US3458017A - Hydraulic cylinder with automatic adjustment of retraction of its piston - Google Patents

Description

July 2 1969 E. J. szmsm 3, ,0 7

HYDRAULIC CYLINDER WITH AUTOMATIC ADJUSTMENT 0F v RETRACTION OF ITS PISTON Filed Nov. 1, 1967 3 Sheets-Sheet 1 FIESEJ f7? Z/erz 2'07".- fa yerze 2153 971254! y 1969 E. J. SZYMSKI 3,458,017

HYDRAULIC CYLINDER WITH AUTOMATIC ADJUSTMENT OF V RETRACTION OF ITS PISTON Filed Nov. 1. 1967 s SheetsSheet' 2 FI'iE July 29, 1969 E. J. SZYMSKI 1 HYDRAULIC CYLINDER WITH AUTOMATIC ADJUSTMENT OF RETRACTIQN OF ITS PISTON 3 Sheets-Sheet 3 Filed Nov. 1, 1967 .77? @7210 7". Zzyerze 153522251?! United States Patent 3,458,017 HYDRAULIC CYLINDER WITH AUTOMATIC ADJUSTMENT 0F RETRACTION OF ITS PISTON Eugene J. Szymski, Skokie, Ill., assignor to General American Transportation Corporation, a corporation of New York Filed Nov. 1, 1967, Ser. No. 679,910 Int. Cl. F16d 65/40; B60t 17/00 US. Cl. 188196 6 Claims ABSTRACT OF THE DISCLOSURE A hydraulic cylinder has a piston that is retracted by a spring to a non-working position. In a preferred use, wear of a brake lining mounted on the front face of the piston results in a change of the pistons working position. A narrow range of piston retraction is automatically maintained by pawl means and ratchet means through their disengagement by cam means upon forward movement of the piston and by their relative movement parallel to the axial movement of the piston. This relative movement is provided by the force developed in the spring.

BACKGROUND OF THE INVENTION Field of the invention This invention pertains to a hydraulic cylinder that has its piston moved to a working position that changes with repeated use and more particularly to an automatic retractable disc brake wear-compensating hydraulic cylinder.

Description of the prior art Many automatic adjusters have been developed to limit the return of a piston of a hydraulic cylinder from its working position where the return is provided by a spring. An example of such an automatic adjuster is disclosed and claimed in US. Patent No. 3,043,406. In that construction a push rod is disposed in telescoping relationship with a piston rod moved forwardly by a piston but retracted by a spring. For the adjustment the push rod is advanced relative to the piston rod. Another automatic adjuster for a hydraulic cylinder is provided by a construction that mounts the spring in a recess in the back face of the piston and has a rod slidably mounted in a frictional manner through the back wall of the housing of the cylinder. The rod has an enlarged front end engaging the front end of the spring. The spring has its rear end mounted for movement with the piston. By this construction increased movement of the piston by fluid pressure due to wear on the front face of a brake lining mounted on the front of the piston provides sufficient force through the spring to slide forwardly the rod frictionally mounted on the wall of the housing. This provides a substantially uniform compression of the spring even though the piston has moved to a new working position for the front face of the brake lining. Upon release of fluid pressure the spring will retract the piston only by the desired distance and will not move the rod rearwardly only if the friction between the rod and its mounting remains sufficiently great. With repeated use the "ice friction will decrease and the automatic adjustment will be partially or completely lost.

SUMMARY OF THE INVENTION This invention relates to an automatically adjustable hydraulic cylinder to provide substantially the same amount of travel of the piston by fluid pressure to a working position regardless of the change of location of that working position. The automatically adjustable hydraulic cylinder includes (1) a housing having at least one port to selectively provide and release fluid pressure, (2) a piston in the chamber, (3) a spring mounted for movement of one of its ends by the piston during the forward movement of the piston upon the application of fluid pressure to the chamber at the rear of the piston, (4) means engaging the other end of the spring, (5) ratchet means, (6) pawl means, one of said ratchet means and pawl means being fixedly mounted relative to said housing and the other of said means being mounted for movement with the piston upon disengagement with the other of said means, and (7) cam means, rearwardly extending means mounted on said piston and constructed to engage and provide forward movement of said cam means during each forward movement of the piston, said cam means being constructed to disengage radially said ratchet means and said pawl means during each forward movement and said means engaging said other end of the spring being constructed to move with it one of said ratchet means and said pawl means.

In its preferred use, the hydraulic cylinder of the invention includes a brake lining mounted on the front face of the piston and forward of the housing of the cylinder.

The hydraulic cylinder of this invention has a relatively simple construction and is fairly compact. The construction provides a nearly constant spring retraction force from the use of the brake lining when new until the lining is sufliciently worn to be replaced. The construction that provides the automatic adjustment as the brake lining wears, maintains a nearly constant clearance between the brake lining and a disc to which it is applied for braking the rotation of the latter. Thus, the time for the advancement of the piston to the braking position is minimized.

BRIEF DESCRIPTION OF DRAWINGS The hydraulic cylinder in combination with a brake lining and a disc on a vehicle is illustrated in the drawings which present a preferred embodiment of the hydraulic cylinder of this invention in a specific form of application. In the drawings like parts are assigned the same numeral.

FIG. 1 is a cross-section of the hydraulic cylinder with a brake lining in brake applied position and with a cooperative mounting which also supports another brake lining, along with a fragmentary part of a disc brake as viewed along line 11 of FIG. 3.

FIG. 2 is an enlargement of a fragmentary portion of the hydraulic cylinder and the brake lining as seen in FIG. 1.

FIG. 3 is a rear elevational view of the hydraulic cylinder of the invention and a fragmentary portion of the brake disc.

FIG. 4 is an enlarged view of substantially the same portion of FIG. 2 but showing the hydraulic cylinder in brake release position.

FIG. 5 is an enlarged fragmentary view showing the hydraulic cylinder in the brake applied position after a substantial amount of wear of the brake lining mounted on the piston of the hydraulic cylinder.

FIG. 6 is a longitudinal cross-section of a cam sleeve used in the hydraulic cylinder of the invention.

FIG. 7 is a front elevational view of the ring pawl of the hydraulic cylinder of the invention.

FIG. 8 is a cross-section of the ring pawl taken along the line 8-8 of FIG. 7.

DETAILED DESCRIPTION Referring to FIG. 1 the hydraulic cylinder of the present invention is indicated generally at 11 and includes a housing generally indicated at 12 that is open at its front end and has a rear wall 13 with an opening 14. A piston 15 having a front face 16 is in housing 12. A brake lining 17 is mounted on front face 16 of piston 15 by screws 18. The opening 14 is concentric with piston 15.

The piston 16 and housing 12 enclose a chamber 19 into which pressurized fluid, such as oil is introduced through one of ports 20 in the sides of housing 12. That port 20 is connected by pipe 21 to an oil source (not shown) to fill chamber 19. When this is done, bleeder valves 22 in ports 23 in the sides of housing 12 are open until oil bleeds out. A bleeder valve 24 in port 23 in the top of housing 12 is also open until air is displaced by oil and the latter starts to flow out valve 24. The pipe 21 is then still full of oil and by a valve (not shown) is disconnected from the oil source to a piston and pipe system (not shown). The piston is forced against the oil to provide hydraulic pressure by pressurized air in a convention- :al manner for brake systems using air of lower pressure to provide oil at substantially higher pressure. Release of air pressure releases hydraulic pressure and the piston is displaced by displacement of oil in chamber 19 by piston 15.

The piston 15 has a central opening 25 that extends axially and has a larger diameter at its front and rear ends to provide a front recess 26 and a larger rear recess 27. A cylindrical shaft 28 extends from recess 26 through central opening 25 and rearwardly of recess 27. The shaft 28 has an enlarged head 29 at its rear end providing a forwardly facing peripheral shoulder. The shaft 28 has a front end of smaller diameter to provide a shoulder 30 and is held in place by a retaining ring 31 mounted on an annular reaess 32 in the front end portion and the ring 31 cooperates with shoulder 30 that abuts piston 16 at the base of recess 27. The shaft 28 has another annular recess between shoulder 30 and retaining ring 31 to receive a hydraulic seal 33 to prevent loss of pressurized fluid in a forward direction. The housing 12 is provided with a dirt seal 34 in an annular recess in its sidewall. The ring 34 is engaged by piston 15. The piston 15 has an annular recess 35 in which is mounted a hydraulic seal 36 that engages housing 12.

A sleeve 37 is mounted on shaft 28. Adjacent its rear end sleeve 37 has an annular elongated recess 38 with a base surface that is forwardly converging, i.e. that tapers inwardly from its rear to its front. The sleeve 37 has a larger diameter at its rear end and spaced from recess 38 to provide a forwardly facing shoulder 40.

A spring pawl 41 is slidably mounted on sleeve 37 to abut shoulder 40. The spring pawl 41 is mounted on sleeve 37 by sliding it over the front end of sleeve 37 until its rear portion is past recess 38. The spring pawl 41 is a hollow cylinder having a thicker wall at its front end portion to provide an outer cam surface 42 that is outwardly diverging in the forward direction relative to the axis. The spring pawl 41 also has a number of longitudinal slots 43 extending from the front end to a short distance from the rear end so as to provide a number of individual spring members 44 pivoting adjacent the rear end and movable radially inward until the distal ends of surfaces 42 of members 44 are aligned with the outer surface of the rear portion of spring pawl 41. This inward movement i provided by a cam sleeve 45 mounted on sleeve 37. The front end of sleeve 45 is beveled to have an end surface 46 at the same angle from the longitudinal axis as cam surface 42. Then the front part of cam surfaces 42 of spring members 44 are in contact with cam surface 46.

The rear end of cam sleeve 45 abuts head 29 of shaft 28 when the brake is applied, as described later. When piston 15 is retracted to the brake release position, head 29 is spaced from cam sleeve 45. At the brake release position, a rear part of cam surfaces 42 of spring members 44 are in contact with cam surface 46.

A sleeve 47 is mounted on sleeve 37 between recess 38 and a ring 48 which is also mounted on sleeve 37. The ring 48 is prevented from movement to the front end of sleeve 37 by a retaining ring 49 in an annular recess 50 of sleeve 37. The ring 48 is thus mounted adjacent the front end of sleeve 37.

A Belleville spring 51 is mounted on sleeve 47 between ring 48 and a retaining ring 52 in an annular recess 53 in rear recess 27 of piston 15. The spring 51 comprises a number of annular cupped discs 54. The spring 51 is in a preloaded condition when piston 15 is at its retracted position.

The sleeve 37 and ring 48 constitute a retractor tube mounted on shaft 28 with ring 48 being a radial flange of the retractor tube. The sleeve 37 extends outside housing 12 through opening 14, but is within a retractor housing generally indicated at that comprises a cylindrical pipe 61 closed at its rear end by a circular plate 62 by the use of screws 63. The housing 60 extends into opening 14 and has its front end coplanar with the front surface of wall 13 of housing 12.

The outer diameter of tube 61 is stepped at its front portion to provide a shoulder 64 that abuts the rear face of wall 13. The tube 61 has an annular recess 65 in which is mounted a packing ring 66 that engages wall 13 adjacent and in front of shoulder 64. The retractor housing 60 is secured to wall 13 by suitable means, such as by threading (not shown). The front end of tube 61 has an inwardly directed radial flange 67 that extends toward sleeve 47.

The housing 12 has integral with its rear wall 13 a pair of strengthening ribs '68 that are on opposite sides of housing 60. The housing 12 has a downwardly extending (as viewed in FIGS. 1 and 3) lateral flange 70 having a number'of cylindrical bores 71. Bolts 72 extend through bores 71 to mount housing 12 to a mounting flange (not shown). A brake lining 73 is mounted by screws 74 on a support plate75. The rear face of brake lining 73 is forwardly spaced from and directly opposite the front face of brake l7ining 17. The support 75 is secured to housing 12 by bolts A ring ratchet generally indicated at 76 is mounted in pipe 61. The ring ratchet 76 comprises a stack of annular discs 77, each having their inner surface beveled at an angle corresponding to the angle of inclination of cam surface 42 and end surface 46 of sleeve 45. The ring ratchet 76 is fixed in position between flange 67 and a retainer sleeve 78 in housing 60 and abutting plate 62. The total of the longitudinal lengths of ring ratchet 76 and sleeve 78 corersponds to the distance between flange 67 and plate 62 of housing 60 so that ring ratchet 76 is stationary. The sleeve 78 has a reduced wall thickness at its front by a recess. The longitudinal length of this thinner wall is sufficiently great to insure positioning of the thicker front end of spring pawl 41 just back of ring ratchet 76.

When the threaded ends of bolts 72 are secured to support plate 75 they extend through openings in a mounting flange (not shown) mounted on the vehicle (not shown) for which the illustrative cylinder of the invention is used. The three bolts 72 maintain housing 12 and support 75 at a fixed location on the vehicle. The mounting flange on the vehicle is between and abuts housing 12 and support 75.

A ring disc having a number of peripheral notches 91 (FIG. 3). The inner and outer diameters of disc 90 are such that when mounted concentric to a wheel axle has a surface portion facing brake linings 17 and 73. The outer peripheral margin of the disc 90 has notches 91 and is radially outside housing 12 and support 75.

The disc 90 is rotated by engagement with lugs mounted on a wheel of the vehicle (both not shown). The lugs in notches 91 rotate disc 90 but do not prevent some axial movement of disc 90.

OPERATION In the following description of the operation of the illustrative hydraulic cylinder of this invention it is assumed that hydraulic oil, not under pressure, is in chamber 19 and pipe 21 which is in communication with a cylinder having its piston to be moved by the application of pressurized air. It is also assumed that piston 15 is in the brake release position as shown in FIG. 4 and that a new brake lining 17 is mounted on retracted piston 15. The piston 15 abuts the front end of sleeve 37 but the enlarged head 29 of shaft 28 is spaced from sleeve 37 and spaced from sleeve 45. The cam surface 42 of spring pawl 41 are merely abutted by cam surface 46 of sleeve 45. The spring members 44 are in their normal position. The front end of spring pawl 41 abuts the rear end of ratchet 76. The Belleville spring 51 is in its preloaded condition.

The vehicle is moving and thus disc 90 is being rotated about its axis. The brake lining 17 is spaced from ring disc 90 but brake lining 73, which is also assumed to be new, is in slight rubbing contact with the disc 90.

To stop the vehicle the brake pedal of the vehicle is depressed and this results in oil being forced into chamber 19. This pressurized fiow of oil forces piston 15 to the right (as viewed in FIG. 1) until brake lining 17 is forced against the disc 90. The disc 90 is forced against brake lining 73. As a result both brake lining 17 and 73 engage disc 90 to slow or stop the vehicle.

When piston 15 is moved to the right, spring 51 is further compressed between ring 48 and ring 52. Movement of ring 48 is prevented because sleeve 37 is prevented from moving to the right by spring pawl 41 that has its front end abutting ratchet 76.

When piston 15 is moved to the right shaft 28 and its enlarged head 29 are moved to the right. Upon braking engagement of brake lining 17 and 73 against disc 90 the movement to the right of shaft 28 and its head 29 are only sufficient to bring head 29 into contact with the rear end of cam sleeve 45. As a result cam sleeve 45 is not moved relative to spring pawl 41. Thus, the front end of spring members 44 are not moved radially inwardly to an unlatching position.

When the brake is released, the pressure of oil in chamber 19 is released. The spring 51 expands to its normal pre-loaded condition. This expansion of spring 51 provides a force against retaining ring 52 to move piston 15 rearwardly. When piston 15 is thus retracted brake lining 17 is no longer in contact with disc 90 and thus disc 90 is no longer forced against brake lining 73. The head 29 of shaft 28 is returned to its position where it is spaced from the rear end of sleeve 45.

By a number of cycles of operation of brake application and brake release, as described above, there will be an amount of wear of brake linings 17 and 73. When the wear has been sufficient the application of the brakes will provide a greater movement of piston 15 to the right as compared with its movement with the new brake lining 17. This greater forward movement results in a greater movement of head 29 of shaft 28. In the last stage of the movement of head 29 it will move cam sleeve 45 to the right. During this movement of cam sleeve 45, spring members 44 of spring pawl 41 have their front ends moved inwardly further into recess 38 of sleeve 37. If this last stage of movement of head 29 is sufficiently long, due to wear of brake lining 17, the inward radial movement will be sufficient for spring members 44 to be completely unlatched and thereby no longer engage ring ratchet 76. The Belleville spring 51 being compressed now can move sleeve 37 to the right. This movement of sleeve 37 moves spring pawl 41 to the right and thereby provides relative movement between cam surface 42 of spring pawl 41 and cam surface 46 of cam sleeve 45. This permits spring members 44 to return to their normal positions. During this return, spring pawl 41 engages ratchet 76 thereby preventing further forward movement of sleeve 37. By this time cam surface 46 is now in contact with the bottom portion of cam surface 42 of spring pawl 41. When the oil pressure is released, piston 15 is retracted as described earlier, except its retracted position is advanced at least one ratchet spacing.

Until there is a sufficient amount of further wear of brake lining 17 to provide the foregoing unlatching of spring pawl 41 with respect to ratchet 76, spring members 44 remain in their normal positions and are merely abutted by the front end of sleeve 45.

It is seen from the foregoing that the repositioning to the right of spring pawl 41 is in a longiutdinal or axial direction relative to ring ratchet 76 to a new latched position. The distance of return of piston 15 is limited by the new position of sleeve 37 that, when moved to new position right as described above, releases some of the force produced by the compression of spring -51 when piston 15 was moved to the right. Accordingly, piston 15 moves in its retraction until it abuts sleeve 37 and there is no force remaining to move it further rearwardly. Thus the piston is now at a new position from which it is moving only by same initial distance to apply the brakes.

Further movement of the right-hand end of spring 51 occurs with subsequent wear of lining 17 and subsequent unlatching of spring pawl 41 from ratchet 76 and relative movement of spring pawl 41, as described above. This maintains piston in a non-working position that is a substantially fixed distance from its working position even though wear of brake lining 17 occurs.

It is seen from the foregoing description of the hydraulic cylinder of the invention (1) that spring means retracts the piston, (2) that one end of the spring by pawl means and ratchet means is maintained at a fixed location until the piston moves a greater distance to new working position, (3) that the greater movement of the piston, due to brake lining wear, unlatches the pawl means from the ratchet means by cam means moved with the piston during its increased portion of movement, (4) that the spring provides a force to move One of the pawl means and the ratchet means in direction of movement of the piston to its working position, (5) that at the same time the springs force moves that end of the spring means to a new fixed position, and (6) that upon retraction of the piston the cam means is rendered ineffective so that there is a latching of the pawl means to theratchet means to maintain that end of the spring means at the new fixed location. Thus the construction provides a nearly constant spring retraction force from the time that new brake lining is installed until they are worn to the extent requiring its replacement. Because the position at which the pawl means latches to the ratchet means advances as the lining wears, a nearly constant clearance is maintained between the disc and the brake lining. This minimizes piston advancement delay.

It is apparent that piston 15 and shaft 28 can be of one-piece construction. Thus the piston is one that has a rearwardly extending shaft with its distal end being constructed to abut and then provide a forward movement of cam means when the piston is moved forwardly by a distance greater than a predetermined distance.

The foregoing description of a preferred embodiment of the hydraulic cylinder of the invention is illustrative only. For example, the invention is described in a brake system in which the automatic adjustment is made only for one of the pair of opposed brake linings. Obviously. a hydraulic cylinder ofthe present invention can be used in place of support 75 and its brake lining 73'. The illustrative embodiment is a simple modification of a disc brake system that utilizes disc 90 on an existing vehicle.

Various other modifications of the hydraulic cylinder of this invention will be obvious to one of ordinary skill in this art in view of the foregoing disclosure. For example, Belleville spring 51 may be replaced by other spring means. As another example, ring ratchet 76 can be replaced by a ratchet fixedly mounted on sleeve 37. Other pawl means can be provided. In such case the substitute ratchet means has its detents facing outwardly and these are engaged by the replacement pawl means. The ratchet means, which would be slidably mounted, is moved by shaft 28 upon its movement beyond a predetermined amount. At the same time shaft 28 will move cam means to disengage the pawl means.

It is also obvious that the hydraulic cylinder of the invention can be utilized for other than disc brake systems to control the location of the non-working position of piston 15 when its working position shifts.

I claim:

1. A hydraulic cylinder, having an automatic adjustment to provide a nearly constant distance of retraction of the piston of the cylinder by a spring regardless of the increased advance of the piston to new working positions in the cycles of use of the cylinder, which comprises:

(1) a housing having a port;

(2) a piston in the housing and with the housing defining a chamber in communication with the port;

(3) spring means mounted to provide an opposing force to the piston and having one end movable by and with said piston upon the application of fluid pressure in the chamber suflicient to move the piston;

(4) means slidably mounted on the housing;

(5) pawl means;

(6) ratchet means engaged by said pawl means; and

(7) means mounted to be moved by said piston during said piston movement to disengage said pawl means from said ratchet means and rendered ineffective to maintain said disengagement during movement of the piston in the opposite direction,

one of said pawl means and said ratchet means being mounted to be fixed relative to the housing and the other being mounted to move with said means slidably mounted on the housing, and said spring means having its other end mounted to be fixed relative to said means slidably mounted on the housing and movable relative to the housing during said piston movement provided by the fluid pressure and in the same direction only upon disengagement between said pawl means and said ratchet means.

2. The hydraulic cylinder of claim 1 and further comprising a brake lining mounted on said piston for movement with and ahead of the piston during the piston movement provided by the fluid pressure.

3. The hydraulic cylinder of claim 2 herein 1) said housing is open at the front end and has the port at the rear wall,

(2) said rear wall has an opening coaxial with said piston,

(3) said piston has an annular concentric recess in its rear wall,

(4) said spring means is mounted in the recess and has its rear end mounted to be moved forward with and by the piston,

(5) the piston has from the base of the recess a coaxial rearward extension through the spring means and through the opening in the rear wall and has its rear end of larger diameter,

(6) said means slidably mounted on the housing is a tube on said rearward extension of the piston and at its front end has a radial flange abutting the front end of the spring means and has an elongated recess in its rear portion with the depth of the recess increasing in the forward direction for at least the front part of the recess,

(7) the pawl means is a spring pawl mounted in the elongated recess and constructed with a front end extending further radially with a cam surface facing rearwardly and outwardly to be moved radially inward at its front end to be disengaged from the ratchet means for forward movement of the pawl,

(8) the ratchet means has detents disposed longitudinally of the tube and in alignment with said extension of the front end of the spring pawl,

(9) said disengaging means comprises cam means slidably mounted on the tube and has a cam surface at its front end to engage said cam surface of the spring pawl to provide said radially inward movement upon forward abutting movement of said cam sleeve relative to said spring pawl upon engagement by and movement with the larger diameter rear end of the piston extension, and

(10) said housing having a rear extension enclosing said piston extension, spring pawl, cam means, and ratchet means, said ratchet being mounted on said housing extensions.

4. A hydraulic cylinder, having an automatic adjustment to provide a nearly constant distance of retraction of the piston of the cylinder by a spring regardless of the increased advance of the piston to new working positions in the cycles of use of the cylinder, which comprises:

(1) a housing open at its front end and having a port through a wall of the housing, a cylindrical cavity and an opening in the rear wall coaxial with the cavity;

(2) a piston in the cylindrical cavity of the housing and with the housing defining a chamber in communication with the port, said piston having a central opening with a central recess at the front of the piston and a central larger recess at the rear of the piston;

(3) a shaft having an enlarged head at its rear end and a front end portion of smaller diameter, said shaft having its front end portion in the central opening of the piston forward of the rear recess and extending into the front recess, said shaft extending through the opening in the rear wall of the housing;

(4) means securing the shaft to the piston;

(5) an extension housing mounted on the rear wall of the housing to enclose the shaft extending beyond said rear wall;

(6) a retractor tube slidably mounted on the shaft forward of the enlarged rear end and having a radially outward flange at the front end of the tube and in the rear recess of the piston and having an elongated annular recess at its outer surface adjacent the rear end of the tube, said recess at its front portion having an inwardly converging bottom wall in the forward direction;

(7) means fixedly mounted on the piston in its rear recess rearwardly of the flange;

(8) a spring mounted on the sleeve between the flange and the fixedly mounted means;

(9) a cylindrical pawl in said recess and having 1ongitudinal slots from its front end to contain pawl members having their front ends movable radially, said pawl having a greater wall thickness at the front end With an outwardly diverging surface in the forward direction that provides the front ends of the pawl members with rearwardly and outwardly face cam surfaces;

(10) a cam sleeve slidably mounted on the rear end of said sleeve having the elongated recess rearwardly and over said pawl rearwardly of said cam surfaces, said cam sleeve having a beveled front end as a complementary cam surface abutting the cam surfaces of the pawl members; and

(11) a ratchet having annular teeth coaxial with said shaft, fixed in said extension housing, and engageable by the front ends of the pawl members between adjacent teeth except when the pawl members are cammed inwardly by the cam sleeve.

5. The hydraulic cylinder of claim 4 and further including a brake lining mounted on the front face of the piston.

6. The hydraulic cylinder of claim 5 wherein the spring is a Belleville springs DUANE A.

1 0 References Cited UNITED STATES PATENTS 9/ 1951 Kovac. 2/ 1965 Gold. 8/ 1967 Trachte. 9/ 1968 Hoenick.

REGER, Primary Examiner US. Cl. X.R.

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