JP2646764B2 - Driving force distribution control device for four-wheel drive vehicle - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a driving force distribution control device for a torque split four-wheel drive vehicle in which the driving force distribution of front and rear wheels is variably controlled.

(Prior Art) First, as a front and rear wheel driving force distribution control device of a four-wheel drive vehicle, for example, a device described in Japanese Patent Application Laid-Open No. 63-141831 is known. In a four-wheel drive vehicle in a wheel drive space, as the difference between the front and rear wheel rotational speeds increases, the drive force transmitted to the front wheels increases, and the drive force distribution is shifted to the four-wheel drive side. The rate of increase of the driving force transmitted to the front wheels with respect to the occurrence is reduced.

Japanese Patent Application Laid-Open No. 61-33325 discloses a four-wheel drive state and a two-wheel drive state which automatically switch between a four-wheel drive state and a two-wheel drive state by using a longitudinal acceleration sensor and a lateral acceleration sensor to determine a traveling state based on these sensor signals. An automatic switching device for a wheel drive vehicle is shown.

(Problems to be Solved by the Invention) In the former four-wheel drive vehicle front and rear wheel drive force distribution control device, the drive force distribution ratio is gradually changed in response to the occurrence of lateral acceleration due to drive wheel slip and turning. It is preferable that the yaw control of the vehicle is performed by the driving force distribution control, and the optimum front and rear wheel driving force distribution corresponding to the running condition and the road surface condition is obtained.

However, since four wheel speed sensors are required to obtain the front and rear wheel rotational speed difference information, the apparatus cost is disadvantageous.

In the latter automatic switching device for four-wheel drive vehicles,
It is advantageous in terms of cost because the device is composed of two sensors of longitudinal acceleration and lateral acceleration.

However, it is not a device that gradually changes the drive power distribution ratio between the front and rear wheels.It is a device that rapidly changes the drive power distribution, such as 2WD → 4WD or 4WD → 2WD, so it is optimal for driving conditions and road surface conditions Not only cannot it be handled, but also a sudden change in the steering characteristic and a sudden change in the vehicle behavior occur due to the switching of the driving force distribution.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. In a driving force distribution control device for a four-wheel drive vehicle using a two-wheel drive-based electronically controlled torque split, the front and rear wheel rotation is reduced while the device cost is advantageously reduced. It is an object to achieve torque split control equivalent to a case where a speed difference is used as input information.

(Means for Solving the Problems) In order to solve the problems described above, in the driving force distribution control device for a four-wheel drive vehicle, torque split control is performed using longitudinal acceleration information instead of longitudinal wheel rotational speed difference information. The means to do it.

That is, as shown in the claim correspondence diagram of FIG. 1, a variable drive force distribution clutch a provided in the middle of the drive system to the other of the front and rear wheels with respect to the drive system directly connected to the engine to one of the front and rear wheels.
A longitudinal acceleration detecting means b for detecting the longitudinal acceleration of the vehicle, a lateral acceleration detecting means c for detecting the lateral acceleration of the vehicle, and increasing the driving force transmitted to the clutch engagement driving wheels as the longitudinal acceleration increases. The driving force distribution is set to the four-wheel drive side, and the variable driving force distribution clutch a is engaged by controlling the decrease in the rate of increase in the driving force transmitted to the clutch engagement driving wheels with respect to the occurrence of longitudinal acceleration as the lateral acceleration increases. And front and rear wheel driving force distribution control means d for performing force control.

(Operation) In straight running, the front and rear wheel drive force distribution control means d increases the drive force transmitted to the clutch engagement drive wheels as the longitudinal acceleration detected by the longitudinal acceleration detection means b increases, thereby increasing the drive force distribution. Control for the four-wheel drive side is performed.

Therefore, at the time of sudden start or acceleration, the drive power distribution is controlled steplessly up to 50:50 in accordance with the acceleration situation, and the drive wheel slip due to excessive transmission drive force to the engine directly connected drive wheel is transmitted to the clutch. It is suppressed by the distribution of the driving force to the driving force, and the driving performance and the running stability are achieved.

At the time of turning, the front and rear wheel driving force distribution control means d controls the increase rate of the transmission driving force to the clutch engagement driving wheel with respect to the occurrence of the longitudinal acceleration as the lateral acceleration detected by the lateral acceleration detecting means c increases. Is performed.

Therefore, at the time of low μ road acceleration turning where the occurrence of lateral acceleration is small, control is performed to increase the distribution of driving force to the clutch engagement driving wheels in accordance with the acceleration strength.
In the case of a rear-wheel drive-based vehicle, the distribution of driving force to the front wheels increases in accordance with the level of acceleration, thereby preventing a sudden increase in oversteer and improving the controllability of the vehicle.

In addition, during high-μ road acceleration turning where the occurrence of lateral acceleration is large, control is generally performed in which the driving force distribution to the clutch engagement driving wheels is small. For example, in the case of a rear-wheel drive-based vehicle, By reducing the distribution of the driving force to the front wheels and suppressing the decrease in the cornering force of the front wheels, the turning performance can be improved.

In addition, the control for increasing the distribution of the driving force to the clutch engagement driving wheels according to the acceleration level is performed at the time of the high μ road acceleration turning, similarly to the low μ road acceleration turning, thereby improving the controllability of the vehicle. Increase.

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

 First, the configuration will be described.

FIG. 2 is an overall system diagram showing a driving force distribution control device for a four-wheel drive vehicle according to an embodiment.
Engine 1, transmission 2, rear propeller shaft 3, rear differential 4, left and right rear drive shafts 5,6, left and right rear wheels 7,8, wet multi-plate clutch 9
(Variable driving force distribution clutch), a front propeller shaft 10, a front differential 11, left and right front drive shafts 12, 13, and left and right front wheels 14, 15.

The road surface transmission driving force is directly transmitted to the rear wheels 7 and 8, but is transmitted to the front wheels 14 and 15 via the wet multi-plate clutch 9. That is, the distribution of the driving force to the front and rear wheels is controlled by controlling the engagement force of the wet type multi-plate clutch 9 by hydraulic pressure, and the front wheel with zero hydraulic pressure: rear wheel = 0: 100 (rear wheel drive) to the front wheel with maximum hydraulic pressure: rear wheel = 50: 50 (rigid 4WD state).

The front / rear wheel driving force distribution control device for controlling the engagement force of the wet multi-plate clutch 9 includes a longitudinal acceleration sensor 20, a first lateral acceleration sensor 21 and a second lateral acceleration sensor 22 as an electronic control system.
And ETS controller (ETS is Electronic Torque Split
), And an oil pump 24 as a hydraulic control system.
And a solenoid control valve 25 and a control pressure oil passage 26.

Then, the ETS controller 26 receives the signals from the respective sensors 20 to 23, the engagement force control of the wet multi-plate clutch 9 based on the longitudinal acceleration X _G and the lateral acceleration Y _G, longitudinal acceleration
Before and after the lateral acceleration Y _G reduces the gain k (increase rate) for the front wheel transmission torque T _f for the longitudinal acceleration X _G according increases with X _G increases the transmission torque T _f to the front wheels 14, 15 in accordance with increased Wheel drive force distribution control is performed.

 Next, the operation will be described.

FIG. 3 is a flowchart showing the flow of the front and rear wheel driving force distribution control operation performed by the ETS controller 26 at a predetermined control cycle. The operation of each step will be described below in order.

In step 41, the longitudinal acceleration _XG , the first lateral acceleration _YG1 , and the second lateral acceleration _YG2 are input.

In step 42, the lateral acceleration Y _G is calculated by the average value between the first lateral acceleration Y _G1 and the second lateral acceleration Y _G2.

In step 43, the gain k of the front wheel side transmitted torque T _f for the longitudinal acceleration X _G is calculated by the following formula based on the reciprocal of the lateral acceleration Y _G.

K = α / Y _G (where K ≦ β), and when expressed as a characteristic diagram, the characteristics as shown in FIG. 4 are exhibited.

In step 44, the gain k and the front-wheel-side transfer by the acceleration X _G longitudinal torque _{T f {= K · f (} X G)} is calculated.

In addition, when it is expressed as a characteristic diagram, it shows characteristics as shown in FIG.

In step 45, the front-wheel-side transmission torque _Tf obtained in step 44 is converted to a solenoid drive current i according to a _Tf- i characteristic table given in advance.

In step 46, a dither current i ^* (for example, i ± 0.1 A100 Hz) is output to the solenoid control valve 28.

By fastening force of the wet multi-plate clutch 9 as described above is controlled in accordance with the longitudinal acceleration X _G and the lateral acceleration Y _G, straight running, during turning, at the time of deceleration, running performance described below Is shown.

* During straight running straight running, since the lateral acceleration Y _G becomes zero or very small value, based on the greatest control characteristic gain K, the front wheel transmission torque T _f according to the magnitude of the longitudinal acceleration X _G
Is controlled, that is, the front / rear wheel driving force distribution ratio is set to 0: 100 to 50:50 depending on the acceleration intensity.

Therefore, at the time of sudden start where the longitudinal acceleration _XG is very large,
Since the vehicle is substantially in the rigid 4WD state in which the front wheel side transmission torque _Tf is large, the startability and stability of the vehicle are enhanced.

In addition, during straight-ahead acceleration, the drive power distribution is controlled steplessly up to 50:50 in accordance with the acceleration situation, so rear wheel slip due to excessive transmission drive force to the rear wheels 7, 8 causes the front wheels 14, 15 to slip. The driving force is distributed to the vehicle, and acceleration performance and stability are enhanced.

* When cornering during cornering, a small gain K as the lateral acceleration Y _G is large also, based on the control characteristics due to a large gain K as the lateral acceleration Y _G is small, the front-wheel-side transmission in accordance with the magnitude of the longitudinal acceleration X _G Control for increasing the torque _Tf is performed.

Therefore, at the time of low-μ road acceleration turning where the occurrence of lateral acceleration is small, the front-wheel-side transmission torque _Tf increases in accordance with the acceleration intensity, thereby preventing a sudden increase in oversteer and improving the controllability of the vehicle.

In addition, during acceleration turning on a high μ road where lateral acceleration is large, the front wheel side transmission torque _Tf is generally controlled to be small, whereby a decrease in the cornering force of the front wheels 14, 15 is suppressed, and the steering effectiveness is maintained. In addition, the turning property can be improved.

Also, at the time of high μ road acceleration turning, similarly to at the time of low μ road acceleration turning, control to increase the front wheel side transmission torque _Tf according to the acceleration intensity is performed, thereby preventing a sudden increase in oversteer, and Controllability increases.

* During deceleration When the vehicle decelerates, as shown in the control characteristic diagram of FIG.
Control is performed to increase the front-wheel-side transmission torque _Tf according to the degree of deceleration.

Therefore, at the time of braking operation or braking by the engine brake, a braking torque corresponding to the braking amount is transmitted to the front wheels 14, 15, and the braking effect is enhanced by the braking force balance between the front and rear wheels.

As described above, in the driving force distribution control device for a four wheel drive vehicle of Example, instead of the conventional front and rear wheel rotational speed difference information, and an apparatus for performing torque split control using the longitudinal acceleration X _G Therefore, torque split control equivalent to the case where the front and rear wheel rotational speed difference is used as input information can be achieved while using only one longitudinal acceleration sensor 20 to improve the apparatus cost.

Although the embodiment has been described with reference to the drawings, the specific configuration and control contents are not limited to this embodiment.

For example, in the embodiment, the example in which the front and rear wheel drive force distribution control device is applied to the rear wheel drive base vehicle is described, but the front and rear wheel drive force distribution control device may be applied to the front wheel drive base vehicle.

Further, in the embodiment, as the front and rear wheel driving force distribution device, an example is shown in which a multi-plate friction clutch that can change the transmission torque by an external control hydraulic pressure is used, but any clutch that can change the transmission torque by external control is used. For example, a control type viscous clutch, a control type orifice clutch, an electromagnetic clutch, or the like may be used.

Further, in the embodiment, the apparatus for performing the front and rear wheel driving force distribution control using the characteristic shown in FIG. 5 as the front wheel side transmission torque characteristic is shown, but as shown in FIG. In a region exceeding a predetermined deceleration, the control may be performed based on the front wheel side transmission torque characteristic in which the front wheel side transmission torque _Tf is a constant value.

In this case, ABS to prevent wheel lock during sudden braking
(Anti-skid braking system) can be prevented from interfering with control, and a moderate tack-in can be caused during sudden braking.

(Effects of the Invention) As described above, according to the present invention, in the driving force distribution control device for the four-wheel drive vehicle using the electronically controlled torque split based on the two-wheel drive, instead of the front and rear wheel rotational speed difference information, Since the means for performing the torque split control using the longitudinal acceleration information is employed, the effect that the torque split control equivalent to the case where the difference between the front and rear wheel rotational speeds is used as the input information can be achieved with the advantage of the apparatus cost is obtained. Can be

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram showing a driving force distribution control device for a four-wheel drive vehicle of the present invention, FIG. 2 is an overall system diagram of a four-wheel drive vehicle to which the driving force distribution control device of the embodiment is applied, FIG. 4 is a flowchart showing the flow of the front and rear wheel driving force distribution control operation by the ETS controller of the embodiment apparatus. FIG. 4 is a gain characteristic diagram with respect to the lateral acceleration set in the ETS controller. FIG. FIG. 6 is a control characteristic diagram showing another example of the front wheel side transmission torque characteristic with respect to the longitudinal acceleration. a: Variable driving force distribution clutch b: Forward / backward acceleration detecting means c: Lateral acceleration detecting means d: Front / rear wheel driving force distribution controlling means

Claims (1)

(57) [Claims] 1. A variable driving force distribution clutch provided in the middle of a driving system to the other of the front and rear wheels with respect to a driving system directly connected to the engine to one of the front and rear wheels, and a longitudinal acceleration detecting means for detecting a longitudinal acceleration of the vehicle. Lateral acceleration detecting means for detecting the lateral acceleration of the vehicle; and increasing the longitudinal driving acceleration to increase the transmission driving force to the clutch engagement driving wheels to increase the driving force distribution to the four-wheel drive side and to increase the lateral acceleration. Control means for controlling the engagement force of the variable drive force distribution clutch according to the control content for decreasing the increase rate of the transmission drive force to the clutch engagement drive wheel with respect to the occurrence of the longitudinal acceleration. A driving force distribution control device for a four-wheel drive vehicle.