US3182443A - Operating mechanism including an assist device - Google Patents

Description

y 1965 M. J. HERMANNS 3,182,443

OPERATING MECHANISM INCLUDING AN ASSIST DEVICE Filed June 21, 1962 .2 Sheets-Sheet 1 I 3 Y g i r N (O F May 11, 1965 M. J. HERMANNS 3,182,443

OPERATING MECHANISM INCLUDEENG AN ASSIST DEVICE- Filed June 21, 1962 2 Sheets-Sheet 2 United States Patent 3,132,443 OYERATHNG MEQHANESWI ENQLUDENG AN ASSEST DEVICE Martin J. Hermauns, Toledo, Ghio, assignor to Dana Corporation, Toledo, Ohio, a corporation of Virginia Filed June 21, 1962, Ser. No. 204,254 6 Claims. (Ci. 6ti10.5)

This invention relates to operating mechanisms in general and more particularly to an operating mechanism having an assist device incorporated therein.

Many operating mechanisms have been disclosed by the prior art; however, where assist devices have been incorporated therewith, they have been of a highly complicated and unsatisfactory nature in that they are not compact, do not operate with suflicient ease, nor does the operator have a constant control of the operation thereof.

It is therefore an object of this invention to provide an operating mechanism having an assist mechanism incorporated therewith.

It is another object of this invention to provide a fluid pressure operating mechanism having a fluid pressure as sist mechanism incorporated therewith which assist mechanism is capable of continuous control by the operator.

It is a still further object of this invention to provide, as an integral portion of a primary operating piston, a metering device for metering the desired amount of assist fluid pressure to assist in moving the primary piston.

It is a yet further object of this invention to provide an operating mechanism having a first and a second piston, the first piston being operated manually by a first fiuid pressure, and the second piston being operated by a second fluid pressure controlled in response to the first fluid pressure and assisting in movement of the first piston.

Further and other objects of this invention will be apparent from the following specification when taken in conjunction with the drawings wherein:

FIG. 1 is a partially diagrammatic view of a clutch and an operating linkage therefor incorporating the operating mechanism of this invention;

FIG. 2 is a longitudinal sectional View of the operating mechanism of this invention; and

FIG. 3 is an enlarged fragmentary view of the valve portion of the operating mechanism of FIG. 2.

A preferred embodiment of this invention comprises a piston housing which is adapted to be attached to a stationary member. Axially slidable within the housing is a first piston, the outboard end thereof being adapted to be attached to the device desired to be operated. A primary supply of fluid pressure of controllable magnitude is introduced into the housing and reacts against the first piston moving the same axially thereby energizing the device. Carried by the first piston is a second or assist piston received within the housing and adapted to be operated upon by an assist pressure fluid. The assist pressure fluid is metered through a valve which is carried integrally within the first piston and which is regulated by means of the primary pressure fluid as the same-energizes the first piston. Upon primary fluid entering the housing and causing movement of the first piston, the primary fluid also causes the integral valve to open thereby metering assist pressure fluid into the housing where it may react against the second piston. Means are provided whereby the integral valve will admit only a con- 3,1824 3 Patented May ll, 19%5 trolled assist pressure which pressure varies in magnitude in response to the primary pressure acting upon the first piston and the assist pressure fluid acting against the econd" piston, which pressures are both adapted to act upon the valve. In this manner the assist fluid and the assist piston are both responsive to the primary pressure fluid and are constantly controlled thereby. The primary fluid is controlled by the pressure manually supplied from a master cylinder.

Referring now to the drawings and more particularly to FIG. 1, a clutch shown generally at 10 is of any well known spring loaded type; however, other types of clutches are satisfactory for use with this invention by merely making adaptations in the linkage hereinafter explained. Since the clutch it is of a well known type, it is sufficient to explain that the pressure plate 12 is biased into engagement with the driven disk 14 by means or" a plurality of compression springs 16. To unload the clutch 10, a plurality of levers 18 are provided which levers, when the radially inner ends are pivoted to the left by a throwout bearing 28, displace the pressure plate 12. to the right against the biasing effect of the springs 1% thereby releasing the clutch. The usual throwout lever 22 engages :a groove 21 in the throwout bearing 2%! and upon clockwise rotation about point 23 is adapted to move the bearing to the left. A linkage rod 24 connects the throwout lever 22 with a piston extension 25 of the operating mechanism shown generally at 2d. The rod 24 is threadedly attached to the extension 25 and fixedly positioned by :a lock nut 27 The operating mechanism 26 is pivotally attached to the frame of the vehicle shown fragmentarily at 23 by means means of a pivot pin 30 which extends through an opening 32 in the operating mechanism 26 and through a registering opening in a bracket 34 fixedly attached to the frame.

A conventional clutch pedal shown generally at 36 is pivotally mounted as shown at 38 on another portion of the frame shown fragmentarily at 39 and spring biased in a clockwise direction against a stop pin 49 by means of a tension spring 42 also carried by the frame 39. In this position the clutch pedal is disposed upwardly and the clutch it) is in the engaged position.

A piston rod 44 is pivotally mounted to the clutch pedal 36 by means of a pivotal connection shown generally at 46. The piston rod 44 moves into a hydraulic pump or master cylinder 48 upon counterclockwise movement of the clutch pedal 36, which movement is limited by a stop pin 59 fixedly attached to the frame 39. Upon movement to the left of the piston 44, the pump 48 produces a fluid pressure (preferably hydraulic) in a line 52. which pressure is introduced into the operating mechanism shown generally at 26, and is dependent upon the degree of displacement of the piston rod 44. A source of assist fluid 53 of constant pressure supplies the operating mechanism 26 by means of a fluid pressure line 53a.

Referring now to FIGS. 2 and 3 where the operating mechanism is shown in detail, a housing 54 is provided with a first axially extending opening 55 which terminates at the right end thereof at an inner face 56 of the housing and at the left end thereof is enlarged to a second a xially extending opening 57. A primary piston assembly 58 is received within the opening 55 and axially slidable therein.

The primary piston 58 includes an annular piston sleeve 6i) pressed on and suitably fixedly secured as by brazing to an inner power piston rod portion'62. The sleeve 6t? and the power piston 62 may be formed integrally if desired, but have been shown as separate fixedly secured elements for manufacturing purposes. The sleeve has a portion 61 which, extends axially to the right beyond the power piston 62 and terminates in a shoulder 64 which isadapted to be spaced from the face 56 of the housing receives a double acting diaphragm 65 comprisednof a pair of flexible diaphragms 66 and 68, preferably prepared from an elastomeric material, and three annular spacer rings 6?, and 71;'-the ring 69 being disposed between v the diaphragm 6S and a snap ring '72 secured .in theouter end of the sleeve 60, the ring 70 being disposed between the periphery of the diaphragms 66 and 68,"and the ring 71 being disposed between the diaphragm 66 and a shoul der 74 formed on the sleeve 69 'at theinner end of the counterbore 61 and a shoulder 75 formed on the right end of a bushing 76 (hereinatter'further described). 7

' The medial portions of the diaphragrns 66 and 68 are enlarged so that the same engage each other and movement to the right of the diaphragm 66 is transferred to the diaphragm 68 while movement to the left of the diaphragm 63 is transferred .to the diaphragm 66. It is apparent that the etiective area of the diaphragm 66 and 63 for being acted upon by a fluid pressure to urge the same against the other diaphragm isthe area lying within the engagement thereof and the spacers 71 and 69 respectively. As shown, the spacer 71 is tapered concavely with respect to the diaphragm 66 while the spacer 69 is tapered convexly with respect to the diaphragm 68 so that the effective area of the diaphragm 66 is greater than that of the diaphragm 68; therefore, a lower pressure is required on the diaphragm 66 than on the diaphragm 68.

.to bias the same and the diaphragm 68 to the right. These areas can be varied to achieve the desired results.

The housing 54 is provided with an opening 78 into which the line 52 from the hydraulic pump 48 is threadedly attached and which is confluent with a chamber 8t) formed in the housing. The chamber 8% is bounded by the 'inner face 56 of the housing and the rightend of the piston assembly 58. A bleeder valve assembly 82 is also threadedlysecuredto' the housing 54- in a confluent relationship with thechamber so that when a primary fluid of the hydraulic type is used any air in the system may plate 12 against the bias of the engaging springs 16.

The structure described to this point represents a conventional fluid actuated power cylinder, which cylinder is operative to actuate the clutch 1h inthe usual manner.

' Such a cylinder has deficiencies in operating heavy duty clutches having springs 16 of relatively high biasing effect which have to be overcome to disengage the clutch. In order to operate such a clutch comfortably, the linkage between the clutch pedal 36 and the clutchlt) must result in a high mechanical advantage for the operator,

since in a vehicle there are limits, such as size, to the amount-the mechanical advantage which can be built into I By increasing the diameter of the piston such a cylinder. assembly 58 and the chamberfiii a greatermechanical advantage could be obtained. However, by so enlarging the above parts, the foot pedal 36'would have to travel i piston 58.

a 10 or the master cylinder 43 would have to begreatly enlarged.

Accordingly, to decrease the efiort required to disengage the clutch 14 while still maintaining the move ment of the pedal 36 and the size of the master cylinder 43 at a minimum, means has been incorporated in the operating mechanism 26 toassist in the movcmentof the More particularly, a secondary piston 84', shown with a greaterdiameter than the primary piston 53,

is unitarily formedwith :the power piston 62 and is slidably received in the segond axially extending opening 57 and the housing 54. Suitable sealing means shown'ge norally at SSare interposed between the piston fie and the opening 57 in a Well known manner. A secondary chamber Slla is formed in the housing 54 'andidefined by the right tace'sda of the secondary piston 84 and the right Wall 57a of the opening 57. The wall 57a also includes a plurality'of spaced bosses'5'7b provided to maintain the piston 84 spaced from the wall 572; and the pistonSS spaced frorn'the wall 56.

Means is provided'for'metering fluid pressure into the housing 54 to operatively react ,upon the piston 84. The

metering'means takes the form of a valve-86 disposed within the piston 58. The power piston 62 of the primary pistonassembly 5 8 is provided with three co-axial axially extending bores; a first bore .88 commencing at the left endof the power piston 62'and extending inwardly, a secondbore 90 intermediate the ends of the power piston 62 and disposed in an annular boss )2 within .the piston and confluent witl'ithe bore 88, and a third bore 94', of greater diameter than the bore 90 extending from the boss 92 to the right end of the powerpiston. The left end of the bore '38 threadedly receives and is closed bythe piston extension-25 which is secured to the power piston by a locked nut 87, while the-piston 621s provided with a radial opening 89 extending'from the bore 63 to the surface of the power piston 62 to the leftrof the piston 84. V

The right end' of the bore 94-is counterbored and receives'the shouldered bushing 76 which is pressed therein and secured by the spacer 71 and'the snap ring 72 as previously described. A seal in the form of an O-ring 96 is disposed between the bushing 76 and the power piston 62 within the counterbor e'to prevent the passage of fluid therebetween. The piston assembly '58 is formed with a radial opening 97 extending through the power plston 62 and thesleeve 60 joining the .bore 94 with a V radially reduced portion'99 of; the sleeve "'69 formed between the sealing means 63;

line 53a is threadedlysecured in an opening in the housing 54 positioned so as to be confluent with the reduced portion 9 9 of the sleeve 60. v

The bushing 76is provided with a bore 98 at its right end co-axial with and preferably of a diameter equal to the bore 90, which bores slidably receive an annularelongated valve stem 101. The left end of a bore 98 is counterbored as at 162 to a diameter greater than thebore Q8.

The bushing 7 6 at its right end is provided with a radially extending slot 104 formed confluent with the counterfvalve stern 10.1 has a bore 1% extending through the a proportionately increased distance toaccomplish sufiicient movement of the piston 58 to disengage the clutch same and is' formed with an annular flange 116 on its right end, which flange serves as a seat .forthe enlarged medial portion of thediaphragm66. 1

, The stem 161 has'fixedly secured thereto an annular bushing 112 which is formedlofa suitable. sealingjmaterial and is adaptedto sealingly engage the left end 114 of the bushing 76 which functions as avalveseahthereby sealing the bore 94 from the counter-bore I162. An an- The assist fluid pressure nular compression spring 116 surrounds the valve stem 101 and engages the left end of the bushing 112 and an annular ring 118 positioned in the bore 94, which ring 'abuttingly engages a seal in the form of an O-ring 121. The O-ring 121 axially engages the boss 92 and radially engages the bore 94 and the valve stem 101 thereby sealing the bore 94 from the bore 88. The spring 116 biases the valve stem 101 to the right until the bushing 112 engages the valve seat 1 14.

The enlarged part of the housing 54 containing the large opening 57 is surrounded by a boot 120 having an annular lip 122 securing the same to an annular groove 124 in the housing 54. The boot 120 has a central opening 126 which sealingly receives the piston extension 25. In this manner the open end of the housing 54 is sealed from contamination. The boot 120 is provided with an opening 130 so that the opening 39 in the power piston 62 is confluent with the atmosphere. A snap ring 132 is secured in a groove 134 at the outer end of the opening 57 to serve as a stop means and limit the outward travel of the pistons 84 and 58.

A bar 136 having an opening 138, through which the piston extension 25 extends, is secured to linkage rod 24- by means of the lock nut 27 and extends radially from the piston extension 25. A bolt 140 is threadedly received in an opening 142 provided in the housing 54 and suitably secured by a lock nut 144. The head of the belt 140 is provided with an annular groove 146 which receives one end of a tension spring 145. The other end of the spring 148 is received in an opening 150 in the bar 136. The spring 148 functions to return the piston assembly 58, the piston extension 25, and linkage rod 24 to the right when the mechanism 26 is inoperative, thereby unloading the throw out bearing 20 and therefore need only have a minimum biasing effect.

Operation As shown in the drawings, the clutch is engaged and the operating mechanism 26 has not been operated. The following conditions exist in the mechanism 26 at this time; the chamber 80 is exhausted from the fluid pres sure and the return spring 148 is maintaining the piston 84 against the bosses 57b; the diaphragms 66 and 68 are unloaded with the diaphragm 66 spaced from the seat 110 of the valve stem 101 so that the chamber 005: is confluent with the bore 55 to the left of the sealing means 63, the opening 108, the slot 104 in the bushing 76, the chamber 106, the bore 109 in the valve stem 110, the bore 88 and opening 89 in the power piston 62, and the opening 130 in the boot 120 thereby venting the chamber 80a to the atmosphere; and the bushing 112 on the valve stem 101 is biased by the spring 116 against the valve seat 114 thereby closing the bore 94- from the counterbore 102, the slot 104 and the chamber 106 so that the secondary or assist fluid pressure in the line 53a, the reduced portion 99 of the piston sleeve 60, and in the bores 97 and 94 may not flow past the bushing 112 to energize the secondary piston 84.

In operating the above mechanism to disengage the clutch 10, which is shown in the engaged position in FIG. 1, the operator depresses the foot pedal 36 which forces the piston rod 44 into the hydraulic pump mechanism 43. Depending upon the amount of the depression of the pedal 36, a fluid pressure is created in the line 52 and in the chamber 80 and the housing 54.

The fluid pressure in the chamber 80 serves two functions. A first function is to react against the entire end area of the piston assembly 58 thereby urging the same to move to the left, which movement urges the piston extension 25, rod 24, lever 22, throw out collar 20, and clutch lever 18 against the bias of the clutch springs 16 and the return spring 148. While performing as above,

'the pressure fluid serves a second function and reacts against the surface of the diaphragm 68 whose effective area for this function lies within the contact area thereof and the convex space ring 69.

The diaphragm 68 is flexed to the left by the pressure in chamber 80, carrying therewith the diaphragm 66 until the latter is seated on the flange 110 of the valve stem 101. This seating closes the bore 109 in the stem 101 so that the chamber 106, between the bushing 76 and the dia phragm 66, and the secondary chamber a confluent therewith are no longer open to vent to the atmosphere. Further movement to the left of the diaphragms 66 and 68 is resisted by the stem 101 which is being biased to the right by the combined reactive force of the spring 116 and the reaction of the pressure fluid in the bore 94 against the left shoulder of bushing 112 until the bushing 112 carried by the valve 101 abuts the valve seat 114.

When the force of the pressure in the chamber 80 acting on the diaphragm 68 is suflicient to bias the diaphragms 66 and 68 and the valve stem further to the left against the reactive force on the valve stem, the bushing 112 is moved from the valve seat 1114 creating a confluent relationship between the secondary or assist fluid line 53a the chamber 106 and secondary chamber 80a.

The assist fluid pressure in the chambers 106 and 80a also serves two functions. A first function in the chamber 80a is to react against the face 84a of the piston 84 urging the same to the left thereby imposing an assist force to the leftward movement of the power piston 62. While performing the above function, the assist pressure fluid in the chamber 106 reacts against the surface of the diaphragm 66, whose effective area for this purpose lies within the contact area thereof and the concave spacer ring 71.

When the combined biasing effects of the assist fluid in the chambers 106 and 80a and the reactive force on the valve stem 101 acting on the diaphragm 66 exceed the biasing effect of the primary fluid in the chamber 80 acting upon the diaphragm 68, the diaphragm 66 will be urged to the right carrying the diaphragm 68 therewith until the bushing 112 is biased against the valve seat 114-. At this time the biasing effect of the reactive forces on the valve stem 101 no longer bias the diaphragm 66 to the right and only the assist fluid trapped in chamber 106 further reacts against the diaphragm 66 and the flow of the assist fluid into the chambers 106 and 80a is terminated.

At this time, if the effective force of the assist fluid on the diaphragm 66 is less than the effective force of the primary fluid in the chamber 80 on the diaphragm 68, the diaphragm 66 will remain seated on the valve seat 110 preventing the venting of assist fluid through the bore 109 of the valve stem and equilibrium is established. If the effective force of the trapped assist fluid on the diaphragm 66 is greater than the effective force of the primary fluid on the diaphragm 68, then the diaphragm 66 will be biased to the right carying the diaphragm 68 therewith so that the bore 109 in the valve stem 110 opens the chambers 106 and 30a to vent to the atmosphere. The diaphragm 66 will remain biased to the right until the effective force of the assist fluid thereon falls below the effective force on the diaphragm 68 so that the latter again biases the diaphragm 66 to the left and seats the same on the seat 110 preventing further venting of the assist fluid and establishing equilibrium.

In the absence of undesirable pressure leaks, the equilibrium will remain until the operator further presses the pedal 36, thereby increasing the pressure in the chamber 80, or allows the pedal 36 to move upwardly, thereby decreasing the pressure in the chamber 80. It is therefore apparent that the operator has a constant control over the force of the primary and assist fluids.

By varying the diameters of the pistons 58 and 84, the source of pressure of the assist and primary fluids, the effective areas of the diaphragms 66 and 68 and the re action force on the valve stem 101, the amount of assisting rendered by the assist fluid can be varied as desired. As

shown, the device 26 is adapted to use air as the assist fluid, however, hydraulic fluid can be utilized by providing means for returning the vented fluid to the sump of the source of the assist fluid. I

From the foregoing it is apparent that an operating mechanism has been described having an assist mechanism incorporated therein; which operating mechanism may be of the hydraulic type having a fluid pressure assist mechanism incorporated therein, which assist mechanism is capable of continuous control by the operator; that the device for controlling the amount of fluid pressure to the assist mechanism is formed as a portion of the primary controllable portion of the operatingmechanisrn; which'mechanism has a first and second piston, the first piston being operated manually by first fluid pressure, and the second piston being operated by a second fluid pressure control in response to at least the firstfluid pressure and assisting'in the movement of the first piston.

The preferred embodiments of this invention have been shown and described, but changes and modifications can be made'and it is understood that this description isillustrative only and not for the purpose of rendering this invention limited to the details illustrated or described except insofar as they have been limited by the terms of the following claims.

What is claimed is:

1. An operating mechanism having an assist device incorporated therein comprising in combination,

(A) ahousing mean,

(B) a piston rod disposed in said housing,

(C) a first and a second piston means disposed in said housing for cooperatively imposing urging forces on said piston rod and urging the latter relative-to said housing means,

(D) a first fluid pressure of manually controllable magnitude and first supply means for supplying the same,

(E) a second fluid pressure and second supply means for supplying the same,

(F) a first conducting means connecting said first supply means to said housing for conducting said first fluid pressure thereto and having a portion thereof disposed in said housing whereby saidfirst fluid pressure is operative to act upon said first'piston means,

(G) a second conducting means connecting said second supply means to said housing for conducting. said second fluid pressure thereto and having a porengaging surface in said first bore therein cooperable with said first engaging surface and e (1) engageable therewith to block saidsecond conducting means, and a (2) disengageable therewith'to open said second conducting means whereby said second fluid pressure may pass through said second conducting meansperipherally' of said plunger means,

(L) said biasing means normally biasing said plunger means for biasing said engaging surfaces into engagement with each other, 7

(M) said second surface of said actuating means is (1) engageable with said plunger for blocking said venting, bore and urging ,said'plunger against the biasing effect of said biasing means thereby moving said engaging surfaces into a disengaged relationship with each other,

(2) radially larger than said plunger means and therefore 'having'a portion thereof extending radially beyond said plunger means whereby (a) said second fluid pressure in said chamber is operative to act upon said extending portion of said second surface while the latter is engaged with said plunger means and blocking said venting bore and impose an urging force on said actuating means in opposition to the urging force thereon of said first fluid pressure on said first surface, V I (b) when said urging force of said second fluid pressure actingyuponv said actuating means exceeds the urging force of said first fluid pressure acting upon said actuating means the latter "moves .from engagement with saidplunger means and opens said venting bore While allowing said biasing means to bias said engaging surfaces into engagement with each' other.

a 2. The combination according to claim 1 wherein at least a portion of said valve means is carried by one of said piston means for movement, therewith while being movable relative thereto.

3. The combination according to claim 2 wherein-said one piston means is said first piston means andsaid ention thereof disposed in said housing whereby said second fluid pressure is operative to act upon said second piston means,

(H) said second conducting means including therein a first bore and a chamber formed'axially adjacent said bore with said chamber being radially larger than saidtfirst bore,

(I) valve means for'regulating the pressure magnitude of said second fluid pressure including (1) a plunger means slidably mounted in said first bore of said conducting means and axially movable relative thereto,

(2) anaetuating means having opposed first and second actuating surfaces with said first surface being disposed in said first conducting means and operable to be acted upon by said first fluid pressure and said second surface being 7 disposed in said chamber of said second, con

by said second fluid pressure,

(3) sealing means carried by said actuating portion for sealing said first and second conducting means from each other, and (4) biasing means,

(J) said plunger means being a hollow cylinder (lQ-f tire valve means is carired by said first piston means. 4. The combination according to claim 3 wherein (A) said valve means includes.

(l) a plunger means slidably mounted in said piston means, and j (2) an actuating means carried by said first piston means for actuating said plunger means, (B) said actuating means 7 (1) being exposed .to and acted-upo'n'by both said first and second fluid pressures, (2) forming a part of said first piston means, and (3) is movable relative to said firstpiston means to actuate said plunger means. 5. The combination according to claim 4 wherein said plunger means'is disposed in' said second conducting ducting means andoperable to be acted upon means, and cooperates therewith 'toregulatei the flow of said second fluid pressure.

- on the periphery thereof, 7 I (B) said first-piston means includes an elongated bore, (C) at least a portion of said elongated bore forms a part of said secondconducting means and, carries a second engaging surface therein cooperable with pressure fluid through said second conductingmeans, (D) vent'means are formed insaid first piston means and is confluent with said venting bore, and (E) said actuating means is a venting bore and having a first engaging surface said first engaging surface to, block the flow of said (1) operative to engage said plunger means thereby blocking said venting bore,

(2) radially larger than said plunger means and therefore having a portion thereof extending radially beyond said plunger means, and

(3) operative to urge said plunger means whereby said first and second engaging means are moved away from each other thereby opening said second conducting means,

(F) whereby said second pressure means acts upon the extending portion of said actuating means.

References Cited by the Examiner UNITED STATES PATENTS Cash 192-13 Rockwell 6010.5 Rockwell 6054.6 Price et a1 60-545 Schnell 60--10.5 X Stelzer 60-52 Stelzer 6054.6

JULIUS E. WEST, Primary Examiner.

ROBERT R. BUNEVICH, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,182,443 May 11, 1965 Martin J. Hermanns It is hereby certified that error appears in the above numbered patent reqiiring correction and that the said Letters Patent should read as correcteibelow.

Column 2, line 33, strike out "means"; 45, for "carired" read carried "piston" insert first column 8, line line 48, before Signed and sealed this 21st day of September 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Atlcsting Officer Commissioner of Patents

Claims (1)

1. AN OPERATING MECHANISM HAVING AN ASSIST DEVICE INCORPORATED THEREIN COMPRISING IN COMBINATION, (A) A HOUSING MEAN, (B) A PISTON ROD DISPOSED IN SAID HOUSING, (C) A FIRST AND A SECOND PISTON MEANS DISPOSED IN SAID HOUSING FOR COOPERATIVELY IMPOSING URGING FORCES ON SAID PISTON ROD AND URGING THE LATTER RELATIVE TO SAID HOUSING MEANS, (D) A FIRST FLUID PRESSURE OF MANUALLY CONTROLLABLE MAGNITUDE AND FIRST SUPPLY MEANS FOR SUPPLYING THE SAME, (E) A SECOND FLUID PRESSURE AND SECOND SUPPLY MEANS FOR SUPPLYING THE SAME, (F) A FIRST CONDUCTING MEANS CONNECTING SAID FIRST SUPPLY MEANS TO SAID HOUSING FOR CONDUCTING SAID FIRST FLUID PRESSURE THERETO AND HAVING A PORTION THEREOF DISPOSED IN SAID HOUSING WHEREBY SAID FIRST FLUID PRESSURE IS OPERATIVE TO ACT UPON SAID FIRST PISTON MEANS, (G) A SECOND CONDUCTING MEANS CONNECTING SAID SECOND SUPPLY MEANS TO SAID HOUSING FOR CONDUCTING SAID SECOND FLUID PRESSURE THERETO AND HAVING A PORTION THEREOF DISPOSED IN SAID HOUSING WHEREBY SAID SECOND FLUID PRESSURE IS OPERATIVE TO ACT UPON SAID SECOND PISTON MEANS, (H) SAID SECOND CONDUCTING MEANS INCLUDING THEREIN A FIRST BORE AND A CHAMBER FORMED AXIALLY ADJACENT SAID BORE WITH SAID CHAMBER BEING RADIALLY LARGER THAN SAID FIRST BORE, (I) VALVE MEANS FOR REGULATING THE PRESSURE MAGNITUDE OF SAID SECOND FLUID PRESSURE INCLUDING (1) A PLUNGER MEANS SLIDABLY MOUNTED IN SAID FIRST BORE OF SAID CONDUCTING MEANS AND AXIALLY MOVABLE RELATIVE THERETO, (2) AN ACTUATING MEANS HAVING OPPOSED FIRST AND SECOND ACTUATING SURFACES WITH SAID FIRST SURFACE BEING DISPOSED IN SAID FIRST CONDUCTING MEANS AND OPERABLE TO BE ACTED UPON BY SAID FIRST FLUID PRESSURE AND SAID SECOND SURFACE BEING DISPOSED IN SAID CHAMBER OF SAID SECOND CONDUCTING MEANS AND OPERABLE TO BE ACTED UPON BY SAID SECOND FLUID PRESSURE, (3) SEALING MEANS CARRIED BY SAID ACTUATING PORTION FOR SEALING SAID FIRST AND SECOND CONDUCTING MEANS FROM EACH OTHER, AND (4) BIASING MEANS, (J) SAID PLUNGER MEANS BEING A HOLLOW CYLINDER DEFINING A VENTING BORE AND HAVING A FIRST ENGAGING SURFACE ON THE PERIPHERY THEREOF, (K) SAID SECOND CONDUCTING MEANS HAVING A SECOND ENGAGING SURFACE IN SAID FIRST BORE THEREIN COOPERABLE WITH SAID FIRST ENGAGING SURFACE AND (1) ENGAGEABLE THEREWITH TO BLOCK SAID SECOND CONDUCTING MEANS, AND (2) DISENGAGEABLE THEREWITH TO OPEN SAID SECOND CONDUCTING MEANS WHEREBY SAID SECOND FLUID PRESSURE MAY PASS THROUGH SAID SECOND CONDUCTING MEANS PERIPHERALLY OF SAID PLUNGER MEANS, (L) SAID BIASING MEANS NORMALLY BIASING SAID PLUNGER MEANS FOR BIASING SAID ENGAGING SURFACES INTO ENGAGEMENT WITH EACH OTHER, (M) SAID SECOND SURFACE OF SAID ACTUATING MEANS IS (1) ENGAGEABLE WITH SAID PLUNGER FOR BLOCKING SAID VENTING BORE AND URGING SAID PLUNGER AGAINST THE BIASING EFFECT OF SAID BIASING MEANS THEREBY MOVING SAID ENGAGING SURFACES INTO A DISENGAGED RELATIONSHIP WITH EACH OTHER, (2) RADIALLY LARGER THAN SAID PLUNGER MEANS AND THEREFORE HAVING A PORTION THEREOF EXTENDING RADIALLY BEYOND SAID PLUNGER MEANS WHEREBY (A) SAID SECOND FLUID PRESSURE IN SAID CHAMBER IS OPERATIVE TO ACT UPON SAID EXTENDING PORTION OF SAID SECOND SURFACE WHILE THE LATTER IS ENGAGED WITH SAID PLUNGER MEANS AND BLOCKING SAID VENTING BORE AND IMPOSE AN URGING FORCE ON SAID ACTUATING MEANS IN OPPOSITION TO THE URGING FORCE THEREON OF SAID FIRST FLUID PRESSURE ON SAID FIRST SURFACE, (B) WHEN SAID URGING FORCE OF SAID SECOND FLUID PRESSURE ACTING UPON SAID ACTUATING MEANS EXCEEDS THE URGING FORCE OF SAID FIRST FLUID PRESSURE ACTING UPON SAID ACTUATING MEANS THE LATTER MOVES FROM ENGAGEMENT WITH SAID PLUNGER MEANS AND OPENS SAID VENTING BORE WHILE ALLOWING SAID BIASING MEANS TO BIAS SAID ENGAGING SURFACES INTO ENGAGEMENT WITH EACH OTHER.

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