Hydrostatic axial piston machine

Abstract

A hydrostatic axial piston machine (1) with a cylinder barrel (2) having at least one piston bore (3) in which is located a power unit piston (4) supported on a cam disk (18). A control surface (5) is stationary relative to the housing and is on a control base (6), against which control surface the cylinder barrel (2) is in contact. In the control base (6) there are a kidney-shaped inlet connection (8) and a kidney-shaped outlet connection (9). The sealing web surface on the control surface 5 on the control base (6) in the vicinity of the inlet connection (8) is reduced, so that in operation as a motor, when there is a pressurization of the inlet connection (8), a reduction of the hydrostatic relief force is achieved. In operation as a motor, a residual application of the cylinder barrel (2) against the control surface (5) from a hold-down force of a hold-down spring (24) that is in an operative connection with the cylinder barrel (2) and/or pressing cylinder compression forces is preserved. In addition or alternatively, the terminal areas of the kidney-shaped inlet connection (8) of the control base (6) have a transitional contour (K) in the shape of a flattened arc in the radially outer area.

Claims

1. A hydrostatic axial piston machine, comprising: a cylinder barrel rotatable around an axis of rotation; at least one piston bore located in the cylinder barrel; a power unit piston located in the at least one piston bore and supported on a cam disk so that it can move longitudinally; a control surface stationary relative to a housing and located on a control base, against which an end face surface of the cylinder barrel is in contact; a kidney-shaped inlet connection formed in a first half of the control base and a kidney-shaped outlet connection formed in a second half of the control base; and a displacement chamber formed between the at least one piston bore and the power unit piston, which during rotation of the cylinder barrel around the axis of rotation is placed in communication alternately with the inlet connection and the outlet connection, wherein the axial piston machine is operable as a pump and as a motor in a same direction of rotation of the cylinder barrel and a same direction of flow of hydraulic fluid, wherein when the cylinder barrel is driven in pump operation, the axial piston machine takes in hydraulic fluid via the inlet connection and delivers it into the outlet connection, wherein when operated as a motor, the axial piston machine is driven by hydraulic fluid under pressure delivered by the inlet connection, wherein a sealing web surface on the control surface on the control base in a vicinity of the inlet connection is smaller than a sealing web surface on the control surface of the control base in a vicinity of the outlet connection, so that in operation as a motor, when there is a pressurization of the inlet connection, a reduction of a hydrostatic relief force is achieved, and so that, in operation as a motor, a residual application of the cylinder barrel against the control surface from a hold-down force of a hold-down spring that is in an operative connection with the cylinder barrel or pressing cylinder compression forces is preserved, and wherein the first half of the control surface of the control base has a single outside diameter and a single inside diameter, wherein the second half of the control surface of the control base has an outside diameter and an inside diameter, wherein the single outside diameter of the control surface of the first half of the control base is smaller than the outside diameter of the control surface on the second half of the control base and/or the single inside diameter of the control surface on the first half of the control base is larger than the inside diameter of the control surface on the second half of the control base.

2. The hydrostatic axial piston machine as recited in claim 1, wherein the control base includes at least one cutout in the control surface to reduce the sealing web surface area in the vicinity of the inlet connection.

3. The hydrostatic axial piston machine as recited in claim 2, wherein terminal areas of the kidney-shaped outlet connection of the control base or terminal areas of the kidney-shaped inlet connection of the control base at a radially outer region have a transitional contour that is flattened.

4. The hydrostatic axial piston machine as recited in claim 2, wherein a transitional contour in a radially outer terminal area of the kidney-shaped inlet connection or of the kidney-shaped outlet connection is formed by an oval contour.

5. The hydrostatic axial piston machine as recited in claim 1, wherein the control base includes in the vicinity of the control surface a stepped outside diameter and/or a stepped inside diameter within the second half of the control base.

6. The hydrostatic axial piston machine as recited in claim 5, wherein terminal areas of the kidney-shaped outlet connection of the control base or terminal areas of the kidney-shaped inlet connection of the control base at a radially outer region have a transitional contour that is flattened.

7. The hydrostatic axial piston machine as recited in claim 5, wherein a transitional contour in the radially outer terminal area of the kidney-shaped inlet connection or of the kidney-shaped outlet connection is formed by an oval contour.

8. The hydrostatic axial piston machine as recited in claim 1, wherein terminal areas of the kidney-shaped outlet connection of the control base or terminal areas of the kidney-shaped inlet connection of the control base at a radially outer region have a transitional contour that is flattened.

9. The hydrostatic axial piston machine as recited the claim 1, wherein a transitional contour in a radially outer terminal area of the kidney-shaped inlet connection or of the kidney-shaped outlet connection is formed by an oval contour.

10. A hydrostatic drive system with a hydrostatic axial piston machine, the axial piston machine comprising: a cylinder barrel rotatable around an axis of rotation; at least one piston bore located in the cylinder barrel; a power unit piston located in the at least one piston bore and supported on a cam disk so that it can move longitudinally; a control surface stationary relative to a housing and located on a control base, against which an end face surface of the cylinder barrel is in contact; a kidney-shaped inlet connection formed in a first half of the control base and a kidney-shaped outlet connection formed in a second half of the control base; a displacement chamber formed between the at least one piston bore and the power unit piston, which during rotation of the cylinder barrel around the axis of rotation is placed in communication alternately with the inlet connection and the outlet connection, wherein the axial piston machine is operable as a pump and as a motor in a same direction of rotation of the cylinder barrel and a same direction of flow of hydraulic fluid, wherein when the cylinder barrel is driven in pump operation, the axial piston machine takes in hydraulic fluid via the inlet connection and delivers it into the outlet connection, wherein when operated as a motor, the axial piston machine is driven by hydraulic fluid under pressure delivered by the inlet connection, wherein a sealing web surface on the control surface of the control base in a vicinity of the inlet connection is smaller than a sealing web surface on the control surface on the control base in a vicinity of the outlet connection, so that in operation as a motor, when there is a pressurization of the inlet connection, a reduction of a hydrostatic relief force is achieved, and so that, in operation as a motor, a residual application of the cylinder barrel against the control surface from a hold-down force of a hold-down spring that is in an operative connection with the cylinder barrel or pressing cylinder compression forces is preserved; and a drive motor comprising an internal combustion engine, wherein the axial piston machine is in drive connection with the drive motor, wherein the axial piston machine, when operated as a pump, supplies at least one consumer, and when operated as a motor functions as a hydraulic starter of the drive motor and/or as a booster drive, and wherein the first half of the control surface of the control base has a single outside diameter and a single inside diameter, wherein the second half of the control surface of the control base has an outside diameter and an inside diameter, wherein the single outside diameter of the control surface of the first half of the control base is smaller than the outside diameter of the control surface on the second half of the control base and/or the single inside diameter of the control surface on the first half of the control base is larger than the inside diameter of the control surface on the second half of the control base.

11. A mobile machine comprising a drive system as recited in claim 10.

12. A stationary power unit with a drive system as recited in claim 10.

13. A hydrostatic axial piston machine, comprising: a cylinder barrel rotatable around an axis of rotation; at least one piston bore located in the cylinder barrel; a power unit piston located in the at least one piston bore and supported on a cam disk so that it can move longitudinally; a control surface stationary relative to a housing and located on a control base, against which an end face surface of the cylinder barrel is in contact; a kidney-shaped inlet connection formed in a first half of the control base and a kidney-shaped outlet connection formed in a second half of the control base; and a displacement chamber formed between the at least one piston bore and the power unit piston, which during rotation of the cylinder barrel around the axis of rotation is placed in communication alternately with the inlet connection and the outlet connection, wherein the axial piston machine is operable as a pump and as a motor in a same direction of rotation of the cylinder barrel and a same direction of flow of hydraulic fluid, wherein when the cylinder barrel is driven in pump operation, the axial piston machine takes in hydraulic fluid via the inlet connection and delivers it into the outlet connection, wherein when operated as a motor, the axial piston machine is driven by hydraulic fluid under pressure delivered by the inlet connection, wherein a sealing web surface on the control surface of the control base in a vicinity of the inlet connection is smaller than a sealing web surface on the control surface on the control base in a vicinity of the outlet connection, so that in operation as a motor, when there is a pressurization of the inlet connection, a reduction of a hydrostatic relief force is achieved, and so that, in operation as a motor, a residual application of the cylinder barrel against the control surface from a hold-down force of a hold-down spring that is in an operative connection with the cylinder barrel or pressing cylinder compression forces is preserved, wherein terminal areas of the kidney-shaped inlet connection of the control base at a radially outer region have a transitional contour that is flattened, and wherein the first half of the control surface of the control base has a single outside diameter and a single inside diameter, wherein the second half of the control surface of the control base has an outside diameter and an inside diameter, wherein the single outside diameter of the control surface of the first half of the control base is smaller than the outside diameter of the control surface on the second half of the control base and/or the single inside diameter of the control surface on the first half of the control base is larger than the inside diameter of the control surface on the second half of the control base.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional advantages and details of the invention are explained in greater detail below with reference to the exemplary embodiments illustrated in the accompanying schematic figures, in which like reference numbers identify like parts throughout.

(2) FIG. 1 shows an axial piston machine of the prior art in longitudinal section;

(3) FIG. 2 is a plan view of the control surface of the control base of the axial piston machine illustrated in FIG. 1;

(4) FIG. 3 shows an axial piston machine of the invention in a longitudinal section;

(5) FIG. 4 is a plan view of the control surface of the control base of the axial piston machine illustrated in FIG. 3; and

(6) FIG. 5 is a plan view of the control surface of a second embodiment of the control base of the axial piston machine illustrated in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) FIG. 1 shows, in a longitudinal section, a hydrostatic axial piston machine 1 of the prior art utilizing a swashplate construction which is operated in an open circuit and is optimized for operation as a pump.

(8) The axial piston machine 1 has a cylinder barrel 2 that is arranged so that it can rotate around an axis of rotation D and is provided with a plurality of piston bores 3 that are concentric to the axis of rotation D and are located on a pitch circle TK. The piston bores 3 are preferably formed by cylindrical borings. A power unit piston 4 is mounted in each piston bore 3 so that it can be displaced longitudinally.

(9) The cylinder barrel 2 is supported in the axial direction with one end face on a control surface 5 which is stationary with reference to a housing and is located on a disk-shaped control base 6 which is non-rotationally fastened to a housing 7 or to a corresponding housing cover 7a of the housing 7. The control base 6 is provided with kidney-shaped control slots which form an inlet connection 8 and an outlet connection 9. The inlet connection 8 is in communication with a suction channel 10 in the housing 7 or in the housing cover 7a. Connected to the outlet connection 9 is a delivery channel 11 in the housing 7 or in the housing cover 7a. The piston bores 3 are each provided on the end face of the cylinder barrel 2 with a preferably kidney-shaped connection channel 12 to place the displacement chambers formed by the power unit pistons 4 and the piston bores 3 alternately in communication with the inlet connection 8 and the outlet connection 9 during rotation of the cylinder barrel 2 around the axis of rotation D.

(10) The cylinder barrel 2 is traversed by a central boring through which a drive shaft 15 that is concentric to the axis of rotation D is guided through the cylinder barrel 2. The drive shaft 15 is rotationally mounted in the housing 7 by bearings 16, 17. The cylinder barrel 2 is connected with the drive shaft 15 in a rotationally synchronous manner although it can move axially, for example by means of teeth 22 in the vicinity of a cylinder barrel neck of the cylinder barrel 2 which is formed onto the cylinder barrel 2 and which extends in the axial direction toward a cam disk 18.

(11) The power unit pistons 4 are each supported in the area in which they project out of the cylinder barrel 2 by a support element which can be in the form of a slipper 19, on the cam disk 18, such as a swashplate which is inclined with respect to the axis of rotation D and generates the displacement. The cam disk 18 can be formed onto or fastened to the housing 7, in which case the axial piston machine 1 has a fixed displacement volume. It is also possible, however, to make the inclination of the cam disk 18 variable by an adjustment device, such as a pivotable cradle, in a pivoting direction, as a result of which the axial piston machine 1 has a variable displacement volume and can be adjusted unilaterally.

(12) The support elements in the form of slippers 19 are prevented from lifting up from the cam disk 18 by a hold-down plate 20 in the form of a ring-shaped disk. The hold-down plate 20 rotates together with the cylinder barrel 2 and is pressed toward the cam disk 18 by a hold-down device 21 which is in the form of a spherical cap shaped or a concave shaped hold-down disk. The hold-down device 21 is connected with the drive shaft 15 in a rotationally synchronous manner but so that it can be displaced axially, for example by means of teeth 23. A hold-down spring 24 in the form of a compression spring is located in the space between the drive shaft 15 and the cylinder barrel 2. The hold-down spring 24 is supported on a first end by a stop 25, such as a retaining ring, on the cylinder barrel 2. On the second end, the hold-down spring 24 is connected with the hold-down device 21 by pins 26. By means of the hold-down spring 24, the cylinder barrel 2 is thereby pressed against the control surface 5 and the slippers 19 are pressed against the cam disk 18 by the hold-down device 21.

(13) Cylinder compression forces pressing the cylinder barrel 2 down onto the control surface 5 also act on the cylinder barrel 2. The applied cylinder compression forces result from the pressure originating in the piston bores 3 and the pressurized surface F which corresponds to the difference in the cross-section surfaces of the piston bores 3 and the cross-section surface of the connection channels 12.

(14) A gap in which a hydrostatic lubrication film can be formed is located between the cylinder barrel 2 and the control surface 5. In the gap there is a hydrostatic relief force which results from the pressure present in the gap and the surface areas of sealing webs on the control surface 5 of the control base 6.

(15) As shown in FIGS. 1 and 2, on the axial piston machine 1 optimized for pump operation, the suction channel 10 and the kidney-shaped inlet connection 8 in the control surface 5 have larger flow cross-sections than the delivery channel 11 and the kidney-shaped outlet connection 9. The width BE of the kidney-shaped inlet connection 8 is greater than the flow cross-section BA of the kidney-shaped outlet connection 9 (as illustrated in FIG. 2, which is a plan view of the control surface 5 of the control base 6).

(16) The inside radius R1 of the kidney-shaped inlet connection 8 is smaller than the inside radius R2 of the kidney-shaped outlet connection 9 and the outside radius R3 of the kidney-shaped inlet connection 8 is larger than the outside radius R4 of the kidney-shaped outlet connection 9, so that the inlet connection 8 is wider than the outlet connection 9 on the inside and on the outside.

(17) The kidney-shaped outlet connection 9 is also interrupted by a plurality of webs 30, 31, 32, to reduce the stresses and deformations in the vicinity of the delivery-side outlet connection 9, which is also pressurized at the delivery pressure during operation as a pump.

(18) The two peripheral-side terminal areas of the kidney-shaped inlet connection 8 in the control base 6 are semi-circular and/or rounded, each with a radius RE.

(19) The control base 6 is provided in the vicinity of the control surface 5 which is on the end surface with a uniform outside diameter DA and a uniform inside diameter DI. The area of the control surface 5 between the outer edge of the inlet connection 8 and the outside diameter DA of the control surface 5 forms a radially outer sealing web SA. The area of the control surface 5 between the inner edge of the inlet connection 8 and the inside diameter DI of the control surface 5 correspondingly forms a radially inner sealing web SI. In the vicinity of the top dead center OT and the bottom dead center UT of the movement of the power unit pistons 4, there are respective reversing areas 33, 34 on the control surface 5.

(20) If the axial piston machine 1 is operated as a pump, the cylinder barrel 2 is driven by the drive shaft 15, for example, by a drive motor in the form of an internal combustion engine. The axial piston machine 1, when operated as a pump, sucks hydraulic fluid via the suction channel 10 and the inlet connection 8 of the control surface 5 from a reservoir and delivers the hydraulic fluid via the outlet connection 9 of the control base 6 into the delivery channel 11. The consumers of the working hydraulics of the machine that are supplied with hydraulic fluid by the axial piston machine 1 functioning as a pump are preferably connected to the delivery channel 11. On account of the design of the suction channel 10 and of the inlet connection 8 with flow cross-sections that are larger than those of the delivery channel 11 and the outlet connection 9 and the design of the outlet connection 9 with the additional webs 30, 31, 32, the axial piston machine 1 is optimized for operation as a pump, to make high suction speeds possible.

(21) The axial piston machine 1 of the prior art can also be operated as a motor in the same direction of rotation of the cylinder barrel 2 and the same direction of flow of the hydraulic fluid. Hydraulic fluid under pressure, for example, from a hydraulic accumulator, is supplied via the suction channel 10 in the inlet connection 8 of the control base 5, and the axial piston machine 1 delivers into a reservoir via the outlet connection 9 of the control base 5 and the delivery channel 11. In this mode of operation of the axial piston machine 1 as a motor, a torque can be output by the drive shaft 15. When operated as a motor, the axial piston machine 1 can be used as a hydraulic starter for the internal combustion engine connected with the drive shaft 15 in a start-stop system and/or as a booster drive to assist the internal combustion engine.

(22) When operated as a motor, the axial piston machine 1 of the prior art, on account of the large sealing web surface area in the vicinity of the inlet connection 8, which is formed by the cylindrical sealing webs SI and SA on the control surface 5 in the vicinity of the inlet connection 8, generates a large pressure field in the vicinity of the inlet connection 8 of the control surface 5, which at an appropriately high pressure in the inlet connection 8 results in a correspondingly high hydrostatic relief force, which in turn results in the lifting up of the cylinder barrel 2 from the control surface 5, which cannot be prevented by the hold-down spring 24 and the cylinder compression forces.

(23) In addition, when the axial piston machine 1 of the prior art is operated as a motor, forces from the pressure present in the inlet connection 8 are acting on the cylinder surfaces of the inlet connection 8 in the control base 6, which forces can exceed the allowable stresses in the material in the terminal areas of the inlet connection 8 characterized by the radii RE and lead to a destruction of the control base 6. It has been shown that the radially outer areas of the semicircular rounded terminal areas of the inlet connection 8 lead to an unfavorable stress curve with high material stresses in the control base 6.

(24) FIGS. 3 to 5 illustrate an axial piston machine 1 of the invention.

(25) As illustrated in FIG. 4, on the control surface 5 of the control base 6 in the vicinity of the inlet connection 8, the sealing web surface area formed by the radially inner sealing web SI and the radially outer sealing web SA is smaller than the prior art embodiment illustrated in FIG. 2.

(26) The sealing webs SI and SA on the inlet connection 8 are cylindrical sealing webs. To make the surface areas of the sealing webs SI and SA on the inlet connection 8 smaller than those in FIG. 2, the control base 6 is provided in the vicinity of the control surface 5 with a stepped outside diameter DA and a stepped inside diameter DI. To reduce the surface area of the sealing webs in the vicinity of the inlet connection 8, the outside diameter DA of the control surface 5 on the inlet connection 8 is smaller than the outside diameter DA of the control surface 5 on the outlet connection 9. Accordingly, the inside diameter DI of the control surface 5 on the inlet connection 8 is greater than the inside diameter DI of the control surface 5 on the outlet connection 9. The diameter transitions 40, 41 on the inside diameter DI and on the outside diameter DA, with reference to the dead center points OT, UT, are located on the geometric half plane that contains the outlet connection 9.

(27) With this design of the control base 6 and the width B of the cylindrical sealing webs SI, SA, which is less than that indicated in FIG. 2 on account of the stepped outside diameter DA and the stepped inside diameter DI, a reduction of the surface area of the sealing web on the control surface 5 on the inlet connection 8 is achieved, so that during operation as a motor, a reduction of the hydrostatic relief force is achieved when the inlet connection 8 is pressurized. The sealing web surface area on the inlet connection 8 is selected so that when the axial piston machine 1 is operated as a motor, even at an elevated pressure level of the pressure in the inlet connection 8, the sum of the relieving forces does not exceed the hold-down forces applied, so that a residual pressing of the cylinder barrel 2 against the control surface 5 from the hold-down force applied by the hold-down spring 24 that is in an operative connection with the cylinder barrel 2 and the applied cylinder compression forces is preserved and thus the cylinder barrel 2 is prevented from lifting up from the control surface 5.

(28) The construction of the control base 6 illustrated in FIG. 4 makes it possible, on account of the widths B of the inner sealing web SI and of the outer sealing web SA which are each adapted to the inlet connection 8 and the outlet connection 9 respectively, to achieve an optimal hydrostatic relief for both pump operation as well as for motor operation of the axial piston machine 1.

(29) As a result of the reduction of the sealing web surface area on the inlet connection 8, the axial piston machine 1 of the invention can also be operated, in contrast to the axial piston machine of the prior art illustrated in FIGS. 1 and 2 which are optimized for operation as a pump, at an elevated and increased pressure level at the inlet connection 8 in operation as a motor, so that the axial piston machine 1 of the invention, when operated as a motor, can output an elevated torque on the drive shaft 15.

(30) As a result of the corresponding adaptation and size of the sealing webs SI, SA, a defined residual hold-down pressure of the cylinder barrel 2 can be set for both motor operation as well as for pump operation of the axial piston machine of the invention, which makes low friction losses possible.

(31) FIG. 5 illustrates a control base 6 of an axial piston machine 1 of the invention in which an additional measure is implemented to increase the pressure level present at the inlet connection 8 when the axial piston machine is operated as a motor.

(32) The peripheral-side terminal areas of the kidney-shaped inlet connection 8 of the control base 6 are provided in the half that lies in the radial direction outside the pitch circle TK, and, thus, in the radially outer area, with a transitional contour K which is in the shape of a flattened arc. In FIG. 5, the transitional contours K of the invention are drawn in solid lines. The terminal areas of the control base 6 of the prior art formed by an arc, which are formed by a radius RE in FIG. 2, are drawn in broken lines to more clearly illustrate the invention.

(33) In the exemplary embodiment illustrated in FIG. 5, the transitional contours K on the radially outer terminal area of the kidney-shaped inlet connection 8 are each formed by an oval contour and, thus, an oval geometry.

(34) The transitional contours K on the radially outer terminal area of the kidney-shaped inlet connection 8 make it possible to adapt the external contour of the inlet connection 8 in the terminal areas to the resulting stress curve during operation as a motor. On account of the transitional contours K adapted to the stress curve on the radially outer terminal areas of the inlet connection 8, the pressure level for operation of the axial piston machine 1 of the invention as a motor can be increased compared to the axial piston machine of the prior art optimized for operation as a pump illustrated in FIGS. 1 and 2, so that an increased drive torque is available on the drive shaft 15 without damaging the control base 6. The constructive design of the transitional contours K of the invention makes it possible, when the axial piston machine 1 is operated as a motor, to advantageously absorb the stresses and forces in the material of the control base 6 in spite of the increased pressure level in the inlet connection 8. The transitional contours K on the radially outer terminal area of the kidney-shaped inlet connection 8 result in only a slight reduction of the flow cross-section of the inlet connection 8, so that on account of the geometry of the inlet connection 8, which is optimized in terms of stress for operation as a motor, there is no adverse effect on the suction capacity and the suction limit speed of the axial piston machine 1 when it is operated as a pump.

(35) The invention is not restricted to the exemplary embodiments illustrated in FIGS. 4 and 5, in which the measures in FIGS. 4 and 5 are implemented separately and individually to increase the pressure level when operated as a motor. It goes without saying that both measures can be implemented jointly on an axial piston machine 1 of the invention to increase the pressure in motor operation as illustrated in FIGS. 4 and 5.

(36) With the geometry and constructive design of the control base 6 adapted for the operation of the axial piston machine 1 as a motor, by means of a corresponding design of the sealing web services on the inlet connection 8 and/or a corresponding design of the peripheral-side terminal areas of the inlet connection 8 on an axial piston machine 1 operated in an open loop, the pressure present at the inlet connection 8 can be increased, so that the axial piston machine 1 can output a torque sufficient to start an internal combustion engine which is in a drive connection with the axial piston machine 1. Therefore, on a mobile machine, an axial piston machine 1 in the form of a pump which is already present to supply the consumers of the working hydraulics can be used as a hydraulic starter for a start-stop system of the internal combustion engine.

(37) It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.