JP2615082B2 - Torque split control device for four-wheel drive vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque split control device for positively controlling 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. The correction of the torque distribution according to.

[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 slit 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. In view of the above, the present invention optimally electronically controls the torque split control in a four-wheel drive system capable of variably controlling the torque split with a center differential, and also constantly secures the stability of the vehicle with respect to road surface conditions. It is an object of the present invention to provide a torque split control device for a four-wheel drive vehicle.

[Means for solving the problems]

In order to achieve the above object, the present invention provides a torque split device including 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 the center differential device has a split clutch with a variable clutch torque. In a four-wheel drive vehicle connected by bypass, a sensor for detecting various information and a control unit for inputting and processing signals from the sensor are provided, and a clutch control signal of the control unit is used together with a torque of the split clutch. A circuit is configured to control the torque distribution to the front and rear wheels, and the control unit determines a high μ torque distribution ratio and a low μ torque distribution ratio according to a vehicle speed based on a steering angle. Detects the output of the stock section and the high μ torque distribution ratio map stock section and the output of the low μ torque distribution ratio map stock section A target torque distribution ratio determining unit for obtaining a torque distribution ratio by interpolation calculation based on the determined road surface condition, and a means for determining a clutch torque according to a torque movement amount based on the torque distribution ratio and outputting a clutch control signal according to the clutch torque. And the torque split of the front and rear wheels is variably controlled according to the road surface condition.

[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, at least at the time of turning, the target torque distribution ratio of the front wheels and the rear wheels set by the steering angle and the vehicle speed is:
By performing correction and control according to the road surface μ using the maps for high μ and low μ, the torque split of the front and rear wheels during turning is optimally controlled depending on the turning state and the road surface state. Here, the target torque distribution ratio is obtained by interpolating and calculating the respective outputs of the high and low μ torque distribution ratio map stock parts based on the detected road surface condition. And the control element can be simplified, and the torque distribution ratio according to the actually detected road surface condition can be set steplessly. Thus, according to the present invention, it is possible to improve both the vehicle stability and the turning performance according to the road surface condition at the time of turning in the active torque split control.

【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 front drive shaft 7 parallel to the output shaft 4 via reduction gears 5 and 6 rotatably provided from the large-diameter ring gear 22 to the transmission output shaft. The front drive shaft 7 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 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 torque 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 by the center differential device 20 is γ, the transmission torque of the front drive shaft 7 is γ · Ti, and the torque of the rear drive shaft 11 is (1−γ ) ・ Ti
Distributed to Therefore, the clutch torque is set to Tc, gears 28 and 29
Assuming that the gear ratio K is K, the torque TF, TR of the front drive shaft 7 and the rear drive shaft 11 by the torque movement becomes TF = γ · Ti−Tc TR = (1−γ) · Ti + KTc. Due to the change in Tc, the distribution ratio of the front side torque TF continuously changes below the distribution ratio in the center differential device 20, and the distribution ratio of the rear side torque TR continuously changes above the distribution ratio in the center differential device 20. Acts on 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. On the other hand, a stock unit 63, which stores a map of the rear wheel torque distribution ratio SH for high μ on a dry road as a correction for road surface conditions,
It has a stock unit 64 for storing a map of the rear wheel torque distribution ratio SL for low μ such as a snowy road. These maps show a high-μ rear wheel torque distribution ratio SH with a high friction coefficient μH and a low μ rear wheel torque distribution ratio SL with a low friction coefficient μL in relation to the steering angle λ and the vehicle speed V.
The steering angle λ of the steering angle sensor 42 and the vehicle speed V of the vehicle speed calculating unit 54 are both input to these map stock units 63 and 64, and the rear wheels for high μ corresponding to the steering angle λ and the vehicle speed V are input. The torque distribution ratio SH and the low-μ rear wheel torque distribution ratio SL are output. In the high μ map, as shown in FIG. 4 (a), in the region where the steering angle at the medium speed is relatively large, the rear wheel torque distribution ratio SH for high μ is set large in order to emphasize the turning performance of the vehicle. In the high-speed small steering angle area, the rear wheel torque distribution ratio SH for high μ is set small in order to emphasize the stability of the vehicle, and in the other area, the rear wheel torque distribution ratio SH for high μ is intermediate and the turning property is emphasized. It is designed for stability. The map for low μ has a rear wheel torque distribution ratio S for low μ as shown in parentheses in FIG.
L is smaller than the high-μ rear wheel torque distribution ratio SH in each of the above-mentioned regions, and there is a tendency that stability is emphasized as a whole. Output of map stock units 63 and 64 and friction coefficient detection means 65
Is input to the target torque distribution ratio determining unit 55, and the rear wheel torque distribution ratio SR is determined by the parameters of the steering angle λ, the vehicle speed V, and the friction coefficient μ. That is, the high friction coefficient μH for high μ, the rear wheel torque distribution ratio SH for high μ, the low friction coefficient μL for low μ, the rear wheel torque distribution ratio SL for low μ, and the actual road surface μ The wheel torque distribution ratio SR is calculated by the following formula for interpolation calculation. SR = {(SH−SL) / (μH−μL)} (μ−μL) + SL Thus, the rear wheel torque distribution ratio SR set by the steering angle λ and the vehicle speed V is linearly corrected according to the road surface μ. This target torque distribution ratio determining unit 55 rear wheel torque distribution ratio S
R and the vehicle body acceleration G detected by the vehicle body acceleration sensor 45 are input to an acceleration correction unit 56. When the acceleration G is substantially zero, the vehicle is regarded as normal running and the rear 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 the 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 ・ Gt 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. Further, 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. As shown in FIG. 4 (d), Pc = g (Tc ). 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 correcting unit 56 determine running conditions based on the steering angle λ, the vehicle speed V, and the vehicle body acceleration G.
Is detected to determine the road surface condition, and the rear wheel torque distribution ratio SR is determined based on the road condition. Further, 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 based on the shift speed Gr to input the input torque Ti. Is calculated. Therefore, in the case of a high μ road during normal traveling, the target torque distribution ratio determining unit 55 determines the rear wheel torque distribution ratio from the high μ map of the stock unit 63 and the low torque map of the map stock unit 64 from the low μ map. The target rear wheel torque distribution ratio SR calculated by interpolation calculation using the rear wheel torque distribution ratio according to the current road surface friction coefficient μ becomes equal to the rear wheel torque distribution ratio SH for high μ. The steering angle λ and the vehicle speed V based on the pattern of FIG.
Are variously determined. That is, under conditions where the center differential input torque is sufficiently large, for example, the steering angle at a medium speed is relatively large,
The rear wheel torque distribution ratio SR is set large, and a duty signal corresponding to this is output, so that the hydraulic unit
30 and the hydraulic pressure of the hydraulic clutch 27 is further increased.Accordingly, the moving torque from the front wheel side to the rear wheel side increases, and a large amount of torque moves to the rear wheel side to increase the rear wheel torque. A very large state of distribution. 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 tire slip between the front wheel and the rear wheel at the time of turning with four-wheel drive always keeps the coefficient of friction with the road surface large, and promotes a reliable line 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. Next, the case where the road surface is deteriorated as compared with the above-mentioned dry road will be described. Input to the torque distribution ratio determining unit 55, and the friction coefficient detecting means
A torque distribution ratio SR is calculated by interpolation calculation in proportion to 65 road surfaces μ. Therefore, as the value of μ decreases, the value of the torque distribution ratio SR also decreases, thereby reducing the clutch pressure of the hydraulic clutch 27 and the amount of torque movement to the rear wheels. Therefore, when turning on a low μ road or the like, the vehicle turns with a torque distribution closer to the front wheels as compared with the case of a high μ road, making it difficult to spin, thereby promoting vehicle stability. Although the embodiment of the present invention has been described above, the present invention is not limited to this. In particular, in determining the torque distribution ratio, a three-dimensional map of the steering angle, the vehicle speed, and the road surface μ may be used. The correction based on the road surface μ may be performed stepwise.

【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 shifted to the rear of the rear wheels 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 torque control is corrected according to the road surface condition, and the torque distribution is closer to the front wheels on the low μ road than on the high μ road, so that the stability of the vehicle particularly when turning is improved. The determination of the front and rear wheel torque distribution ratio according to the road surface condition is set steplessly in accordance with the detected road surface μ, and the torque distribution ratio is determined by detecting each output of the high and low μ torque distribution ratio map stock parts. Since it is obtained by interpolation calculation based on the road surface condition, only two types of map stocks to be provided, one for high μ and one for low μ, are required, and the control elements can be simplified.

[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, 63: torque distribution ratio map stock unit for high μ, 64
…… Low μ torque distribution ratio map stock part, 65 …… Friction coefficient detecting means

Claims (2)

(57) [Claims] 1. A center differential device for distributing motive power to front and rear wheels with a predetermined torque distribution in a drive system, and connected to the center differential device by bypassing a torque split device having a split clutch having a variable clutch torque. In a four-wheel drive vehicle, a sensor for detecting various information, a control unit for inputting and processing signals from the sensor, and a torque distribution to the front and rear wheels together with a torque for the split clutch by a clutch control signal of the control unit. The control unit is configured to determine a high and low μ torque distribution ratio according to the steering angle based on the vehicle speed.
The target of obtaining the torque distribution ratio by interpolating the output of the high torque distribution ratio map stock part and the output of the low μ torque distribution ratio map stock part based on the detected road surface condition. A torque distribution ratio determining unit, and means for determining a clutch torque according to a torque movement amount based on the torque distribution ratio, and outputting a clutch control signal according to the clutch torque, wherein a torque split between the front and rear wheels is determined according to a road surface condition. A torque split control device for a four-wheel drive vehicle, wherein the torque split control device variably controls the torque split. 2. The high-μ torque distribution ratio map stock section outputs a rear-wheel-side torque distribution ratio, and the low-μ torque distribution ratio map stock section outputs a front-wheel-side torque distribution ratio. The torque split control device for a four-wheel drive vehicle according to claim 1, characterized in that: