Park brake system for a hydrostatic radial piston unit

Abstract

Provided is a hydrostatic radial piston unit of the cam-lobe type of construction comprising a non-rotary, stationary housing at least partially enclosing an interior cavity. A rotary cylinder block with radially oriented cylinder bores is arranged in the interior cavity and is rotatable around a rotational axis of the hydrostatic radial piston unit. The hydrostatic unit further includes a park brake device comprising at least one non-rotary brake disc which is in torque-proof connection with a non-rotary element of the hydrostatic radial piston unit and at least one rotary brake disc which is in torque-proof connection with a rotary element of the hydrostatic radial piston unit. The park brake device is at least partially radially enclosed by the cylinder block.

Description

[0001] Description

[0002] Park Brake System for a Hydrostatic Radial Piston Unit

[0003] The present invention relates to hydrostatic radial piston units, more particular to cam lobe motors or pumps, or to orbital motors or pumps. In detail the present invention relates to a park brake device for hydrostatic radial piston units, in particular for a hydrostatic radial piston units of the cam-lobe type of construction.

[0004] Radial piston units, i.e. radial piston pumps and radial piston motors, are widely used in the art, e.g. for heavy duty applications like the construction, agricultural or forestry industry. Radial piston units are particularly useful for hydraulic applications in which a high torque is required. Further, radial piston units have a reduced axial length in comparison to axial piston units.

[0005] One specific application of radial piston units is propelling of work vehicles or compaction equipment, e.g. of track loaders or asphalt rollers. Often, one radial piston unit is installed at either side of a frame / body of a work vehicle. Therefore, the geometry of the frame and of the propel mechanism is influenced significantly by the dimensions of the radial piston unit. As radial piston units driving work vehicles have to be integrated into the vehicle frame, the frame has to be designed in a manner to be capable of receiving stationary parts, e.g. a stationary casing, of the radial piston unit in order to be able to support the torque generated in operating conditions. It is therefore desirable to reduce the dimensions of the used radial piston units, especially in the axial direction, as much as possible, in order to reduce the required adaption in the design of the frame, the radial piston unit is installed to.

[0006] If hydrostatic radial piston units are used in propel applications, park brakes are required to prevent, for example a work vehicle motion down an incline, when motive power is not present, e.g. a vehicle in park mode with engine off, or to ensure a fail-safe operation of the hydrostatic radial piston units, e.g. to provide emergency fail safe dynamic braking to stop a vehicle in the event of a system failure which disables hydraulic transmission braking. Thereby the park brake doesn’t have to stop the hydraulic motor driving, as the motor function can be disabled when in park mode. Here the park brake functions like a handbrake of cars, e.g. In this case, the park brakes only allow movement of the vehicle, if they are actively released. In an inactive state of the park brake, movement of the hydrostatic radial piston unit and therewith of the vehicle is blocked. In the state of the art, there are different concepts available for providing a park brake mechanism to hydrostatic radial piston units. E.g., a disc brake may be attached to the outside of the housing of a hydrostatic radial piston unit. As an alternative, the brake could be arranged inside the casing of a hydrostatic radial piston unit, where it is guarded from dirt or similar negative influences. Disadvantageously, this arrangement significantly increases the axial length of the hydrostatic radial piston unit.

[0007] It is an objective of the invention to provide a radial piston unit with reduced dimensions, especially with reduced axial length, but also with reduced radial dimensions. Simultaneously the provided radial piston unit shall comprise a park brake device which is arranged inside the housing respectively casing of the radial piston unit without increasing the axial or the radial dimensions of the radial piston unit significantly.

[0008] The objective is solved by a hydrostatic radial piston unit according to claim 1. Preferred embodiments are presented in the dependent claims.

[0009] A hydrostatic radial piston unit according to the invention may be of the cam-lobe type of construction. However, the concept may be applicable to other types of radial piston units as well, e.g. to orbital motors.

[0010] The hydrostatic radial piston unit comprises a non-rotary, stationary housing. The housing at least partially encloses an interior cavity formed, e.g. by a front casing part and a rear casing part. Additionally the housing can be closed in axial direction at an rear end by an end cover. A rotary cylinder block with radially oriented cylinder bores is arranged in the interior cavity. The cylinder block is rotatable around a rotational axis of the hydrostatic radial piston unit. According to the invention, the terms “radially” and “axially” are seen with respect to the rotational axis of the hydrostatic radial piston unit. Thus, “radially” means “in radial direction with respect to the rotational axis” or “orthogonal to the rotational axis”. “Axially” means “in axial direction with respect to the rotational axis” or “parallel to the rotational axis”. In the scope of this application, “stationary” means non-rotary around the rotational axis, when the radial piston unit is installed, e.g., to a work vehicle or other equipment.

[0011] The hydrostatic radial piston unit further includes a park brake device. The park brake device comprises at least one non-rotary brake disc which is in torque-proof connection with a non-rotary element of the hydrostatic radial piston unit. The park brake device further includes at least one rotary brake disc which is in torque-proof connection with a rotary element of the hydrostatic radial piston unit. Preferably, the park brake device comprises a plurality of non-rotary brake discs and a plurality of rotary brake discs which are arranged in alternating order. Therewith, the contact area by means of which a frictional contact between the brake discs can be established is increased. Preferably, the brake discs are movable in the axial direction such that they can pressed against each other. The park brake device is arranged at least partially radially inside of the cylinder block.

[0012] In particular, the park brake device may be at least partially radially enclosed by the cylinder block. This means that at least one element of the park brake device is arranged radially inside of the cylinder block. Additionally, the element of the park brake device which is arranged radially inside of the cylinder block is arranged axially in the same position as the cylinder block.

[0013] As the park brake device is at least partially arranged radially inside or is at least partially radially enclosed by the cylinder block, the axial length of the hydrostatic radial piston unit is reduced. Due to the reduced axial length, integrating the radial piston unit into work vehicles or other devices is facilitated. Furthermore, when the park brake device is at least partially radially enclosed by the rotary cylinder block, the number of parts required for transmitting motion from the cylinder block towards the brake discs is reduced. Additionally, the manufacturing and assembling costs for a hydrostatic radial piston unit are lowered due to facilitated and simplified assembling and the lower number of parts.

[0014] Preferably at least one brake disc is arranged radially inside the cylinder block or is radially enclosed by the cylinder block. In addition or as an alternative, other elements of the park brake device may be arranged radially inside or may be radially enclosed by the cylinder block. In particular, a stop element can be provided radially inside of the cylinder block against which the brake discs can be pressed in axial direction in order push / press the brake discs together and to establish a frictional contact between the rotary brake discs and the non-rotary brake discs. Additionally or alternatively, an actuating element of the brake device may be arranged radially inside or may be radially enclosed by the cylinder block, e.g. a brake pin, a brake piston, a brake shim, a disc spring and / or a sealing element, such as a brake seal ring, may be arranged radially inside or may be enclosed by the cylinder block. In one embodiment of the invention, all of the brake discs are radially enclosed by the cylinder block.

[0015] In a preferred embodiment, at least a part of the park brake device is arranged radially inside or is radially enclosed by a non-rotary hydraulic fluid distributor being in torque-proof connection with the housing. In other words: The park brake device is at least partially arranged radially inside or at least partially radially enclosed by the non- rotary distributor, wherein the distributor may be in torque-proof connection with the housing, e.g. the rear casing part.

[0016] A front face of the stationary distributor may be arranged axially adjacent to the cylinder block, such that the front face faces a lateral surface of the cylinder block and hydraulic fluid is guidable to and from the cylinder bores in the cylinder block via timing holes in the front face of the distributor. Thus, depending on the rotational position of the cylinder bores, the distributor is used for providing pressurized hydraulic fluid to some of the cylinder bores and to drain hydraulic fluid from other cylinder bores. The distributor may comprise at least one outer groove in an outer circumferential surface of the distributor, wherein the at least one outer groove forms a circular conduct in combination with at least one internal groove in the circumferentially inner surface of the housing. Preferably, at least two separate circular conducts may be formed by outer grooves in the distributor’s outer surface and inner grooves in the housing, such that fluid under high working pressure is guidable in one of the conducts and fluid at low pressure is guidable in the other conduct.

[0017] When the park brake device is at least partially arranged inside of the distributor, the axial length of the hydrostatic radial piston unit may be further reduced, such that the advantages mentioned above in connection with the park brake device being at least partially enclosed by the cylinder block are further enhanced.

[0018] Preferably at least one brake disc is arranged radially inside or is radially enclosed by the distributor. In addition or as an alternative, other elements of the park brake device may be arranged radially inside or may be radially enclosed by the distributor. In one embodiment, similarly to the cylinder block, a stop element can be provided radially inside of the distributor against which the brake discs can be pressed in axial direction. Additionally or alternatively, an actuating element of the brake device may be arranged radially inside or may be enclosed by the distributor, e.g. a brake pin, a brake piston, a brake shim, a disc spring and / or a sealing element, such as a brake seal ring, may be arranged radially inside or may be enclosed by the distributor.

[0019] The distributor may be axially pre-tensioned towards the cylinder block by means of a wave spring arranged between the distributor and the housing. Providing a wave spring avoids the need for drillings in the distributor and / or the housing, which are required in known solutions to accommodate coil spring sets. Preferably, the wave spring is made of spring steel and shows a, in general, axially waved disc shape .

[0020] In a preferred embodiment, at least one brake disc is in torque-proof connection with a shaft. The shaft has a central axis that is identical to the rotational axis of the hydrostatic radial piston unit defined by the rotary cylinder block. Preferably, the shaft is entirely arranged in the interior cavity. Thus, the shaft does not protrude from the hydrostatic radial piston unit in axial direction. Therewith, the axial length of the radial piston unit is short and the shaft is guarded by the housing of the radial piston unit, e.g., from dirt.

[0021] Additionally or alternatively, the shaft may be hollow. Providing a hollow shaft with a central opening may be particularly beneficial when it is required that other parts, like cables or a shaft with a smaller diameter are routed through the opening of the hollow shaft. Additionally a hollow shaft reduces the overall weight of the hydrostatic radial piston unit.

[0022] In a preferred embodiment, the shaft may be non-rotary. In particular, the shaft may be in torque-proof connection with the non-rotary housing. Therefore, the at least one brake disc being connected to the shaft in a torque-proof manner is non-rotary. This configuration of the hydrostatic radial piston unit may be preferred, e.g., if the shaft is hollow and cables or other equipment extend through shaft, as no relative motion between the stationary cables or equipment and the stationary shaft is present. A hollow shaft might accommodate other equipment going through the shaft, e.g. a rotating orbiting shaft which can be driven at a different rotational velocity than the cylinder block. A main advantage of a non-rotating shaft is the easier sealing between the static brake piston and the static shaft.

[0023] Further preferred, the at least one rotary brake disc is in torque-proof connection with the cylinder block. Thus, the rotational motion of the cylinder block is directly forwarded to the at least one rotary brake disc without requiring any additional parts for transmitting the motion from the cylinder block to the brake discs.

[0024] In another embodiment the shaft can be rotary, too. In particular, the shaft may be in torque-proof connection with the cylinder block. Thus, the at least one brake disc being in torque-proof connection with the shaft is rotary and the at least one non-rotary brake disc may be in torque-proof connection with the housing or with the non-rotary distributor. In a preferred embodiment, an end cover may be provided which closes the housing in axial direction. The end cover may comprise an opening, such that cables or other equipment can extend from the outside of the housing towards the inside of the hollow shaft. Preferably, the diameter of the opening of the end cover is at least of equal size as the diameter of the opening of the hollow shaft.

[0025] The end cover may pre-tension a disc spring of the brake device against a discshaped brake piston of the brake device, wherein the disc spring and the brake piston are both located in a rear end portion of the stationary housing. Thus, in a blocking position of the brake, also called fail-safe position or park mode, which preferably is the default position of the brake, an axially oriented spring force is generated, in order to press the brake discs of the brake device against each other by means of the brake piston, and, e.g., against a shoulder of the cylinder block or a shaft nut on the opposite axial end of the break device remote from the brake piston.

[0026] To release the brake, a pressure chamber may be provided opposite to the disc spring and sealed by the brake piston. Pressurized hydraulic fluid may be feed to the pressure chamber to generate an opening force on a front face of the brake piston in order to release the compressing force from the brake discs.

[0027] Therefore, if no hydraulic pressure is present in the pressure chamber opposite to the disc spring, the park brake mechanism is in its blocking position in which the brake discs are pressed against each other and the rotational position of the rotary elements of the radial piston unit is fixed in relation to the stationary elements of the radial piston unit. To release the park brake, the pressure chamber may be pressurized by hydraulic fluid.

[0028] In an alternative embodiment, an end cover - with or without an opening - closes the housing in axial direction. The end cover pre-tensions a disc spring of the brake device against a disc-shaped brake piston of the brake device both located in a rear end portion of the stationary housing to generate an axially oriented spring force. By contrast to the above described embodiment, the axially oriented force is forwarded by the brake piston to at least one brake pin of the brake device arranged in an axially oriented bore in the stationary housing. The brake pin transmits the force towards the brake discs in order to press the brake discs against each other and, e.g., against a shoulder of the cylinder block or a shaft nut on the other axial end of the brake device, to hold the park brake in a blocking position.

[0029] The brake piston may seal a pressure chamber opposite to the disc spring and pressurized hydraulic fluid may be guided to the pressure chamber to generate an opening force on a front face of the brake piston in order to release the compressing force from the brake discs, and therewith releasing or opening the brake.

[0030] A person with skills in the relevant art will select the number, shape and arrangement of the brake pins and the corresponding axially oriented bores according to the requirements of the distinct application. E.g., it might be preferable to arrange at least three or more brake pins equidistantly distributed on a circular arc which comprises the rotational axis as center, in order to guarantee for a uniform distribution of the actuation force over the entire front face of the brake discs.

[0031] Apart from the above explained options for switching the park brake into open / released position, further options are available.

[0032] For a first option, the brake pin at least contributes to sealing the pressure chamber that is formed, e.g. in the stationary part of the casing at the rear end of the radial piston unit. As explained above, the chamber can be formed by multiple parts, e.g. by the shaft, by the stationary casing, the brake pins and by the brake piston. Hence, the rear end of the brake pins is preferably attached in a fluid tight manner to the brake piston. An additional sealing is provided between the front end of the brake pin and the stationary casing. Therefore, a pressure chamber is formed by the stationary casing in combination with the shaft, the brake pin guiding holes and the brake piston. If pressurized hydraulic fluid is supplied to this pressure chamber, a force on a releasing surface of the brake piston is generated in order to counteract against the pre-tensioning force of the disc spring and release the brake. Thus, the compressing force is no longer transmitted to the brake discs by means of the brake pin, and the rotary elements of the radial piston unit are able to rotate relative to the stationary elements.

[0033] The release pressure, which is required to release the brake, depends on the dimensions of the releasing surface of the brake piston in comparison to pre-tensioning force provided by the disc-spring. The pre-tensioning force of the spring might be adjustable, e.g. by adjusting the relative position of the brake piston to the end cover by an adjustable shoulder or an adjusting screw in the end cover. The length of the brake pack, i.e. the number of brake disks, may be adjusted. Additionally or alternatively, in order to adjust the pre-tensioning force exerted by the disc spring, a brake shim of the brake device may be provided axially between the brake piston and the disc spring.

[0034] Preferably, the rear end of the brake pin which faces in the direction of the brake piston, comprises a higher diameter than the front end of the brake pins. This design of the brake pins ensures that the pins are always in contact with the brake piston, no matter if the brake is in its blocking state or in the released state.

[0035] If pressurized hydraulic fluid is supplied to the before mentioned pressure chamber in order to generate a force on the releasing surface of the brake piston, the same pressure is applied to the end surfaces of the brake pin. This pressure generates a force acting on the end surfaces of the brake pins. Due to the higher diameter of the rear end of the brake pins, a higher force will be generated on this side. Therefore, the brake pin is moved in the direction of the brake piston until it is in contact with the brake piston. Then the brake pin remains in contact with the brake piston, even if the brake piston moves in the direction towards the disc spring, i.e. in direction of the end cover of the stationary casing.

[0036] For the second option representing an alternative embodiment of the invention, a pressure chamber is formed inside of the axially oriented bores in which the brake pins are arranged and guided in axial direction. Sealings are provided at the front and at the rear end of the brake pins to close the pressure chamber. Preferably, also in this embodiment, the rear end of the brake pins which faces the brake piston, comprises a higher diameter than the front end of the brake pins. If pressure is supplied to the pressure chamber, a higher force will be generated at the rear end of the brake pins due to the higher diameter. Therefore, the brake pin moves in the direction of the rear end of the hydrostatic radial piston unit, i.e. in the direction of the brake piston. If there is a gap between the brake pin and the brake piston, the brake pin will move towards the rear side until it is in contact with the brake piston. Then, the force generated by the pressure in the pressure chamber is transmitted to the brake piston by means of the brake pin. If the generated force is high enough to overcome the pre-tensioning force of the disc-spring, the disc-spring is compressed and the park brake is released.

[0037] Preferably, the pressure chamber extends in axial direction from a brake seal ring of the brake device, provided between the shaft and the housing, towards the brake piston, wherein the brake piston is sealed at the radially inner side by the shaft and is sealed at the radially outer side by the housing.

[0038] Further preferred, the brake seal ring limits the axial movement of the shaft with respect to the housing. Thus, in order to reduce the number of parts required for assembling a hydrostatic radial piston unit, the brake seal ring simultaneously fulfills the function of sealing the pressure chamber as well as fixing or limiting the axial movability of the shaft with respect to the housing.

[0039] The shaft may be centered with respect to the brake piston and / or with respect to the cylinder block by means of the brake seal ring. Additionally or alternatively, the shaft may be centered by means of a shaft seal arranged axially on an end of the shaft opposite to the end cover and radially in between the shaft and the cylinder block. As the brake seal ring and / or the shaft seal fulfill two functions as one part, i.e. sealing against fluid leakage and centering the shaft, the number of parts of a hydrostatic radial piston unit can be reduced. Thus, assembling of the hydrostatic radial piston unit is facilitated and simplified and the manufacturing costs of the hydrostatic radial piston unit are reduced.

[0040] Especially, when the end cover of the hydrostatic radial piston unit comprises an central opening, the parts arranged in the interior cavity should be sealed against fluid leakage. For this purpose, in a preferred embodiment, a seal plate of the brake device is provided inside of the interior cavity adjacent to the end cover. Further preferred, the shaft is hollow, and a collar of the seal plate radially engages with the inner surface of the shaft to form a radially inner sealing connection. The seal plate extends in radial direction at least to the housing, where a radially outer sealing connection may be provided. E.g., the seal plate may be pressed against the housing by means of the end cover, or the seal plate may be fixed to the housing together with the end cover. Therefore, the interior cavity of the housing is fluidly separated from the outside of the housing and leakage of hydraulic fluid is avoided.

[0041] The hydrostatic radial piston unit may comprise a mechanical brake release mechanism capable of axially pulling the brake piston against the force of the disc spring towards the end cover closing the housing in order to open respectively release the brake. The mechanical brake release mechanism may be used, when no hydraulic actuation of the brake is possible, e.g. due to a failure of a hydraulic or electrohydraulic actuation system. By means of the mechanical brake release mechanism the brake can be released after breakdown, e.g. in order to enable towing a damaged vehicle onto a truck or a workshop.

[0042] In one embodiment, the mechanical brake release mechanism comprises at least one brake release screw, which is provided in a threaded blind bore in the end cover or the housing. Thus, the brake release screw can be considered to be a spare part that does not serve a particular use during operation of the hydrostatic unit. When the brake shall be mechanically released, the brake release screw is removed from the threaded blind bore. Then, the brake release screw may be put through a clearance hole in the end cover and screwed into a threaded bore in the brake piston, while the head of the brake release screw abuts against the outer surface of the end cover. Thus, by tightening the brake release screw, the brake piston is mechanically pulled towards the end cover against the pretensioning force of the disc spring, such that a clearance is achieved between the rotary and non-rotary brake discs allowing a rotary motion of the rotary parts of the hydrostatic unit and therewith towing or pushing a vehicle equipped with a hydrostatic unit according to the invention. In a further embodiment of the hydrostatic radial piston unit according to the invention a two-speed, three-speed or multiple-speed-control-valve is provided in the housing. The speed-control-valve is switchable at least between a first position and a second position. In the first position, all cylinder bores of the cylinder block can be supplied with hydraulic fluid under high pressure from a high pressure inlet of the hydrostatic radial piston unit. In other words: All cylinder bores are used for generating torque on the rotary cylinder block, i.e. all cylinder bores can be supplied with fluid under a high pressure, e.g. working pressure. When a cylinder bore is supplied with hydraulic fluid under a high pressure, the piston which is arranged in the cylinder bore is forced to move radially outwards. When the piston is moving radially inwards, e.g., because it follows the shape of a cam of an internal cam-lobe surface of the housing, the corresponding cylinder bore is connected to an outlet timing hole and hydraulic fluid is drained from the cylinder bore.

[0043] In the second position, e.g., only a portion or a subset of the cylinder bores shows the same working behavior as in the first position, i.e. only a portion of cylinder bores is supplied via an inlet timing hole with hydraulic fluid under high pressure and only a portion of the cylinder bores is supplied with fluid under high pressure. Another portion of the cylinder bores is hydraulically short circuited, such that the cylinder bores and the corresponding pistons do not contribute to the generation of torque. In this case, the cylinder bores may be supplied with hydraulic fluid at a reduced pressure, e.g. charge pressure, independently from the movement of the working pistons. Thus, a low force is generated on the pistons which urges the corresponding piston rollers against the camlobe surface, and an abrupt movement of the pistons is avoided when the speed-control valve is switched.

[0044] In other words, in the first position of the control valve, the working volume of the hydrostatic radial piston unit is the sum of all working volumes enclosed between the cylinder bores and their corresponding working cylinders. In the second position, only a part of the cylinder bores may be supplied with fluid at high pressure. Therefore, only this part of the working pistons and the corresponding cylinder bores contribute to the working volume of the radial piston unit. The other working pistons are supplied with a reduced pressure sufficient to assure contact of the piston rollers with the cam-lobe-surface of the rotating casing. They do not contribute to the actual working volume of the radial piston unit as the corresponding pressure chamber is not supplied with hydraulic fluid under high pressure. In the short-circuited case, the hydraulic fluid volume necessary to move one piston outwards is displaced by another inwardly moving piston.

[0045] In a preferred embodiment, the stationary housing comprises a front casing part and a rear casing part. The front casing part comprises a first radially extending shoulder. The rear casing part comprises a second radially extending shoulder. A first tapered roller bearing and a second tapered roller bearing are provided on opposite sides with respect to the cylinder bores of the cylinder block, such that the first and second roller bearing form an X-arrangement for rotary support of the rotary cylinder block against the stationary housing.

[0046] The front casing part is axially fixed to the rear casing part such that the first tapered roller bearing is axially trapped between the first shoulder and the cylinder block, and the second tapered roller bearing is axially trapped between the cylinder block and the second shoulder. Thus, the bearing arrangement has a slimline design which requires only a minimum number of components, especially in axial direction. Further, as both of the bearings are in direct contact with the cylinder block, a direct transmission of forces to be supported from the cylinder block to the bearings is guaranteed, and the axial length of the hydrostatic unit is further reduced.

[0047] Preferably, the first tapered roller bearing and the second tapered roller bearing are arranged on bearing surfaces of the cylinder block, preferably directly adjacent to a respective shoulder of the cylinder block. Thus, the axial extension of the bearing arrangement is minimized, as the bearings are positioned as close as possible to the cylinder bores.

[0048] A pre-tensioning force of the bearing arrangement is determined by the axial distance between the first shoulder on the front casing part and the second shoulder on the rear casing part in comparison to the axial dimensions of the first tapered roller bearing, the second tapered roller bearing and the portion of the cylinder block which is arranged between the first and second tapered roller bearing. A pre-tensioned bearing arrangement is especially advantageous as it allows a play free transmission of torque and forces. Further it is ensured that the position of the power-take-off, i.e. the area of the cylinder block via which mechanical torque can be transferred to another component, e.g. a wheel of a vehicle, remains with tight tolerances.

[0049] The distance between the first shoulder and the second shoulder may be varied, e.g., by tightening a fixation means by means of which the front casing part is fixed to the rear casing part or vice versa.

[0050] In order to provide a simple yet effective way to adjust the pre-tensioning force of the bearing arrangement, at least one bearing shim may be provided axially between the first shoulder and the first tapered roller bearing, or axially between the first tapered roller bearing and the cylinder block, or axially between the cylinder block and the second tapered roller bearing, and / or axially between the second tapered roller bearing and the second shoulder. One the one hand, a bearing shim serves the purpose of adjusting the pre-tensioning of the bearing arrangement. When the distance between the first shoulder and the second shoulder remains the same, the thicker the bearing shim is, the higher the pre-tensioning force of the bearing arrangement will be. On the other hand, the bearing shim can be used for compensating manufacturing and assembling tolerances, such that the pre-tensioning force of the bearing arrangement of various hydrostatic radial piston units can be adjusted to a target value during the manufacturing of the hydrostatic units.

[0051] According to a preferred embodiment, the housing is formed only by the front casing part and the rear casing part, such that the number of required connections between the casing parts and the required assembling time is minimized. Optionally, e.g. when the housing shall be sealed on one side, an end cover may be provided by means of which the housing is closed on one side, wherein the housing is open on the opposite side. The housing may also be closed on both sides in axial direction. As explained above, the cylinder block comprises radially reciprocatable working pistons which are disposed in the cylinder bores. Preferably, the hydrostatic unit is of the cam-lobe-type of construction, and a circumferential cam surface with which the working pistons can interact, is formed integrally with the stationary front casing part or stationary the rear casing part on its radially inner side. The front casing part and / or the rear casing part each being of single-piece design such that the integrally formed cam surface is formed at an inner surface of the front casing part or of the rear casing part.

[0052] The cylinder block may comprise at least one additional row of cylinder bores and radially reciprocating working pistons. Each row of cylinder bores is arranged axially spaced from the adjacent rows. The cylinder bores and the corresponding working pistons can be arranged in axial direction adjacent to, i.e. with the same rotational position, or with an offset in circumferential direction to the first row of cylinder bores and can interact with the cam surface.

[0053] The hydrostatic radial piston unit may further comprise a second cylinder block, whose working pistons interact with the same cam-lobe surface or with another, second cam-lobe surface arranged in parallel to the first one. The second cylinder block is arranged axially parallel to the first cylinder block. Providing a cylinder block with more than one row of cylinder bores or a second cylinder block increases the potential working volume significantly, wherein the diameter of the hydrostatic radial piston unit stays the same. In this embodiment it is preferred that the before mention bearing arrangement with two sets of tapered roller bearings encompasses both rows of cylinder bores.

[0054] A second circumferential cam surface may be formed integrally with the housing on its radially inner side. The working pistons of the additional row of cylinder bores or of the additional cylinder block may interact with the second cam surface. Thereby the two cam surfaces can be each on a different casing part or both on the same casing part.

[0055] In order to tailor the behavior of the hydrostatic radial piston unit to a specific application, the number of cylinder bores and the number of radially reciprocating working pistons of the axially spaced rows of cylinder bores or of the second cylinder block may differ from the number of cylinder bores and the number of radially reciprocating working pistons of the first cylinder block. In this case, a second circumferential cam lobe surface can be provided at the radially inner side of the rotary casing. The working pistons of the second cylinder block or of the second or a further row of cylinder bores can interact with the second cam lobe surface. In one embodiment, the second circumferential cam-lobe surface is formed integrally with the rotary casing.

[0056] Preferably, a mechanical output of the hydrostatic radial piston unit is provided on a front face of the cylinder block, in particular on the front face of the cylinder block facing away from the end cover. In this configuration of the hydrostatic radial piston unit, one side of the housing is closed in axial direction by an end cover, with or without opening, and the other side of the housing remains open to provide a mechanical interface for transmitting torque.

[0057] In the following annexed Figures, exemplary embodiments of the hydrostatic radial piston unit according to the invention as wells as specific subassemblies of a hydrostatic radial piston unit according to the invention are described. The presented embodiments do not limit the scope of the invention. The Figures show:

[0058] Figure 1 shows a sectional view along the rotational axis of a first embodiment of the hydrostatic radial piston unit according to the invention;

[0059] Figure la an alternative of the first embodiment shown with Figure 1;

[0060] Figure 2 shows a sectional view along the rotational axis of a second embodiment of the hydrostatic radial piston unit according to the invention,

[0061] Figure 2a an alternative of the second embodiment shown with Figure 2;

[0062] Figure 3 shows a sectional view along the rotational axis of a third embodiment of the hydrostatic radial piston unit according to the invention; and Figure 3a an alternative of the third embodiment shown with Figure 3.

[0063] For illustration and legibility purposes only, in all presented Figures the same functional parts are indicated with same reference numbers.

[0064] Figure 1 shows a sectional view along the rotational axis 10 of a first embodiment of the hydrostatic radial piston unit 1. The hydrostatic radial piston unit 1 comprises a housing 20 which can be installed to a vehicle frame, e.g. Therefore, the housing is considered to be stationary with respect to the rotational axis 10. The housing 20 comprises a front casing 30 and a rear casing 40, which are attached to each other. For fixing the hydrostatic radial piston unit 1 on an external machine flanges 35 are provided at the front casing 30.

[0065] The housing 20 encloses an interior cavity 23, in which a cylinder block 50 is arranged. The cylinder block 50 comprises a plurality of circumferentially distributed cylinder bores 55, wherein one working piston 60 is arranged in each of the cylinder bores 55. Working pistons 60 are reciprocatably movable in the cylinder bores 55 and abut on a radially outer side against an inwardly oriented cam surface 80 by means of piston rollers 62. The cylinder block 50 is rotatable around the rotational axis 10 of the hydraulic radial piston unit 1. When the cylinder block 50 rotates, the pistons 60 are forced to conduct a back-and-forth movement in the cylinder bores 55 due to their interaction with the cam surface 80.

[0066] In the presented embodiment, the cam-lobe surface 80 is formed integrally with the front casing part 30, e.g. by 3D-milling, casting, turning, forging or a different manufacturing method. However, the cam-lobe surface 80 might also be formed integrally with the rear casing part 40, or it might be a separate part, sandwiched between the front casing 30 and the rear casing 40.

[0067] Thus, in the case of using the hydrostatic radial piston unit as a hydraulic pump, the cylinder block 50 is rotated by mechanical torque provided at a mechanical torque transmission element 57 on a front face of the cylinder block 50. In consequence, the pistons 60 are guided by the cam surface 80, and hydraulic fluid is pushed out of a cylinder bore 55 when the piston 60 is forced due to the shape of the cam-lobes of the cam surface 80 to move radially inwards.

[0068] When the hydrostatic radial piston unit 1 is used as hydraulic motor, hydraulic energy provided to the cylinder bores 50 is converted into mechanical torque for take-off at the torque transmission element 57. In order to urge the working pistons 60 against the cam-lobe surface 80, pressurized fluid is supplied to the cylinder bores 55 of the cylinder block 50. The force on the pistons 60 generated by the pressure of the hydraulic fluid in the cylinder bores 55 is supported by the cam surface 80 formed at the stationary housing 20. Due to the shape of the cam surface 80 a torque is generated. When a piston 60 is moved radially inwardly following the shape of the cam surface 80, hydraulic fluid is drained from the corresponding cylinder bore 55. Therefore, in the course of one revolution of the cylinder block 50, the cylinder bores 55 have to be alternately connected to a pressure inlet of the hydrostatic radial piston unit 1 and to a pressure outlet of the hydrostatic radial piston unit 1.

[0069] For this purpose, a stationary distributor 70 is provided. The distributor 70 is capable of selectively connecting the pressure inlet of the hydrostatic unit 1 or the pressure outlet of the hydrostatic unit 1 with the appropriate cylinder bores 55 via timing holes that are arranged in a front face 72 of the distributor 70 which is in fluid connection with an adjacent front face of the cylinder block 50. The distributor 70 may be arranged directly adjacent to the cylinder block 50, or the distributor 70 may be at least fluidly connected to the cylinder block 50, e.g. when a bearing plate is arranged in between the distributor 70 and the cylinder block in order to lower frictional forces between the two components.

[0070] According to one embodiment of the invention distributor springs 76 are provided in axial holes in the body of the distributor 70. The distributor springs 76 are capable of providing a pre-tensioning force onto the distributor 70 which urges the front face 72 of the distributor against the adjacent front face of the cylinder block 50. Thereby, the force generated by distributor springs 76 is supported by a rear end portion 25 of the stationary housing 20.

[0071] The distributor 70 is fluidly connected to the pressure inlet and to the pressure outlet of the hydrostatic unit 1 by means of annular conducts which are formed by outer grooves 74 in the outer circumferential surface of the distributor 70 in combination with inner grooves 44 provided in an internal circumferential surface of the housing 20, in particular of the rear casing part 40.

[0072] Depending on whether high pressure shall be supplied to a specific cylinder bore 55 via the timing holes or whether hydraulic fluid shall be drained from the specific cylinder bore 55 via the timing holes, the appropriate circular / annular conduct is connected to the specific passing cylinder bore by means of the timing holes.

[0073] In order to support the rotary cylinder block 50 in the stationary housing 20, a spacesaving bearing arrangement is provided. The bearing arrangement consists in a first embodiment of the invention of a first tapered roller bearing 90 and a second tapered roller bearing 100. The two roller bearings 90 and 100 are arranged on opposite sides of the cylinder block 50, preferably on opposite sides of the cylinder bores 55, i.e. the radial distance of the roller bearings 90 and 100 with respect to the rotational axis 10 is approximately the same as of the cylinder bores 55. The roller bearings 90 and 100 are radially supported by circumferential surfaces of the cylinder block 50, and abut in the direction towards the cylinder bores 55 against a respective first and second stop surface 52, 53 of the cylinder block 50 with its inner bearing shells 91 and 101, respectively. Thus, the first and second tapered roller bearing 90, 100 do not protrude from the cylinder block 50 in axial direction. In other words, the cylinder block 50 extends further in axial direction from the first and second stop surface 52, 53 than the first and second tapered roller bearing 90, 100. However, it is preferred by the invention that the two roller bearings are arranged in close axial proximity to the cylinder bores 55 such that the overall axial length of the hydrostatic radial piston unit is kept as short as possible. On the other side arranging the roller bearing 90 and 100 close to the cylinder bores 55 provides for compact and robust design as mounting / support forces can be received at short distance to their occurrence, i.e. with short leverage.

[0074] The front casing part 30 comprises a first radially extending shoulder 32. The rear casing part 40 comprises a second radially extending shoulder 42. The first radially extending shoulder 32 and the second radially extending shoulder 42 may be brought into contact with the outer bearing shell 92 of the first tapered roller bearing 90 and with the outer bearing shell 102 of the second tapered roller bearing 100, respectively, when the rear casing 40 is fixed to the front casing 30, or vice versa. In the present embodiment screws 34 (see Figure 3) are provided for fixing the rear casing 40 to the front casing 30. When the screws are tightened the first tapered roller bearing 90 is axially trapped between the first shoulder 32 of the front casing 30 and the cylinder block 50, in particular the first stop surface 52. Similarly, the second tapered roller bearing 100 is axially trapped between the cylinder block 50, in particular the second stop surface 53, and the second shoulder 42 of the rear casing 40.

[0075] Once a contact between the first shoulder 32, the first tapered roller bearing 90, the cylinder block 50, the second tapered roller bearing 100 and the second shoulder 42 is established, the screws 34 may be further tightened in order to increase the bearings pretensioning force. However, this way of adjusting the pre-tensioning force may lead to a statically overderminate bearing arrangement. In order to avoid statical overdetermination of the bearing arrangement, one or more bearing shims 110 may be integrated in the bearing arrangement, in particular between the first shoulder 32 and the first tapered roller bearing 90 and / or between the second shoulder 42 and the second tapered roller bearing 100. The at least one bearing shim 110 may be capable of compensating manufacturing tolerances of the front casing part 30 and the rear casing part 40 as well as of adjusting the pre-tensioning force of the bearing arrangement. Thus, when the dimensions of the front casings 30 and the rear casing 40 of various hydrostatic units deviates from each other, the pre-tensioning force of the bearing may be adjusted to a pre-termined level by means of selecting the appropriate number and thickness of bearing shims 110. The hydrostatic unit 1 may comprise a park brake device 150 for ensuring that the rotating elements of the hydrostatic radial piston unit 1 are held stationary, when the system is de-energized or de-pressurized. The park brake device 150 includes at least one non-rotary brake disc 152 and at least one rotary brake disc 154. Preferably, the brake device 150 comprises a plurality of non-rotary brake discs 152 and rotary brake discs 154 which are arranged in alternating order. The non-rotary brake discs 152 are connected in a torque-proof manner to a non-rotary element of the hydrostatic unit 1 , whereas the rotary brake discs 154 are connected in a torque-proof manner to a rotary element of the hydrostatic unit 1.

[0076] In the embodiment shown with Figure 1, a stationary shaft 12 is provided which is in torque-proof connection with the rear end portion 25 of the housing 20, e.g. via a splined shaft connection. The brake pack, i.e. all the rotary brake discs 154 and the non- rotary brake discs 152, is entirely radially enclosed by the cylinder block 50. The rotary brake discs 154 are in torque proof connection with an inner circumferential surface of the cylinder block 50. The non-rotary brake discs 152 are in torque proof connection with an outer circumferential surface of the shaft 12. On one end of the shaft 12 a stop element 164 is provided against which the axially movable brake discs 152, 154 can be pressed.

[0077] The rear end portion 25 of the housing 20 is at least partially closed by an end cover 130. The end cover 130 and the shaft 12 comprise a central opening for allowing the passage of equipment, like cables, or a shaft with a smaller diameter than the opening of the hollow shaft.

[0078] A disc spring 158 is supported by the end cover 130 and is pressed against a brake piston 156 to generate a pre-tensioning force for holding the brake device 150 in a closed position by pressing the brake discs 152, 154 against the stop element 164 and against each other. Thereby a frictional contact between the brake discs 152, 154 is ensured. As long as the brake piston 156 is not pressurized at its releasing surface facing away from the end cover 130, the spring force of the disc spring 158 is transferred via the brake piston 156 to at least one brake pin 155 arranged in an axially oriented bore 28 in the stationary housing 20. Preferably, to provide a more balanced actuation of the brake discs 152, 154, more than one brake pin 155 is provided. For this, e.g. axial bores 28 in which the brake pins 155 are arranged, are distributed circumferentially in the stationary housing 20 around the rotational axis 10. The at least one brake pin 155 applies / transfers the pre-tensioning force of the disc spring 158 on / to the brake discs 152, 154 which are pressed against each other and supported by the stop element 164, e.g. Therewith relative movement between the rotary cylinder block 50 and the stationary shaft 12 / the stationary housing 20 is avoided, e.g., when a working vehicle is at standstill.

[0079] If relative movement between the rotary cylinder block 50 and the stationary housing 20 shall be enabled, pressurized fluid is conducted to the pressure chamber 27 and hydraulic pressure is applied to a releasing surface of the brake piston 156 located opposite to the disc spring 158. The hydraulic pressure generates a force on the releasing surface of the brake piston 156, which is directed towards the rear side of the stationary housing 20, i.e. in the direction of the disc spring 158 or the end cover 130. As the generated force is directed opposite to the pre-tensioning force of the disc spring 158, the brake pins 155 no longer transmit an axial oriented force to the brake discs 152, 154, and the park brake 150 is released. Thus, relative movement between the brake discs 152, 154 and therewith relative movement of the stationary housing 20 and the rotary cylinder block 50 is possible.

[0080] Preferably, the end / the head 161 of a brake pin 155 which is facing in the direction to the brake piston 156 comprises a higher diameter than the end facing in the direction of the brake discs 152, 154. The head 161 of the brake pin 155 is accommodated in the brake piston 156 in a fluid tight manner. The brake pins 155 are sealed with respect to the housing 20. Additionally, a brake seal ring 160 is provided radially in between the shaft 12 and the housing 20. The brake seal ring 160 is axially fixed with respect to the housing 20 and the shaft 12 by means of securing rings. Thus, apart from a sealing function, the brake seal ring 160 also provides for an axial fixation of the shaft 12 with respect to the housing 20. The brake piston 156 forms a radially outer sealing connection in combination with the housing 20 and a radially inner sealing connection in combination with the shaft 12. Thus, the pressure chamber 27 extends in axial direction from the sealing of the brake pin 155 and the brake seal ring 160 towards the brake piston 156. The pressure chamber 27 extends in radial direction from the shaft 12 to the housing 20.

[0081] Preferably, in order to adjust the pre-tensioning force generated by the disc spring 158, at least one brake shim 159 is provided axially between the brake piston 156 and the disc spring 158. The higher the number of brake shims 159 and / or the higher the thickness of the brake shims 159, the higher the pre-tensioning force, provided by the disc spring 158. Another way of adjusting the pre-tensioning force of the brake device 150 may be to adjust the axial position of the end cover 130 with respect to the shaft 12 or with respect to the housing 20, e.g. by tightening or loosening a fixation means, like a screw, of the end cover 130.

[0082] A collar of a seal plate 157 radially engages the circumferentially inner surface of the hollow shaft 12. From there, the seal plate 157 extends in radial direction to fluidly close the housing 12 and to avoid fluid leakage through the opening in the end cover 130. At a radially outer location, the seal plate 157 may be fixed to the housing 20, to the end cover 130 or between the housing 20 and the end cover 130 in a fluid tight manner. Between the collar of the seal plate 157 and the hollow shaft 12 a dust or dirt seal 167 can be arranged in an axial or radial sealing contact with the shaft 12. Means that the dust or dirt seal 167 can seal the seal plate 157 against a front face of the shaft 12 (Figure 1) or against a radial inner surface of the hollow shaft and against a radial outer surface of the collar of the seal plate 157 (Figure 2).

[0083] The shaft 12 may be centered by means of a bearing, e.g. a plain bearing 163, arranged in between the shaft 12 and the cylinder block 50, in particular in-between the shaft 12 and the stop element 164. A shaft seal 162 may be arranged adjacent to the plain bearing 163 to hold back in hydraulic fluid, e.g. at an inner side of the plain bearing 163. Further, a dirt seal 167 is arranged on the opposite, outer side of the plain bearing 163 to prevent dirt from entering the interior of the housing 20. An alternative or additional shaft seal 162 may be provided in-between the shaft 12 and the brake piston 156 for sealing and centering. The shaft 12 may be additionally or alternatively be centered by the brake seal ring 160.

[0084] As shown with Figure la on the other axial end opposite to the end cover 130 a cover plate 170 can be fixed to the cylinder block 50, e.g. to the torque transmission element 157 and rotates with the cylinder block 50 around the rotational axis 10. Such a cover plate 170 covers the front casing part 30 from entering dirt or dust into hydrostatic radial piston unit 1. Preferably an axial seal 172 is arranged axially between the front casing part 30 and the cover plate 170 to improve the sealing conditions when the hydrostatic radial piston unit is operated. To further improve the sealing of the casing also in radial direction the cover plate may comprise a collar which encompass the front casing part 30 over the whole circumference. Additionally a radial seal can be provided between the collar of the cover plate 170 and a radial outer surface of front casing part 30. Here a kind of shaft seal can be used to achieve a sealing between the two parts - the cover plate 170 and the front casing part 30 - moving relative to each other.

[0085] The Figures 2 and 3 show similar embodiments of hydrostatic radial piston units 1. To avoid repetitions, only the differences between the embodiments will be explained in more detail.

[0086] Figure 2 shows a second embodiment of a hydrostatic radial piston unit 1.

[0087] The end cover 130 of the second embodiment is fully closed, such that the housing 20 is closed in one axial direction. This can be preferred, e.g., when the environment in which the hydrostatic unit 1 is intended to be used is harsh or dirty. In such situations, it may be beneficial to avoid that dirt enters the hydrostatic unit 1, as the behavior of the hydrostatic unit 1 may be negatively influenced. Similarly the other side of the stationary housing 20 can be closed as well by a cover plate 170 at the front casing part 30, and / or the hollow shaft 12 can be closed by a plate or cap on the front side end of hydrostatic radial piston unit . the front side in the embodiments shown in the Figures 1 to 3a is the left side of the illustrations of the hydrostatic radial piston units 1. As can readily be seen by a person skilled in the relevant art one or both ends of the hollow shaft 12 can be closed to prevent the entrance of dust and / or dirt or even water into the hollow shaft 12 area, especially in case if the use of the hydrostatic radial piston unit according to the invention is planned for harsh environments.

[0088] In comparison of Figures la and 2a it can be seen that the cover plate 170 may be a thin plate which is, e.g. sandwiched by the front side of cylinder block 55 and a machine / tool flange when the torque transmission elements are connected to a machine or tool which should be driven by or drives the hydrostatic radial piston unit 1 according to the invention.

[0089] In further difference to the embodiment of Figure 1 the shaft 12 in the embodiment of Figure 2 is integrally formed with the stationary housing 20. Therefore, no seal ring 160 is required for sealing the connection of the shaft 12 with the stationary housing 20. Further, no spline connection between the shaft 12 and the housing 20 has to be provided. The functionality of the bearing arrangement and of the brake device 150 is very similar to the embodiment shown with Figure 1 such that a detailed description is not presented.

[0090] Figure 3 shows a third embodiment of a hydrostatic radial piston unit 1 according to the invention. Here, the shaft 12 is rotationally coupled to the cylinder block 50, e.g., by means of a spline connection, such that the shaft 12 is rotary around the rotational axis 10 together with the cylinder block 50. The rotary brake discs 154 are rotationally connected to an outer circumferential surface of the rotary shaft 12. The stationary brake discs 152 are rotationally connected to an inner circumferential surface of the housing 20. The stop element 164 is held axially between a circlip and a protrusion of the housing 20 and is radially enclosed by the cylinder block 50. A torque proof connection of the stopelement 164 with the housing 20 is not required. However, such a torque-proof connection with the housing 20 may be provided.

[0091] To achieve this, a protrusion 29 extends in axial direction from the rear end portion 25 of the housing 20 towards the cylinder block 50, such that the protrusion 29 is preferably partially radially enclosed by the cylinder block 50 to reduce to the overall axial length of the hydrostatic radial piston unit 1 according to the invention. Thereby the protrusion 29 can be an integral part of the rear casing part 40 or a separate part fixed to the rear end portion 25 of the rear casing part 40. In this embodiment the brake discs 152, 154 are also partially radially enclosed by the cylinder block 50.

[0092] The brake device 150 of this embodiment includes an actuation mechanism without brake pins 155, such that the spring force of the disc spring 158 is directly transmitted by means of the brake piston 156 to the brake discs 152, 154 and presses the brake discs together, when a pressure chamber 27 is not pressurized. The pressure chamber 27 extends in axial direction from a sealing between the shaft 12 and the cylinder block 50, or from a sealing 165 between the shaft 12 and the housing 20, towards the brake piston 156. In radial direction, the pressure chamber 27 extends from the shaft 12 to the housing 20. Apart from that, the functionality of the brake device 150 is similar to the aboveexplained in context with Figures 1 and 2.

[0093] In summary, due to the arrangement of elements of the brake device 150 at least in parts radially inside of the cylinder block 50, the hydrostatic radial piston unit 1 can be designed with a shorter axial length in comparison to known embodiments. The compact bearing arrangement with the first tapered roller bearing 90 and the second tapered roller bearing 100 is also capable of reducing the axial length of known radial piston units. Thus, the two design features enhance each other, and in combination lead to a hydraulic radial piston unit 1 of short axial length.

[0094] From the above disclosure and accompanying Figures and claims, it will be appreciated that the hydrostatic radial piston unit 1 according to the invention offers many possibilities and advantages over the prior art. It will be appreciated further by a person skilled in the relevant art that further modifications and changes known in the art could be made to radial piston unit 1 according to the invention without parting from the spirit of this invention. Therefore all these modifications and changes are within the scope of the claims and covered by them. It should be further understood that the examples and embodiments described above are for illustrative purposes only and that various modifications, changes or combinations of embodiments in the light thereof, which will be suggested to a person skilled in the relevant art, are included in the spirit and purview of this application.

[0095] Reference list:

[0096] 1 Hydrostatic radial piston unit

[0097] 40 80 Cam surface

[0098] 10 Rotational axis

[0099] 12 Shaft 90 First tapered roller bearing

[0100] 91 Inner bearing shell

[0101] 20 Stationary housing 92 Outer bearing shell

[0102] 23 Interior cavity 45

[0103] 25 Rear end portion 100 Second tapered roller bearing

[0104] 27 Pressure chamber 101 Inner bearing shell

[0105] 28 Axially oriented bore 102 Outer bearing shell

[0106] 29 Housing protrusion

[0107] 50 110 Bearing shim

[0108] 30 Front casing / Front casing part

[0109] 32 First radially extending shoulder 130 End cover

[0110] 34 Screw

[0111] 150 Park brake device

[0112] 35 Flange

[0113] 55 152 Non-rotary brake disc

[0114] 40 Rear casing / Rear casing part 154 Rotary brake disc

[0115] 42 Second radially extending 155 Brake pin shoulder 156 Brake piston

[0116] 44 Inner groove 157 Seal plate

[0117] 60 158 Disc spring

[0118] 50 Cylinder block 159 Brake shim

[0119] 52 First stop surface 160 Brake seal ring

[0120] 53 Second stop surface 161 Head of brake pin

[0121] 55 Cylinder bores 162 Shaft seal

[0122] 57 Torque transmission element 65 163 Plain bearing

[0123] 164 Stop element

[0124] 60 Working pistons 165 Seal

[0125] 62 Piston rollers 167 Dust / Dirt seal

[0126] 70 Distributor 70 170 Cover Plate

[0127] 72 Front face 172 Axial seal

[0128] 174 Radial seal

[0129] 74 Outer groove

[0130] 76 Distributor springs

Claims

Claims1. Hydrostatic radial piston unit (1) of the cam-lobe type of construction comprising: a non-rotary, stationary housing (20) at least partially enclosing an interior cavity (23); a rotary cylinder block (50) with radially oriented cylinder bores (55), the cylinder block (50) being arranged in the interior cavity (23) and being rotatable around a rotational axis (10) of the hydrostatic radial piston unit (1); a park brake device (150) comprising at least one non-rotary brake disc (152) which is in torque-proof connection with a non-rotary element of the hydrostatic radial piston unit (1) and at least one rotary brake disc (154) which is in torque-proof connection with a rotary element of the hydrostatic radial piston unit (1); wherein the park brake device (150) is at least partially radially enclosed by the cylinder block (50).

2. Hydrostatic radial piston unit (1) according to claim 1, wherein at least one brake disc (152, 154) is radially enclosed by the cylinder block (50).

3. Hydrostatic radial piston unit (1) according to any of the preceding claims, wherein at least a part of the park brake device (150) is radially enclosed by a non-rotary distributor (70) being in torque-proof connection with the housing (20), wherein a front face (72) of the stationary distributor (70) is arranged axially adjacent to the cylinder block (50), such that hydraulic fluid is guidable to and from the cylinder bores (55) in the cylinder block (50) via timing holes in the front face (72), wherein at least one outer groove (74) in an outer circumferential surface of the distributor (70) forms a circular conduct in combination with at least one internal groove (44) in the circumferentially inner surface of the housing (20).

4. Hydrostatic radial piston unit (1) according to claim 3, wherein at least one brake disc (152, 154) is radially enclosed by the distributor (70).

5. Hydrostatic radial piston unit (1) according to any of claims 3 or 4, wherein the distributor (70) is axially pre-tensioned towards the cylinder block (50) by means of a wave spring arranged between the distributor (70) and the housing (20).

6. Hydrostatic radial piston unit (1) according to any of the preceding claims, wherein at least one brake disc (152, 154) is in torque-proof connection with a shaft (12) with a central axis that is identical to the rotational axis of the hydrostatic radial piston unit (1).

7. Hydrostatic radial piston unit (1) according to claim 6, wherein the shaft is entirely arranged in the interior cavity (23).

8. Hydrostatic radial piston unit (1) according to claim 6 or 7, wherein the shaft (12) is hollow.

9. Hydrostatic radial piston unit (1) according to any of claims 6 to 8, wherein the shaft (12) is rotary, in particular in torque-proof connection with the cylinder block (50).

10. Hydrostatic radial piston unit (1) according to claim 9, wherein the at least one nonrotary brake disc (152) is in torque-proof connection with the housing (20).

11. Hydrostatic radial piston unit (1) according to any of claims 6 to 8, wherein the shaft (12) is non-rotary, in particular in torque-proof connection with the non-rotary housing (20).

12. Hydrostatic radial piston unit (1) according to claim 11, wherein the at least one rotary brake disc (154) is in torque-proof connection with the cylinder block (50).

13. Hydrostatic radial piston unit (1) according to claims 6 to 12, wherein an end cover (130) closing the housing (20) in axial direction pre-tensions a disc spring (158) ofthe brake device (150) against a disc-shaped brake piston (156) of the brake device (150) both located in a rear end portion (25) of the stationary housing (20) to generate an axially oriented spring force, in order to press the brake discs (152, 154) of the brake device (150) against each other by means of the brake piston (156), wherein the brake piston (156) seals a pressure chamber (27) opposite to the disc spring (158) and pressurized hydraulic fluid is guidable to the pressure chamber (27) to generate an opening force on a front face of the brake piston (156) in order to release the compressing force from the brake discs (152, 154).

14. Hydrostatic radial piston unit (1) according to claims 6 to 12, wherein an end cover (130) closing the housing (20) in axial direction pre-tensions a disc spring (158) of the brake device (150) against a disc-shaped brake piston (156) of the brake device (150) both located in a rear end portion (25) of the stationary housing (20) to generate an axially oriented spring force which is forwarded by the brake piston (156) to at least one brake pin (155) of the brake device (150) arranged in an axially oriented bore (28) in the stationary housing (20), in order to press the brake discs (152, 154) against each other by means of the brake pin (155), wherein the brake piston (156) seals a pressure chamber (27) opposite to the disc spring (158) and pressurized hydraulic fluid is guidable to the pressure chamber (27) to generate an opening force on a front face of the brake piston (156) in order to release the compressing force from the brake discs (152, 154).

15. Hydrostatic radial piston unit (1) according to claim 13 or 14, wherein the pressure chamber (27) extends in axial direction from a brake seal ring (160) of the brake device (150), provided between the shaft (12) and the housing (20), towards the brake piston (156), wherein the brake piston (156) is sealed at the radially inner side by the shaft (12) and is sealed at the radially outer side by the housing (20).

16. Hydrostatic radial piston unit (1) according to claim 15, wherein the brake seal ring (160) limits the axial movement of the shaft (12) with respect to the housing (20).

17. Hydrostatic radial piston unit (1) according to claim 15 or 16, wherein the shaft (12) is centered with respect to the brake piston (156) and / or with respect to the cylinder block (50) by means of the brake seal ring (160) and / or by means of a shaft seal (162) and / or by means of a plain bearing (163) arranged axially on an end of the shaft (12) opposite to the end cover (130) and radially in between the shaft (12) and the cylinder block (50).

18. Hydrostatic radial piston unit (1) according to any of claims 13 to 17, wherein a brake shim (159) of the brake device (150) is provided axially between the brake piston (156) and the disc spring (158).

19. Hydrostatic radial piston unit (1) according to any of claims 13 to 18, wherein a seal plate (157) of the brake device (150) is provided inside the interior cavity (23) adjacent to the end cover (130), wherein a collar of the seal plate (153) radially engages with the shaft (12) to form a sealing connection, and the seal plate (157) extends in radial direction at least to the housing (20).

20. Hydrostatic radial piston unit (1) according to any of claims 13 to 19, wherein the hydrostatic radial piston unit (1) comprises a mechanical brake release mechanism capable of axially pulling the brake piston (156) against the force of the disc spring (158) towards the end cover (130) to open the brake.

21. Hydrostatic radial piston unit (1) according to claim 20, wherein the mechanical brake release mechanism comprises at least one brake release screw provided in a threaded blind bore in the end cover (130) or the housing (20), which brake release screw is, after removal from the threaded blind bore, screwable into a threaded bore in the brake piston (156) while protruding through a clearance hole in the end cover (130) to pull the brake piston (156) towards the end cover (130).

22. Hydrostatic radial piston unit (1) according to any of the preceding claims, wherein a multiple-speed-control-valve (120) is provided in the housing (20), the multiple- speed-control-valve (120) being switchable at least between a first position in whichall cylinder bores (55) of the cylinder block (50) can be supplied with hydraulic fluid under high pressure from a high pressure inlet of the hydrostatic radial piston unit (1) and a second position in which only a portion of the cylinder bores (55) is supplied with fluid under high pressure and pairs of cylinder bores (55) are hydraulically short-circuited.

23. Hydrostatic radial piston unit (1) according to any of the preceding claims, wherein the stationary housing (20) comprises a front casing part (30) and a rear casing part (40), the front casing part (30) comprising a first radially extending shoulder (32) and the rear casing part (40) comprising a second radially extending shoulder (42), and wherein a first tapered roller bearing (90) and a second tapered roller bearing (100) are provided on opposite sides with respect to the cylinder bores (55) of the cylinder block (50) for forming an X-arrangement for rotary support of the rotary cylinder block (50) against the stationary housing (20), wherein the front casing (30) is axially fixed to the rear casing (40) such that the first tapered roller bearing (90) is axially trapped between the first shoulder (32) and the cylinder block (50), and the second tapered roller bearing (100) is axially trapped between the cylinder block (50) and the second shoulder (42).

24. Hydrostatic radial piston unit (1) according to claim 23, wherein at least one bearing shim (110) is provided axially between the first shoulder (32) and the first tapered roller bearing (90), axially between the first tapered roller bearing (90) and the cylinder block (50), axially between the cylinder block (50) and the second tapered roller bearing (100) and / or axially between the second tapered roller bearing (100) and the second shoulder (42).

25. Hydrostatic radial piston unit (1) according to claim 23 or 24, wherein the housing (20) is formed only by the front casing part (30) and the rear casing part (40), and wherein, optionally, the housing (20) is closed by the end cover (130) on one side and is open on the opposite side.

26. Hydrostatic radial piston unit (1) according to any of claims 23 to 25, wherein the cylinder block (50) comprises radially reciprocatable working pistons (60) which are disposed in the cylinder bores (55), wherein a circumferential cam surface (80) with which the working pistons (60) can interact, is formed integrally with the front casing part (30) or the rear casing part (40) on its radially inner side, the front casing part (30) and / or the rear casing part (40) each being of single-piece design.

27. Hydrostatic radial piston unit (1) according to claim 26, wherein the cylinder block (50) comprises at least one additional row of cylinder bores (55) and radially reciprocating working pistons (60) which are arranged in axial direction adjacent to or with an offset in circumferential direction to the first row of cylinder bores (55) and can interact with the cam surface (80).

28. Hydrostatic radial piston unit (1) according to claim 27, wherein a second circumferential cam surface (82) is formed integrally with the housing (20) on its radially inner side.

29. Hydrostatic radial piston unit (1) according to claim 28, wherein the working pistons (60) of the additional row of cylinder bores (55) interact with the second cam surface (82).

30. Hydrostatic radial piston unit (1) according to any of the preceding claims, wherein a mechanical torque transmission element (57) is provided on a front face of the cylinder block (50).

31. Hydrostatic radial piston unit (1) according to any of the preceding claims, wherein a cover plate (170) is arranged on an outside facing side of the cylinder block (50) and rotates with the cylinder block (50).

32. Hydrostatic radial piston unit (1) according to claim 31, wherein the cover plate (170) comprises a collar encompassing a radially outside of front casing part (30).

3. Hydrostatic radial piston unit (1) according to claim 31 or 32, wherein an axial seal (172) and / or a radial seal (174) is provided to seal the front face of and / or the radial outer side the front casing part with the cover plate (170).

Images