JPS6274711A - Control mechanism for four-wheel-drive vehicle - Google Patents

Abstract

PURPOSE:To prevent occurrence of a tight corner braking phenomenon, by supplying the pressure of accumulator control which exhibits such a characteristic that it is low in a range where the opening degree of a throttle valve is small, into a center clutch, as a clutch engaging pressure clutch. CONSTITUTION:When a throttle valve 16 is controlled in such a throttle valve opening range that a center clutch 2 slips, the throttle pressure is adjusted to a throttle modulator pressure by a throttle modulator valve 18. Accordingly, this pressure is fed into an accumulator control valve 15 which therefore controls a line pressure fed thereinto, and delivers an accumulator control pressure which is lower than the line pressure into an oil passage 1K. Further, this control pressure is controlled by a fourth solenoid valve in a center clutch control valve 1, and thereafter, is fed into the center clutch 2. With this arrangement, it is possible to control the center circuit 2, simply and smoothly, and thereby it is possible to prevent occurrence of tight corner phenomena.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a control mechanism for a four-wheel drive vehicle, and particularly to a four-wheel drive vehicle that switches between two-wheel drive and four-wheel drive with a horizontally mounted engine. Regarding control i structure.

(Prior Art) In a conventional four-wheel drive vehicle, when turning while turning the steering wheel in a four-wheel drive state, a rotation difference occurs between the front and rear wheels due to a difference in turning locus. In particular, when the front wheels and rear wheels are connected in a one-to-one correspondence or when the vehicle turns with a small turning radius, the difference in rotation becomes significant. If such a difference in rotation occurs between the front and rear wheels, a tight corner braking phenomenon will occur, causing problems such as tire wear, deterioration of fuel efficiency, and poor controllability, so it is necessary to absorb this difference in rotation. (
Ru. For this reason, various proposals have been made in the past.

First, in order to absorb the difference in rotation, a transmission mechanism was developed in which a central differential device called a center differential was installed between the front and rear wheels.
This is proposed in Japanese Patent No. 5-83617. However, this mechanism requires a differential lock mechanism, resulting in a very complex structure.

Next, in the case of four-wheel drive, a transmission mechanism in which the front and rear wheels are directly connected mechanically by a center clutch (transfer clutch) is proposed in Japanese Patent Laid-Open No. 56-43031. In this mechanism, when turning with four-wheel drive, the front wheels have a larger turning radius than the rear wheels, so the front wheels try to rotate faster than the rear wheels, creating twisting torque between the front and rear drive shafts. This is similar to a braking action, and causes the so-called tight corner braking phenomenon. Therefore, in a 4-wheel drive vehicle in which the front and rear wheels are directly connected using a transfer clutch, a transmission mechanism is proposed in JP-A-57-15019 that disconnects the transfer clutch based on the steering wheel rotation angle or the rotation difference between the front and rear wheels. . However, with this mechanism, when the transfer clutch is disengaged, the rear wheels lose all driving force, which is the same as switching to two-wheel drive. Therefore, when turning on slippery surfaces such as rough roads or muddy roads, the driving performance inherent to a four-wheel drive vehicle, which doubles the tire grip force, cannot be demonstrated.

Next, a microcomputer is installed to create a transmission mechanism that automatically switches to four wheels when the actual driving condition deviates from this curve based on a running resistance curve set based on the vehicle specifications of a four-wheel drive vehicle. This is proposed in Japanese Patent Application Laid-Open No. 58-126224. This mechanism immediately switches to four-wheel drive if the actual driving condition deviates significantly from the driving resistance curve.
If there is a small deviation, the degree of deviation is determined after a delay to prevent hunting when switching to 4-wheel drive.
Lack of responsiveness. Furthermore, the running resistance curve takes into account the actual running conditions and estimates the switching range for switching to four-wheel drive. For this reason, the switching width makes it difficult to realize switching to four-wheel drive that is suitable for actual driving conditions.

Finally, as a recent example, a tight corner braking phenomenon is determined, a signal based on the determination is used to drive a solenoid valve in pulses, and the solenoid valve supplies and drains oil to the transfer clutch, causing the clutch to engage, resulting in a half-clutch state. A transmission mechanism that creates this is proposed in Japanese Patent Laid-Open No. 60-33127. ,: This is because the solenoid valve is driven in pulses to supply and drain oil to the clutch, which is repeated in short cycles, so the clutch is engaged and disengaged depending on the presence or absence of pulses. As a result, there is no connection state of the necessary degree in the middle of connection and disconnection, and it is not possible to set the continuous connection state or continuous disconnection state that is required depending on the situation.
In addition to making it difficult to transmit power smoothly, it is also necessary to provide a judgment circuit and a clutch and hydraulic mechanism that can operate in response to the output pulses of the judgment circuit, which inevitably increases the cost.

(Problems to be Solved by the Invention) The various proposals described above require complicated configurations, and furthermore, there is a problem that the avoidance operation of the tight corner braking phenomenon in four-wheel drive does not lead to smooth driving. Ta.

Therefore, in order to solve the above problems, the present invention has been developed to automatically and smoothly perform tight corner braking while maintaining four-wheel drive by simply adding a simple configuration to the conventional transmission mechanism. It is an object of the present invention to provide a control mechanism for a four-wheel drive vehicle that avoids this.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a control mechanism for a four-wheel drive vehicle that switches from two wheels to four wheels using a center clutch. By supplying an accumulator control pressure exhibiting low pressure characteristics to the center clutch as engagement pressure, the clutch is caused to slip, thereby preventing the occurrence of tight corner braking during four-wheel drive. be.

(Operations and Effects of the Invention) According to the present invention, as shown in FIG. Then, as shown in FIG. 2, it is applied to the piston 33 of the center clutch 2 via the oil passage 34 and the oil passage 38. The center clutch 2 connects the differential case 32 and the rear wheel side output member 35 from a state where slip occurs to a state where no slip occurs as the accumulator pressure changes from low to high throttle opening.

According to the present invention, the effects of the invention described below can be achieved.

(1) Effectively use the low accumulator control pressure in the region where the opening degree of the throttle valve 16 is low. 2
can be used for control.

(2) Since the center clutch 2 can be smoothly and continuously controlled in any control state with a simple configuration,
The occurrence of tight corner braking phenomenon can be effectively prevented.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

Fig. 1 is a circuit diagram of a hydraulic control mechanism of an automatic transmission according to the present invention, Fig. 2 is a sectional view of an automatic transmission according to the present invention, Fig. 3 is a hydraulic characteristic diagram, and Fig. 4 is a torque capacity characteristic diagram. It is.

First, an overview of the configuration of the present invention will be explained.

4 to prevent tight corner braking phenomenon
It is necessary to slip the clutch of the wheel drive transmission, and for this purpose a certain hydraulic pressure is required in the clutch. Therefore, as shown in Fig. 3, we focused on the fact that the accumulator control pressure in the region T ball where the throttle opening is low is lower than the line pressure, and set this low accumulator control pressure as the center clutch engagement pressure. As shown in FIG. 4, an experimental result was obtained in which the center clutch torque capacity is smaller than the torque transmitted to the center clutch (torque from the engine input to the center clutch) in the throttle opening range Ob. This region a'c' in which the center clutch torque capacity is small means that the center clutch slips, so to speak, and it has been found that this slip is effective in preventing the occurrence of tight corner braking.

Therefore, the present invention adjusts the line pressure using hydraulic pressure via the throttle modulator valve 18 and the accumulator control valve 15 based on the hydraulic output according to the opening degree of the throttle valve 16 in the center clutch type four-wheel drive transfer mechanism 50. The pressurized accumulator valve controls the center clutch 2 for coupling two wheels to four wheels.

Next, one embodiment of the present invention will be described in detail using FIGS. 1 to 4.

First, the hydraulic control mechanism mainly includes a center clutch control valve 1, a center clutch 2, a fourth solenoid valve 3,
Accumulator 11.12.13, accumulator control valve 15, throttle valve 16, torque converter 17, throttle modulator valve 18, secondary regulator valve 80, exhaust pressure relief valve 81, kickdown valve 82, cooler bypass valve 83, mouth, cup-up Control valve 84, cutback valve 85, third solenoid valve 86
, lock-up signal valve 87, oil pump 88, primary regulator valve 89, manual valve 90.2-
3 shift valve 91, -2 shift valve 92.3-4 shift valve 93, first solenoid valve 94, low coast modulator valve 95.2nd coast modulator valve 96, second solenoid valve 97, from accumulator 98.99 It is configured.

The details of this hydraulic control mechanism are described in the previously filed Japanese Patent Application No. 59-267784.

■The automatic transmission includes a hydraulic torque converter 17,
It is composed of a transmission 100, a four-wheel drive transfer mechanism, and a hydraulic control mechanism shown in FIG.

The transmission 100 is a front planetary gear U
D. , Rear plane clear gear UD2, two multi-plate clutches C5 and C2 operated by hydraulic servo, 1
One handbrake B1. Two multi-disc brakes B2 and B3. One one-way latch F, one one-way brake F2, underdrive transmission a200 with three forward speeds and one reverse speed, planetary gear LIDff, and hydraulic servo. The second underdrive transmission includes one multi-disc latch C3 and one multi-disc brake F3. The four-wheel drive transfer mechanism 50 is
Front differential device 60 and center clutch (C/C)
2 and a rear wheel propulsion mechanism 70. The center clutch 2 is a multi-plate wet clutch, and this clutch is connected to the piston 33 via an oil passage 34 provided in a transfer case 37 and an oil passage 3B provided in a differential case 32.
The differential gear case 32 screwed to the large drive gear 31 and the rear wheel side output member 35 are
connect and disconnect.

The center clutch control valve 1 uses the accumulator control pressure from the accumulator control valve 15 as a human power, and applies the accumulator control pressure controlled by the fourth solenoid valve 3 to the center clutch 2. The accumulator control pressure is determined by converting the throttle pressure corresponding to the opening degree of the throttle valve 16 into the throttle modulator pressure via the throttle modulator valve 1B, and inputting this as a control input to the accumulator control valve 19.
The line pressure input to the IK is regulated and output to the oil passage IK.

Next, the effect of the control mechanism of the automatic transmission of this embodiment on the opening degree of the throttle valve will be explained.

When the throttle valve 16 is controlled within the throttle opening range 7T where the center clutch slips, the throttle pressure is adjusted to the throttle modulator pressure by the throttle modulator valve 18, and the throttle modulator pressure is adjusted by the accumulator control valve 15. The line pressure input to the accumulator control valve 15 is regulated and output to the oil passage IK as an accumulator control pressure lower than the line pressure. This low accumulator control pressure is controlled by the fourth solenoid valve 3 in the center clutch control valve l, and then the operation of the piston 33 connects and disconnects the center clutch 2 via the oil passages 34 and 38 of the center clutch 2. , transmits the rotation of the large drive gear 31 to the differential case 32, the center clutch 2, and the rear wheel side output member 35, and transmits the rotation of the large drive gear 31 to the rear wheel propulsion mechanism 7.
Drive 0.

As is clear from the above description, according to the present invention, (1) the operation to eliminate the tight corner braking phenomenon can lead to smooth running.

(2) The control means for the center clutch 2 can be easily configured by simply connecting the center clutch control valve 1 to the accumulator control hydraulic system.

(3) The center clutch control valve 1 is hydraulically controlled and can be easily controlled by the solenoid valve 3 as in the conventional case.

In this way, the configuration can be simplified, resulting in lower costs, and since the center clutch can be placed between the front differential device for the front wheels and the rear wheel propulsion mechanism for the rear wheels, the length of the transmission in the vehicle width direction can be reduced. Together with the shortening effect, the vehicle width can be effectively shortened.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a hydraulic control mechanism of an automatic transmission according to the present invention, Fig. 2 is a sectional view of an automatic transmission according to the present invention, Fig. 3 is a hydraulic characteristic diagram, and Fig. 4 is a torque capacity characteristic diagram. It is. l...Center clutch control valve, 2...
Center clutch, 3... Fourth solenoid valve, 15...
-Accumulator control valve, 16... Throttle valve, 34, 38... Oil passage.

Claims (2)

[Claims] (1) In a control mechanism for a four-wheel drive vehicle that uses a center clutch to switch between two-wheel drive and four-wheel drive, the accumulator control pressure, which exhibits low pressure characteristics in the region of low throttle opening, is used as the engagement pressure for the center clutch. A control mechanism for a four-wheel drive vehicle, characterized in that the control mechanism is configured to supply a four-wheel drive vehicle. (2) The control mechanism for a four-wheel drive vehicle according to claim 1, wherein the center clutch is disposed between a front differential device and a rear wheel propulsion mechanism.