GEROTOR-TYPE FLUID MOTOR

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority benefits under 35 U.S.C. § 119 from European Patent Application No. 24217407.6 filed Dec. 4, 2024, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to a port plate segment for a rotary fluid pressure device that comprises an inner recess for receiving a valve drive shaft that is orbiting and rotating within the port plate segment, and that further comprises a plurality of circumferentially arranged fluid throughput ports for selectively fluidly connecting a valve spool segment and a Gerotor-type fluid displacement segment of the rotary fluid pressure device.

The invention further relates to a rotary fluid pressure device that comprises at least a valve spool segment, at least a port plate segment and at least a Gerotor-type fluid displacement segment and a valve drive shaft.

BACKGROUND

In a wide variety of technical fields, pressurised fluids are used for various purposes. To have such pressurised fluid available, unpressurised fluid has to be pressurised using hydraulic pumps, or generally using fluid working machines (in particular machines that can be operated as a fluid pump and as a fluid motor interchangeably). Due to the widespread use of pressurised fluid, and hence of fluid pumps to pressurise such fluids, a wide variety of fluid pumps have been suggested in the prior art. Similarly, a wide variety of fluid motors have been proposed to convert energy stored in pressurised fluid back to mechanical energy. Generally speaking, depending on the technical requirements (and also on monetary considerations), a suitable fluid pump design is chosen out of the vast variety of available fluid pumps designs in the prior art. Just to name some considerations that influence the choice of the design of the fluid pump: available mechanical energy; the way how the mechanical energy is available (for example high torque and low rpm versus low torque and high rpm; and the like), required fluid pressure; required fluid flux and the like. The same applies mutatis mutandis to fluid motors.

One of those basic designs of fluid pumps is the so-called Gerotor-type design. Here, an axially offset, orbiting part is orbiting and rotating around within a surrounding housing, thus creating reciprocally varying volumes, typically alternating between essentially 0 to a certain maximum design volume. Hence, fluid can be pumped at high output pressure but usually comparatively limited fluid flow rate. The Gerotor-type pumping member typically rotates and orbits at a comparatively low speed with high torque. However, Gerotor-type pumps are usually designed to comprise a planetary type gear, so that the actuation of the Gerotor-type pump is done with low input torque and high input rpm, where the actuation is translated into high torque, low rpm of the Gerotor-type member by means of the planetary type gear. In particular, the Gerotor member is the planet, while the driving shaft is the sun.

A possible design of such a Gerotor-type fluid pump is disclosed in United States patent U.S. Pat. No. 11,377,953 B2. Admittedly, this design works well in practice. However, experience has shown that the assembly process of the plurality of parts of the Gerotor-type fluid pressure device that is disclosed in this United States patent at the manufacturing plant is problematic in that it is prone to assembly errors. In particular, experience has shown that the drive retainer ring that is used to axially hold the valve drive shaft in place, in particular in a way that it does not tend to push the spool valve member of the valve spool segment away from the neighbouring port plate segment is regularly missed during assembly. Such an absence of a drive retainer ring frequently results in a significant deterioration of pumping performance and pumping efficiency.

Missing to assemble the drive retainer ring is particularly problematic since the absence of the drive retainer ring is quite often not noticed during a testbed run at the manufacturing side. Then, the customer is plagued with machine problems and a costly refurbishment of the final machine he built, using the deficient Gerotor-type pump. This has not only problematic with respect to cost, but is also highly problematic with respect to strongly decaying customer trust and customer satisfaction.

Even in case the missing absence of a drive retainer ring is noticed in a testbed run, a quite cumbersome reassembly of the Gerotor-type pump is required at the assembling factory.

In light of these problems, even a somewhat moderate increase in part cost and/or in assembly costs can be tolerated if the problem can be avoided with a sufficient probability.

It is therefore no surprise that there is a desire for a design of Gerotor-type pumps that is less error-prone/more failsafe during assembly of the arrangement.

SUMMARY

It is therefore an object of the present invention to suggest a port plate segment for a rotary fluid pressure device that comprises an inner recess for receiving a valve drive shaft that is orbiting and rotating within the port plate segment, wherein the port plate further comprises a plurality of circumferentially arranged fluid throughput ports for selectively fluidly connecting a valve spool segment and a Gerotor-type fluid displacement segment of the rotary fluid pressure device in a way that is improved over such port plate segments as they are known in the state of the art.

It is another object of the present invention to suggest a rotary fluid pressure device that comprises at least a valve spool segment, at least a port plate segment and at least a Gerotor-type fluid displacement segment, and that further comprises a valve drive shaft that is designed and arranged to translate an orbiting and rotating movement of the Gerotor-type fluid displacement segment to a rotating movement of the valve spool segment in a way that it is improved over such rotary fluid pressure devices as they are known in the prior art.

A port plate segment for a rotary fluid pressure device according to claim 1 solves at least one of these objects.

Similarly, a rotary fluid pressure device according to claim 4 solves at least one of these objects.

It is suggested to design and arrange a port plate segment for a rotary fluid pressure device, comprising an inner recess for receiving a valve drive shaft that is orbiting and rotating within said port plate segment, the port plate further comprising a plurality of circumferentially arranged fluid throughput ports for selectively fluidly connecting a valve spool segment and a Gerotor-type fluid displacement segment of the rotary fluid pressure device, in a way that the inner recess comprises at least two axially aligned segments with different diameters.

In particular, due to the Gerotor-type design of the fluid displacement segment, the rotary fluid pressure device may also be referred to as a Gerotor-type fluid pressure device. Such a design is, as such, known in the prior art and described, for example in U.S. Pat. No. 11,377,953 B2. The disclosure thereof is hereby fully incorporated into the present application. The design of the inner recess with the at least two axially aligned segments is usually done in a way that the various parts (if present) are fixedly connected to each other, in particular in an undetachable way. This applies at least to the sections of the port plate segment neighbouring the inner recess. This way, it is not possible that during assembly of the port plate segment, and in particular the assembly of the various segments, to ultimately achieve a rotary fluid pressure device, the valve drive shaft support ring may be omitted, as it is the case in U.S. Pat. No. 11,377,953 B2. As already mentioned, this at first glance minuscule change has large implications, since a non-present valve drive shaft support ring is frequently not detected during a comparatively short testbed run. This, in turn, will lead to major efficiency losses and/or fluid pump performance losses for the customer of the rotary fluid pressure device, when the full machinery, the rotary fluid pressure device is used in, is operated in the field. As already described, this creates a major problem for the end customer, therefore severely deteriorating the trust of the buyer in the supplier of the rotary fluid pressure device.

It is to be noted that the presently proposed design is usually somewhat more problematic to manufacture and assemble. This is because usually less standard structural components may be used, and instead specialised tools and machines have to be used for manufacturing the port plate segment. In particular, the so far used valve drive shaft support ring is readily and cheaply available on the market, as it is a standard structural component for a plurality of use cases. However, the special design of the inner recess of the port plate with usually undetachable components around the inner recess is more complicated, requires additional manufacturing steps, and the like.

Furthermore, the handling of the parts during assembly of the resulting rotary fluid pressure device becomes more complicated, since heavier parts have to be handled relative to each other with high preciseness. This particular applies to fitting the valve drive shaft through the narrow section of the inner recess of the port plate segment. It is to be noted that the diameter difference of the smaller diameter section of the inner recess and the outer diameter of the respective end part of the valve drive shaft is typically quite small.

Nevertheless, the additional effort - and hence the additional cost that is involved with this—is usually more than compensated by the benefit according to the present proposal.

While different transient regimes are possible, it is suggested to preferably design and arrange the port plate segment in a way that the inner recess comprises a stepped change between the at least two axially aligned segments with different diameters. In other words, there are usually two (and possibly more) sections, wherein the diameter is essentially constant within the respective section. Preferably, there are exactly two axially aligned segments provided with a stepped change therebetween. It is to be noted that a stepped change in the strict mathematical sense is not possible to manufacture, and at least not feasible to manufacture. Nevertheless, despite this deviation from the strict mathematical shape, the notion of a stepped change will be used in the present context. This is obvious for a person skilled in the present technical field.

It is to be noted that the at least two axially aligned segments may show a more or less identical diameter within the respective section. However, even within one, both or even more segments, the diameter may change somewhat (for example a tapered shape of the respective segment).

In particular, it is suggested to design and arrange the port plate segment in a way that the housing of the port plate segment is designed arranged to be a single piece unit. This particularly applies to the sections of the port plate segment that are neighbouring the inner recess. This way, the resulting port plate segment, and ultimately the rotary fluid pressure device, may become particularly stable and may hence show a particularly high lifetime. Furthermore, the risk of misalignment of subparts when connecting them together may be mitigated. The single piece unit design may be realised by moulding techniques (possibly with some finishing work, like polishing or the like), by material removing techniques (for example by turning on a turning machine), or by standard fixation techniques of two subunits, as they are known in the prior art (for example welding).

Further, it is suggested to design and arrange a rotary fluid pressure device that comprises at least a valve spool segment, at least a port plate segment and at least a Gerotor-type fluid displacement segment, and that further comprises a valve drive shaft that is designed and arranged to translate an orbiting and rotating movement of the Gerotor-type fluid displacement segment to a rotating movement of the valve spool segment, in a way that the port plate segment is designed and arranged as a port plate segment according to the present disclosure. This way, the port plate segment, and hence the rotary fluid pressure device may show the intrinsic advantages and features of an arrangement according to the present disclosure in a particularly profound way. In particular, the rotary fluid pressure device may be a Gerotor-type fluid pressure device.

Yet further, it is suggested to design and arrange the rotary fluid pressure device in a way that it further comprises a main shaft support casing with an inner recess, and a main drive shaft that is arranged within the main shaft support casing, wherein the main drive shaft is designed and arranged to translate a rotating input action into a rotating and orbiting movement of the Gerotor-type fluid displacement segment. This way, a particularly advantageous rotary fluid pressure device may be realised. As an example, the rotary fluid pressure device may then be actuated by a standard actuating machine, for example by an electric motor, a combustion engine or the like. In particular, the port plate segment, and hence the rotary fluid pressure device may show the intrinsic advantages and features of an arrangement according to the present disclosure in a particularly profound way.

Also, it is suggested to design and arrange the rotary fluid pressure device in a way that the main drive shaft and the valve drive shaft are connected to each other in a torque-proof way, while allowing a pivoting movement between the main drive shaft and the valve drive shaft. This way, the particular driving requirements for a Gerotor-type fluid pressure device may be dealt with particularly well. In particular, the torque proof connection may be realised by some kind of cog wheels, where the gear rims may be crowned rims and/or may show some kind of a convex and/or concave shape in the axial direction.

Another possibility is to design and arrange the rotary fluid pressure device in a way that the valve drive shaft comprises two end sections that are connected by a middle section, wherein at least the end section facing toward the Gerotor-type fluid displacement section, preferably both end sections, comprise a diameter that is larger than that of the middle section. While the end sections of the valve drive shaft may show (essentially) the same diameter, it is preferred if the end sections show a different diameter. In particular the end section pointing towards the valve spool segment typically shows a larger diameter as compared to the end section pointing towards the Gerotor-type fluid displacement segment. This way, the valve drive shaft may be held in place, when seen in the axial direction, when the rotary fluid pressure device is operated in its assembled state. This way, an axial movement of the valve drive shaft that could lead to a gap between the port plate segment and the valve spool segment, which again would lead to a major decrease of efficiency and/or to decreased operational characteristics of the rotary fluid pressure device may be advantageously avoided.

In particular it is suggested to design and arrange the rotary fluid pressure device in a way that the (usually) smaller end section of the valve drive shaft that faces toward the Gerotor-type fluid displacement section has a diameter that is slightly smaller than the inner diameter of the smaller diameter of the inner recess of the port plate segment. This way, an unwanted axial displacement of the valve drive shaft with its consequent disadvantages may be suppressed to a particularly large extent.

Moreover, it is suggested to design and arrange the rotary fluid pressure device in a way that the neighbouring end face surfaces of the inner recess of the port plate segment and of the (usually) smaller end section of the valve drive shaft are designed and arranged in a way that they are essentially in a sliding contact when the rotary fluid pressure device is assembled. Again, this way the operational characteristics and efficiency of the resulting rotary fluid pressure device may be particularly high. It is to be noted that in a sliding contact the respective surfaces are in a hard material-hard material contact (solid state-solid state contact). In principle, this would give rise to a grinding contact with a substantial friction and the potential of material abrasion. However, when using a lubricant, the friction and wear can be severely limited, resulting in a sliding contact. It is to be noted that in fluid motors/fluid pumps, lubricating fluid cannot only be easily provided, but is even frequently present anyhow (and in particular in inner voids) due to leakage issues. Even further, quite often drainage channels or the like have to be provided to dispense with such leakage hydraulic fluid. Hence, lubrication is usually not a problem when it comes to hydraulic machinery.

It further, it is suggested to design and arrange the rotary fluid pressure device in a way that the larger diameter of the at least two axially aligned segments with different diameters of inner recess of the port plate segment is chosen to be essentially the same as the receiving recess of the valve spool segment for the corresponding end section of the valve drive shaft, or is chosen to be smaller than the receiving recess of the valve spool segment for the corresponding end section of the valve drive shaft. This way, an additional fixation of the valve drive shaft in the axial direction may be realised, when the rotary fluid pressure device is operated in its assembled state.

Yet further, it is suggested to design and arrange the rotary fluid pressure device in a way that the neighbouring end face surfaces of the inner recess of the port plate segment and of the (usually) larger end section of the valve drive shaft are designed and arranged in a way that they are essentially in a sliding contact when the rotary fluid pressure device is assembled. Again, this way the operational characteristics and efficiency of the resulting rotary fluid pressure device may be particularly high.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features, and objects of the invention will be apparent from the following detailed description of the invention in connection with the associated drawings, wherein the drawings show:

FIG. 1: a perspective view of an example low-speed, high torque Gerotor motor 100;

FIG. 2: a cross-sectional view of the Gerotor motor 100 of FIG. 1;

FIG. 3: a rearward exploded view of the Gerotor motor 100 of FIG. 1;

FIG. 4: a forward exploded view of the Gerotor motor 100 of FIG. 1;

FIG. 5: a cross-sectional view of the area, neighbouring the valve drive shaft, according to another embodiment of a Gerotor motor according to the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, an example low-speed, high torque Gerotor hydraulic motor 100 is provided in accordance with the principles of the present disclosure. In this document, the hydraulic motor 100 is also referred to as a rotary fluid pressure device. The hydraulic motor 100 may include a shaft support casing segment 102, a wear plate segment 104, a Gerotor-type displacement segment 106, a port plate segment 108, and/or a valve housing segment 110. The shaft support casing 102 includes a mounting flange 112 configured to mount the motor 100 to a predetermined location. The shaft support casing segment 102, the wear plate segment 104, the Gerotor-type displacement segment 106, the port plate segment 108, and the valve housing segment 110 may be secured together by a plurality of fasteners 114 configured to pass through fastening holes 115 (see FIG. 3).

Referring to FIG. 2, the hydraulic motor 100 includes an output shaft 116 that is positioned within the shaft support casing segment 102 and rotatably supported therein by one or more bearing elements 118 and 120. Disposed adjacent a rearward end of the bearing element 118 is the wear plate segment 104 configured to retain the output shaft 116 and the bearing elements 118 and 120 in place within the shaft support casing segment 102.

The wear plate segment 104 defines an axial end surface 122 configured to engage an adjacent end surface of the Gerotor-type displacement segment 106 (e.g., its ring member 126 and star member 128). In some examples, an annular sealing member (e.g., an O-ring) 124 is disposed between the engaging end surfaces of the wear plate segment 104 and the shaft support casing segment 102.

The Gerotor-type displacement segment 106 may be a rotary-type positive displacement device and include an internally-toothed ring member 126 and an externally-toothed star member 128. In some examples, the ring member 126 includes a plurality of rollers 130 serving as the internal teeth. The star member 128 is eccentrically disposed within the ring member 126 and may have one less tooth than the ring member 126. In some examples, the star member 128 orbits and rotates relative to the ring member 126, and this orbital and rotational movement defines a plurality of expanding and contracting fluid volume chambers 132. Although it is described that the ring member is fixed and the star member orbits and rotates, it should be clearly understood by those skilled in the art that either the ring member or the star member can have either the orbital or rotational movement, or both, in accordance with the principles of the present disclosure. Further, it is apparent that the present disclosure is not necessarily limited to a Gerotor as the fluid displacement mechanism. An example Gerotor-type displacement segment 104 is further described in United states patens U.S. Pat. Nos. 4,533,302 and 4,992,034, both of which are hereby incorporated by reference in their entireties.

Referring to FIGS. 3 and 4, the port plate 108 defines a plurality of fluid passages 136, each of which is disposed to be in continuous fluid communication with the adjacent volume chamber 132. In the depicted example, the port plate 108 includes seven fluid passages 136 as the ring member 126 has seven internal teeth and thus defines seven fluid volume chambers 132.

As depicted in FIG. 2, an annular sealing member (e.g., an O-ring) 133 is disposed between the opposing axial end surfaces of the wear plate segment 104 and the Gerotor-type displacement segment 106. Disposed also is another annular sealing member (e.g., an O-ring) 135 between the opposing axial end surfaces of the Gerotor-type displacement segment 106 and the port plate segment 108.

Turning again to FIG. 2, the valve housing segment 110 is configured to rotatably support a valve spool 140. The valve housing segment 110 includes a fluid inlet port 142 (see also FIG. 1) in communication with an annular chamber 144 which surrounds the valve spool 140. The valve housing segment 110 further includes a fluid outlet port 146 (see also FIG. 1) in fluid communication with a center chamber 148 disposed between the valve housing segment 110 and the valve spool 140. The valve housing segment 110 also includes a case drain port 150 (see FIG. 3) that is plugged to force the case drain fluid to flow to whichever port 142 or 146 is at return pressure. The valve spool 140 defines a plurality of first valve passages 152 and a plurality of second valve passages 154. The first and second valve passages 152 and 154 are alternately arranged around the valve spool 140. The first valve passages 152 are in continuous fluid communication with the annular chamber 144, and the second valve passages 154 are in continuous fluid communication with the center chamber 148. In the depicted example, there are six first valve passages 152 and six second valve passages 154, corresponding to the six external teeth of the star member 128. The valve spool 140 may also define one or more angled drain passages 156.

The valve spool 140 may be biased toward the port plate segment 108 to maintain the valve spool 140 in sealing engagement with an adjacent surface 164 of the port plate segment 108, thereby preventing cross port leakage between the fluid chambers 144 and 148. In some examples, a valve seating mechanism 160 is employed to bias the valve spool 140 toward the port plate segment 108. The valve seating mechanism 160 is seated within an annular groove 162 defined by the valve housing segment 110. The valve seating mechanism 160 can be in fluid communication with the drain passages 156. An example of the valve seating mechanism 160 is disclosed in U.S. Pat. Nos. 3,572,983 and 4,533,302, both of which are hereby incorporated by reference in their entireties.

Referring again to FIG. 2, the hydraulic motor 100 includes a main drive shaft 170 and a valve drive shaft 172. The output shaft 116 includes a set of internal, straight splines 174, which is configured to engage a set of forward splines 176 of the main drive shaft 170. The forward splines 176 of the main drive shaft 170 may be external, crowned splines formed on a forward end 175 of the main drive shaft 170. Formed at a rearward end 177 of the main drive shaft 170 is a set of rearward splines 178 of the main drive shaft 170. The rearward splines 178 may be external, crowned splines that are configured to engage a set of internal, straight splines 180 formed on an inner circumferential surface of the star member 128. In the depicted example, the ring member 126 includes seven internal teeth, and the star member 128 includes six external teeth. Thus, six orbits of the star member 128 result in one complete rotation thereof, and one complete rotation of the main drive shaft 170 and the output shaft 116.

Referring to FIGS. 2 and 3, the valve drive shaft 172 is at least partially received within the main drive shaft 170 and engaged with the main drive shaft 170 such that an interface between the main drive shaft 170 and the valve drive shaft 172 is generally aligned with the Gerotor-type displacement segment 106.

In some examples, the main drive shaft 170 includes a hollow 184 at the rearward end 177 and has a set of inner splines 186 formed on an inner circumferential surface of the hollow 184. The inner splines 186 of the main drive shaft 170 may be straight splines. The hollow 184 of the main drive shaft 170 is configured to receive at least a portion of a forward end 192 of the valve drive shaft 172, and the inner splines 186 of the main drive shaft 170 at the rearward end 177 engages a set of forward external splines 196 formed around the forward end 192 of the valve drive shaft 172. In some examples, the forward splines 196 of the valve drive shaft 172 may be crowned splines. The valve drive shaft 172 has a set of rearward external splines 198 at a rearward end 194 thereof, which are configured to engage a set of internal splines 200 formed about an inner periphery (a recess 201 of valve spool 140, comprising the internal splines 200) of the valve spool 140. In some examples, the rearward splines 198 of the valve drive shaft 172 may be external, crowned splines, and the internal splines 200 of the valve spool 140 may be straight splines.

As illustrated, the engagement between the inner splines 186 of the main drive shaft 170 and the external splines 196 of the valve drive shaft 172 is arranged between opposite planes P1 and P2, which are defined by axial end faces 206 and 208 (see also FIGS. 3 and 4) of the Gerotor displacement mechanism 106, respectively. For example, a first plane P1 is defined by the axial end face 206 of the gerotor displacement mechanism 106, and a second plane P2 is defined by the axial end face 208 of the Gerotor-type displacement segment 106. In some examples, the interface between the inner splines 186 of the main drive shaft 170 and the external splines 196 of the valve drive shaft 172 is generally aligned with the interface between the external splines 178 of the main drive shaft 170 and the internal spline 180 of the star member 128.

As such, the configuration of the external splines 196 of the valve drive shaft 172 nested in the hollow 184 of the main drive shaft 170 requires a shorter axial length of the internal splines 180 of the star member 128 of the Gerotor-type displacement segment 106, and thus maximizes the efficiency in use of the splines 180 of the star member 128. In certain cases, the lengths of the splines 186 of the main drive shaft 170 and the splines 196 of the valve drive shaft 172 can be maximized as a shorter axial length of the internal splines 180 of the star member 128 is required. Because the required spline length is reduced, the design of the present disclosure also provides a high eccentricity on a small displacement motor for improved starting torque efficiency. Further, this configuration also allows using the Gerotor-type displacement segment 106 with a smaller width along axis of rotation A. The design in accordance with the present disclosure also reduces the running angles for both the main drive shaft 170 and the valve drive shaft 172, thereby increasing the life of the hydraulic motor 100. The design can reduce the need for case flow (e.g., leakage slots) and, thus, increase volumetric efficiency.

Referring again to FIGS. 2 to 4, the hydraulic motor 100 includes an inner recess 224 that works as a drive retainer arrangement 220 for preventing lift-off of the spool valve 140 away from port plate 108. According to the present disclosure, this is realised in that the inner recess 224 comprises two different sections 221, 222 with different diameters, namely a first section 222 with a larger diameter (which could be addressed as the nominal diameter of inner recess 224) and a second section 221 with a smaller diameter. The changeover between the first section 222 and the second section 221 is presently realised as a steplike changeover. In the present disclosure, the lift-off can be defined as an axial separation of the spool valve 140 from the stationary port plate segment 108. The lift-off can occur when the main drive shaft 170 and/or the valve drive shaft 172 axially slide toward the spool valve 140 as the main drive shaft 170 and the valve drive shaft 172 rotate and orbit, cooperating with the Gerotor-type displacement segment 106 comprises a Gerotor displacement mechanism. The lift-off can cause substantial cross-port leakage and stalling of the motor 100.

As presently proposed, the drive retainer member 220 comprises two different sections 221, 222 with different diameters, wherein the two different sections 221, 222 are designed and arranged as an integral arrangement of undetachable parts 221, 222 on the inside (inner recess 224) of port plate segment 108. Preferably, the drive retainer arrangement 220 is designed as a single piece unit with the neighbouring housing part of the port plate segment 108. The second section 221 with the smaller diameter of drive retainer arrangement 220 is arranged adjacent an axial end surface of the star member 128 as the star member 128 rotates and orbits around the ring member 126 of the Gerotor-type displacement segment 106. In some examples, the second section 221 with the smaller diameter of drive retainer arrangement 220 is arranged and configured to contact the axial end surface of the star member 128 during the rotation and orbiting of the star member 128.

According to a possible embodiment, the second section 221 with the smaller diameter of drive retainer 220 may be configured to be provided as an initially separate sub-unit that will be connected to a standard port plate segment 108 (for example, so as to utilize existing castings and/or blanks for manufacturing the port plate segment 108, thereby limiting increase in cost and speeding up implementation of the presently suggested design), for example using positive substance locking connections like soldering or welding. In other examples, a port plate segment 108 may be used that is specifically designed and arrange to comprise the drive retainer arrangement 220 in place as a single piece unit.

As depicted, the drive retainer arrangement 220 includes an inner recess 224 with a nominal diameter (presently equivalent to the inner diameter of the first, larger sized section 222 of the drive retainer arrangement) that is configured for a stem 226 (see FIG. 3) of the valve drive shaft 172 to pass therethrough when the valve drive shaft 172 is installed in place. The nominal opening of the drive retainer arrangement 220 is configured to hold the forward end 192 of the valve drive shaft 192 within the hollow 186 of the main drive shaft 170 when the star member 128, the main drive shaft 170, and the valve drive shaft 172 together orbit about the ring member 126 of the Gerotor displacement mechanism/the Gerotor-type displacement segment 106. In some examples, the center of the nominal opening of the drive retainer arrangement 220 is aligned with the axis of rotation A.

In some examples, like it is done in the embodiment of a hydraulic motor 100 according to FIGS. 1 to 4, the nominal opening of the drive retainer arrangement 220 (i.e. inner diameter of first section 222) is designed as a hole having a diameter, where diameter is configured to be larger than the largest diameter of the valve drive shaft 172 at the forward end 192 such that the valve drive shaft 172 passes through the nominal opening of the first section 222 of the drive retainer arrangement 220 during installation.

The opening of first section 222 is also configured to be smaller than the largest, outmost trace defined by the valve drive shaft 172 (i.e., the external splines 196 thereof) at the forward end 192 as the valve drive shaft 172 rotates and orbits around the ring member 128 of the Gerotor-type displacement segment 106. The same applies mutatis mutandis for the second section 221 of the drive retainer arrangement 220, although the inner diameter of the second section 221 is smaller as compared to the inner diameter of the first section 222. Therefore, the process of introducing the valve drive shaft 172 through the second section 221 is more delicate, as compared to the first section 222. This configuration is to prevent the valve drive shaft 172 from disengaging off or sliding out from the hollow 186 of the main drive shaft 170 and thus from the Gerotor-type displacement segment 106. The largest, outmost orbital trace of the valve drive shaft 172 is defined by the external splines 196 of the valve drive shaft 172 at the forward end 192 when the valve drive shaft 172 is tilted and deviates from the axis of rotation A and orbits around the ring member 126 of the Gerotor-type displacement segment 106.

In the embodiment of a hydraulic motor 100 according to FIGS. 1 to 4, the diameter of the inner recess 201 of valve spool 140 is chosen to be of approximately the same size as the diameter of the first section 222 of drive retainer member 220. (The diameter of inner recess 201 of valve spool 140 may be defined by the protruding peaks of the internal splines 200, by the bottom recesses of the internal splines 200, or by a more or less averaged value.)

In FIG. 5, there is a modification in that the diameter of the first section 222 of drive retainer member 220 is chosen to be clearly smaller than the diameter of the inner recess 201 of valve spool 140. This may result in a sliding contact between (parts of) neighbouring surfaces of the rearward end 194 of the valve drive shaft 172 and adjacent surface 164 of the port plate segment 108 (vicinity around the hole of first section 222 of drive retainer member 220). This may result in an advantageous fixation of valve drive shaft 172 in an axial direction. It is to be understood that in inner voids of the Gerotor hydraulic motor 100 (like it is also the case with essentially all types of moving hydraulic machinery), hydraulic fluid due to fluid leakage is usually around in sufficient quantities, if not in abundance, even without special provisions. Hence, the (present) metal-to-metal contact will be lubricated to an extent that a low friction sliding contact will result (with appropriately low mechanical wear of the contacting surfaces).

In some examples, the opening diameters of both the first section 222 and second section 221 of inner recess 224 have a diameter smaller than the largest diameter of the main drive shaft 170 at the rearward end 177 so that the main drive shaft 170 is also prevented from being slid out from the Gerotor-type displacement segment 106 during rotating and orbiting movement. In other examples, the opening diameters of both the first section 222 and second section 221 of inner recess 224 have a diameter smaller than the largest trace defined by the main drive shaft 170 (i.e., the external splines 178 thereof) at the rearward end 177 as the main drive shaft 170 orbits around the ring member 128 of the Gerotor-type displacement segment 106.

As such, the drive retainer arrangement 220 is configured to prevent lift-off of the spool valve 140 from other valve components, such as the port plate segment 108. The lift-off would otherwise reduce volumetric efficiency and cause freewheeling.

In this document, the shaft support casing segment 102 and the wear plate segment 104 can be regarded as a unit and referred to as an output shaft housing. In some examples, the shaft support casing segment 102 and the wear plate segment 104 can be configured as an integral part. The output shaft housing (including the shaft support casing segment 102 and the wear plate segment 104) and the valve housing segment 110 can be considered as a unit and referred to herein as a housing assembly. Further, the valve spool 140 can be regarded as a valve mechanism. In some examples, the valve mechanism can further include the port plate segment 108.

It is noted that identical reference numerals are used throughout the present disclosure for parts that are sufficiently similar in design and/or in function to justify the use of identical reference numerals, although the respective parts may not be identical. This is done for brevity and to improve the understandability of the description.

It is also to be noted that a single one or a plurality of the features of one, several or all of the presently disclosed detailed embodiments may be used in combination with the generic description of the present disclosure (even across the present and the other aforementioned applications).

While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.