JP6039967B2 - Vehicle tuck-in suppression control device - Google Patents

Description

  The present invention relates to a vehicle tack-in suppression control device that suppresses tack-in that occurs when a vehicle is turning.

  In general, in a vehicle such as an automobile, when the accelerator is turned off in a driving state with a high lateral acceleration, a cornering force on the front wheel side may increase and a tuck-in phenomenon may occur that suddenly becomes oversteered.

  For this reason, Patent Document 1 includes a torque moving mechanism that transfers torque between the left and right wheels by limiting the differential between the left and right wheels, and tack-in based on the reference lateral acceleration of the vehicle and the engine brake operation amount. When it is predicted that this will occur, a technique has been proposed in which the torque moving mechanism is controlled to increase the torque on the inner turning side, and the tack-in is appropriately suppressed without impairing the turning performance.

JP-A-7-108842

  However, the technique of Patent Document 1 is directed to a vehicle that distributes driving force to the front wheel side and the rear wheel side via a center differential by a planetary gear mechanism and includes a torque moving mechanism in the rear differential. For this reason, the driving force transmitted to the rear wheel cannot be eliminated, and not only the braking force is generated on the rear wheel during engine braking due to the accelerator off during turning, and the lateral force of the rear wheel is reduced. Since the torque on the inner ring side is increased in consideration of turning performance, the lateral force on the inner ring side is insufficient, and there is a possibility that the suppression of tack-in may be insufficient.

  The present invention has been made in view of the above circumstances, and at the time of engine braking for turning, the rear wheel side braking force is weakened and the tolerance to the inner wheel difference is reduced to increase the lateral force of the rear wheel, thereby effectively preventing tack-in. An object of the present invention is to provide a tack-in suppression control device for a vehicle that can be suppressed.

A vehicle tack-in suppression control device according to the present invention includes a center clutch that distributes driving force to a front wheel side and a rear wheel side, and left and right rear wheels interposed between a rear wheel final reduction gear and left and right rear drive shafts. A tuck-in suppression control device that suppresses the occurrence of tuck-in when a vehicle having a clutch is turned, wherein the tuck-in is performed based on the amount of change in the accelerator opening degree when turning in the all-wheel drive mode in which the center clutch is engaged. A tuck-in suppression mode determination unit that determines a state of occurrence of a tuck-in and instructs a switch to a tuck-in suppression mode that suppresses the occurrence of tuck-in. When instructed to switch to the tuck-in suppression mode, A center clutch control unit that reduces the driving force toward the rear wheels, and switches to the tack-in suppression mode. And a rear clutch control unit that increases the engagement torque of the left and right rear clutches when instructed to change, and reduces the tolerance for the inner wheel difference between the left and right rear wheels.

  According to the present invention, it is possible to weaken the braking force on the rear wheel side during engine braking during turning and reduce the tolerance for the inner wheel difference to increase the lateral force of the rear wheel, thereby effectively suppressing tuck-in.

Configuration diagram of vehicle powertrain system Explanatory drawing which shows the clutch fastening state of FWD mode Explanatory drawing which shows the clutch fastening state of AWD mode Explanatory drawing which shows the clutch fastening state of tuck-in suppression mode Explanatory drawing showing the relationship between tire longitudinal force and lateral force Tuck-in suppression control routine flowchart Characteristic diagram showing the amount of reduction in center clutch engagement torque Characteristic diagram showing the amount of increase in rear clutch engagement torque Explanatory drawing showing a decrease in center clutch engagement torque Explanatory drawing showing increase in rear clutch engagement torque

Embodiments of the present invention will be described below with reference to the drawings.
First, a vehicle powertrain system will be described. In FIG. 1, reference numeral 1 denotes an engine disposed in the front part of the vehicle. In the present embodiment, a front engine in which the driving force of the engine 1 is variably distributed between the front wheels and the rear wheels with the front wheels serving as main driving wheels. Applies to all-wheel drive (AWD) vehicles based on front drive vehicles (FF base).

  Specifically, the driving force of the engine 1 is transmitted to the transfer 3 from the automatic transmission (including a torque converter) 2 behind the engine 1 through the transmission output shaft 2a. Further, the driving force transmitted to the transfer 3 is input to a rear wheel final reduction device 7 composed of a bevel gear mechanism or the like via a rear drive shaft 4, a propeller shaft 5, and a drive pinion shaft portion 6, while a reduction drive gear. 8, the reduction driven gear 9 and the front drive shaft 10 serving as a drive pinion shaft portion are input to the front wheel final reduction gear 11. The driving force input to the front wheel final reduction gear 11 is transmitted to the left front wheel 14FL via the front wheel left drive shaft 13FL, and is transmitted to the right front wheel 14FR via the front wheel right drive shaft 13FR.

  The automatic transmission 2, the transfer 3, the front wheel final reduction gear 11 and the like are integrally provided in the case 12.

  The transfer 3 is a wet multi-plate clutch (center clutch) as a torque transmission capacity variable type clutch configured by alternately stacking a drive plate 20a provided on the reduction drive gear 8 side and a driven plate 20b provided on the rear drive shaft 4 side. ) 20 is mainly configured. The center clutch 20 is provided with a clutch piston 20c that variably applies the fastening force of the center clutch 20, and by controlling the pressing force by the clutch piston 20c, the fastening force of the center clutch 20 is varied to change the rear wheel. The driving force input to the final reduction gear 7 can be controlled, and the torque distribution ratio between the front wheels and the rear wheels can be varied.

  The driving force input to the rear wheel final reduction gear 7 is transmitted from the rear wheel left drive shaft 13RL to the left rear wheel 14RL via the left rear clutch 21RL, and also to the rear wheel right via the right rear clutch 21RR. It is transmitted from the drive shaft 13RR to the right rear wheel 14RR. The left and right rear clutches 21RL and 21RR are torque transmission capacity variable clutches similar to the center clutch 20.

  Specifically, the left rear clutch 21RL includes a drive plate 21RLa provided on the rear wheel final reduction gear 7 side, a driven plate 21RLb provided on the rear wheel left drive shaft 13RL side, and a clutch piston that applies a clutch fastening force. 21RLc. The right rear clutch 21RL includes a drive plate 21RRa provided on the rear wheel final reduction gear 7 side, a driven plate 21RRb provided on the rear wheel right drive shaft 13RR side, and a clutch piston 21RRc for applying a clutch fastening force. Yes. In these rear clutches 21RL and 21RR, the pressing force by the clutch pistons 21RLc and 21RRc is individually controlled, and the driving force transmitted to the left and right wheels is differentially limited.

  Next, an electronic control system that controls the powertrain of the vehicle will be described. The electronic control system of the power train is configured by a plurality of control units connected to a communication bus 100 such as a CAN (Controller Area Network), and the engine 1 and the automatic transmission are controlled by cooperative control via the plurality of control units. The device 2 is controlled. Each of the plurality of control units is composed mainly of a microcomputer, and includes an engine control unit (ECU) 50 that controls the engine 1, a transmission control unit (TCU) 60 that controls the automatic transmission 2, and vehicle dynamics that controls vehicle behavior. Represented by a control (VDC; Vehicle Dynamics Control) unit 70.

  These control units 50, 60, and 70 mutually exchange control information such as various calculation values and control parameter information detected by various sensors via an in-vehicle network formed by the communication bus 100, and control engine and driving force. Transmission control including control, vehicle behavior control, etc. are executed. Examples of signals input to the control units 50, 60, and 70 include sensor signals as shown below.

  Sensor signals input to the ECU 50 include signals from a crank angle sensor 51 that detects the engine speed, an accelerator sensor 52 that detects the driver's accelerator operation (accelerator pedal depression amount: accelerator opening), and the like. Further, the TCU 60 includes various ranges in the select operation unit of the automatic transmission 2 such as a parking (P) range, a reverse (R) range, a neutral (N) range, a drive (D) range, a manual (M) range, and the like. Signals such as an inhibitor switch 61 for detecting the transmission and a transmission output shaft rotation sensor 62 for detecting the rotation speed of the transmission output shaft 2a are input.

  Further, the VDC unit 70 includes wheel speed sensors 15FL, 15FR, 15RL, and 15RR that detect wheel speeds of the wheels 14FL, 14FR, 14RL, and 14RR, a steering angle sensor 71 that detects a steering angle, and a lateral acceleration of the vehicle. Signals from the lateral acceleration sensor 72 that detects the yaw rate of the vehicle and the yaw rate sensor 73 that detects the yaw rate of the vehicle are input.

  Here, the vehicle in the present embodiment can vary the torque distribution ratio between the front wheels and the rear wheels via the center clutch 20, and the FWD mode (front wheel drive mode) with the torque distribution ratio of the front and rear wheels being 100: 0. ) And 50:50 AWD mode (all-wheel drive mode) can be switched. Further, when it is determined that a tuck-in occurs during turning in the AWD mode, the operation state of the center clutch 20 and the left and right rear clutches 21RL, 21RR is controlled to switch to the tuck-in suppression mode, and the occurrence of tuck-in is determined. Suppress.

  Specifically, switching of each driving force mode (FWD mode, AWD mode, tack-in suppression mode) is performed via a clutch driving unit 65 configured by a hydraulic circuit having a plurality of solenoid valves and the like. The clutch drive unit 65 controls the hydraulic pressure supplied to the clutch pistons 20c, 21RLc, and 21RRc of each clutch in response to a command from the TCU 60, thereby changing the engaged state of the center clutch 20 and the left and right rear clutches 21RL, 21RR. , AWD mode and tuck-in suppression mode are switched.

  In the FWD mode, as shown in FIG. 2, the center clutch 20 and the rear clutches 21RL and 21RR are all released, and the power train elements between the propeller shaft 5 and the rear wheel final reduction gear 7 are separated. This FWD mode is a mode that enables fuel-saving driving with reduced friction loss and internal circulation torque.

  In the AWD mode, as shown in FIG. 3, the center clutch 20 and the rear clutches 21RL and 21RR are all operated (fastened). This AWD mode is a mode that enables stable driving by controlling the driving force of the four wheels including the vectoring effect.

  On the other hand, in the tack-in suppression mode, as shown in FIG. 4, the fastening force of the center clutch 20 is weakened (substantially released), and the rear clutches 21RL and 21RR are controlled in a direction in which the fastening force increases. This tuck-in suppression mode is switched when a situation where tuck-in is likely to occur is detected, and the occurrence of tuck-in is suppressed.

  Control of the center clutch 20 and the rear clutches 21RL and 21RR for switching between these modes is performed based on the traveling state of the vehicle and the driving operation of the driver. Hereinafter, the control in the tack-in suppression mode, which is the gist of the present invention, will be mainly described. As shown in FIG. 1, the functional configuration of the TCU 60 relating to the tack-in suppression mode includes functional units represented by a tack-in suppression mode determination unit 60a, a center clutch control unit 60b, and a rear clutch control unit 60c.

  The tack-in suppression mode determination unit 60a determines a situation where tack-in is likely to occur based on the change in accelerator opening, and instructs switching to the tack-in suppression mode. In the present embodiment, determination is made based on the accelerator opening change amount ΔACC in the accelerator return direction of the accelerator opening degree ACC detected by the accelerator sensor 52, and the accelerator opening change amount ΔACC exceeds a preset threshold value Hc. The center clutch control unit 60b and the rear clutch control unit 60c are instructed to switch to the tack-in suppression mode.

  Note that the determination to switch to the tack-in suppression mode based on the accelerator opening change amount ΔACC as described above may be performed when it is determined that the vehicle is turning based on a signal from the lateral acceleration sensor 72. Further, the accelerator opening change speed may be added as a determination condition to the condition based on the accelerator opening change amount ΔACC.

  The center clutch control unit 60b receives a switching instruction to the tack-in suppression mode from the tack-in suppression mode determination unit 60a, and the amount of reduction relative to the engagement torque of the center clutch 20 set according to the operation state immediately before switching to the tack-in suppression mode. Set. And the fastening torque of the center clutch 20 is reduced via the clutch drive part 65, and the torque transmission to the rear-shaft side is reduced.

  The amount of reduction with respect to the engagement torque of the center clutch 20 is set based on the lateral acceleration of the vehicle and the vehicle speed (average value of the wheel speeds of the four wheels), and is controlled in a direction in which torque transmission between the front and rear axes by the center clutch 20 is divided. By doing so, the braking force of the rear wheel is brought close to 0 so that the lateral force of the rear wheel can be used more. In other words, the braking force generated by the engine brake is mainly generated only on the front wheels, and the tuck-in is suppressed by increasing the lateral force margin of the rear wheels.

  FIG. 5 shows the relationship between the longitudinal force (horizontal axis) and lateral force (vertical axis) of the tire for each slip angle. The greater the slip angle, the greater the change in lateral force with respect to the change in longitudinal force. Is shown. As can be seen from FIG. 5, it is possible to suppress the tuck-in by increasing the lateral force margin of the rear wheel by reducing the tire front-rear force of the rear wheel by reducing the fastening force of the center clutch 20 during turning. Become.

  At the same time, the rear clutch control unit 60c receives an instruction to switch to the tack-in suppression mode and sets an increase amount with respect to the engagement torque immediately before switching the rear clutches 21RL and 21RR to the tack-in suppression mode. In the present embodiment, the same increase amount is set for the left and right rear clutches 21RL and 21RR, and the torque transmission between the front and rear shafts by the center clutch 20 is weakened via the clutch drive unit 65, and at the same time The engagement torque of the clutches 21RL and 21RR is increased to make it difficult to allow the difference between the inner wheels of the rear wheel left and right trajectory bases (to reduce the tolerance for the inner wheel difference).

  That is, when the tack-in suppression mode determination unit 60a determines that a situation where tack-in is likely to occur is generated, the center clutch control unit 60b decreases the fastening torque of the center clutch 20 to reduce the longitudinal force of the rear wheel, and the lateral force of the rear wheel. Increase margins. At the same time, the rear clutch control unit 60c increases the engagement torque of the rear clutches 21RL and 21RR, thereby making it difficult to allow the difference between the rear wheel left and right trajectory base inner wheels.

  This increases the lateral force margin of the rear wheel by controlling the torque transmission between the front and rear shafts, and reduces the tolerance for the inner wheel difference between the left and right rear wheels to reduce the yaw moment in the direction opposite to the turning direction. Can be generated. As a result, tuck-in can be effectively suppressed by canceling entrainment during turning.

  The processing related to the tuck-in suppression mode is specifically realized by the program processing shown in the flowchart of FIG. Hereinafter, the tack-in suppression control routine shown in the flowchart of FIG. 6 will be described.

  In this tuck-in suppression control routine, first, in the first step S1, the accelerator opening change amount ΔACC in the accelerator return direction of the accelerator opening ACC detected by the accelerator sensor 52 is set to a threshold value Hc (for example, with respect to 100% of the accelerator fully open) It is examined whether or not the amount of accelerator return (exceeding 60 to 70% in running on a dry road) is exceeded. As a result, if ΔACC ≦ Hc, the routine is exited, and if ΔACC> Hc, the process proceeds from step S1 to step S2 and subsequent steps in order to switch to the tack-in suppression mode. In the processing after step S2, in steps S2 and S3, a reduction amount ΔTC with respect to the engagement torque of the center clutch 20 and an increase amount ΔTR with respect to the engagement torque of the rear clutches 21RL and 21RR are set.

  The reduction amount ΔTC of the engagement torque of the center clutch 20 is obtained by averaging the lateral acceleration Gy (absolute value) detected by the lateral acceleration sensor 72 and the wheel speeds of the four wheels detected by the wheel speed sensors 15FL, 15FR, 15RL, and 15RR, respectively. Is set based on the vehicle speed V obtained in this way. The engagement torque reduction amount ΔTC using the lateral acceleration Gy and the vehicle speed V as parameters is set to a characteristic as shown in FIG. 7, for example, and the engagement torque of the center clutch 20 is referred to by referring to a map of such a characteristic. A reduction amount ΔTC is set.

  In the example shown in FIG. 7, as the lateral acceleration Gy increases and the vehicle speed V increases, that is, as the vehicle travels on a traveling path with a high curvature and a small radius of curvature, the center clutch 20 approaches the disengaged state (for example, the tightening torque is substantially reduced). 0 to 5Nm), the lateral force margin is increased by reducing the longitudinal force of the rear wheels. On the other hand, in the situation where the lateral acceleration Gy is small and the vehicle speed V is low, that is, the vehicle is traveling on a traveling path with a low curvature and a large radius of curvature, the influence of tuck-in is small. The fastening torque will be slightly weakened when not switched.

  Similarly, the increase amount ΔTR of the engagement torque of the rear clutches 21RL and 21RR is the absolute value of the lateral acceleration Gy detected by the lateral acceleration sensor 72 and the four wheels detected by the wheel speed sensors 15FL, 15FR, 15RL, and 15RR, respectively. Is set based on the average value (vehicle speed) V of the wheel speeds. FIG. 8 shows a characteristic example of the increase amount ΔTR of the engagement torque using the lateral acceleration Gy and the vehicle speed V as parameters, and referring to a map of such characteristics, the engagement torque of the rear clutches 21RL and 21RR is shown. An increase amount ΔTR is set.

  In the example shown in FIG. 8, the engagement torque of the rear clutches 21RL and 21RR is increased as the lateral acceleration Gy is larger and the four-wheel wheel speed average value V is higher, that is, as the vehicle travels on a traveling road with a higher curvature radius. Increase the yaw moment, which makes it difficult to allow the difference between the inner wheels of the left and right rear wheels and cancels the entrainment when turning. On the contrary, in the situation where the lateral acceleration Gy is smaller and the four-wheel wheel speed average value V is lower, that is, in a situation where the vehicle travels on a traveling path with a low curvature and a large curvature radius, the influence of tuck-in is small. The increase amount of the fastening torque is reduced and maintained in a direction allowing the inner wheel difference between the left and right rear wheels.

  Thereafter, the process proceeds to step S4, where the engagement torque of the center clutch 20 is reduced by a reduction amount ΔTC from the engagement torque TC corresponding to the normal operation state (AWD mode), and the engagement torques of the left and right rear clutches 21RL, 21RR are reduced. Each is switched to the tack-in suppression mode by increasing the fastening torques TRL and TRR according to the driving state by an increase amount ΔTR.

  The engagement torque of the center clutch 20 in the normal operation state before switching to the tack-in suppression mode is set using, for example, the accelerator opening ACC (or longitudinal acceleration) and the lateral acceleration Gy as parameters as shown in FIG. The In the example of FIG. 9, for the same accelerator opening degree ACC, a characteristic is set such that the fastening torque TC increases as the lateral acceleration Gy increases.

  Similarly, the engagement torque of the rear clutches 21RL and 21RR in the normal operation state before switching to the tack-in suppression mode is similarly set using the accelerator opening ACC (or longitudinal acceleration) and the lateral acceleration Gy as parameters. As shown in FIG. 10, the fastening torques of the rear clutches 21RL and 21RR increase the fastening torque TRo on the outer ring side by a predetermined amount with respect to the fastening torque TR determined from the fastening torque TC of the center clutch 20, and The fastening torque TRi is reduced by a predetermined amount to generate a differential limiting torque.

  When the change amount ΔACC of the accelerator opening exceeds the threshold value Hc and enters the tack-in suppression mode, the center clutch 20 has an engagement torque reduced by a reduction amount ΔTC from the engagement torque determined by the accelerator opening and the lateral acceleration at that time. It is controlled to become. At this time, since the accelerator is returned and the accelerator opening is reduced, the engagement torque of the center clutch 20 is also reduced. As shown in FIG. 9, the engagement torque of the center clutch 20 is further reduced by a reduction amount ΔTC. Therefore, the driving force distribution to the rear wheel side is close to zero, and the braking force can be generated only on the front wheel to increase the lateral force margin of the rear wheel. At this time, the engagement torque of the rear clutches 21RL and 21RR is increased by an increase amount ΔTR, as shown in FIG. By increasing the fastening torque of the rear clutches 21RL and 21RR, it is possible to reduce the tolerance for the difference between the left and right inner wheels and generate a yaw moment in the direction opposite to the turning direction, and to cancel the entrainment during turning. .

  As described above, in the present embodiment, when tack-in is likely to occur, the rear wheel side lateral force margin is increased by reducing the engagement torque of the center clutch 20, and the engagement torque of the rear clutches 21RL and 21RR is increased. Due to the synergistic effect with the additional yaw moment in the direction of canceling the entrainment during turning, tack-in during turning can be suppressed extremely effectively.

DESCRIPTION OF SYMBOLS 1 Engine 2 Automatic transmission 3 Transfer 7 Rear wheel final reduction gear 20 Center clutch 21RL, 21RR Rear clutch 60 Transmission control unit 60a Tuck-in suppression mode determination unit 60b Center clutch control unit 60c Rear clutch control unit ΔACC Accelerator opening change amount Gy Lateral Acceleration Hc Threshold ΔTC Amount of decrease in engagement torque of the center clutch ΔTR Amount of increase in engagement torque of the rear clutch

Claims (4)

When a vehicle having a center clutch that distributes driving force to the front wheel side and the rear wheel side, and a left and right rear clutch interposed between the rear wheel final reduction gear and the left and right rear drive shafts, A tuck-in suppression control device that suppresses occurrence,
When turning in the all-wheel drive mode in which the center clutch is engaged, it is determined whether or not tack-in occurs based on the amount of change in the accelerator opening, and an instruction to switch to the tack-in suppression mode that suppresses the occurrence of tack-in is given. A tuck-in suppression mode determination unit;
A center clutch control unit that reduces the engagement torque of the center clutch and reduces the driving force toward the rear wheel when instructed to switch to the tack-in suppression mode;
And a rear clutch control unit that increases the fastening torque of the left and right rear clutches and reduces the tolerance for the inner wheel difference between the left and right rear wheels when instructed to switch to the tack-in suppression mode. Tuck-in suppression control device. The tuck-suppression mode determination unit, when the change amount of the accelerator opening exceeds a threshold value, according to claim 1, wherein the instructions for the changeover is determined that the situation where the tuck is generated to tuck suppression mode Vehicle tuck-in suppression control device.   3. The vehicle tack-in suppression control device according to claim 1, wherein the center clutch control unit sets a reduction amount of an engagement torque of the center clutch based on a lateral acceleration and a vehicle speed of the vehicle.   4. The vehicle tuck-in suppression control device according to claim 3, wherein the rear clutch control unit sets an increase amount of an engagement torque of the left and right rear clutches based on a lateral acceleration and a vehicle speed of the vehicle.

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