Vehicle braking system with a plunger assembly

Abstract

Braking system (10), with: first and second wheel brakes (16a, 16b, 16c, 16d); a brake pedal assembly (12) comprising a brake pedal unit (20) which has a housing (24), a pair of output pistons (38, 40) slidably arranged in the housing (24) and a pedal simulator (100) which is accommodated within the brake pedal unit (20), wherein the pair of output pistons (38, 40) is movable, to generate a brake actuation pressure at first and second outputs during a manual push-through mode to actuate the first and second wheel brakes (16a, 16b, 16c, 16d), respectively; and a hydraulic control unit (14) with a plunger assembly (300, 502, 700, 900) for actuating the first and second wheel brakes (16a, 16b, 16c, 16d) during normal braking, wherein the plunger assembly (300, 502, 700, 900) comprises: a case (340, 540, 706, 902); a motor (352) attached to the housing (340, 540, 706, 902) for driving an actuator; a first piston (344, 544, 744) connected to the actuator, wherein the first piston (344, 544, 744) is slidably mounted within the housing (340, 540, 706, 902) to pressurize a first fluid chamber in the housing (340, 540, 706, 902), wherein the first fluid chamber is connected to the first wheel brake (16c, 16d); and a second piston (346, 546, 746) arranged slidably within the housing (340, 540, 706, 902) to pressurize a second fluid chamber in the housing (340, 540, 706, 902), the second fluid chamber being connected to the second wheel brake (16a, 16b); comprising a pumpless control valve arrangement: a first control valve that regulates the fluid flow between the first fluid chamber and the first wheel brake (16c, 16d), and a second control valve that regulates the fluid flow between the second fluid chamber and the second wheel brake (16a, 16b); and a shut-off valve arrangement for switching the brake system (10) between the normal brake mode, in which boost pressure is supplied from the plunger assembly (300, 502, 700, 900) to the wheel brakes (16a, 16b, 16c, 16d), and the manual push-through mode, in which actuation pressure is supplied from the brake pedal unit (20) to the wheel brakes (16a, 16b, 16c, 16d), characterized in that the pedal simulator (100) is accommodated between an input piston (34) of the brake pedal unit and one of the output pistons (38, 40).

Description

REFERENCE FROM RELATED APPLICATIONS

[0001] This application claims priority over US patent application no. 13 / 843845, filed on March 15, 2013. BACKGROUND OF THE INVENTION

[0002] This invention relates generally to vehicle braking systems. Vehicles are usually slowed down and brought to a stop by hydraulic braking systems. These systems vary in complexity, but a basic braking system typically 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 depressed, the master cylinder generates hydraulic forces in both brake circuits by pressurizing brake fluid. This pressurized fluid travels through the fluid lines in both circuits to actuate brake cylinders at the wheels, thus slowing the vehicle.

[0003] Basic braking systems typically use a brake booster to supply force to the master cylinder, assisting the pedal force applied by the driver. The booster can be vacuum-operated or hydraulically driven. 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 in turn generate pressurized fluid in the line connected to 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 amount of pressurized fluid supplied to the master cylinder.

[0004] Controlled braking of a vehicle under adverse conditions requires precise brake application by the driver. In such 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-up conditions can lead to longer braking distances and a potential loss of directional control.

[0005] Advances in braking technology have led to the introduction of anti-lock braking systems (ABS). An ABS system monitors wheel rotation and selectively builds up and releases brake pressure in the relevant wheel brakes to maintain wheel speed within a selected slip range to achieve maximum braking force. While such systems are typically designed to control the braking of each braked wheel of the vehicle, some systems have been developed to control the braking of only a portion of the total number of braked wheels.

[0006] Electronically controlled ABS valves, comprising pressure application 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. When activated, these ABS valves typically operate in three pressure control modes: pressure application, pressure release, and pressure hold. The application valves allow pressurized brake fluid to flow into the corresponding wheel brakes to increase pressure during the application mode, and the release valves release brake fluid from their associated wheel brakes during the release mode. During the hold mode, the wheel brake pressure is maintained by closing both the application and release valves.

[0007] To achieve maximum braking force while maintaining vehicle stability, it is desirable to achieve optimal wheel slip values ​​at both 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 should be proportioned between the front and rear brakes 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 control the brake pressures at the front and rear wheels independently, dynamically achieving optimal braking performance at the front and rear axles under the prevailing conditions.

[0008] A further development in brake technology has led to the introduction of traction control systems (TC systems). Typically, valves were added to existing ABS systems to provide a braking system that regulates wheel speed during acceleration. Excessive wheel speed during vehicle acceleration leads to wheel slip and a loss of traction. An electronic control system 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.

[0009] During vehicle maneuvers such as cornering, dynamic forces are generated that can reduce vehicle stability. A vehicle stability control (VSC) brake system improves vehicle stability by counteracting these forces through selective brake application. These forces and other vehicle parameters are detected by sensors that signal an electronic control unit. The electronic control unit automatically actuates pressure control devices to regulate the amount of hydraulic pressure applied to specific individual wheel brakes. To achieve optimal vehicle stability, brake pressures greater than the master cylinder pressure must be readily available at all times.

[0010] Braking systems can also be used for regenerative braking to recover energy. Regenerative braking uses the electromagnetic force of an electric motor / generator to provide the vehicle with some of its braking torque to meet its braking needs. A control module in the braking system communicates with a powertrain control module to provide coordinated braking during regenerative braking, as well as braking in case of wheel lock and slippery conditions. For example, once the driver begins to brake during regenerative braking, electromagnetic energy from the motor / generator is used to apply braking torque to the vehicle (i.e., electromagnetic resistance to provide torque to the powertrain).If it is determined that there is no longer a sufficient amount of storage medium to store the energy recovered from regenerative braking, or if the regenerative braking does not meet the driver's requirements, hydraulic braking is activated to complete part or all of the braking action requested by the operator. Preferably, the hydraulic braking operates as a regenerative braking mixture, so that the braking mixture is effectively and imperceptibly resumed where the electromagnetic braking left off. It is desirable that the vehicle's movement exhibits a smooth transition to hydraulic braking, such that the change remains imperceptible to the driver.

[0011] Some braking systems are configured such that the pressures at each of the wheel brakes can be controlled independently (also known as multiplex operation), even though the braking system may only contain a single pressure source. Thus, valves downstream of the pressure source are controlled between their open and closed positions to provide different braking pressures within the wheel brakes. Such multiplex systems, all of which are disclosed by reference to the contents of this document, are disclosed in U.S. Patent 8,038,229, U.S. Patent Application Publication No. 2010 / 0026083, U.S. Patent Application Publication No. 2012 / 0013173, and U.S. Patent Application Publication No. 2012 / 0306261. A braking system with a tandem master cylinder and a tandem auxiliary cylinder is known from U.S. Patent 2008 / 0290726 A1.US 2003 / 0038541 A1 discloses an electronic braking system with a motor-driven master cylinder, the motor of which is driven based on the operation of a decoupled pedal. US 6 494 546 B1 discloses a brake pressure control device comprising a master cylinder and a pressure supply unit with a motor-driven pump.

[0012] The object of the invention is to overcome the disadvantages of the prior art. This object is achieved by the subject matter of claim 1. SUMMARY OF THE INVENTION

[0013] This invention relates to vehicle braking systems, such as a braking system with first and second wheel brakes and a brake pedal assembly comprising a housing and a pair of output pistons slidably arranged within the housing. The pair of output pistons is movable to generate brake actuation pressure at first and second outputs for actuating the first and second wheel brakes, respectively, during a manual depressor mode. A plunger assembly for actuating the first and second wheel brakes during normal braking comprises a housing and a motor mounted on the housing for driving an actuator. A first piston is connected to the actuator. The first piston is slidably mounted within the housing to pressurize a first fluid chamber within the housing. The first fluid chamber communicates with the first wheel brake.A second piston is slidably mounted within the housing to pressurize a second fluid chamber within the housing. This second fluid chamber communicates with the second wheel brake. A pumpless control valve assembly includes a first control valve that regulates the fluid flow between the first fluid chamber and the first wheel brake. A second control valve regulates the fluid flow between the second fluid chamber and the second wheel brake. A shut-off valve assembly switches the braking system between normal braking mode, in which boost pressure is supplied to the wheel brakes from the plunger assembly, and manual override mode, in which brake actuation pressure is supplied to the wheel brakes from the brake pedal assembly.

[0014] Various aspects of this invention will become apparent to experts in this field from the following detailed description of the preferred embodiment when reading it with reference to the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES Fig. Figure 1 is a schematic representation of a first embodiment of a braking system. Fig. Figure 2 is an enlarged schematic sectional view of the brake pedal assembly of the braking system. Fig. 1, shown in their resting position. Fig. Figure 3 is an enlarged schematic sectional view of the plunger assembly of the brake system. Fig. 1, shown in its resting position. Fig. Figure 4 is a schematic representation of a second embodiment of a braking system. Fig. Figure 5 is an enlarged schematic sectional view of the plunger assembly of the brake system. Fig. 4, shown in its resting position. Fig. Figure 6 is a cross-sectional view of a third embodiment of a plunger assembly, which is part of the braking system. Fig. 5 can be used, with the plunger assembly shown in a rest position. Fig. Figure 7 is a cross-sectional view of a plunger assembly made of Fig. 6, shown in a full-stroke position. Fig. Figure 8 is a cross-sectional view of a fourth embodiment of a plunger assembly. DETAILED DESCRIPTION OF THE PREFERRED VERSION

[0015] Referring now to the characters, in Fig. Figure 1a schematically illustrates a first embodiment of a vehicle braking system, which is generally characterized by 10. The braking system 10 is a hydraulically augmented braking system in which increased fluid pressure is used to generate braking forces. The braking system 10 is suitable for use in a land vehicle, such as a four-wheeled motor vehicle with a wheel brake for each wheel. Furthermore, the braking system 10 can be equipped with additional braking functions, such as anti-lock braking systems (ABS) and other slip control functions, to effectively decelerate the vehicle, as will be explained below.

[0016] The brake system 10 generally comprises a first block or brake pedal assembly, indicated by dashed lines 12, and a second block or hydraulic control unit, indicated by dashed lines 14. The various components of the brake system 10 are housed within the brake pedal assembly 12 and the hydraulic control unit 14. The brake pedal assembly 12 and the hydraulic control unit 14 may comprise one or more blocks or housings made of a solid material, such as aluminum, which has been drilled, machined, or otherwise formed to accommodate the various components. Fluid lines may also be formed within the housings to provide fluid passages between the various components. The housings of the brake pedal assembly 12 and the hydraulic control unit 14 may be single structures or composed of two or more parts.As shown schematically, the hydraulic control unit 14 is located remotely from the brake pedal assembly 12, with hydraulic lines hydraulically connecting the brake pedal assembly 12 and the hydraulic control unit 14. Alternatively, the brake pedal assembly 12 and the hydraulic control unit 14 can be arranged in a single housing. It should be noted that the grouping of components as in . Fig. 1 is not to be understood as limiting and any number of components can be accommodated in each of the housings.

[0017] The brake pedal assembly 12 interacts with the hydraulic control unit 14 to actuate the wheel brakes 16a, 16b, 16c, and 16d. The wheel brakes 16a, 16b, 16c, and 16d can be any suitable wheel brake structure operated by the application of pressurized brake fluid. For example, the wheel brake 16a, 16b, 16c, and 16d can include a brake caliper mounted on the vehicle to engage with a friction element (such as a brake disc) that rotates with a vehicle wheel to cause braking of that wheel. The wheel brakes 16a, 16b, 16c, and 16d can be assigned to any combination of front and rear wheels of the vehicle in which the brake system 10 is installed. For example, in a vertically divided system, wheel brakes 16a and 16d can belong to the wheels of the same axle.In a diagonally split braking system, wheel brakes 16a and 16b can be considered front wheel brakes.

[0018] The brake pedal assembly 12 includes a fluid reservoir 18 for storing and maintaining hydraulic fluid for the brake system 10. The fluid in the reservoir 18 can generally be stored at atmospheric pressure or, if desired, at other pressures. The brake system 10 may include a fluid level sensor 19 for detecting the fluid level in the reservoir. The fluid level sensor 19 can be helpful in determining whether a leak has occurred in the system 10.

[0019] The brake pedal assembly 12 includes a brake pedal unit (BPU), which is generally designated 20. The brake pedal unit 20 is enlarged in Fig. 2 is also shown schematically. It should be noted that the structural details of the components of the brake pedal unit 20 represent only one example of a brake pedal unit 20. The brake pedal unit 20 could be configured differently, with components other than those shown. Fig. 1 and Fig. 2 components shown.

[0020] The brake pedal unit 20 includes a housing 24 (in Fig. (2 shown in a broken-up view) with various bores formed therein for the slidable accommodation of various cylindrical pistons and other components. The housing 24 can be formed as a single unit or comprise two or more separately formed, coupled sections. The housing 24 generally includes a first bore 26, a middle second bore 28, and a third bore 30. The second bore 28 has a larger diameter than the first bore 26 and the third bore 30. The brake pedal assembly 20 further includes an input piston 34, a primary piston 38, and a secondary piston 40. The input piston 34 is slidably arranged in the first bore 26. The primary piston 38 is slidably arranged in the second bore 28. The secondary piston 40 is slidably arranged in the third bore 30.

[0021] A brake pedal that is in the Fig. 1 and Fig. Figure 2, schematically depicted and labelled 42, is connected to a first end 44 of the input piston 34 via an input rod 45. The input rod 45 can be directly coupled to the input piston 34 or indirectly connected to it via a coupling piece (not shown). The input piston 34 has an enlarged second end 52, which defines a shoulder 54. In the Fig. 1 and Fig. In the rest position shown in Figure 2, the shoulder 54 of the inlet piston engages with a shoulder 56 formed between the first and second bores 26 and 28 of the housing 24. An outer cylindrical surface 57 of the inlet piston 34 engages with a seal 58 and a lip seal 60, which are fitted in grooves formed in the housing 34. The outer cylindrical surface 57 can be continuous along its length or stepped with two or more different diameter sections. The inlet piston 34 includes a central bore 62 formed by the second end 52. One or more lateral passages 64 are formed by the inlet piston 34. The lateral passages 64 extend from the outer cylindrical surface 57 to the central bore 62 to establish a fluid connection between them. The brake pedal assembly 20 is located, as shown in Figure 2. Fig. 1 and Fig. Figure 2 shows the vehicle in a "rest position." In the "rest position," the pedal 42 is not depressed by the driver. In the rest position, the passages 64 of the inlet piston 34 are located between the seals 58 and 60. In this position, the passages 64 are in fluid communication with a line 66 formed by the housing 24. The line 66 is in fluid communication with a line 68 formed in the housing 24. The line 68 is in fluid communication with a reservoir connection 70 connected to the reservoir 18. A filter 69 can be arranged in the connection 70 or in the line 68. The lines 66 and 68 can be formed by various bores, grooves, and passages provided in the housing 24. In the rest position, the passages 64 are also in fluid communication with a line 72 formed in the housing 24, which leads to a simulator valve 74. The simulator valve 74 can be a shut-off valve that can be electrically operated.The simulator valve 74 can be installed in the housing 24 or located away from it.

[0022] The primary piston 38 is slidably arranged in the second bore 28 of the housing 24. An outer wall 79 of the primary piston 38 engages with a lip seal 80 and a lip seal 81, which are fastened in grooves formed in the housing 24. The primary piston 38 has a first end 82 with a cavity 84 formed therein. A second end 86 of the primary piston 38 includes a cavity 88 formed therein. One or more passages 85 are formed in the primary piston 38, extending from the cavity 88 to the outer wall of the primary piston 38. As in Fig. As shown in Figure 2, the passage 85 is located between the lip seals 80 and 81 when the primary piston 38 is in its rest position. For reasons explained below, the passage 85 is in selective fluid communication with a line 154, which is in fluid communication with the container 18.

[0023] The central bore 62 of the input piston 34 and the cavity 84 of the primary piston 38 accommodate various components that form a pedal simulator, generally designated 100. A captive spring assembly, generally designated 102, is formed by a pin 104, a retainer 106, and a soft simulator spring 108. The pin 104 is schematically depicted as part of the input piston 34 and located in the central bore 62. The pin 104 could be configured as a pin with a first end that is press-fitted or screw-fit into the input piston 34. The pin 104 extends axially within the central bore 62 and into the cavity 84 of the primary piston 38. A second end 112 of the pin 104 has a circular collar 114 that projects radially outward from the pin. The second end 112 is spaced apart from an elastomeric cushion 118, which is arranged in the cavity 84.The elastomeric cushion 118 is axially aligned with the second end 112 of the pin 104, the reason for which will be explained below. The holder 106 of the captive spring assembly 102 includes a stepped bore 122. The stepped bore 122 defines a shoulder 124. The second end 112 of the pin 104 extends through the bore 122. The collar 114 of the pin 104 engages the shoulder 124 of the holder 106 to prevent the pin 104 and the holder 106 from separating. One end of the soft simulator spring 108 engages the second end 52 of the input piston 34, and the other end of the soft simulator spring 108 engages the holder 106 to bias the holder 106 in a direction away from the pin 104.

[0024] The pedal simulator 100 further includes a rigid simulator spring 130 arranged around the pin 104. The terms rigid and soft are used for descriptive purposes and are not intended to be restrictive. It should be noted that the various springs of the pedal simulator 100 can have any suitable spring coefficient or spring constant. In the illustrated embodiment, the rigid simulator spring 130 preferably has a higher spring constant than the soft simulator spring 108. One end of the rigid simulator spring 130 engages in the bottom of the central bore 62 of the input piston 34. The other end of the rigid simulator spring 130 is in Fig. 2 is shown in a non-engaging position and spaced from one end of the holder 106. The housing 24, the inlet piston 34 (and its seals), and the primary piston 38 (and its seals) generally define a fluid simulation chamber 144. The simulation chamber 144 is in fluid communication with a line 146, which is in fluid communication with the simulator valve 74. A filter 145 may be accommodated within the line 146.

[0025] As explained above, the brake pedal assembly 20 includes the primary and secondary pistons 38 and 40, which are arranged in the second and third bores 28 and 32, respectively, formed in the housing 24. The primary piston 38 and the secondary piston 40 are generally coaxial with each other. A primary outlet line 156 is formed in the housing 24 and is in fluid communication with the second bore 28. The primary outlet line 156 can be extended by means of external piping or a hose connected to the housing 24. A secondary outlet line 166 is formed in the housing 24 and is in fluid communication with the third bore 30. The secondary outlet line 166 can be extended by means of external piping or a hose connected to the housing 24. As will be explained in detail below, a consideration of the Fig. 1 and Fig. 2. The primary and secondary pistons 38 and 40 move to the right, forcing a pressurized fluid outwards through lines 156 and 166 respectively. A return spring 151 is housed in the second bore 28 and biases the primary piston 38 in the leftward direction.

[0026] The secondary piston 40 is slidably arranged in the third bore 30. An outer wall 152 of the secondary piston engages with a lip seal 153 and a lip seal 154, which are installed in grooves formed in the housing 24. A secondary pressure chamber 228 is generally defined by the third bore 30, the secondary piston 40, and the lip seal 154. When considering the Fig. 1 and Fig. 2. A movement to the right of the secondary piston 40 causes a build-up of pressure in the secondary pressure chamber 228. The secondary pressure chamber 228 is in fluid communication with the secondary outlet line 166, so that pressurized fluid is selectively supplied to the hydraulic control unit 14. One or more passages 155 are formed in the secondary piston 40. The passage 155 extends between the outer wall of the primary piston 38 and a right end of the secondary piston 40. As in Fig. As shown in Figure 2, the passage 155 is located between the seal 153 and the lip seal 154 when the secondary piston is in its rest position, the reasons for which are explained below. For reasons explained below, the passage 155 is in selective fluid communication with a line 164, which is in fluid communication with the container 18.

[0027] A primary pressure chamber 198 is generally defined by the second bore 28, the primary piston 38, the secondary piston 40, the lip seal 81, and the seal 153. Although the various seals shown in the figures are schematically represented as O-rings or lip seals, it is understood that they can be configured arbitrarily. When considering the Fig. 1 and Fig. 2 causes a movement to the right of the primary piston 38, resulting in a build-up of pressure in the primary pressure chamber 198. The primary pressure chamber 198 is in fluid communication with the primary outlet line 156, so that pressurized fluid can be selectively supplied to the hydraulic control unit 14.

[0028] The primary and secondary pistons 38 and 40 can be mechanically linked, allowing limited clearance or movement between them. This linkage enables the primary and secondary pistons 38 and 40 to move relative to each other in relatively small increments to compensate for pressure and / or volume differences in their respective output circuits. However, in certain fault modes, it is desirable for the secondary piston 40 to be linked to the primary piston 38. For example, if the brake system 10 is in a manual override mode, as explained below, and additionally, fluid pressure is lost in the output circuit relative to the secondary piston 40, such as in line 166, the secondary piston 40 will be forced or biased to the right due to the pressure within the primary chamber 1798.If the primary and secondary pistons 38 and 40 were not connected, the secondary piston 40 would be viewed when considering the . Fig. 1 and Fig. 2 could move freely to its far right position, and the driver would have to press the pedal 42 a certain distance to compensate for this loss of travel. However, since the primary and secondary pistons 38 and 40 are connected, the secondary piston 40 is prevented from this movement, and the loss of travel in this type of disturbance is comparatively small.

[0029] The primary and secondary pistons 38 and 40 can be connected to each other in any suitable way. For example, as shown in the Fig. 1 and Fig. As shown schematically in Figure 2, a locking element 180 is arranged and trapped between the primary and secondary pistons 38 and 40. The locking element 180 has a first end 182 and a second end 184. The first end 182 is trapped within the cavity 88 of the second end 86 of the primary piston 38. The second end 184 of the locking element 180 is trapped within a recess or cavity 186 formed in the secondary piston 40. The first and second ends 182 and 184 may have enlarged head sections, each trapped behind narrower openings 192 and 194 of the cavities 88 and 186, respectively. A first spring 188 is received within the cavity 88 of the primary piston 38 and pre-tensions the locking element 180 in a direction towards the primary piston 38 and away from the secondary piston 40.A second spring 190 is housed within the cavity 186 of the secondary piston 40 and biases the locking element 180 in a direction towards the primary piston 38 and away from the secondary piston 40. The springs 188 and 190 and the locking element 180 hold the first and second output pistons apart, while allowing limited movement towards and away from each other by compressing the springs 188 or 190. This mechanical connection with limited play allows the primary and secondary pistons 38 and 40 to move relative to each other in small increments to compensate for pressure and / or volume differences in their respective output circuits.

[0030] Referring back to Fig. 1. System 10 can also include a displacement sensor that is located in Fig. The system 10, shown schematically at 240, may include a circuit 252 for generating a signal indicative of the length of the input piston 34's travel, which corresponds to the pedal travel. The system 10 may also include a circuit 252 for generating a signal to activate a brake light and for providing a signal indicative of movement of the input piston 34. Furthermore, the brake system 10 may include sensors such as pressure transducers 257 and 259 for monitoring the pressure in lines 156 and 166, respectively.

[0031] System 10 further includes a pressure source in the form of a plunger assembly, generally designated 300. As detailed below, System 10 uses the plunger assembly 300 to supply each of the wheel brakes 16a-d with a desired pressure level. Fluid from the wheel brakes 16a-d is returned to the plunger assembly 300.

[0032] System 10 further includes a first shut-off valve 302 and a second shut-off valve 304 (also referred to as changeover valves or changeover valve assembly). The shut-off valves 302 and 304 can be solenoid-operated valves. The shut-off valves 302 and 304 can generally be switched between an open position 302a, as shown in Fig. Figure 1 schematically illustrates the first shut-off valve 302, which is operated in a closed position 302b. The first shut-off valve 302 is in fluid communication with the primary outlet line 156, so that when the first shut-off valve 302 is in its open position 302a, a fluid flow between the first output pressure chamber 198 and the plunger assembly 300 is permitted via the primary outlet line 156 and a line 306. When the first shut-off valve 302 is in its closed position 302b, a fluid flow is prevented from flowing through the primary outlet line 156 to the line 306. The second shut-off valve 304 is in fluid communication with the secondary outlet line 166, so that when the second shut-off valve 304 is in its open position 304a, a fluid flow between the second output pressure chamber 228 and the plunger assembly 300 is allowed via the secondary outlet line 166 and a line 308.When the second shut-off valve 304 is in its closed position 304b, a fluid flow is prevented from flowing through the secondary outlet line 166 to the line 308.

[0033] System 10 can further include various valves, such as a slip control valve arrangement, to allow controlled braking operations, such as ABS, traction control, vehicle stability control, and regenerative brake mixing. In the Fig. In the embodiment shown in Figure 1, the system comprises 10 first, second, third, and fourth control valves 310, 312, 314, and 316. Similar to the shut-off valves 302 and 304, the control valves 310, 312, 314, and 316 can be solenoid-operated valves that are movable between open and closed positions and are designed to allow a high-pressure fluid to flow through the valve in both directions. Control valve 310 is in fluid communication with the plunger assembly 300 via a line 320. Control valve 310 is also in fluid communication with the wheel brake 16a via a wheel line 322. Control valve 312 is in fluid communication with the plunger assembly 300 via a line 324. Control valve 312 is also in fluid communication with the wheel brake 16b via a wheel line 326. The control valve 314 is in fluid communication with the plunger unit 300 via line 324.The control valve 314 is also in fluid communication with the wheel brake 16b via a wheel line 328. The control valve 316 is in fluid communication with the plunger assembly 300 via line 320. The control valve 316 is also in fluid communication with the wheel brake 16b via a wheel line 328. A pressure transducer 321 or another sensor may be included in the system 10 to monitor the pressure within line 320. The system 10 may also include a pressure transducer or a sensor (not shown) to monitor the pressure within line 324.

[0034] As stated above, system 10 includes a pressure source in the form of the plunger unit 300 to supply each of the wheel brakes 16a-d with a desired pressure level. As in Fig. As best shown in Figure 3, the plunger assembly 300 includes a housing 340 with a bore 342 formed therein. First and second pistons 344 and 346 are slidably arranged in the bore 342. The plunger assembly 300 further includes a ball screw mechanism, generally designated 350. The ball screw mechanism 350 is provided to impart a translational or linear movement to the first piston 344 along an axis defined by the bore 342 in both an actuation direction (when considering the Fig. 1 and Fig. 3 to the left) as well as a retraction direction (when viewing the Fig. 1 and Fig. 3 to the right) within the bore 342 of the housing 340. In the embodiment shown, the ball screw mechanism 350 includes a motor 352 that rotates a screw shaft 354. A motor 352 can include a sensor 353 for detecting a rotational position of the motor 352 and / or ball screw mechanism 350, which is indicative of the position of the first piston 344. This can be particularly useful for a motor 352 capable of very precise control, including controlling the motor to minute movements to provide multiplex control, as will be explained below. The first piston 344 includes a threaded bore 356 and acts as the driven nut of the ball screw mechanism 350.The ball screw mechanism 350 comprises a plurality of balls 358 held within the helical raceways formed in the screw shaft 354 and the threaded bore 356 of the first piston 344 to reduce friction. Although a ball screw mechanism 350 is shown and described in relation to the plunger assembly 300, it should be noted that other suitable mechanical linear actuators can be used to drive the first piston 344. It should also be noted that although the first piston 344 acts as the nut of the ball screw mechanism 350, the first piston 344 could also be configured to act as the screw shaft of the ball screw mechanism 350. Naturally, in this case, the screw shaft 354 would be configured to act as a nut with internal helical raceways formed therein.

[0035] The first piston 344 has an outer cylindrical surface 360. An O-ring 362 is fitted within a groove 364 formed in the bore 342. A lip seal 366 is fitted within a groove 368 formed in the bore 342. The O-ring 362 and the lip seal 366 engage sealingly with the outer cylindrical surface 360 ​​of the first piston 344. The first piston 344 has a pin or extension 370 that extends toward the second piston 346. The extension 370 has an enlarged head 372. The enlarged head 372 is held within a cavity 374 formed in the second piston 356 by an inwardly extending collar 376. The first piston 344 is mechanically connected to the second piston 346 by the interaction of the extension 370 and the collar 376, although a predetermined degree of movement between them is still permitted.The first piston 344 is biased in a direction away from the second piston 346 by a spring 380. The spring 380 generally acts on the end faces of the pistons 344 and 346 that face each other. The spring 380 can generally be accommodated within a recess 382 formed in the first piston 344.

[0036] The second piston 346 has an outer cylindrical surface 384. An O-ring 386 is fitted within a groove 387 formed in the bore 342. A lip seal 388 is fitted within a groove 389 formed in the bore 342. The O-ring 386 and the lip seal 388 engage in a sealing manner with the outer cylindrical surface 384 of the second piston 346. It should be noted that any suitable sealing structure can be used for the O-rings 362 and 386 and the lip seals 366 and 388. The second piston 346 has a pin or extension 390 that extends towards the end of the bore 342. The extension 390 has an enlarged head 392. The enlarged head 392 is trapped within a cavity 394 formed in the end of the bore 342 of the housing 340 by an inwardly extending collar 396.The second piston 346 is mechanically connected to the housing 340 by the interaction of the extension 390 and the collar 396, although a predetermined degree of movement between them is still permitted. The second piston 346 is biased in a direction away from the end of the bore 340 (and towards the first piston 344) by a spring 400. The spring 400 can generally be accommodated within a recess 402 formed in the second piston 346. The springs 380 and 400 generally position the second piston 346 relative to the first piston 344 within the bore 342. The springs 380 and 400 also act as return springs, returning the first and second pistons 344 and 346 to their rest positions as shown in the diagram. Fig. 1 and Fig. 3 shown pre-tensioning.

[0037] The plunger assembly 300 comprises a first pressure chamber 410 and a second pressure chamber 412. The first pressure chamber 410 is generally defined by the bore 340, the first and second pistons 344 and 346, the lip seal 366, and the O-ring 386. The first pressure chamber 410 communicates with line 308, which is in selective communication with the secondary outlet line 166 via the second shut-off valve 304. The first pressure chamber 410 is also in fluid communication with line 324, which is in selective fluid communication with the wheel brakes 16b and 16c via the control valves 312 and 314. The second pressure chamber 412 is generally defined by the bore 340, the second piston 346, and the lip seal 388. The second pressure chamber 412 communicates with the line 306, which selectively communicates with the primary outlet line 156 via the first shut-off valve 302.The second pressure chamber 412 is also in fluid communication with the line 320, which is in selective fluid communication with the wheel brakes 16a and 16d via the control valves 310 and 316.

[0038] The gap between the O-ring 362 and the lip seal 366 is vented or is in fluid communication with the container 18 via the line 296. Similarly, the gap between the O-ring 386 and the lip seal 388 is vented or is in fluid communication with the container 18 via the line 296.

[0039] As explained above, the brake pedal assembly 12 includes a simulation valve 74, which can be mounted in the housing 24 or remotely from the housing 24. As shown schematically in the Fig. 1 and Fig. As shown in Figure 2, the simulation valve 74 can be a solenoid-actuated valve. The simulation valve 74 includes a first port 75 and a second port 77. Port 75 is in fluid communication with line 146, which is in fluid communication with the simulation chamber 144. Port 77 is in fluid communication with line 72, which is in fluid communication with the container 18 via lines 66 and 68. The simulation valve 74 is movable between a first position 74a, in which the flow of fluid from the simulation chamber 144 to the container 18 is limited, and a second position 74b, which allows the flow of fluid between the container 18 and the simulation chamber 144.The simulation valve 74, as long as it is not actuated, is in the first position or normally closed position, so that a fluid is prevented from flowing out of the simulation chamber 144 through the line 72, as will be explained in more detail below.

[0040] The following is a description of how to operate brake system 10. Fig. 1 and Fig. Figure 2 represents the brake system 10 and the brake pedal unit 20 in their rest position. In this state, the driver does not depress the brake pedal 42. Even in the rest state, the simulation valve 74 may be energized or not. During a typical braking operation, the driver depresses the brake pedal 42. The brake pedal 42 is coupled to the position sensor 240 to generate a signal indicating the travel distance of the input piston 34 and to deliver this signal to an electronic control module (not shown). The control module may include a microprocessor. The control module receives and processes various signals and controls the operation of numerous electrical components of the brake system 10 in response to the received signals. The control module may be connected to various sensors, such as pressure sensors, position sensors, circuits, wheel speed sensors, and steering angle sensors.The control module can also be connected to an external module (not shown) to obtain information regarding the yaw rate, lateral acceleration, and longitudinal acceleration of the vehicle, e.g., for controlling the braking system 10 during a vehicle stabilization procedure. In addition, the control module can be connected to the instrument cluster to collect and provide information regarding warning indicators such as an ABS warning light, a brake fluid warning light, and a traction control / vehicle stability control indicator light.

[0041] During normal braking (a normal braking operation with brake booster), the plunger unit 300 is operated to supply boost pressure to lines 320 and 324 for actuating the wheel brakes 16a-d. In certain driving conditions, the control unit communicates with a powertrain control unit (not shown) and other auxiliary brake control units of the vehicle to provide coordinated braking during extended brake control schemes (e.g., anti-lock braking (ABS), traction control (TC), vehicle stability control (VSC), and regenerative brake mixing). During normal braking with brake booster, the flow of pressurized fluid from the brake pedal unit 20, generated by depressurizing the brake pedal 42, is directed to the internal pedal simulation arrangement 100.The simulation valve 74 is actuated to divert fluid from the simulation chamber 144 through the simulation valve 74 to the container 18 via the lines 146, 72, 66, and 68. It should be noted that fluid flow from the simulation chamber 144 to the container 18 is shut off as soon as the passages 64 in the inlet piston 34 move past the seal 60. Before any movement of the inlet piston 34, as shown in the... Fig. 1 and Fig. As shown in Figure 2, the simulation chamber 144 is in fluid communication with the container 18 via the lines 66 and 68.

[0042] During a normal braking process, the simulation valve 74 remains open, allowing the fluid to flow from the simulation chamber 144 to the reservoir 18. The fluid within the simulation chamber 144 is not pressurized and is under very low pressures, such as atmospheric pressure or low reservoir pressure. This unpressurized configuration has the advantage of not subjecting the sealing surfaces of the pedal simulator to high frictional forces from seals acting against the surfaces due to a high-pressure fluid. In conventional pedal simulators, the piston(s) are subjected to increasingly high pressures as the brake pedal is depressed, thus subjecting them to high frictional forces from the seals and adversely affecting pedal feel.

[0043] Even during normal braking with brake booster operation, the first and second shut-off valves 302 and 304 are energized to their closed positions 302b and 304b, respectively, to prevent fluid flow from lines 156 and 166 to the plunger assembly 300 and the wheel brakes 16a-d. This fluidly locks the fluid within the first and second output pressure chambers 198 and 228 of the brake pressure unit 20, generally preventing the first and second output pistons 38 and 40 from moving further. More precisely, during the initial phase of normal braking with brake booster operation, movement of the input rod 45 causes movement of the input piston 34 into a position that, when considering the Fig. 2. Right-hand direction. An initial movement of the inlet piston 34 causes a movement of the primary piston 38 via the soft simulator spring 108. A movement of the primary piston 38 causes an initial movement of the secondary piston 40 due to the mechanical connection between them by the locking element 180 and the springs 188 and 190. It should be noted that during this initial movement of the primary piston 38, the fluid can flow unhindered from the primary pressure chamber 198 to the reservoir 18 via lines 85, 154, and 68 until line 85 passes the seal 81. Likewise, during the initial movement of the secondary piston 40, the fluid can flow unhindered from the secondary pressure chamber 228 to the reservoir 18 via lines 155 and 164 until line 155 passes the seal 154.

[0044] After the primary and secondary pistons 38 and 40 stop moving (by closing lines 85 and 155 and closing the first and second base brake valves 320 and 322), the input piston 34 moves when considering the Fig. 1 and Fig. 2 continues to move to the right with further movement by the driver, who depresses the brake pedal 42. Further movement of the input piston 34 compresses the various springs of the pedal simulator assembly 100, thereby providing the driver of the vehicle with a feedback force.

[0045] During normal braking (normal braking with brake booster), in which the pedal simulator assembly 100 is actuated by depressing the brake pedal 42, the plunger assembly 300 can be actuated by the electronic control unit to provide actuation of the wheel brakes 16a-d. Actuation of the shut-off valves 302 and 304 to their closed positions 302b and 304b isolates the brake pedal assembly 12 from the wheel brakes 16a-d. The plunger assembly 300 can provide "boosted" or higher pressure levels to the wheel brakes 16a-d compared to the pressure generated by the brake pedal assembly 12 by the driver depressing the brake pedal 42.Therefore, the system 10 provides assisted braking, whereby increased pressure is supplied to the wheel brakes 16a-d during normal braking with amplification, which helps to reduce the force required by the driver to act on the brake pedal 42.

[0046] To actuate the wheel brakes 16a-d via the plunger assembly 300, the electronic control unit actuates the motor 352 in a first direction of rotation to rotate the screw shaft 354 in the first direction of rotation. A rotation of the screw shaft 354 in the first direction of rotation causes the first piston 344 to move forward in the direction of actuation (when viewing the Fig. 1 and Fig. 3 (directed to the left). Movement of the first piston 344 causes the spring 380 to press against the second piston 346, thereby initiating movement of the second piston 346. Further movement of the first piston 344 also causes a pressure increase in the first pressure chamber 410 and causes fluid to flow out of the first pressure chamber 410 and into line 324. It should be noted that fluid flow from the first pressure chamber 410 into line 308 is prevented because the shut-off valve 304 is in its closed position 304b. A pressure increase in the first pressure chamber 410 can also cause the second piston 412 to move in the direction of actuation, thereby causing a pressure increase in the second pressure chamber 412. Fluid flows out of the second pressure chamber 412 through line 320.It should be noted that the flow of fluid from the second pressure chamber 412 into line 306 is prevented because the shut-off valve 302 is in its closed position 302b. Pressurized fluid flowing into lines 320 and 324 and through the open control valves 310, 312, 314, and 316 actuates the wheel brakes 16a-d. The braking force can be increased by advancing the first and second pistons using the screw shaft 354 of the ball screw mechanism 350.

[0047] When the driver releases the brake pedal 42, the pressurized fluid from the wheel brakes 16a-d can retract the ball screw mechanism 350, thereby moving the first and second pistons 344 and 346 back to their rest positions. Under certain circumstances, it may also be desirable to actuate the motor 352 in a second direction of rotation opposite to the first direction of rotation in order to cause the first and second pistons 344 and 346 to move in a retraction direction (when considering the Fig. 1 and Fig. 3 to the right), thereby draining the fluid from the wheel brakes 16a-d and refilling the first and second pressure chambers 410 and 412. The motor 352 of the plunger assembly 300 can be actuated in the first and second directions of rotation to increase or decrease the brake pressure at the wheel brakes 16a-d. All control valves 310, 312, 314, and 316 can be controlled (in the unenergized state) to an open position to apply braking to all wheel brakes 16a-d simultaneously. Alternatively, as will be described below, the control valves 310, 312, 314, and 316 can be actuated individually between their open and closed positions to provide different brake pressures within the wheel brakes 16a-d.

[0048] As described above, the control valves 310, 312, 314, and 316 can be individually actuated between their open and closed positions to provide different brake pressures within the wheel brakes 16a-d. This can be used during various braking functions, such as anti-lock braking, traction control, dynamic brake force distribution, vehicle stability control, hill hold, and regenerative braking. The plunger assembly 300 and the control valves 310, 312, 314, and 316 are operated by the electronic control unit (not shown). The plunger assembly 300 is preferably configured and operated by the electronic control unit (not shown) such that comparatively small rotational steps of the motor 352 and / or the ball screw mechanism 350 can be achieved. Therefore, small fluid volumes and comparatively low pressure levels can be applied to and drawn from lines 320 and 324.For example, motor 352 can be actuated to rotate by 0.5 degrees to deliver a comparatively small amount of fluid and pressure increase. This enables a multiplex arrangement such that the plunger unit 300 can be controlled to provide individual wheel pressure control. For example, if the electronic control unit determines that the wheel brakes 16a and 16d require a pressure increase to stabilize the vehicle, control valves 310 and 316 can be actuated to their open positions. The remaining control valves 312 and 314 are actuated to their closed positions. Then, motor 352 of the plunger unit 300 is actuated to deliver the required pressure level to the wheel brakes 16a and 16d via pressure chamber 412 and lines 320, 322, and 330.To maintain the pressure level within the wheel brakes 16a and 16d, the control valves 310 and 316 can be actuated to their closed positions. To decrease the pressure within the wheel brakes 16a and 16d, the motor 352 can be actuated in its opposite direction of rotation, and the control valves 310 and 316 will be actuated accordingly. If, during this process, the electronic control unit detects that different pressures are required in the wheel brakes 16a and 16d, the control valves 310 and 316 can be controlled individually to allow an increase or decrease in pressure via lines 310 and 330, respectively, as needed.Thus, the plunger unit 300 and the system 10 can be operated to provide individual control of the wheel brakes 16a-d, or they can be used to control one or more wheel brakes 16a-d simultaneously by opening or closing the corresponding control valves 310, 312, 314, and 316.

[0049] Although system 10 is shown using individual control valves 310, 312, 314, and 316 for each of the wheel brakes 16a-d, the system can be configured to include a pair of solenoid-actuated control valves (not shown) for each of the wheel brakes 16a-d. Each pair of valves would be arranged in parallel with respect to the lines between the plunger assembly 300 and the corresponding wheel brakes 16a-d. Thus, the illustrated system 10 would include eight control valves instead of the four control valves 310, 312, 314, and 316. The paired valves are actuated simultaneously between their open and closed positions. It can be more economical to actuate two smaller valves simultaneously than to have a single, larger control valve. To generally provide the same volume flow and pressure flow, the pair of valves can have smaller springs with smaller spring constants compared to the single valve configuration.This can reduce overall costs and result in a quieter system, as the solenoid required to overcome the spring preload can be smaller. For the dual control valve arrangement (not shown), the dual valves within the system 10 can be arranged such that the fluid flow through one of the dual valves is reversed relative to the other dual valve. The dual valves can incorporate a valve seat arrangement in which fluid can flow through the valve seat in one of two directions. In the first direction, the fluid first flows through the valve seat and around the ball or valve element. In the second direction, the fluid first flows around the ball or valve element and then through the valve seat. Although the dual valves can generally be of identical construction, they can be arranged in a reversed manner within the housing of the hydraulic control unit 14.The use of a pair of dual valves with smaller spring constants in a reverse flow arrangement can provide better proportional control than a single, larger valve. Proportional control occurs when pressure increases or decreases are applied to more than one wheel brake simultaneously, with the wheel brakes operating at different pressures. Proportional control can be achieved in brake system 10 by using the plunger assembly 300 in conjunction with the respective control valve(s) for a first wheel brake, and then simultaneously using only the control of the respective control valve(s) for a second wheel brake. The use of dual valves in a parallel arrangement can also prevent unwanted hydraulic braking in both directions of fluid flow.

[0050] In the event of a loss of electrical power supply in parts of the brake system 10, the brake system 10 provides a manual depressor or manual application, such that the brake pedal assembly 20 can supply fluid under comparatively high pressure to the primary output line 156 and the secondary output line 166. During an electrical fault, the motor 352 of the plunger assembly 300 could cease to operate, thus preventing the generation of pressurized hydraulic brake fluid from the plunger assembly 300. The shut-off valves 302 and 304 are operated as described in Fig. Figure 1 shows the valves 302a and 304a oscillating (or remaining) in their open positions. In these positions, the shut-off valves 302 and 304 allow fluid flow from lines 156 and 166 to the wheel brakes 16a-d through the plunger assembly 300. Specifically, the fluid flow is allowed to pass from the primary outlet line 156, then through the open shut-off valve 302, line 306, the secondary pressure chamber 412, line 320, the open control valves 310 and 316, lines 322 and 330, and to the wheel brakes 16a and 16d. Similarly, the fluid flow is allowed to flow from the secondary outlet line 166 then through the open shut-off valve 304, the line 308, the primary pressure chamber 410, the line 324, the open control valves 312 and 314, the lines 326 and 328, and to the wheel brakes 16b and 16c.Thus, the brake pedal unit 20 can now provide a manual application to pressurize lines 320 and 324 for actuating the wheel brakes 16a-d. The simulation valve 74 swings to its closed position 74a, as in the [reference]. Fig. 1 and Fig. Figure 2 shows that this prevents fluid from flowing from simulation chamber 144 to container 18. Therefore, moving the simulation valve 74 to its closed position 74a hydraulically locks the simulation chamber 144 and traps the fluid within it. During manual pressure application, the primary and secondary output pistons 38 and 40 will move forward to the right, pressurizing chambers 198 and 228 respectively. Fluid flows from chambers 198 and 228 into lines 156 and 166, respectively, to actuate the wheel brakes 16a-d as described above.

[0051] During manual actuation, an initial movement of the input piston 38 forces the spring(s) of the pedal simulator to begin moving pistons 38 and 40. After further movement of the input piston 34, during which the fluid is trapped or hydraulically locked within the simulation chamber 144, a further movement of the input piston 34 pressurizes the simulation chamber 144 and causes movement of the primary piston 38, which in turn triggers movement of the secondary piston 40 because the primary chamber 144 is pressurized. As described in the Fig. 1 and Fig. As shown in Figure 2, the inlet piston 34 has a smaller diameter (around the seal 60) than the diameter of the primary piston 38 (around the seal 80). Since the hydraulically effective area of ​​the inlet piston 34 is smaller than the hydraulically effective area of ​​the primary piston 38, the inlet piston 34 can be considered when viewing the Fig. 1 and Fig. 2. The input piston 34 moves axially further to the right than the primary piston 38. One advantage of this configuration is that, although a smaller effective diameter of the input piston 34, compared to the larger effective diameter of the primary piston 38, requires a longer travel distance, the force input from the driver's foot is reduced. Therefore, compared to a system where the input piston and the primary piston have identical diameters, the driver needs less force to apply pressure to the wheel brakes when acting on the brake pedal 42.

[0052] In another example of a malfunction of the brake system 10, as explained above, the hydraulic control unit 12 may fail, and in addition, one of the output pressure chambers 198 and 228 may be reduced to zero pressure or reservoir pressure, e.g., due to a malfunction of a seal or a leak in one of the lines 156 or 166. The mechanical connection of the primary piston and the secondary piston 38 and 40 prevents a larger gap or distance between the pistons 38 and 40 and prevents the pistons 38 and 40 from having to be moved over a comparatively large distance without any increase in pressure in the functional circuit.For example, if the brake system 10 is in a manual depressor operation and additional fluid pressure is lost in the output circuit relative to the secondary piston 40, such as in line 166, the secondary piston 40 will be forced or biased to the right due to the pressure within the primary chamber 198. If the primary and secondary pistons 38 and 40 were not connected, the secondary piston 40 would, if one [were to...] Fig. 1 and Fig. Considered as 2, the primary and secondary pistons 38 and 40 could move freely to their far right position, and the driver would have to depress the pedal 42 a certain distance to compensate for this loss of travel. However, since the primary and secondary pistons 38 and 40 are connected to each other by the locking element 180, the secondary piston 40 is prevented from this movement, and the loss of travel in this type of disturbance is comparatively small. Thus, the maximum volume of the primary pressure chamber 198 would be limited if the secondary piston 40 were not connected to the primary piston 38.

[0053] In another example, if the brake system 10 is in a manual depressor operation and additional fluid pressure is lost in the output circuit relative to the primary piston 40, such as in line 156, the secondary piston 40 is forced or biased to the left due to the pressure within the secondary chamber 228. Due to the configuration of the brake pedal assembly 20, the left end of the secondary piston 40 is located relatively close to the right end of the primary piston 38. Therefore, the movement of the secondary piston 40 towards the primary piston 38 during this pressure loss is reduced compared to a conventional master cylinder, where the primary and secondary pistons have the same diameter and are slidably arranged in the same diameter bore.To achieve this advantage, the housing 24 of the brake pedal unit 20 incorporates a stepped bore arrangement such that the diameter of the second bore 28, which accommodates the primary piston 38, is larger than that of the third bore 30, which accommodates the secondary piston 40. A section of the primary chamber 198 includes an annular area that surrounds a left section of the secondary piston 40 in such a way that the primary and secondary pistons 38 and 40 can remain relatively close to each other during a manual actuation. In the configuration shown, the primary and secondary pistons 38 and 40 move together during a manual actuation in which both of the circuits corresponding to lines 156 and 166 are intact. This equal speed of movement is due to the fact that the hydraulically effective areas of the pistons 38 and 40 are approximately equal for their respective output pressure chambers 198 and 228.In a preferred embodiment, the area of ​​the diameter of the secondary piston 40 is approximately equal to the area of ​​the diameter of the primary piston 38 minus the area of ​​the diameter of the secondary piston 40. Of course, the brake pedal assembly 20 could be configured differently such that the primary and secondary pistons 38 and 40 move at different speeds and distances during a manual depress operation.

[0054] During a manual pedal stroke, when both circuits corresponding to lines 156 and 166 are intact, such as during an electrical fault as explained above, the combined hydraulically effective area of ​​the primary and secondary pistons 38 and 40 is equal to the diameter of the primary piston 38. However, during a fault in one of the two circuits corresponding to lines 156 and 166, such as a leak in line 166, the hydraulically effective area is halved, such that the driver can now generate twice the pressure within the primary chamber 198 and the undamaged line 156 when the primary piston 38 is advanced during a manual pedal stroke by depressing the brake pedal 42. Although the driver only operates two of the wheel brakes 16a and 16d during this manual pressing process, a greater pressure can thus be achieved in the undisturbed primary chamber 198.Naturally, the stroke length of the primary piston 38 must be increased to compensate.

[0055] The plunger assembly 300 also incorporates features to assist during certain fault conditions. The extension 370 and the enlarged head 372 of the first piston 344, and the extension 390 and the enlarged head 392 of the second piston 346, restrict the movement of the second piston 346 relative to the first piston 344. A backward movement of the second piston 346 is also limited by the configuration of the enlarged head 392 relative to the housing 340. This configuration limits the maximum volume of the first and second pressure chambers 410 and 412. This limitation of movement can be helpful during a downstream fault condition in which one of the two circuits, corresponding to lines 320 and 324, is leaking.For example, in the event of a detected fault condition where fluid leaks within one or more lines 320, 322, and 330, the electronic control unit can enter a manual push-through mode, such that the shut-off valves 302 and 304 are actuated to their open positions and the brake pedal unit 20 is used to provide pressure within the output lines 156 and 166. In this manual push-through situation, fluid flows through the pressure chambers 410 and 412 of the plunger assembly 300. In this example of a fault condition, fluid leaks from line 320. The configuration of the plunger assembly 300 prevents the first pressure chamber 410 from expanding due to the pressure increase relative to the second pressure chamber 412, which is connected to the point of leakage.If the secondary piston 346 were not mechanically connected and not allowed to move, the first pressure chamber 410 would expand, and the pistons of the brake pedal assembly 20 would have to be advanced to accommodate the expanding first pressure chamber 410, causing a loss of pedal travel that the driver would feel. Similarly, a malfunction in which fluid leaks within one or more of the lines 324, 326, and 328 would result in a loss of pressure within the first pressure chamber 410. The extension 390 and the enlarged head 392 prevent significant retraction of the second piston 346 in the retraction direction (when considering the...). Fig. 1 and Fig. 3 (right-facing) due to the greater pressure within the second pressure chamber 412 relative to the first pressure chamber 410.

[0056] During a normal power-assisted operation of system 10, in which the plunger assembly 300 supplies pressure to one of the lines 320 and / or 324, the first and second pistons 344 and 346 are advanced in the actuation direction by the ball screw assembly 350. If a fault occurs in this state, in which the electronic control unit puts system 10 into a manual push-through mode, the shut-off valves 302 and 304 can be de-energized from a closed position to an open position. When the shut-off valves 302 and 304 are moved to their open positions, the pressure within the first and second pressure chambers 410 and 412 would either cause the ball screw assembly 350 to retract, such that the first piston 344 is moved in the retraction direction (when considering the Fig. 1 and Fig. 3 (right-handed), or cause the pressure within lines 156 and 166 to force the pistons of the brake pedal assembly 20 backward, which would also force the pedal 42 back. The driver can compensate for the retracted ball screw mechanism 350 by continuing to depress the pedal 42 to advance the pistons of the brake pedal assembly 20 and thereby compensate for the lost travel. Although this may be perfectly acceptable during such a malfunction, the valve components of the shut-off valves 302 and 304 could be configured to hydraulically lock during this situation to prevent any backward movement of the pistons of the brake pedal assembly 20, even though the shut-off valves 302 and 304 are de-energized.Therefore, even in the event of an electrical failure of system 10 during a normal power amplification mode, the shut-off valves 302 and 304, which would be de-energized in their normally open positions, would remain in an internally closed (hydraulically locked) state, such that the internal valves of the shut-off valves 302 and 304 would prevent fluid from flowing from the first and second chambers 410 and 412 into the lines 156 and 166. Consequently, this pressure build-up in the plunger assembly 300 would initially not force the pistons of the brake pedal assembly 20 backward, thus also forcing the pedal 42 backward.The shut-off valves 302 and 304 could also be configured such that when the driver depresses the pedal 42 to generate pressure within the brake pedal assembly 20 during a manual depress mode, the increase in pressure within lines 156 and 166 opens the internal valves of the shut-off valves 302 and 304, thus allowing flow to the wheel brakes 16a-d, as in a normal manual depress operation described above. Preferably, the shut-off valves 302 and 304 are configured such that they do not hydraulically close in other states, such as during a pressure spike or rapid application. Thus, the shut-off valves 302 and 304 can be configured such that a low pressure level acting on the valves 302 and 304 unlocks the valves from their temporarily hydraulically closed state.

[0057] Schematically represented in Fig. 4 is a second embodiment of a vehicle braking system, generally designated 500. Similar to the braking system 10 described above, braking system 500 is suitable for a land vehicle, such as a four-wheeled motor vehicle with a wheel brake for each wheel. Furthermore, braking system 500 can be provided with other braking functions, such as anti-lock braking (ABS), other slip control features, and regenerative brake mixture to effectively decelerate the vehicle. Braking system 500 is similar to braking system 10 in some aspects of its function and structure; therefore, the same numbers and / or designations are used to refer to similar components.

[0058] Similar to brake system 10, brake system 500 includes a brake pedal assembly, indicated by the dashed line 12, comprising a brake pedal unit 20, a reservoir 18, a brake pedal 42, and a simulation valve 74, which are similar in function and structure to those described above in relation to brake system 10. Brake system 500 also includes wheel brakes 16a-d, first and second shut-off valves 302 and 304, and control valves 310, 312, 314, and 316, which are similar in function and structure to those described in relation to system 10. The components located outside the brake pedal assembly 12 may be housed within a hydraulic control unit housing or may be located separately.

[0059] The brake assembly 500 further includes a plunger assembly, generally designated 502. Although the plunger assembly 502 is similar to the plunger assembly 300 described above in relation to system 10, there are some differences, which are explained below. As is best understood in Fig. As shown in Figure 5, the plunger assembly 502 includes a housing 540 with a bore 542 formed therein. The first and second pistons 544 and 546, respectively, are slidably mounted in the bore 542. The plunger assembly 502 further includes a ball screw mechanism, generally designated 550. The ball screw mechanism 550 is designed to provide the first piston 544 with translational or linear movement along an axis defined by the bore 542 in both an actuation direction (when considering the Fig. 4 and Fig. 5 downwards) as well as a retraction direction (when considering the Fig. 4 and Fig. 5 upwards) within the bore 542 of the housing 540. In the embodiment shown, the ball screw mechanism 550 includes a motor 552 that rotates a screw shaft 554. A motor 552 may include a sensor 553 for detecting the rotational position of the motor 552 and / or the ball screw mechanism 550, which is indicative of the position of the first piston 544. This can be particularly useful for a motor 552 capable of very precise control, including controlling the motor to minute movements to provide multiplex control, as will be explained below. The first piston 544 includes a threaded bore 556 and functions such as a driven nut of the ball screw mechanism 550.The ball screw mechanism 550 includes a multitude of balls 558 which are held within spiral raceways formed in the screw shaft 554 and the threaded bore 556 of the first piston 544 to reduce friction.

[0060] The first piston 544 has an outer cylindrical surface 560. A seal, or O-ring 562, is fitted within a groove 564 formed in the bore 542. A lip seal 566 is fitted within a groove 568 formed in the bore 542. The O-ring 562 and the lip seal 566 engage sealingly with the outer cylindrical surface 560 of the first piston 544. The first piston 544 includes a pin or extension 570 that extends toward the second piston 546. The extension 570 includes an enlarged head 572. The enlarged head 572 is held within a cavity 574 formed in the second piston 556 by an inwardly extending collar 576. The first piston 544 is mechanically connected to the second piston 546 by the interaction of the extension 570 and the collar 576, although a predetermined amount of movement between them is still permitted.The first piston 544 is biased in a direction away from the second piston 546 by the spring 580. The spring 580 generally acts on the end faces of the pistons 544 and 546 that face each other. The spring 580 can generally be accommodated within a groove 582 formed in the first piston 544.

[0061] The second piston 546 has an outer cylindrical surface 584. An O-ring 586 is fitted within a groove 587 formed in the outer cylindrical surface 584 of the second piston 546. The O-ring 586 engages the wall of the bore 542 in a sealing manner. Instead of having a pin or extension, the movement of the second piston 546 is restricted by an outwardly extending collar 590 and is trapped within a recess 592 formed in the bore 542. The recess 592 defines a pair of shoulders 593 and 594 that can engage with the collar 590 of the second piston 546 to mechanically connect the second piston 546 to the housing 540, although a predetermined amount of movement is still permitted between them. The second piston 546 is biased by a spring 600 in a direction away from the end of the bore 550, towards the first piston 544.Springs 580 and 600 generally position the second piston 546 relative to the first piston 544 within the bore 542. Springs 580 and 600 also act as return springs, holding the first and second pistons 544 and 546 in their rest positions, as shown in the diagram. Fig. 4 and Fig. Shown in section 5, pre-tension.

[0062] The plunger assembly 502 has a first pressure chamber 610 and a second pressure chamber 612. The first pressure chamber 610 is generally defined by the bore 540, the first and second pistons 544 and 546, the lip seal 566, and the O-ring 586. The first pressure chamber 610 communicates with a line 324a, which is in fluid communication with line 324. The second pressure chamber 612 is generally defined by the bore 540, the second piston 546, and the O-ring 586. The second pressure chamber 612 communicates with a line 320a, which is in fluid communication with line 320. Unlike the plunger assembly 300, adjacent areas of the seals of the plunger assembly 502 are not vented or in fluid communication with the reservoir 18.

[0063] The brake system 500 operates similarly to the system 10 described above. To actuate the wheel brakes 16a-d via the plunger assembly 502, the electronic control unit actuates the motor 552 in a first direction of rotation to rotate the screw shaft 554 in the first direction of rotation. A rotation of the screw shaft 554 in the first direction of rotation causes the first piston 544 to move in the direction of actuation (when viewing the Fig. 4 and Fig. 5 downwards), causing an initial movement of the second piston 612 by the spring 570. Movement of the first piston 544 causes an increase in pressure in the first pressure chamber 610, causing fluid to flow out of the first pressure chamber 610 and into line 324a. It should be noted that fluid is prevented from flowing out of the first pressure chamber 610 into the secondary outlet line 166 because the shut-off valve 304 is in its closed position. An increase in pressure in the first pressure chamber 610 will also cause the second piston 612 to move in the direction of actuation, causing an increase in pressure in the second pressure chamber 612. Fluid flows out of the second pressure chamber 612 through line 324a.It should be noted that fluid is prevented from flowing from the second pressure chamber 612 into line 320 because the shut-off valve 302 is in its closed position. Pressurized fluid flowing into lines 320 and 324 and through the open control valves 310, 312, 314, and 316 actuates the wheel brakes 16a-d. Similar to system 10, braking can be intensified by advancing the first and second pistons 544 and 546 via the screw shaft 554 of the ball screw mechanism 550. To relieve pressure within the wheel brakes 16a-d, the motor 552 is actuated in a second direction of rotation opposite to the first, causing the first and second pistons 544 and 546 to move in a retraction direction (when considering the...). Fig. 4 and Fig. 5 downwards), thereby drawing the fluid away from the wheel brakes 16a-d and refilling the first and second pressure chambers 610 and 612. The motor 552 of the plunger assembly 502 can be actuated in the first and second directions of rotation to provide an increase or decrease in brake pressure at the wheel brakes 16a-d. All of the control valves 310, 312, 314, and 316 can be controlled (unenergized) to an open position to provide simultaneous braking at all wheel brakes 16a-d. Alternatively, the control valves 310, 312, 314, and 316 can be actuated individually between their open and closed positions to provide different brake pressures within the wheel brakes 16a-d.

[0064] Similar to the plunger assembly 300, the plunger assembly 502 incorporates features to provide support during certain fault conditions, such as limiting the maximum volume of the first and second pressure chambers 410 and 412. A fault condition in which fluid escapes within line 324a would lead to a pressure loss within the first pressure chamber 610. The interaction of the collar 590 and the shoulder 593 of the recess 592 prevents significant retraction of the second piston 346 in the retraction direction (when considering the Fig. 4 and Fig. 5 upwards) due to the greater pressure within the second pressure chamber 612 relative to the first pressure chamber 610.

[0065] One of the advantages of the 502 plunger assembly compared to the 300 plunger assembly is the reduced number of seals. The 300 plunger assembly incorporates four seals (362, 366, 386, and 388) compared to the 502 plunger assembly's three (562, 566, and 586). Fewer seals allow for a reduction in the overall length of the 502 plunger assembly. Another advantage is that at higher pressures within the plunger assembly, the reduced number of seals can lower friction. Friction is also reduced because the differential pressure during a normal amplification process is mitigated by a seal on the secondary piston.

[0066] Another difference between the plunger units 300 and 502 is that the plunger unit 300 has a line 296 connecting the reservoir 18 to the plunger unit 300. Line 296 branches into a pair of lines such that a gap between the O-ring 362 and the lip seal 366, and a gap between the O-ring 386 and the lip seal 388, are in fluid communication with the reservoir 18 via line 296. This configuration allows for easier detection of a malfunction in one of the seals of the plunger unit 300 compared to the plunger unit 502. Line 296 enables fault detection during a normal amplification process by detecting an unusual movement path that lies outside the range of the expected pressure.During non-braking operations, the electronic control unit on the system can perform 10 checks to detect a malfunction of the seals by monitoring the unusual fluid flow into line 296 behind a malfunctioning seal within the plunger assembly 300.

[0067] In the Fig. 6 and Fig. Figure 7 shows a third embodiment of a plunger assembly, generally designated 700. The plunger assembly 700 is similar to the plunger assemblies 300 and 502 in terms of structure and function. One of the differences is that the plunger assembly 700 includes a hollow outer sleeve 702, which is mounted within a bore 704 of a housing 706. First and second pistons 744 and 746 are slidably arranged in a stepped inner bore of the outer sleeve 702, as will be explained below. The outer sleeve 702 can be helpful for emptying and evacuating the plunger assembly 700 compared to a plunger assembly with first and second pistons mounted in a bore of the housing. If the housing 706 were made of aluminium, a separate sleeve 702 made of a stiff-coated, anodised material to accommodate the first and second pistons 744 and 746 may be desirable.Due to the stepped bore configuration, the sleeve 702 can also provide support during assembly. As described below, one of the advantages of the plunger assembly 700 is that the pistons 744 and 746 and their associated pressure chambers are arranged in an overlapping manner, which helps to reduce the overall length of the plunger assembly 700.

[0068] The plunger assembly 700 further includes a ball screw mechanism, generally designated 750. The ball screw mechanism 750 is designed to provide the first piston 744 with translational and linear movement along an axis defined by the bore 704 in both an actuation direction (when considering the Fig. 1 and Fig. 3 left-directed) as well as a retraction direction (when viewing the Fig. 1 and Fig. 3 (right-handed). In the embodiment shown, the ball screw mechanism 750 includes a motor (not shown) that drives an actuator 754. The actuator 754 can be prevented from rotating by an anti-rotation device with a pair of rollers 714 that move in corresponding tracks 716, as shown in Fig. Figure 6 shows that the actuator 754 is moved linearly by the ball screw mechanism 750. The actuator 754 engages in a holder 720, which is screwably connected to one end of the first piston 744. The holder 720 includes a seal 722 to seal the interior of the first piston 744 against the ball screw mechanism 750.

[0069] The first piston 744 has an outer cylindrical surface 760. A pair of seals 762 and 766 are attached to the outer sleeve 702 and engage sealingly with the surface 760 of the first piston 744. The plunger assembly 700 also includes a mechanical coupling to the second piston 746 via a captured spring assembly, generally designated 747. The captured spring assembly 747 includes an extension pin 770, which is screwably connected to the end of the second piston 746 and has an enlarged head 772 that is contacted and captured by an inwardly extending collar 774 of the first piston 744. A spring 780 biases the second piston 746 in a direction away from the first piston 744.

[0070] The second piston 746 has an outer cylindrical surface 784. An O-ring 786 is attached to the second piston 746. A captured spring assembly, generally designated 789, includes an extension pin 790, which is screwably connected to the second piston 746 and has an enlarged head 792 that is contacted and captured by a holder 796 located in the end of the bore 704. A spring 800 pre-tensions the holder away from the second piston 746 by a predetermined distance.

[0071] The plunger assembly 700 has a first pressure chamber 810 and a second pressure chamber 812. The first pressure chamber 810 includes an expanding and a contracting section, generally arranged around the outer surface of the piston 746 to help reduce the length of the plunger assembly 700. The first pressure chamber 810 can communicate with the line 324a via passages 813 formed through the outer sleeve 702, as in the Fig. 4 system 500 shown. The second chamber 812 can communicate with the line 320a via columns 815 formed in the holder 796, as in system 500.

[0072] The outer sleeve 702 has a first bore section 703 and a second bore section 705. The first bore section 703 is defined by a diameter D1 that is slightly smaller than the diameter D2 of the second bore section 705. This configuration of the outer sleeve 702 allows communication between the primary chamber 810 and the line 324a even with long stroke lengths of the first piston 744, as shown in Fig. 7 shown, with the end of the first piston 744 moving past the passages 813.

[0073] The trapped spring assemblies 747 and 789 each limit the maximum volume of the first and secondary pressure chambers 810 and 812, thereby reducing the movement path in certain disturbance conditions as explained above with regard to the other plunger assemblies and shown here.

[0074] It is shown in Fig.8 A fourth embodiment of a plunger assembly, generally designated 900. The plunger assembly 900 is similar in structure and function to the plunger assemblies described above. The plunger assembly 900 has a housing 902 with a bore 904 formed therein. First and second pistons 910 and 912 are slidably arranged in the bore 904 to generate pressure within first and second pressure chambers 920 and 922, respectively. The bore 904 includes a pair of gap sections 906 to provide a fluid connection between the first and second pressure chambers 920 and 922 and the lines 930 and 932. The lines 930 and 932 can be in fluid communication with the wheel brakes of a brake system, which is shown and described above in relation to the other plunger assemblies described herein. Column 906 also provides flow paths from the tank connections to the pressure chambers behind the restoring lip seals.

[0075] The plunger assembly 900 can also include trapped spring assemblies 936 and 938 to limit the maximum volume of the first and secondary pressure chambers 920 and 922. The plunger assembly 900 can further include a threaded cap 942, which is screwably connected to a holder 944 of the trapped spring assembly 938 to seal an opening 943 at the end of the bore 904 by means of a gasket 946. The removable cap 942 allows the installation of various components of the plunger assembly 900 through the openings 943 and also provides access for screwing together various components during installation, such as the trapped spring assembly 938. The plunger assembly 900 can be pre-assembled and inserted into the bore. The opening 943 provides access for adjusting the screw connection at the end of the bore. The cap 942 seals the opening 943 and locks the screw connection.

[0076] The principle and operation of this invention have been explained and illustrated in its preferred embodiment. It is understood, however, that this invention can be implemented differently than specifically explained and illustrated without departing from its scope of protection.

Claims

[1] Braking system (10), with: first and second wheel brakes (16a, 16b, 16c, 16d); a brake pedal assembly (12) comprising a brake pedal unit (20) which has a housing (24), a pair of output pistons (38, 40) slidably arranged in the housing (24) and a pedal simulator (100) which is accommodated within the brake pedal unit (20), wherein the pair of output pistons (38, 40) is movable, to generate a brake actuation pressure at first and second outputs during a manual push-through mode to actuate the first and second wheel brakes (16a, 16b, 16c, 16d), respectively; and a hydraulic control unit (14) with a plunger assembly (300, 502, 700, 900) for actuating the first and second wheel brakes (16a, 16b, 16c, 16d) during normal braking, wherein the plunger assembly (300, 502, 700, 900) comprises: a case (340, 540, 706, 902); a motor (352) attached to the housing (340, 540, 706, 902) for driving an actuator; a first piston (344, 544, 744) connected to the actuator, wherein the first piston (344, 544, 744) is slidably mounted within the housing (340, 540, 706, 902) to pressurize a first fluid chamber in the housing (340, 540, 706, 902), wherein the first fluid chamber is connected to the first wheel brake (16c, 16d); and a second piston (346, 546, 746) arranged slidably within the housing (340, 540, 706, 902) to pressurize a second fluid chamber in the housing (340, 540, 706, 902), the second fluid chamber being connected to the second wheel brake (16a, 16b); comprising a pumpless control valve arrangement: a first control valve that regulates the fluid flow between the first fluid chamber and the first wheel brake (16c, 16d), and a second control valve that regulates the fluid flow between the second fluid chamber and the second wheel brake (16a, 16b); and a shut-off valve arrangement for switching the brake system (10) between the normal brake mode, in which boost pressure is supplied from the plunger assembly (300, 502, 700, 900) to the wheel brakes (16a, 16b, 16c, 16d), and the manual push-through mode, in which actuation pressure is supplied from the brake pedal assembly (20) to the wheel brakes (16a, 16b, 16c, 16d), characterized by , that the pedal simulator (100) is located between an input piston (34) of the brake pedal unit and one of the output pistons (38, 40). [2] Braking system (10) according to claim 1, wherein the motor (352, 552) is operable to drive the actuator in a reverse direction to supply fluid to the first and second fluid chambers of the plunger assembly (300, 502, 700, 900). [3] Braking system (10) according to claim 1, further comprising an electronic controller which provides multiplex control to the first and second control valves to control the pressures at each of the first and second wheel brakes (16a, 16b, 16c, 16d) independently of each other. [4] Brake system (10) according to claim 1, wherein the first control valve is a valve arrangement with a pair of valves arranged in a parallel arrangement that controls the fluid flow between the first fluid chamber and the first wheel brake (16c, 16d), and wherein the second control valve is a valve arrangement with a pair of valves in a parallel arrangement that controls the fluid flow between the second fluid chamber and the second wheel brake (16a, 16b). [5] Brake system (10) according to claim 1, wherein the shut-off valve arrangement comprises a first shut-off valve (304) arranged between the first outlet of the brake pedal unit (20) and the first fluid chamber of the plunger assembly, and wherein the shut-off valve arrangement comprises a second shut-off valve (302) arranged between the second outlet of the brake pedal unit (20) and the second fluid chamber of the plunger assembly (300, 502, 700, 900). [6] Brake system (10) according to claim 5, wherein the first and second shut-off valves (304, 302) are solenoid-actuated valves. [7] Brake system (10) according to claim 6, wherein the first and second shut-off valves (304, 302) are solenoid-actuated valves configured to lock hydraulically into a closed position during a power loss at the solenoids. [8] Brake system (10) according to claim 1, wherein the brake pedal unit (20) further comprises an input piston (34) which is slidably arranged in the housing (24), can be actuated by the brake pedal and is capable of operating a pedal simulator (100) during a normal amplified braking process. [9] Brake system (10) according to claim 1, wherein the brake pedal assembly (12) and the hydraulic control unit (14) are arranged in a single housing. [10] Brake system (10) according to claim 1, wherein the first and second pistons are arranged such that sections of the first and second pistons (344, 544, 744, 346, 546, 746) are positioned within the housing (340, 540, 706, 902) with respect to a radial direction in an overlapping manner. [11] Braking system (10) according to claim 1, wherein the plunger assembly (300, 502, 700, 900) is configured to limit the maximum volume of the first and second fluid chambers in a fault condition in which fluid escapes from one of the first and second fluid chambers. [12] Brake system (10) according to claim 11, wherein the first and second pistons (344, 544, 744, 346, 546, 746) are mechanically connected to each other and at the same time allow a predetermined degree of movement relative to each other. [13] Brake system (10) according to claim 12, in which the second piston (346, 546, 746) is mechanically connected to a section of the housing (340, 540, 706, 902) and at the same time a predetermined degree of movement of the second piston relative to the housing (340, 540, 706, 902) is permitted. [14] Brake system (10) according to claim 13, wherein the second piston (546) comprises a collar (590) which selectively engages with a shoulder (593, 594) which is formed in a bore of the housing (540) in which the second piston is slidably arranged. [15] Brake system (10) according to claim 1, wherein the plunger assembly (700) comprises a sleeve (702) which is immovably mounted in a bore (704) of the housing (706), and wherein the first and second pistons (744, 746) are slidably arranged within a bore of the sleeve (702). [16] Brake system (10) according to claim 15, wherein the bore (704) of the sleeve (702) has a stepped configuration defining a first diameter section and a second diameter section which is larger than the first diameter section, and wherein the first piston (744) is slidably arranged in the first diameter section and engages sealingly with it, and wherein the second piston (746) is slidably arranged in the second diameter section and engages sealingly with it. [17] Brake system (10) according to claim 16, wherein the first and second pistons (744, 746) are arranged such that end sections of the first and second pistons are positioned inside the housing in a manner overlapping with respect to a radial direction.

Images