JPS6277225A - Automatic change over device for four-wheel-drive vehicle - Google Patents

Abstract

PURPOSE:To prevent the reduction of a braking force and the occurrence of a tight corner braking phenomenon by detecting tire lock or a premonition thereof in braking to lock a center differential gear and connect the front wheel side directly to the rear wheel side. CONSTITUTION:Power from an engine is transmitted to a torque converter 1, a main transmission 2 and an auxiliary transmission 3 the outputs of which are transmitted to a center differential gear 7 through a drive gear 5 and a center differential gear input shaft 6. And if any tire lock condition or premonition thereof is detected in braking, a center differential gear lock clutch 6 and a front wheel output shaft 8 are switched to be connected directly to each other so that the center differential gear 7 is locked. Thus the reduction of a braking force and the increase of braking distance can be prevented while a tight corner braking phenomenon is prevented and a power transmission system is prevented from the action of an excessive force.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a four-wheel drive system equipped with a center differential device.
The present invention relates to an automatic switching device for preventing an increase in braking distance due to tire locking in a wheel drive vehicle.

[Conventional technology]

In a four-wheel drive vehicle, if the front wheels and rear wheels are directly connected via a power transmission system, tight corner braking cannot absorb the rotational speed difference between the front and rear wheels during steering. There is a problem in that it causes a ringing phenomenon. For this reason, a mechanism has been developed that transmits power to the front wheel drive shaft and the rear wheel drive shaft via a center differential device in order to absorb the rotation difference between the front and rear wheels.

However, when braking to stop the vehicle, in the case of a four-wheel drive system where the front and rear axles are directly connected via a power transmission system, the rotational speed of the front and rear axles is the same. A single-wheel tire lock, in which one wheel stops, cannot occur, but a four-wheel tire lock with a center differential device cannot occur.
In the case of a wheel drive vehicle, the front and rear axles each rotate freely, resulting in a tire lock phenomenon, which reduces the coefficient of friction between the road surface and the tires, resulting in a slightly longer braking distance.

For this reason, so-called anti-lock brakes, which are mechanisms that electrically detect the state of tire lock or a sign thereof and reduce the braking force to release or prevent tire locking, have been used. In addition, in 4-wheel drive vehicles equipped with a center differential device, the system detects brake signals and prevents tire locking by switching to 4-wheel drive in which the front and rear wheels are directly connected via the power transmission system during braking. [Problems to be Solved by the Invention] Conventional anti-lock brakes, however, have a problem in that the braking force itself is weaker than normal braking force, resulting in a longer braking distance. In addition, in 4-wheel drive vehicles equipped with a center differential device, the system detects brake signals and prevents tire locking by switching to 4-wheel drive in which the front and rear wheels are directly connected via the power transmission system during braking. In this mechanism, there is a problem in that during braking during normal driving, the front wheels and the rear wheels are always connected directly to each other via a power transmission system, resulting in a four-wheel drive system. That is, during steering, the phenomenon of tight corner braking occurs because the difference in rotation between the front and rear wheels cannot be absorbed, resulting in disadvantages such as excessive force acting on the power transmission system and tire wear.

The present invention solves the above-mentioned problems, and is a four-wheel drive vehicle that prevents a decrease in braking force, prevents tight corner braking, and prevents excessive force from acting on the power transmission system. The purpose is to provide an automatic switching device.

[Means for solving problems]

To this end, the automatic switching device for a four-wheel drive vehicle of the present invention detects a state of tire lock or a sign of tire lock during braking in a four-wheel drive vehicle that transmits engine power to the front wheels and rear wheels via a center differential device. The feature is that the center differential device is automatically locked upon detection, and switching is performed so that the front wheels and the rear wheels are directly connected via the center differential device.

[Action and effect of the invention]

The automatic switching device for a four-wheel drive vehicle of the present invention detects the state of tire lock or a sign of tire lock during braking, and automatically connects the front wheels and rear wheels directly via the center differential device. This function prevents the phenomenon of tire locking, which prevents a reduction in braking force and an increase in braking distance.It also prevents tight corner braking, which prevents excessive force from being applied to the power transmission system and causing tire wear. This solves the problem of

〔Example] Examples will be described below with reference to the drawings.

FIGS. 1 and 2 are flowcharts of control according to each embodiment of the present invention, and FIG. 3 is a diagram showing a power transmission system of a four-wheel drive vehicle equipped with a center differential device. In the diagram, A is an automatic transmission, l is a torque converter, and 2
is the main transmission, 3 is the sub-transmission, 5 is the drive gear, 6 is the center differential input shaft, 7 is the center differential device,
8 is a front export power shaft, 9 is a front wheel differential, 10 is a front wheel drive shaft, 11 is a rear export power shaft, 12 is a bevel gear, 13 is a rear wheel drive propeller shaft 71, and 14 is a center differential lock clutch. show.

Generally, in a four-wheel drive vehicle equipped with a center differential, when the engine is placed horizontally,
As shown in Figure 3, power from the engine is transmitted to automatic transmission A.
The output is transmitted to a torque converter 1, a main transmission 2, and an auxiliary transmission 3, which are arranged inside the engine, and the output is transmitted to a drive gear 5, and then a center differential input shaft 6 installed integrally with the drive gear 5. The signal is transmitted to the center differential device 7. The center differential device 7 transmits power to a front wheel drive shaft 10 via a front export power shaft 8 and a front wheel differential device 9, and also transmits power to a front drive shaft 10 via a front export power shaft 8 and a front wheel differential device 9.
The power is also transmitted to the rear wheel drive propeller shaft 13 via 2. Furthermore, a center differential lock clutch 14 for directly connecting or disconnecting the center differential input shaft 6 and the front export force shaft 8 is disposed between the center differential input shaft 6 and the front export force shaft 8.

During normal travel, the center differential input shaft 6 and the front export force shaft 8 are switched to separate, and the front and rear wheels are driven via the center differential device 7.
Wheel drive is performed, and during steering, the difference in rotation between the front and rear wheels is absorbed by the center differential device 7, thereby preventing tight corner braking. When braking to stop the vehicle, if the tires are locked or a sign thereof is locked, the condition is detected and the center differential lock clutch 14 is automatically activated to connect the center differential input shaft 6 and the front export force shaft. By switching the center differential device 8 to be directly connected and locking the center differential device 7, locking of only one wheel can be prevented and an increase in braking distance can be prevented.

Next, a control method during braking will be explained using flowchart 1 shown in FIGS. 1 and 2. First, the flow of processing will be explained using the embodiment shown in FIG. 2. (1) When the vehicle starts and runs, it is determined whether the solenoid that operates the center differential lock clutch 14 is OFF;
That is, check whether the center differential human power axis 6 and the front export force axis 8 are disconnected.

If the answer is No, the process is repeated until the answer is YES, and if the answer is YES, the next process is performed.

■ Check whether the foot brake is ON. N
In the case of O, the process ``■'' is performed, and in the case of YES, the process ``■'' is performed.

■ Turn off the solenoid and return to the process in ■.

■ Input the tire rotation speed S and then perform the process in ■.

(2) Check S#0, that is, whether the rotational speed of the tire is O or near O (tire lock state or its precursor state ai). If NOO, the process returns to (2), and if YES, then the process (2) is performed.

■ Turn on the solenoid, that is, transfer clutch 1
4, the center differential input shaft 6 and the front export force shaft 8 are directly connected, the center differential device 7 is locked, and the front and rear wheels are switched to be directly connected without going through the center differential device 7. return.

Next, the flow of processing will be explained using the embodiment shown in FIG. The processing of ①, ②, ②, and O is the same as that in FIG. 1, so the explanation thereof will be omitted.

(2) Input the wheel deceleration a and the brake pressure p calculated from the change in the wheel rotation speed, and then perform the process (2).

(2) Calculate the deceleration f (p>) of the wheels or vehicle from the brake pressure p, and then process the [phase].

Check whether @a>f(p). That is, it is checked whether the deceleration in the state of tire lock or its precursor is greater than the deceleration in normal braking.

If NO, the process returns to 0, and if YES, process O is performed.

As is clear from the above description, according to the present invention, the state of tire lock or a sign thereof is detected and the center differential device 7 is switched to lock, so the braking force is greater than that of conventional anti-lock brakes. This increases the braking distance and shortens the braking distance.

In addition, since the center differential device 7 is switched to lock only when the tires are locked or a sign of that, unreasonable force is applied to the power transmission system and the tires wear out, compared to a system where the center differential device 7 is always switched during braking. can be prevented from happening.

It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made. For example, in the above embodiment, the deceleration is detected based on the number of rotations of the wheels, and the state of tire lock or its precursor is detected by comparing it with the deceleration corresponding to the brake pressure. It is also possible to directly detect the deceleration of the vehicle and compare it with the deceleration corresponding to the brake pressure to detect the state of tire lock or a sign thereof.

Also, when calculating the deceleration corresponding to the brake pressure,
The vehicle weight due to occupants may be automatically detected and the deceleration may be calculated from the brake pressure and vehicle weight. Furthermore, a table of decelerations corresponding to brake pressures may be set and compared with decelerations actually detected based on the number of rotations of the wheels or an accelerometer.

[Brief explanation of drawings]

FIGS. 1 and 2 are flowcharts of control according to each embodiment of the present invention, and FIG. 3 is a diagram showing a power transmission system of a four-wheel drive vehicle equipped with a center differential device. A... Automatic transmission, 1... Torque converter, 2...
... Main transmission, 3... Sub-transmission, 5... Drive gear,
6... Center differential input shaft, 7... Center differential device, 8... Front export force shaft, 9... Front differential device, 10... Front wheel drive shaft, 11... Rear export Power shaft, 12... Bevel gear, 13... Propeller shaft for rear wheel drive, 14... Center prowl clutch. Figure j

Claims (3)

[Claims] (1) In a four-wheel drive vehicle that transmits engine power to the front and rear wheels via a center differential device, the center differential device is automatically locked by detecting the state of tire lock or a sign of tire lock during braking. An automatic switching device for a four-wheel drive vehicle, characterized in that switching is performed so that front wheels and rear wheels are directly connected via a center differential device. (2) The automatic switching device for a four-wheel drive vehicle according to claim 1, wherein the state of the tire lock or a sign of the tire lock is detected based on the number of rotations of the wheels. (3) The state of the tire lock or the sign of the tire lock is determined by comparing the deceleration of the wheels or the vehicle with the deceleration corresponding to the brake pressure. Automatic switching device for wheel drive vehicles.