JP3223629B2 - Braking force 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 vehicle braking force control device.

[0002]

2. Description of the Related Art As a braking force control device, there is one described in, for example, Japanese Patent Application Laid-Open No. 56-53944.
This is to start the anti-skid control when the wheel deceleration reaches a predetermined deceleration during braking of the vehicle. Anti-skid control, for example, for low μ
It is effective in preventing wheel lock when braking on the road.

[0003]

However, there is room for improvement in such control in consideration of the following points. That is, when the vehicle is traveling on a rough road, an irregular road, or the like, the wheel deceleration reaches the predetermined deceleration, so that the anti-skid control starts, and the brake hydraulic system is controlled. As a result, even when the brake pedal is depressed, the wheel cylinder hydraulic pressure is not transmitted from the master cylinder side, and the brake force may be insufficient.

In view of the above, the present invention has improved braking force control for controlling the fluid pressure of a wheel cylinder to at least one of pressure reduction, holding, and pressure increase based on a wheel speed detection signal. A braking force control device capable of appropriately suppressing early operation of undesired control that may cause a braking force shortage even on a rough road or the like and increasing the effectiveness of braking force control. It is intended to provide.

[0005]

According to the present invention, the following braking force control device is provided (FIG. 1). A master cylinder that generates brake fluid pressure by driver's operation, a wheel cylinder that is disposed on each wheel and generates braking force by supplying brake fluid pressure, and wheel speed detection means that detects the rotational speed of the wheel. And a control means for controlling the fluid pressure of the wheel cylinder to at least one of pressure reduction, holding, and pressure increase based on the detection signal of the wheel speed detection means, wherein the hydraulic pressure of the master cylinder is detected. A master cylinder pressure detecting means, and a threshold setting means for setting a threshold value when the control means starts operating, a first threshold value at which the control means starts operating as a threshold value set by the threshold setting means. And a second threshold value that is set so that the control means is unlikely to start operating when the master cylinder pressure is zero or extremely low pressure, and A braking force control device comprising a first threshold value with the change to become provided a third threshold value which varies toward the second threshold.

[0006]

In the present invention, the control means is provided on each wheel based on the detection signal of the wheel speed detection means for detecting the rotation speed of the wheel, and is provided on each wheel to generate a braking force by supplying brake fluid pressure. Is controlled to at least one of pressure reduction, holding and pressure increase, and further, master cylinder pressure detection means for detecting a hydraulic pressure of a master cylinder that generates brake hydraulic pressure by operation of a driver, and the control means Providing a threshold setting means for setting a threshold at the start of operation, and, as a threshold set by the threshold setting means,
A first threshold value at which the control means starts operating, a second threshold value set such that the control means does not easily start operating at a master cylinder pressure of zero or extremely low pressure, and a first threshold value with a change in the master cylinder pressure. And a third threshold value that changes from the threshold value to the second threshold value.

Thus, a threshold value for controlling the wheel cylinder pressure to decrease, hold, and increase the pressure by the control means is set by the master cylinder pressure, and the threshold value can be switched in a direction in which control is difficult to be performed at an extremely low pressure. Even when the vehicle is traveling on a rough road, the threshold value for starting the anti-skid control can be changed based on the master cylinder pressure to a direction in which the control is difficult to start when the master cylinder pressure is zero or extremely low pressure. In addition to preventing the early operation of the anti-skid control due to rough road traveling and avoiding a situation where the braking force tends to be insufficient, the threshold value is changed from the first threshold value according to the change of the master cylinder pressure. If the third threshold is set to change toward the second threshold, the control state does not change abruptly even if the master cylinder pressure changes. There can be realized. Here, FIG. 5 is a diagram to be referred in later, speaking with reference to this, the driver slowly depressing the master cylinder pressure and the brake pedal (P _M) is increased slowly in the third threshold value region when passing through the (area), by the action of such regions, since moves gradually to the state easy to enter from the anti-skid control is difficult to enter the state, the second threshold value (alpha ₀₎
In this case, it is easier to enter the anti-skid control than in the case of (area), and it is possible to prevent wheel lock on an icy road or the like. At the same time, the area (area) in which the first threshold value (α ₁ ) is taken enters the anti-skid control more frequently. Therefore, it is possible to prevent the brake force from becoming insufficient even on a rough road, and even if the master cylinder pressure (P _M ) changes, the control state does not change suddenly, and appropriate control can be realized.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows the configuration of an embodiment of the apparatus of the present invention.
In this embodiment, the vehicle to be applied is a four-channel vehicle capable of controlling the left and right brake fluid pressures of the front and rear wheels.

In the drawings, 1L and 1R denote left and right front wheels, 2L and 2R denote left and right rear wheels, 3 denotes a brake pedal, and 4 denotes a tandem master cylinder (M / C). In addition, 3a is a booster as a booster of a brake, and 4a is a reservoir. Each of the wheels 1L, 1R, 2L, 2R is provided with a wheel cylinder 5L, 5R, 6L, 6R for applying a braking force to each wheel by frictionally holding a brake disk by supplying hydraulic pressure. When (W / C) is supplied with hydraulic pressure from the master cylinder 4, each wheel is individually braked.

In the present embodiment, the brake fluid pressure (braking fluid pressure) system of the braking device includes a front wheel brake system 7F from the master cylinder 4 and pipelines 8F, 9F, 10F, and a hydraulic pressure control valve 1.
Left and right front wheel cylinders 5L, 5F after 1F, 12F
R, the rear wheel brake system 7R from the master cylinder 4 is connected to the pipelines 8R, 9R, 10R and the hydraulic pressure control valve 11
R, 12R, left and right rear wheel cylinders 6L, 6R
To reach.

[0011] Hydraulic pressure control valves 11F, 12F, 11R, 12
R is a wheel cylinder 5L, 5 of the corresponding wheel, respectively.
By individually controlling the brake fluid pressure toward R, 6L, 6R,
Used for anti-skid (ABS) control.
At the FF position, the brake fluid pressure is increased toward the original pressure at the pressure increase position shown in the figure, and the brake fluid pressure is increased or decreased without increasing or decreasing the first stage ON brake fluid pressure, and the second stage ON brake fluid pressure is increased. It is assumed that a decompression position is reached where the pressure is released to a part of the reservoirs 13F and 13R (reservoir tanks) and lowered.

The control of these hydraulic pressure control valves is performed by currents (control valve driving currents) I _{1 to} I ₄ from a controller (control unit) described later to the solenoids of the corresponding valves, and currents I _{1 to} I ₄ Is 0 A (pressure increase control signal), the pressure increase position, and when the currents I _{1 to} I ₄ are 2 A (hold control signal), the pressure increase position, and the currents I _{1 to} I ₄ are 5 A (pressure decrease control signal). At this time, it is assumed that the pressure reducing position is set.

The brake fluid in the reservoirs 13F, 13R is supplied to the pump
F and 14R return to the pipelines 8F and 8R, and return to the accumulators 15F and 15R of these pipelines for reuse. Thus, in the above-mentioned brake hydraulic system, the master cylinder 4 that generates the brake hydraulic pressure by the driver's depressing operation of the brake pedal 3, and the wheel cylinders 5L, 5R that generate the braking force by supplying the hydraulic pressure from the master cylinder, Between 6L and 6R, the hydraulic pressure control valve 11F, 1
2F, 11R, and 12R are interposed, and the fluid pressure of each wheel cylinder can be switched to three states of pressure reduction, holding, and pressure increase by these control valves.

The hydraulic pressure control valves 11F, 12F, 11R, 12
R is ON / OFF controlled by a controller 16, and the controller 16 controls the brake pedal 3 when the brake pedal 3 is depressed.
Signal from the brake switch 18 to perform N, wheels 1L, 1
Signals from wheel speed sensors 19 to 22 for detecting the rotational peripheral speeds (wheel speeds) V _{w1 to} V _w4 of R, 2L, and 2R are input, respectively.

Further, the fluid pressure P _M in the master cylinder 4 to the controller 16 (front wheel system pressure P _M1, the rear wheels based fluid pressure P _M2)
Signals from the hydraulic sensors 33 _1, 33 ₂ to be detected is inputted to. As for the detection of the master cylinder pressure, for example, the detection may be performed by only the front wheel system and represented. The signal from the wheel speed sensor is used for anti-skid control performed by the controller 16, and the output of the master cylinder hydraulic pressure sensor is used as an input value for setting a variable control threshold in the control as described later.

The controller 16 includes an input detection circuit, an operation processing circuit, a storage circuit for storing various control programs executed by the operation processing circuit, operation results, and the like.
It comprises a microcomputer including an output circuit for supplying a control signal to the hydraulic control valve. In the arithmetic processing circuit,
Based on predetermined input information input from the sensors, according to a control program of anti-skid control described later,
The mode of pressure increase, pressure reduction, and holding is determined, and a control signal corresponding to the mode is output to the hydraulic pressure control valve.

In the anti-skid control, basically, in the four-channel, four-sensor system as in this embodiment, a wheel speed detection value is obtained for each wheel, and the pressure is reduced so that the slip amount of the corresponding wheel falls within a predetermined range. By performing the wheel cylinder pressure control in the holding and pressure increasing mode (skid cycle), the individual wheels can be subjected to anti-skid control, whereby the maximum braking efficiency can be achieved for each wheel.
Avoid wheel locks.

The controller 16 controls the wheel cylinder pressure to increase, hold, and reduce the pressure based on the detection signal from the wheel speed sensor in this manner. In monitoring the pressure and setting a variable control threshold value in the anti-skid control performed by the controller 16 as described above and described later, the output of the master cylinder pressure sensor (detection of the master cylinder pressure sensor) Signal) as an input value, a threshold for starting anti-skid control is set as a value corresponding to the master cylinder pressure, and the set threshold is based on the detected master cylinder pressure, and is set to the master cylinder pressure P _M At very low pressures including zero, the control is changed in a direction in which control is difficult to enter. To return gradually the normal threshold value (alpha ₁₎ in accordance with the over increase in cylinder pressure P _M), with such a characteristic, it varied according to the master cylinder pressure P _M.
Here, as will be described later, the normal threshold value can be set with emphasis on the effect of anti-skid control (ABS control) on a low μ road. The controller 16 also executes threshold value change control that changes in accordance with the master cylinder pressure.

In the storage circuit of the controller 16, in addition to the above-described anti-skid control program, for example, a threshold setting map (see FIG. 5) for such a threshold change process applied by the program, and an ABS control map for mode determination (see FIG. 5). 6 can be stored in advance.

FIGS. 3 and 4 are flowcharts showing an example of a braking force control program including the above-described threshold value changing process executed by the controller 16, and this program is executed at regular intervals. In FIG. 3, first, step 1
00, wheel speed sensor, based on the output of the master cylinder pressure sensor, read the wheels 1L, 1R, 2L, wheel speed V _wj of 2R (V _w1 ~V _w4), the master cylinder pressure P _M, respectively. Subsequent step 101, each such step execution, seeing the threshold value setting map that is stored in advance in the memory circuit, the search of the control threshold value according to the read master cylinder fluid pressure P _M at that time, the determination process Execute.

FIG. 5 shows an example of a threshold setting map applicable to such processing. In this example, a control threshold α (m / s
² ) relates specifically to the reference values of the wheel acceleration and the wheel acceleration as the control parameters of the control map (ABS control table) of the hydraulic pressure control valve shown in FIG. The provision of the above processing is performed by setting the hydraulic pressure control threshold value in accordance with the master cylinder pressure, changing the threshold value to a direction in which control is difficult to enter at an extremely low pressure including zero, and gradually increasing the hydraulic pressure in accordance with an increase in the hydraulic pressure. In order to return to the normal threshold value, in the illustrated example, the control threshold value α is, as a predetermined value, a normal control threshold value α ₁ (first threshold value) and a lower value α ₀ (second threshold value). ) Is determined, and takes a value α _{0 in a} region where the master cylinder pressure P _M (Kgf / cm ² ) is low, and a value in the range between the value α ₀ and the value α ₁ (a Α data is set so as to take a third threshold value) and to take a value α _{1 in the} region, with the characteristic of the tendency as shown in the figure.

After obtaining α in accordance with the master cylinder pressure P _M , every time step 103 is executed, the retrieved value α is applied as a reference wheel acceleration value to execute steps 110 to 113 as shown in FIG. The hydraulic pressure control routine is executed. In the hydraulic control routine, the wheel acceleration (differential value of the value V _wj ) is determined for each wheel based on the read wheel speed V _wj as in a known anti-sud control method using the slip amount and the wheel acceleration as parameters. , The slip amount is calculated, and the calculated slip amount and wheel acceleration are applied to the ABS control table (step 110).
Pressure increase, hold, and pressure reduction (Step 1)
11, 112, 113) The braking force is adjusted. In this case, the search value α is used as a reference value with which the calculated wheel acceleration is to be compared, and the wheel acceleration reference value is changed.

As shown in FIG. 6, with respect to the wheel acceleration, a reference value α ₂ and another reference value on the negative side are set, and a mode pattern as shown in the drawing is determined. By comparing with the reference value,
The anti-sood control is executed according to the control pattern of the control table. In this control, in this case,
When applicable, the negative reference value of the wheel acceleration is variable in the range of α _{0 to} α ₁ corresponding to the master cylinder pressure, and the control of the hydraulic pressure control valve is performed in this manner. You. For example, if the calculated wheel acceleration is lower than the variable reference wheel acceleration, the wheel cylinder pressure is held as a locking tendency, the pressure is reduced if the wheel is still locked, and the pressure is increased if the wheel speed is restored. Is controlled.

According to the above control, the control threshold value can be appropriately changed by the master cylinder hydraulic pressure.
Prevention of early operation of the hydraulic pressure control valve due to stepping on the driver who does not recognize that the driver is stepping on the brake pedal 3 or bad stepping when it is stepping slightly, It is possible to achieve compatibility with hydraulic pressure control. More specifically, referring to FIGS. 5 and 6, as shown in FIG. 5, in the area at the time of slow braking (the stepping on or the stepping state as described above), even if the wheel is on a bad road. The threshold α is as low as α = α ₀ even if a rapid decompression occurs,
That is, it is in a state where it is difficult to maintain the liquid pressure control and enter the pressure reduction state (see α _{0 in} a broken line state in FIG. 6). Therefore, at this time, the normal brake (in FIG. Is determined).

On the other hand, in the region where the driver depresses the brake pedal 3 more, or in the region, the following is obtained. That is, in the region, according to the master cylinder pressure P _M, relates threshold alpha, as the control valve early operation of the rough road suppress this, and on the other hand, slow motion in frozen road or the like -
In order to prevent this, the lock is gradually increased in the range of α ₀ to α to α ₁ to prevent this, and in the region, α = α ₁ (predetermined Value). Here, as the α ₁ value itself, AB on a low μ road
The effect of the S control can be set with emphasis.

In this manner, as shown in the ABS control table of FIG. 6, in the region of FIG. 5, the reference wheel acceleration, which is the threshold value, becomes a value α ₀ (second threshold value). And the holding mode zone becomes narrower. This means that the ABS control is in a direction in which it is difficult to operate. In contrast, in the region, according to the master cylinder pressure P _M, α ₀ α ₁ from (second threshold value)
(The first threshold), gradually increasing the holding mode zone, and in the region, the reference value of the wheel speed acceleration as the threshold returns to the above-described normal state of the value α ₁ (the first threshold). become.

Thus, in this embodiment, the threshold α for starting the anti-skid control is set to the master cylinder pressure P _M
The basis, when the master cylinder pressure P _M is zero or very low pressure, it is possible to realize a control for changing the hard direction starting control, therefore, traveling the vehicle rough road or illegal road or the like, the evil Undesirable early operation of the anti-skid control due to running on the road or the like is prevented, and in such a case, the driver needs to brake from, for example, a stepped state, and the wheel cylinder is moved from the master cylinder side even though the brake pedal is depressed. A state in which the hydraulic pressure is not transmitted and the hydraulic pressure becomes insufficient can be solved.

FIG. 7 shows a wheel speed sensor, a brake switch (S / W), a controller by a microcomputer which receives signals from these sensors and outputs a hydraulic pressure control signal, and a fluid operated by the output control signal. FIG. 10 shows a control time chart of a braking force control device including a pressure control valve and in which a program as shown in FIG. 8 is formed. This does not have the control as described above. That is, FIG. 7A shows the transition of the wheel speed, and FIG. 7B shows the transition of the differential change rate. The comparison value α ₁ in FIG. 7B does not depend on the master cylinder pressure as shown in FIG. 7 (c) and (d).
Fig. 3 shows the timing of switching between the pressure reduction, holding, and pressure increase modes in such a case, and changes in the master cylinder pressure and the wheel cylinder pressure.

The following is a comparison between this and the control according to the present embodiment. As shown in the program of FIG. 8, in this case, the determination of the fluid pressure control is performed based on the brake switch signal, and the brake switch is turned off.
If so, the hydraulic pressure control is not performed. When it is determined that the brake switch signal is OFF by looking at the ON / OFF state of the brake switch signal, the brake fluid pressure control routine is passed, and in this state of the brake switch OFF, if the brake switch signal is OFF, as shown in FIGS. ), Even if there is a sharp drop in wheel speed,
If the brake hydraulic pressure control routine is executed, the early operation of switching the hydraulic pressure control valve from the pressure increasing position to the holding position and the pressure reducing position as shown in FIG. 7C does not occur.

On the other hand, a scene in which the driver predicts braking and only puts his foot on the brake pedal to prepare for the braking may occur while the vehicle is running, and the master cylinder pressure becomes zero (see FIG. 7). (Refer to (d)), but when the brake switch is ON or at extremely low pressure (for example,
If the vehicle is suddenly decelerated on a rough road as shown in FIGS. 7A and 7B at a pressure of about 0 to 5 Kgf / cm ² with a slight step, the brake fluid pressure shown in FIG. in the control routine at the time below a predetermined value alpha ₁ as shown in FIG. 7 (c), the switching of the holding position of a liquid pressure control valve to the pressure increase position of normal, even switched to pressure reducing position is performed, Thus, the hydraulic control valve is operated. Then, in this case, if the driver who had put his foot on the brake pedal depresses the brake pedal with the intention of braking at the timing as shown in FIG. However, even when the driver starts to step on the wheel, the wheel cylinder pressure changes as shown in the figure against the rise in the master cylinder pressure caused by this, and as a result, in such a situation, the driver's intended It is difficult to obtain a braking force. On the other hand, in the present embodiment, it is possible to cope with the above-described situation, and it is possible to avoid a state in which the wheel cylinder hydraulic pressure is not transmitted from the master cylinder side and the hydraulic pressure becomes insufficient, as described above. It is.

A sensor for detecting a wheel speed and a controller for operating a hydraulic control valve in accordance with a slip state are provided. The sensor for detecting the hydraulic pressure of the master cylinder is used to operate the hydraulic control valve in accordance with a road surface condition. The present control that can change the threshold value to be applied can be used other than the above method. For example, in the embodiment, the threshold value α for the reference wheel acceleration is changed. There is no hindrance to setting a threshold value for the rate λ and changing the threshold value λ.

[0032]

According to the present invention, in the braking force control for controlling the fluid pressure of the wheel cylinder to at least one of pressure reduction, holding, and pressure increase based on the wheel speed detection signal, the master cylinder has a threshold value for starting the control. When the master cylinder pressure is zero or extremely low based on the pressure, the control can be appropriately changed to a direction in which control is difficult to start. Premature operation can be prevented, and it is possible to prevent the braking force from becoming insufficient. Moreover, according to the present invention, the control means for performing the so-called anti-skid control for preventing the wheel lock is used as a threshold when the control is started.
With the increase of the master cylinder pressure, from the second threshold value that is set so that the anti-skid control is difficult to enter, toward the first threshold value that can be set as a normal value so that the anti-skid control enters on the low μ road A variable third threshold can be provided, so that when the driver depresses the brake pedal slowly and the master cylinder pressure slowly increases and passes through the third threshold region, the action of such region allows the anti-skid Since the state gradually shifts from a state where control is difficult to enter to a state where control is easy to enter, it is easier to enter anti-skid control than when the second threshold is taken, and it is possible to prevent wheel lock on icy roads and the like, and at the same time take the first threshold. Since the anti-skid control is not entered as often, it is possible to prevent the brake force from becoming insufficient even on rough roads, and to reduce the master cylinder pressure. It is varied, control state is not a sudden change,
Appropriate control can be realized. Preventing early operation of the control due to a bad road or the like and achieving sufficient controllability when necessary enhances the effectiveness of such braking force control.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a braking force control device according to the present invention.

FIG. 2 is a system diagram of a braking force control device according to one embodiment of the present invention.

FIG. 3 is a partial flowchart showing an example of a braking force control program executed by a controller.

FIG. 4 is another partial flowchart.

FIG. 5 is a diagram showing an example of a threshold setting map applicable to the program.

FIG. 6 is a diagram showing an example of a hydraulic control map.

FIG. 7 is an example of a time chart according to a comparative example shown in comparison with the present embodiment.

FIG. 8 is a control flowchart of the comparative example.

[Explanation of symbols]

 1L, 1R Left and right front wheels 2L, 2R Left and right rear wheels 3 Brake pedal 4 Master cylinder 5L, 5R, 6L, 6R Wheel cylinder 11F, 11R, 12F, 12R Hydraulic pressure control valve 16 Controller 18 Brake switch 19-22 Wheel speed sensor

Continuation of the front page (72) Inventor Shinji Matsumoto 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-63-184557 (JP, A) JP-A-2-141356 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B60T 8/32

Claims (1)

(57) [Claims] 1. A master cylinder for generating brake fluid pressure by operation of a driver, a wheel cylinder disposed on each wheel for generating a braking force by supplying brake fluid pressure, and detecting a rotational speed of the wheel. A braking force control device comprising: a wheel speed detection unit; and a control unit that controls a fluid pressure of a wheel cylinder to at least one of pressure reduction, holding, and pressure increase based on a detection signal of the wheel speed detection unit. as for the master cylinder pressure detecting means for detecting the fluid pressure, pre-SL control means provided with a threshold value setting means for setting a threshold value at the time of starting operation, the threshold set by the threshold value setting means, said control means operating a first threshold value for starting, a second threshold value by the master cylinder pressure is the control means at the zero and extremely low pressure is set so as difficult to start the operation, Ma As the star cylinder pressure changes, the second
A third threshold value that changes toward the threshold value .