JP2615083B2 - 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 four-wheel drive vehicle with a center differential device.

[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, since only the center differential device is used, only one torque distribution is determined thereby. Further, the control system is a control for switching between two- and four-wheel drive and a 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 equipped with a heavy object such as an engine or a transmission at one of a front side and a rear side of a vehicle body and a predetermined torque distribution in a drive system from a transmission output side to front and rear wheels. In a four-wheel drive vehicle provided with a center differential device for distributing power to front and rear wheels, power is transmitted from one of the outputs of the center differential device to a final reduction device for front wheels via a first gear device, Power is transmitted from one of the outputs of the differential device to the final reduction gear of the rear wheel via a second gear device, and the center differential device is provided between the first gear device and the second gear device. A torque splitting device comprising a split clutch capable of changing a clutch torque by bypassing the first gear device, a reduction ratio of the front wheel final reduction device, and a reduction ratio of the second gear device and the rear wheel. The reduction ratio by the device, the reduction ratio of the side where the heavy object is not disposed is small, and when the split clutch is fully engaged, the rotational speed of one of the front and rear wheels on which the gravity object is not disposed is reduced. A control unit for setting the rotation speed to be higher than the rotation speed of the wheel on which the gravity object is disposed, detecting a variety of information, and inputting and processing a signal of the sensor; A circuit is 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, and the control unit controls the steady, acceleration, and turning running conditions by the elements of the steering angle, the vehicle speed, and the vehicle body acceleration. A torque distribution ratio determining unit for determining a target torque distribution ratio by making a determination; a clutch torque calculating unit for determining a clutch torque according to a torque movement amount based on the torque distribution ratio; An operation amount setting section for outputting a clutch control signal in response to the torque, a torque split clutch by the clutch torque control signal, characterized by variably controlling the torque split between the front and rear wheels according to the driving conditions.

[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. Then, the target torque distribution ratio of the front and rear wheels is determined and controlled in each of the steady, acceleration, and turning travel conditions, so that the torque split is optimally controlled in each of the travel conditions. In addition, the reduction ratio of the power transmission device from the output of the center differential device to the final reduction device for the front wheels or the rear wheels is set in consideration of the weight distribution between the front and rear of the vehicle, and the wheels on the side where the heavy objects of the front and rear wheels are not disposed. Is set to be higher, torque can be distributed to the required side regardless of the weight distribution of the vehicle when the split clutch is fully engaged. Therefore, even in a general vehicle in which an engine or the like is disposed in front, a sufficient driving force can be distributed to the rear wheels when the split clutch is completely engaged. Thus, according to the present invention, turning performance, acceleration performance, safety, traction effect, and the like can be significantly improved by active torque split control under each traveling condition.

【Example】

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 its drum 27b is 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 is set to, for example, “1”, and the gear ratios of the gears 28 and 29 are set slightly smaller than that.
Since the reduction ratio of the rear differential device 12 is set equal,
When the hydraulic clutch 27 is fully engaged, the reduction gears 5, 6
The rotation speed of the rear wheel is set to be high due to the difference in reduction ratio between the gears 28 and 29. Also hydraulic clutch 27
The clutch can generate clutch torque by supplying 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 gear ratio of the clutch torque Tc and the gears 28 and 29 is K, the torque TF and TR of the front drive shaft 7 and the rear drive shaft 11 by 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 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 large in order to emphasize the turning characteristics of the vehicle. The torque distribution ratio SR is set small,
In the other regions, the rear wheel torque distribution ratio SR is intermediate and the stability is achieved with emphasis on turning performance. The 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 an acceleration correction unit 56. When the acceleration G is substantially zero, it is regarded that the vehicle is traveling normally, and the rear wheel torque distribution ratio is determined. No SR correction is performed. 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 with a rotation difference caused by the gear ratio between the reduction gears 5, 6 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 traction under torque split control is promoted to increase the rear wheel torque distribution in accordance with the rearward movement of the vehicle body load. Also, when the center differential input torque Ti is substantially zero, the clutch pressure becomes zero in any state of the rear wheel torque distribution ratio SR.
Thereby, the tight corner braking phenomenon is avoided. The following table summarizes the torque split control patterns described above. Although the embodiment of the present invention has been described above, the present invention is not limited to this. Particularly in an electronic control system, sensors may be provided on the front and rear drive shafts to directly detect the average rotational speed of the front and rear wheels. When the torque converter is not used, the calculation of the torque ratio becomes unnecessary. The duty ratio may be reversed depending on the characteristics of the solenoid valve. Although the embodiment of the hydraulic clutch has been described as the split clutch, the present invention can be applied to other clutches, and the clutch pressure control signal may be adapted to the clutch. The target torque distribution ratio may be the front-wheel-side torque distribution ratio, and is similarly applicable to a method of moving the torque to the front wheels.

【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. In straight running, the traction effect is improved by the torque split control according to the load distribution of the vehicle. At this time, the split clutch is inoperative especially during steady running,
There is no power loss, which is advantageous in terms of fuel efficiency, clutch heat generation, and the like. 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. In the acceleration running, the torque is moved to the rear wheel side more than usual, so that the torque split control according to the change in the load distribution of the vehicle improves the traction effect and the acceleration performance. The target torque distribution ratio can be determined by accurately judging the running conditions based on the steering angle, the vehicle speed, and the vehicle body acceleration, and the traveling torque amount can be accurately calculated and controlled based on the target torque distribution ratio and the center differential input torque.

[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. 20 …… Center differential device, 25 …… Torque split device, 27 …… Hydraulic clutch, 30 …… Hydraulic unit, 50 ……
Control unit, 55 …… Target torque distribution ratio determining unit, 56 ……
Acceleration correction unit, 61 ... Clutch pressure calculation unit, 62 ... Operation amount setting unit

Claims (3)

(57) [Claims] An engine, a transmission, or other heavy object is provided at one of the front and rear sides of a vehicle body, and power is supplied to the front and rear wheels by a predetermined torque distribution in a drive system from the transmission output side to the front and rear wheels. In a four-wheel drive vehicle provided with a center differential device for sorting, power is transmitted from any one of the outputs of the center differential device to a final reduction device for the front wheels via a first gear device, and any of the outputs of the center differential device is output. And power from the other to the final reduction gear of the rear wheel through the second gear device,
A torque split device including a split clutch having a variable clutch torque bypassing the center differential device between the first gear device and the second gear device;
The reduction ratio of the first gear unit and the final reduction unit of the front wheel and the reduction ratio of the second gear unit and the final reduction unit of the rear wheel are reduced by the reduction ratio of the side where the heavy object is not disposed. When the split clutch is fully engaged, the rotation speed of one of the front and rear wheels, on which the gravitational object is not disposed, is set to be higher than the rotation speed of the wheel on which the gravitational object is disposed. A sensor for detecting various information; and a control unit for inputting and processing signals from the sensor. The clutch control signal from the control unit controls the torque distribution to the front and rear wheels together with the torque of the split clutch. The control unit determines a target torque distribution ratio by determining steady, acceleration, and turning traveling conditions based on the steering angle, the vehicle speed, and the vehicle body acceleration. A clutch torque calculating unit that determines a clutch torque according to a torque transfer amount according to a torque distribution ratio; and an operation amount setting unit that outputs a clutch control signal according to the clutch torque. A torque split device for a four-wheel drive vehicle, wherein torque split of front and rear wheels is variably controlled according to each traveling condition. And a torque distribution ratio determining section for determining a torque distribution ratio according to a change in vehicle load distribution during acceleration, a torque distribution according to a change in vehicle load distribution during acceleration, and a torque distribution closer to the rear wheel according to a turning state during turning. 3. The torque split control device for a four-wheel drive vehicle according to claim 1, wherein the torque split control device determines the torque split. 3. The split clutch is a hydraulic clutch, and a hydraulic unit having a duty solenoid valve is formed in the hydraulic clutch as a circuit. A duty signal is input from the operation amount setting unit to the solenoid valve to torque the hydraulic clutch. The torque split control device for a four-wheel drive vehicle according to claim 1, wherein the torque split control is performed.