US2852918A

US2852918A - Hydraulic control circuit with unloading means

Info

Publication number: US2852918A
Application number: US477512A
Authority: US
Inventors: Robert E Schwary
Original assignee: New York Air Brake LLC
Current assignee: New York Air Brake LLC
Priority date: 1954-12-24
Filing date: 1954-12-24
Publication date: 1958-09-23
Anticipated expiration: 1975-09-23

Description

Sept. 23, 1958 HYDRAULIC CONTROL CIRCUIT WITH UNLOADING MEANS Filed Dec.

R. E. scHwARY 2,852,918

5 Sheets-Sheet 1 SUMP INVENTOR Rober BSchwarg ATTORNE YQ Fie. l

Sept. 23, 1958 R. E. scHwARY 2,852,918

HYDRAULIC CONTROL .CIRCUIT WITH UNLOADING MEANS Filed Dec. 24, 1954 3 Sheets-Sheet 2 i i 59 'fmf 6.1 15 54 l /66 61'? 1w; O 65 6g' 56 1f 6l a 66 59 l l l j I j ll MOTOR 12J PUMP INVENTOR F162 Roberc E Schwary BY A9452/ fw ATTORNEYS SePt- 23 1958 R. E. scHwARY 2,852,918

HYDRAULIC CONTROL CIRCUIT WITH UNLOADING MEANS United States Patent() HYDRAULIC CNTRQL ClRCUlT WITH UNLGA-.DlNG MEANS Robert E. Schwary, Euclid, Ghia, assigner to The New York Air Brake Company, a corporation New Jersey Applicatioanecember 24, 19754, sont Ns. 477,512

s Claims. (ci. news2) This invention relates to automatic transmissions. Speciiically it concerns a transmission which includes an hydraulic motor connected to be driven by one or more of a plurality of pumps which are connected -in parallel between a `sump and the motor. Valve means are provided which provide initial sequential loading of the pumps.` A valve responsive to back pressure in the motor `inlet unloads therpumps sequentially as the back pressure increases whereby the load is carried by the remaining pumps. The remaining pumps, since theytreceive the entire outputof the prime mover, can deliver Vagainst a higher back pressure wherebythe motor can overcome a nected to the open center whereby the vehicle may coastV or be pushed against low internal resistance. The control valve may be moved toeither of two operating positions, themotor moving in opposite directions depending upon the selection` between these two positions.

It is desirable in a system in which a gasoline engine is used that the motor be `started with the pumps unloaded. The valve means which initially loads thepumps assumes a position, when the prime mover is stopped, in which the discharge from. the pumps is connected to the Sump. These discharge connections are provided with restrictions and as engine speed increases the back pressure between the restriction and the pump discharge is increased. The valve means are shifted in response to this rising back pressure to direct pump flow toward the control valve. Preferably the pumps are loaded sequentially by this valve means. i

An unloading valve is provided which is actuated by back pressure in excess of a predetermined amount to divert discharge oW from one of the pumps toward the sump. i

A preferred embodiment of the invention will be described having `reference to the accompanying drawings. Figures l and 2 placed side by side from left to right in the order stated comprise a diagram, certain parts being in axial section, of a complete circuit according to the invention.

Figure 3 is an axial section of a modified form of the invention.

`For purposes of illustration, all of the ports and pipe connections` are shown` lying in a single plane. Obviously in the `actual apparatus these need not be coplanar. In the specification all statements of direction refer to the apparatus as shown inthe drawings.

` Thesystem includes pumps 11 and 12.which comprise a idual unit, driven` by a single prime over, notshown.

Pumps

11 and 12 haveitheir inlets connected in parallel ricc and draw fluid from the sump 13 and deliver it to the valve 14 through parallel connected outlets. The

pumps

11 and 12 are of the constant-delivery, positive displace ment type. Pump displacement is therefore a function of the speed of the prime mover. Fluid from the pump 11 is directed from the valve 14 directly to the open* center control Valve 15. Fluid from the pump 12 is supplied to the open-center valve 15 through the diverting or unloading valve 16. The valve 16 is pressure actuated by back pressure `and connects the pump 12 to the sump when the back pressure exceeds a predetermined amount. The open-center valve 15 controls uid flow to the reversible rotary motor 17.

The valve 14 includes a ported valve seat bore 18. Two

hollow plunger valves

19 and 21 are slidable into bore 18 and spring biased to the positions shown. To the right of its mid-point the `bore is encircled by three

annular grooves

22, 23, 24 which are respectively connected to the sump 13, pump 11 and to open-center con trol valve 15. To the left of its midpoint bore 18 is encircled by

grooves

25, 26 and 27 respectively connected with sump 13, pump 12 and valve 16. The sump connections are provided with adjustable restrictions such as needle valves 28. The

plunger valves

19 and 21 are mirror duplicates. Referring to valve 19, it will be seen that it is provided with three sets of radial ports 29, 31 and 32. An encircling groove .33 is formed in plunger valve 19 and interconnects ports 31 and 32. Adjacent ends of the hollow valve plungers are closed, and the space 34 defined between themis connected with the sump 13 as shown in the drawings.

Valve 16 comprises a body having a bore therethrough closed at opposite ends by screw plugs 35. Pressed into the bore is a bushing 36 having alined

bores

37 and 38 of different diameters. Abutting hollow plungers 39 and 41 are fitted to and sli-dable in the alined bores, `37 and 38.

Annular grooves

42, 43 and 44 are formed in the bushing surface and are connected respectively with the groove 27 of valve 14, with thesurnp 13 and with the valve 15 and groove 24 of valve 14. Plunger 39 carries adjacent its open end a check valve 45 `which is biased closed vby spring 46. Space 47 is connected with valve 15 and with groove 24 of valve 14. Plonger 39 has three sets of radial ports 4S, 49 and 50, formed therein. Spring 54 biases the plungers 39 and 41 to the position shown. Pressure fluid in the groove 44 is admitted to the right of plunger 41 by ports 52 in the stop 53. In the illustrated position ports 5t) communicate with space 47; ports 48 register with the groove 42 and ports 49 are obstructed. In the unloading position ports 50 are obstructed and ports 49 unload the pump 12 by direct ing tlow therefrom to the sump 13 via groove 43.

The open center control vvalve 15 comprises a housing having a ported valve bore 54 therein. A central annular groove 55 is formed in thefbore yand is connected with the sump 13 as shown. On each side of the groove 55 are grooves 56 and `56 which each connect to inlet chamber 57 which is connected with the

grooves

24 and 44 and space 47. This -inlet chamber 57 is also in communication with sump 13 through check valve `58 which permits flow from the sump but inhibits reverse flo-W. Between each o-f the grooves 56 and 56' and the corresponding end of the bore 54 are 4grooves 59 and 59' which are connected with `the motor17.` A cored chamber 61 is formed in thehousingand is connected with the sump at all times. Arelief valve assembly is provided as generally indicated at 62.

A valve plunger 63 `is reciprocable in the bore 54 and is shiftable selectivelyto fthree positionsin each of `which animpositive detent 64 is eiiective to holditagainst accidental movement.. Theiplunger isprovided with adjacent point. Between each of the

grooves

65 and 65 and the corresponding end of plunger 63 are encircling

grooves

66 and 66 which register, at all times, with

Agrooves

59 and 59 respectively.

Grooves

65 and 66 are connected by port 67,

ports

65 and 66 are similarly connected by a port 67.

In the illustrated position the inlet chamber 57 and the motor connected

grooves

59 and 59 are connected with the sump through

grooves

65 and 65. When the plunger 63 is raised, inlet chamber 57 and

grooves

56 and 59 are connected together through port 67 and groove 59 is connected to the sump 13 through port 67 and groove 55. A reverse condition is established when plunger is in its lowermost position and the motor 17 will rotate in the reverse direction. The open-center valve is generally conventional, and no claims are directed to its construction.

In the drawings the parts are shown in the position assumed when the prime mover is idling and the vehicle is at rest or coasting. As shown pumps 11 and l2 are connected through valve 14 past needle valves 28 with the sump 13. The pumps are also unloaded by valve 15. If Valve 1S is shifted up or down to drive motor 17 either forward or backward as the case may be, the

pumps

11 and 12 initially remain unloaded. As prime mover speed is increased

plungers

19 and 21 will move toward each other and will, respectively, connect pump 12 with groove 27 and the valve 16, and pump 11 with the groove 24 and inlet chamber 57 of valve 15. The two needle valves 28 are preferably dierently adjusted so that the pumps are loaded successively, pump 11 being the first loaded. This aords smoother operation.

Under normal operating conditions when the load is not excessive the check valve 45 in valve 16 is open and both

pumps

11 and 12 supply fluid to the inlet chamber 57 of open-center valve 15. The pressure in chamber 57 is a direct function of the load on motor 17. This pressure acts on the open ends of plungers 39 and 41. Plunger 39 is of a larger area than plunger 41. It will be apparent that plungers 39 and 41 constitute a differential piston motor which biases the plungers toward the right when they are subject to pressure. This bias increases as the load increases. When it reaches a predetermined amount, the plungers 39 and 41 will be shifted to the right against the bias of spring 54 thereby obstructing port S0 and opening port 49 whereby pump 12 kis unloaded.

When pump 12 is unloaded, pump 11 continues to operate against the same back pressure. The vehicle will slow, but can be accelerated within the limits established by the setting of the relief valve 62 and by the maximum speed of the prime mover. With pump 11 operating alone its discharge pressure may be further increased by accelerating the prime mover. The maximum pressure attainable in the system is determined by the setting of relief valve 62.

When the load is reduced the back pressure in the system is reduced and plungers 39 and 41 ofvalve 16 resume their illustrated position whereby pump 12 is again effective to supply iiuid to the system. It will be obvious that maximum speed is attained when both pumps are operating under a light load, whereas heavy loads can be handled, at a lower speed, by a single pump. The transition is smooth and automatic.

In addition to loading the pumps serially, the valve 14 serves a second useful purpose. It unloads the pumps when the prime mover is not operating. Hence regardless of the position of valve 15, the prime mover is started without being initially subject to load.

The open-center control valve 15 has' a central float position in which the inlet chamber 57 is connected to the I sump as are the motor connected

grooves

59 and 59. This permits the vehicle to coast freelywhen desired.

When the vehicle is being driven downhill and is permitted to coast without shifting the valve 15 to its midposition, the motor 17 will operate as a pump and may displace more fluid than it is receiving from

pumps

11 and 12. Check valve 58 will open under these conditions to supply fluid to the motor inlet, whereby cavitation in the motor 17 is prevented. Check valve 58 could be replaced by two check valves, one between a sump conneetion, such as chamber 61, and each of the pipe connections to the motor 17 from grooves 59 and 59'.

Figure 3 shows a modification of the valve 14. It comprises a body 101 having a bore 102 therein. Opposite ends of bore 102 are closed by screw caps 103 having threaded apertures which receive adjusting screws 104. Lock nuts 105 and protecting cap nuts 106 are provided on screws 104. An abutment 107 is adjnstably mounted in each cap 103. Spring biased against the grooved inner face of abutments 107 are hollow plungers 108 and 109 which are reciprocable in bore 102. Adjacent ends of these plungers are closed. A manifold sump connection 111 is connected to each of the three encircling

grooves

112, 113 and 114 formed in the bore surface. Threaded

connections

115 and 116 are provided near opposite ends of bore 102 and may be connected respectively to

pumps

11 and 12. An encircling groove 117 is provided between grooves 112 and 113 and may be connected to valve 16. A corresponding groove 118 is located between grooves 114 and 113 and may be connected to valve 15. The plungers 108 and 109 are provided with three sets of radial ports, 119, 120, and 121, and 119', 120 and 121. respectively.

In Figure 3 the valve is shown in the position it would assume when the prime mover is idling. As shown the

ports

112 and 120 register as do

ports

114 and 120. This initial position of the ports may be adjusted by moving abutments 107. In this way the throttling effect imposed on the fluid owing to the sump may be varied, whereby the shifting of the valves to operating position when the prime mover is accelerated can be controlled. As the back pressure to the left of plunger 109 increases, the plunger is shifted to the right to bring

ports

119 and 117 into registry. Plunger 108 is shifted in a similar fashion. By adjustment of the abutments 107, the plungers 108 and 109 can be made to shift serially in the order stated or in the reverse order. It is preferred that plunger 108 shift firstas has already been pointed out in connection with Figures 1 and 2.

It will be apparent the valve of Figure 3 may be .substituted for valve 14 shown in Figure 1.

If desired the three

valves

14, 15 and 16 can be built using a single cast housing or body in which theppipe connections wouldv be replaced by cored passages. The design of such single valve housing is deemed to be within the skill of a person skilled in the art of valve construction and is therefore not illustrated.

What is claimed is:

l. In a hydraulic transmission of the type including a prime mover, a plurality of pumps driven thereby and connected in parallel flow relation between a sump and a control valve having a float position, and an unloader for one of said pumps serving to unload that pump whenever the pressure of the liquid supplied to said control valve exceeds a perdetermined maximum, the combination of a secondary unloader for each of said pumps comprising a valve seat having an inlet connection from a pump, an outlet connection to the control valve, and a restricted unloading path connected with said sump; a

valve member; means biasing said member toward an initial position in which it interconnects said unloader path and said inlet from the pump; and motor means actuated by pressure in the inlet from said pump to shift said valve against said bias progressively toward a position in which it establishes communication between the inlet from said pump and said outlet connection, and closes said unloader path.

2. The combination defined in claim l in which the restrictionin each of said unloaded paths is variable independently of the restriction in the other unloader path.

3. The combination dened in claim 1 in which the restriction in said unloader path comprises an adjustable stop for said valve member and against which it is biased by said biasing means whereby the interconnection between said unloader path and the inlet from said pump may be varied in size.

4. In an hydraulic system of the type including a pump, a motor and a control valve arranged to control the ow of liquid from said pump to said motor; an unloader valve for said pump comprising a valve seat having a 10 supply port connected with the pump discharge, a discharge port connected with the control valve and an eX- haust port connected with the sump; flow restricting means for said exhaust port; a ported valve member biased toward an unloading position in which it interconnects said supply and exhaust ports; motor means actuated in response to rising pressure in said supply port to urge said valve member iu a direction to interconnect said supply and discharge ports and close said exhaust port.

5. The combination deiined in claim 4 in which the iiow restricting means comprises an adjustable stop effective to limit the transverse arca of the iiow path from the supply to the exhaust port in said unloading position.

References Cited in the le of this patent l UNITED STATES PATENTS Eames Mar. 6, 1956