JP2612718B2 - Torque split control device for four-wheel drive vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a torque split control device that positively controls the torque distribution of front and rear wheels according to running conditions in a full-time type four-wheel drive vehicle with a center differential device, and more particularly to a torque split control device for rear wheel torque distribution during turning. About settings.

[Prior art]

A four-wheel drive vehicle with a center differential has the advantage of absorbing the difference in rotation between the front and rear wheels during turning, and ensures smooth turning performance with four-wheel drive. Therefore, a torque split control having such performance and further varying the torque distribution of the front and rear wheels according to running conditions is conceivable. That is, in straight running, acceleration, and deceleration running, if the torque split control is performed according to the weight distribution of the vehicle on the front and rear wheels, the driving force distribution on the front and rear wheels is optimally exhibited according to the weight distribution of the vehicle. That is, the effect of the traction control can be obtained. When turning, if the torque split control is performed according to the state, the front engine
Understeer tendency of front drive (FF) vehicles,
It is possible to obtain the optimum turning performance in consideration of stability and turning performance while suppressing the oversteer tendency of the front engine rear drive (FR) vehicle. Furthermore, if the torque split control is performed in consideration of the road surface friction coefficient μ, wheel spin, etc., the driving safety will be improved, and it will have a function equal to or more than the differential lock function of the center differential. Will be possible. As described above with respect to an example, it is expected that the torque split control of a four-wheel drive vehicle will maximize its performance and achieve a great effect. Therefore, a drive system of a four-wheel drive vehicle capable of actively variably controlling the torque split has been proposed by the present applicant, but there is still room for development of other systems. Also, an optimal electronic control system for realizing the torque split is being developed. Conventionally, with respect to a four-wheel drive vehicle with a center differential, there is a prior art disclosed in Japanese Patent Application Laid-Open No. 55-83617, for example, in which the output side of a transmission is input to a center differential device, and the two output sides from the center differential device are connected. A transmission structure is provided for the front and rear wheels. In addition, it is shown that the center differential device is controlled by adding a clutch, a brake, and a selective clutch device.

[Problems to be solved by the invention]

By the way, in the above-mentioned prior art, only the center differential device is used, so that only one torque distribution ratio is determined thereby. The control system is 2,4
This is switching control between wheel drive and differential lock, and does not perform torque split control. SUMMARY OF THE INVENTION In view of the above, the present invention provides a torque split control device for a four-wheel drive vehicle in which a torque split control is optimally electronically controlled in a four-wheel drive system capable of variably controlling a torque split with a center differential. The purpose is to provide.

[Means for solving the problems]

In order to achieve the above object, the present invention provides a vehicle in which a heavy object such as an engine or a transmission is mounted on one of a front portion and a rear portion of a vehicle body, and a predetermined portion is provided in a drive system from a transmission output side to front and rear wheels. It has a center differential device for distributing power to the front and rear wheels with a torque distribution, and a torque split device having a split clutch with variable clutch torque, and inputs and processes signals for detecting various information and signals from the sensors. A circuit configured to control the torque distribution to the front and rear wheels together with the torque of the split clutch by a clutch control signal of the control unit.
In a wheel drive vehicle, power is transmitted from one of the output sides of the center differential to a final reduction device for front wheels via a first gear unit, and a second gear unit is transmitted from the other output side of the center differential unit. And a torque split device having the split clutch with a variable clutch torque between the first gear device and the second gear device. The transmission is arranged so as to be bypassed with the differential device, and the reduction ratio of the transmission system to the final reduction device for the front wheels via the first gear device, and the transmission ratio to the final reduction device for the rear wheels via the second gear device. The relationship with the speed reduction ratio of the system, the reduction ratio of the wheel side where the heavy object is not arranged is reduced, and when the split clutch is fully engaged, the rotational speed of the wheel on which the heavy object is not arranged is set to the other Is heavy The control unit sets the target torque distribution ratio for the front and rear wheels based on the steering angle and the vehicle speed as the torque distribution during turning. Unit, a center differential input torque calculating unit for obtaining a center differential input torque, a clutch pressure calculating unit for determining a clutch pressure by obtaining a moving torque amount based on a target torque distribution ratio, a center differential input torque and an initial torque distribution ratio by the center differential device. The torque split of the front and rear wheels at the time of turning is controlled according to the turning state, the power transmission state, and the initial torque distribution by the center differential device.

[Action]

Based on the above configuration, the four-wheel drive vehicle equipped with the center differential device and the torque split device generates a split clutch torque of the torque split device by a clutch control signal from the control unit, so that a part of the torque of the front and rear wheels is changed from one side. Moving to the other side, the torque split is actively variably controlled. At the time of turning, the rear wheel moving torque amount is calculated based on, for example, the target torque distribution ratio on the rear wheel side, the initial torque distribution ratio by the center differential device, and the center differential input torque, which are set in advance based on the steering angle and the vehicle speed. , An appropriate amount of torque moves to the rear wheel side according to the turning state and the power transmission state, and the torque distribution is controlled to the optimal rear wheel side torque distribution. Thus, according to the present invention, the turning performance and the like can be significantly improved by the active torque split control using the target torque distribution ratio during turning.

【Example】

Further, according to the present invention, before the torque is distributed, the reduction ratio on the side where no heavy object is disposed (for example, on the rear wheel side in a normal vehicle having an engine at the front part of the vehicle body) is reduced with respect to the rear wheel. When the split clutch is completely engaged, the gear ratio is set such that the wheel rotation speed on the rear wheel side is increased, so that a driving force greater than the weight distribution ratio of the vehicle body can be moved. Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the outline of the torque split control device of the present invention will be described. First, as a drive system of a four-wheel drive vehicle capable of torque split control with a center differential, which is a vertically mounted front engine and has an automatic transmission with a torque converter, an engine 1, a torque converter 2, and The automatic transmission 3 is disposed in the front-rear direction of the vehicle, and is connected to be capable of transmitting power. The output shaft 4 of the automatic transmission 3 is input to a center differential device 20, and a torque split device 25 is provided in the center differential device 20 in a bypass manner. The center differential device 20 is of a planetary gear type and includes a sun gear 21, a ring gear 22, a pinion 23 meshing with the sun gear 21 and the ring gear 22, and a carrier 24.
4, the transmission output shaft 4 is coaxially connected. In the two sun gears 21 and ring gears 22 on the output side, a reduction gear 5 rotatably provided on the transmission output shaft from the large-diameter ring gear 22, and a front gear parallel to the output shaft 4 via a reduction gear 6. The front drive shaft 7 is connected to the drive shaft 7 and is transmitted to the left and right front wheels 10L and 10R via the front differential device 8 and the axle 9. On the other hand, the small-diameter sun gear 21 is connected to the rear drive shaft 11, and the rear drive shaft 11 is configured to transmit power to the left and right rear wheels 14L, 14R via the rear differential device 12, the axle 13, and the like. Thus, the center differential device 20 transmits the transmission output to the front and rear wheels with a predetermined torque distribution, and absorbs the rotation difference between the front and rear wheels. Here, the drive system corresponds to the case where the static load is larger at the front of the vehicle body than at the rear, and the torque transmitted from the ring gear 22 to the front wheels is larger than the torque transmitted from the sun gear 21 to the rear wheels. I have. The torque split device 25 has a bypass shaft 26 coaxial with the front drive shaft 7 and a hydraulic clutch 27 as a clutch capable of variably controlling the torque. The bypass shaft 26 is connected to a hub 27a of the hydraulic clutch 27, and the drum 27b is connected to a pair of drums 27b. Gear 2
It is configured to transmit power to the rear drive shaft 11 via 8, 29. Here, the reduction gears 5 and 6 are also components in this case, and the gear ratio thereof is set to, for example, “1”, and the gear ratios of the gears 28 and 29 are set slightly smaller than that. Also hydraulic clutch
Numeral 27 is such that clutch torque can be generated by supply of hydraulic oil from the hydraulic unit 30. Thus, in the hydraulic clutch 27, the drum 2 is
7b produces a slightly lower rotation difference, so that when clutch pressure is applied to the hydraulic clutch 27 to generate clutch torque, torque movement corresponding to the clutch pressure is performed from the front wheel side of the hub 27a to the rear wheel side of the drum 27b. Then, the torque distribution between the front wheel side and the rear wheel side is varied. That is, assuming that the input torque of the center differential device 20 is Ti and the front side distribution ratio of the center differential device 20 is γ, the transmission torque of the front drive shaft 7 is γ
The torque of the rear drive shaft 11 is allocated to (1−γ) · Ti. Therefore, assuming that the clutch torque Tc and the gear ratio of the gears 28 and 29 are K, the torque TF and TR of the front drive shaft 7 and the rear drive shaft 11 due to the torque movement are as follows: TF = γ · Ti−Tc TR = (1−γ ) · Ti + KTc. Thus, the distribution ratio of the front side torque TF continuously changes below the distribution ratio in the center differential device 20 due to the change in the clutch torque Tc, and the distribution ratio of the rear side torque TR continuously increases above the distribution ratio in the center differential device 20. And acts as a torque split. Next, regarding the electronic control system of the torque split, the left and right front wheel and rear wheel speed sensors 40L, 40R, 41L, 41R,
The control unit 50 includes a steering angle sensor 42, an engine speed sensor 43, a throttle opening sensor 44, a vehicle body acceleration sensor 45, and a shift stage sensor 46 on the automatic transmission side. The control unit 50 determines the torque distribution ratio of the front and rear wheels based on the running conditions and the slip state of the front and rear wheels, and determines the clutch pressure according to the torque distribution ratio. The control unit 50 outputs this clutch pressure control signal to the hydraulic unit 30. I do. In FIG. 2A, the hydraulic unit 30 will be described. Reference numeral 31 denotes, for example, an oil passage to which a line pressure for controlling an automatic transmission is supplied, and this line pressure is guided to a pressure regulating valve 32. The pressure regulating valve 32 constantly generates a constant pilot pressure in the oil passage 33 while interrupting the communication between the oil passage 31 that supplies the line pressure and the oil passage 33. The oil passage 33 is a duty solenoid valve.
Connect to 34. The duty solenoid valve 34 controls the discharge pressure according to the duty signal from the control unit 50 to generate a duty pressure in the oil passage 35. A duty pressure acts on the clutch control valve 36, and a line pressure oil passage 31 and an oil passage 37 of the hydraulic clutch 27 communicate with each other. Generates a clutch torque corresponding to. Here, for example, the clutch pressure has a characteristic as shown in FIG. 2B with respect to the duty ratio of the duty signal. When the duty ratio is substantially zero, the clutch pressure becomes zero. From this state, the duty ratio increases. Accordingly, the clutch pressure also increases. The dashed line in FIG. 2 indicates the characteristic of the duty pressure. In FIG. 3, the control unit 50 will be described. First, a front wheel speed calculation unit 51 to which the left and right front wheel rotation speeds NFL and NFR of the rotation speed sensors 40L and 40R are input, and a rear wheel speed calculation unit 52 to which left and right rear wheel rotation speeds NRL and NRR of the rotation speed sensors 41L and 41R are input. The front and rear wheel speeds NF and NR are calculated by the front wheel speed calculation unit 51 and the rear wheel speed calculation unit 52.
NF = (NFL + NFR) / 2 NR = (NRL + NRR) / 2 The front and rear wheel speeds NF and NR of the front wheel speed calculation unit 51 and the rear wheel speed calculation unit 52 are input to the wheel speed calculation unit 53, and the average wheel speed N of the four wheels is calculated by N = (NF + NR) / 2. The wheel speed N is input to the vehicle speed calculation unit 54, and the vehicle speed V is calculated in consideration of the tire diameter. The steering angle λ of the steering angle sensor 42 and the vehicle speed V of the vehicle speed calculation unit 54 are input to a target torque distribution ratio determining unit 55, and the torque distribution ratio of the rear wheels is determined by the parameters of the steering angle λ and the vehicle speed V. Here, for example, the rear wheel torque distribution ratio SR is set as shown in FIG. That is, in a region where the steering angle at a medium speed is relatively large, the rear wheel torque distribution ratio SR is set to be large in order to emphasize the turning characteristics of the vehicle. The wheel torque distribution ratio SR is set to a small value, and in the other region, the rear wheel torque distribution ratio SR is intermediate to achieve stability while emphasizing turning characteristics.
This target torque distribution ratio determining unit 55 rear wheel torque distribution ratio SR
And the acceleration G of the acceleration sensor 45 are input to the acceleration correction unit 56,
When the acceleration G is substantially zero, it is regarded that the vehicle is traveling normally, and the outer wheel torque distribution ratio SR is not corrected. Further, at the time of acceleration at which the acceleration G occurs, the rear wheel torque distribution ratio SR is corrected so as to correspond to a change in vehicle weight distribution. The engine speed Ne of the engine speed sensor 43 and the throttle opening θ of the throttle opening sensor 44 are input to an engine torque calculator 57, and an engine torque Te is determined based on the torque characteristics shown in FIG. 4 (b). Wheel speed of wheel speed calculator 53
N, engine speed Ne, and speed Gr of the speed sensor 46
Is input to the torque converter rotation ratio calculation unit 58 and the wheel speed N
Calculate the turbine speed Nt, which is the output side of the torque converter 2, by calculating backward from the gear stage Gr, and calculate the rotation ratio Rw with the engine speed Ne as the input side of the torque converter 2 by Rw = Nt / Ne. The rotation ratio Rw is input to the torque converter torque ratio calculation section 59, and the torque ratio Rt is obtained from the characteristics shown in FIG. Then, the engine torque Te, the torque converter torque ratio Rt, and the shift speed Gr are input to the center differential input torque calculation unit 60, and the center differential input torque Ti is calculated as follows. Ti = Te ・ Rt ・ Gr The above rear wheel torque distribution ratio SR and center differential input torque T
i is input to the clutch pressure calculating unit 61, and the clutch torque Tc
Also, the clutch pressure Pc is determined. As described above, assuming that the front side torque is TF and the rear side torque is TR,
The rear wheel torque distribution ratio SR is represented by SR = TR / (TF + TR). Therefore, when the above equations of the front side distribution ratio γ, the input torque Ti, the clutch torque Tc, and the gear ratio K are substituted into the above equation, Tc = f (SR, Ti), and the rear wheel torque distribution ratio SR, the input torque As the Ti increases, the value of the clutch torque Tc increases. The relationship between the clutch torque Tc and the clutch pressure Pc has a characteristic peculiar to parameters such as the number of clutch plates constituting the hydraulic clutch 27 and the friction coefficient, and Pc = g (Tc) as shown in FIG. Is represented by The clutch pressure Pc is input to the operation amount setting unit 62, and is converted into a signal having a duty ratio corresponding to the clutch pressure Pc using the characteristics shown in FIG. Next, the operation of the thus configured torque split control device will be described. First, when the automatic transmission 3 is shifted to a driving range such as a drive (D) while the vehicle is running, the power of the engine 1 is input to the automatic transmission 3 via the torque converter 2 and the power for shifting is output. Is the carrier of the center differential device 20
Communicate to 24. The ring gear 22 and the sun gear 21 distribute the static load to the front and rear wheels at a torque distribution ratio of, for example, 60:40 to the wheels of the vehicle. The power from the ring gear 22 is transmitted through the reduction gears 5, 6, the front drive shaft 7, the front differential device 8, etc., to the front wheels 10L, 10R.
Further, the power from the sun gear 21 is transmitted to the rear wheels 14L, 14R via the rear drive shaft 11, the rear differential device 12, and the like, and thus, a full-time four-wheel drive traveling with a center differential is provided. At this time, the hydraulic clutch 27 of the torque split device 25
Is rotated by a rotation difference caused by the gear ratio between the reduction gears 5, 8 and the gears 28, 29, so that torque can be transferred to the rear wheels. On the other hand, various information is detected by each sensor of the electronic control system, and is input to the control unit 50. The target torque distribution ratio determining unit 55 and the acceleration correction unit 56 determine running conditions based on the steering angle λ, the vehicle speed V, and the vehicle body acceleration G, and the rear wheel torque distribution ratio SR is determined based on this. The center differential input torque calculation unit 60 uses the engine torque Te, the shift speed Gr, the engine speed Ne, the wheel speed N, and the rotation ratio Rw and the torque ratio Rt of the torque converter 2 according to the shift speed Gr to obtain a center differential input. The torque Ti is calculated. Therefore, during normal driving, the target torque distribution ratio determining unit
At 55, the rear wheel torque distribution ratio SR becomes the fourth according to the steering angle λ and the vehicle speed V.
Various determinations are made based on the pattern shown in FIG. That is,
Under conditions where the center differential input torque is sufficiently large, for example, when the steering angle at medium speed is relatively large, the rear wheel torque distribution ratio SR is set large, and the duty signal of the hydraulic unit 30 is reduced by outputting a duty signal corresponding to this. The hydraulic pressure of the hydraulic clutch 27 is increased, and the traveling torque from the front wheels to the rear wheels increases accordingly, and a large amount of torque moves to the rear wheels, resulting in a very large rear wheel torque distribution. become. On the other hand, when the vehicle speed V and the steering angle λ decrease, the rear wheel torque distribution decreases accordingly, and thus the rear wheel torque distribution is variably controlled according to the turning state. For this reason, the slip of the front and rear tires at the time of turning with four-wheel drive always keeps the coefficient of friction with the road surface large, and promotes reliable turning along the target turning radius. Further, in the pattern of FIG. 4 (a), it is possible to positively improve the turning performance of the vehicle by setting a larger torque distribution ratio to the rear wheels, thereby enabling more sporty traveling. . In particular, when the vehicle is running straight and the vehicle acceleration G is substantially zero, the target rear wheel torque distribution ratio SR is held at 40% of the torque distribution ratio by the center differential device 20. Therefore, the clutch pressure calculating section 61 sets the clutch pressure Pc = 0 since the rear wheel moving torque amount is zero. Therefore, the operation amount setting unit 62
, A signal having a duty ratio of 0% is input to the solenoid valve 34 of the hydraulic unit 30, the duty pressure is maximized, and the hydraulic clutch 27 is drained by the clutch control valve 36, whereby the hydraulic pressure and torque of the hydraulic clutch 27 are reduced. Becomes zero. In such running conditions, the hydraulic clutch 27 is not operated, and only the torque distribution by the center differential device 20 is performed.
Initial torque split control corresponding to the vehicle body load distribution. On the other hand, in the acceleration traveling output by the acceleration G, when the vehicle is traveling straight or turning, the acceleration correction unit 56 corrects the rear wheel torque distribution ratio SR to increase according to the acceleration G, that is, the backward movement of the vehicle body load. For this reason, the clutch pressure Pc becomes a value larger than that during normal running where the acceleration G is zero, and a duty signal corresponding to this is input to the solenoid valve 34, and the clutch control valve 36 supplies oil to the hydraulic clutch 27 to reduce the clutch pressure. Occurs. Therefore, a part of the torque to the front drive shaft 7 is moved to the rear drive shaft 11 by the hydraulic clutch 27 and added to increase the rear wheel torque. Thus, under these running conditions, the torque split control is performed so as to increase the rear wheel torque distribution in accordance with the rearward movement of the vehicle body load, and the traction is improved. When the center differential input torque Ti is substantially zero, the clutch pressure becomes zero regardless of the rear wheel torque distribution ratio SR in any state, thereby avoiding the tight corner braking phenomenon. The following table summarizes the torque split control patterns described above. Although the embodiment of the present invention has been described above, the target torque distribution ratio may be determined on the front wheel side, and the center differential input torque may be directly detected by a torque sensor or the like. The initial torque distribution of the center differential device is not limited to the embodiment.

【The invention's effect】

As described above, according to the present invention, in a four-wheel drive vehicle with a center differential, active torque split control is performed under steady, accelerated, and turning traveling conditions. Power performance is obtained. When turning, the torque split control according to the turning state improves the turning performance. In addition, it is possible to turn accurately along a target turning radius by four-wheel drive, so that turning performance is greatly improved and safety is secured. The torque distribution ratio at the time of turning can be appropriately set by a map of the target torque distribution ratio based on the steering angle and the vehicle speed. For example, the rear wheel moving torque amount is directly determined by the target torque distribution ratio on the rear wheel side, the initial torque distribution ratio by the center differential device, and the center differential input torque, so that the torque split control toward the rear wheel according to the turning state can be easily performed. It can be performed accurately. Further, torque control of the clutch according to the moving torque amount is also facilitated. Further, according to the present invention, before the torque is distributed, the reduction ratio on the side where no heavy object is disposed (for example, on the rear wheel side in a normal vehicle having an engine at the front part of the vehicle body) is reduced with respect to the rear wheel. When the split clutch is completely engaged, the gear ratio is set such that the wheel rotation speed on the rear wheel side is increased, so that a driving force greater than the weight distribution ratio of the vehicle body can be moved.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing an embodiment of a torque split control device according to the present invention, FIG. 2 (a) is a circuit diagram of a hydraulic unit, FIG. 2 (b) is a hydraulic characteristic diagram thereof, and FIG. FIG. 4 is a block diagram showing various characteristics. 2 ... Torque converter, 20 ... Center differential device, 25
…… Torque split device, 27 …… Hydraulic clutch, 30…
... hydraulic unit, 50 ... control unit, 55 ... target torque distribution ratio determination unit, 60 ... center differential input torque calculation unit, 61 ... clutch pressure calculation unit

Claims (2)

(57) [Claims] A heavy object such as an engine or a transmission is mounted on one of a front portion and a rear portion of a vehicle body, and power is distributed by a predetermined torque distribution in a drive system from a transmission output side to front and rear wheels. A center differential device for distributing to the front and rear wheels, a torque split device having a split clutch having a variable clutch torque, a sensor for detecting various information, and a control unit for inputting and processing a signal of the sensor, In a four-wheel drive vehicle configured to control the torque distribution to the front and rear wheels together with the torque of the split clutch by a clutch control signal of the control unit, a first gear unit is provided from one of the output sides of the center differential device. The power is transmitted to the final reduction gear of the front wheel through the second differential gear, and the power is transmitted to the final reduction gear of the rear wheel through the second gear device. A torque split device having a split clutch capable of changing the clutch torque is disposed between the first gear device and the second gear device so as to bypass the center differential device. And the relationship between the reduction ratio of the transmission system to the final reduction gear of the front wheels via the first gear device and the reduction ratio of the transmission system to the final reduction gear of the rear wheels via the second gear device, The reduction ratio of the wheel on which the heavy object is not disposed is reduced, and when the split clutch is fully engaged, the rotational speed of the wheel on which the heavy object is not disposed is changed to the rotational speed of the wheel on which the other heavy object is disposed. A target torque distribution ratio determining unit that determines a target torque distribution ratio of the front and rear wheels based on a steering angle and a vehicle speed as a torque distribution during turning. A center differential input torque calculating unit for determining a differential input torque, a target torque distribution ratio, a center differential input torque, and a clutch pressure calculating unit for determining a clutch pressure by determining a moving torque amount based on an initial torque distribution ratio by the center differential device; A torque split control device for a four-wheel drive vehicle, wherein the torque split of front and rear wheels during turning is controlled according to a turning state, a power transmission state, and an initial torque distribution by a center differential device. 2. The torque split control device for a four-wheel drive vehicle according to claim 1, wherein the target torque distribution ratio is determined by a function of a rear wheel torque distribution ratio and a steering angle and a vehicle speed.