JP3426265B2 - Drive torque distribution control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive torque distribution control device for a vehicle, and more particularly to a drive torque of a type used together with an antilock control device for estimating a vehicle speed from wheel speeds and performing antilock control. The present invention relates to a distribution control device.

[0002]

2. Description of the Related Art It has already been carried out to mount an antilock control device on a vehicle in order to shorten the braking distance while ensuring the running stability of the vehicle during vehicle braking. Then, as one form of this anti-lock control, the vehicle speed is estimated based on the wheel speeds of a plurality of wheels of the vehicle, and the relationship between the estimated vehicle speed and the wheel speed of each wheel is used to determine that each wheel is in braking. There is a form in which the brake pressure of each wheel is controlled so as not to fall into a locked state.

On the other hand, for the purpose of appropriately distributing the driving torque of the engine to each wheel to improve the driving performance, the differential limitation between the front and rear wheels in the drive system is performed based on the vehicle speed, the rotational speed difference between the front and rear wheels, and the like. It has already been carried out to equip a vehicle with a drive torque distribution control device for controlling the ratio of the drive torque of the vehicle engine distributed to the front and rear wheels by controlling the amount.

A conventional example of this drive torque distribution control device is described in Japanese Patent Application Laid-Open No. 62-53232. This is a drive torque distribution control device that increases the differential limiting amount of the front and rear wheels and increases the torque transmission amount to the front wheels in the vehicle braking state than in the non-braking state. If the front and rear wheels are strongly coupled when the vehicle is braked, even if one of the plurality of wheels is locked, that wheel is driven through the drive system,
As the wheels are not locked and continue to rotate, the timing of occurrence of the locking tendency is delayed and the locking limit is improved.At the time of limit braking, the locking tendency is generated at the front and rear wheels at the same time. The vehicle can be braked by making the most effective use of.

[0005]

However, when this conventional device is used, the front and rear wheels are strongly connected to each other when the vehicle is in a braking state regardless of whether the vehicle is in a straight traveling state or in a turning state. Therefore, the following problems occur.

When the vehicle turns, the turning radii of the wheels do not match each other, and the wheel speeds when the wheels roll on the road surface without slip usually do not match each other. Therefore, even if the same amount of slip occurs in each wheel under a situation where the front and rear wheels have a large differential limitation amount, the wheel speeds of the respective wheels do not match each other. On the other hand, the vehicle speed is estimated based on the wheel speeds of a plurality of wheels, and the determination as to whether or not the antilock control should be started considers the relative relationship between the wheel speed of each wheel and the estimated vehicle speed. Done.
Therefore, when the vehicle is turning, if there is an excessive slip on each wheel, the difference between the wheel speed of each wheel and the estimated vehicle speed tends to increase, so the antilock control is not started for any wheel. Does not occur.

However, when the vehicle goes straight, the wheel speeds when the wheels roll on the road surface without slipping coincide with each other. Therefore, under the situation where the front and rear wheels have a large differential limit amount, the same amount of slip occurs on each wheel. Then, the wheel speeds of the respective wheels coincide with each other, and the estimated vehicle speed is determined to be equal to the wheel speed. Therefore, when the conventional device is used, when the vehicle goes straight, the differential limitation amount of the front and rear wheels is large, and even if excessive slip occurs on each wheel, the difference between the wheel speed of each wheel and the estimated vehicle speed increases. Since the tendency to run is weak, the slip cannot be detected, and a situation may occur in which antilock control does not start unexpectedly for any of the wheels.

In short, regardless of whether the vehicle is in a straight traveling state or in a turning state, when using the conventional device that always strengthens the front and rear wheels when the vehicle is in the braking state,
There is a problem in that the antilock control may not start unexpectedly in the straight traveling state, and the present invention has been made to solve this problem.

[0009]

In order to solve this problem, the present invention, as shown in FIG. 1, is provided on each of a plurality of wheels and operates by hydraulic pressure to suppress the rotation of each wheel. A plurality of brakes 1, a differential limiting device 3 that limits the differential between the front and rear wheels 2 in the drive system, and the differential limiting device 3 thereof.
The vehicle speed is estimated based on the wheel speeds of the front and rear wheels 2 whose differentials are limited by, and the relationship between the estimated vehicle speed and the wheel speeds of the respective wheels is used to prevent the wheels from falling into a locked state during vehicle braking. As described above, the vehicle is provided with the anti-lock control device 4 for controlling the hydraulic pressure of the brake, and by controlling the differential limiting amount of the differential limiting device 3, the driving torque of the engine is transmitted to the front and rear wheels 2. In the drive torque distribution control device 5 that controls the distribution ratio, at least when the vehicle is being braked by the operation of the brake 1 and the antilock control device 4 is in the non-operation state, at least the friction coefficient is the reference.
In a straight braking state on a low μ road that is lower than the value, the differential limiting amount of the front and rear wheels 2 is reduced to a value smaller than that in the turning braking state and is not zero, and in the operating state of the antilock control device 4, It is characterized in that a differential limiting amount control means 6 for setting the differential limiting amount of the front and rear wheels 2 to zero is provided regardless of whether the vehicle is in a straight braking state or a turning braking state.

One mode of the "differential limiting amount control means" here is to determine whether the vehicle is in the braking state from the ON / OFF state of the stop switch for detecting the brake operation, and use the lateral acceleration sensor. It is determined from the magnitude of the detected lateral acceleration whether or not the vehicle is in the straight traveling state, and when it is determined that the vehicle is in the braking state and the straight traveling state, it is determined that the vehicle is in the braking state and in the turning state. From time to time, the differential limiting amount of the front and rear wheels can be reduced.

Another mode is to turn on / off the stop switch.
From the FF state, it is determined whether the vehicle is in the braking state, and from the operation angle of the steering wheel detected by the steering sensor, it is determined whether the vehicle is in the straight traveling state,
When it is determined that the vehicle is in the braking state and the straight traveling state, it is possible to reduce the differential limiting amount of the front and rear wheels more than when it is determined that the vehicle is in the braking state and the turning state.

Further, the form of the differential limiting amount control in the "differential limiting amount control means" is a center differential which connects the front wheels and the rear wheels to each other, and the differential limiting amounts of the front and rear wheels are variable by the clutch pressure. However, it is possible to control the height of the clutch pressure . One embodiment of the present invention, is to <br/> et al, vehicle, high coefficient of friction is higher than the reference value μ road
In certain cases in the straight braking state, you in the low-μ road
In addition, it includes means for increasing the differential limitation amount of the front and rear wheels more than when the vehicle is in the straight braking state .

[0013]

In the drive torque distribution control device 5 according to the present invention, when the vehicle is braked by the operation of the brake 1 and the antilock control device 4 is in the non-operating state, the differential limiting amount of the front and rear wheels 2 becomes the differential limiting quantity control means 6, small
In the straight braking state on the low μ road where the friction coefficient is at least lower than the reference value, it is reduced to a value smaller than the turning braking state and not zero . Is the bond before rear wheel 2 is weakened. Further, in the operating state of the anti-lock control device 4, the differential limiting amount of the front and rear wheels 2 is set to zero regardless of the straight braking state or the turning braking state.

[0014]

As described above, according to the present invention, when the vehicle is being braked by the operation of the brake 1 and the antilock control device 4 is not in operation, at least on a low μ road.
In the straight-ahead braking state, the coupling between the front and rear wheels 2 is weakened more than in the turning braking state, and therefore, the effect that the antilock control does not start unexpectedly in the straight-ahead braking state is obtained. Moreover,
When the antilock control is started, the differential limiting amount of the front and rear wheels 2 is set to zero, so that the coupling between the front and rear wheels 2 is weakened and the operation of the antilock control device 4 is not hindered. It is also possible to obtain the effect that the antilock control is performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drive torque distribution control device according to an embodiment of the present invention will be described in detail below with reference to the drawings.

2 to 5 show a drive torque distribution control device according to an embodiment of the present invention. This drive torque distribution control device (hereinafter simply referred to as distribution control device) 10 is
As shown in FIG. 2, it is mounted on a vehicle together with the antilock control device 12.

As shown in FIG. 1, the antilock control device 12 includes a wheel speed sensor 20, a stop switch 22, a longitudinal G sensor 24 and a lateral G sensor 26. The wheel speed sensor 20 is provided on each of four wheels arranged on the front, rear, left, and right of the vehicle, and detects the wheel speed V _W that is the rotation speed of each wheel. The stop switch 22 is
Detects the depression of the brake pedal by the driver, that is, the brake operation. Specifically, it detects that the brake operation state is in the ON state, and detects that the brake operation state is not in the OFF state. The longitudinal G sensor 24 detects an acceleration G _X generated in the longitudinal direction of the vehicle body. As shown in FIG. 3, the front-rear G sensor 24 detects the front-rear acceleration G _X that occurs in the front direction of the vehicle body as positive and the rear-direction acceleration G _X that occurs in the rear direction as negative. The lateral G sensor 26 detects an acceleration G _Y generated in the lateral direction of the vehicle body. As shown in the figure, the lateral G sensor detects the lateral acceleration G _Y that is generated when turning right and that that is generated when turning left is negative.

In the antilock controller 12, as shown in FIG. 2, the input side of the controller 30 is connected to the wheel speed sensors 20 and the like. Controller 30
Is mainly composed of computers, and its R
A vehicle speed estimation routine, an antilock control routine, etc. are stored in the OM. A brake pressure control means 32 such as a solenoid valve is connected to the output side of the controller 30. The brake pressure control means 32 electrically controls the hydraulic pressure of a wheel cylinder that operates a brake 34 that suppresses the rotation of each wheel.

The vehicle speed estimation routine of the ROM is premised on the fact that the wheel speed V _WO of the fastest wheel having the maximum wheel speed V _W among the four wheels is likely to match the actual vehicle speed. It is a routine for estimating the vehicle speed V based on the wheel speed V _W of each wheel. Specifically, a routine that is repeatedly executed every time a predetermined computation period t has elapsed, at the time of each round of execution, the wheel speed of the fastest wheel is the maximum wheel speed V _W Out of four wheels V _WO and the upper limit vehicle speed V _{S UP} and the lower limit vehicle speed V _{S LO} that the vehicle body can take are respectively acquired,
This is a routine for determining an intermediate value among these three candidate values as the current estimated vehicle speed V _{SO (n)} .

The "upper limit vehicle speed V _{S UP} " is obtained by using the formula V _{SO (n-1)} + α _UP · t, while the "lower limit vehicle speed V _{S LO} " is obtained.
Is obtained using the formula V _{SO (n−1)} + α _LO · t.

Here, "V _{SO (n-1)} " is the previously estimated vehicle speed. Further, “α _UP ” and “α _LO ” are based on the combined acceleration G _XY (= (G _X ² + G _Y ² ) ^1/2 ) which is the combined value of the longitudinal acceleration G _X and the lateral acceleration G _Y. Is the maximum acceleration and the minimum acceleration (= maximum deceleration) that are determined by the constants a ₁ , a ₂ and a
₃ is used to obtain α _UP = a ₁ −G _XY α _LO = − (a ₂ · G _XY + a ₃ ).

On the other hand, the antilock control routine of the ROM is a routine which is repeatedly executed while the brake operation is detected by the stop switch 22, and specifically, the estimated vehicle speed V _SO and the wheel speed of each wheel. Whether it is necessary to execute the antilock control is sequentially determined from the relationship with V _W, and when it is determined that it is necessary, the estimated vehicle speed V _SO , the wheel speed V _W , the wheel acceleration V _W ′ and This is a routine for determining the control characteristic of the brake pressure based on the synthetic acceleration G _XY and controlling the brake pressure according to the control characteristic.
It should be noted that this routine is a routine for determining the control characteristic of the brake pressure to the pressure increasing side when the combined acceleration G _XY is large and when it is small.

The antilock control device 12 has been described above. Next, the distribution control device 10 will be described.

The distribution control device 10 also includes the stop switch 22, the longitudinal G sensor 24, and the lateral G sensor 26, which are also used as the antilock control device 12. The distribution control device 10 further includes a throttle sensor 4 for detecting an opening θ of the throttle valve of the engine.
0, a vehicle speed sensor 42 that detects the average value of the left and right front wheels as the vehicle speed, and a rear wheel speed sensor 44 that detects the average value of the left and right rear wheels as the rear wheel speed. The stop switch 22 and the like are connected to the input side of the controller 50, and the clutch pressure control means 52 including an electromagnetic valve and the like is connected to the output side of the controller 50. This clutch pressure control means 52 is a center differential clutch 54 such as a hydraulic multi-plate type provided on a center differential that distributes the drive torque from the engine to the front and rear wheels, and limits the differential amount of the front and rear wheels according to the clutch pressure. The clutch pressure of the center differential clutch 54 is controlled.
In this center differential clutch 54, the higher the clutch pressure, the larger the differential limiting amount.

The controller 50 is mainly composed of a computer, and executes a drive torque distribution control routine (represented by a flow chart in FIG. 4) stored in the ROM of the computer to drive the front and rear wheels. Properly control torque distribution.

The drive torque distribution control routine will be described below. First, its outline will be described.

In this routine, as shown in FIG. 5, the state of the vehicle is first classified into the antilock control state and the non-antilock control state, and further, the non-antilock control state is set to the non-antilock control state. The braking state is classified into a braking state and a braking state, and further, the braking state is classified into a high μ road straight traveling state, a high μ road turning state, and a low μ road rolling state and a low μ road straight traveling state. ing.

In this routine, the case where the vehicle is in the "antilock control state" is defined as the case where the antilock control device 12 is in the operating state, and the vehicle is in the "non-braking state". Is defined as a case where the stop switch 22 is in the OFF state, and the vehicle is in any one of the high μ road straight traveling state, the high μ road turning state, and the low μ road turning state. As shown in the graph of FIG. 6, when the absolute value of the longitudinal acceleration G _X is the reference acceleration G _N1 or more or the lateral acceleration G _{Y is} the absolute value of the reference acceleration G _L or more. It is defined as a certain case (region indicated by to in the figure), and the case where the vehicle is in the “low μ straight road state” means that the absolute value of the longitudinal acceleration G _X is as shown in the figure. Is smaller than the reference acceleration G _N1 and laterally applied It is defined as a case where the absolute value of the speed G _Y is smaller than the reference acceleration G _L (area indicated by in the figure). That is, in this embodiment, the longitudinal acceleration G _X is used as the vehicle state quantity that reflects the friction coefficient μ of the road surface, and the lateral acceleration G _Y is used as the vehicle state quantity that reflects the strength of the turning state of the vehicle. It has been done.

Then, in this routine, when the vehicle is in the anti-lock control state, the clutch pressure of the center differential clutch 54 is set to 0 and the center differential is set in the free state.
During the anti-lock control, the differential limiting amount of the front and rear wheels is set to substantially 0 to weaken the coupling between the front and rear wheels so that the operation of the anti-lock control device 12 is not hindered.
On the other hand, the vehicle is in the non-braking state or
When the vehicle is traveling straight on the road, the clutch pressure is controlled based on the input signal so that the optimum driving state is realized. That is, normal control for controlling the center differential according to a certain rule is performed. Further, when the vehicle is in any of the high μ road straight traveling state, the high μ road turning state and the low μ road turning state, the clutch pressure is set to the maximum value and the center differential is locked.

In the vehicle braking state, the center differential is locked to prevent the tendency of early locking of each wheel from occurring, but in the present embodiment, the center differential is always locked in the braking state. Instead of being put into a state, it goes straight to a high μ road, turns to a high μ road, and has a low μ.
When the vehicle is in one of the road turning states, the lock state is set, and when it is in the other braking state, that is, the low μ road straight traveling state, the normal control state is set. Vehicle is low μ
When the vehicle is traveling straight on the road, the clutch pressure is made lower than that in the locked state to weaken the coupling between the front and rear wheels. Less than,
The reason for this will be described.

When the vehicle is in a straight traveling state, the four wheel speeds V _W are substantially equal to each other, while in a turning state, the turning radii of the wheels are different from each other, and thus the wheels slip. Wheel speed V _W when rolling on the road without
Are also different from each other. Therefore, even if the four slip amount of the wheel is increased uniformly, the difference increases between the estimated vehicle speed V _SO and the wheel speed V _W of each wheel, to start the antilock control for either wheel There is a strong tendency to be judged as. As described above, at the time of turning braking, the antilock control tends to be started as planned even if the coupling between the front and rear wheels is strengthened. Therefore, in this embodiment, the vehicle is in a turning state, that is, the lateral acceleration G _Y. The center differential is locked on condition that the absolute value of is large.

The antilock control device 12 used together with the distribution control device 10 estimates the vehicle speed V from the wheel speed V _W ,
Antilock control is performed based on it. On the other hand, on low μ roads, it is 4
It is usual that the wheel speed V _W has a strong tendency to fall with respect to the vehicle speed V almost uniformly for each wheel. Therefore, the estimated vehicle speed V _SO in the antilock control device 12 becomes lower than the actual vehicle speed V, the difference from the wheel speed V _W becomes smaller than the original value, and there is a strong tendency that the antilock control is not started unexpectedly. . On the other hand, when the coupling between the front and rear wheels is strong, the tendency that the wheel speed V _W changes substantially uniformly among the four wheels is usually stronger than when the coupling is weak. Therefore, in the present embodiment, the vehicle must be on a high μ road in order to prevent the wheel speeds V _W of the four wheels from decreasing substantially uniformly on the low μ road and the accuracy of the estimated vehicle speed V _SO from deteriorating. , That is,
The center differential is locked on the condition that the absolute value of the longitudinal acceleration G _X is large.

In this embodiment, the lateral acceleration G _Y
Even if the absolute value of is small, the center differential is locked when the absolute value of the longitudinal acceleration G _X is large. This is because the absolute value of the longitudinal acceleration G _X is large. In this case, it is considered that the vehicle is on a high μ road. Therefore, even when the center differential is locked, it is common that the wheel speeds V _{W of the} four wheels do not decrease uniformly during sudden braking. This is because the estimated vehicle speed V _SO may be lower than the actual vehicle speed as compared with the case where the absolute value of the longitudinal acceleration G _X is small.

Next, this routine will be described in detail with reference to FIG.

In each execution of this routine, first, in step S1 (hereinafter referred to simply as S1; the same applies to other steps), the antilock controller 12 is executed.
From the status signal, which is indicative of its operating state, is received, and it is judged from the status signal whether or not the antilock control is being performed. If this is the case this time, the determination is YES, and the clutch pressure is set to 0 in S2 to set the center differential in the free state. Thus, one execution of this routine is completed.

On the other hand, assuming that the antilock control is not being executed this time, the determination in S1 is NO and S3
At, it is determined whether or not the stop switch 22 is in the ON state, that is, whether or not the stop switch 22 detects a brake operation. In S4, it is determined whether the absolute value of the lateral acceleration G _Y is less than or equal to the reference acceleration G _L. Further, in S5, it is determined whether or not the absolute value of the longitudinal acceleration G _X is less than or equal to the reference acceleration G _N1 . This time, the vehicle is in a high μ road straight braking state (Fig. 6).
2)), the high μ road turning braking state (the area shown in the same figure) and the low μ road turning braking state (the area shown in the same figure), that is, the non-braking state. Or, assuming that the vehicle is in a low μ road straight traveling state (area shown by in the figure), the determination in S3 is NO, or the determinations in S4 and S5 are YES,
In S6, the center differential is normally controlled. Thus, one execution of this routine is completed.

On the other hand, this time, assuming that the vehicle is in the high-μ road turning braking state or the low-μ road turning braking state, the absolute value of the lateral acceleration G _Y becomes larger than the reference acceleration G _L. If the determination in S4 is NO, the process proceeds to S7. On the other hand, this time, assuming that the vehicle is in the high μ road straight braking state, the absolute value of the lateral acceleration G _Y becomes equal to or less than the reference acceleration G _L , The determination in S4 is YES, the absolute value of the longitudinal acceleration G _X is larger than the reference acceleration G _N1 , the determination in S5 is NO, and the process proceeds to S7. In any case, S7
At, the clutch pressure is set to the maximum value so that the center differential is locked. Thus, one execution of this routine is completed.

As is apparent from the above description, in this embodiment, the controller 50 of the controllers S3 and S4 of FIG.
The part that executes steps 6 and 6 constitutes one aspect of the "differential limiting amount control means" in the present invention.

[0039] While an embodiment of the present invention have been described in detail with reference to the drawings, without departing from the scope of the appended claims in addition to this, various modifications based on the knowledge of those skilled in the art, facilities improved The present invention can be implemented in such a manner.

[Brief description of drawings]

FIG. 1 is a diagram conceptually showing a configuration of the present invention.

FIG. 2 is a system diagram conceptually showing the structure of a drive torque distribution control device according to an embodiment of the present invention together with the structure of an antilock control device.

FIG. 3 is a plan view for explaining respective detection characteristics of the front-rear G sensor and the lateral G sensor in FIG. 2 and also for explaining the relationship between G _X and G _Y detected by them and the resultant acceleration G _XY . is there.

FIG. 4 is a flowchart showing a drive torque distribution control routine used by the controller of the drive torque distribution control device in FIG.

FIG. 5 is a diagram for explaining a part of the execution content of the drive torque distribution control routine that is closely related to the present invention.

FIG. 6 is a graph for explaining a part of the execution content of the drive torque distribution control routine, which is closely related to the present invention.

[Explanation of symbols]

10 Drive torque distribution control device 12 Anti-lock control device 20 wheel speed sensor 22 Stop switch 24 Front and rear G sensor 26 Horizontal G sensor 30 controller 32 Brake pressure control means 50 controller 52 Clutch pressure control means 54 Center differential clutch

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-110530 (JP, A) JP 62-265030 (JP, A) JP 2-193719 (JP, A) JP 4- 24154 (JP, A) Actually opened 63-22236 (JP, U) Actually opened 61-73430 (JP, U) Actually opened 2-98027 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) B60K 17/35 B60T 8/58

Claims (2)

(57) [Claims] 1. A plurality of brakes, which are provided on each of a plurality of wheels and actuated by hydraulic pressure to suppress rotation of each wheel, and a differential limiting device that limits a differential between front and rear wheels in a drive system, The vehicle speed is estimated based on the wheel speeds of the front and rear wheels whose differentials are limited by the differential limiting device, and each wheel is locked during vehicle braking by using the relationship between the estimated vehicle speed and the wheel speed of each wheel. It is provided in a vehicle equipped with an anti-lock control device that controls the hydraulic pressure of the brake so as not to fall into a state, and by controlling the differential limiting amount of the differential limiting device, the front and rear wheels of the drive torque of the engine are controlled. in the driving torque distribution control device for controlling the distribution ratio of the a when the vehicle braking by actuation of the brake, in the non-operating state of the anti-lock control device, less the
In a straight braking state on a low μ road where the friction coefficient is lower than the reference value , the differential limiting amount of the front and rear wheels is reduced to a value smaller than that in the turning braking state and not zero, and the operation state of the antilock control device is reduced. In
A drive torque distribution control device comprising a differential limiting amount control means for setting the differential limiting amount of front and rear wheels to zero regardless of whether the vehicle is in a straight braking state or a turning braking state. To 2. A further, vehicle, when the friction coefficient is in the straight ahead braking state with high high μ road than the reference value,
2. The drive torque distribution control device according to claim 1, further comprising means for increasing the differential limiting amount of the front and rear wheels more than when the vehicle is in a straight braking state on the low μ road .