JPH03279026A - Power transmission device for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To restrain the degree of slip for preventing the excessive variation of a body upon occurrence of the slip by providing a control means to control a differential limiting force for the increase thereof with time elapsed during the occurrence of the slip. CONSTITUTION:Hydraulic pressure in a clutch 16 is adjusted by controlling the opening degree of a hydraulic control valve 19. Namely, the lock conditions of a front wheel propeller shaft 4 and a rear wheel propeller shaft are controlled, depending upon the value of a lock signal LCK for controlling the aforesaid opening degree. Also, a differential limiting force LCK generated by a controller 18 increases, with time elapsed time during slip occurrence, and torque transmitted between wheels is nearly equalized correspondingly. The more equalized is the torque, the higher is the stability of a body. According to the aforesaid gradual increase and control of a differential limiting force, the excessive variation of torque transmitted to a wheel before and after the occurrence of slip is restrained, and the behavior of the body is thereby stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power transmission device for a four-wheel drive vehicle that has a function of limiting the differential between wheels according to a slip ratio, and in particular,
The present invention relates to a technique for suppressing a sudden increase in differential limiting force and preventing vehicle fluctuations when differential limiting is applied.

(Prior Art) For four-wheel drive vehicles, many techniques have been proposed that attempt to cope with various driving conditions by providing a limiting mechanism that limits the differential of a center differential and performing torque distribution.

For example, Japanese Patent Laid-Open No. 63-2729 attempts to ensure the stability of a vehicle body by detecting road resistance and controlling the amount of torque to be distributed to the wheels in accordance with this resistance value.

Furthermore, in JP-A No. 62-261539, a center differential and a limiting mechanism for limiting the differential are interposed between the front wheels and the rear wheels, and the differential is adjusted according to the difference between the rear wheel rotation speed and the front wheel rotation speed. It controls the limiting force.

(Problems to be Solved by the Invention) By the way, the amount of wheel slip varies depending on changes in the road surface and weight distribution in the vehicle. According to the above-mentioned prior art, when slip occurs in the wheels, the torque transmitted between the wheels is uniformly distributed. That is, before the slip occurs, torque is distributed between the wheels at an appropriate distribution ratio, but when the slip occurs, the torque is controlled so that there is no difference in the distribution ratio between the wheels. As the amount of slip increases, the fluctuation in the torque distribution ratio increases. This fluctuation in the torque distribution ratio causes sudden fluctuations in the torque transmitted to the wheels before and after slip occurs.
This is a factor that hinders the stability of the vehicle body.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to propose a power transmission device for a four-wheel drive vehicle that is capable of suppressing slip so as not to cause sudden fluctuations in the vehicle body when slip occurs. .

(Means and operations for achieving the object) The configuration of the present invention for achieving the above object includes means for detecting the slip rate of the wheels, and limiting the differential between the wheels according to the detected slip rate. The present invention is characterized by comprising a differential limiting means and a control means for controlling the differential limiting force so as to increase as time passes while a slip occurs.

That is, when a slip occurs, the differential limiting force only increases gradually over time, and a sudden increase is suppressed, so that running stability is ensured.

(Example) An example to which the present invention is applied will be described below with reference to the accompanying drawings. This embodiment is a four-wheel drive vehicle in which torque is transmitted to the front and rear four wheels via a center differential, and when the center differential is engaged, a multi-plate clutch is used to secure the front and rear propeller shafts. This is an embodiment applied to a four-wheel drive vehicle of the type.

FIG. 1 is a diagram schematically showing a driving force transmission system of a four-wheel drive vehicle according to this embodiment. In the figure, 1 is the engine and transmission, 3 is the center differential, 6 is the front wheel differential,
7 is the rear wheel differential. The output of the engine 1 is transmitted to a center differential 3 via a drive shaft 2. A signal G indicating the current gear shift position is sent from the engine/transmission l.
P is sent to the controller 18. The front wheel driving force is transmitted to the front wheel differential 6 via the propeller shaft 4, and further transmitted to the left and right front wheels 9.8 via the left front wheel drive shaft 13 and the right front wheel drive shaft 12, respectively.

On the other hand, the engine torque for the rear wheels is transmitted to the rear wheel differential 7 via the center differential 3 and the rear wheel propeller shaft 5, and furthermore, the left rear wheel drive shaft 15 is transmitted to the left and right rear wheels 11.10, respectively.
．． The power is transmitted via the right rear wheel drive shaft 14.

The front propeller shaft 4 and the rear propeller shaft 5 are connected by a hydraulically driven multi-plate clutch 16. The oil pressure within the clutch 16 is adjusted by controlling the opening ratio of the oil pressure control valve 19. That is, the locked state of the front wheel propeller shaft 4 and the rear wheel blower shaft is controlled according to the value of the lock signal LCK that controls the aperture ratio.

In FIG. 1, 20a, 20b, 20c, and 20d are sensors that detect the rotational speed of the wheels (RFll, RFL, R**, R*L). Further, 21 is a sensor that detects vehicle speed. This sensor 21 is a sensor that rotates following the movement of the vehicle and detects the rotation speed Rv. still,
Instead of a driven type sensor, a refund value of a signal obtained by excluding signals with extremely large variations from among the outputs of the wheel rotation speed sensor may be used as the vehicle speed.

An overview of the control of this embodiment will be explained with reference to FIGS. 2 and 3.

Figure 2 shows the vehicle speed rotation speed Rv and the slip wheel rotation speed Ro.
This is a map that determines the magnitude of the amount of slip based on the correspondence with the amount of slip. Here, check the wheel that is considered to be slipping (
As an example, the rotation speed R0 of the slip wheel (hereinafter referred to as a slip wheel) is as follows: Ro = MAX (Rr*, RrL, R111RFI
L) (1) Defined by: Further, the slip rate S is defined by, for example. In this embodiment, if Rv≧R0, it is determined that no slip has occurred.

FIG. 3 explains the control principle of this embodiment. In the figure, line segment ~m is a signal LC that controls the engagement state of the clutch 16.
The change characteristics of K over time are shown. Time t on the horizontal axis
1 memory is 1 second.

Constant AIt °C, , I2. is I2. , <ρ2<ρ3, then the characteristic I is LCK=j2.・t・・・・・・(3
) Characteristic ■ is LCK=12.・t...(4) Characteristic (2) is expressed as LCK=ρ3・t...(5). Regardless of the characteristics, the signal LCK that controls the engagement state of the clutch 16 increases with time. That is, as time passes, the differential limiting force LCK
becomes larger, and the torque transmitted between the wheels becomes more equal. The more even it is, the more stable the vehicle will be. By controlling the differential limiting force to gradually increase as described above, fluctuations in the torque transmitted to the wheels before and after the occurrence of slip are suppressed from increasing, and the behavior of the vehicle body is stabilized.

Which of the characteristics I to ■ is selected depends on the slip weight S. That is, the threshold constants of the slip rate are SM, SL (
SM < SL ), if the slip rate S calculated by equation (2) is S < S11, then the characteristic work (increase rate 2□
) is selected, and if SM≦S<SL, the characteristic ■ (increase rate β
2) is selected, and if S > SL, the characteristic ■ (increase rate ρ,)
chooses. That is, the larger the slip rate is, the larger the rate of increase ρ of the differential side eye power LCK with respect to time is.

As shown in FIG. 3, and more specifically, as shown in FIGS. 4B and 5, the differential limiting force is gradually increased by 5
It only takes place for seconds. In this embodiment, this gradual increase control is
If the slip is not suppressed after repeating this for several seconds, set the differential limiting force LCK to the maximum LMAX.

LCK=LMAX ・・・・・・(6)
The reason why the gradual increase control is limited to a certain period of time in this way is to prevent the stability of the vehicle body from being impaired for a long time due to the slip state continuing for a long time due to the gradual increase control of the differential limiting force. Therefore, if the slip is not suppressed even after 5 seconds of incremental control, the differential is completely stopped to improve the stability of the vehicle body. However, even if the differential limiting force is maximized in this way, it is fully expected that the torque fluctuation will be small when the differential limiting force is maximized due to the gradual increase in the limiting force up to that point.

The control procedure of this embodiment will be explained in detail with reference to FIGS. 4A to 4C. First, in step S2, the rotation speed Ro of the slipping wheel and the vehicle speed rotation speed RV+slip ratio S are determined. The details of step S2 are shown in FIG. 4C.

In step S4, a timer T, which will be described later, is reset. In step S6, the vehicle speed and rotational speed Rv are compared with the rotational speed R0 of the slip wheel. If RV≧R0, slip has not substantially occurred, so in view of improving fuel efficiency, LCK=O is set to allow the center differential 3 to be free in order to allow differential movement between the wheels.

If it is determined in step S6 that RV<RO, it is considered that slipping has occurred, so control is performed to limit the differential between the wheels in steps 86 and subsequent steps.

In step S8, it is determined whether the slip rate S is large or small. That is, if the slip rate S is S<S, step SIO
Then, the characteristic (increase rate ρ1) is selected, and LCK=Ni.

In addition, in step S'12, the gradual increase amount △L becomes △L=
It is assumed to be 12°. Moreover, in step S8, SM≦S<S L
If so, the characteristic ■ (increase rate of 2) is selected (LCK=2) in step S14, and ΔL=ff a (step 816). Also, if S > S L, the characteristic ■ (increase rate I23) is selected in step S18 (LC
K=β3), and ΔL=123 in step S20.

In other words, the differential limiting force according to the slip ratio S is applied to the center differential 3.
join.

In FIG. 4B, steps 330 to S36→
The loop of step S46→step S48→step S30 is a control to gradually increase the differential limiting force LCK for 5 seconds.

That is, in step S30, one second is measured, and in step S30, one second is measured.
In step S32, the timer T is counted up, and in step S32
Now, measure the latest rotational speeds Ro, Rv, etc.

If it is determined in step S36 that the time is within 5 seconds, the process advances to step S46. Until it is determined in step S46 that the slip condition has not subsided (RV<R,), the differential limiting force LCK is increased by ΔL in step S48. That is, LCK=LCK+△L...
...(7), where ΔL is β1. ρ2. ρ.

Figure 5 shows the differential limiting force L as time changes for 5 seconds.
It is shown that CK gradually increases by ρ. Furthermore, Fig. 5 shows a case where the slip does not subside even if the differential limiting force is gradually increased for 5 seconds, and if the slip subsides before the 5 seconds elapse (Rv≧Re). and step S4
If it is determined in step S44, the differential limiting force is set to "0", the center differential 3 is freed, and the process proceeds to step S44.
Return to 2.

If the slip is not suppressed even after gradually increasing the differential limiting force for 5 seconds, the answer is NO in step S36.

It is determined that the differential limiting force LCK is
is maximized according to equation (6). This control to maintain the differential limiting force at the maximum is effective when the slip has subsided (RV≧R0)
The process continues until it is determined in step S42. Rv≧
If it becomes R0, the differential limiting force is set to "0" in step S44, the center differential 3 is freed, and the process returns to step S2. In FIG. 5, control is performed to gradually increase the differential limiting force for 5 seconds. A case is shown in which the differential limiting force is later controlled to be maximized and the slip subsides at time t1.

According to the embodiment described above, (1) When slippage occurs, the signal LCK that controls the engagement state of the clutch 16 is controlled to increase with the passage of time, that is, the differential limiting force LCK increases with the passage of time.
becomes larger, and the torque transmitted between the wheels becomes more equal. Thus, by controlling the differential limiting force to gradually increase, the fluctuations in the torque transmitted to the wheels before and after the occurrence of slip are suppressed, and the behavior and movement of the vehicle body are stabilized. In other words, Even on roads with low resistance, straight-line stability, cornering performance, and acceleration are improved.

(2) The larger the slip ratio is, the larger the rate of increase 2 of the differential limiting force LCK with respect to time is. In other words, whether the slip is large or small, the slip converges within the same time span.

(2): The above-mentioned gradual increase control of the differential limiting force is performed for only 5 seconds. If the slip is not suppressed after performing this gradual increase control for 5 seconds, the differential limiting force LCK is set to the maximum LMAX. As a result, the gradual increase control of the differential limiting force prevents the stability of the vehicle body from being impaired for a long time due to the slip state continuing for a long time. As described above, even if the differential limiting force is maximized, it is fully expected that the torque fluctuation will be small when the differential limiting force is maximized due to the gradual increase in the limiting force up to that point.

The present invention can be modified in various ways without departing from the spirit thereof.

In the above embodiment, slip control is performed by controlling the differential of the center differential. However, there are various types of four-wheel drive vehicles, and the present invention is also applicable to such four-wheel drive vehicles.

The four-wheel drive vehicle shown in FIG. 6 is not equipped with a center differential, and is driven in principle by rear wheels, and when necessary, engine output is transmitted to the front wheels to provide four-wheel drive. Further, torque split control is performed by controlling the oil pressure applied to the fluid clutch 30.

FIG. 7 shows a vehicle that is normally front-wheel drive, and torque split control is performed between the front wheels and the rear wheels as necessary.

(Effects of the Invention) As explained above, the present invention includes a means for detecting the slip rate of wheels, a differential limiting means for limiting the differential between the wheels according to the detected slip rate, and a differential limiting means for limiting the differential between the wheels according to the detected slip rate. and control means for controlling the force to increase over time while the slip is occurring.

That is, when a slip occurs, the differential limiting force only increases gradually over time, and a sudden increase is suppressed, so that running stability is ensured.

Further, by increasing the rate of increase in the differential limiting force gradual increase control according to the slip rate, the time for slip to converge becomes constant regardless of the magnitude of the slip amount.

In addition, the gradual increase control is limited to a certain period of time, after which the differential limiting force is maximized, thereby preventing the slip occurrence state from continuing for a long time.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIGS. 2 and 3 are diagrams explaining the outline of control of this embodiment. FIGS. 4A to 4C are control procedures of this embodiment. FIG. 5 is a timing chart showing an example of the control according to this embodiment. FIGS. 6 and 7 are diagrams illustrating the configuration of a modification of the embodiment shown in FIG. In the diagram, 1...engine/transmission, 2...output shaft, 3...
Center differential, 4... Front wheel propeller shaft, 5...
Rear wheel propeller shaft, 6... Front wheel differential, 7... Rear wheel differential, 8.9, 10.11... Wheels, 12.13,
14゜15・・・Wheel drive shaft, 16, 30.40
...Multi-disc clutch, 17...Oil pipe, 18...Controller, 19...Pressure control valve, 20a
, 20b, 20c, 20d... wheel speed sensor, 21
...Vehicle speed sensor. Figure 2 Figure 3 Figure 4C

Claims (3)

[Claims] (1) means for detecting the slip rate of the wheels; differential limiting means for limiting the differential between the wheels according to the detected slip rate; 1. A power transmission device for a four-wheel drive vehicle, comprising: control means for controlling the power to increase over time. (2) The power of the four-wheel drive vehicle according to claim 1, wherein the control means controls the increase rate of the differential limiting force with respect to time to increase as the slip ratio increases. transmission device. (3) The control for increasing the differential limiting force with respect to time by the control means is performed for a fixed period of time regardless of the slip rate, and when the slip does not converge, the differential limiting force is maximized. A power transmission device for a four-wheel drive vehicle according to claim 1.