AXIAL PISTON MACHINE, IN PARTICULAR AN AXIAL PISTON PUMP OR AN AXIAL PISTON MOTOR

Abstract: An axial piston machine of the axial piston pump or motor type, having a first subassembly (1), including a plurality of circumferentially spaced cylinder-piston units (2) around a central axis (3), a second subassembly (29) rotatable in relation to the first subassembly in a force-transmitting manner with the cylinder-piston units in a coupling plane (30) at a predetermined angle to the central axis, wherein one of these subassemblies is rotatably arranged within a housing (10) and coupled with rotational drive means, with the driving subassembly including two spaced first bearings (33, 34) that act at least substantially in a radial direction and a swivel-joint type second bearing (35) having a pivot center (36) located at about the mid point of the center-to-center distance between the two first bearings, with this type of construction being applicable to swash-plate, skew-plate and skew-drum type machines.

Description: AXIAL PISTON MACHINE, IN PARTICULAR AN AXIAL PISTON PUMP OR AN AXIAL PISTON MOTOR CROSS REFERENCE TO RELATED APPLICATIONS This application claims the priority of Swiss Application No. 02566/92-4, filed 6 August, 1992, the disclosure of which is incorporated herein by reference in its entirety. BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to an axial piston machine, in particular an axial piston pump or motor of the type having a first subassembly, including a plurality of circumferentially- spaced cylinder-piston units around a central axis; a second subassembly rotatably connected with the first assembly in a force-transmitting manner with the cylinder piston units in a coupling plane arranged at a predetermined angle to the central axis, wherein one of these subassemblies is rotatably arranged within a housing and coupled with rotational drive means. 2. Discussion of the Background of the Invention and Material Information Different types of such axial piston machines, namely "swash-plate machines", "skew-plate machines" and "skew-drum machines" are known in the art, e.g. from printed lecture notes entitled "Grundlagen der Oelhydraulik" (Fundamentals of oil Hydraulics) , by Prof. . Backe, Institut fϋr hydraulische und pneumatische Antriebe und Steuerungen der Rheinisch- estfalischen Technischen Hochschule Aachen, 2nd edition 1974, p. 116, together with illustrations 4-22 to 4-25, which are incorporated herein by reference. The genus of axial piston machines is subdivided into the following types: I. swash-plate machines; II. skew-plate machines; and III. skew-drum machines. All three types are deemed to be encompassed by this invention, wherein in a type I. machine the first subassembly is represented by a cylinder-piston arrangement fixed in a housing, and the second subassembly is represented by a rotating swash-plate, with the second subassembly, therefore, being a drive subassembly. In a type II. machine the first subassembly is represented by a rotating drum containing a cylinder-piston arrangement, with this first subassembly thus being a drive subassembly, while the second subassembly is represented by a fixed skew-plate. In a type III. machine the first subassembly again is represented by a rotating drum, containing a cylinder-piston arrangement, while the second subassembly is represented by a rotating drive plate arranged perpendicular to its axis of rotation. The rotational axes of both subassemblies are arranged at an angle relative to each other. In this embodiment the second subassembly is the drive subassembly. Substantially no drive torque is transferred to the first subassembly. SUMMARY OF THE INVENTION With reference to the previous definition of the axial piston machines encompassed by this invention, a first objective of the invention is to improve the construction of the axial bearing assembly, which mainly functions to transfer the piston forces that are produced by the hydraulic working pressure of the machine. The solution to this problem according to the invention is defined by an axial piston machine, in particular an axial piston pump or axial piston motor, which comprises a first subassembly including a plurality of cylinder-piston units, arranged at a distance from and in parallel to, or at acute angle to a central axis as well as being circumferentially offset, relative to each other around the central axis by a predetermined angle; a second subassembly being rotatably connected with the first subassembly, the second subassembly having a force- transmitting connection with the cylinder-piston units within the range of a coupling plane, being arranged at a predetermined angle to the central axis, so as to receive the oscillating drive forces of the cylinder-piston units; one of the first and second subassemblies being a driving subassembly rotatably arranged in a housing and being coupled with rotational drive means; the driving subassembly having a bearing assembly including two first bearings, acting at least substantially in a radial direction and situated at a predetermined axial distance from each other, and a swivel- joint type second bearing acting in both the axial and radial directions; and the second bearing having a pivot center, with the pivot center being located at a about the axial mid point of the center-to-center distance between the first two bearings. These previously-noted features make it possible or facilitate the use of a self-aligning or swivel-joint roller bearing, particularly a spherical roller bearing, for the axial or longitudinal support of the driving subassembly, preferably in connection with axially movable radial bearings for the transverse support, such radial bearings being free of load in the axial or longitudinal direction. The axial forces occurring in axial piston machines act eccentrically and in a circulating manner in relation to the central axis. Within the limits given by the clearance of the radial bearings the axial forces entail circulating and oscillating swivel-type movements of the driving subassembly. The danger of edge pressures in the axial bearings contained therein are avoided to a large extent by the previously-recited measures. A further objective of the invention refers to the type I. and II. machines. This objective aims at an improvement in supporting or bearing the pistons on a preferably disk-like coupling member, which is rotatably connected with a driving subassembly, in the manner of previously-noted illustration 4- 22. The solution to this objective takes the form of an axial piston machine comprising a first subassembly including a plurality of cylinder-piston units arranged at a distance from and in parallel to or under an acute angle to a central axis as well as being circumferentially offset, relative to each other around the central axis by a predetermined angle; a second subassembly having a force-transmitting connection with the cylinder-piston units so as to receive the oscillating drive forces of the cylinder-piston units; these subassemblies being rotatably arranged relative to each other, around the central axis; with one of the subassemblies being rotatably arranged in a housing and functioning as a driving subassembly and being coupled with rotational drive means; wherein a preferably disk-like coupling member is rotatably connected to the second subassembly in relation thereto around a swash axis arranged at a predetermined angle relative to the central axis, the coupling member further being connected to the first subassembly so as to be blocked against continuous rotation around the central axis, the coupling member also having a force-transmitting connection with the cylinder-piston unit within the range of a coupling plane, the coupling plane being at least approximately perpendicular to the swash axis, so as to receive the oscillating drive forces of the cylinder-piston units; and the coupling member having a rotation-blocking connection with the first subassembly by means of a positively-acting holding device. The connection thus defined hereinabove between the coupling member and the first subassembly greatly reduces the relative motion in the force-transmitting coupling faces. This produces a desired reduction of friction and wear. It should be clear at this time that such a rotation-blocking coupling connection, in the case of a stationary first subassembly ("swash-plate type") , entails a stationary rotational blocking of the coupling member. A further embodiment of the invention provides a cardanic holding device. Due to special advantages, relating to stability and operational safety, the holding device is designed so as to comprise a cardan ring extending along the external perimeter of the coupling member which is connected both therewith and with the first subassembly by means of a pair of diametrical joints. Preferably, the first subassembly is fixedly secured in a housing, while the cardan ring is fixed at the housing by means of a pair of diametrical joints. In this context a further embodiment utilizes double-jointed rods, preferably double ball-jointed rods, for the force transmission between the cylinder-piston units and the coupling member. Each of the double-jointed rods are connected by means of a first joint to a corresponding piston and by means of a second joint to a corresponding junction apparatus of the coupling member. Such a design offers the advantage of minimizing the transverse piston forces without impeding the freedom of the coupling member for necessary minor angular oscillation against the first subassembly around the central axis. Finally, a further extension of the objective of the invention is directed to improvements of axial piston machines, particularly type I. machines, with regard to a desired structural combination of machine parts that come into contact with the hydraulic working medium, which is often dangerous or corrosive, and with regard to offering easy access to valves, auxiliary units and the like for service and repair. The solution to this objective is defined by an axial piston machine including a plurality of cylinder-piston units which are arranged at a distance from and parallel to or at an acute angle to a central axis as well as being circumferentially offset relative to each other around the central axis by a predetermined angle; a second subassembly being coaxially with and located rotationally around the central axis on a drive shaft, the second subassembly further having a force-transmitting connection with the cylinder- piston units so as to receive the oscillating drive forces of the cylinder-piston units; wherein the drive shaft, which preferably includes at least two rotationally coupled longitudinal sections, extending coaxially with the central axis from its drive input end through a corresponding central opening of the first subassembly or of the housing respectively, to a head-subassembly which includes at least one auxiliary unit coupled with the drive shaft. Accordingly, valves, auxiliary units and the like, can be positioned in a comparatively freely accessible head- subassembly. A special advantage of such a design is that the pistons, located in the first subassembly and connected thereto, are also easy accessible. Preferably the head-subassembly includes a feed pump coupled with the drive shaft and/or a pump or motor valve assembly. A further advantage made possible by the subject design is restricting the use of corrosion resistant materials to the head-subassembly. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein throughout the various figures of the drawings, there have generally been used the same reference characters to denote the same or analogous components and wherein: Fig. 1 is an axial section of a portion of a type I. axial piston pump; and Fig. 2 is an axial section of a further portion of the type I. axial piston pump of Fig. 1, with Figs. 1 and 2 showing two axially adjacent parts of this pump. The common radial plane of the two adjacent pump portions is identified by lines 0-0. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described in detail with reference to the example of a type I. swash-plate axial piston pump illustrated in the drawings. It should also be understood that all the features of the invention can be constructed with reference to the illustrated embodiment, with particular reference to the previously-noted type II. and III. machines. Specifically, in Fig. 2, a first subassembly 1 is comprised of a plurality of, for example five, cylinder-piston units 2, which units are arranged at a radial distance from and parallel to a central longitudinal axis 3 as well as being circumferentially offset, relative to each other around the central axis by an appropriate angle, for example 72°. Each cylinder-piston unit is comprised of a piston 4 slidably arranged in a cylinder 5 with piston 4 and cylinder 5 being shown in axial sections only over a part of their axial length. Specific design details of cylinder 5 and piston 4 are only of minimal interest in the present context, since cylinder-piston units 2 may be of any type well known in the art. A pretensioned return coil or compression spring 6 surrounds cylinder 5 and acts through a sleeve 7 against a radially projecting bottom flange 8 of piston 4, thus tending to push piston 4 in its restoring or cylinder-filling direction (in the Figures from the left to the right) . The inner (in Fig. 2 the left) end of spring 6 abuts on the right end face of a support sleeve 9 fixedly retained in an axial bore of a machine housing 10. Support sleeve 9, on its right side, is fixedly secured to the left end portion of cylinder 5. It should also be understood that, instead of an arrangement of cylinders 5 in parallel to axis 3, a design may be adopted with the cylinder axes being arranged at an acute angle, e.g. between 5° and 10°, relative to axis 3. This may be advantageous in view of the space available between the cylinders for auxiliary elements or units. The left end face of housing 10 is tightly connected, e.g. by means of highly pretensioned axial screws 11, with a head-subassembly 12, which among other parts houses a valve assembly 13 and a filler or feed pump 14 attached to a section 15 of a drive shaft 16 (Fig.l). Drive shaft section 15 is coupled, by means of -a toothed-clutch 17, to a central drive shaft section 18. Filler pump 14 serves to enhance the input hydraulic pressure for the cylinder-piston units 2 to a value sufficient for avoiding cavitation. Drive shaft section 18 also drives a lubricant pump 19, which in turn feeds a lubricant channel system 20 via a lubricant filter 21. Coaxially attached to each cylinder-piston unit 2 is a combined inlet-outlet valve 22 having an inlet side 23 connected, via in inlet channel system 24, to the output 25 of filler pump 14. Pump 14 e.g. is of the well-known "side- channel" type and will not be described in detail here since it is not material for the essence or function of the invention. Filler pump 14 is connected, via an input 26, to a non-illustrated external low-pressure hydraulic feed system. Inlet/outlet valve 22 further has an output side 27, connected through an output channel system 28, to a non-illustrated external high-pressure hydraulic system. Valve 22 has substantially coaxial internal flow channel systems and spring-loaded check valve members for both flow directions, i.e. to and from the corresponding cylinder-piston unit 2. The internal structure of valve 22 is of no specific interest for the invention and thus will not be described in further detail. In principle, instead of the noted example of the combined inlet/outlet valve 22 described here, other conventional and well-known valve types may be used. In Fig. 1, a second subassembly 29 is rotatably arranged relative to first subassembly 1. Subassembly 29 is in force- transmitting connection with cylinder-piston units 2 within the range of a coupling plane 30, arranged at least approximately right-angled or perpendicular to the central longitudinal axis 3, so as to absorb the oscillating drive forces produced by cylinder-piston units 2. Subassembly 29 is constructed as a driving subassembly that is rotatably arranged in housing 10 and coupled with a main section 31 of drive shaft 16. Drive shaft sections 18 and 31 are coupled by means of any type of a conventional clutch. It should also be mentioned that different design modes or types of subassembly 29 may be utilized. Thus, cylinder-piston subassembly 2 may be designed as a rotating drum, i.e. in the sense of previously-noted machine types II. and III. In the latter case, this subassembly would be a substantially torqueless rotating unit. Driving subassembly 29 includes a bearing assembly comprising two first bearings 33, 34, which act at least substantially in the radial direction and are arranged at a predetermined axial distance or spacing from each other, and a swivel-joint or pivot-type second bearing 35 acting both axially and radially. In the noted example, bearings 33 and 34 may take the form of axially movably cylindrical roller bearings, while bearing 35 may be a mainly axially acting spherical roller bearing. The swivel or pivot center 36 of second bearing 35 is located at about the axial mid-point (center-to-center distance) 37 between the mid-points 38, of the bearing axial width 39, of axially spaced first bearings 33, 34. Subassemblies 1 and 29 are arranged so as to be rotatable, in relation to each other, around their common central axis 3. Only one of these subassemblies, here subassembly 29, is arranged to be rotatable in housing 10 and functions as a driving subassembly, coupled with the drive shaft 16. However, as already noted earlier, a design according to machine type III. may also be utilized. In addition, a disk-like coupling member 40 is rotatably connected to second subassembly 29 around a swash axis 41, which is arranged at an angle relative to the central axis 3. Coupling member 40 is ' further connected to first subassembly l in a manner so as to be blocked against continuous rotation around central axis 3, and is connected in a force- transmitting manner with the cylinder-piston units 2 within the range of coupling plane 30. Coupling plane 30 is arranged at least approximately right-angled or perpendicularly to swash axis 41. Thus, coupling member 40 takes over or absorbs the substantially axial, oscillating drive forces produced by cylinder-piston units 2 and transmits such forces to second subassembly 29. It should be understood that coupling member 40 can also be regarded as a part of second subassembly 29. The noted rotation-blocking connection between coupling member 40 and first subassembly 1 is accomplished by means of a positively-acting holding device 42. In the illustrated embodiment, holding device 42 is a cardan type of device 10 comprising a cardan ring 43, which extends along the external perimeter of coupling member 40 and which is connected with each of coupling members 40 and subassembly 1 by means of a pair of diametrical pivots 44. In view of first subassembly 1 being fixedly arranged in machine housing 10, cardan ring 43 is fixed to housing 10 by means of a further pair of non- illustrated diametrical pivots. In the illustrated embodiment, double-jointed rods 45, preferably double ball- jointed rods, are provided for the force transmission between cylinder-piston units 2 and coupling member 40. Each of double-jointed rods 45 is connected by means of a first joint 46 to a corresponding piston 2 and by means of a second joint 47 to a corresponding junction assembly 48 of coupling member 40. As already previously noted, in the illustrated embodiment, drive shaft 16 is comprised of three rotationally coupled sections 31, 18 and 15. Drive shaft 16 extends coaxially with central axis 3 from its drive input end 49 through a corresponding central opening of first subassembly 1 and of housing 10 to head-subassembly 12 with feed pump 14 and valve assembly 13. Obviously, the mode of design according to the invention, as specifically depicted in the illustrated embodiment, can also be utilized for axial piston motors. Of course, the valve assembly then must be positively coupled to and synchronized with the rotation of the drive shaft, which then functions as a power output shaft. The filler pump can be omitted or replaced by other useful auxiliary units. While there are shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope 11 of the following claims and the reasonably equiva l ent structures thereto. In particular it is to be understood that the angle between the swash axis and the central axis may be predetermined so as to be of a fixed acute angle value or so as to be variably adjustable in operation between 0° and a maximum acute angle value, and this with angle variation to both sides of the zero angle value if desired for purposes of hydraulic flow direction reversal. Such variation obviously entails a corresponding variation of the angle between the coupling plane and the central axis, which is the complementary angle to the one between the swash axis and the central axis and determinative for the magnitude of the piston stroke. This type of of swash plate axial piston machines with variable swash-angle is well known in the art per se. Thus the realization of the subject of the present invention for such variable-swash- angle machines can be established by usual structures near at hand and needs no further explanation. 12

Claims: WHAT IS CLAIMED IS: 1. An axial piston machine, in particular one of an axial piston pump and an axial piston motor comprising: a) a first subassembly including a plurality of cylinder- 5 piston units, said cylinder-piston units being arranged at a distance from and in one of being parallel to and being at an acute angle to a central axis as well as being circumferentially offset, relative to each other around said central axis by a predetermined angle; 10 b) a second subassembly being arranged rotatably in relation to said first subassembly, said second subassembly having a force-transmitting connection with said cylinder- piston units within the range of a coupling plane, said coupling plane being arranged at a predetermined angle to said 15 central axis, so as to receive the oscillating drive forces of said cylinder-piston units; c) one of said first and second subassemblies being a driving subassembly rotatably arranged in a housing and being coupled with rotational drive means; ■20 d) said driving subassembly having a bearing assembly including two first bearings, said two first bearings acting at least substantially in a radial direction and situated at a predetermined axial distance from each other, and a swivel- joint type second bearing acting in both the axial and radial 25 directions; and e) said second bearing having a pivot center, with said pivot center being located at about the axial mid point of the center-to-center distance between said two first bearings. 2. An axial piston machine, in particular one of an 30 axial piston pump and an axial piston motor comprising: a) a first subassembly including a plurality of cylinder- piston units, said cylinder-piston units being arranged at a 13 distance from and in .one of being parallel to and being at an acute angle to a central axis as well as being circumferentially offset, relative to each other around said central axis by a predetermined angle; b) a second subassembly having a force-transmitting connection with said cylinder-piston units so as to receive the oscillating drive forces of said cylinder-piston units; c) said subassemblies being rotatably arranged relative to each other, around said central axis; d) one of said subassemblies being rotatably arranged in a housing and functioning as a driving subassembly and being coupled with rotational drive means; e) a preferably disk-like coupling member being rotatably connected to said second subassembly in relation thereto around a swash axis arranged at a predetermined angle relative to said central axis, said coupling member further being connected to said first subassembly so as to be blocked against continuous rotation around said central axis, said coupling member also having a force-transmitting connection with said cylinder-piston units within the range of a coupling plane, said coupling plane being at least approximately perpendicular to said swash axis, so as to receive the oscillating drive forces of said cylinder-piston units; and f) said coupling member having a rotation-blocking connection with said first subassembly by means of a positively-acting holding device. 3. The axial piston machine of claim 2, wherein said positively-acting holding device takes the form of a cardanic holding device. 4. The axial piston machine of claim 3, wherein said holding device comprises a cardan ring, said cardan ring 14 extending along the external perimeter of said coupling member and being connected with each of said coupling members and said first subassembly by means of a pair of diametrical pivots. 5. The axial piston machine of claim 4, wherein said first subassembly is fixedly secured in a housing and said cardan ring is fixed at said housing by means of a pair of diametrical pivots. 6. The axial piston machine of claim 2, wherein double- jointed rods, preferably double ball-jointed rods, are provided for the force transmission between said cylinder- piston units and said coupling member, each of said double- jointed rods being connected by means of a first joint to a corresponding piston and by means of a second joint to a corresponding junction apparatus of said coupling member. 7. The axial piston machine of claim 3, wherein double- jointed rods, preferably double ball-jointed rods, are provided for the force transmission between said cylinder- piston units and said coupling member, each of said double- jointed rods being connected by means of a first joint to a corresponding piston and by means of a second joint to a corresponding junction apparatus of said coupling member. 8. The axial piston machine of claim 4, wherein double- jointed rods, preferably double ball-jointed rods, are provided for the force transmission between said cylinder- piston units and said coupling member, each of said double- jointed rods being connected by means of a first joint to a corresponding piston and by means of a second joint to a corresponding junction apparatus of said coupling member. 15 9. The axial piston machine of claim 5, wherein double- jointed rods, preferably double ball-jointed rods, are provided for the force transmission between said cylinder- piston units and said coupling member, each of said double- jointed rods being connected by means of a first joint to a corresponding piston and by means of a second joint to a corresponding junction apparatus of said coupling member. 10. An axial piston machine, in particular one of an axial piston pump and an axial piston motor comprising: a) a first subassembly including a plurality of cylinder- piston units, said cylinder-piston units being arranged at a distance from and in one of being parallel to and being at an acute angle to a central axis as well as being circumferentially offset relative to each other around said central axis by a predetermined angle; b) a second subassembly being coaxial with and arranged rotationally around said central axis on a drive shaft, said second subassembly further having a force-transmitting connection with said cylinder-piston units so as to receive the oscillating drive forces of said cylinder-piston units; and c) said drive shaft, which preferably includes at least two rotationally coupled longitudinal sections, extending coaxially with said central axis from a drive input end ' through at least one of a corresponding central opening of said first subassembly and of said housing respectively, to a head-subassembly, said head-subassembly including at least one auxiliary unit coupled with said drive shaft. 11. The axial piston machine of claim 10, wherein said head-subassembly comprises a feed pump coupled with said drive shaft. 16 12. The axial piston machine of claim 11, wherein one of a pump and motor valve assembly is housed in said head- subassembly. 17 S

Inventors: FREY BERNHARD, FREY, BERNHARD
Applicants: FREY BERNHARD, HYDROWATT SYST, HYDROWATT SYSTEMS LTD.
Application year: 1993
Main classification: F01B3
IPC codes: F01B3, F02B75, F04B1