Vehicle brake pressure control unit

Abstract

A vehicle brake pressure control unit is provided. A BRK_ECU 11 detects a brake trigger object based on images captured by an onboard camera 12 and sets a target brake pre-pressure release distance Lpr based on a relative speed between the brake trigger object and a subject vehicle 1. When an actual distance Lbr between the subject vehicle 1 and the brake trigger object reaches the target brake pre-pressure release distance Lpr, the BRK_ECU 11 outputs an actuation signal, which generates a brake pre-pressure Ppr, to a brake actuation unit 17 to minimize the brake gap S of a disc brake 2.

Description

[0001] The present invention relates to vehicle brake pressure control devices that detect in advance a braking point at which a driver applies a brake to brake wheels and provide a brake pre-pressure that brings a friction element of a brake into light contact or close proximity to a rotating element.

[0002] Conventional disc brakes create resistance when a brake pad remains in contact with a brake disc under non-braking conditions. This resistance not only reduces performance but also contributes to brake pad wear.

[0003] Therefore, under non-braking conditions, a return spring separates the brake pad or brake lining from the brake disc with a predetermined gap. However, when the driver presses the brake pedal, the brake gap between the brake pad and the brake disc becomes a free stroke, which generates braking deceleration. The brake gap is therefore preferably reduced to a minimum.

[0004] Japanese unexamined patent application publication (JP-A) No. 2002-321609 discloses a technique for performing what is called an initial filling operation. More precisely, at an early stage, when the driver depresses the brake pedal, brake fluid is rapidly supplied to the brake from a master cylinder to immediately bridge the free stroke of the brake pedal.

[0005] Regarding another example, JP-A No. 201-239929 discloses a motor-driven brake control system. More precisely, when the driver depresses the brake pedal, a position control is first performed to bring the brake pad close to the brake disc, and then a power control is performed to press the brake pad against the brake disc.

[0006] However, the technology disclosed in JP-A No. 2002-321609 requires a brake fluid pressure chamber in the master cylinder to perform the initial filling operation, which is complex in terms of its structure, increases the size of the master cylinder, and also increases production costs.

[0007] The technology disclosed in JP-A No. 2001-239929 requires an electric motor, which increases the number of components as well as the weight, and the installation of the electric motor restricts the design of the components.

[0008] DE 10 2012 101 954 A1 describes a vehicle driving assistance device.

[0009] DE 10 2007 049 249 A1 describes a system for reducing the braking distance of a vehicle.

[0010] DE 10 2005 012 037 A1 describes a method for operating a collision avoidance or collision consequence mitigation system of a vehicle as well as a collision avoidance or collision consequence mitigation system.

[0011] DE 10 2005 011 415 A1 describes a vehicle brake control device and a vehicle brake control method.

[0012] EP 1 557 332 A2 describes a control device for motor vehicles.

[0013] JP 2006-298310 A describes a vehicle control device.

[0014] US 6 415 230 B1 describes a method and device for assisting the driver in braking.

[0015] The internet publication "Notbremsassistent" (Emergency Brake Assistant) on Wikipedia, dated September 15, 2012; DOI: https: / / de.wikipedia.org / w / index.php?title=Notbremsassistent&oldid=108098649, describes emergency brake assistants.

[0016] Brake Handbook; 4th edition; Ed.: Breuer, B.; Bill, KH. H.; Springer-Vieweg-Verlag; 2012; pp. 10-12 describe electronic brake control systems.

[0017] In view of the circumstances described above, it is an object of the present invention to provide a vehicle brake pressure control device that does not use a special component for the brake system including the master cylinder, the brake and the brake fluid pressure circuit, which is suitable to reduce or minimize the free stroke to zero when the driver presses the brake pedal, and achieves an improvement in brake feel as well as a reduction in brake friction.

[0018] The problem is solved by the features of claim 1. Advantageous embodiments are described in the dependent claims.

[0019] According to one aspect of the present invention, a vehicle brake pressure control device is provided, comprising: a non-volatile memory, a driving environment detection unit attached to a vehicle to detect a driving environment in front of the vehicle, a brake detection unit for detecting the pressing of a brake pedal, a brake drive unit for providing brake fluid pressure to a brake provided in the vehicle and for pressing a friction element against a rotating element that rotates together with a shaft of the brake, and a brake control unit for controlling the brake fluid pressure supplied to the brake by the brake drive unit.The brake control unit includes: a brake release object detection unit for detecting a brake release object based on the driving environment detected by the driving environment detection unit; a target brake pre-pressure release distance setting unit for setting a target brake pre-pressure release distance based on a relative speed between the brake release object and the vehicle when the brake release object detection unit detects a brake release object; and a brake pre-pressure output unit for outputting a drive signal to the brake drive unit when a distance between the vehicle and the brake release object reaches the target brake pre-pressure release distance, the drive signal generating a brake pre-pressure to bring the friction element into light contact with or close to the rotating element and to reduce or minimize a brake gap against the preload force of a return spring.A table and a learning correction table are stored in non-volatile memory. The table contains a predetermined base brake pre-release distance related to the relative speed between the brake triggering object and the vehicle, and the learning correction table contains a learning correction factor related to the vehicle speed. The target brake pre-release distance setting unit sets the target brake pre-release distance to a value obtained by multiplying the base brake pre-release distance read from the table by the learning correction factor read from the learning correction table. The base brake pre-release distance is set based on the relative speed between the brake triggering object and the vehicle, and the learning correction factor is set based on the vehicle speed.The brake control unit has a brake pre-pressure learning correction factor update unit for updating the learning correction factor stored in the learning correction table according to a difference between the target brake pre-pressure release distance and the distance to the brake release object, wherein the brake release object is detected by the driving environment detection unit when the brake detector detects the depressing of the brake pedal.

[0020] Preferably, the vehicle brake pressure control unit further comprises an accelerator pedal opening degree detection unit to detect the degree of accelerator pedal opening. When accelerator pedal depressurization is detected, based on the degree of accelerator pedal opening detected by the accelerator pedal opening degree detection unit, the brake pre-pressure output unit does not output the drive signal that generates the brake pre-pressure to the brake drive unit, even if the distance between the vehicle and the brake release object reaches the target brake pre-pressure release distance.

[0021] Preferably, the brake control unit includes a brake pre-pressure release control unit to send a signal to the brake drive unit that releases the brake pre-pressure after a set delay time has elapsed, when the brake pre-pressure output unit outputs the drive signal that generates the brake pre-pressure, and the brake detection unit detects the release of the brake pedal after the pressing of the brake pedal has been detected.

[0022] Preferably, the brake pre-pressure release control unit clears the set delay time when the brake detector detects the pressing of the brake pedal within the set delay time.

[0023] Preferably, the brake pre-pressure release control unit sends a signal to the brake drive unit to release the brake pre-pressure when the accelerator pedal opening degree detection unit detects the pressing of the accelerator pedal within the set delay time.

[0024] The invention will be further explained below with reference to an exemplary embodiment and the drawings in which Fig. 1 is a schematic representation that depicts an overall configuration of a brake control device, Fig. 2 is a sectional view of a vehicle disc brake, Fig. 3 is a flowchart showing a brake pre-pressure control program, Fig. 4 is a flowchart showing a brake pre-pressure release control program, Fig. 5 is a flowchart showing a brake pre-pressure learning correction factor update program, the Fig. 6A and Fig. 6B Represent brake pre-pressure actuation time and brake pre-pressure release time, wherein Fig. 6A is a time sequence diagram of a pre-printed flag and Fig. 6B is a timing diagram showing a brake pre-pressure actuation state, Fig. 7 is an exemplary view representing a brake pre-pressure timing setting state of a subject vehicle following a vehicle ahead, Fig. 8A is an exemplary view showing a brake pre-pressure timing setting state before a curve, and Fig. 8B is an exemplary view showing a brake pre-pressure setting state before a narrow road, Fig. 9A is an exemplary view showing a brake pre-pressure timing set state when a traffic light is red at an intersection where a traffic light is installed, and Fig. 9B is an exemplary view showing a brake pre-pressure timing state before a stop line, and Fig. 10A is an exemplary view that represents a brake pre-pressure timing set state when the vehicle comes close to a stopped vehicle, and Fig. Figure 10B is an example view showing a brake pre-pressure timing set state when a pedestrian is detected.

[0025] An embodiment of the present invention will now be described with reference to the drawings. As shown in Fig. Figure 1 shows a disc brake 2, which serves as a brake in the present invention, provided in each of the four wheels of the vehicle (subject vehicle) 1. Each disc brake 2 comprises a brake disc 2a and a brake caliper 3. The brake disc 2a corresponds to the rotating element according to the present invention and is attached to a hub of each axle to rotate integrally. The brake caliper 3 is attached to the vehicle body and is designed to grip the brake disc 2a.

[0026] As in Fig. As shown in Figure 2, the disc brake 2 according to the present embodiment is of the opposing piston type: cylinders 3a are formed in the brake disc 2a on opposite surfaces of the brake caliper 3, and a piston 3b is arranged in each of the cylinders 3a. A metallic back 4a of a brake pad 4 is attached to the front surface of the piston 3b, and a brake lining 4b, which serves as a friction element, is attached to the metallic back 4a.

[0027] When brake fluid pressure is applied from a brake drive unit 17, described below, to a brake cylinder chamber 3c enclosed by the cylinder 3a and the piston 3b, the piston 3b is pushed outwards, pressing the brake disc 2a and engaging it with the brake pads 4b, thereby applying a braking force. The brake pads 4 are pre-tensioned by a return spring 5 in the direction in which they separate from each other. When the brake fluid pressure applied to the brake cylinder chamber 3c is released, the brake pads 4 return to their original position according to the pre-tension force of the return spring 5, and each brake pad 4b is in contact with the brake disc 2a with a predetermined braking gap S.

[0028] The brake fluid pressure applied to the disc brake 2 is essentially provided by a master cylinder 10. The master cylinder 10 generates brake fluid pressure according to a measure of pressure or pressure force applied to a brake pedal 10a. The master cylinder 10 is equipped with a vacuum booster that utilizes the vacuum from the intake manifold of an engine.

[0029] When a driver presses the brake pedal 10a, the brake fluid in the master cylinder 10 is pressurized and then applied by the brake drive unit 17 to the disc brake 2, which is provided in each of the four wheels. There is a delay during which no braking force is generated until the brake clearance S is reduced sufficiently for the brake pad 4b to press against the brake disc 2a.

[0030] Therefore, if the brake pad 4b is brought into slight contact with or close to the brake disc 2a, the brake clearance S becomes zero or minimal, thus improving the brake's response. However, it is not desirable to always bring the brake pad 4b into slight contact with or close to the brake disc 2a, as this leads to brake drag or rubbing.

[0031] For this reason, in the present embodiment, the point in time (braking point) at which the driver depresses the brake pedal 10a is detected in advance, and a brake pre-pressure is supplied to the brake cylinder chamber 3c of the disc brake 2 immediately before a braking operation is carried out, so that the idle stroke (the delay time) is reduced to zero or minimized when the driver depresses the brake pedal 10a. In other words, the brake pad 4b is brought into light contact with the brake disc 2a, or brought close to it, by the brake pre-pressure in order to reduce the brake gap S to zero or minimize it against the preload force of the return spring 5.

[0032] The brake pre-pressure control is carried out by a brake electronic control unit (BRK_ECU) 11 in Fig. 1, which serves as the brake control unit of the present invention. The BRK_ECU 11 is mainly represented by a microcomputer with a CPU and known non-volatile memory such as a ROM, RAM, and an EEPROM. According to a control program stored in the memory, the CPU supplies a brake pre-pressure to the disc brake 2, sets a release point for the supplied brake pre-pressure, and updates a learning correction factor Kpr, described below, which is used to correct a brake pre-pressure Ppr by learning. Various types of fixed data, such as a table and a characteristic map, are stored in the ROM in addition to the control program. A learning correction table is also stored in the non-volatile memory.

[0033] An onboard camera 12 is mounted at an upper point on the inside of the windshield of the vehicle 1. The onboard camera 12 is a stereo camera unit comprising a main camera 12a and a secondary camera 12b. Cameras 12a and 12b capture images of the driving environment in front of the subject vehicle 1 in one direction of travel. The images captured by cameras 12a and 12b undergo predetermined image processing and are then output by an image processing unit (IPU) 13. The onboard camera 12 and the IPU 13 together serve as the driving environment recognition unit according to the present invention.

[0034] An input port of the BRK_ECU 11 receives, for example, an image signal processed by the IPU 13, a vehicle speed (subject vehicle speed) Vsp of the subject vehicle 1, which is detected by a vehicle speed sensor 14, an accelerator pedal opening degree θacc, which is detected by an accelerator pedal opening degree sensor 15, which serves as the accelerator pedal opening degree detection unit according to the present invention, and ON / OFF signals, which are output by a brake switch 16, which serves as the brake detection unit according to the present invention and is switched to ON when the brake pedal 10a is pressed.

[0035] The brake drive unit 17, which serves as the brake drive unit according to the present invention, is connected to an output port of the BRK_ECU 11. The brake drive unit 17 is inserted between the master cylinder 10 and each disc brake 2 and includes a hydraulic control unit (HCU) that increases and decreases the brake fluid pressure supplied to each disc brake 2. The HCU includes a pump that pressurizes the brake fluid, an accumulator or reservoir, and a solenoid valve that regulates the brake fluid pressure.

[0036] When the brake drive unit 17 receives a brake pre-pressure signal from the BRK_ECU 11, it applies the pre-set brake pre-pressure Ppr to each disc brake 2 to actuate the piston 3b, thereby reducing or minimizing the brake clearance S. In other words, the brake pad 4b is brought into light contact with, or close to, the brake disc 2a. The brake pre-pressure Ppr is set to a value optimal for the vehicle.

[0037] When the brake drive unit 17 receives a brake pre-pressure release signal from the BRK_ECU 11, it releases the brake pre-pressure Ppr that is supplied to each disc brake 2.

[0038] More precisely, in the BRK_ECU 11, the supply control of the brake pre-pressure Ppr is carried out according to a brake pre-pressure control program, as described in Fig. As shown in Figure 3, the release control of the brake pre-pressure Ppr is carried out according to a brake pre-pressure release control program, as described in Fig. 4 is shown, and the update of the learning correction factor Kpr is set according to a brake pre-pressure learning correction factor update program, as shown in Fig. 5 is shown.

[0039] The program according to Fig. Step 3 is performed in each set calculation period. First, in step S1, the image signal output from the IPU 13 is read to detect the driving environment in front of the subject vehicle 1, a brake trigger object is identified using a known pattern matching procedure, and an actual distance Lbr between the subject vehicle 1 and the brake trigger object is obtained.

[0040] The term "brake trigger object" used here refers to a fixed object against which the driver initiates a braking maneuver when the driver becomes aware of it in front of the subject vehicle 1 in the direction of travel. Fig. Numbers 7 to 10 show brake release objects. Fig. Figure 7 shows a vehicle ahead. Fig. 8A and Fig. 8B shows street shapes: Fig. 8A shows a curve input and Fig. 8B shows an entrance to a narrow street. Fig. 9A and Fig. 9B shows lane lines: Fig. Figure 9A shows a stop line drawn in front of a red traffic light on a road, and Fig. Figure 9B shows a stop line painted on a road before a priority road. Fig. 10A and Fig. 10B shows obstacles in front of the subject vehicle 1 in the direction of travel: Fig. 10A indicates a stopped vehicle and Fig. Figure 10B shows a pedestrian (which could also be an animal such as a cat) crossing the street. The vehicle shown by dashed lines in each drawing indicates a position to which the subject vehicle 1 will move after a predetermined time has elapsed.

[0041] The program then proceeds to step S2 to check whether the brake trigger object is detected. If the brake trigger object is detected, the program proceeds to step S3, and if it is not detected, to step S11. The process steps in steps S1 and S2 correspond to the brake trigger object detection unit of the present invention.

[0042] In step S3, a relative vehicle speed Vre is obtained between the brake-trigger object and the subject vehicle 1, and the program proceeds to step S4. If the brake-trigger object is a lane line, such as a stop line, a fixed object, such as a curve, or a pedestrian crossing the road, the relative vehicle speed Vre is equal to the subject vehicle speed Vsp. The relative vehicle speed Vre is obtained by differentiating the distance between the subject vehicle 1 and the brake-trigger object with respect to time.

[0043] In step S4, a basic brake pre-pressure release distance Lb is set based on the relative vehicle speed Vre by referencing a table. The program then proceeds to step S5. For the basic brake pre-pressure release distance Lb, the time at which an ordinary driver depresses the brake pedal 10a is obtained in advance by trial or similar means, based on the relative vehicle speed Vre, and the table is generated by adding a predetermined safety margin m (for example, 5 to 10 [m]) to the time at which the driver presses the brake pedal 10a.

[0044] The program then proceeds to step S5, where the learning correction factor Kpr is set based on the subject vehicle speed Vsp, detected by vehicle speed sensor 14, by referencing the learning correction table stored in non-volatile memory. The program then proceeds to step S6. The learning correction factor Kpr is used to adjust the brake pre-pressure release point to the driver actually operating subject vehicle 1. The learning correction factor Kpr is stored in the learning correction table for each subject vehicle speed Vsp. The learning correction factor Kpr is updated sequentially by the brake pre-pressure learning correction factor update program.

[0045] In step S6, the base brake pre-pressure release distance Lb is corrected by the learning correction factor Kpr, and a target brake pre-pressure release distance Lpr is set (Lpr ← Kpr · Lb). The program then proceeds to step S7. Steps S3 to S6 of the process correspond to the target brake pre-pressure release distance setting unit according to the present invention.

[0046] In step S7, the actual distance Lbr between the subject vehicle 1 and the brake release object is compared with the target brake pre-pressure release distance Lpr to determine whether the target brake pre-pressure release distance Lpr reaches the actual distance Lbr. If the target brake pre-pressure release distance Lpr does not reach the actual distance Lbr (Lbr > Lpr), the program proceeds to step S11. If the target brake pre-pressure release distance Lpr reaches the actual distance Lbr (Lbr ≤ Lpr), the program proceeds to step S8.

[0047] In step S8, the accelerator pedal opening degree θacc detected by the accelerator pedal opening degree sensor 15 is read and compared with the accelerator pedal opening degree (accelerator pedal opening degree at release) θaco when the accelerator pedal is released. If the accelerator pedal opening degree θacc is greater than the accelerator pedal opening degree θaco (θacc > θaco), it is assumed that the accelerator pedal (not shown) is being pressed and the program proceeds to step S11. On the other hand, if the accelerator pedal opening degree θacc is less than or equal to the accelerator pedal opening degree θaco (θacc ≤ θaco), it is determined that the accelerator pedal is being released, i.e., that the driver is about to press the brake pedal 10a, and the program proceeds to step S9.

[0048] In step S9, the drive signal is output to the brake drive unit 17 to generate the brake pre-pressure Ppr. The program then proceeds to step S10. Program steps S7 to S9 correspond to the brake pre-pressure output unit according to the present invention.

[0049] In step S10, a brake pre-pressure flag Fbr is set (Fbr ← 1). The program then exits. As a result, the brake pre-pressure Ppr is supplied to the brake cylinder chamber 3c of each disc brake 2 by the brake drive unit 17, and the piston 3b is moved forward against the preload force of the return spring 5 by the brake pre-pressure Ppr. Since the brake pre-pressure Ppr is set to the value that ensures that the brake gap S becomes zero or is minimized against the preload force of the return spring 5, the brake pad 4b is brought close to the brake disc 2a or into slight contact with the brake disc 2a.

[0050] Since the brake pad 4b is brought close to the brake disc 2a or is brought into slight contact with the brake disc 2a, the free stroke becomes zero or minimized when the driver presses the brake pedal 10a, thereby improving the braking feel.

[0051] On the other hand, if the program continues from step S2, S7 or S8 to step S11, the brake pre-pressure flag Fbr is cleared (Fbr ← 0) and the program is exited.

[0052] The brake pre-pressure flag Fbr is read by the brake pre-pressure release control program according to Fig. 4. The process of the program according to Fig. 4 corresponds to the brake pre-pressure release control device according to the present invention.

[0053] The program according to Fig. Step 4 is performed in each set calculation period. In step S21, reference is made to the value of the brake pre-pressure flag Fbr. The program proceeds to step S22 if the brake pre-pressure flag Fbr is set (Fbr = 1), meaning the brake pre-pressure Ppr is supplied to each disc brake 2, and the program proceeds to step S30 if the brake pre-pressure flag Fbr is cleared (Fbr = 0).

[0054] In step S22, the signal from brake switch 16 is read. If brake switch 16 is switched OFF, it is determined that the brake pedal 10a is released, and the program proceeds to step S23. If brake switch 16 is switched ON, it is determined that the brake pedal 10a is pressed, and the program proceeds to step S24.

[0055] In step S23, the accelerator pedal opening degree θacc is compared with the accelerator pedal opening degree upon release θaco to check whether the accelerator pedal is depressed. If the accelerator pedal is released (θacc ≤ θaco), the program exits and the supply of brake pre-pressure Ppr continues. Conversely, if the accelerator pedal is depressed (θacc > θaco), the program proceeds to step S29.

[0056] In step S24, the signal from brake switch 16 is read. When brake switch 16 is switched ON, the program proceeds to step S25 to clear a count value Tim of the delay timer (Tim ← 0). The program then continues to step S24. The program therefore remains in standby mode until brake switch 16 is switched OFF, in other words, until the driver releases the brake pedal 10a.

[0057] When brake switch 16 is switched to OFF, the program proceeds to step S26 to increment the count value Tim of the delay timer (Tim ← Tim + 1). The program then proceeds to step S27. In step S27, the accelerator pedal opening degree θacc is compared with the accelerator pedal opening degree upon release θaco to check if the accelerator pedal is being depressed. The program proceeds to step S28 if the accelerator pedal is released (θacc ≤ θaco) and to step S29 if the accelerator pedal is depressed (θacc > θaco).

[0058] When the program progresses from step S27 to step S28, the counter value Tim is compared to a set delay time To (for example, 2 to 5 seconds). If the counter value Tim does not reach the set delay time To (Tim < To), the program returns to step S24. Therefore, if the driver depresses the brake pedal 10a within the set delay time To, the counter value Tim of the delay timer is cleared in step S25. As a result, even if the driver performs a pumping action, the brake pre-pressure Ppr is not released with each pumping action, thus maintaining good brake feel.

[0059] When the counter value Tim reaches the set delay time To (Tim = To), the program continues from step S28 to step S29. If the program moves from step S23, S27, or S28 to step S29, the brake pre-pressure flag Fbr is cleared (Fbr ← 0). The program then continues to step S30.

[0060] When the program progresses from step S21 or step S29 to step S30, a signal is sent to the brake actuator 17 to release the brake pre-pressure Ppr, and the program exits. The brake actuator 17 releases the brake pre-pressure Ppr, which is supplied to each disc brake 2, reducing the brake fluid pressure to an initial pressure. As a result, the preload force of the return spring 5 returns the brake pad 4b to an initial position, i.e., to the rear, to establish the brake clearance S.

[0061] Even with the set delay time To, when the driver presses the accelerator pedal, the brake pre-pressure Ppr supplied to disc brake 2 is immediately released, as the program continues from step S27 to step S29 to step S30. Therefore, no brake drag is generated during acceleration after deceleration, thus preventing a reduction in performance.

[0062] The following describes the brake pre-pressure learning correction factor update program according to Fig. 5 described. The parts of the process in the brake pre-pressure learning correction factor update program correspond to the brake pre-pressure learning correction factor update unit according to the present invention.

[0063] In step S31 of the brake pre-pressure learning correction factor update program, the value of the brake pre-pressure flag Fbr is read to check whether the brake pre-pressure flag Fbr is set or not. The program proceeds to step S32 if the brake pre-pressure flag Fbr is set (Fbr = 1), and the program exits if the brake pre-pressure flag Fbr is cleared (Fbr = 0).

[0064] In step S32, the signal from brake switch 16 is read to check if the brake switch 16 is switched ON. If the brake switch 16 is switched OFF, the program exits without performing the learning process. Conversely, if the brake switch 16 is switched ON, in other words, if the driver depresses the brake pedal 10a, the program proceeds to step S33.

[0065] In step S33, it is checked whether there is a difference (Lpr - Lbr) between the last target brake pre-pressure release distance Lpr, which was determined in step S6 according to Fig. The current distance Lbr to the current brake trigger object falls within a dead zone width ± γ (for example, γ = 2 to 3 [m]) around the allowed safety margin m. If the difference (Lpr - Lbr) falls within the set range (m ± γ) (Lpr - Lbr = m ± γ), the program exits without performing the learning process. If the difference (Lpr - Lbr) is outside the set range (m ± γ), the program proceeds to step S34 and compares the difference (Lpr - Lbr) with the set range (m ± γ). If the difference (Lpr - Lbr) is greater than the set range (m ± γ) (Lpr - Lbr > m ± γ), the program proceeds to step S35. On the other hand, if the difference (Lpr - Lbr) is less than or equal to the set range (m ± γ) (Lpr - Lbr ≤ m ± γ), the program proceeds to step S36.

[0066] In step S35, a new learning correction factor Kpr is set (Kpr ← Kpr - β1) by subtracting a set value β1 from the learning correction factor Kpr, which was set in step S5 according to Fig. 3 is set. The program then proceeds to step S37. In step S36, the new learning correction factor Kpr is set (Kpr ← Kpr + β2) by adding a set value β2 to the learning correction factor Kpr, which was set in step S5 according to Fig. 3 is set. The program then proceeds to step S37. The set values, or rather the set values ​​β1 and β2, can be the same or different. In this example, the set values ​​β1 and β2 are set to approximately 0.1 to 0.2. In the learning correction table, each learning correction factor Kpr, which is stored for each vehicle speed Vsp, has the initial value 1.

[0067] When the program continues from step S35 or step S36 to step S37, the learning correction factor Kpr, which is stored in an address corresponding to the subject vehicle speed Vsp, which was determined in step S5 according to Fig. Once the value 3 is read, it corresponds and is updated to the currently received learning correction factor Kpr. The program then exits.

[0068] The learning correction factor Kpr is continuously updated as the driver operates subject vehicle 1, and the learning correction factor Kpr, which is unique to the driver, is eventually set for each vehicle speed Vsp. Therefore, if the driver operates subject vehicle 1 on a continuous basis, the braking point specific to the driver is anticipated, and the application of brake pre-pressure Ppr can begin at an optimal time.

[0069] Examples of a brake pre-pressure control operation and a brake pre-pressure release control operation are given below with reference to a timing table in Fig. 6 explained. When the actual distance Lbr between the subject vehicle 1 and the brake release object reaches the target brake pre-pressure release distance Lpr, the brake pre-pressure flag Fbr is set and the brake pre-pressure Ppr is supplied to each disc brake 2 by the brake drive unit 17, thereby reducing or minimizing the brake clearance S between the brake pad 4b and the brake disc 2a.

[0070] When the driver depresses the brake pedal 10a, almost no free play (no delay time) is generated by the brake clearance S, thus maintaining good brake feel. Since the brake pre-pressure Ppr is continuously supplied while the driver depresses the brake pedal 10a, no unpleasant sensation is generated when the driver applies the brakes. The brake pre-pressure Ppr is not normally supplied, as it is supplied by the prior detection of the driver's brake application. Therefore, no brake drag is generated, and a reduction in the vehicle's performance 1 or unnecessary wear of the brake pad 4b can be avoided, thereby improving fuel consumption.

[0071] Since the brake fluid pressure supplied by the brake drive unit 17 reduces or minimizes the brake gap S, it is not necessary to provide a special component for a brake system including the master cylinder 10, the disc brake 2, and the brake fluid pressure circuit. As a result, a reduction in the number of components and a simplification of the design can be achieved, thereby reducing production costs.

[0072] Even after the driver releases the pressure on the brake pedal 10a, the brake pre-pressure Ppr is not immediately released; instead, the set delay time To is applied. If the driver depresses the brake pedal 10a again within the set delay time To, the counter value Tim of the delay timer is reset (Tim ← 0), and the brake pre-pressure Ppr is continuously applied. Therefore, even if the driver pumps the brake pedal during deceleration, the brake clearance S is maintained at zero or a minimum value, and no free play is generated, thus preserving good brake feel.

[0073] The present invention is not limited to the above embodiment. While, for example, the driving environment in front of the subject vehicle 1 is detected in this embodiment based on the image captured by the onboard camera 12, the driving environment can alternatively be detected using millimeter-wave radar or laser radar. The brake pre-pressure Ppr can be set according to the driver's preference, or the brake pre-pressure Ppr can be related to the vehicle speed. When related to vehicle speed, a lower brake pre-pressure Ppr is set for low vehicle speeds, and a higher brake pre-pressure Ppr can be set as the vehicle speed increases. Similarly, the safety margin m can be set variably according to the driver's preference.

[0074] The brake can be a hydraulic drum brake. In this case, the rotating element corresponds to a brake drum, the friction element corresponds to a brake shoe, and the brake clearance corresponds to a gap between the brake drum and the brake shoe.

Claims

[1] Vehicle brake pressure control device, comprising: a non-volatile memory, a driving environment detection unit (12, 13) mounted on the vehicle (1) and configured to detect a driving environment in front of the vehicle (1), a brake detection unit for detecting the pressing of a brake pedal (10a), a brake drive unit (17) for supplying brake fluid pressure to a brake (2) provided in the vehicle (1) and for pressing a friction element (4b) against a rotating element (2a) which rotates together with a shaft of the brake (2), and a brake control unit (11) for controlling the brake fluid pressure supplied to the brake (2) by the brake drive unit (17), the brake control unit (11) comprises: a brake release object detection unit for detecting a brake release object, based on the driving environment detected by the driving environment detection unit (12, 13), a target brake pre-pressure release distance (Lpr) setting unit for setting a target brake pre-pressure release distance (Lpr) based on a relative velocity (Vre) between the brake release object and the vehicle (1) when the brake release object detection unit detects a brake release object, and a brake pre-pressure output unit for outputting a drive signal to the brake drive unit (17) when a distance between the vehicle (1) and the brake release object reaches the target brake pre-pressure release distance (Lpr), wherein the drive signal generates a brake pre-pressure (Ppr) to bring the friction element (4b) into light contact with or close to the rotating element and to reduce or minimize a brake gap (S) against the preload force of a return spring (5), where a table and a learning correction table are stored in the non-volatile memory, wherein a predetermined basic brake pre-pressure release distance (Lb) is stored in the table in relation to the relative speed (Vre) between the brake release object and the vehicle (1), where a learning correction factor (Kpr) is stored in the learning correction table in relation to the vehicle speed (Vsp), wherein the target brake pre-pressure release distance setting unit sets the target brake pre-pressure release distance (Lpr) to a value obtained by multiplying the base brake pre-pressure release distance (Lb) read from the table by the learning correction factor (Kpr) read from the learning correction table, wherein the base brake pre-pressure release distance (Lb) is set based on the relative velocity (Vre) between the brake release object and the vehicle (1), and wherein the learning correction factor (Kpr) is set based on a vehicle velocity (Vsp) of the vehicle (1), wherein the brake control unit (11) has a brake pre-pressure learning correction factor update unit for updating the learning correction factor (Kpr) stored in the learning correction table according to a difference between the target brake pre-pressure release distance (Lpr) and the distance to the brake release object, wherein the brake release object is detected by the driving environment detection unit (12, 13) when the brake detector detects the depressing of the brake pedal (10a). [2] Vehicle brake pressure control device according to claim 1, further comprising an accelerator pedal opening degree detection unit for detecting the opening degree of an accelerator pedal, wherein, when the depressing of the accelerator pedal is detected, based on the opening degree of the accelerator pedal detected by the accelerator pedal opening degree detection unit, the brake pre-pressure output unit does not output the drive signal generating the brake pre-pressure (Ppr) to the brake drive unit (17), even when the distance between the vehicle (1) and the brake release object reaches the target brake pre-pressure release distance (Lpr). [3] Vehicle brake pressure control device according to claim 1 or 2, wherein the brake control unit (11) has a brake pre-pressure release control unit to send a signal to the brake drive unit (17) to release the brake pre-pressure (Ppr) after a set delay time has elapsed, when the brake pre-pressure output unit sends the drive signal that generates the brake pre-pressure (Ppr), and the brake detection unit detects the release of the brake pedal (10a) after the pressing of the brake pedal (10a) has been detected. [4] Vehicle brake pressure control device according to claim 3, wherein the brake pre-pressure release control unit clears the set delay time when the brake detector detects the pressing of the brake pedal (10a) within the set delay time. [5] Vehicle brake pressure control device according to claim 3 or 4, wherein the brake pre-pressure release control unit outputs a signal to release the brake pre-pressure (Ppr) to the brake drive unit (17) when the accelerator pedal opening degree detection unit detects the pressing of the accelerator pedal within the set delay time.

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