Brake mechanism for radial piston unit

Abstract

The hydrostatic radial piston unit of cam lobe type construction comprises a non-rotating stationary casing. The stationary casing comprises a through hole defining the rotation axis of the hydrostatic radial piston unit. The rotating casing is rotatably mounted to the non-rotating stationary casing in an axial overlapping region. The parking brake mechanism comprises at least two brake discs arranged adjacent to each other in the overlapping region. An end cover closes the non-rotating casing at a rear end side of the hydrostatic radial piston unit facing away from the rotating casing. The end cover pretensions a disc spring against a disc-shaped brake piston, both of which are arranged in the rear end portion of the stationary casing, to generate an axially directed spring force. When the brake piston on the opposite face of the disc spring is not forced to move towards the end cover, a force can be transmitted by the brake piston to at least one brake pin arranged in an axially directed bore of the stationary casing to press the brake discs against each other.

Description

[Technical field]

[0001] The present invention relates to a hydrostatic radial piston unit, more particularly to a cam lobe or orbital motor or pump. In particular, the present invention relates to a brake mechanism for a hydrostatic radial piston unit of cam lobe type construction. [Background technology]

[0002] Radial piston units, i.e. radial piston pumps and radial piston motors, are widely used in the art, e.g. for heavy load applications. For example, radial piston units are used in the field of construction machinery, agricultural equipment or forestry machinery. Radial piston units are characterized in that their working pistons move radially relative to a central longitudinal / rotational axis when supplied with pressurized hydraulic fluid, in the case of radial piston motors. In general, radial piston units are used in hydraulic applications that do not require high rotational speeds but do require high torque. Radial piston units show the advantage over axial piston units of reduced axial construction space.

[0003] One particular application of radial piston units is the propulsion of work vehicles, for example track loaders. In many cases, one radial piston unit is installed on either side of the frame / body of the work vehicle. The geometry of the frame and the propulsion mechanism is therefore significantly influenced by the size of the radial piston unit. The position at which the radial piston unit transmits torque to the drive means is in many applications pre-set by other components than the radial piston unit, which interact with the drive means. However, radial piston units in the known technical field exhibit a relatively large axial length and a relatively large diameter. Since the radial piston unit driving the work vehicle must be integrated into the vehicle frame, the frame must be designed in such a way that it is possible to receive the fixed part of the radial piston unit, for example the fixed casing, in order to be able to support the torque generated / applied in the operating state. It is therefore desirable to make the size of the radial piston unit used as small as possible, in particular in the axial direction, in order to reduce the changes in the design of the frame on which the radial piston unit is installed.

[0004] When hydrostatic radial piston units are used in propulsion applications, a parking brake is often required to ensure a fail-safe operation of the hydrostatic radial piston unit. In this case, the brake only allows the vehicle to move if it is actively released. In the inactive state of the parking brake, the movement of the hydrostatic radial piston unit and thus the vehicle is prevented. In the prior art, there are different concepts available to provide a parking brake mechanism for a hydrostatic radial piston unit, for example a disk brake that is mounted on the outside of the casing of the hydrostatic radial piston unit. As an alternative, the brake can be arranged inside the casing of the hydrostatic radial piston unit, where it is protected from dust or similar negative influences. Unfortunately, this arrangement significantly increases the axial length of the hydrostatic radial piston unit.

[0005] WO 2013 / 160145 A2 discloses a radial piston engine with a rotating output shaft. In order to reduce the axial length of the radial piston engine, at least a part of the parking brake is arranged between the housing and a part of the output shaft. The output shaft is designed to rotate, for example, to drive wheels, which can be fastened to an output flange at the output shaft. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a radial piston unit with reduced size, in particular reduced axial length, but also reduced radial size / diameter, which at the same time comprises a parking brake mechanism arranged inside the casing of the radial piston unit, such that neither the axial nor radial size of the radial piston unit increases significantly. [Means for solving the problem]

[0007] This object is achieved by a hydrostatic radial piston unit according to claim 1. Preferred embodiments are given in the dependent claims.

[0008] The hydrostatic radial piston unit according to the invention comprises a stationary casing with a through hole that defines a longitudinal axis, which is also the axis of rotation of the hydrostatic radial piston unit, which is provided for coupling to a frame of a working vehicle, i.e. in the sense of the present specification, the stationary part of the radial piston unit according to the invention forms, for example, a rear end region that can be fixedly fastened to a frame or a support.

[0009] In this specification, the terms "radial" and "axial" refer to directions relative to the longitudinal axis of a fixed shaft. In the context of this application, "fixed" means that the radial piston unit does not rotate about the longitudinal axis, for example when installed in a work vehicle.

[0010] The cylindrical rotating casing is rotatably mounted to the non-rotating stationary casing in an axial overlap region. In this region, the front end portion of the non-rotating casing and the rear end portion of the rotating casing overlap axially. As a result, in the overlap region, at least a part of the rotating casing is arranged radially outside or inside the stationary casing. Thereby, the rear end portion of the rotating casing is sealed against the front end portion of the stationary casing when the rotating casing can rotate relative to the stationary casing around the rotation axis of the radial piston unit. The sealing between the rotating casing and the stationary casing is performed such that both casings together form a closed fluid-tight cavity. The connection between the rotating casing and the stationary casing allows the rotating casing to rotate relative to the stationary casing around the rotation axis, i.e. the longitudinal axis.

[0011] Essentially, the axial position of the seal between the stationary casing and the rotating casing defines a sealing surface perpendicular to the axis of rotation, so that, in a view from the outside, the sealing surface divides the casing of the hydrostatic radial piston unit into a stationary part (rear end) on one side of the sealing surface and a rotating part (front end) on the other side of the sealing surface.

[0012] In a preferred embodiment of the invention, the stationary casing accommodates the stationary shaft in a torque-resistant manner at its rear end portion, meaning that neither the stationary shaft nor the stationary casing rotate relative to each other. The stationary shaft is arranged coaxially with the axis of rotation in an internal cavity formed by the stationary casing and the rotating casing. At a front end portion of the stationary shaft protruding from the stationary casing, a stationary cylinder block is arranged in torque-resistant connection with the stationary shaft. The cylinder block comprises a number of cylinder bores extending radially inward from a circumferential surface of the cylinder block.

[0013] The hydrostatic radial piston unit according to the invention further comprises a parking brake mechanism with at least two brake discs arranged adjacently in an overlapping region, one brake disc being rotatably fixed to the non-rotating casing and the other brake disc being rotatably fixed to the rotating casing, whereby at least one brake disc is axially movable. If the hydrostatic radial piston unit comprises more than two brake discs, the brake discs are rotatably fixed alternately to the stationary and rotating casings, and an axial mobility must be provided in order to achieve the braking effect by (fully) pressing the brake discs together, and to release the brake by lowering the compression force. According to the invention, the rotatably fixed parts cannot rotate relative to each other.

[0014] The parking brake mechanism comprises a blocking position, in which the brake discs are pressed against each other and the rotational position of the rotating casing is fixed relative to the fixed casing. According to a preferred embodiment of the invention, the brake discs can be arranged in the axial overlap area between the fixed casing and the rotating casing, axially adjacent to the sealing surface.

[0015] The parking brake mechanism can be pretensioned towards its blocking position by a disc spring providing a pretensioning force acting axially on the brake piston and can be supported, for example, by an end cap / end cover fixed to the rear end of the stationary casing, which closes the non-rotating stationary casing on the end side of the hydrostatic radial piston unit facing away from the rotating casing, i.e. facing away from the axial overlap area where the rotating casing is attached to the stationary casing.

[0016] The axial pretensioning force of the disc spring can be transmitted to the brake disc via the brake piston by at least one brake pin extending axially between the brake piston and the brake disc. The at least one brake pin is preferably arranged in an axially oriented bore in the non-rotating stationary casing on the opposite side of the brake piston from the disc spring. As a result, the brake piston transmits the pretensioning force of the disc spring to the brake pin which presses the brake disc against each other.

[0017] Those skilled in the art will select the number, shape and arrangement of the brake pins and corresponding axially oriented bores according to the requirements of a particular application. For example, it may be preferable to arrange at least three brake pins equidistantly distributed on a circular arc having the axis of rotation as its center.

[0018] Different options are available for switching the parking brake into the open / released position. For the first option, the brake pin seals a chamber formed, for example, in the fixed part of the casing at the rear end of the radial piston unit. The chamber can also be formed by several parts, for example, by the shaft, the fixed casing, the brake pin and the brake piston.

[0019] Thus, the rear end of the brake pin is preferably mounted fluid-tight on the brake piston. An additional seal is provided between the front end of the brake pin and the fixed casing. Thus, a pressure chamber is formed by the fixed casing together with the fixed shaft, the brake pin guide hole and the rear end front face of the brake piston. If pressurized hydraulic fluid is supplied to this pressure chamber, a force on the release face of the brake piston is generated to counteract the pretensioning force of the disc spring and release the brake. The compression force of the brake pin is thereby released from the brake disc and the rotating casing can rotate relative to the fixed casing. The release pressure required to release the brake depends on the size of the release face of the brake piston in comparison with the pretensioning force provided by the disc spring. The pretensioning force of the spring may be adjustable, for example, by adjusting the relative position of the brake piston to the end cover with an adjustable shoulder or an adjustment screw on the end cap / end cover. Alternatively, the length of the brake pack, i.e. the number of brake discs, may also be adjusted.

[0020] Preferably, the rear end of the brake pin, which faces the brake piston, has a larger diameter than the front end of the brake pin. This design of the brake pin ensures that the pin is always in contact with the brake piston, whether or not the brake is preventing the relative rotation of the stationary and rotating casings. In the blocking position, or if the hydrostatic radial piston unit is moved towards the blocking position, the brake piston presses the brake pin against the brake disc which is pressed against it, for example against a shoulder of the stationary casing.

[0021] When pressurized hydraulic fluid is supplied to the aforementioned pressure chamber in order to generate a force on the release face of the brake piston, the same pressure is applied to the end face of the brake pin. This pressure generates a force acting on the end face of the brake pin. Due to the larger diameter of the rear end of the brake pin, a larger force is generated on this side. The brake pin therefore moves towards the brake piston until it comes into contact with the brake piston. In that case, 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. towards the end cap of the fixed casing.

[0022] With regard to a second option, which represents an alternative embodiment of the invention, the pressure chamber is formed in an axially oriented bore in which the brake pin is arranged and guided axially. Sealings are provided at the front and rear ends of the brake pin to close the pressure chamber. Preferably, also in this embodiment, the rear end of the brake pin, which faces the brake piston, has a larger diameter than the front end of the brake pin. If pressure is supplied to the pressure chamber, due to the larger diameter, a larger force is generated at the rear end of the brake pin. The brake pin therefore moves in the direction of the rear end of the hydrostatic radial piston unit, i.e. in the direction of the brake piston. In the event of a gap between the brake pin and the brake piston, the brake pin moves towards the rear side until it comes into contact with the brake pin. The force generated by the pressure in the pressure chamber is then transmitted by the brake pin to the brake piston. If the generated force is large enough to overcome the pretensioning force of the disc spring, the disc spring is compressed and the parking brake is released.

[0023] In one embodiment according to the invention, the non-rotating stationary casing comprises an annular groove on the inner surface of the through hole, which forms a first circular guide together with a first groove on the outer peripheral surface of the non-rotating stationary shaft. According to the invention, a brake pin is used to fill the axial gap between the brake piston and the brake disc, which may be arranged in the axial overlap area. Preferably, the axially oriented bore with the brake pin is arranged radially outside the first circular guide of the stationary casing. This ensures that it is possible to provide sufficient space on the outer surface of the shaft for the annular groove and sufficient space on the inner surface of the stationary casing for the first groove.

[0024] The brake design according to the invention allows the centrally located brake disc to be located close to the area where the rotating part of the hydrostatic radial piston unit overlaps with the fixed part. At the same time, the hydraulic connections required to provide hydraulic fluid to the pressure chamber of the brake device to release the brake can be located in the fixed part of the hydrostatic radial piston unit as well as in the mechanical part of the parking brake except for the rotating brake disc, which is fixed to the rotating part. The brake pin provides a functional connection between the brake disc in the overlap area / near the rotating part and the pressure chamber in the fixed part. Therefore, it is not necessary to provide hydraulic fluid with brake release pressure to the rotating part from the fixed part. As a result, fewer sealed joints are required and the complexity of assembly and machining of the hydrostatic radial piston unit according to the invention is reduced. Furthermore, the amount of potential leak points is reduced.

[0025] The stationary cylinder block at the front end portion of the radial piston unit comprises a number of cylinder bores extending radially inward from the circumferential surface of the cylinder block. A number of working pistons may be arranged to be radially movable within the cylinder bores, with each cylinder bore housing one working piston. Each working piston seals a pressure chamber within the cylinder bore to which pressurized hydraulic fluid may be supplied via a hydraulic channel to generate a force on the head of the associated working piston that moves the working piston radially outward. Hydraulic fluid may likewise be evacuated from the cylinder bore via a hydraulic channel if the working piston is mechanically urged inward, for example by a cam.

[0026] The rotating casing includes an internal cam lobe surface. When pressurized fluid is supplied to the pressure chamber, the working piston is urged against the cam lobe surface. Because the cylinder block is fixed and supported to the stationary casing via a fixed shaft, radially outward movement of the working piston generates a force on the cam lobe surface that causes the rotating casing to rotate relative to the stationary casing.

[0027] In order to guide the pressurized fluid to the pressure chamber, according to the invention, a rotary distributor is provided, which comprises a hollow shaft section and a disk-shaped section, which are preferably formed integrally with each other, but may for example be attached fluid-tight to each other. The disk-shaped section is in torque-resistant connection with the rotating casing, i.e. rotates together with the rotating casing. In a preferred embodiment, the disk-shaped section of the distributor presents a radial height that matches the lobes of the cam lobe surface. The rotary distributor further comprises timing holes in the disk-shaped section for the supply of hydraulic fluid to and the discharge of hydraulic fluid from the cylinder bores of the cylinder block via hydraulic channels. Furthermore, the rotary distributor comprises a second internal groove, which together with a second groove on the outer surface of the non-rotating fixed shaft forms a second circular guide. The second groove on the outer surface of the non-rotating shaft is connected with the first circular guide by an internal channel of the shaft. The skilled person is familiar with the working principle of radial piston units, so further details of the functioning of radial piston units are not necessary here.

[0028] According to the invention, a pair of roller bearings support the rotating casing for rotation relative to the stationary casing. According to the invention, the roller bearings are arranged radially outside the rotating distributor, but near the front end portion of the stationary casing, and substantially in the same axial position as the hollow shaft portion of the distributor, respectively near the rear end portion of the rotating casing. In other words, the roller bearings are arranged adjacent to or near the sealing surfaces to allow relative movement between the rotating casing and the stationary casing and to avoid large tilting moments of both casings. This also facilitates the sealing of both casings.

[0029] The roller bearings according to the invention are arranged in pairs, and in one embodiment are preferably arranged next to or adjacent to each other. Arranged substantially axially in the same position with the hollow shaft part of the rotary distributor means that the bearing is arranged in an axial region adjacent to the cylinder block side facing the stationary casing and at least partially surrounds the rotary distributor, for example in its cylindrical part. In this region too, the stationary casing and the rotary casing overlap, or at least an extension or protrusion of one or both casings overlaps axially, and at the same time are arranged coaxially so that a rotating part, for example a rotating casing or a rotary distributor, can rotate relative to a fixed part, for example a stationary casing or a stationary shaft. The pair of bearings may have an axial length different from the distributor. Since the bearing is arranged radially outside (with respect to the longitudinal axis) of the hollow shaft part of the distributor and at least partially overlaps the distributor in the axial direction instead of being axially adjacent to it, the axial length of the hydrostatic radial piston unit is reduced. Those skilled in the art will appreciate that the use of roller bearings is only a preferred embodiment, however, the use of journal bearings to rotatably support the rotating casing relative to the stationary casing is also encompassed by the present invention.

[0030] According to one preferred embodiment of the invention, the stationary casing of the radial piston unit can be provided with a fixed extension, which extends axially beyond the sealing surface into the volume of the rotating casing and has a substantially cylindrical shape. The extension, for example, accommodates the inner shell of the bearing. The extension, for example, provides a fixed support for the pair of bearings radially outside the rotary distributor, as the pair of bearings are received in the space between the rotating casing and the rotary distributor. The extension is therefore arranged in the radial space between the two rotating parts, the rotary distributor and the rotating casing.

[0031] In one embodiment according to the invention, the extension may be integrally formed with the stationary casing. However, in another embodiment according to the invention, the extension is provided as an additional part and attached to the stationary casing. The extension may be attached to the stationary casing, for example, by screwing, welding, joining, pressing, heat shrinking, clamping, crimping or plastic deformation. The connection between the stationary casing and the additional extension must be a torque-resistant connection, so that the bearing support force can be statically transferred to the stationary casing via the extension. This separate part design increases the possibilities of designing and assembling the radial piston unit according to the invention. Preferably, the extension comprises a hollow cylindrical sleeve-like shape, the outer surface of which is adapted to accommodate a pair of bearings, preferably O-devices. To support the bearing axially, the extension may comprise on its outer surface fixing means for the bearing, for example a shoulder for supporting the bearing axially, a groove for receiving a retaining ring and / or a thread on which a shaft nut can be screwed.

[0032] According to the invention, the pair of roller bearings can be positioned not only at substantially the same axial position or near the distributor, but also at substantially the same axial position on the outer circumferential surface of the rotating casing as a flange, a sprocket or a similar torque transmission device. In a motor operation mode, a rotating part such as a wheel or a sprocket can be driven by the hydrostatic radial piston unit. In a pump operation mode, the rotating part can drive the hydrostatic radial piston unit. The torque transmission device serves as an interface to which the rotating part, or a track or a chain, can be fixed. Since the bearings are essentially arranged at the same axial position as the torque transmission device, no tilting moment is generated by the rotating casing with respect to the longitudinal axis, or at least it is reduced, with respect to the position of the pair of bearings. The bearings can therefore be designed smaller and with a smaller load factor. This leads to a reduction in the cost of the bearings and also to a reduction in the manufacturing cost of the hydrostatic radial piston unit. At the same time, the bearing device according to the invention reduces the axial length of the radial piston unit and thus the distance required between the torque transmission point and the fixing means of a fixed casing on which the radial piston unit can be mounted, for example on the frame of a vehicle.

[0033] In another embodiment according to the invention, the hydrostatic radial piston unit comprises a fixed (non-rotating) two-speed, three-speed or multi-speed control valve. For example, the control valve in the two-speed embodiment is switchable between a first position and a second position. In the first position, for example, all cylinder bores are used to generate torque on the rotating casing, i.e. the cylinder bores can be supplied with fluid under high pressure, e.g. working pressure. This means that the cylinder bores are supplied with hydraulic fluid under high pressure which moves the pistons arranged in the cylinder bores radially outward. When the pistons are moving radially inward to follow the shape of the cams on the cam lobe surfaces, the corresponding cylinder bores are connected to the outlet timing holes and the hydraulic fluid is discharged from the cylinder bores. In the second position, for example, only a part of the cylinder bores exhibits the same working behavior as in the first position, i.e. only a part of the cylinder bores can be supplied with hydraulic fluid under high pressure via the inlet timing holes. However, another part of the cylinder bores is supplied with hydraulic fluid at a lower pressure, e.g. charge pressure, independent of the movement of the working pistons. Here, for example, groups of cylinder bores can also be hydraulically short-circuited under low water pressure.

[0034] 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 the working volumes enclosed between the cylinder bores and their corresponding working cylinders. In the second position, only a part of the cylinder bores is supplied with high pressure fluid. Thus, only this part of the working pistons and their corresponding cylinder bores contribute to the working volume of the radial piston unit. The other working pistons are supplied with a pressure low enough to ensure the contact of the piston rollers with the cam lobe surfaces of the rotating casing. Since the corresponding pressure chambers are not supplied with hydraulic fluid under high pressure, they do not contribute to the actual working volume of the radial piston unit. If they are short-circuited, the hydraulic fluid volume required to move one piston outward is displaced by another piston moving inward.

[0035] In another preferred embodiment according to the invention, the cam lobe surface is integrally formed with the rotating casing. If the casing is assembled from multiple parts, the necessary connections and seals require additional radial and axial space. By integrally forming the rotating casing together with the cam lobe surface, the complexity of the assembly process is reduced. Furthermore, this integral concept allows the diameter, i.e. the radial dimension, of the hydrostatic radial piston unit to be reduced, since connections between the parts can be eliminated. This also reduces the manufacturing and assembly costs, since precisely machined connection surfaces and additional assembly steps are avoided.

[0036] The synchronizing pin can be accommodated in an axially oriented hole of the rotating casing, preferably in the extension of the lobe, and engages with a corresponding hole in one of the radial heights of the disk-shaped part of the distributor. Thereby, the synchronizing pin can simultaneously interact with the rotating casing and the rotating distributor. Thereby, the synchronizing pin ensures that the distributor, or rather the disk-shaped part of the rotating distributor, is correctly oriented when the distributor is installed in the rotating casing. Furthermore, the synchronizing pin synchronizes the rotation of the distributor with that of the rotating casing, i.e. prevents any relative movement between these two parts.

[0037] According to the invention, the radial piston unit may further comprise distributor springs which press the rotary distributor with its disk-shaped portion towards the cylinder block. According to the invention, these distributor springs are preferably received in the axially extending bore of the rotary casing in the axial extension direction of the lobes. Preferably, the disk-shaped portion of the rotary distributor presents a complementary contour to the cam lobe surface. The distributor springs bias the rotary distributor towards the cylinder block. The front face of the disk-shaped portion of the rotary distributor and the adjacent front face of the cylinder block thereby form a hydrostatic bearing between the disk-shaped portion of the rotary distributor and the fixed cylinder block.

[0038] The hydrostatic bearing is arranged in front of the disk-shaped part of the rotary distributor and is supplied with pressurized fluid by timing holes that allow the hydraulic fluid to be fed to and discharged from the cylinder bores of the cylinder block. The arrangement of the distributor spring in the rotary casing with torque-resistant connection with the distributor ensures that there is no relative movement in the circumferential direction between the distributor spring and the distributor. If there was a relative movement between the two components, the spring would likely tend to wear intensively and / or buckle. Furthermore, the axial accommodation of the distributor spring in the extension / extension of the lobes of the cam lobe surface reduces the loads and stresses on the synchronizing pin resulting from the frictional resistance between the rotary distributor and the fixed shaft.

[0039] When the spring is housed within the axial thickness of the distributor, another benefit is realized: the axially oriented bore of the front housing for housing the spring can be moved toward the distributor, thereby reducing the axial length of the front housing, which further reduces the axial length of the hydrostatic radial piston motor.

[0040] The first cylinder block may include more than one row of cylinder bores having radially reciprocating working pistons, each row of cylinder bores spaced axially from an adjacent row, the cylinder bores and corresponding working pistons may be circumferentially adjacent, i.e., in the same rotational direction, or may be staggered, and may interact with a first cam lobe surface.

[0041] According to the invention, the hydrostatic radial piston unit may further comprise a second cylinder block, the working pistons of which interact with the same cam lobe surface or with another cam lobe surface arranged parallel to the first cylinder block. The second cylinder block is arranged axially parallel to the first cylinder block on a non-rotating shaft. By providing a cylinder block or a second cylinder block with more than one row of cylinder bores, the potential working volume is significantly increased, while the diameter of the hydrostatic radial piston unit remains the same.

[0042] In order to adapt the operation 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 row of cylinder bores or of the second cylinder block may be different from the number of cylinder bores and the number of radially reciprocating working pistons of the first cylinder block. In this case, a second peripheral cam lobe surface may be provided radially inside the rotating casing. The working pistons of the second cylinder block or of the second or further row of cylinder bores may interact with the second cam lobe surface. In one embodiment, the second peripheral cam lobe surface is integrally formed with the rotating casing.

[0043] In a further embodiment according to the invention, a reinforced disk-shaped cover is attached to the front end of the rotating casing, which is also the front end of the hydrostatic radial piston unit. The cover closes the rotating casing and preferably seals it, for example by an O-ring, so that leakage of hydraulic fluid from inside the cavity formed by the rotating casing and the stationary casing is prevented. Furthermore, the front end and the reinforced cover are designed so that the reinforced cover can absorb radial forces acting on the rotating casing due to the cam lobe working principle.

[0044] In another embodiment, the reinforcing cover comprises a sleeve-like collar and the rotating casing comprises a complementary shoulder, or vice versa. The sleeve-like collar can be arranged in form-blocking connection with the complementary shoulder at least in the radial direction, whereby the rotating casing can be reinforced in the radial direction. Preferably, the thickness of the reinforcing cover is designed such that the reinforcing cover rotates with the rotating casing but has a small rotating mass, since it provides a high radial stiffness. The higher radial stiffness of the reinforced rotating casing reduces possible slippage between the cam lobe surface and the working piston interacting with the cam lobe surface. The reinforcing cover thus ensures a better contact between the cam lobe surface and the working piston, thereby preventing increased wear of the components, since during operation of the radial piston unit it is favorable for the line contact of the piston roller to be pressed against the cam lobe surface.

[0045] In one preferred embodiment according to the invention, the hydrostatic radial piston unit operates as a hydraulic motor, which drives, for example, the track drive or the wheels of a working machine, for example a track loader, by means of a torque transmission device. Particularly in the field of track drives, it is important that the axial length of the radial piston unit is small in order to be able to select the design of the working machine as flexibly as possible.

[0046] In the following attached drawings, exemplary embodiments of a hydrostatic radial piston unit according to the invention as well as specific subassemblies of a hydrostatic radial piston unit according to the invention are illustrated, the embodiments shown not limiting the scope of the invention. [Brief description of the drawings]

[0047] [Figure 1] 1 shows a first cross-sectional view along the axis of rotation of a hydrostatic radial piston unit according to the invention; [Diagram 2] 2 shows a second cross-sectional view along the axis of rotation of the hydrostatic radial piston unit according to the invention; [Diagram 3] 3 shows a third cross-sectional view perpendicular to the axis of rotation of the hydrostatic radial piston unit according to the invention; [Figure 4] FIG. 2 shows an isometric view of the rotating casing of a hydrostatic radial piston unit according to the present invention. [Diagram 5] FIG. 2 shows an isometric cross-sectional view of a rotating casing with a distributor mounted thereon of a hydrostatic radial piston unit according to the present invention. [Figure 6] 1 shows a partial cross-sectional view of the front end of a hydrostatic radial piston unit according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] For ease of explanation and visibility only, the same functional parts are designated with the same reference numerals in all the illustrated figures.

[0049] FIG. 1 discloses a hydrostatic radial piston unit 1 according to the invention. The hydrostatic radial piston unit 1 comprises a stationary non-rotating casing 20 with a through hole 26 defining a rotation axis 10. The non-rotating casing 20 accommodates a stationary shaft 12 arranged coaxially with the rotation axis 10 and is in a torque-resistant connection with the non-rotating casing 20. The rotating casing 40 is supported by a pair of roller bearings 90 so as to be rotatable about the rotation axis 10 relative to the stationary casing 20. Thereby, the rear end portion of the rotating casing 40 is sealed against the front end portion of the stationary casing 20 by a seal 37. The axial position of the seal 37 is defined by a sealing surface 35 perpendicular to the rotation axis 10. Viewed from the outside, the sealing surface 35 divides the housing 3 of the radial piston unit 1 into a rotating casing part 40 on one side of the sealing surface 35 and a stationary casing part 20 on the other side of the sealing surface 35.

[0050] A pair of roller bearings 90 is arranged on the extension 25 of the stationary casing 20, the extension 25 according to the embodiment shown in FIG. 1 being provided as an additional extension part. The extension 25 protrudes across the sealing face 35 into the cavity formed by the rotating casing 40. In the embodiment shown in FIG. 1, the roller bearings 90 are arranged as a pair, i.e. substantially directly next to each other in the direction of the axis of rotation, in an O-arrangement. The O-arrangement of the bearings is preferred if the bearing support spacing is increased, for example when components are guided with small tilting clearances or when large tilting forces have to be supported. In other cases, an X-arrangement or a locating / non-locating bearing arrangement may be selected.

[0051] According to the invention, a pair of bearings 90 are arranged in the axial overlap region 30 where the stationary non-rotating casing part 20 and the rotating casing 40 overlap. In other words, in the overlap region 30, the stationary casing 20 is arranged coaxially with the rotating casing 40 and vice versa. However, both the stationary casing 20 and the rotating casing 40 are radially spaced apart from each other. This means that in the case of the example shown, the rotating casing 40 surrounds the stationary casing 20 or vice versa.

[0052] The rotating casing 40 comprises a torque transmission device 44, i.e. a flange at its outer circumferential surface 48. Depending on the application, components that can be driven by or drive the hydrostatic radial piston unit 1 can be mounted on the flange 44. The torque transmission device 44 is preferably arranged in the same axial position as the pair of bearings 90 in order to reduce the axial lever between the bearing 90 and the torque transmission device 44 and thereby eliminate the tilting moment that would otherwise occur.

[0053] The rotating casing 40 is provided with an inwardly facing cam lobe surface 80 against which the working piston 60 can press (see also FIG. 3). In the embodiment shown, the cam lobe surface 80 is formed integrally with the rotating casing 40, for example by 3D milling, casting, turning, forging or different manufacturing methods. The working piston 60 is accommodated in a cylinder bore 55 of the cylinder block 50. The cylinder block 50 is designed to be stationary with respect to the fixed shaft 12 and the fixed casing 20. Thus, biasing / pressing the working piston 60 against the cam lobe surface 80 generates a force on the cam lobe surface 80 supported by the fixed cylinder block 50. Due to the shape of the cam lobes, this force causes the rotating casing 40 to rotate.

[0054] Pressurized fluid is supplied to the cylinder bores 55 of the cylinder block 50 in order to bias the working pistons 60 against the cam lobe surfaces 80. In the opposite case, when the working pistons 60 are driven radially inwards to follow the shape of the cam lobe surface, i.e. the cam, hydraulic fluid is exhausted from the corresponding cylinder bores 55. The cylinder bores 55 must therefore be alternately connected to the inlets of the hydrostatic radial piston units 1 and to the outlets of the hydrostatic radial piston units 1. This is achieved by means of a rotary distributor 70.

[0055] The rotary distributor 70, having a T-shaped cross section due to the disk-shaped portion 71 and the hollow shaft portion 74, is partially arranged in the axial overlap region 30. As a result, the pair of bearings 90 can be arranged axially at the same position as the hollow shaft portion 74 of the rotary distributor 70, but radially outside the hollow shaft portion 74 of the rotary distributor 70 in a region exhibiting a smaller diameter. However, in some designs, the pair of bearings 90 may also be arranged radially inside the hollow shaft portion 74 of the rotary distributor 70.

[0056] Preferably, the rotating casing 40 and the stationary casing 20 seal the internal cavity. For this purpose, end covers 45, 130 are provided at the rear end side 24 and at the front end 42 of the radial piston unit 1 in order to facilitate the manufacturing and mounting performance of the components of the radial piston unit 1 according to the invention. In addition to its function for closing the casing cavity, the front cover 45 is designed to radially reinforce the rotating casing 40 and therewith the cam lobe surface 80. The front cover 45 comprises a substantially flat disk-shaped base from which a hollow cylindrical collar 46 extends. A step 47, complementary to the collar 46, is provided on the outer peripheral surface 48 of the rotating casing 40. After the front cover 45 is mounted on the rotating casing 40, the collar 46 provides support for the radial step 47. This additional support ensures that the cam lobe surface 80 maintains its shape even if the working piston 55 is pressed against it. The thickness of the collar 46 and base plate can be selected depending on the increased stability required.

[0057] Furthermore, the front cover 45 may be provided with a lightweight construction, for example by reinforcing ribs in the areas where the stress is mainly applied and notches / recesses in the areas where the stress is less applied. A person skilled in the art will understand that the functional principle of the front cover 45 providing the collar 46 and the casing 40 providing the step may be reversed, so that the front cover 45 may be provided with a step 47 and the casing 40 may be provided with a collar 46. However, other stability increasing designs capable of absorbing the forces acting radially on the rotating casing 40 are also within the scope of the present invention, for example by providing a dowel joint between the substantially flat front cover 45 and the rotating front casing 40.

[0058] In addition to its function for closing the rear end side 24 of the cavity of the two-part casing of the radial piston unit 1, the end cover 130 is part of the parking brake mechanism 100, whose actuation mechanism is arranged in the stationary casing 20. The parking brake mechanism 100 comprises at least two brake discs 112, one of which is torque-resistantly attached to the rotating casing 40 and the other of which is non-rotatably attached to the stationary casing 20. The brake discs 112 are axially movable relative to the stationary casing 20 and the rotating casing 40. If the parking brake mechanism 100 comprises more than two brake discs 112, the discs 112 are connected to the stationary casing 20 and the rotating casing 40 in alternating order. A disc spring 118 supported by the end cover 130 provides a pretensioning force on the brake piston 116. As long as the brake piston 116 is not pressurized at its release face 117 , the spring force is transmitted via the brake piston 116 to at least one brake pin 114 arranged in an axially oriented bore 28 in the stationary casing 20 .

[0059] Preferably, more than one brake pin 114 is provided to provide a more balanced actuation of the brake disc. Each brake pin 114 is arranged in one of the circumferentially distributed axial bores 28. The at least one brake pin 114 exerts / transmits the pretensioning force of the disc spring 118 onto the brake disc 112, which is pressed against each other and supported, for example, by a shoulder or extension 25 of the stationary casing 20. Thereby, relative movement between the rotating casing 40 and the stationary casing 20 can be prevented, for example, when the work vehicle is stopped.

[0060] If a relative movement between the rotating casing 40 and the stationary casing 20 is permitted, hydraulic pressure is applied to a release face 117 of the brake piston 116 arranged opposite the disc spring 118. The hydraulic pressure generates a force on the release face 117 directed towards the rear side of the stationary casing 20, i.e. in the direction of the disc spring 118. As the generated force is directed against the pretensioning force of the disc spring 118, the brake pin 114 is released from the brake disc 112. Thus, a relative movement between the brake discs 112 and therefore between the stationary casing 20 and the rotating casing 40 is possible.

[0061] Preferably, the brake pin 114 has a particular geometric shape. The end of the brake pin 114 facing towards the brake piston 116 has a larger diameter than the end facing towards the brake disc 112. Furthermore, the brake pin 114 is sealed against the fixed casing 20 and the fixed shaft 12. A pressure chamber is thus formed between the end faces of the brake pin 114 and the casing 20 of the hydrostatic radial piston unit 1. If the brake piston 116 is biased towards the brake disc 112, it presses the brake pin 114 against the brake disc 112. If in the other case pressure is supplied to the sealed pressure chamber and a force is generated on the end face of the brake pin 114, due to the different diameters of the end faces, the pressure generates a force biasing the brake pin 114 towards the brake piston 116. After the brake pin 114 contacts the brake piston 116 , the brake pin 114 presses the brake piston 116 against the disc spring 118 , thereby relieving the axial force from the brake disc 112 .

[0062] However, it is also encompassed by the concept according to the invention that a specific design of the brake pin 114 ensures that the pin 114 is always in contact with the brake piston 116, regardless of whether the release face is pressurized or not. In this embodiment, the brake pin 114 is sealed against the stationary casing 20 at the end facing away from the brake piston 116. The rear end of the brake pin 114, which has a larger diameter, is received in the brake piston 116 and a seal is provided between the rear end of the brake pin 114 and the brake piston 116. In that case, hydraulic pressure can be present on the rear / end face of the brake pin 114 when the brake piston 116 moves due to the force generated by hydraulic pressure in the pressure chamber formed by the brake piston 116 together with the shaft 12, the front end of the brake pin 114 and the stationary casing 20. Due to the larger diameter of the end face facing towards the brake piston 116, a larger force is generated by the hydraulic pressure on the side facing away from the brake piston 116 and the brake pin 114 is held in contact with the brake piston 116.

[0063] 2 shows a cross-sectional view of the hydrostatic radial piston unit 1 according to FIG. 1 in different cross sections. In the view according to FIG. 2, some of the hydraulic guides of the hydrostatic radial piston unit 1 according to the invention are shown. In the center of the hydrostatic radial piston unit 1, a fixed non-rotating shaft 12 is provided which is provided with a first group of grooves 13 in the area towards the end side 24 of the hydrostatic radial piston unit 1 according to the invention. The fixed shaft 12 further comprises a second group of grooves 14 in the area towards the front end 42 of the hydrostatic radial piston unit 1. The first group of grooves 13 together with the annular grooves 22 provided in the fixed non-rotating casing form first circular guides 33. These first circular guides 33 are used to distribute the hydraulic fluid guided from the inlet of the hydrostatic radial piston unit 1 towards the outlet of the hydrostatic radial piston unit 1.

[0064] The second circular guide 43 is formed by the second groove 14 together with a second internal groove 73 of the hollow shaft portion 74 of the rotary distributor 70. The first circular guide 33 is fluidly connected to the second circular guide 43 by a channel (not visible in FIG. 2) arranged in the fixed shaft 12.

[0065] 1 and 2 reveal the internal structure of the rotary distributor 70. The rotary distributor 70 can selectively connect the second circular guide 43 with the appropriate cylinder bore 55 depending on whether high pressure is to be supplied to the particular cylinder bore 55 or whether hydraulic fluid is to be exhausted from the particular cylinder bore 55 via the timing holes.

[0066] In the illustrated embodiment of the invention, the extension 25 is provided as an additional part that is attached to the stationary casing 20. In addition to supporting the pair of bearings 90, the extension 25 provides a shoulder against which the brake disc 112 can press. Both functions require close manufacturing tolerances to ensure reliable bearing and braking of the hydrostatic radial piston unit 1. Realizing both of these functions with a relatively small additional part includes the advantage that only a relatively small additional part has to be machined, whereas if the stationary casing 20 had to provide a shoulder and / or a bearing surface, a larger part of the stationary casing 20 would not require such complex machining that would be performed in this respect.

[0067] The stationary non-rotating shaft 12 further comprises an axial bore 15, which in the example shown is arranged coaxially with the rotating shaft 10. A two-speed valve 120 is arranged in the axial bore 15. The two-speed valve 120 comprises two positions. In a first position, all cylinder bores 55 can be supplied with hydraulic fluid at high pressure. In a second position, only a part of the cylinder bores 55 can be supplied with hydraulic fluid at high pressure. The other cylinder bores 55 are supplied with a lower pressure, sufficient to make the rollers of the working pistons 60 follow the cam lobe surfaces. At the same time, the cylinder bores 55 supplied with the lower pressure can be hydraulically short-circuited. Thus, in the first position, all cylinder bores 55 comprise the working volume of the hydrostatic radial piston unit 1. In the second position, the short-circuited cylinder bores 55 do not contribute to the working volume of the hydrostatic radial piston unit 1, and when all working pistons 60 move outwards, another piston moves inwards in its associated cylinder bore 55.

[0068] In the embodiment shown, the two-speed valve 120 is hydraulically actuated. However, the two-speed valve 120 may also be mechanically or electromechanically actuated. In other embodiments, as one skilled in the art will appreciate, the two-speed valve 120 may be a multi-speed valve 120 that provides additional positions to vary the rotational speed and torque of the hydrostatic radial piston unit 1 over a larger range.

[0069] FIG. 3 shows a cross-section of a hydrostatic radial piston unit 1 according to the invention in a plane arranged perpendicular to the axis of rotation 10. The fixed shaft 12 shown in the center of FIG. 3 is in a torque-resistant connection with a cylinder block 50. The cylinder block 50 is therefore also stationary. The cylinder block 50 comprises radially arranged cylinder bores 55, which are distributed equidistantly on the circumference of the cylinder block 50. All the cylinder bores 55 receive a working piston 60 so that the working piston 60 can slide radially in the cylinder bore 55. At its radially outer end, the working piston 60 comprises a roller 65. The roller 65 is forced into contact with a cam lobe surface 80 formed on the radially inner side of the rotating casing 40 when pressure is supplied to the cylinder bore 55. The pressure generates a force on the working piston 60 which is directed radially outwards. When the rotating casing is forced to rotate, the roller 65 interacts with the cam lobe surface 80, or vice versa, depending on whether the roller 65 is moving from a lobe to a cam. If the roller 65 moves from a lobe to a cam, i.e. if the shape of the cam lobe surface is directed radially inwards, the roller 65 and the corresponding piston 60 are forced inwards by the shape of the cam lobe surface 80, and hydraulic fluid is expelled from the associated cylinder bore 55. In the opposite case, i.e. if the roller moves from a cam to a lobe, which means that the shape of the cam lobe surface 80 in this section is directed radially outwards, the roller and the corresponding piston 60 are forced outwards and follow the cam lobe surface by the pressure inside the cylinder bore 55.

[0070] FIG. 4 shows an isometric view of the rotating casing 40 used in one embodiment of the hydrostatic radial piston unit 1 according to the invention. In addition to the features already mentioned above, FIG. 4 shows axially oriented holes 75 arranged radially inside the cam lobe surface 80 in a plane perpendicular to the rotation axis 10. The axially oriented holes 75 receive a distributor spring 72 that can provide a pretensioning force on the adjacently arranged rotary distributor 70. The disk-shaped part 71 of the rotary distributor 70 and the rotating casing 40 can be rotatably coupled by a synchronizing pin 78 arranged in one of the axially extending holes 75 of the rotating casing 40 in combination with the axially oriented holes 75 and the accommodated distributor spring 72. As a result, the rotary distributor 70 and the distributor spring 72 rotate at the same rotational speed.

[0071] 1 or 2, the skilled person will notice from FIG. 4 that the axially oriented holes 75 can also move towards the distributor 70 and abut against the bottom surface of the associated lobe. Placing the distributor spring 72 in the hole 75 of the distributor 70 achieves the same function, pressing the disk-shaped portion 71 of the distributor 70 against the front surface of the cylinder block 50.

[0072] In figure 4, the synchronizing pin 78 is also shown, which is arranged on a larger diameter than usual in the art. This reduces the shear moment acting on the synchronizing pin 78. These shear forces are generated in the operation of the hydraulic motor by friction forces between the outer circumferential surface of the shaft 12 and the inner circumferential surface of the distributor 70, which seals between the surface of the shaft 12 and the circular distribution channel (see also figures 1 or 2). Here, the synchronizing pin 78 is received in an axial bore 75 of the front housing 40 and in a corresponding hole in the distributor 70.

[0073] FIG. 5 discloses a cross-sectional view of the rotating casing 40 in which the rotating distributor 70 is arranged. The outer surface of the disk-shaped portion 71 of the distributor 70 is formed complementarily to the cam lobe surface 80 in order to support the functionality of the synchronizing pin 78 housed in the rotating casing 40. The synchronizing pin 78 ensures that the rotational direction of the distributor 70 is correct when the distributor 70 is received in the rotating casing 40. Furthermore, the synchronizing pin 78 synchronizes the rotation of the distributor 70 with that of the rotating casing 40. Furthermore, it is shown (not shown in FIG. 5) how the distributor spring 72 abuts against the base of the axially oriented hole 75, thereby pushing the distributor 70 in the direction of the front end 42, i.e. towards the cylinder block 50. The rotating distributor 70 has a lightweight design, reducing the rotational inertia of the assembly. For this purpose, a gap is partially provided in the radially extending plate-like part 71 of the distributor 70. Further shown is a second internal groove 73 formed on the radially inner side of the distributor 70. The groove 73 has an annular shape and can guide the fluid to and from a timing hole 77 arranged on the front face of the distributor 70.

[0074] 6 shows how the stiffening front cover 45 is attached to the rotating casing 40 by threads that are distributed equidistantly along an imaginary arc. The above described combination of the collar of the front cover 45 and the step of the rotating casing 40 not only stiffens the cam lobe face 80, but also ensures that the cover 45 is accurately centered relative to the rotating casing 40. It will be understood that other techniques for attaching the cover to the rotating casing are within the knowledge of one skilled in the art.

[0075] From the above disclosure and the accompanying drawings, as well as the claims, it will be understood that the hydrostatic radial piston unit 1 according to the present invention offers many possibilities and advantages over the prior art. Moreover, it is obvious to those skilled in the art that further modifications and changes known in the art may be made to the radial piston unit 1 according to the present invention without departing from the spirit of the present invention. Accordingly, all these modifications and changes are within the scope of the claims and are encompassed therein. It should be further understood that the above-mentioned examples and embodiments are for illustrative purposes only, and various modifications, changes, or combinations of the embodiments may be suggested to those skilled in the art in light thereof and are within the spirit and scope of the present application. [Explanation of symbols]

[0076] 1 Hydrostatic radial piston unit 3. Housing 10 Rotation axis 12 Fixed non-rotating shaft 13 First Groove 14 The Second Groove 15 Axial Bore 20 Fixed non-rotating casing part 22 Annular groove 24 End side 25 Extension 26 Through hole 28 Axially oriented bores for brake pins 30 Axial overlap area 33 First circular guide 35 Sealing surface 37 Seal 40 Rotating Casing 42 Front end 43 Second circular guide 44 Torque transmission device 45 Reinforced front cover 46 Color 47 Step / Shoulder 48 Outer surface 49 Screw 50 Cylinder block 55 Cylinder bore 60 Working piston 65 Lola 70 RPM distributor 71 Disk-shaped part 72 Distributor spring 73 Second internal groove 74 Hollow shaft section 75 Axially Oriented Holes 77 Timing Hole 78 Synchronization pin 80 First cam lobe surface 90 Roller bearing pair 100 Parking brake mechanism 112 Brake disc 114 Brake pin 116 Brake piston 117 Release plane 118 Disc Spring 120 Two-speed valve / multiple-speed control valve 130 End cover

Claims

1. A hydrostatic radial piston unit (1) of cam lobe type construction, a non-rotating stationary casing (20) with a through hole (26) defining the axis of rotation (10) of said radial hydrostatic piston unit (1); a cylindrical rotating casing (40) rotatably mounted on the non-rotating stationary casing (20) in an axial overlap region (30) in which a front end portion of the non-rotating casing (20) and a rear end portion of the rotating casing (40) overlap such that the rotating casing (40) can rotate relative to the stationary casing (20) around the rotation axis (10); a parking brake mechanism (100) comprising at least two brake discs (112) arranged adjacent to each other in said overlapping region (30), one brake disc (112) being rotatably fixed to said non-rotating casing (20) and the other brake disc (112) being rotatably fixed to said rotating casing (40); an end cover (130) closing said non-rotating casing (20) at the rear end side (24) of said hydrostatic radial piston unit (1) facing away from said rotating casing (40); Equipped with the end cover (130) pretensioning a disc spring (118) against a disc-shaped brake piston (116), both of which are arranged in the rear end portion of the stationary casing (20), and generating an axially directed spring force which can be transmitted by the brake piston (116) to at least one brake pin (114) arranged in an axially directed bore (28) in the stationary casing (20) in order to press the brake discs (112) against each other, when the brake piston (116) on the opposite face of the disc spring (118) is not forced to move towards the end cover (130). Hydrostatic radial piston unit (1).

2. 2. The hydrostatic radial piston unit (1) according to claim 1, further comprising a fixed shaft (12) arranged coaxially with the rotating shaft (10) in an internal cavity formed by the fixed casing (20), the rotating casing (40), the end cover (130) and the front cover (45), and a cylinder block (50) non-rotatably accommodated in a front end portion of the rotating casing (40) is in torque-resistant connection with the fixed shaft (12).

3. 3. The hydrostatic radial piston unit (1) of claim 2, wherein forward and rearward ends of the at least one brake pin (114) seal a pressure chamber in the axially oriented bore (28) that can be pressurized, whereby the brake pin (114) is urged toward the end cover (130) causing the brake piston (116) to compress the disc spring (118), thereby relieving compression force from the brake disc (112).

4. 3. The hydrostatic radial piston unit (1) of claim 2, wherein the brake piston (116), the at least one brake pin (114), the non-rotating shaft (12), and the non-rotating casing (20) seal a pressure chamber that can be pressurized such that the brake piston (116) is urged toward the end cover (130) to compress the disc spring (118), thereby relieving compression force from the brake disc (112).

5. 5. The hydrostatic radial piston unit (1) according to claim 1, wherein the at least one brake pin (114) comprises, at an end facing the brake piston (116), a portion having a larger diameter.

6. 6. A hydrostatic radial piston unit (1) according to any one of claims 2 to 5, wherein the non-rotating casing (20) comprises an annular groove (22) on its inner surface which forms, together with a first groove (13) on the outer surface of the fixed shaft (12), a first circular guide (33).

7. A rotary distributor (70) having a disk-shaped portion (71) and a hollow shaft portion (74) by which said distributor (70) is disposed around a front end portion of said fixed shaft (12) and is rotatably received by said rotating casing (40) in a fixed relationship with said disk-shaped portion (71), said rotary distributor (70) distributing hydraulic fluid through timing holes (78) in said disk-shaped portion (71) to working pistons (60) of said cylinder block (50).

7. A hydrostatic radial piston unit (1) according to claim 2, further comprising a second internal groove (73) for guiding hydraulic fluid from the working piston (60) of the cylinder block (50) and for guiding hydraulic fluid therefrom, the second internal groove (73) being provided inside the hollow shaft portion (74) and forming, together with a second groove (14) on the outer surface of the fixed shaft (12), a second circular guide (43), which second circular guide (43) is connected to the first circular guide (33) by a fluid channel arranged in the fixed shaft (12).

8. 8. The hydrostatic radial piston unit (1) according to claim 1, further comprising a pair of roller bearings (90) for rotatably mounting the rotating casing (40) to the stationary casing (20), the pair of roller bearings (90) being arranged in the overlapping region (30) between the rotating casing (40) and the stationary casing (20) radially outward of the hollow shaft portion (74) of the rotary distributor (70).

9. 9. A hydrostatic radial piston unit (1) according to claim 8, wherein the overlap area (30) of the front end portion of the radial piston unit (1) is defined by an extension (25) of the stationary casing (20), which extends axially beyond a sealing surface (35) into the volume of the rotating casing (40) and extends radially between the hollow shaft portion (74) of the rotary distributor (70) and the rotating casing (40), the extension (25) being provided to accommodate inner shells of the pair of roller bearings (90).

10. 10. A hydrostatic radial piston unit (1) according to claim 9, wherein the extension (25) is provided as an add-on part and is attached to the stationary casing (20).

11. 11. The hydrostatic radial piston unit (1) according to any one of claims 1 to 10, comprising a fixed multi-speed control valve (120) switchable between a first position in which all cylinder bores (55) 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 some of the cylinder bores (55) can be supplied with fluid under high pressure and pairs of cylinder bores (55) are hydraulically short-circuited.

12. 12. The hydrostatic radial piston unit (1) according to claim 11, wherein the fixed multi-speed control valve (120) is arranged in an axial bore (15) of the fixed shaft (12), the axial bore (15) being preferably arranged coaxially with the axis of rotation (10).

13. 13. The hydrostatic radial piston unit (1) according to claim 11 or 12, wherein the multi-speed control valve (120) is a two-speed control valve (120) or a three-speed control valve (120).

14. A hydrostatic radial piston unit (1) according to any one of the preceding claims, wherein a cam lobe surface (80) capable of acting against the working piston (60) is formed integrally with the rotating casing (40).

15. 15. A hydrostatic radial piston unit (1) according to any one of claims 7 to 14, wherein the rotary distributor (70) is biased together with its disk-shaped area (71) against the outer surface of the cylinder block (50) by a distributor spring (72) and / or a distributor piston, both of which are housed in the rotary casing (40) or in the disk-shaped area (71) of the rotary distributor (70) and axially oriented.

16. 16. The hydrostatic radial piston unit (1) according to claim 15, wherein the distributor spring (72) and / or the distributor piston are received in an axially oriented hole (75) in the rotating casing, the hole being located in a recess in the cam lobe surface (80).

17. 17. A hydrostatic radial piston unit (1) according to any one of claims 1 to 16, wherein the first cylinder block (52) comprises more than one row of cylinder bores (55) arranged adjacently or staggered in the circumferential direction and capable of interacting with the cam lobe surfaces (80), the cylinder bores having radially reciprocating working pistons (62).

18. A hydrostatic radial piston unit (1) according to any one of claims 1 to 17, wherein a second cylinder block, the working piston (60) of which interacts with the first one, the cam lobe surface (80), is arranged parallel to the first cylinder block (50) on the fixed shaft (12).

19. The number of cylinder bores (55) and radially reciprocating working pistons (60) of the second cylinder block are different from the number of cylinder bores (55) and radially reciprocating working pistons (60) of the first cylinder block (50); 19. The hydrostatic radial piston unit (1) according to claim 18, wherein a second peripheral cam lobe surface (82) with which the working piston (60) of the second cylinder block can interact is disposed on the forward casing (40) radially inward therefrom.

20. 20. A hydrostatic radial piston unit (1) according to any one of claims 1 to 19, wherein a reinforcing front cover (45) is attached to a front end (42) of the rotating casing (40) facing away from the stationary casing (20) to close the rotating casing (40), the front end (42) of the rotating casing (40) and the reinforcing cover (45) being designed such that the reinforcing cover (45) is at least partially able to absorb forces acting on the rotating casing (40), in particular in the radial direction.

21. 20. A hydrostatic radial piston unit (1) according to claim 19, wherein the reinforcing cover (45) comprises a sleeve-like collar (46) and the rotating casing (40) comprises a complementary shoulder (48) or vice versa.

Images