JPH0231935A - Control method for front and rear wheel differential control clutch - Google Patents

Abstract

PURPOSE:To improve the durability of a differential control clutch by judging the difference of the temperature of two parts at least, and forcedly reducing the slide of the clutch when the temperature of the clutch for controlling the differential of front and rear wheels rises, preceding to other part. CONSTITUTION:The temperature of two parts at least, the temperature T of a differential control clutch including a clutch for switchin two wheel drive four wheel drive or of the part substituting for it and the temperature T of the preset reference part, are detected. The compared value of the temperature (the difference of the temperature or the ratio of the temperature) of the two pats is compared with the preset value T1, and when the obtained compared value is more than the preset value T1, the clutch is controlled so as to reduce the slide of a friction plate of the clutch.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method of controlling a clutch that controls differential rotation between front and rear wheels of a four-wheel drive vehicle.

Conventional technology Four-wheel drive that transmits driving force to both front and rear wheels! 11
81 is equipped with a center differential and a friction clutch that limits its differential operation, and a friction clutch that transmits power from the rear wheel drive shaft to the front wheel drive shaft, or vice versa, from the front wheel drive shaft to the rear wheel drive. A method is known in which this is done through The former example is schematically shown in Fig. 2. In Fig. 2, a differential case 2 of a center differential (hereinafter referred to as center differential) 1 changes gears via a driven gear 3 and a drive gear 4 that meshes with it. One side gear 6 in the center differential 1 is connected to a ring gear mounting case 7;
A ring gear 8 is attached to the rear wheel drive shaft 9, and a hypoid gear 10 connected to a rear wheel drive shaft 9 meshes with the ring gear 8. The other side gear 11 in the center differential 1 is a front differential (hereinafter referred to as front differential).
It is connected to a differential case 13 at 12, which distributes power to left and right front wheel drive shafts 14. A differential control clutch 15 that limits the differential operation of the center differential 1 is located at a position that limits the relative rotation between the differential case 2 of the center differential 1 and the other side gear 11, that is, the ring gear mounting case 16 to which the driven gear 3 is attached and the front differential 12. A hydraulic servo 17 for engaging and disengaging the differential control clutch 15 is also provided.

Then, the hydraulic pressure generated by the hydraulic pump 18 is controlled by the hydraulic control system@
After the pressure is regulated to a predetermined level by 19, the hydraulic servo 17
By supplying the torque to the differential control clutch 15, the transmission torque capacity of the differential control clutch 15, that is, the differential limiting force is adjusted.

An example of the latter is shown in FIG. 3. In FIG. 3, the rear wheel drive shaft 20 is integrated with the input shaft 22 which is the output shaft of the transmission 21; On the other hand, a friction clutch 23 is provided concentrically. A drum 24 of the friction clutch 23 is connected to the rear wheel drive shaft 20, and a drive gear 26 is attached to the clutch hub 25, and the drive gear 26 meshes with a counter driven gear 28 attached to a counter shaft 27. The drive gear 29 attached to the shaft 27 is the front wheel drive shaft 30.
It meshes with the driven gear 31 attached to the. The hydraulic pressure supplied to the hydraulic servo 32 that engages the friction clutch 23 is controlled by a hydraulic control unit 33, thereby adjusting the torque transmitted to the rear wheels and the front wheels.

In the four-wheel drive systems with each of the above configurations, each clutch directly transmits driving force to the front wheel drive shaft or the rear wheel drive shaft, so the torque is distributed between the front wheels and the rear wheels according to the transmitted torque capacity. The rate will change. Therefore, in recent years, in order to improve driving performance such as braking performance, driving stability, and acceleration, differential control force has been adjusted according to driving conditions. Further, in the configuration shown in FIG. 3, by completely engaging the clutch, a four-wheel drive state with no differential between the front and rear wheels can be achieved, and by completely releasing the clutch, a two-wheel drive state can be achieved.

When controlling the torque distribution ratio between the front and rear wheels appropriately depending on the driving condition using each of the clutches described above, - If a large difference in rotational torque between the front and rear wheels occurs due to wheel slippage or continuous cornering, the clutches will In this case, the durability of the clutch is greatly affected by the degree of slippage, that is, the magnitude of the frictional force and the relative rotational speed of the friction plates, and the length of the duration of the slippage.

Furthermore, even in a friction clutch that switches between two-wheel drive and four-wheel drive, transient slippage occurs during engagement and disengagement, and depending on the degree of slippage, it has a significant effect on durability.

The durability of the clutch decreases as the above-mentioned values such as the duration of slipping increase, and this can be shown in a diagram as shown in FIG. 4. That is, in FIG. 4, the left side of each curve is the permissible region, and the longer the differential duration, the larger the differential rotation speed, and the larger the engagement force, the narrower the permissible region.

Therefore, if the clutch slips, in order to maintain its durability, the clutch is released to prevent slippage when the differential rotation speed of the front and rear wheels and the duration of the differential rotation exceed a predetermined set value. A control method that prevents this from occurring is effective, and it is conceivable to carry out such control based on the diagram in FIG.

Furthermore, conventionally, the clutch shown in FIG.
``1j'' is a method that detects the temperature and, when the detected temperature exceeds a set value, releases or fully engages the clutch to eliminate the slippage of the friction plate, as disclosed in Japanese Patent Laid-Open No. 6.
1-178232.

Furthermore, conventionally, when the four-wheel drive control clutch was controlled by hydraulic pressure, the oil temperature affected the control characteristics, so if the oil temperature exceeded a set value, quantitative control of the four-wheel drive control clutch was prohibited. However, a method for preventing control that differs from the initial control characteristics and a decrease in durability is disclosed in Japanese Patent Application Laid-Open No. 63-3.
It is described in Publication No. 1826.

Problem to be Solved by the Invention However, when controlling the clutch release based on the above-mentioned FIG. 4, as is clear from FIG. This is not practical. Therefore, if control is performed using a plurality of appropriate representative values, a problem arises in that reliability decreases.

In addition, the limit PJ of the allowable slipping range shown in Figure 4 changes due to changes in oil pressure, usage environment, etc., but the set value that serves as the basis for judgment must be a fixed value, so it is reliable in this respect as well. There was a risk that it would lack sex.

Furthermore, in the method described in JP-A-61-178232, the temperature of the clutch itself is compared with a set value, so even if excessive slippage occurs from time to time, the accompanying temperature rise will be If the set value is not reached, control to reduce slippage, that is, control to release or fully engage the clutch, will not be executed, and as a result, excessive slippage will continue.In other words, the delay in control will increase. There was a risk that this would occur.

Furthermore, the method described in Japanese Patent Application Laid-Open No. 63-31826 is a method for preventing a decrease in clutch durability caused by the control characteristics being different from the initial characteristics due to an increase in oil temperature. Even if some slippage occurs and the oil temperature rises, there is a risk that excessive clutch slippage will be allowed until the oil temperature reaches a level that causes fluctuations in control characteristics, and there is room for improvement in this regard. .

This invention was made against the background of the above-mentioned circumstances, and aims to provide a method capable of quickly responding to a sudden temperature rise in a differential control clutch and improving its durability. be.

Means for Solving the Problems The present invention is a method for achieving the above object by comparing the difference in temperature at at least three predetermined locations with a set value.More specifically, the method of the present invention comprises: In controlling the front and rear wheel differential control clutch that allows differential movement between the front and rear wheels and limits the differential movement between the front and rear wheels, the temperature of the front and rear wheel differential control clutch or the temperature of a predetermined location substituted for that temperature, This method is characterized by controlling to reduce the slippage between the friction plates when the comparison value of the temperature of at least three locations with the temperature of a predetermined reference location exceeds a set value.

How this invention works: two-wheel drive! Humidity is detected in at least three locations: the differential control clutch, including the J0 four-wheel drive switching clutch, or a location substituted for it, and a predetermined reference location, and a comparison value (temperature difference or The temperature ratio) is compared with a set value, and if the comparison value obtained is greater than or equal to the set value, the clutch is controlled to reduce the slippage of the friction plates of the clutch. Specifically, the clutch is released or engaged so that no slippage occurs. Therefore, if the clutch temporarily slips excessively when the oil temperature or ambient temperature is low, the above comparison value will increase, and the clutch will be disengaged or fully engaged, causing light heat generation. This prevents excessive slippage, resulting in improved durability.

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

The method of this invention is based on the center differential 1 shown in FIG.
The present invention can be applied to both the clutch 15 that performs differential restriction and the clutch 23 that transmits the driving force from the rear drive shaft 20 to the front drive shaft 30 shown in FIG. The flowchart shown in Figure 1 shows a method for applying these differential control clutches to a four-wheel drive system that is configured to automatically control as differential rotation occurs between the front and rear wheels. In step 1, it is determined whether the select switch is set to AUTOJ. By setting this select switch to AUTOJ, the differential limiting device including the differential limiting clutch is operated based on vehicle conditions such as the differential rotation speed of the front and rear wheels, vehicle speed, and throttle opening. ! Contrary to this, by executing the i-slip restriction control and setting IFF J, the non-operating state, specifically the differential-slip restriction clutch is released.Therefore, the judgment result in step 1 is "No". In this case, control is performed to make the differential limiting device "free", that is, to cancel the differential limiting (step 2). Then, the control flag FA is set to 0'' (step 3) and the process returns.

On the other hand, if the determination result in step 1 is "yes", that is, if the select switch is set to "80TOJ", it is determined whether the control flag F^ is 1n (step 4).Control flag FA is set to "0" in step 3, and is set to "0" except when controlling to reduce the slippage of the differential limiting clutch as described later, and is further set to "O" by initialization. Therefore, if step 4 is reached first, the determination result is "no", and in this case, the process proceeds to step 5 to determine the temperature difference. The temperature difference that is subject to this judgment is the temperature of the differential limiting clutch or the temperature of the location substituted for the differential limiting clutch (hereinafter referred to as clutch temperature) and the temperature of a predetermined reference location (hereinafter referred to as tentatively referred to as clutch temperature). (referred to as reference temperature) is the difference between TB (TA - TB). Specifically, the clutch temperature TA is the temperature of the drum, friction plate, clutch hub, etc. of the differential limiting clutch, the temperature of the lubricating oil in the differential limiting clutch, the ambient temperature of the clutch, and the like. In addition, the reference temperature TB is essentially the average temperature of the entire differential device and transmission including the differential limiting clutch, or the temperature of a location that can be substituted for them, and specifically, the temperature of the oil pan drain in the automatic transmission. The average temperature can be the oil temperature, the oil temperature at the outlet of the oil cooler, the oil temperature near the strainer in the oil pan, etc. If the above-mentioned temperature difference is equal to or higher than the predetermined set value 611, that is, if the judgment result in step 5 is "yes", control is immediately executed to reduce the slippage of the differential l1% J-limit clutch (step 7 ).

Specifically, the control content of step 7 is to disengage the differential limiting clutch or reduce the engagement force to lower the frictional force, or to completely engage the differential limiting clutch to reduce the friction plate relative to each other. This is a control that does not cause any slippage.

On the other hand, if the above temperature difference is lower than the set value ΔT1, that is, if the determination result in step 5 is "no", it is determined whether the clutch temperature T^ is equal to or higher than the clutch upper limit temperature T2 (step 6). This is because when the overall temperature is high, even if the temperature difference mentioned above is low, the differential limiting clutch may reach high temperatures that greatly affect its durability. If the judgment result in step 7 is "no", the process returns; on the other hand, if it is "yes", that is, if the clutch temperature T^ is equal to or higher than the clutch upper limit temperature T2,
Proceeding to step 7, control is executed to reduce slippage of the differential limiting clutch. When the control for forcibly reducing the slippage of the differential limiting clutch is performed in this way, the control flag l''A is set to 1' (step 8), and the process then returns.

By the way, the judgment result in step 4 will be "yes" if the differential limiting clutch slip reduction 11tlJ control has been executed as described above and the select switch is continuously set to rAUTOJ, in which case step 9
Then the clutch temperature TA becomes the second clutch upper limit temperature T.
3 (<T2) or not (step 9). This step 9 is for determining whether the conditions for canceling the forced slip reduction control in step 7 described above are satisfied, and the result of this determination is U-no.
If so, return and continue the control executed in step 7. Further, if the clutch temperature TA becomes lower than the second clutch upper limit temperature T3 and the determination result in step 9 becomes "yes", the process proceeds to step 10. The reason why the second clutch upper limit temperature T3, which is the criterion in step 9, is made different from the first clutch upper limit temperature T2 described above is to prevent hunting.

Step 10 also determines whether the conditions for canceling the control in step 7 described above are satisfied.
A determination is made as to whether the temperature difference between the clutch temperature TA and the reference temperature TB is lower than a second set value ΔT4 (ΔT). Note that the reason why the second set value ΔT4 is different from the first set value ΔT1 is to prevent hunting. If the result of this judgment is "no",
Returns and continues control to forcibly reduce the slippage of the differential vJ limiting clutch, and if the judgment result is "yes", permission control for applying differential limiting force according to vehicle conditions is performed.
After performing (step 11), the control flag FA is
O'' (step 12). Therefore, the forced slip reduction control of the differential limiting clutch is released.Then, the scanning process returns.

Note that if the select switch is set to [IFF J after performing control to forcibly reduce the slippage of the differential limiting clutch in step 7, the process proceeds to step 2 and sets the differential limiting device to the non-operating state, that is, the differential Release the limit clutch.

The above detailed description of the present invention is directed to a differential limiting clutch, but this invention transmits torque between a front wheel drive shaft and a rear wheel drive shaft to set a four-wheel drive state. However, it goes without saying that the present invention can also be applied to the case of controlling a clutch that differentially operates the front and rear wheels by allowing slippage. Further, the number of temperature measurement points is not limited to three, but may be three or more.

Further, in the present invention, when comparing the obtained temperatures at at least three locations, a ratio may be taken and compared with a set value instead of taking the difference.

Furthermore, the present invention can be applied to the case of eliminating transient slippage when a friction clutch is engaged or released for switching between two-wheel drive and four-wheel drive.

Effects of the Invention As is clear from the above explanation, according to the method of the present invention, by detecting the temperature at at least three locations and determining the temperature difference, the clutch that controls the differential between the front and rear wheels is connected to the other location. If the temperature rises in advance of this, the slippage of the clutch will be forcibly eliminated or reduced, so if excessive friction occurs in the clutch, the temperature will not necessarily reach a high enough temperature to cause damage to the clutch. It also eliminates slippage, which is a cause of heat generation, and therefore improves the durability of differential control clutches by quickly dealing with excessive friction and avoiding wear.

[Brief explanation of the drawing]

Fig. 1 is a flowchart for explaining an example of the method of the present invention, Fig. 2 is a skeleton diagram showing an example of differential limiting 8@, and Fig. 3 is an example of another device that can perform differential limiting. FIG. 4 is a diagram showing the permissible slippage range of the differential limiting clutch in relation to the differential duration time and the differential rotation speed using the engagement force as a parameter. 9.20...Rear wheel drive shaft, 14.30...Front wheel drive shaft, 15...Differential limiting clutch, 23...Friction clutch. Figure 1 Applicant Toyota Motor Corporation Agent Patent Attorney Yutaka 1) Oxygen deficiency (1 other person)

Claims (1)

[Scope of Claims] In controlling the front and rear wheel differential control clutch that allows differential movement between the front and rear wheels and limits the differential movement between the front and rear wheels, the temperature of the front and rear wheel differential control clutch or the temperature can be substituted for the temperature of the front and rear wheel differential control clutch. Front and rear wheels characterized in that control is performed to reduce slippage between friction plates when a comparison value of the temperature at at least two locations, that is, the temperature at a predetermined location and the temperature at a predetermined reference location, exceeds a set value. Control method of differential control clutch.