Patent Description:
As electric and hybrid vehicles continue to proliferate in markets around the world, it is well understood that significant lengthening of battery life can be obtained by utilizing the motor-generator output capabilities of that device during braking. However, the input torque in the generator mode used to recharge batteries is not consistent with driver input function of pedal force/travel verses vehicle deceleration. In order to achieve that complex function, the hydraulic brakes of the vehicle must supply the difference between generator braking torque and driver requested braking torque.

The engineering world has understood this requirement for a number of years commonly known as regenerative brake blending. A most efficient way to achieve this is to use a "brake-by-wire" technique. To accomplish this, the brake pedal in effect becomes a joystick, so it must be connected to a travel and/or force sensor in order to send a signal to the system ECU that will interpret this as driver's intent of a desired vehicle deceleration. In addition, the brake pedal "feel" must be simulated by the appropriate force-travel relationship and must also have the ability to be isolated from directly applying the master cylinder to the wheel brakes.

Brake-by-wire systems typically include a pressure supply unit (PSU) to provide a supply of pressurized fluid for actuating the wheel brakes. Document <CIT> discloses an electro-hydraulic brake apply system with emulator latch. An electro-hydraulic brake apply system includes an emulator that effects pedal feel simulation by allowing compliance at a selective variable rate. This provides a vehicle driver with the preferred pedal travel and feedback characteristics of a conventional master cylinder/power booster apply system. As a secondary function, the emulator is utilized to latch the modulator. This locks the modulator apply piston in place when electrical power is removed from the drive motor. Further, the emulator operates to hydraulically isolate the master cylinder from the wheel brakes during normal system operation. Document <CIT> discloses a vehicle brake system with front axle overboost. A brake system having a wheel brake and being operable under a non-failure normal braking mode and a manual push-through mode. The system includes a master cylinder operable by a brake pedal during the manual push-through mode to provide fluid flow at an output for actuating the wheel brake. A first source of pressurized fluid provides fluid pressure for actuating the wheel brake under the normal braking mode. A second source of pressurized fluid generates brake actuating pressure for actuating the wheel brake under the manual push-through mode. Document <CIT> discloses an actuating system for a vehicle brake and method of operating the actuating system. The invention relates to an actuating system for a vehicle brake, with an actuating arrangement, in particular a brake pedal, at least one (first) piston-cylinder unit, which is connected via a hydraulic line to the vehicle brake (braking circuit) in order to supply the braking circuit with pressure medium and apply pressure to the vehicle brake, and with a drive for the piston-cylinder unit. According to the invention, pressure medium can be fed to the braking circuit in controlled manner in both piston movement directions, in particular the advance stroke and the return stroke, by means of at least one, in particular stepped, piston of the piston-cylinder unit.

The present invention provides an electro-hydraulic brake system and a control system comprising any feature described, either individually or in combination with any feature, in any configuration.

The present invention provides an electro-hydraulic brake system. The electro-hydraulic brake system comprises a master cylinder (MC) fluidly coupled to a first MC fluid passageway and configured to supply fluid into the first MC fluid passageway in response to pressing force on a brake pedal coupled thereto. The electro-hydraulic brake system also comprises a pressure supply unit (PSU) including an electric motor coupled to an actuator rod, a piston bore including a terminal end opposite the electric motor, and a PSU piston disposed within the piston bore and movable by the actuator rod through the piston bore and dividing the piston bore into a first chamber and a second chamber. The electro-hydraulic brake system also comprises an inner cylinder within the piston bore, the inner cylinder extending from the terminal end towards the PSU piston and defining a balance bore. The PSU piston includes a balance piston extending into the balance bore and having a cross-sectional area equal to a cross-sectional area of the actuator rod. The electro-hydraulic brake system also comprises a check valve configured to allow fluid flow from the second chamber of the PSU to the first chamber of the PSU and to block fluid flow in an opposite direction. The electro-hydraulic brake system also comprises a pedal feel emulator (PFE) including a PFE piston movable through a PFE bore and separating an upper chamber from a lower chamber. The lower chamber of the PFE is fluidly coupled to the second chamber of the PSU to convey fluid from the lower chamber of the PFE to the second chamber of the PSU in response to a compression of the PFE. The first MC fluid passageway is fluidly coupled to the upper chamber of the PFE to provide a fluid path from the master cylinder into the upper chamber of the PFE.

The present invention also provides a pressure supply unit (PSU) for an electro-hydraulic brake system. The pressure supply unit comprises an electric motor; and a piston bore including a terminal end opposite the electric motor. The pressure supply unit also comprises a PSU piston disposed within the piston bore. The PSU piston is movable through the piston bore by the electric motor and dividing the piston bore into a first chamber and a second chamber, the first chamber extending between the PSU piston and the terminal end. The pressure supply unit also comprises a first supply port in fluid communication with the first chamber for discharging fluid therefrom in response to the PSU piston moving through the piston bore toward the terminal end. The pressure supply unit also comprises an inner cylinder within the piston bore and extending from the terminal end towards the PSU piston and defining a balance bore. The PSU piston includes a balance piston extending through the first chamber and into the balance bore.

The present invention also provides an electro-hydraulic brake system. The electro-hydraulic brake system comprises a single-circuit master cylinder (MC) having a single piston and fluidly coupled to a MC fluid passageway and configured to supply fluid into the MC fluid passageway in response to pressing force on a brake pedal coupled thereto. The electro-hydraulic brake system also comprises a pressure supply unit (PSU) including an electric motor and a PSU piston disposed within a piston bore. The PSU piston is movable through the piston bore by the electric motor and divides the piston bore into a first chamber and a second chamber, the piston bore including a terminal end opposite the electric motor. The electro-hydraulic brake system also comprises a PSU fluid passageway for conveying fluid from the pressure supply unit to at least one wheel brake. The PSU includes a first supply port in fluid communication with the first chamber for conveying fluid therefrom and to the PSU fluid passageway in response to the PSU piston moving through the piston bore toward the terminal end. The PSU also includes a second supply port in fluid communication with the second chamber for discharging fluid therefrom and to the PSU fluid passageway in response to the PSU piston moving through the piston bore away from the terminal end.

Further details, features and advantages of designs of the invention result from the following description of embodiment examples in reference to the associated drawings.

Referring to the drawings, the present invention will be described in detail in view of following embodiments.

<FIG> shows a schematic block diagram of a brake-by-wire system <NUM> in a vehicle, such as an automobile. Basic brake-by-wire (BBW) architecture is now well-established in the automotive industry. The vehicle's master cylinder <NUM> either applies the brakes directly in a failed system fallback mode or is isolated from the wheel brakes <NUM> and connected to a pedal feel emulator <NUM> that replicates force, travel, and damping of a traditional brake system. The brake pedal travel and/or force, and/or brake pressure is used by the system <NUM> as an input signal to a brake electronic control unit (ECU) <NUM>. It in turn sends the appropriate signal to a pressure supply unit (PSU) <NUM>. The PSU <NUM> may include a high efficiency brushless motor and ballscrew assembly displacing one or two pistons, which can be thought of as an electric master cylinder. The master cylinder <NUM> and/or the PSU <NUM> may be coupled to the wheel brakes <NUM> via a series of control valves <NUM>, which may include an apply valve and a release valve (not shown) for each of the wheel brakes <NUM> to provide functions such as antilock braking (ABS), electronic traction control, etc..

The brake pedal inputs define driver intent which determines how fast and how hard the brakes are applied with the goal to replicate the feel of a conventional vacuum booster brake system. The brake ECU <NUM> may also send a signal to a drive control unit (DCU) <NUM>, which may also be called a powertrain control module (PCM), to slow the vehicle using one or more electric motors in a regenerative mode.

<FIG> shows a schematic diagram of a conventional H-bridge circuit <NUM> as part of a brake-by-wire (BbW) system 20a for controlling operation of the wheel brakes 22a, 22b, 22c, 22d of the vehicle. One or more of the wheels of vehicles using BbW systems may be powered by an internal combustion engine <NUM>. Additionally or alternatively, one or more of the wheels of vehicles using BbW systems may be powered by an electric motor <NUM>, such as with pure electric vehicles. Additionally or alternatively, and as is the case with some hybrid vehicles, one or more of the wheels of vehicles using BbW systems may be powered by both an electric motor <NUM> and an internal combustion engines <NUM> in a sharing configuration. Most vehicle using BbW systems fall into the latter two categories. An example of a sharing configuration is shown in <FIG>, with the two front wheels each being coupled to an internal combustion engine <NUM> and an electric motor <NUM>. However, this is merely an example, and other configurations may be used, including any or all of wheels being driven by either or both of the internal combustion engine <NUM> and/or the electric motor <NUM>. Furthermore, either or both of the internal combustion engine <NUM> and/or the electric motor <NUM> may be configured to drive any number of the wheels, e.g. through a direct-drive, a differential, and/or other powertrain components.

The H-Bridge type of BbW system 20a includes a fluid reservoir <NUM> holding a hydraulic fluid and supplying the hydraulic fluid to a dual-circuit master cylinder <NUM>. A fluid level sensor <NUM>, such as a float switch, monitors a level of the hydraulic fluid in the fluid reservoir <NUM>. A reservoir test valve <NUM> selectively controls fluid flow from the fluid reservoir <NUM> to the dual-circuit master cylinder <NUM>. The dual-circuit master cylinder <NUM> is configured to supply fluid pressure in each of a first master cylinder (MC) fluid passageway <NUM> and a second MC fluid passageway <NUM> in response to application of a brake pedal <NUM>. The brake pedal <NUM> is coupled to press a brake linkage <NUM> which, in turn, presses a primary piston <NUM> of the dual-circuit master cylinder <NUM>. The MC fluid passageways <NUM>, <NUM> may be fluidly isolated from one another to provide redundancy in case of a failure, such as a leak, in in of the two MC fluid passageways <NUM>, <NUM>. A travel sensor <NUM> monitors a position of the brake pedal <NUM>. A first pressure sensor <NUM> monitors the pressure in the first MC fluid passageway <NUM>.

A pedal feel emulator (PFE) <NUM> includes a PFE bore <NUM>. A PFE piston <NUM> is slidably disposed within the PFE bore <NUM> to divide the PFE bore <NUM> into an upper chamber 42a and a lower chamber 42b. The PFE piston <NUM> is biased by a spring <NUM> to compress the upper chamber 42a. The upper chamber 42a is selectively fluidly coupled to the first MC fluid passageway <NUM> via a PFE isolation valve <NUM> to selectively provide a natural feeling of brake operation, particularly when the dual-circuit master cylinder <NUM> is decoupled from operating the wheel brakes. A first check valve <NUM> is connected in parallel with the PFE isolation valve <NUM> to allow fluid flow from the PFE <NUM> back to the first MC fluid passageway <NUM> while preventing fluid flow in a reverse direction. The lower chamber 42b is fluidly coupled to the fluid reservoir <NUM> via a return fluid passageway <NUM>.

A pressure supply unit (PSU) <NUM> includes an electric motor <NUM> and a PSU pump <NUM> to supply the hydraulic fluid from the fluid reservoir <NUM> to a PSU fluid passageway <NUM>. A rotor angle sensor <NUM> may be coupled to the electric motor <NUM> to determine a position of the rotor in the motor, and thus a position of the PSU pump <NUM>. A second check valve <NUM> allows fluid flow from the fluid reservoir <NUM> into the PSU fluid passageway <NUM> while blocking fluid flow in an opposite direction. A second pressure sensor <NUM> monitors the pressure in the PSU fluid passageway <NUM>.

This hydraulic layout includes an H-bridge circuit <NUM> having four valves that control the switching between the MC fluid passageways <NUM>, <NUM> of the dual-circuit master cylinder <NUM> and the PSU <NUM>. This basic safety circuit of normally-open valves connecting wheel brakes 22a, 22b, 22c, 22d to the dual-circuit master cylinder <NUM> and normally-closed brakes connecting wheel brakes 22a, 22b, 22c, 22d to the PSU <NUM> is described in U. Patent <CIT>.

A control valve manifold <NUM> fluidly connects the two brake circuits <NUM>, <NUM> to the corresponding wheel brakes 22a, 22b, 22c, 22d. The control valve manifold <NUM> includes an apply valve 68a and a release valve 68b corresponding to each of the wheel brakes 22a, 22b, 22c, 22d to selectively control fluid flow between the corresponding one of the of the wheel brakes 22a, 22b, 22c, 22d and an associated one of the two brake circuits <NUM>, <NUM>. The apply valves 68a and the release valves 68b may collectively be called antilock brake system (ABS) valves for their use in such an ABS. However, the apply valves 68a and the release valves 68b may be used for other functions, such as for traction control and/or for torque vectoring.

Besides the eight standard ABS valves 68a, 68b, and the four H-bridge control valves <NUM>, conventional brake-by-wire systems include two more valves <NUM>, <NUM>, bringing the total to fourteen (<NUM>) valves. The PFE isolation valve <NUM> is a normally-closed valve and its sole purpose is to lock out the PFE <NUM> in the event of a failed pressure supply unit when master cylinder backup is required. The reservoir test valve <NUM> may be used to shut off the primary master cylinder return path to the fluid reservoir <NUM> so that the system may conduct a self-test to make sure the PFE isolation valve <NUM> is functioning properly. This is extremely important as the pedal may be locked up if the PFE isolation valve <NUM> were to fail to open when first commanded.

An electronic control unit (ECU) <NUM> may include one or more processors, microcontrollers, and/or electric circuits for controlling operation of one or more of the valves <NUM>, 68a, 68b, <NUM>, <NUM> and/or for monitoring one or more sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and to thereby coordinate operation of the H-Bridge BbW system 20a.

<FIG> shows a schematic diagram of a <NUM>-valve BbW system 20b. The <NUM>-valve BbW system 20b may be similar or identical to the H-Bridge BbW system 20a, except for the changes described herein. The <NUM>-valve BbW system 20b may provide some advantages over the H-Bridge BbW system 20a shown in <FIG>, such as reduced cost, mass, and size while meeting requirements for performance and safety. The <NUM>-valve brake-by-wire system 20b includes a single-circuit master cylinder <NUM> having a single piston, instead of the dual-circuit master cylinder <NUM> of the H-Bridge BbW system 20a. The single-circuit master cylinder <NUM> receives hydraulic fluid from the fluid reservoir <NUM> via parallel combination of a master cylinder (MC) orifice <NUM> and an MC check valve <NUM>. The single-circuit master cylinder <NUM> feeds the fluid to a first MC fluid passageway <NUM> in response to application of the brake pedal <NUM>. A fourth check valve <NUM> allows fluid flow from the fluid reservoir <NUM> to the PSU <NUM> while blocking fluid flow in an opposite direction.

In place of the H-bridge circuit <NUM>, the <NUM>-valve BbW system 20b has a <NUM>-valve arrangement 60a, 60b, 60c configured to selectively couple either the first master cylinder (MC) fluid passageway <NUM> or the PSU fluid passageway <NUM> to one or both of the two brake circuits <NUM>, <NUM>, which, in turn, are fluidly coupled to two of the wheel brakes 22a, 22b, 22c, 22d. The <NUM>-valve arrangement 60a, 60b, 60c includes a MC isolation valve 60a configured to selectively fluidly couple the first master cylinder (MC) fluid passageway <NUM> with the first brake circuit <NUM>. The <NUM>-valve arrangement 60a, 60b, 60c also includes a PSU isolation valve 60b configured to selectively fluidly couple the PSU fluid passageway <NUM> with the second brake circuit <NUM>. The <NUM>-valve arrangement 60a, 60b, 60c also includes a middle circuit connecting valve 60c configured to selectively fluidly couple the first brake circuit <NUM> with the second brake circuit <NUM>.

The <NUM>-valve BbW system 20b includes a control valve manifold <NUM> fluidly connecting the two brake circuits <NUM>, <NUM> to the corresponding wheel brakes 22a, 22b, 22c, 22d. The control valve manifold <NUM> may be similar or identical to the control valve manifold <NUM> of the H-Bridge BbW system 20a.

The <NUM>-valve BbW system 20b may provide a reduced performance to achieve the cost, size, and mass reduction also sought after by our industry. There are downsides to this layout as well in that it may only be suited for Front/Rear systems due to a lag that may be caused by the middle circuit connecting valve 60c, and the valves 60a, 60b, 60c will need to be large enough to flow the same fluid carried out by two valves in parallel in the H-bridge circuit <NUM> of the H-Bridge BbW system 20a.

<FIG> shows a schematic diagram of a first BbW system <NUM> of the present invention. The first BbW system <NUM> is a <NUM>-valve system, with a single-circuit master cylinder <NUM> and a dual-circuit pressure supply unit (PSU) <NUM> with a pressure-balanced piston <NUM>. It should be appreciated one or more aspects of the first BbW system <NUM> may be implemented in a brake system having a different number of valves. The first BbW system <NUM> is significantly different from the conventional BbW systems previously described, as described below.

The first BbW system <NUM> includes a single-circuit master cylinder <NUM>. Hydraulic fluid can flow from the fluid reservoir <NUM> into the single-circuit master cylinder <NUM> via a parallel combination of the MC orifice <NUM> and the MC check valve <NUM>. The hydraulic fluid is discharged from the single-circuit master cylinder <NUM> and into the first MC fluid passageway <NUM> in response to application (i.e. pressing) of the brake pedal <NUM>.

The first BbW system <NUM> includes the upper chamber 42a of the PFE <NUM> fluidly coupled to the first MC fluid passageway <NUM> via a second orifice <NUM> connected in parallel with a first check valve <NUM>. The first check valve <NUM> is configured to allow fluid flow from the PFE <NUM> back to the first MC fluid passageway <NUM>, while preventing fluid flow in a reverse direction. A third pressure sensor <NUM> monitors fluid pressure in the upper chamber 42a of the PFE <NUM>. A fourth pressure sensor <NUM> monitors fluid pressure in the PSU fluid passageway <NUM>.

The dual-circuit PSU <NUM> of the first BbW system <NUM> includes a first fluid port <NUM>, a second fluid port <NUM>, a third fluid port <NUM>, a fourth fluid port <NUM>, and a fifth fluid port <NUM>. A PSU piston <NUM> is moved linearly by the electric motor <NUM> to supply the hydraulic fluid under pressure to the PSU fluid passageway <NUM> via the second fluid port <NUM>.

The second fluid port <NUM> may also be called a first supply port because of its function for supplying fluid from the dual-circuit PSU <NUM> when the PSU piston <NUM> is extended away from the electric motor <NUM>. The fourth fluid port <NUM> may also be called a second supply port because of its function for supplying fluid from the dual-circuit PSU <NUM> when the PSU piston <NUM> is retracted toward the electric motor <NUM>. The third fluid port <NUM> may also be called a third supply port because of its function for supplying fluid from the dual-circuit PSU <NUM> when the PSU piston <NUM> is extended away from the electric motor <NUM>. A PSU reservoir isolation valve (PRIV) <NUM>, which is a normally-closed valve, selectively controls fluid communication between the fluid reservoir <NUM> and an intake passage <NUM> that is fluidly coupled to the first fluid port and the fourth fluid port <NUM> of the dual-circuit PSU <NUM>.

A PSU replenish check valve <NUM> is connected between the intake passage <NUM> and the PSU fluid passageway <NUM> and configured to allow fluid flow from the intake passage <NUM> into the PSU fluid passageway <NUM> while blocking fluid flow in an opposite direction. A PSU balance check valve <NUM> is connected between the third fluid port <NUM> and the PSU fluid passageway <NUM> and configured to allow fluid flow from the third fluid port <NUM> into the PSU fluid passageway <NUM> while blocking fluid flow in an opposite direction. In some embodiments, the PSU balance check valve <NUM> may not be used, and the third fluid port <NUM> may be directly fluidly coupled to the PSU fluid passageway <NUM>.

The lower chamber 42b of the PFE <NUM> is connected to the fluid reservoir <NUM> via a fifth check valve <NUM>. The fifth check valve <NUM> is configured to allow fluid flow from the fluid reservoir <NUM> to flow into the PFE <NUM> while blocking fluid flow in the opposite direction. A makeup conduit <NUM> is also connected to the lower chamber 42b of the PFE <NUM>. The makeup conduit <NUM> is connected to the fifth fluid port <NUM> of the dual-circuit PSU <NUM> via a sixth check valve <NUM>. The sixth check valve <NUM> is configured to allow fluid flow from the makeup conduit <NUM> into the fifth fluid port <NUM> of the dual-circuit PSU <NUM> while blocking fluid flow in the opposite direction.

A master cylinder isolation valve (MCIV) <NUM>, which is a normally-open valve, selectively controls fluid communication between the first MC fluid passageway <NUM> and the PSU fluid passageway <NUM>.

The PSU fluid passageway <NUM> is directly fluidly connected to each of the first brake circuit <NUM> and the second brake circuit <NUM>. A first bi-directional check valve <NUM> controls fluid flow between the PSU fluid passageway <NUM> and the ABS valves 68a, 68b in the first brake circuit <NUM>, and a second bi-directional check valve <NUM> controls fluid flow between the PSU fluid passageway <NUM> and the ABS valves 68a, 68b in the second brake circuit <NUM>. The purpose and operation of the bi-directional check valves <NUM>, <NUM>, is described in further detail, below.

<FIG> shows a cut-away diagram of the dual-circuit PSU <NUM>. The dual-circuit PSU <NUM> includes the electric motor <NUM> configured to move an actuator nut <NUM> in a linear path through an actuator bore <NUM>. Specifically, the electric motor <NUM> rotates a threaded rod <NUM> to move the actuator nut <NUM> in the linear path through the actuator bore <NUM>. In some embodiments, the actuator nut <NUM> may be prevented from rotating, e.g. by a key and slot, as the actuator nut <NUM> moves in the linear path through the actuator bore <NUM>. In some embodiments, one or more ball bearings may be disposed between the threaded rod <NUM> and the actuator nut <NUM>, providing a ball-screw interface. A gear set <NUM>, which may include one or more planetary reduction gears, mechanically couples the motor shaft of the electric motor <NUM> and the threaded rod <NUM>, reducing the speed and increasing torque applied to the threaded rod <NUM>.

An actuator rod <NUM> is coupled to the actuator nut <NUM> and extends to a ball end <NUM> opposite from the electric motor <NUM>. The actuator rod <NUM> extends through a partition <NUM> and is sealed by a first O-ring <NUM>. The ball end <NUM> of the actuator rod <NUM> fits within a corresponding pocket <NUM> in the PSU piston <NUM> with a tight snap fit, thereby allowing the PSU piston <NUM> to be pushed or pulled by the actuator rod <NUM>. The PSU piston <NUM> is disposed within a piston bore <NUM> and configured to move linearly therethrough in response to being pressed by the ball end <NUM> of the actuator rod <NUM>. The piston bore <NUM> extends between the partition <NUM> and a terminal end <NUM>. The PSU piston <NUM> divides the piston bore <NUM> into a first chamber <NUM> and a second chamber <NUM>. The first chamber <NUM> extends between the terminal end <NUM> and the PSU piston <NUM>. The interlocking fit between the ball end <NUM> of the actuator rod <NUM> fits and the corresponding pocket <NUM> in the PSU piston <NUM> may allow the dual-circuit PSU <NUM> to function without a return spring, which may otherwise be required, providing a cost savings over alternative designs.

The second chamber <NUM> extends between the PSU piston <NUM> and the partition <NUM>. The second fluid port <NUM> provides fluid communication into the first chamber <NUM> adjacent to the terminal end <NUM> for fluid to exit from the first chamber <NUM> in response to the PSU piston <NUM> being pushed toward the terminal end <NUM>. The fourth fluid port <NUM>, and the fifth fluid port <NUM> each provide fluid communication into the second chamber <NUM>.

The PSU piston <NUM> includes a top face <NUM> that spans across the piston bore <NUM> and which engages the ball end <NUM> of the actuator rod <NUM>. The PSU piston <NUM> also includes cylindrical skirt <NUM> extending away from the top face <NUM> and into the first chamber <NUM> adjacent to the piston bore <NUM>. The cylindrical skirt <NUM> defines an intake passage <NUM> that aligns with the first fluid port <NUM> for allowing fluid into the first chamber <NUM> with the dual-circuit PSU <NUM> in a retracted position, as shown in <FIG>. A set of second O-rings <NUM> seal between the piston bore <NUM> and the PSU piston <NUM> for preventing the fluid from leaking around the PSU piston <NUM>.

The dual-circuit PSU <NUM> includes an inner cylinder <NUM> within the piston bore <NUM> and extending from the terminal end <NUM> toward the electric motor <NUM> and defining a balance bore <NUM> on an inner surface thereof. The balance bore <NUM> may be coaxial with the piston bore <NUM>. The PSU piston <NUM> also includes a balance piston <NUM> extending opposite from the top face <NUM> and having a cross-sectional area that is equal to the cross-sectional area of actuator rod <NUM>. The balance piston <NUM> extends through the balance bore <NUM>. The third fluid port <NUM> provides fluid communication into the balance bore <NUM>. A third O-Ring <NUM> extends around the balance piston <NUM> for sealing with the balance bore <NUM>.

When the driver applies the brake, the master cylinder isolation valve (MCIV) <NUM> is closed, and the PSU reservoir isolation valve (PRIV) <NUM> remains opened. Master cylinder fluid is directed to the PFE <NUM> to simulate normal brake pedal force and travel. That same travel information is sent to the electronic control unit ECU <NUM> which subsequently applied the appropriate current to the electric motor <NUM> to rotate the ballscrew and mechanically displace the PSU piston <NUM>. This causes the fluid to travel through the bi-directional check valves <NUM>, <NUM>, through the ABS apply valves 68a and finally reaching the wheel brakes 22a, 22b, 22c, 22d to apply pressure and slow the vehicle.

Since this is an "open" system, meaning the fluid released from the wheel brakes in an ABS stop is not captured but flows back to the reservoir at atmospheric pressure, it is necessary to replenish the PSU. This is accomplished by first closing the PSU reservoir isolation valve (PRIV) <NUM> which traps pressure behind the PSU piston <NUM>. The ball screw is retracted the actuator rod <NUM> to pull the PSU piston <NUM> back away from the terminal end <NUM>. This forces fluid behind the PSU piston <NUM> to flow to the front of the PSU piston <NUM> via the replenish check valve <NUM>. Pressure on both sides of the PSU piston <NUM> is maintained during replenishment since due to the balance piston <NUM>, both sides of the PSU piston <NUM> now displace equal volumes as the PSU piston <NUM> moves through the piston bore <NUM>.

The dual-circuit PSU <NUM> may be filled at an assembly plant using an "evac. and fill" procedure. That is, the entire brake system may be evacuated and then brake fluid added so there is no trapped air. In that case, the balance check valve <NUM> may have a very low cracking pressure, and the balance bore <NUM> in front of the balance piston <NUM> would be filled with fluid. After the first apply, the balance bore <NUM> in front of the balance piston <NUM> could not replenish but simply create a partial vacuum. Alternatively, if an evac. and fill is not used, but a simple pressure or gravity bleed, then a small volume of air may be trapped in the balance bore <NUM> in front of the balance piston <NUM>. This small volume of air would not impede operation, but would most likely slowly go back into the brake system and be absorbed. In either of the two cases above, the balance bore <NUM> in front of the balance piston <NUM> may be maintained at or near atmospheric pressure, so it balances out force applied by the actuator rod <NUM> on the top side of the PSU piston <NUM>.

<FIG> shows an enlarged section of the dual-circuit PSU <NUM>, showing how the ball end <NUM> of the actuator rod <NUM> fits within the corresponding pocket <NUM> in the PSU piston <NUM>. The actuator rod <NUM> may include a plastic and stamped assembly that fits into the pocket <NUM> in the PSU piston <NUM>. The ball end <NUM> may then be snapped and retained into the PSU piston <NUM> to form a solid couple with substantially high pull-out forces.

<FIG> shows a section of the schematic diagram of the first BbW system <NUM> of <FIG>, indicating a fluid path from the dual-circuit PSU <NUM> to the control valve manifold <NUM>, which may also be called the ABS valves. <FIG> shows a section of the schematic diagram of the H-bridge type BbW system 20a of <FIG>, indicating a fluid path from the PSU <NUM> to the control valve manifold <NUM>, with the isolation valves in the fluid path between the PSU and the control valve manifold <NUM> circled. <FIG> shows a section of the schematic diagram of the <NUM>-valve BbW system 20b system of <FIG>, indicating a fluid path from the PSU <NUM> to the control valve manifold <NUM>, with the isolation valves in the fluid path between the PSU <NUM> and the control valve manifold <NUM> circled.

These schematics show an advantage of the first BbW system <NUM> regarding the important aspect of braking response time. In both the H-bridge BbW system 20a and the <NUM>-valve BbW system 20b designs, fluid must flow through one or two isolation valves from the PSU <NUM> to the wheel brakes. In the first BbW system <NUM>, there are no isolation valves between the dual-circuit PSU <NUM> and the wheel brakes. This gives the first BbW system <NUM> a distinct advantage in that typical orifice equivalent sizes of valve range from <NUM> to <NUM> which can cause a significant flow restriction, thus reducing braking response time.

It should also be noted that this situation may be worse for the <NUM>-valve BbW system 20b, in that by necessity the valve will need to be larger to achieve equivalent flow rates to the parallel valves in the H-bridge BbW system 20a. In addition, this design is may only be applicable to Front/Rear hydraulic base brake splits due to the cross-over valve added flow restriction.

<FIG> shows a section of the schematic diagram of the first BbW system <NUM> system of <FIG>, indicating details of the dual-circuit PSU <NUM>. The first BbW system <NUM> design is unique and adds a degree of safety to the brake system in that there is always fluid behind the PSU piston <NUM>. This virtually eliminates the leakage concern of seal failure. When the PSU piston <NUM> displaces to the left (i.e. during a discharge stroke), the PRIV <NUM> is opened, and fluid can enter the second chamber <NUM> via the fourth fluid port <NUM>. Fluid can also enter the second chamber <NUM> via the a fifth fluid port <NUM> and sixth check valve <NUM>. During replenishment (i.e. when the PSU piston <NUM> moves to the right), the PRIV <NUM> is closed, sealing the second chamber <NUM> behind the PSU piston <NUM>. When the actuator rod <NUM> retracts, the PSU piston <NUM> is pulled away from the terminal end <NUM>, which in turn pushes the fluid out of the fourth fluid port <NUM> into the second fluid port <NUM> and the third fluid ports <NUM>, all the while maintaining system pressure since the areas on both sides of the piston are equal.

<FIG> shows a section of the schematic diagram of the H-bridge BbW system 20a of <FIG>, indicating details of the PSU <NUM>. The <NUM>-valve BbW system 20b may incorporate a PSU <NUM> having a similar or identical design having fluid on only one side of the piston. Such a dry-piston PSU can suffer from fluid leaking past the PSU piston seals into the motor assembly. Furthermore, to establish replenishment, the PSU outlet valves must be closed, and a vacuum created in order to allow fluid to enter into the PSU bore. This creates further concern for air ingestion. Finally, should there be a ballscrew failure, the PSU piston will only travel the displacement equivalent of the pushrod piston before being hydraulically locked into place.

<FIG> shows a section of the schematic diagram of the first BbW system <NUM> of <FIG>. <FIG> shows a section of the schematic diagram of the H-bridge BbW system 20a of <FIG>, indicating a faulty PFE isolation valve. <FIG> shows a section of the schematic diagram of the <NUM>-valve BbW system 20b of <FIG>, indicating a faulty PFE isolation valve. <FIG> illustrate another area where the first BbW system <NUM> design is inherently safer is for initiation of brake-by-wire mode. In the H-bridge BbW system 20a, and the <NUM>-valve BbW system 20b, the pedal feel emulator (PFE) is locked out by a normally-closed valve for fallback mode operation. If the other control valves all operate properly (blocking master cylinder flow to the wheel brakes) and the PFE isolation valve fails to open, then the pedal may be locked, and therefore unable to transmit travel information to the ECU, potentially resulting in failed brakes. The first BbW system <NUM> of the present invention does not require a PFE isolation valve because of its unique balanced piston design. Thus, brake pedal displacement is guaranteed each brake apply and the pedal lockout problem is eliminated.

<FIG> shows a schematic diagram of the first BbW system <NUM> of <FIG>, indicating a leak in a brake line to the right-front wheel brake. This illustrates a main purpose of the dual check valves in the main brake system is to prevent long term (e.g. overnight) leakage of the brake system should a leak be present such as a faulty brake hose. The check valves require a small pressure differential to actuate, which is sufficient to prevent leakage from the effects of gravity. This adds another measure of safety to a system using a single master cylinder circuit for backup. In other words, each of the bi-directional check valves <NUM>, <NUM> may prevent fluid from flowing therethrough, unless there the differential pressure thereacross is greater than a predetermined pressure value. In cases of a leak, the differential pressure across a corresponding one of the of the bi-directional check valves <NUM>, <NUM> may fall below the predetermined value, after which the corresponding bi-directional check valve <NUM>, <NUM> blocks the flow, preventing further leakage.

<FIG> shows a cut-away diagram of a release valve <NUM>. The release valve <NUM> may be a conventional design. <FIG> shows a cut-away diagram of a bi-directional check valve <NUM>, <NUM> that may use many of the same tooling and components as the release valve <NUM> shown in <FIG> shows a perspective cut-away view of the bi-directional check valve <NUM>, <NUM>.

A block <NUM> defines a valve bore <NUM> from an open end <NUM>. A valve core <NUM> is disposed within the valve bore <NUM>. The valve core <NUM> is generally tubular and defines an interior passage <NUM> extending axially therethrough between a first end <NUM> and a second end <NUM>. A cap <NUM> encloses the open end <NUM>, holding the valve core <NUM> within the valve bore <NUM>. The block <NUM> defines a first fluid passage <NUM> that is in fluid communication with a first end <NUM> of the interior passage <NUM> via first holes <NUM> in the valve core <NUM>. The block <NUM> also defines a second fluid passage <NUM> that is aligned with and in fluid communication with the second end <NUM> of the valve core <NUM>. A ball seal <NUM>, ball <NUM>, and spring <NUM> are disposed within the valve bore <NUM>, forming a first check valve to allow fluid flow through the interior passage <NUM> of the valve core <NUM> from the first fluid passage <NUM> to the second fluid passage <NUM>, while preventing fluid flow in an opposite direction. The valve core <NUM> includes a smaller portion <NUM> adjacent to the second end <NUM>, and a wider portion <NUM> spaced apart from the second end <NUM> toward the first end <NUM>. A lip seal <NUM> is disposed around the smaller portion <NUM> of the valve core <NUM> and engaging a corresponding shoulder <NUM> formed in the block <NUM>. The lip seal <NUM> functions as a second check valve, allowing fluid to flow around a periphery of the valve core <NUM> from the second fluid passage <NUM> to the first fluid passage <NUM>, while preventing fluid flow in an opposite direction.

<FIG> show additional views of the core of the bi-directional check valve <NUM>, <NUM>.

<FIG> shows a schematic diagram of a second BbW system <NUM> of the present invention. The second BbW system <NUM> may be similar or identical to the first BbW system <NUM>, with a couple of differences discussed herein. This second BbW system <NUM> variation offers the additional safety benefit of a <NUM>-circuit master cylinder <NUM> having a first circuit and a second circuit. The first circuit of the <NUM>-circuit master cylinder <NUM> is configured to supply fluid to the first brake circuit <NUM> via the first MC fluid passageway <NUM> and the PSU fluid passageway <NUM>. The second circuit of the <NUM>-circuit master cylinder <NUM> is configured to supply fluid to the second brake circuit <NUM> via the second MC fluid passageway <NUM>. A master cylinder isolation valve (MCIV) <NUM>, which is a normally-open valve, selectively controls fluid communication between the first MC fluid passageway <NUM> and the PSU fluid passageway <NUM>. A circuit isolation valve <NUM>, which is a normally-closed valve, selectively controls fluid communication between the two brake circuits <NUM>, <NUM>. The circuit isolation valve <NUM> may also be called a primary/secondary circuit isolation valve. A secondary MC isolation valve <NUM>, which is a normally-open valve, selectively controls fluid communication between the second MC fluid passageway <NUM> and the second brake circuit <NUM>.

The addition of these components <NUM>, <NUM>, <NUM> may provide another layer of safety in that positive failure mode management for leak isolation at a wheel brake is no longer required, and the system will fall back to a half system even in case of a dual failure of a leak and an electrical shut down. Otherwise, the same additional safety benefits of the first BbW system <NUM> are realized, with its balanced PSU piston eliminating leakage concerns and/or air ingestion.

<FIG> shows a schematic diagram of third BbW system <NUM> of the present invention. The third BbW system <NUM> may be similar or identical to the first BbW system <NUM>, with a couple of differences discussed herein. This design variation is slightly different than the others in that it requires the removal of the bypass check valves from the ABS apply valves 68a. This may require that the valve internal return spring in each of the ABS apply valves 68a to be increased to avoid self-closure on relief by the Bernoulli effect. However, the benefit of this change means the PSU outlet circuit can be completely isolated during a regeneration cycle and pull fluid directly from the fluid reservoir <NUM>. The added safety benefit is that there is still fluid captured behind the PSU piston <NUM> in event of a mechanical failure, which is why the design is now called "fluid balanced," This also virtually eliminates concern for air ingestion as well. If the electric motor <NUM> fails, the single-circuit master cylinder <NUM> will supply fluid directly to the wheel brakes 22a-22d. Any displacement of the PFE <NUM> will be recovered from the fluid entering from behind the PSU piston <NUM>. A bi-directional check valve <NUM> may take the place of the sixth check valve <NUM> between the dual-circuit PSU <NUM> and the lower chamber 42b of the PFE <NUM>. This permits fluid flow in both directions between the dual-circuit PSU <NUM> and the lower chamber 42b of the PFE <NUM>. This assures that lower chamber 42b remains full of fluid since retraction of PSU piston <NUM> after a brake application can force fluid back into the PFE <NUM> lower chamber 42b.

The BbW systems <NUM>, <NUM>, <NUM> may be packaged in any configuration. For example, any of the BbW systems <NUM>, <NUM>, <NUM> may have an axial configuration 620a, with the PSU axially aligned with the master brake cylinder, as shown in <FIG>. Additionally or alternatively, any of the BbW systems <NUM>, <NUM>, <NUM> may have a motor-down configuration 620b, as shown in <FIG>. Additionally or alternatively, any of the BbW systems <NUM>, <NUM>, <NUM> may be configured with a transverse motor configuration 620c, with the electric motor <NUM> having a motor shaft that extends transverse to the master brake cylinder, as shown in <FIG>.

According to an aspect of the invention, a brake system for motor vehicles in a brake-by-wire operating mode can be activated both by a vehicle driver in the normal brake-by-wire operating mode and can also be operated by the same driver in at least one fallback operating mode in which only operation of the brake system by the vehicle driver is possible.

The brake system includes a brake pedal for actuating a brake master cylinder having a housing and a single piston and which defines a single pressure chamber which is subsequently connected to the wheel brakes, wherein an actuating force exerted by the brake pedal is exerted on the single piston upon actuation of the brake system by the vehicle driver and the piston is positioned in a starting position by a return spring when the brake pedal is not actuated.

The brake system also includes a pressure medium reservoir for a pressure medium which is exposed to atmospheric pressure and has a reservoir chamber associated with the pressure chamber; a travel detection device which detects the actuation travel of the brake pedal or at least the piston connected to the brake pedal; and a pedal feel emulator which conveys a desired haptic brake pedal feel to the vehicle driver in the brake-by-wire mode, being connected hydraulically directly to the master cylinder pressure chamber.

The brake system also includes an electrically controllable pressure supply unit which delivers a brake system pressure and consists of a piston sealed to the main housing bore displaced by an independently actuated push rod on one end to supply brake system pressure which is also sealed to the main housing in a corresponding bore and an extending rod on the other side that is part of the main piston and is sized exactly as the push rod and sealed in a separate bore proportional to its size such as when the piston and push rod displace, equal volumes of fluid are displaced on both sides.

Claim 1:
An electro-hydraulic brake system comprising:
a master cylinder (MC) (<NUM>) fluidly coupled to a first MC fluid passageway (<NUM>) and configured to supply fluid into the first MC fluid passageway (<NUM>) in response to pressing force on a brake pedal (<NUM>) coupled thereto;
a pressure supply unit (PSU) (<NUM>) including an electric motor (<NUM>) coupled to an actuator rod (<NUM>), a piston bore (<NUM>) including a terminal end (<NUM>) opposite the electric motor (<NUM>), and a PSU piston (<NUM>) disposed within the piston bore (<NUM>) and movable by the actuator rod (<NUM>) through the piston bore (<NUM>) and dividing the piston bore (<NUM>) into a first chamber (<NUM>) and a second chamber (<NUM>);
characterized in that the electro-hydraulic brake system further comprises an inner cylinder (<NUM>) within the piston bore (<NUM>) and extending from the terminal end (<NUM>) towards the PSU piston (<NUM>) and defining a balance bore (<NUM>);
the PSU piston (<NUM>) including a balance piston (<NUM>) extending into the balance bore (<NUM>) and having a cross-sectional area equal to a cross-sectional area of the actuator rod (<NUM>);
a check valve configured to allow fluid flow from the second chamber (<NUM>) of the PSU (<NUM>) to the first chamber (<NUM>) of the PSU (<NUM>) and to block fluid flow in an opposite direction;
a pedal feel emulator (PFE) (<NUM>) including a PFE piston (<NUM>) movable through a PFE bore (<NUM>) and separating an upper chamber (42a) from a lower chamber (42b);
wherein the lower chamber (42b) of the PFE (<NUM>) is fluidly coupled to the second chamber (<NUM>) of the PSU (<NUM>) to convey fluid from the lower chamber (42b) of the PFE (<NUM>) to the second chamber (<NUM>) of the PSU (<NUM>) in response to a compression of the PFE (<NUM>); and
wherein the first MC fluid passageway (<NUM>) is fluidly coupled to the upper chamber (42a) of the PFE (<NUM>) to provide a fluid path from the master cylinder (<NUM>) into the upper chamber (42a) of the PFE (<NUM>).