JPS6341246A - Four wheel drive control method - Google Patents

Abstract

PURPOSE:To stabilize driving by locking either a 4-wheel drive condition or a center differential immediately when a sudden maneuver is performed on a steering wheel at a high vehicle speed, thereby enhancing limit values of maneuverability and stability of the vehicle. CONSTITUTION:An oil pressure generated by drawing oil up from an oil sump 20 by means of an oil pump 21 is regulated to a line oil pressure by means of a regulator valve 22. The line oil pressure, after passing through an orifice 23, is further regulated by means of a solenoid valve 24 capable of duty control and supplied to a clutch C4. The solenoid valve 24, using an electromagnetic force generated by a solenoid 25, makes a valve body 26 advance to close a port 27. As a result, a specified oil pressure is given to the clutch C4, magnet ism of the solenoid 25 is erased, the valve body 26 is returned by means of a return spring 28, and the port 27 is opened so that the clutch C4 is communi cated with a drain. The solenoid valve 24 is connected to a microcomputer 29 to regulate duty rates and to give oil pressures to the clutch C4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a four-wheel drive control method for changing the transmission state of driving force to a four-wheel drive transfer of a vehicle by controlling frictional engagement means such as a clutch. It is something.

As is well known in the art, four-wheel drive types can be broadly divided into part-time four-wheel drive and full-time four-wheel drive.
Examples are shown in FIGS. 8 and 9. FIG. 8 shows an example of part-time four-wheel drive, in which the output of the engine 1 is transmitted to the transfer gear 13 via the transmission 2. 3 has a first output shaft (for example, a rear export power shaft) 4 connected to the transmission 2 and a second output shaft (for example, a front export power shaft) 5 that is selectively driven, and a clutch C4 By engaging the first output shaft 4 and the drive sprocket 6, the first output shaft 4 and the drive sprocket 6 are integrated, and the rotation thereof is transmitted to the second output shaft 5 by the driven sprocket 7 and the chain 8. Therefore, engaging clutch C4 provides four-wheel drive, and conversely, releasing clutch C4 provides two-wheel drive.

FIG. 9 shows an example of full-time four-wheel drive, in which the transfer 9 connects the first output shaft 4 and the second output shaft 5 to two output elements of the center differential 10, and A driven gear 11 integrated with the input element 10 is meshed with a drive gear 12 attached to the output shaft of the transmission 2, and a differential limiting element is provided between the input element of the center differential 10 and one of the output elements. The configuration includes a clutch C4.

By the way, in the part-time four-wheel drive system shown in Fig. 8,
As mentioned above, it is possible to switch between two-wheel drive and four-wheel drive by engaging and disengaging the clutch C4, but even if the clutch C4 is in an engaged state with slippage, such as a so-called half-clutch, Therefore, by performing slip control on the clutch C4, it is possible to appropriately set the torque distribution ratio between the front wheels and the rear wheels. This situation is the 9th
The same applies to the full-time four-wheel drive system shown in the figure; if clutch C4 is released, the torque distribution ratio to the front and rear wheels will be a preset value, but clutch C4
If the differential operation of the center differential 10 is limited to some extent by slip control, the torque distribution ratio can be set appropriately.

This so-called slip control of the latch C4 is necessary to prevent tight corner braking and to ensure stable driving in response to rough roads and road surface conditions. proposed by. The proposed device is equipped with an electromagnetic clutch that switches between two-wheel drive and four-wheel drive, and is configured so that when turning, the larger the steering angle is, the smaller the clutch current is, increasing the slippage of the clutch. .

Problems to be Solved by the Invention However, when the radius of a corner is small or when entering a corner at high speed, it is desirable to quickly control the clutch that distributes torque between the front and rear wheels. Since such a device performs slip control based only on the magnitude of the steering angle, a delay in the response of the control system may cause the clutch to disengage, for example, while driving around a corner, resulting in a sudden change in the behavior of the vehicle. In any case, since the vehicle speed during steering is not reflected in the torque distribution control, there is a high possibility that running stability will be impaired.

In order to solve this problem, it is possible to set the control system to have the fastest response in advance, but if the response of the control system is extremely fast, it may cause problems such as when driving around a gentle curve during normal driving. Even when the steering wheel is operated slowly, as in the example shown in FIG.

In other words, since the torque transmission amount is changed by changing the amount of slip, for example, in the case of FIG. 8, the torque of the front export force shaft 5 changes suddenly, causing problems such as occurrence of shock. .

This invention has been made under the above circumstances, and provides a four-wheel drive control method that can ensure running stability by optimizing torque distribution to front and rear wheels according to vehicle speed during steering. It is intended for that purpose.

Means for Solving the Problems In order to achieve the above object, the present invention controls a friction engagement means that acts to reduce the difference in torque distribution ratio between the front and rear wheels as the engagement force increases. In order to do this, the steering angular velocity when changing the steering angle is compared with a steering angular velocity limit value corresponding to the vehicle speed at that time, and if the comparison result exceeds a predetermined set value, the friction coefficient is changed. This method is characterized by increasing the engagement force of the coupling means.

In addition, in the method of the present invention, after increasing the engagement force of the friction engagement means as described above, it is preferable that the control is prohibited within a predetermined time, or that the control is prohibited depending on the vehicle speed. It is preferable to continue the process until the speed reaches a predetermined setting speed or less.

Function: In the method of the present invention, by adjusting the engagement force of the friction engagement means, the slip amount is changed, and the torque distribution ratio between the front and rear wheels is adjusted. When the steering angle is changed while the vehicle is running, the amount of change in the steering angle per time, that is, the steering angular velocity, is calculated and determined, while the steering angular velocity limit value is determined based on the vehicle speed at that time, and these two values are compared. If the comparison result exceeds a predetermined set value, the engagement force of the frictional engagement means is increased to maintain four-wheel drive (in the case of part-time four-wheel drive) or the center differential differential limited state (in the case of full-time four-wheel drive). (in case of drive).

For example, if the vehicle speed is high, the steering angular velocity limit value becomes a low value, so even if the steering is performed relatively slowly while driving at high speed, the steering angular velocity becomes relatively large, and the engagement force of the frictional engagement means increases, causing the The torque distribution ratio to the wheels becomes nearly equal, and as a result, there are no sudden changes in behavior, resulting in high driving stability.

Embodiments Next, embodiments of the present invention will be described with reference to the accompanying drawings.

1 and 2 are schematic diagrams showing an example of a system in which the clutch C4 is subjected to slip control, in which the oil pressure generated by pumping up the oil pump 21 from the oil reservoir 20 is transferred to the line oil pressure by the regulator valve 22. After the line oil pressure passes through an orifice 23, the pressure is further adjusted by a duty-controllable solenoid valve 25 and then supplied to the clutch C4. Here, the solenoid valve 24 moves the valve body 26 forward and closes the port 27 by the electromagnetic force generated by the solenoid 25. As a result, a predetermined oil pressure is applied to the clutch C4, and the solenoid 25 is demagnetized to close the valve body 26. Return spring 28
The clutch C4 is returned to its original state to open the port 27, thereby communicating the clutch C4 with the drain and discharging the pressure. Roughly speaking, the solenoid valve 24 is connected to a microcomputer 29 to adjust the duty rate and apply hydraulic pressure to the clutch C4 according to the duty rate. The microcomputer 29 contains various signals such as the front wheel rotation speed, rear wheel rotation speed, throttle opening, C4 clutch oil pressure, brake status, and oil temperature as data for controlling the solenoid valve 24, as well as the pulse gear installed on the steering shaft. A steering angle signal is inputted from a steering angle sensor 30 such as an electromagnetic pickup, a foot sensor, or a sensor whose contacts are composed of several bits of gray code.

As shown in FIG. 2, the clutch C4 engages or disengages the disk 33 and the plate 34 by means of a hydraulic servo 32 mainly composed of a piston 31, or engages the disc 33 and the plate 34 in a slip state, thereby causing the input member 35 to engage or disengage. From the output member 36
It is configured to transmit torque to and cut off the torque. That is, the clutch C4 can change the amount of slip and the resulting torque transmission amount depending on the oil pressure supplied to the hydraulic servo 32, and in order to change the oil pressure supplied, the clutch control means 37 and the steering angular velocity detection means 38 are used.
and vehicle speed detection means 39, steering angular velocity comparison means 40,
Clutch forced engagement means 41 is provided. These means 37. ... 41 is constituted by the solenoid valve 24 and a part of the microcomputer 29, and the clutch control means 37 controls the solenoid valve 24 on/off based on an input signal, or controls the duty rate. The hydraulic pressure supplied to the hydraulic servo 32 is adjusted by controlling the hydraulic pressure. Also, the steering angular velocity detection means 38
is configured to determine the amount of change in the steering angle per time, that is, the steering angular velocity, based on the output signal of the steering angle sensor 30 and output a signal to the steering angular velocity comparing means 40. The system detects the rotational speed of a rotating member (not shown) such as a shaft or a rear export force shaft as a vehicle speed, and is configured to input the vehicle speed as an electric signal to the steering angular velocity comparison means 40.

Further, the steering angular velocity comparison means 40 calculates a steering angular velocity limit value corresponding to the vehicle speed based on the input signal from the vehicle speed detection means 39, and also receives the input signal from the steering angular velocity detection means 38 and the steering angular velocity limit value. The steering angular velocity is compared with the steering angular velocity, and when the comparison result exceeds a predetermined 8th constant value, (i) is output to the clutch forced engagement means 41.

Then, the clutch forced engagement means 41 outputs a signal to the clutch control means 37 based on the input signal from the steering angular velocity comparison means 40, and as a result, hydraulic pressure is sent to the hydraulic lever 32 to engage the clutch C4, etc. The engagement force is increased.

Next, to explain the method of the present invention targeted at the above-mentioned system, FIG. 3 shows its control flowchart.
), and if F=0, the microcomputer 29
reads various signals (step 101), and then calculates the steering angular velocity limit value ωC (step 102). Here, the steering angular velocity limit (direction ωC is determined by the vehicle speed V, ωc
It can be expressed as = f(V), and to give an example, the fourth
As shown in the figure, the steering angular velocity limit value ωC and the vehicle speed V are in an inversely proportional relationship. The steering angular velocity comparison means 40 includes:
In addition to calculating the above-mentioned steering angular velocity limit value ωC, the actual steering angular velocity ω1 inputted from the steering angular velocity detecting means 38 and the steering angular velocity limit value ωC are compared by taking the ratio thereof (step 103). Then, the comparison result ωH/ωC is determined by a predetermined setting value C (≦1.0>
If it is below, the solenoid valve 24 is controlled based on various signals (step 104). On the other hand, when it is determined that the steering wheel operation is sudden relative to the traveling speed, that is, when it is determined that ω[1/ωc>C, the clutch forcible engagement means 41 outputs a signal. Output and solenoid valve 2
The duty rate of 4 is increased (step 105). The relationship between the duty rate and the clutch oil pressure is as shown in FIG. 5. As the duty rate increases, the clutch oil pressure increases and the engagement force of the clutch C4 becomes stronger. In other words, if you have part-time four-wheel drive, you will have to switch from two-wheel drive to four-wheel drive, and if you have full-time four-wheel drive, the differential of the center differential will be limited, and in either case, the torque to the front and rear wheels will be limited. The difference in distribution rates is controlled to decrease. Then, at the same time as turning on the solenoid valve 24, the timer T starts counting (step 106), and the flag F is set to 1'' (step 107).
).

On the other hand, if it is determined in step 100 that the flag F=1 because a sudden steering wheel operation was performed just before, the scanning process reaches step 108, and the count value of timer T and the predetermined set time To Compare with. The comparison result is TNT. In this case, the vehicle speed V is compared with a predetermined set speed vo (step 110). If the actual vehicle speed V is faster than the set speed vo, that is, T<
T. and when v>Vo, control of the electromagnetic valve 24 is prohibited and the ON state that was switched immediately before is maintained.

On the other hand, if T≧To or ■≦vo,
Reset flag F and timer T (step 1
11).

Here, we will explain how to calculate the steering angular velocity.
In the steering angular velocity detection means 38, as shown in FIG.
When the trigger detects the signal emitted by the steering angle sensor 30 (step 120), and the trigger is turned on, that is, when the steering wheel is rotated to a predetermined angle, the timer value T1 is read (step 121). This timer value T1
is the value from the time when the turning steering wheel is steered, and therefore the steering angular velocity ω is determined by ω, (=1/T1 (step 122). Then, the timer value T1 is cleared in step 123), and the following Prepare for calculation.

In other words, according to the above method, as shown in FIG. 7, if the steering angular velocity ω is lower than the limit value ωC determined according to the vehicle speed, the steering angular velocity ω is slowly adjusted to reach the target slip amount. However, when the steering angular velocity ωH is high, the engagement force of the clutch C4 is immediately increased to control the amount of slip to almost zero, and therefore the drive state of the front and rear wheels will be in accordance with the driving state. Stability can be ensured.

Effect of Excusation As is clear from the above explanation, according to the control method of the present invention, if the vehicle speed is high and the steering wheel is operated suddenly, the vehicle will be in a four-wheel drive state or a state in which the center differential is locked. As a result, the limit value of the vehicle's steering stability becomes higher, and as a result, more stable driving can be ensured.

Furthermore, in this invention, the above-mentioned control of the friction engaging means based on sudden steering wheel operation is continued for a predetermined time or until the vehicle speed slows down to a certain extent, so that changes in the torque distribution between the front and rear wheels while driving on a curve and the accompanying It is possible to prevent sudden changes in the behavior of the vehicle.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of the system targeted by this invention, Fig. 2 is a schematic diagram showing the main parts of the system in different clothing formats, and Fig. 3 is the same as Figs. 1 and 2. A control flowchart showing an example of the method of the invention for the system shown in FIG. 4 shows the relationship between the vehicle speed V and the steering angular velocity limit value ωC. Fig. 6 is a flowchart explaining a method for controlling the steering angular velocity, Fig. 7 is a diagram showing changes in slip suspension over time when the steering angular velocity is high and slow, and Fig. 8 The figure is a schematic diagram of a part-time four-wheel drive system, and FIG. 9 is a schematic diagram of a full-time four-wheel drive system. 24... Solenoid valve, 29... Microcomputer, 30... Steering angle sensor, 32... Hydraulic servo,
37... Clutch control means, 38... Steering angular velocity detection means, 39... Vehicle speed detection means, 40... Steering angular velocity comparison means, 41... Clutch forced engagement means,
C4...Clutch. Applicant Toyota Motor Corporation Agent Patent Attorney Yutaka 1) Takehisa (and 1 other person) Figure 1 Figure 3 Figure 4 Factor Figure 5 Duty rate c%) Figure 6

Claims (3)

[Claims] (1) In controlling the friction engagement means that acts to reduce the difference in torque distribution ratio between the front and rear wheels as the engagement force increases, the steering angular velocity when the steering angle is changed and the vehicle speed at that time are determined. A four-wheel drive control method, comprising: comparing a steering angular velocity limit value corresponding to a steering angular velocity limit value, and increasing the engagement force of the frictional engagement means when the comparison result exceeds a predetermined set value. (2) Prohibiting control of the frictional engagement means within a predetermined set time after increasing the engagement force of the frictional engagement means in response to the comparison result exceeding a predetermined set value; A four-wheel drive control method according to claim 1, characterized in that: (3) After the engagement force of the frictional engagement means is increased in response to the comparison result exceeding a predetermined set value, the frictional engagement means remains active until the vehicle speed becomes equal to or less than the predetermined set speed. The four-wheel drive control method according to claim 1, characterized in that the control is prohibited.