US3311026A

US3311026A - Bypass valve for hydraulic jacks

Info

Publication number: US3311026A
Application number: US516619A
Authority: US
Inventors: Chester A Crisp
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1965-12-27
Filing date: 1965-12-27
Publication date: 1967-03-28
Anticipated expiration: 1984-03-28
Also published as: GB1126725A; SE304921B; DE1279908B; BE691819A; FR1506058A

Description

March 28, 1967 c. CRISP BYPASS VALVE FOR HYDRAULIC JACKS 2 Sheets-Sheet 1 Filed Dec. 27, 1965 INVENTOR. CHESTER A. CRISP T a 7. PW 2 ATTORNEYS March 28, 1967 c. A. CRISP BYPASS VALVE FOR HYDRAULIC JACKS 2 Sheets-Sheet 2 Filed Dec. 27, 1965 INVENTOR. CHESTER A. CRISP I "9%,? W HORNEYS United States Patent Ofiice 3,311,026 Patented Mar. 28, 1967 3,311,026 BYPASS VALVE FOR HYDRAULIC JACKS Chester A. Crisp, Wilmington, Ill., assignor to Caterpillar Tractor Co., Peoria, 111., a corporation of California Filed Dec. 27, 1965, Ser. No. 516,619 2 Claims. (Cl. 91-401) This invention relates to hydraulic jacks and particularly to improvements in the bypass valves employed in some jacks to relieve the shock when the piston reaches the end of its travel and abuts the end of the cylinder.

It is common practice to provide double acting check valves controlling flow through passages which extend through the piston of a hydraulic jack. Such valves have stems projecting from opposite sides of the piston. They are held closed by actuating pressure on one side of the piston and, when the piston approaches the end of its stroke, they are opened by engagement of the stems with the end of the cylinder or a part thereof. This permits bleeding of actuating pressure to the low pressure end of the jack and to a sump so that only enough pressure remains to hold the piston in its load sustaining position.

The valves described above often relieve or bypass too much fluid too quickly so that the piston travels on by pressure and inertia to the end of its stroke where shock is produced which is damaging to the jack and its supporting structure.

It is the object of the present invention to improve bypass valves of the kind described by simple and inexpensive means in a manner to modulate the fiow of bypassed fluid and thus decrease the speed of the piston prior to bypassing the full capacity of the valves.

The above and further objects and advantages of the invention are made apparent in the following specification wherein the invention is described in detail by reference to the accompanying drawings.

In the drawings:

FIG. 1 is a view in side elevation of the front portion of a track-type tractor with a bulldozer secured thereto and illustrating a conventional jack for raising and lowering the bulldozer blade with respect to the ground;

FIG. 2 is an enlarged fragmentary sectional view of the jack shown in FIG. 1 illustrating valves embodying the present invention controlling flow of fluid through the jack piston;

FIG. 3 is a fragmentary detail showing a constructional feature of one of the valves shown in FIG. 2; and

FIG. 4 is a sectional view taken on the line IV-IV of FIG. 3.

In FIG. 1, the forward end of a tractor indicated generally at is shown as supporting a bulldozer blade 11 by means of push arms 12 which may be raised and lowered about their pivotal connections 13 with truck frames 14 of the tractor, there being only one push arm and connection shown in FIG. 1. A tilt brace is only partially shown at 15 and a hydraulic jack 16 is provided for raising and lowering the blade. The jack is pivotally supported on a trunnion 17 shown in dotted lines and supported on a bracket 18 which is secured to the radiator guard 19 of the tractor.

The jack has the usual piston and extensible rod 20 pivoted to the blade 11 as at 21. The jack is of the double acting type and fluid from a suitable source under pressure, which is not shown, may be introduced to either end of the jack for raising and lowering the blade. When a jack of this type is fully extended or fully retracted under the high pressures required for operating devices of this type, an undesirable shock is often encountered as the piston reach-es the end of the stroke and damage results not only to the jack but to associated parts of the tractor itself. It has been common practice to provide ports extending through the piston from the rod end to the head end of the cylinder and to control flow through these ports with double acting check valves of the kind shown in FIGS. 2, 3 and 4.

In FIG. 2, the jack piston is shown at 23 as fitted over a reduced end of the rod 20 and secured thereon as by a nut 24. The piston is generally of solid material With suitable seals such as shown at 25 and 26 and has ports extending therethrough for reception of

check valves

27 and 28 which have

stems

29 and 30, respectively, guided in sleeves 31 pressed into opposite ends of the port. The sleeves are retained in position by washers 33 and 34 encircling the reduced portion of the shaft 20 and overlying the edges of the sleeves. The sleeves are generally hollow and have cutaway portions, best shown in FIGS. 3 and 4 at 35, communicating with their interiors to permit flow of fluid from one side of the piston to the other. Thus as the piston approaches the end of its stroke in either direction, the projecting ends of the valve stems 29 and 30 engage the end of the cylinder being approached and the valves, having been held closed by the pressure which causes the stroke, are opened to bleed pressure to the opposite sides of the piston. For example with pressure on the rod side of the piston as indicated in FIG. 2, the valves are normally urged to the closed position such as illustrated for the valve 28 and as the end of the stroke is approached, the valves are opened to the position shown in connection with the valve 27 to permit bleeding of pressure from the rod side to the head side and this pressure is exhausted as through a passage 36 and conduit 37 through which it is returned to the sump (not shown). One disadvantage of the earlier bypass valves of this type was that both valves engaged the end of the cylinder at the same time and were opened simultaneously so that a great deal of pressure was exhausted at once and the force of fluid behind the piston as well as inertia cause it to strike the end of the cylinder with -a resultant destructive shock.

The improvement of the present invention resides in providing one of the valves, this being the valve 27 in FIG. 2, with a stem which is considerably longer in both directions than the stem of the other valve. Consequently as the piston approaches the end of the stroke, this stem is engaged first and the one valve opened first bleeding a small quantity of fluid thus reducing speed prior to opening of the second valve. Consequently the inertial force has been reduced and contact between piston and the end of the cylinder is prevented.

The present disclosure shows the piston as having two ports and two valves but obviously any number of valved ports may be employed and any desired number of the valves mayhave longer stems for producing the modulating effect which is produced by opening of one or more valves prior to opening of the others.

What is claimed is:

1. In a hydraulic jack having a piston rod and piston and check valves in the piston which are closed by pres- 3,311,026 3 4 sure on either side of the piston and having stems pro- References Cited by the Examiner jecting from the piston for engagement with the end UNITED STATES PATENTS of the, cylinder at the opposite side of the piston to re-' duce, shock when the piston approaches the end of its 841'527 1/1907 Imler 91-422 7 stroke, the improvement which comprises means for 5 1,985,361 12/1934 Anthony et a1 91-401 opening one of said check valves prior to opening others 2752'890 7/1956 Rogneby 91 401 to modulate the escape of pressure through the'piston 290L007 9/1959 ROFkWeH 91 401 and reduce the shock occurring at the end of its stroke. 3,182,563 5/1965 Nellan 91401 2. The combination of claim 1 in which the means for opening is a stem on said one check valve which is longer 10 MARTIN SCHWADRON Primary Exammer' than that of the others. P. E. MASLOUSKY, Assistant Examiner.

Claims

1. IN A HYDRAULIC JACK HAVING A PISTON ROD AND PISTON AND CHECK VALVES IN THE PISTON WHICH ARE CLOSED BY PRESSURE ON EITHER SIDE OF THE PISTON AND HAVING STEMS PROJECTING FROM THE PISTON FOR ENGAGEMENT WITH THE END OF THE CYLINDER AT THE OPPOSITE SIDE OF THE PISTON TO REDUCE SHOCK WHEN THE PISTON APPROACHES THE END OF ITS STROKE, THE IMPROVEMENT WHICH COMPRISES MEANS FOR OPENING ONE OF SAID CHECK VALVES PRIOR TO OPENING OTHERS TO MODULATE THE ESCAPE OF PRESSURE THROUGH THE PISTON AND REDUCE THE SHOCK OCCURRING AT THE END OF ITS STROKE.