Abstract:
Master cylinder pressure of either or both of the primary and secondary braking circuits is sensed by a pressure sensor or sensors mounted in a manifold which is installed directly on a brake pressure modulator housing when the modulator is manufactured. The pressure sensors receive power and are grounded through the electronic control unit which is an integral component of the modulator; accordingly, the sensors do not require external electrical connections other than those already provided on the modulator. Since the sensing manifold is installed and tested for leaks when the modulator is manufactured and before the modulator is shipped to the vehicle assembly plant, assembly operations in addition to those required in installation of the modulator in the vehicle braking system are not required.

Description:
TECHNICAL FIELD 
     This invention relates to a brake pressure modulator having a pressure sensing manifold for sensing master cylinder braking pressure. 
     BACKGROUND OF THE INVENTION 
     Modern passenger cars and light trucks are equipped with split circuit hydraulic brakes in which the vehicle operator generates braking pressure in primary and secondary braking circuits by operating a brake pedal connected to a master cylinder (usually through a booster that amplifies the force applied by the vehicle operator). More recently, vehicles have commonly been equipped antilock braking systems (ABS), traction control systems (TCS), and vehicle stability control (VSC). Adaptive cruise control (ACC) and panic brake assist (PBA) systems have also been proposed. All of these systems require a brake pressure modulator connected in the primary and secondary braking circuits to control braking pressure communicated to the vehicle brakes. The modulator is equipped with an electronic control unit (ECU), which generates electronic control signals controlling the braking pressure. Commonly, actual master cylinder braking pressure in the primary and secondary master cylinder braking circuits is not sensed. However, it is desirable that the actual braking pressure being developed at the master cylinder be sensed and used by the ECU to control braking pressure. 
     However, direct sensing of braking pressures has associated cost and reliability considerations. For example, such sensors require separate fluid connections in the braking system, thus creating potential leakage points; require extra assembly operations when the vehicle is manufactured, since the pressure sensor must be installed separately; and require an additional external power connection as well as connections transmitting the signal or signals representing braking pressure. It has also been proposed that pressure sensors be mounted directly on or in the master cylinder itself, but such sensing would still require additional external electrical connections. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a pressure sensor or sensors are mounted in a manifold which is installed directly on the modulator housing when the modulator is manufactured. The pressure sensors receive power and are grounded through the electronic control unit which is an integral component of the modulator; accordingly, the sensors do not require external electrical connections other than those already provided on the modulator. Since the sensing manifold is installed and tested for leaks when the modulator is manufactured and before the modulator is shipped to the vehicle assembly plant, assembly operations in addition to those required in installation of the modulator in the vehicle braking system are not required. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view in perspective of a brake pressure modulator with a pressure sensing manifold made pursuant to the teachings of the present invention; and 
     FIG. 2 is an exploded view in perspective of the modulator shown in FIG. 1, with portions shown in cross section or cut away to show internal components. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, a brake pressure modulator assembly generally indicated by the numeral  10  includes a modulator housing generally indicated by the numeral  12  having a pair of inlet ports  14 ,  16  connected to the primary and secondary master cylinder braking circuits when the modulator assembly  10  is installed on an automotive vehicle and four outlet ports  18 ,  20 ,  22  and  24 . Each of the outlet ports  18 - 24  is connected to a corresponding one of the vehicle brakes when the modulator assembly  10  is installed on the vehicle for communication of braking pressure to the brakes when a brake application is effected, in a manner well known to those skilled in the art. An electronic control unit generally indicated by the numeral  26  includes a housing  28  mounted on surface  30  of modulator housing  12 . Within the housing  28  is mounted circuit mounting structure such as a circuit board  32  (FIG.  2 ), which mounts conventional electronic components, such as one or more microprocessors, which generate control signals in response to wheel speed signals generated by wheel speed sensors (not shown). The wheel speed signals vary in accordance with the wheel speed of the corresponding vehicle wheel. The wheel speed signals are transmitted to the electronic control unit  26  through a socket  34  mounted on the housing  28 , which receives a plug (not shown) connected to wiring connected to the aforementioned speed sensors at each of the vehicle wheels. The plug and socket  34  also transmit electrical power to electrical control unit  26 , and also include a conductor providing grounding. 
     Within the modulator housing  12  are multiple solenoid valves, a pump, and other fluid control components that respond to the electrical signals generated by the electronic control unit  26  in response to incipient skidding conditions of the vehicle wheels. The electronic control unit  26 , and the various solenoid valve, pump, and other components within the housing  12  are conventional and will not be described in detail herein. The pump mounted within the housing  12  is powered by an electric motor (not shown), which is housed within electric motor housing  36  mounted on surface  38  of the modulator housing  12 , which is opposite the surface  30 . Signals generated by the electronic control unit  26  are transmitted to the corresponding electrically responsive components, such as solenoid valves, through internal electrical circuitry. Power to operate the pump within the pump housing is common with the power supplied through the socket  34  to power the electronic control unit  26 . 
     Also mounted on the upper surface  38  of the modulator housing  12  is a pressure sensing manifold generally indicated by the numeral  40 . It will be noted that the pressure sensing manifold  40  extends around a segment of the motor housing  36  and is wholly within the volume defined between the motor housing  36  and an existing mounting bracket  42 . Accordingly, addition of the pressure sensing manifold  40  does not change the overall package size of the modulator  10 , so that packaging and installation of the modulator  10  on a vehicle is not affected. The manifold  40  includes a housing  44  which extends over apertures  46 , 48  in the surface  38 . Each of the apertures  46 , 48  terminates a corresponding one of fluid passages  50 , 52  within the modulator housing  12 , which communicate with a corresponding one of the inlet ports  14 ,  16 . Each of these passages  50 , 52  accordingly communicate the pressure levels in the primary and secondary master cylinder circuits at all times. These passages are also communicated to the solenoid valves and other fluid control components within the modulator housing  12 , but, as discussed above, these passages  50  and  52  are isolated from the brake pressure build and decay cycles during antilock operation of the modulator  10  and hence the pressure level at the apertures  46 , 48  is representative of master cylinder pressure at all times. 
     Mounted within the housing  44  is a circuit board, flex circuit, or equivalent structure generally indicated by the numeral  54 . Mounted on the circuit board  54  are a pair of coin-shaped pressure sensors  56 , 58 . The spacing between the pressure sensors  56 , 58  is such that the pressure sensors will register with the apertures  46 , 48  when the manifold  40  is installed on the housing  12 . The pressure sensors  56 , 58  may be of the piezo-resistive, strain gauge, ceramic capacitive, or any other pressure sensor well known to those skilled in the art. The pressure sensors  56 , 58  generate an electrical signal which varies in accordance with the pressure sensed. Power and grounding are provided to the pressure sensor  56 , 58 , through the circuit board  54 , and the signal generated by the pressure sensors  56 , 58  is also transmitted through the conductors within the circuit board. 
     An electrical connecting member generally indicated by the numeral  60  is mounted on the circuit board  54  and extends downwardly therefrom, viewing FIG.  2 . The electrical connecting member  60  contains at least four conductors, two of which provide conditioned power and grounding to the circuit board  54  (and, therefore, to the pressure sensors  56 , 58 ), and two of which transmit the signals representing pressure sensed by the pressure sensors  56 , 58 . The connecting member  60  extends through bore  62  in modulator housing  12 , which extends all of the way through the modulator housing  12  between the surfaces  38  and  30 . The length of the connecting member  60  is such that it extends all of the way through the modulator housing  12  with the end of the member  60  opposite the end connected to circuit board  54  being received within the housing  28  of electrical control unit  26 . The member  60  terminates in a plug  64  which plugs into a socket  66  provided on circuit board  32  mounted within the housing  28  of electrical control unit  26 . Accordingly, power and grounding are supplied to the sensors  56  and  58  through the electronic control unit  26 , and the signals representing master cylinder pressure sensed by the sensors  56 , 58  are transmitted back to the electronic control unit  26 , which processes the signals along with the signals representing wheel speed to control the electrically responsive components within the modulator housing  12 . 
     Fasteners  68  secure the manifold  40  to the surface  38  of the modulator housing  12 . The fasteners  68  each extend through corresponding apertures  70  in the housing  44 , through corresponding apertures  72  in a plate  74 , which is clamped between the housing  44  and the surface  38  when the manifold  40  is installed on the modulator housing  12 , and into corresponding bores  76  in the modulator housing  12  to secure the manifold  44  to the modulator housing  12 . The plate  74  further includes a pair of apertures  78 , 80  which are spaced to register with the apertures  46 , 48  and with the pressure sensors  56 , 58  when the manifold  40  is installed on the modulator housing  12 . Each of the apertures  78 , 80  are provided with a pair of circumferentially extending seals  82 , 84  which seal against the surface  38  and the pressure sensors  56 , 58  to provide a fluid tight connection between the manifold and the modulator housing  12 . 
     It will be noted that in some applications of the modulator  10  the pressure sensing capabilities of the present invention are not necessary. In that event, the manifold  40  is omitted, and the apertures  46 , 48  and bore  62  are plugged. Accordingly, modulators both with and without pressure sensing abilities can be manufactured using the same tooling and equipment. Furthermore, power and grounding is provided to the manifold  40  through the electronic control unit  26  and the pressure signals are also processed by the electronic control unit  26 ; accordingly, a separate electrical connection for the pressure sensor is not required. The manifold is installed and tested for leaks when the modulator  10  is manufactured; accordingly, separate assembly operations involving fluid connections are not required at the vehicle assembly plant. 
     Although the invention has been described with regard to sensing pressures in both the primary and secondary master cylinder pressure circuits, it will be noted that in many cases it is acceptable to sense only a single pressure (usually, the pressure in the primary circuit). In this case, only one of the pressure sensors  56 , 58  is provided, and the corresponding one of the apertures  46  or  48  is either omitted or plugged.