JP2643231B2 - 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 running on a road with a low friction coefficient, the differential limiting force suddenly increases, causing a tail swing, and even when running on a road with a high friction coefficient, 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 device, even if the above-described problems can be solved, the differential limiting force is not generated when the turning radius is small and the centripetal acceleration is small in order to ensure low speed and small turning performance. Due to the configuration, when turning on a split μ road where one side of the road surface is frozen, the differential limiting force does not occur, the tires on the low μ road side idle, and the driving force decreases significantly However, there is a problem that the running ability on the split μ road is inferior.

(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 conceptual diagram of the claim in 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 including: a differential limiting clutch that variably controls the differential limiting force of the left and right drive wheels by controlling the engagement force. Means c, a centripetal acceleration detecting means d for detecting the centripetal acceleration of the vehicle, and a drive wheel slip detecting means e for detecting slippage of the left and right driving wheels.
The differential limiting force command value is a value obtained by adding a value that increases according to the drive wheel slip amount to a value that increases according to the turning radius value and the absolute value of the centripetal acceleration obtained from the detection units c and d. It is characterized by being a means.

(Operation) When traveling straight at low to medium speeds, the turning radius becomes infinite because the vehicle is traveling straight, and the differential limiting force control means 2 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.

In the first half of turning at low to medium speeds, the turning radius becomes smaller as the steering wheel is turned from straight ahead, and a command value for reducing the differential limiting force to zero or near zero is output from the differential limiting force control means a. In addition, the centripetal acceleration is in a range from a small centripetal acceleration to a medium centripetal acceleration. Therefore, the tendency of understeer, such as when turning while applying a high differential limiting force, is suppressed.

In the latter period of turning at low speed to medium speed, the turning radius is almost constant but the centripetal acceleration increases, and a command to increase the differential limiting force again is output from the differential limiting force control means a. Therefore,
In the latter half of the turn, spin of the inner wheel is prevented, sufficient drive torque is obtained, and the turn traction capability is improved.

A command value for setting a high differential limiting force from the differential limiting force control means a regardless of whether the vehicle is traveling straight or turning at high speeds, such that the turning radius becomes infinite at high speed straight running and the centripetal acceleration becomes very large at high speed turning. Is output. Therefore, vehicle stability is ensured by a high differential limiting force against disturbances such as crosswinds during high-speed straight traveling, and
During 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.

When turning with a small radius on a split μ road where one side of the road surface is frozen, the turning radius is small and the centripetal acceleration is small, but due to the occurrence of slip of the left and right driving wheels, the differential limiting force control means a Outputs a command value for giving a differential limiting force. Accordingly, the tires on the low μ road side are prevented from spinning, and the driving force for the tires on the high μ road side is secured, so that the running ability on the turning on the split μ road can be improved.

(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 front right wheel speed sensor 33, a front left wheel speed sensor 34, a rear right wheel speed sensor 35,
A left rear wheel speed sensor 36 is 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 right front wheel speed _NFR , the left front wheel speed _NFL , the right rear wheel speed _NRR, and the left rear wheel speed _NRL are read.

In steps 101 and 102, the right front wheel speed N _FR
And the left front wheel speed _NFL , the turning radius R is calculated in step 101, and the centripetal acceleration Yg is calculated in step 102.

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) | where, K1, K2, K3 is a proportionality constant determined by vehicle specifications, r
Is the tire radius.

In step 103, the turning radius R and the centripetal acceleration Yg obtained at step 101 and 102, based on the control characteristic function and control characteristic map is set in advance, is determined differential limiting force instruction value [Delta] T _1.

In addition, as the control characteristic map, for example, step 103
The two-dimensional map is such that the differential limiting force command value ΔT ₁ increases in proportion to the turning radius R and the centripetal acceleration Yg, respectively, as described in the frame.

In step 104, the right and left rear wheel rotation speed difference ΔN _R is calculated by the right rear wheel speed N _RR and the left rear wheel speed N _RL .

The arithmetic expression is ΔN _R = | N _RR −N _RL |.

In step 105, on the basis of the left and right rear wheel rotational speed difference .DELTA.N _R, the differential limiting force instruction value [Delta] T ₂ is determined.

Incidentally, the differential limiting force instruction value [Delta] T ₂ is as described in the frame of step 105, a value proportional to the left and right rear wheel rotational speed difference .DELTA.N _R is obtained.

In step 106, the differential limiting command sum _{ΔTtotal (= ΔT 1 + ΔT 2} ) is calculated by adding the command value [Delta] T ₂ in the command value [Delta] T ₁ and step 105 in step 103.

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 total value ΔTtotal.

By performing the above-described control, each running mode exhibits the following operation.

When traveling straight at low speed to medium speed When traveling straight at low speed to medium speed, the turning radius R becomes infinite due to straight traveling, and a valve drive signal based on a command value from controller 32 that maximizes differential limiting force ΔT. (I)
Is output.

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 speed to medium speed In the first half of turning at low speed to medium speed, the turning radius R becomes smaller as the steering wheel is turned from straight ahead, and the controller 32 issues a command value for reducing the differential limiting force ΔT to zero or near zero. , A valve drive signal (i) is output. In addition, the centripetal acceleration Yg is in the range from small centripetal acceleration to medium centripetal acceleration.

Therefore, the tendency of understeer, such as when turning while applying a high differential limiting force, is suppressed.

In the latter half of the turn at low to medium speeds, the turning radius R is substantially constant but the centripetal acceleration Yg increases, and the controller 32 sends a valve drive signal (i) based on a command value to increase the differential limiting force ΔT again. Is output. Therefore, in the latter half of the turn, the inner wheel spin is prevented by the increased differential limiting force ΔT, and a sufficient drive torque is obtained, and the turn traction capability is improved.

At high speeds When turning straight at high speed, the turning radius R becomes infinite, and when turning at high speeds, the centripetal acceleration Yg becomes extremely large.
At high speed, the controller 32 outputs a valve drive signal (i) based on a command value for a high differential limiting force ΔT regardless of whether the vehicle is traveling straight or turning.

Therefore, a high differential limiting force ΔT secures vehicle stability against disturbances such as crosswinds during high-speed straight running, and a high torque limiting force ΔT generates an understeer moment during high-speed turning. Turning stability is improved by increasing the amount of understeer of the vehicle.

When turning on a small radius on a split μ road When turning on a small radius on a split μ road where one side of the road surface is frozen, the turning radius R is small, the centripetal acceleration Yg is small, and the differential limit command value ΔT ₁ Is almost zero, but the left and right rear wheels
Due to the occurrence of the slips 16 and 17, the controller 32 outputs a command value ΔTtotal (≒ ΔT ₂ ) for giving the differential limiting force ΔT.

Accordingly, the tires on the low μ road side are prevented from spinning, and the driving force for the tires on the high μ road side is secured, so that the running ability on the turning on the split μ road can be improved.

Next, the second embodiment will be described with reference to the flowchart shown in FIG.

The second embodiment is the same as the first embodiment in the basic content of the differential limiting control, but the difference between the left and right rear wheel rotational speeds Δ
Even N _R is generated, when the vehicle speed V is high, the turning radius R and the centripetal acceleration Yg and the differential limiting force [Delta] T ₁ or more differential limiting force Δ by
For impairing the contrary drivability the addition of T _2, is an example of prohibiting additional [Delta] T ₂ at the set vehicle speed greater than or equal _to V _0.

In the flowchart, a comparison step (step 108) of the vehicle speed V obtained when calculating the turning radius R is performed.
And a command value setting step for setting ΔT ₂ = 0 (step
109) is added to the flow of the first embodiment.

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 ₁ are not limited to those shown in the embodiments, and the command value ΔT ₁ can be determined by various characteristics as described in the prior application (Japanese Patent Application No. 62-264525).

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.

(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 detecting means and a driving wheel slip detecting means for detecting a slip of the left and right driving wheels, wherein the differential limiting force control means sets a value which increases according to a turning radius value and a centripetal acceleration absolute value obtained from the detecting means. Since the value obtained by adding a value that increases in accordance with the amount of drive wheel slip is used as the differential limiting force command value, understeer can be reduced during low- to medium-speed turns, and traveling performance on a split μ road can be improved. It is possible to obtain the effect that optimal differential limiting force control according to various road surface conditions and driving modes can be achieved with a simple device that does not directly detect the turning state and the road surface friction coefficient, and one side of the road surface is frozen. When the small radius turning in such a split μ road is, the effect is obtained that it is possible to improve the running performance capability by the application of differential limiting force.

[Brief description of the drawings]

FIG. 1 is a conceptual view 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 first embodiment is applied, FIG. 4 is a flowchart showing a control operation flow in the controller of the first embodiment device, and FIG. 4 is a flowchart diagram showing a control operation flow in the controller of the second embodiment device. a: differential limiting force control means b: differential limiting clutch c: turning radius detecting means d: centripetal acceleration detecting means e: drive wheel slip 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 detection means for detecting a centripetal acceleration of the vehicle, and a drive wheel slip detection means for detecting a slip of the left and right drive wheels, wherein the differential limiting force control means includes a turning radius value obtained from the detection means, A differential limiting force control device, wherein a value obtained by adding a value increasing according to a drive wheel slip amount to a value increasing according to an absolute value of a centripetal acceleration is used as a differential limiting force command value.