BRAKE SYSTEM WITH PEDAL SIMULATOR

Abstract

Electronic hydraulic braking system, comprising: a brake pedal (10) to be operated by a driver to brake a vehicle; a brake cylinder connected to the brake pedal (10) for generating hydraulic pressure upon receiving a foot force from the driver via the brake pedal (10); and a pedal simulator (30) connected to the brake cylinder via a pedal-side hydraulic line (24) to create a pedal feel based on the driver's foot force by means of the hydraulic pressure generated by the brake cylinder, where the brake cylinder has: a master brake cylinder (21) connected to the brake pedal (10) while being connected to the pedal simulator (30) via the pedal-side hydraulic line (24), and an auxiliary brake cylinder (22) connected to the brake pedal (10) while being connected to the pedal simulator (30) and to a fluid reservoir (23b) via the pedal-side hydraulic line (24), wherein a first simulator valve (26) is installed in a section of the pedal-side hydraulic line (24) between the master brake cylinder (21) and the pedal simulator (30), and wherein a second simulator valve (27) is installed in a portion of the pedal-side hydraulic line (24) between the auxiliary brake cylinder (22) and the fluid reservoir (23b), and wherein a check valve (25) is installed in a portion of the pedal-side hydraulic line (24) between the auxiliary brake cylinder (22) and the pedal simulator (30) to prevent backflow of fluid from the pedal simulator (30) to the auxiliary brake cylinder (22) while allowing fluid to flow only from the auxiliary brake cylinder (22) to the pedal simulator (30).

Description

The present invention relates to a brake system for a vehicle, and more particularly to a hydraulic booster brake system including a pedal simulator for generating a pedal feel based on a degree of driver intervention, generating hydraulic pressure required for braking based on a braking intention of the driver, and supplying the generated hydraulic pressure to a wheel brake.Recently developed vehicles use brake-by-wire technology for controlling braking, which uses an electronic control system instead of a conventional general hydraulic control system. In such an electronically controlled brake system, hydraulic pressure required for braking is generated based on a braking intention of the driver by an electric motor. The hydraulic pressure generated based on the drive of the motor is transmitted to a wheel brake (wheel cylinder) of each wheel, and accordingly, a braking force is generated. Such an electronically controlled brake system that controls hydraulic pressure by means of an electronic actuator is typically referred to as an "electro-hydraulic brake system (EHB)", i.e., an "electronic hydraulic brake system".The electronic hydraulic brake system controls braking forces generated at respective wheels in an independent manner. Accordingly, it may be possible to realize functions associated with, for example, an electronic stability control (ESC) or an anti-lock brake system (ABS). A pump is frequently used as an electronic actuator used in a general hydraulic booster brake system, i.e., an electronic hydraulic brake system, as mentioned above. The pump converts a rotational force generated during driving of a motor into a linear force to move a piston in a forward and rearward direction. According to the movement of the piston, brake fluid in a chamber of a cylinder is pressurized to thereby generate hydraulic pressure.In this electronic hydraulic brake system, a sensor is configured to detect a pedal stroke generated based on a pedal depression (e.g., degree of intervention) of the driver, and the pump generates hydraulic pressure based on the detected results by driving the motor, and thus braking forces of the respective wheels are controlled. In addition, the electronic hydraulic brake system is equipped with a pedal simulator that allows the driver to feel a pedal feeling as in a general hydraulic brake system. Specifically, when the driver depresses or operates a pedal connected to a master cylinder, hydraulic pressure of the brake fluid in the master cylinder is increased. The hydraulic pressure from the master cylinder is transmitted to the pedal simulator through a pedal-side hydraulic line, and thus a pedal feeling is generated from the pedal simulator.In addition, in response to a driver depressing the brake pedal, a controller is configured to calculate a target hydraulic pressure desired by the driver based on a pedal input (e.g., brake input) of the driver detected by a brake pedal sensor (e.g., pedal stroke sensor), i.e., a pedal stroke value. Based on the calculated target hydraulic pressure, the controller is configured to drive the motor to cause the pump to generate hydraulic pressure. The hydraulic pressure generated by the pump is transmitted to each wheel cylinder, and thus a desired braking force is obtained.Meanwhile, in a conventional electronic hydraulic brake system, the master cylinder side and the pedal simulator side are connected to each other via a pedal-side hydraulic line. Moreover, in such a conventional electronic hydraulic brake system, the operation of a motor in an electronic actuator is stopped when the system fails. Specifically, a check valve is opened to allow hydraulic pressure generated by the master cylinder based on a foot force of the driver to be directly transmitted to the wheel brake (wheel cylinder). Therefore, a braking force is generated by the hydraulic pressure of the master cylinder.In connection with this, for an increase in the braking force generated by the driver's foot force when the system has failed, it is necessary to reduce the inner diameter of the master cylinder. However, when the inner diameter of the master cylinder is reduced, the hydraulic pressure on the pedal simulator side connected to the master cylinder via the pedal-side hydraulic line may be increased to a certain pedal stroke. In particular, the durability of members of the pedal simulator, for example, a spring and a rubber damper, may be insufficient.In order to increase the durability of the spring and the damper of the pedal simulator, it is necessary to increase the size of the pedal simulator. However, there is a limitation in increasing the size of the pedal simulator due to an increase in the sealing function of the pedal simulator and a limited arrangement space in the engine room. In view of this, the reduction in the inner diameter of the master cylinder results in a restriction in the increase in backup braking performance, i.e., a function of generating the braking force by hydraulic pressure generated from the master cylinder by a foot force (e.g., an engagement degree) of the driver in an open state of the check valve when the system has failed.DE 10 2013 216 477 A1 describes an electronic hydraulic brake system, comprising a brake pedal which is to be operated by a driver for braking a vehicle, a brake cylinder which is connected to the brake pedal in order to generate a hydraulic pressure after receiving a foot force of the driver via the brake pedal, and a pedal simulator which is connected to the brake cylinder via a pedal-side hydraulic line in order to generate a pedal feeling based on the foot force of the driver by means of the hydraulic pressure generated by the brake cylinder, wherein the brake cylinder comprises a master brake cylinder which is connected to the brake pedal while being connected to the pedal simulator via the pedal-side hydraulic line, and an auxiliary brake cylinder which is connected to the brake pedal while being connected to the pedal simulator and to a fluid reservoir via the pedal-side hydraulic line, wherein a first simulator valve is installed in a portion of the pedal-side hydraulic line between the master cylinder and the pedal simulator, and wherein a second simulator valve is installed in a portion of the pedal-side hydraulic line between the master cylinder and the fluid reservoir.Further electronic hydraulic brake systems are known from the post-published DE 10 2014 225 962 A1 and DE 10 2014 215 379 A1.Proceeding from the prior art, the object of the invention is to provide a hydraulic booster brake system having a pedal simulator which is suitable for achieving an increase in the safety brake output and an increase in the design freedom of the pedal simulator.The object is achieved according to the invention by an electronic hydraulic brake system having the features of claim 1. Advantageous refinements are described in the dependent claims.According to an aspect of the invention, there is provided an electronic hydraulic brake system including a brake pedal to be operated by a driver for braking a vehicle, a brake cylinder connected to the brake pedal to generate a hydraulic pressure after receiving a foot force (e.g., an engagement degree or a pedal depression) of the driver via the brake pedal, and a pedal simulator connected to the brake cylinder via a pedal-side hydraulic line to provide a pedal feeling based on the foot force of the driver using the hydraulic pressure generated by the brake cylinder, wherein the brake cylinder includes a master cylinder connected to the brake pedal while being connected to the pedal simulator via the pedal-side hydraulic line, and an auxiliary brake cylinder connected to the brake pedal, while being connected to the pedal simulator and to a fluid reservoir via the pedal-side hydraulic line. In addition, a first simulator valve is installed in a portion of the pedal-side hydraulic line between the master cylinder and the pedal simulator, and a second simulator valve is installed in a portion of the pedal-side hydraulic line between the master cylinder and the fluid reservoir.According to the invention, a check valve is installed in a portion of the pedal-side hydraulic line between the auxiliary brake cylinder and the pedal simulator to prevent a backflow of fluid from the pedal simulator to the auxiliary brake cylinder while allowing fluid to flow only from the auxiliary brake cylinder to the pedal simulator. In an exemplary embodiment, the electronic hydraulic brake system may further include a controller configured to perform opening and closing operations of the first and second simulator valves to open the first simulator valve while closing the second simulator valve after receiving a brake input generated based on an operation of the brake pedal by the driver.In addition, the pedal-side hydraulic line may include a hydraulic line portion branched from a hydraulic line portion between the auxiliary brake cylinder and the second simulator valve and connected to the pedal simulator. The branched hydraulic line portion may be connected to a hydraulic line portion between the pedal simulator and the first simulator valve, and a check valve may be installed in the branched hydraulic line portion to prevent a backflow of fluid from the pedal simulator to the auxiliary brake cylinder while allowing fluid to flow only from the auxiliary brake cylinder to the pedal simulator.Further, the electronic hydraulic brake system may further include a controller configured to perform opening and closing operations of the first and second simulator valves to open the first simulator valve while closing the second simulator valve after receiving a brake input generated based on an operation of the brake pedal by the driver. The controller may be configured to perform opening and closing operations of the first and second simulator valves based on a mode selected by the driver among pedal feel modes after receiving a brake input generated based on an operation of the brake pedal by the driver.The pedal feel modes may include a normal pedal feel mode in which the first simulator valve is opened and the second simulator valve is closed, and a smooth pedal feel mode in which the first and second simulator valves are opened. The electronic hydraulic brake system may further include a pressure generator configured to generate a brake hydraulic pressure, wheel brakes each configured to receive the brake hydraulic pressure generated by the pressure generator to generate a braking force limiting the rotation of each of the corresponding wheels, and a hydraulic pressure supply line connecting the pressure generator to the wheel brakes to supply the brake hydraulic pressure generated by the pressure generator to the wheel brakes, wherein at least one check valve may be installed in a fluid line connecting the hydraulic pressure supply line to the pedal-side hydraulic line.In addition, the electronic hydraulic brake system may further include a controller configured to perform opening and closing operations of the first and second simulator valves and opening and closing operations of the check valve. The controller may be configured to, when a failure of the pressure generator occurs, close the first simulator valve while open the second simulator valve and the shut-off valve.The hydraulic pressure supply line may include a first sub hydraulic pressure supply line configured to supply a brake hydraulic pressure from the pressure generator to one pair of the wheel brakes and a second sub hydraulic pressure supply line configured to supply the brake hydraulic pressure from the pressure generator to another pair of the wheel brakes. A first check valve may be installed in a fluid line connecting the second sub hydraulic pressure supply line to a portion of the pedal side hydraulic line between the first simulator valve and the master cylinder, and a second check valve may be installed in a fluid line connecting the first sub hydraulic pressure supply line to the master cylinder.The electronic hydraulic brake system may further include a controller configured to perform opening and closing operations of the first and second simulator valves and opening and closing operations of the first and second cut valves. The controller may be configured to, when a failure of the pressure generator occurs, close the first simulator valve while opening the second simulator valve and the first and second shut-off valves.In addition, the electronic hydraulic brake system may further include a pressure generator configured to generate a brake hydraulic pressure, wheel brakes each configured to receive the brake hydraulic pressure generated by the pressure generator to generate a braking force that limits the rotation of each of the corresponding wheels, and a hydraulic pressure supply line connecting the pressure generator to the wheel brakes to supply the brake hydraulic pressure generated by the pressure generator to the wheel brakes. A boost valve may be installed in the hydraulic pressure supply line connecting the pressure generator to the wheel brakes. A pressure reducing valve may be installed in a liquid line branched from the hydraulic pressure supply line and connected to a liquid reservoir.The electronic hydraulic brake system may further include a controller configured to perform an operation of the boost valve and an operation of the pressure reducing valve, and operate the pressure generator or the boost and pressure reducing valves based on a depression force of the driver, thereby adjusting a brake hydraulic pressure supplied to the wheel brakes via the hydraulic pressure supply line.The hydraulic pressure supply line may include a first sub hydraulic pressure supply line configured to supply a brake hydraulic pressure from the pressure generator to one pair of the wheel brakes and a second sub hydraulic pressure supply line configured to supply the brake hydraulic pressure from the pressure generator to another pair of the wheel brakes. Boost valves may be installed in the first and second sub hydraulic pressure supply lines, respectively. Pressure reducing valves may be installed in each of liquid lines branched from each of the corresponding sub hydraulic pressure supply lines and connected to the liquid container.In still another exemplary embodiment, the controller may be configured to operate the boost valves and the pressure reducing valves and operate the pressure generator or the boost and the pressure reducing valves based on a depression force of the driver, to thereby adjust a brake hydraulic pressure supplied to the wheel brakes via the sub hydraulic pressure supply lines.The invention will be explained in more detail with reference to the drawings. In the drawing, the following are shown: FIG. 1 is a schematic diagram of a brake system according to an exemplary embodiment of the present invention; FIGS. 2 and 3 are switching diagrams illustrating operating states of the brake system according to the exemplary embodiment of the invention; FIG. 4 is a diagram illustrating an operation state of the brake system according to the exemplary embodiment of the invention in a normal pedal feel mode; FIG. 5 is a diagram illustrating an operation state of the brake system according to the exemplary embodiment of the invention in a soft pedal feel mode; FIG. 6 is a graph illustrating foot forces depending on pedal strokes in a brake system according to the exemplary embodiment of the invention in the normal pedal feel mode and the soft pedal feel mode; and FIG. 7 is a diagram illustrating a backup braking state in the event of failure of the brake system according to the exemplary embodiment of the invention.It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. In the figures, reference numerals refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.It is understood that the term "vehicle" or "vehicular" or other similar term as used herein includes general motor vehicles such as passenger cars including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, as well as hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle having two or more sources of power, for example both gasoline propulsion and electric propulsion.Although the example embodiment is described as using a plurality of units to perform the example process, it should be appreciated that the example processes may be performed by one or more modules. It should also be understood that the term controller / controller refers to a hardware device that includes a memory and a processor. The memory is configured to store the modules, and the processor is specifically configured to apply the modules to perform one or more processes described below.Further, the control logic according to the present invention may be embodied as a non-transitory computer readable medium on a computer readable medium containing executable program instructions executed by a processor, controller, or the like. Examples of the computer readable media include, but are not limited to, ROM, RAM, CD-ROMs, magnetic tapes, floppy disks, memory sticks, smart cards, and optical data storage devices. The computer readable storage medium may also be distributed in network coupled computer systems such that the computer readable medium is stored and executed in a distributed manner, e.g., by a telematics server or a control area network (CAN).The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, describe the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.Reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. Although the invention has been described in connection with exemplary embodiments, it is to be understood that the present description is not intended to limit the invention to these exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.FIG. 1 is a schematic diagram of a brake system according to an exemplary embodiment of the present invention. The invention provides a brake system capable of improving a hydraulic booster brake system having a pedal simulator, i.e., achieving improvement in backup brake performance and increase in design freedom of the pedal simulator.According to an exemplary embodiment of the invention, a hydraulic booster brake system is provided, which can be realized as an electronic hydraulic brake system. Specifically, in the electronic hydraulic brake system, as an electronic actuator, a pump may be used to convert the rotational force generated during driving of a motor 41 into a linear force to move a piston 43 in the forward and rearward directions. According to the movement of the piston 43, brake fluid in a pressure chamber 44 aof a cylinder 44 may be pressurized to thereby generate hydraulic pressure.According to an exemplary embodiment of the invention, the electronic hydraulic brake system may include a brake pedal 10 as a brake input unit to be operated by a driver for braking a vehicle, a brake input detection sensor 11 configured to detect a brake input value from the brake pedal 10, a pressure generator 40 configured to generate a brake hydraulic pressure, and wheel cylinders 50 each configured to receive the brake hydraulic pressure generated by the pressure generator 40 to generate a braking force capable of limiting the rotation of each of the respective wheels. The electronic hydraulic brake system may further include a hydraulic pressure supply line 60 connecting the pressure generator 40 to the wheel cylinders 50 to supply the brake hydraulic pressure generated by the pressure generator 40 to the wheel cylinders 50, and a controller 80 configured to operate the pressure generator 40 to generate a target brake hydraulic pressure based on a signal from the brake input detection sensor 11.The configuration of the above-described electronic hydraulic brake system will now be described in more detail. The electronic hydraulic brake system may further include fluid reservoirs 23 aand 23 bconfigured to store brake fluid therein, master and auxiliary brake cylinders 21 and 22 connected to the fluid reservoirs 23 aand 23 b, respectively, and the brake pedal 10 to generate hydraulic pressure when the driver depresses the brake pedal 10 (e.g., when a foot force of the driver is applied to the brake pedal 10 or a pressure is applied to the brake pedal 10), and a pedal simulator 30 connected to the master and auxiliary brake cylinders 21 and 22 via a pedal side hydraulic line 24 to generate pedal feeling based on a foot force of the driver using the hydraulic pressure generated by the two brake cylinders 21 and 22. Therefore, in the electronic hydraulic brake system according to the exemplary embodiment of the invention, the master cylinder connected to the brake pedal 10 may be constituted by two brake cylinders, i.e., the master cylinder 21 and the auxiliary brake cylinder 22, which are connected in parallel with each other between the brake pedal 10 and the pedal simulator 30.In the above-described configuration, the brake pedal 10 may be connected to both the master cylinder 21 and the auxiliary brake cylinder 22, and thus hydraulic pressure may be generated from both the master cylinder 21 and the auxiliary brake cylinder 22 when the driver depresses the brake pedal 10 and then a foot force may be applied to the brake pedal 10. In addition, in a soft pedal feel mode as described later, it is possible to generate hydraulic pressure for generating pedal feel by only one brake cylinder, specifically, the master cylinder 21, through the operation of first and second simulator valves 26 and 27.The master cylinder 21 is not different in configuration from a master cylinder mounted in a general electronic hydraulic brake system. However, the electronic hydraulic brake system according to the exemplary embodiment of the invention is different from the general electronic hydraulic brake system in that, in addition to the master cylinder 21, another brake cylinder to which the brake pedal 10 is connected, namely, the auxiliary brake cylinder 22 is provided separately from the master cylinder 21.In particular, master brake cylinder 21 and auxiliary brake cylinder 22 may be connected in parallel to pedal simulator 30 via pedal-side hydraulic line 24. The pedal simulator 30 is not different in configuration from a pedal simulator mounted in the general electronic hydraulic brake system. The pedal simulator 30 may include a housing 31, at least one spring 33, a damper 32, and a piston 34 supported by the spring 33. The piston 34 may be moved by hydraulic pressure generated by the two brake cylinders 21 and 22 (or the master cylinder 21), and thus the pedal simulator 30 may be configured to generate a pedal reaction feeling, i.e., a pedal feeling, and may be configured to give (e.g., transmit) the generated pedal feeling to the driver through the brake pedal 10. In the same manner as the connection of the fluid reservoir 23 awith the master brake cylinder 21, the fluid reservoir 23 bmay be connected with the auxiliary brake cylinder 22. Although one liquid reservoir is provided for each of the brake cylinders 21 and 22 in the illustrated exemplary embodiment, a common liquid reservoir connected to the two brake cylinders may be used.In the above-described configuration, when the brake pedal 10 is depressed, a foot force of the driver can be transmitted to respective pistons (not numbered) of the master and slave brake cylinders 21 and 22 via the brake pedal 10. As a result, the pistons can be moved forward, thus pressurizing the liquid in the brake cylinders 21 and 22, thereby generating hydraulic pressure. The generated hydraulic pressure may be transmitted to the pedal simulator 30 via the pedal-side hydraulic line 24.Further, in a hydraulic line portion between the auxiliary brake cylinder 22 and the pedal simulator 30, in the pedal-side hydraulic line 24 installed to transmit the pressure of the pressurized fluid to the pedal simulator 30, a check valve 25 may be installed to prevent a backflow of the fluid from the pedal simulator 30 to the auxiliary brake cylinder 22 while allowing the fluid to flow only from the auxiliary brake cylinder 22 to the pedal simulator 30. The check valve 25 may be configured to prevent hydraulic pressure generated by the master cylinder 21 from being transmitted to the pedal-side hydraulic line portion on the side of the auxiliary brake cylinder 22.Therefore, since both the master cylinder 21 and the auxiliary brake cylinder 22 may be coupled to the brake pedal 10 while being connected to the pedal simulator 30 via the pedal-side hydraulic line 24, the master cylinder 21 and the auxiliary brake cylinder 22 may be configured to simultaneously generate hydraulic pressure when the driver depresses the brake pedal 10, and thus the hydraulic pressure generated by the master cylinder 21 and the hydraulic pressure generated by the auxiliary brake cylinder 22 may be simultaneously transmitted to the pedal simulator 30.In addition, the first simulator valve 26 may be installed in the pedal-side hydraulic line 24 between the master cylinder 21 and the pedal simulator 30. The second simulator valve 27 may be installed in a fluid line connecting the auxiliary brake cylinder 22 to the fluid reservoir 23 b. Further, it may be determined by a controller whether hydraulic pressure is generated in the pedal-side hydraulic piping portion on the side of each brake cylinder 21 or 22 for the operation of the pedal simulator 30 based on the opening or closing operation of the two simulator valves, i.e., the first and second simulator valves 26 and 27.Referring to FIG. 1, it can be seen that in the configuration of the pedal-side hydraulic line 24, a hydraulic line portion branching from a hydraulic line portion between the auxiliary brake cylinder 22 and the second simulator valve 27 may be connected to the pedal simulator 30. In addition, it can be seen that, in the configuration of the pedal-side hydraulic line 24, a hydraulic line portion in which the check valve 25 is installed may be connected to a hydraulic line portion between the pedal simulator 30 and the first simulator valve 26, and a first check valve 71 may be installed in a fluid line 69 that connects the hydraulic pressure supply line 60 to a hydraulic line portion between the first simulator valve 26 and the master cylinder 21.Meanwhile, in the electronic hydraulic brake system according to the exemplary embodiment of the invention, the pressure generator 40 may include a reciprocating pump driven by the motor 41. The operation of the pump may be performed by the controller 80. In other words, while the controller 80 drives the motor 41, the pump may be configured to generate a target brake hydraulic pressure. In this regard, the pump is not different in configuration from a piston-type pressure pump used in the general electronic hydraulic brake system. In other words, the pump may be a piston (plunger) pressure pump in which the piston 43 is configured to generate and adjust hydraulic pressure while moving forward or backward based on a linear force converted from the rotational force of the motor 41. Such a configuration is well known in the art, so a detailed description thereof will be omitted.For example, in the pump described above, the conversion of the rotational force of the motor 41 into the linear force of the piston 43 can be achieved by the configuration described below. A ball screw 42 may be mounted on a rotation shaft of the motor 41 so as to be rotatable together with the rotation shaft, and the plunger 43 may be engaged with an outer surface of the ball screw 42 and thus moved forward or backward along an inner side of the cylinder 44 during rotation of the ball screw 42. When the piston 43 moves forward, the liquid in the pressure chamber 44 aof the cylinder 44 may be pressurized to thereby generate hydraulic pressure.The lines and accessories such as a liquid line 46 installed between the pump and a liquid reservoir 45 and a check valve 47 installed in the liquid line 46 are not different from those of the plunger type pump used in the general electronic hydraulic brake system. The pump including the motor 41 and the piston 43 may be connected to the hydraulic pressure supply line 60 to supply hydraulic pressure to the wheel cylinders 50. Specifically, the hydraulic pressure supply line 60 may be connected to the pump pressure chamber 44 aand the wheel cylinder 50 of each wheel to transmit the hydraulic pressure.Therefore, the hydraulic pressure generated during the operation of the pump can be supplied to the wheel cylinder 50 of each wheel via the hydraulic pressure supply line 60. A boost valve 61 may be installed in the hydraulic pressure supply line 60 that connects the pump to the wheel cylinder 50 of each wheel. The hydraulic pressure supply line 60 in which the boost valve 61 is installed may be connected to the wheel cylinder 50 of each wheel via an inlet valve 64 to supply the hydraulic pressure generated by the pump. In addition, a return line 65 may be branched from the hydraulic pressure supply line 60 connected to the wheel cylinder 50 of each wheel. The return line 65 can be connected to a liquid container 73 via an outlet valve 66.In an exemplary embodiment, the inlet valve 64 may be a normally open (NO) valve and the outlet valve 66 may be a normally closed (NC) valve. In the exemplary embodiment shown, as the inlet valve 64 and the outlet valve 66, an NO and an NC valve for ABS per wheel may be installed, respectively, to independently adjust the pressure of each wheel. In the illustrated exemplary embodiment, the hydraulic pressure supply line 60 connected to the pump pressure chamber 44 amay include two branched hydraulic pressure supply lines, i.e., a first sub hydraulic pressure supply line 62 and a second sub hydraulic pressure supply line 63.In addition, the branched sub hydraulic pressure supply lines 62 and 63 may be branched into two hydraulic pressure supply lines, i.e., lines 62 aand 62 b, and lines 63 aand 63 b, respectively. The finally branched hydraulic pressure supply lines 62 a, 62 b, 63 a, and 63 bmay be connected to the respective wheel cylinders 50 of the wheels. Liquid lines 67 branched from the first and second sub hydraulic pressure supply lines 62 and 63 may be connected to the liquid container 45. Each liquid line 67 may be connected to a line portion above the check valve 47 of the liquid line 46 connecting the pump to the liquid container 45.A pressure reducing valve 68 may be installed in each liquid line 67 connected to the liquid container 45 and branched from the first and second sub hydraulic pressure supply lines 62 and 63. In addition, the adjustment of the wheel pressure by each wheel cylinder 50 (wheel brake) configured to generate a braking force on the corresponding wheel may be performed by the operation of the motor 41 or the boost valve 61 and the pressure reducing valve 68. A boost valve 61 and a pressure reducing valve 68 may be installed per hydraulic circuit, i.e., in a primary hydraulic circuit including the first sub hydraulic pressure supply line 62 and a secondary hydraulic circuit including the second sub hydraulic pressure supply line 63.In addition to the type in which hydraulic pressure is generated based on the conversion of a rotational motion of the motor 41 into a linear motion of the piston 43, other types may be used in the brake system according to the invention. For example, the brake system according to the invention may employ a type in which hydraulic pressure of the fluid pumped from the pump driven by rotation of the motor 41 is stored in a high-pressure accumulator, and then the wheel pressure (e.g., wheel cylinder hydraulic pressure) for generating the braking force may be adjusted by operating the pressure reducing valve 68 and the boosting valve 61.Further, the hydraulic pressure supply line 60, i.e., the first sub hydraulic pressure supply line 62 and the second sub hydraulic pressure supply line 63 may be connected to the pedal-side hydraulic line 24 and the master cylinder 21 via fluid lines 70 and 69 branched from the first sub hydraulic pressure supply line 62 and the second sub hydraulic pressure supply line 63, respectively, downstream of the respective boost valves 61. The first check valve 71 may be installed in the liquid line 69 that connects the second sub hydraulic pressure supply line 63 to the pedal-side hydraulic line 24. A second check valve 72 may be installed in the fluid line 70 connecting the first sub hydraulic pressure supply line 62 to the master cylinder 21. The first shut-off valve 71 and the second shut-off valve 72 may be configured to shut off supply of hydraulic pressure generated based on a foot force (e.g., a depression amount) of the driver and hydraulic pressure generated by the pump for generating braking force, i.e., wheel pressure set for generating braking force, from each other.As described above, in an electronic hydraulic brake system according to the illustrated exemplary embodiment of the invention, a brake cylinder configuration is provided in which two brake cylinders, i.e., the master cylinder 21 and the slave cylinder 22, may be disposed in parallel with the pedal simulator 30, and accordingly, the pressurizing area of the brake cylinder may be increased in a normal control mode. Thus, improvement in design freedom of the pedal simulator 30 can be achieved.In view of this, the hardness of the spring 33 and the damper 32 can be reduced, so that it is possible to achieve an increase in the durability of the pedal simulator 30 and an improvement in the pedal feel (e.g., prevention of a large depression of the pedal at an initial stage of braking). In addition, a deviation between constituent elements in the pedal simulator can be reduced, and thus a deviation in pedal feel can be advantageously reduced. If the system fails, the pressurizing area of the brake cylinder (by using only the master cylinder) can be minimized. Accordingly, it is possible to increase the backup braking performance of generating a braking force by hydraulic pressure generated from the master cylinder by a foot force of the driver in an open state of the first and second cut valves 71 and 72. In addition, under the condition that the desired hardness of the spring 33 and the damper 32 of the pedal simulator 30 has already been secured even with a reduced brake cylinder diameter, it is possible to variably set a pedal feeling based on a setting operation of the operator by operating the first and second simulator valves 26 and 27, and thus the marketability of the vehicle can be improved.Next, a method of controlling the above-described brake system according to the illustrated exemplary embodiment of the invention and operating states according to the control method will be described. FIG. 2 is a diagram illustrating a standby state before braking of the brake system according to the illustrated exemplary embodiment of the invention. FIG. 3 is a diagram illustrating a control state during braking.Referring to FIG. 2 illustrating a state before the brake pedal 10 is depressed, the first simulator valve 26 is an NC valve, and the second simulator valve 27 is an NO valve, the first and second cut valves 71 and 72 are NO valves, and the boost valve 61 and the pressure reducing valve 68 are NC valves, as can be seen from the states of the respective valves before the valve drive control.In contrast to the state in FIG. 2, a state in which brake hydraulic pressure is generated while the driver depresses the brake pedal 10 is shown in FIG. 3. In other words, FIG. 3 shows a state in which, while each wheel cylinder 50 receives a brake hydraulic pressure, a braking force can be generated at the corresponding wheel brake by hydraulic pressure of the wheel cylinder 50. When the brake pedal 10 is depressed or engaged, the brake input detection sensor 11, which may be, for example, a pedal stroke sensor, may be configured to detect a pedal stroke. Based on information regarding the detected pedal stroke, the controller 80 may be configured to determine a driver's desire or intention to brake.In addition, the controller 80 may be configured to acquire a target hydraulic pressure for generating braking force by using a pedal stroke value, which is the brake input value from the driver. Using the target hydraulic pressure as a target value, the controller 80 may be configured to drive the motor 41 of the pump to generate and adjust a brake hydraulic pressure to be transmitted to each wheel cylinder 50 via the hydraulic pressure supply line 60. Therefore, the brake hydraulic pressure generated by the pump can be transmitted to each wheel cylinder 50 (e.g., wheel brake) via the hydraulic pressure supply line 60, and thus the deceleration of the vehicle can be achieved.In the above-described braking state, based on a control signal from the controller 80, the first simulator valve 26 may be opened, the second simulator valve 27 may be closed, and both the first shut-off valve 71 and the second shut-off valve 72 may be closed.Specifically, hydraulic pressure can be generated by both the master cylinder 21 and the auxiliary cylinder 22, and therefore pedal feeling can be given to the driver by the hydraulic pressure acting in the pedal-side hydraulic line 24 between the pedal simulator 30 and the two brake cylinders 21 and 22 based on a foot force of the driver.Further, based on the closing of the first check valve 71 and the second check valve 72, the pedal-side hydraulic line 24 and the hydraulic pressure supply line 60 may be disconnected from each other, and therefore, the pressure (e.g., hydraulic pressure) generated by the driver's foot force and the brake hydraulic pressure set by the pump may be disconnected from each other. In addition, the brake pressure transmitted to each wheel cylinder 50 after being generated in the hydraulic pressure supply line 60 may be adjusted by the motor 41 of the pump, the corresponding boost valve 61 (supply control), and the corresponding pressure reducing valve 68 (release control). Specifically, the boost valve 61 and the pressure reducing valve 68 installed in the primary hydraulic circuit and the boost valve 61 and the pressure reducing valve 68 installed in the secondary hydraulic circuit can be independently operated based on the respective hydraulic circuits, and thus the hydraulic pressure of each hydraulic circuit can be independently adjusted.Accordingly, it is possible to independently adjust the brake hydraulic pressure and the braking force in the wheel cylinders 50 included in the primary hydraulic circuit and the brake hydraulic pressure and the braking force in the wheel cylinders 50 included in the secondary hydraulic circuit based on the respective hydraulic circuits.Specifically, the primary hydraulic circuit may include the first sub hydraulic pressure supply line 62, the boost valve 61 installed in the first sub hydraulic pressure supply line 62, the liquid line 67 branched from the first sub hydraulic pressure supply line 62, the pressure reducing valve 68 installed in the liquid line 67, the hydraulic pressure supply lines 62 aand 62 bbranched from the first sub hydraulic pressure supply line 62, a pair of wheel cylinders 50 connected to the hydraulic pressure supply lines 62 aand 62 b, the inlet valve 64 and the outlet valve 66 installed respectively for the wheel cylinders 50, and the return line 65 in which the outlet valve 66 is installed.Meanwhile, the secondary hydraulic circuit may include the second sub hydraulic pressure supply line 63, the boost valve 61 installed in the second sub hydraulic pressure supply line 63, the liquid line 67 branched from the second sub hydraulic pressure supply line 63, the pressure reducing valve 68 installed in the liquid line 67, the hydraulic pressure supply lines 63 aand 63 bbranched from the second sub hydraulic pressure supply line 63, a pair of wheel cylinders 50 connected to the hydraulic pressure supply lines 63 aand 63 b, the inlet valve 64 and the outlet valve 66 installed respectively for the wheel cylinders 50, and the return line 65 in which the outlet valve 66 is installed.Next, with reference to FIGS. 4 and 5, a process of generating a pedal feeling during braking will be described. FIG. 4 is a diagram illustrating a typical normal pedal feel mode. In the normal pedal feel mode, it is possible to achieve a mode change to a smooth pedal feel mode by operating the first and second simulator valves 26 and 27, as shown in FIG. 5.In FIG. 3, the first simulator valve 26 and the second simulator valve 27 are illustrated as being in the state of a normal pedal feeling mode as in FIG. 4. Referring to FIG. 5, the pedal-side hydraulic line 24 on the master cylinder 21 side may be isolated from the pedal-side hydraulic line 24 on the auxiliary cylinder 22 side by the check valve 25. When the two simulator valves 26 and 27 are operated to be opened in the normal pedal feel mode, the hydraulic pressure of the auxiliary brake cylinder 22 and the hydraulic pressure of the pedal-side hydraulic line 24 on the auxiliary brake cylinder 22 side become atmospheric pressure, and therefore, hydraulic pressure for creating a pedal feel can be created by the pedal simulator 30 on the master brake cylinder 21 side and the pedal-side hydraulic line 24 corresponding thereto.Accordingly, the amount of fluid and hydraulic pressure introduced into the pedal simulator 30 can be increased as compared with that of the normal pedal feel mode in FIG. 4 under the condition of the same foot force of the driver, and thus smooth pedal feel can be transmitted to the driver. Thus, it is possible to set and set a pedal feeling for the driver in a normal mode or a smooth mode based on the mode set by the driver by using the two brake cylinders 21 and 22 and the two simulator valves 26 and 27 and operating each simulator valve.Specifically, under the condition that the driver has selected a desired pedal feel mode by operating an operating device such as a switch or other input device, the controller may be configured to drive each simulator valve based on the mode selected by the driver, and thus a foot force and a pedal feel may be provided in one of the normal mode and the smooth mode.Referring to FIG. 6, it can be seen that under the same pedal stroke conditions, a lower foot force is required in the soft pedal feel mode than in the normal pedal feel mode.Meanwhile, FIG. 7 is a diagram illustrating a backup braking state when the system has failed. For example, when a failure occurs in the pressure generator 40 or the like due to a failure in the motor 41 or other elements of the pump, the operation of the motor 41 of the pump and the operation of the pressure reducing valve 68 and the boosting valve 61 may be stopped (e.g., by a closed state of both the pressure reducing valve 68 and the boosting valve 61), and the first shut-off valve 71 and the second shut-off valve 72 may be opened by the controller.Specifically, the first simulator valve 26 may be closed and the second simulator valve 27 may be opened, and therefore, the side of the auxiliary brake cylinder 22 is under atmospheric pressure. In other words, no hydraulic pressure is generated in the auxiliary brake cylinder 22. As a result, no pressure is generated in the pedal simulator 30. Accordingly, the hydraulic pressure generated from the master cylinder 21 by the driver's foot force can be transmitted to each wheel cylinder 50 via the pedal-side hydraulic line 24 and the hydraulic pressure supply line 60, and a braking force can be generated. Therefore, the foot force generated when the operator depresses the brake pedal 10 can be used only for generating hydraulic pressure by the master cylinder 21, and an increased hydraulic pressure can be transmitted to each wheel cylinder 50, thereby generating an increased braking force. Accordingly, an increase in the backup braking performance can be achieved.As is apparent from the above description, the present invention provides a brake system capable of improving a hydraulic booster brake system having a pedal simulator, i.e., achieving an increase in backup brake performance and an improvement in the freedom of design of the pedal simulator. In addition, it is possible that by controlling valves, different pedal feel modes may be set to desired pedal feel modes selected by the driver.

Claims

An electronic hydraulic brake system comprising: a brake pedal (10) to be operated by a driver for braking a vehicle; a brake cylinder connected to the brake pedal (10) for generating a hydraulic pressure after receiving a foot force of the driver via the brake pedal (10); and a pedal simulator (30) connected to the brake cylinder via a pedal side hydraulic line (24) for providing a pedal feeling based on the foot force of the driver by means of the hydraulic pressure generated by the brake cylinder, wherein the brake cylinder comprises: a master cylinder (21) connected to the brake pedal (10) while being connected to the pedal simulator (30) via the pedal side hydraulic line (24), and an auxiliary cylinder (22) connected to the brake pedal (10), while being connected to the pedal simulator (30) and a fluid reservoir (23b) via the pedal-side hydraulic line (24), a first simulator valve (26) is installed in a portion of the pedal-side hydraulic line (24) between the master cylinder (21) and the pedal simulator (30), and a second simulator valve (27) is installed in a portion of the pedal-side hydraulic line (24) between the auxiliary cylinder (22) and the fluid reservoir (23b), and a check valve (25) is installed in a portion of the pedal-side hydraulic line (24) between the auxiliary cylinder (22) and the pedal simulator (30) to prevent a backflow of fluid from the pedal simulator (30) to the auxiliary cylinder (22) while allowing fluid to flow only from the auxiliary cylinder (22) to the pedal simulator (30).The electronic hydraulic brake system according to claim 1, further comprising: a controller (80) configured to perform opening and closing operations of the first and second simulator valves (26, 27) to open the first simulator valve (26) while closing the second simulator valve (27) after receiving a brake input generated based on an operation of the brake pedal by the driver.The electronic hydraulic brake system according to claim 1, wherein the pedal-side hydraulic line (24) includes a hydraulic line portion branched from a hydraulic line portion between the auxiliary brake cylinder (22) and the second simulator valve (27) and connected to the pedal simulator (30).The electronic hydraulic brake system according to claim 3, wherein the branched hydraulic line portion is connected to a hydraulic line portion between the pedal simulator (30) and the first simulator valve (26), and a check valve (25) is installed in the branched hydraulic line portion to prevent a backflow of liquid from the pedal simulator (30) to the auxiliary brake cylinder (22) while allowing liquid to flow only from the auxiliary brake cylinder (22) to the pedal simulator (30).The electronic hydraulic brake system according to claim 3 or 4, further comprising: a controller (80) configured to perform opening and closing operations of the first and second simulator valves (26, 27) to open the first simulator valve (26) while closing the second simulator valve (27) after receiving a brake input generated based on an operation of the brake pedal by the driver.The electronic hydraulic brake system according to claim 1, further comprising: a controller (80) configured to perform opening and closing operations of the first and second simulator valves (26, 27) based on a mode selected by an operator from pedal feel modes after receiving a brake input generated based on an operation of the brake pedal by the driver.The electronic hydraulic brake system according to claim 6, wherein the pedal feel modes include: a normal pedal feel mode in which the first simulator valve (26) is opened and the second simulator valve (27) is closed; and a smooth pedal feel mode in which the first and second simulator valves (26, 27) are opened.The electronic hydraulic brake system according to claim 1, further comprising: a pressure generator (40) configured to generate a brake hydraulic pressure; wheel brakes (50) each configured to receive the brake hydraulic pressure generated by the pressure generator (40) to generate a braking force that limits the rotation of each of the corresponding wheels; and a hydraulic pressure supply line (60) connecting the pressure generator (40) to the wheel brakes (50) to supply the brake hydraulic pressure generated by the pressure generator (40) to the wheel brakes (50), wherein a shut-off valve is installed in a fluid line (69) connecting the hydraulic pressure supply line (60) to the pedal-side hydraulic line (24).The electronic hydraulic brake system according to claim 8, further comprising: a controller (80) configured to perform opening and closing operations of the first and second simulator valves (26, 27) and opening and closing operations of the check valve (71), wherein the controller (80) is configured to, when a failure of the pressure generator (40) occurs, close the first simulator valve (26) while opening the second simulator valve (27) and the check valve (71).The electronic hydraulic brake system according to claim 8, wherein the hydraulic pressure supply line (60) includes: a first sub hydraulic pressure supply line (62) configured to supply a brake hydraulic pressure from the pressure generator (40) to one pair of the wheel brakes (50), and a second sub hydraulic pressure supply line (63) configured to supply the brake hydraulic pressure from the pressure generator (40) to another pair of the wheel brakes (50), and wherein the shut-off valve includes: a first shut-off valve (71) installed in a fluid line (69) connecting the second sub hydraulic pressure supply line (63) to a portion of the pedal-side hydraulic line (24) between the first simulator valve (26) and the master cylinder (21), and a second shut-off valve (72) installed in a fluid line (70), which connects the first secondary hydraulic pressure supply line (62) to the master brake cylinder (21).The electronic hydraulic brake system according to claim 10, further comprising: a controller (80) configured to perform opening and closing operations of the first and second simulator valves (26, 27) and opening and closing operations of the first and second shut-off valves (71, 72), wherein the controller (80) is configured to, when a failure of the pressure generator (40) occurs, close the first simulator valve (26) while opening the second simulator valve (27) and the first and second shut-off valves (71, 72).The electronic hydraulic brake system according to claim 1, further comprising: a pressure generator (40) configured to generate a brake hydraulic pressure; wheel brakes (50) each configured to receive the brake hydraulic pressure generated by the pressure generator (40) to generate a braking force that limits the rotation of each of the corresponding wheels; and a hydraulic pressure supply line (60) connecting the pressure generator (40) to the wheel brakes (50) to supply the brake hydraulic pressure generated by the pressure generator (40) to the wheel brakes (50), wherein a boost valve (61) is installed in the hydraulic pressure supply line (60) connecting the pressure generator (40) to the wheel brakes (50); and wherein a pressure reducing valve (68) is installed in a liquid line (67) connected to a liquid reservoir (45) and branched from the hydraulic pressure supply line (60).The electronic hydraulic brake system according to claim 12, further comprising: a controller (80) configured to perform an operation of the boost valve (61) and an operation of the pressure reducing valve (68), and perform an operation of the pressure generator (40) or operations of the boost and pressure reducing valves (61, 68) based on a foot force of the driver to adjust a brake hydraulic pressure supplied to the wheel brakes (50) via the hydraulic pressure supply line (60).The electronic hydraulic brake system according to claim 12, wherein the hydraulic pressure supply line (60) includes: a first sub hydraulic pressure supply line (62) configured to supply a brake hydraulic pressure from the pressure generator (40) to one pair of the wheel brakes (50), and a second sub hydraulic pressure supply line (63) configured to supply the brake hydraulic pressure from the pressure generator (40) to another pair of the wheel brakes (50); the boost valve (61) includes boost valves (61) respectively installed in the first and second sub hydraulic pressure supply lines (62, 63); and the pressure reducing valve (68) includes pressure reducing valves (68) respectively installed in liquid lines (67) connected to the liquid reservoir (45) and respectively branched from one of the corresponding sub hydraulic pressure supply lines (62, 63).The electronic hydraulic brake system according to claim 14, further comprising: a controller (80) configured to perform operations of the boost valves (61) and operations of the pressure reducing valves (68), and perform an operation of the pressure generator (40) or operations of the boost and pressure reducing valves (61, 68) based on a foot force of the driver to adjust a brake hydraulic pressure supplied to the wheel brakes (50) via the sub hydraulic pressure supply lines (62, 63).

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