Patent Publication Number: US-2003234574-A1

Title: Electro-hydraulic control unit with integral precharge pump for a controlled braking apparatus

Description:
[0001] This application claims the benefit of commonly assigned: U.S. Provisional patent application bearing the serial No. 60/389,973 titled ELECTRO-HYDRAULIC CONTROL UNIT WITH INTEGRAL PRE-CHARGE PUMP, by Reuter, et al; and U.S. Provisional patent application bearing the serial No. 60/439,935, titled CONTROLLED BRAKE SYSTEMS FOR VEHICLES, by Reuter, et al. 
    
    
     
       TECHNICAL FIELD OF THE INVENTION  
       [0002] This invention relates to vehicle brakes, and more particularly to a vehicle with a brake apparatus including both a controlled braking pump for providing brake fluid during controlled braking operation of the vehicle, and a pre-charge pump for augmenting fluid flow to the inlet of the controlled braking pump.  
       BACKGROUND OF THE INVENTION  
       [0003] Since the mid 1930s, vehicles such as automobiles and light trucks have predominantly utilized hydraulic brake systems having a pedal operated master cylinder supplying pressurized hydraulic fluid to disk or drum braking devices at each wheel.  
       [0004] Early hydraulic brake systems utilized a single hydraulic fluid circuit supplying pressurized fluid from the master cylinder to all four comers of the vehicle. A break in the fluid circuit anywhere rendered the entire hydraulic brake system inoperative.  
       [0005] In order to prevent a total loss of hydraulic braking in the event of a failure of part of the system, failsafe hydraulic split brake systems were developed that provided two separate fluid circuits from the master cylinder, configured such that a failure of either of the two fluid circuits would still leave hydraulic brakes operative on at least two corners of the vehicle. In rear wheel drive automobiles and light trucks, one fluid circuit typically served the front wheels, and the other fluid circuit served the rear wheels, to provide a front/rear (F/R) failsafe hydraulic split system. Front wheel drive vehicles typically used a diagonal failsafe hydraulic split system, having one front comer and the diagonally opposite rear comer of the vehicle on one fluid circuit, and the other front corner and its diagonally opposite rear comer on the second fluid circuit. Government stopping distance regulations were passed in regards to failed brake system performance that, in order to comply, required brake systems to be configured such that a single failure of the braking system would still leave the brakes on at least two corners of the vehicle operational.  
       [0006] In the years since hydraulic brake systems became the norm, many additional features have been added to further enhance safe operation and optimize vehicle performance. Modem brake systems often include a booster that amplifies force exerted on the brake pedal, to provide power brakes that allow a person operating the vehicle to control the brakes with significantly less force on the brake pedal than is required in a non-boosted brake system. Anti-lock brake systems (ABS) were developed in which valves controlling fluid flow to each comer of the vehicle were pulsed, in response to signals received from rotation sensors monitoring each wheel, to preclude locking the brakes on slippery road surfaces. Traction control systems (TCS) were added that controlled both the brakes and the engine throttle setting to improve traction and handling of the vehicle during maneuvers, such as acceleration or turning, when the brakes are not being applied by the operator. Vehicle dynamics control (VDC) further advanced the level of sophistication of brake systems to utilize a number of sensors throughout the vehicle, and a more advanced onboard computer with higher throughput, to monitor forces acting on the vehicle, together with inputs indicating operational commands from the operator applied to the steering, braking, and drive systems. VDC analyzes the data received from the sensors and coordinates operation of the various elements of the vehicle brake system, power-train, and suspension to provide enhanced vehicle safety or performance of the vehicle.  
       [0007] The addition of all of these enhancements has made hydraulic brake systems very complex. Numerous valves, sensors, and electronic control components are required. Brake systems offering one or more types of automated control operating modes, such as ABS, TCS and VDC, are known as “controlled braking systems.” 
       [0008] Recent advances in technology have made it feasible to develop a controlled brake system that utilizes electrically actuated brakes, rather than hydraulic brakes, on at least the rear corners of a vehicle. Such brake systems are known as “Hybrid” brake systems. Commonly assigned U.S. patent application Ser. No. 10/121,454, titled Hybrid. Brake System for a Vehicle, by Reuter, et al, describes such a system, and is incorporated herein by reference.  
       [0009] To provide a flow of pressurized brake fluid during controlled braking operation in modes such as TCS and VDC where there is no brake pressure being produced by the master cylinder because the brake pedal is not depressed, controlled braking systems typically include a controlled braking pump driven by an electric motor for recirculating pressurized brake fluid through the controlled braking circuit during one or more of the controlled braking operations. Such controlled braking pumps must also be capable of starting and producing braking pressure m a fraction of a second when the braking system recognizes the need for and initiates a controlled braking operation.  
       [0010] A controlled braking pump must further be an efficient suction-type pump, since fluid must be drawn from the remote master cylinder reservoir and subsequently pumped through extended brake lines to the wheel brake. At low ambient operating temperatures, the brake fluid becomes more viscous and flows through the fluid passages in the brake circuit at a significantly slower rate, making it difficult to get the controlled braking pump primed quickly enough to provide adequate braking pressure during a controlled braking event, such as VDC during a quick swerving maneuver, for example.  
       [0011] Prior controlled braking systems ‘A’, such as the one shown in FIG. 1, have incorporated a pre-charge circuit connected in parallel with the master cylinder, and in series with the hydraulic brake circuit to provide a pressurized flow of brake fluid through the hydraulic brake circuit lines to the inlet of the controlled braking pump under cold ambient operating conditions.  
       [0012] The prior controlled braking system A shown in FIG. 1 includes a master cylinder  12 , as shown in FIG. 2, having a cylinder bore  14 , a fluid reservoir  16  for brake fluid, a bleed port  18  providing fluid communication between the cylinder bore  14  and the fluid reservoir  16 , and a primary piston  20  movable in the bore  14  for closing off the bleed port  18  and generating hydraulic braking pressure in the bore  14 .  
       [0013] A primary hydraulic brake circuit  22 , indicated by dashed lines in FIG. 1, is connected in a series fluid circuit relationship to the bore  14  of the master cylinder  12  for delivering pressurized brake fluid at the braking pressure to an inlet/outlet  24  of a hydraulically actuated braking device  26  and receiving a return flow of brake fluid from an inlet/outlet  24  of the hydraulically actuated braking device  26 . It will be noted that the brake system A shown in FIG. 1 includes a primary hydraulic braking circuit  22  having a number of components for controlling the flow and pressure of brake fluid to both a left and right front braking device LF, RF, and a secondary braking circuit, generally indicated by arrow  28 , for controlling both a left and right rear braking device LR, RR.  
       [0014] Because the components in the primary and secondary braking circuits  22 ,  28  are generally identical, only the components in the primary circuit  22  will be described in detail below. It will also be noted that in the system A shown in FIG. 1 the inlet and outlet to the braking device  26  is indicated by a single line  24 . It should be noted that, although FIG. 1 shows a front/rear split hydraulic system, the same basic circuit arrangement may also be utilized for a diagonal split hydraulic system where, for example, the RF and LR braking devices are connected to the master cylinder primary hydraulic outlet circuit  66  and the LF and RR braking devices are connected to the secondary master cylinder hydraulic outlet circuit  28 .  
       [0015] The primary hydraulic brake circuit  22  includes a normally open inlet control valve  30  and a normally closed outlet control valve  32  for controlling flow in and out of each of the LF and RF braking devices  26 . Each of the control valves  30 ,  32  also has associated therewith a check valve  34  allowing reverse flow, in a direction toward master cylinder  12 , through the check valve  34  when its associated control valve  30 ,  32  is in the closed position. The primary brake circuit also includes an isolation valve  36  and an associated check valve  38 , allowing flow through the check valve  38  in a forward direction, toward the braking device  26 , when the isolation valve  36  is in the closed position. The isolation valve  36  is utilized for regulating or closing off the flow of brake fluid through a portion of the hydraulic brake circuit  22  from the master cylinder  12  during certain controlled braking operations.  
       [0016] A controlled braking pump  40  has an inlet  42  operatively connected through a check valve  46  for receiving brake fluid from the primary hydraulic brake circuit  22 . An accumulator  48  is also connected to both the primary brake circuit and the check valve  46  for storing brake fluid received from the primary brake circuit  22 , and delivering the stored brake fluid through the check valve  46  to the inlet  42  of the controlled braking pump  40 . The controlled braking pump  40  also includes an outlet  44  operatively connected through a damper  50  and an orifice  52  for providing pressurized brake fluid to the hydraulic brake circuit  22  at the braking pressure. The controlled braking pump  40  is driven by a motor  54 .  
       [0017] From the description above, it will be evident that controlled braking systems include a substantial number of components, connected by a number of complex shaped hydraulic conduits or internal passages within the components. At cold operating temperatures, the brake fluid becomes thick and viscous, and it can be difficult for the controlled braking pump  40  to generate enough suction at its inlet to quickly generate an adequate flow of fluid for controlled braking operation. To address this problem, some prior controlled braking systems have included a pre-charge circuit, including a pre-charge pump, to help supply an adequate flow of fluid to the inlet of the controlled braking pump  40  at all operating temperatures, for priming the controlled braking pump  40 .  
       [0018] The prior controlled braking system A, shown in FIG. 1, incorporates a pre-charge circuit, generally indicated by arrow  56 , including a pre-charge pump  58  having an inlet  60  operatively connected to the fluid reservoir  16 , and an outlet  62  operatively connected via an outlet check valve  64  to an inlet portion  66  of the primary hydraulic circuit  22 , with the inlet portion  66  being further connected to bore  14  of the master cylinder  12 . The outlet check valve  64  is required, between pre-charge pump  58  and primary hydraulic brake circuit  22 , to prevent reverse flow of fluid from the primary circuit  22  through the pre-charge pump  58  and pressure relief valve  76 .  
       [0019] As will be seen from FIG. 2, the master cylinder  12  also includes a secondary piston  68  and a secondary bleed port  70  in the bore  14 . The secondary piston  68  is separated axially from the primary piston  20  by a space, indicated by arrow  72 , between the primary and secondary pistons  20 ,  68 . The connections between the outlet  62  of the pre-charge pump  58  and the inlet portion  66  of the primary hydraulic brake circuit  22  are made to the bore  14  in the space  72  between the primary and secondary pistons  20 ,  68 , such that pre-charge pressure generated by the pre-charge pump  58  will be communicated directly to the primary hydraulic brake circuit  22  via the inlet  66 , and indirectly to the secondary hydraulic brake circuit  28  by movement of the secondary piston  68  in the bore caused by the existence of the pre-charge pressure in the space  72  between the primary and secondary pistons  20 ,  68  generating an axially acting force on the secondary piston  68 . Some of the flow from the pre-charge pump  58  is lost though primary bleed orifice  18 , but the pre-charge pump  58  is adequately sized to allow for this loss.  
       [0020] The pre-charge circuit  56  further includes a second motor  74  driving the pre-charge pump  58 , and a pressure relief valve  76  connected between the inlet to the outlet  60 ,  62  of the pre-charge pump  58  for regulating the pre-charge pressure generated by the pre-charge pump  58 .  
       [0021] The pre-charge circuit  56  also includes a prime valve  78 , having an inlet  80  connected to the input  66  of the primary hydraulic brake circuit  22 , and an outlet  82  connected to the inlet  42  of the controlled braking pump  40 , for selectively blocking and allowing a flow of brake fluid through the prime valve  78  between the inlet  66  of the primary hydraulic circuit  22  and the inlet  42  of the controlled braking pump  40 . A check valve  84  allows reverse flow of brake fluid through the check valve  84  when the prime valve  78  is blocking flow.  
       [0022] The brake apparatus A also includes a control circuit  86  including a number of sensors, and a control unit (ECU) for sensing when the brake apparatus A should be operated in a controlled braking mode, and connections to the control elements of the apparatus for controlling these elements during the controlled braking operation.  
       [0023] Prior brake systems of the type described above have several drawbacks. Because the prime valve  78  and its associated check valve  84  are connected to the bore  14  and the inlet  66  to the primary hydraulic circuit  22 , they must be designed to withstand and operate at typical braking pressures of about 2000 pounds per square inch. The need to withstand and operate at maximum braking pressures significantly increases the size, weight and cost of the prime valve  78 .  
       [0024] As shown in FIG. 3, in the past it has been common practice to split the various components of a controlled braking system having a pre-charge circuit  56 , such as the system A shown in FIG. 1, into two packages.  
       [0025] A first grouping of components, known as an electro-hydraulic control unit (EHCU)  200  includes a hydraulic control unit (HCU)  210  and an electronic control unit (ECU)  212  for controlling the HCU  210 . The HCU  210  typically includes a block  214  containing the controlled braking pump  40  and other hydraulic components of the controlled braking system A required for operation of the controlled braking system A in its various operational modes. The motor  54  is attached to the block  214  of the HCU  210 , for driving the controlled braking pump  40 . The EHCU  200  is typically mounted to a body panel in the under-hood area of the vehicle, remotely from the master cylinder  12 , fluid reservoir  16 , and brake booster  216 , wherever there is a sufficient space.  
       [0026] The second grouping of components includes the pre-charge pump  58 , a second motor  74  for driving the pre-charge pump  58 , and sometimes a second block including hydraulic components of the pre-charge circuit, such as the pressure relief valve  76 , and check valve  64 , as shown in FIG. 1. This second grouping of components including the pre-charge pump  58  and its associated motor  74  are typically mounted separately from the EHCU  200 , preferably in close proximity to the fluid reservoir  16  of the master cylinder  12 .  
       [0027] Mounting the pre-charge pump  58 , its drive motor  74 , and associated components of the pre-charge circuit remotely from the EHCU  200 , as illustrated in FIG. 3 is undesirable for a number of reasons. Having the pre-charge pump  58 , together with its associated drive motor  74  and hydraulic components, mounted separately from the EHCU  200  adds a large undesirable volume, on the order of about 500 cubic centimeters to the brake system A, as well as additional weight, complexity and cost. The additional volume consumes valuable space, in under-hood area of the vehicle, which could be more advantageously used for other purposes.  
       [0028] Commonly assigned United States utility patent application, Ser. No. 10/174,601, titled BRAKE SYSTEM FOR A VEHICLE HAVING AN INTEGRAL PRECHARGE PUMP, by Reuter, et al, filed on Jun. 19, 2002, and commonly assigned United States utility patent application, bearing Assignee&#39;s docket number DP-309725, titled BRAKE SYSTEM FOR A VEHICLE HAVING AN INTEGRAL PRECHARGE PUMP AND BACK-FLOW PROTECTION, by Reuter, et al, filed on ______, provide a controlled braking apparatus that resolves a number of the problems with prior controlled braking systems having pre-charge circuits, as described above.  
       [0029] Although controlled braking systems practicing the teachings of Reuter, et al, Ser. No. 10/174,601, and docket number DP-309725 provide considerable improvement over prior controlled braking systems, further improvement is desirable. In particular, it is desirable to provide hardware configurations that further reduce the under-hood volume, weight and component cost for providing a controlled braking system including a pre-charge circuit. It is also desired that the improved brake apparatus be applicable to hybrid as well as conventional totally hydraulic controlled brake systems, and that such an improved brake apparatus be applicable to a wide range of embodiments of controlled braking systems, including braking systems according to Reuter, et al, Ser. No. 10/174,601, and docket number DP-309725.  
       SUMMARY OF THE INVENTION  
       [0030] Our invention provides an improved controlled brake apparatus, meeting the requirements discussed above through use of a hydraulic control unit (HCU) including a controlled braking pump and a pre-charge pump driven by a single motor. The HCU may also include one or more hydraulic components for controlling a flow of hydraulic fluid in the braking apparatus. Combining both the controlled braking pump and pre-charge pump into the HCU and driving them with the same motor considerably reduces under-hood volume of the controlled braking apparatus, in comparison to prior controlled braking systems having pre-charge pumps, where the pre-charge pump was driven by different motor than the controlled braking pump and the pre-charge pump and its drive motor were mounted remotely from the HCU. Our invention may also take the form of an electro-hydraulic control unit EHCU, having an electronic control unit ECU attached to the HCU.  
       [0031] Our invention is applicable to a variety of controlled braking systems including hydraulic, hybrid and electrically actuated braking devices including electro-mechanical and electro-hydraulic brake devices, and may also take the form of a method for operating a controlled braking apparatus including an HCU of the type described herein.  
       [0032] The foregoing and other features and advantages of our invention will become further apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of our invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0033]FIG. 1 is a schematic representation of a prior controlled brake system having a pre-charge pump mounted remotely from the controlled braking pump, and driven by a separate motor from the controlled braking pump;  
     [0034]FIG. 2 is a cross section of a typical master cylinder of the type used in the prior brake system of FIG. 1, and in exemplary embodiments of brake systems, according to our invention, as shown in FIGS.  3 - 10 ;  
     [0035]FIG. 3 is a perspective view of several components of the prior braking system of FIG. 1 showing the manner in which the components were mounted in two groups of components, with the controlled braking pump and a motor for driving the controlled braking pump mounted in an electro-hydraulic control unit (EHCU), and the re-charge pump together with its separate drive motor in a second grouping of components mounted remotely from the EHCU;  
     [0036]FIG. 4 is a perspective view of an EHCU according to our invention, including a controlled braking pump and a pre-charge pump driven by a single motor;  
     [0037]FIG. 5 is a schematic of a first exemplary embodiment of a controlled braking apparatus, according to our invention;  
     [0038]FIGS. 6 and 7 show alternate exemplary embodiments of a hydraulic control unit (HCU) having a controlled braking pump and a pre-charge pump driven by a single motor, for use in the EHCU of FIG. 4 and the controlled braking apparatus of FIG. 5;  
     [0039]FIGS. 8 and 9 are respectively a schematic of an exemplary embodiment of a controlled braking system according to our invention having a pair of controlled braking pumps and a pair of pre-charge pumps all driven by the same motor, and a perspective view of an EHCU, according to our invention, including the pair of controlled braking pumps and a pair of pre-charge pumps all driven by the same motor, together with other hydraulic components, in an HCU.  
     [0040] FIGS.  10 - 12  are respectively a schematic of an exemplary embodiment of a hybrid controlled braking system, according to our invention, a perspective view of an HCU for use in the braking system of FIG. 10, including a controlled braking pump and a pre-charge pump driven by a single motor, together with other hydraulic components, and a cross sectional view taken through the pumps of the HCU of FIG. 11; and  
     [0041] FIGS.  12 - 15  are schematic representations of alternate exemplary embodiments of braking systems incorporating an HCU or EHCU, according to our invention. 
    
    
     DETAILED DESCRIPTION  
     [0042]FIG. 5 shows a first exemplary form of a brake apparatus  10 . FIG. 4 and FIG. 6 show components of the brake apparatus, including an EHCU  200 , having an ECU  212  attached to an HCU  210 , according to our invention. The embodiment depicted in FIGS.  4 - 6  includes many of the same components as the prior apparatus A discussed above with regard to FIGS.  1 - 3 .  
     [0043] To facilitate understanding of our invention, and the distinctions between our invention and prior brake systems, the components in FIGS.  4 - 6  and subsequent FIGS.  7 - 15  that are substantially equivalent or similar to the components described above, in the Background of the Invention, will be given the same reference numbers used in the Background of the Invention. For the sake of brevity, where components bearing similar reference numbers are substantially equivalent or similar in function to the components described in detail above, the description of those components and their functions will not be repeated below. For the sake of clarity, the reference numerals for a particular component may be omitted in a subsequent drawing where that component has been identified in a previous drawing.  
     [0044] The exemplary embodiment of the brake apparatus  10  depicted in FIG. 5, includes a master cylinder  12  similar to the one depicted in FIG. 2, having a cylinder bore  14 , a fluid reservoir  16  for brake fluid, a bleed port  18  providing fluid communication between the cylinder bore  14  and the fluid reservoir  16 , and a primary piston  20  movable in the bore  14  for closing off the bleed port  18  and generating hydraulic braking pressure in the bore  14 .  
     [0045] A primary hydraulic brake circuit  22 , indicated by dashed lines, is connected in a series fluid circuit relationship to the bore  14  of the master cylinder  12  for exchanging pressurized brake fluid at the braking pressure with an inlet/outlet  24  of the hydraulically actuated braking devices  26 . The hydraulically actuated braking devices take the form of front brakes on the front wheels of a vehicle.  
     [0046] The brake apparatus  10  also includes a secondary brake circuit, generally designated by reference numeral and arrow  28 , connected in a series fluid circuit relationship to the bore  14  of the master cylinder  12  for delivering pressurized brake fluid at the braking pressure to the rear front brakes, and for receiving a return flow of brake fluid from the rear brakes. The primary and secondary brake circuits  22 ,  28  are substantially identical. Accordingly, for the sake of brevity the following description will generally be directed to the primary brake circuit  22 .  
     [0047] In both the primary and secondary brake circuits  22 ,  28 , a controlled braking pump  40  has an inlet  42  for receiving brake fluid from the hydraulic brake circuit  22  and an outlet  44  for providing pressurized brake fluid to the hydraulic brake circuit  22  at the braking pressure. A pre-charge circuit  88  including a single pre-charge pump  58  supplies fluid to the inlets  42  of the controlled braking pumps  40  in both the primary and secondary brake circuits  22 ,  28 .  
     [0048] The pre-charge circuit  88  has an inlet  90  operatively connected to the fluid reservoir  16 , and an outlet  92  operatively connected to the inlet  42  of the controlled braking pump  40  in each of the primary and secondary brake circuits  22 ,  28 , to thereby form a pair of parallel circuits to the series circuit formed by the cylinder bore  14  and the hydraulic brake circuit  22  for providing a pre-charge flow of brake fluid to the inlets  42  of the controlled braking pumps  40  at a pre-charge pressure.  
     [0049] The pre-charge circuit  88  includes a back-flow check valve  46  near the inlet  42  of each controlled braking pump  40 , for allowing the pre-charge flow of brake fluid to pass through the back-flow check valve  46  from the fluid reservoir  16  to the inlet  42  of the controlled braking pump  40  and blocking a flow of brake fluid from the inlet  42  of the controlled braking pump  42  to the fluid reservoir  16 . The primary brake circuit  22  of the brake apparatus  19  further includes an accumulator  48  commonly connected in fluid communication with the inlet  42  of the controlled braking pump  40 , the inlet/outlet  24  of the hydraulically actuated braking devices  26 , and the outlet  92  of the pre-charge circuit  88 . The connection to the inlet/outlet  24  of the hydraulically actuated braking devices  26  is provided via an outlet  27  of the primary braking circuit  22  flowing through the series-connected control valve  32 . The secondary brake circuit  28  also includes a similar arrangement of hydraulic components including an accumulator  48 , connected in similar fashion to the inlet/outlet of the rear brakes.  
     [0050] The pre-charge pump  58  has an inlet  60  operatively connected to the fluid reservoir  16 , and an outlet  62  operatively connected to the inlets  42  of the controlled braking pumps  40 . Specifically, the outlet  62  of the pre-charge pump  58  is connected in a series circuit relationship to the inlet  80  of a prime valve  78  in each of the primary and secondary brake circuits, and the outlet  82  of the prime valve  78  is connected in a series circuit relationship through the back-flow check valve  46  to the inlet  42  of the controlled braking pump  40  in that circuit, for selectively blocking or passing a flow of brake fluid through the prime valve  78  in that circuit.  
     [0051] Also in contrast to the prior brake apparatus A shown in FIG. 1, the brake apparatus  10  shown in FIG. 5 includes a single motor  54  operatively connected for driving the controlled braking pumps  40  in both the primary and secondary brake circuits  22 ,  28  and the pre-charge pump  58 .  
     [0052] The pre-charge circuit  88  shown in FIG. 5 further includes a pressure operated relief valve  76  operatively connected from the outlet to the inlet of the pre-charge pump  58 . A bleed orifice  98 , of small diameter, on the order of 0.010 inch, is connected in parallel to the pressure operated relief valve  76  to facilitate bleeding air from the controlled braking system  10  to facilitate filling the braking system  10  with hydraulic brake fluid, utilizing the commonly practiced evacuation and filling techniques employed in many vehicle assembly plants.  
     [0053] The pre-charge circuit  88  further includes a check valve  84  operatively connected from the outlet  82  of the prime valve  78  to the outlet  62  of the pre-charge pump  58  for blocking flow through the check valve  84  from the inlet to the outlet  80 ,  82  of the prime valve  78 , and allowing flow through the check valve  84  from the outlet  82  to the inlet  80  of the prime valve  78 .  
     [0054] As shown in FIG. 4, the controlled braking pumps  40 , and the pre-charge pump  58  are incorporated into a hydraulic control unit (HCU)  210  of an EHCU  200 , and are driven by a single motor  54 , thereby allowing the separate drive motor  74  used for driving the pre-charge pump  58  in the prior controlled braking system A, as shown in FIGS. 1 and 3, to be eliminated, so that no components of the pre-charge circuit need to be mounted remotely from the EHCU  200 .  
     [0055] As shown in FIGS. 4 and 6 the HCU  210  in the first exemplary embodiment thereof includes a block  214 . The controlled braking pumps  40  are mounted within the block  214 , and the pre-charge pump  58  is mounted on an outside surface  218  of the block  214 .  
     [0056] The HCU  210  includes a drive shaft apparatus operatively connected for driving both the pre-charge pump  58  mounted outside of the block  214  and the controlled braking pumps  40  mounted inside of the block  214 . Specifically, in the embodiment of the HCU  210  shown in FIG. 6, the controlled braking pumps  40  are piston pumps driven by an eccentric of self-supported stub shaft  220 , journaled by a pair of bearings  224 ,  226  in the block  214 , and adapted for operative connection to a motor shaft  222  extending from the motor  54 . The motor shaft  222  extends through the pre-charge pump  58  mounted on the outside surface  218  of the block  214  and engages the stub shaft  220  driving the controlled braking pumps  40  mounted inside of the block  214  for driving the controlled braking pumps  40 . The motor-shaft  222  is journaled within the pre-charge pump  58  on a pair of bearings  228 ,  230 .  
     [0057] In the embodiment of FIG. 6, the controlled braking pumps  40 , and the pre-charge pump  58  are piston pumps driven by eccentrics on the stub shaft  220  and the motor shaft  22  respectively. The pre-charge pump  58  includes a pair of opposed pistons  58   a,    58   b,  connected together by porting within the body of the pump  58  and/or the block  214  in a single stage parallel pumping arrangement, or alternatively in a two stage series pumping arrangement, for supplying fluid from a common outlet  62 , shown in FIG. 5, of the pre-charge pump  58  to the controlled braking pumps  40  in both the primary and secondary circuits  22 ,  28 .  
     [0058] It will be understood by those skilled in the art that either or both of the controlled braking pump  40 , and a pre-charge pump  58  according to our invention may utilize other types of pumping mechanisms, such as gerotor pump, a gear pump, vane pump, etc. It will also be understood that the relative positions of the controlled braking pump  40 , and the pre-charge pump  58  could be reversed in other embodiments, with pre-charge pump  58  being mounted within the block  214 , and the controlled braking pump  40  being mounted on the outside surface  218  of the block  214 . It will be further understood that the motor  54  may be mounted directly on the outer surface  218  of the HCU  210  and engage the stub shaft  222  for driving whichever pump  40 ,  58  is mounted inside of the block  214 , and the other of the pumps  40 ,  58  may be mounted on a second outside surface  219  of the block  214  opposite the surface  218  to which the motor  54  is mounted, with the stub shaft  22  extending out of the block  214  through the second outside surface  219  of the block  214  for engaging and driving whichever pump  40 ,  58  is mounted on the second surface  119  of the block  214 .  
     [0059]FIG. 7 shows an embodiment of an HCU  210  having a pair of controlled braking pumps  40 , and a pre-charge pump  58  mounted within the block  214  and driven by a stub shaft  232 , journaled within the block by a pair of bearings  234 ,  236 . A quill shaft  238  operatively connects the stub shaft  232  to the shaft  222  of the motor  54 , which is mounted on the outer surface  218  of the block  214 . This embodiment provides several advantages over the embodiment shown in FIG. 6, in that the number of bearings  234 ,  236  is reduced from four to two, and there are fewer seals required. It will be noted that the pre-charge pump  58  in this configuration could also have been housed in a separate pump housing mounted on the second side  219  of the block  214 . Furthermore, although the embodiment of FIG. 7 is shown with the controlled braking pumps  40  as eccentric driven piston pumps, and the pre-charge pump  58  as a gerotor pump, other types of pumping devices could be used for the pumps  40 ,  58  in other embodiments.  
     [0060]FIG. 8 shows an alternate exemplary embodiment of a brake apparatus  10 , according to our invention, having a second pre-charge circuit  94  connected between the fluid reservoir  16  and the inlet  96  of the controlled braking pump  40  of the secondary hydraulic braking circuit  28 , in-such a manner that the primary brake circuit  22  as shown in FIG. 5, and the secondary brake circuit  28  each have their own pre-charge circuits  88 ,  94 . The second pre-charge circuit  94  is identical in all other respects to the pre-charge circuit  88  described above. The second pre-charge circuit also includes a second pre-charge pump  58  driven by the same motor  54  used for driving the controlled braking pumps  40  in the primary and secondary braking circuits  22 ,  28 . An HCU  210 , as shown in FIG. 6, having two pairs of opposed piston pumps, may be used in the brake apparatus  10  of FIG. 8. The pair of piston pumps  40  mounted within the block  214 , can be connected individually to the primary and secondary brake circuits  22 ,  28 , to function as controlled braking pumps  40 , and a second pair of piston pumps  58  mounted on the outer surface  218  of the block  214 , which may be connected individually to the first and second pre-charge circuits  88 ,  94 , to function as the pre-charge pumps  58  for those circuits  88 ,  94 .  
     [0061]FIG. 9 shows an exemplary embodiment of an EHCU  200  that may be used with a braking apparatus  10 , such as the one shown in FIG. 8, having a pair of controlled braking pumps  40  and a pair of pre-charge pumps  58 , all driven by a single motor  54 . The EHCU of FIG. 9 includes an HCU  210 , having a first pair of opposed piston pumps  40  mounted within the block  214 , and a second pair of opposed piston pumps  58  mounted in a pre-charge pump housing  240 , attached to the outer surface  218  of the block  214 , and driven by a single motor  54  in the manner shown in FIG. 6. Only the pump shown in the second pre-charge circuit  28  is labeled in FIG. 8.  
     [0062] The HCU  210  of FIG. 9 also includes a number of the hydraulic components shown in FIG. 5 and FIG. 8 for controlling the flow of fluid in the controlled braking apparatus  10 . Mounted in the block  214  are a number of solenoid-operated valves, including four apply valves  30 , four release valves  32 , two prime valves  36 , two isolation valves  78 . The armatures  242  (only 2 of 12 of which are labeled in FIG. 9) for the solenoids that actuate these valves  30 ,  32 ,  36 ,  78  extend outward from the second surface  119  of the block  214  of the HCU  210 . The two inlet accumulators  48  for the primary and secondary circuits  22 ,  28  also extend outward from the second surface  219  of the block  214 . Inside of the block  210  are internal passages interconnecting the valves  30 ,  32 ,  36 ,  78 , the accumulators  48  and many other hydraulic components housed within bores internal to the HCU  210 , including relief valves, orifices, check valves, and dampers. The check valves  34 ,  38 ,  84  across the solenoid operated valves  30 ,  32 ,  36 ,  78  may either be stand alone devices, or be provided by one-way lip seals in the valves  30 ,  32 ,  36 ,  78  as is known in the art. Mounted on the outside surface  218  of the block  214  is a sensor package  244 , connected through ports opening toward the outside surface  218  of the block  214  to the internal passages in the block  214 .  
     [0063] An ECU  212  is mounted on the second face  219  of the block  214  of the HCU  210 , to form the EHCU  200 . The ECU includes 12 electrical coils (not shown), one surrounding the armature  242  of each solenoid actuated valve  30 ,  32 ,  36 ,  78 . The coils are selectively actuated by control electronics within the ECU  212  for opening and closing the solenoid actuated valves  30 ,  32 ,  36 ,  78 .  
     [0064]FIG. 10 shows a hybrid brake apparatus  10  according to our invention, having front hydraulic brakes LF, RF, and electrically actuated rear brakes LR, RR. The hybrid brake apparatus  10  includes a pre-charge circuit  88  as described above, with the motor  54  driving both the controlled braking pump  40  and the pre-charge pump  58 . The secondary hydraulic circuit  28  includes a pedal-feel emulator  100  and a pressure sensor  102  operatively connected to receive pressurized brake fluid from the secondary piston  68  of the master cylinder  12 .  
     [0065] As shown in FIG. 2, the master cylinder  12  in the exemplary embodiment of the brake system  10  shown in FIG. 9, includes a secondary piston  68  in the cylinder bore  14 , separated from the first piston  20  to form a primary fluid cavity  72  in the bore  14  between the primary and secondary pistons  20 ,  68 . The primary fluid cavity is connected in fluid communication through a primary port  13  of the master cylinder  12  to the hydraulic brake circuit  22 . The master cylinder  12  also includes a secondary fluid cavity  73  between the second piston  68  and the bore  14 , and connected to a secondary fluid port  15  of the master cylinder  12 .  
     [0066] A brake pedal feel emulator  100 , according to the present invention, has a first and a second fluid cavity  104 ,  106  on opposite sides of a movable wall  108 . The first fluid cavity  104  of the pedal feel emulator  100  is connected in fluid communication to the secondary fluid cavity  73  of the master cylinder  12 , through the secondary fluid port  15  of the master cylinder  12 . The second fluid cavity  106  of the pedal feel emulator  100  is connected in fluid communication to the primary fluid cavity  72  of the master cylinder  12 , through the primary fluid port  13  of the master cylinder  12 . By virtue of adding the second fluid cavity  106  in the pedal feel emulator  100  of the present invention, connected in fluid communication with the primary fluid cavity  72  of the master cylinder  12 , as shown in FIG. 5, the pressure existing in the primary cavity  72  of the master cylinder is applied directly to the back side of the movable wall  108 , and indirectly to the front side (first fluid cavity  104 ) of the pedal feel emulator  100 , to thereby provide a hydraulic lock against movement of the movable wall  108  of the pedal feel emulator  100  until hydraulic pressure is lost in the primary fluid cavity  72  of the master cylinder  12 . Thus, when the primary circuit is functional, there are no additional travel losses occurring-from the pedal feel emulator  108 .  
     [0067] Once pressure in the primary cavity  72  is lost, the pressure on the back side of the movable wall  108  of the pedal feel emulator  100  will drop to atmospheric pressure, and the primary piston  20  will move forward under pedal pressure to a lower pedal position, whereas the primary piston  20  will bear against the secondary piston  68 . Further pedal movement will then move the secondary piston  68  in the bore  14  to expel fluid from the secondary fluid cavity  73  of the master cylinder  12  into the pedal feel emulator  100 . A spring mechanism  110  in the pedal feel emulator  100  resists movement of the movable wall  108  of the pedal feel emulator  100 , to simulate normal pedal feel to the operator, albeit at a lower pedal height than normal.  
     [0068] An HCU  210 , as shown in FIGS. 11 and 12, may be used in the brake apparatus  10  of FIG. 10. The HCU  210  of FIGS. 11 and 12 includes a first and a second piston pump  40 ,  58  mounted within the block  214  and driven by a single motor  54 , which may be connected individually, one to the primary brake circuits  22 , to function as the controlled braking pump  40 , and the other to the pre-charge circuit  88 . The HCU  210  of FIG. 11 also includes a number of the hydraulic components shown in the system of FIG. 10, including two apply valves  30 , two release valves  32 , a prime valve  78 , an isolation valve  36 , and a pedal feel emulator  100 .  
     [0069] FIGS.  13 - 15  illustrate several more embodiments of controlled braking systems  10  in which the controlled braking pumps  40  and pre-charge pumps  58 , driven by a single motor  54 , together with hydraulic components for controlling the brake apparatus  10 , can be combined into an HCU  210  or an EHCU  200 , according to our invention, in the embodiments shown in FIGS. 4, 6,  7 ,  9 ,  11  or  12 , or in other configurations not specifically disclosed herein but within our contemplation and the scope of the appended claims.  
     [0070]FIG. 13 shows an embodiment of a brake apparatus  10 , according to our invention, having a pre-charge pump  58  driven by a common motor  54  with a pair of controlled braking pumps  40 , in the same manner as described above with regard to the embodiment of FIG. 5, but having the outlet  62  of the pre-charge pump and the inlet  80  of a prime valve  78  connected to the inlet  66  of only the primary hydraulic brake circuit  22  and bore  14 , as described above in relation to FIG. 1. An outlet check-valve  64  is located between pre-charge pump  58  and primary hydraulic brake circuit  22  to prevent reverse flow of fluid from the primary circuit  22  through the pre-charge pump  58  and pressure relief valve  76 . An HCU  210  or an EHCU  200  as shown in FIGS.  4 , and  6 - 7  can be used with the brake apparatus of FIG. 13.  
     [0071]FIG. 14 shows an embodiment of our brake apparatus  10  that is similar to the embodiment in FIG. 8, but having a second pre-charge pump  58  and a second prime valve  78  connected in the same manner as the first pre-charge pump and prime valve  58 ,  78  described above with respect to FIG. 8, and both pre-charge pumps  58  being driven in common by motor  54  with two controlled braking pumps  40 . An outlet check valve  64  is located between each pre-charge pump  58  and its respective hydraulic brake circuit  22 ,  28  to prevent reverse flow of fluid from either the primary or secondary circuit  22 ,  28  through the pre-charge pump  58  and pressure relief valve  76  serving that circuit  22 ,  28 . An HCU  210  or an EHCU  200  as shown in FIGS. 8 and 9 can be used with the brake apparatus of FIG. 14.  
     [0072] Those having skill in the art will recognize that, while we presently consider it preferable to have the components according to our invention arranged as described above, we contemplate many other arrangements within the scope of our invention.  
     [0073] For example, FIG. 15 shows an embodiment of our invention in a hybrid brake system having the pre-charge circuit in series with the primary brake circuit, in a manner similar to the embodiment shown in FIG. 1, but having a pedal feel emulator  100  and an HCU  210 , according to the present invention, as described above with regard to FIGS.  10 - 12 . FIG. 15 shows a hybrid brake apparatus  10 , according to our invention having a pre-charge pump  58  and a controlled braking pump  40  both driven by a common motor  54 , as described above in relation to FIGS.  10 - 12 , but having the output  62  of the pre-charge pump  58  and the inlet  80  of a prime valve  78  connected to the inlet  66  of the hydraulic brake circuit  22  and bore  14 , as described above in relation to FIGS. 1 and 2.  
     [0074] Those skilled in the art will recognize that any embodiment of an HCU according to our invention may include one or more components for controlling the brake apparatus, in the same manner as is specifically disclosed for the HCU of FIG. 9 and FIG. 11.  
     [0075] We also contemplate that the hydraulic locking method and apparatus of our invention, as disclosed above with regard to the embodiments shown in FIGS. 10 and 15, may be utilized for locking a pedal feel emulator against movement until hydraulic pressure is lost in the primary brake circuit in all hydraulic or other types of brake systems that may or may not include a pre-charge circuit.  
     [0076] In summary therefore, while the embodiments of our invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes or modifications within the meaning and range of equivalents are intended to be embraced therein.