JP4129222B2 - Brake control device - Google Patents

Description

  The present invention belongs to the technical field of a brake control device that controls the brake pressure of each wheel and controls the distribution of front and rear brake torque in 4WD.

In a conventional 4WD vehicle, as the longitudinal acceleration detected by the longitudinal acceleration sensor increases to the negative side and the degree of deceleration increases, the restraint torque of the center differential is increased, and the braking force is distributed along with the torque distribution to the front and rear wheels. (For example, refer to Patent Document 1).
JP 2002-87104 A (page 2-6, full view)

  However, in the conventional brake control device, the brake fluid pressure is maintained or reduced when a rear slip occurs, or the vehicle deceleration is detected and the 4WD fastening force is increased. Will occur and the feeling will deteriorate.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a brake control device capable of preventing excessive operation of the 4WD coupling.

In order to achieve the above-mentioned object, a solenoid valve that adjusts the brake hydraulic pressure supplied to the wheels, a 4WD coupling that can linearly adjust the fastening torque of the front and rear axles, and a deceleration state of the vehicle are detected to detect brake torque. In a control device that performs front-rear distribution,
Based on the difference between the front wheel speed and the rear wheel speed,
When the wheel speed difference is smaller than the first control threshold, the brake control is performed by adjusting the pressure increase state using the brake fluid pressure by operating the electromagnetic valve and setting the fastening torque of the 4WD coupling to 0 Nm. And do
When the wheel speed difference exceeds the first control threshold, the fastening force of the 4WD coupling is controlled stepwise or continuously, and the brake control is performed by adjusting the brake fluid pressure by the operation of the electromagnetic valve. did.
Therefore, excessive operation of the 4WD coupling can be prevented.

Hereinafter, an embodiment for realizing a brake control device of the present invention will be described based on examples.
(Example)
First, the configuration will be described.
FIG. 1 is a configuration diagram of an ABS (EBD) system portion of a brake control device according to an embodiment. FIG. 2 is a main part hydraulic circuit diagram of the brake device of the embodiment. FIG. 3 is a configuration diagram of a 4WD system portion of the brake control device of the embodiment.
The brake control device of this embodiment is largely composed of an ABS (EBD) system part and a 4WD system part.

As shown in FIGS. 1 and 2, the ABS system portion mainly includes a brake unit 1, a control unit 2, a master cylinder 3, G switches 41 and 42, wheel speed sensors 51 to 54, and a wheel cylinder 6.
As shown in FIG. 2, the brake unit 1 mainly includes switching valves 11 and 12, a reservoir 13, a pump 14, and a motor 15 that drives the pump 14.

The switching valve 12 switches between a state in which the brake hydraulic pressure from the master cylinder 3 communicates with the wheel cylinder 6 and a state in which the hydraulic pressure in the wheel cylinder 6 communicates with the reservoir 13.
The switching valve 11 switches the state in which the brake fluid pressure from the master cylinder 3 is communicated with the wheel cylinder 6 and the oil path between the master cylinder 3 and the wheel cylinder 6 is in a non-communication state.

The reservoir 13 temporarily stores the brake fluid in order to reduce the brake fluid pressure increased to the wheel cylinder 6.
The pump 14 is driven by the motor 15 to return the brake fluid temporarily stored in the reservoir 13 to a brake fluid reserve tank (not shown) on the master cylinder 3 side.
The master cylinder 3 increases the brake fluid pressure to the wheel cylinder 6 due to the driver's brake operation.
The wheel cylinder 6 operates the brake of the wheel by the brake fluid pressure from the master cylinder 3.
Wheel speed sensors 51 to 54 detect wheel speeds of the respective wheels.
The G switches 41 and 42 detect the vehicle acceleration in the vehicle traveling direction and the yaw direction.

  The control unit 2 (corresponding to engine state determination means and failure determination means) calculates the road surface friction coefficient, vehicle deceleration, etc. from the wheel speed from the wheel speed sensors 51 to 54 and the vehicle acceleration from the G switches 41 and 42. The brake unit 1 is controlled by calculating.

As shown in FIG. 3, the 4WD system portion first transmits the drive of the engine 71 to the power transmission unit 73 via the transmission 72.
The power transmission unit 73 is provided so as to connect the front and rear propeller shafts 77, and transmits the driving force from the engine 71 to the propeller shaft 77.
The power transmission unit 73 in the embodiment does not distribute the driving force according to the front and rear loads, but simply transmits the driving force to the propeller shaft 77.
A front differential 74 is provided at the front end of the propeller shaft 77 so as to connect the left and right drive shafts 78 for driving the front left and right wheels 81 and 82, and the driving force from the propeller shaft 77 is adjusted according to the load. The drive shaft 78 is distributed.

A 4WD coupling 76 is provided at the rear end of the propeller shaft 77. The 4WD coupling 76 changes the degree of transmission of the driving force of the propeller shaft 77 rearward by changing the coupling fastening force by pressure control by the controlled electromagnetic valve.
The 4WD coupling 76 is connected to the rear differential 75 so as to connect the left and right drive shafts 79 that drive the left and right wheels 83 and 84, so as to transmit the driving force.
The control during braking of the 4WD coupling 76 is performed by the control unit 2 as shown in FIG.
In this 4WD system, the driving torque of the vehicle is calculated based on the difference in speed between the front and rear wheels due to acceleration slip, the front and rear G, and the engine torque, etc., and the fastening torque of the 4WD coupling is changed to improve startability and running performance. It is increasing.

Next, the function and effect will be described.
[Rear wheel torque distribution / braking force distribution control]
FIG. 4 is a flowchart showing a flow of processing of rear wheel torque distribution / braking force distribution control executed by the control unit of the embodiment. Each step will be described below.
In the following description, VIFE represents the vehicle body speed, VWFR, VWFL, VWRR, VWRL represents the wheel speed, VWR represents the rear wheel average speed, λa to λc represent the control threshold, and k represents the 4WD torque control gain. .

  In step S1, VIFE = (VWFR + VWFL) / 2 is calculated, and the vehicle body speed is calculated in a pseudo manner.

  In step S2, VWR = (VWRR + VWRL) / 2 is calculated to calculate the rear wheel average speed.

  In step S3, the control threshold λa and the control threshold λb are calculated from the formulas λa = Vi × 0.98 and λb = Vi × 0.98-2 km / h (in the above formula, Vi indicates VIFE). And).

In step S4, it is determined whether or not the average rear wheel speed VWR is greater than the control threshold λa. If greater than λa, the process proceeds to step S5, and if less than λa, the process proceeds to step S6.
In this embodiment, the VWR is set not to be smaller than λa (λa = Vi × 0.98) when the vehicle deceleration is small on a high μ road.

  In step S5, the brake hydraulic pressure to the wheel cylinder 6 is increased, the torque transmitted to the rear wheel by the 4WD coupling 76 is set to 0 Nm, and the process is returned.

  In step S6, it is determined whether the rear wheel average speed VWR is greater than the control threshold λb. If it is greater than λb, the process proceeds to step S7, and if it is less than λb, the process proceeds to step S8.

  In step S7, torque control by 4WD torque distribution is performed. That is, a predetermined torque (for example, 98 Nm) is transmitted to the rear wheel, or (VIFE-VWR) × k is performed so that a torque corresponding to the speed difference between the front and rear wheels is transmitted to the rear wheel. The process is terminated.

  In step S8, it is determined whether or not the rear wheel average speed VWR is greater than the brake control threshold λc. If greater than λc, the process proceeds to step S8, and if less than λc, the process proceeds to step S10.

  In step S9, the brake force distribution system (EBD) using the ABS system is used to operate the solenoid valve so that the brake fluid pressure is maintained or reduced, and the pressure is gradually increased and decreased repeatedly. The braking force is distributed to finish the process.

  In step S10, torque control by 4WD torque distribution is performed. That is, a predetermined torque (for example, 490 Nm) is transmitted to the rear wheel, or (VIFE-VWR) × k is performed to control the torque corresponding to the speed difference between the front and rear wheels to be transmitted to the rear wheel. The process is terminated.

  Although the detailed description of this flowchart is omitted, it is incorporated in the main routine of ABS, EBD control, or electronic control 4WD, and is executed every 10 ms.

[Brake force control to distribute 4WD torque]
In this embodiment, the torque distribution control for performing the 4WD torque distribution shown in FIG. 4 is incorporated in the ABS system and the braking force front / rear distribution system (EBD) using the ABS system.
<1> When the vehicle deceleration is small and VWR> λa on a high μ road When a vehicle equipped with the brake control device 1 of this embodiment enters a braking operation with a low vehicle deceleration on a high μ road, slip is relatively low. This is unlikely to occur and the front and rear wheels follow the vehicle speed well, so the speed difference between the front and rear wheels is small.
In step S4, λa to be compared with the rear wheel average speed VWR is obtained by multiplying the front wheel average speed by a coefficient close to 1 (for example, 0.98) equal to or less than 1. Therefore, comparing VWR and λa, VWR is larger than λa because there is no speed difference between the front and rear wheels.
Therefore, when the vehicle deceleration is small and VWR> λa on the high μ road, the 4WD torque distribution is not performed during the braking operation, and therefore there is no occurrence of longitudinal vibration due to torque transmission of the 4WD coupling 76.

<2> When the vehicle deceleration is high on a high μ road and λa ≥ VWR> λb When the vehicle deceleration becomes medium when the vehicle deceleration is slightly high on a high μ road, the preload The rear wheel becomes more slippery because the tendency becomes slightly stronger.
Then, in the comparison determination in step S4, the VWR having a difference from the front wheel speed becomes smaller than λa with respect to λa reflecting the front wheel speed. However, since the deceleration is moderate, it becomes larger than λb (step S6). In this case, the 4WD coupling 76 is controlled so that a constant torque (98 Nm) or a torque corresponding to the speed difference between the front and rear wheels is transmitted to the rear wheels by the process of step S7.

Here, the torque generated during braking is driven by the inertia of the vehicle body. As this definition, braking torque is generated because positive rotation and negative torque are generated on the front wheel side. On the other hand, when torque is distributed to the rear wheel side via the 4WD coupling 76, the rotational speed of the rear wheel side increases in the upward direction, and positive rotation and positive torque are generated, so that drive torque is generated. In this way, when the driving torque is distributed to the rear wheels during the deceleration operation, the wheel deceleration is reduced by increasing the driving torque at the rear wheels, whereas the torque using the inertia of the vehicle body as the driving source at the front wheels. Decreasing increases the wheel deceleration. That is, the braking effect is improved while reducing the difference between the front and rear wheel decelerations and preventing slipping.
In addition, transmitting torque to the rear wheels increases the braking load (for four wheels), so the torque using the inertia of the vehicle body as a drive source is quickly reduced, improving the braking effect. Contribute to.

<3> When the vehicle deceleration is large on high μ road and λb ≧ VWR> λc If the vehicle deceleration further increases on high μ road (compared to <1> and <2> above), the tendency of preload is Since it becomes stronger, the rear wheel is more likely to slip.
Here, in the comparison determination in step S4, VWR is smaller than λa and λb and larger than λc.
In this case, the EBD control in the ABS control system is performed by the process of step S8. In the braking force front / rear distribution system (EBD) using the ABS system, the switching valves 11 and 12 are operated to release the brake fluid pressure of the wheel cylinder 6 to the reservoir 13 to reduce or hold the brake fluid pressure. Then, while monitoring the state of the slip, the pressure is gradually increased and held repeatedly, and the rear wheel slip is prevented to stabilize the vehicle behavior (FIG. 5 shows the held state). .

  At the time of such deceleration, the difference between the rear wheel speed and the front wheel speed gradually increases, so that the torque transmission control by the 4WD coupling 76 is performed by the above processing (processing <2>). Therefore, torque transmission control to the rear wheels is continued, and then EBD control by the ABS system is performed. In this way, when the control for reducing the difference in wheel deceleration between the front and rear wheels is performed by torque transmission control to the rear wheels and EBD control, a predetermined control amount can be obtained by torque transmission. High control can be performed.

<4> When the vehicle deceleration is even larger and λc ≥ VWR on a high μ road If the vehicle deceleration is even greater than in <3> above, the tendency of the preload is due to the size of the vehicle deceleration. Since it becomes stronger, the rear wheels are more likely to slip. Then, in the comparison judgment of steps S4 → S6 → S8, VWR having a difference from the front wheel speed becomes smaller than λc. In this case, the 4WD coupling 76 is controlled so as to transmit a constant torque (490 Nm) larger than step S7 or torque according to the speed difference between the front and rear wheels to the rear wheel by the process of step S10.

<5> When the vehicle deceleration is even larger and λ1 ≧ VWR on a high μ road The control shown in FIG. 5 is performed by being incorporated in the ABS system. In the case where the vehicle body deceleration is further larger than the above <4> and falls below the ABS pressure reduction threshold λ1, in the control shown in FIG. 5, 4WD torque transmission control is performed by the process of step S10. However, the ABS control (not shown) ends the control of FIG. 5 so that the ABS control is performed. At this time, the 4WD coupling 76 is controlled so that torque is not transmitted to the rear wheels.
As a result, more effective braking control can be performed in cooperation with the ABS control without any problems.
Thus, in this embodiment, when the necessity is low, the 4WD torque control that does not operate and operates when the necessity increases can be performed.

[Preventing excessive operation of 4WD coupling]
In the embodiment, when there is no speed difference between the front and rear wheels, the control process for the 4WD coupling 76 is not performed by the determination process (VWR> λa) in step S4. Therefore, torque distribution is not performed when the vehicle body deceleration is small on a high μ road where a sufficient braking performance is easily obtained. Therefore, the number of times that the 4WD coupling 76 operates is reduced. As a result, excessive operation of the 4WD coupling 76 can be prevented.
As a result, the 4WD coupling 76 is relieved of severe operating durability, and can transmit torque to the rear wheel with sufficient performance when necessary.
This also leads to cost reduction of the 4WD coupling 76.

[Improvement in feeling]
In the embodiment, torque distribution by the 4WD coupling 76 is not performed when the vehicle body deceleration is small on a high μ road as described above. Then, since the number of operations is reduced, the number of times the shock of longitudinal vibration during torque transmission by the 4WD coupling 76 is transmitted to the driver is reduced.
Thereby, feeling can be improved.
When the driver feels the necessity, the driver of the operation shock of the device related to the brake control device may rather feel that the operation shock is transmitted as a feeling. . However, in the situation where ABS (EBD) does not operate strongly as in the case where the vehicle deceleration is small on a high μ road, such a shock is transmitted to the driver. It feels bad because you don't feel it.
The present invention improves the feeling by providing a threshold value so as not to operate when the vehicle body deceleration is small on a high μ road.

As mentioned above, although the brake control apparatus of this invention has been demonstrated based on the Example, about a concrete structure, it is not restricted to these Examples, The summary of the invention which concerns on each claim of a claim is shown. Unless it deviates, design changes and additions are allowed.
For example, in the embodiment, EBD control and torque transmission by 4WD coupling are incorporated into ABS control. However, torque transmission by 4WD coupling may be incorporated into ABS control without EBD control.

Furthermore, technical ideas other than the claims that can be understood from the above-described embodiments and examples will be described together with the effects thereof.
(B) A solenoid valve that adjusts the brake fluid pressure supplied to the wheels, a 4WD coupling that can linearly adjust the fastening torque of the front and rear axles, and a control device that detects the deceleration state of the vehicle and distributes the brake torque before and after When the wheel speed difference is smaller than the first control threshold based on the wheel speed difference between the front wheel and the rear wheel, the solenoid valve is increased and the fastening torque of the 4WD coupling is set to 0 Nm. When the wheel speed difference is larger than the first control threshold and smaller than the second control threshold, the brake control for increasing / decreasing the engagement torque of the 4WD coupling is performed. When the wheel speed difference exceeds the second control threshold value, the fastening torque of the 4WD coupling is set to a predetermined amount, and brake control by the electromagnetic valve is further performed. Brake control device.

  That is, in coordination with ABS (EBD) control, braking control more than necessary is not performed by 4WD coupling, and both improved feeling and high braking performance can be achieved. In addition, the control that makes it difficult to slip first by the torque transmission control of the 4WD coupling reduces the frequency of operation of the electromagnetic valve that controls the brake fluid pressure, thereby improving the sound vibration performance.

(B) In the brake control device according to (A) above, when the wheel speed difference exceeds the first control threshold and the second control threshold and further exceeds the ABS control threshold, the ABS control is performed. A brake control device characterized by not transmitting torque by 4WD coupling.
In other words, the control to make a good braking state close to the slip limit by ABS control is coordinated so that the good braking state is not changed by transmitting torque by 4WD coupling. However, since the braking effect is obtained by torque transmission to the rear wheels by the 4WD coupling as a stage before the ABS control is performed, a synergistic braking effect is obtained in the ABS control performed thereafter.

1 is an overall view of an ABS (EBD) system portion of a brake control device of an embodiment. It is a principal part hydraulic circuit diagram of the brake device of an Example. It is a block diagram of the 4WD system part of the brake control apparatus of an Example. It is a flowchart which shows the flow of a process of rear-wheel torque transmission and braking force distribution control performed with the control unit of an Example. It is a time chart which shows operation | movement of the brake device of an Example. It is a time chart figure which shows operation | movement of the conventional brake device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brake unit 2 Control unit 3 Master cylinder 6 Wheel cylinder 11 Switching valve 12 Switching valve 13 Reservoir 14 Pump 15 Motor 41 G switch 42 G switch 51 Wheel speed sensor 52 Wheel speed sensor 53 Wheel speed sensor 54 Wheel speed sensor 71 Engine 72 Shift Machine 73 Power transmission part 74 Front differential 75 Rear differential 76 Coupling 77 Propeller shaft 78 Drive shaft 79 Drive shaft 81 Wheel (FL)
82 wheels (FR)
83 wheels (RL)
84 wheels (RR)

Claims (3)

A solenoid valve that adjusts the brake fluid pressure supplied to the wheels;
4WD coupling that can linearly adjust the fastening torque of the front and rear axles,
In the control device that detects the deceleration state of the vehicle and distributes the front and rear brake torque,
Based on the difference between the front wheel speed and the rear wheel speed,
When the wheel speed difference is smaller than the first control threshold, the brake control is performed by adjusting the pressure increase state using the brake fluid pressure by operating the electromagnetic valve and setting the fastening torque of the 4WD coupling to 0 Nm. And do
When the wheel speed difference exceeds the first control threshold, the fastening force of the 4WD coupling is controlled stepwise or continuously, and brake control is performed by adjusting the brake fluid pressure by the operation of the solenoid valve. Brake control device.   A solenoid valve that adjusts the brake fluid pressure supplied to the wheels;
  4WD coupling that can linearly adjust the fastening torque of the front and rear axles,
  In the control device that detects the deceleration state of the vehicle and distributes the front and rear brake torque,
  Based on the wheel speed difference between the front wheels and the rear wheels,
  When the wheel speed difference is smaller than the first control threshold, the electromagnetic valve is increased to perform brake control to set the fastening torque of the 4WD coupling to 0 Nm, and the wheel speed difference is the first control. When it is larger than the threshold value and smaller than the second control threshold value, brake control for increasing or decreasing the engagement torque of the 4WD coupling is performed, and when the wheel speed difference exceeds the second control threshold value, the 4WD is controlled. A brake control device characterized in that a coupling fastening torque is set to a predetermined amount and brake control is performed by the electromagnetic valve.   The brake control device according to claim 2,
  When the wheel speed difference exceeds the first control threshold and the second control threshold, and further exceeds the ABS control threshold, the ABS transmission is not performed, so that torque transmission by 4WD coupling is not performed. Brake control device.

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