JP3327964B2 - Automotive differential limiter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential control system for a motor vehicle, and more particularly to a differential control system for a motor vehicle having a differential unit between axles for front wheels, rear wheels and front and rear wheels.

[0002]

2. Description of the Related Art A four-wheel drive vehicle has a center differential disposed between axles of front and rear wheels, a front differential disposed between front wheels, and a front differential for compensating for a difference in trajectory between front and rear wheels when turning. And a rear differential disposed between the rear wheels. By the function of these differentials, it is possible to eliminate a so-called tight corner braking phenomenon or the like. However, in vehicles with these differentials,
If any of the four wheels spins during start / acceleration, the driving force will not be sufficiently transmitted to the other wheels, and it will be difficult to start / accelerate stably, resulting in reduced steering stability, braking performance, and acceleration performance. There was a problem of doing it.

In view of such a problem, Japanese Patent Application Laid-Open No. 62-16 / 1987
Japanese Patent No. 6114 discloses a differential limiting device in which operating states of a front differential, a rear differential, and a center differential are set according to an operation state by a hydraulic pressure in a locked state and an unlocked state, respectively. A wheel drive vehicle is disclosed. This differential limiting device inputs a wheel speed signal and a steering angle signal of each wheel to a control circuit, performs a rough road determination, a straight traveling determination, an acceleration determination, and a braking determination based on these values, and performs various driving states. In response to the above, the operations of the front differential, the rear differential, and the center differential are controlled, thereby improving steering stability, braking performance, acceleration performance, and the like.

Further, in this type of differential limiting device, there has been proposed a type which is configured to control a transmission torque capacity of the differential limiting device based on a difference in rotation speed between front and rear wheels (Japanese Patent Laid-Open No. Sho 62). No. 166113). The differential limiting device is configured to reduce the transmission torque capacity when the rotational speed difference between the front and rear wheels is relatively small, thereby providing an appropriate differential or limiting the differential according to the operating condition. .

Further, there has been proposed a differential lock control device configured to detect a starting state of a vehicle and to automatically lock a center differential when the vehicle starts moving (Japanese Patent Laid-Open No. 63-251327). This differential lock device eliminates the need for a driver's manual differential lock operation at the time of starting, and attempts to ensure a reliable differential lock operation at the time of starting.

[0006]

However, in such a differential limiter, when a differential is locked, a plurality of differentials are locked substantially synchronously. This may cause a so-called torque shock. Also, since all differential limiters lock or unlock substantially simultaneously under substantially the same conditions, under certain operating conditions, all differential limiters may cause hunting at once. Conceivable. Furthermore, the differential limiting device generally includes an electromagnetic or hydraulically actuated multi-plate clutch that regulates the differential of each differential, but when an electromagnetic clutch is used as such a clutch, the clutch in each differential May impose a sudden electrical load on the control system of the differential limiter.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a differential limiting device for an automobile, which can suppress a torque shock during traveling due to a differential locking operation. It is in.
Another object of the present invention is to provide a differential limiting device for a vehicle which can effectively prevent wheel slippage, particularly when the vehicle starts or accelerates, and thus has good running performance.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a differential limiting device for a motor vehicle having a control system for limiting all differentials of a plurality of differentials under a predetermined condition. The differential includes a first differential provided between the axles, a second differential provided between the rear wheels, and a third differential provided between the front wheels. The first differential is attached to the first differential and the first differential is provided. A first differential limiting means for limiting a differential of the differential, a second differential limiting means provided on the second differential for limiting the differential of the second differential, and a second differential limiting means provided on the third differential; Third differential limiting means for limiting the differential of the third differential, and a maximum driving torque at which the wheels rotate without slipping.
The torque limit value of each wheel ,
A coefficient of friction of a road surface on which a wheel comes into contact with the ground, a limit torque calculating means for calculating from a radius of the wheel, a difference between a limit torque value between front wheels from a limit torque value of each wheel, and a limit torque value between rear wheels . Limit torque value for calculating the difference between the difference and the limit torque value between axles
Calculating means; operating order determining means for operating the differential limiting means in the order of increasing the difference between the limit torque values; and differential determining the differential torque of each of the differential limiting means according to the difference between the limit torque values. And torque determining means.

[0009] The ground contact load of the wheel is determined by accelerating the vehicle in the forward direction.
The correction is based on the degree. In addition,
The ground contact load of the wheel is corrected based on the turning state of the vehicle
You can also.

Furthermore, more <br/> considering the change in radius of the wheel, thereby enabling more precise control. Further, since the load on the wheels changes in accordance with the turning state, the slip can be reduced by operating the differential limiting means based on the turning state of each wheel instead of the limit torque value. In another aspect, the differential limiting means does not selectively control whether the differential is completely locked or unlocked, but changes the value of the differential torque itself so as to continuously change the torque transmission of the differential. Attention may be paid to this.

For example, the differential limiting means is constituted by an electromagnetic clutch and the current supplied to the electromagnetic clutch is continuously controlled, whereby the differential torque can be controlled continuously.

[0012]

According to the present invention, the differential of each differential is set based on the limit driving torque of each wheel. The limit driving torque of the wheel can be obtained by the following equation. T = W × μ × R where T: limit driving torque of the wheel, W: ground contact load of the wheel, μ: coefficient of road surface friction at which the wheel contacts the ground, R, radius of the wheel. The limit drive torque of the wheel can be grasped as the maximum drive torque that allows the wheel to rotate without slipping.
Therefore, efficient running can be ensured by controlling this limit driving torque to be the maximum and the driving torque difference to be the minimum.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram showing an overall configuration of a vehicle control device according to one embodiment of the present invention. First, the power transmission system of the vehicle shown in FIG. 1 will be described. The automobile includes an engine 10, and a transmission 11 is connected to the engine 10. On the output side of the transmission 11, a center differential 12 is arranged. The center differential 12 is connected to a front propeller shaft 13 for transmitting the output from the engine 10 to the front wheels and a rear propeller shaft 14 for transmitting the outputs to the rear wheels. A front wheel 16 is connected to the front propeller shaft 13 via a front axle 15. A rear wheel 18 is connected to the rear propeller shaft 14 via a rear axle 17. The front axle 15 has a front differential 19 (hereinafter, referred to as a front differential), and the rear axle 15 has a rear differential 20 (hereinafter, a rear differential).
Are provided respectively.

The vehicle of this embodiment is provided with an anti-skid brake device and a brake device control unit 21 (hereinafter referred to as an ABS control unit) for controlling this device. Further, the vehicle of this example includes a power train control unit 22 that controls the transmission 11 and the engine.

These control units 21 and 22
, Signals representing various running states are input. First,
A wheel speed sensor for detecting the wheel speed of each wheel is attached to each front wheel 16 and each rear wheel 18, and a signal from the wheel speed sensor is input to the ABS control unit 21. A brake switch 23 for detecting an operation state of the brake is provided, and a signal from the brake switch 23 is detected. The intake system of the engine is provided with a throttle sensor for detecting a throttle opening.

The control unit 22 includes a throttle opening from a throttle sensor, a lateral acceleration of the running vehicle from a lateral acceleration sensor 31, an engine speed from an engine speed sensor, and a rotation of the steering wheel 24, that is, a steering angle. Is input from a steering angle sensor or the like for detecting the steering angle. The control unit 22 outputs a throttle opening signal to the engine 10 to adjust the throttle opening, and outputs a fuel injection signal to control the fuel injection valve. Further, an ignition signal is output to control the ignition timing. Also,
A shift signal is output to the transmission 11 to perform shift control. Powertrain control unit 22
Is connected to the ABS control unit 21, through which a wheel speed signal and an estimated μ (estimated road surface friction coefficient) for each wheel are input. Further, the control unit 22 outputs a fail signal to the ABS control unit 21 to release the differential lock when an emergency or the like is necessary.

The control units 21 and 22 include input / output sections 25 and 26, CPUs 27 and 28, respectively.
And memories 29 and 30. All of the above input / output signals are sent via the input / output section. In the differential control, the control unit 22 supplies a center differential current to the center differential 12, a front differential current to the front differential 19, and a rear differential current to the rear differential 20 based on each input value. 12, the front differential 19 and the rear differential 20 are provided with an unlocked state, an intermediate locked state and a completely locked state. In the intermediate lock state, the differential torque changes continuously according to the amount of current.

FIG. 2 is a sectional view showing an electromagnetic multi-plate clutch provided in the center differential. Each of the center differential 12, the front differential 19 and the rear differential 20 is provided with an electromagnetic multi-plate clutch 50. The electromagnetic multi-plate clutch 50 allows the center differential 12, the front differential 19 and the rear differential 2 to be mounted.
0 indicates that the differential state changes continuously from the unlocked state to the completely locked state. This electromagnetic multi-plate clutch 50
May be of any type as long as the differential between the front propeller shaft 13 and the rear propeller shaft 14 can be limited. An example is shown in FIG. In FIG. 2, an electromagnetic multi-plate clutch 50 includes a clutch plate 51 including a plurality of inner disks and an outer disk, and an actuator 5 for generating a pressing force on the clutch plate 51.
2 is comprised. Further, 53 is a bearing, 54 is a transmission member that is operatively connected to one propeller shaft, and 55 is a transmission member that is operatively connected to the other propeller shaft. The actuator 52 is configured such that the armature 57 presses the clutch plate 51 by a magnetic force generated when a current flows through the solenoid 56. In the electromagnetic multi-plate clutch 50, since the current flowing through the solenoid 56 and the pressing force for frictionally engaging the clutch plate 51, that is, the torque generated by the electromagnetic multi-plate clutch 50, are in a proportional relationship, the center differential 12, the front differential 19, and the Rear differential 2
1 can be continuously changed by increasing or decreasing the current.

FIG. 3 is a flowchart showing the control of the differential gear according to the present invention. The control unit 22 calculates the weight distribution of the vehicle applied to the wheels as the ground load W of each wheel 16 and 18 based on the various input signals. In this case, as shown in FIG. 3, the ground contact load W of the wheel is corrected based on the forward acceleration acting on the vehicle. That is, when the vehicle is in an acceleration state, the vehicle load distribution to the rear wheels is larger than that of the front wheels due to the inertial force. On the other hand, in the decelerating state, the ground contact load of the front wheels increases. Therefore, regarding the forward acceleration of the vehicle, the front and rear wheels have symmetrical characteristics as shown in FIG. Further, when the vehicle is in a turning state, the load distribution of the vehicle changes, so that even in such a situation, the value of the ground contact load W of each wheel is corrected. When the wheels are steered as shown in FIG. 5, a larger load is applied to the turning outer wheel than to the turning inner wheel. Therefore, this correction coefficient increases the correction amount for the left wheel when the wheel turns right, and increases the correction amount for the right wheel when the wheel turns left. Further, the control unit 22 calculates the diameter R of each wheel (step S1). Further, μ of the ground contact road surface of each wheel, that is, a road surface friction coefficient is obtained. In the embodiment, the road surface friction coefficient μ is calculated by the ABS control unit 41 and input to the control unit 22. Next, the control unit 22 calculates the limit driving torque Ti = Wi · μi · Ri for each wheel (step S2).
This limit drive torque means the maximum drive force when each wheel rotates without substantially slipping. Next,
The control unit 22 calculates a limit driving torque difference between the front and rear wheels C, the front wheels F, and the rear wheels R (step S).
3). In this case, the gear ratio FGR is considered between the front and rear wheels based on the sum of the left and right front wheels and the total torque of the left and right wheels.

Next, the front and rear wheels between the limit driving torque difference C, compared rear wheel between the limit driving torque difference R, and the value of the front wheel between the limit driving torque difference F descending order differential order according to their size
Is determined (step S4), and a current value to be supplied to the electromagnetic clutch is set based on the chart as shown in FIG. 6 (step S5). Then, control is performed such that the determined current is supplied to the electromagnetic clutch corresponding to the differential (steps S6, S7, S8).

[0021]

As described above, according to the present invention,
Since the differential is controlled based on the limit driving torque of each wheel, the slip of each wheel can be minimized. As a result, the running performance of the vehicle can be improved. In addition, since the three differentials are individually controlled, it is possible to prevent the differentials from performing the locking operation at the same time, and therefore, it is possible to suppress the torque shock during traveling due to the locking operation of the differentials.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an overall configuration of a vehicle control device to which a differential limiting device according to the present invention is applied.

FIG. 2 is a sectional view showing an electromagnetic multi-plate clutch provided in a center differential.

FIG. 3 is a flowchart showing a routine of differential control of each differential.

FIG. 4 is a characteristic diagram of a correction value based on a forward acceleration of a contact load.

FIG. 5 is a characteristic diagram of a correction value based on a turning acceleration of a ground contact load.

FIG. 6 is a graph showing a relationship between a supply current to an electromagnetic clutch for controlling a differential torque of a differential and a limit driving torque difference.

[Explanation of symbols]

 20 Center differential (Center differential) 21 Front differential (Rear differential) 22 Rear differential (Rear differential) 43 Control unit for differential 50 Electromagnetic multi-plate clutch

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yuji Shiya 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Corporation (56) References JP-A-1-309825 (JP, A) JP-A Sho 62-4632 (JP, A) JP-A-62-292529 (JP, A) JP-A-62-155135 (JP, A) JP-A-61-9341 (JP, A) JP-A-62-166114 (JP, A) A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B60K 17/28-17/36 B60K 23/04 F16H 48/20

Claims (3)

(57) [Claims] 1. A differential limiting device for a motor vehicle having a control system for limiting all differentials of a plurality of differentials under a predetermined condition, wherein the plurality of differentials includes a first differential provided between axles and a rear differential. First differential limiting means comprising a second differential provided between the wheels and a third differential provided between the front wheels, the first differential limiting means being attached to the first differential and limiting a differential of the first differential; A second differential limiting means attached to the second differential for limiting the differential of the second differential; a third differential limiting means attached to the third differential for limiting the differential of the third differential And the maximum drive torque at which the wheels rotate without slipping
The limit torque value of a certain wheel is
The coefficient of friction of the road surface to be ground, the limit torque calculating means for calculating the radius of the wheel, the limit torque value between the front wheel from the limit torque value of the respective wheel
The difference, the critical torque value calculating means for calculating a difference between the limit torque value between the difference and the axle threshold torque value between the rear wheel, actuating order determination means for actuating the differential limiting means in order difference is large該限field torque value And a differential torque determining means for determining a differential torque of each of the differential limiting means according to the difference between the limit torque values. 2. The ground load of the wheel according to claim 1,
Is characterized by correcting based on the forward acceleration of the vehicle
Differential limiter for automobiles. 3. The ground load of the wheel according to claim 1,
Is corrected based on the turning state of the vehicle.
That motor vehicles of a limited slip differential.