GB2158993A - Electrical switch for use in combination with a hydraulic master cylinder - Google Patents

Abstract

An electrical switch operated by the input member of a hydraulic master cylinder of a motor vehicle clutch or brake control system has a linearly displaceable input member or push rod 16 carrying a plunger 34 which carries contacts 64, and 66 which in a "home" position of the input member and remote from fixed contacts 48, 50. The contacts 48 and 50 have a relatively considerable length so that when the input member is moved so that contacts 64, 66 bridge contacts 48, 50 an extended operative position is provided. Additional fixed contacts 49, 51 may be bridged between the "home" and operative positions of the impact member 16. <IMAGE>

Description

SPECIFICATION Electrical switch for use in combination with a hydraulic master cylinder The present invention relates to an electrical switch for use in combination with a hydraulic master cylinder such as the master cylinder of a motor vehicle clutch hydraulic control system, the master cylinder of a motorvehicle hydraulic brake system, and the like.

An electrical switch is often associated with the master cylinder of motor vehicle hydraulic brake systems for the purpose of, for example, energizing the electrical circuitturning on the motor vehicle stop signal lights, or/and for operating a cruise control system from an active mode to an inactive mode, upon application ofthe brakes bythedriver. Such electrical switches are generally of the pressure operated type. They are operated by the increase of hydraulicfluid pressure when the brake pedal is displaced such as to cause a corresponding displacement of the master cylinder piston, thus increasing the pressure ofthe hydraulic fluid in the master cylinder in front of the piston. Pressure operated switches are costly to manufacture and they must be installed, at least partly, within the master cylinder.They are often unreliable as they must be activated by a slight increase in the hydraulic fluid pressure for providing an appropriate stop signal even upon slight application of the brakes orfor disconnecting the cruise control system as a result of a slight foot tap on the brake pedal.

Thefunctioning of pressure actuated switches may be somewhat erratic under certain conditions, hydraulicfluid back pressure surges in the master cylinder caused, for example, by heat expansion ofthe brake linings and ofthe hydraulic fluid. Such erratic functioning of pressure-actuated switches causes erraticturning on and off ofthe motor vehicle stop signal lights, particularly irritating to the driver of a motor vehicle immediately following.

Hydraulic control apparatus for motor vehicle mechanical clutches are rapidly becoming the stan dard ofthe industry for operating the clutch release mechanism of a motorvehicle provided with a mechanical clutch and a conventional manually shiftable transmission or gearbox. An example of such a hydraulic control system for mechanical clutches is disclosed in U.S. Patent No. 4,407,125.It has become general practice in the automobile industry to interlock the operation of the engine starter motor with othercontrolsofthe motorvehiclesuchthatthe starter motor is rendered inoperative unless the transmission is in neutral or park in motorvehicles provided with an automatic transmission or, in motor vehicles provided with a foot operated clutch and a manually operated gea rshift transmission, unless the transmission is in neutral and/orthe clutch pedal is fully depressed to fully release the clutch. In addition, it is convenient, in motorvehicles provided with a cruise control and a mechanical clutch, to shut off the operation ofthe cruise control upon, for example, down shifting which in turn requires release ofthe clutch.However, it is desirable thatthe cruise control be disconnected even before the clutch is fully released, to enable the driverto cut off the cruise control by a slight foot tap on the clutch pedal, and perhaps to discourage "riding" the clutch, i.e. resting one's foot on the clutch pedal at all times.

According to one aspect of the present invention there is provided an electrical switch for use in combination with a hydraulic master cylinder having a linearly displaceable input member, said electrical switch being operable by said input member during displacement of said input memberfrom a home position to an operative position and comprising a pair of movable elements and a pair of stationary elements whereby said movable elements are displaceable from a first position in non-operative relation with regard to said stationary elements to a second position in which they co-operate with said stationary elements said first position of the movable elements corresponding to the home position ofthe input member and said second position of the movable elements corresponding to the beginning of said operative position, said movable elements remaining in co-operation with said stationary elements from the beginning of the operative position to the end thereof, said switch being arranged to control an electrical circuit, which, in use, includes said stationary elements and which is operable as a function ofthe position of said input member.

Preferably means is provided for returning the movable elements to said first position wherebythe movable elements are moved into non-operative relation with regard to said stationary elements automatically upon return of said input member to said home position.

The switch may further comprise a second pair of stationary elements included, in use, in a second electrical circuit, whereby said movable elements will be in non-operative relation with regard to said first and second stationary elements in the home position of said input member and said movable elements co-operate first with said second pair of stationary elements upon initial displacement of said input memberfrom said home position to said operative position.

In one embodiment said stationary elements are on a housing mounted on an end of said master cylinder, said movable elements are mounted on an end of a plunger projecting within said housing and having another end extended from said housing, and said input member has a surface in engagement with said other end of said plunger.

In another embodiment said stationary elements are mounted on a housing mounted on said input member and displaceable therewith, and said movable elements are mounted on an end of a plunger projecting within said housing and having another end in engagementwith a stationary portion of said master cylinder.

According to another aspect of the invention there is provided an electrical switch for use in combination with a hydraulic master cylinder having a linearly displaceable input member, said electrical switch being operable by said input member during displacement of said input member from a home position to an operative position and comprising a movable element, first and second stationary elements included, in use, in respective first and second electrical circuits whereby said movable element is displaceablefrom a first position in non-operative relation with regard to thestationarypartsto a second position co-operable with one ofthefirstand second stationary elements to control the electrical circuit associated therewith, said first position ofthe movable element corresponding to the home position of said input member and said second position ofthe movable element corresponding to the beginning of a first operative position, said movable element remaining co-operable with said one stationary elementfrom the beginning of said first operative position to the end thereof, said movable element being movable from the first operative position to a second operative position into cooperation with the other ofsaid first and second stationary elements to control the other electrical circuit Preferably means is provided for returning the movable element to said first position wherebythe movable element is moved into non-operative relation with regard to said stationary elements automatically upon return of said input memberto said home position.

In one embodiment said stationary elements are on a housing mounted on an end of said master cylinder, said movable element is mounted on an end of a plunger projecting within said housing and having another end extended from said housing, and said input member has a surface in engagementwith said other end of said plunger.

In another embodiment said stationary elements are mounted on a housing mounted on said input memberanddisplaceabletherewith,andsaid movable element is mounted on an end of a plunger projecting within said housing and having another end in engagement with a stationary portion of said mastercylinder.

The switch may be used in combination with a mastercylinderwhich forms partofa motorvehicle hydraulic system. Where the hydraulic system is a brake system said circuit may be a stop signal circuit.

Where the switch is arranged to control two electrical currents, both said circuits may be stop signal circuits.

One ofthe stationary elements may be included in a third electrical circuit. In the lattercase,thethird electrical circuit may be a cruise control disconnect circuit. Where the hydraulic system is a hydraulic clutch control system the switch may be arranged to control a starter with relay interlock circuit.

Preferably each said stationary element is an electrical contact and the or each moving element may be an electrical contact.

Switches in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: FIG. lisa partial elevational view of a hydraulic master cylinder and input memberassemblyfora clutch hydraulic control, provided with an electrical switch, according to the present invention; FIG. 1 a is a view similarto FIG. 1, but showing a master cylinder and input member assemblyfora hydraulic brake system; FIG. 2 is an end view fro line 2-2 of FIG. 1; FIG. 3 is a longitudinal sectional viewthereoffrom line 3-3 of FIG. 2; FIGS. 4through6areviewssimilarto FIG. 3, but illustrating progression in the operation ofthe invention; FIG. 7 is a cross-sectional view along 7-7 of FIG. 3; FIGS. 8 and 9 are views similarto FIGS.1 and 2 respectively, but illustrating a modification ofthe invention; FIGS. 8 and 9 are views similarto FIGS. 1 and 2 respectively, but illustrating a modification ofthe invention; FIG. 10 is a view similarto FIG. 1, but showing a further modification of the invention; FIG. 11 is an end view along a line 11-11 of FIG. 10; FIG. 12 is a longitudinal section thereof along line 12-12ofFlG. 10; and FIGS. 13 and 14areviewssimilarto FIG. 12, but showing the operation ofthe illustrated embodiment ofthe invention.

Referring to the drawing, and more particularly to FIGS. 1-2 thereof, the present invention takesthe form of an electric switch 10 enclosed in a dielectric plastic housing 12 mounted on the end of a hydraulic master cylinder 14. The hydraulic master cylinder 14 may, for example,bethemastercylinderofa motorvehicle clutch hydraulic control system, FIG. las described in detail in the aforesaid U.S. patent and copending applications, orthe master cylinder of a motor vehicle hydraulic brake system, FIG. la.

As is well known in the art, a linear input member in theformofapushrod 16 is disposed reciprocable through an end 18, FIGS. 3-6, ofthe hydraulic master cylinder 14which is closed by an end cap, not shown, provided with an appropriate central aperture accepting the pushrod 16 therethrough.An end ofthe push rod 16 is coupled to a piston, not shown, slidably disposed within the master cylinder 14, and displacement ofthe piston causes in turn a portion ofthe hydraulic fluid in front ofthe piston in the master cylinder 14to be displaced through a tubular conduit, not shown, to a slave cylinder, such asthewheel brake slave cylinders of a hydraulic brake system orthe slave cylinder actuating a mechanical clutch release mechanism.Theend l8ofthemastercylinderl4 through which reciprocates the pushrod 16 is generally, in conventional structures, protected by an elastomeric boot.In the present structure, the elastomeric boot is replaced bytheswitch housing 12 which may be attached to the hydraulic master cylinder 14 proximate its end 18 by any convenient means such as being screwed on, cemented on, or the like. In the structure illustrated, the peripheral surface ofthe master cylinder 14 is provided proximate its end 18 with a peripheral annular groove 20, andthe switch housing 12 has a cylindrical recess 22 at an end with an annular ridge 24 projecting from the internal surface of the recess 22 elastically engaging the groove 20 for snap fit ofthe switch housing 12 overthe peripheral surface of the mastercylinderl4proximate its end 18.

The switch housing 12 has a cylindrical bore 26 closed at one end by an end cap 28 having a central aperture 30 in which is slidably disposed the body 32 of a plunger 34. The plunger 34, also made of a dielectric plastic material, is provided with an integral radially disposed flange portion 36. The plunger 34 has a central bore 38 loosely accepting therethrough the push rod 16. The other end of the switch housing 12 is closed by an end wall 40, cemented or heat-welded thereto, having a central aperture 42 affording free passage therethrough to the pushrod 16. A return coil spring 44 is disposed surrounding the pushrod 16.

One end ofthe coil spring 44 engages the end wall 40 and the other end engages the bottom of an annular recess 46 disposed in the plunger 32. The annular recess 46 acts as a pilot meansforthe coil spring 44 and as a recess in which the coil spring, when compressed, retracts, FIGS. 4-6, such as not to cause any interference with full displacement of the plunger 34, and thus enables the switch 1 Oto be of a relatively short length.

Two pairs of separate longitudinally disposed stationary contacts 48-50 and 49-51 are affixed in recesses in portions ofthe internal surface of the bore 26 ofthe switch housing 12. The stationary contacts 48 and 50 are disposed about 180from each other, and the contacts 49 and 50 are similarly disposed. The stationary contact 48 is connected through a wire 52 to a terminal 54, and the stationary contact 50 is connected through a wire 56to a terminal 58,the terminals 54 and 58 being in a connector 61 mounted, for example and as illustrated, on the end ofthe switch housing end cap 28.The stationary contact 49 is connected through a wire 53to a terminal 55, and the contact 51 is connected through a wire 57to a terminal 59,theterminals 55 and 59 being in a connector63 also mounted, in the example of structure illustrated, on the end ofthe switch housing end cap 28.

The plunger end flange 36 has a pair of diametrically aligned radial bores 60 and 62, FIGS. 3-6. A sliding brush contact 64 is slidably disposed in the radial bore 60 and a sliding brush contact 66 is similarly disposed in the radial bore 62, the brush contacts 64 and 66 being respectively urged outwardly by coil springs 68, 70, respectively. Means are provided, such as for example a key and key slot arrangement, as shown at 72 at FIG. 7, for preventing the plungerflange 36 from rotating relative to the switch housing 12,the key and key slotarrangement72 permitting only relative longitudinal motions therebetween.The two sliding contacts 64 and 66 are interconnected by a wire, shown schematicallyat74 at FIG. 7, such thatwhen the sliding contacts 62 and 64shortcircuitthe stationary contact pair 49-51, FIG. 4, orthe stationary contact pair48-50, FIGS. 5 and 6, according tothe linear position occupied by the plungerflange 36, any electrical circuit connected acrosstheterminals55-59, or any electrical circuit across theterminals 54-58, is individually closed. In the position illustrated at FIG. 3, or home position, both circuits are open as a result of the sliding contacts 64 and 66 engaging portions 76 and 78 ofthe surface ofthe housing bore 26 proper beyond the leading end ofthe stationary contacts 49 and 51.

The switch plunger34 has an annular end face 80 engageable by an annular abutment 82 provided on the push rod 16. The annular abutment 82 may be on the end face of a collar 83 clamped around the pushrod 16, FIG. 8, or, in the example of structure illustrated at FIGS. 1-7, it is formed atthe end of an extension rod 84 having at its other end an eye 86, FIGS. 1 and 1 a, for swivelling connection to a brake control pedal orto a clutch control pedal, not shown, the extension rod 84 being connected to the pushrod 16 by any convenient means, such as press-fit thereon of the tubular end of the extension rod 84 orthreaded fit, brazing or swaging.

The annularabutment 82 may alsotaketheform of the end of a spacer disposed between the end of the extension rod 84 and the plunger annular end face 80, ortheform of a spring clip snapped around the rod 16 at an appropriate position in engagement with the plunger annular end face 80 orin proximity therewith.

In hydraulic control systems for mechanical clutches utilizing the present invention, and where it is desired to disconnect a cruise control mechanism upon shifting gears, or pressing slightly or tapping the clutch pedal, the terminals 55-59 in the connector 63 are connected to the cruise control disconnect circuit, as schematically represented at FIG. and as soon as the plunger 34 is displaced by the annular abutment 82 ofthe pushrod 16fromthe position shown at FIG. 3 of the drawing tothe position causing engagementof the sliding brush contacts 64 and 66 with the stationary contacts 49 and 51, FIG. 4, the cruise control disconnect circuit is closed and the cruise control is turned off.Further depressing the clutch pedal causes the annular abutment 82 to furtherdisplace the switch plunger34to a position, FIG. 5, wherein the circuit across the terminals 54-58 is closed. As the terminals 54-58, in the connector61, are connected across the engine starter motor relay circuit, the starter motor relay circuit is enabled, thus allowing the motor vehicle operator to startthe vehicle engine. The position ofthe plunger 34 causing engagement ofthe sliding brush contacts 64 and 66 with the stationary contacts 48 and 50 connected across the terminals 54-58 corresponds to a position ofthe clutch pedal fully releasing the clutch.

However, the stationary contacts 48 and 50 are provided with a relatively considerable length as compared to the length of the contacts 49 and 51, such as to correspond to a full stroke of the clutch pedal, and consequently a full stroke ofthe master cylinder pushrod 16, from the beginning ofthe clutch release until the clutch pedal hitsthefloorboard, such positions being shown approximately at FIGS. and 6 respectively.

In installation where there is no cruise control on the motorvehicle, the structure ofthe switch 10 may remain the same, the terminals 54-58 remaining unconnected but available if a cruise control is subsequently installed on the motorvehicle.

In installations wherein the switch 10 is mounted on the end ofthe master cylinder 14 of a hydraulic brake system, FIG. 1 a, the terminals 54-58 in the connector 63 are connected in series in the motor vehicle stop signal light circuit, and the contacts 49 and 51 are madesuchastoextend Iongitudinallyonthesurface of the bore 26 ofthe switch housing 12, such that the stop signal lights remain on irrespective of the position of the brake control pedal.However, by keeping two separate pairs of contacts 49-51 and 48-50 as shown, the switch 10 becomes of universal use, thus decreasing the inventory of parts, and both pairs of terminals 55-59 in the connector 63 and 54-58 in the connector 61 may be connected in parallel with each otherandtheircommon junction point connected in series in the stop signal light circuit, with the result thatthestop signal lights remain on as long as the brake pedal is depressed, on the condition thatthe insulating portions 88 and 90 ofthe surface ofthe bore 26 between, respectively, the stationary contacts 48 and 49 and the stationary contacts 50 and 51 be narrower than the width of the sliding brush contacts 64and 66, such thatthe brush contacts 64 and 66 remain simultaneously engaged respectively with the contacts 48 and 49 on one hand and 50 and 51 on the other hand while passing overthe insulating portions 88 and 90 ofthe switch housing bore 26. The structure ofthe switch 10, with two separate pairs of stationary contacts, also permits to provide a motorvehicle brake application progressive warning system,for example by connecting the terminals 55-59 in the connector 63 in series in the stoplight circuitofa differentcolour, such as amberoryellow (stop signal No. 1), and connecting the terminals 54-58 in the connector61 in a circuit for red stop signal lights (stop signal No. 2).The terminals 55-59 in the connector 63 are also availableforconnectionto a cruise control disconnect circuit FIG. 1 a, for enabling the motor vehicle driver two cut offthe operation ofthe cruise control upon application ofthe brakes or as a result of a slighttap upon the brake pedal.

Instead oftaking the cylindrical form illustrated at FIGS. 1-7,theswitch housing 12maytakeany convenientform such as, for example, the switch 10' illustrated at FIGS. 8 and 9 having a housing 12 providedwith agenerallycylindrical peripheral surface portion 92, FIG. 9, and a generallyflat side surface portion 94, FIG. 8. The housing 12 ofswitch 10' encloses a switch assembly identical to that of FIGS.

3-7, exceptthatthe bore 26 and the plunger and flange 36 extend cirumferentially over less than 360". The housing 12 ofthe switch 10' is elastically snapped sideways over the master cylinder 14 proximate the end i8thereof.Thehousing 12 oftheswitch 10' has a longitudinal slit 96 permitting sideways passage over themastercylinderpushrod 16, and the plunger switch 34 is substantially U-shaped such as to be disposed around approximately one-half ofthe periphery of the pushrod 16.The housing 12 ofthe switch 10' has a generally U-shaped end recess 98 with wings 99 that elastically spread for pushing over a portion ofthe peripheral surface of the cylinder 14 proximate its end 18, and spring back elasticallyfor snap fit ofthe housing 12 overthe end ofthe master cylinder 14.

Itwill be readily apparentto those skilled in the art thatthe invention encompasses other structures than those specifically illustrated at FIGS. 3-7 and described hereinbefore. Also, it will be readily apparent that instead of being mounted on the end of the master cylinder 14, the electrical switch may be installed on the pushrod 16, itself, as illustrated at FIGS. 10-14.

The electrical switch 10" of FIGS. 10-14 comprises a housing 12, made of plastic, having a bifurcated portion forming a pair of wings 102 and 104, as shown more particularly at FIG. 11, defining therebetween a partially cylindrical recess with a cylindrical surface 106 extending over an arc of slightly more than 1800, suchastoenablethehousing 12to be attachedtothe pushrod 16 by resilient spreading apart of the wings 102 and 104, while pushing the housing 12 sideways upon the pushrod 16, with an end ofthe housing 12 abutting against the annular abutment 82 formed, for example, on the end ofthe pushrod extension 84. A plunger 34 projects from the other end of the housing 12, and the end face 108 ofthe plunger 34 normally abuts a closure plate 110 atthe end 18 ofthe master cylinder 14through which reciprocate the pushrod 16.

For the purpose of clarity ofthe disclosure ofthe invention, the outerface ofthe end plate 110 of the master cylinder 14 is shown as being flush with the end 18 ofthe housing of the master cylinder 1 4while, in most structures, the closure plate may be slightly recessed from the cylinder end. The plunger 34 reciprocatesthroughan end bore 112inthe housing 12. A key 114, FIG. 11 formed longitudinally integral with the body ofthe plunger34 engages a corresponding longitudinal groove 116 in the housing 12for preventing the plunger34 from rotating about its axis during reciprocation thereof.

The plunger34 is tubular and is provided with an axially disposed pilot pin 118, a coil spring 120 being disposed around the pilot pin 118. One end ofthe coil spring 120 engages the bottom wall 122 of the tubular plunger34, while the other end of the coil spring 120 engages the end wall 124 ofthe housing 18, a short integral pilot pin 126 projecting from the housing end wall 124 being disposed coaxiallywithin the coil spring 120.

The end of the tubular plunger34 is provided with a metallic ring 128 affixed thereon. The annular ring 128 supports, or is made integral with, a pair of spring sliding contacts 64 and 66, whose function is the same as the brush contacts 64 and 66 of the embodiment of FIGS. 1-7. The bore 26 ofthe housing 12 is provided with two separate pairs of stationary contact plates 49-51 and 48-50, and functions are the same asthetwo pair of contacts 49-51 and 48-50 ofthe embodiment of FIGS. 3-7. The contacts 49 and 51, and 48 and 50 are connected through appropriate electrical conductors, not shown, embedded in the housing 12 to a four-pin orfour-socket plug 130, FIGS. 10 and 11, for connection ofthe switch 10"to appropriate control circuits as hereinbefore explained in detail with regard to the embodiment of FIGS. 1-7.

FIG. 12 illustratesschematicallythe home position ofthe plunger 34, and consequentlyoftheintercon- nected sliding contacts 64 and 66, relative to the stationary contacts 49-51 and 48-50, when the master cylinder pushrod 16 is fully extended and the switch 10" is open, FIG. 12. As soon as the pushrod 16 begins to be displaced, underthe action of a clutch pedal or a brake pedal,the plunger 38 engaged at its end against the closure plate 110 ofthe master cylinder 14 is caused to be retracted againstthe pressure ofthe spring 120 within the bore 26 in the housing 12, thus causing the sliding contact 64 and 66, interconnected through the metallic annular ring 128, to close the circuit connected across the stationary contacts 49 and 51, FIG. 13. Further displacement of the plunger34 within the bore 26 ofthe housing 12 results in the sliding contacts 64 and 66 becoming engaged with the stationary contacts 48 and 50. The circuit across the stationary contacts 48 and 50 remains closed to the end of the permissible amount of retraction of the plunger 34, as illustrated at FIG. 14, causing end engagement of the pins 118and 126.

Having thus described the present invention byway of examples of structure well designed to accomplish the objects of the invention, modification whereof will be apparent to those skilled in the art, what is claimed as new is as follows: The movable and stationary contacts referred to above constitute the aforesaid movable and stationary elements respectively.

Claims (19)

1. An electrical switch for use in combination with a hydraulic master cylinder having a linearly displaceable input member, said electrical switch being operable by said input member during displacement of said input memberfrom a home position to an operative position and comprising a pair of movable elements and a pair of stationary elements whereby said movable elements are displaceable from a first position in non-operative relation with regard to said stationary elements to a second position in which they co-operate with said stationary elements said first position of the movable elements corresponding to the home position of the input member and said second position of the movable elements corresponding to the beginning of said operative position, said movable elements remaining in co-operation with said stationary elements from the beginning ofthe operative position to the end thereof, said switch being arranged to control an electrical circuit which, in use, includes said stationary elements and which is operable as a function ofthe position of said input member.

2. A switch according to Claim 1 wherein means is provided for returning the movable elements to said first position wherebythe movable elements are moved into non-operative relation with regard to said stationaryelementsautomaticallyupon return of said input memberto said home position.

3. A switch accordingto claim 1 or 2 further comprising a second pair of stationary elements included, in use, in a second electrical circuit, whereby said movable elements are in non operative relation with regard to said first and second stationary elements in the home position of said input member and said movable elements co-operate first with said second pair of stationary elements upon initial displacement of said input member from said home position to said operative position.

4. A switch according to any preceding claim in combination with said master cylinder wherein said stationary elements are on a housing mounted on an end of said master cylinder, said movable elements are mounted on an end of a plunger projecting within said housing and having another end extended from said housing, and said input member has a surface in engagementwith said other end of said plunger.

5. A switch according to any of Claims 1 to 3 in combination with a master cylinderwherein said stationary elements are mounted on a housing mounted on said input member and displaceable therewith, and said movable elements are mounted on an end of a plunger projecting within said housing and having another end in engagement with a stationary portion of said master cylinder.

6. An electrical switch for use in combination with a hydraulic master cylinder having a linearly displaceable input member, said electrical switch being operable by said input member during displacement of said input member from a home position to an operative position and comprising a movable ele ment,first and second stationary elements included, in use, in respective first and second electrical circuits wherebysaidmovableelementisdisplaceablefrom a first position in non-operative relation with regard to the stationary parts to a second position co-operable with one of the first and second stationary elements to control the electrical circuit associated therewith, said first position ofthe movable element corresponding to the home position of said input member and said second position ofthe movable element corresponding to the beginning of a first operative position, said movable element remaining cooperable with said one stationary elements from the beginning of said first operative position to the end thereof, said movable element being movablefrom the first operative position to a second operative position into cooperation with the other of said first and second stationary elements to control the other electrical circuit.

7. A switch according to Claim 6 wherein means is provided for returning the movable elementto said first position whereby the movable element is moved into non-operative relation with regard to said stationary elements automatically upon return of said input member to said home position.

8. A switch according to Claim 6 or 7 in combination with said master cylinder wherein said stationary elements are on a housing mounted on an end of said master cylinder, said movable element is mounted on an end of a plunger projecting within said housing and having another end extended from said housing, and said input member has a surface in engagement with said other end of said plunger.

9. Aswitch accordingtoClaim6,7or8in combination with said master cylinder wherein said stationary elements are mounted on a housing mounted on said input member and displaceable therewith, and said movable element is mounted on an end of a plunger projecting within said housing and having another end in engagement with a stationary portion of said master cylinder.

10. A switch according to any preceding claim in combination with a master cylinder wherein the master cylinder forms part of a motor vehicle hydrau lic system.

11. A switch according to Claim 10 when appendantto Claim 1 or 2 wherein the hydraulic system is a brake system and said circuit is a stop signal circuit.

12. Aswitch according to Claim 10 and in the case where the switch is arranged to control two electrical circuits, wherein both said circuits are stop signal circuits.

13. Aswitch according to Claim 10 when appendantto Claim 6,7,8 or9 wherein one of said stationary elements is included in a third electrical circuit.

14. Aswitch accordingtoClaim 13whereinsaid third electrical circuit is a cruise control disconnect circuit.

15. Aswitch according to Claim 10 wherein said hydraulic system is a hydraulic clutch control system

16. Aswitch according to Claim 15 in which the switch is arranged to control a starter motor relay interlock circuit.

17. A switch according to any preceding claim wherein each stationary elements is an electrical contact.

18. Aswitch according to any preceding claim wherein the or each moving element is an electrical contact.

19. An electrical switch for use in combination with a hydraulic master cylinder having a linearly displaceable input member, the switch being constructed and arranged substantially as described herein with reference to Fig. 1 to 7, Figs. 8 and 9 or Figs. 10to 13 of the accompanying drawings.