JPH06305338A - Power transmission of vehicle - Google Patents

Abstract

PURPOSE:To prevent deterioration of maneuvering stability at braking when differential limiting force of differential devices provided between wheels and between axles are controlled by detecting the low (mu) road surface condition and the brake condition of a vehicle, and reducing the differential limiting force while maintaining it based on the detected result. CONSTITUTION:A transmission 11 coupled with the output side of an engine 10 is connected in order to a transfer 12, and front and rear both propeller shafts 13, 14, and these are respectively connected to center, front, and rear differentials 20, 21, 22. In the respective differentials 20-22, differential limiting force is controlled according to control current supplied to each electromagnetic type variable joint force multiple disc clutch. In this case, a control unit 43 for differentials judges the low (mu) road surface condition based on the respective detected signals of respective wheel speed sensors 30, and judges the brake condition of a vehicle based on the detected signal of a brake switch 31. According to the result, the differential limiting force is reduced while being maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential limiting means for controlling a differential limiting force with respect to a differential device provided between wheels or between axles, and the occurrence of a locked state of the wheels during vehicle braking. The present invention relates to a power transmission device of a vehicle including an anti-lock brake device for prevention.

[0002]

2. Description of the Related Art As is well known, in a vehicle such as an automobile, when the output of the engine is transmitted to the wheels, a difference in rotational speed occurs between wheels due to a difference in wheel locus such as vehicle turning. In order to prevent the occurrence of tire slip and ensure sufficient maneuverability of the vehicle as well, in the middle of the power transmission system from the engine to each wheel side, the rotational speed difference is mechanically affected by the differential action. Is provided with a differential device (differential device, or abbreviated as differential).

That is, in order to absorb the rotational speed difference between the left and right front wheels in a front-wheel drive vehicle, and between the left and right rear wheels in a rear-wheel drive vehicle, the front and rear wheels are used. In the four-wheel drive vehicle, in addition to the differential device between the left and right wheels, a differential device (so-called front differential or rear differential) is provided between the front wheel side and the rear wheel side. Is also provided with a differential device (so-called center differential).

Further, while the differential device is provided between the wheels or between the axles, the differential limiting force for limiting the differential by the differential device is set to a predetermined parameter in order to properly transmit the torque to each wheel. It is known that a differential limiting control device including a variable engagement force clutch for performing control based on the above is provided.

On the other hand, in order to improve safety during vehicle braking by preventing the wheels from locking tendency during vehicle braking and controlling the slip state thereof, the wheels receive sudden braking force. When the wheels are about to lock, the brake pressure is reduced to control the braking force so that the braking force is released. When the risk of wheel locking disappears, the braking pressure is increased to increase the braking force. However, such a series of wheel braking force control is continuously performed until the vehicle stops, for example, a so-called anti-lock brake device (hereinafter referred to as ABS).
(Abbreviated as device) is generally well known.

By installing such an ABS device, it is possible to prevent the wheels from becoming locked or skid during sudden braking even on a so-called low μ road where the friction coefficient μ of the road surface is low. It is possible to secure driving stability and to stop at the shortest braking distance possible.

By the way, in a vehicle equipped with both the ABS device and the differential limiting control device, for example, the center differential is in a differential lock state by the action of the differential limiting control device when the ABS device is activated during vehicle braking. In this case, since the front wheels and the rear wheels rotate integrally and the respective rotation states interfere with each other, the ABS device can detect the independent slip states of the front wheels and the rear wheels. No, and therefore it becomes difficult to control each brake pressure according to its slip condition.

With regard to such a problem, for example, Japanese Patent Laid-Open No.
In the Japanese Patent Laid-Open No. 3-78823, particularly on a low μ road where the ABS device is easy to operate, the differential limiting device controls the operation limiting force to the center differential in a non-operational state to activate the differential mechanism of the center differential, thereby enabling the ABS device. There is disclosed a control device for a vehicle which is capable of sufficiently exhibiting the function of.

[0009]

However, if the differential limiting force by the differential control device is released with the start of braking on a low μ road, for example, turning while pushing the brake pedal will occur. In this case, the steer characteristic (the steering characteristic such as understeer and oversteer) suddenly changes due to the sudden change of the transmission torque to the wheel, which causes a problem that the steering stability deteriorates.

Particularly on a so-called split μ road in which the road surface friction coefficients μ on the left and right wheel sides are significantly different from each other, if the differential limiting force by the differential control device is released with the start of braking, the behavior of the vehicle body will change. There was a problem that the change was remarkable.

In view of the above-mentioned circumstances, the present invention provides a differential limiting means for controlling a differential limiting force with respect to a differential device provided between wheels or between axles, and a lock state of the wheels during vehicle braking. Provided is a vehicle power transmission device including an anti-lock brake device for preventing occurrence of the vehicle power transmission device, which prevents deterioration of steering stability during braking on a low μ road or a split μ road. The purpose is to

[0012]

A power transmission device for a vehicle according to the present invention detects a state in which a road surface friction coefficient μ is low or a road surface friction coefficient μ on each of the left and right wheel sides is significantly different and detects a low μ signal or a split μ. When a road surface condition detecting means for outputting a signal, a braking condition detecting means for detecting a braking condition of the vehicle and outputting a braking signal, and both of the low μ signal or the split μ signal and the braking signal are inputted. And a control means for reducing the differential limiting force with respect to the differential device while maintaining the differential limiting force.

In one mode in which the control means reduces the differential limiting force with respect to the differential device while maintaining the differential limiting force, the differential limiting force is stepwise reduced.

In another mode in which the control means reduces the differential limiting force with respect to the differential device while maintaining the differential limiting force, the differential limiting force is reduced by a predetermined amount and then the differential limiting force is maintained for a predetermined time. I am trying to do it.

[0015]

According to the present invention, when the vehicle is braked on the low μ road or the split μ road, the differential limiting force for the differential device is controlled so as to decrease while being maintained. Sudden changes are prevented, which makes it possible to prevent deterioration of steering stability without impairing ABS performance.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a case in which an embodiment of the present invention is applied to a four-wheel drive vehicle will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing an overall structure of a driving force transmission system of a vehicle according to an embodiment of the present invention. In FIG. 1, a transfer 12 is connected to a transmission 11 connected to the output side of an engine 10, and the transfer 12 is connected to one ends of front and rear propeller shafts 13 and 14, respectively.

The front end side of the front propeller shaft 13 is connected to a front axle 15 via a front differential 21 (hereinafter abbreviated as front differential), and the output of the engine 10 is output from the transmission 11 and the transfer 12. The front propeller shaft 13, the front differential 21, and the front axle 15 are sequentially transmitted to the left and right front wheels 16L, 16R.

The rear end side of the rear propeller shaft 14 is connected to a rear axle 17 via a rear differential 22 (hereinafter abbreviated as rear differential),
The output of the engine 10 is transmitted from the transmission 11 and the transfer 12 to the left and right rear wheels 18L and 18R via the rear propeller shaft 14, the rear differential 22, and the rear axle 17 in that order.

The front differential 21 and the rear differential 22
Is between the left and right front wheels 16L, 16R and the rear wheels 18L, 1
When a rotational speed difference occurs between the 8Rs, the rotational speed difference is mechanically absorbed, and the output of the engine 10 transmitted through the propeller shafts 13 and 14 is transmitted to the front wheels 16L and
When transmitting to 16R and rear wheels 18L and 18R, respectively, left and right front wheels 16L and 16R and rear wheels 18L and 18L,
The torque distribution to 18R is controlled respectively.

Further, the transfer 12 includes front wheels 16
In order to control the torque distribution between the L, 16R side and the rear wheels 18L, 18R side, the center differential 20
(Hereinafter, abbreviated as a center differential) is provided. Each of the front, rear and center differentials 21, 22 and 20 is provided with an electromagnetic fastening force variable multi-plate clutch so that the differential limiting force is controlled in accordance with the control current supplied to this clutch. Is configured.

Each of the wheels 16L, 16R, 18L, 18
A wheel speed sensor 30 for detecting the rotation speed of each wheel is arranged near R, and the detection output (wheel speed signal) of each wheel speed sensor 30 is used as an antilock brake device control unit 41 (hereinafter, It is input to the ABS control unit).

Further, the engine 10 includes
A throttle sensor 32 for detecting the throttle opening degree is attached, and the detection output (throttle opening signal) of the throttle sensor 32 is input to the engine control unit 40.

Further, a brake switch 31 for detecting ON / OFF of the brake is provided on the front side of the vehicle, and the detection output (brake signal) of the brake switch 31 is a differential control unit 43.
Has been entered in. The differential control unit 43 is connected to a manual switch 44 for selecting a diff lock mode and a battery 45.

In addition to the brake signal from the brake switch 31, the throttle opening signal from the throttle sensor 32 is input to the differential control unit 43, and the ABS device is operated from the ABS control unit 41. ABS data signal indicating whether or not each wheel 16L, 16R,
Wheel speed signals representing the rotational speeds of 18L and 18R are input. Further, a mode signal is input from the manual switch 44.

Based on these input signals, the differential control unit 43 determines whether the brake switch 31 is turned on or whether the ABS device is operating, and based on the determination result, It is determined whether the normal control or the differential limiting force reduction control is executed, and the control current values to be supplied to the front, rear and center differentials 21, 22 and 20 are calculated and supplied. . Then, in accordance with the supplied control currents (front differential current If, rear differential current Ir, and center differential current Ic), the differentials 21 and 22 are supplied.
The differential limiting force (locking force) of 20 and 20 is controlled.

In the above-mentioned normal control, the differential lock mode selected by the manual switch 44 is set to A,
There are four modes of C, R, and F, and when both the ABS signal and the brake signal are OFF, in the A mode, I
f = 0 (unlocked) and Ic and Ir are controlled,
In C mode, If = 0, Ic = maximum value (complete lock)
Therefore, only Ir is controlled. In R mode,
If = 0, Ic = Ir = maximum values, and in F mode,
If, Ic, and Ir are all maximum values.

Next, a vehicle brake control system according to this embodiment will be described.

FIG. 2 is a system configuration diagram schematically showing the overall configuration of the vehicle brake control system. As shown in this diagram, each wheel 16L, 16R, 18L, 1
8R includes brake devices 61L and 61L that are composed of a disc that rotates integrally with these wheels and a caliper that receives the supply of braking pressure to brake the rotation of the disc.
R, 62L, 62R are provided respectively, and a booster 67 for increasing the stepping force of the brake pedal 66 by the driver in order to perform a braking operation of these brake devices 61L, 61R, 62L, 62R, and this doubler. A brake control mechanism 65 having a master cylinder 68 that generates a braking pressure according to the stepping force increased by the force device 67 is provided.

The front wheel braking pressure supply line 69 led from the master cylinder 68 is branched into two paths, and these front wheel branch braking pressure lines 69L and 69R are applied to the brake devices 61 of the left and right front wheels 16L and 16R.
The first front wheel branch braking pressure line 69L, which is connected to the L and 61R calipers and communicates with the left front wheel 16L brake device 61L, is composed of an electromagnetic relief valve and an electromagnetic relief valve. Valve unit 70
Is provided.

Similarly to the first valve unit 70, the other front wheel branch braking pressure line 69R leading to the brake device 61R for the right front wheel 16R has a second valve unit including an electromagnetic on-off valve and a relief valve. 71 is installed.

On the other hand, the rear wheel braking pressure supply line 72 led from the master cylinder 68 is connected to the first and second brake wheels.
A third valve unit 73 similar to the valve units 70 and 71 is installed, and the rear wheel braking pressure supply line 72 is branched into two paths downstream of the third valve unit 73, and these Branch braking pressure line 72 for wheels
L and 72R are connected to the calipers of the brakes 62L and 62R on the left and right rear wheels 18L and 18R, respectively.

That is, in the brake control system of this embodiment, the first channel that variably controls the braking pressure of the brake device 61L on the left front wheel 16L by the operation of the first valve unit 70 and the right channel by the operation of the second valve unit 71. Brake device 61R for front wheel 16R
The second channel for variably controlling the braking pressure of the rear wheel 18L, 18R
And a third channel for variably controlling the braking pressure of both brake devices 62L and 62R in the above.
The third channel is controlled independently of each other.

The brake control system includes an A as a control device for controlling the first to third channels.
A BS control unit 41 is provided, and the control unit 41 turns on / off the brake pedal 66.
A brake signal from a brake switch 31 that detects OFF and a wheel speed signal from each wheel speed sensor 30 that detects the rotation speed of each wheel are input, and a braking pressure control signal corresponding to these signals is first input. ~ Third valve unit 7
By outputting to 0, 71, 73 respectively, braking control for slips of the left and right front wheels 16L, 16R and rear wheels 18L, 18R, that is, ABS control, is performed by the first to third.
It is designed to be performed in parallel for each channel.

That is, the ABS control unit 41 determines the first to third valve units 7 based on the wheel speed indicated by the wheel speed signal from each wheel speed sensor 30.
The open / close valves and the relief valves at 0, 71, 73 are controlled by the duty control so that the front wheels 16L,
The braking force is applied to the 16R and the rear wheels 18L and 18R.

The first to third valve units 70, 7
The brake oil discharged from the relief valves 1 and 73 is returned to the reservoir tank 68a of the master cylinder 68 via a drain line (not shown).

In the ABS non-controlled state, the braking pressure control signal is not output from the ABS control unit 41, so that the relief valves in the first to third valve units 70, 71 and 73 are shown as shown. Are each held closed, and each unit 70, 71, 7
The open / close valves of No. 3 are kept open, and the master cylinder 68
The braking pressure generated in 1) is applied to the left and right front wheels 16 via the front wheel braking pressure supply line 69 and the rear wheel braking pressure supply line 72.
L, 16R and the rear wheels 18L, 18R are supplied to the braking devices 61L, 61R, 62L, 62R, and braking forces corresponding to these braking pressures are applied to the front wheels 16L, 16L.
It is directly applied to the R and the rear wheels 18L and 18R.

Next, the differential limiting force control routine executed by the differential control unit 43 will be described with reference to the flowcharts of FIG.

First, in S1 of FIG. 3, the above various input signals are read, and the current value (I value) corresponding to the differential limiting force for each differential 21, 22, and 20 is determined (S2).

Next, it is judged whether or not the road surface μ is low μ (S3). The following method is known as an example of a known method for determining the road surface μ. That is, on low μ roads,
Since wheels with a small shared load tend to slip,
The rotation speed difference between the front and rear wheels is obtained from the front wheel rotation speed and the rear wheel rotation speed, and the allowable rotation speed difference is set in advance for each throttle opening, and the actual rotation speed difference is set in advance. If it is larger than the difference, it is determined to be a low μ road. If the result of such determination is a low μ road (S3, YES),
The low μ road flag F is set to 1 (S4), and if the medium μ road is high (S3, NO), F = 0 is set (S5).

Next, it is judged whether or not the brake is ON (S
6) If the brake is ON (S6, YES), low μ
It is determined whether the road flag F is 1 (S7). Then, during non-braking (S6, NO) or during braking (S6, Y
Even if ES), the low μ road flag F = 0 (S7, N
For O), the normal control described above is executed (S8). When braking (S6, YES) and the low μ road flag F is 1 (S7, YES), the differential limiting force lowering control described below is executed (S9).

The same control is performed when the road surface is a split μ road, but in that case, step S3 in FIG.
Instead of this, step S3 ′ for determining whether or not the road is the split μ road is provided, and the low μ road flag F may be read as the split μ road flag. As an example of this split μ road determination method, the rotation speed difference between the left and right wheels is obtained from the left wheel rotation speed and the right wheel rotation speed, and the allowable rotation speed difference is preset for each throttle opening. If the actual difference in the number of revolutions is larger than the preset difference in the number of revolutions, there is a method of determining the split μ road.

An example of the differential limiting force lowering control routine is shown in the flowchart of FIG. 4 and the timing chart of FIG. 5. In the flowchart of FIG. 4, first, the current current value (I value) for differential limiting is present. (S11),
A timer for counting a preset short predetermined time T _N (see FIG. 5) is started (S12). Then, it is determined whether or not the predetermined time T _N has passed (S13), and if the predetermined time T _N has not passed (S13, NO), the timer is incremented (S14), and then the brake is turned on. It is determined whether or not the state is continued (S15),
If the brake is not ON (S15, NO), this control routine ends.

On the other hand, if the brake is ON (S15,
YES), it is determined whether the ABS device is turned on (S16), and while the ABS device is not turned on (S1).
6, NO), the process returns to S13, and the determination as to whether or not the predetermined time T _N has elapsed is repeated. Then, when it is determined that the predetermined time T _N has passed (S13, YES), the timer is reset (S17), and the current I value is the predetermined minute value set as the current reduction amount. It is determined whether or not ΔI (see FIG. 5) or more (S18). If ΔI or more (S18, YES), ΔI is subtracted from the current I value (S19), and the I value is output. (S20). Then, while the I value is not 0 (S21, NO), the process returns to step S12 and the above-described flow is repeated.

Next, when the I value is less than the minute value ΔI (S18, NO), the I value is set to 0 (S22),
The I value is output (S23), and this control routine ends. Also, when the ABS device is turned on (S1
6, YES), the I value is set to 0 (S22), the I value is output (S23), and the control routine ends.

By such control, when the brake pedal is depressed on the low μ road or the split μ road,
As shown in FIG. 5, the current value (I value) according to the differential limiting force
Is reduced stepwise, so that it is possible to reduce it while maintaining the differential limiting force.

Another example of the differential limiting force lowering control routine is shown in the flowchart of FIG. 6 and the timing chart of FIG. In the flowchart of FIG. 6, first, the current value (I value) for differential limiting is input (S31),
Next, it is determined whether or not this I value is greater than or equal to a predetermined current reduction amount I ₁ (see FIG. 7) (S32), and if it is greater than or equal to I ₁ (S32, YES), the current I value is changed to I ₁ Is subtracted (S33), the I value is output (S34), and at the same time, the timer is started (S35), and it is determined whether a predetermined time T _M (see FIG. 7) has elapsed (S36). And
If the predetermined time T _M has not elapsed (S36, N
O), the timer is incremented (S37), and then it is determined whether the brake ON state continues (S3).
8) If the brake is not ON (S38, NO), this control routine ends.

On the other hand, if the brake is ON (S38,
YES), it is determined whether the ABS device is turned on (S39), and while the ABS device is not turned on (S3).
(9, NO), the process returns to S36 and the determination of whether the predetermined time T _M has elapsed is repeated. When it is determined that the predetermined time T _M has elapsed (S36, YES), the timer is reset (S40), and the I value is set to 0 (S4).
1), the I value is output (S42), and this control routine ends. Also, when the ABS device is turned on (S39, YES), the I value is set to 0 (S41), and the I
A value is output (S42) and this control routine ends.

By such control, when the brake pedal is depressed on the low μ road or the split μ road,
As shown in FIG. 7, the current value (I value) according to the differential limiting force
Is once decreased by a predetermined value I ₁ , and then the current value is held for a predetermined time T _M, so that it can be decreased while maintaining the differential limiting force.

As described above, according to the above-mentioned embodiment, the low μ
When the vehicle is braked on a road or on a split μ road, the differential limiting force for the differential device is controlled to decrease while being maintained, so that a sudden change in the steer characteristic is prevented, and thus ABS performance is not impaired. It is possible to prevent deterioration of steering stability.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an overall configuration of a driving force transmission system of a vehicle according to an embodiment of the present invention.

FIG. 2 is a block diagram of a vehicle brake control system according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a control routine.

FIG. 4 is a flowchart showing an example of a differential limiting force lowering control routine.

5 is a timing chart used to explain the operation of the control routine of FIG.

FIG. 6 is a flowchart showing another example of the differential limiting force lowering control routine.

7 is a timing chart used to explain the operation of the control routine of FIG.

[Explanation of symbols]

 15 Front Axle 16L, 16R Front Wheel 17 Rear Axle 18L, 18R Rear Wheel 20 Center Differential 21 Front Differential 22 Rear Differential 41 ABS Control Unit 43 Differential Control Unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroaki Higashi 3-1, Shinchi Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Kazuaki Nada 3-3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Within the corporation

Claims (6)

[Claims] 1. A differential limiting means for controlling a differential limiting force with respect to a differential device provided between wheels or between axles, and an antilock for preventing a wheel from being locked during vehicle braking. In a power transmission device for a vehicle equipped with a braking device, a road surface condition detecting means for detecting a condition of a low road friction coefficient μ and outputting a low μ signal, and a braking device for detecting a braking condition of the vehicle and outputting a braking signal. And a control means for reducing the differential limiting force while maintaining the differential limiting force with respect to the differential device when both the low μ signal and the braking signal are input. Power transmission device for a vehicle. 2. The power transmission device for a vehicle according to claim 1, wherein the control means reduces the differential limiting force in a stepwise manner. 3. The power transmission system for a vehicle according to claim 1, wherein the control means maintains the differential limiting force for a predetermined time after reducing the differential limiting force by a predetermined amount. 4. A differential limiting means for controlling a differential limiting force with respect to a differential device provided between wheels or between axles, and an anti-lock for preventing a locked state of wheels during vehicle braking. In a vehicle power transmission device including a braking device, a road surface condition detecting means for detecting a condition where road surface friction coefficients μ on the left and right wheel sides are significantly different and outputting a split μ signal, and a vehicle braking condition are detected. A braking state detecting means for outputting a braking signal; and a controlling means for reducing the differential limiting force for the differential device while maintaining the differential limiting force when both the split μ signal and the braking signal are input. A power transmission device for a vehicle characterized by the following. 5. The power transmission device for a vehicle according to claim 4, wherein the control means reduces the differential limiting force stepwise. 6. The power transmission device for a vehicle according to claim 4, wherein the control means maintains the differential limiting force for a predetermined time after reducing the differential limiting force by a predetermined amount.