Patent ID: 12208777

DESCRIPTION OF THE ENABLING EMBODIMENTS

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

FIG.1shows a schematic block diagram of a brake-by-wire system10in a vehicle, such as an automobile. Basic brake-by-wire (BBW) architecture is now well-established in the automotive industry. The vehicle's master cylinder12either applies the brakes directly in a failed system fallback mode or is isolated from the wheel brakes13and connected to a pedal feel emulator14that 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 system10as an input signal to a brake electronic control unit (ECU)17. It in turn sends the appropriate signal to a pressure supply unit (PSU)16. The PSU16may 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 cylinder12and/or the PSU16may be coupled to the wheel brakes13via a series of control valves15, which may include an apply valve and a release valve (not shown) for each of the wheel brakes13to 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 ECU17may also send a signal to a drive control unit (DCU)18, 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.2shows a schematic diagram of a conventional H-bridge circuit60as part of a brake-by-wire (BbW) system20afor controlling operation of the wheel brakes22a,22b,22c,22dof the vehicle. One or more of the wheels of vehicles using BbW systems may be powered by an internal combustion engine6. Additionally or alternatively, one or more of the wheels of vehicles using BbW systems may be powered by an electric motor8, 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 motor8and an internal combustion engines6in a sharing configuration. Most vehicle using BbW systems fall into the latter two categories. An example of a sharing configuration is shown inFIG.2, with the two front wheels each being coupled to an internal combustion engine6and an electric motor8. 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 engine6and/or the electric motor8. Furthermore, either or both of the internal combustion engine6and/or the electric motor8may 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 system20aincludes a fluid reservoir24holding a hydraulic fluid and supplying the hydraulic fluid to a dual-circuit master cylinder30. A fluid level sensor25, such as a float switch, monitors a level of the hydraulic fluid in the fluid reservoir24. A reservoir test valve26selectively controls fluid flow from the fluid reservoir24to the dual-circuit master cylinder30. The dual-circuit master cylinder30is configured to supply fluid pressure in each of a first master cylinder (MC) fluid passageway32and a second MC fluid passageway34in response to application of a brake pedal36. The brake pedal36is coupled to press a brake linkage38which, in turn, presses a primary piston40of the dual-circuit master cylinder30. The MC fluid passageways32,34may 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 passageways32,34. A travel sensor37monitors a position of the brake pedal36. A first pressure sensor33monitors the pressure in the first MC fluid passageway32.

A pedal feel emulator (PFE)41includes a PFE bore42. A PFE piston44is slidably disposed within the PFE bore42to divide the PFE bore42into an upper chamber42aand a lower chamber42b. The PFE piston44is biased by a spring45to compress the upper chamber42a. The upper chamber42ais selectively fluidly coupled to the first MC fluid passageway32via a PFE isolation valve46to selectively provide a natural feeling of brake operation, particularly when the dual-circuit master cylinder30is decoupled from operating the wheel brakes. A first check valve47is connected in parallel with the PFE isolation valve46to allow fluid flow from the PFE41back to the first MC fluid passageway32while preventing fluid flow in a reverse direction. The lower chamber42bis fluidly coupled to the fluid reservoir24via a return fluid passageway27.

A pressure supply unit (PSU)50includes an electric motor52and a PSU pump54to supply the hydraulic fluid from the fluid reservoir24to a PSU fluid passageway56. A rotor angle sensor53may be coupled to the electric motor52to determine a position of the rotor in the motor, and thus a position of the PSU pump54. A second check valve58allows fluid flow from the fluid reservoir24into the PSU fluid passageway56while blocking fluid flow in an opposite direction. A second pressure sensor57monitors the pressure in the PSU fluid passageway56.

This hydraulic layout includes an H-bridge circuit60having four valves that control the switching between the MC fluid passageways32,34of the dual-circuit master cylinder30and the PSU50. This basic safety circuit of normally-open valves connecting wheel brakes22a,22b,22c,22dto the dual-circuit master cylinder30and normally-closed brakes connecting wheel brakes22a,22b,22c,22dto the PSU50is described in U.S. Pat. No. 6,533,369, which is incorporated herein by reference in its entirety.

A control valve manifold66fluidly connects the two brake circuits62,64to the corresponding wheel brakes22a,22b,22c,22d. The control valve manifold66includes an apply valve68aand a release valve68bcorresponding to each of the wheel brakes22a,22b,22c,22dto selectively control fluid flow between the corresponding one of the of the wheel brakes22a,22b,22c,22dand an associated one of the two brake circuits62,64. The apply valves68aand the release valves68bmay collectively be called antilock brake system (ABS) valves for their use in such an ABS. However, the apply valves68aand the release valves68bmay be used for other functions, such as for traction control and/or for torque vectoring.

Besides the eight standard ABS valves68a,68b, and the four H-bridge control valves60, conventional brake-by-wire systems include two more valves26,46, bringing the total to fourteen (14) valves. The PFE isolation valve46is a normally-closed valve and its sole purpose is to lock out the PFE41in the event of a failed pressure supply unit when master cylinder backup is required. The reservoir test valve26may be used to shut off the primary master cylinder return path to the fluid reservoir24so that the system may conduct a self-test to make sure the PFE isolation valve46is functioning properly. This is extremely important as the pedal may be locked up if the PFE isolation valve46were to fail to open when first commanded.

An electronic control unit (ECU)70may include one or more processors, microcontrollers, and/or electric circuits for controlling operation of one or more of the valves60,68a,68b,26,46and/or for monitoring one or more sensors25,33,37,53,57and to thereby coordinate operation of the H-Bridge BbW system20a.

FIG.3shows a schematic diagram of a 12-value BbW system20b. The 12-value BbW system20bmay be similar or identical to the H-Bridge BbW system20a, except for the changes described herein. The 12-value BbW system20bmay provide some advantages over the H-Bridge BbW system20ashown inFIG.2, such as reduced cost, mass, and size while meeting requirements for performance and safety. The 12-value brake-by-wire system20bincludes a single-circuit master cylinder130having a single piston, instead of the dual-circuit master cylinder30of the H-Bridge BbW system20a. The single-circuit master cylinder130receives hydraulic fluid from the fluid reservoir24via parallel combination of a master cylinder (MC) orifice132and an MC check valve134. The single-circuit master cylinder130feeds the fluid to a first MC fluid passageway32in response to application of the brake pedal36. A fourth check valve136allows fluid flow from the fluid reservoir24to the PSU50while blocking fluid flow in an opposite direction.

In place of the H-bridge circuit60, the 12-value BbW system20bhas a 3-value arrangement60a,60b,60cconfigured to selectively couple either the first master cylinder (MC) fluid passageway32or the PSU fluid passageway56to one or both of the two brake circuits62,64, which, in turn, are fluidly coupled to two of the wheel brakes22a,22b,22c,22d. The 3-value arrangement60a,60b,60cincludes a MC isolation valve60aconfigured to selectively fluidly couple the first master cylinder (MC) fluid passageway32with the first brake circuit62. The 3-valve arrangement60a,60b,60calso includes a PSU isolation valve60bconfigured to selectively fluidly couple the PSU fluid passageway56with the second brake circuit64. The 3-value arrangement60a,60b,60calso includes a middle circuit connecting valve60cconfigured to selectively fluidly couple the first brake circuit62with the second brake circuit64.

The 12-valve BbW system20bincludes a control valve manifold66fluidly connecting the two brake circuits62,64to the corresponding wheel brakes22a,22b,22c,22d. The control valve manifold66may be similar or identical to the control valve manifold66of the H-Bridge BbW system20a.

The 12-valve BbW system20bmay 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 valve60c, and the valves60a,60b,60cwill need to be large enough to flow the same fluid carried out by two valves in parallel in the H-bridge circuit60of the H-Bridge BbW system20a.

FIG.4shows a schematic diagram of a first BbW system120of the present disclosure. The first BbW system120is a 10-valve system, with a single-circuit master cylinder130and a dual-circuit pressure supply unit (PSU)150with a pressure-balanced piston160. It should be appreciated one or more aspects of the first BbW system120may be implemented in a brake system having a different number of valves. The first BbW system120is significantly different from the conventional BbW systems previously described, as described below.

The first BbW system120includes a single-circuit master cylinder130. Hydraulic fluid can flow from the fluid reservoir24into the single-circuit master cylinder130via a parallel combination of the MC orifice132and the MC check valve134. The hydraulic fluid is discharged from the single-circuit master cylinder130and into the first MC fluid passageway32in response to application (i.e. pressing) of the brake pedal36.

The first BbW system120includes the upper chamber42aof the PFE41fluidly coupled to the first MC fluid passageway32via a second orifice144connected in parallel with a first check valve47. The first check valve47is configured to allow fluid flow from the PFE41back to the first MC fluid passageway32, while preventing fluid flow in a reverse direction. A third pressure sensor145monitors fluid pressure in the upper chamber42aof the PFE41. A fourth pressure sensor146monitors fluid pressure in the PSU fluid passageway56.

The dual-circuit PSU150of the first BbW system120includes a first fluid port152, a second fluid port154, a third fluid port155, a fourth fluid port156, and a fifth fluid port158. A PSU piston160is moved linearly by the electric motor52to supply the hydraulic fluid under pressure to the PSU fluid passageway56via the second fluid port154.

The second fluid port154may also be called a first supply port because of its function for supplying fluid from the dual-circuit PSU150when the PSU piston160is extended away from the electric motor52. The fourth fluid port156may also be called a second supply port because of its function for supplying fluid from the dual-circuit PSU150when the PSU piston160is retracted toward the electric motor52. The third fluid port155may also be called a third supply port because of its function for supplying fluid from the dual-circuit PSU150when the PSU piston160is extended away from the electric motor52. A PSU reservoir isolation valve (PRIV)126, which is a normally-closed valve, selectively controls fluid communication between the fluid reservoir24and an intake passage128that is fluidly coupled to the first fluid port and the fourth fluid port156of the dual-circuit PSU150.

A PSU replenish check valve172is connected between the intake passage128and the PSU fluid passageway56and configured to allow fluid flow from the intake passage128into the PSU fluid passageway56while blocking fluid flow in an opposite direction. A PSU balance check valve173is connected between the third fluid port155and the PSU fluid passageway56and configured to allow fluid flow from the third fluid port155into the PSU fluid passageway56while blocking fluid flow in an opposite direction. In some embodiments, the PSU balance check valve173may not be used, and the third fluid port155may be directly fluidly coupled to the PSU fluid passageway56.

The lower chamber42bof the PFE41is connected to the fluid reservoir24via a fifth check valve174. The fifth check valve174is configured to allow fluid flow from the fluid reservoir24to flow into the PFE41while blocking fluid flow in the opposite direction. A makeup conduit176is also connected to the lower chamber42bof the PFE41. The makeup conduit176is connected to the fifth fluid port158of the dual-circuit PSU150via a sixth check valve178. The sixth check valve178is configured to allow fluid flow from the makeup conduit176into the fifth fluid port158of the dual-circuit PSU150while blocking fluid flow in the opposite direction.

A master cylinder isolation valve (MCIV)170, which is a normally-open valve, selectively controls fluid communication between the first MC fluid passageway32and the PSU fluid passageway56.

The PSU fluid passageway56is directly fluidly connected to each of the first brake circuit62and the second brake circuit64. A first bi-directional check valve162controls fluid flow between the PSU fluid passageway56and the ABS valves68a,68bin the first brake circuit62, and a second bi-directional check valve164controls fluid flow between the PSU fluid passageway56and the ABS valves68a,68bin the second brake circuit64. The purpose and operation of the bi-directional check valves162,164, is described in further detail, below.

FIG.5Ashows a cut-away diagram of the dual-circuit PSU150. The dual-circuit PSU150includes the electric motor52configured to move an actuator nut202in a linear path through an actuator bore204. Specifically, the electric motor52rotates a threaded rod205to move the actuator nut202in the linear path through the actuator bore204. In some embodiments, the actuator nut202may be prevented from rotating, e.g. by a key and slot, as the actuator nut202moves in the linear path through the actuator bore204. In some embodiments, one or more ball bearings may be disposed between the threaded rod205and the actuator nut202, providing a ball-screw interface. A gear set206, which may include one or more planetary reduction gears, mechanically couples the motor shaft of the electric motor52and the threaded rod205, reducing the speed and increasing torque applied to the threaded rod205.

An actuator rod208is coupled to the actuator nut202and extends to a ball end209opposite from the electric motor52. The actuator rod208extends through a partition212and is sealed by a first O-ring210. The ball end209of the actuator rod208fits within a corresponding pocket211in the PSU piston160with a tight snap fit, thereby allowing the PSU piston160to be pushed or pulled by the actuator rod208. The PSU piston160is disposed within a piston bore222and configured to move linearly therethrough in response to being pressed by the ball end209of the actuator rod208. The piston bore222extends between the partition212and a terminal end228. The PSU piston160divides the piston bore222into a first chamber224and a second chamber226. The first chamber224extends between the terminal end228and the PSU piston160. The interlocking fit between the ball end209of the actuator rod208fits and the corresponding pocket211in the PSU piston160may allow the dual-circuit PSU150to function without a return spring, which may otherwise be required, providing a cost savings over alternative designs.

The second chamber226extends between the PSU piston160and the partition212. The second fluid port154provides fluid communication into the first chamber224adjacent to the terminal end228for fluid to exit from the first chamber224in response to the PSU piston160being pushed toward the terminal end228. The fourth fluid port156, and the fifth fluid port158each provide fluid communication into the second chamber226.

The PSU piston160includes a top face230that spans across the piston bore222and which engages the ball end209of the actuator rod208. The PSU piston160also includes cylindrical skirt232extending away from the top face230and into the first chamber224adjacent to the piston bore222. The cylindrical skirt232defines an intake passage234that aligns with the first fluid port152for allowing fluid into the first chamber224with the dual-circuit PSU150in a retracted position, as shown inFIG.5A. A set of second O-rings236seal between the piston bore222and the PSU piston160for preventing the fluid from leaking around the PSU piston160.

The dual-circuit PSU150includes an inner cylinder241within the piston bore222and extending from the terminal end228toward the electric motor52and defining a balance bore242on an inner surface thereof. The balance bore242may be coaxial with the piston bore222. The PSU piston160also includes a balance piston240extending opposite from the top face230and having a cross-sectional area that is equal to the cross-sectional area of actuator rod208. The balance piston240extends through the balance bore242. The third fluid port155provides fluid communication into the balance bore242. A third O-Ring244extends around the balance piston240for sealing with the balance bore242.

When the driver applies the brake, the master cylinder isolation valve (MCIV)170is closed, and the PSU reservoir isolation valve (PRIV)126remains opened. Master cylinder fluid is directed to the PFE41to simulate normal brake pedal force and travel. That same travel information is sent to the electronic control unit ECU70which subsequently applied the appropriate current to the electric motor52to rotate the ballscrew and mechanically displace the PSU piston160. This causes the fluid to travel through the bi-directional check valves162,164, through the ABS apply valves68aand finally reaching the wheel brakes22a,22b,22c,22dto 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)126which traps pressure behind the PSU piston160. The ball screw is retracted the actuator rod208to pull the PSU piston160back away from the terminal end228. This forces fluid behind the PSU piston160to flow to the front of the PSU piston160via the replenish check valve172. Pressure on both sides of the PSU piston160is maintained during replenishment since due to the balance piston240, both sides of the PSU piston160now displace equal volumes as the PSU piston160moves through the piston bore222.

The dual-circuit PSU150may 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 valve173may have a very low cracking pressure, and the balance bore242in front of the balance piston240would be filled with fluid. After the first apply, the balance bore242in front of the balance piston240could 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 bore242in front of the balance piston240. 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 bore242in front of the balance piston240may be maintained at or near atmospheric pressure, so it balances out force applied by the actuator rod208on the top side of the PSU piston160.

FIG.5Bshows an enlarged section of the dual-circuit PSU150, showing how the ball end209of the actuator rod208fits within the corresponding pocket211in the PSU piston160. The actuator rod208may include a plastic and stamped assembly that fits into the pocket211in the PSU piston160. The ball end209may then be snapped and retained into the PSU piston160to form a solid couple with substantially high pull-out forces.

FIG.6Ashows a section of the schematic diagram of the first BbW system120ofFIG.4, indicating a fluid path from the dual-circuit PSU150to the control valve manifold66, which may also be called the ABS valves.FIG.6Bshows a section of the schematic diagram of the H-bridge type BbW system20aofFIG.2, indicating a fluid path from the PSU50to the control valve manifold66, with the isolation valves in the fluid path between the PSU and the control valve manifold66circled.FIG.6Cshows a section of the schematic diagram of the 12-value BbW system20bsystem ofFIG.3, indicating a fluid path from the PSU50to the control valve manifold66, with the isolation valves in the fluid path between the PSU50and the control valve manifold66circled.

These schematics show an advantage of the first BbW system120regarding the important aspect of braking response time. In both the H-bridge BbW system20aand the 12-value BbW system20bdesigns, fluid must flow through one or two isolation valves from the PSU50to the wheel brakes. In the first BbW system120, there are no isolation valves between the dual-circuit PSU150and the wheel brakes. This gives the first BbW system120a distinct advantage in that typical orifice equivalent sizes of valve range from 0.7 to 1.0 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 12-value BbW system20b, 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 system20a. 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.7Ashows a section of the schematic diagram of the first BbW system120system ofFIG.4, indicating details of the dual-circuit PSU150. The first BbW system120design is unique and adds a degree of safety to the brake system in that there is always fluid behind the PSU piston_160. This virtually eliminates the leakage concern of seal failure. When the PSU piston160displaces to the left (i.e. during a discharge stroke), the PRIV126is opened, and fluid can enter the second chamber226via the fourth fluid port156. Fluid can also enter the second chamber226via the a fifth fluid port158and sixth check valve178. During replenishment (i.e. when the PSU piston160moves to the right), the PRIV126is closed, sealing the second chamber226behind the PSU piston160. When the actuator rod208retracts, the PSU piston160is pulled away from the terminal end228, which in turn pushes the fluid out of the fourth fluid port156into the second fluid port154and the third fluid ports155, all the while maintaining system pressure since the areas on both sides of the piston are equal.

FIG.7Bshows a section of the schematic diagram of the H-bridge BbW system20aofFIG.3, indicating details of the PSU50. The 12-value BbW system20bmay incorporate a PSU50having 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.8Ashows a section of the schematic diagram of the first BbW system120ofFIG.4.FIG.8Bshows a section of the schematic diagram of the H-bridge BbW system20aofFIG.2, indicating a faulty PFE isolation valve.FIG.8Cshows a section of the schematic diagram of the 12-value BbW system20bofFIG.3, indicating a faulty PFE isolation valve.FIGS.8A-8Cillustrate another area where the first BbW system120design is inherently safer is for initiation of brake-by-wire mode. In the H-bridge BbW system20a, and the 12-value BbW system20b, 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 system120of the present disclosure 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.9shows a schematic diagram of the first BbW system120ofFIG.4, 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 valves162,164may 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 valves162,164may fall below the predetermined value, after which the corresponding bi-directional check valve162,164blocks the flow, preventing further leakage.

FIG.10shows a cut-away diagram of a release valve166. The release valve166may be a conventional design.FIG.11shows a cut-away diagram of a bi-directional check valve162,164that may use many of the same tooling and components as the release valve166shown inFIG.10.FIG.12shows a perspective cut-away view of the bi-directional check valve162,164.

A block300defines a valve bore302from an open end304. A valve core310is disposed within the valve bore302. The valve core310is generally tubular and defines an interior passage312extending axially therethrough between a first end314and a second end316. A cap318encloses the open end304, holding the valve core310within the valve bore302. The block300defines a first fluid passage320that is in fluid communication with a first end314of the interior passage312via first holes322in the valve core310. The block300also defines a second fluid passage324that is aligned with and in fluid communication with the second end316of the valve core310. A ball seal330, ball332, and spring334are disposed within the valve bore302, forming a first check valve to allow fluid flow through the interior passage312of the valve core310from the first fluid passage320to the second fluid passage324, while preventing fluid flow in an opposite direction. The valve core310includes a smaller portion340adjacent to the second end316, and a wider portion342spaced apart from the second end316toward the first end314. A lip seal344is disposed around the smaller portion340of the valve core310and engaging a corresponding shoulder346formed in the block300. The lip seal344functions as a second check valve, allowing fluid to flow around a periphery of the valve core310from the second fluid passage324to the first fluid passage320, while preventing fluid flow in an opposite direction.

FIGS.13A and13Bshow additional views of the core of the bi-directional check valve162,164.

FIG.14shows a schematic diagram of a second BbW system420of the present disclosure. The second BbW system420may be similar or identical to the first BbW system120, with a couple of differences discussed herein. This second BbW system420variation offers the additional safety benefit of a 2-circuit master cylinder422having a first circuit and a second circuit. The first circuit of the 2-circuit master cylinder422is configured to supply fluid to the first brake circuit62via the first MC fluid passageway32and the PSU fluid passageway56. The second circuit of the 2-circuit master cylinder422is configured to supply fluid to the second brake circuit64via the second MC fluid passageway34. A master cylinder isolation valve (MCIV)170, which is a normally-open valve, selectively controls fluid communication between the first MC fluid passageway32and the PSU fluid passageway56. A circuit isolation valve423, which is a normally-closed valve, selectively controls fluid communication between the two brake circuits62,64. The circuit isolation valve423may also be called a primary/secondary circuit isolation valve. A secondary MC isolation valve424, which is a normally-open valve, selectively controls fluid communication between the second MC fluid passageway34and the second brake circuit64.

The addition of these components422,423,424may 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 system120are realized, with its balanced PSU piston eliminating leakage concerns and/or air ingestion.

FIG.15shows a schematic diagram of third BbW system520of the present disclosure. The third BbW system520may be similar or identical to the first BbW system120, 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 valves68a. This may require that the valve internal return spring in each of the ABS apply valves68ato 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 reservoir24. The added safety benefit is that there is still fluid captured behind the PSU piston160in 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 motor52fails, the single-circuit master cylinder130will supply fluid directly to the wheel brakes22a-22d. Any displacement of the PFE41will be recovered from the fluid entering from behind the PSU piston160. A bi-directional check valve522may take the place of the sixth check valve178between the dual-circuit PSU150and the lower chamber42bof the PFE41. This permits fluid flow in both directions between the dual-circuit PSU150and the lower chamber42bof the PFE41. This assures that lower chamber42bremains full of fluid since retraction of PSU piston240after a brake application can force fluid back into the PFE41lower chamber42b.

The BbW systems120,420,520may be packaged in any configuration. For example, any of the BbW systems120,420,520may have an axial configuration620a, with the PSU axially aligned with the master brake cylinder, as shown inFIG.16. Additionally or alternatively, any of the BbW systems120,420,520may have a motor-down configuration620b, as shown inFIG.17. Additionally or alternatively, any of the BbW systems120,420,520may be configured with a transverse motor configuration620c, with the electric motor52having a motor shaft that extends transverse to the master brake cylinder, as shown inFIG.18.

According to an aspect of the disclosure, 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.

The brake system also includes a fluid connection between the bore of the extending rod and the main system pressure path with a check valve assembly dividing the two area with said check valve permitting flow from the bore of the extending rod to the main system pressure path; a master cylinder isolation valve for isolating the master cylinder from the brake circuit; a pressure supply unit reservoir isolation valve for isolating the push rod side of the electrically controllable pressure source to the reservoir; a forward flow and reverse flow check valve in parallel to each other and located between the pressure supply unit and two of the wheel brakes with a second forward flow and reverse flow check valve in parallel to each other and located between the pressure supply unit and the remaining two-wheel brakes; and an inlet valve and outlet valve for each of the wheel brakes for setting wheel-individual brake pressures which are derived from signals generated by the electronic control unit, where the inlet valves transmit fluid to the wheel brakes in an unactivated state and limit or prevent a build-up of wheel pressure in an activated state and the outlet valves prevent an outflow of the pressure medium from the wheel brakes to the reservoir in an unactivated state and permit and control the outflow in an activated state, the inlet valves being closed, so that a reduction in wheel brake pressure takes place.

The foregoing description is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.