Patent Publication Number: US-2003234052-A1

Title: Hydraulic contol unit

Description:
TECHNICAL FIELD  
       [0001] This invention relates generally to braking systems for motor vehicles, and relates more particularly to a hydraulic control unit for an anti-lock braking system of a motor vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002] Antilock brake systems (“ABS”) are hydraulic braking systems for motor vehicles. A typical ABS system senses when the wheels on a vehicle begin to lock up during braking, and modulates at a relatively high rate hydraulic pressure at the affected wheel brake(s). The high rate of braking cycles creates a certain degree of vibration and corresponding noise in the ABS assembly, which can intrude into the passenger compartment of the vehicle. Such vibration and noise may be objectionable to the passengers in the vehicle.  
       [0003] A vehicle braking system typically includes a number of devices that cooperate to control fluid pressure in the vehicular braking system, and in particular within the anti-lock braking system. One such device is a hydraulic control unit. An ABS hydraulic unit normally includes positive displacement pumps that may weep a small amount of brake fluid during operation. This residual fluid must be routed away from any nearby electrical components, and is typically vented outside the ABS hydraulic assembly.  
       SUMMARY OF THE INVENTION  
       [0004] This invention is a grommet for a bore in a hydraulic modulator. The grommet comprises a plurality of ribs disposed about a periphery of the grommet, and a lip seal extending between the ribs. The ribs are adapted to engage the bore, and the lip seal is adapted to engage the bore at an interface to prevent passage of fluid in one direction past the interface.  
       [0005] Accordingly, it is an object of the present invention to provide a grommet of the type described above that allows fluid weeping from the reciprocating piston pump assemblies within the brake control unit to be released outside the unit, while maintaining an external environmental seal.  
       [0006] Another object of the present invention is to provide a hydraulic control unit that includes an isolated mounting interface to the vehicle.  
       [0007] Still another object of the present invention is to provide an isolation boot for the terminals of a motor for the hydraulic modulator.  
       [0008] The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 is a side view of an electro-hydraulic control unit for the braking system of a motor vehicle;  
     [0010]FIG. 2 is a perspective view of one embodiment of a grommet for use with the electro-hydraulic control unit;  
     [0011]FIG. 3 is a cross-sectional view of the grommet;  
     [0012]FIG. 4 is a perspective view of a motor terminal boot for use with the electrohydraulic control unit;  
     [0013]FIG. 5 is a cross-sectional view of the motor terminal boot; and  
     [0014]FIG. 6 is a cross-sectional view a portion of the electro-hydraulic control unit and another embodiment of the motor terminal boot. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS  
     [0015]FIG. 1 shows an electro-hydraulic control unit (EHCU)  10  including an electrical control unit (ECU)  12  and a hydraulic modulator  14 . As is well known, the ECU  12  normally contains the electronic components, and the hydraulic modulator  14  normally contains the hydraulic components, for modulating fluid pressure in the braking system of a motor vehicle. The hydraulic modulator  14  includes a motor  16  that powers a reciprocating piston pump (not shown). The pump in turn develops fluid pressure to return fluid to a vehicle master cylinder, or to generate a braking force at the wheels of the motor vehicle.  
     [0016] The motor  16  extends into a cavity in the hydraulic modulator  14 . An egress path for hydraulic fluid that may accumulate in the cavity is provided through a vertically oriented, generally orthogonal drainage hole  20  that originates at a pump bore/motor cavity in the hydraulic modulator. The drainage hole  20  passes through a motor terminal bore  42  that facilitates the connection of the terminals of the motor  16  to the ECU  12 , and opens into a larger diameter bore  22  machined into the body of the hydraulic modulator  14 . A grommet  24  is disposed into the bore  22 .  
     [0017]FIGS. 2 and 3 show the grommet  24  in greater detail. The grommet  24  includes a plurality of extruded ribs  26  disposed about its periphery, and a lip seal  32  extending between each pair of ribs. The grommet  24  also includes a central bore  34  which is adapted to accept a solid peg or other mounting member for mounting the modulator  14  to the vehicle. Because the modulator  14  develops some vibrations in operation, the grommet  24  is preferably formed of an elastomer such as rubber to facilitate the isolation of these vibrations.  
     [0018] The grommet  24  is inserted tapered end first into the bore  22 . The ribs  26 , preferably three of which are equally spaced around the outside of the grommet, ensure consistent location of the grommet  24  with the inside diameter of the bore  22 . The insertion of the ribs  26  within the bore  22  also radially compresses the grommet  24 , and in particular a plurality of open areas  36  and  38  extending from opposite faces of the grommet, to facilitate tuning of the vibrational damping. When in place, the tapered shape of the lip seal  32  around the periphery of the grommet  24  essentially functions as a check valve to prevent entry of external environmental debris, while allowing any excess brake fluid from the pump assemblies traversing down through the drain hole  20  to pass the lip seal and exit out of the bottom of the modulator  14 .  
     [0019] Referring again to FIG. 1, the EHCU  10  also includes a boot  40  for the terminals electrically connecting the ECU  12  with the motor  16 . The motor terminal boot  40  is closely disposed in the orthogonally drilled bore  42  in the modulator body, and extends between the underside of the motor  16  and a location proximate the underside of the ECU  12 . Residual brake fluid may also accumulate in the motor terminal bore  42 . To accommodate this, the motor terminal boot  40  is configured to prevent brake fluid from traveling into the motor  16 , as well as to prevent fluid from traveling into the ECU  12 .  
     [0020]FIGS. 4 and 5 show the motor terminal boot  40  in greater detail. The motor terminal boot  40  is generally cylindrical, and includes a tapered end  44  and an opposite, motor-side end  46 . The tapered end  44  has a lip seal  48  to prevent any fluid in the terminal bore  42  from entering the ECU  12 , while at the same time allowing the ECU to vent back through the lip during any high temperature excursions. The end  46  of the motor terminal boot includes an enlarged diameter region  50  that may either be wedged into the terminal bore  42 , or disposed against a shoulder  52  in the modulator body as shown in FIG. 1. In the latter case, the enlarged region  50  may be flattened to more effectively abut against the shoulder  52 . In either case, any residual brake fluid that accumulates in the motor terminal bore  42  and outside the boot  40  may travel down the vertical drill  20  and out through the grommet  24 , as discussed above.  
     [0021]FIG. 6 shows an alternative embodiment  60  of the motor terminal boot. The motor terminal boot  60  is stepped to include separate face seals  62  and  64 . To accommodate the shape of the motor terminal boot  60 , the terminal bore  42 ′ is correspondingly stepped to include sections  66 ,  68  and  70 . Upon installation, the larger outside diameter face seal  62  is compressed between the motor  16  and a shoulder  72  extending between the sections  66  and  68 . This compressive force ensures that the smaller outside diameter face seal  64  remains viable at a shoulder  74  extending between the sections  68  and  70  for protection of the ECU  12 . As with the motor terminal boot  40 , any residual brake fluid that accumulates in the motor terminal bore  42 ′ and outside the double-faced motor terminal boot  60  may travel down the vertical drill  20  and out through the grommet  24 .  
     [0022] While the embodiments of the 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 that come within the meaning and range of equivalents are intended to be embraced therein.