US3918847A

US3918847A - Accumulator charging circuit for high pressure hydraulic system

Info

Publication number: US3918847A
Application number: US440145A
Authority: US
Inventors: John A Junck; Howard L Johnson
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1974-02-06
Filing date: 1974-02-06
Publication date: 1975-11-11
Anticipated expiration: 1992-11-11

Abstract

An accumulator charging arrangement for a high pressure hydraulic system. The arrangement includes a pair of relatively small volumetric capacity fixed-displacement pumps each of which is combined with a separate accumulator charging valve. The pumpcharging valve combinations are disposed in parallel to feed pressure fluid to a pair of accumulator devices for use of the hydraulic circuit upon specific demand. One pump-charging valve combination supplies pressure fluid only within a certain pressure range. The second pump-charging valve combination supplies fluid at a second discrete pressure range which is higher than that within which the first combination operates. For system demands within a lower pressure range, both pump-charging valve combinations are operative to supply fluid, however, upon a demand for pressure only within the higher pressure range, only the second pump-valve combination is operative to supply the separate accumulator devices associated with the combinations.

Description

United States Patent [191 J unck et al.

1 1 Nov. 11, 1975 1 ACCUMULATOR CHARGING CIRCUIT FOR HIGH PRESSURE HYDRAULIC SYSTEM [75] Inventors: John A. Junck; Howard L. Johnson,

both of Joliet, ll].

[73] Assignee: Caterpillar Tractor Company,

Peoria, 111.

[22] Filed: Feb. 6, 1974 [21] Appl. N0.: 440,145

[52] US. Cl. 417/288; 60/416; 60/418;

Primary Examiner-C. J. Husar Assistant Examiner-Leonard Smith Attorney, Agent, or Firm-Phillips, Moore, Weissenberger, Lempio & Strabala [57] ABSTRACT An accumulator charging arrangement for a high pressure hydraulic system. The arrangement includes a pair of relatively small volumetric capacity fixeddisplacement pumps each of which is combined with a separate accumulator charging valve. The pump charging valve combinations are disposed in parallel to feed pressure fluid to a pair of accumulator devices for use of the hydraulic circuit upon specific demand. One pump-charging valve combination supplies pressure fluid only within a certain pressure range. The second pump-charging valve combination supplies fluid at a second discrete pressure range which is higher than that within which the first combination operates. For system demands within a lower pressure range, both pump-charging valve combinations are operative to supply fluid, however, upon a demand for pressure only within the higher pressure range, only the second pump-valve combination is operative to supply the separate accumulator devices associated with the combinations.

2 Claims, 1 Drawing Figure US. Patent Nov. 11, 1975 3,918,847

TO BRAKES ACCUMULATOR CHARGING CIRCUIT FORHIGH PRESSURE HYDRAULIC SYSTEM BACKGROUND or THE INVENTION This invention relates to an accumulator charging circuit which includes a pair of fixed-displacement pumps in combination with a pair of' accumulator charging valves for charging separate accumulator means to provide a system which simulates a variabledisplacement pump arrangement for charging of one or more accumulators in a hydraulic system.

Earthmoving vehicles, such as motor graders and the like, commonly employ accumulators in their hydraulic systems to ensure a constant supply of working fluid for actuating various fluid operated components, such as brakes, steering, and the like. Since the output of an engine driven pump varies with the speed of the vehicle engine, pumps chosen in prior art systems had to have volumetric capacities sufficiently large to ensure that the required volume would be available to the accumulator circuit even at minimum pumping rates.

In the past, a single fixed-displacement pump and an accumulator charging valve were utilized to charge the accumulator of such hydraulic systems. It is obvious that such pumps operated much of the time with a volumetric output in excess of that required'by the accumulator circuit. This is so because sucha pump, as mentioned above, had to be large enough to handlethe largest capacity requirements demanded. With such large capacity pumps charging prior art accumulators, considerable horsepower had to be diverted from the vehicle engine for pump actuation and this resulted in a loss of power to perform other usefulwork. Such. diversion of power is particularly undesirable in vehicles such as motor graders because the intermittent lugging of the grader engine due to on'and off cycling of the pump makes critical handling and control functions difficult to perform. I

One rather effective solution to the problem has been the utilization of a variable displacement pump such as that shown in U.S. Pat. application Ser. No. 373,612, filed by Hein, et al., of common assignment herewith. Unfortunately the substitution of a variable displacement pump in a system normally utilizing a--fixeddisplacement pumps is not always practical due to the relative complexity and expense of the variabledisplacement pump.

Additional prior art systems utilizing variable displacement means are shown in U.S. Pat. applications Ser. Nos. 283,855 to Hein, et al., and 272,408 to Ferre, et al., both of common assignment herewith.

SUMMARY AND OBJECTS OF THE INVENTION The instant invention provides an accumulator charging arrangement for a hydraulic system utilizing a plurality of fixed-displacement pumps having relatively small capacities and being individually operative only upon specific system demands. Each pump is combined with an accumulator charging valve which provides operating fluid to an accumulator device within a given predetermined pressure range. At low volume, high pressure system demands only one or a few pumpcharging valve combinations will be operative, whereas at maximum volume, low pressure demands, all pumpvalve combinations will be operative to supply the accumulator means.

The main object of the present invention is to provide a charging arrangement for the accumulators of a hydraulic system which arrangement does not utilize expensive variable -displacement pumps.

Another object of the invention is to provide a system utilizing a plurality of fixed-displacement pumps connected in parallel to'provide individual or combined flow to meet specific system requirements.

A still further object of the present invention is to provide a plurality offixed-displacement pumps each arranged in a parallel circuit with an accumulator charging valve and a separate'accumulator device and operated upon demand to charge the respective accumulators. I

Other objects-and advantages of the invention will become apparent from the following description and drawing.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE of the drawing is a partially schematic representation of the instant accumulator charging arrangment shown coupled to hydraulic user circuitry of a grader vehicle.

DETAILED DESCRIPTION With reference to the drawing, the preferred embodiments of the instant charging arrangement are shown generally at 10. The arrangement is shown in association with a hydraulic system, shown generally at 12, for a motor grader not shown. The particular hydraulic system illustrated is supplied by two

parallel circuits

14 and 16. The circuit 14 includes, in series, a check valve 22, an accumulator 24, and a priority valve 26. This circuit is adapted tosu'pply pressure fluid to a brake valve 18 and an implement valve 20. The priority valve gives priority to the brake valve 18 over the implement valve 20. The circuit 16 supplies fluid under pressure to a steering valve 28 and includes, in series, a check valve 30, an accumulator '32, and a reducing valve 34.

Both circuitsare uniformly'supplied with fluid under pressure from the accumulator charging circuit 10 of the presentinvention. The circuit includes a pair of

accumulator charging valves

36 and 38 disposed in a parallel with respect to the user circuit. The accumulator charging valves utilized in the preferred embodiment are essentially identical to the valve assembly fully disclosed in U.S. Pat. No. 3,570,519, to Bianchetta, of common assignment herewith, and will not be discussed in detail herein. The valve 36 functions to charge in a high pressure range, for example from 3,100 to 3,500 psi, whereas the valve 38 functions to charge in a lower pressure range, on the order of 2,700 to 3,100 psi.

The charging circuit also includes a relatively small capacity fixed displacement pump 40 for supplying fluid under pressure to the high range accumulator valve 36, and a relatively large capacity constant displacement pump 42, for supplying fluid to the lower range accumulator charging valve 38. In a typical example, the pump 40 would have a capacity of 15 gallons per minute while the pump 42 would provide some 25 gallons per minute.

In operation, when the pressure in either or both of the

accumulators

24 or 32 falls below 2,700 psi, i.e.,

the minimum charging pressure of the

accumulator charging valves

36 and 38, fluid under pressure from both of the

pumps

40 and 42 would be directed to the

accumulators

24 and 32. Upon reaching the maximum charging pressure of the valve 38, i.e., 3,100 psi, such valve will dump fluid pumped by the larger capacity pump 42 to a tank 11 through a line 39 in the manner disclosed particularly in the above-mentioned patent to Bianchetta. The smaller capacity pump 40 will continue to charge both the accumulators until a maximum pressure of 3,500 psi is reached, whereupon the accumulator charging valve 36 will cease charging and will dump the excess output of the smaller pump to the tank 11 through an outlet line 37.

During operation of the vehicle, the accumulator pressure will frequently drop below 3,100 psi due to the use of the various of the control valves 18, and 28. When this occurs, the charging valve 36 will automatically shift to redirect fluid from the smaller capacity pump 40 to the accumulators. The larger pump 42 will be utilized only to charge the accumulators during periods of extreme fluid demand when system pressure would tend to drop grossly. Consequently, it will be appreciated that substantial savings in engine horsepower may be realized by charging with only the smaller capacity pump during most vehicle operations and by utilizing the larger capacity pump 42 only at such times as is necessary as determined by the flow requirements of the system. It is also obvious that it is preferable to have a small low capacity pump cutting on and off instead of a larger one, which would lug the engine during charging and interfere with ancillary control and implement functions.

While the invention has been described with reference to the preferred embodiments thereof, it is apparent that the variations and modifications are possible within the purview of the inventive concepts. No limitation with respect to such variations and modifications is intended, except by the scope of the appended claims.

We claim:

1. An accumulator charging system for charging accumulator means which supply fluid under pressure to a fluid user circuit, said system comprising; accumulator means, a source of fluid, first pump means in fluid communication with said source, first fluid communication means for communicating the output of said first pump means with said accumulator means, said first pump means having a fixed displacement and maximum pumping capacity of a first predetermined value, first automatic charging valve means in said first fluid communication means for controlling the flow of fluid from said first pump means to said accumulator means, said first automatic charging valve means being responsive to the pressure extant in said accumulator means for permitting fluid flow from said first pump means to said accumulator means only when the pressure within said accumulator means is within a first predetermined range of positive pressures and for returning fluid from said first pump means to said source when said accumulator means pressure is above said first predetermined range of pressures, second pump means in communication with said source, second fluid communication means for communicating the output of said sec- 0nd pump means with said accumulator means, second automatic charging valve means in said second fluid communication means for controlling the flow of fluid from said second pump means to said accumulator means, said second pump means having a fixed dis placement and constant volumetric capacity of a given second predetermined value which is less than said first predetermined value, said second automatic charging valve means permitting fluid flow from said second pump means to said accumulator means when the pressure extant in said accumulator means is within a second predetermined range of positive pressures extending to a higher pressure than said first predetermined range of pressures, said second charging valve means being effective to return fluid from said second pump means to said source when accumulator pressure rises above the maximum pressure of said second predetermined range of pressures, said accumulator means including first and second fluid accumulator devices each said accumulator device being connected for fluid communication with both of said first and second automatic charging valve means at least partially through common conduit means, first check valve means in said first fluid communication means between said common conduit means and said first accumulator device for permitting flow from said first charging valve means to said first accumulator device but preventing reverse flow.

2. The invention of claim 1 including second check valve means in said second fluid communication means between said common conduit means and said second accumulator device for permitting flow from said second charging valve means to said second accumulator device but preventing reverse flow.

Claims

1. An accumulator charging system for charging accumulator means which supply fluid under pressure to a fluid user circuit, said system comprising; accumulator means, a source of fluid, first pump means in fluid communication with said source, first fluid communication means for communicating the output of said first pump means with said accumulator means, said first pump means having a fixed displacement and maximum pumping capacity of a first predetermined value, first automatic charging valve means in said first fluid communication means for contorlling the flow of fluid from said first pump means to said accumulator means, said first automatic charging valve means being responsive to the pressure extant in said accumulator means for permitting fluid flow from said first pump means to said accumulator means only when the pressure within said accumulator means is within a first predetermined range of positive pressures and for returning fluid from said first pump means to said source when said accumulator means pressure is above said first predetermined range of pressures, second pump means in communication with said source, second fluid communication means for communicating the output of said second pump means with said accumulator means, second automatic charging valve means in said second fluid communication means for controlling the flow of fluid from said second pump means to said accumulator means, said second pump means having a fixed displacement and constant volumetric capacity of a given second predetermined value which is less than said first predetermined value, said second automatic charging valve means permitting fluid flow from said second pump means to said accumulator means when the pressure extant in said accumulator means is within a second predetermined range of positive pressures extending to a higher pressure than said first predetermined range of pressures, said second charging valve means being effective to return fluid from said second pump means to said source when accUmulator pressure rises above the maximum pressure of said second predetermined range of pressures, said accumulator means including first and second fluid accumulator devices each said accumulator device being connected for fluid communication with both of said first and second automatic charging valve means at least partially through common conduit means, first check valve means in said first fluid communication means between said common conduit means and said first accumulator device for permitting flow from said first charging valve means to said first accumulator device but preventing reverse flow.