JPH0367725A - Differential limiting control device for vehicle - Google Patents

Abstract

PURPOSE:To allow the braking stability to be compatible with shorter braking distance by judging whether the road is a split mu road or not corresponding to the state of occurrence of the difference between in rotative speed between right and left wheels, and controlling the maximum value of added differential limiting torque in response to the vehicle speeds. CONSTITUTION:A differential limiting mechanism (a) is installed in a driving system for distributing-transmitting the driving force of an engine to right and left driving wheels while allowing the differential. The differential limiting mechanism (a) is controlled by a differential limiting control means (c) based on detection signals from a specified detecting means (b). In the above-stated devices, respective means b1 - b3 for detecting braking operation, vehicle speed, and the difference in rotative speed between right and left wheels respectively are provided as the above detecting means (b). The above control means (c) increases differential limiting torque in accordance with the increase in the difference in rotating speed between right and left wheels when the brake is applied. Further, the control means controls the maximum value of the differential limiting torque in accordance with the vehicle speed so that the value is changed to become smaller at higher speeds compared with the value at lower speeds.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a differential limiting torque that is applied by an external control force,
The present invention relates to a differential limiting control device for a vehicle that controls differential limiting according to predetermined control conditions.

(Prior Art) As a conventional vehicle differential limiting control device, for example, a device described in Japanese Patent Application Laid-open No. 110530/1982 is known.

This control device performs control to cancel differential restriction when an anti-skid device (anti-lock brake system) that prevents wheel locking by increasing and decreasing brake fluid pressure during a braking operation is activated.

(Problem to be solved by the invention) However, in such conventional vehicle differential limiting control devices, when the anti-skid device is activated, only a free differential function that does not have a differential limiting function is exerted. Therefore, when braking suddenly on a split μ road where the friction coefficients of the road surfaces where the left and right wheels are in contact are different, the low μ
The anti-lock system sends low brake fluid pressure to each wheel cylinder to prevent wheels from locking on the roadside, leaving the problem of longer braking distances.

That is, in a 3-sensor, 3-channel anti-lock brake system, the brake fluid pressure is controlled so that the wheel on the low-μ road side does not lock, and in a 4-sensor, 3-channel anti-lock brake system, the brake fluid pressure is controlled so that the wheel on the low-μ road side does not lock. The brake fluid pressure is controlled by selecting the speed using the select low.

On the other hand, in an attempt to solve the above-mentioned problem of longer braking distance, when the anti-lock brake system is activated during sudden braking on a split-μ road, applying a large differential limiting torque and directly connecting the left and right wheels, the road Yaw moment is generated due to unbalanced braking force due to difference in friction coefficient,
This will result in changes in vehicle behavior and reduced braking stability.

The above-mentioned problem also occurs when brake fluid pressure is sent to each wheel cylinder by the driver's brake pedal operation during sudden braking using the split circuit.

Therefore, in Japanese Patent Application No. 63-325380 (filed on December 23, 1988), the present applicant proposed that when the brake is applied by either the anti-lock brake system or the normal brake, and when the vehicle speed is high, By applying a differential limiting torque that corresponds only to the vehicle speed that makes the differential limiting torque smaller than that at low speeds, the split μ
We proposed a device that improves braking performance on roads.

However, in this prior art, the differential and limiting force sufficient to ensure sufficient braking stability with a split circuit are set based only on the vehicle speed, and it is difficult to determine whether or not the split circuit is used.
Because the configuration was such that the differential limiting force described above was applied uniquely to the differential limiting mechanism during braking without any special action, when the actual road surface was a split μ road with a large imbalance between the left and right wheels, Braking stability is obtained when the brakes are applied, but if the road surface μ is uniform on the left and right sides, when the brakes are applied, the differential limiting torque described above creates a moment (hereinafter referred to as under moment) that suppresses the turning rate of the vehicle when turning. There is a problem in that the vehicle is difficult to turn because it occurs more than necessary.

The present invention has been made with attention to the above-mentioned problems, and is a differential limiting control device for a vehicle that applies differential limiting torque between left and right wheels by external control. The objective is to achieve both braking stability and shortening of braking distance on split μ roads without sacrificing the verbal performance of the vehicle.

(Means for Solving the Problems) In order to solve the above problems, the differential limiting control device for a vehicle of the present invention determines whether or not it is a split μ road based on the occurrence of the difference in rotational speed between the left and right wheels. In addition, the maximum value of differential limiting torque to be applied is controlled by vehicle speed.

In other words, as shown in the complaint diagram in Figure 1, a differential is installed in a drive system that distributes and transmits engine driving force to the left and right drive wheels while allowing a differential, and generates a differential limiting torque by an external control force. A differential limiting control device for a vehicle comprising a limiting mechanism a and a differential limiting control means C that controls increasing or decreasing differential limiting torque based on a signal from a predetermined detection means,
The detection means includes brake operation detection means b1 for detecting whether or not the brake is being applied, vehicle speed detection means b2 for detecting vehicle speed, and left and right wheel rotational speed difference detection means b3 for detecting the rotational speed difference between the left and right wheels. The differential limiting control means C increases the differential limiting torque in accordance with an increase in the rotational speed difference between left and right wheels when the brake is applied, and increases the maximum value of the differential limiting torque in accordance with the vehicle speed. The present invention is characterized in that it is a means for carrying out differential limiting control corresponding to vehicle speed, which changes characteristics to be smaller at high speeds than at low speeds.

(Function) When the brake operation detection means b1 detects that the brake is being applied, the differential limiting control means C controls the increase in the difference in rotational speed between the left and right wheels detected by the left and right wheel rotational speed difference detection means b3. Differential limiting control is performed to increase the differential limiting torque accordingly and to change the maximum value of the differential limiting torque in accordance with the vehicle speed from the vehicle speed detecting means b2.

Therefore, when braking is applied on a split μ road where there is a large difference in road grip between the left and right wheels and a large difference in rotational speed between the left and right wheels, the differential limiting torque corresponding to the difference in rotational speed between the left and right wheels becomes a large value. Since the optimum differential limiting torque is applied by limiting the maximum value of the differential limiting torque according to the vehicle speed, braking stability on split μ roads can be ensured and the braking distance can be shortened.

In addition, when braking is applied in a left-right uniform circuit where the difference in road grip force between the left and right wheels is small and the difference in rotational speed between the left and right wheels is small, a small difference corresponding to the difference in rotational speed between the left and right wheels is almost unrestricted by the maximum value. Since dynamic limiting torque is applied, excessive undermoment is prevented from occurring, and the vehicle's turning performance is ensured when turning.

(Example) Embodiments of the present invention will be described below based on the drawings.

First, the configuration will be explained.

Fig. 2 shows an overall system diagram of a differential limiting control device for a rear wheel drive vehicle equipped with a multi-disc friction clutch mechanism operated by external hydraulic pressure, including a differential 10 and a multi-disc friction clutch mechanism 11 (differential limiting mechanism). , a hydraulic pressure generator 12, and a control unit 13 (differential limit control means), and the input sensors 14 of the control unit 13 include a vehicle speed sensor 141 (vehicle speed detection means), an accelerator opening sensor 142, and a left wheel rotation speed sensor. 144, a right wheel rotation speed sensor 145, and a brake switch 146.

Each configuration will be described below with reference to FIGS. 3 to 5.

The above-mentioned differential 10 has a differential function that creates a speed difference between the left and right wheels in accordance with the rotational speed difference in driving conditions where a rotational speed difference occurs between the left and right wheels, and equally distributes engine driving force to the left and right driving wheels. It is a device with a driving force distribution function that distributes and transmits the driving force to the vehicle body, and is housed in a housing 16 that is attached to the vehicle body by a stud port 15.
, side gears 21, 21°.

The differential case 18 includes a housing 16
In contrast, it is rotatably supported by tapered roller bearings 22, 22'.

The ring gear 17 is connected to a differential case 18.
The propeller shaft 23 is fixed to the propeller shaft 23 and meshes with a drive pinion 24 provided on the propeller shaft 23, from which rotational driving force is input.

The side gears 21, 21° include a left wheel drive shaft 25 and a right wheel drive shaft 2, which are drive output shafts.
6 are provided for each.

The multi-plate friction clutch machine lateral 11 is provided between the drive input part and the drive output part of the differential 10,
This is a mechanism that generates differential limiting torque using clutch engagement force from external hydraulic pressure, and is housed within the housing 16 and differential case 18, and includes a multi-disc friction clutch 27.27' and a pressure ring 28.2.
8', a rear axle plate 29, 29', a thrust bearing 30, 30', a spacer 31, 31', a bushing rod 32, a hydraulic piston 33, an oil chamber 34, and a hydraulic port 35.

The multi-plate friction clutch 27, 27' includes friction plates 27a, 27'a fixed to the differential case 18 in the rotational direction, and side gears 21, 21.
a friction disk 27b fixed in the rotational direction to
27"b, and a pressure ring 28.28" and a rear axis fin plate 29.29' are arranged on both end faces in the axial direction.

The pressure rings 28, 28' are provided in a fitted state on the pinion mate shaft 19 as members receiving the clutch engagement force, and the fitting portion has a rectangular cross section as shown in FIG. The shaft end portion 19a is fitted into the shaft end portion 19a through square grooves 28a, 28°a, and has a structure in which no thrust force is generated due to a difference in rotation, unlike the conventional torque proportional differential limiting mechanism.

The hydraulic piston 33 moves in the axial direction (to the right in the drawing) by supplying hydraulic pressure to the hydraulic port 35, and engages both multi-disc friction clutches 27, 27' according to the hydraulic pressure level. In the clutch 27, the engagement force is transmitted from the bushing rod 32 to the spacer 31 to the thrust bearing 30 to the reaction plate 29, and the clutch 27 is engaged using the pressure ring 28 as a reaction force receiver. The fastening reaction force becomes the fastening force and the product is fastened.

The hydraulic pressure generating device 12 is an external device that generates hydraulic pressure as a clutch engagement force, and includes a hydraulic pump 40 and a pump motor 4.
1. Control pressure oil passage 42, check valve 43, first drain oil passage 44, relief valve 45, reserve tank 46
, a second drain oil passage 47, a switching valve 48, a valve solenoid 49, and a pressure switch 50.

The pump motor 41 is a motor that is activated and deactivated by a motor signal from the control unit 13.
When driving, a energizing signal is output when differential limiting is being performed or there is a possibility of differential limiting, and a de-energizing signal is output when differential limiting is not required at all, such as when stopped. Output.

The control pressure oil passage 42 is an oil passage connected to a control pressure oil vibe 51 that supplies hydraulic oil at a control pressure to the hydraulic port 35, and is provided with an orifice 52 in the middle to slow the rise of oil pressure. .

The relief valve 45 is a valve that releases pressure to the reserve tank 46 side for pressure regulation when the pump pressure flowing through the control pressure oil path 42 is equal to or higher than a predetermined pressure.

The switching valve 48 is a valve actuator that switches between supplying pump pressure oil to the hydraulic port 35 side and returning it to the reserve tank 46. When the valve solenoid 49 receives the control current value 1* from the control unit 13, Operate.

The pressure switch 50 is an input sensor that checks the pressure level of the control pressure oil passage 42, outputs a switch signal to the control unit 13 when the pressure level is above a predetermined value, and performs feedback control to lower the pressure level. .

The control unit 13 is an electronic control circuit mainly using an in-vehicle microcomputer, and includes an input circuit 131, a memory 132 such as RAM or ROM, a CPU 133, and an output circuit 134.

The vehicle speed sensor 141 is a sensor that detects the vehicle speed V by detecting the rotational speed of the transmission output shaft, the rotational speed of one or more driven wheels, a Doppler radar type ground vehicle speedometer, etc., and outputs a vehicle speed signal.

The accelerator opening sensor 142 is provided at the throttle valve position of the engine, detects the accelerator opening A, and outputs an accelerator opening signal.

The left wheel rotation speed sensor 144 and the right wheel rotation speed sensor 145 are arranged close to the sensor rotor provided on the axle, and are means for detecting the wheel rotation speed using magnetism or light. Signals corresponding to the left wheel rotational speed VWL and the right wheel rotational speed VWR, which are input information for obtaining the rotational speed VWL and the right wheel rotational speed VWR, are respectively output.

The brake switch 146 is provided at the brake pedal position, and the brake switch signal Bsw is an OFF signal when the brake is not operated, and an ON signal when the brake is operated.
Output.

Next, the effect will be explained.

FIG. 6 is a flowchart showing the flow of the differential limiting control operation in the control unit 13, and each step will be explained in order below.

At step 60, the vehicle speed V, the accelerator distance A, and the left wheel rotation speed VWL*right wheel rotation speed VWR+brake switch signal SSW are read.

In step 61, the accelerator opening degree A read this time and the accelerator opening degree A read in one control cycle or several control cycles before. The accelerator opening differential value A is calculated based on the control cycle time dt and the control cycle time dt using the following formula.

A=(A-A.)/dt In step 62, the left and right wheel rotational speed difference ΔVw is calculated from the left wheel rotational speed VWL and the right wheel rotational speed VWR using the following formula.

ΔvW=vwFl−vwL At step 63, the brake switch signal BSW is turned ON.
It is determined whether or not it is a signal, that is, whether or not the brake is normally activated.

If the brake switch signal Bsw is an OFF signal, the process proceeds to step 64, and if the brake switch signal Elsw is an ON signal, the process proceeds to step 68.

In step 64, the accelerator opening degree differential value A, the accelerator opening degree A, the vehicle speed V, and FIGS. 7a and 7b.

The differential limiting torque Tc is determined based on the maps shown in FIGS. 7c and 7d.

In step 68, the vehicle speed V is used to calculate the differential limiting torque Vmax below the maximum value according to the characteristics shown in FIG.

T AVmax = f + (V) Step 69
Now, the differential limiting torque TΔV corresponding to the left and right wheel rotational speed difference ΔVw is calculated according to the characteristics shown in FIG.

TΔv=1,0002 (Δvw) = k*Δvw In step 70, it is determined whether the differential limiting torque TΔV calculated in 69 is less than the maximum differential limiting torque ΔVmax obtained in steps 66 and 68d, respectively. If it is determined that TΔV<TΔVmax, step 7
Differential limiting torque T commanded in 1.

is set to TΔV and TΔV≧TΔVmax, the differential limiting torque T commanded in step 72
It is set to ctJ<TΔVmax.

In step 73, the control current value l* that provides the differential limiting torque Tc is calculated and output to the valve solenoid 49.

Next, each characteristic shown in FIGS. 8 and 9 will be explained.

Figure 8 shows the maximum value characteristic of the differential limiting torque when the brake is applied, and shows that when the vehicle speed is high (vehicle speed v2 or higher), the maximum value of the differential limiting torque (AVmax) is lower than when the vehicle speed is low (vehicle speed v1 or less).
is set small, and the vehicle speed v1~V
7, the maximum value lower AVmax is gradually lowered.

This is to achieve both shortening of braking distance during low-speed braking on a split μ road and stability of vehicle behavior during high-speed braking.

FIG. 9 shows the characteristics of the differential side, limiting torque TΔV with respect to the left and right wheel rotational speed difference Δvw, and the differential limiting torque TΔV also increases as the left and right wheel rotational speed difference ΔVW increases.

In this way, the characteristic that the differential limiting torque T△V increases as the left and right wheel rotational speed difference △vw increases is due to the split circuit where the left and right wheel rotational speed difference △vW is large and the left and right wheel rotational speed. This is to distinguish between left and right uniform μ paths where the difference ΔvW is small.

Next, the operation of the differential limiting control when the brake is not applied and when the brake is applied will be explained.

(B) When the brake is not activated During normal driving with the brake not activated, a differential limiting torque corresponding to the vehicle speed V and accelerator opening A is obtained, and high-speed driving stability and high-speed driving safety are achieved. By including the accelerator opening degree differential value A in the control conditions,
When the accelerator operation speed is high, such as during sudden acceleration, differential limiting control is performed with high response.

(b) When the brakes are applied When the brakes are applied on a split μ road, there is a large difference in the coefficient of friction between the left and right road surfaces, so if the same braking force is applied, a large difference in rotational speed between the left and right wheels ΔvW will occur, mainly due to the differential The maximum value AVmax of the limit torque will be given.

However, at high speeds where braking stability is a problem, the maximum value TΔVmax of the differential limiting torque is limited to a small value as shown in the characteristics of FIG. 8, so that turning braking stability can be obtained with a split circuit.

Furthermore, when braking with the split circuit, at low vehicle speeds when the driver's corrective steering ability is high, a larger differential limiting torque is applied than at high vehicle speeds, as shown in the characteristics in Figure 8. The braking force on the high-μ road side, which has greater road surface grip, is utilized to shorten the braking distance. In this case, a yaw moment will be generated due to the unbalanced braking force between the left and right sides, but the change in vehicle behavior due to this yaw moment can be sufficiently compensated for by the corrective steering due to the driver's high corrective steering ability at low vehicle speeds. I can do it.

In addition, when braking is applied on a road with uniform left and right μ roads, the difference in the coefficient of friction between the left and right road surfaces is small, so the rotational speed difference Δvw between the left and right wheels is only small for the same braking force, and the maximum value of the differential limiting torque is Regardless of the lower ΔVmax, a small differential limiting torque is applied according to the characteristics shown in FIG.

Therefore, excessive under-moment is not generated due to the activation of the brakes during a turn in the left-right uniform circuit, and the turning performance of the vehicle during the turn is ensured.

Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments.

For example, in the embodiment, an example was shown in which brake operation is detected by a brake switch, but in the case of a car equipped with an anti-lock brake system, a signal indicating the operating state of the system is used as a brake operation detection signal, An adaptive example may be such that when the signal is output, the same vehicle speed-dependent differential limiting control as described above is performed.

Further, the normal differential limiting control when the brake is not activated is not limited to the control content of the embodiment, and may be controlled based on other driving conditions such as the difference in rotational speed between left and right wheels.

In addition, in the embodiment, an example was shown in which a differential device and a differential limiting clutch were combined as a differential limiting mechanism. It can also be applied to a differential limiting mechanism equipped with a functional clutch.

(Effects of the Invention) As described above, in the present invention, in a vehicle differential limiting control device that applies differential limiting torque between left and right wheels by external control, whether or not a split circuit is used. This is done based on the occurrence of the difference in rotational speed between the left and right wheels, and the maximum value of differential limiting torque to be applied is controlled by the vehicle speed, so that splitting can be achieved without impairing the turning performance of the vehicle on roads with uniform left and right μ. This provides the effect of achieving both braking stability on μ roads and shortening of braking distance.

[Brief explanation of drawings]

Fig. 1 is a claim correspondence diagram showing a vehicle differential limiting control device of the present invention, Fig. 2 is an overall system diagram showing a differential limiting control device of an embodiment, and Fig. 3 is a differential diagram of the embodiment device. FIG. 4 is a sectional view showing the Z direction in FIG. A flowchart showing the flow of operation; Figures 7a, 7b, 7C, and 7d are differential limit control characteristic maps when the brake is not applied; Figure 8 is the differential limit torque corresponding to vehicle speed when the brake is applied. The maximum value characteristic diagram, FIG. 9, is a differential limiting torque characteristic diagram with respect to the rotational speed difference between the left and right wheels. a...-Differential limiting mechanism b...Detecting means bl...-Brake operation detecting means b2...Vehicle speed detecting means b3...Left and right wheel rotational speed difference detecting means C...Differential limiting control means

Claims (1)

[Claims] 1) A differential limiting mechanism that is provided in a drive system that distributes and transmits engine driving force to left and right drive wheels while allowing differential, and that generates a differential limiting torque by an external control force, and a predetermined In a differential limiting control device for a vehicle, the differential limiting control device includes differential limiting control means that increases or decreases differential limiting torque based on a signal from the detecting device, wherein the detecting device includes a brake operation detection device that detects whether or not the brake is being applied. means, vehicle speed detection means for detecting vehicle speed, and left and right wheel rotational speed difference detection means for detecting a rotational speed difference between the left and right wheels; Means for performing differential limiting control corresponding to vehicle speed, increasing the differential limiting torque in accordance with an increase in the differential limiting torque, and changing the maximum value of the differential limiting torque in accordance with the vehicle speed with a characteristic that it becomes smaller at high speeds than at low speeds. A differential limiting control device for a vehicle characterized by the following.