JP5235957B2 - Hydraulically driven vehicle, and control method and control apparatus therefor - Google Patents

Description

  The present invention relates to a hydraulically driven vehicle (for example, a forklift) and its control.

  A vehicle having an engine, a hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, and a load device (for example, driving wheels) driven by the hydraulic motor is known (for example, a patent) Reference 1). Typical examples are found in industrial vehicles, agricultural machinery and construction machinery. In such a vehicle, for example, in its power train (driving power transmission device), a hydrostatic transmission (hereinafter referred to as HST) is used to transmit the power from the engine to the drive wheels. The In general, an HST is composed of a variable displacement hydraulic pump (hereinafter referred to as “HST pump”) and a variable or fixed displacement hydraulic motor (hereinafter referred to as “HST pump”) interconnected to form a closed hydraulic circuit. HST motor "). In principle, HST has advantages such as energy loss is extremely small compared to HDT (Hydrodynamic Transmission) typified by a torque converter, the gear can be steplessly shifted, and has a braking function.

  The HST incorporated in the vehicle powertrain transmits the power from the engine to the drive wheels of the vehicle as follows. When the engine is driven, the HST pump mechanically connected to the engine is driven. When the hydraulic fluid is supplied from the HST pump to the HST motor, the HST motor rotates. Further, the HST motor drives and rotates the drive wheels of the vehicle.

  A vehicle having an HST further has a control system. In recent years, electronic control systems have been favored. The control system controls the fuel injection amount to the engine and the capacity of the HST pump in response to an accelerator operation such as an accelerator pedal provided in the vehicle. Thereby, the pressure and flow rate of the HST pump are controlled, and the torque and rotational speed of the drive wheels of the vehicle are controlled.

  The control system disclosed in Patent Document 1 determines the target value of the engine speed in response to the accelerator operation amount, and the relationship between the target value of the engine speed and the capacity of the HST hydraulic pump is The capacity of the HST hydraulic pump is controlled so as to have a predetermined relationship.

Japanese Patent Laid-Open No. 9-301016

  A method of controlling the absorption torque of the HST hydraulic pump (product of the capacity of the hydraulic pump and the effective output pressure) in response to the rotational speed of the engine or the accelerator operation amount is known. However, in both cases of controlling the absorption torque of the HST hydraulic pump in response to only the engine speed and controlling the absorption torque of the HST hydraulic pump in response to only the accelerator operation amount, There are several problems.

  First, in a vehicle that controls the absorption torque of the HST hydraulic pump in response to only the rotational speed of the engine, when the vehicle is started, the vehicle must start after the accelerator pedal is depressed until the vehicle actually starts running. There is a problem that a time lag of a length that cannot be ignored in terms of operation responsiveness may occur.

  The occurrence of the problem is caused by variations in engine rotation speed (low idle rotation speed) in an engine low idle state (an idle state in which the accelerator operation amount is zero and the engine is operating at a low rotation speed). For example, even if the rated low idle rotational speed is 800 rpm, the actual low idle rotational speed varies within a certain range (for example, within a range of 750 rpm to 850 rpm) due to individual differences between engines.

  HST does not transmit the power from the engine to the drive wheels when the capacity of the hydraulic pump is zero. When the accelerator pedal is depressed and the accelerator operation amount starts to increase from zero when starting, the engine rotation speed starts to increase from the low idle rotation speed, and in response, the absorption torque of the HST hydraulic pump starts from zero. Start increasing. As a result, the power transmitted from the engine to the drive wheels increases from zero, and the vehicle starts to travel.

  In this case, in order not to generate a creep phenomenon (a phenomenon in which the vehicle starts if the brake is not applied in a low idle state) in all manufactured vehicles, the starting point for increasing the absorption torque of the HST hydraulic pump from zero at the start is set. It is conceivable to set the maximum value (for example, 850 rpm) in the above-described low idle rotation speed variation range (for example, 750 rpm to 850 rpm).

  However, in a vehicle having a characteristic of a low idle rotation speed (for example, 750 rpm) lower than the above maximum value (set value), the engine rotation speed is set to the set value (for example, from the time when the driver starts stepping on the accelerator pedal). Up to 850 rpm), the absorption torque of the hydraulic pump is zero and the vehicle does not start. Thereafter, the vehicle starts traveling after the rotational speed of the engine reaches the set value (for example, 850 rpm). That is, when starting, an unnecessary time lag occurs from when the accelerator pedal is depressed until when the vehicle starts running. With such a time lag, the driver is unhappy with the poor response of the vehicle.

  On the other hand, in the vehicle that controls the absorption torque of the hydraulic pump of the HST in response to only the accelerator operation amount, the above time lag problem is solved. However, when the driver depresses the accelerator pedal deeply and runs the vehicle, the following two types of problems occur.

  One of the problems is that when the driver suddenly loosens the accelerator pedal, the engine overruns (the rotational speed exceeds an allowable value) and overdeceleration occurs. The cause is that the absorption torque of the HST hydraulic pump suddenly greatly decreases in response to the sudden decrease in the accelerator operation amount, so that the large inertial force of the vehicle trying to continue traveling from the drive wheels through the HST This is because it is returned to the engine (regenerative braking action). In other words, it is a problem that HST braking is excessively applied (even if braking is not applied separately), which is a feature of HST.

  Another problem is that the engine stalls when a large load is suddenly applied to the drive wheels while the vehicle is traveling, for example, when the vehicle starts climbing from a flat road. The cause of the engine stall is that when a heavy load is applied to the drive wheels, the amount of operation of the accelerator pedal is still large, so the absorption torque of the HST is still kept large according to the large amount of accelerator operation. This is because an excessive load is applied.

  The problems described above are particularly noticeable in forklifts. This is because forklifts often stop and start frequently during the loading operation, and the driver tends to frequently perform an operation of depressing the accelerator pedal to the maximum or returning it to zero at a stroke. Furthermore, it is necessary for the forklift to prevent excessive impact load and load collapse on the load loaded with the fork for safety and prevention of damage to the load.

  Conventionally, a technique for solving the above-described problems has not been known. Accordingly, one object of the present invention is a hydraulically driven vehicle configured to transmit power from an engine to a load device through a hydraulic power transmission device represented by HST. The purpose is to improve the control of the power transmission device according to the change of the drive command to the engine and the change of the drive state of the engine.

  A vehicle provided according to one aspect of the present invention includes an engine, a variable displacement hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, and driven by the hydraulic motor. An engine control unit that controls the engine in response to an accelerator operation amount, and controls the hydraulic pump in response to the accelerator operation amount and the engine rotation speed. A pump control means. In response to the accelerator operation amount, the pump control means determines the first target value such that the first target value of the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases. In response to the one absorption torque control means and the engine rotation speed, the second target value is determined such that the second target value of the maximum absorption torque of the hydraulic pump increases as the engine rotation speed increases. In response to the second absorption torque control means and the engine rotation speed, the third target value is determined such that the third target value of the maximum absorption torque of the hydraulic pump increases as the engine rotation speed increases. The third absorption torque control means, the small selection means for selecting the smaller one of the first and second target values, the target value selected by the small selection means and the third target value A large selection means for selecting the larger of, so that the maximum absorption torque of said hydraulic pump becomes the target value selected by the large selection unit, and a absorption torque control means for controlling the hydraulic pump.

  According to this vehicle, by appropriately setting the first, second, and third target values, the maximum absorption torque of the hydraulic pump is appropriately determined based on either the accelerator operation amount or the engine rotation speed, depending on the situation. Select to control the hydraulic pump.

  First, when the driver slowly increases the accelerator operation amount and starts the vehicle, the control is performed so that the first target value is selected and the maximum absorption torque of the hydraulic pump becomes the first target value. Done. That is, the maximum absorption torque of the hydraulic pump is controlled according to the accelerator operation amount. As a result, the problem of creep and acceleration delay (time lag) when starting is improved.

  In addition, when the driver increases the accelerator operation amount at a stroke and starts the vehicle, the control is performed so that the second target value is selected and the maximum absorption torque of the hydraulic pump becomes the second target value. Is called. That is, the maximum absorption torque of the hydraulic pump is controlled according to the engine speed. As a result, the engine stall is prevented and the problem of acceleration delay (time lag) at the start is also improved.

  In addition, when the vehicle is traveling at a certain high speed and the driver suddenly decreases the accelerator operation amount, the third target value is selected, and the maximum absorption torque of the hydraulic pump is the third absorption torque. The control is performed so that the target value becomes. That is, the maximum absorption torque of the hydraulic pump is controlled according to the engine speed. As a result, the maximum absorption torque of the hydraulic pump is maintained at a relatively large value, and the problem of engine overrun is improved.

  In addition, when the vehicle is traveling on a flat road at a certain high speed, the load on the drive wheels suddenly increases due to, for example, going uphill, and the engine speed is significantly reduced. A value is selected and the maximum absorption torque of the hydraulic pump is controlled according to the engine speed. As a result, the maximum absorption torque of the hydraulic pump is reduced to a relatively small value, improving the engine stall problem.

In the vehicle described above, the first, second and third target values can be set as follows, for example, in order to obtain the above-described action. That is, the first target value is mapped to the engine rotation speed by converting the accelerator operation amount into the engine rotation speed based on the control characteristic of the engine control means, and the second and second If three target values are also mapped to the engine speed and the mapped first, second and third target values are compared,
Over the entire variable range of the engine speed,
In a low speed region where the relationship of second target value ≧ first target value ≧ third target value is established and the engine speed is equal to or lower than a predetermined value,
The first, second and third target values can be set so that the relationship of second target value> first target value> third target value is established.

  As a result, when the engine speed is low and the accelerator operation amount is small (for example, when making a call or when traveling normally at low speed), the first target value 61 is selected. The vehicle can be controlled as intended.

  Further, according to an embodiment of the present invention, the pump control means controls the maximum absorption torque of the hydraulic pump according to the accelerator operation amount or the engine rotation speed when the vehicle starts, so that a predetermined high speed region is obtained. When the accelerator operation amount decreases from a predetermined large operation amount region to a predetermined small operation amount region while the engine is operating at the engine rotation speed, the maximum absorption of the hydraulic pump according to the engine rotation speed When the engine speed is reduced to a predetermined low speed region while the engine is operating at the engine speed in the high speed region, the maximum absorption torque of the hydraulic pump is controlled according to the engine rotational speed. To control.

A vehicle provided in accordance with another aspect of the present invention includes an engine, a variable displacement hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, and a load device driven by the hydraulic motor. An engine control means for controlling the engine in response to an accelerator operation amount, and a pump control means for controlling the hydraulic pump in response to the accelerator operation amount and the engine rotational speed. Is provided. The pump control means includes
(1) In a state where the engine rotation speed is in a predetermined low speed region including a low idle state and the accelerator operation amount is constant or changes within a predetermined small operation amount region, in response to the accelerator operation amount The hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases.
(2) In a state where the engine rotation speed is in a predetermined high speed region higher than the low speed region, the accelerator operation amount is smaller than the predetermined large operation amount region and smaller than a predetermined small value including zero. In response to the engine speed, the hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases as the engine speed increases in response to the engine speed.
(3) In a state where the accelerator operation amount is in a predetermined large operation amount region that is larger than the small operation amount region, when the engine rotation speed decreases from the high speed region to the low speed region, the engine rotation speed is increased. In response, the hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases as the engine speed increases.

  According to this vehicle, the following effects can be obtained.

  (1) When the driver starts the vehicle while stepping on the accelerator pedal slowly, the accelerator operation amount increases within a predetermined small operation amount region while the engine speed is in the low speed region. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the accelerator operation amount. As a result, the creep phenomenon is prevented, and the vehicle starts smoothly without a time lag with respect to the accelerator operation.

  (2) When the driver takes his foot off the accelerator pedal while the vehicle is traveling at a certain high speed, the accelerator operation amount is reduced from the large operation amount region while the engine speed is in the high speed region. Decrease to the manipulated variable area. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the engine speed. As a result, the maximum absorption torque of the hydraulic pump is gently reduced, preventing engine overrun.

  (3) When the vehicle is traveling on a flat road at a certain high speed, when entering the uphill driving, the engine speed is changed from the high speed region to the low speed region while the accelerator operation amount is in the large operation amount region. Decrease. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the engine speed. As a result, the maximum absorption torque of the hydraulic pump rapidly decreases, so that excessive torque is not applied to the engine, and engine stall is prevented.

In the above vehicle, the pump control means further includes:
(4) When the accelerator operation amount increases from the small operation amount region to the large operation region while the engine rotation speed is in the low speed region, the engine rotation speed is high in response to the engine rotation speed. The hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases.
(5) When the accelerator operation amount is constant or changes within the large operation amount region in a state where the engine rotation speed is in the high speed region, the larger the accelerator operation amount is in response to the accelerator operation amount. , Controlling the hydraulic pump so that the maximum absorption torque of the hydraulic pump is increased,
It may be constituted as follows.

  According to such a configuration, the following operation is obtained.

  (4) When the driver depresses the accelerator pedal deeply and starts the vehicle, the engine operation speed is in the low speed region, and the accelerator operation amount increases from the small operation amount region to the large operation region. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the engine speed. As a result, engine stall can be prevented, and (according to the sudden increase in the amount of accelerator operation, the engine rotation speed instantaneously exceeds the range of variation in the rotation speed of the low idle state Li) The vehicle can be started without time lag.

  (5) When the vehicle is traveling at a high speed and the accelerator operation amount is large, the accelerator operation amount is constant or changes within the large operation amount region while the engine speed is in the high speed region. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the accelerator operation amount. As a result, the speed of the vehicle can be controlled according to the accelerator operation.

A vehicle provided in accordance with another aspect of the present invention is driven by an engine, a variable displacement hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, and the hydraulic motor. An engine control means for controlling the engine in response to an accelerator operation amount, and a pump for controlling the hydraulic pump in response to the accelerator operation amount and the engine rotation speed. Control means. The pump control means includes
(1) When the engine rotational speed is in a predetermined low speed region including a low idle state and the accelerator operation amount is in a predetermined small operation amount region including zero, in response to the accelerator operation amount, The hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases.
(2) When the engine rotation speed is in a predetermined high speed region higher than the low speed region and the accelerator operation amount is in the small operation amount region, the engine rotation speed is high in response to the engine rotation speed. The hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases.
(3) When the engine rotation speed is in the low speed region and the accelerator operation amount is in a predetermined large operation amount region that is larger than the small operation amount region, the engine rotation is performed in response to the engine rotation speed. The hydraulic pump is controlled such that the maximum absorption torque of the hydraulic pump increases as the speed increases.

  According to this vehicle, the following effects can be obtained.

  (1) When the driver starts the vehicle while stepping on the accelerator pedal slowly, the engine speed is in the low speed region and the accelerator operation amount is in the small operation amount region. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the accelerator operation amount. As a result, the creep phenomenon is prevented, and the vehicle starts smoothly without a time lag with respect to the accelerator operation. When the accelerator operation amount is small during low-speed traveling, the speed of the vehicle can be controlled according to the accelerator operation.

  (2) When the driver removes his / her foot from the accelerator pedal while the vehicle is traveling at a certain high speed, the engine speed is in the high speed region and the accelerator operation amount is in the small operation amount region. become. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the engine speed. As a result, even if the accelerator operation amount suddenly decreases during traveling at a certain high speed, the maximum absorption torque of the hydraulic pump is gently decreased, so that engine overrun is prevented.

  (3) The engine speed is low when the vehicle is traveling on a flat road at a certain high speed, or when the vehicle starts to go uphill, or when the driver depresses the accelerator pedal deeply and starts the vehicle. The accelerator operation amount is in the large operation amount region. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the engine speed. As a result, when the engine speed is suddenly drastically reduced while the vehicle is traveling at a certain high speed, the maximum absorption torque of the hydraulic pump is suddenly reduced, so that excessive torque is not applied to the engine.・ Stall is prevented. In addition, when the driver depresses the accelerator pedal deeply and starts the vehicle, engine stall can be prevented, and the engine speed can be instantaneously reduced to a low idle state due to a sudden increase in the amount of accelerator operation. The vehicle can be started without a time lag with respect to the accelerator operation (because it exceeds the variation range of the engine speed of Li).

  In the above vehicle, the pump control means may further comprise (4) when the engine rotation speed is in the high speed region and the accelerator operation amount is in the large operation amount region, in response to the accelerator operation amount. The hydraulic pump may be controlled so that the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases.

  According to such a configuration, when the vehicle is traveling at high speed and the accelerator operation amount is large, the engine speed is in the high speed region and the accelerator operation amount is in the large operation amount region. In this case, the maximum absorption torque of the hydraulic pump is controlled according to the accelerator operation amount. Therefore, when the accelerator operation amount is large during high-speed traveling, the vehicle speed can be controlled in accordance with the accelerator operation.

  According to the present invention, in a hydraulically driven vehicle configured to transmit power from an engine to a load device through a hydraulic power transmission device represented by HST, driving to the engine is performed. It is possible to improve the control of the power transmission device according to the change in the command and the change in the driving state of the engine.

1 is a side view showing a schematic appearance of a vehicle (for example, a forklift) according to an embodiment of the present invention. The block diagram which shows the structural example of the power train which has HST integrated in the embodiment (Several systems adjacent to a power train are also shown together). The graph which shows the rotational speed-torque characteristic of the engine and HST pump in the embodiment. The block diagram which shows the functional structural example of the HST controller in the power train of the embodiment. The figure which shows an example of the maximum absorption torque characteristic of the engine speed-HST pump employ | adopted by the same embodiment. The figure which shows the modification of the engine speed-maximum absorption torque characteristic of the HST pump which can be employ | adopted by the embodiment. The figure which shows another modification of the engine speed-maximum absorption torque characteristic of the HST pump which can be employ | adopted by the same embodiment. 6 is a flowchart showing a control operation performed by the HST controller of the embodiment. The figure explaining an example of how the maximum absorption torque of an HST pump is determined at the time of start in the embodiment. The figure explaining an example of how the maximum absorption torque of an HST pump is determined when the accelerator operation amount decreases suddenly and significantly during traveling at a certain high speed in the same embodiment. The figure explaining an example of how the maximum absorption torque of the HST pump is determined when the engine rotation speed is suddenly drastically decreased during traveling at a certain high speed in the embodiment.

  Hereinafter, an embodiment of the present invention will be described. Hereinafter, as an illustrative example, an embodiment of the present invention in which the vehicle is a forklift will be described, but it goes without saying that the present invention can also be applied to other types of vehicles.

  FIG. 1 shows a schematic appearance of a hydraulically driven vehicle (for example, a forklift) according to this embodiment. As shown in FIG. 1, the forklift 1 includes a driving wheel 3, an accelerator pedal 5 (not a pedal, but may be another operating device such as a rotary dial, a lever, or a slide rod), a forward / reverse switching lever 7, and the like. Have.

  FIG. 2 shows a configuration example of a power train (travel power transmission system) having a hydraulic power transmission device, particularly an HST, mounted on a vehicle (for example, a forklift) according to the present embodiment. Shows not only the powertrain, but also some systems related to it).

  As shown in FIG. 2, the powertrain 10 includes an accelerator pedal 5, a forward / reverse switching lever 7, an engine 13, an engine controller 11, an HST 21, an HST controller 15, a drive wheel system (differential, axle, and drive wheel) 31. . The HST 21 has a variable displacement type HST pump 23 (typically a swash plate type variable displacement pump is used) and a variable or fixed displacement type (variable displacement type in the illustrated example) HST motor 25. Both 23 and 25 are connected to each other via a hydraulic pipe 22 through which hydraulic oil flows to form a closed hydraulic circuit. The HST pump 23 is connected to the output shaft 9 of the engine 13 and is driven by the engine 13 to rotate. When hydraulic fluid is supplied from the HST pump 23 to the HST motor 25, the HST motor 25 is driven to rotate. The drive wheel system 31 is connected to the output shaft of the HST motor 25, and the HST motor 25 drives and rotates the drive wheel 3. Note that the output shaft 9 of the engine 13 is not limited to the HST pump 23 but also other hydraulic pumps (for example, in the case of a forklift, a hydraulic pump 27 for raising and lowering and tilting the fork and a brake device for driving the brake device). A hydraulic pump 29 etc.) can also be connected. Here, the engine 13 may be driven by various fuels such as a gasoline engine, a diesel engine, or an LPG engine.

  An operation amount (actual accelerator operation amount) of the accelerator pedal 5 by the driver is detected as an electric signal by a sensor (for example, a potentiometer) (not shown) provided on the accelerator pedal 5. Further, the rotational speed of the engine 13 is detected as an electrical signal by a rotational speed sensor 14 provided on the output shaft 9 of the engine 13. The engine controller 11 receives an actual accelerator operation amount detection signal from the accelerator pedal 5 and an engine rotation speed detection signal from the rotation speed sensor 14. The engine controller 11 controls the throttle opening of the electronically controlled throttle (not shown) of the engine 13 or the fuel injection amount from the injector (not shown) in response to the detected accelerator operation amount and engine speed, thereby The output torque of the engine 13 is controlled. Further, the engine controller 11 transmits a detection signal of the engine rotation speed detected by the rotation speed sensor 14 to the HST controller 15.

  The HST controller 15 determines the maximum absorption torque of the HST pump 23 based on the detection signal of the engine rotation speed and the detection signal of the accelerator operation amount received from the rotation speed sensor 14 through the engine controller 11, and indicates the maximum absorption torque. The maximum absorption torque command to be output is output to EPC (Electric Proportional Control) valves 17 and 18 for the HST pump in the form of electrical signals. Here, one EPC valve 17 is a forward EPC valve 17 that functions when forward movement is selected by the forward / reverse switching lever 7, and the other EPC valve 18 is selected for backward movement by the forward / backward switching lever 7. A reverse EPC valve 18 that sometimes functions. The pump EPC valves 17 and 18 operate by receiving the maximum absorption torque command input from the HST controller 15 as an electrical signal, and hydraulically drive the HST pump capacity variable unit 20. The variable capacity unit 20 of the HST pump 23 has a capacity of the HST pump 23 (typical) so that the absorption torque of the HST pump 23 becomes an appropriate value within the range having the maximum absorption torque instructed by the maximum absorption torque command as an upper limit. Specifically, the angle of the swash plate is controlled.

  In the illustrated example, the capacity of the HST motor 25 is also controlled through the motor EPC valve 19 and the HST motor capacity variable unit 24 according to a command from the HST controller 15, but detailed description thereof is omitted here.

  FIG. 3 shows a typical example of the rotational speed-torque characteristics of the engine 13 and the HST pump 23 shown in FIG.

  A solid characteristic line (maximum output torque characteristic line) 51 shows a typical characteristic example of the maximum output torque corresponding to the rotational speed of the engine 13. Here, the maximum output torque of the engine 13 means the maximum torque that can be output by the engine 13 in a full throttle state in which the operation amount of the accelerator pedal is maximum.

  The operating point Li is a low idle point (that is, an operating point when the engine 13 operates at a low rotational speed, the accelerator operation amount is zero, and the transmission torque to the drive wheels 3 is also zero). The operating point Hi is a high idle point (that is, an operating point when the engine operates at a high rotational speed, the accelerator operation amount is maximum, and the transmission torque to the drive wheels 3 is zero).

  An alternate long and short dash line characteristic line (maximum absorption torque characteristic line) 53 is a typical characteristic of the maximum absorption torque of the HST pump 23 in accordance with the engine rotation speed, which is determined by the HST controller 15 as described with reference to FIG. An example is shown. The HST controller 15 outputs a torque value corresponding to the current engine speed on the maximum absorption torque characteristic line 53 to the pump EPC valves 17 and 18 as a maximum absorption torque command. Thereby, the absorption torque of the HST pump 23 is controlled within the range of the maximum absorption torque characteristic line 53 or less. The occasional absorption torque of the HST pump 23 varies within the range of the maximum absorption torque characteristic line 53 or less depending on the load applied to the drive wheels 3. However, when the forklift starts, the load applied to the drive wheels 3 is considerably large, and therefore the absorption torque of the HST pump 23 is often a value on or close to the maximum absorption torque characteristic line 53.

  A broken characteristic line (output torque characteristic line) 55 shows a typical characteristic example of the output torque of the engine 13 according to the rotational speed of the engine 13 when the actual accelerator operation amount is constant. That is, as described with reference to FIG. 2, the engine controller 11, particularly the all speed governor (ASG), determines the throttle opening or fuel injection amount of the engine 13 according to the accelerator operation amount and the engine speed. To control. Thus, the engine output torque is controlled so as to follow one output torque characteristic line 55 in the figure corresponding to the accelerator operation amount at each time. When the accelerator operation amount increases under the control of ASG, the output torque characteristic line 55 moves to the right in the figure. As one feature of ASG control in forklifts and construction machines, the gradient of the output torque characteristic line 55 (ratio of torque change to rotational speed change) is set to be steep (high ratio) as shown in the figure. Thereby, even if the load from the outside suddenly changes greatly (even if the torque changes drastically), the fluctuation of the engine speed is small, and the workability is high. Thus, as a result of setting the output torque characteristic line 55 corresponding to each accelerator operation amount to have a steep slope, when the accelerator operation amount is determined, the engine rotation speed is determined in a substantially one-to-one relationship, It can be said roughly that the engine speed increases as the accelerator operation amount increases.

  Hereinafter, the control operation of the maximum absorption torque of the HST pump 23 performed by the HST controller 15 in the power train 10 shown in FIG. 2 will be described in more detail.

  The HST controller 15 has the following control functions. First, when the forklift starts, the HST controller 15 controls the maximum absorption torque of the HST pump 23 according to the accelerator operation amount. Further, when the accelerator operation amount is reduced to a predetermined decrease or more during traveling at an engine rotation speed equal to or higher than a predetermined speed, the HST controller 15 controls the maximum absorption torque of the HST pump 23 according to the engine rotation speed. Further, when the engine speed is reduced to a predetermined decrease or more during traveling at an engine speed equal to or higher than a predetermined speed, the HST controller 15 controls the maximum absorption torque of the HST pump 23 according to the engine speed.

  FIG. 4 shows a more specific functional configuration example of the HST controller 15 for realizing the above functions. FIG. 5 shows an example of the engine rotation speed employed in the power train 10 and the maximum torque characteristic of the HST pump.

  As shown in FIG. 4, the HST controller 15 includes a first absorption torque control unit 15a, a second absorption torque control unit 15b, a third absorption torque control unit 15c, a small selection unit 15d, and a large selection unit 15e. Yes.

  The accelerator operation amount detected by the accelerator pedal 5 is input to the first absorption torque control unit 15a, and the first target value 61 of the maximum absorption torque of the HST pump 23 is determined based on the accelerator operation amount ( As a determination method, calculation or reference to a preset lookup table can be adopted). The first target value 61 is determined so that the first target value 61 increases as the accelerator operation amount increases. Here, as will be described later with reference to FIG. 5, when the accelerator operation amount is within a certain value (for example, approximately 60%) or more, the first target value 61 is the maximum absorption torque of the HST pump 23. The upper limit value of the variable range is reached and becomes constant at the upper limit value. However, in the present specification, this is included in the concept of “the first target value 61 increases as the accelerator operation amount increases”.

  As shown in FIG. 4, the engine speed detected by the speed sensor 14 is input to the second absorption torque control unit 15b, and the second maximum absorption torque of the HST pump 23 is calculated based on the engine speed. The target value 62 is determined (as a determination method, calculation or reference to a preset look-up table can be adopted). The second target value 62 is determined so that the second target value 62 increases as the engine speed increases. Here, as will be described later with reference to FIG. 5, when the engine speed is in a range of a certain value (for example, about 1600 rpm), the second target value 62 is a variable of the maximum absorption torque of the HST pump 23. The upper limit of the range is reached and becomes constant at that upper limit. However, this is included in the above-mentioned concept of “the second target value 62 increases as the engine speed increases”.

  As shown in FIG. 4, the third absorption torque control unit 15c receives the engine rotation speed detected by the rotation speed sensor 14, and based on the engine rotation speed, the third absorption torque control unit 15c determines the third absorption torque of the HST pump 23. The target value 63 is determined (as a determination method, calculation or reference to a preset look-up table can be adopted). The third target value 63 is determined such that the third target value 63 increases as the engine speed increases. Here, as will be described later with reference to FIG. 5, when the engine speed is in a range of a certain value (for example, about 1850 rpm), the third target value 63 is a variable of the maximum absorption torque of the HST pump 23. When the upper limit value of the range is reached and becomes constant at the upper limit value, and when the engine speed is within a certain value (for example, about 1050 rpm), the third target value 63 is the maximum absorption torque of the HST pump 23. The lower limit value (zero) of the variable range is reached and becomes constant at the lower limit value. However, this is included in the above-described concept of “the third target value 63 increases as the engine speed increases”.

  As described above, the second and third target values 62 and 63 are determined as a function of the engine speed. On the other hand, the first target value 61 is determined as a function of the accelerator operation amount.

  Here, the accelerator operation amount can be converted into the engine rotation speed based on the control characteristic of the engine controller 11 (this is indicated by the output torque characteristic line 55 in FIGS. 3 and 5). There can be a plurality of conversion methods. An example of the simplest method is as follows. For example, in FIG. 5, a characteristic line 55 corresponding to each accelerator operation amount from 0% to 100% is a line corresponding to a predetermined output torque value (for example, a line of torque “0”, that is, a horizontal line in FIG. Find the point that intersects the axis. Then, each accelerator operation amount is converted into an engine rotation speed at each intersection. In the example of FIG. 5, the accelerator operation amounts 0%, 25%, 50%, 75%, and 100% are converted into engine rotation speeds of 800 rpm, 1150 rpm, 1500 rpm, 1850 rpm, and 2200 rpm, respectively.

  Thus, by converting the accelerator operation amount into the engine rotation speed, the first target value 61 can be mapped to the engine rotation speed (that is, the first target value is converted into the engine rotation corresponding to the accelerator operation amount). Can be expressed as a function of speed). A characteristic example of the first target value 61 mapped to the engine rotation speed in this way is shown by a solid line 61 in FIG. Further, a characteristic example of the second target value 62 mapped with respect to the engine speed is shown by a dashed line 62 in FIG. 5, and a characteristic example of the third target value 63 mapped with respect to the engine speed is shown. 5 is shown by a two-dot chain line 63.

  As shown in FIG. 5, the first target value 61 is set as follows. First, when the accelerator operation amount is 0% (the engine rotational speed in the low idle state Li), the first target value 61 is zero. The first target value 61 increases as the accelerator operation amount increases (that is, as the engine speed converted from the accelerator operation amount increases). When the accelerator operation amount is a predetermined large value (for example, about 60%) or more, in other words, when the engine speed converted from the accelerator operation amount is a predetermined high value (for example, about 1600 rpm) or more, the first target value 61 is set. Reaches the upper limit value of the variable range of the maximum absorption torque and is constant at the upper limit value.

  The second target value 62 is set as follows. First, in the low speed region from the engine rotation speed in the low idle state Li to a predetermined value (for example, 1300 rpm), a value larger than the first target value 61 is shown. The second target value 62 increases as the engine speed increases. In the middle to high speed region where the engine speed is equal to or higher than the predetermined value (for example, about 1300 rpm), the characteristic line of the second target value 62 overlaps with the characteristic line of the first target value 61.

  The third target value 63 is set as follows. First, when the engine speed is between a low idle state Li and a predetermined value (for example, about 1050 rpm), the lower limit value of the variable range of the maximum absorption torque is zero. When the engine speed is equal to or higher than the predetermined value, the third target value 63 increases as the engine speed increases. Then, in a low speed to medium speed range where the engine rotation speed is lower than a predetermined very high value (for example, about 1850 rpm) and a certain high speed range, the engine speed is lower than the first target value and is equal to or higher than the very high value (for example, about 1850 rpm). In the very high speed region, the characteristic line of the third target value 63 overlaps the characteristic line of the first target value 61.

  The characteristic examples of the first, second, and third target values 61, 62, and 63 shown in FIG. 5 are merely examples, and other characteristic examples can be used. For example, the target values 61, 62, and 63 can be set so that the characteristic example shown in FIG. 6 or 7 is obtained.

  The characteristic example shown in FIG. 6 has a higher engine rotation speed region where the first target value 61 and the second target value 62 overlap with each other (for example, the characteristic example shown in FIG. (High speed range of about 1600 rpm or more). In the characteristic example shown in FIG. 7, the engine rotational speed region where the first, second, and third target values 61, 62, and 63 overlap is lower than that in the characteristic example shown in FIG. 5. (For example, in the medium to high speed range of about 1300 rpm or more).

What is common to the characteristic examples shown in FIGS. 5, 6 and 7 is as follows. That is, in this embodiment, over the entire variable range of the engine rotation speed,
Second target value 62 ≧ first target value 61 ≧ third target value 63
The first, second, and third target values 61, 62, and 63 are determined so that the relationship is established. In particular, in a low speed region where the engine speed is below a predetermined value (in the example shown, about 1300 rpm or less),
Second target value 62> First target value 61> Third target value 63
The relationship has been established.

  Refer to FIG. 4 again. The small selection unit 15d of the HST controller 15 compares the first target value 61 determined by the first absorption torque control unit 15a with the second target value 62 determined by the second absorption torque control unit 15b. The smaller target value α of 61 and 62 is selected.

  The large selection unit 15e compares the target value α selected by the small selection unit 15d with the third target value 63 determined by the third absorption torque control unit 15c, and the larger of both α and 63 is compared. Select the target value β.

  The target value β selected by the large selection unit 15e is output from the HST controller 15 to the EPC valves 17 and 18 as the above-described maximum absorption torque command. As already described with reference to FIG. 2, the EPC valves 17 and 18 and the pump displacement variable unit 20 operate. Thereby, the maximum absorption torque of the HST pump 23 is controlled to be the selected target value β.

  FIG. 8 shows a flow of a control operation performed by the HST controller 15.

  As shown in FIG. 8, a first target value (A) 61 is determined by the first absorption torque control unit 15a based on the current accelerator operation amount (S1). Further, the second target value (B) 62 and the third target value (C) 63 are respectively calculated by the second absorption torque control unit 15b and the third absorption torque control unit 15c based on the current engine speed. (S2).

  The small selection unit 15d compares the magnitudes of the first target value (A) 61 and the second target value (B) 62 (S3), and the smaller target value (A or B) is an intermediate target value α. (S4 or S5).

  Thereafter, the large selection unit 15e compares the intermediate target value α with the third target value (C) 63 (S6), and the larger target value (α or C) is determined as the final target value. It is determined as the value β (S7 or S8). This final target value β is output as a maximum absorption torque command from the HST controller 15 (S9). As a result, the maximum absorption torque of the HST pump 23 is controlled to be the final target value β.

  FIG. 9 shows one example of how the maximum absorption torque of the HST pump is determined when the forklift starts in this embodiment. Here, the case where the maximum absorption torque of the HST pump 23 is determined will be described based on the characteristic example shown in FIG.

  As shown in FIG. 9, at the time of start, the accelerator operation amount increases from the low idle point Li (accelerator operation amount 0%). The first target value 61 increases from the low idle point Li as indicated by an arrow 61A. In parallel with this, the engine speed increases as the accelerator operation amount increases. Thereby, the second and third target values 62 and 63 also increase as indicated by arrows 62A and 63A. In this case, the smaller one of the first target value 61 and the second target value 62, that is, the first target value 61 is selected by the small selection unit 15d. Then, the larger one of the first target value 61 and the third target value 63, that is, the first target value 61 is selected by the large selection unit 15e. As a result, the maximum absorption torque of the HST pump 23 is controlled to the first target value 61. That is, the maximum absorption torque of the HST pump 23 is controlled according to the accelerator operation amount. As a result, if the accelerator operation is not performed, the HST pump 23 does not generate absorption torque, so that the creep phenomenon is prevented and the vehicle starts smoothly without a time lag with respect to the accelerator operation.

  FIG. 10 shows how the HST pump in the present embodiment shows that when the accelerator operation amount suddenly drastically decreases during traveling at a certain high speed (for example, when the driver removes his / her foot from the accelerator pedal 5). One example of how the maximum absorption torque of 23 is determined is shown.

  As shown in FIG. 10, in this case, the accelerator operation amount decreases rapidly from a considerably large value (about 50% in the illustrated example) to a considerably small value (about 10% in the illustrated example). Therefore, the first target value 61 decreases rapidly as the accelerator operation amount, as indicated by the arrow 61B. However, due to the inertial force of the vehicle, the engine speed decreases more gradually and is still relatively high. Therefore, the second target value 62 and the third target value 63 are slightly decreased and are still relatively large values as indicated by arrows 62B and 63B, respectively. In this case, the smaller one of the first target value 61 and the second target value 62, that is, the first target value 61 is selected by the small selection unit 15d. Then, the larger one of the first target value 61 and the third target value 63, that is, the third target value 63 is selected by the large selection unit 15e. As a result, the maximum absorption torque of the HST pump 23 is controlled to the third target value 63. That is, the maximum absorption torque of the HST pump 23 is controlled according to the engine speed. As a result, even if the accelerator operation amount suddenly decreases, the maximum absorption torque of the HST pump 23 decreases gently, so that overrun of the engine 13 is prevented and damage to the engine 13 can be prevented.

  FIG. 11 shows how the maximum of the HST pump is increased when the engine rotation speed is suddenly drastically decreased during traveling at a certain high speed (for example, when a forklift travels uphill while carrying a load). An example of how the absorption torque is determined is shown.

  As shown in FIG. 11, the engine speed rapidly decreases from a considerably high value (about 1500 rpm in the illustrated example) to a considerably low value (about 1000 rpm in the illustrated example). Therefore, the second target value 62 and the third target value 63 rapidly decrease and become considerably small values as indicated by arrows 62C and 63C, respectively. On the other hand, since the driver keeps stepping on the accelerator pedal considerably deeply, the accelerator operation amount is still at a considerably high value (about 50% in the illustrated example). Therefore, since the first target value 61 is determined according to the accelerator operation amount, it is still a considerably high value as indicated by the dot 61C. In this case, the smaller one of the first target value 61 and the second target value 62, that is, the second target value 62 is selected by the small selection unit 15d. Then, the larger one of the second target value 62 and the third target value 63, that is, the second target value 62 is selected by the large selection unit 15e. As a result, the maximum absorption torque of the HST pump 23 is controlled to the second target value 62. That is, the maximum absorption torque of the HST pump 23 is controlled according to the engine speed. Therefore, since the maximum absorption torque of the HST pump 23 decreases rapidly, it is possible to avoid applying excessive torque to the engine 13 and to prevent engine stall.

  The embodiment of the present invention has been described above. Hereinafter, the control in the present embodiment will be described from the viewpoint of how to control the absorption torque of the HST pump when the accelerator operation amount or the engine rotation speed changes.

  First, as shown in FIG. 9, FIG. 10, or FIG. 11, a small operation amount region including 0% within a variable range of the accelerator operation amount and a large operation amount region larger than the small operation amount region are assumed. Further, a low speed region including the low idle state Li and a high speed region higher than the low speed region are assumed in the variable range of the engine rotation speed. In the illustrated example, the small operation amount region and the low speed region correspond to the range of the engine rotation speed from the low idle state Li (at least about 750 rpm) to about 1300 rpm, and the large operation amount region and the high speed region correspond to 1450 rpm. Corresponds to the range of engine speed in the high idle state Hi (about 2200 rpm) (specific values defining each region may be different values. In addition, the small operation amount region and the low speed region are partially The large operation amount area and the high speed area may be partially different.

  The HST controller 15 controls the maximum absorption torque of the HST pump 23 as in the following (1) to (5).

  (1) When the accelerator operation amount is constant or changes within a predetermined small operation amount region with the engine speed being in the low speed region (for example, when the driver slowly starts the forklift while stepping on the accelerator pedal) ), In response to the accelerator operation amount, the HST controller 15 controls the HST pump 23 so that the maximum absorption torque of the HST pump 23 increases as the accelerator operation amount increases. Thus, the creep phenomenon is prevented, and when the driver starts the forklift while slowly depressing the accelerator pedal, the vehicle starts smoothly without a time lag with respect to the accelerator operation.

  (2) When the accelerator operation amount decreases from the large operation amount region to the small operation amount region while the engine speed is in the high speed region (for example, driving while the forklift is traveling at a certain high speed) When the person lifts his / her foot from the accelerator pedal), the HST controller 15 responds to the engine speed so that the maximum absorption torque of the HST pump 23 increases as the engine speed increases. To control. As a result, even if the accelerator operation amount suddenly decreases during traveling at a certain high speed, the maximum absorption torque of the HST pump 23 decreases gently, so that overrun of the engine 13 is prevented.

  (3) When the engine rotation speed decreases from the high speed area to the low speed area while the accelerator operation amount is in the large operation amount area (for example, from the state where the forklift is traveling on a flat road at a certain high speed, The HST controller 15 controls the HST pump 23 so that the maximum absorption torque of the HST pump 23 increases as the engine speed increases in response to the engine speed. . As a result, when the engine rotational speed suddenly and drastically decreases during traveling at a certain high speed, the maximum absorption torque of the HST pump 23 decreases rapidly, so that excessive torque is not applied to the engine 13. Stalls are prevented.

  (4) When the engine speed is in the low speed region and the accelerator operation amount increases from the small operation amount region to the large operation region (for example, when the driver depresses the accelerator pedal deeply and starts the forklift) ), The HST controller 15 controls the HST pump 23 in response to the engine rotation speed so that the maximum absorption torque of the HST pump 23 increases as the engine rotation speed increases. Specifically, by depressing the accelerator pedal at once, the accelerator operation amount is detected as a large value and becomes a large operation region, but the engine speed does not increase immediately, so the engine speed detected by the speed sensor Is in the low speed region, the HST controller 15 selects the maximum absorption torque near the rise of the line 62 in the characteristic example of the second target value 62 in FIG. 5 (the engine speed is near Li). Even if the pedal is depressed at once, the HST pump 23 operates with a certain amount of pump absorption torque. As a result, engine stall can be prevented, and the forklift can be started without a time lag with respect to the accelerator operation.

  (5) When the accelerator operation amount is constant or changes within the large operation amount region in a state where the engine rotation speed is in the high speed region (for example, when the accelerator operation amount is large while traveling at high speed), the HST controller 15 In response to the accelerator operation amount, the HST pump 23 is controlled so that the maximum absorption torque of the HST pump 23 increases as the accelerator operation amount increases. Thereby, when the vehicle is traveling at high speed and the amount of accelerator operation is large, the speed of the vehicle can be controlled in accordance with the accelerator operation.

  Further, hereinafter, the control in the present embodiment will be described from the viewpoint of how to control the absorption torque of the HST pump when the accelerator operation amount or the engine rotation speed is in any state. The HST controller 15 controls the maximum absorption torque of the HST pump 23 as follows (11) to (14).

  (11) When the engine rotational speed is in the low speed region and the accelerator operation amount is in the small operation amount region (for example, when the driver starts the forklift while slowly depressing the accelerator pedal), the HST controller 15 In response to the accelerator operation amount, the HST pump 23 is controlled so that the maximum absorption torque of the HST pump 23 increases as the accelerator operation amount increases. As a result, the creep phenomenon is prevented, and the vehicle starts smoothly without a time lag with respect to the accelerator operation. When the accelerator operation amount is small during low-speed traveling, the speed of the vehicle can be controlled according to the accelerator operation.

  (12) When the engine speed is in the high speed region and the accelerator operation amount is in the small operation amount region (for example, while the forklift is traveling at a certain high speed, the driver removes his / her foot from the accelerator pedal). The HST controller 15 controls the HST pump 23 so that the maximum absorption torque of the HST pump 23 increases as the engine speed increases in response to the engine speed. As a result, even if the accelerator operation amount suddenly decreases during traveling at a certain high speed, the maximum absorption torque of the HST pump 23 decreases gently, so that overrun of the engine 13 is prevented.

  (13) When the engine rotational speed is in the low speed region and the accelerator operation amount is in the large operation amount region (for example, from the state where the forklift is traveling on a flat road at a certain high speed, the vehicle enters the uphill traveling Or when the driver depresses the accelerator pedal deeply and starts a forklift), the HST controller 15 responds to the engine speed and the maximum absorption of the HST pump 23 increases as the engine speed increases. The HST pump is controlled to increase the torque. As a result, when the engine rotational speed suddenly and drastically decreases during traveling at a certain high speed, the maximum absorption torque of the HST pump 23 decreases rapidly, so that it is possible to avoid applying excessive torque to the engine 13.・ Stall is prevented. In addition, when the driver depresses the accelerator pedal deeply and starts the forklift, engine stall can be prevented, and HST with a certain amount of pump absorption torque due to a sudden increase in accelerator operation amount. Since the pump 23 is controlled, the forklift can be started without time lag with respect to the accelerator operation.

  (4) When the engine speed is in the high speed region and the accelerator operation amount is in the large operation amount region (for example, when traveling at high speed and the accelerator operation amount is large), the HST controller 15 In response to this, the HST pump 23 is controlled so that the maximum absorption torque of the HST pump 23 increases as the accelerator operation amount increases. As a result, when the accelerator operation amount is large during high-speed traveling, the vehicle speed can be controlled according to the accelerator operation.

  As mentioned above, although preferred embodiment of this invention was described, this is an illustration for description of this invention, and is not the meaning which limits the scope of the present invention only to this embodiment. The present invention can be implemented in various modes different from the above-described embodiments without departing from the gist thereof. The controller 15 may perform the function, or the function of the accelerator increase rate limiting unit 15a of the HST controller 15 may be performed by the engine controller 11. Moreover, the same problem can be solved by applying the present invention not only to forklifts but also to cargo handling vehicles such as wheel loaders and crane cars. Furthermore, not only the vehicle configured to transmit the power from the engine to the drive wheels through a hydraulic power transmission device such as HST, but also requires some rotational drive through the hydraulic power transmission device. The present invention can also be applied to industrial machines configured to transmit to other types of devices.

DESCRIPTION OF SYMBOLS 1 Forklift 3 Drive wheel 5 Accelerator pedal 7 Forward / reverse switching lever 9 Output shaft 10 Power train 11 Engine controller 13 Engine 14 Rotational speed sensor 15 HST controller 15a 1st absorption torque control part 15b 2nd absorption torque control part 15c 3rd absorption torque Control unit 15d Small selection unit 15e Large selection unit 17, 18 EPC valve for HST pump 20 Pump capacity variable unit 21 HST
23 HST pump 25 HST motor 61 1st target value 62 2nd target value 63 3rd target value

Claims (10)

In a vehicle having an engine, a variable displacement hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, and a load device driven by the hydraulic motor,
Engine control means for controlling the engine in response to an accelerator operation amount;
Pump control means for controlling the hydraulic pump in response to the accelerator operation amount and the engine rotation speed,
The pump control means includes
In response to the accelerator operation amount, first absorption torque control means for determining the first target value so that the first target value of the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases. ,
Second absorption torque control means for determining the second target value so that the second target value of the maximum absorption torque of the hydraulic pump increases as the engine rotation speed increases in response to the engine rotation speed; ,
Third absorption torque control means for determining the third target value such that the third target value of the maximum absorption torque of the hydraulic pump increases as the engine rotation speed increases in response to the engine rotation speed; ,
Small selection means for selecting the smaller one of the first and second target values;
A large selection means for selecting a larger one of the target value selected by the small selection means and the third target value;
A vehicle comprising absorption torque control means for controlling the hydraulic pump so that the maximum absorption torque of the hydraulic pump becomes a target value selected by the large selection means. The vehicle according to claim 1,
The first target value is mapped to the engine rotation speed by converting the accelerator operation amount into the engine rotation speed based on a control characteristic of the engine control means, and the second and third target If a value is also mapped to the engine speed and the mapped first, second and third target values are compared,
Over the entire variable range of the engine speed,
The relationship of the second target value ≧ the first target value ≧ the third target value is established, and
In a low speed region below a predetermined value of the engine speed,
The first, second and third target values are determined so that a relationship of second target value> first target value> third target value is established.
vehicle. In the vehicle according to claim 1 or 2,
The pump control means includes
When starting the vehicle, the maximum absorption torque of the hydraulic pump is controlled according to the accelerator operation amount or the engine speed,
When the accelerator operation amount decreases from a predetermined large operation amount region to a predetermined small operation amount region while the engine is operating at the engine rotation speed within a predetermined high speed region, the hydraulic pressure is increased according to the engine rotation speed. Control the maximum absorption torque of the pump,
When the engine speed is reduced to a predetermined low speed area while the engine is operating at the engine speed in the high speed area, the maximum absorption torque of the hydraulic pump is controlled according to the engine speed.
vehicle. In a vehicle having an engine, a variable displacement hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, and a load device driven by the hydraulic motor,
Engine control means for controlling the engine in response to an accelerator operation amount;
Pump control means for controlling the hydraulic pump in response to the accelerator operation amount and the engine rotation speed,
The pump control means includes
(1) In a state where the engine rotation speed is in a predetermined low speed region including a low idle state and the accelerator operation amount is constant or changes within a predetermined small operation amount region, in response to the accelerator operation amount The hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases.
(2) In a state where the engine rotation speed is in a predetermined high speed region higher than the low speed region, the accelerator operation amount is smaller than the predetermined large operation amount region and smaller than a predetermined small value including zero. In response to the engine speed, the hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases as the engine speed increases in response to the engine speed.
(3) In a state where the accelerator operation amount is in a predetermined large operation amount region that is larger than the small operation amount region, when the engine rotation speed decreases from the high speed region to the low speed region, the engine rotation speed is increased. In response, the hydraulic pump is controlled such that the maximum absorption torque of the hydraulic pump increases as the engine speed increases.
vehicle. 5. The vehicle according to claim 4, wherein the pump control means further includes:
(4) When the accelerator operation amount increases from the small operation amount region to the large operation region while the engine rotation speed is in the low speed region, the engine rotation speed is high in response to the engine rotation speed. The hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases.
(5) When the accelerator operation amount is constant or changes within the large operation amount region in a state where the engine rotation speed is in the high speed region, the larger the accelerator operation amount is in response to the accelerator operation amount. , Controlling the hydraulic pump so that the maximum absorption torque of the hydraulic pump is increased,
vehicle. In a vehicle having an engine, a variable displacement hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, and a load device driven by the hydraulic motor,
Engine control means for controlling the engine in response to an accelerator operation amount;
Pump control means for controlling the hydraulic pump in response to the accelerator operation amount and the engine rotation speed,
The pump control means includes
(1) When the engine rotational speed is in a predetermined low speed region including a low idle state and the accelerator operation amount is in a predetermined small operation amount region including zero, in response to the accelerator operation amount, The hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases.
(2) When the engine rotation speed is in a predetermined high speed region higher than the low speed region and the accelerator operation amount is in the small operation amount region, the engine rotation speed is high in response to the engine rotation speed. The hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases.
(3) When the engine rotation speed is in the low speed region and the accelerator operation amount is in a predetermined large operation amount region that is larger than the small operation amount region, the engine rotation is performed in response to the engine rotation speed. Controlling the hydraulic pump such that the maximum absorption torque of the hydraulic pump increases as the speed increases,
vehicle. 7. The vehicle according to claim 6, wherein the pump control means further comprises: (4) the accelerator operation amount when the engine rotation speed is in the high speed region and the accelerator operation amount is in the large operation amount region. In response, the hydraulic pump is controlled so that the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases.
vehicle. The vehicle according to any one of claims 1 to 7, wherein the vehicle is configured as a forklift. An engine, a variable displacement hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, a load device driven by the hydraulic motor, and controlling the engine in response to an accelerator operation amount In a pump control device for controlling the hydraulic pump for a vehicle having an engine control means for
In response to the accelerator operation amount, first absorption torque control means for determining the first target value so that the first target value of the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases. ,
Second absorption torque control means for determining the second target value so that the second target value of the maximum absorption torque of the hydraulic pump increases as the engine rotation speed increases in response to the engine rotation speed; ,
Third absorption torque control means for determining the third target value such that the third target value of the maximum absorption torque of the hydraulic pump increases as the engine rotation speed increases in response to the engine rotation speed; ,
Small selection means for selecting the smaller one of the first and second target values;
A large selection means for selecting a larger one of the target value selected by the small selection means and the third target value;
A pump control device comprising absorption torque control means for controlling the hydraulic pump so that the maximum absorption torque of the hydraulic pump becomes a target value selected by the large selection means. An engine, a variable displacement hydraulic pump driven by the engine, a hydraulic motor driven by the hydraulic pump, a load device driven by the hydraulic motor, and controlling the engine in response to an accelerator operation amount In a method for controlling the hydraulic pump for a vehicle having engine control means for
A first absorption torque control step for determining the first target value such that the first target value of the maximum absorption torque of the hydraulic pump increases as the accelerator operation amount increases in response to the accelerator operation amount; ,
A second absorption torque control step for determining the second target value such that the second target value of the maximum absorption torque of the hydraulic pump increases as the engine rotation speed increases in response to the engine rotation speed; ,
A third absorption torque control step for determining the third target value such that the third target value of the maximum absorption torque of the hydraulic pump increases as the engine rotation speed increases in response to the engine rotation speed; ,
A small selection step of selecting a smaller one of the first and second target values;
A large selection step of selecting a larger one of the target value selected by the small selection means and the third target value;
An absorption torque control step for controlling the hydraulic pump so that the maximum absorption torque of the hydraulic pump becomes a target value selected by the large selection means.

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