JP2013036275A - Work machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent engine stall and improve a travelling speed during work and facilitate the restoration of an engine speed when greatly dropping, in a work machine equipped with a HST for driving a travel device.SOLUTION: The work machine includes a pressure control valve 34 for controlling a travelling primary side pressure and a control device CU for controlling the pressure control valve 34. The control device CU controls the pressure control valve 34 to create a drop characteristic line Z showing a relationship between an actual engine speed and the travelling primary side pressure when a predetermined or greater load works on an engine 29. The drop characteristic line Z is bent on its way, and has a first characteristic line part E1 which is set so that the travelling primary side pressure rapidly drops as the actual engine speed is down from a target engine speed, and a second characteristic line part E2 which is set so that the travelling primary side pressure more gently drops than that in the first characteristic line part E1 as the actual engine speed is down when the engine speed is further down.

Description

  The present invention relates to a self-propelled working machine such as a compact truck loader (CTL), a skit loader, or a backhoe.

As a self-propelled working machine, there are truck loaders described in Patent Documents 1 and 2.
This truck loader is connected by a closed circuit by an HST pump comprising a swash plate type variable displacement pump driven by an engine, and a pair of speed change oil passages, and is driven by oil discharged from the HST pump. Accordingly, an HST including an HST motor that drives the traveling device is provided.

The truck loader includes a main pump and a pilot pump driven by an engine, a work device driven by discharge oil of the main pump, and a swash plate of the HST pump by discharge oil of the pilot pump. A traveling operation device.
The working device has an arm that is vertically swung, and a bucket that is attached to the distal end side of the arm.

In the truck loader, when a load is applied to the HST motor, for example, when the truck loader is moved forward and a bucket is thrust into piled earth and sand, the load applied to the HST motor is passed through the HST pump. It is transmitted to the engine and the engine speed drops.
At this time, if the bucket is squeezed at the same time and a high load is applied to the bucket, the load acting on the main pump from the bucket is transmitted to the engine and the engine may be stalled. In order to prevent engine stall, a bleed circuit is provided for draining part of the pilot oil supplied from the pilot pump to the travel operation device through the throttle.

  By providing this bleed circuit, when the engine speed drops, the pilot pump speed decreases and the pilot pump discharge rate decreases. The ratio of oil leakage from the bleed circuit to the pilot pump discharge rate Therefore, the primary pressure of the travel operation device (this is referred to as travel primary side pressure) decreases and the pilot pressure output from the travel operation device decreases as the engine speed decreases. The swash plate angle of the HST pump is automatically adjusted so as to reduce the rotational speed (so that the swash plate returns to the neutral side), thereby reducing the engine load and preventing engine stall.

JP 2010-270527 A JP 2010-270528 A

In the conventional truck loader, when the climbing operation is performed in a state where the bucket load is excessive, there is a problem that the drop amount of the engine speed is large and the climbing speed is slow.
In order to cope with this problem, it has been considered that the primary pressure on the traveling side is rapidly decreased when the engine rotation drops. When the engine speed drops, the primary pressure on the traveling side is drastically decreased, so that the load acting on the engine from the HST pump side is reduced early and balanced at a higher actual engine speed. The speed increase due to the increase in the HST pump flow rate caused by the engine speed is greater than the speed reduction due to the HST pump flow rate decrease due to the swash plate angle decrease. As a result, the traveling speed can be improved.

However, for example, even when working with the target engine speed set to the maximum speed, if the bucket is pushed into the piled earth and the like by moving the track loader forward, the engine speed will be close to 1200 rpm. However, when the engine rotation drops so far, if the amount of decrease in the primary pressure of the running against the drop amount is large, the engine torque is insufficient and the engine rotation returns slowly, for example, it is piled up If the engine speed is low and the traveling primary side pressure is low when the bucket is pushed into the ground after being pushed into the earth and sand, etc., and the traveling primary pressure is low, there is a problem that the engine rotation is difficult to return and cannot be smoothly backed up.

  Then, this invention makes it a subject to solve the said problem.

The technical means taken by the present invention to solve the technical problems are characterized by the following points.
In the invention according to claim 1, the HST pump is composed of a swash plate type variable displacement pump driven by an engine, and the HST pump is connected to the HST pump in a closed circuit by a pair of transmission oil passages. An HST motor that drives the traveling device by being driven, a pilot pump driven by the engine, a traveling operation device that controls the swash plate of the HST pump by pilot oil discharged by the pilot pump, and the traveling operation device A pressure control valve that controls the traveling primary side pressure that is the primary side pressure, and a control device that controls the pressure control valve,
By controlling the pressure control valve by the control device, a drop characteristic line indicating a relationship between the actual engine speed and the traveling primary side pressure when a load exceeding a predetermined value is applied to the engine is generated. The first characteristic line portion that is bent in the middle and set so that the traveling primary side pressure rapidly decreases as the actual engine speed decreases from the target engine speed, and when the engine speed further decreases, And a second characteristic line portion that is set so that the traveling primary side pressure gradually falls as compared to the first characteristic line portion as the actual engine speed decreases.

  The invention according to claim 2 is characterized in that the traveling primary side pressure at the bent portion of the drop characteristic line is a pressure capable of traveling even at idling speed.

The present invention has the following effects.
According to the first aspect of the present invention, the first characteristic line portion that is set so that the traveling primary pressure rapidly decreases can prevent the engine stall when a load is applied, and can reduce the traveling speed during work. After the second characteristic line that is improved and the primary pressure on the traveling side is set so that it drops more slowly than the first characteristic line, an excessive load is applied and the engine rotation drops greatly. The engine speed can be easily restored.

  According to the second aspect of the present invention, it is possible to satisfactorily achieve prevention of engine stall and improvement of traveling speed, and a return effect of engine rotation after a large drop in engine rotation.

It is a whole side view of a truck loader. It is a side view which shows a part of track loader of the state which raised the cabin. 1 is a hydraulic circuit of a truck loader hydraulic system. It is a hydraulic circuit of a traveling system. It is a hydraulic circuit of a work system. It is a characteristic figure of engine speed-traveling primary side pressure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2, reference numeral 1 denotes a track loader exemplified as a work machine according to the present invention. The track loader 1 can travel on a machine body 2, a work device 3 attached to the machine body 2, and the machine body 2. The cabin 5 (driver protection device) is mounted near the upper front part of the airframe 2.

The airframe 2 includes a bottom wall 6, a pair of left and right side walls 7, a front wall 8, and a support frame 9 provided at the rear part of each of the left and right side walls 7, and the space between the side walls 7 is open upward. A lid member 10 that closes the rear end opening between the pair of left and right support frame bodies 9 is provided at the rear end portion of the machine body 2 so as to be freely opened and closed.
The cabin 5 has a front lower end placed on the upper end of the front wall 8 of the airframe 2, and a back and forth middle part is swingable about a support shaft 12 in the left-right direction on a support bracket 11 provided on the airframe 2. The interior of the machine body 2 can be maintained by swinging the cabin 5 upward around the support shaft 12.

A driver's seat 13 is provided in the cabin 5, and a traveling operation device 14 for operating the traveling device 4 is arranged on one side (for example, the left side) of the driver's seat 13. A work operation device 15 for operating the work device 3 is arranged on the side (for example, the right side).
The cabin 5 is covered with a roof on the upper surface, the left and right side surfaces are closed with side walls formed with a number of square holes, the upper back is covered with rear glass, and the center in the front-rear direction is closed with the bottom wall. The front side is formed in a box shape, and the front side is the entrance.

Each of the left and right traveling devices 4 includes a pair of front and rear driven wheels 16, a drive wheel 17 disposed between the front and rear driven wheels 16 and closer to the rear, and a plurality of wheels 18 disposed between the front and rear driven wheels 16. And a crawler type traveling device including an endless belt-like crawler belt 19 wound around the front and rear driven wheels 16, the drive wheels 17, and the rollers 18.
The front and rear driven wheels 16 and the rolling wheels 18 are attached to a track frame 20 attached and fixed to the airframe 2 so as to be rotatable about a horizontal axis, and the drive wheels 17 are hydraulically driven travel motors 21L, The crawler belt 19 is circulated in the circumferential direction by rotating the drive wheels 17 around the left and right axes by the travel motors 21L and 21R. Is configured to move forward and backward.

The working device 3 includes a pair of left and right arms 22 and a bucket 23 (working tool) attached to the distal end side of the arms 22.
The arms 22 are arranged on both the left and right sides of the cabin 5, and the left and right arms 22 are connected to each other by a connecting body at a midway portion on the front side.
Each of the left and right arms 22 has a first lift link 24, a second lift link 25, and a base side (rear side) at the rear upper part of the body 2 so that the distal end side of the arm 22 moves up and down on the front side of the body 2. Is supported so as to be swingable up and down.

A lift cylinder 26 composed of a double-acting hydraulic cylinder is provided between the base side of each of the left and right arms 22 and the rear lower part of the airframe 2. The arm 22 swings up and down.
A mounting bracket 27 is pivotally connected to the front end side of each of the left and right arms 22 so as to be rotatable about a left and right axis, and the back side of the bucket 23 is attached to the left and right mounting brackets 27.

A bucket cylinder 28 composed of a double-acting hydraulic cylinder is interposed between the mounting bracket 27 and the middle part on the tip side of the arm 22, and the bucket 23 swings (squeeze / dump operation) by the expansion and contraction of the bucket cylinder 28. ) Is configured to.
The bucket 23 is detachable with respect to the mounting bracket 27. By removing the bucket 23 and attaching various hydraulic attachments (hydraulic drive working tools) to the mounting bracket 27, various operations other than excavation (or Other excavation operations) can be performed.

An engine 29 is provided on the rear side on the bottom wall 6 of the body 2, and a fuel tank 30 and a hydraulic oil tank 31 are provided on the front side on the bottom wall 6 of the body 2.
A hydraulic drive device 32 that drives the left and right traveling motors 21L and 21R is provided in front of the engine 29, and first to third pumps P1, P2, and P3 are provided in front of the hydraulic drive device 32, and the right side of the airframe 2 A work device control valve 33 (hydraulic control device) is provided in the middle of the wall 7 in the front-rear direction.

Further, an accelerator pedal 53 (accelerator operation member) that increases / decreases the rotation speed of the engine 29 by a foot operation and an accelerator lever that increases / decreases the rotation speed of the engine 29 by a hand operation are provided at the front of the body 2. 54 (accelerator operating member).
The accelerator lever 54 is linked to the accelerator pedal 53 via a cable or the like. When the accelerator lever 54 is operated, the accelerator pedal 53 swings in conjunction with the operation. Further, the accelerator lever 54 can be held at a position operated by a frictional force. The accelerator pedal 53 can be stepped on from the position operated by the accelerator lever 54. When the stepping operation is released, the accelerator pedal 53 is returned to the original position before the stepping by the return spring.

On the lower side of the accelerator pedal 53, an accelerator sensor AS that detects the amount of depression of the accelerator pedal 53 (accelerator operation amount) is provided.
Next, the hydraulic system of the truck loader 1 will be described with reference to FIGS.
The first to third pumps P1, P2, and P3 are constituted by constant displacement gear pumps that are driven by the power of the engine 29.

The first pump P1 (main pump) is used to drive a hydraulic actuator of an attachment attached to the tip side of the lift cylinder 26, bucket cylinder 28 or arm 22.
The second pump P2 (pilot pump, charge pump) is mainly used for supplying control signal pressure (pilot pressure).

The third pump P3 (sub-pump) increases the flow rate of hydraulic oil supplied to the hydraulic actuator when the hydraulic actuator of the hydraulic attachment attached to the distal end side of the arm 22 is a hydraulic actuator that requires a large capacity. used.
A discharge oil path q through which the discharge oil discharged from the first pump P1 flows is connected to the discharge port of the first pump P1, and a discharge discharged from the second pump P2 to the discharge port of the second pump P2. A discharge oil passage a through which oil (pilot oil) flows is connected, and a discharge oil passage k through which discharge oil discharged from the third pump P3 flows is connected to a discharge port of the third pump P3.

The first to sixth supply paths b to g are branched from the discharge oil path a of the second pump P2, and the terminal end of the discharge oil path a of the second pump P2 is connected to the seventh supply path w. A relief valve 52 that sets the maximum pressure of the second pump P2 is connected to the downstream side of the fifth supply path f.
With reference to FIG.3 and FIG.5, the hydraulic system of a working system is demonstrated first.
The working operation device 15 includes an arm raising pilot valve 86, an arm lowering pilot valve 87, a bucket dumping pilot valve 88, a bucket squeeze pilot valve 89, and these pilot valves 86, 87, 88, 89. And a common (one) operation lever 90.

  A fifth supply path f is connected to the work operation device 15, and a work lock valve 91 including an electromagnetic two-position switching valve is provided in the fifth supply path, and the work lock valve 91 is excited. Thus, the oil discharged from the second pump P2 can be supplied to the pilot valves 86, 87, 88, 89 via the fifth supply path f. Further, when the work lock valve 91 is demagnetized, the pressure oil from the second pump P2 cannot be supplied to the pilot valves 86, 87, 88, and 89, and the work operation device 15 cannot be operated.

  The work device control valve 33 controls an arm control valve 92 that controls the lift cylinder 26, a bucket control valve 93 that controls the bucket cylinder 28, and an attachment hydraulic actuator attached to the tip side of the arm 22. SP control valve 94, and each control valve 92, 93, 94 is a pilot-type direct acting spool type three-position switching valve.

The arm control valve 92, the bucket control valve 93, and the SP control valve 94 are connected to the discharge oil path q of the first pump P1 so as to constitute a series circuit, and the discharge oil of the first pump P1 is lifted. Each cylinder 26, bucket cylinder 28, or attachment hydraulic actuator can be supplied.
The operation lever 90 of the work operation device 15 can be tilted from the neutral position in an oblique direction between front and rear, left and right, front and rear, and left and right. By operating the operation lever 90 to tilt, each operation lever 90 of the work operation device 15 is operated. The pilot valves 86, 87, 88 and 89 are operated, and a pilot pressure proportional to the operation amount from the neutral position of the operation lever 90 is output from the operated pilot valves 86, 87, 88 and 89.

In the present embodiment, when the operation lever 90 is tilted rearward (in the direction of arrow B1 in FIG. 5), the arm raising pilot valve 86 is operated, and the arm control valve 92 is operated in the direction in which the lift cylinder 26 is extended. Then, the arm 22 is raised at a speed proportional to the tilting amount of the operation lever 90.
When the operation lever 90 is tilted forward (in the direction of arrow B2 in FIG. 5), the arm lowering pilot valve 87 is operated to operate the arm control valve 92 in a direction to reduce the lift cylinder 26, and the operation lever 90 is tilted. The arm 22 is lowered at a speed proportional to the amount.

When the operation lever 90 is tilted to the right (in the direction of arrow B3 in FIG. 5), the bucket dump pilot valve 88 is operated to operate the bucket control valve 93 in the direction in which the bucket cylinder 28 is extended. The bucket 23 dumps at a speed proportional to the amount of tilt.
When the operation lever 90 is tilted to the left (in the direction of arrow B4 in FIG. 5), the bucket squeeze pilot valve 89 is operated, the bucket control valve 93 is operated in a direction to reduce the bucket cylinder 28, and the operation lever 90 The bucket 23 squeezes at a speed proportional to the amount of tilt.

Further, when the operation lever 90 is tilted in an oblique direction, a combined operation of the raising or lowering operation of the arm 22 and the squeeze or dumping operation of the bucket 23 can be performed.
A pair of hydraulic oil supply / discharge joints 71a and 71b of a joint unit 71 for connecting a hydraulic hose is connected to the SP control valve 94 via a hydraulic line, and a hydraulic hose or the like is connected to the joints 71a and 71b. By connecting the hydraulic actuator of the attachment via the attachment, the attachment can be operated by the SP control valve 94.

The joint unit 71 is provided with a drain joint 71c.
The SP control valve 94 can be operated by a pair of SP operation valves 79 and 80 constituted by a proportional electromagnetic pilot valve. These SP operation valves 79 and 80 are provided on the operation lever 90 of the work operation device 15. It can be operated by a slide button provided on the top side.

One SP operation valve 79 is provided in the fourth supply path d, the fourth supply path d is connected to a pressure receiving portion on one side of the SP control valve 94, and the other SP operation valve 80 is connected to the fifth supply path e. The fifth supply path e is connected to the pressure receiving portion on the other side of the SP control valve 94.
When a slide button provided on the operation lever 90 is slid to one side, an operation signal is input to the control unit CU, and a command signal is output from the control unit CU to one SP operation valve 79. A pilot pressure proportional to the operation amount is output to a pressure receiving portion on one side of the SP control valve 94.

When the slide button is slid to the other side, a command signal is output from the control unit CU to the other SP operation valve 80, and the pilot pressure proportional to the operation amount is output from the other SP operation valve 80 to the other SP control valve 94. Is output to the pressure receiving part on the side.
The discharge oil passage k of the third pump P3 is connected to a high flow valve 83.
The high flow valve 83 is composed of a pilot-type two-position switching valve, and a non-increasing position for returning the discharge oil of the third pump P3 to the hydraulic oil tank 31 and the discharge oil of the third pump P3 via the increase oil passage n. The position can be switched to an increase position to be passed through one joint 71b, biased in a direction to be switched to a non-increase position by a spring, and switched to an increase position by a pilot pressure acting on the pressure receiving portion.

Whether or not the pilot pressure is applied to the pressure receiving portion of the high flow valve 83 is determined by a switching valve 84 made up of an electromagnetic two-position switching valve. By exciting the switching valve 84, the second branching from the fifth supply path f is performed. The pilot pressure of the 8 supply path r acts on the pressure receiving portion of the high flow valve 83, and the pilot pressure does not act on the pressure receiving portion of the high flow valve 83 by demagnetizing the switching valve 84.
Next, a traveling hydraulic system will be described with reference to FIGS.

  The traveling operation device 14 includes a forward pilot valve 36, a reverse pilot valve 37, a right turn pilot valve 38, a left turn pilot valve 39, and these pilot valves 36, 37, 38, 39, common (one) travel lever 40, first to fourth shuttle valves 41, 42, 43, 44, pump port 50 for inputting pressure oil from the second pump P2, and hydraulic oil tank 31 A tank port 51 communicating therewith.

  A second supply path c is connected to the pump port 50 of the travel operation device 14, and the discharge oil of the second pump P <b> 2 is supplied to the travel operation device 14 as pilot oil and supplied to the travel operation device 14. Pilot oil can be supplied to the primary ports of the pilot valves 36, 37, 38, 39 of the traveling operation device 14, and unused pilot oil is drained from the tank port 51.

  Each of the left and right traveling motors 21L and 21R has an angle of an HST motor 57 (traveling hydraulic motor) configured by a swash plate type variable capacity axial motor that can change speed between high and low speeds, and the swash plate angle of the HST motor 57. A swash plate switching cylinder 58 that shifts the HST motor 57 to high and low speeds by switching, a brake cylinder 59 that brakes the output shaft 57a of the HST motor 57 (the output shaft 57a of the travel motors 21L and 21R), and a flushing valve 60 And a relief valve 61 for flushing.

A seventh supply path w is connected to the swash plate switching cylinder 58, and when the pilot oil of the seventh supply path w is not acting on the swash plate switching cylinder 58, the HST motor 57 is set to the first speed state, When pilot oil in the seventh supply passage w is acting on the swash plate switching cylinder 58, the HST motor 57 is switched to the second speed state.
Whether or not pressure oil is applied to the swash plate switching cylinder 58 is determined by a cylinder switching valve 63 formed of a pilot-type two-position switching valve. The cylinder switching valve 63 is an electromagnetic wave provided in the seventh supply path w. Switching operation is performed by a two-speed switching valve 64 comprising a two-position switching valve of the type.

The brake cylinder 59 has a built-in spring for braking the output shaft 57a of the HST motor 57 and is connected to a sixth supply path g. The brake is composed of an electromagnetic two-position switching valve provided in the sixth supply path g. Excitation of the release valve 65 causes the pilot oil in the sixth supply path g to act on the brake cylinder 59 to release the braking of the output shaft 57a of the HST motor 57.
The hydraulic drive device 32 includes a drive circuit 32A (left drive circuit) for the left travel motor 21L and a drive circuit 32B (right drive circuit) for the right travel motor 21R.

  Each drive circuit 32A, 32B includes an HST pump (travel hydraulic pump) 66 connected in a closed circuit to the HST motor 57 of the corresponding travel motor 21L, 21R by a pair of speed change oil paths h, i, and a high-pressure side When the pressure in the speed change oil passages h, i exceeds the set value, the high pressure relief valve 67 that escapes to the low pressure side oil passages h, i and the pressure oil from the second pump P2 through the check valve 68 And a charging circuit j for replenishing the shifting oil passages h and i.

The HST pump 66 of each drive circuit 32A, 32B is a swash plate type variable displacement axial pump driven by the power of the engine 29, and a pilot type hydraulic pump (swash plate type) in which the angle of the swash plate is changed by the pilot pressure. Variable displacement hydraulic pump).
That is, the HST pump 66 includes a forward pressure receiving portion 66a to which a pilot pressure acts and a reverse pressure receiving portion 66b, and the angle of the swash plate is changed by the pilot pressure acting on the pressure receiving portions 66a and 66b. The oil discharge direction and the discharge amount are changed, so that the rotation output of the traveling motors 21L and 21R is steplessly changed in the direction in which the track loader 1 is moved forward (forward rotation direction) or the direction in which the track loader 1 is moved backward (reverse rotation direction). It is configured to be able to shift.

The first supply path b is connected to each charge circuit j, and the discharge oil of the second pump P2 can be supplied to each charge circuit j. The right drive circuit 32B is provided with a charge relief valve 78 for setting the circuit pressure of the charge circuit j of each of the drive circuits 32A and 32B.
The flushing valve 60 of the travel motors 21L, 21R is switched by the pressure of the high pressure side shifting oil passages h, i to connect the low pressure side shifting oil passages h, i to the flushing relief oil passage m. A part of the hydraulic fluid in the low-pressure side shifting oil passages h, i through the flushing relief oil passage m in order to replenish the operating oil in the side shifting oil passages h, i. It escapes to the oil reservoir inside. The flushing relief valve 61 is interposed in the flushing relief oil passage m.

The HST motor 57 and the flushing valve 60 of the travel motors 21L and 21R, the drive circuits 32A and 32B, and the pair of speed change oil passages h and i constitute a separate HST (hydrostatic transmission).
The travel lever 40 of the travel operation device 14 can be tilted from the neutral position in an oblique direction between front and rear, left and right, front and rear, left and right, and each pilot of the travel operation device 14 is operated by tilting the travel lever 40. The valves 36, 37, 38, 39 are operated, and a pilot pressure proportional to the operation amount from the neutral position of the travel lever 40 is output from the secondary port of the operated pilot valves 36, 37, 38, 39. It is configured to be.

  When the traveling lever 40 is tilted forward (in the direction of arrow A1 in FIG. 4), the forward pilot valve 36 is operated to output pilot pressure from the pilot valve 36, and the pilot pressure is output from the first shuttle valve 41. It acts on the forward pressure receiving portion 66a of the HST pump 66 of the left drive circuit 32A via the first flow path 46, and from the second shuttle valve 42 to the forward pressure receiving portion 66a of the right drive circuit 32B via the second flow path. Works. As a result, the output shafts 57a of the left and right traveling motors 21L, 21R rotate forward (forward rotation) at a speed proportional to the tilting amount of the traveling lever 40, and the track loader 1 moves straight forward.

  When the traveling lever 40 is tilted rearward (in the direction of arrow A2 in FIG. 4), the reverse pilot valve 37 is operated and pilot pressure is output from the pilot valve 37. The pilot pressure is the third shuttle valve. 43 acts on the reverse pressure receiving portion 66b of the HST pump 66 of the left drive circuit 32A via the third flow path 48 and from the fourth shuttle valve 44 via the fourth flow path to the HST pump 66 of the right drive circuit 32B. It acts on the reverse pressure receiving portion 66b.

As a result, the output shafts 57a of the left and right traveling motors 21L and 21R are reversely rotated (reversely rotated) at a speed proportional to the tilting amount of the traveling lever 40, and the track loader 1 moves straight forward.
Further, when the traveling lever 40 is tilted to the right (in the direction of arrow A3 in FIG. 4), the right turn pilot valve 38 is operated and pilot pressure is output from the pilot valve 38, and the pilot pressure is the first shuttle. The valve 41 acts on the forward pressure receiving portion 66a of the HST pump 66 of the left drive circuit 32A through the first flow path 46, and the HST of the right drive circuit 32B from the fourth shuttle valve 44 through the fourth flow path 49. It acts on the reverse pressure receiving portion 66b for the backward movement of the pump 66.

As a result, the output shaft 57a of the left traveling motor 21L rotates in the forward direction and the output shaft 57a of the right traveling motor 21R rotates in the reverse direction, so that the track loader 1 turns to the right.
When the traveling lever 40 is tilted to the left (in the direction of arrow A4 in FIG. 4), the left turn pilot valve 39 is operated to output pilot pressure from the pilot valve 39, and the pilot pressure is the second shuttle valve. 42 acts on the forward pressure receiving portion 66a of the HST pump 66 of the right drive circuit 32B via the second flow path 47, and from the third shuttle valve 43 via the third flow path 43, the HST pump of the left drive circuit 32A. 66 acts on the reverse pressure receiving portion 66b.

As a result, the output shaft 57a of the right traveling motor 21R rotates in the forward direction and the output shaft 57a of the left traveling motor 21L rotates in the reverse direction so that the track loader 1 turns to the left.
Further, when the travel lever 40 is tilted in the oblique direction, the output shafts of the travel motors 21L and 21R are generated by the differential pressure between the pilot pressures acting on the forward pressure receiving portion 66a and the reverse pressure receiving portion 66b of the drive circuits 32A and 32B. The rotational direction and rotational speed of 57a are determined, and the truck loader 1 turns right or left while moving forward or backward.

In other words, when the travel lever 40 is tilted to the left and forward, the track loader 1 turns left at a speed corresponding to the tilt angle of the travel lever 40, and when the travel lever 40 is tilted to the right and forward, the travel lever 40 is moved. When the track loader 1 turns right while moving forward at a speed corresponding to the tilt angle, and the travel lever 40 is tilted to the left rear side, the track loader 1 moves backward at a speed corresponding to the tilt angle of the travel lever 40. When turning left and tilting the traveling lever 40 to the right rear side, the truck loader 1 turns right while moving backward at a speed corresponding to the tilting angle of the traveling lever 40.

  The first to fourth flow paths 46 to 49 are respectively provided with shock reducing throttles 77, and supply of pilot oil from the traveling operation device 14 to the forward pressure receiving portion 66a and the reverse pressure receiving portion 66b of the HST pump 66 or Since the return of the pilot oil from the forward pressure receiving portion 66a and the reverse pressure receiving portion 66b is performed via the shock mitigation throttle 77, rapid fluctuations in the vehicle speed are prevented.

  The engine 29 is operated by the accelerator pedal 53 or the accelerator lever 54 from the idling rotation (1150 rpm) at which the operation amount of the accelerator operation members 53, 54 is 0, and the maximum rotation of the accelerator operation members 53, 54. The number of revolutions can be increased to (2480 rpm), and by increasing the number of revolutions of the engine 29, the number of revolutions of the HST pump 66 is increased, the discharge amount of the HST pump 66 is increased, and the traveling speed is increased.

  In this embodiment, a common rail type electronically controlled fuel supply unit SU is provided, and fuel is supplied to the engine 29 by the electronically controlled fuel supply unit SU. This electronically controlled fuel supply unit SU includes a common rail made of a cylindrical tube for storing fuel, a supply pump for supplying high pressure fuel in the fuel tank 30 to the common rail, and a high pressure fuel stored in the common rail for cylinders of the engine 29. And an ECU for controlling the fuel injection amount of the injector.

An accelerator sensor AS that detects the amount of operation of the accelerator pedal 53 and a rotation sensor RS that detects the actual rotational speed of the engine 29 (actual engine rotational speed) are connected to the controller ECU via a transmission path. Detection signals from the accelerator sensor AS and the rotation sensor RS are input to the controller ECU.
Then, based on the detection signals of the accelerator sensor AS and the rotation sensor RS, the engine 29 rotates according to the operation amount of the accelerator pedal 53 or the accelerator lever 54 (determined by the accelerator operation members 53 and 54) (target engine). The fuel injection amount of the injector is controlled by the controller ECU so that the rotational speed becomes equal to the rotation speed).

In the second supply path c, a pressure control valve 34 for controlling a pilot pressure (primary pressure of each pilot valve 36, 37, 38, 39 of the traveling operation device 14) supplied to the traveling operation device 14 is interposed. Has been. The pressure control valve 34 is constituted by an electromagnetic proportional valve, and the hydraulic system includes a control unit CU that controls the pressure control valve 34.
The proportional solenoid 34a of the pressure control valve 34 is connected to the control unit CU via a transmission line, and the secondary side pressure of the pressure control valve 34 (that is, the pressure side of the pressure control valve 34 by the output current output from the control unit CU to the proportional solenoid 34a) The primary pressures of the pilot valves 36, 37, 38, 39 of the travel operation device 14 are controlled.

The control unit CU is connected to the controller ECU of the electronic control fuel supply unit SU via a transmission path, and information on the target engine speed and the actual engine speed is input from the electronic control fuel supply unit SU to the control unit CU. Is done.
Next, referring to FIG. 6, the control of the primary side pressures of the pilot valves 36, 37, 38, 39 of the traveling operation device 14 by the control unit CU and the pressure control valve 34 (hereinafter simply referred to as traveling primary side pressure). Will be described.

FIG. 6 is a characteristic diagram showing the relationship between the engine speed and the travel primary side pressure (pressure characteristics of the travel primary side pressure with respect to the engine speed), where the travel primary side pressure is the vertical axis and the engine speed is The horizontal axis.
In FIG. 6, M1 indicates the idling speed (1150 rpm), and M2 indicates the maximum engine speed (2480 rpm) that is the target engine speed when the accelerator operation member (accelerator pedal 53, accelerator lever 54) is operated to the maximum. .

A characteristic line X indicates a characteristic line indicating the relationship between the engine speed of the truck loader 1 and the traveling primary pressure of the truck loader 1 of the present embodiment, and is relative to the actual engine speed (= target engine speed) when the engine 29 is not loaded. This is a characteristic line showing a change in the traveling primary pressure (this is called a no-load characteristic line).
A characteristic line Y indicates a characteristic line indicating a relationship between the traveling primary pressure and the engine speed in the conventional hydraulic system, and the actual engine speed in both the no-load state and when the engine is loaded. It is the characteristic line which showed the change of the driving | running | working primary side pressure with respect to.

  A characteristic line Z indicates a characteristic line indicating the relationship between the engine speed of the truck loader 1 of the present embodiment and the traveling primary side pressure, and the target engine speed is fixed to a predetermined speed by the accelerator operation members 53 and 54. Is a characteristic line showing a change in the primary pressure of the traveling with respect to the actual engine speed when the engine 29 is subjected to a load of a predetermined level or more and the actual engine speed drops from the target engine speed (this is referred to as a drop characteristic line). .

  In the truck loader 1 of this embodiment, the no-load characteristic line X is generated when the engine 29 is not loaded, and the drop characteristic is applied when a load exceeding a predetermined value is applied to the engine 29. The control unit CU and the pressure control valve 34 perform control to change the traveling primary pressure according to the engine speed so that the line Z is generated (therefore, no load is applied when a predetermined load or more is applied from the no load state). The time characteristic line X is switched to the drop characteristic line Z).

  As with the conventional characteristic line Y, the no-load characteristic line X is the primary pressure on the traveling side as the engine speed decreases from the maximum engine speed M2 at which the accelerator operating members 53 and 54 are operated to the maximum to the idling engine speed M1. Is set so as to gradually fall, and the traveling primary pressure at the same rotational speed is set higher than that of the conventional characteristic line Y (in FIG. 6, the no-load characteristic line X represents the conventional characteristic line). Located above line Y).

Further, the no-load characteristic line X is set so that the primary pressure on the traveling side is one step higher than that in the past near the idling speed M1.
The drop characteristic line Z1 indicates a characteristic line indicating a change in the traveling primary pressure with respect to the actual engine speed when the engine speed is dropped when the target engine speed is the maximum engine speed M2, and the drop characteristic line Z2 is When the target engine speed is 2000 rpm, a characteristic line showing a change in the primary pressure of traveling with respect to the actual engine speed when the engine speed is dropped is shown. A drop characteristic line Z3 is shown when the target engine speed is 1500 rpm. A characteristic line showing a change in traveling primary pressure with respect to an actual engine speed when the engine speed is dropped is shown. A drop characteristic line Z4 is when the engine speed is dropped when the target engine speed is the idling speed M1. Of the change in the primary pressure of the vehicle with respect to the actual engine speed It is shown.

The drop characteristic lines Z1 to 4 illustrated in FIG. 6 exemplify the drop characteristic lines when the target engine speed is the maximum engine speed M2, 2000 rpm, 1500 rpm, or the idling engine speed M1. Z exists for each target engine speed from idling speed M1 to max speed M2.
Therefore, the drop characteristic line Z exists steplessly from the idling speed M1 to the maximum speed M2, and when the accelerator operation members 53 and 54 are operated, the drop characteristic line Z corresponds to the drop characteristic line Z corresponding to the target engine speed at the operated position. Controlled to switch. Further, the drop characteristic line Z is continuously changed during the operation of the accelerator operation members 53 and 54 (continuously switches).

Each drop characteristic line Z is bent in the middle part (the drop characteristic line Z has an inclination of the characteristic line in the middle part), and the characteristic line in the region where the engine speed is higher than the bent part D A first characteristic line portion E1 which is a portion and a second characteristic line portion E2 which is a characteristic line portion in a region where the engine speed is lower than the bent portion D.
In the example shown in the figure, the drop characteristic line Z is bent at an angle (obtuse angle) at the bent portion D (although the bent portion D is square), but the drop characteristic line Z is curved at the bent portion D. (The bent portion D may be curved).

The first characteristic line E1 is set so that the traveling primary side pressure drops more rapidly than the no-load characteristic line X as the actual engine speed decreases from the target engine speed to the bent portion D (first). The difference between the traveling primary pressure of the first characteristic line portion E1 and the traveling primary pressure of the no-load characteristic line X gradually increases as the actual engine speed decreases).
The second characteristic line portion E2 is set so that the traveling primary side pressure gradually falls as compared to the first characteristic line portion E1 as the actual engine speed decreases from the bent portion D.

Note that the first characteristic line portion E1 and the second characteristic line portion E2 of the drop characteristic line Z in the illustrated example are linear with the inclination of the first characteristic line portion E1 larger than the inclination of the second characteristic line portion E2. However, the first characteristic line portion E1 and the second characteristic line portion E2 may have a curved shape substantially along the first characteristic line portion E1 and the second characteristic line portion E2 in the figure.
In the present embodiment, the drop characteristic line Z1 when the target engine speed is the maximum engine speed M2 is experimentally obtained, and the drop characteristic line Z1 at the maximum engine speed M2 is used as a reference drop characteristic line. The other drop characteristic lines (drop characteristic lines Z2, Z3, Z4 and other drop characteristic lines not shown) are generated by translating the drop characteristic line Z1 along the horizontal axis. Therefore, the inclination of the first characteristic line portion E1 of each drop characteristic line Z is the same, the inclination of the second characteristic line portion E2 of each drop characteristic line Z is also the same, and the bent characteristic D of each drop characteristic line Z is The traveling primary side pressure is the same pressure.

In the present embodiment, the load acting on the engine 29 is detected by calculating the difference between the target engine speed and the actual engine speed in the control unit CU (with respect to the target engine speed). If the actual engine speed is low, it is judged that the load is acting).
Then, when there is no load, the pressure control valve 34 is controlled so that the traveling primary side pressure with respect to the actual engine speed determined by the characteristic line X is reached, and when a predetermined load or more is detected, the drop characteristic line Z The pressure control valve 34 is controlled so that the primary pressure on the traveling side with respect to the actual engine speed determined in step S1 is reached. That is, the characteristic line of the traveling primary side pressure with respect to the actual engine speed is switched between when there is no load and when a load exceeding a predetermined value is applied.

  As described above, the no-load characteristic line X is generated so that the traveling primary pressure with respect to the actual engine speed is higher than in the prior art. For example, the working device 3 is not working, and the climbing slope The speed of traveling is improved in the state where a large load such as is not applied, and in particular, the traveling primary side pressure is set to be one step higher than the conventional high engine speed range near the idling rotation M1. The traveling speed is increased when idling.

Further, when the engine 29 is subjected to a load exceeding a predetermined value, as shown by the first characteristic line portion E1 of the drop characteristic line Z, the traveling primary side pressure is rapidly (largely) decreased as the actual engine speed drops. I am letting.
As a result, it is possible to increase the running speed by preventing the engine from stalling and stabilizing the actual engine speed to a higher level when the engine speed drops.

  That is, by reducing the traveling primary side pressure when the engine rotation drops, the pilot pressure (traveling secondary side pressure) output from the traveling operation device 14 decreases, thereby reducing the rotational speed. The swash plate angle of the HST pump 66 is adjusted (so that the swash plate returns to the neutral side), thereby reducing the load acting on the engine 29 and preventing the engine 29 from stalling.

  Further, when the engine speed drops, the primary pressure on the traveling side is drastically decreased, so that the load acting on the engine 29 from the HST pump 66 side is reduced early, whereby, for example, the target engine speed is set to a maximum. When the actual engine speed drops at the time of the rotation M2, what was conventionally balanced at 1500 rpm can be balanced at a higher actual engine speed of 2200 rpm.

  Since the speed increase due to the increase in the flow rate of the HST pump 66 caused by the engine speed is larger than the speed reduction due to the decrease in the flow rate of the HST pump 66 accompanying the swash plate angle reduction, the actual engine when the engine rotation drops By stabilizing the rotational speed at a high level, the flow rate of the HST pump 66 is secured at a high level, and the traveling speed can be improved in total. Further, if the load acting on the engine 29 from the HST pump 66 side is reduced earlier, the load can be kept at a higher torque.

Thereby, the traveling speed in a work in which a large load acts on the engine 29 can be improved. For example, the traveling speed (climbing speed) is improved when the climbing work is performed in a state where the load of the bucket 23 is excessive. be able to.
As described above, in the present embodiment, by controlling the pressure control valve 34 by the control unit CU to electronically control the traveling primary side pressure, there is no load and when a load exceeding a predetermined value is applied. The characteristic line of the traveling primary pressure with respect to the actual engine speed can be switched. As a result, the traveling primary pressure at no load can be set higher to improve the traveling speed, and when the load more than a predetermined value is applied, the traveling speed is improved while preventing engine stall. be able to.

  Also, for example, even when the accelerator pedal 53 is depressed and the target engine speed is set to the maximum engine speed M1, the truck 23 is moved forward and the bucket 23 is thrust into the piled earth or the like. The actual engine speed drops to around 1200 rpm, but when the actual engine speed drops to that point, if the slope of the drop characteristic line Z is large (the amount of decrease in traveling primary pressure relative to the drop amount is If large, the torque of the engine 29 is insufficient and the actual engine speed returns slowly. And, for example, when the bucket 23 is thrust into piled earth and sand, and when trying to come out at the back, if the actual engine speed is low and the traveling primary side pressure is also low, the actual engine speed is difficult to return. It will not be possible to back smoothly.

Therefore, the drop characteristic line Z is bent in the middle so that the actual engine speed can be easily recovered after the engine rotation has dropped greatly, so that the slope of the second characteristic line part E2, which is an excessive drop area, is increased. The slope is gentler than the slope of the first characteristic line portion E1, and the amount of decrease in the traveling primary pressure with respect to the drop amount is reduced when the load is high.
This makes it easier for the actual engine speed to recover after the engine speed drops extremely large. When the bucket 23 is pushed into the piled earth and sand, etc., when it is about to come out, it quickly returns. be able to.

If the traveling primary pressure at the bent portion D is too high, the above-described effect of improving the traveling speed in the climbing operation when the bucket load is excessive will not be obtained, and if it is too low, the engine rotation will drop greatly. Since the effect of returning the actual engine speed later cannot be obtained, in this embodiment, the traveling primary pressure at the bent portion D is set to a pressure (predetermined pressure) at which the vehicle can travel even at the idling engine speed M1. Specifically, it is set to 14 kg / m ² .

That is, the second characteristic line portion E2 having a gentle slope is generated based on the traveling primary pressure that can be traveled even at the idling speed M1, and the travel is performed even at the idling speed M1 even if the engine speed drops greatly. The primary pressure on the traveling side does not drop much more than the pressure that can be used.
In the present embodiment, the engine speed has a low-rotation characteristic line G in a low-speed region where the engine speed is less than the idling speed M1.

The low-rotation characteristic line G is generated so as to extend from the idling rotation-side end portion of the no-load characteristic line X, and is generated so that the traveling primary side pressure decreases as the engine speed decreases.
Further, each drop characteristic line Z intersects with the low speed characteristic line G, and the low primary speed characteristic line G is a portion where each drop characteristic line Z intersects, and the traveling primary side pressure increases as the engine speed decreases. It is set so as to drop larger (rapidly) than the second characteristic line portion E2.

In a state where the target engine speed is the idling speed M1 (a state where the accelerator operating members 53 and 54 are not operated), when the traveling lever 40 is operated and a load exceeding a predetermined value is applied, the characteristic line becomes a drop characteristic. Switching to the line Z4 controls the traveling primary pressure, but if the engine speed is low and the traveling primary pressure is high, it becomes easy to stall.
Therefore, in order to prevent engine stall when the target engine speed is the idling engine speed M1, when the drop characteristic line Z4 intersects the low speed characteristic line G, the characteristic line switches to the low speed characteristic line G and travels. The primary pressure is controlled.

Similarly, when the traveling primary pressure is controlled by the other drop characteristic line Z, if the drop characteristic line Z intersects the low rotation characteristic line G, the characteristic line becomes the low rotation characteristic line G. The primary side pressure of the traveling is controlled by switching.
In the present embodiment, as described above, the drop characteristic line Z exists for each target engine speed, and when the accelerator operation is performed (when the accelerator pedal 53 or the accelerator lever 54 is operated), the target engine speed that is operated by the accelerator is determined. However, since the drop characteristic line Z is continuously switched during the accelerator operation, the operation feeling of the accelerator operation is good.

  Also, when the accelerator operation is performed, if the drop characteristic line Z corresponding to the target engine speed after the accelerator operation is switched instantaneously according to the accelerator operation, there is a sense of incongruity of the operation or a shock. Control is performed to delay the switching speed of the characteristic line Z (a time lag is provided between the accelerator operation and switching of the drop characteristic line).

  That is, for example, when the accelerator operation is performed so that the target engine speed is 1500 rpm, when the actual engine speed is dropping to 1000 rpm, the target engine speed is increased to 2000 rpm by the accelerator operation. In this case, the drop characteristic line is switched from Z3 to Z2. At this time, the drop characteristic line is changed from Z3 to Z2 while there is a response delay (time lag) in response to the accelerator operation when the actual engine speed increases. When switching instantaneously, the traveling primary side pressure temporarily decreases to a pressure in the vicinity of 1000 rpm of the drop characteristic line Z2 before the actual engine speed increases. That is, a phenomenon occurs in which the primary pressure on the traveling side temporarily decreases while the engine speed is being increased, and the operator feels uncomfortable or feels shock.

  Conversely, when the accelerator operation is performed so that the target engine speed is 2000 rpm, when the actual engine speed is dropping to 1000 rpm, the target engine speed is decreased to 1500 rpm by the accelerator operation. In this case, when the drop characteristic line is instantaneously switched from Z2 to Z3, a phenomenon occurs in which the traveling primary pressure temporarily decreases.

  Therefore, in the present embodiment, when the accelerator operation is performed, the switching speed of the drop characteristic line Z is delayed with respect to the accelerator operation so as to synchronize with the increase speed or the decrease speed of the engine speed ( In other words, when the accelerator operation members 53 and 54 are operated, the drop characteristic line Z before the operation of the accelerator operation members 53 and 54 is matched with the response delay of the engine speed with respect to the operation of the accelerator operation members 53 and 54. The speed of switching to the drop characteristic line Z after the operation of the accelerator operation members 53 and 54 is delayed).

As a result, the switching speed of the drop characteristic line Z when the accelerator operation is performed matches the increase speed or the decrease speed of the engine speed, and the traveling speed smoothly increases or decreases according to the accelerator operation. 54, the operation feeling becomes good.
The switching speed of the drop characteristic line Z has been experimentally determined. When the responsiveness of the engine speed is considered to be considerably slow with respect to the accelerator operation, for example, the time when the engine speed increases when the accelerator operation is performed while the bucket 23 is climbing while applying an excessive load or In the present embodiment, the switching speed of the drop characteristic line Z is determined so as to match the time to decrease, and in this embodiment, when increasing from any target engine speed to any target engine speed The switching speed of the drop characteristic line Z is constant, and the switching speed of the drop characteristic line Z is constant even when any target engine speed is reduced to any target engine speed. .

However, since the responsiveness of the engine speed is different between the case where the accelerator operation is performed to increase the engine speed and the case where the accelerator operation is performed to decrease the engine speed, the engine speed is decreased compared to the case where the engine speed is increased. In some cases, the switching speed of the drop characteristic line Z is changed.
Since the load on the engine 29 is relatively lighter when the engine speed is decreased than when the engine speed is increased, the drop is caused when the accelerator operation members 53 and 54 are operated in the direction of increasing the engine speed. The speed at which the drop characteristic line Z is switched when the accelerator operation members 53 and 54 are operated in the direction of decreasing the engine speed is set higher than the speed at which the characteristic line Z is switched.

In the present embodiment, when the actual engine speed is higher than the target engine speed determined by the accelerator operation members 53 and 54, the traveling primary pressure set by the no-load characteristic line X is controlled. .
The present invention includes a traveling device 3 that is operated by a hydraulic motor that is driven by discharge oil of a hydraulic pump that is driven by an engine 29, and a work device that is driven by discharge oil of a hydraulic pump that is driven by the engine 29. The self-propelled working machine provided, for example, a working machine such as a backhoe can also be employed.

4 traveling device 14 traveling operation device 29 engine 34 pressure control valve 53 accelerator pedal (accelerator operating member)
54 Accelerator lever (accelerator operating member)
57 HST motor 66 HST pump CU control unit D bent part E1 first characteristic line part E2 second characteristic line part M1 idling rotational speed M2 max rotational speed P2 pilot pump X load characteristic line Z drop characteristic line h transmission oil path i Shift oil passage

Claims (2)

An HST pump (66) composed of a swash plate type variable displacement pump driven by an engine (29), and the HST pump (66) and a pair of transmission oil passages (h, i) are connected in a closed circuit, and the HST pump An HST motor (57) that drives the traveling device (4) by being driven by oil discharged from the pump (66), a pilot pump (P2) that is driven by the engine (29), and this pilot pump (P2) The traveling operation device (14) for controlling the swash plate of the HST pump (66) by the pilot oil discharged by the pressure control valve, and the pressure control valve for controlling the traveling primary pressure which is the primary pressure of the traveling operation device (14) (34) and a control unit (CU) for controlling the pressure control valve (34),
A drop characteristic line showing the relationship between the actual engine speed and the traveling primary side pressure when a load of a predetermined level or more is applied to the engine (29) by controlling the pressure control valve (34) by the control unit (CU). (Z) is generated, and the drop characteristic line (Z) is bent halfway, and the first primary pressure is set so that the traveling primary pressure rapidly decreases as the actual engine speed decreases from the target engine speed. When the engine speed has further decreased with the characteristic line portion (E1), the primary pressure on the traveling side is set to drop more slowly than the first characteristic line portion (E1) as the actual engine speed decreases. A working machine comprising a second characteristic line portion (E2).   2. The operation according to claim 1, wherein the primary pressure on the traveling side at the bent portion (D) of the drop characteristic line (Z) is a pressure that allows traveling even at the idling rotational speed (M1). Machine.

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