Vehicle braking system and self-diagnostic tests

Abstract

Method for performing a diagnostic test to determine leaks within a brake system, the method comprising: (a) Providing a braking system (10) comprising: a piston arrangement (18) with a housing defining a bore therein, wherein the piston arrangement (18) has a piston slidably arranged therein such that the movement of the piston pressurizes a pressure chamber when the piston is moved in a first direction, and wherein the pressure chamber of the piston arrangement (18) is in fluid communication with an outlet, and wherein the piston arrangement (18) further comprises an electrically operated linear drive for moving the piston within the bore; (b) Actuating the linear drive of the piston assembly (18) to provide pressure at a first predetermined level at the outlet of the piston assembly (18); (c) Maintaining the pressure at the outlet of the piston assembly (18) for a predetermined period of time; and (d) Determine whether a condition criterion is met which indicates a leak within the brake system (10), wherein the brake system (10) further comprises: a brake pedal unit (14) with a housing defining a bore therein, wherein the brake pedal unit (14) further comprises a first piston slidably arranged therein such that the movement of the first piston pressurizes a first pressure chamber, and wherein the brake pedal unit (14) further comprises a second piston slidably arranged therein such that the movement of the second piston pressurizes a second pressure chamber; a first pressure build-up valve for selectively enabling a fluid flow to a first wheel brake; and characterized by a first separating valve (30, 32) which is movable between a first position which allows a fluid connection between the outlet of the piston assembly (18) and the first pressure build-up valve, and a second position which allows a fluid connection between the first pressure chamber of the brake pedal assembly (14) and the first pressure build-up valve; where, following step (a), the first separating valve (30, 32) is actuated to prevent the fluid flow from the outlet of the piston assembly (18) to the first pressure build-up valve and to allow the fluid flow to one of the first and second pressure chambers of the brake pedal assembly (14).

Description

GENERAL STATE OF THE ART

[0001] This invention relates generally to vehicle braking systems. Vehicles are typically slowed down and stopped by hydraulic braking systems. These systems vary in complexity, but a basic braking system generally includes a brake pedal, a tandem master cylinder, fluid lines arranged in two similar but separate brake circuits, and wheel brakes in each circuit. The driver of the vehicle operates a brake pedal connected to the master cylinder. When the brake pedal is operated, the master cylinder generates hydraulic forces in both brake circuits by pressurizing a brake fluid. The pressurized fluid flows through the fluid lines in both circuits to actuate brake cylinders at the wheels and slow the vehicle.

[0002] Basic braking systems typically use a brake booster that applies force to the master cylinder, assisting the pedal force applied by the driver. The booster can be vacuum- or hydraulically operated. A typical hydraulic booster detects the movement of the brake pedal and generates pressurized fluid that is fed into the master cylinder. The fluid from the booster assists the pedal force acting on the master cylinder pistons, which generate pressurized fluid in the line, in fluid communication with the wheel brakes. This increases the pressures generated by the master cylinder. Hydraulic boosters are usually located adjacent to the master cylinder pistons and use a booster valve to control the pressurized fluid applied to the booster.

[0003] Controlled braking of a vehicle under adverse conditions requires precise brake application by the driver. Under these conditions, a driver can easily apply excessive braking pressure, causing one or more wheels to lock up, resulting in excessive slippage between the wheel and the road surface. Such wheel lock-ups can lead to longer braking distances and a potential loss of directional control.

[0004] Advances in braking technology have led to the introduction of anti-lock braking systems (ABS). An ABS system monitors wheel rotation and selectively applies and releases brake pressure in the relevant wheel brakes to maintain wheel speed within a selected slip range and achieve maximum braking force. Such systems are typically designed to control the braking of each braked wheel of the vehicle. However, some systems have been developed to control the braking of only a subset of the many braked wheels.

[0005] Electronically controlled ABS valves, which include pressure build-up valves and pressure release valves, are located between the master cylinder and the wheel brakes. The ABS valves regulate the pressure between the master cylinder and the wheel brakes. Typically, when activated, these ABS valves operate in three pressure control modes: pressure build-up, pressure release, and pressure hold. The pressure build-up valves allow pressurized brake fluid to enter the respective wheel brakes to increase the pressure in pressure build-up mode, and the pressure release valves release the brake fluid from the corresponding wheel brakes in pressure release mode. In hold mode, the wheel brake pressure is maintained at a constant level by closing both the pressure build-up and pressure release valves.

[0006] To achieve maximum braking force while maintaining vehicle stability, it is desirable to achieve optimal wheel slip values ​​at the front and rear axles. During deceleration, different braking forces are required at the front and rear axles to achieve the desired slip values. Therefore, the brake pressures between the front and rear brakes should be proportionally distributed to achieve the highest braking force at each axle. ABS systems with this capability, known as Dynamic Rear Proportioning (DRP) systems, use the ABS valves to regulate the brake pressure at the front and rear wheels independently and dynamically achieve optimal braking performance at both axles under the prevailing conditions.

[0007] Advances in braking technology have led to the introduction of traction control (ASR) systems. Typically, valves were added to existing ABS systems to provide a braking system that regulates wheel speed during acceleration. Excessive wheel speed during acceleration causes wheel slip and loss of traction. An electronic control unit detects this condition and automatically applies brake pressure to the wheel cylinders of the slipping wheel to reduce slip and increase available traction. To achieve optimal vehicle acceleration, pressurized brake fluid is supplied to the wheel cylinders even when the master cylinder is not being actuated by the driver.

[0008] During vehicle movements, such as cornering, dynamic forces are generated that can affect vehicle stability. A Vehicle Stability Control (VSC) braking system improves vehicle stability by counteracting these forces through selective brake application. These forces and other vehicle parameters are detected by sensors and reported to an electronic control unit (ECU). The ECU automatically actuates pressure control devices to regulate the level of hydraulic pressure applied to specific individual wheel brakes. To achieve optimal vehicle stability, brake pressures exceeding the master cylinder pressure must be available quickly and at all times.

[0009] Braking systems can also be used for regenerative braking to recover energy. During regenerative braking, the electromagnetic force of an electric motor / generator is used to provide a portion of the braking torque to the vehicle to meet its braking requirements. A control module in the braking system communicates with a powertrain control module to ensure coordinated braking during regenerative braking, as well as braking in cases of wheel lock-up and skidding. For example, when the driver begins to brake during regenerative braking, the electromagnetic energy of the motor / generator is used to apply the braking torque (i.e., the electromagnetic resistance to generate torque in the powertrain) to the vehicle.If it is determined that insufficient storage capacity is available to store the energy recovered from regenerative braking, or if regenerative braking cannot meet the driver's requirements, hydraulic braking is activated to generate all or part of the braking effect requested by the driver. Preferably, the hydraulic brake operates within a regenerative braking system, so that the system effectively and imperceptibly resumes the process where the electromagnetic brake left off. It is desirable that the vehicle's movement exhibits a smooth transition to hydraulic braking, ensuring that the driver remains unaware of the change.

[0010] Braking systems can also include autonomous braking capabilities, such as adaptive cruise control (ACC). During autonomous braking, various sensors and systems monitor the traffic conditions ahead of the vehicle and automatically activate the braking system to slow the vehicle if necessary. Autonomous braking can be programmed to react quickly to prevent emergency situations. The braking system can be activated without the driver pressing the brake pedal, or even if the driver does not apply sufficient pressure. Advanced autonomous braking systems are designed to operate the vehicle without driver intervention, relying solely on the various sensors and systems that monitor traffic conditions in the vehicle's vicinity.

[0011] A braking system and diagnostic procedures are known, for example, from DE 10 2015 106 089 A1.

[0012] The object of the invention is to overcome the disadvantages of the prior art, in particular to increase vehicle safety through diagnostic methods for brake systems with an electric motor pressure generator.

[0013] This problem is solved by the independent claims procedure, with optional further developments specified in the dependent claims. BRIEF SUMMARY OF THE INVENTION

[0014] This invention relates to a method for performing a diagnostic test to determine leaks within a brake system, wherein a brake system is initially provided with a piston assembly having a housing that defines a bore therein. The piston assembly includes a piston that is slidably arranged therein, such that the movement of the piston pressurizes a pressure chamber when the piston is moved in a first direction. The pressure chamber of the piston assembly is in fluid communication with an outlet, and wherein the piston assembly further includes an electrically operated linear actuator for moving the piston within the bore. The linear actuator of the piston assembly is actuated to provide pressure at a first predetermined level at the outlet of the piston assembly. The pressure at the outlet of the piston assembly is maintained for a predetermined period of time.The procedure also includes determining whether a condition criterion is met that indicates a leak within the brake system.

[0015] This invention further relates to a method for performing a self-diagnostic test to determine leaks within a brake system, wherein a brake system is first provided with a brake pedal unit having a housing that defines a bore therein. The brake pedal unit further comprises a first piston slidably arranged therein, such that the movement of the first piston pressurizes a first pressure chamber, and wherein the brake pedal unit further comprises a second piston slidably arranged therein, such that the movement of the second piston pressurizes a second pressure chamber.The braking system further comprises a piston assembly with a housing defining a bore therein, wherein the piston assembly has a piston slidably arranged therein such that the movement of the piston pressurizes a pressure chamber when the piston is moved in a first direction, and wherein the pressure chamber of the piston assembly is in fluid communication with an outlet, and wherein the piston assembly further comprises an electrically operated linear actuator for moving the piston within the bore. The braking system further comprises a first pressure build-up valve to selectively allow a fluid flow to a first wheel brake, and a second pressure build-up valve to selectively allow a fluid flow to a second wheel brake.A first isolating valve is movable between a first position, which allows fluid flow between the outlet of the piston assembly and the first pressure build-up valve, and a second position, which allows fluid flow between the first pressure chamber of the brake pedal assembly and the first pressure build-up valve. A second isolating valve is movable between a first position, which allows fluid flow between the outlet of the piston assembly and the second pressure build-up valve, and a second position, which allows fluid flow between the second pressure chamber of the brake pedal assembly and the second pressure build-up valve. The first isolating valve is actuated to prevent fluid flow from the outlet of the piston assembly to the first pressure build-up valve. The second isolating valve is actuated to allow fluid flow from the outlet of the piston assembly to the second pressure chamber of the brake pedal assembly.The piston assembly is actuated to provide pressure at its outlet at a first predetermined level. A pressure increase at the piston assembly's outlet causes a pressure increase in the first and second pressure chambers of the brake pedal assembly. The pressure at the piston assembly's outlet is maintained for a predetermined period. The system determines whether the pressure in the second pressure chamber of the brake pedal assembly is below a second predetermined level, which is lower than the first. If the pressure in the second pressure chamber of the brake pedal assembly is not below the second predetermined level, the proper functioning of the second piston within the brake pedal assembly is confirmed.

[0016] Various aspects of this invention will become clear to the person skilled in the art by reading the following detailed description of the preferred embodiment together with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a first embodiment of a braking system. Fig. Figure 2 is an enlarged schematic representation of the piston arrangement of the brake system of Fig. 1. Fig. Figure 3 is a schematic representation of the braking system of Fig. 1, illustrating its function during a self-diagnostic test in which a possible leak within the brake pedal unit is detected. Fig. Figure 4 is a schematic representation of the braking system of Fig. 1, illustrating its function during a self-diagnostic test in which a possible leak within the pedal simulator is detected. Fig. Figure 5 is a schematic representation of the braking system of Fig. Figure 1, illustrating the operation of the brake system during a self-diagnostic test in which a possible leak is detected via the first and second separating valves to the piston assembly. Fig. Figure 6 is a schematic representation of the braking system of Fig. 1, illustrating its function during a self-diagnostic test in which the proper movement of the pistons of the brake pedal unit is verified during a manual full actuation event. DETAILED DESCRIPTION OF THE PREFERRED VERSION

[0017] Referring to the drawings, in Fig. Figure 1 schematically illustrates a first embodiment of a vehicle braking system, generally characterized by 10. The braking system 10 is a hydraulic braking system in which fluid pressure is applied from a source to generate braking forces for the braking system 10. The braking system 10 can be suitably used on a ground vehicle, such as a four-wheeled motor vehicle. Furthermore, the braking system 10 can be equipped with additional braking functions, such as anti-lock braking (ABS) and other traction control functions, for effective braking of the vehicle, as explained below. In the illustrated embodiment of the braking system 10, four wheel brakes 12a, 12b, 12c, and 12d are provided. The wheel brakes 12a, 12b, 12c, and 12d can have any suitable wheel brake design that is actuated by the application of pressurized brake fluid.The wheel brakes 12a, 12b, 12c, and 12d can, for example, have a brake caliper mounted on the vehicle for engaging a friction element (such as a brake disc) that rotates with a vehicle wheel to brake that wheel. The wheel brakes 12a, 12b, 12c, and 12d can be assigned to any combination of front and rear wheels of the vehicle in which the brake system 10 is installed. A diagonally split brake system is shown such that wheel brake 12a is assigned to the left rear wheel, wheel brake 12b to the right front wheel, wheel brake 12c to the left front wheel, and wheel brake 12d to the right rear wheel. Alternatively, in a vertically split system, wheel brakes 12a and 12b can be assigned to the front wheels, and wheel brakes 12c and 12d to the rear wheels.

[0018] The brake system 10 comprises a brake pedal unit, generally designated 14, a pedal simulator 16, a piston assembly, generally designated 18, and a reservoir 20. The reservoir 20 stores and holds hydraulic fluid for the brake system 10. The fluid in the reservoir 20 is preferably kept at or around atmospheric pressure, but can also be stored at other pressures if desired. The brake system 10 may include a fluid level sensor (not shown) for detecting the fluid level in the reservoir 20. Note that in the schematic representation of Fig. 1 Flow lines may not be explicitly drawn leading to the reservoir 20, but may be represented by lines ending with T1, T2, or T3, which are labeled to indicate that these different lines are connected to one or more reservoirs or parts of the reservoir 20. Alternatively, the reservoir 20 may also have several separate housings. As explained in more detail below, the piston assembly 18 of the brake system 10 acts as a pressure source to impart a desired pressure level to the wheel brakes 12a, 12b, 12c, and 12d during typical or normal brake application. Fluid from the wheel brakes 12a, 12b, 12c, and 12d can be returned to the piston assembly 18 and / or diverted to the reservoir 20.

[0019] The braking system 10 includes an electronic control unit (ECU) 22. The ECU 22 may contain microprocessors. The ECU 22 receives various signals, processes these signals, and controls the operation of various electrical components of the braking system 10 in response to the received signals. The ECU 22 may be connected to various sensors, such as pressure sensors, displacement sensors, switches, wheel speed sensors, and steering angle sensors. The ECU 22 may also be connected to an external module (not shown) to receive information about the vehicle's yaw rate, lateral acceleration, and longitudinal acceleration, for example, to control the braking system 10 during vehicle stability control operation. Additionally, the ECU 22 may be connected to the instrument cluster to receive and provide information via warning indicators, such as an ABS warning light, a brake fluid level warning light, and a traction control / vehicle stability control light.

[0020] The brake system 10 further comprises a first and second isolating valve 30 and 32. The isolating valves 30 and 32 can be magnetically actuated three-way valves. The isolating valves 30 and 32 are generally operable in two positions, as shown in Fig. Figure 1 is shown schematically. The first and second isolating valves 30 and 32 each have an opening in selective liquid connection with an outlet line 34, which is generally connected to an outlet of the piston assembly 18, as explained below. The first and second isolating valves 30 and 32 also contain openings that are selectively in liquid connection with the lines 36 and 38 when the first and second isolating valves 30 and 32 are de-energized, as shown in Figure 1. Fig. 1 shown. The first and second separating valves 30 and 32 further have openings which are in fluid communication with the lines 40 and 42 and supply the fluid to and from the wheel brakes 12a, 12b, 12c and 12d.

[0021] In a preferred embodiment, the first and / or second isolating valves 30 and 32 can be mechanically designed such that, in the de-energized position, the flow can proceed in the reverse direction (from line 34 to line 36 or 38) and bypass the normally open seat of the valves 30 and 32. Although the three-way valves 30 and 32 are not shown schematically to indicate this fluid flow position, it should be noted that the valve design can allow such a fluid flow. This can be helpful when performing self-diagnostic tests of the brake system 10, as explained below.

[0022] System 10 further comprises various magnetically actuated valves (slip control valve arrangement) that enable controlled braking operations, such as ABS, traction control, vehicle stability control, and regenerative brake mixing. A first set of valves includes a first pressure build-up valve 50 and a first pressure release valve 52 in fluid connection with line 40 for the cooperative supply of fluid received from the first separating valve 30 to the wheel brake 12a and for the cooperative discharge of pressurized fluid from the wheel brake 12a to a reservoir line 53 in fluid connection with the reservoir 20.A second set of valves comprises a second pressure build-up valve 54 and a second pressure release valve 56 in fluid connection with line 40 for the cooperative supply of fluid received from the first isolating valve 30 to the wheel brake 12b and for the cooperative discharge of hydraulic fluid from the wheel brake 12b to the reservoir line 53. A third set of valves comprises a third pressure build-up valve 58 and a third pressure release valve 60 in fluid connection with line 42 for the cooperative supply of fluid received from the second isolating valve 32 to the wheel brake 12c and for the cooperative discharge of hydraulic fluid from the wheel brake 12c to the reservoir line 53.A fourth set of valves comprises a fourth pressure build-up valve 62 and a fourth pressure release valve 64 in fluid connection with line 42 for the cooperative supply of fluid received from the second isolating valve 32 to the wheel brake 12d and for the cooperative release of hydraulic fluid from the wheel brake 12d to the reservoir line 53. Note that during a normal braking event, fluid flows through the de-energized, open pressure build-up valves 50, 54, 58, and 62. Additionally, the pressure release valves 52, 56, 60, and 64 are preferably in their de-energized closed positions to prevent fluid flow to the reservoir 20.

[0023] The brake pedal unit 14 is connected to a brake pedal 70 and is actuated by the vehicle driver by pressing the brake pedal 70. A brake sensor or switch 72 can be connected to the ECU 22 to provide a signal indicating actuation of the brake pedal 70. As explained below, the brake pedal unit 14 can be used as a reserve source of hydraulic fluid to essentially replace the normally supplied source of hydraulic fluid from the piston assembly 18 under certain failure conditions of the brake system 10. The brake pedal unit 14 can supply hydraulic fluid, if required, to the lines 36 and 38 (which are normally closed at the first and second isolating valves 30 and 32 during normal brake application) of the wheel brakes 12a, 12b, 12c, and 12d.

[0024] The brake pedal assembly 14 has a housing with a multi-stage bore 80 formed therein for the sliding accommodation of various cylindrical pistons and other components. The housing can be designed as a single unit or have two or more separately formed sections that are coupled together. An input piston 82, a primary piston 84, and a secondary piston 86 are slidably arranged within the bore 80. The input piston 82 is connected to the brake pedal 70 via a linkage arm 76. A counterclockwise movement of the input piston 82, the primary piston 84, and the secondary piston 86 can, under certain conditions, cause a pressure increase in an input chamber 92, a primary chamber 94, or a secondary chamber 96, respectively. Various seals of the brake pedal assembly 14, as well as the design of the housing and the pistons 82, 84, and 86, define the chambers 92, 94, and 96.For example, the inlet chamber 92 is generally defined between the inlet piston 82 and the primary piston 84. The primary chamber 94 is generally defined between the primary piston 84 and the secondary piston 86. The secondary chamber 96 is generally defined between the secondary piston 86 and an end wall of the housing formed by the bore 80.

[0025] The inlet chamber 92 is in fluid communication with the pedal simulator 16 via a line 100; the reason for this is explained below. The inlet piston 82 is slidably arranged in the bore 80 of the housing of the brake pedal unit 14. An outer wall of the inlet piston 82 engages with a lip seal 102 and a seal 104, which are fitted in grooves formed in the housing. A passage 106 (or several passages) is formed by a wall of the piston 82. As shown in Fig. As shown in Figure 1, the passage 106 is located between the lip seal 102 and the seal 104 in the rest position of the brake pedal assembly 14 (the driver is not depressing the brake pedal 70). In the rest position, the passage 106 allows a fluid connection between the inlet chamber 92 and the reservoir 20 via a line 108. Sufficient leftward movement of the inlet piston 82, as shown in Figure 1, is required. Fig. As shown in Figure 1, the passage 106 moves past the lip seal 102, thus preventing the flow of fluid from the inlet chamber 92 into the line 108 and the reservoir 20. A further leftward movement of the inlet piston 82 pressurizes the inlet chamber 92, causing fluid to flow through the line 100 into the pedal simulator 16. As fluid is diverted into the pedal simulator 16, a simulation chamber 110 in the pedal simulator 16 expands, causing a piston 112 in the pedal simulator 16 to move. The movement of the piston 112 compresses a spring assembly, schematically represented as a spring 114. The compression of the spring 114 generates a feedback force to the driver of the vehicle, simulating the forces a driver would feel at the brake pedal 70, for example, in a conventional hydraulic vacuum braking system.The spring 114 of the pedal simulator 16 can comprise any number and any type of spring elements. For example, the spring 114 can have a combination of spring elements with low and high spring constants to enable nonlinear force feedback. The spring 114 of the pedal simulator 16 can be housed in a pressureless chamber 122 in fluid communication with the reservoir 20 (T1).

[0026] The simulation chamber 110 of the pedal simulator 16 is in fluid communication with line 100, which is in fluid communication with the inlet chamber 92. A magnetically actuated simulator closing valve 116 is arranged within line 100 to selectively prevent the fluid flow from inlet chamber 92 into simulation chamber 110, for example, during a failure condition in which the brake pedal unit 14 is used to provide a pressurized fluid source for the wheel brakes. In its energized open position, the simulator valve 116 allows fluid communication between the inlet chamber 92 of the brake pedal unit 14 and the simulation chamber 110 of the pedal simulator 16. The brake system 10 may also include a check valve 118, which is arranged in a parallel-path configuration with a constricted opening 120 in line 100.The check valve 118 and the constricted orifice 120 could be integrated into or formed within the simulator valve 116, or they could be separate components. The constricted orifice 120 provides damping during peak actuation, when the driver rapidly and forcefully depresses the brake pedal 70. This damping provides force feedback, making the actuation of the brake pedal 70 feel more like a conventional vacuum booster, which can be a desirable characteristic of the brake system 10. The damping can also establish a more accurate relationship between brake pedal travel and vehicle deceleration by generally preventing excessive brake pedal travel for the vehicle deceleration that can be provided by the brake system 10. The check valve 118 provides a simple flow path and allows for rapid return of the brake pedal 70, enabling the associated brake pressure to dissipate quickly, depending on the driver's intent.

[0027] As explained above, the inlet chamber 92 of the brake pedal unit 14 is selectively connected to the reservoir 20 via a line 108 and the passage 106 formed in the inlet piston 82. The brake system 10 may optionally include a simulator test valve 130 located within the line 108. The simulator test valve 130 can be electronically switched between an open position, as in Fig. The simulator test valve 130 is shown in Figure 1 and is controlled by a motor in a closed position. It is not strictly necessary during normal, amplified brake application or in a manual full-actuation mode. The simulator test valve 130 can be moved to a closed position during various test modes to determine the correct function of other components of the brake system 10. For example, the simulator test valve 130 can be moved to a closed position to prevent venting into the reservoir 20 via line 108, allowing pressure build-up in the brake pedal assembly 14 to be used to monitor fluid flow and determine whether there are any leaks at seals of various components of the brake system 10.

[0028] The primary chamber 94 of the brake pedal assembly 14 is connected to the second separating valve 32 via line 38. The primary piston 84 is slidably arranged in the bore 80 of the housing of the brake pedal assembly 14. An outer wall of the primary piston 84 engages with a lip seal 132 and a seal 134, which are fitted in grooves formed in the housing. One or more passages 136 are formed by a wall of the primary piston 84. The passage 136 is located between the lip seal 132 and the seal 134 when the primary piston 84 is in its rest position, as shown in Fig. Figure 1 shows that the lip seal 132 is located only slightly to the left of the passage 136 in the rest position, thus enabling a liquid connection between the primary chamber 94 and the reservoir 20.

[0029] The secondary chamber 96 of the brake pedal assembly 14 is in fluid communication with the first separating valve 30 via line 36. The secondary piston 86 is slidably arranged in the bore 80 of the housing of the brake pedal assembly 14. An outer wall of the secondary piston 86 engages with a lip seal 140 and a seal 142, which are fitted in grooves formed in the housing. One or more passages 144 are formed by a wall of the secondary piston 86. As shown in Fig. As shown in Figure 1, the passage 144 is located between the lip seal 140 and the seal 142 when the secondary piston 86 is in its rest position. Note that in the rest position, the lip seal 140 is located only slightly to the left of the passage 144, thus allowing a fluid connection between the secondary chamber 96 and the reservoir 20 (T2).

[0030] If desired, the primary and secondary pistons 84 and 86 can be mechanically connected, limiting their movement. This mechanical connection prevents a large gap or distance between them and prevents them from having to be advanced over a relatively large distance without a pressure increase in the non-failing circuit. For example, if the brake system 10 is in manual full-actuation mode and fluid pressure is lost in the output circuit relative to the secondary piston 86, such as in line 36, the pressure in the primary chamber 94 will push or preload the secondary piston 86 to the left. If the primary and secondary pistons 84 and 86 were not connected, the secondary piston 86 would move freely to a further, extreme left position, as shown in Fig. Figure 1 shows that the driver would have to depress the pedal 70 degrees to compensate for this loss of travel. However, since the primary and secondary pistons 84 and 86 are connected, the secondary piston 86 is prevented from this movement, and relatively little travel loss occurs with this type of fault. Any suitable mechanical connection between the primary and secondary pistons 84 and 86 can be used. For example, as shown in Figure 1, the primary and secondary pistons 84 and 86 can be connected by a mechanical linkage. Fig. Figure 1 schematically shows that the right end of the secondary piston 86 has an outwardly extending flange that engages in a groove formed in an inner wall of the primary piston 84. The groove has a width greater than the width of the flange, resulting in a relatively small stroke between the first and second pistons 84 and 86 relative to each other.

[0031] The brake pedal assembly 14 may include an input spring 150, which is generally arranged between the input piston 82 and the primary piston 84. Additionally, the brake pedal assembly 14 may include a primary spring (not shown), which is generally arranged between the primary piston 84 and the secondary piston 86. A secondary spring 152 may be inserted and arranged between the secondary piston 86 and a bottom wall of the bore 80. The input, primary, and secondary springs may have any suitable configuration, such as a cage spring arrangement, to preload the pistons in a direction away from each other and also to correctly position the pistons within the housing of the brake pedal assembly 14.

[0032] The brake system 10 can further include a pressure sensor 156 in fluid connection with line 36 to detect the pressure in the secondary pressure chamber 96 and transmit the signal indicating the pressure to the ECU 22. Additionally, the brake system 10 can further include a pressure sensor 158 in fluid connection with line 34 to transmit a signal indicating the pressure at the outlet of the piston assembly 18.

[0033] As in Fig. As shown schematically in Figure 2, the piston assembly 18 has a housing with a multi-stage bore 200 formed therein. The bore 200 has a first section 202 and a second section 204. A piston 206 is slidably arranged within the bore 200. The piston 206 has an enlarged end section 208, which is connected to a central section 210 with a smaller diameter. The piston 206 has a second end 211, which is connected to a ball screw drive, generally characterized by 212. The ball screw drive 212 is designed to enable translational or linear movement of the piston 206 along an axis defined by the bore 200, both in the forward direction (to the left, as shown in Figure 2). Fig. 1 and Fig. 2 shown) as well as in reverse (to the right, as in Fig. 1 and Fig. 2 shown) within the bore 200 of the housing. In the illustrated embodiment, the ball screw drive 212 includes a motor, which is shown schematically and generally at 214, and which is electrically connected to the ECU 22 for actuating it. The motor 214 rotatably drives a spindle 216. The motor 214 generally has a stator 215 and a rotor 217. In the embodiment shown Fig. In the schematically depicted embodiment 2, the rotor 217 and the spindle 216 are formed as a single unit. The second end 211 of the piston 206 has a threaded bore 220 and functions as the driven nut of the ball screw drive 212. The ball screw drive 212 has a plurality of balls 222 contained in helical raceways 223 formed in the spindle 216 and the threaded bore 220 of the piston 206 to reduce friction.

[0034] Although a ball screw drive 212 is shown and described in relation to the piston assembly 18, it should be noted that other suitable mechanical linear drives can also be used to effect movement of the piston 206. It should also be noted that while the piston 206 functions as the nut of the ball screw drive 212, it can also be configured as the spindle of the ball screw drive 212. Naturally, in this case, the spindle 216 would be configured to function as a nut with internal helical raceways. The piston 206 can incorporate features (not shown) that interact with other features in the housing of the piston assembly 18 to prevent rotation of the piston 206 when the spindle 216 rotates around it.For example, the piston 206 can have outwardly directed wedge springs or tongues (not shown) arranged in longitudinally extending grooves (not shown) formed in the housing of the piston assembly 18, so that the tongues slide along inside the grooves as the piston 206 moves in the bore 200.

[0035] As explained below, the piston assembly 18 is preferably designed to exert pressure on the line 34 when the piston 206 is moved in both the forward and reverse directions. The piston assembly 18 includes a seal 230, which is attached to the enlarged end section 208 of the piston 206. The seal 230 provides a sliding seal against the inner cylindrical surface of the first section 202 of the bore 200 while the piston 206 moves within the bore 200. A seal 234 and a seal 236 are mounted in grooves formed in the second section 204 of the bore 200. The seals 234 and 236 provide a sliding seal against the outer cylindrical surface of the central section 210 of the piston 206. A first pressure chamber 240 is generally defined by the first section 202 of the bore 200, the enlarged end section 208 of the piston 206 and the seal 230.An annular second pressure chamber 242, generally arranged behind the enlarged end section 208 of the piston 206, is generally defined by the first and second sections 202 and 204 of the bore 200, the seals 230 and 234, and the central section 210 of the piston 206. The seals 230, 234, and 236 may have any suitable sealing design.

[0036] Although the piston assembly 18 can be configured in any suitable size and arrangement, in one embodiment the effective hydraulic area of ​​the first pressure chamber 240 is larger than the effective hydraulic area of ​​the annular second pressure chamber 242. The first pressure chamber 240 generally has an effective hydraulic area equal to the diameter of the central section 210 of the piston 206 (the inner diameter of the seal 234), since the fluid is guided through the lines 254, 34, and 243 when the piston 206 is moved forward. The second pressure chamber 242 generally has an effective hydraulic area equal to the diameter of the first section 202 of the bore 200 minus the diameter of the central section 210 of the piston 206.This design provides that during the return stroke, when the piston 206 moves backward, the motor 214 requires less torque (or power) to maintain the same pressure as during the forward stroke. In addition to lower power consumption, the motor 214 can also generate less heat during the piston 206's return stroke. In certain circumstances, when high braking pressure is desired, the piston assembly 34 could be operated from a forward stroke to a return stroke. Thus, while a forward stroke is used in most braking applications, a return pressure stroke can also be utilized.Even in circumstances where the driver presses the pedal 90 for a longer period of time, the brake system 10 could be actuated to maintain brake pressure (instead of continuously exciting the piston assembly 34) by controlling the first and second piston valves 250 and 252 (as discussed below) to closed positions and then switching off the motor or the piston assembly 34.

[0037] The piston assembly 18 preferably includes a sensor, schematically represented as 218, for indirectly detecting the position of the piston 206 within the bore 200. The sensor 218 is connected to the ECU 22. In one embodiment, the sensor 218 detects the rotational position of the rotor 217, in which metallic or magnetic elements may be embedded. Since the rotor 217 is formed integrally with the shaft 216, the rotational position of the shaft 216 corresponds to the linear position of the piston 206. Thus, the position of the piston 206 can be determined by detecting the rotational position of the rotor 217 via the sensor 218.

[0038] The piston 206 of the piston assembly 18 includes a passage 244 formed therein. The passage 244 defines a first opening 246 that extends through the cylindrical outer wall of the piston 206 and is in fluid communication with the secondary chamber 242. The passage 244 also defines a second opening 248 that extends through the cylindrical outer wall of the piston 206 and is in fluid communication with a section of the bore 200 between the seals 234 and 236. The second opening 248 is in fluid communication with a line 249, which is in fluid communication with the reservoir 20 (T3). In the rest position, as shown in Fig. As shown in Figure 2, pressure chambers 240 and 242 are connected to the reservoir 20 via line 249. This helps to ensure proper pressure relief at the outlet of the piston assembly 18 and in the pressure chambers 240 and 242 themselves. After an initial forward movement of the piston 206 from its rest position, the opening 248 moves past the lip seal 234, thus closing off the fluid connection between the pressure chambers 240 and 242 and the reservoir 20, allowing the pressure chambers 240 and 242 to build up pressure as the piston 206 continues to move.

[0039] With reference to Fig. The brake system 10 further comprises a first piston valve 250 and a second piston valve 252. The first piston valve 250 is preferably a magnetically actuated normally open valve. Thus, the first piston valve 250 is in a closed position when de-energized, as shown in Fig. Figure 1 shows the second piston valve 252, preferably a magnetically actuated normally closed valve. Thus, the second piston valve 252 is in an open position when de-energized, as shown in Figure 1. Fig. Figure 1 shows that a check valve can be arranged inside the second piston valve 252 so that, when the second piston valve 252 is in its closed position, the fluid can still flow through the second piston valve 252 towards a first outlet line 254 (from the first pressure chamber 240 of the piston assembly 18) to the line 34, which leads to the separating valves 30 and 32. Note that during a return stroke of the piston 206 of the piston assembly 18, pressure can be generated in the second pressure chamber 242 for output into the line 34.

[0040] In general, the first and second piston valves 250 and 252 are controlled to allow fluid flow at the outlets of the piston assembly 18 and, if necessary, to enable venting of the reservoir 20 (T3) through the piston assembly 18. For example, the first piston valve 250 can be moved to its open position during a normal braking event, so that both the first and second piston valves 250 and 252 are open (which can reduce the noise level during operation). Preferably, the first piston valve 250 is almost always activated during an ignition cycle with the engine running. Of course, the first piston valve 250 can also be deliberately moved to its closed position, e.g., during a pressure-generating reverse stroke of the piston assembly 18.The first and second piston valves 250 and 252 are preferably in their open position when the piston 206 of the piston assembly 18 is operating in its forward stroke to maximize flow. When the driver releases the brake pedal 70, the first and second piston valves 250 and 252 preferably remain in the open positions. Note that, depending on the stroke direction of the piston 206 of the piston assembly 18, fluid can flow through the check valve within the closed second piston valve 252, as well as through a check valve 258 from the reservoir 20.

[0041] It may be desirable to design the first piston valve 250 with a relatively large opening in the open position. A relatively large opening in the first piston assembly 250 helps to ensure a smooth flow path within it. The second piston valve 252 can be provided with a significantly smaller opening in its open position compared to the first piston valve 250. One reason for this is to prevent the piston 206 of the piston assembly 18 from being rapidly pushed back in the event of a failure due to the rise of fluid through the first outlet line 254 into the first pressure chamber 240 of the piston assembly 18, thus preventing damage to the piston assembly 18. Since the fluid flow is restricted by the relatively small opening, power loss occurs because some of the energy is converted into heat.Therefore, the opening should be sufficiently small to prevent a sudden, catastrophic reverse movement of the piston 206 of the piston assembly 18 in the event of a failure of the brake system 10, such as when power is lost to the motor 214 and the pressure in the line 34 is relatively high. As in . Fig. As shown in Figure 2, the piston assembly 18 may optionally include a spring element, such as a spring washer 277, to assist in damping such a rapid rearward movement of the piston 206. The spring washer 277 may also help to dampen the piston 206 as it moves at any speed when approaching a rest position near its most retracted position within the bore 200. As shown in Fig. As shown schematically in Figure 2, the spring washer 277 is located between the enlarged end section 208 and a shoulder 279 formed in the bore 200 between the first and second sections 202 and 204. The spring washer 277 can have any suitable configuration that deflects or compresses upon contact with the piston 206 when the piston 206 moves backward. For example, the spring washer 277 can be in the form of a metallic conical spring washer. Alternatively, the spring washer 277 can also be in the form of a wave spring. Although the spring washer 277 is located in the bore 200 of the piston assembly 18, the spring washer 277 can alternatively be mounted on the piston 206 so that the spring washer 277 moves with the piston 206. In this configuration, the spring washer 277 would engage with the shoulder 279 and compress when the piston 206 moves sufficiently forward.

[0042] The first and second piston valves 250 and 252 ensure an open parallel path between the pressure chambers 240 and 242 of the piston assembly 18 during normal braking. Although a single open path may suffice, the advantage of both the first and second piston valves 250 and 252 is that the first piston valve 250 can provide a free flow path through its relatively large opening, while the second piston valve 252 can provide a restricted opening path under certain failure conditions (when the first piston valve 250 is de-energized to its closed position).

[0043] During a typical or normal braking process, the brake pedal 70 is depressed by the driver of the vehicle. In a preferred embodiment of the braking system 10, the brake pedal unit 14 comprises one or more position sensors 270 (for redundancy) for generating signals transmitted to the ECU 22, indicating the travel distance of the input piston 82 of the brake pedal unit 14.

[0044] During normal braking, the piston assembly 18 is actuated to supply pressure to line 34 for actuating the wheel brakes 12a, 12b, 12c, and 12d. Under certain driving conditions, the ECU 22 communicates with a powertrain control module (not shown) and other additional vehicle brake controls to enable coordinated braking in the case of advanced brake control systems (e.g., anti-lock braking system (ABS), traction control (TC), vehicle stability control (VSC), and regenerative braking).

[0045] During a normal braking process, the pressurized fluid flow generated by depressing the brake pedal 70 is diverted from the brake pedal unit 14 to the pedal simulator 16. The simulator valve 116 is actuated to divert fluid from the inlet chamber 92 through the simulator valve 116. Note that the simulator valve 116 is in Fig. Figure 1 shows the valve in the switched-on state. Thus, the simulator valve 116 is a normally open solenoid valve. Note also that the fluid flow from the inlet chamber 92 to the reservoir 20 is closed as soon as the passage 106 in the inlet piston 82 moves past the seal 104.

[0046] During a normal braking event, the simulator valve 116 preferably remains open. Also during normal braking, the isolating valves 30 and 32 are switched to secondary positions to prevent fluid flow from lines 36 and 38 through the isolating valves 30 and 32. Preferably, the isolating valves 30 and 32 are activated for the entire duration of an ignition cycle, e.g., when the engine is running, rather than being switched on and off, in order to minimize noise. Note that the primary and secondary pistons 84 and 86 are not in fluid contact with the reservoir 20 due to their passages 136 and 144, which are arranged past the lip seals 132 and 140. Preventing the flow of fluid by the separating valves 30 and 32 hydraulically blocks the primary and secondary chambers 94 and 96 of the brake pedal unit 14 and prevents further movement of the primary and secondary pistons 84 and 86.

[0047] It is generally desirable for the isolating valves 30 and 32 to remain activated during normal braking mode to ensure venting of the reservoir 20 by the piston assembly 18, such as when the driver releases the brake pedal 70. As is best done in Fig. As shown in Figure 1, the passage 244 formed in the piston 206 of the piston arrangement 18 enables this ventilation.

[0048] During normal brake application, when the pedal simulator 16 is actuated by depressing the brake pedal 70, the piston assembly 18 can be actuated by the ECU 22 to actuate the wheel brakes 12a, 12b, 12c, and 12d. The piston assembly 18 is actuated to provide the desired pressure levels to the wheel brakes 12a, 12b, 12c, and 12d, compared to the pressure generated by the brake pedal unit 14 when the driver depresses the brake pedal 70. The electronic control unit 22 actuates the motor 214 to rotate the spindle 216 in the first direction of rotation. The rotation of the spindle 216 in the first direction of rotation moves the piston 206 forward (to the left as shown in the diagram). Fig. 1 and Fig. (2 shown). The movement of piston 206 causes a pressure increase in the first pressure chamber 240, and fluid flows from the first pressure chamber 240 into line 254. The fluid can flow into line 34 via the open first and second piston valves 250 and 252. Note that the fluid is allowed to flow into the second pressure chamber 242 via line 243 when piston 206 moves forward. Pressurized fluid from line 34 is directed into lines 40 and 42 via the separating valves 30 and 32. The pressurized fluid from lines 40 and 42 can be directed to the wheel brakes 12a, 12b, 12c, and 12d through open pressure build-up valves 50, 54, 58, and 62, while the pressure release valves 52, 56, 60, and 64 remain closed.When the driver releases the brake pedal 70, the ECU 22 can actuate the motor 214 to rotate the spindle 216 in the second direction, causing the piston 206 to withdraw fluid from the wheel brakes 12a, 12b, 12c, and 12d. The speed and distance of the piston 206's retraction are based on the driver's demands when releasing the brake pedal 70, as detected by the sensor 218. If the driver releases the brake pedal 90 quickly, the piston assembly 14 can, of course, be actuated to prevent such an immediate pressure drop. Under certain conditions, such as with non-amplified traction control, the hydraulic fluid from the wheel brakes 12a, 12b, 12c, and 12d can help to rotate the ball screw mechanism 212 back and move the piston 206 to its rest position.Note that when the driver releases the brake pedal 90, the first and second piston valves 250 and 252 preferably remain in their open position during an anti-slip control operation.

[0049] In some situations, the piston 206 of the piston assembly 18 can reach its full stroke length within the bore 200 of the housing, and it is still desirable to supply additional boosted pressure to the wheel brakes 12a, 12b, 12c, and 12d. The piston assembly 18 is a double-acting piston assembly designed to also supply boosted pressure to line 34 when the piston 206 is moved rearward (to the right) or in the opposite direction. This has the advantage over a conventional piston assembly, where the piston must first be returned to its rest or retracted position before it can move forward again to build up pressure in a single pressure chamber. For example, if the piston 206 has reached its full stroke and additional boosted pressure is still desired, the second piston valve 252 is switched to its closed check valve position.The first piston valve 250 is de-energized to its closed position. The electronic control unit 22 actuates the motor 214 in a second direction of rotation, opposite to the first direction, to rotate the spindle 216 in the second direction. By rotating the threaded spindle 216 in the second direction, the piston 206 retracts or moves in the reverse direction (to the right as in ). Fig. 1 and Fig. (2 shown). The movement of piston 206 causes a pressure increase in the second pressure chamber 242, and the fluid flows from the second pressure chamber 242 into line 243 and line 34. Hydraulic fluid from line 34 is routed via the separating valves 30 and 32 into lines 40 and 42. The hydraulic fluid from lines 40 and 42 can be routed through the open pressure build-up valves 50, 54, 58, and 62 to the wheel brakes 12a, 12b, 12c, and 12d, while the pressure release valves 52, 56, 60, and 64 remain closed. Similar to a forward stroke of the piston 206, the ECU 22 can also selectively actuate the pressure build-up valves 50, 54, 58 and 62 as well as the pressure release valves 52, 56, 60 and 64 to give the wheel brakes 12a, 12b, 12c and 12d a desired pressure level.When the driver releases or depresses the brake pedal 70 during a pressurized return stroke of the piston assembly 18, the first and second piston valves 250 and 252 are preferably moved to their open positions, although it would generally suffice if only one of the valves 250 and 252 were open. Note that during the transition from a slip control event, the ideal situation would be that the position of the piston 206 and the displaced volume within the piston assembly 18 correlate exactly with the given pressures and fluid volumes within the wheel brakes 12a, 12b, 12c, and 12d. However, if the correlation is not exact, fluid from the reservoir 20 can be drawn into the chamber 240 of the piston assembly 18 via the check valve 258.

[0050] During a braking event, the ECU 22 can selectively actuate the pressure build-up valves 50, 54, 58, and 62 and the pressure release valves 52, 56, 60, and 64 to apply a desired pressure level to the wheel brakes. The ECU 22 can also control the braking system 10 during ABS, DRP, TC, VSC, regenerative braking, and autonomous braking by generally actuating the piston assembly 18 in conjunction with the pressure build-up and pressure release valves. Even if the vehicle's driver does not press the brake pedal 70, the ECU 22 can actuate the piston assembly 18 to provide a source of hydraulic fluid directed to the wheel brakes, as in an autonomous vehicle braking event.

[0051] In the event of a power failure affecting parts of the brake system 10, the brake system 10 provides for manual full actuation or manual actuation so that the brake pedal assembly 14 can supply lines 36 and 38 with fluid under relatively high pressure. During an electrical fault, the motor 214 of the piston assembly 18 may cease operation and thus fail to generate pressurized hydraulic brake fluid from the piston assembly 18. The isolating valves 30 and 32 switch (or remain in their positions) to allow fluid flow from lines 36 and 38 to the wheel brakes 12a, 12b, 12c, and 12d. The simulator valve 116 switches to its closed position to prevent fluid from escaping from the inlet chamber 92 into the pedal simulator 16.During manual full actuation, the input piston 82, the primary piston 84, and the secondary piston 86 move to the left, causing the passages 106, 136, and 144 to move past the seals 102, 132, and 140, respectively, thus preventing fluid flow from their respective fluid chambers 92, 94, and 96 to the reservoir 20 and pressurizing the chambers 92, 94, and 96. The fluid flows from chambers 94 and 96 into lines 38 and 36 to actuate the wheel brakes 12a, 12b, 12c, and 12d.

[0052] It may be desirable to perform checks or tests, such as self-diagnostic tests, to determine whether a leak might have occurred anywhere within the brake system 10. It may also be desirable to perform self-diagnostic tests to determine whether the brake system 10 is functioning properly. These self-diagnostic tests can be performed at any suitable time. For example, these tests can be performed with the vehicle stationary, such as at the end of an ignition cycle when the driver switches off the engine. The tests can also be performed after a time delay, such as 90 seconds or several minutes after the end of an ignition cycle. This delay would help ensure that the driver is not disturbed during tests that may generate noise, as it is likely that the driver and / or passengers will have moved away from the vehicle after a few minutes.

[0053] Such a self-diagnostic test includes the detection of a possible leak within the brake pedal assembly 14. This test can also help to determine the correct movement of one or more pistons within the brake pedal assembly 14, e.g., the secondary piston 86. For the sake of simplicity, this test is referred to here as the "brake pedal assembly test". Fig. Figure 3 is a schematic representation of the brake system 10, in which the states and positions of various components of the brake system 10 during at least one section of the brake pedal unit test are schematically depicted. To initiate the brake pedal unit test, various components of the brake system 10 are controlled by the ECU 22. For example, it is preferred that the first three-way isolating valve 30 is moved to a position in which the fluid flow from the secondary pressure chamber 96 of the brake pedal unit 14 via line 36 to the wheel brakes 12a and 12b via line 40 is prevented. Note that in this position, the fluid is not prevented from flowing through the first isolating valve 30 from the outlet of the piston assembly 18 via line 34 to line 40.During this test, however, the ECU 22 preferably also brings all pressure build-up valves 50, 54, 58 and 62 into their closed positions, thereby blocking the fluid flow in line 40.

[0054] Preferably, the ECU 22 actuates the second isolating valve 32 in the unactuated state during the brake pedal unit test, as shown in Fig. Figure 3 illustrates this. As discussed above, the first and second isolating valves 30 and 32 are preferably mechanically designed such that the flow can actually flow in the reverse direction from line 34 into lines 36 and 38, bypassing the normally open seat of the de-energized second three-way isolating valve 32. Although the second isolating valve 32 is not shown schematically to indicate this fluid flow direction, it should be noted that the valve design can accommodate such a fluid flow. Thus, fluid can flow through the de-energized second isolating valve 32 from the outlet of the piston assembly 18, via line 34, into line 38, which leads to the primary pressure chamber 94 of the brake pedal assembly 14.

[0055] During the brake pedal unit test, the first piston valve 250 is preferably brought into its open position, as shown in Fig. Figure 3. Additionally, the simulator test valve 130 is preferably moved to its closed position to prevent fluid flow from the primary pressure chamber 94 to the reservoir 20. It should be noted that the simulator test valve 116, the second piston valve 252, and the pressure relief valves 52, 56, 60, and 64 are preferably moved to their unactuated states during the brake pedal unit test, as shown in Figure 3. Fig. 3 shown.

[0056] After the ECU 22 has controlled the various valves to their states as described above for the brake pedal unit test, the ECU 22 preferably actuates the piston assembly 18 to pressurize line 34 (the outlet of the piston assembly 18) to a first predetermined pressure level, e.g., approximately 30 bar. It should be clear that, of course, the piston assembly 18 can be actuated to generate an outlet pressure of any desired level. The pressure in line 34 causes a pressure increase in the brake pedal unit 14 via line 38. More precisely, the pressure in line 38 enables fluid flow into the primary chamber 94 and the inlet chamber 92 via line 108, resulting in a pressure increase in these chambers 92 and 94. Accordingly, a pressure increase in the primary chamber 94 causes movement of the secondary piston 86, which pressurizes the secondary chamber 96.Pressurizing the secondary chamber 96 pressurizes the fluid in line 36, which is monitored by pressure sensor 156. The piston assembly 18 is actuated to maintain this pressure at the first predetermined level (e.g., 30 bar). The ECU 22 then monitors the brake system 10 to determine the possibility of a leak within the brake pedal assembly 14. More specifically, the ECU 22 monitors the pressure in line 36 via pressure sensor 156. If the pressure in line 36 falls below a second predetermined value, e.g., approximately 20 bar, within a predetermined time period, e.g., approximately 100 ms, the test is considered failed. Failure of this brake pedal assembly test may be related to leaks within the brake pedal assembly 14 or in the lines connected to the brake pedal assembly 14.Another possible cause is that the secondary piston 86 is not moving correctly or is not functioning correctly within the brake pedal unit 14.

[0057] Another way to determine whether the brake pedal assembly test has passed or failed is to monitor the movement of piston 206 of piston assembly 18. If it is determined that piston 206 has to move more than would normally be required to build up the pressure in line 34 to the first predetermined pressure level under normal operating conditions, the brake pedal assembly test can be considered to have failed. For example, if the information received from sensor 218 indicates that piston 206 has moved more than 4 mm, the brake pedal assembly test can be considered to have failed, since piston 206 should not need to move more than 4 mm to build up the pressure to the first predetermined pressure under normal operating conditions.

[0058] Failure to meet the requirements of the brake pedal assembly test described above indicates that a leak related to the brake pedal assembly 14 has likely occurred, or that one or more pistons of the brake pedal assembly 14 are not functioning properly. In this scenario, the ECU 22 may issue a warning to the vehicle's driver that the brake system 10 requires service. Warnings or alarms may include, for example, indicator lights, screen displays, audible warnings, or tactile warnings (vibration). These warnings or alarms may be triggered if any of the self-diagnostic tests specified here fail.

[0059] Another such self-diagnostic test involves detecting a possible leak within the pedal simulator 16. For the sake of simplicity, this test is referred to here as the "pedal simulator test". Fig. Figure 4 is a schematic representation of the brake system 10, in which the states and positions of various components of the brake system 10 during at least one section of the pedal simulator test are schematically depicted. To initiate the pedal simulator test, the ECU 22 controls various components of the brake system 10. The pedal simulator test is preferably performed following a successful brake pedal unit test, as described above. Of course, the pedal simulator test can also be performed separately and independently of the brake pedal unit test.

[0060] When the pedal simulator test is performed following the brake pedal unit test, the ECU 22 preferably de-energizes the simulator test valve 130 to relieve the pressure within the brake pedal unit 14, allowing fluid to flow from the brake pedal unit 14 to the reservoir 20. After the pressure is relieved, the simulator test valve 130 is moved to its closed position, preventing fluid flow from the brake pedal unit 14 to the reservoir 20. The simulator valve 116 is moved to its open position, allowing fluid to flow into the pedal simulator 16. The piston assembly 18 is actuated by the ECU 22 to generate an output pressure at a third predetermined pressure level, e.g., approximately 10 bar. It should be clear that, of course, the piston assembly 18 can be actuated to generate an output pressure at any desired pressure level.The piston assembly 18 is actuated to maintain and sustain the third predetermined pressure level. Under normal operating conditions, the pressure in pressure chamber 110 of the pedal simulator 16, as well as the pressure in chambers 92, 94, and 96 of the brake pedal assembly 14, is maintained. The pedal simulator test is considered to have failed if the pressure detected by pressure sensor 156 cannot maintain the third predetermined pressure, e.g., approximately 10 bar, and falls below a fourth predetermined value, e.g., 7 bar, for a predetermined time period, e.g., 100 ms. The pedal simulator test can also be considered to have failed if the information received from sensor 218 indicates that the piston 206 has moved more than a predetermined distance to normally maintain the third predetermined pressure of, e.g., approximately 10 bar.If the pedal simulator test fails, the ECU 22 can issue a warning to the driver of the vehicle that the brake system 10 requires service.

[0061] Another such self-diagnostic test involves detecting a possible leak via the first and second three-way isolating valves 30 and 32 to the piston assembly 18, which would prevent the proper functioning of a manual full actuation of the brake pedal unit 14. For the sake of simplicity, this test is referred to here as the "isolating valve test". Fig. Figure 5 is a schematic representation of the brake system 10, in which the states and positions of various components of the brake system 10 during at least one section of the isolation valve test are schematically depicted. To initiate the isolation valve test, the ECU 22 controls various components of the brake system 10. The isolation valve test is preferably performed following a successful pedal simulator test, as described above. Of course, the isolation valve test can also be performed separately and independently of the previously discussed tests.

[0062] When the isolation valve test is performed following the pedal simulator test / pedal unit test, the ECU 22 preferably activates the first and second three-way isolation valves 30 and 32, thereby isolating the brake pedal unit 14. This leaves chambers 92, 94, and 96 of the brake pedal unit 14 at the third predetermined pressure, e.g., 10 bar. The ECU 22 then actuates the motor 214 of the piston assembly 18 to move the piston 206 rearward until the piston assembly 18 is in its rest position. The movement of the piston assembly 18 to its rest position releases the boost pressure in line 34. The ECU 22 then actuates the motor 214 of the piston assembly 18 forward, increasing the pressure in line 34 to a fifth predetermined pressure, e.g., 10 bar. Thus, the pressure in line 34 is now approximately the same as the pressure in lines 36 and 38. The first and second separating valves 30 and 32 are then opened to their positions. Fig. The five positions shown are de-energized. The ECU 22 then actuates the motor 214 of the piston assembly 18 to move the piston 206 backward until the piston assembly 18 is in its rest position. The movement of the piston assembly 18 to its rest position releases the boost pressure in line 34 to approximately 0 bar. The ECU 22 then monitors the pressure within the brake pedal assembly 14, particularly the secondary chamber 96, via the pressure sensor 156. The isolation valve test can be considered failed if the pressure within the secondary chamber 96 drops below a predetermined pressure, e.g., 7 bar, after a specified time interval, e.g., 100 ms.

[0063] In another such self-diagnostic test, the proper movement of the pistons of the brake pedal unit 14 is detected, e.g., during a manual full-actuation event. For the sake of simplicity, this test is referred to here as the "brake pedal unit piston test". Fig. Figure 6 is a diagram of the brake system 10, schematically showing the states and positions of various components of the brake system 10 during at least part of the brake pedal unit piston test. To initiate the brake pedal unit piston test, the ECU 22 controls various components of the brake system 10. The brake pedal unit piston test is preferably performed following a successful isolation valve test, as described above. Of course, the brake pedal unit piston test can also be performed separately and independently of the previously discussed tests.

[0064] When the brake pedal unit piston test is performed following the isolation valve test, the ECU 22 preferably de-energizes all pressure build-up valves 50, 54, 58, and 62, allowing fluid to flow to the wheel brakes 12a, 12b, 12c, and 12d, respectively. The pressure release valves 52, 56, 60, and 64 can be pulsed individually or collectively between their open and closed positions to release the pressure from the wheel brakes 12a, 12b, 12c, and 12d at a predetermined pressure drop rate.

[0065] The ECU 22 then monitors the pressure release rates from the secondary chamber 96 via the pressure sensor 156. The brake pedal unit piston test can be considered to have failed if the fluid pressure is trapped or remains in the secondary chamber 96 for too long, and it can be assumed that the pistons 82, 84, and 86 of the brake pedal unit 14 are not functioning properly. For example, in one embodiment of the brake pedal unit piston test, the pressure release valves 52, 56, 60, and 64 are held in their open positions for 200 ms, which would normally release the pressure in the secondary chamber 96. If sufficient pressure is present in the secondary chamber 96, as detected by the pressure sensor 156, the test is considered to have failed.

[0066] As mentioned above, the self-diagnostic tests (brake pedal unit test, pedal simulator test, isolating valve test, and brake pedal unit piston test) can be performed after each ignition cycle with the vehicle off or after a certain time delay. However, instead of after every ignition or driving cycle, it may be desirable to restrict the test to when certain vehicle conditions or triggering conditions are met. One such condition could be that the self-diagnostic tests are not performed if the vehicle has not traveled more than a predetermined distance, e.g., 800 meters, in an ignition cycle. Another condition could be that the vehicle must complete a driving cycle after ignition. A driving cycle can be defined as maintaining the vehicle speed above a certain speed, e.g., 14.4 m / s, for a predetermined period, e.g., 30 seconds, during an ignition cycle.Another condition may be that the vehicle's idle or standstill time during the ignition cycle is shorter than a predetermined period, e.g., 270 seconds. If the above conditions prevent the self-diagnostic tests from being performed multiple times, e.g., ten times consecutively, the ECU 22 may still force the execution of one or more self-diagnostic tests regardless of the driving distance and waiting time conditions.

[0067] Other conditions may also prevent the self-diagnostic tests from starting. One condition may be that the piston assembly 18 must be functioning normally and without faults. It may also be desirable to monitor the actuation of the brake pedal 70 and not perform the self-diagnostic tests if the driver depresses the brake pedal. The tests can be aborted if it is determined that the driver has depressed the brake pedal 70 during the tests. In this situation, the test is aborted, and the ECU 22 actuates the brake system 10 accordingly to provide the desired boost pressure as in a normal braking event. The ECU 22 can then wait for the brake pedal 70 to be released and restart the test. This can be done for a number of trials, e.g., a total of two times, before the tests are aborted.The self-diagnostic tests might also fail if it is determined that the parking brake is not engaged. If, for example, it is determined that an electric parking brake is engaged before the tests begin, the tests will proceed normally. Preferably, the ECU 22 will also abort the test if the ignition is switched on and will not attempt it again during that ignition cycle.

[0068] With regard to the various valves of the brake system 10, the terms “operate” or “bring” (or “actuate,” “move,” “position”) used herein (including in the claims) do not necessarily refer to energizing the solenoid coil of the valve, but rather to moving or switching the valve into a desired position or state. For example, a magnetically actuated normally closed valve can be moved to an open position simply by leaving the valve in its de-energized open state. Actuating the normally closed valve may involve energizing the solenoid coil to move internal mechanisms of the valve to block or prevent the flow of fluid.The term "actuate" should therefore not be understood as meaning that the valve is moved to a different position or that an associated solenoid coil of the valve is always supplied with power.

[0069] The principle and operation of this invention have been explained and illustrated in its preferred embodiment. However, it should be noted that this invention can be implemented differently than specifically explained and illustrated without deviating from its essence or scope.

Claims

[1] Method for performing a diagnostic test to determine leaks within a brake system, the method comprising: (a) Providing a braking system (10) comprising: a piston arrangement (18) with a housing defining a bore therein, wherein the piston arrangement (18) has a piston slidably arranged therein such that the movement of the piston pressurizes a pressure chamber when the piston is moved in a first direction, and wherein the pressure chamber of the piston arrangement (18) is in fluid communication with an outlet, and wherein the piston arrangement (18) further comprises an electrically operated linear drive for moving the piston within the bore; (b) Actuating the linear drive of the piston assembly (18) to provide pressure at a first predetermined level at the outlet of the piston assembly (18); (c) Maintaining the pressure at the outlet of the piston assembly (18) for a predetermined period of time; and (d) Determine whether a condition criterion is met which indicates a leak within the brake system (10), wherein the brake system (10) further comprises: a brake pedal unit (14) with a housing defining a bore therein, wherein the brake pedal unit (14) further comprises a first piston slidably arranged therein such that the movement of the first piston pressurizes a first pressure chamber, and wherein the brake pedal unit (14) further comprises a second piston slidably arranged therein such that the movement of the second piston pressurizes a second pressure chamber; a first pressure build-up valve for selectively enabling a fluid flow to a first wheel brake; and characterized by a first separating valve (30, 32) which is movable between a first position which allows a fluid connection between the outlet of the piston assembly (18) and the first pressure build-up valve, and a second position which allows a fluid connection between the first pressure chamber of the brake pedal assembly (14) and the first pressure build-up valve; where, following step (a), the first separating valve (30, 32) is actuated to prevent the fluid flow from the outlet of the piston assembly (18) to the first pressure build-up valve and to allow the fluid flow to one of the first and second pressure chambers of the brake pedal assembly (14). [2] Method according to claim 1, wherein in step (d) the condition criterion is met if the pressure at the outlet of the piston arrangement (18) is below a second predetermined level, wherein the second predetermined level is lower than the first predetermined level. [3] Method according to claim 1, wherein in step (d) the condition criterion is met if the stroke distance of the piston of the piston arrangement (18) is greater than a first predetermined distance. [4] Method for performing a self-diagnostic test to determine leaks within a brake system (10), the method comprising: (a) Providing a braking system (10) comprising: a brake pedal unit (14) with a housing defining a bore therein, wherein the brake pedal unit (14) further comprises a first piston slidably arranged therein such that the movement of the first piston pressurizes a first pressure chamber, and wherein the brake pedal unit (14) further comprises a second piston slidably arranged therein such that the movement of the second piston pressurizes a second pressure chamber; a piston arrangement (18) with a housing defining a bore therein, wherein the piston arrangement (18) has a piston slidably arranged therein such that the movement of the piston pressurizes a pressure chamber when the piston is moved in a first direction, and wherein the pressure chamber of the piston arrangement (18) is in fluid communication with an outlet, and wherein the piston arrangement (18) further comprises an electrically operated linear drive for moving the piston within the bore; a first pressure build-up valve for selectively enabling a fluid flow to a first wheel brake; a second pressure build-up valve to selectively allow a fluid flow to a second wheel brake; a first separating valve (30, 32) which is movable between a first position which allows a fluid connection between the outlet of the piston assembly (18) and the first pressure build-up valve, and a second position which allows a fluid connection between the first pressure chamber of the brake pedal assembly (14) and the first pressure build-up valve; a second separating valve (32, 30) which is movable between a first position which allows a fluid connection between the outlet of the piston assembly (18) and the second pressure build-up valve, and a second position which allows a fluid connection between the second pressure chamber of the brake pedal assembly (14) and the second pressure build-up valve; (b) Actuating the first separating valve to prevent the flow of fluid from the outlet of the piston assembly (18) to the first pressure build-up valve; (c) Actuating the second separating valve to allow the fluid flow from the outlet of the piston assembly (18) to the second pressure chamber of the brake pedal assembly (14); (d) Actuating the piston assembly (18) to provide pressure at the outlet of the piston assembly (18) at a first predetermined level, wherein a pressure increase at the outlet of the piston assembly (18) causes a pressure increase in the first and second pressure chambers of the brake pedal assembly (14); (e) Maintaining the pressure at the outlet of the piston assembly (18) for a predetermined period of time; and (f) following step (e) Determine whether the pressure of the second pressure chamber of the brake pedal assembly (14) is below a second predetermined level, wherein the second predetermined level is smaller than the first predetermined level, such that if the pressure of the second pressure chamber of the brake pedal assembly (14) is not below the second predetermined level, the proper functioning of the second piston within the brake pedal assembly (14) is determined. [5] Method according to claim 4, wherein before step (d) the first and the second pressure build-up valve are actuated to prevent the fluid flow from the outlet of the piston arrangement (18) to the first and second wheel brake respectively. [6] Method according to claim 4, wherein the brake pedal unit (14) further comprises a third piston which is slidably arranged in the bore such that the movement of the third piston pressurizes a third pressure chamber, and wherein the brake system (10) further comprises a pedal simulator in selective fluid connection with the third chamber, and wherein the brake system (10) further comprises a simulator valve which is arranged between the third chamber and the pedal simulator, and wherein the method further comprises: (g) Actuating the simulator valve to allow fluid flow from the third chamber to the pedal simulator; (h) Actuating the piston assembly (18) to provide pressure at the outlet of the piston assembly (18) with a third predetermined pressure level that is higher than the first predetermined pressure level, wherein a pressure increase at the outlet of the piston assembly (18) causes a pressure increase in the first, second and third pressure chambers of the brake pedal assembly (14); and (i) Maintaining the pressure at the outlet of the piston assembly (18) for a second predetermined time period. [7] Method according to claim 6, wherein following step (i) it is determined whether the pressure of the second pressure chamber of the brake pedal unit (14) is below a fourth predetermined level, wherein the fourth predetermined level is smaller than the third predetermined level, such that if the pressure of the second pressure chamber of the brake pedal unit (14) is not below the fourth predetermined level, the proper operation of the pedal simulator is determined. [8] Method according to claim 6, wherein following step (i) it is determined whether the pressure at the outlet of the piston arrangement (18) is below a fourth predetermined level, wherein the fourth predetermined level is lower than the third predetermined level, such that if the pressure of the second pressure chamber of the brake pedal unit (14) is not below the fourth predetermined level, the proper operation of the pedal simulator is determined. [9] Method according to claim 6, wherein during step (h) the stroke distance of the piston of the piston assembly (18) is assessed and compared with a previously determined stroke distance of the piston of a proper operation of the piston assembly (18). [10] The method of claim 6, further comprising the following steps: (j) Actuating the first and second separating valves to prevent the flow of fluid from the outlet of the piston assembly (18) to the brake pedal assembly (14); (k) Maintaining the pressure at the outlet of the piston assembly (18) for a third predetermined time period; and (l) Determine whether the pressure of the second pressure chamber of the brake pedal assembly (14) is below a fifth predetermined level. [11] Method according to claim 10, wherein following step (i) the pedal simulator valve is actuated to prevent a fluid flow from the third pressure chamber of the brake pedal unit (14) to the pedal simulator. [12] Method according to claim 10, wherein the brake system (10) further comprises a first pressure relief valve arranged between the first wheel brake and the reservoir, and wherein the brake system (10) further comprises a second pressure relief valve arranged between the second wheel brake and the reservoir, and further comprising the following steps: (m) Actuating the first and second pressure build-up valves to allow fluid flow from the first and second separating valves (30, 32) to the wheel brakes; (n) Pulsing of at least one of the pressure relief valves; (o) Monitoring the rate of pressure reduction of the pressure at the wheel brake connected to at least one of the pressure relief valves; and (p) Determine whether the pressure reduction rates are above a predetermined reduction rate.

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