JPS6357334A - Controlling method for four-wheel drive device - Google Patents

Abstract

PURPOSE:To improve not only a braking performance but also an acceleration performance by controlling the transmitting torque capacity of a differential control clutch in accordance with deceleration at the time of braking, in the captioned device in which the differential action of a center differential device is restricted by said differential control clutch. CONSTITUTION:A transfer device 14 for four-wheel driving which is connected to an internal combustion engine 10 via an automatic transmission 12 including a continuously variable transmission 18, houses a differential control clutch 64 which selectively connects the differential case 46 of a center differential device 42 and a front wheel driving shaft 62. And, the clutch 64 is controlled by a hydraulic control device 74, which, in turn, is controlled by a control device 100. In this case, the hydraulic control device 74 controls so that the transmitting torque capacity of the differential control clutch 64 is gradually reduced from a reference transmitting torque capacity under a totally closed throttle, as the deceleration which is obtained from the output of a vehicle speed sensor 104 at the time of braking is increased, to become the least transmitting torque capacity right before an ABS operation point.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method of controlling a four-wheel drive system having a center differential device that differentially operates front and rear wheels and a clutch that performs differential control thereof, and in particular, It concerns a method of control.

2. Description of the Related Art In this type of four-wheel drive system, by releasing the clutch, the center differential device is freed and the front and rear wheels are differentially operated, thereby preventing tight corner braking during sharp turns. By engaging the clutch and limiting the differential operation of the center differential device to create a so-called direct-coupled four-wheel drive state, it is possible to improve maneuverability (handling stability) and acceleration performance. Furthermore, in the above-mentioned four-wheel drive system equipped with a differential control clutch, it is possible to control the differential control clutch in a variety of ways depending on the driving condition of the vehicle. For example, when making a sharp turn, the throttle opening degree is generally reduced. It has been proposed to release the differential control clutch when the throttle opening falls below a certain opening, thereby preventing tight corner braking. Also, JP-A-61-1539 and JP-A-61-1539
No. 3541 describes a system that completely releases a differential control clutch or releases a clutch provided on the drive shaft of the front or rear wheels when the ABS (Anti-Skid Control Brake System) operates.

Problems to be Solved by the Invention However, even if the purpose is to prevent tight corner braking, if the differential control clutch is released when the throttle opening decreases below a certain opening, the differential control clutch will be released during braking. The problem arises that the dynamic control clutch is disengaged, making it impossible to take advantage of engine braking in direct-coupled four-wheel drive mode, which has the best braking performance.

In addition, in the system described in each publication of #Jt8, AB
If the differential operation of the center differential device is completely restricted during S operation, the standard speed cannot be set to 1q because all four wheels behave in the same way, and the vehicle speed signal may be affected by torsional vibration in the drive system of the front and rear wheels. For reasons such as disorder, A.
When the BS operates, the differential control clutch is released. However, if the differential control clutch is configured to be hydraulically controlled, for example, when ABS operates on a sharp curve while driving in a mountainous area, especially on a low μ road, and then suddenly accelerates at the exit of a corner, the differential Since the control clutch is once released and the center differential device is in a free state, even if you try to limit the differential of the center differential device during sudden acceleration after handling a corner,
Since oil pressure is being extracted from the hydraulic servo system of the differential control clutch, there is a time lag before the differential control clutch operates, resulting in a problem of deterioration in acceleration performance.

This invention was made against the background of the above-mentioned circumstances, and it is an object of the present invention to provide a control method for a four-wheel drive device that can improve not only braking performance but also acceleration performance.

Means for Solving the Problems In order to achieve the above object, the present invention transmits driving force to a rear wheel drive shaft and a front wheel drive shaft through a center differential device, and When controlling a four-wheel drive system in which the differential operation of the differential control clutch is limited by a differential control clutch with a variable transmission torque capacity, it is necessary to change the transmission torque capacity of the differential control clutch according to the deceleration during braking. This method is characterized by

Further, in the present invention, when the deceleration is equal to or greater than a predetermined value, it is effective to maintain the transmission torque capacity at a predetermined low capacity.

Roughly, in this invention, when the deceleration is below a predetermined value, the transmission torque capacity is increased according to the deceleration, and when the deceleration is above the predetermined value, the transmission torque capacity is increased. It is preferable to maintain it at a predetermined low value.

Operation Therefore, in the method of the present invention, when braking is performed by reducing the throttle opening or stepping on the brake, the output signal from the vehicle speed sensor is differentiated to calculate the deceleration obtained by 1q or the deceleration obtained from the acceleration sensor. The transmission torque capacity of the differential control clutch of the center differential device is controlled according to the speed. For example, when the deceleration is above a certain level, the transmission torque capacity is maintained at a predetermined value, or the transmission torque capacity is increased or decreased according to the deceleration. ,
As a result, all four wheels are not in a free state but are connected to the engine in a state in which a predetermined torque can be transmitted, resulting in high braking performance. In addition, with the provision of ABS, if the transmission torque capacity is to be reduced to give priority to ABS operation when deceleration exceeds a certain value, the differential control clutch will not be completely disengaged, but will operate at a predetermined level. The differential 11 is maintained at a low transmission torque capacity during braking followed by acceleration.
The first period is performed quickly and the acceleration performance is improved.

EXAMPLES Next, the method of the present invention will be explained in detail based on examples.

FIG. 1 is a flowchart showing an example of the method of the present invention, and the method shown here is implemented with the apparatus shown in FIGS. 2 and 3 as a target. That is, in FIG. 2, reference numeral 10 indicates an internal combustion engine, and the internal combustion engine 10 is placed horizontally at the front of the vehicle. Transfer devices 14 are connected in sequence. The automatic transmission 12 for a vehicle includes a hydraulic torque converter 16 having a general structure and a transmission 18.

The hydraulic torque converter 16 is connected to the output shaft 11 of the internal combustion engine 10 by an input member 16a, and is connected to the output shaft 11 of the internal combustion engine 10.
The output member 16b is given rotational driving force from the output member 16b.
is connected to the transmission 18.

The transmission 18 may be of conventional construction including a planetary gear arrangement and is adapted to change between a plurality of forward gears and at least one reverse gear.

The speed change control of the transmission device 18 is performed using hydraulic pressure by a hydraulic control device 40.

The four-wheel drive transfer device 14 has a center differential device 42. The center differential device 42 is rotatably held by a differential case 46 integrally provided with an input gear 44 that meshes with the output gear 38 of the transmission 18, and a pinion shaft 48 provided in the differential case 46, and is opposed to each other. It has a pair of disposed differential pinions 50, and a side gear 52 for rear export force and a side gear 54 for front export force that mesh with these differential pinions 50.

A rear export force gear 56 is connected to the rear export force side gear 52, and a rear wheel drive gear 60 of a rear wheel drive shaft 58 meshes with the rear export force gear 56.

A hollow front wheel drive shaft 62 is directly connected to the front export force side gear 54.

The four-wheel drive transfer device 14 is configured to selectively transmit torque between the differential case 46, which is an input member of the center differential device 42, and the front wheel drive shaft 62, which is an output member of the center differential device 42. Connecting hydraulically operated differential control clutch 6
4 is provided. The differential control clutch 64, as shown in FIG. By moving to the right in the figure against the spring force, the differential case 46 and the front wheel drive shaft 62 are connected to enable torque transmission, and the transmission torque capacity increases as the servo oil pressure supplied to the oil chamber 68 increases. It is designed to increase proportionally.

Servo hydraulic pressure is supplied to the oil chamber 68 of the hydraulic servo device 66 by a hydraulic control device 74. The hydraulic control device 74 includes a pressure regulator valve 7 that receives hydraulic pressure from an oil pump 76 built into the vehicle automatic transmission 12 and regulates the hydraulic pressure to line hydraulic pressure.
8 and an electromagnetic servo hydraulic control valve 8Q to which line hydraulic pressure is applied from a pressure regulator valve 78. The servo hydraulic control valve 80 has a port a connected to the oil chamber 68, a hydraulic board b supplied with line hydraulic pressure from the pressure regulator valve 78, and a drain port C. When energized, the port a is connected to the port a. The port a is connected to the hydraulic port b, while the port a is connected to the drain port C when the power is not energized. A pulse signal with a predetermined duty ratio is given to the servo hydraulic control valve 80 from the control device 100, and thereby the servo hydraulic control valve 80 supplies servo hydraulic pressure to the oil chamber 68 with a magnitude corresponding to the duty ratio of the pulse signal. It is supposed to be done.

The front wheel drive shaft 62 is a front differential device 82
The differential case 84 is connected to the differential case 84. The front differential device 82 includes two differential pinions 88 that are rotatably held in a differential case 84 by a pinion shaft 86 and are arranged opposite to each other.
and a right side gear 90 and a left side gear 92 that mesh with these differential pinions 88, and the right side gear 9
0 is connected to a right axle 94, and one end of a left side axle 96 is connected to the left side gear 92.

The hydraulic control device 40.74 operates based on a control signal from the electric control device 100. The control device 100 receives information regarding the throttle opening of the internal combustion engine 10 from the throttle opening sensor 102, information regarding the vehicle speed from the vehicle speed sensor +j 104, and information regarding the manual shift range of the transmission 18 from the manual shift position sensor 106. However, information regarding whether or not the vehicle is braking is transmitted from the brake switch 108.
Information regarding brake fluid pressure representing braking force is provided from the brake fluid pressure sensor 110.
This control device 100 basically outputs a control signal for controlling the gear position of the transmission 18 to the hydraulic control device 40 according to a predetermined shift pattern according to the manual shift range, vehicle speed, and throttle opening. Further, during vehicle braking, a pulse signal with a predetermined duty ratio is output to the servo hydraulic control valve 80 of the hydraulic control device 74 for controlling the transmission torque capacity of the differential control clutch 64 in accordance with the deceleration. It has become.

Next, an example of the control method of the present invention for the above-mentioned device will be explained. As shown in FIG. ), if the judgment result is YES, the process proceeds to step 201 where the deceleration (dv/dt) is calculated from the signal of the vehicle speed sensor, and step 200
If the judgment result is no, return. Step 2
After determining the deceleration (dv/dt) in step 01, step 20
In step 2, the transmission torque capacity Tc of the differential control clutch 64 is determined according to the deceleration (dv/dt). Specifically, as shown in FIG. 4(A), the transmission torque capacity ITC gradually decreases from the reference transmission torque capacity Tco at full throttle as the deceleration increases, and immediately before the ABS operation point. The transmission torque capacity may be the smallest at , and thereafter maintain that low transmission torque capacity, or, as shown in Figure 4 (B), the transmission torque capacity may be the smallest as the deceleration increases until just before the ABS operation point. The transmission torque capacity may be increased to a certain value, and thereafter maintained at the smallest transmission torque capacity. Note that "R is also a small transmission torque capacity" does not mean that the transmission torque capacity is zero, and the above-mentioned hydraulic servo device 6
A slight hydraulic pressure is applied to Yuzu 68 of No. 6.

In order to realize the above transmission torque capacity, in step 203, a duty ratio corresponding to the transmission torque capacity Tc is determined, and a pulse signal corresponding to the duty ratio is given to the servo oil pressure control valve 80 to cause the differential control clutch 64 to perform servo control. Apply hydraulic pressure (step 204).

Therefore, in the above method, the differential operation of the center differential device 42 is limited by controlling the transmission torque capacity of the differential control clutch 64 according to the deceleration when braking the vehicle, so that the internal combustion engine 10 is transmitted to all four wheels. Torque is applied in accordance with the weight distribution of the vehicle, providing engine braking in a state similar to direct four-wheel drive, and improving braking performance. Furthermore, if the deceleration becomes greater than the deceleration at which ABS operates, ABS can be effectively activated by maintaining the transmission torque capacity at the smallest value immediately above the ABS operating point. At the time of re-acceleration, a small amount of oil pressure is already applied to the hydraulic servo of the differential control clutch 64, so the differential control clutch 64 is immediately strongly engaged and the differential operation of the center differential device 42 is restricted. It approaches a direct four-wheel drive state, resulting in high acceleration performance.

In the above explanation, the case where deceleration is detected based on a change in vehicle speed has been taken as an example, but in this invention, deceleration is detected using an appropriate acceleration sensor, and the transmitted torque capacity is determined according to the detected value. It may also be controlled.

As described in detail, according to the control method of the present invention, each set of transmission torque of the differential control clutch is controlled according to the deceleration, so that the differential operation of the center differential device is limited during braking. This invention improves braking performance by bringing the center differential closer to a free state when ABS is operating, allowing ABS to operate effectively.Also, in this invention, even when ABS is operating, a low transmission torque capacity is applied to the differential control clutch. Therefore, when re-accelerating after braking, the differential control clutch can be engaged immediately to limit the differential of the center differential device, bringing it closer to a direct-coupled four-wheel drive state. Acceleration performance can be improved like never before.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing an example of the method of the present invention;
Figure 2 is a simplified diagram of the device targeted by this method, Figure 3 is a simplified diagram of the differential control clutch control system, and Figure 4 (A> is an example of the relationship between deceleration and transmitted torque capacity. 18 is a diagram showing another example of the relationship between deceleration and transmission torque capacity. 18...Transmission device, 42... Center differential device, 58... Rear Wheel drive shaft, 62...Front wheel drive shaft, 64...Differential control clutch, TC...
・Transmission torque capacity.

Claims (3)

[Claims] (1) Transmitting driving force to the rear wheel drive shaft and the front wheel drive shaft via the center differential device,
In controlling a four-wheel drive device in which the differential operation of the center differential device is limited by a differential control clutch having a variable transmission torque capacity, the transmission torque capacity of the differential control clutch is changed in accordance with the deceleration during braking. A four-wheel drive device control method characterized by: (2) The method for controlling a four-wheel drive device according to claim 1, characterized in that, when the deceleration is equal to or higher than a predetermined value, the transmission torque capacity is maintained at a predetermined low capacity. (3) If the deceleration is less than a predetermined value, the transmission torque capacity is increased according to the deceleration, and if the deceleration exceeds the predetermined value, the transmission torque capacity is determined in advance. 2. The method of controlling a four-wheel drive device according to claim 1, wherein the four-wheel drive device is maintained at a low value.