Braking system

Abstract

This invention improves the practicality of braking systems that perform ABS (Anti-lock Braking System) actions. The braking system of this invention includes: a braking device that applies braking force to the wheels; and a controller that, when the wheel slip ratio exceeds a threshold, causes the braking device to perform ABS action, the ABS action including a reduction mode that reduces the braking force and an increase mode that increases the braking force after the reduction mode to restore the braking force, wherein, based on the start time of ABS action (t... AS The braking force is used to determine the time at which the ABS action ends (t). AE The braking force (P) should be restored. W The braking force (P) to reach the target W * Furthermore, the action cycle (T) for triggering ABS is determined based on the road conditions on which the vehicle is traveling. CYC Without the need for complex processing such as determining the braking force increase gradient based on factors like vehicle weight, appropriate ABS action can be achieved through a relatively simple process.

Description

Technical Field

[0001] This invention relates to a braking system that performs ABS (Antilock Brake System) operation. Background Technology

[0002] In braking systems, ABS (anti-lock braking system) control is typically used to prevent wheel lock-up. In this ABS control, when the wheel slip ratio exceeds a set slip ratio, the braking device performs ABS action, including a depressurization mode and a boost mode. Many technologies have been developed regarding ABS control to date. For example, in the technology described in the following patent document concerning a hydraulic braking system, when one of the left or right wheels is set to depressurization mode, the boost gradient of the other wheel in boost mode is adjusted.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-110716

[0006] In the aforementioned patent literature, the boost gradient is set to constant. However, depending on the road surface friction coefficient, it's difficult to say that setting the boost gradient to constant will necessarily result in appropriate ABS activation. Furthermore, ideally, to ensure appropriate ABS activation, many factors such as the driving environment (primarily the road surface friction coefficient) and the vehicle's weight should be considered. However, when the number of factors increases, the controller performs more computational processing for ABS activation, potentially placing an excessive load on the braking system. Therefore, there is still much room for improvement in ABS control, and improvements can enhance the practicality of braking systems that implement ABS activation. This invention was made in view of these realities, and its objective is to provide a highly practical braking system. Summary of the Invention

[0007] To address the aforementioned problems, the present invention provides a braking system mounted on a vehicle, comprising: a braking device that applies braking force to the wheels; and a controller that, when the wheel slip ratio exceeds a threshold, causes the braking device to perform ABS operation, the ABS operation including a reduction mode that reduces the braking force and an increase mode that increases the braking force after the reduction mode to restore the braking force, the controller being configured to: determine a target braking force as the braking force to be restored at the end of the ABS operation based on the braking force at the start of the ABS operation, and determine an operating cycle as the time for performing the ABS operation based on the state of the road surface on which the vehicle is traveling.

[0008] Invention Effects

[0009] According to the braking system of the present invention, the target braking force is determined based on the braking force at the start of ABS action, and the action cycle, i.e., the time from the start to the end of one ABS action, is determined based on the road conditions on which the vehicle is traveling. Therefore, without performing complex processing such as determining the increase gradient of braking force in the increased mode based on other factors such as vehicle weight, appropriate ABS action can be achieved through a relatively simple process.

[0010] [Invention Scheme]

[0011] As the braking device in the braking system of the present invention, a so-called hydraulic braking device can be used. More specifically, it is a braking device comprising a rotating body that rotates together with the wheel, a friction member pressed against the rotating body, a hydraulic cylinder that operates to press the friction member against the rotating body, and a working fluid supply device that supplies working fluid to the hydraulic cylinder. Furthermore, not limited to a hydraulic braking device, a braking device having an actuator that moves a piston by an electric motor as a drive source, i.e., an electric braking device, can also be used.

[0012] When using the aforementioned hydraulic braking device, the pressure of the working fluid in the hydraulic cylinder is used as an indicator of braking force. Therefore, the controller can be configured to activate the ABS system based on the pressure of the working fluid in the hydraulic cylinder, rather than on the braking force. It should be noted that, in this configuration, the aforementioned "reduction mode" can be called "pressure reduction mode," and the "increase mode" can be called "pressure boosting mode." Furthermore, the "holding mode," which will be described later, can be called "hydraulic holding mode," the "steep increase mode" can be called "steep pressure boosting mode," and the "gradual increase mode" can be called "gradual pressure boosting mode."

[0013] The aforementioned "controller" can be configured primarily as a computer, which may include, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). Furthermore, the "controller" can be configured to include a driver (drive circuit) that constitutes the actuating components of the braking device. In the case of a hydraulic braking device, the driver may include a drive unit for driving valves used to control hydraulic pressure; in the case of an electric braking device, it may include a drive circuit for an electric motor that serves as the drive source.

[0014] The "road surface condition on which the vehicle is traveling" is most usually indicated by the "road surface friction coefficient (hereinafter, sometimes referred to as "road surface μ")", and the braking device can be activated to perform ABS based on this road surface μ.

[0015] The aforementioned "target braking force" can be determined to be the same value as the braking force at the start of the ABS action. Alternatively, it can be based on the braking force at the start of the ABS action and the road surface μ; the smaller the road surface μ, the smaller the value compared to the braking force at the start of the ABS action. The aforementioned "action cycle" refers to the time from the start to the end of one ABS action, specifically, the time from the start time of the deceleration mode to the end time of the acceleration mode. The action cycle can also be called the ABS action cycle time.

[0016] To achieve efficient ABS operation, the aforementioned braking mode can be configured to include the following modes: a steep increase mode, where the braking force increases with a steep gradient; and a gradual increase mode, where the steep increase mode is followed by a gradual increase in braking force with a gentler gradient than the steep increase gradient. Ideally, the steep increase time should be determined based on the road conditions on which the vehicle is traveling. Furthermore, the braking force used to transition from the steep increase mode to the gradual increase mode should be determined as a predetermined ratio relative to the target braking force, and the steep increase gradient should be determined based on the steep increase time and the difference between the braking force at the start of the steep increase mode and the transition braking force.

[0017] Furthermore, a reference gradual increase gradient is determined based on the time from the start of the gradual increase mode to the predetermined end time of the ABS action, determined based on the action cycle, and the difference between the braking force at the start of the gradual increase mode and the target braking force. The braking force is then increased in the gradual increase mode based on this reference gradual increase gradient. If it is considered that the wheel slip ratio will be significantly improved in the gradual increase mode, the gradual increase gradient can be determined, for example, by correcting the reference gradual increase gradient based on the wheel slip ratio. In this case, to end the ABS action as early as possible, the gradual increase mode can be terminated even before the determined action cycle is reached when the braking force reaches the target braking force.

[0018] Furthermore, the ABS operation can be configured to include a holding mode that maintains braking force between the deceleration mode and the increase mode. In this case, the system is configured to switch from the deceleration mode to the holding mode when the deceleration of the wheel rotation is below a set deceleration, and switch from the holding mode to the increase mode when the acceleration of the wheel rotation is above a set acceleration. The terms "deceleration of the wheel rotation" and "acceleration of the wheel rotation" can be understood as the unified concept of "acceleration and deceleration of the wheel rotation (hereinafter, sometimes referred to as "wheel acceleration and deceleration")". Wheel acceleration and deceleration are positive when the wheel rotation speed is increasing and negative when the wheel rotation speed is decreasing. Ideally, when using wheel acceleration and deceleration, the aforementioned "set deceleration" should be set to a negative value close to 0 (hereinafter, sometimes referred to as "hold mode transition set wheel acceleration and deceleration"), and the system should switch from the deceleration mode to the holding mode when the wheel acceleration and deceleration reaches or exceeds this hold mode transition set wheel acceleration and deceleration. Similarly, ideally, the above "set acceleration" should also be set to a positive value close to 0 for wheel acceleration and deceleration (hereinafter, sometimes referred to as "increase mode change set wheel acceleration and deceleration"). Attached Figure Description

[0019] Figure 1 This is a diagram illustrating the hardware configuration of the braking system in an embodiment.

[0020] Figure 2 It is a diagram that shows the change in wheel speed when braking force is applied to the vehicle and a summary of the ABS action performed on that wheel based on that change.

[0021] Figure 3 It is a graph showing the change in braking force over time during ABS operation.

[0022] Figure 4 It is a mapping diagram used to determine some parameters in ABS action.

[0023] Figure 5 This is a flowchart of the ABS control program executed in the braking system of the embodiment.

[0024] Figure 6 This is a flowchart of the decompression mode subroutine that constitutes the ABS control program.

[0025] Figure 7 This is a flowchart of the hydraulic holding mode subroutine that constitutes the ABS control program.

[0026] Figure 8 This is a flowchart of the steep boost mode subroutine and the slow boost mode subroutine that constitute the ABS control program.

[0027] Explanation of reference numerals in the attached figures

[0028] 1: Hydraulic braking device; 2: ABS actuator (working fluid supply device); 3: ABS electronic control unit (controller); 11: Brake pedal (working fluid supply device); 12: Negative pressure booster (working fluid supply device); 13: Master cylinder (working fluid supply device); 14, 15: Wheel brake (rotating body), (friction component), (hydraulic cylinder); 16, 17: Pressure boosting valve; 21, 22: Pressure reducing valve; 34, 35: Wheel brake (rotating body), (friction component), (hydraulic cylinder); 36, 37: Pressure boosting valve; 41, 42: Pressure reducing valve; SLP: Slip ratio; SLP S : ABS action start threshold slip ratio [threshold]; SLP I : Boost mode transition threshold slip ratio; dSLP: Slip ratio change rate; μ: Road surface friction coefficient (road surface condition); v: Vehicle speed; v W Wheel rotation speed (wheel speed); dv W Wheel acceleration and deceleration; dv WM Hydraulic hold mode switching setting deceleration; dv WI : Boost mode switching setting acceleration; t ISS : The start time of steep boost; t ISE : The scheduled time point for the end of the steep boost; t AS : ABS action start time; t AE : ABS motion end predetermined time point [ABS motion end predetermined time point]; T CYC Action cycle; T IS : Steep boost time [steep increase time]; P W Wheel cylinder pressure (braking force); P W * : Target pressure (reaching target braking force) at the end of ABS action; P ISE : Steep pressure increase ends hydraulic [conversion of braking force]; dP D : Decompression gradient; dP IS Steep pressure gradient (sharply increasing gradient); dP IG Gradual pressure gradient (gradient increase); dP IG0 : Baseline gradual pressure increase gradient (baseline gradual increase gradient); α: Hydraulic determination coefficient for steep pressure increase end (set ratio); β: Gradual pressure increase gradient correction coefficient; MIng: Mode indicator; Norm: Non-ABS operating state; Dec: Pressure reduction mode (reduction mode); Main: Hydraulic holding mode (holding mode); IncS: Steep pressure increase mode (steep increase mode); IncG: Gradual pressure increase mode (gradual increase mode). Detailed Implementation

[0029] Hereinafter, a braking system as an embodiment of the present invention will be described in detail with reference to the accompanying drawings, as a means of carrying out the present invention. It should be noted that, in addition to the embodiments described below, the present invention can also be implemented in various ways, with various modifications and improvements made based on the knowledge of those skilled in the art, primarily as described in the item "Solution to the Invention".

[0030] [Example]

[0031] [A] Hardware configuration of the braking system

[0032] As in Figure 1 As shown in the hydraulic circuit diagram, this braking system is configured with a hydraulic braking device 1 (hereinafter, sometimes simply referred to as "braking device 1") as the central component. In order for the braking device 1 to perform ABS operation, the braking device 1 includes an ABS actuator 2 (hereinafter, sometimes simply referred to as "actuator 2"). The operation of the actuator 2 is controlled by the ABS electronic control unit 3 (hereinafter, sometimes referred to as "ABS-ECU3"), which serves as the controller of the braking system.

[0033] In addition to actuator 2, braking device 1 also includes brake pedal 11 as a braking operation component, negative pressure booster 12 as an assist unit, master cylinder 13, and four wheel brakes 14, 15, 34, and 35 respectively located on the four wheels (specifically, left front wheel FL, right rear wheel RR, right front wheel FR, and left rear wheel RL). Wheel brakes 14, 15, 34, and 35 are each so-called disc brakes, typically configured to include: a disc rotor, which is a rotating body that rotates with the wheel; brake pads as friction components; and wheel cylinders as hydraulic cylinders supplied with working fluid to press the brake pads against the disc rotor. ABS actuator 2, brake pedal 11, negative pressure booster 12, and master cylinder 13 function as working fluid supply devices to supply working fluid to the wheel cylinders.

[0034] When the brake pedal 11 is pressed by the driver, the force of the press is assisted by the negative pressure booster 12, pressing the pressure pistons 13a and 13b located in the master cylinder 13. This pressing generates hydraulic pressure (hereinafter referred to as "main pressure P") in the pressure chambers 13c and 13d formed within the master cylinder 13 at the same height. M The main cylinder 13 is equipped with a reservoir 13e that communicates with the pressurization chambers 13c and 13d. The reservoir 13e has the function of supplying working fluid to the main cylinder 13 or storing excess working fluid in the main cylinder 13.

[0035] The main pressure P generated in the main cylinder 13 MThe braking force is directed to the wheel cylinders of each wheel brake 14, 15, 34, and 35 via the ABS actuator 2. The ABS actuator 2 has a first system for generating braking force on the left front wheel FL and the right rear wheel RR, and a second system for generating braking force on the right front wheel FR and the left rear wheel RL, and the two systems are configured to be identical to each other.

[0036] The first system of ABS actuator 2 has a function for transferring the main pressure P M The main fluid passage A is introduced into the wheel cylinder of the wheel brake 14 located on the left front wheel FL and the wheel cylinder of the wheel brake 15 located on the right rear wheel RR. Through the main fluid passage A, hydraulic pressure (hereinafter sometimes referred to as "wheel cylinder pressure P") is generated in each of these wheel cylinders. W In detail, the main fluid passage A is divided into two fluid passages A1 and A2. Fluid passage A1 is connected to the wheel cylinder of wheel brake 14, and fluid passage A2 is connected to the wheel cylinder of wheel brake 15.

[0037] Liquid passages A1 and A2 are respectively equipped with pressure P for the corresponding wheel cylinder. W The added pressure boosting valves 16 and 17 are normally open on-off valves that are open in the non-excited state and closed in the excited state. They are configured to operate based on PWM (pulse width modulation). Specifically, by changing the duty ratio (the ratio of excited to non-excited time), i.e., by performing so-called duty operation, the amount of working fluid passing through per unit time (passage speed) can be changed. In other words, pressure boosting valves 16 and 17 are configured to change the corresponding cylinder pressure P. W The gradient is increased, i.e., the pressure gradient.

[0038] Additionally, check valves 16a and 17a are respectively provided alongside the booster valves 16 and 17. These check valves 16a and 17a are designed to, during the ABS operation of the braking system 1 (described later), when the booster valves 16 and 17 are closed and the driver resets the brake pedal 11, adjust the wheel cylinder pressure P of the wheel brakes 14 and 15 according to this operation. W It is set to reduce.

[0039] Furthermore, a reservoir 20 is provided in the first system. A pressure reducing valve 21 and 22 are provided in the discharge passage B, which connects the reservoir 20 to the respective pressure boosting valves 16 and 17 of the fluid passages A1 and A2 and to the wheel brakes 14 and 15. The pressure reducing valves 21 and 22 are normally closed type on / off valves that are closed in the non-energized state, and like the pressure boosting valves 16 and 17, they are configured to operate in a PWM-based manner. By enabling the pressure reducing valves 21 and 22 to operate in a so-called duty cycle, the amount of working fluid passing through per unit time (passage speed) can be changed. That is, the pressure reducing valves 21 and 22 are configured to change the corresponding wheel cylinder pressure P. W The reduction gradient, also known as the decompression gradient.

[0040] Furthermore, the first system includes a return path C that connects the reservoir 20 to the main fluid passage A. A pump 24 is installed in this return path C, which draws working fluid from the reservoir 20 into the upstream portion (master cylinder 13 side) of the pressure boosting valves 16 and 17 in the main fluid passage A. The pump 24 is driven by a motor 23 shared by both the first and second systems. It should be noted that a one-way valve 24a is installed on the discharge side of the pump 24 to prevent backflow of working fluid via the pump 24. It should also be noted that, at the start timing of the ABS operation (described later), the motor 23 operates to drive the pump 24; at the end timing of the ABS operation, the motor 23 stops operating to stop driving the pump 24.

[0041] In addition, the reservoir 20 has a reservoir chamber 20a, a piston 20b that divides the reservoir chamber 20a, and a spring 20c that applies force to the piston 20b. The reservoir 20 is configured to receive working fluid discharged from the wheel cylinders of the wheel brakes 14 and 15 in the reservoir chamber 20a until a predetermined amount is reached.

[0042] The above describes the first system of the ABS actuator 2. The second system, similar to the first system, includes a main fluid passage D, a discharge passage E, and a return passage F, and also includes a wheel cylinder pressure P for controlling the wheel brakes 34 and 35 for the right front wheel FR and the left rear wheel RL. W The pressure boosting valves 36 and 37, check valves 36a and 37a, liquid reservoir 40 and its constituent elements 40a to 40c, pressure reducing valves 41 and 42, pump 44, and check valve 44a.

[0043] It should be noted that the ABS actuator 2 is also equipped with a device for detecting the main pressure P. M The main pressure sensor 50. In addition, each wheel FL, RR, FR, RL is equipped with a sensor for detecting its own rotational speed (hereinafter sometimes referred to as "wheel speed v"). W Wheel speed sensors 4, 5, 6, and 7.

[0044] The ABS-ECU3, serving as the controller for the ABS operation of the braking device 1, includes: a computer configured to include a CPU, ROM, RAM, input / output interfaces, and a bus connecting them; and a driver (drive circuit) that operates based on instructions from the computer to drive the components of the braking device 1. Specifically, it includes: a driver for the motor 23 that drives the pumps 24 and 44; and a driver for opening and closing the pressure boosting valves 16, 17, 36, 37, and the pressure reducing valves 21, 22, 41, and 42 and for performing duty cycles. The computer receives information about the main pressure P from the main pressure sensor 50 via the input / output interface. M The signals from wheel speed sensors 4, 5, 6, and 7 regarding the wheel speed v of each wheel. W The signal.

[0045] [B] ABS Control Instructions

[0046] i) Overview of ABS control

[0047] ABS control is used to prevent wheel lock-up when braking force is applied to the wheels. As a prerequisite for ABS control, the computer needs to have information on the wheel speeds (v) of each wheel. W This computer has the function of sensing the vehicle's speed (hereinafter, sometimes referred to as "vehicle speed" or "body speed") v. In addition, the computer has the function of sensing the slip ratio SLP of each wheel, as shown in the following formula.

[0048] SLP=(v-r·v W ) / vr: Effective radius of the wheel

[0049] A slip ratio SLP = 1 indicates that the wheels are completely locked. Furthermore, the computer has a slip ratio SLP based on each wheel and a slip ratio P based on the mains pressure. M The function derives the braking force applied to the wheels to estimate the coefficient of friction (the so-called "road surface μ") of the road surface on which the vehicle is traveling. The methods for sensing vehicle speed v, slip ratio SLP, and estimating the road surface friction coefficient μ are well-known techniques and therefore are omitted here.

[0050] Furthermore, ABS control is performed individually for each of the four wheels. Therefore, this description will only concern ABS control for a specific wheel, and the reference numerals for the components used in the above description of the hardware configuration of the braking system will be omitted.

[0051] exist Figure 2 The diagram illustrates, in graphical form, the change in vehicle speed v when braking force is applied to the wheels, and the wheel speed v of one wheel. WChanges in the wheel cylinder pressure P of the wheel brake installed on this wheel W The change. Additionally, in the graph, the wheel speed v W It is shown in the same dimension as the vehicle speed v, that is, as the value obtained by multiplying by the effective wheel radius r. Furthermore, this braking system is configured to include a hydraulic braking device 1, therefore the wheel cylinder pressure P... W The braking force applied to the wheels is used as an indicator. Considering this, the wheel cylinder pressure P is sometimes used below. W To explain this in place of braking force.

[0052] Reference Figure 2 The chart illustrates this, showing the time point t when the vehicle is traveling at a certain speed v. BS When braking begins on the brake pedal, that is, when a certain amount of braking force is applied, from that time point t... BS Initially, the vehicle speed v decreases. Without wheel slippage, the wheel speed v W It will decrease as the vehicle speed v decreases, but in the case of wheel slippage, according to Figure 2 The chart shows that the wheel speed v W It will decrease significantly. That is to say, the slip ratio (SLP) will increase.

[0053] In ABS control, such as Figure 2 As shown in the graph, the controller detects when the wheel slip ratio SLP exceeds the threshold (hereinafter, sometimes referred to as the "ABS action start threshold slip ratio") SLP. S Time, that is, from the start time t of the ABS action AS Upon activation, the braking system performs ABS (Anti-lock Braking System) action. This ABS action includes a reduction mode that decreases braking force and an increase mode that increases the reduced braking force to restore it. In other words, it causes the braking system to perform actions including increasing wheel cylinder pressure P... W Reduced decompression mode and increased wheel cylinder pressure P W The ABS activation is enhanced with a boost mode. It should be noted that the ABS activation in this braking system includes a holding mode to maintain wheel cylinder pressure P, used to maintain braking force between the decompression and boost modes. W Hydraulic holding mode.

[0054] In ABS control, as long as the slip ratio SLP exceeds the ABS action start threshold, the slip ratio SLP will be affected. S The ABS action is performed repeatedly during a single braking operation. Furthermore, during each braking operation, the wheel slip ratio (SLP) falls within the target slip ratio area indicated by the shaded line in the graph, thus preventing wheel lock-up.

[0055] ii) Details of ABS actions

[0056] The following is for reference Figure 3 The diagrams will be used to provide a detailed explanation of the ABS action. Figure 3 This is a graph showing the change in braking force over time during ABS operation; specifically, it represents the wheel cylinder pressure P. W The graph shows the changes. As previously explained, when the wheel slip ratio SLP exceeds the ABS action initiation threshold, the slip ratio SLP... S Time, that is, from the start time t of the ABS action in the chart. AS Begin the ABS action.

[0057] When ABS is initiated, the ABS-ECU determines the time at which ABS is activated, i.e., the time from the start of ABS activation, t. AS From the scheduled time point t until the ABS action ends AE The action cycle T up to the end of the time CYC This decision refers to Figure 4 The motion cycle determination mapping shown in (a) is used for this purpose. This mapping represents the road surface friction coefficient μ as the state of the road surface on which the vehicle travels, and the motion cycle T. CYC According to this mapping diagram, the smaller the road surface friction coefficient μ, the shorter the action cycle T. CYC The shorter the time, the more frequent the shorter the ABS action can be performed on slippery surfaces.

[0058] Furthermore, this braking system does not have a function for detecting wheel cylinder pressure P. W The wheel cylinder pressure sensor. When ABS is not activated, the wheel cylinder pressure P can be considered as... W With the main pressure P M They are equal. Therefore, the ABS-ECU will register the ABS activation at time t. AS cylinder pressure P W The principal pressure P at that point in time was identified. M Then, the ABS-ECU bases its response on the time point t at the start of ABS action. AS Braking force, i.e., wheel cylinder pressure P W To determine the target braking force that causes the ABS to terminate, i.e., the wheel cylinder pressure P that causes the ABS to terminate. W The target pressure P at the end of the ABS action W * Specifically, in this braking system, the target pressure P at the end of ABS activation... W * Set to be at the start time t of the ABS action AS cylinder pressure P W equal.

[0059] During ABS operation, the ABS-ECU first executes the decompression mode. In decompression mode, the ABS-ECU closes the pressure boosting valve of the ABS actuator and puts the pressure reducing valve into idle operation. The reduction gradient of braking force in decompression mode, i.e., the wheel cylinder pressure P, is... W decompression gradient dP D Reference via ABS-ECU Figure 4 The decompression gradient is determined by the mapping shown in (b). Specifically, the ABS-ECU considers the rate of change of slip ratio dSLP as the rate of change of slip ratio SLP. The closer the rate of change of slip ratio dSLP is to 0, the more the ABS-ECU will determine the decompression gradient dP. D The gentler the gradient, the better. The ABS-ECU bases its decompression gradient dP on this gradient. D This allows the pressure reducing valve to operate in a duty cycle. Additionally, the pressure reduction gradient dP D The slip ratio change rate dSLP is negative in decompression mode. It should be noted that the ABS-ECU is based on the ABS activation start time t. AS cylinder pressure P W The time elapsed since that point in time and the determined decompression gradient dP D In decompression mode, the wheel cylinder pressure P is estimated at any time. W .

[0060] On the other hand, the ABS-ECU is based on the wheel speed v detected by the wheel speed sensor. W To determine as the wheel speed v W The change in speed of the wheel's acceleration and deceleration dv W Additionally, the wheel acceleration / deceleration dv W When the value is positive, it represents wheel acceleration; when the value is negative, it represents wheel deceleration. In decompression mode, although the wheel speed v... W The wheel descends, but after descending to a certain extent, its rate of descent becomes quite low. Therefore, when the wheel can be considered to be decelerating to a stop, that is, when the wheel's acceleration / deceleration dv... W The hydraulic holding mode transition setting deceleration dv was set to a negative value close to 0. WM At this time, the ABS-ECU ends the decompression mode, causing it to switch to hydraulic holding mode.

[0061] When switching to hydraulic holding mode, the ABS-ECU also closes the pressure relief valve of the ABS actuator. As a result, the wheel cylinder pressure P at that point in time... W It is maintained. In this hydraulic holding mode, the wheel deceleration stops and begins to accelerate. Therefore, when it can be considered that the wheel has begun to accelerate, that is, when the wheel acceleration / deceleration dv... WThe boost mode transition setting acceleration dv was achieved, which was set to a positive value close to 0. WI At this time, the ABS-ECU ends the hydraulic holding mode and switches to boost mode.

[0062] In boost mode, with the pressure reducing valve of the ABS actuator closed, the boost valve operates in idle mode. In this braking system, to achieve the wheel cylinder pressure P... W For efficient and appropriate recovery, as a boost mode, it is set with: steep boost mode, wheel cylinder pressure P W The boost gradient is set to a relatively steep boost gradient dP. IS ; and a gradual boost mode, followed by a steep boost mode, with wheel cylinder pressure P W The pressurization gradient is set to a relatively gentle pressurization gradient dP. IG In other words, the gradient for increasing braking force is set to a steep increase mode with a relatively steep gradient, and the gradient for increasing braking force is set to a gradual increase mode with a relatively gentle gradient.

[0063] In this braking system, before engaging the steep boost mode, the ABS-ECU refers to... Figure 4 The steep boost time determination mapping shown in (c) is used to determine the steep boost time T as the time for executing the steep boost mode. IS This mapping represents the road surface friction coefficient μ as a state of the road surface on which the vehicle travels, in relation to the steep boost time T. IS The relationship, through this mapping, is related to the action cycle T. CYC Similarly, the smaller the road surface friction coefficient μ, the shorter the steep pressurization time T. IS The shorter the time, the more frequent the shorter the ABS action can be performed on slippery surfaces.

[0064] On the other hand, the ABS-ECU measures the time from the start of ABS activation and determines the current time point as the start time point t of the steep boost. ISS And by analyzing the steep boost start time t ISS Plus steep boost time T IS To determine the predetermined time point t for the steep boost mode to end. ISE .

[0065] In addition, the ABS-ECU determines the wheel cylinder pressure P that should be reached at the end of the steep boost mode. W The steep pressurization ends the hydraulic P ISE Specifically, the hydraulic pressure P at the end of the steep pressurization... ISE By measuring the target pressure P at the end of the ABS action W *The hydraulic pressure at the end of the boost is determined by multiplying it by the boost-end hydraulic pressure determination factor α. In this braking system, the boost-end hydraulic pressure determination factor α is set to, for example, around 0.6. Then, the ABS-ECU determines the boost-end hydraulic pressure P by multiplying it by the boost-end hydraulic pressure... ISE The wheel cylinder pressure P estimated at the start time of the steep boost mode, which is also the end time of the hydraulic holding mode. W Difference divided by steep boost time T IS To determine the wheel cylinder pressure P that should be achieved in steep boost mode. W The steep boost gradient dP IS Regarding braking force, in other words, the ABS-ECU will determine the braking force that causes the braking force to change from a steep increase mode to a gradual increase mode as a braking force at a set ratio relative to the target braking force, and will determine the steep increase gradient based on the difference between the braking force at the start of the steep increase mode and the transition braking force during the steep increase time.

[0066] In steep boost mode, the ABS-ECU determines the steep boost gradient dP as described above. IS This allows the boost valve to operate in idle mode. Furthermore, similar to the decompression mode, the ABS-ECU determines the boost gradient dP based on the time elapsed since the start of the steep boost mode. IS Even in steep boost mode, the wheel cylinder pressure P is constantly estimated. W Furthermore, the predetermined time point t for the sharp boost to end was reached within the timeframe from the start of ABS activation. ISE At this time, the steep boost mode ends, and the system switches to a gentle boost mode.

[0067] When switching to the gentle boost mode, the ABS-ECU determines the reference gentle boost gradient dP as the reference for the boost gradient in this mode. IG0 Specifically, this is achieved by adjusting the target pressure P from the end of the aforementioned ABS action. W * Subtract the wheel cylinder pressure P at the start time of the slow boost mode W The obtained value is divided by the action cycle T. CYC The base ramp gradient dP is determined by subtracting the time from the start of ABS activation to the start of the ramp-up mode. IG0 Regarding braking force, it is based on the period from the start of the gradual increase mode to the action cycle T. CYC The reference gradual increase gradient is determined by the time from the predetermined end point of the ABS action to the difference between the braking force at the start of the gradual increase mode and the braking force at the target braking force.

[0068] In boost mode, the ABS-ECU adjusts the reference boost gradient dP. IG0Corrections are made to determine the gradual ramp-up gradient dP, which serves as the ramp-up gradient in this mode. IG In detail, by adjusting the baseline gradual pressure gradient dP... IG0 It is determined by multiplying by the gradual increase gradient correction factor β. The gradual increase gradient correction factor β is referenced. Figure 4 The gradient correction factor β is determined by the gradient map shown in (d). This map represents the gradient correction factor β relative to the slip ratio SLP. According to this map, when the slip ratio SLP is high enough, the gradient correction factor β is determined to be 1. When the slip ratio SLP becomes low enough, the gradient correction factor β is determined to gradually increase from 1.

[0069] In boost mode, the ABS-ECU determines the boost gradient dP as described above. IG This allows the booster valve to operate in idle mode. When the slip ratio SLP is high enough, the wheel cylinder pressure P... W According to the baseline gradual pressure gradient dP IG0 Increase, but when the slip ratio SLP decreases to a certain level midway through the slow boost mode, for example, as by Figure 3 As shown by the dashed line, the wheel cylinder pressure P W It will be based on the baseline gradual pressure gradient dP IG0 A steeper gradient is added.

[0070] Similar to the steep boost mode, the ABS-ECU determines the gradual boost gradient dP based on the time elapsed since the start of the gradual boost mode. IG Even in the slow boost mode, the wheel cylinder pressure P is constantly estimated. W At time t, the start point of the ABS action AS The time elapsed after the start of the action cycle T has elapsed. CYC At that time, or the estimated wheel cylinder pressure P W The target pressure P was reached at the end of the ABS operation. W * At that time, the ABS-ECU terminates the gradual boost mode. Therefore, when the slip ratio SLP remains high to a certain extent, at the time point t from the start of ABS activation... AS The time elapsed after the start of the action cycle T has elapsed. CYC At that time, the slow boost mode ends, but when the slip ratio SLP decreases to a certain level in the middle of the slow boost mode, it ends again at the start of the action cycle T. CYC Previously, the slow pressurization mode would end. Upon the end of the slow pressurization mode, the pressurization valve would close.

[0071] ABS activation is as described above. In this braking system, the target pressure P is reached at the end of ABS activation. W* Based on the ABS action start time t AS cylinder pressure P W To determine, and the action cycle T CYC The coefficient of friction μ is determined based on the road surface condition on which the vehicle travels. Therefore, in this braking system, appropriate ABS action can be achieved through relatively simple processing. Furthermore, the steep boost gradient dP in steep boost mode... IS It is also determined based on the road surface friction coefficient μ. This also helps to achieve proper ABS action through relatively simple processing.

[0072] iii) ABS control process

[0073] The computer of the ABS-ECU repeatedly executes the command for each wheel at short time intervals (e.g., a few milliseconds) Δt. Figure 5 The ABS control program shown in the flowchart executes the aforementioned ABS control. The following explanation describes the processing flow in the ABS control according to this flowchart.

[0074] In the ABS control procedure, firstly, in step 1 (hereinafter referred to as "S1"; other steps are the same), the wheel slip ratio SLP and the slip ratio change rate dSLP are determined. In S2, the wheel acceleration / deceleration dv is determined based on the detection of the wheel speed sensor. W Next, in S3, the timer t used to measure the time increments to count the execution interval Δt of the program.

[0075] Regarding ABS control, a mode indicator MIng is provided to indicate which of the various modes described earlier should be implemented or is being implemented. When ABS action is not performed, i.e., in the normal mode, the mode indicator MIng is set to "Norm". In decompression mode, hydraulic holding mode, steep pressure increase mode, and slow pressure increase mode, the mode indicator MIng is set to "Dec", "Maint", "IncS", and "IncG", respectively. In S4 to S7, the mode indicator MIng is judged. When the judgment is "Dec", "Maint", "IncS", or "IncG", the processing of the decompression mode subroutine, hydraulic holding mode subroutine, steep pressure increase mode subroutine, and slow pressure increase mode subroutine, which will be described later, is executed.

[0076] When the ABS action is not performed, in S12, it is determined whether the slip ratio SLP exceeds the ABS action start threshold slip ratio SLP. S When the slip ratio SLP does not exceed the ABS action initiation threshold, the slip ratio SLP... SIn the case of S13, the friction coefficient μ of the road surface on which the vehicle is traveling is obtained; in S14, the pressure boosting valve is kept open; and in S15, the pressure reducing valve is kept closed.

[0077] In S12, the slip ratio SLP is determined to exceed the ABS action initiation threshold slip ratio SLP. S In this case, to initiate ABS operation, processing after S16 is executed. Specifically, in S16, the main pressure P is obtained based on the detection of the main pressure sensor. M In S17, the wheel cylinder pressure P at the current time point is... W Assuming the principal pressure P M Furthermore, in S18, the target pressure P at the end of the ABS action is... W * The cylinder pressure P at the current time point is set as follows. W Next, in S19, based on the obtained road surface friction coefficient μ, according to... Figure 4 The mapping diagram of (a) determines the motion cycle T of the subsequent ABS action. CYC Then, in S20, the timer t is reset, and in S21, in order to implement the decompression mode, the mode indicator Ming is set to "Dec".

[0078] If the mode indicator Ming is determined to be "Dec" in S4, then execute... Figure 6 The flowchart shows the decompression mode subroutine. In the processing according to this subroutine, firstly, in S31, the pressure boosting valve is closed. Then, in S32, based on the slip ratio change rate dSLP, according to... Figure 4 The mapping diagram of (b) is used to determine the wheel cylinder pressure P in the decompression mode. W decompression gradient dP D In S33, the decompression gradient dP determined by this is... D This allows the pressure reducing valve to operate in idle mode. Then, in S34, based on the pressure reduction gradient dP... D To estimate the cylinder pressure P at the current time point W In the following S35, the wheel acceleration / deceleration dv is determined. W Has the hydraulic hold mode transition been reached? Deceleration setting dv WM In the acceleration and deceleration dv of the wheel W The hydraulic holding mode has not been reached, so the deceleration setting has not been changed. WM In this case, the processing of this subroutine ends, and the wheel acceleration / deceleration dv... W Reaching hydraulic hold mode change setting deceleration dv WM In the case of S36, in order to implement the hydraulic holding mode, the mode indicator Ming is set to "Maint".

[0079] If S5 determines that the mode indicator Ming is "Maint", then execute... Figure 7 The flowchart shows the hydraulic holding mode subroutine. In the processing according to this subroutine, firstly, in S41, the pressure reducing valve is closed; secondly, in S42, it is assumed that the wheel cylinder pressure P is maintained. W Then, in S43, the wheel acceleration / deceleration dv is determined. W Has the boost mode transition setting acceleration been achieved? WI In S44, it is determined whether the slip ratio SLP is lower than the boost mode transition threshold slip ratio SLP. I In the acceleration and deceleration dv of the wheel W The boost mode transition setting acceleration dv was not reached. WI Furthermore, the slip ratio SLP is the threshold for boost mode transition. I Under the above circumstances, the execution of this subroutine ends. (Regarding wheel acceleration / deceleration dv) W Achieve boost mode switching and set acceleration dv WI Or the slip ratio SLP is lower than the boost mode transition threshold. I In order to switch to steep boost mode, the processing after S45 is executed.

[0080] Specifically, in S45, the mode indicator Ming is set to "IncS". Then, in S46, based on the road surface friction coefficient μ, according to... Figure 4 The mapping diagram of (c) is used to determine the steep boost time T. IS Furthermore, in S47, the current time point is determined as the steep boost start time point t. ISS In S48, based on these steep boost times T IS The start time of steep boost is t ISS To determine the predetermined time point t for the steep boost to end ISE Furthermore, in S49, the target pressure P at the end of the determined ABS action is... W * The hydraulic pressure P at the end of the steep boost is determined by multiplying by the aforementioned hydraulic pressure determination coefficient α at the end of the steep boost. ISE In S50, the hydraulic P is based on the steep pressurization termination. ISE The cylinder pressure P at the current time point W and steep boost time T IS To determine the steep boost gradient dP that should be achieved in steep boost mode. IS .

[0081] If the mode indicator Ming is determined to be "IncS" in S6, then execute... Figure 8The flowchart shows the steep boost mode subroutine. In the processing according to this subroutine, firstly, in S61, based on the determined steep boost gradient dP... IS To enable the booster valve to operate in idle mode, in S62, based on the determined steep boost gradient dP IS To estimate the cylinder pressure P at the current time point W Next, in S63, it is determined whether the time t from the start of the ABS action has reached the predetermined time t for the end of the steep boost. ISE Before the predetermined time point t for the steep boost to end. ISE In this case, the processing according to this subroutine will end, and the predetermined time point t for the steep boost will be reached. ISE In order to switch to the slow-increase mode, in S64, the mode indicator Ming is set to "IncG", and in S65, the target pressure P is based on the end of the ABS action. W * The wheel cylinder pressure P at the current time point W Action cycle T CYC The time t from the start of ABS action determines the gradual boost gradient dP that should be achieved in the gradual boost mode. IG The benchmark gradient dP IG0 .

[0082] If the mode indicator Ming is determined to be "IncG" in S7, then execute... Figure 8 The flowchart shows the slow ramp-up mode subroutine. In the processing according to this subroutine, firstly, in S71, the slow ramp-up gradient dP is determined. IG Specifically, by adjusting the baseline gradual pressure gradient dP... IG0 Conduct based on Figure 4 The correction of the gradual ramp-up gradient correction coefficient β in the mapping diagram of (d) is used to determine the gradual ramp-up gradient dP. IG Then, in S72, based on the determined gradual pressure gradient dP... IG To enable the booster valve to operate in idle mode, in S73, based on the determined gradual booster gradient dP IG To estimate the wheel cylinder pressure P W .

[0083] Next, in S74, it is determined whether the time since the start of the ABS action has reached the action period T. CYC In S75, the estimated wheel cylinder pressure P is determined. W Has the target pressure P at the end of the ABS action been reached? W * The time from the start of the ABS action has not reached the action cycle T. CYC And the cylinder pressure P WThe target pressure P at the end of the ABS action was not reached. W * In this case, processing based on that subroutine ends. The time from the start of the ABS action reaches the action cycle T. CYC Or the cylinder pressure P W The target pressure P is reached at the end of the ABS action. W * In the case of S76, in order to end the ABS operation, the mode indicator Ming is set to "Norm", and in S77, the booster valve is opened.

Claims

1. A braking system mounted on a vehicle, the braking system comprising: Braking devices apply braking force to the wheels; and The controller activates the ABS system when the wheel slip ratio exceeds a threshold. The ABS activation includes a reduction mode that decreases the braking force and an increase mode that increases the braking force to restore braking force after the reduction mode. The controller is configured to: determine the target braking force that should be restored at the end of the ABS action based on the braking force at the start of the ABS action, and determine the action cycle for the duration of the ABS action based on the road conditions on which the vehicle is traveling. The addition modes include: The steep increase mode increases braking force in a steep gradient. And then the steep increase mode is implemented, which increases the braking force at a gradual increase gradient that is more gentle than the steep increase gradient. The controller is configured to determine the steep increase time as the time for implementing the steep increase mode based on the state of the road surface on which the vehicle is traveling.

2. The braking system according to claim 1, wherein, The controller is configured to: determine the transition braking force, which is the braking force that causes the transition from the steep increase mode to the gradual increase mode, as a braking force at a set ratio relative to the target braking force, and determine the steep increase gradient based on the difference between the braking force at the start of the steep increase mode and the transition braking force at the steep increase time.

3. A braking system mounted on a vehicle, the braking system comprising: Braking devices apply braking force to the wheels; and The controller activates the ABS system when the wheel slip ratio exceeds a threshold. The ABS activation includes a reduction mode that decreases the braking force and an increase mode that increases the braking force to restore braking force after the reduction mode. The controller is configured to: determine the target braking force that should be restored at the end of the ABS action based on the braking force at the start of the ABS action, and determine the action cycle for the duration of the ABS action based on the road conditions on which the vehicle is traveling. The increase pattern comprises: The steep increase mode increases braking force in a steep gradient. And then the steep increase mode is implemented, which increases the braking force at a gradual increase gradient that is more gentle than the steep increase gradient. The controller is configured to: determine a reference gradual increase gradient as a reference for the gradual increase gradient based on the time from the start of the gradual increase mode to the predetermined end time of the ABS action determined based on the action cycle and the difference between the braking force at the start of the gradual increase mode and the target braking force, and increase the braking force in the gradual increase mode based on the reference gradual increase gradient.

4. The braking system according to claim 3, wherein, The controller is configured to determine the gradual gradient by correcting the baseline gradual gradient based on the wheel slip ratio.

5. The braking system according to claim 4, wherein, The controller is configured to terminate the gradual increase mode when the braking force reaches the target braking force, even if the action cycle has not yet ended.

6. The braking system according to claim 1 or 3, wherein, The ABS operation includes a holding mode that maintains braking force between the reduction mode and the increase mode. The controller is configured to: switch from the deceleration mode to the holding mode when the deceleration of the wheel's rotation is below a set deceleration, and switch from the holding mode to the increasing mode when the acceleration of the wheel's rotation is above a set acceleration.

7. The braking system according to any one of claims 1 to 5, wherein, The controller causes the braking device to perform the ABS action based on the road surface friction coefficient, which is the state of the road surface on which the vehicle is traveling.

8. The braking system according to any one of claims 1 to 5, wherein, The braking device includes: a rotating body that rotates together with the wheel; a friction member pressed against the rotating body; a hydraulic cylinder that operates to press the friction member against the rotating body; and a working fluid supply device that supplies working fluid to the hydraulic cylinder. The pressure of the working fluid in the hydraulic cylinder is used as an indicator of braking force, and the controller is configured to cause the braking device to perform the ABS action based on the pressure of the working fluid in the hydraulic cylinder instead of the braking force.

Images