JP2549875B2 - Torque split controller 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 for actively controlling torque distribution between front and rear wheels in a full-time four-wheel drive vehicle equipped with a center differential device, and more particularly to a torque split control during steady running.

[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 the traveling condition can be considered. 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 in the above example, it is expected that torque split control of a four-wheel drive vehicle will maximize its performance and obtain 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
It 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 problems]

In order to achieve the above object, the present invention includes a center differential device that distributes power to front and rear wheels with a predetermined torque distribution in the middle of a drive system, and a torque split device having a split clutch with a variable clutch torque in the center differential device. In a four-wheel drive vehicle that is connected by bypass, it has a sensor for detecting various information and a control unit for inputting and processing the signals of the sensor, and a clutch control signal of the control unit together with the torque of the split clutch. A circuit is configured to control the torque distribution to the front and rear wheels, and the initial driving force distribution ratio by the center differential device is set to be approximately equal to the static load distribution ratio of the front and rear wheels of the vehicle, and It is configured to control the torque split to the initial drive force distribution.

[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 initial drive force distribution ratio by the center differential device is set so as to match the static load distribution ratio of the vehicle, the split clutch is released during steady running, and the torque distribution ratio to the front and rear wheels is set by the center differential device. By allocating it, the traction performance of the front and rear wheels during this driving is sufficiently secured. Thus, according to the present invention, it is possible to release the split clutch in the steady-state torque split control to prevent clutch heat generation and the like, and obtain optimum traction performance.

【Example】

Embodiments of the present invention will be described below 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 with a center differential capable of torque split control, a front engine that is vertically installed and has an automatic transmission with a torque converter will be described. The automatic transmission 3 is arranged in the front-rear direction of the vehicle and is connected so that power can be transmitted. 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. Further, in the two output side sun gears 21 and ring gears 22, a reduction gear 5 rotatably provided on the transmission output shaft from the large-diameter ring gear 22 and a front face 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, 10R via a front differential device 8 and an 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. In this way, 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, for example, as a clutch capable of variable torque control. The bypass shaft 26 is a hub 27a of the hydraulic clutch 27 and its drum 27b is a pair. 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 T i and the front side distribution ratio by the center differential device 20 is γ, the transmission torque of the front drive shaft 7 is γ.
・ T i is the torque of the rear drive shaft 11 (1-γ) ・ T i
Be distributed to. Therefore, the clutch torque is T c, gears 28,2
If the gear ratio of 9 is K, the torque TF, TR of the front drive shaft 7 and the rear drive shaft 11 due to the torque movement becomes TF = γ · T i−T c TR = (1−γ) · T i + KT c . 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 of the clutch torque Tc, and the distribution ratio of the rear side torque TR continuously exceeds the distribution ratio in the center differential device 20. Change and the torque split works. Next, to describe the torque split electronic control system, the left and right front wheel and rear wheel rotation speed sensors 40L, 40R, 41L, 41R,
The steering angle sensor 42, the engine speed sensor 43, the throttle opening sensor 44, the vehicle body acceleration sensor 45, and the gear stage sensor 46 on the automatic transmission side are provided, and these sensor signals are input to the control unit 50. 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. The hydraulic unit 30 will be described with reference to FIG. 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 intermittently connecting the oil passage 31 and the oil passage 33 which supply the line pressure, and 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, the front wheel calculation output unit 51 input by the left and right front wheel rotation speeds NFL, NFR of the rotation speed sensors 40L, 40R and the rear wheel speed calculation unit 52 input by the left and right rear wheel rotation speeds NRL, NRR of the rotation speed sensors 41L, 41R. The front wheel speed calculation unit 51 and the rear wheel speed calculation unit 52 have front and rear wheel speeds NF and NR.
Is calculated by 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 the target torque distribution ratio determination 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. The rear wheel torque distribution ratio SR is set to a large value in order to emphasize the turning ability of the vehicle in the area where the steering angle at high and medium speeds is relatively large. The rear wheel torque distribution ratio SR is set to a small value, and in other regions, the rear wheel torque distribution ratio SR is intermediate and the turning performance is emphasized and stability is achieved.
This target torque distribution ratio determination 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 as steady running and the rear wheel torque distribution ratio SR is not corrected. Further, at the time of acceleration that causes the acceleration G, the rear wheel torque distribution ratio SR is corrected so as to correspond to the change in the vehicle weight distribution. The engine speed N e of the engine speed sensor 43 and the throttle opening θ of the throttle opening sensor 44 are input to the engine torque calculation unit 57, and the engine torque T e is determined based on the torque characteristic of FIG. 4 (b). . The wheel speed N of the wheel speed calculation unit 53, the engine speed N e, and the shift speed Gr of the shift speed sensor 46 are input to the torque converter rotation ratio calculation unit 58, and back calculated by the wheel speed N and the shift speed Gr. Torque converter 2
The turbine rotation speed N t, which is the output side of, is calculated, and the rotation ratio R w with the engine rotation speed Ne, which is the input side of the torque converter 2, is calculated by R w = N t / N e. w is input to the torque converter torque ratio calculation unit 59, and the torque ratio R t is obtained from the characteristics of FIG. 4 (c). Then, the engine torque T e, the torque converter torque ratio R t, and the gear G r are input to the center differential input torque calculation unit 60, and the center differential input torque T
i is calculated as follows. T i = T e · R t · G r Above rear wheel torque distribution ratio SR and center differential input torque T
i is input to the clutch pressure calculation unit 61, and the clutch torque T
Determine the clutch pressure P c together with c. As described above, when the front torque is TF and the rear torque is TR, the rear wheel torque distribution ratio SR is given by SR = TR / (TF + TR). Therefore, by substituting the above equations for the float side distribution ratio γ, the input torque T i, the clutch torque T c, and the gear ratio K into the above formula, T c = f (SR, T i) and the rear wheel torque distribution ratio The value of the clutch torque T c increases as the SR and the input torque T i increase. The relationship between the clutch torque T c and the clutch pressure P c is the hydraulic clutch.
It has its own characteristics depending on the parameters such as the number of clutch plates and friction coefficient that make up 27, and is represented by P c = g (T c) as shown in Fig. 4 (d). Then, the clutch pressure P c is input to the manipulated variable setting unit 62, is converted into a signal having a duty ratio corresponding to the clutch pressure P c using the characteristic of FIG. There is. Next, the operation of the torque split control device thus configured 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. Then, the target torque distribution ratio determination unit 55 and the acceleration correction unit 56 determine the traveling 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 the traveling conditions. Further, in the center differential input torque calculation unit 60, the engine torque T e, the gear G r, the engine speed N e, the wheel speed N, and the gear G
Rotation ratio R w and torque ratio of torque converter 2 by r
The center differential input torque T i is calculated using R t. Therefore, during normal driving, the target torque distribution ratio determining unit
At 55, the rear wheel torque distribution ratio SR is 4th depending on 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 corresponding to this is output to change the duty pressure of the hydraulic unit 30. When the hydraulic pressure of the hydraulic clutch 27 is further increased, the moving torque from the front wheel side to the rear wheel side increases accordingly, and a large amount of torque moves to the rear wheel side, and the rear wheel torque distribution is very large. 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 tires of the front wheels and the rear wheels at the time of turning with four-wheel drive always maintains a large friction coefficient with the road surface, and surely promotes turning along a 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, which enables more sporty running. . Further, particularly during steady running in which the vehicle body acceleration G is substantially zero during straight traveling, the target rear wheel torque distribution ratio SR is held at 40% of the torque distribution ratio by the center differential device 20. Therefore, in the clutch pressure calculation unit 61, since the rear wheel moving torque amount is zero, the clutch pressure P c becomes 0. Therefore, the manipulated variable setting unit 6
A signal with a duty ratio of 0% is input to the solenoid valve 34 of the hydraulic unit 30 from 2 to maximize the duty pressure to drain the hydraulic clutch 27 by the clutch control valve 36, which causes the hydraulic pressure and torque of the hydraulic clutch 27. 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, in the case of straight traveling or turning, the acceleration correction unit 56 corrects so as to increase the rear wheel torque distribution ratio SR according to the acceleration G and the backward movement of the speed vehicle load. . For this reason, the clutch pressure P c becomes a value larger than that during normal running when the acceleration G is zero, a duty signal corresponding to this is input to the solenoid valve 34, and the clutch control valve 36 refuels the hydraulic clutch 27 to provide the clutch pressure. Cause 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. Needless to say, when the center differential input torque T i 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 torque split control patterns described above are summarized in the following table. Although one embodiment of the present invention has been described above, the center differential device 20 may be a bevel gear type when the static load distribution ratio of the front and rear wheels is approximately 50:50, and in the case of a rear engine a planetary gear and a ring gear. The swing by the sun gear may be reversed from that in the embodiment. Further, when the load distribution ratio changes due to cargo loading in a freight vehicle, torque split control can be performed accordingly.

【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 normal, acceleration, and turning traveling conditions, so that optimum four-wheel drive performance is exhibited. Power performance is obtained. In straight-ahead steady running, the traction effect is improved by the torque split control according to the load distribution of the vehicle. At this time, since the split clutch is not operated, there is no power loss, which is advantageous in terms of fuel consumption, heat generation of the clutch, and the like. In the center differential device, the initial torque distribution can be reliably determined according to the vehicle load distribution, and the split clutch can be completely released during steady running. In the torque split control, the split clutch can be set to the disengaged state during steady traveling, the control is simplified, and various durability is improved.

[Brief description of 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, 56… Acceleration correction unit

Claims (1)

(57) [Claims] 1. A center differential device for distributing power to front and rear wheels according to a predetermined torque distribution in the middle of a drive system, and a torque split device having a split clutch with a variable clutch torque is bypassed and connected to the center differential device. A four-wheel drive vehicle has a sensor for detecting various kinds of information and a control unit for inputting and processing signals from the sensor. The clutch control signal from the control unit is used to distribute the torque of the split clutch to the front and rear wheels. The center differential device sets the initial drive force distribution ratio to the static load distribution ratio of the front and rear wheels of the vehicle to set the torque split of the front and rear wheels during steady running to the initial drive. A torque split control device for a four-wheel drive vehicle, which is characterized by controlling the force distribution.