JPH0790707B2 - 4-wheel drive vehicle with front and rear wheel engagement mechanism control function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a four-wheel drive vehicle with a function of controlling a front-rear wheel engagement mechanism that prevents a tight corner braking phenomenon from occurring.

[Conventional technology]

Generally, when driving a car, front-wheel drive has better straight-line stability than rear-wheel drive, but when cornering, it is necessary to apply force to the tire to return with the steering wheel, so front-wheel drive tends to bend less easily. There is. In that respect, the rear-wheel drive is more likely to bend, but if the driving force is too strong, it has the drawback of overturning. Therefore, it is ideal for driving a car to drive with front and rear wheels at half-power.
In that respect, the four-wheel drive vehicle is extremely excellent. By the way, since the turning radii of the left and right wheels of the automobile are different during cornering, this effect is absorbed, and in order to perform smooth cornering, the difference in rotational speed between the left and right wheels is absorbed according to the difference in turning radius. A mechanism, that is, a differential mechanism (front differential, rear differential) is provided. Since this difference in turning radius also occurs between the front wheels and the rear wheels, in a four-wheel drive vehicle, a mechanism that absorbs the difference in rotation speed between the front wheels and the rear wheels according to the difference in turning radius, that is, a center differential mechanism. The one with is proposed.

However, since this center differential mechanism has a function of distributing the torques of the front wheels and the rear wheels in an equal ratio, the driving force transmission limit should be balanced with the lower value of the driving force of the front wheels or the rear wheels. Becomes For example, if one of the front wheels spins, drive energy escapes there,
The driving force of the rear wheels becomes extremely small. For this reason,
A four-wheel drive vehicle with a center differential may be inferior in transmission driving force to a four-wheel drive vehicle without a center differential when the road surface friction coefficient is low. This is manifested as a phenomenon such as slippage (idling) of front wheels or rear wheels when a large driving force is generated, such as during acceleration, and the driving force cannot be sufficiently transmitted to the road surface.

In order to prevent such an adverse effect, conventionally, a lock mechanism that directly connects the differential limitation between the front wheels and the rear wheels without using a center differential is provided, and a large driving force is required such as when accelerating or traveling on a rough road. In this case, the center differential mechanism was manually locked, and the lock was manually unlocked during normal driving that does not require a large driving force.

FIG. 5 is a diagram for explaining a drive force transmission mechanism of a full-time four-wheel drive vehicle with a center differential in which an engine is mounted on the front side. In this drive force transmission mechanism, the power from the engine is transmitted to the torque converter 31, the main transmission 32, and the auxiliary transmission 33 arranged in the automatic transmission 30, and the output thereof is the drive gear 34 and then the drive gear. It is transmitted to the front wheel drive shaft 36 via 34, and the front wheels are driven. Here, the front differential device 35 is a differential mechanism between the right wheel and the left wheel of the front wheels. On the other hand, the rear wheel drive propeller shaft 37 is connected via a bevel gear 38 to a center differential device 39, which is a differential mechanism between the front and rear wheels, and the center differential device 39 is connected to a rear wheel transmission device 40. Has been done. Further, a center differential lock clutch 41 is provided in parallel with the center differential device 39.
Are arranged. Therefore, the lock of the center differential is controlled by controlling the engagement state of the clutch 41 by the hydraulic circuit 42.

In general, as a four-wheel drive vehicle, there is a part-time four-wheel drive vehicle without a center differential as opposed to a full-time four-wheel drive vehicle with a center differential as described above. Normally, either the front wheels or the rear wheels are driven, and when the driving force on the snowy road is required, the remaining wheels are directly connected to the drive shaft via a clutch or the like so as to drive the two-wheel drive and the four-wheel drive. And is switched intermittently.

By the way, full-time type 4 with such a center differential
In a wheel drive vehicle, since the steering angle of the steered wheels and the lock control of the center differential are irrelevant, the center differential is locked when traveling on a bad road,
When returning to a normal road with a large friction coefficient and trying to turn at a large steering angle without releasing the lock of the center differential,
The rotation speed on the front wheel side cannot be higher than that on the rear wheel side, negative torque is generated on the front wheel side, and a tight corner braking phenomenon occurs.

Therefore, conventionally, there has been proposed a four-wheel drive vehicle in which the center differential mechanism is unlocked when the steering angle is equal to or greater than a predetermined value and the center differential mechanism is locked (Japanese Patent Laid-Open No. 59-59). -206228).

[Problems to be solved by the invention]

However, in the method of releasing the lock of the center differential mechanism when the steering angle becomes a predetermined value or more, for example, if the steering wheel is turned over a predetermined angle on a snowy road, the center differential mechanism will always be free and slip very much. The problem arises that it becomes easier.

The present invention is to solve the above problems, and provides a four-wheel drive vehicle with a control function of front and rear wheel engagement mechanism that can prevent the occurrence of a tight corner braking phenomenon and the occurrence of slip. The purpose is to do.

[Means for solving problems]

Therefore, in the four-wheel drive vehicle with the control function of the front and rear wheel engaging mechanism of the present invention, the differential limitation between the front wheel and the rear wheel is controlled from the direct connection through the slip region by controlling the engagement degree of the front and rear wheel engaging mechanism. A four-wheel drive vehicle that can be controlled up to release, corresponding to a detected steering angle from a front wheel torque detection means, a steering angle detection means, and a reference torque value set corresponding to each steering angle stored in a built-in memory. The reference torque value is read and compared with the detected torque value, and an electronic control unit that outputs a control signal according to the comparison result, and a drive unit that is controlled by the electronic control unit and that drives the front and rear wheel engagement mechanism, When the detected torque value is smaller than the reference torque value, the drive means is controlled by the electronic control means so as to drive the front and rear wheel engagement mechanism in the disengagement direction.

[Action and effect]

The four-wheel drive vehicle with the control function of the front and rear wheel engagement mechanism of the present invention is
Front wheel torque and steering angle are detected in a four-wheel drive vehicle in which the differential limitation between the front wheels and the rear wheels can be controlled from the direct connection to the release through the slip area by controlling the degree of engagement of the front and rear wheel engagement mechanisms. When the reference torque value corresponding to the detected steering angle is read from the reference torque value set corresponding to each steering angle stored in the internal memory and compared with the detected torque value, when the detected torque value is smaller than the reference torque value, By controlling the engagement of the front and rear wheel engagement mechanisms in the releasing direction, it is possible to prevent the occurrence of a tight corner braking phenomenon and prevent the occurrence of slips in advance, and it is set according to each steering angle. By increasing the reference torque value when the steering angle is large and decreasing it when the steering angle is small, the reference torque value is controlled to release the engagement of the front and rear wheel engagement mechanism earlier when the steering angle is large. It is possible to reduce the shock due to the release by, it is unnecessary to determine erroneously engine brake when the steering angle is small and tight corner braking.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a diagram showing the overall configuration of a control device for a full-time type four-wheel drive vehicle with a center differential according to the present invention, and FIG. 2 is a center differential lock release curve in which the horizontal axis is the steering angle and the vertical axis is the front wheel torque. 3 and 4 are diagrams in which the release curve of FIG. 2 is converted into data for storing in the memory of the electronic control unit, and FIG.
The figure is a flow chart for explaining the control flow. In the figure, 1 is a steering sensor, 2 is a front wheel torque sensor, 3 is an electronic control device, 4 is a hydraulic circuit, and 5 is a center clutch composed of friction engagement elements. In the figure, the steering sensor 1 is attached to the steering wheel and the torque sensor 2 is attached to the front wheels, and the steering angle and the front wheel torque detected by each sensor are input to the electronic control unit 3. The electronic control unit 3 stores each torque value data on the center differential lock release curve corresponding to the steering angle in FIG. 2 in a built-in memory. The center clutch 5 can control the differential limitation between the front wheels and the rear wheels from direct connection to release through the slip region by controlling the degree of engagement.

Next, the operation will be described. The electronic control unit 4 reads the detected front wheel torque at the step of the control flow shown in FIG. 4, and reads the detected steering angle at the step. In step, the torque value A stored in the memory corresponding to the steering angle read in step is read. In step, it is determined whether the front wheel torque is larger than A. NO
In this case, it is determined that the tight corner braking phenomenon is occurring, and the hydraulic circuit 4 is controlled in a step to reduce the hydraulic pressure of the center clutch 5 to release the lock of the center differential. If YES, it is determined that the tight corner braking phenomenon has not occurred.

The release curve of the center diff lock in FIG. 2 is that when the steering angle is large, the reference torque value is increased. The shock when releasing the lock is reduced. When the steering angle is small, the reference torque value is reduced to determine that the tight corner braking phenomenon does not occur even if the torque slightly decreases. I try not to make a mistake.

Although the full-time four-wheel drive vehicle has been described in the above embodiment, the four-wheel drive vehicle with the control function of the front and rear wheel engagement mechanism according to the present invention can be applied to the part-time four-wheel drive vehicle. . In this case, as the front and rear wheel engaging mechanism, the former controls the clutch of the differential limiting mechanism of the center differential, while the latter controls the clutch that directly connects the front wheel and the rear wheel. The clutch may be an electromagnetic type or any other clutch that can control the differential limitation between the front wheels and the rear wheels from direct connection to release through the slip region by controlling the degree of engagement.

As described above, according to the present invention, not only the steering angle but also the front wheel torque is used as the criterion for determining the occurrence of tight corner braking. Therefore, tight corner braking may not occur when the steering angle is large. On the road surface, the engagement of the front and rear wheel engagement mechanism will not be released,
It is possible to prevent the occurrence of slip. Further, since the reference torque value to be compared with the front wheel torque is small when the steering angle is small and is large when the steering angle is large, engine braking when the steering angle is small can be erroneously determined as tight corner braking, and When the steering angle is large, the engagement of the front and rear wheel engagement mechanism is released earlier, so the shock associated with the release of the engagement can be reduced.

[Brief description of drawings]

FIG. 1 shows a front and rear wheel engaging mechanism according to the present invention with a control function 4
FIG. 2 is a diagram showing the overall configuration of a wheel drive vehicle, and FIG.
FIG. 3 is a diagram showing a center differential lock release curve in which the vertical axis is the front wheel torque, FIG. 3 is a diagram in which the release curve of FIG. 2 is converted into data for storage in the memory of the electronic control unit, and FIG. 4 is the front and rear wheels of the present invention. FIG. 5 is a diagram showing a flow chart of a four-wheel drive vehicle with a control function of an engagement mechanism, and FIG. 5 is an explanatory diagram of a drive force transmission mechanism of a full-time four-wheel drive vehicle with a center differential in which an engine is mounted on the front side. 1 ... Steering sensor, 2 ... Torque sensor, 3 ...
… Electronic control device, 4 …… Hydraulic circuit, 5 …… Center clutch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsugu Tatsuda 10 Takane, Fujii-cho, Anjo City, Aichi Prefecture, within Aisin Warner Co., Ltd. (56) References JP 59-206228 (JP, A)

Claims (4)

[Claims] 1. A four-wheel drive vehicle capable of controlling a differential limitation between a front wheel and a rear wheel from direct connection to release through a slip region by controlling a degree of engagement of front and rear wheel engaging mechanisms,
The reference torque value corresponding to the detected steering angle is read from the front wheel torque detection means, the steering angle detection means, and the reference torque value set corresponding to each steering angle stored in the internal memory and compared with the detected torque value. An electronic control unit that outputs a control signal according to the comparison result; and a drive unit that is controlled by the electronic control unit and drives the front-rear shaft engaging mechanism. A four-wheel drive vehicle with a control function for the front and rear wheel engagement mechanism, which is controlled by the electronic control means so as to drive the front and rear wheel engagement mechanism in a releasing direction when it is small. 2. The reference torque value set corresponding to each of the steering angles is large when the steering angle is large and small when the steering angle is small. 4-wheel drive vehicle with front and rear wheel engagement mechanism control function. 3. The front and rear wheel engaging mechanism according to claim 1 or 2, wherein the front and rear wheel engaging mechanism is a center clutch that locks the center differential device when completely engaged. 4-wheel drive vehicle with integrated mechanism control function. 4. The four-wheel drive vehicle with a control function for the front and rear wheel engagement mechanism according to claim 1 or 2, wherein the drive means is a hydraulic circuit.