Patent Description:
A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacements, i.e. rotation. In radial piston hydraulic motors, the pistons are arranged radially inside a piston frame and they are reciprocating in radial direction. The outer end of each piston has a piston roller which are pushed against a cam ring with multiple lobes. By the pressure of hydraulic fluid, the pistons are pushed outwards against the lobes of the cam ring, which causes the piston frame to rotate.

In known solutions, the piston frame also forms the shaft of the motor, i.e. it is uniform part rotating inside the motor. Therefore, the piston frame extends through the motor from rear to front in axial direction and forms a cavity inside the motor for receiving a drive shaft to which the rotational movement is transferred.

The hydraulic fluid is distributed to the piston via distribution channels, which are provided in non-rotating part, e.g. a frame, of the motor. Typically, the distribution channels are located at the rear part of the motor. The distribution channels are connected to supply holes in the piston frame and the hydraulic fluid is provided under the pistons through said supply holes. The size, i.e. the diameter, of the supply holes determines the possible speed of the motor. The hydraulic fluid is provided in axial direction and, therefore, the pressure of the hydraulic fluid causes axial force, which strives to form a gap between the frame and the piston frame. To avoid this, a counter axial force must be created. In known motors, the counter force is created by providing bearings at both ends of the motor, i.e. front end and rear end, in the form of tapered roller bearings. The bearings are provided between the shaft part of the piston frame and the frame of the motor. The tapered roller bearings are tapered from the ends of the motor towards the center of the motor and, thus, they form mechanical stop, i.e. form the counter force for the axial force caused by the pressure of the hydraulic fluid. However, such arranged tapered roller bearing transfers the force to the shaft part of the piston frame and the shaft must have very rigid structure, i.e. the shaft needs a big wall thickness and/or greater diameter.

Radial piston hydraulic motors are used for example to drive industrial machinery. A drive shaft of a machinery is installed inside the piston frame of the radial piston hydraulic motor and the torque and the rotational movement from the motor may be transferred to the machinery.

See <CIT>, disclosing a device according to the state of the art.

The objective of the device is to alleviate the disadvantages mentioned above.

In particular, it is an objective of the present device to provide a more efficient radial piston hydraulic motor. This is achieved by providing a motor structure in which smaller bearings may be used and less forces are directed to the rotating shaft structure inside the motor. Therefore, the hydraulic fluid channels, which distribute the hydraulic fluid to the pistons, i.e. causes the motor rotate, have more space and less pressure and fluid speed reduction occurs, i.e. the motor is more efficient.

According to a first aspect, the present invention provides a radial piston hydraulic motor comprising a hollow rotating shaft inside the motor, which rotating shaft is arranged to rotate around its axial central axis A for providing torque from the radial piston hydraulic motor, wherein the rotating shaft comprises a piston frame with pistons, which are arranged to move radially, the piston frame comprises.

The rotating shaft comprises a half shaft having a second inner surface extending in axial direction around the axial central axis A, wherein piston frame and the half shaft are arranged adjacent to each other so that the first inner surface and the second inner surface form a surface, in axial direction, forming a cavity inside the rotating shaft for receiving a drive shaft.

In an embodiment, the radial piston hydraulic motor comprises a box frame with a cam ring connected thereto, which box frame comprises a distribution channel for hydraulic fluid, and a front end part and a rear end part so that the front end part is arranged at one side of the piston frame, in axial direction, and the rear end part is arranged on other side of the piston frame, in axial direction, and.

wherein the pistons are engageable against an inner surface of the cam ring by means of the pressure of the hydraulic fluid.

In an embodiment, the first inner surface comprises first projections extending inwards into the cavity.

In an embodiment, the second inner surface comprises second projections extending inwards into the cavity.

In an embodiment, the motor comprises a cover plate for covering the cavity at the rear end part side of the motor, wherein the cover plate is fastened to the rear end part with fastening means.

In an embodiment, the motor comprises bearings and a shimming is provided between the cover plate and the rear end part for pre-loading the bearings.

In an embodiment, the motor comprises a brake arranged at the rear end part of the motor so that the brake is engageable with the drive shaft when the drive shaft is introduced inside the cavity, and the cover plate is configured to cover the brake.

In an embodiment, the front end part is connected to the piston frame via a first bearing.

In an embodiment, the first bearing is tapered roller bearing, which is tapered towards the front end of the motor, arranged to support axial force from the piston frame towards the front end.

In an embodiment, the rear end part is connected to the half shaft via bushing.

In an embodiment, the rear end part (<NUM>) is connected to the half shaft via a second bearing.

In an embodiment, the second bearing is tapered roller bearing, which is tapered towards the rear end of the motor, arranged to support axial force from the piston frame towards the rear end.

The first tapered roller bearing and the second roller bearing are tapered towards the ends of the motor, front end and rear end respectfully, i.e. the bearings are in X-montage.

In an embodiment, the half shaft comprises circumferential flange extending outwards.

In an embodiment, the circumferential flange is arranged to extend outwards of the half shaft into a space between the second bearing and the rear end part.

In an embodiment, the distribution surface is made by lapping.

It is to be understood that the aspects and embodiments of the invention described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the invention.

In the description, the front end should be understood to be the end through which a drive shaft, for example from a machinery, is pushed inside the motor, and the back end is the other end of the motor.

<FIG> shows one example of currently used radial piston hydraulic motors. The motor <NUM> comprises a rotating shaft structure <NUM> having monolithic structure, i.e. a piston frame and shaft are uniform structure. The shaft structure <NUM> is rotatably connected to the frame <NUM>, i.e. the non-rotating part, of the motor at both ends via tapered roller bearings <NUM>. In <FIG>, the right end is the front end, through which the drive shaft is assembled inside the motor, and the left end is the rear end. The bearings are used as mechanical stops for the axial force from the non-rotating parts, which is caused by the pressure of the hydraulic fluid. To work as the mechanical stops, the bearings are tapered towards the center of the motor. With such bearing design, at least part of the axial forces is transferred from the frame to the shaft structure and, therefore, the wall thickness of the shaft structure must be big enough to support the forces. Further mechanical stop for the bearing is achieved by providing an end plate at the rear end of the motor. The end plate is fastened to the walls of the shaft structure by screws in axial direction. Thus, the wall thickness must be big enough to allow the screws to be fastened.

As the bearings must support significant forces from the frame, the size of the bearings <NUM> must be quite big. Therefore, the bearings <NUM>, especially at the rear end, needs a lot of space. The hydraulic fluid is provided to the pistons through distribution channels <NUM> inside the frame. As the bearing needs significant amount of space, the space for distribution channels <NUM> is limited.

<FIG> show a new design of radial piston hydraulic motor <NUM> having a hollow rotation shaft inside the motor <NUM>. The rotation shaft <NUM> is arranged to rotate around its axial central axis A for providing torque from the radial piston hydraulic motor <NUM> to, for example, a drive shaft of a machinery, which may be installed inside the rotating shaft <NUM>. In the new design, the monolithic rotating shaft <NUM> is replaced with a rotating shaft <NUM> with separate piston frame <NUM> and half shaft <NUM>. Pistons <NUM> are provided inside the piston frame <NUM> and the pistons <NUM> are arranged to move radially. Further, the piston frame <NUM> comprises a distribution surface <NUM>, which is a flat surface in parallel plane with the radial movement of the pistons <NUM>, and a first inner surface <NUM>, which is extending in axial direction around the axial central axis A. Further, the rotating shaft <NUM> comprises a half shaft <NUM> having a second inner surface <NUM>, which is extending in axial direction around the axial central axis A. The piston frame <NUM> and the half shaft <NUM> are arranged adjacent to each other so that the first inner surface <NUM> and the second inner surface <NUM> form a surface, in axial direction, forming a cavity <NUM> inside the rotating shaft <NUM> for receiving the drive shaft from an application to which the rotation force is transferred, i.e. the surface formed by the first inner surface <NUM> and the second inner surface <NUM> are engageable with the drive shaft. The piston frame <NUM> and the half shaft <NUM> may be adjacent to each other so that they are partly overlapping, i.e. the half shaft <NUM> is partly inside the piston frame <NUM> as seen in some figures.

The radial piston hydraulic motor <NUM> may comprise a box frame <NUM> with a cam ring <NUM> connected thereto. The box frame <NUM> comprises a distribution channels <NUM>, through which the hydraulic fluid is conducted to the pistons <NUM>. The box frame <NUM> comprises a front end part <NUM> and a rear end part <NUM> so that the front end part <NUM> is arranged at one side of the piston frame <NUM>, in axial direction, and the rear end part <NUM> is arranged on other side of the piston frame <NUM>, in axial direction.

The radial piston hydraulic motor <NUM> may comprise pressure channels <NUM> inside the piston frame <NUM> to provide hydraulic fluid to each piston <NUM>. Each pressure channel <NUM> comprises a hydraulic fluid inlet <NUM> at the distribution surface <NUM> and the pressure channels <NUM> are connectable with the distribution channel <NUM> via the hydraulic fluid inlet <NUM>. The pistons <NUM> are engageable against an inner surface of the cam ring <NUM> by means of the pressure of the hydraulic fluid, such as hydraulic oil. The inner surface of the cam ring <NUM> is a waveshaped structure so that when the piston is pressed against the cam ring <NUM>, the piston conforms the shape of the cam ring <NUM>, which causes the piston frame <NUM>, and the rotating shaft <NUM>, to rotate.

The first inner surface <NUM> of the piston frame <NUM> may comprise first projections <NUM> extending inwards into the cavity <NUM>. The first projections <NUM> are configured to be engaged with the drive shaft so that the rotation movement, and torque, is transferred from the rotating shaft <NUM> to the drive shaft.

The second inner surface <NUM> of the half shaft <NUM> may comprise second projections <NUM> extending inwards into the cavity <NUM>. Said second projections <NUM> are configured to be engaged with the drive shaft.

In an embodiment, both, the first inner surface <NUM> and the second inner surface <NUM>, comprise projections <NUM>, <NUM> which are engageable with the drive shaft.

The projections or part of the projections may be splines.

The connection between the half shaft and the inner surface may be cylindrical and with or without projections towards the cavity.

The radial piston hydraulic motor <NUM> may comprise a cover plate <NUM> for covering the cavity <NUM> at the rear end part <NUM> side of the motor <NUM>, wherein the cover plate <NUM> is fastened to the rear end part <NUM> with fastening means. The fastening means may be for example screws or bolts.

The rotation movement in relation to the static parts are achieved by providing bearings between the rotating parts and the static parts.

A shimming may be provided between the cover plate <NUM> and the rear end part <NUM> for pre-loading bearings.

The rear end part side of the motor may comprise a brake which is arranged between the cover plate and the rear end part so that it is engageable with the drive shaft when the drive shaft is installed inside the cavity. The brake may be for example an additional motor, encoder for direct speed and position measurement or any other braking device. With such arrangement, the brake may be mounted on the drive shaft directly without using the motor for transmitting the torque to the drive shaft.

The front end part <NUM> of the radial piston hydraulic motor <NUM> may be connected to the piston frame <NUM> via a first bearing <NUM>, which allows the rotating shaft <NUM> structure to rotate around its axial central axis. The first bearing <NUM> may be a tapered roller bearing, which is tapered towards the front end of the motor <NUM>, arranged to support axial force from the piston frame <NUM> towards the front end. The tapered roller bearing is a circumferential bearing arranged around the axial central axis of the rotating shaft <NUM>, and between the piston frame <NUM> and the front end part <NUM>. As the tapered roller bearing is tapered towards the front end of the motor <NUM>, the axial force from the piston frame <NUM> is transferred through the tapered roller bearing towards the front end part <NUM>.

The rear end part <NUM> may be connected to the half shaft <NUM> via bushing <NUM> (in <FIG>), which allows the half shaft <NUM> part, and the rotating shaft <NUM>, to rotate around its axial central axis. The bushing is a circumferential part around the axial central axis, and arranged between the half shaft <NUM> and the rear end part <NUM> allowing the half shaft to rotate in relation to the rear end part.

<FIG> shows has similar structure as in <FIG>, except, instead of the bushing, the rear end part <NUM> is connected to the half shaft <NUM> via a second bearing <NUM>, which allows the half shaft <NUM> to rotate around its axial central axis. Other parts of the motor <NUM> may be the same as in <FIG>, which are capable to be implemented to the motor <NUM> of <FIG>.

The second bearing <NUM> may tapered roller bearing, which is tapered towards the rear end of the motor <NUM>, and arranged to support axial force from the piston frame <NUM> towards the rear end of the motor <NUM>. The tapered roller bearing is a circumferential bearing arranged around the axial central axis of the rotating shaft <NUM>, especially around the half shaft <NUM>, and between the half shaft <NUM> and the front end part <NUM>. The second bearing <NUM> may be arranged to support at least part of the axial force from the rear end part <NUM> of the motor <NUM>, i.e. the second bearing <NUM> acts as a mechanical stop for the axial forces. The axial forces from the rotating shaft <NUM> and the rear end part <NUM> is transferred through the second bearing <NUM> into the cover plate <NUM>, which is arranged to engage with the second bearing <NUM> and to act as a mechanical stop for the axial force through the second bearing <NUM>. The cover plate <NUM> may also be arranged to act as a mechanical stop for the axial force from the non-rotating part, i.e. the rear end part <NUM> of the motor <NUM>.

As the axial force from the rear end part <NUM> is not transferred through the bearing to the rotating shaft <NUM>, as in known motors (e.g. in <FIG>), the bearing needs to support less forces. Thus, the bearing may be much smaller and there is more space for the distribution channels and distribution fluids. Thus, it is possible to have more efficient motor without increasing the size of the motor.

The half shaft <NUM> may comprise a circumferential flange <NUM> extending outwards. The circumferential flange <NUM> may be arranged to extend outwards of the half shaft <NUM> into a space between the second bearing <NUM> and the rear end part <NUM>, whereby the axial force from the half shaft <NUM> may be transferred to the second bearing <NUM> via the circumferential flange <NUM>.

Because the rotating shaft <NUM> is made of two separate parts, i.e. the piston frame <NUM> and the half shaft <NUM>, it allows more flexible and efficient manufacturing processes. For example, the distribution surface <NUM> may be made by lapping which results very smooth surface with reduced costs comparing for example to grinding.

By having the described structure, the motor may be more efficient without need to increase the size of the motor. The rotating shaft, i.e. the half shaft, does not need to be so rigid and smaller diameter and/or wall thickness is sufficient. Thus, the structure is more simpler and a drive shaft with greater diameter may be installed inside the cavity of the motor.

Claim 1:
A radial piston hydraulic motor (<NUM>) comprising a hollow rotating shaft (<NUM>) inside the motor, which rotating shaft (<NUM>) is arranged to rotate around its axial central axis A for providing torque from the radial piston hydraulic motor, wherein the rotating shaft (<NUM>) comprises a piston frame (<NUM>) with pistons (<NUM>), which are arranged to move radially, the piston frame (<NUM>) comprises
- a distribution surface (<NUM>), which is a flat surface in parallel plane with the radial movement of the pistons (<NUM>), and
- a first inner surface (<NUM>) extending in axial direction around the axial central axis A,
characterized in that
the rotating shaft (<NUM>) comprises a half shaft (<NUM>) having a second inner surface (<NUM>) extending in axial direction around the axial central axis A,
wherein piston frame (<NUM>) and the half shaft (<NUM>) are arranged adjacent to each other so that the first inner surface (<NUM>) and the second inner surface (<NUM>) form a surface, in axial direction, forming a cavity (<NUM>) inside the rotating shaft (<NUM>) for receiving a drive shaft.