JP2016011081A - Electric parking brake control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric parking brake control device capable of exhibiting desired brake force with a simple structure.SOLUTION: An electric parking brake control device comprises: a liquid pressure sensor for detecting brake liquid pressure of a service brake; a motor for operating a parking brake; and a control part for controlling a current for driving the motor. The control part sets a target current value for allowing the parking brake to perform brake operation by a target load value, based on a measurement pressure value detected by the liquid pressure sensor at an inflection point where grade of the current to time becomes smaller, and the value of the current on the inflection point, during operation of the service brake and parking brake, and controls the current so that the current value becomes the target current value.

Description

  The present invention relates to an electric parking brake control device.

  Devices for braking automobiles (brakes) can be broadly classified into service brakes (also referred to as service brakes) that are mainly used during traveling and parking brakes that are mainly used when the vehicle is stopped.

  The service brake is a hydraulic type in a general passenger car or the like, and generates a pressure in the brake fluid by a pedal depression force to perform a braking operation. On the other hand, the parking brake is a brake system different from the service brake and is mechanically operated.

  As a parking brake, a technique called an electric parking brake is known. The electric parking brake uses, as a configuration for operating or releasing the parking brake, an actuator that pulls or returns a cable driven by a motor and a control device that controls the actuator (see, for example, Patent Document 1). There is also known a technique in which the electric parking brake and the service brake share the same configuration.

  For service brakes, a hydraulic pressure sensor is installed in the vehicle to check the braking operation status, but for electric parking brakes, the load sensor that checks the braking operation status is omitted for weight reduction and space saving. It is hoped that.

U.S. Pat. No. 8,820,653

  The electric parking brake sets a target current value to be supplied to the motor so as to operate the brake with a predetermined load. At this time, it is necessary to set a target load value larger than the required load in advance in consideration of variations in current values due to temperature characteristics and variations in individual differences among devices such as motors. For this reason, in order to ensure the durability of the parts, the member is strengthened by increasing the thickness of the member, so that the apparatus configuration becomes large and the cost increases. Moreover, in order to obtain a load more than necessary, the operating stroke of the parking brake is increased, and the operating time and release time are lengthened. As a result, merchantability is deteriorated.

  An object of the present invention is to provide an electric parking brake control device that exhibits a desired braking force with a simple configuration.

  An electric parking brake control device according to an aspect of the present invention includes a hydraulic pressure sensor that detects a brake hydraulic pressure of a service brake, a motor that operates a parking brake, and a control unit that controls a current that drives the motor. The control unit includes a measured pressure value detected by the hydraulic pressure sensor at an inflection point at which a gradient with respect to time of the current becomes small when the service brake and the parking brake are operated, and the inflection point. The target current value for the parking brake to perform a braking operation with a target load value is set based on the current value at, and the current is controlled with the target current value as a target.

  According to the present invention, when the service brake and the parking brake are operated, the measured pressure value detected by the hydraulic pressure sensor at the inflection point where the gradient with respect to time of current becomes small and the current value at the inflection point are obtained. Based on this, setting the target current value for the parking brake to perform the braking operation with the target load value makes it possible to bring the target load value closer to the required load. Can be demonstrated.

The block diagram which shows schematic structure of the electric parking brake system which concerns on one embodiment of this invention Graph showing time change of load and current Flow chart showing operation of electric parking brake system A diagram comparing various variations considered by the current electric parking brake system with various variations considered by the electric parking brake system of the present invention Flow chart showing other operation of electric parking brake system

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an electric parking brake system according to an embodiment of the present invention. The electric parking brake system includes a control device (for example, ECU) 1, an actuator 2 controlled by the control device 1, and a pulling operation and a return operation of the cable 3 performed by the actuator 2. And a brake assembly 4 that is released. Further, the electric parking brake system is provided with an operation switch 5 that sends a signal to the control device 1 in order to operate and release the parking brake. Furthermore, the electric parking brake system is provided with a gradient sensor 6 that detects the gradient of the road in the longitudinal direction of the vehicle and sends the detection result to the control device 1.

  The actuator 2 includes a motor 11 that can be rotated in the forward and reverse directions by the control device 1, a speed reduction mechanism 12 that includes a plurality of gears that reduce the rotation speed of the motor 11, and an output of the speed reduction mechanism 12. The screw 13 is driven to rotate, and the nut 13 and the like that constitute an equalizer mechanism are reciprocated in the axial direction of the screw 13 by the rotation of the screw 13.

  A cable 3 on the left side in the drawing is connected to one end of the nut 14, a cable 3 on the right side in the drawing is connected to the other end of the nut 14, and the other end of both cables 3 is connected to the brake assembly 4. Connected to each side. As the cable 3 is pulled and returned, the shaft 15 reciprocates in the axial direction.

  In addition, when driving the motor 11 of the actuator 2 and pulling the cable 3, the control device 1 drives the motor 11 until the preset motor current (current that drives the motor 11) is reached. When the motor current reaches a preset value, the motor 11 is stopped and the pulling operation of the cable 3 is also stopped.

  The brake assembly 4 is also provided with a wheel cylinder 7 for operating and releasing the service brake 20 and shares the same structure as the parking brake. The wheel cylinder 7 is provided with a hydraulic pressure sensor 8, and the hydraulic pressure sensor 8 measures and detects the hydraulic pressure of the wheel cylinder 7. Measurement is detected by the hydraulic pressure sensor, and the hydraulic pressure is output to the control device 1.

  FIG. 2 is a graph showing temporal changes in load and current when the parking brake is operated during service brake operation for the electric parking brake system of FIG. In the figure, the left vertical axis shows the load (N) in the brake assembly 4 when the parking brake is operated, the right vertical axis shows the current (A) supplied to the motor 11, and the horizontal axis shows time (msec). ). A solid line indicates a change in current, and a dotted line indicates a change in load.

  Around 750 msec, the current value, which had been increasing at a constant or moderate rate at about 1 A, rapidly increases to about 4 A, and then continues to increase at a constant gradient. That is, at around 750 msec, the current gradient with respect to time changes from a small gradient to a large gradient, and further changes to a small gradient. As described above, when the current value changes with time, the change from a small gradient to a large gradient occurs, for example, with respect to a drum brake, when the brake assembly is operated by the service brake and the brake shoe is in contact with the drum, the parking brake is operated. Therefore, it does not require a large driving force to move the brake shoe to a position close to the drum, and if a braking force is generated by operating the parking brake and generating a braking force by the brake shoe, a large driving force is required. This is due to the need for increased power. Furthermore, when the parking brake is operated to increase the braking force by the parking brake, the required parking brake driving force changes from a sudden increase to a driving force increase proportional to the parking brake operation. . Therefore, the current value necessary for driving the motor has an inflection point at which the current gradient with respect to time becomes small.

  That is, the inflection point at which the current gradient with respect to time becomes smaller is the second in which the parking brake load contributes to the braking operation from the first load in which the parking brake does not contribute to the braking operation due to the operation of the service brake. It is also a point that switches to a load. Therefore, there is a relationship between the load at the time when the brake assembly contributes to braking and the load at the inflection point at which the current gradient with respect to time decreases, so the load and current value are based on the current value at this inflection point. The current value required for the load when the parking brake is sufficiently operated can be easily calculated.

  Next, the operation of the electric parking brake system described above will be described with reference to FIG. In step ST01, the service brake 20 is operated, and in step ST02, the hydraulic pressure sensor 8 detects the hydraulic pressure of the wheel cylinder 7.

  In step ST03, the control device 1 calculates the load of the service brake 20 from the hydraulic pressure detected in step ST02. The control device 1 has a calculation formula or a graph that associates the hydraulic pressure with the brake load in advance. For example, when the hydraulic pressure is 10 MPa, the brake load is calculated as 500N. In step ST04, the control device 1 issues a parking brake operation command.

  In step ST05, the control device 1 starts control of the current that drives the motor 11 with the initial target current value, which is a preset target of current supply at startup, as a target. In step ST06, the control device 1 changes. It is determined whether or not a music point has been detected. If the inflection point is detected, the process proceeds to step ST07. If the inflection point cannot be detected, the current control is continued until the initial target current value reaches the target. When the target is reached, the current control is terminated. .

  In step ST07, the control device 1 associates the current value of the inflection point detected in step ST06 (here, assumed to be 3.6A) with the brake load (500N) calculated in step ST03. In step ST08, A gradient sensor 6 detects the gradient of the road in the longitudinal direction of the vehicle.

  In step ST09, the control device 1 calculates the required load (1000 N) from the slope gradient (assumed to be 30%) detected in step ST08, and takes into account various variations, and the target current value from the target load (1300 N). (3.6A × 1300N / 500N = 9.4A) is calculated, and in step ST10, the control device 1 performs current control up to the target current value (9.4A) calculated in step ST09. Exit. However, the method of calculating the target current value in step ST09 is an example, and other methods may be used.

  FIG. 4 is a diagram comparing various variations considered by the current electric parking brake system with various variations considered by the electric parking brake system of the present invention. In FIG. 4, ◯ indicates a variation that is considered in calculating the target load, and − indicates a variation that is not considered.

  In the current system, variations in individual motors, variations in reduction gear efficiency (gear ratio), variations in current values due to temperature characteristics, changes in current values due to durability such as durability degradation, variations in reading of current values by ECUs, individual gradient sensors It is necessary to consider the difference variation.

  On the other hand, in the system of the present invention, the current value reading variation by the ECU, the individual difference variation of the gradient sensor, and the individual difference variation of the wheel cylinder may be considered.

  As described above, in the system of the present invention, there is less variation to be considered than in the current system, and the margin to be added to the necessary load can be reduced. Thereby, the target load can be made smaller than that of the current system, it is not necessary to improve the durability of the parts, and an increase in the scale and cost of the apparatus configuration can be avoided. Further, it is not necessary to increase the operation stroke of the parking brake, and the operation time and release time can be shortened.

  As described above, according to the present embodiment, when the service brake and the parking brake are operated, the inflection point is detected, and the brake load calculated from the service brake fluid pressure at the inflection point is changed. When calculating the target load from the required load of the parking brake by correlating the motor current at the inflection point, setting the target current value of the parking brake, and controlling the motor current with the target current value as the target Since the variation can be reduced, the target load can be set lower than when many variations are taken into consideration. For this reason, it is not necessary to improve the durability of the components, and an increase in the size and cost of the apparatus configuration can be avoided. Further, it is not necessary to increase the operation stroke of the parking brake, and the operation time and release time can be shortened. Therefore, the parking brake can exhibit a desired braking force with a simple configuration.

  In the present embodiment, the current control is performed according to the procedure shown in FIG. However, the present invention is not limited to this. For example, the procedure shown in FIG. 5 may be used. In FIG. 5, step ST11 is added to FIG. In step ST11, the control device 1 calculates a difference between the initial target current value and the target current value calculated in step ST09 as a correction value. In step ST12, current control is performed using the correction value calculated in step ST11.

  The present invention is applicable to a control device that controls an electric parking brake that operates and releases a parking brake.

DESCRIPTION OF SYMBOLS 1 Control apparatus 2 Actuator 3 Cable 4 Brake assembly 5 Operation switch 6 Gradient sensor 7 Wheel cylinder 8 Fluid pressure sensor 11 Motor 12 Gear, reduction mechanism 13 Screw 14 Nut 15 Shaft 20 Service brake

Claims (3)

A fluid pressure sensor for detecting the brake fluid pressure of the service brake;
A motor for operating the parking brake;
A control unit for controlling a current for driving the motor;
Comprising
The controller is
When the service brake and the parking brake are operated, the measured pressure value detected by the hydraulic pressure sensor at the inflection point where the gradient of the current with respect to time becomes small, and the current value at the inflection point. Based on this, the target current value for the parking brake to perform a braking operation with a target load value is set, and the current is controlled with the target current value as a target.
Electric parking brake control device. The controller is
Based on the operation command of the parking brake, the control of the current is started with the initial target current value as a target,
When the inflection point is detected, the target current value is calculated from the current value at the inflection point and the measured pressure value,
The difference between the initial target current value and the target current value is calculated as a correction value,
Control using the correction value,
The electric parking brake control device according to claim 1. The service brake and the parking brake are configured to perform a braking operation by a common brake mechanism,
The inflection point is that a load of the parking brake is changed from a first load at which the parking brake does not contribute to the braking operation by an operation of the service brake to a second load at which the parking brake contributes to the braking operation. Is the point of switching,
The electric parking brake control device according to claim 1 or 2.

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