JPS6390444A - Four-wheel drive vehicle provided with slip preventing function - Google Patents

Abstract

PURPOSE:To avoid occurrence of a tight corner brake phenomenon, by detecting a slip and by selecting a road surface map having a friction coefficient lower than that of the present road surface map when a slip occurs. CONSTITUTION:A signal is delivered from a pattern select switch to determine the position of the latter. If it is locked, a solenoid is driven (1 3, 1 4) in such a way that a center differential gear clutch is engaged while if is free, the center differential gear is released. When it is at the automatic position other than the above-mentioned positions, a vehicle speed, a rear wheel rotational speed and a throttle opening degree are read. Then, a subroutine 8 for estimating a road surface friction coefficient mu is carried out, and in accordance with the result, a subroutine 9 for controlling a center differential gear is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a four-wheel drive vehicle with an anti-slip function applied to part-time or full-time four-wheel drive vehicles.

[Conventional technology]

Traditionally, 4-wheel drive vehicles have developed a drive system that differs from simple 4-wheel drive as needed to ensure that appropriate driving conditions are obtained even when driving conditions such as road surface conditions and acceleration/deceleration change. Four-wheel drive vehicles have been proposed that can also be switched to different modes.

One of them is a part-time four-wheel drive vehicle, which can be divided into two-wheel drive, in which either the front or rear wheels are the driving wheels, and four-wheel drive, in which both the front and rear wheels are the driving wheels, depending on road conditions. For example, if the engine is mounted on the front side, the driving force transmission mechanism will be as shown in Fig. 7, and the power from the engine will be transferred to the automatic transmission 5.
Torque converter 51 and main transmission 52 located in 0
and the auxiliary transmission 53, the output of which is transmitted to the drive gear 55.
The signal is transmitted to the four-wheel drive transfer 56 via. That is, the power is transmitted to the front wheel drive shafts 58,58 through the front differential device 57 installed integrally with the drive gear 55, and the two
It is configured to have wheel drive. On the other hand, a rear wheel drive propeller shaft 59 is connected to a rear wheel transmission device 61 via a bevel gear 60, and a rear export force device 62 is integrally installed on the rear wheel transmission device 61 and the drive gear 55. 2
Wheel drive 74 is arranged to be freely switchable by a wheel drive switching clutch 63, and when the switching clutch 63 is engaged, power is transmitted from the automatic transmission j1150 to the propeller shaft 59, and the rear wheels are also driven. Another drive system is a full-time four-wheel drive vehicle, which is configured to have four-wheel drive. It is equipped with a center differential mechanism as a differential mechanism.

Even in this full-time four-wheel drive vehicle with a center differential, in order to make it possible to switch the drive system according to road conditions, etc., there is a restriction mechanism that directly connects power transmission between the front wheels and rear wheels without going through the center differential mechanism. is provided so that the center differential mechanism can be disabled (locked Li) when a large driving force is required, such as during acceleration or when driving on a rough road.

For example, when the engine is mounted on the front side, the driving force transmission mechanism becomes as shown in FIG. transmitted to the sub-transmission 73,
The output is transmitted to a four-wheel drive transfer 76 via a drive gear 75. If the center differential clutch 77, which is the front and rear wheel engagement mechanism, is released, the rotation of the drive gear 75 is controlled via the front and rear export force device 78 to the center differential device 79, which is the differential mechanism between the front and rear wheels. transmitted to
Furthermore, the front differential device 8
1, and the left and right front wheel drive shafts 82, 82 are driven. The output of the center differential device 79 is also transmitted to a rear wheel transmission device 83, and further transmitted to a rear wheel drive propeller shaft 86 via a bevel gear 85 to drive the rear wheels.

Therefore, when the center differential clutch 77 is released, the vehicle is driven in four-wheel drive where the center differential device 79 operates a differential mechanism between the front and rear wheels.

On the other hand, when the center differential clutch 77 is engaged, the rotation of the drive gear 75 is directly transmitted to the front differential device 81 via the clutch 77, and the left and right front wheel drive shafts 82
．． 82 is driven. At the same time, the front and rear export force device 7
8. Since the front wheel transmission device 80 and the center differential device 79 are integrated, the rotation of the drive gear 75 is controlled by the rear wheel transmission device 8.
3, and is further transmitted to the rear wheel drive propeller shaft 86 via the bevel gear 85 to drive the rear wheels. Therefore, when the center differential clutch 75 is engaged, the differential mechanism by the center differential device 77 is not activated and the vehicle is driven in four-wheel drive.6 However, one of the conditions for the vehicle to slip is that the driving force of the vehicle is There are cases where it is large. Therefore, we focused on the fact that changing to 4-wheel drive rather than 2-wheel drive increases the tire grip force and prevents slips, as described above, so we switched from 2-wheel drive to 4-wheel drive at the position of the select lever that has the highest driving force, and the tire grip force increases and slips can be prevented. A technique for preventing this is proposed, for example, in Japanese Unexamined Patent Publication No. 58-26634. Specifically, it is applied to a part-time four-wheel drive vehicle, and automatically switches from two-wheel drive to four-wheel drive when the select lever is shifted to the first or second speed range. Similarly, when the driving force is large, 2
As a method of switching from wheel drive to four-wheel drive, a method of automatically switching based on the accelerator opening has also been attempted.

[Problem that the invention seeks to solve]

In the above part-time or full-time four-wheel drive vehicles, there is a problem that the front wheels or rear wheels slip during two-wheel drive or four-wheel drive when the center differential mechanism is activated. In particular, the center differential mechanism has the function of distributing torque between the front and rear wheels in an equal ratio, so the drive power transmission limit is balanced to the value of the lower drive power of the front or rear wheels. For example, if one of the front wheels spins, the driving energy will escape there, and the driving force of the rear wheel will become extremely small.For this reason, a 4-wheel drive vehicle with a center differential is different from a 4-wheel drive vehicle without a center differential. The transmitted driving force may be inferior when the road surface friction coefficient is low. For example, when a large driving force is generated, such as during acceleration, the driving force cannot be sufficiently transmitted to the road surface, and this appears as phenomena such as front or rear wheels slipping (spin).

However, the driving force in particular is greatly influenced by the gear ratio, and the lower the gear, the greater the driving force becomes.Furthermore, in the case of an automatic transmission, as shown in Figure 2, the driving force depends on the accelerator opening,
It varies greatly depending on vehicle speed. Therefore, there is a problem in that slips cannot be completely prevented only by adjusting the accelerator opening or the position of the select lever by manual operation. For example, in a vehicle equipped with an automatic transmission, the main action for rapid acceleration is to press the accelerator.
Since the operation of moving the shift lever is rarely performed, a method of switching from two-wheel drive to four-wheel drive based on the position of the select lever cannot be expected to function effectively as a slip prevention.

On the other hand, if the differential of the four-wheel drive or center differential is too limited in order to completely prevent slipping, the front and rear wheels will not be differentially operated, resulting in tight corner braking during low-speed turns. When driving at high speeds, there is a problem that if there is an imbalance in air pressure or load between the front and rear wheels, fuel consumption will increase.

In order to solve the above problem, the present applicant filed a patent application filed in 1986-2.
In No. 94753, IM of the road surface is obtained by photographing the road surface and processing the image! We have proposed detecting the friction coefficient and controlling the switching between 2-wheel/4-wheel drive or the differential limiting mechanism of the center differential mechanism depending on the road surface condition, but it is difficult to directly detect the friction coefficient of the road surface. The problem is that the software configuration becomes complicated.

The present invention solves the above problems, and has a slip prevention function that can reliably avoid slips while avoiding tight corner braking and improve fuel efficiency with a simple configuration. The purpose is to provide a four-wheel drive vehicle equipped with the following.

[Means for solving problems]

For this purpose, a four-wheel drive vehicle equipped with the anti-slip function of the present invention is a four-wheel drive vehicle equipped with a front and rear wheel engagement mechanism that makes it possible to control the differential limit between the front wheels and the rear wheels. , a detection means for detecting a gear position and a slip;
7) A road surface map stored in an electronic control device for each of a plurality of road surfaces having different coefficients of friction and used to control the front and rear wheel engagement mechanisms based on signals of vehicle speed, throttle opening, and gear position; The presence or absence of slip is detected by the signal of the detection means, and if slip occurs, a road surface map with a lower friction coefficient than the current road surface map is selected, and if no slip occurs, a road surface map with a friction coefficient lower than the current road surface map is selected. This is characterized by selecting a high road surface map.

[Action and effect of the invention]

In the four-wheel drive vehicle equipped with the anti-slip function of the present invention, as shown in FIGS. 5 and 6, for example, when a slip occurs, the map is set to lock the center differential mechanism in the process @~0. and (
By searching the map in which the vehicle speed and throttle opening are in the lock range by processing O to ■ from the highest coefficient of friction μ to the lowest, the center map is set using the map with the highest μ as possible. This allows more free opportunities and avoids the tight corner braking phenomenon. Also,
If no slip occurs, the map is changed to one with as high a μ as possible through processing (1) to [phase], thereby increasing the chances of the center differential mechanism being free and avoiding the tight corner braking phenomenon.

Therefore, since the road surface map is estimated without directly detecting the friction coefficient μ, a simple configuration can reliably prevent slips while avoiding tight corner braking, and improve fuel efficiency.

〔Example〕

Examples will be described below with reference to concave surfaces.

FIG. 1 is a diagram showing the configuration of one embodiment of a control system for a four-wheel drive vehicle equipped with a slip prevention function according to the present invention, FIGS. 2 and 3 are diagrams for explaining a clutch control map, FIG. 4 is a diagram for explaining an example of the flow of processing by the electronic control unit, FIG. 5 is a flow diagram of the road surface μ estimation subroutine in FIG. 4, and FIG. 6 is a flow diagram of the road surface discrimination subroutine based on slip in FIG. It is a flow diagram.

In FIG. 1, 1 is a vehicle speed sensor, 2 is a front wheel or rear wheel rotation speed sensor, 3 is a throttle sensor, 4 is a gear stage detection unit, 5 is a pattern select switch, 6 is a snow road sensor, 7 is a steering sensor, 8 is the electronic control unit, 9 is the I10 boat, 10 is the CPU, 11 is the RA
M, 12 indicates a ROM 113 and an actuator.

The vehicle speed sensor 1 is a sensor that detects the output rotation speed of the transmission or the average value of the rotation speed of the front wheels and rear wheels,
In the case of an automatic transmission, the gear position detection unit 4 reads the control signal from the gear change control device or the maintenance oil pressure signal used in the gear position, and in the case of a manual transmission, reads the shift lever position. be. Furthermore, by selecting the lock or free button switch, the pattern select switch 5 engages or releases the two-wheel/four-wheel drive switching clutch 63 or center differential clutch 77, which is the aforementioned front and rear wheel engagement mechanism. By selecting the automatic button switch, these clutches 63 and 77 are automatically controlled as described later.

The electronic control unit 8 includes, for example, a RAM 11 and a ROM 12 that store control programs and road maps for clutch control.
memory, CPU (computation processing bag FF) 10, I10
A computer controlled unit with a boat 9 and an I
10 Each sensor, switch, etc. (1 to 7
), and the actuator 13 is controlled by referring to a clutch control road map as described later based on the signals of the gear ratio, vehicle speed, accelerator opening, snowy road, and steering angle.

The actuator 13 is a solenoid that supplies hydraulic pressure to the hydraulic clutch, and engages and releases the two-wheel/74-wheel drive switching clutch 63 or the center differential clutch 77 by turning on/off the solenoid. The actuator 13 may be a duty solenoid, in which case the oil pressure (duty ratio) of the hydraulic clutch is set (continuously, stepwise) to control the hydraulic clutch from direct engagement through a slip region to disengagement. Further, the front and rear wheel engagement mechanisms may not be hydraulic clutches, but the actuator 13 may be an electric motor.

Next, the contents of the road surface map for clutch control will be explained with reference to FIGS. 2 and 3. FIG. 2 shows the relationship between vehicle speed, throttle opening θ, gear position, and vehicle driving force. The drive transmission limit line shown in the figure indicates the area where the vehicle slips, and changes depending on the road surface condition and vehicle weight. The slip area corresponding to this road surface condition and vehicle weight is calculated, and as shown in Figure 3, the switching between 2-wheel and 74-wheel drive or the locking of the center differential mechanism is controlled for each of several types of road surface conditions with different road surface friction coefficient μ. For example, a normal road surface (a), a wet road surface (b), a snowy road with chains (C), a snowy road without chains (d). A two-wheel/four-wheel drive switching region or a center differential mechanism locking region is provided for road surfaces with high to low road friction coefficient μ, corresponding to vehicle speed and throttle opening.

In addition, in Fig. 3, 2 is determined by vehicle speed and throttle opening.
Although shown as dimensional data, it may be formed as three-dimensional data that also includes the parameters of the gear position.

Next, the flow of processing by the electronic control unit when controlling the center differential mechanism in a full-time four-wheel drive vehicle will be explained with reference to FIGS. 4 to 6.

In Fig. 4, first input the pattern select switch signal, check its position, and set the solenoid to engage the center differential clutch in the case of rLOcK and release the center differential clutch in the case of rFREEJ. drive (■→■, ■-■), and in the case of rAUTO, which is not in any of the above positions, read the vehicle speed, rear wheel rotation speed, and throttle opening signal (■ to ■) 0. Then, the road surface friction coefficient μ The estimation subroutine (2) is executed, and the center differential control subroutine [F] is executed according to the result.

The above-mentioned road surface friction coefficient μ estimation subroutine (■) will be explained with reference to FIG. A subroutine for determining the road surface based on slip, which stores the vehicle speed and throttle opening in the memory, then executes a subroutine for determining the road surface based on slip, which will be described later, and stores the road surface map determined in the subroutine in memory (■~[phase]). 0, as shown in Figure 6,
``LOCK'' the vehicle speed and throttle opening that caused the slip.
Search the road surface map for the J area from the higher μ to the lower μ, and assume that the road surface of the map found here matches the current road surface (@-@), for example, the third
If you are using the wet road map (b) in the figure and a slip occurs when the vehicle speed and throttle opening are 0, then the vehicle speed,
A map in which the throttle opening is in the rLOcKJN region at 0 point is searched from the higher μ to the lower μ, and in this case, it is assumed to be a snowy road map (C) with a chain.

If it is determined that there is no slip in step ◎ in FIG. If the predetermined time has elapsed, repeat the above routine, and if the predetermined time has elapsed, at step [phase],
Is the point of the vehicle speed and throttle opening that caused the previous slip on the currently used road surface map rLOcKJ? Check whether it is in the +i region or the rFREEJ region. rLOcK
If it is in the J area, a road surface map that is one μ higher than the currently stored road surface map is assumed to be the current road surface and stored in the memory (O~[phase]).Continuing with the example mentioned above, if there is a chain From the snowy road map (c) to the wet road map (b)
) will be changed. rFREEJff in step O
If it is determined that the vehicle is in the i range, it is determined whether or not the vehicle is currently running at the same speed and throttle opening that caused the slip before.If NO, the above routine is repeated and Y
In the case of ES, a map with one μ higher than the currently stored road surface map is assumed as the current road surface and stored in memory ([phase] to [phase]). The road surface map (b) is changed to a normal road surface map (a).

The above processes @ ~ [phase] estimate and change the road surface map so as to lock the center differential mechanism in the event of a slip. In particular, the processes ~ ~ O are based on the vehicle speed and throttle opening. By searching the map where the lock area is from the higher μ to the lower μ, the center differential mechanism uses a map with as high μ as possible to increase the chances of free movement and avoid the tight corner braking phenomenon. It is something. In addition, processing [phase] ~ ◎ is a process in which if no slip occurs, the map is sequentially changed to a map with as high μ as possible to increase the chances of the center differential mechanism being free and avoid the tight corner braking phenomenon. It is.

The snowy road sensor 6 may be used to estimate the road surface condition, and in the case of a snowy road, the snowy road map shown in FIG. 3 may be used.

Further, when the steering angle is changed in a certain driving state, the difference in turning radius between the front wheels and the rear wheels increases as the steering angle increases.

In such a case, if the center differential is changed from locked to free or from free to locked, there is a risk that the behavior of the vehicle will worsen. Control may not be performed.

It should be noted that the present invention can be modified in various ways and is not limited to the above-mentioned embodiment. For example, in the above-mentioned embodiment, the explanation has been made as applied to a full-time four-wheel drive vehicle with a center differential. It is equally applicable to part-time four-wheel drive vehicles.

In addition, in the above embodiment, in subroutine 0 for determining the road surface based on slip, the map in which the vehicle speed and throttle opening are in the lock range is searched from the higher μ to the lower μ, but maps are searched at random. Good too.

In the above embodiment, the presence or absence of slip is detected using signals of vehicle speed and front wheel or rear wheel rotation speed, but the presence or absence of slip is detected using a torque sensor that detects the torque acting on the drive shaft, vehicle acceleration and wheel speed. Various methods have been considered, such as a method for detecting by comparing the acceleration of the front and rear wheels, a method for detecting by comparing the vehicle speed and the rotational speed ratio of the front and rear wheels, a method for detecting by comparing the rotational acceleration of the front and rear wheels, etc. It will be done.

As is clear from the above explanation, the disadvantage of restricting (locking) the differential of the center differential mechanism is that the front and rear wheels are not differentially operated, resulting in tight corner braking when turning at low speeds and deterioration of fuel efficiency when driving at high speeds. However, according to the present invention, if a slip occurs, the clutch control map is changed to lock the center differential mechanism, and if no slip occurs, the clutch control map is changed to lock the center differential mechanism, and if no slip occurs, the clutch control map is changed to lock the center differential mechanism. By changing to a road surface map with a high μ, it is possible to increase the chances of the center differential mechanism being free, avoid the tight corner braking phenomenon, and reliably prevent slips, thereby solving the above-mentioned problems.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the configuration of a control system for a four-wheel drive vehicle equipped with a slip prevention function according to the present invention, and FIGS. 2 and 3 are diagrams for explaining a road surface map for clutch control. , FIG. 4 is a diagram for explaining an example of the flow of processing by the electronic control unit, FIG. 5 is a flow diagram of the road surface μ estimation subroutine in FIG. 4, and FIG. 6 is a subroutine for determining the road surface by slip in FIG. 5. 7 is a diagram for explaining the driving force transmission mechanism of a part-time four-wheel drive vehicle, and FIG. 8 is a diagram for explaining the driving force transmission mechanism of a full-time four-wheel drive vehicle with a center differential. This is a diagram. 1...Vehicle speed sensor, 2...Front wheel or rear wheel rotation speed sensor, 3...Throttle sensor, 4...i speed detection unit, 5...Pattern select switch,
6... Snow road sensor, 7... Steering sensor,
8...Electronic control unit, 9...I10 boat, 1
0...CPU, 11...RAM, 12...ROM
, 13... Actuator, ■... Road surface μ estimation subroutine, ■... Road surface discrimination subroutine based on slip. Applicant Aisin Warner Co., Ltd. (1 other person) Representative Patent Attorney Hiroki Shirai (2 others) Figure 1 Figure 2 Figure 3 (0) (b) ζC) (d) Death 1
Figure 4 Figure 7

Claims (3)

[Claims] (1) In a four-wheel drive vehicle equipped with a front and rear wheel engagement mechanism that makes it possible to control the differential limit between the front wheels and the rear wheels, a detection means for detecting vehicle speed, throttle opening, gear stage, and slip;
a road surface map stored in an electronic control device for each of a plurality of road surfaces having different coefficients of friction, and for controlling the front and rear wheel engagement mechanisms based on vehicle speed, throttle opening, and gear stage signals; The system detects the presence or absence of slips based on signals, and if slips occur, it selects a road surface map with a lower friction coefficient than the current road surface map, and if no slips occur, it selects a road surface map with a higher friction coefficient than the current road surface map. A four-wheel drive vehicle with an anti-slip function that features a selection of features. (2) A full-time four-wheel drive vehicle equipped with a center differential mechanism that absorbs the difference in turning radius between the front and rear wheels, and four wheels equipped with an anti-slip function as set forth in claim 1. driving car. (3) When a slip occurs, the road surface map with the highest friction coefficient is searched from the one with the highest friction coefficient to the one with the lowest friction coefficient among the road surface maps to enable engagement of the front and rear wheel engagement mechanisms. A four-wheel drive vehicle equipped with an anti-slip function according to claim 1 or 2, wherein: