US3887308A

US3887308A - Valve porting arrangement for a gerotor

Info

Publication number: US3887308A
Application number: US355411A
Authority: US
Inventors: Karl-Heinz Liebert
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1972-04-29
Filing date: 1973-04-30
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03
Also published as: FR2183460A5; AU471742B2; JPS5754636B2; AU5502573A; ES414169A1; PL85459B1; GB1400108A; BG29725A3; HU165168B; JPS4954905A; DD104128A5; YU110173A; AR194331A1; YU35660B; DE2221183A1; SE381627B; DE2221183C2; BR7303066D0

Abstract

A fluid displacing device having a fixed internal gear in mesh with a planetating external gear to expand and contract pressure chamber formed between the teeth of the internal gear causing flow of fluid to and from the pressure chambers alternately placed in fluid communication with inflow and outflow ports by a flow distributing arrangement which includes an externally grooved, rotary slide coaxially coupled to the power shaft and mounted on the coupling shaft to which the external gear is pinned. Continuous fluid communication is maintained by the external grooves at the end of the rotary slide in sliding contact with the external gear.

Description

United States Patent Liebert June 3, 1975 [54] VALVE PORTING ARRANGEMENT FOR A 3,283.723 11/1966 Charlson 418/61 13 3,289,542 12/1966 Fikse 1 1 .7 418/61 B GEROTOR 3,289,601 12/1966 Compton .6 418/61 B Inventor: Karl-Heinz Liebert. Schwabisch 3,385,057 5/1968 P1111161 et a1... 418/61 B Gmund, Germany 3,446,153 5/1969 Easton 418/61 8 [73] Assignee: Zahnradtabrik Friedrichshafen AG,

Germany Primary Examiner-John J. Vrabhk Attorney, Agent, or Firm-Zalkind, Hornet & Shuster [22] Filed: Apr. 30, 1973 A fluid displacing device having a fixed internal gear [30] Forelgn Apphcauon Pflomy Dam in mesh with a planetating external gear to expand and P 1 1972 Germany 2221183 contract pressure chamber formed between the teeth of the internal gear causing flow of fluid to and from Cl 418/61 l37/625-24 the pressure chambers alternately placed in fluid com- [5l] lnt- C Flllc U F03C munication with inflow and outflow ports by a flow [53] Field 01 Search 418/61 B; di tributing arrangement which includes an externally 13 /6 5-2 grooved, rotary slide coaxially coupled to the power shaft and mounted on the coupling shaft to which the 156] e fi Cited external gear is pinned. Continuous fluid communica- UNITED STATES PATENTS tion is maintained by the external grooves at the end 2,121 455 6/1938 Ten Broek 64 7 of the rotary shde sliding with the external 2,153,093 4/1939 Magee et a1. 64/7 g 3,270,683 9/1966 McDermott 1 1 1 418/61 B 3,277,833 10/1966 Hudgens 418/61 B 16 Clam, 8 D'hwmg F'ghres 28 17 11 III 1V V 24 13 VI h 11 12 A I r-/ I 8 5 /i\\ I'n iv v IV 2 l 6 IL 15 3 PATENTEUJM 3 1975 SHEET FIG.1

PATENTEDJUH 3 ms SHEET FIGZ PATENTEDJUH .975 v .887.308

FIG. 6

VALVE PORTING ARRANGEMENT FOR A GEROTOR This invention relates to a hydrostatic pump or fluid motor, particularly useful in hydrostatic power steering systems for motor vehicles.

Fluid displacing devices having a fixed toothed ring with an internal tooth profile and an external gear having one tooth less than said ring so as to produce a planetary movement of an external gear, are well known. A fluid distributing arrangement is generally rotatable with the external gear about its axis and includes a control valve having channels leading to each fluid pressure chamber formed between the teeth of the tooth ring. Control openings corresponding in number to twice the number of teeth of the toothed ring are disposed in the housing for cooperation with said channels. The fluid distributing arrangement alternately establishes fluid communication between the pressure chambers and separate fluid conduits conducting fluid medium to and from the fluid displacement device.

Such rotary fluid displacing devices with a rotating distributor control valve deliver a relatively large mass of fluid per rotation of the driving shaft at a low speed, in the case ofa pump operation, or in the case of motor operation, a relatively large driven torque and fluid absorption volume for a low driven speed. Such devices are therefore used in hydrostatic steering systems for motor vehicles as a hydraulic auxiliary power assist under control of the steering wheel or as a hydraulic auxiliary power source operable by the steering wheel.

In one known type of rotary fluid displacing device fluid pressure channels are formed in the gear and lead to gaps between the teeth and to openings in fixed walls of the housing forming part of a fluid distribution system, so that movement of the gear around its center by one tooth pitch, completes a control cycle of the distribution system.

In another type of fluid displacing device, a cylindrical rotating slide valve rotating with the driving or driven shaft in coaxial relation thereto, has longitudinal grooves on its outside cylindrical surface, which are alternately connected with separate pressure lines, and to channels leading to the pressure chambers formed between the teeth of the internally toothed ring.

In yet another known type of fluid displacing device operating as a rotating piston engine, a rotary piston is mounted in a housing, the cross section of which constitutes a triangle with rounded corners and connected by means of a drive shaft with the driving or driven shaft, so that the rotary piston upon one turn of the shaft by 360 rotates a number of times about its center, corresponding to the number of teeth of the rotary piston, as it travels along a circular path around the axis of the housing, in a direction opposite to the rotational direction of the shaft. In such case, discharge of the operating medium is controlled by cooperation between control channels in one surface of the rotary piston and a number of control openings arranged in a wall of the housing adjacent to said channels, as a result of which said openings alternately communicate with the control channels of the rotary piston.

In still another known rotary piston engine, the gear is connected with the main shaft by means of a drive shaft, so that the cylindrical, rotary slide of the distributor at the rotational speed of the main shaft and coaxial therewith, rotates synchronously with the rotational movement of the piston about its own axis. The rotary slide at the same time has a number of longitudinal grooves corresponding to double the number of teeth of the gear, which are connected in an alternating sequence each time with a separate pressure line and cooperate with channels disposed in the housing leading to the root of the teeth of the toothed ring.

In the foregoing rotary piston engines, the flow of pressure liquid is throttled abruptly because of the arrangement of channels leading from the displacement chamber to the connecting lines and by the directional flow changes and cross sectional passage constrictions. As a result of these flow losses, the mass of fluid displaced in the case of a liquid pump, is reduced by the cavitation occurring in the suction lines, while in the case of a liquid motor, drive torque is decreased by reason of pressure losses.

Therefore an important object of the present invention is to provide a rotary piston engine with rotating distributor control, wherein an optimum degree of filling is effected with small losses of pressure in the supply channels conducting flow to the pressure medium operating chambers formed between the toothed profiles of the external gear and the internally toothed ring.

In order to achieve the foregoing objective, the invention includes a rotary slide, rotatable with the external gear which in turn is coupled in a manner known to the driving shaft by means of coupling shaft. The rotary slide is connected slidingly at one axial end with a surface of the gear and has longitudinal grooves extending axially on its radially outer or outside cylindrical sur face communicating on said one axial end with the gaps between the teeth of the gear. The grooves are also axially aligned with control openings in the housing to provide alternating fluid communication with separate pressure lines along the cylindrical surface.

Also, the longitudinal grooves disposed on the outside surface of the rotary slide, have enlargements at the ends in a sliding contact with one axial surface of the gear to advantageously conduct flow between the operating chambers and the inflow and outflow ports with a minimal amount of throttling.

The invention will be explained in more detail hereafter with additional features shown constituting part of one embodiment shown by way of example in the drawings, in which:

FIG. 1 shows a longitudinal section view through a rotary piston engine constructed in accordance to the present invention.

FIGS. 26 are transverse section views taken through planes indicated by section lines lI-II, lII--III, IVIV, V-V and VI-VI of FIG. 1.

FIG. 8 shows a modified form of the rotary piston engine constructed in accordance to the present invention.

FIG. 7 is a side elevation view of the rotary slide.

An internal toothed ring or gear 1 as shown in FIG. 1, is disposed between an end cover 2 and a housing body 3 to which it is fixed by means of screws 4. An externally toothed gear 5 having one tooth less than the toothed ring 1, forms with said toothed ring 1 operating chambers 6 radially between the teeth of the two gears and axially between the confronting surfaces of the cover wall 2 and the housing 3.

The gear 5 is connected for rotation with a driving shaft 8 by means of a coupling shaft 7. Two driver pins 9 and and the coupling shaft 7 fonn a universal, articulated connection between the gear 5 and the driving shaft 8. The coupling shaft 7 is fixed in an axial direction in the driving shaft 8 by a front surface 11 and in the gear 5 by a buffer disk 12 abutting the cover wall 2.

A flow controlling member in the form of a rotary slide 13 is coaxially mounted relative to the driving shaft 8 in the housing 3 and coupled to the driving shaft 8 by means of a coupling pin 14 for rotation therewith. In order to avoid misalignment between the driving shaft 8 and the rotary slide 13, limited radial displacement relative to each other is accomodated by the coupling. Alternatively, the rotary slide 13 could be made an integral component of the driving shaft 8 as shown in FIG. 8 to avoid misalignment.

A needle thrust bearing 15, axially positions the driving shaft 8 relative to an adjusting disk 16, the thickness of which is selected to obtain the required axial clearances for sliding contact between the rotary slide 13 at one axial end and the gear 5 as shown in FIG. 1.

The gear 5 is coupled to the driving shaft 8 as aforementioned so that upon each revolution of the driving shaft 8, the gear 5 will rotate about its own axis in a reverse direction a number of revolutions corresponding to the relative numbers of teeth of the gear 5 and ring 1, as the gear 5 is carried in a circular path about the axis of the fixed toothed ring 1.

Longitudinal grooves 17, leading to the gaps between the teeth of the gear 5, are formed on the outside cylindrical valve surface of the rotary slide 13. The longitudinal grooves 17 have enlargements 18 on the front axial end surface of the rotary slide 13 adjacent to the gear 5, to enlarge the transitional flow area to the operating chambers 6. Since both the rotary slide 13 as well as the gear 5 are rotatably coupled to the driving shaft 8, and the gear 5 planetates in a direction opposite to the rotary movement of the driving shaft, during expansion and contraction of the volume of the operating chamber 6 there is relative displacement between the rotary slide 13 and the gear 5 in synchronism with the rotational movements. In this manner, as expansion of each operating chamber 6 occurs, there is a corresponding enlargement of the transitional flow area to an associated longitudinal groove 17 in the rotary slide 13 and thus a continuous filling and emptying of the operating chambers 6. In order to avoid abrupt change in flow of fluid pressure medium, a continuous transition passage from the longitudinal grooves 17 to the volumetrically variable pressure spaces or operating chambers 6, is provided.

The longitudinal grooves 17 are axially aligned with control openings 21 or 22 formed in the housing 3 as shown in FIGS. 4 and 5 so that the grooves 17 communicate alternately with

separate ports

19 or 20 for the inflow or the return flow of a fluid pressure medium. The number of control openings 21 and 22 correspond to double the number of teeth of the toothed ring 1. The control openings 21 or 22 which are circumferentially spaced from each other by one tooth pitch of the internal teeth of ring one, are displaced from the internal teeth on either side by one-fourth of the tooth pitch of the internally toothed ring 1 shown in the drawings.

The control openings 21 are connected with an annular channel 23 disposed in the housing 3 and the control openings 22 with a corresponding annular channel 24. The annular channel 23 is connected by an axial passage to the port 19 while the annular channel 24 is connected by passage 26 to the port 20.

The longitudinal grooves 17 in the rotary slide 13 act, together with the control openings 21 and 22 in the housing 3, in such a way, that the operating chambers 6 lying on one side of a line passing through the centers of the gear 5 and toothed ring 1 as viewed in FIG. 2, are connected by the control openings 21 with one port 19 while the operating chambers 6 lying on the other side of the separating line are connected to the other port 20 by the other control openings 22.

The control openings 21 as viewed in FIG. 4 are circumferentially spaced from the control openings 22 by one half of the tooth pitch of the teeth of the toothed ring 1. In order to obtain large transitional flow areas during transitional flow from the longitudinal grooves 17 to the

annular channels

23 and 24, the control openings 21 and 22 are developed as longitudinal slits running axially in the housing 3.

One of the ports 20 is effectively connected with an annular channel 27 disposed in the housing 3 as seen in FIG. 6, in order that all spaces in the bores formed in the gear 5, the rotary slide 13, the driving shaft 8 as well as the housing 3, can be vented through one of the pressure fluid lines and filled with a fluid pressure medium.

To radially fix the driven pin 10, it is necked down to flats 10a parallel to one another in its central part, which are engaged by the fork-shaped end of the coupling shaft 7.

A cylindrical casing or shell 28 enclosing the housing 3, the toothed ring 1 and the coverwall 2, seals the

annular channels

23 and 24 from each another and also seals the toothed ring 1 against leakage past the cover wall 2.

It will be apparent that flow to and from the operating chambers 6 is conducted through the longitudinal grooves 17 in the rotary slide 13 which communicate with the operating chambers. The transitional flow passages 18 between the longitudinal grooves and the operating chambers, having enlarged flow areas, reduce the flow velocity of the fluid pressure medium to and from the operating chambers. The inflow and discharge of the fluid medium to and from the operating chambers occurs with only one directional change in the fluid stream within the control channels. Also, the transitional flow passage at 18 between each operating chamber and a longitudinal groove of the rotary slide, increases in flow area in synchronism with expansion of the associated operating chamber. The rotary fluid displacing device described, thus operates as a pump or motor with reduced fluid flow losses.

I claim:

1. In a fluid displacing device, a housing (3) having separate ports (24 and 25) and to which an internal gear (1) is fixed, an external gear (5) in mesh with the internal gear to form pressure chambers (6) within the internal gear, a power shaft (8) and articulated means (7) coupling the shaft to the external gear for imparting planetary movement thereto causing expansion and contraction of said pressure chambers, a fluid distributing system including a flow controlling member (13) mounted on the coupling means having a radially outer valve surface and an axial end surface in sliding contact with the external gear, means directly connecting the flow controlling member to the power shaft for rotation thereof at the same speed as the external gear to control flow of fluid at said valve surface to and from the ports and conduit means (17-18) mounted in the flow controlling member to form passages in continuous fluid communication with the pressure chambers and said valve surface of the flow controlling member for conducting said flow of fluid between said ports and said pressure chambers during rotation of the power shaft.

2. The combination of claim 1 including axial thrust bearing means axially positioning the flow controlling member within the housing for establishing a predetermined clearance between the external gear and the flow controlling member.

3. The combination of claim 1 wherein said coupling means includes a coupling shaft having opposite ends, one of which is provided with a fork formation, a driver pin having and bearing portions pivotally connected to the power shaft and an intermediate portion of reduced cross-section presenting parallel flats engaged by the fork formation at said one of the ends of the coupling shaft and means pivotally connecting the other of the ends of the coupling shaft to the external gear.

4. The combination of claim 1 including a common sealing shell enclosing both the housing and the internal gear for confining flow between the pressure chambers and the separate passages in the housing.

5. The combination of claim 1 wherein the flow controlling member is made an integral component of the power shaft.

6. The combination of claim 1 wherein said conduit means comprises a plurality of external grooves opening radially outwardly and extending axially from one axial end of the flow controlling member, said grooves being circumferentially spaced from each other by one tooth pitch of the external gear, each of said grooves having a flow transition enlargement at said one axial end in fluid communication with the pressure chambers.

7. The combination of claim 1 wherein said conduit means comprises separate, axially extending grooves (17) formed externally on said flow controlling member and opening radially outwardly, said grooves being cross-sectionally enlarged (18) adjacent one axial end of the flow controlling member and opening in an axial direction to establish said continuous fluid communication with the pressure chambers.

8. The combination of claim 7 wherein said housing includes axially extending openings (21 and 22) aligned with the grooves to establish separate passages from the ports.

9. The combination of claim 8 wherein said control openings are circumferentially spaced from the teeth of the internal gear by one quarter of the circular tooth pitch associated with the internal gear.

10. The combination of claim 9 wherein the control openings in one of the separate passages are circumferentially spaced from the control openings in the other of the separate passages by one half the circular tooth pitch of the internal gear.

11. The combination of claim 8 including axial thrust bearing means axially positioning the flow controlling member within the housing for establishing a predetermined clearance between the external gear and the flow controlling member.

12. The combination of claim 11 wherein said control openings are circumferentially spaced from the teeth of the internal gear by one-quarter of the circular tooth pitch associated with the internal gear.

13. The combination of claim 12 wherein the control openings in one of the separate passages are circumferentially spaced from the control openings in the other of the separate passages by one half the circular tooth pitch of the internal gear.

14. The combination of claim 13 wherein said coupling means includes a coupling shaft having opposite ends, one of which is provided with a fork formation, a driver pin pivotally connected to the power shaft having end bearing portions and an intermediate portion of reduced cross-section presenting parallel flats engaged by the fork formation at said one of the ends of the coupling shaft and means pivotally connecting the other of the ends of the coupling shaft to the external gear.

15. The combination of claim 14 including a common sealing shell enclosing both the housing and the internal gear for confining flow between the pressure chambers and the separate passages in the housing.

16. In combination with a fluid displacing device having a housing (3) provided with inlet and outlet ports (19 and 20), an internal gear (1) fixed to the housing, an external gear (5 enmeshed with the internal gear to form volumetrically variable pressure spaces (6) within the internal gear, a power shaft (8), and articulated coupling means (7) drivingly connecting the power shaft to the external gear; fluid distributing means for conducting a pressure medium between the ports in the housing and said pressure spaces, comprising an axially elongated member (13) having opposite axial ends and an external cylindrical valve surface, a plurality of Iongitudinal grooves (17) formed in said external valve surface and extending from one of said axial ends toward locations spaced from the other of the axial ends, means coupling the member at said other of the axial ends to the power shaft for rotation at the same speed as the external gear to control fluid communication between the ports and the grooves at said external valve surface of the member, said one of the axial ends of the member being in sliding contact with the external gear and provided with enlargements of the grooves to form continuous transitional passages between the grooves and the pressure spaces.

I! i l l

Claims

3. The combination of claim 1 wherein said coupling means includes a coupling shaft having opposite ends, one of which is provided with a fork formation, a driver pin having end bearIng portions pivotally connected to the power shaft and an intermediate portion of reduced cross-section presenting parallel flats engaged by the fork formation at said one of the ends of the coupling shaft and means pivotally connecting the other of the ends of the coupling shaft to the external gear.