JP2876209B2 - Control device for continuously variable transmission - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a belt-type continuously variable transmission for a vehicle, and more particularly, to a measure for improving a poor downshift return failure to a low-speed stage during rapid deceleration. About. 2. Description of the Related Art In a continuously variable transmission of this type, it has been considered to perform speed change control so as to perform convergence satisfactorily so as not to cause overshoot, hunting, and the like, in addition to followability in a transient state. For this reason, for example, it has been proposed that the shift amount is determined by calculating the operation amount by the shift speed by using a difference between the target value of the target speed ratio and the actual value of the actual speed ratio, an element considering convergence, and the like. There is a tendency that the target value and the operation amount are further corrected and optimized according to various special running conditions, the state of the engine or the drive system, and the like. Here, at the time of deceleration, the target gear ratio is gradually increased from a state where the high gear is small, and the actual gear ratio is down-shifted so as to follow this target gear ratio in response to a decrease in the vehicle speed, etc., contrary to the case of acceleration. By the way, when the vehicle is suddenly decelerated by the brake operation during this deceleration, the change in the target gear ratio is sharp, but at a high speed stage, the line pressure is low and the differential pressure from the primary pressure is small, so that the belt has a secondary pulley side. , That is, the change in the actual gear ratio is delayed as shown in FIG. As a result, it may not be possible to return to the maximum gear ratio iL when the vehicle stops. Therefore, when starting immediately after stopping, the engine is in an idling state, the discharge amount of the oil pump is insufficient, and an upshift is performed from the vicinity of the intermediate speed ratio ip, thereby suppressing an increase in line pressure, and The belt and pulley may be damaged due to slippage. Conventionally, in the shift control of the above-described continuously variable transmission, particularly with respect to downshift control during braking,
There is a prior art of -170958. Here, it is shown that when a brake operation signal is input, the downshift is started immediately by the reduction ratio control mechanism. Problems to be Solved by the Invention Meanwhile, in the above-mentioned prior art, since the downshift is started only by the brake signal, it lacks coasting at the time of slow deceleration. Further, the downshift start point is set arbitrarily, and the downshift is not performed along the lowest speed change line, which undesirably increases the engine speed and the line pressure. SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a control device for a continuously variable transmission that promotes an increase in a shift speed of an actual gear ratio only at the time of sudden deceleration to prevent a return failure. . Means for Solving the Problems In order to achieve the above object, the present invention always applies a line pressure to a hydraulic cylinder of a secondary pulley, and supplies and discharges oil to a hydraulic cylinder of a primary pulley according to a target gear ratio. The control system for following control of the actual gear ratio has a rapid deceleration determining unit that determines based on the brake operation and the deceleration of the vehicle speed. When the rapid deceleration is determined, the secondary pressure due to the line pressure of the hydraulic cylinder of the secondary pulley is increased. It is configured to correct. According to the above configuration, in the case of rapid deceleration in which the downshift is likely to be delayed from the deceleration state during braking, the secondary pressure is corrected to the maximum together with the line pressure, for example, so that the hydraulic pressure is reduced and the downshift is performed. The differential pressure between the primary pressure and the secondary pressure increases, so that the belt between the primary pulley and the secondary pulley easily shifts to the secondary pulley side, thereby increasing the speed of shifting to the downshift. Thus, according to the present invention, it is possible to prevent a return failure by rapidly downshifting due to an increase in the shift speed during sudden deceleration. Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the overall configuration of a drive system in which a belt-type continuously variable transmission is combined with an electromagnetic clutch will be described. The engine 1 is connected to a continuously variable transmission 4 via an electromagnetic clutch 2 such as an electromagnetic powder type and a forward / reverse switching device 3, and is connected to the continuously variable transmission 4 from the continuously variable transmission 4.
The transmission gears are configured to be transmitted to drive wheels 9 via a set of reduction gears 5, output shafts 6, differential gears 7, and axles 8. The electromagnetic powder type clutch 2 has a drive member 2a on an engine crankshaft 10 and a driven member 2b having a clutch coil 2c on an input shaft 11. And clutch coil 2c
The electromagnetic powder is coupled and accumulated in the gap between the two members 2a and 2b in a chain by the clutch current flowing through the clutch, and the clutch engagement / disengagement and clutch torque are variably controlled by the coupling force. The forward / reverse switching device 3 is synchronously meshed with a gear, a hub, and a sleeve between the input shaft 11 and the transmission main shaft 12, and includes a forward position at which the input shaft 11 is directly connected to the main shaft 12, and an input shaft. And a retracted position for transmitting the rotation of the rotation 11 to the main shaft 12 in the reverse direction. The continuously variable transmission 4 includes a main shaft 12 and a sub shaft arranged in parallel with the main shaft 12.
The primary shaft 12 is provided with a primary pulley 14 having a hydraulic cylinder 14a having a hydraulic cylinder 14a and the secondary shaft 13 is similarly provided with a secondary pulley 15 having a hydraulic cylinder 15a. A drive belt 16 is wound around both pulleys 14 and 15, and both cylinders 14a and 15a are configured as a hydraulic control circuit 17. Then, a line pressure according to the transmission torque is supplied to both cylinders 14a and 15a to apply a pulley pressing force, and the primary pressure changes the ratio of the winding diameter of the drive belt 16 to the pulleys 14 and 15 to continuously change the speed. It is configured to control. Next, an electronic control system of the electromagnetic powder type clutch 2 and the continuously variable transmission 4 will be described. Engine speed sensor 19 for engine 1 and primary pulley speed sensor 2 for continuously variable transmission 4
1, a secondary pulley rotation speed sensor 22, and sensors 23 and 24 for detecting the operation status of the air conditioner and the choke. Also,
The shift lever 25 of the operation system is mechanically coupled to the forward / reverse switching device 3 and has a shift position sensor 26 for detecting each range of reverse (R), drive (D), and sporty drive (Ds). Further, the accelerator pedal 27 has an accelerator switch 28 for detecting an accelerator depression state,
A throttle opening sensor 29 is provided on the throttle valve side. The various signals of the switches and the sensors are input to the electronic control unit 20 and processed by software using a microcomputer or the like. The clutch control signal output from the electronic control unit 20 is input to the electromagnetic clutch 2 and the shift control signal and the line pressure control signal are input to the hydraulic control circuit 17 of the continuously variable transmission 4 to perform each control operation. I have. 2, the electromagnetic clutch control system and the continuously variable transmission control system of the control unit 20 will be described. First, the electromagnetic clutch control system includes a reverse excitation mode determination unit 32 to which signals in the parking (P) and neutral (N) ranges other than R, D, and Ds of the engine speed Ne and the shift position sensor 26 are input. For example, if Ne <300 rpm,
Alternatively, in the case of the P and N ranges, the mode is determined to be the reverse excitation mode, and the output determining unit 33 allows a small current to flow in a direction opposite to the normal direction. Then, the electromagnetic clutch 2 is completely released except for the residual magnetism.
An energization mode determination unit to which the determination output signal of the reverse excitation mode determination unit 32, the depression signal of the accelerator switch 28, and the vehicle speed V signal of the secondary pulley rotation speed sensor 22 are input.
The running state such as starting is determined, and this determination signal is input to the starting mode current setting unit 35, the drag mode current setting unit 36, and the direct connection mode current setting unit 37. The start mode current setting unit 35 sets the start characteristics individually in relation to the engine speed Ne and the like in the case of normal start or start using the air conditioner and choke. Then, the starting characteristics are corrected based on the travel ranges of the throttle opening θ and the vehicle speeds V, R, D, and Ds, and the clutch current is set. The drag mode current setting unit 36 determines a small drag current when the accelerator is released at a low vehicle speed in each of the R, D, and Ds ranges,
A drag torque is generated in the electromagnetic clutch 2 to reduce the play of the belt and the drive system, thereby smoothly starting the vehicle. In this mode, the current is determined to be zero current until just before the vehicle stops after the clutch in the D range is released, thereby ensuring the coasting. The direct-coupling mode current setting unit 37 determines the direct-coupling current based on the relationship between the vehicle speed V and the throttle opening θ in each of the ranges of R, D, and Ds, fully engages the electromagnetic clutch 2, and saves power in the engaged state. . The output signals of these current setting units 35, 36, and 37 are input to the output determination unit 33, and the clutch current is determined according to the instruction. Next, regarding the speed change control system of the stepless speed change control, the primary speed Np and the secondary speed Ns of the primary pulley speed sensor 21 and the secondary pulley speed sensor 22 are input to the actual speed ratio calculating unit 40, Gear ratio Actual gear ratio Is calculated. This actual gear ratio And the throttle opening θ of the throttle opening sensor 29 are input to the target primary rotational speed search unit 41, and are based on the shift pattern for each of the R, D, and Ds ranges. The target primary rotational speed _NPD is searched using the map shown in FIG. The target primary speed _NPD and the secondary speed Ns are input to the target speed ratio calculating unit 42, and the target speed ratio is is = _NPD /
Calculated by Ns. The target gear ratio is input to the target gear ratio change speed calculator 43, and the target gear ratio is
The target gear ratio change speed dis / dt is calculated from the change amount of is. And these actual gear ratios The target gear ratio is, the target gear ratio change speed dis / dt, and the coefficients K ₁ and K ₂ of the coefficient setting unit 44 are input to the gear speed calculator 45, and the gear speed di / dt is calculated as follows. In the above equation, Is the control amount of the target and actual gear ratio deviation, and dis / dt is the delay correction factor of the control system. Gear speed di / dt and actual gear ratio Is input to the duty ratio search unit 46. Here, the duty ratio D of the manipulated variable is The duty ratio D is set in the upshift and the downshift. Is searched using the map. Then, the value of the duty ratio D of the operation amount is output to the shift speed control solenoid valve 48 of the hydraulic control circuit 17 via the drive unit 47. Subsequently, a line pressure control system of the continuously variable transmission control will be described. Engine speed sensor 19, throttle opening sensor 29
And an engine torque search unit 50 to which the engine speed Ne and the throttle opening θ are inputted, and obtains the engine torque T from the torque characteristic map of θ-Ne. This engine torque T
And the actual gear ratio of the actual gear ratio calculator 40 Is input to the target line pressure setting section 51, and the required line pressure and the actual gear ratio according to the engine torque are input. The target line pressure P _Ld is determined by the product of On the other hand, the line pressure maximum value fluctuates as the pump discharge pressure changes depending on the engine speed. Has a maximum line pressure search unit 52 to input, The maximum line pressure P _Lm is obtained from the map shown in FIG. The target line pressure P _Ld and the maximum line pressure P _Lm are input to the pressure reduction value calculation unit 53, and the line pressure P _LR is calculated by the ratio of the target line pressure P _Ld to the maximum line pressure P _Lm . Five
4 to determine the duty ratio D according to the line pressure _PLR . The duty signal is output to the line pressure control solenoid valve 56 via the drive unit 55. Therefore, as a countermeasure for increasing the shift speed at the time of sudden deceleration in the above control system, the brake switch 60 for detecting the brake operation and the secondary rotation speed Ns according to the vehicle speed of the secondary pulley rotation speed sensor 22 are input, and the change per unit time is input. It has a deceleration calculation unit 61 that calculates the deceleration dNs / dt from the amount. These brake and deceleration signals are input to the rapid deceleration determination section 62, and if the deceleration is equal to or greater than a predetermined deceleration during braking, it is determined that rapid deceleration is performed. Further, a duty ratio correction unit 63 is added to the output side of the duty ratio search unit 54 of the line pressure control system, and when the rapid deceleration signal is input, the duty ratio for maximizing the line pressure for a certain period of time including after the vehicle stops. Is corrected. Next, the operation of the thus-configured control device for a continuously variable transmission will be described. First, the power corresponding to the depression of the accelerator from the engine 1 is input to the primary pulley 14 of the continuously variable transmission 4 via the electromagnetic clutch 2 and the forward / reverse switching device 3, and the drive belt 16,
The power is shifted by the secondary pulley 15 and is transmitted to the drive wheels 9 to travel. During the above-mentioned traveling, the actual gear ratio The target line pressure is set to be larger as the engine torque T is larger in the low speed stage where the value of the pressure is larger, and a duty signal corresponding to this is input to the solenoid valve 56 to generate a control pressure, and the line pressure control is performed by the averaged pressure. by, increasing the line pressure P _L. And as the gear shifts to the higher gear, the gear ratio Becomes smaller and the engine torque T also becomes smaller, so that the line pressure P _L is controlled to be reduced. Thus, the pulley pressing force corresponding to the transmission torque of the drive belt 16 is always applied. I do. The line pressure P _L is always supplied to the secondary cylinder 15a, and the shift speed is controlled by supplying and discharging oil to and from the primary cylinder 14a by a shift speed control valve (not shown) by the control pressure of the solenoid valve 48. This will be described below. First, the signals Np, Ns, and θ from the primary pulley rotation speed sensor 21, the secondary pulley rotation speed sensor 22, and the throttle opening sensor 29 are read, and the actual speed ratio is calculated by the actual speed ratio calculation unit 40 of the control unit 20. Ask for. Also, the target primary rotational speed search unit 41 uses the actual gear ratio The target primary rotational speed _{NPD is} temporarily determined by the throttle opening θ.
Is retrieved from the map, and the target speed ratio calculating section 42 calculates the target speed ratio is corresponding to the target primary rotational speed _NPD . Therefore, in the region where the primary speed is constant, the target speed ratio is the same fixed value as calculated by the Ns-θ method, but in the region where the primary speed is variable, the target speed ratio is Is set to be offset toward the lower gear, and the target speed ratio is becomes a value that changes by itself. These actual gear ratios The target gear ratio is and the value of dis /
dt, the shift speed calculating unit 4 using the coefficients K ₁ and K ₂ of the coefficient setting unit 44
In step 5, the shift speed di / dt is obtained. Then, the duty ratio search unit 46 searches the duty ratio D based on the shift speed di / dt and the actual speed ratio i. The duty signal is input to a solenoid valve 48 to generate a pulse-like control pressure, whereby the shift speed control valve is repeatedly operated at two positions of oil supply and oil discharge. Here, when the duty ratio becomes small, the operation time at the refueling position becomes longer due to the off time, and the primary cylinder
Refueling at 14a, thus upshifting. On the other hand, when the duty ratio increases, the operating time at the oil discharge position becomes longer due to the on-time, and the primary cylinder 14a is drained, thereby causing a downshift.
Since the shift speed di / dt in this case corresponds to the change in the duty ratio, the target speed ratio is and the actual speed ratio Is small, the change in the duty ratio is small and the change in the flow rate of the primary cylinder 14a is small, so that the shift speed is reduced. On the other hand, the target gear ratio is and the actual gear ratio As the deviation increases, the change in the duty ratio causes the change in the flow rate of the primary cylinder 14a to increase, and the shift speed increases. In this way, in the entire shift range of the low-speed gear and the high-speed gear, the upshift or downshift is performed while changing the shift speed, and the gear is continuously changed. Next, the operation of the downshift at the time of sudden deceleration will be described with reference to the flowchart of FIG. 3 and the characteristic diagram of FIG. First, at the time of deceleration accompanied by a brake operation, an ON signal of the brake switch 60 is input to the rapid deceleration determination unit 62 to enable determination. On the other hand, at this time, the deceleration is calculated by the sudden deceleration calculation unit 61, and is not corrected when the deceleration is slower than the set value. For this reason, in the speed change control system, the target speed ratio is gradually increased, and the primary pressure Pp of the hydraulic cylinder 14a of the primary pulley 14 decreases, so that the primary pulley 1
4, the belt 16 of the secondary pulley 15 is the secondary pulley 15
To the actual gear ratio Is also down-shifted by gradually increasing to follow.
At this time, the actual gear ratio As the pressure increases, the line pressure control system also controls the line pressure and the secondary pressure Ps of the hydraulic cylinder 15a of the secondary pulley 15 to increase. Meanwhile, when the deceleration is a sudden deceleration equal to or greater than the set value, the timer Tm sets a fixed time A as shown in FIG. 3, and the duty ratio correction unit 63 of the line pressure control system corrects the line pressure to increase. Therefore, as shown in FIG. 4, the secondary pressure Ps suddenly increases to a maximum, for example, and the pressure difference between the secondary pressure Ps and the primary pressure Pp during a decrease in the hydraulic pressure becomes much larger than the above. Therefore, the primary pulley 14, the secondary pulley 15, and the belt 16 which are wound around the primary pulley 14 for the high-speed gear are quickly shifted to the secondary pulley 15 due to the large differential pressure. Thus, during such a rapid deceleration, the target speed ratio is and the actual speed ratio are In addition to the increase in the shift speed due to the deviation from the above, the shift speed further mechanically increases due to the differential pressure between the primary pressure Pp and the secondary pressure Ps, and as shown in FIG. Is the maximum gear ratio while downshifting with a small delay Return to On the other hand, the maximum correction of the secondary pressure together with the line pressure is continued even after the vehicle stops, so that even if a large torque is input due to re-acceleration before returning, a belt slip occurs because the line pressure is sufficiently secured. The torque is transmitted without the need. Although the embodiment of the present invention has been described above, the present invention can be similarly applied to a case where the control method is different. As described above, according to the present invention, in a downshift at the time of deceleration, in the case of sudden deceleration, the differential pressure between the primary pressure and the secondary pressure mechanically promotes the increase of the shift speed. In addition, poor return of the actual gear ratio at or near the stop of the vehicle is prevented. At this time, since the line pressure has been corrected to increase, it is possible to prevent the pulley and the belt from being damaged due to the belt strip at the time of re-acceleration. Since it is only necessary to judge the sudden deceleration and to correct the increase of the line pressure, the control is easy and the line pressure control is advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram schematically showing an embodiment of a control device for a continuously variable transmission according to the present invention, FIG. 2 is a block diagram of an electronic control system, and FIG. FIG. 4 is a characteristic diagram at the time of sudden deceleration, and FIG. 5 is a characteristic diagram of a conventional example. 4 ... continuously variable transmission, 14 ... primary pulley, 14a ... hydraulic cylinder, 15 ... secondary pulley, 15a ... hydraulic cylinder, 1
6 ... belt, 48 ... shift control solenoid valve, 56 ... line pressure control solenoid valve, 60 ... brake switch, 61 ... deceleration calculation unit, 62 ... sudden deceleration determination unit, 63 ... duty ratio correction unit

Claims (1)

(57) [Claims] In the control system that constantly applies line pressure to the hydraulic cylinder of the secondary pulley, and supplies and discharges oil to the hydraulic cylinder of the primary pulley according to the target gear ratio to follow the actual gear ratio, it is determined based on the brake operation and the deceleration of the vehicle speed When the sudden deceleration is determined by the sudden deceleration determining means, the line pressure control system for controlling the line pressure is used to increase and correct the secondary pressure based on the line pressure of the hydraulic cylinder of the secondary pulley. A control device for a continuously variable transmission, comprising a correction unit.