Operating mechanism for steering systems or the like
United States Patent {19] Termansen et al.  
  [111 3,880,554 51 Apr. 29, 1975 [751 Inventors: Poul Erik Term-ansen; Johannes Vagn Baatrup, both of Sonderborg.  
 Denmark [73] Assignee: Danfoss A/S, Nordhorg. Denmark [22] Filed: Oct. 25, 1973 21 Appl. No: 409,698  
 [30] Foreign Application Priority Data Nov. 2. i973 Germany 2253575 [52] U.S. Cl. ..4l8/6lB:4l8/104 [51] Int. Cl. F0lc 1/02; F03c 3/00; Ftl4e 1/02 [58] Field of Search 4l8/6l B. l04; 60/384 [56] References Cited UNITED STATES PATENTS 3.286.645 11/1966 Alhcrs 4l8/6l B 3.289.542 l2/l966 Fikse 4l8/6l B 3.302584 2/1967 McDcrmott 4l8/6l B i la l Fl 7 Tl? Ma Primary Exumim&#39;r.|ohn Jr Vrablik [57] ABSTRACT The invention relates to a metering type control unit for a power steering system. Units of this type most commonly utilize gerotor type gear sets for the metering operation. A problem with this unit is that highly pressurized fluid leaks from the expansible chambers formed between the star and ring members of the gerotor to the central bore of the star. Control units of this type require a universal drive between the rotatable valve thereof and the star which has a combination rotating and orbiting movement In this invention the universal drive has a sealing flange associated therewith which serves to enclose the central bore of the star so that a fluid tight chamber is formed Fluid is trapped in this central bore with the result that the pressure differential between the expansible chambers and this central bore is minimized and leakage is consequently minimized 4 Claims, 10 Drawing Figures OPERATING MECHANISM FOR STEERING SYSTEMS OR THE LIKE The invention relates to an operating mechanism for steering systems or the like in which the pressure medium for moving a work motor is passed to the supply side through a rotary-piston metering motor. the rotat ing and circulating piston of which is connected by way of a compensating coupling, which extends into a cavity in the piston, to an outer rotary-slide sleeve which, together with a bore in the casing of the mechanism, forms a distributor valve for the metering motor, and in which a steering shaft is connected to an inner rotary-slide sleeve which is rotatable relatively to the outer rotary-slide sleeve, against the force of a return spring, through an angle delimited by stops and which. together with this sleeve, forms a reversing valve optionally having neutral-position holes.  
  In a known operating mechanism of this kind (British Patent Specification No. 897,768) the rotary piston which takes the form of an externally toothed wheel is connected to the outer rotary-slide sleeve by way of a universal-joint shaft and a pin extending through the inner rotary-slide sleeve. there being clearance between the pin and sleeve. The return spring consists of two curved strips which extend substantially in the diametral direction and which pass through complementary openings in the two rotary-slide sleeves. The pump-side port communicates with an outer channel in the outer rotary-slide sleeve from which extend on the one hand the neutral-position holes and on the other further pressure-side distributing openings. The cavity in the piston and the interior of the inner rotary-slide sleeve are connected to the discharge-side port by way of openings, extending through the two sleeves, and annular channels.  
  The object ofthe present invention is to increase the operating accuracy of a mechanism of this kind.  
  According to the invention this object is achieved by bringing a seal between the inner cavity in the piston and the discharge-side port, at least while the metering motor is operating.  
  The seal&#34; in question does not need to be absolutely tight; it suffices if a flow restricting seal is created the effect of which is so pronounced that a pressure building up in the cavity in the piston is permitted to relax very slowly towards the discharge side.  
  In an operating mechanism of this kind, the leakages from the metering motor are extremely small. Consequently rotation of the metering motor constitutes a precise image of the displacement of the working motor. Since the metering motor is disposed on the supply side, a pressure in the order of magnitude of I atmos, e.g. 7O I40 atmos, obtains in its displacement chambers. The cavity in the piston is normally filled with oil. Because of the presence of the seal this oil acquires a pressure corresponding to that in the displacement chambers as soon as a trace of leaked oil passes along the end face of the piston and into the cavity. However, any further leakage is thus inhibited or kept negligibly small. Instead of this, the pressure in the cavity can be constantly held at a correspondingly high level by means of a suitable connection with the pumpside port.  
  It is particularly advantageous to form the seal by utilizing parts of the compensating coupling and/or at least one rotary slidev The required effect can then be achieved without the use of additional components.  
  In a preferred arrangement the compensating coupling is a cross-disc-type coupling (Oldham coupling), and the seal is formed along the periphery of a part coaxial with the rotary-slide sleeves. Even with a simple sliding fit, the cavity in the piston can be closed off satisfactorily.  
  In particular the co-axial part carries a sealing flange which is disposed on that side of the end disc remote from the piston.  
  In accordance with a further feature of the invention, the interior of the inner rotary-slide sleeve is connected to the pump-side port. In this case this rotary-slide sleeve acts as a sealing element which permits the pressure in the cavity in the piston to be maintained irrespective of whether the interior of the sleeve communicates directly with the cavity in the piston or whether it communicates with the pressure chamber adjoining the sealing flange.  
  The invention will now be described in greater detail by reference to a form of construction illustrated in the annexed drawing, in which:  
  FIG. 1 is a longitudinal section through an operating mechanism of the invention, on the line HH of FIG. 2-  
  FIG. 2 is an end view from the left of the mechanism shown in FIG. 1,  
 FIG. 3 is a section on the line 33 of FIG. 1,  
 FIG. 4 is a section on the line 44 of FIG. 1,  
 FIG. 5 is a section on the line 5-5 of FIG. 1,  
 FIG. 6 is a section on the line 66 of FIG. 1.  
 FIG. 7 is a section on the line 77 of FIG. 1,  
 FIG. 8 is a section on the line 88 of FIG. 1,  
 FIG. 9 is a section on the line 9-9 of FIG. I, and FIG. 10 is a section on the line 10-10 of FIG. 2. The operating mechanism has a casing l which includes a port 2 for connection to a pump 3, a port 4 for discharge of oil into a tank 5, and ports 6 and 7 for connection to a working motor 8. An internally toothed ring 10 with an end plate II is screwed onto one end of the casing, an end disc 9 being interposed between the ring and the casing. A cover plate I2 is secured to the opposite end face of the casing. The parts are held together by means of screw-bolts 13.  
  A steering shaft 14 is formed integrally with a valve tube I5 which together with a closure tube I6 forms an inner rotary-slide sleeve 17. The latter is surrounded by an outer rotary-slide sleeve 18 which in turn is accommodated in a bore 19 of the casing.  
  The outer rotary-slide sleeve 18 is connected by means of a compensating coupling 20 to a rotary piston 21 in the form of an externally toothed wheel. Displacement chambers are formed between this wheel and the toothed ring 10. The piston 21 has a cavity 22 which, with the piston, is able to execute a circulating and rotary movement. The compensating coupling is designed as a cross-disc-type or Oldham coupling. It  
 consists of a first part 23 which is disposed co-axially with the rotary-slide sleeves I7 and I8 and has a projection 24 which extends into a complementary channel in an intermediate part 25 which in turn. by way of a projection 26 extending at right angles to the projection 24, is displaceable in a channel formed in the piston 2I.  
  A duct 28 leads from the pump-side port 2 to a pressure chamber 29 which is provided between the end faces of the rotary-slide sleeves 17 and 18 and a sealing flange on part 23 ofthe coupling and which communicates with the interior 3] of the inner rotary-slide sleeve 17. At the periphery of the sealing flange there is created a seal between the piston cavity 22 and the interior 31 of the sleeve 17. The rotary-slide sleeves 17 and 18 are pressed against associated stops 32 and 33 at the opposite end by the pump pressure obtaining in the pressure chamber 29. The interior 3] of the sleeve 17 can be caused to communicate with the dischargeside port 4 only by way of neutral-position holes 34 which are formed in the rotary-slide sleeves 17 and 18 and are gradually closed as the steering shaft 14 is rotated. and by way of an annular channel 35 formed at that end of the bore 19 in the casing remote from the metering motor.  
  Part 23 of the coupling also has a radial projection 36 which engages in matching recesses 37 at the uncovered end face of the outer rotary-slide sleeve 18 and in larger recesses 38 at the uncovered end face of the inner rotary-slide sleeve 17. Consequently the outer rotary-slide sleeve 18 is connected to the coupling part 23 so that the two rotate together. Furthermore, relative rotation of the inner and outer rotary-slide sleeves 17 and 18 is possible, this rotation being limited by the recesses 38. A return spring 39 is formed as a ring, the in wardiy bent ends 40 of which engage in mutually similar openings 41 and 42 at the uncovered end-faces of the two rotary-slide sleeves 17 and 18. This spring returns both sleeves to their neutral positions upon completion of each steering movement (FIG. 9).  
  Also provided in the casing is a combination valve 43, and the only fact concerning this valve that is of interest here is that its closing member 44 operates as a return valve and opens when the neutral-position holes 34 are throttled. A duct leading to an annular channel 45 in the casing is then opened and is connected. through radial bores 46 in the outer rotary-slide sleeve 18 (FIG. 4) and axial channels 47 in the inner rotaryslide sleeve 17, to each second control opening 49a in the outer rotary-slide sleeve 18, each of these second control openings, together with the control openings 49b, disposed between them. and the control openings 50 in the bore 19 in the casing, forming a distributor valve which, through duct 51, connects the displacement Chambers to the supply and discharge of the metering motor in the correct manner for operating this motor. The control openings 4% are connected to an annular channel 56 in the bore 19 of the casing (FIG. 5) by way of bores 52a in the valve tube 15, axial channels 53a in the closure tube 16 (FIG. 3), bores 54a in the valve tube 15 and bores 55 in the outer rotary-slide sleeve 18. Bores 52b and axial channels 53b are used when the mechanism is operating in the other direction when, instead of the annular channel 56, the annular channel 57 alongside it and formed in the bore 19 of the casing, is connected to the discharge side of the metering motor. Each of the annular channels 56 and 57 is connected to one side of the working motor 8. Disposed between them is a two-way excess-pressure valve which is likewise accommodated in the casing 1.  
  Leading to the discharge-side annular channel 35 in the bore 19 of the casing from the annular channel 57 now acting as a return channel, are bores 59 (FIG. 6) in the outer rotary slide sleeve 18. control openings 60a in the valve tube 15, axial channels 61 in the closure tube 16 (FIG.6), control openings 62 in the valve tube 15 and bores 63 in the outer rotary-slide sleeve 18 (FIG. 7 FIGS. 5 and 6 show similar constructions with bores 54b and 60b. The functions of the corresponding ducts are transposed when the direction of rotation changes.  
  As shown in FIGS. 3 to 8, the inner rotary-slide sleeve 17 is turned so far relatively to the outer rotaryslide sleeve 18 in the position illustrated that the metering motor turns in one of the directions corresponding to the rotation of the steering shaft 14, and when this happens the motor causes the outer rotary-slide sleeve to follow the inner rotary&#39;slide sleeve. As soon as the neutral position is reached, the neutral-position holes 34 move into register again on the one hand, whereas on the other hand the axial channels 47 (FIG. 3) in the inner rotary-slide sleeve 17 are separated from the control openings 49a in the outer rotary-slide sleeve 18. Flow to the metering motor and to the work motor is thus interrupted. When the two rotary-slide sleeves rotate relatively to each other in the opposite direction, the axial channel 17 which conveys the pump pressure communicates with the control opening 49b so that the metering motor turns in the opposite direction. When such rotation through the neutral position occurs. the bores 55 and 59 (FIGS. 5 and 6) in the outer rotaryslide sleeve 18 also transpose from the bores 54 and 60 respectively in the inner rotary-slide sleeve 17 to the adjacent bores in the inner rotary-slide sleeve 17, so that the direction in which the work motor 8 moves is also reversed. The two rotary-slide sleeves therefore act as a reversing valve.  
  When the neutral-position holes 34 are opened in the at-rest position of the operating mechanism, there obtains in the interior 31 of the inner rotary-slide sleeve 17 a pressure corresponding to the throttle resistance of the holes 54. The pressure in the cavity 22 ofthe pis ton 21 is also equal to this pressure. When the steering shaft 14 is rotated and the neutral-position holes 34 thus more or less closed, the closure member 44 of the return valve opens, and pressure fluid is supplied to the metering motor. At the same time however the sealing flange 30 is pressed against the end disc 9 by the pump pressure obtaining the pressure chamber 29, so that the cavity 22 is tightly closed off. If oil leaking from the displacement chambers now seeks to pass into the cavity 22, the pressure there rises immediately to the pressure obtaining in the displacement chambers, so that no further leakage oil passes over. The required precise operation of the mechanism is thus achieved.  
 We claim:  
  1. A metering unit for steering systems comprising a casing, a rotary piston in said casing having a rotatable movement relative to its own axis and an orbitable movement relative to the casing axis, a toothed ring member surrounding said piston, said piston having a central bore. a disk having a central bore attached to one side of said ring member, and a closure member attached to the other side of said ring member, said disk and said closure member constituting walls for expansible chambers formed between said rotary piston and said ring member, a rotary valve rotatable about said casing axis, a drive mechanism between said valve and said piston, said drive mechanism being in sealing engagement with said disk to enclose said piston central bore along with said closure member so that said piston central bore forms a fluid tight chamber.  
 ing a central bore. neutral position valve means for selectively providing fluid communication between said rotary valve means central bore and said outlet port.  
 4. A metering unit according to claim I wherein said drive means is an Oldham coupling.