Patent Description:
The electric machine is usually configured as an electric motor and is connected to a hydraulic unit configured as a pump. The electric machine comprises a stator and a rotor connected to the shaft or forming the shaft. However, it can also be provided that the hydraulic unit drives the electric machine as a generator.

In order to transmit the torques between the (first) shaft of the electric machine and the (second) shaft of the hydraulic unit, it is known to provide a so-called bell housing, which spaces the electric machine and the hydraulic unit apart from one another in a connecting manner and inside which a transmission shaft connects the first shaft and the second shaft to one another. The bell housing and the transmission shaft have the advantage that the electric machine and the hydraulic unit can be aligned with respect to one another to a certain extent during assembly so that the manufacturing tolerances in particular relative to the bearings of the first shaft of the electric machine and the bearings of the second shaft of the hydraulic unit can be compensated. A disadvantage however is that the length of the entire system (in the direction of the direction of extension of the shafts) is substantially increased by the bell housing and the transmission shaft. In addition, a large number of parts with corresponding assembly expenditure and costs is necessary to construct the complete system.

In order to construct a more compact system which requires fewer components, it is known to insert the first shaft of the electric machine and the second shaft of the hydraulic unit directly into one another thereby forming a positive and direct shaft-hub connection. Such a more compact system is known, for example, from <CIT>. It is proposed there that the shaft-hub connection is lubricated by means of the hydraulic fluid conveyed by the hydraulic unit. For this purpose a leakage oil channel running in the axial direction of the pump shaft is proposed, which extends over the entire length of the pump shaft. Hydraulic fluid which passes from a pressurized conveying chamber of the pump along a bearing of the pump head into a leakage oil chamber inside the hydraulic unit can thus enter into the end of the leakage oil channel which is disposed at the front-side end of the pump shaft inside the hydraulic unit. The leakage oil flowing through the central leakage oil channel, after exit from the leakage oil channel at the end assigned to the shaft-hub connection flows along the shaft-hub connection and lubricates the shaft-hub connection. In order to facilitate this leakage oil flow, a drain is proposed through which the leakage oil drains off after lubrication of the shaft-hub connection. A separate drain is therefore required which must be formed between the electric machine and the hydraulic unit or in the electric machine. An apparative adaptation of the electric machine or an adapter piece disposed between the electric machine and the hydraulic unit is therefore necessary.

Other examples of electric machine-hydraulic unit assemblies are disclosed in <CIT> and <CIT>.

It is therefore the object of the present invention to provide a system comprising an electric machine and a hydraulic unit as well as an electric machine and a hydraulic unit by means of which it is possible to further integrate the leakage oil drain in the hydraulic unit.

The object is achieved by a system, a hydraulic unit, an electric machine having the features of the respective independent claim. Advantageous further developments of the system, the hydraulic unit, the electric machine are specified in the dependent claims and in the description, wherein individual features of the advantageous further developments can be combined with one another in a technically meaningful manner. In particular, the features described with reference to the system can be applied to the hydraulic unit or the electric machine and vice versa.

The object is achieved in particular by a system according to claims <NUM> and <NUM>.

The object is also achieved by a hydraulic unit, wherein a shaft of the hydraulic unit has a central recess and at least one transverse channel, and the at least one transverse channel extends from the central recess to an external circumference of the shaft.

The object is also achieved by an electric machine, wherein a shaft of the electric machine has a central recess and at least one transverse channel, wherein the at least one transverse channel extends from the central recess to an external circumference of the shaft.

The invention will be discussed hereinafter with reference to the system. However, the embodiments described also explicitly relate to the independent hydraulic unit, the independent electric machine.

In an embodiment of the system the first shaft and the second shaft are inserted directly into one another to form the shaft-hub connection, in which case the first shaft or the second shaft comprises the central recess, wherein the at least one transverse channel extends from the central recess to an external circumference of the respective shaft. Preferably, the central recess and the at least one transverse channel are formed in the second shaft of the hydraulic unit.

The first shaft and the second shaft may be directly inserted into one another to form the shaft-hub connection so that no further components (such as bell housing and transmission/intermediate shaft) need to be provided in order to connect the shaft of the electric machine to the shaft of the hydraulic unit.

In an alternative embodiment the first shaft and the second shaft may be indirectly connected by an intermediate shaft. In this case, the shaft-hub connection comprises an intermediate shaft for connecting the first shaft and the second shaft, wherein the central recess and the at least one transverse channel may be formed in the intermediate shaft.

Preferably a plurality (at least two, preferably at least four, particularly preferably no more than eight) of transverse channels adjoin the central recess, which extend in particular rectilinearly in each case from the central recess to an external circumference of the shaft. The at least one transverse channel can extend outwards strictly in the radial direction and therefore at a right angle to a longitudinal axis of the shaft. However, it is also possible that the at least one transverse channel is aligned at a different angle to the longitudinal axis of the shaft. The transverse channel(s) can, for example, be formed by a bore.

The invention is based on the finding that fluid located in the at least one transverse channel (in particular leakage oil from a leakage oil chamber of the hydraulic unit) is subjected to a centrifugal force during operation of the system, whereby fluid can be conveyed from the central recess into a chamber surrounding the external circumference of the shaft, wherein fluid can be sucked in as a result of the negative pressure formed thereby in the recess, with the result that a specific conveying direction of the fluid is predefined.

In other words: the invention provides in its basic idea that the first shaft of the electric machine, the second shaft of the hydraulic unit or the intermediate shaft has transverse channels running outwards in particular in the radial direction for conveying the leakage oil along the shaft-hub connection. Thus, leakage oil can be specifically conveyed for lubrication of the contact points between the shafts and in particular can be circulated back into a leakage oil chamber of the hydraulic unit. Thus, no additional drain is required for leakage oil.

According to the invention, the hydraulic unit comprises a leakage oil chamber. The leakage oil chamber is in particular a chamber inside the hydraulic unit into which hydraulic oil enters during operation from the pressurized conveying chamber of the hydraulic unit. For example, hydraulic fluid enters along bearings of the components conveying the pressurized hydraulic fluid. In this case, the central recess can be disposed in the (second) shaft of the hydraulic unit or in the intermediate shaft, wherein the at least one transverse channel extends from the central recess to the leakage oil chamber. The recess is preferably formed in the (second) shaft of the hydraulic unit as an axial channel and extends from the at least one transverse channel through the second shaft to the direct shaft-hub connection. Alternatively, the central recess may be formed in the in the intermediate shaft as an axial channel and extends from the at least one transverse channel through the intermediate shaft to a front-side end of the intermediate shaft. The axial channel extending in the axial direction of the shaft therefore has an inlet at a front-side end facing the electric machine through which leakage oil (after lubricating the shaft-hub connection) can enter into the axial channel. Therefore, the axial channel does not extend completely through the second shaft or through the intermediate shaft. Accordingly, the axial channel is to be considered a blind hole extending from the front-side end through the shaft to the at least one transverse channel.

In an alternative embodiment, it can be provided that the (first) shaft of the electric machine has the recess and the adjoining at least one transverse channel. In this case, the recess is arranged in particular directly adjoining a receptacle for the (second) shaft of the hydraulic unit or for the intermediate shaft. In this embodiment, leakage oil which has already flowed along the contact points of the shaft-hub connection is conveyed through the (first) shaft of the electric machine into the chamber surrounding the shaft.

Preferably in this embodiment, it is possible that a separate drain is provided for the leakage oil conveyed through the at least one transverse channel of the first shaft of the electric machine.

In one embodiment it is preferably provided that the shaft-hub connection is connected fluidically outside the second shaft via at least one passage to a leakage oil chamber inside of the hydraulic unit. A first passage or a first group of such passages is provided so that leakage oil flows out from the leakage oil chamber inside the hydraulic unit to the shaft-hub connection.

Such a first passage can be implemented, for example, by mounting the (second) shaft of the hydraulic unit without a shaft seal in a housing of the hydraulic unit in a direction towards the shaft-hub connection. In this case, therefore, leakage oil flows from the leakage oil chamber along the surface of the (second) shaft through the housing of the hydraulic unit in the direction of the shaft-hub connection. In the case of the first embodiments described above, according to which the central recess and the at least one transverse channel are formed in the (second) shaft of the hydraulic unit or in the intermediate shaft, the fluid that has come from the leakage oil chamber enters into the axial channel in the second shaft (or in the intermediate shaft) after it has flowed along contact points of the shaft-hub connection. In the second embodiment described above, according to which the central recess and the at least one transverse channel are formed in the (first) shaft of the electric machine, the fluid that has come from the leakage oil chamber along the second shaft is conveyed into a chamber surrounding the first shaft.

A passage for the fluidic connection of the leakage oil chamber inside the hydraulic unit and the shaft-hub connection can additionally or alternatively be formed by at least one, preferably a plurality of opening(s) (which is/are formed in particular as a recess and preferably as a hole), which is/are disposed adjacent to the second shaft in a housing or a housing component (for example, in a cover cap or a bearing) of the hydraulic unit. In the case of the first embodiments described above, the leakage oil can flow out from the leakage oil chamber through the at least one opening in the housing to the shaft-hub connection and then into the axial channel in the second shaft or in the intermediate shaft. In the case of the second embodiment described above, the leakage oil conveyed through the at least one transverse channel can flow back through the opening into the leakage oil chamber. In this connection it is preferable if a front end face of the first shaft is sealed with respect to the hydraulic unit so that leakage oil can flow from the leakage oil chamber inside the hydraulic unit along the outside of the shaft and along the shaft-hub connection to the recess in the (first) shaft of the electric machine and from there can be conveyed back through the at least one transverse channel to the openings in the housing, which are radially outwardly offset in relation to the sealed end face of the shaft, into the leakage oil chamber.

Preferably the at least one opening can be closed and preferably has an internal thread for this purpose. Thus, in a delivery state the opening can be closed by, for example, a screw. In this case, the opening can be closed until shortly before attachment of the hydraulic unit to the electric machine.

In an example, the shaft-hub connection has a splined connection, wherein the spline connection comprises at least one pin having an external toothed structure and at least one receptacle having an internal toothed structure.

The pin preferably having the external toothed structure can be formed on the first shaft of the electric machine in which case the receptacle having the internal toothed structure is preferably disposed on a front-side end of the second shaft of the hydraulic unit. Alternatively, the pin preferably having the external toothed structure can be formed on the (second) shaft of the hydraulic unit, in which case the receptacle preferably having the internal toothed structure is disposed on a front-side end of the (first) shaft of the electric machine.

In an example, the first shaft of the electrical machine and the second shaft of the hydraulic unit may each comprise a receptacle on its front-side ends preferably having the internal toothed structure, wherein the intermediate shaft forms two pins each having an external toothed structure for insertion into the receptacles, in case the first shaft is connected to the second shaft via the intermediate shaft.

In order to fix the electric machine on the hydraulic unit, a housing of the electric machine and a housing of the hydraulic unit can be connected to one another in a suitable manner (for example, by corresponding screw connections) for example, by forming at least one flange or a cover cap.

The first shaft is in particular mounted by means of two bearings in the electric machine. The second shaft is in particular mounted by means of two bearings in the hydraulic element. In particular, if the pin with the external toothed structure is formed on the second shaft of the hydraulic unit, the pin projects beyond one of the bearings and beyond the housing of the hydraulic unit in the direction of the electric machine.

When specifically implementing the system, it has been found that the internal toothed structure and the external toothed structure of the spline connection are severely worn. The background of this severe wear could be that as a result of the forces acting on the shaft inside the hydraulic unit during operation, it can occur that the pin projecting beyond the bearing is deflected from its neutral position and thus does not maintain its position/alignment in the rest state in the receptacle of the electric machine. Another reason for the severe wear could be that as a result of tolerances of the electric machine or of the hydraulic unit, when connecting the electric machine to the hydraulic unit the pin in the receptacle does not occupy the desired position/alignment.

It has been shown that in order to reduce the wear of the spline connection inter alia, a certain ratio range of pitch circle diameter to external toothed structure length of the external toothed structure on the pin is advantageous.

Thus, the external toothed structure of the pin, which can be formed either on the first shaft of the electric machine, on the second shaft of the hydraulic unit or on the intermediate shaft, has an external toothed structure length and a pitch circle diameter. The external toothed structure length is the length of the teeth in the direction of extension of the shaft. It is now preferred that the ratio of pitch circle diameter to external toothed structure length is less than <NUM>, particularly preferably less than <NUM> and quite particularly preferably less than <NUM>. On the other hand, the ratio of pitch circle diameter to external toothed structure length should be at least <NUM>, preferably at least <NUM> and particularly preferably at least <NUM>. In a particularly preferred embodiment, the ratio of pitch circle diameter to external toothed structure length is between <NUM> and <NUM> and is particularly preferably equal to <NUM>. An independent invention is also seen in this ratio of pitch circle diameter to external toothed structure length which can be claimed independently of the above-described solution for a system comprising electric machine and hydraulic unit.

The hydraulic unit is preferably embodied as a swash plate unit which can be operated as pump or motor. In a swash plate unit the deflection of the pin of the shaft projecting beyond the housing during operation is particularly great as a result of the forces acting on the shaft inside the swash plate pump. The pin of the shaft of the swash plate pump projecting beyond the housing of the swash plate pump is therefore inserted immediately and directly into a corresponding receptacle of the electric machine. Alternatively, the hydraulic unit that can be operated as pump or motor can be executed as an angled piston unit, a gear unit, a rotary vane unit or a screw spindle unit.

The spline connection is preferably a spline in which the tapered teeth of the external toothed structure engage in the internal toothed structure. Such a spline is defined, for example, in ANSI B92. <NUM> from <NUM>.

The invention and the technical background are explained hereinafter by reference to the figures as an example. In the figures schematically.

The hydraulic unit <NUM> shown in <FIG> and configured as a swash plate pump comprises a housing <NUM> which has a cover cap <NUM>. Mounted in the housing <NUM> is a shaft <NUM> which projects with a pin <NUM> beyond the cover cap <NUM>. The pin <NUM> has an external toothed structure <NUM> with an external toothed structure length <NUM> and a pitch circle diameter <NUM>. The shaft <NUM> with the pin <NUM> is also shown as a single component in <FIG>.

<FIG> shows an electric machine <NUM> with its connecting region to the hydraulic element <NUM>. A shaft <NUM> of the electric machine <NUM> has a receptacle <NUM> with an internal toothed structure <NUM>.

The pin <NUM> of the shaft <NUM> of the hydraulic unit <NUM> is inserted in the receptacle <NUM> of the electric machine <NUM> to form a system. The shaft <NUM> of the electric machine <NUM> is thus connected directly to the shaft <NUM> of the electric hydraulic unit <NUM> forming a positive locking shaft-hub connection. Thus, no additional components are required to connect the shafts <NUM>, <NUM> of the electric machine <NUM> and of the hydraulic unit <NUM> to one another.

In order that a tolerance deviation of the bearings of the shafts <NUM> and <NUM> can be compensated, the ratio of the pitch circle diameter <NUM> to external toothed structure length <NUM> is between <NUM> and <NUM> and preferably between <NUM> and <NUM>. For the same reason the internal toothed structure <NUM> has a tolerance in class <NUM>.

<FIG> and <FIG> each show a region of a system consisting of an electric machine <NUM> and a hydraulic unit <NUM>. Thus, the end of the hydraulic unit <NUM> facing the electric machine <NUM> and that of the hydraulic unit <NUM> facing the electric machine <NUM> are shown. In all the exemplary embodiments, it can be seen that the hydraulic unit <NUM> has a housing <NUM> which can comprise a cover cap <NUM> as a component. A leakage oil chamber <NUM> is formed inside the housing <NUM> into which hydraulic fluid can flow from the conveying chamber of the hydraulic unit along corresponding bearings (not shown) of the pump head. In addition, a leakage oil outlet <NUM> can be provided from which the leakage oil can emerge from the leakage oil chamber <NUM>.

In addition, the receptacle <NUM> already described above can be seen at one end of the first shaft <NUM> in which the pin <NUM> of the second shaft <NUM> of the hydraulic unit <NUM> is inserted.

In the exemplary embodiment of <FIG>, a central recess <NUM> configured as an axial channel is formed in the second shaft <NUM> of the hydraulic unit <NUM>. This recess <NUM> configured as an axial channel is adjoined by two transverse channels <NUM> extending in the radial direction to an external circumference <NUM>. The transverse channels <NUM> thus run from the end of the recess <NUM> into the leakage oil chamber <NUM>. The recess <NUM> ends on the side facing the electric machine <NUM> on an end face of the second shaft <NUM>.

In the exemplary embodiments shown in <FIG> a recess <NUM> is formed in the first shaft <NUM> of the electric machine <NUM> which adjoins the receptacle <NUM> for the pin <NUM>. Starting from the recess <NUM> two transverse channels <NUM> extend to an external circumference <NUM> of the first shaft <NUM>.

In both exemplary embodiments a passage <NUM> is formed along the external circumferential surface or through a bearing of the second shaft <NUM> of the hydraulic unit <NUM> through which leakage oil can flow from the leakage oil chamber <NUM> under appropriate pressure conditions. The exemplary embodiment of <FIG> provides a separate leakage oil outlet <NUM> in the electric machine <NUM> which is fluidically connected via the transverse channels <NUM> to the recess <NUM> in the first shaft <NUM>.

During operation the first shaft <NUM> and the second shaft <NUM> rotate about their longitudinal axes. This has the result that leakage oil located in the transverse channels <NUM> is conveyed outwards as a result of centrifugal forces and a negative pressure is formed in the recess <NUM>.

In the exemplary embodiment shown in <FIG> this again has the result that a negative pressure is also formed in the region of the receptacle <NUM> so that leakage oil flows from the leakage oil chamber <NUM> through the passage <NUM> and along the coupling point between the pin <NUM> and the receptacle <NUM>. Thus, the coupling point between the pin <NUM> and the receptacle <NUM> is permanently lubricated. The leakage oil then enters into the recess <NUM> formed as an axial channel and passes from the transverse channels <NUM> back into the leakage oil chamber <NUM>.

In the exemplary embodiments shown in <FIG>, the rotation of the shafts <NUM>, <NUM> also has the result that as a result of the centrifugal forces acting on the leakage oil in the transverse channels <NUM>, a negative pressure is formed in the recess <NUM> with the result that leakage oil (hydraulic fluid) flows along the outer side of the second shaft <NUM> through the first passage <NUM> and along the coupling point between the receptacle <NUM> and the pin <NUM>, with the result that the coupling point is lubricated. The fluid conveyed through the transverse channels <NUM> flows to the separate leakage oil outlet <NUM> of the electric machine <NUM>.

<FIG> shows a region of a further embodiment of a system consisting of an electric machine <NUM> and a hydraulic unit <NUM>, which hydraulic unit <NUM> might be embodied as gear pump, for example. In the following mainly the differences with regard to the above described embodiments will be described.

In this embodiment the first shaft <NUM> of the electric machine <NUM> is indirectly connected to the second shaft <NUM> of the hydraulic unit <NUM>. The first shaft <NUM> is connected to the second shaft <NUM> via an intermediate shaft <NUM>, which is inserted with its one end having an external toothed structure into a receptacle <NUM> of the first shaft <NUM> and with its other end having also an external toothed structure into a receptacle formed within the second shaft <NUM>. Accordingly, the intermediate shaft <NUM> connects the first shaft <NUM> and the second shaft <NUM> in a torque proof manner, so that a rotational movement of the first shaft <NUM> is transferred into a rotational movement of the second shaft <NUM>. Thereby, a shaft-hub connection is formed between the first shaft <NUM> and the second shaft <NUM>.

The intermediate shaft <NUM> has a central recess <NUM> which extends from and end face of the intermediate shaft <NUM> facing the first shaft <NUM> to transverse channels <NUM>, the transverse channels <NUM> extending radially outwards towards an external circumference of the intermediate shaft <NUM>. Within the housing <NUM> of the hydraulic unit <NUM> a leakage oil chamber <NUM> is formed, which surrounds the external circumference of the intermediate shaft <NUM> in an area, in which the transverse channels <NUM> exit.

During operation centrifugal forces acting on the leakage oil in the transverse channels <NUM> produce a negative pressure in the central recess <NUM>, so that leakage oil from the leakage oil chamber <NUM> flows along the outer circumference of the intermediate shaft <NUM> into the receptacle <NUM> of the first shaft <NUM> and enters from there into the central recess <NUM>. The leakage oil within the central recess <NUM> is expelled through the transverse channels <NUM> back into the leakage oil chamber <NUM>. Accordingly, the positive locking connection between the first shaft <NUM> and the intermediate shaft <NUM> is lubricated by the leakage oil.

In order to enhance the leakage oil flow along the external circumference of a shaft a tooth of the external or internal toothed structure may within the shaft-hub connection may be omitted.

Claim 1:
System comprising
- an electric machine (<NUM>), wherein the electric machine (<NUM>) comprises a first shaft (<NUM>), and
- a hydraulic unit (<NUM>), wherein the hydraulic unit (<NUM>) comprises a second shaft (<NUM>), a housing (<NUM>) and a leakage oil chamber (<NUM>) inside the housing (<NUM>),
wherein
• the first shaft (<NUM>) and the second shaft (<NUM>) are connected to one another to form a shaft-hub connection,
• the shaft-hub connection comprises a central recess (<NUM>) and
• the shaft-hub connection is fluidically connected to an interior (<NUM>) of the hydraulic unit (<NUM>) for lubrication, wherein
the central recess (<NUM>) adjoins at least one transverse channel (<NUM>), wherein the at least one transverse channel (<NUM>) extends from the central recess (<NUM>) to an external circumference (<NUM>) of the shaft-hub connection,
characterised in that,
the at least one transverse channel (<NUM>) ends at a point on the external circumference of one of shaft which does not overlap with the other shaft in the connected state, so that leakage oil can be conveyed from the leakage oil chamber (<NUM>) inside the hydraulic unit (<NUM>) along the shaft-hub connection arranged outside the housing (<NUM>) of the hydraulic unit (<NUM>), and wherein the first shaft (<NUM>) and the second shaft (<NUM>) are inserted into one another to form the shaft-hub connection, and in that the first shaft (<NUM>) and/or the second shaft (<NUM>) comprises the central recess (<NUM>), wherein the at least one transverse channel (<NUM>) extends from the central recess (<NUM>) to an external circumference (<NUM>) of the shaft.