Vehicle braking system

Abstract

To prevent a reduction in brake force after lowering pressing force of a hydraulic drive system in a brake device mounted with both the hydraulic drive system and a mechanical drive system.SOLUTION: When shifting brake force from hydraulic system pressing force H with a hydraulic drive system to mechanical system pressing force M with a mechanical drive system, a vehicle brake device reduces the hydraulic system pressing force H according to an increase in the mechanical system pressing force M. Thus, concurrent progression of an increase in the mechanical system pressing force M and a reduction in the hydraulic system pressing force H prevents total pressing force T, brake force, from being reduced.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a brake system for a vehicle, and more particularly to a brake system equipped with an electric parking brake. [Background technology]

[0002] Electric parking brakes are known that use an electric actuator to mechanically press a braking element, such as a brake pad, against a braked element, such as a disc rotor, to restrict wheel movement. Patent Document 1 below discloses an electric parking brake (2) in which a piston (19), to which the driver's brake pedal operation is transmitted via fluid, is mechanically pushed out by a linearly acting member (18) driven by an EPB motor (10), thereby pressing a brake pad (11) against a disc rotor (brake disc 12). The component names and symbols in parentheses above are those used in Patent Document 1 below and are unrelated to the component names and symbols used in the description of the embodiments of the present application. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-26122 Summary of the Invention [Problem to be solved by the invention]

[0004] When hydraulic pressure is applied to the piston to generate a pressing force of the braking member against the braked member, if the piston is pushed out by the electric actuator via the transmission member to add pressing force, and then the hydraulic pressure is reduced, the reaction force of the braking member pressing force that had previously been borne by the hydraulic pressure is applied to the mechanical transmission member. The mechanical transmission member is compressed and shortened by this reaction force, reducing the pressing force of the braking member and the frictional force generated between the braking member and the braked member, i.e., the braking force.

[0005] The present invention suppresses a reduction in the braking force applied by the mechanical transmission member after reducing the hydraulic pressure when transitioning from braking force applied by hydraulic pressure to braking force applied by the mechanical transmission member in a vehicle brake device. [Means for solving the problem]

[0006] The vehicle brake device of the present invention comprises a piston that pushes out a braking member toward a braked member that rotates integrally with a wheel, a hydraulic drive system that drives the piston by hydraulic pressure to push out the braking member and generate a pressing force against the braked member, and a mechanical drive system that mechanically and directly drives the piston to push out the braking member and generate a pressing force against the braked member, When applying the parking brake, When a pressing operation is started by the mechanical drive system while a pressing force is being generated by the hydraulic drive system against the member to be braked, the hydraulic drive system reduces the pressing force of the hydraulic drive system in response to an increase in the pressing force caused by the pressing operation of the mechanical drive system. When the pressing force of the mechanical drive system reaches the necessary pressing force required for parking, the pressing force of the hydraulic drive system is reduced so that the pressing force of the hydraulic drive system becomes zero.

[0007] As the pressing force of the hydraulic drive system decreases as the pressing force due to the pressing operation of the mechanical drive system increases, the mechanical drive system gradually begins to bear the reaction force of the pressing force of the brake member that was previously borne by the hydraulic drive system as the pressing force of the mechanical drive system increases. Therefore, compression (shortening) of the mechanical drive system member due to the reaction force applied to the mechanical drive system member corresponding to the decrease in pressing force by the hydraulic drive system has already occurred as the pressing force of the mechanical drive system increases. Then, as the pressing force of the mechanical drive system increases, the pressing force of the mechanical drive system increases, taking into account the decrease in pressing force corresponding to this compression. Therefore, when the pressing force of the mechanical drive system reaches a predetermined value, the mechanical drive system has already borne the reaction force that was borne by the hydraulic drive system, and after the pressing force of the hydraulic drive system decreases, compression and shortening of the transmission member of the mechanical drive system is suppressed, thereby suppressing a decrease in the total pressing force.

[0008] In the above-described vehicle brake device, the sum of the increasing pressing force of the mechanical drive system and the decreasing pressing force of the hydraulic drive system can be made constant, thereby making it possible to keep the total pressing force constant. [Effects of the Invention]

[0009] By reducing the pressing force of the hydraulic drive system in accordance with an increase in the pressing force of the mechanical drive system, it is possible to suppress a decrease in braking force after the pressing force of the hydraulic drive system has decreased. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a schematic configuration of a brake device according to an embodiment of the present invention; [Figure 2] 5 is a diagram illustrating an example of control of a pressing force of the brake device according to the embodiment. FIG. [Figure 3] 10A and 10B are diagrams illustrating another example of control of the pressing force of the brake device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a vehicle brake device 10 according to this embodiment. The brake device 10 includes a disk-shaped disc rotor 12 that rotates integrally with the vehicle wheel, and brake pads 14 that come into sliding contact with the rotating disc rotor 12 and apply braking force to the disc rotor 12 by friction. The disc rotor 12 is an example of a braked member that rotates integrally with the wheel, and another example of a braked member is a brake drum. The brake pads 14 are an example of a braking member that comes into sliding contact with the braked member. A brake shoe is an example of a braking member that corresponds to the brake drum.

[0012] The brake device 10 further includes a brake caliper 16 (hereinafter referred to as the caliper 16) in which the brake pads 14 are incorporated, and the caliper 16 further includes a brake piston 18 (hereinafter referred to as the piston 18) for pushing the brake pads 14 toward the disc rotor 12, which is slidably incorporated in a cylinder chamber 20 defined within the caliper 16. The piston 18 includes a hollow cylindrical portion 18a and an end surface portion 18b provided to close the end of the cylindrical portion 18a on the brake pad 14 side. The brake device 10 includes a hydraulic drive system 22 that drives the piston 18 via hydraulic pressure, and a mechanical drive system 24 that directly mechanically drives the piston 18 without using fluid pressure such as hydraulic pressure.

[0013] The hydraulic drive system 22 includes a master cylinder 28 that generates hydraulic pressure according to the amount of depression of the brake pedal 26, and a hydraulic circuit 30 that can increase or decrease the hydraulic pressure generated by the master cylinder 28. The hydraulic circuit 30 includes a hydraulic pump (not shown) that increases the hydraulic pressure supplied to the cylinder chamber 20 when the master cylinder pressure is insufficient. The hydraulic circuit 30 may be a hydraulic circuit of a device called a vehicle behavior control device, an anti-skid device, or the like. A vehicle behavior control device individually controls the braking force generated at each wheel, and generates a yaw moment of the vehicle using the braking force to stabilize the vehicle's behavior. Hydraulic pressure from the master cylinder 28 is supplied to the cylinder chamber 20 via the hydraulic circuit 30. This pressure drives a piston 18, which pushes the brake pad 14 toward the disc rotor 12. As a result, the disc rotor 12 is sandwiched between the brake pads 14 facing each other across the disc rotor 12, generating braking force.

[0014] The mechanical drive system 24 includes an electric motor 32 (hereinafter referred to as the motor 32) and a mechanical transmission mechanism 34 that transmits the rotation of the motor 32, converts it into linear motion, and drives the piston 18. Therefore, the mechanical drive system 24 is an electric actuator that electrically drives the piston 18. The mechanical transmission mechanism 34 includes a gear train 36 that reduces the rotation of the motor 32 before transmitting it, a feed screw shaft 38 that is rotationally driven by the gear train 36, and a thrust nut 40 that is threadedly coupled to the feed screw shaft 38. The feed screw shaft 38 and the thrust nut 40 are disposed coaxially with the piston 18 inside the cylindrical portion 18a of the piston 18. The thrust nut 40 is restricted from rotating relative to the piston 18 and the caliper 16, and moves along the axial direction of the feed screw shaft 38 when the feed screw shaft 38 rotates. The feed screw shaft 38 and the thrust nut 40 constitute a motion conversion mechanism that converts the rotational motion of the motor 32 into linear motion. When the thrust nut 40 is driven toward the end face portion 18b of the piston 18, the piston 18 pushes the brake pads 14 toward the disc rotor 12. As a result, the disc rotor 12 is sandwiched between the brake pads 14 that face each other across the disc rotor 12, generating a braking force.

[0015] The disc rotor 12, caliper 16, hydraulic drive system 22, and mechanical drive system 24 are provided for each of a plurality of wheels, and Fig. 1 shows the configuration for one wheel. The mechanical drive system 24 may be provided for only some of the wheels, for example, for only the two rear wheels in a four-wheel vehicle such as a typical passenger car.

[0016] The brake device 10 includes a control unit 42 that controls the operation of the hydraulic drive system 22 and the mechanical drive system 24 of each wheel. The control unit 42 controls the hydraulic circuit 30 to control the hydraulic pressure supplied to the cylinder chamber 20 by the hydraulic drive system 22. At this time, feedback control may be performed based on the hydraulic pressure detected by a hydraulic pressure sensor 44 that detects the hydraulic pressure of the hydraulic drive system 22. The control unit 42 also controls the current supplied to the motor 32 to control the driving force of the piston 18 by the mechanical drive system 24. The driving force of the piston 18 can be detected based on the value of the current supplied to the motor 32. Furthermore, the control unit 42 controls the drive of the motor 32 based on the operation of an electric parking brake switch 46 (hereinafter referred to as the EPB switch 46) by the occupant, thereby advancing and retracting the thrust nut 40. When the EPB switch 46 is turned on, the thrust nut 40 is driven to advance toward the end surface 18b of the piston 18, and when the EPB switch 46 is turned off, the thrust nut 40 is driven to retract in the opposite direction.

[0017] Fig. 2 is a diagram illustrating the operation of the brake device 10, particularly the operation when applying the parking brake. In Fig. 2, the upper region shows the pressing force of the brake pad 14 against the disc rotor 12, and the lower region shows the drive current I of the motor 32. In Fig. 2, the pressing force H by the hydraulic drive system 22 (hereinafter referred to as hydraulic system pressing force H) is shown by a dashed line, the pressing force M by the mechanical drive system 24 (hereinafter referred to as mechanical system pressing force M) is shown by a thick solid line, and the total pressing force T, which is the sum of the hydraulic system pressing force H and the mechanical system pressing force M, is shown by a thin solid line. Furthermore, pressing force F is the pressing force required for parking, for example, the pressing force required to generate a braking force sufficient to stop the vehicle on a road with a predetermined inclination angle, and will hereinafter be referred to as required pressing force F.

[0018] At time t1, when the EPB switch 46 is turned on, the control unit 42 first controls the hydraulic circuit 30 to generate a hydraulic system pressing force H. The control unit 42 controls the hydraulic circuit 30 based on the hydraulic pressure of the hydraulic drive system 22 detected by the hydraulic pressure sensor 44. At time t2, when the hydraulic system pressing force H reaches the required pressing force F, the control unit 42 stops driving the hydraulic circuit 30, maintains the hydraulic system pressing force H, and starts driving the motor 32. The driving of the motor 32 advances the thrust nut 40 toward the end surface 18b of the piston 18. At time t3, when the thrust nut 40 abuts against the piston 18 and mechanical system pressing force M begins to be generated, the control unit 42 starts controlling the hydraulic circuit 30 to reduce the hydraulic system pressing force H. Based on the motor current I associated with the mechanical system pressing force M, the control unit 42 controls the hydraulic circuit 30 to reduce the hydraulic system pressing force H in response to an increase in the mechanical system pressing force M. At this time, the increase in the mechanical pressure M and the decrease in the hydraulic pressure H proceed simultaneously or in parallel. If the rate of increase in the mechanical pressure M and the rate of decrease in the hydraulic pressure H are controlled to be equal, the total pressure T remains constant even while the mechanical pressure M and the hydraulic pressure H are changing. At time t4 when the mechanical pressure M reaches the required pressure F, the control unit 42 stops the supply of power to the motor 32 and terminates control of the mechanical drive system 24. Furthermore, if the rate of increase in the mechanical pressure M and the rate of decrease in the hydraulic pressure H are equal, the hydraulic pressure of the hydraulic drive system 22 becomes 0 at time t4. The rate of increase in the mechanical pressure M and the rate of decrease in the hydraulic pressure H do not have to be constant between time t3 and t4.

[0019] When applying the parking brake, a pressing force is first generated by the hydraulic drive system, and then generated by the mechanical drive system, thereby reducing the load on the mechanical drive system and allowing the motor 32 to be a small, low-output motor.

[0020] In Fig. 2, no pressing force (braking force) is generated at time t1 when the EPB switch 46 is turned on, but if the driver turns on the EPB switch 46 while depressing the brake pedal 26, a hydraulic system pressing force H is generated at time t1. The hydraulic system pressing force H at this time may differ from the required pressing force F. When the EPB switch 46 is turned on, the control unit 42 increases or decreases the hydraulic system pressing force H to the required pressing force F (time t2), and from time t2 onwards controls the mechanical drive system 24 and the hydraulic drive system 22 in the same manner as described above.

[0021] FIG. 3 illustrates another example of control when a pressure is being applied when the EPB switch 46 is turned on. If the hydraulic pressure H exceeds the required pressure F when the EPB switch 46 is turned on at time t1, the control unit 42 immediately supplies power to the motor 32 while maintaining the hydraulic pressure H, thereby operating the mechanical drive system 24 (time t2). When the mechanical pressure M increases at time t3, the control unit 42 reduces the hydraulic pressure H in response to the increase in the mechanical pressure M. Because the hydraulic pressure H at the beginning of the reduction is greater than the required pressure F, the control unit 42 reduces the hydraulic pressure H by a greater amount than the increase in the mechanical pressure M. As a result, the hydraulic pressure H becomes zero at time t4 when the mechanical pressure M reaches the required pressure F. In other words, the control unit 42 determines the amount of reduction and controls the hydraulic circuit 30 so that the hydraulic pressure H becomes zero at time t4.

[0022] The above describes an example in which the brake device 10 starts operating when the driver or the like turns on the EPB switch 46. When the brake device 10 is installed in a vehicle that runs autonomously without a driver, the control unit 42 may operate in accordance with the operation plan of the vehicle. For example, when the operation plan calls for the vehicle to stop or park for a long period of time, longer than a predetermined time, before the next run, the brake device 10 may perform the operation described with reference to FIG. 2 or FIG. 3. [Explanation of symbols]

[0023] 10 Brake device, 12 Disc rotor (brake member), 14 Brake pad (brake member), 16 Caliper, 18 Piston, 20 Cylinder chamber, 22 Hydraulic drive system, 24 Mechanical drive system, 26 Brake pedal, 28 Master cylinder, 30 Hydraulic circuit, 32 Motor, 38 Feed screw shaft, 40 Thrust nut, 42 Control unit, 44 Hydraulic pressure sensor, 46 Electric parking brake (EPB) switch, F Required pressing force, H Hydraulic system pressing force, I Motor current, M Mechanical system pressing force, T Total pressing force.

Claims

1. a piston that pushes the braking member toward a member to be braked that rotates integrally with the wheel; a hydraulic drive system that drives the piston by hydraulic pressure to push out the braking member and generate a pressing force against the member to be braked; a mechanical drive system that mechanically and directly drives the piston to push out the braking member and generate a pressing force against the member to be braked; Equipped with In an operation of applying the parking brake, if a pressing operation is started by the mechanical drive system while a pressing force is being generated by the hydraulic drive system on the member to be braked, the hydraulic drive system reduces the pressing force of the hydraulic drive system in accordance with an increase in the pressing force due to the pressing operation of the mechanical drive system, and reduces the pressing force of the hydraulic drive system so that the pressing force of the hydraulic drive system becomes 0 when the pressing force of the mechanical drive system reaches the necessary pressing force required for parking. Vehicle braking system.

2. 2. The vehicle brake device according to claim 1, wherein the sum of the increasing pressing force of the mechanical drive system and the decreasing pressing force of the hydraulic drive system is constant.

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