Abstract:
A master cylinder assembly for controlling a motor vehicle clutch including switches for controlling functions such as enabling the starter motor, disabling the cruise control, or signaling the engine computer. The assembly includes an annular seal disposed in an internal groove in the wall of the cylinder sealingly engaging the piston of the cylinder and dividing the cylinder into a pressurized chamber on one side of the seal and an unpressurized chamber open to atmosphere on the other side of the seal. The plurality of axially spaced pairs of contacts are provided on the inner wall of the cylinder in the unpressurized chamber for coaction with an annular contact carried by a flange structure defined by the piston so that as the piston moves axially within the cylinder in response to depression of the clutch the annular contact on the piston successively closes circuits associated with the successive spaced pairs of contacts on the inner wall of the cylinder whereby to successively enable or disable motor vehicle control devices associated with the pairs of cylinder contacts.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to hydraulic master cylinder assemblies and more particularly to a hydraulic master cylinder assembly incorporating switching functions. 
     It has become general practice in the automobile industry to interlock the operation of the engine starter motor with other controls of the motor vehicle such that the starter motor is rendered inoperative unless the transmission is in neutral or park in motor vehicles provided with an automatic transmission or, in motor vehicles provided with a foot operated clutch and a manually operated gear shift transmission, unless the transmission is in neutral and/or the clutch pedal is fully depressed to fully release the clutch. In addition, it is convenient in a motor vehicle provided with a cruise control and a mechanical clutch to shut off the operation of the cruise control upon, for example, downshifting which in turn requires release of the clutch. Specifically, it is necessary that the cruise control be disconnected even before the clutch is fully released to enable the driver to cut out the cruise control by a slight foot tap on the clutch pedal. It is also desirable, upon clutch disengagement, to generate a signal for transmission to the engine computer indicating that the torque path is going to be disengaged so that the computer may take appropriate action such as shutting down the fuel injection or reducing the fuel injection. 
     Many arrangements have been provided for providing switching functions in association with the master cylinder assembly to accomplish the various desired switching operations as the clutch pedal is depressed. Examples of such switches are shown for example in U.S. Pat. Nos. 4,878,041; 4,719,444; 4,742,193; 4,649,238; and 5,343,005. The switch devices shown in these prior art patents are all of the type in which the switch mounts on the push rod of the master cylinder assembly and in which the switch includes a plurality of axially spaced switches which can be sequentially actuated in response to depression of the clutch to generate a sequential series of control signals with respect to cruise control, starter interlock, fuel injection control, etc. Whereas these prior art switches have proven to be generally satisfactory, generating the required control signals in response to depression of the clutch, the use of a separate switch module on the push rod of the master cylinder adds significantly to the overall cost and complexity of the master cylinder assembly and the sequential arrangement of the various switches along the length of the switch module results in a relatively long switch assembly which is incapatible with the relatively short push rods that are found in many present day motor vehicles. 
     SUMMARY OF THE INVENTION 
     This invention is directed to the provision of an improved switching arrangement for a master cylinder assembly. 
     More specifically, this invention is directed to the provision of a master cylinder assembly in which the switching functions are provided integral with the master cylinder assembly. 
     The invention is applicable to a pressure cylinder apparatus of the type including a hydraulic cylinder structure having a cylindrical wall defining a generally closed left end and a generally open right end; a piston movable axially within the hollow of the cylinder structure; a seal structure between the piston and the cylinder structure defining a fluid pressure chamber within the cylinder on the left side of the piston and an unpressurized chamber on the right side of the piston; a fluid pressure fitting communicating with the pressure chamber for connection to a fluid pressure conduit communicating with a coacting fluid pressure device; and a piston rod extending through the open end of the cylinder and into the unpressurized chamber for connection to the right side of the piston. 
     According to the invention, a contact is carried by the piston at a location on the piston to the right of the seal structure and within the unpressurized chamber; a contact is disposed at an interior surface of the cylinder within the unpressurized chamber for selective coaction with the piston contact in response to axial movement of the piston in the hollow of the cylinder; and an electrical lead is connected to one of the contacts and extends to a location external to the cylinder for providing an electrical control signal generated in response to closing of the cylinder contact by the piston contact. This switching arrangement provides a switching function required in association with a typical pressure cylinder apparatus while reducing the overall cost and complexity of the total pressure cylinder apparatus and minimizing the overall size of the total pressure cylinder apparatus. 
     According to a further feature of the invention, a plurality of axially spaced contacts are disposed at the interior surface of the cylinder within the unpressurized chamber for selective coaction with the piston contact in response to axial movement of the piston in the hollow of the cylinder, and a plurality of electrical leads are connected to the respective cylinder contacts and extend to locations external to the cylinder for providing respective electrical control signals generated in response to selective closing of the cylinder contacts by the piston contact. This switching arrangement provides all of the switching functions required in association with a typical pressure cylinder apparatus while reducing the overall cost and complexity of the total pressure cylinder apparatus and minimizing the overall size of the total pressure cylinder apparatus. 
     According to a further feature of the invention, the seal structure comprises an annular elastomeric seal positioned in an annular groove provided in the interior surface of the cylinder and arranged for wiping engagement with an exterior surface of the piston as the piston moves axially in the cylinder. This arrangement maximizes the length of the unpressurized chamber in which the cylinder contacts are disposed. 
     According to a further feature of the invention, the cylinder is a compound structure constituted by a left cylinder structure defining the pressure chamber and a right cylinder structure coupled to the left cylinder structure and carrying the plurality of axially spaced cylinder contacts. This arrangement allows the switching functions of the apparatus to be embodied in a separate module for inventory and quality control purposes. 
     According to a further feature of the invention, the right cylinder structure is a compound structure constituted by a cartridge and a right cylinder member having a cylindrical wall having an open right end and including an axially extending slot opening into the hollow interior of the right cylinder and opening at the right end of the right cylinder; the cartridge is sized to fit in the slot; the axially spaced cylinder contacts are provided on an inner surface of the cartridge; and the electrical leads are carried by the cartridge. This specific arrangement allows the switching functions of the apparatus to be totally isolated from the remainder of the apparatus for inventory and quality control purposes. 
     Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
     FIG. 1 is a partial schematic view of a motor vehicle incorporating a master cylinder apparatus according to the invention; 
     FIG. 2 is a cross-sectional view of the master cylinder apparatus; 
     FIG. 3 is a cross-sectional view taken on line  3 — 3  of FIG. 2; 
     FIG. 4 is a perspective exploded view of the master cylinder apparatus; and 
     FIG. 5 is a bottom detail view of a switch cartridge embodied in the master cylinder apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention master cylinder apparatus  10  is seen in FIG. 1 in association with a motor vehicle of the type including a firewall  12 , a clutch pedal  14 , a slave cylinder  16 , and a clutch  18 . The master cylinder  10  is fixedly secured to firewall  12  in known manner and clutch pedal  14  is pivotally secured to the free end of the push rod  20  of the master cylinder so that depression of the clutch pedal  14  by a vehicle operator transmits pressurized hydraulic fluid through a conduit  22  to slave cylinder  16  which operates a release lever  24  which acts upon a clutch release bearing  26  to disengage the clutch  18  in known manner. 
     Master cylinder  10  (FIGS. 2 and 3) includes a cylinder structure  28 , a seal assembly  30 , a cartridge  32 , push rod  20 , a piston assembly  34 , and a reservoir  36 . 
     The designations left and right as hereinafter employed are with respect to FIG.  2  and the designations forwardly and rearwardly as hereinafter employed designate leftward and rightward movement, respectively, as viewed in FIG.  2 . 
     Cylinder structure  28  includes a left cylinder structure  38  and a right cylinder structure  40 . The cylinder structures are shown in their coupled relationship in FIG.  2  and in an exploded relationship in FIG.  3 . 
     Left cylinder structure  38  includes a left relatively small diameter portion  38   a  and a right relatively large diameter portion  38   b . Left portion  38   a  defines a bore  38   c  and a fluid pressure outlet  38   d . Right portion  38   b  defines a bore  38   e , a counter bore  38   f , a conical bore  38   g  interconnecting bores  38   e  and  38   f , a further counter bore  38   h , a conical bore  38   i  interconnecting bores  38   f  and  38   h , an external mounting flange  38   j , a reservoir fitting  38   k , and an annular shoulder  38   l  interconnecting bores  38   c  and  38   e.    
     Right cylinder member  40  includes a main body tubular portion  40   a  including an axially extending slot  40   b  opening at the right face  40   c  of the main body tubular portion, an enlarged diameter flange portion  40   d  joined to main body portion  40   a  by an annular shoulder  40   e , and circumferentially spaced finger portions  40   f  extending rearwardly from flange portion  40   e  in radially spaced relation to main body portion  40   a . The left portion of flange portion  40   d  has an angled exterior surface  40   g  defining an annular interior groove  40   h . Flange portion  40   d  further defines an annular external groove  40   i  for receipt of an elastomeric O-ring  42 . Right cylinder member  40  is fitted telescopically into left cylinder member  38  with flange portion  40   d  slidably received in bore  38   f , O-ring  42  sealingly engaging bore  38   f , and nubs  40   n  carried by the free ends  40   j  of fingers  40   f  snappingly received in respective arcuate slots  38   m  in portion  38   b  to preclude inadvertent withdrawal of part  40  from part  38 . 
     Seal assembly  30  includes a primary annular elastomeric seal  44 , a secondary annular elastomeric seal  46 , and an annular spacer  48 . Primary seal  44  is received in an annular groove  38   m  defined between shoulder  38   l  and bore  38   e , secondary seal  46  is received in annular groove  40   h , and annular spacer  48  is positioned between the primary and secondary seals proximate conical bore  38   g.    
     Cartridge  32  (see also FIG. 4) includes a main body portion  32   a  formed of a suitable insulative material and a plurality of conductors or leads  50  embedded in main body portion  32   a  and formed of a suitable conductive material. Main body portion  32   a  is sized to fit in slot  40   b  and has an arcuate cross-sectional configuration conforming to the radius of cylinder main body portion  40   a  so as to, when fitted into slot  40   b , form a continuation of the arcuate circumferential curve of main body portion  40   a . When fitted into slot  40   b  the inner arcuate surface  32   b  of the main body portion is flush with bore  40   k  of cylinder main body portion  40   a , the left end  30   c  of the main body portion is seated against the end  40   l  of slot  40   b  and telescopically positioned in cylinder bore  38   h , and the main body portion is positioned circumferentially between circumferentially spaced finger portions  40   f . Leads  50  extend axially through main body portion  32   a  and define terminal ends  50   a  for connection to external leads and contacts  50   b  positioned in exposed relation flush with the inner surface  32   b  of the main body portion. 
     A plurality of pairs of leads are provided. For example, and as shown, two pairs of leads are provided with the first pair of leads terminating in a pair of circumferentially spaced contacts  50   c  and the second pair of leads terminating in a pair of circumferentially spaced contacts  50   d  spaced axially from contacts  50   c.    
     Push rod  20  includes a main body shaft portion  20   a , a swivel portion  20   b  for pivotal connection to clutch pedal  14 , and a spherical ball end portion  20   c.    
     Piston assembly  34  includes a piston member  52 , a pair of insert halves  54 , and a piston contact  56 . 
     Piston member  52  is formed of a suitable sheet metal material and includes a main body outer shell portion  52   a , an inner tubular portion  52   b  positioned concentrically within the left end of outer shell portion  52   a  and joined to the left end of shell portion  52   a  by annular shoulder  52   c , and an inwardly directed flange portion  52   d  at the right end of outer shell portion  52   a . Piston  52  is sized to fit slidably within bore  40   k  and to sealingly engage at its left end with the inner lip seal portions of primary seal  44  and secondary seal  46 . 
     Each insert half  54  is formed of a suitable plastic material in a suitable molding operation and includes a right end flange portion  54   a , a hemispherical portion  54   b  adjoining flange portion  54   a , and a main body portion  54   c  extending rearwardly from hemispherical portion  54   b  and defined by a plurality of circumferentially spaced ribs  54   d  and a flat inner face  54   e.    
     In the assembled relation of the piston assembly, insert halves  54  are received within piston member  52  with nubs  54   e  on the ribs  54   d  engaging the inner piston member walls, the left end  54   f  of the insert halves bearing against the blind end  52   e  of the inner tubular portion  52   b  of the piston member, and the flange  52   d  of the piston member crimped over the ends  54   g  of the ribs  54   d  to firmly lock the piston member over the main body portions of the insert halves. The spherical portions  54   b  and the flange portions  54   a  of the insert halves project forwardly out of the piston member to define a spherical cavity  54   h  and an annular flange constituted by the fitted together flange halves  54   a  of the upper and lower insert halves. 
     Contact  56  has an annular configuration, is formed of a suitable conductive material, and is fitted over flanges  54   a  in crimping fashion so as to be fixedly mounted on flanges  54   a.    
     In the assembled relation of the piston assembly and the push rod, the ball end  20   c  of the push rod is received in spherical cavity  54   h  and the main body  20   a  of the push rod extends through the open right-hand end of right cylinder member  40 . 
     In the assembled relation of the master cylinder, it will be seen that the piston assembly and the seals coact to define a hydraulic fluid pressure chamber within the bore  38   c  on the left side of the piston and a dry unpressurized atmospheric chamber within the bore  40   k  on the right side of the piston, and it will further be seen that the contact pairs  50   c / 50   d  as well as the annular contact  56  are positioned in the dry, unpressurized chamber defined within the bore  40   k . It further will be understood that fitting  38   k  is connected by a conduit, such as conduit  60  seen in FIG. 1, to an external hydraulic fluid reservoir  62  whereby to deliver hydraulic fluid to the cylinder apparatus and it will be further understood that seal assembly  30  acts in known manner to allow the delivery of hydraulic fluid to the pressure chamber within the bore  38   c  on the left side of the piston assembly while precluding delivery of hydraulic fluid to the unpressurized chamber within the bore  40   k.    
     In operation, the clutch pedal is depressed to move the piston assembly to the left to eject hydraulic fluid under pressure through fitting  38   d  for delivery to a coacting fluid pressure device such as the slave cylinder  16  controlling the clutch  18  and, upon release of the clutch pedal, the piston assembly is returned to the right under the action of a return spring  58  with hydraulic fluid flowing from the reservoir through the conduit  60  and fitting  38   k  and past the collapsed primary seal  44  to fill in the chamber  38   c  behind the retreating piston assembly. The rightward, return movement of the piston is defined by engagement of contact  56  with an annular lip  40   m  on the right end of cylinder member  40  and a coacting annular lip  32   d  on the right end of cartridge  32 . 
     As the piston assembly moves forwardly within the cylinder structure, annular contact  56  first engages the contacts  50   c  to electrically span the circumferential space between the contacts and complete a circuit through the two leads  50  defining the spaced contacts  50   c  whereby to transmit a control signal to an associated cruise control device to disengage the cruise control whereafter, with further leftward movement of the piston assembly in response to further depression of the clutch pedal, contact  56  electrically spans the circumferential space between the contacts  50   d  to complete an electrical circuit through the two leads  50  defining the contacts  50   d  and thereby generate an electrical control signal for transmittal, for example, to the engine starter motor to enable starting of the engine and/or to the engine computer for appropriate action consistent with disengagement of the engine torque path. 
     The invention will be seen to provide a master cylinder assembly in which the switching functions are provided integral with the master cylinder assembly whereby to minimize the overall cost and complexity of the master cylinder and switch assembly and whereby to eliminate the space problems associated with the separate switch assembly positioned on the push rod of the master cylinder assembly. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.