JP2679302B2 - Vehicle differential limiting control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicular differential limiting control device for controlling a differential limit according to a predetermined control condition to which a differential limiting torque is applied by an external control force.

(Prior Art) As a conventional vehicular differential limiting control device, for example, a device described in JP-A-62-103226 (Japanese Patent Application No. 60-244676) is known.

This conventional source discloses a limited slip differential control device that detects the slip condition of each wheel from the rotational speed of the wheel and controls the slip ratio of the turning outer wheel of the drive wheel to a predetermined value.

(Problems to be Solved by the Invention) However, in such a conventional vehicle differential limiting control device, a target slip that is a control target is set based on a slip characteristic of a standard tire or the like mounted on an applicable vehicle. Since it is a device that sets the ratio in advance, if the slip characteristics of the tire are largely changed from the reference slip characteristics, for example, if the tire characteristics change, road surface temperature, tire wear, etc., The lateral force characteristic with respect to tire slip changes, and the vehicle steer characteristic changes to oversteer or understeer.

That is, there are tire brands (A), (B), (C),
A specific example in which each tire has a slip characteristic as shown in FIG. 10 will be described.

When the owner changes the tire brand of the driving wheel (rear wheel) from (A) to (C) at the time of new car, as is clear from FIG. 10, tire-road surface for the same slip ratio S Inter-friction coefficient μ characteristics deteriorate. This coefficient of friction μ
As a result, the magnitude of the lateral force generated at the turning outer wheel also changes during turning.

As a result, if the same control as that performed when the tire brand is (A) is performed, the steer characteristics are different.

By the way, in the above example, the lateral force of the rear wheels, which are the driving wheels, is reduced, resulting in oversteer, which leads to vehicle spin at the turning limit at which high lateral acceleration occurs.

The present invention has been made in view of the above-described problems, and in a vehicle differential limiting control device that applies a differential limiting torque between the left and right wheels by external control, a change in tire slip characteristics occurs. Even if there is, it is an object to prevent the vehicle spin by suppressing the change of the steering characteristic of the vehicle at the turning limit.

(Means for Solving the Problems) In order to solve the above problems, the vehicle differential limiting control device of the present invention detects the vehicle body slip angle, and when the vehicle body slip angle is larger than a set value, that is, the vehicle is A means for performing control to increase or decrease the differential limiting torque applied in the direction of decreasing the vehicle body slip angle when the turning limit at which spin is likely to occur is made.

That is, as shown in the claim correspondence diagram of FIG. 1, a differential system that is provided in a drive system that distributes and transmits the engine driving force to the left and right driving wheels while allowing differential, and that generates a differential limiting torque by an external control force. The limiting mechanism a, a turning differential limiting control means e that applies a differential limiting torque so that the tire slips of the left and right driving wheels reach a target slip state in which turning stability is obtained when turning, the vehicle body center line and the vehicle body advancement. The vehicle body slip angle detecting means b for detecting the vehicle body slip angle which is an angle formed by the direction, the yaw moment direction determining means c for determining the direction of the yaw moment generated by the differential limitation, and the vehicle body slip angle being larger than the set value. In this case, when the yaw moment direction generated by the differential limitation is an under moment, control is performed to increase the differential limiting torque applied, and the difference Differential limit torque increasing / decreasing control means d for performing control to reduce the applied differential limit torque when the yaw moment direction generated by the dynamic limit is an over moment.

The yaw moment direction discriminating means c inputs the inner / outer wheel rotation speed during turning, and when the inner wheel rotation speed is higher than the outer wheel rotation speed, it is judged as an over-moment in the oversteer direction, and the inner wheel rotation speed is the outer wheel rotation speed. When it becomes smaller, it may be a means for discriminating the undermoment in the understeer direction.

(Operation) At the time of turning, in the turning differential limiting control means e, differential limiting torque is applied so that the tire slips of the left and right driving wheels reach a target slip state in which turning stability is obtained, and the vehicle body slip angle detecting means In b, the vehicle body slip angle, which is the angle formed by the vehicle body center line and the vehicle body traveling direction, is detected.

When it is determined that the detected vehicle body slip angle is larger than the set value during this turning, the yaw moment direction generated by the differential limitation is undermoment in the differential limiting torque increase / decrease control means d. When judged by the yaw moment direction judging means c, control is performed to increase the applied differential limiting torque, and the yaw moment direction judging means c determines that the yaw moment direction generated by the differential limiting is an over moment. When the determination is made, control is performed to reduce the applied differential limiting torque.

Therefore, when the yaw moment direction generated by the differential limitation is the under moment, that is, at the turning limit where the steer characteristic shows the oversteer characteristic, the yaw moment in the understeer direction generated by the control that increases the differential limiting torque is generated. The oversteer characteristic is suppressed by.

Further, when the yaw moment direction generated by the differential limitation is an over moment, that is, when the steering limit shows an understeer characteristic as a turning limit, the yaw moment in the oversteer direction generated by the control for reducing the differential limiting torque is generated. The understeer characteristic is suppressed by.

Hereinafter, the present invention will be described with reference to the drawings.

 First, the configuration will be described.

FIG. 2 is an overall system diagram of a vehicular differential limitation control device applied to a rear-wheel drive vehicle.

In FIG. 2, the engine drive system includes an engine 1,
It has a transmission 2, a rear propeller shaft 3, a rear differential 4, rear drive shafts 5 and 6, and rear wheels 7 and 8. Incidentally, 9 and 10 are rear wheels.

A differential between the rear propeller shaft 3 and the rear drive shafts 5 and 6 is provided by a wet multi-plate friction clutch structure capable of changing the differential limiting torque by a clutch engagement pressure P _C applied from the outside. Limiting clutches (differential limiting mechanisms) 11 and 12 are built in the rear differential 4 (for details, see Japanese Patent Laid-Open No. 62-103226).

The differential limiting clutches 11 and 12 have an external device,
A hydraulic control unit 20 to produce a clutch engagement pressure P ^C, the electronic control unit 30 for outputting a command to make the clutch engagement pressure P _C is provided.

The hydraulic control device 20 supplies the hydraulic pressure by the pump pressure from the hydraulic pump 21 to the clutch engagement pressure according to the command current value I _C.
A hydraulic control solenoid valve 22 for adjusting the pressure to P _C is provided.

The electronic control unit 30 includes an LSD control unit 3 having a microcomputer, a drive circuit, etc. in its internal circuit.
1 and input information means 32 for obtaining input information necessary for control calculation in the control unit 31. As the input information means 32, there are a vehicle speed sensor 33 for detecting a vehicle speed V and a steering wheel for detecting a steering angle θ. Angle sensor 34, right rear wheel speed sensor 35 for detecting right rear wheel speed nr, left rear wheel speed sensor for detecting left rear wheel speed nl
36, accelerator opening sensor 3 to detect accelerator opening A _CC
7, the lateral acceleration sensor 38 for detecting a lateral acceleration Yg, the longitudinal direction of the vehicle speed sensor 39 for detecting a vehicle longitudinal direction vehicle speed V _L, the transverse direction of the vehicle speed sensor 40 for detecting a vehicle lateral speed V _Q are provided .

The LSD control unit 31 has a clutch engagement force TΔn calculation unit based on the outer wheel slip velocity, a tack-in countermeasure torque T _T calculation unit, a torque Tψ calculation unit according to the vehicle body slip angle Ψ, and these torques. And a calculation unit of the clutch engagement force T based on the sum of the above.

 Next, the operation will be described.

FIG. 3 is a flowchart of a main routine showing the flow of the differential limiting control operation in the embodiment, and each step will be described below.

In step 100, the vehicle speed, the steering angle θ, the right rear wheel speed nr, the left rear wheel speed nl, the accelerator opening A _CC , the lateral acceleration are detected from the sensors 33 to 40.
yg, vehicle longitudinal direction vehicle speed V _L , vehicle lateral direction vehicle speed V _Q are read.

In step 101, the slip velocity of the turning outer wheel is detected according to the flow shown in FIG. 4, and the clutch torque TΔn is calculated based on the outer wheel slip velocity (tire slip).

In step 102, the tack-in generated when the accelerator is off is detected according to the flow shown in FIG. 5, and the tack-in countermeasure torque T _T is calculated.

In step 103, calculation of the torque Tψ according to the vehicle body slip angle ψ, which is a control featured by the present invention, is performed according to the flow shown in FIG.

In step 104, the clutch engagement force T is calculated from the sum of the torques TΔn, T _T , and Tψ obtained by the above calculation.

T = TΔn + T _T + Tψ where the clutch torque TΔn due to the outer wheel slip velocity
The relation between the torque and the tack-in countermeasure torque T _T when the accelerator is off is described as follows: _T Δn is differentially limited when the inner wheel of the turning wheel spins due to the driving force during turning acceleration, while T _T is decelerated by the accelerator off operation. In that case, differential limitation is performed, so that T _T = 0 when TΔn is positive, and T Δn = 0 when T _T is positive, and they do not affect each other.

Therefore, the clutch engagement force T is substantially T = TΔn + Tψ (during acceleration) T = T _T + Tψ (during deceleration), and the basic control TΔn, T _T during acceleration and deceleration, respectively.
On the other hand, the differential limiting torque is corrected with the torque Tψ according to the vehicle body slip angle ψ, and the control is performed in response to the fluctuation of the road surface condition and the slip condition.

In step 105, the control current Ic with which the clutch engagement force T is obtained is output from the drive circuit to the control solenoid valve 22.

Next, the calculation process of the clutch torque TΔn based on the outer wheel slip velocity will be described according to the flow shown in FIG.

This processing calculates the slip target value ΔW _A (step 200) set according to the accelerator opening A _CC and the actual slip speeds ΔW _R and ΔW _L of the left and right wheels (step 201), Determine the outer turning wheel based on the turning direction, and determine the slip speed of the outer turning wheel △
W _R or △ W _L slip target value △ W a speed determining required to match _A (step 202 to step 208), the clutch torque Tiderutaenu, respectively one control cycle before the clutch torque Tiderutaenu _O to the set value It is calculated by increasing or decreasing A (step 209 to step 214).

Next, the processing for calculating the tack-in countermeasure torque T _T will be described according to the flow shown in FIG.

This process is as a start condition for tuck-in control.
If the accelerator opening A _CC is less than the predetermined value A _O (step 305), the accelerator change speed A _CC is 0 or negative (step 306), and the absolute accelerator change speed | A _CC | exceeds the predetermined value A _1. (Step 307) When the lateral acceleration yg is equal to or greater than the predetermined value Y ₁ (Step 308), when these conditions are satisfied, the tack flag TUCKFLG = 1 is set, and as shown in Step 310, the vehicle speed V and the lateral acceleration Yg. The tack-in countermeasure torque T _T that suppresses the tack-in is calculated according to.

It should be noted that steps 300 to 303 are processing steps for setting the accelerator change speed flag A _CC FLG.
Step 311 and step 312 are steps for determining the release condition of the tuck-in suppression control, and when not controlling, step 31
In 3 the tack flag TUCKFLG = 0 is set, and step 314
The tuck-in countermeasure torque T _T is set to 0.

Next, the vehicle body slip angle Ψ according to the flow shown in FIG.
The calculation process of the torque T ψ according to will be described.

In step 400, the vehicle body slip angle Ψ is calculated from the vehicle longitudinal direction vehicle speed V _L and the vehicle lateral direction speed V _Q by the following formula,
Determine the turning direction and add a code.

Here, the turning direction is the lateral acceleration Yg (or steering angle θ)
Is used to determine whether the vehicle is turning to the right or to the left, and the following signs are attached.

A method of assigning a sign to the vehicle body slip angle Ψ in the case of turning left will be described.

FIG. 7 shows a low speed grip turning, and since the turning center is on the rear axle side from the center of gravity, the lateral vehicle speed V _Q is generated inward of the turning (left in the drawing). Therefore, at this time, the vehicle body slip angle Ψ is negative.

FIG. 8 shows a high-speed limit turning, and since the turning center is on the front axis side from the center of gravity, the lateral vehicle speed V _Q is generated in the turning outward direction (to the right in the drawing). Therefore, at this time, the vehicle body slip angle Ψ is positive.

 In step 401, the turning direction is determined.

 This is done by steering θ or lateral acceleration Yg.

When it is determined in step 401 that the vehicle is turning to the right, the process proceeds to step 402, in which the left rear wheel speed nl is substituted for the outer wheel rotational speed N _OUT and the right rear wheel speed nr is substituted for the inner wheel rotational speed N _IN .

When it is determined in step 401 that the vehicle is turning left, the process proceeds to step 403, in which the right rear wheel speed nr is substituted for the outer wheel rotation speed N _OUT , and the left rear wheel speed nl is substituted for the inner wheel rotation speed N _IN .

In step 404, the direction of generation of the moment due to the limited differential torque is determined based on the magnitudes of the inner and outer wheel rotation speeds N _OUT and N _IN .

That is, when the outer wheel rotation speed N _OUT is higher than the inner wheel rotation speed N _{IN, an} understeer yaw moment is generated due to the differential limitation. Therefore, in step 405, the differential equation is used to reduce the vehicle body slip angle Ψ. Increase the torque limit and generate understeer yaw moment.

_{Tψ = K 2 * (Ψ-} Ψ O) On the other hand, if the wheel rotating speed N _OUT is less than the inner ring rotation speed N _IN, since the yaw moment of oversteer is generated by the differential restriction, in step 406, the vehicle body slip angle [psi The torque of the differential limit is reduced and the yaw moment of the oversteer is reduced by the following equation so as to reduce.

Tψ = K ₁ * (Ψ−Ψ _O ) Here, in steps 405 and 406, as shown in FIG. 9, when the actual vehicle body slip angle Ψ is larger than the vehicle body slip angle set value Ψ _O , the difference Ψ between them. -It has a characteristic of differentially limiting according to Ψ _O.

As described above, the differential limit control is performed,
It has the features listed below.

When the vehicle body slip angle Ψ is detected and the vehicle body slip angle Ψ is larger than the set value Ψ _O , that is, when the vehicle is at a turning limit where the vehicle is likely to spin, the vehicle body slip angle Ψ is reduced and the differential limiting torque is reduced. Since it is a device that controls increase / decrease by the corresponding torque Tψ, for example, different brands of tires,
Even if the tire slip characteristics change due to road surface conditions, tire wear, and the like, the change in the steering characteristics of the vehicle is suppressed at the turning limit, and vehicle spin can be prevented.

Since the differential limiting torque is given by the sum of the clutch torque TΔn due to the outer wheel slip speed, the tack-in countermeasure torque T _T, and the torque Tψ according to the vehicle body slip angle Ψ, wheel spin of the inner wheel during turning is prevented during acceleration turning. As a result, turning stability is ensured, and tack-in is effectively prevented during deceleration turning.
In any turn of acceleration and deceleration, correction of the differential limiting torque by the torque Tψ provides the vehicle spin prevention effect at the turning limit when the slip characteristics of the tire described above are changed.

The embodiments of the present invention have been described in detail with reference to the drawings.
The specific configuration is not limited to this embodiment. For example, in the embodiment, the hydraulic clutch is shown as an example of the differential limiting mechanism, but an electromagnetic clutch, a viscous clutch or the like may be used.

(Effects of the Invention) As described above, according to the present invention, in the vehicle limited slip control device that applies the limited slip differential torque between the left and right wheels to obtain turning stability during turning, the vehicle body slip angle When the vehicle body slip angle is larger than the set value, that is, when the vehicle is at the turning limit where spin is likely to occur, control is performed to increase or decrease the differential limiting torque applied in the direction to reduce the vehicle body slip angle. Since the means is adopted, even if there is a change in the slip characteristic of the tire, it is possible to prevent the vehicle spin by suppressing the change in the steer characteristic of the vehicle at the turning limit.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to a claim showing a vehicle differential limiting control device of the present invention, FIG. 2 is an overall system diagram showing a vehicle differential limiting control device applied to a rear-wheel drive vehicle, and FIG. 3 is an embodiment. A flow chart of the main routine showing the flow of differential limiting control operation performed by the LSD control unit in the device,
FIG. 4 is a flow chart showing the flow of clutch torque calculation processing operation based on the outer wheel slip speed, FIG. 5 is a flow chart showing the flow of calculation processing operation of tack-in countermeasure torque, and FIG. 6 is torque calculation according to vehicle body slip angle. FIG. 7 is a flow chart showing the flow of the processing operation, FIG. 7 is a schematic explanatory view for explaining how to assign the reference sign of the vehicle body slip angle during low-speed grip turning, and FIG. Explanatory schematic diagram for explanation, 9th
FIG. 10 is a characteristic diagram of torque corresponding to vehicle body slip angle, and FIG. 10 is a characteristic diagram of friction coefficient with respect to slip ratio due to difference in tire brand. a ... Differential limiting mechanism b ... Body slip angle detecting means c ... Yaw moment direction determining means d ... Differential limiting torque increase / decrease control means e ... Turning differential limiting control means

Claims (2)

(57) [Claims] 1. A differential limiting mechanism provided in a drive system for distributing and transmitting an engine driving force to left and right driving wheels while allowing differential, and a differential limiting mechanism for generating differential limiting torque by an external control force; The vehicle-body slip angle, which is the angle formed by the vehicle body center line and the vehicle body traveling direction, is set to the vehicle-body centerline and the vehicle body traveling direction, and the vehicle-body centerline and the vehicle body traveling direction are controlled by the vehicle body centerline and the vehicle body traveling direction. A vehicle body slip angle detecting means for detecting, a yaw moment direction determining means for determining the direction of a yaw moment generated by the differential limitation, and a yaw moment generated by the differential limitation when the vehicle body slip angle is larger than a set value. When the direction is under moment, control is performed to increase the differential limiting torque applied, and the yaw moment direction generated by differential limiting Is an over-moment, a differential limit torque increasing / decreasing control means for performing control to reduce the applied differential limit torque, and a differential limit control device for a vehicle. 2. The yaw moment direction discriminating means inputs the rotational speeds of the inner and outer wheels during turning, and when the inner ring rotational speed is higher than the outer wheel rotational speed, it is determined as an overmoment in the oversteer direction, and the inner ring rotational speed is the outer wheel rotational speed. The differential limiting control device for a vehicle according to claim 1, wherein when the rotational speed is lower than the rotational speed, it is determined as an undermoment in the understeer direction.