JPH04325318A - Differential control device - Google Patents

Abstract

PURPOSE:To provide a differential control device capable of correctly controlling the slip of wheels. CONSTITUTION:The differential action of a differential device is controlled in a vehicle driving the right and left wheels via the differential device. A means 22 detecting the speed of the left drive wheel, a means 24 detecting the speed of the right drive wheel, a means 26 detecting the yaw rate, and a controller 28 are provided. The controller 28 is a CPU, it subtracts the smaller speed Vrl and a correction value given as the product of the detected yaw rate gamma and a tread (t) from the larger speed Vrr within the detected right and left wheel speeds to determine the wheel slip value, and the differential action of the differential device 14 is controlled based on this wheel slip value.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a differential control device.
In particular, the present invention relates to a device for controlling the differential of a differential device in a vehicle in which left and right wheels are driven via a differential device.

0002

[Prior Art] A differential limiting mechanism provided in a differential device that transmits driving force to left and right wheels includes a means for detecting the speed of the left wheel, a means for detecting the speed of the right wheel, and a means for detecting the speed of the right wheel. A differential control device has been proposed that is controlled by a means for detecting a steering angle, a means for detecting a steering angle, and a controller that receives signals from these means (Japanese Patent Application Laid-open No. 312238/1983). This differential control device corrects a reference wheel speed difference based on vehicle speed and steering angle to perform fine control.

0003

[Problem to be Solved by the Invention] The speed difference between the left and right wheels includes a difference in turning trajectory and a slip value of the wheels. Even if the speed, vehicle speed, steering angle, etc. are detected and the differential is controlled based on this, the speed component of the left and right wheels due to the difference in turning trajectory is not accurately corrected, so it is difficult to prevent wheel slip. cannot be precisely controlled.

By the way, by determining a target yaw rate from the vehicle speed and steering angle and controlling the differential so that the actual yaw rate approaches the target yaw rate, it is possible to change the steering characteristics of the vehicle and improve the steering stability. However, in the conventional system, control is based on the difference between the target yaw rate and the actual yaw rate, resulting in reverse control when turning left and right, etc.
It does not necessarily achieve its original purpose.

An object of the present invention is to provide a differential control device that can accurately control wheel slip.

Another object of the present invention is to provide a differential control device that can achieve a high level of driving performance that takes into consideration not only wheel slip but also the steering characteristics of the vehicle.

[0007]

[Means for Solving the Problems] The present invention is a device for controlling the differential of a differential device in a vehicle in which left and right wheels are driven via a differential device, the device detecting the speed of the left driving wheel. means for detecting the speed of the right drive wheel, means for detecting the yaw rate, and a controller. The controller calculates a wheel slip value by subtracting the smaller speed and a correction value based on the detected yaw rate from the larger speed of the detected left and right wheel speeds, and controls the differential based on this wheel slip value. do.

The present invention also provides a device for controlling the differential of a differential device in a vehicle in which left and right wheels are driven via a differential device, comprising means for detecting the speed of the vehicle and a means for detecting a steering angle. means for detecting the speed of the left drive wheel, means for detecting the speed of the right drive wheel, means for detecting the yaw rate, and a controller. The controller determines a target yaw rate from the detected vehicle speed and steering angle, and calculates a steering characteristic value by multiplying the value obtained by subtracting the detected yaw rate from the target yaw rate and the detected yaw rate. The controller further calculates a wheel slip value by subtracting the smaller speed and a correction value based on the detected yaw rate from the larger speed of the detected left and right wheel speeds, and calculates the wheel slip value and the steering characteristic value. The differential is controlled based on and.

[0009]

[Operation and Effect] In the first invention, the differential of the differential device is controlled so that a differential limiting force that is substantially proportional to the wheel slip value is applied, and in the second invention, the differential of the differential device is controlled so that the wheel slip value is the same. If the steering characteristic of the vehicle determined from the steering characteristic value is understeer, a small differential limiting force is applied, and if the steering characteristic is oversteer, a large differential limiting force is applied.

[0010] Simply taking the difference between the speed of the wheels on the outside and the speed of the wheels on the inside of the turn, the component of the wheel speed difference caused by the difference in turning trajectory, that is, the component corresponding to the product of the yaw rate and the tread, is However, according to the present invention, since the wheel slip value is obtained by subtracting a correction value based on the yaw rate from the difference, the accuracy can be increased. Can be done. In particular, if the product of the yaw rate and the tread is taken as a correction value based on the yaw rate, the wheel slip value will be the exact difference between the slip of the outer wheel and the slip of the inner wheel. By controlling the differential using the wheel slip values obtained in this way, fine differential control is possible.

In addition, in the second invention, not only the wheel slip value but also the steering characteristic value is considered, and even if the wheel slip value is the same, if the steering characteristic of the vehicle determined from the steering characteristic value is understeered, the differential limiting force is becomes smaller, and if there is oversteer, control can be performed to increase the differential limiting force. This makes it possible to achieve a higher level of vehicle dynamic performance.

0012

[Embodiment] In the embodiment shown in FIG. 1, the differential control device controls the differential of a differential device 14 in a vehicle that drives left and right rear wheels 10, 12 via a differential device 14. , means 16 and 18 for detecting the speed of the vehicle, means 20 for detecting the steering angle θ, means 22 for detecting the speed of the left drive wheel 10, and means 24 for detecting the speed of the right drive wheel 12. , means 26 for detecting yaw rate γ, and a controller 28.

The differential device 14 includes a plurality of friction plates 32
A differential limiting mechanism 30 is provided. The plurality of friction plates 32 are brought into contact with each other by the supplied hydraulic pressure and generate frictional force. This frictional force is proportional to the oil pressure.
This becomes differential limiting force. When a current is supplied to the hydraulic pressure generator 34, a hydraulic pressure proportional to the magnitude of this current is supplied from the hydraulic pressure generator 34 to the differential limiting mechanism 30.

The above-mentioned differential device 14 and differential limiting mechanism 30
, the hydraulic pressure generator 34, and the like are known per se, as described in the above-mentioned publication, and the various detection means described above are also known.

When the rear wheels are driven, it is assumed that the vehicle turns to the left, as shown in FIG. 2, and the wheels 12 on the outside of the turn
When the speed of the inner wheel 10 is Vrr, the speed of the inner wheel 10 is Vrl, and the tread is t, the wheel slip value ΔV is ΔV=Vr
It is given by r-Vrl-tγ (1). Then, the speed V of the vehicle is determined by the inner front wheel 3, which is the non-driven wheel.
6 is Vfl, and the speed of the outer front wheel 38 is Vfr, it is given by V=(Vfl+Vfr)/2 (2).

When the front wheels are driven, the wheel slip value ΔV becomes ΔV=Vfr−Vfl−tγ (3), and the vehicle speed V becomes V=(Vrl+Vrr)/2 (4).

When the vehicle turns to the right, in the above equation giving the wheel slip value ΔV, (Vrr-Vrl)
to (Vrl-Vrr) and (Vfr-Vfl) to (
Vfl-Vfr). Therefore, if we take the absolute value of the wheel slip value and express it as |ΔV|, then the basic algorithm for wheel slip control is: P = Kv |ΔV| (5) If the hydraulic pressure for differential control is P, .

Here, Kv is a control constant and is either a constant value or a variable value with respect to the vehicle speed. Kv
Instead of giving a mathematical formula, a map such as the one shown in FIG. 3 can also be used. The control constant A in the map of FIG. 3 is given by a polygonal line and exhibits nonlinear characteristics, and has a greater degree of freedom in characteristics than B, where the control constant is constant.

The oil pressure P is determined by a controller 28 that is a CPU or a computer. controller 2
8 supplies current to the hydraulic pressure generator 34 to generate the hydraulic pressure P. As a result, the hydraulic pressure P is supplied to the differential limiting mechanism 30,
The differential movement of the differential device 14 is limited by a differential limiting force corresponding to the oil pressure P.

By the way, it is known that by calculating the target yaw rate from the vehicle speed and steering angle and controlling the detected actual yaw rate to approach the target yaw rate, the steering characteristics of the vehicle can be improved and the steering stability can be improved. It is being Conventional control for this purpose is the target yaw rate γ0
Since only the difference between the actual yaw rate γ and the actual yaw rate γ is calculated, the following problem arises.

[0021]

[Table 1]

In the table, the units of the target yaw rate and the actual yaw rate are rad/s or °/s, and left rotation is represented by a plus sign, while right rotation is represented by a minus sign. In case (2), the target yaw rate is 10 in the left direction, and the actual yaw rate is 5 in the left direction. In addition, in ■, the target yaw rate is 10 in the right direction, and the actual yaw rate is 5 in the right direction. This shows that although there is a difference between turning left and turning right, the steering characteristics of the vehicle are the same in both cases. Nevertheless, when taking the difference between the target yaw rate and the actual yaw rate, it is 5 for ■, but -5 for ■.

In ■ and ■, the absolute value of the target yaw rate minus the absolute value of the actual yaw rate, sin
Both cases where γ is used only to determine the sign are 5, indicating correct steering characteristics.

Next, looking at ■ and ■, in ■,
The target yaw rate is 10 in the left direction and the actual yaw rate is 5 in the right direction. In addition, in ■, the target yaw rate is 10 in the right direction, and the actual yaw rate is 5 in the left direction. Therefore, the steering characteristics of the vehicle are the same in both cases. Nevertheless, when we take the difference between the target yaw rate and the actual yaw rate, it is 15 for ■ and -15 for ■. Furthermore, if we take the difference in absolute values, both are 5
, when sin γ is used for sign determination, both are −15
It becomes.

After all, among the determination methods shown in Table 1, those that take a simple difference may result in reverse control because the sign changes depending on the turning direction, and those that take a difference in absolute values may not. , cannot be used because it does not show any tendency of steering characteristics itself. Furthermore, in the case where sin γ is used for sign determination, the sign of the product value in the table changes in areas where this value changes from plus to minus or vice versa. control becomes discontinuous in the state.

A control algorithm using the target yaw rate γ0 and the detected actual yaw rate γ, which was devised to correct the above-mentioned problem, is as follows. Assuming that the detected vehicle speed is V, the steering angle is θ, and it is a first-order lag system,

[Formula 1] Here, γc is a constant, τ is a time constant, which can be given by the map shown in FIG. 4, and s is a Laplace operator. The steering characteristic value Δγ is a value obtained by subtracting the detected yaw rate γ from the target yaw rate γ0, and
As the value multiplied by the detected yaw rate γ, Δγ
= γ(γ0 - γ) (7) is given.

[0027]

[Table 2]

Table 2 shows the target yaw rate γ0 used in Table 1.
The steering characteristic value Δγ is calculated from the detected actual yaw rate γ.
This is what I got. The steering characteristic value does not directly indicate the deviation between the target yaw rate and the actual yaw rate, but the sign does not change even if the turning direction changes, and it does not become discontinuous, so it can be used to determine the tendency of the steering characteristic. can. That is, when the steering characteristic value Δγ is positive, there is an understeer tendency, and as its absolute value increases, the understeer tendency becomes stronger. Conversely, when the steering characteristic value is negative, there is a tendency to oversteer, and as its absolute value increases, the tendency to oversteer becomes stronger.

The basic algorithm for the oil pressure P that performs differential control according to the steering characteristic value Δγ is as follows. P=-Kr Δγ [Δγ≦0] =0 [Δγ>0] (8) Kr is a control constant and can be a constant value or can be variable depending on the vehicle speed. A map shown in FIG. 5 can also be used instead of giving it using a mathematical formula. Since the map C in FIG. 5 is given as a polygonal line and is non-linear, it has a higher degree of freedom in characteristics than the straight line map D. The algorithm given by equation (8) and the map in Figure 5 strengthens the differential limiting force to decrease the yaw rate when there is a tendency to oversteer, and weakens the differential limiting force to increase the yaw rate when there is an understeer tendency. It is something.

Wheel slip control and vehicle steering characteristic control can be performed independently of each other, but it is also possible to combine them. The basic algorithm for combining the two is as follows from equations (5) and (8). P=Kv (1-Kr Δγ) | ΔV | (9) Or, P=Kv ′ | ΔV | (10) K
v' can be determined from the Δγ map shown in FIG. According to the control according to equation (9) or equation (10), a higher level of vehicle motion performance can be achieved because the control is a combination of wheel slip control and vehicle steering characteristic control.

The controller 28 executes composite control according to the flowchart shown in FIG. That is, initialize (100) and set the wheel speeds Vfl, Vfr, Vrl
, Vrr (101), and yaw rate γ (102). Expression (1) of wheel slip value ΔV and vehicle speed V
, (2) (103), and from the map in Figure 4, γ
c and τ are determined (104). After that, the steering angle θ is detected (105), and the target yaw rate γ0 is calculated using equation (6).
(106). Furthermore, the steering characteristic value Δγ is determined from equation (7) (107), the control constant Kv' is determined from the map in FIG. 6 (108), and the pressure P is calculated (
109). Controller 28 outputs a current corresponding to pressure P to pressure generator 34 (110) and repeats the routine. Due to the current output to the pressure generator 34, a pressure proportional to the current is applied to the friction plate 3 of the differential limiting mechanism 30.
2, limiting the differential.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a differential control device.

FIG. 2 is a schematic diagram showing wheel slip control.

FIG. 3 is a graph showing a map that can be used for wheel slip control.

FIG. 4 is a graph showing a map that can be used when calculating a target yaw rate.

FIG. 5 is a graph showing a map that can be used when calculating the oil pressure to be applied to the differential limiting mechanism using the steering characteristic value.

FIG. 6 is a graph showing a map that can be used for complex control.

FIG. 7 is a flowchart of composite control.

[Explanation of symbols]

14 Differential device 16, 18 Vehicle speed detection means 20 Steering angle detection means 22, 24 Wheel speed detection means 26 Yaw rate detection means 28 Controller 30 Differential limiting mechanism 32 Friction plate

Claims (2)

[Claims] 1. A device for controlling the differential of a differential device in a vehicle in which left and right wheels are driven via a differential device, the device comprising means for detecting the speed of the left driving wheel and a means for detecting the speed of the right driving wheel. The controller includes a means for detecting a speed, a means for detecting a yaw rate, and a controller, and the controller is configured to detect a speed from a larger speed to a smaller speed among the detected speeds of the left and right wheels, and a correction value based on the detected yaw rate. A differential control device that calculates a wheel slip value by subtracting the wheel slip value and controls the differential based on this wheel slip value. 2. A device for controlling the differential of a differential device in a vehicle in which left and right wheels are driven via a differential device, the device comprising: means for detecting the speed of the vehicle; and means for detecting a steering angle; means for detecting the speed of the left drive wheel, means for detecting the speed of the right drive wheel, means for detecting the yaw rate, and a controller, the controller configured to detect the detected speed and steering angle of the vehicle. The controller further calculates the steering characteristic value by subtracting the detected yaw rate from the target yaw rate and multiplying the detected yaw rate by the value obtained by subtracting the detected yaw rate from the target yaw rate. Differential control that calculates a wheel slip value by subtracting the smaller speed and a correction value based on the detected yaw rate from the larger speed, and controls the differential based on this wheel slip value and the steering characteristic value. Device.