JP2643233B2 - Differential limiting force control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential limiting force control device for a vehicle capable of variably controlling a differential limiting force of left and right drive wheels by controlling a coupling force of a differential limiting clutch.

(Prior Art) As a conventional differential limiting force control device, for example,
Japanese Patent Application Laid-Open No. 67629/1986 and Japanese Patent Application Laid-Open No. 61-102321 are known.

The former device has vehicle speed as input information, and is a control content for increasing the clutch engagement force as the vehicle speed becomes higher.
The latter device has a control content in which the acceleration state is used as input information and the clutch engagement force is increased as the acceleration state increases.

(Problems to be Solved by the Invention) However, in such a conventional device, the clutch engagement force is controlled only by the input information of the vehicle speed or the acceleration state. If the control content is suitable for a high friction coefficient road,
When the vehicle travels on a road with a low friction coefficient, the differential limiting force increases sharply, causing a tail swing. In addition, even when traveling on a road with a high friction coefficient, a strong understeer occurs when turning in at a tight corner. On the other hand, if the control content is suitable for a low friction coefficient road where the clutch engagement force is weak overall,
When traveling on a road with a high friction coefficient, the spin of the turning inner wheel becomes remarkable because the differential limiting force is low, and the turning acceleration is poor. As a countermeasure, it is conceivable to correct the control content by the road surface friction coefficient, but it is difficult to directly and accurately detect the road surface friction coefficient.

In order to solve the above-mentioned problem, the applicant has disclosed in the specification and drawings of Japanese Patent Application No. 62-264525 that the differential limiting force is increased as the turning radius is larger and the centripetal acceleration is higher. The device was proposed.

However, in this prior apparatus, the differential limiting force is controlled using the turning radius and the centripetal acceleration as parameters, regardless of the turning radius, so that the steering wheel is cut from a constant vehicle speed. In the case of turning, the increase of the moment in the understeer direction becomes remarkable due to the application of the differential limiting force in the first half of turning, which is a large turning radius.
In the case of a small radius turn with the steering wheel turned while accelerating, the turning performance of the vehicle is inferior due to the lack of the differential limiting force in the latter half of the turn, which is a small turning radius. Also in this case, the tack-in prevention effect is inferior due to insufficient differential limiting force.

That is, when the steering wheel is cut from a constant vehicle speed and when the steering wheel is cut while accelerating, even if the same centripetal acceleration and turning radius, in the former case, the inner wheel side driving force is changed by the outer wheel side driving force. In the latter case, the outer wheel side driving force is larger than the inner wheel side driving force. It was difficult to obtain sufficient driving characteristics due to the large outflow of force.

This is, as shown in the relationship of the friction circle of the tire in FIG.
When a large acceleration is performed, the lateral force is reduced, and the lateral flow becomes easy. This results in a difference between understeer and oversteer characteristics of the vehicle.

In addition, when the driving force is increased by the acceleration operation and the driving force exceeds the capacity of the tire, the tire idles.
Since this state starts from the inner wheel having a small wheel load during turning, the state becomes an oversteer direction at the driving moment.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above-mentioned problems, and in order to achieve this object, the present invention provides a method as shown in the conception diagram of FIG. A differential limiting force control means a for outputting a differential limiting force command value determined based on an input detection value from a predetermined detecting means, and an external control based on a command value from the differential limiting force control means 2. A differential limiting force control device comprising: a differential limiting clutch that variably controls the differential limiting force of the left and right driving wheels by controlling the engagement force. Means c, a centripetal acceleration detecting means d for detecting the centripetal acceleration of the vehicle, and a longitudinal acceleration detecting means e for detecting the longitudinal acceleration of the vehicle, wherein the differential limiting force control means a has a turning radius exceeding a predetermined radius. When you are, turn radius value And a value increasing according to the absolute value of the centripetal acceleration is defined as a differential limiting force command value. When the turning radius is equal to or less than a predetermined radius, a value increasing according to the absolute value of the centripetal acceleration and the absolute value of the longitudinal acceleration is referred to as the differential limiting force command value. It is characterized in that it is a means for obtaining a value.

(Operation) At the time of a large turning radius, a value that increases according to the turning radius value and the absolute value of the centripetal acceleration is output from the differential limiting force control unit a as the differential limiting force command value. As a result, the following effects are obtained in each running state.

When the vehicle is traveling straight at low to medium speeds (the turning radius is infinite because the vehicle is traveling straight), the differential limiting force control unit a outputs a command value for maximizing the differential limiting force. Therefore, when traveling on the split μ road, the running performance is improved as in the case of the differential lock due to the differential limitation between the left and right wheels.

When turning at low to medium speeds, assuming that the turning radius is constant, the centripetal acceleration increases as the vehicle speed increases, and a command to increase the differential limiting force is output from the differential limiting force control unit a.

Therefore, when the vehicle turns at a high vehicle speed, the moment in the understeer direction increases, and the turning performance tends to be understeer, which is a safe side.

At high speeds (the turning radius becomes infinite during high-speed straight running and the centripetal acceleration becomes very large during high-speed turning), the differential limiting force control means a issues a command to set a high differential limiting force regardless of whether the vehicle is running straight or turning. The value is output.

Therefore, vehicle stability is ensured by a high differential limiting force against disturbances such as crosswinds during high-speed straight traveling,
Also, at the time of high-speed turning, turning stability is improved by generating a moment in the understeer direction by the differential limiting force and increasing the amount of understeer of the vehicle.

At the time of a small turning radius, a value that increases according to the absolute value of the centripetal acceleration and the entire value of the longitudinal acceleration is output from the differential limiting force control unit a as the differential limiting force command value. As a result, the following effects are obtained in each running state.

In the case of a small radius turning with the steering wheel cut from a constant vehicle speed, regardless of the turning radius, there is almost no longitudinal acceleration, so a small differential limiting force according to the centripetal acceleration is applied from the differential limiting force control means a. Is output.

Therefore, an increase in the moment in the understeer direction is suppressed, and a strong understeer tendency during a constant-speed small radius turn is prevented.

In the case of a small radius turning with the steering wheel being cut while accelerating, since a longitudinal acceleration occurs regardless of the turning radius, the differential limiting force control means a outputs a large differential limiting force according to the longitudinal acceleration and the centripetal acceleration. Is output.

Therefore, the application of the differential limiting force during the acceleration turning increases the moment in the oversteer direction, thereby improving the turning performance of the vehicle, and at the same time, preventing wheel spin of the inner wheel to obtain sufficient driving characteristics.

Also in the case of a small radius turning with the steering wheel being cut while decelerating, similarly to the case of acceleration, a command for applying a large differential limiting force is output from the differential limiting force control means a.

Therefore, the braking force on the outer wheel side is increased by the application of the differential limiting force, and tack-in is prevented.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

 First, the configuration will be described.

As shown in FIG. 2, a rear wheel drive vehicle to which the differential limiting force control device of the embodiment is applied includes an engine 10, a transmission 11, a propeller shaft 12, a differential 13,
Drive shafts 14 and 15, rear wheels 16 and 17, and front wheels 18 and 19 are provided.

The differential limiting force ΔT of the left and right rear wheels 16 and 17 is variably controlled by controlling the engaging force of a differential limiting clutch 20 (such as a wet multi-plate friction clutch) built in the differential 13 similar to the above-described known technology. The differential limiting force control is performed by guiding the pressurized oil from the external hydraulic pressure source 30 to the differential limiting clutch 20 via the differential limiting control valve 31.

Further, a valve drive signal (i) is supplied to the differential limit control valve 31.
Is an electronic control circuit that performs differential limiting force control.

As input sensors to the controller 32, a right front wheel speed sensor 33 and a left front wheel speed sensor 34 are provided.

 Next, the operation will be described.

Based on the flowchart shown in FIG.
The flow of the control operation in will be described.

In step 100, the front right wheel speed _NFR and the front left wheel speed _NFL are read.

At step 101, step 102 and step 103, based on the right front wheel speed N _FR and the left front wheel speed N _FL, turning radius R is computed at step 101, the centripetal acceleration Yg is calculated in step 102, before and after in step 103 The acceleration Xg is calculated.

The arithmetic expression is as follows when the vehicle speed V and the yaw rate are set.

_{V = {(N FL + N} FR) / 2} / r = K1 · | N FL -N FR | R = V / = K2 · | (N FL + N FR) / (N FL -N FR) | Yg = V ^{2 / R = K3 · | (} N FL + N FR) × (N FL -N FR) | Xg == {(FL + FR) / 2} / r where, K1, K2, K3 is a proportionality determined by the vehicle specifications Constant, r
Is the tire radius.

In step 104, the turning radius R calculated in the step 101 it is determined whether the set turning radius R _O below. And R
Proceeds to ≦ R step 105 when the _O, when the R> R _O proceeds to step 106.

In step 105, the differential limiting force command value ΔT is determined based on the turning radius R and the centripetal acceleration absolute value | Yg | obtained in steps 101 and 102, and a preset control characteristic function or control characteristic map.

In addition, as the control characteristic map, for example, step 105
The differential limiting force command value ΔT is proportional to the turning radius R and the centripetal acceleration absolute value | Yg |, respectively, as described in the frame of
Is a two-dimensional map in which is increased.

In step 106, the differential limiting force command value ΔT is determined based on the centripetal acceleration absolute value | Yg | and the longitudinal acceleration absolute value | Xg | obtained in steps 102 and 103, and a preset control characteristic function or control characteristic map. I can decide.

In addition, as the control characteristic map, for example, step 106
Absolute centripetal acceleration | Yg |
And a two-dimensional map in which the differential limiting force command value ΔT increases in proportion to the longitudinal acceleration absolute value | Xg |.

In step 107, a valve drive signal (i) is output to the differential limiting control valve 31 so that the differential limiting clutch 20 sets the engagement force to obtain the differential limiting force command value ΔT obtained in step 105 or step 106. Is done.

The operation will now be described separately for a large turning radius and a small turning radius.

(B) when a large turning radius at R> R _O large turning radius of, as a differential limiting force instruction value ΔT from the controller 32, the turning radius R and the centripetal acceleration absolute value | increasing values are output in response to | Xg . As a result, the following effects are obtained in each running state.

When the vehicle is traveling straight at low to medium speeds (the turning radius R is infinite because the vehicle is traveling straight), the controller 32 outputs a command value ΔT that maximizes the differential limiting force.

Therefore, when traveling on the split μ road, the left and right wheels 16, 17
As a result, the running performance is improved as in the case of the differential lock.

When turning at low to medium speeds, assuming that the turning radius R is constant, the centripetal acceleration Yg increases as the vehicle speed V increases, and the controller 32 outputs a command value ΔT that increases the differential limiting force.

Therefore, when the vehicle turns at a high vehicle speed, the moment in the understeer direction increases, and the turning performance tends to be understeer, which is a safe side.

At high speed (when turning straight at high speed, the turning radius R becomes infinite, and at high speed turning, the centripetal acceleration Yg becomes very large)
The controller 32 outputs a command value ΔT for setting a high differential limiting force regardless of whether the vehicle is traveling straight or turning.

Therefore, vehicle stability is ensured by a high differential limiting force against disturbances such as crosswinds during high-speed straight traveling,
Also, at the time of high-speed turning, turning stability is improved by generating a moment in the understeer direction by the differential limiting force and increasing the amount of understeer of the vehicle.

(B) At the time of the small turning radius of the small turning radius when R ≦ R _O, as a differential limiting force instruction value ΔT from the controller 32, the centripetal acceleration absolute value | Yg | and the longitudinal acceleration absolute value | Xg | value increases with Is output.
As a result, the following effects are obtained in each running state.

In the case of a small radius turning with the steering wheel cut from a constant vehicle speed, regardless of the turning radius R, almost no longitudinal acceleration Xg is generated, so the controller 32 issues a command to apply a small differential limiting force according to the centripetal acceleration Yg. The value ΔT is output.

Therefore, an increase in the moment in the understeer direction is suppressed, and a strong understeer tendency during a constant-speed small radius turn is prevented.

In the case of a small radius turning with the steering wheel being cut while accelerating, since the longitudinal acceleration Xg occurs regardless of the turning radius R, the controller 32 applies a large differential limiting force according to the longitudinal acceleration Xg and the centripetal acceleration Yg. Command value ΔT to be given
Is output.

Therefore, the application of the differential limiting force during the acceleration turning increases the moment in the oversteer direction, thereby improving the turning performance of the vehicle, and at the same time, preventing wheel spin of the inner wheel to obtain sufficient driving characteristics.

Also in the case of a small radius turning with the steering wheel being cut while decelerating, as in the case of the acceleration, since the longitudinal acceleration Xg occurs, the controller 32 outputs a command value ΔT for applying a large differential limiting force. .

Therefore, the braking force on the outer wheel side is increased by the application of the differential limiting force, and tack-in is prevented.

Although the embodiments have been described with reference to the drawings, the specific configuration is not limited to the embodiments.

For example, the characteristics of the command value ΔT are not limited to those shown in the embodiment, and the command value ΔT can be determined by various characteristics as described in the prior application (Japanese Patent Application No. 62-26425).

The turning radius detecting means may be obtained from a steering angle signal from a steering angle sensor in addition to the embodiment, and the centripetal acceleration detecting means may be obtained directly from a centripetal acceleration signal from a centripetal acceleration sensor. And the turning radius may be obtained by calculation, or the longitudinal acceleration detecting means may be obtained directly by a longitudinal G sensor or by differentiating the vehicle speed from a vehicle speed sensor.

(Effect of the Invention) As described above, in the differential limiting force control device according to the present invention, as the detecting means, the turning radius detecting means for detecting the turning radius of the vehicle and the centripetal detecting for detecting the centripetal acceleration of the vehicle. An acceleration detection means and a longitudinal acceleration detection means for detecting a longitudinal acceleration of the vehicle, wherein the differential limiting force control means increases the turning radius value and the centripetal acceleration absolute value when the radius exceeds a predetermined radius. This value is used as a differential limiting force command value. When the turning radius is equal to or smaller than a predetermined radius, a value that increases according to the absolute value of the centripetal acceleration and the absolute value of the longitudinal acceleration is used as the differential limiting force command value. At turning radii, under-steering moment is easily generated by differential limiting force control, which enables safe straight running and turning performance of the vehicle.At small turning radii, understeering moment is minimized. By controlling the differential limiting force, the effect of improving the turning performance of the vehicle, preventing wheel spin of the inner wheel, and preventing tack-in can be achieved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a claim showing a differential limiting force control device of the present invention, FIG. 2 is an overall schematic diagram showing a rear wheel drive vehicle to which the differential limiting force control device of the embodiment is applied, and FIG. FIG. 4 is a flowchart showing the flow of the control operation of the controller of the embodiment, and FIG. 4 is a diagram showing a friction circle of the tire with the lateral force of the tire taken along the horizontal axis and the braking / driving force taken along the vertical axis. a: differential limiting force control means b: differential limiting clutch c: turning radius detecting means d: centripetal acceleration detecting means e: longitudinal acceleration detecting means

Claims (1)

(57) [Claims] 1. A differential limiting force control means for outputting a differential limiting force command value determined based on an input detection value from a predetermined detecting means, and based on a command value from the differential limiting force control means. A differential limiting clutch that variably controls the differential limiting force of the left and right driving wheels by external engagement force control, wherein the detecting means detects a turning radius of the vehicle as the detecting means. Means, a centripetal acceleration detecting means for detecting a centripetal acceleration of the vehicle, and a longitudinal acceleration detecting means for detecting a longitudinal acceleration of the vehicle, wherein the differential limiting force control means turns when the turning radius exceeds a predetermined radius. The value that increases according to the radius value and the absolute value of the centripetal acceleration is defined as the differential limiting force command value. When the turning radius is equal to or less than the predetermined radius, the value that increases according to the absolute value of the centripetal acceleration and the absolute value of the longitudinal acceleration is limited. Force command Differential limiting force control system, characterized in that the means for the.