The present invention relates to a vacuum pump, and particularly to an automotive vacuum pump and a system, comprising an engine and a vacuum pump.

Vacuum pumps may be fitted to road vehicles with gasoline or diesel engines. Typically, the vacuum pump is driven by a camshaft of the engine. Therefore, in most vehicles the vacuum pump is mounted to an upper region of the engine. But also configurations where the vacuum pump is mounted to a lower region of the engine are known. In general, two different construction types of vacuum pumps are known, one is the type incorporating a movable piston, and the other is vane pump. Nowadays, in particular vane pumps are broadly established.

A vane pump of the aforementioned type typically comprises a casing having a cavity and a movable member arranged for rotation inside the cavity, wherein the cavity is provided with an inlet and an outlet and a movable member is movable to draw fluid into the cavity through the inlet and out of the cavity through the outlet so as to induce a reduction in pressure at the inlet. The inlet is connectable to a consumer such as a brake booster or the like. The outlet normally is connected to the engine's crankcase.

Further the vacuum pumps of the aforementioned type also comprise an oil supply conduit for supplying oil from the engines lubrication circuit to the vacuum pump and a check valve having a check valve body arranged in the oil supply conduit. Such a vacuum pump for example is disclosed in WO 2007/1 16 216 A1 in name of the present applicant. The disclosed vacuum pump comprises a check valve which is arranged in an oil supply conduit to prevent the flow of oil to the cavity during periods when the pump is not operating. When the pump is not operating it is possible that oil drains by means of gravity into the cavity or is drawn into the gravity by a residual vacuum inside the cavity. The check valve known from WO 2007/116 216 A1 prevents oil from flowing into the cavity.

However, it can also happen that during operation too much oil is supplied to the cavity. Excess oil inside the cavity leads to inefficient operation of the vacuum pump and increases the vacuum pump power consumption.

Therefore, arrangements have been developed which meter or dose the oil flow to the cavity.

For example, EP 1 972 785 B1 suggests to provide a slidably supported valve member inside the check valve which is slidable in a direction perpendicular to a rotational axis of the shaft of the vacuum pump. The slidably supported valve member is arranged in such a way that rotational speed of the shaft the oil supply conduit is more open so that more oil is supplied to the cavity.

From EP 0 406 800 B1 a vacuum vane pump is known which incorporates dosing the oil flow dependent on rotational speed of a vane pump. The disclosed vane pump comprises a first groove in fluid connection with an oil supply conduit and arranged adjacent to the shaft of the vane pump inside the housing, a through bore perpendicular to the rotational axis of the shaft provided in the shaft and a second groove in fluid communication with the cavity and arranged adjacent to the shaft of the vane pump inside the housing. The through bore is arranged in such a way that on rotation it connects the first with the second groove thus allowing oil flow from the oil supply conduit to the cavity. Further, EP 0 406 800 B1 discloses one or two spherical valve elements inside the through bore to measure or dose the oil flow in such a way that e.g. on every rotation an amount of oil equal to the volume of the through bore is supplied to the cavity.

However, a drawback of the known vacuum pumps is even though some are able to dose the oil flow to the cavity, an excess oil flow to the cavity cannot be effectively prevented.

Therefore, the object of the present invention is to provide a vacuum pump of the aforementioned type, in particular which prohibits an excess oil flow to the cavity

According to the invention the problem is solved by a vacuum pump according to claim 1. The invention also leads to a system of claim 15. The system comprises an engine and a vacuum pump, wherein the vacuum pump is mounted to the engine, in particular wherein the vacuum pump is driven by a camshaft of the engine, in particular an engine of a road vehicle.

The invention starts from a vacuum pump of the aforementioned type, namely a vacuum pump suitable for mounting to an engine, comprising a casing having a cavity, and a moveable member arranged for rotation inside the cavity, wherein the cavity is provided with an inlet and an outlet and the movable member is movable to draw fluid into the cavity through the inlet and out of the cavity through the outlet so as to induce a reduction in pressure at the inlet, further comprising an oil supply conduit for supplying oil from a reservoir to the cavity and a check valve having a check valve body arranged in the oil supply conduit.

According to the invention the check valve meters the oil flow to the cavity dependent on the oil pressure so that on exceeding an upper oil pressure threshold the supply of oil to the cavity is stopped by means of the check valve.

Oil in this application defines oil as such and the like lubrication liquid. A fluid in this application defines any kind of fluid to be pumped, in particular a gaseous fluid or gas, like air e.g. The term oil pressure presently relates to the pressure of oil measured between the oil reservoir side and the cavity side of the check valve. That is, the term "oil pressure" is defined by the pressure difference between the oil reservoir side and the cavity side of the check valve (hence: "oil pressure" = "pressure at oil reservoir side" - "pressure at cavity side").

Examples for an oil reservoir according the invention are an engine lubrication circuit or an oil gallery of the engine.

These and further developed configurations of the invention are further outlined in the dependent claims. Thereby, the mentioned advantages of the proposed concept are even more improved. For each feature of the dependent claims it is claimed independent protection independent from all other features of this disclosure.

The upper oil pressure threshold is preferably predetermined. Thus on exceeding the upper oil pressure threshold the check valve will close and therefore prohibiting oil to enter the cavity on a too high oil pressure level leading to an extensive oil flow to the cavity. Since in the cavity a vacuum is present the pressure inside the cavity is lower than standard pressure. The pressure measured between the oil reservoir side and the cavity side of the check valve normally will be higher than a pressure measured between the oil reservoir side of the check valve and the standard pressure. Additionally, when the check valve closes on exceeding the upper oil pressure threshold, the oil reservoir pressure may directly by applied to a main bearing, in particular main friction bearing, of the vacuum pump. This additional oil pressure on the main bearing supplements the hydro-dynamically generated bearing pressure and significantly reduces the low speed power consumption of the vacuum pump.

According to a first preferred embodiment the check valve meters the oil flow to the cavity dependent on the oil pressure measured between the oil reservoir side and the cavity side of the check valve so that on falling below a lower oil pressure threshold the oil flow is stopped by means of the check valve. This prevents oil from draining or flowing into the cavity when the vacuum pump is not operating. Again oil pressure relates to the pressure between the check valve and the cavity.

Particular preferred is that the check valve body is movable between a first closed position, an open position and a second closed position, and the check valve body is located in the first closed position when the oil pressure is lower than a lower oil pressure threshold, in the open position, when the oil pressure is between a lower oil pressure threshold and an upper oil pressure threshold and in the second closed position when the oil pressure exceeds the upper oil pressure threshold. The both closed positions, namely the first closed position and the second closed position can be spatially separated or be identical.

Therefore when starting from a zero (or even a negative) oil pressure, the check valve body of the check valve is located in the first close position. No oil flow from the oil supply conduit to the cavity is allowed. When the oil pressure (measured between the oil reservoir side and the cavity side of the check valve) rises above the lower oil pressure threshold, the check valve body moves from the first closed position into the open position, thus allowing oil to flow from the oil supply conduit to the cavity. During operation the oil pressure may further rise until it exceeds an upper oil pressure threshold. The check valve body then moves further to the second closed position and is being located in the second closed position, when the oil pressure exceeds the upper oil pressure threshold. Then again the check valve is closed and an oil flow from the oil supply conduit to the cavity is prohibited.

It is further preferred that the check valve comprises first and a second valve seats for engagement with the check valve body. Preferably the check valve body engages the first valve seat in the first closed position and the check valve body engages the second valve seat in the second closed position. Again the valve seats may be spatially separated or identical. If the both valve seats are separated preferably the second valve seat is arranged downstream of the first valve seat in a direction of the oil flow to the cavity. This leads to a simple and compact design of the check valve. According to a further preferred embodiment a biasing member is arranged in the check valve to bias the check valve body in the first closed position. Thus the biasing member is adapted to bias the check valve body to the first valve seat. The biasing member has a biasing force. A biasing force is used to adjust the lower oil pressure threshold. The check valve body has to be moved from the first closed position against the biasing member and thus against the biasing force from the first closed position into the open position. Preferably the biasing force of the biasing member is used to adjust the upper oil pressure threshold.

In a further preferred embodiment at least one of the two valve seats is formed by a plug having a through hole and arranged in the oil supply conduit. In one alternative the first valve seat is formed by the plug having the through hole and arranged in the oil supply conduit. In another alternative the second valve seat is formed by the plug having the through hole and arranged in the oil supply conduit. In a further alternative both, the first and the second valve seats are formed by a plug having a through hole and arranged in the oil supply conduit. The check valve is arranged in the oil supply conduit. Therefore preferably both valve seats are also arranged in the oil supply conduit. Preferably the check valve body is arranged in a cavity of the check valve movable between the first and the second valve seats. The cavity of the check valve may be formed by a diameter enlarged portion of the oil supply conduit. One of the two valve seats may be then formed by tapered wall connecting the diameter enlarged portion of the oil supply conduit with the oil supply conduit. Preferably the valve seat, which is not formed by the plug is formed by tapered wall connecting the diameter enlarged portion of the oil supply conduit with the oil supply conduit. Thus, in an alternative where for example the second valve seat is formed by the plug, the first valve seat is formed by the tapered wall and vice versa. The diameter increased portion of the oil supply conduit may then extend to the cavity of the pump terminating in an oil inlet to the cavity. According to the present embodiment one of the two valve seats, in particular the second valve seat is then formed by a plug, arranged and preferably fixed in the oil supply conduit at the proximal end of the diameter enlarged portion, seen from the cavity of the pump. The plug may be fixed by means of adhering or screwing means. The plug may be pressed into the oil supply conduit or fixed by welding. Preferably the valve seat formed by the plug is formed by a contact line located around the through hole in the plug. Thus the check valve body can close the oil supply conduit when in contact with the plug.

In particular the through hole of the plug connects the oil supply conduit with the cavity, hence forming a fluid connection between the oil supply conduit or the oil reservoir with the cavity of the pump.

The biasing member preferably is a spring, in particular a spiral spring or a spring washer, supported by one of the two valve seats. Particular preferred is the biasing member supported by the plug forming one of the two valve seats. Thus, the biasing member preferably is arranged between the second valve seat, which e.g. is formed by the plug, and the check valve body, biasing the check valve body in the direction of the first closed position thus into the direction of the first valve seat. This leads to a simple and compact design of the check valve. A spiral spring generally has a higher range of spring but a lower force of spring, a spring washer has a lower range of spring, but a higher force of spring. Both types of springs can advantageously be used according to the invention.

Preferably the check valve body is formed as a ball or a pintle. When the check valve body is formed as a ball, the use of a spiral spring is advantageous, in the other case where the check valve body is formed as a pintle, the use of a spring washer is preferred although also a spiral spring can be used in a beneficial way.

Further for the vacuum pump, the pump may comprise a drive shaft for rotationally driving the moveable member and preferably the oil supply conduit extends through the drive shaft. Such a shaft could be connected to or may be formed integral with a rotor. The rotor may comprise a slot for engaging with the vane for rotation inside the cavity. Alternatively the oil supply conduit extends through a portion of the housing of the cavity and terminates at an cavity inlet.

Preferably the oil supply conduit comprises an axial portion extending along a rotational axis of the shaft and in fluid communication with the oil reservoir and the cavity respectively. Thus the proximal portion or the end portion of the oil supply conduit with respect to the cavity of the pump runs substantially through the center of the drive shaft and terminates at the cavity. Preferably the oil supply conduit terminates into the slot of the rotor to supply oil to the slot. This leads to a beneficial lubrication of the slit in which the vane moves back and forth during the operation of the pump. Further when arranging the oil supply conduit along a central rotational axis of the shaft, the oil inside the oil supply conduit is not subjected to any centrifugal forces circumferential rotation of the shaft. The oil supply conduit further preferably comprises a radial portion extending from a circumferential face of the shaft to the rotational axis of the shaft and in fluid communication with the axial portion of the oil supply conduit. Preferably the radial portion connects the axial portion of the oil supply conduit with the oil reservoir. It is not essential that the radial portion of the oil supply conduit extends strictly radial, i.e. perpendicular to the rotational axis of the shaft, but more this embodiment relate to the radial portion of the oil supply conduit connecting the axial portion of the oil supply conduit with a radial outer face of the shaft. Thus, the distal axial end of the shaft with respect to the cavity of the pump is free of oil inlets or outlets and can be used as an engaging portion to engage with a camshaft of an engine or with a driving motor or the like.

According to these embodiments preferably the check valve is arranged in the axial portion of the oil supply conduit. In particular, the axial portion of the oil supply conduit is formed as a cylindrical wall, and the wall of the conduit forming a housing for the check valve. Therefore again the check valve is free of centrifugal forces, since it is arranged with its central axis along the rotational axis of the shaft of the pump. In a further preferred embodiment the radial portion of the oil supply conduit is in fluid communication with an oil gallery. The oil gallery preferably feeds oil into the cavity of the pump. Preferably the oil gallery is defined between the shaft and the casing of the pump. It may be defined by a circumferential groove in the casing and/or the drive shaft. Thus an operation the radial portion of the oil supply conduit is permanently in fluid communication with the oil gallery.

According to such an embodiment, the oil gallery forms a part of a main friction bearing of the drive shaft. When the check valve closes on exceeding the upper oil pressure threshold, the oil reservoir pressure is directly and fully applied to this main friction bearing of the vacuum pump. This additional oil pressure supplements the hydro-dynamically generated bearing pressure and

significantly reduces the low speed power consumption of the vacuum pump.

For a more complete understanding of the invention, the invention will now be described in detail with reference to the accompanying drawing. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and as claimed hereinafter. Further the features described in the description, the drawing and the claims disclosing the invention may be essential for the invention considered alone or in combination. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The wording "comprising" does not exclude other elements or steps. The wording "a" or "an" does not exclude a plurality. The wording, "a number of items, comprises also the number one, i.e. a single item, and further numbers like two, three, four and so forth.

In the accompanying drawing: FIG. 1 shows a perspective view of an open vacuum pump according to the present invention;

FIG. 2 shows a cross-sectional view of a drive shaft connected to a rotor and a check valve inside the drive shaft according to a first embodiment;

FIG. 3A-3C show the working principle of the check valve of FIG. 2;

FIG. 4 shows a cross-sectional view of a drive shaft connected to a rotor and a check valve inside the drive shaft according to a second embodiment;

FIG. 5A-5C show the working principle of the check valve of FIG. 4;

FIG. 6 shows a cross-sectional view of a drive shaft connected to a rotor and a check valve inside the drive shaft according to a third embodiment; and

FIG. 7A-7C show the working principle of the check valve of FIG. 6.

Referring to the drawing in FIG. 1 there is shown a vacuum pump, generally designated 1 , which is intended to be located adjacent to an automotive engine. The vacuum pump 1 comprises a casing 2 enclosing a cavity 4. The casing 2 is shown without cover plate thus leaving the view open to the inside cavity 4 of the vacuum pump 1. The cover plate can be attached to the rim 6 of the casing 2 by means of the fixing portions 8 (only one depicted with a reference sign in FIG. 1). Further the casing includes engine fixing portions 10 (only one depicted with a reference sign) for fixing the vacuum pump 1 to an engine.

Within the cavity 4 there is provided a rotor 12 and a vane 14. The vane 14 is slidingly mounted in a slit 16 of the rotor 12 and is slidable movable relative to the rotor 12 as indicated by the arrow 18. The ends 20, 22 of the vane 14 are provided with seals 24, 26 which ensure that a substantially fluid tight seal is maintained between the vane 14 and the wall 28 of the cavity 4.

The cavity 4 is provided with an inlet 31 and an outlet 33. Additionally first and second bypass ports 30, 32 are provided at the cavity 4 to lower cold start torque

The inlet 31 is connected to a connector 34 which in turn may be connected to a brake booster arrangement of a vehicle (not shown). The cavity outlet 33 may be connected to the exterior of the pump 1 and may be connected to a crankcase chamber of the engine.

As to FIG. 2, the rotor 12 is connected to a shaft 40. The shaft 40 comprises a proximal end 42 connected to the rotor 12 and a distal end 44 which includes an engagement section 46 for engaging for example a cam shaft of an engine or any other drive motor. The shaft 40 further comprises an oil supply conduit 50 which runs through the shaft connecting the cavity 4 with an oil reservoir (not shown), which in most cases would be an engine lubrication circuit or an oil gallery. The direction of oil flow from the reservoir (not shown) to the cavity 4 (see FIG. 1) is indicated by arrow 52. The oil supply conduit 50 comprises a radial portion 54 and an axial portion 56. The radial portion 54 extends from the axial portion 56 to the outer radial surface of the shaft 40 joining a

circumferential groove 58 on the outer surface of the shaft 40. The

circumferential groove 58 forming an oil gallery. Thus the oil gallery formed by the groove 58 is in fluid communication with the inlet 60 of the oil supply conduit 50. The axial portion 56 of the oil supply conduit 50 runs along the rotational axis A of the shaft 40 and the rotor 12. The axial portion 56 of the oil supply conduit 50 comprises a distal portion 62 having substantially the same diameter as the radial portion 54 of the oil supply conduit and a diameter enlarged portion. The diameter enlarged portion 64 is connected to the distal portion 62 by a tapered portion 66. The diameter enlarged portion 64 forms a housing for a check valve 70. The check valve 70 comprises a check valve body 72. The check valve 72 is according to this embodiment (figures 2 to 3C) formed as a spherical ball. The check valve 70 and thus the check valve body 72 are arranged inside the oil supply conduit 50, the check valve body 72 is arranged inside the diameter enlarged portion 64 of the axial portion 56. According to FIG. 2 the check valve body 72 is located in the first closed position 100. The check valve body 72 is in contact with the tapered portion 66 of the oil supply conduit 50 thus forming a first valve seat 74.

At the proximal end of the axial portion 56 of the oil supply conduit 50 with respect to the cavity 4 a plug 76 is provided. The plug 76 comprises a plug body 78 and a through hole 80, the through hole 80 connecting the oil supply conduit 50 with the cavity 4. The plug body 78 has an outer dimension adapted to be fixed inside the oil supply conduit 50 namely according to this embodiment inside the diameter enlarged portion 64. The central axis of the through hole 80 is substantially arranged along the rotational axis A of the shaft 40 and the central axis of the axial portion 56 of the oil supply conduit 50. The plug body 78 further includes a central protrusion 82 protruding from the plug body 78 basically along the rotational axis A of the shaft into the direction of the distal end 44 of the shaft 40 and thus into the direction of the first valve seat 74. The protrusion 82 has a generally cylindrical shape and the through hole 80 generally runs centrally through the protrusion 82 terminating at the top end 84 of the protrusion 82. At the top end 84 the protrusion 82 includes an inwardly sloped surface 86 adapted to engage with the check valve body 72. The plug 76, in particular the sloped surface 86 of the protrusion 82 forms a second valve seat (87; see FIG. 3B). The plug body 78 further has a supporting surface 88 running substantially around the protrusion 82 and arranged substantially perpendicular to the central axis of the through hole 80. The surface 88 serves as a support for the spiral spring 90 forming a biasing member according to this embodiment. The spiral spring 90 is on the first end (on the left side of FIG. 2) in contact with the supporting surface 88 and on the second end (on the right side of FIG. 2) in contact with the check valve body 72 to bias the check valve body 72 against the first valve seat 74 and thus into the first closed position 100. The working principle of the check valve 70 will now be described in detail with reference to FIG. 3A, FIG. 3B and FIG. 3C. Whereas FIG. 3A shows the check valve body 72 in a first closed position 100, FIG. 3B shows the check valve body in an open position 102 and FIG. 3C in the second closed position 104.

FIG. 3A mainly shows the same situation as FIG. 2. The check valve body 72 is in the first closed position 100 and engages the valve seat 74. The oil supply conduit 50 is closed and no oil can flow from the oil supply conduit 50 into the cavity 4. The spiral spring 90 biases the check valve body 72 against the valve seat 74. The oil pressure DP acting on the check valve body 72 is below a lower oil pressure threshold. The oil pressure DP is defined by the pressure difference P1-P2 between the oil reservoir side and the cavity side of the check valve 70. Thus the force of the spring 90 forcing the check valve body 72 against the valve seat 74 is higher than the force resulting of the pressure DP forcing the check valve body 72 away from the valve seat 74 thus into the direction of the plug 76.

When pressure DP rises and exceeds the lower oil pressure threshold the check valve body 72 moves into an open position 102, as shown in FIG. 3B.

In FIG. 3B the check valve body 72 has moved away and disengaged the valve seat 74 formed by the tapered portion 76. As easily can be seen in the figures, the diameter of the spherical formed check valve body 72 is slightly smaller than the interior diameter of the diameter enlarged portion 64 of the oil supply conduit 50. Therefore, when disengaging from the first valve seat 74 the check valve body 72 leaves a gap 92 between the check valve body 72 and the inner surface of the diameter enlarged portion 64 thus allowing oil 52 to flow from the oil supply conduit 50 into the cavity 4. The oil flows through the radial portion 54, the axial portion 56 around the check valve body 72 and through the through hole 80 formed in the plug 76 until reaching the cavity 4. In this open position 102 (see FIG. 3B) the spiral spring 90 is compressed to a certain extend but not fully compressed. The spring force which is equivalent to the range the spring is compressed and therefore equivalent to the way the check valve body 72 moves from the first closed position 100 (FIG. 3A) to the open position 102 (FIG. 3B) substantially corresponds to the pressure DP measured as the difference of the pressure P1 at the oil reservoir side and the pressure P2 measured at the cavity side of the check valve 70 (DP = P1 - P2) and acting on the check valve body 72 .

When the oil pressure P1 inside the oil supply conduit 50 rises further (see FIG. 3C) and thus the oil pressure DP rises accordingly, the spring 90 is being compressed further until the check valve body 72 engages the second valve seat 87 formed by the sloped surface 86 of the protrusion 82. In this second closed position 104 (see FIG. 3C) the check valve body 72 closes the through hole 80 of the plug 76 and oil flow into the cavity 4 is thus stopped. The arrows 53 in FIG. 3C depict oil, which may flow beneath and behind the check valve body 72, however does not enter the cavity 4. Thus when the oil pressure DP exceeds an upper oil pressure threshold the supply of oil to the cavity 4 is stopped by the check valve 70.

FIG. 4 to 5C illustrate a second embodiment of the vacuum pump 1 comprising the check valve 70 which measures the oil flow to the cavity 4. Identical and similar parts are indicated with identical reference signs. Insofar reference is made to the above description of the first embodiment (FIG. 1 - 3C).

According to the cross-sectional view of FIG. 4 the vacuum pump 1 comprises a casing 2 having a cavity 4. The casing 2 has a cover plate 3 which was fixed to the casing 2 by means of screws 106. The screws 106 are engaging the cover fixing portions 8, which are integrally formed with the casing 2 (see also FIG. 1). A seal 108 is arranged between the cover plate 3 and the casing 2 inside a groove formed in the casing 2 for an airtight sealing of the cavity 4.

A rotor and a vane 14 are provided within the cavity 4. The rotor cannot be seen in FIG. 4, since the cross-section cutting plane runs through the plane of the vane 14, so that the rotor is hidden behind the vane 14. The vane 14 includes seals 24, 26 arranged radial ends 20, 22 which are provided with seals 24, 26 for sealing the vane against an inner circumferential wall of the cavity 4 (see also FIG. 1). The rotor (which is not shown in FIG. 4) is connected to a shaft 40 in which a check valve 70 is arranged. The shaft 40 and the check valve 70 will be described in greater detail below with reference to FIG. 5A-5C.

FIG. 5A to 5C illustrate three different working positions 100, 102, 104 of the check valve 70, similar to the illustration in FIG. 3A to 3C. FIG. 5A shows the first closed position 100 corresponding to FIG. 3A, FIG. 5B shows the open position 102, corresponding to FIG. 3B and FIG. 5C illustrates the second closed position 104, corresponding to FIG. 3C.

Now with reference to figure 5A, the shaft 40 which is seated in a cylindrical portion of the casing 2 is connected via a connection portion 112 with the rotor inside the cavity. The cylindrical portion of the casing 2 in which the shaft 40 is seated, forms a main friction bearing for the shaft 40. Inside the shaft 40 the check valve 70 is provided which is in general formed according to the check valve 70 of the first embodiment (see FIG. 2 to 3C).

The check valve 70 according to the second embodiment (FIG. 4 to 5C) is provided inside an oil supply conduit 50, which includes an axial portion 56 extending along the whole axial length of the shaft 40 along the rotation axis A. The oil supply conduit 150 further comprises a radial portion 154 terminating in a circumferential groove 158 which forms part of an oil gallery 159 for the main friction bearing between the shaft 40 and the casing 2.

Different from the first embodiment (see FIG. 2 to 3C) the oil supply conduit 150 is not fed through the radial portion 154 and the oil gallery 159, but through the axial portion 156 in which at a distal end 44 of the shaft 40 an oil coupling 160 is provided. The oil coupling 160 includes an oil passage 157 which is in fluid communication with the oil supply conduit 150 and forms part of the axial portion 156. The oil coupling 160 has a body 161 having an engagement portion 162 for engaging with the axial portion 156 of the conduit 150 formed in the shaft 40 and a connection portion 163 for connecting the oil coupling 160 to a cam shaft of an engine so that oil may be supplied via the oil coupling 160 to the oil supply conduit 150 and thus to the cavity 4. The oil coupling body 161 includes a radially extending collar 164 which abuts against a portion of the shaft 40 for defining the axial relationship between the shaft 40 and oil coupling 160. Further the body 161 of the oil coupling 160 is provided with seals 165, 166, 167, wherein the seals 165, 166 are pressed against an inner

circumferential wall of the axial portion 156 formed inside the distal end 44 of the shaft 40 for sealing the oil coupling 160 against the shaft 40. The seal 167 arranged at the connection portion 163 is adapted for sealing the oil coupling 160 against an oil outlet of a cam shaft (not shown in the FIG.).

The check valve 70 is arranged in the axial portion 156 of the oil supply conduit 150. The check valve 70 includes a check valve body 172 which according to this embodiment (see figures 4 to 5C) is formed as a pintle 172. The pintle 172 is generally shaped in the form of a mushroom and has a stem 171 and a head 173.

A second valve seat 187 is formed as a tapered portion of the circumferential inner wall of the axial portion 156 of the oil supply conduit 150 in the shaft 40. The tapered portion forming the second valve seat 187 encircles an outlet opening 182 of the oil supply conduit 150 leading into the cavity 4. The stem 171 of the pintle 172 includes a tapered portion 175 corresponding to the tapered portion of the second valve seat 187 for engaging the same. Thus, when the pintle 172 is in the first closed position 100 as shown in figure 5A the tapered portion 175 is disengaged from the second valve seat 187 and a gap between the second valve seat 187 and the tapered portion 175 is provided. When in contrast the pintle 172 is in the second closed position 104 as shown in figure 5C, the tapered portion 175 of the stem 171 engages the second valve seat 187 and thus closes the opening 182 so that oil cannot be provided via the oil supply conduit 150 into the cavity 4.

At the same time the stem 171 , which has a substantially cylindrical shape, serves as a guide and holding means for the biasing member 90, which according to this embodiment is formed as a spiral spring. The biasing member 90 is seated about the stem 71 and abuts against the head 173 of the pintle 172 and on the other hand is seated on a inwardly extending collar 183 formed around the opening 182 and the second valve seat 187. Therefore, the second valve seat 187 is arranged between the collar 183 and the opening 182.

Further different to the first embodiment (FIG. 2 to 3C), in which the second valve seat 87 is formed by the plug 76, according to the second embodiment (FIG. 4 to 5C) the first valve seat 174 is formed by the plug 176. The plug 176 according to this embodiment is substantially formed as a cylindrical bushing having a through hole 180 which forms a passage way for the oil and has an inwardly tapered surface forming the first valve seat 174. At the opposite end the plug 176 has a collar 178 which engages a corresponding recess in the inner circumferential surface of the oil supply conduit 150 for defining an axial position of the plug 176 relative to the shaft 40. The plug 176 may be fixed to the shaft 40 by means of a tight fit or by any other suitable fixing means. The plug 176 is adapted to engage with the head 173 of the pintle 172. Therefore the head 173 of the pintle 172 includes a tapered portion 179 which

corresponds to the tapered surface of the plug 176 which forms the valve seat 174. According to FIG. 5A in which the check valve 70 is shown in the first closed position 100 the tapered surface 179 engages the first valve seat 174. The biasing member 90 forces the pintle 172 into the first closed position 100, as can be easily seen in FIG. 5A.

The head 173 of the pintle 172 has a substantially cylindrical outer shape. The outer diameter of the head 173 corresponds substantially to the inner circumferential diameter of the portion of the axial portion 156 of the oil supply conduit 150 in which the pintle 172 is located. Thus, the pintle 172 can be guided inside the axial portion 156, when moving between the three positions 100, 102, 104.

For allowing a flow of oil from the oil coupling 160 to the cavity 4 the pintle 172 comprises a groove 177 formed on an outer portion of the head 173. The groove 177 has a radial depth which is smaller than the wall thickness of the plug 176 so that when the pintle 172 engages the first valve seat 174 (FIG. 5A) the axial portion 156 of the oil supply conduit 150 is sealed in a fluid tight manner.

In FIG. 5B the check valve 70 is shown in the open position 102 and in FIG. 5C in the second closed position 104. The working principle of the check valve 70 of the second embodiment is substantially identical to the working principle of the check valve 70 according to the first embodiment (see FIG. 3A to 3C).

When no oil is supplied via the oil coupling 160 to the check valve 70 and the vacuum pump 1 is in an idle state, pressure P1 is at a normal value and the pintle 172 is forced to engage the first valve seat 174 by means of the biasing member 90. When oil pressure P1 is increased and oil pressure DP which is the difference between P1 and P2 rises accordingly and exceeds a predetermined threshold, the pintle 172 is moved away from the first valve seat 174 into an open position 102 as shown in FIG. 5B. In the open position 102 the pintle 172 is neither engaging the first valve seat 174 nor the second valve seat 187 and thus oil can be supplied from the oil coupling 160 to the cavity 4 via the oil passage 157, the axial portion 156, the through hole 180 in the plug 176, through the gap between the head 173 and the valve seat 174, the groove 177 then through a gap between the tapered surface 175 and the second valve seat 187 through the opening 182 into the cavity 4. When the oil pressure DP rises further, e.g. because pressure P1 relative to the normal pressure rises or pressure P2 relative to the normal pressure is decreased, the pintle 172 is moved further away from the first valve seat 174 and the biasing member 90 is further compressed so that the tapered surface 175 of the stem 171 engages the second valve seat 187 and oil flow from the oil coupling 160 to the cavity 4 is stopped.

Most significantly in the present embodiment (FIG. 5A to 5C), it can be seen that, when the oil pressure DP exceeds the upper oil pressure threshold and the check valve 70 is in the second closed position 104 as shown in FIG. 5C, oil may only flow through the oil coupling 160 and the conduit 157 to the radial portion 154 and the oil gallery 159 for supplying oil to the main friction bearing between the drive shaft 40 and the casing 2. Thus, oil at the high oil pressure is supplied to the oil gallery 159. This additional oil pressure on the main bearing supplements the hydro-dynamically generated bearing pressure and

significantly reduces the low speed power consumption of the vacuum pump 1. The same effect is present at the vacuum pump 1 according to the first embodiment (FIG. 2 to 3C), however the main friction bearing is not shown in FIG. 2 to 3C. The benefits of the described additional oil pressure will be apparent to the person skilled in the art also with respect to first embodiment (FIG. 2 to 3C).

Now referring to FIG. 6 to 7C, a third embodiment of the vacuum pump 1 is shown. Identical and similar parts are shown with identical reference signs. Insofar reference is made to the above description of the first and second embodiments of the vacuum pump.

The vacuum pump 1 of the third embodiment (FIG. 6 to 7C) comprises a casing 2 in which a cavity 4 is formed and a cover 3, which is fixed to the casing 2 by means of screws 106 which engage fixing portions 8 formed in the casing 2. The vacuum pump 1 further includes a rotor 12 and a vane 14 which is arranged in a slot 16 of the rotor 12. The cross-sectional plane of FIG. 6 runs substantially perpendicular to a plane of the vane 14, so that the rotor 12 and parts of the free cavity 4 can be seen in contrast to FIG. 4 above.

The rotor 12 is connected to a drive shaft 40 which is seated in a cylindrical recess of the casing 2 by means of a friction bearing as described above with reference to the second embodiment (FIG. 4 to 5C).

The vacuum pump 1 further includes a check valve 70 which is according to this embodiment (FIG. 6 to 7C) arranged in the casing 2 and not in the shaft 40 as it is in the first and second embodiment (FIG. 2 to 5C). Therefore an oil supply conduit 250 is arranged in the casing 2 which comprises an axial portion 256 and two slanted conduit 257, 258. The first slanted conduit 257 connects the axial portion 256 with an outlet 260 which terminates at the cavity 4 so that oil can supplied via the oil supply conduit 250 to the cavity 4. The second slanted conduit 258 connects the axial portion 256 with an oil gallery 262 at the friction bearing between the shaft 40 and the casing 2.

The check valve 70 will now be described in a greater detail with reference to FIG. 7A to 7C. Again, corresponding to the FIG. 3A to 3C and 5A to 5C, the check valve 70 is shown in FIG. 7A in a first closed position 100 in FIG. 7B in an open position 102 and in FIG. 7C in a second closed position 104. The structure of the check valve 70 according to the third embodiment (FIG. 6 to 7C) is in general similar to the structure of the check valve 70 of the second embodiment (FIG. 4 to 5C). The check valve 70 of the third embodiment (FIG. 6 to 7C) comprises a check valve body 272 which is formed as a pintle 272 similar to the one of the second embodiment. The pintle 272 again comprises a stem 271 and a head 273.

The axial portion 256 of the oil supply conduit 250 comprises a tapered surface forming the second valve seat 287 and a recess 283. A biasing member 90 which according to this embodiment again is formed as a spiral spring 90 is seated in the recess 283 and engages the stem 271 of the pintle 272. The stem 271 includes similar to the stem 171 (see FIG. 5A) a tapered portion 275 corresponding to the tapered portion 175 for engaging the second valve seat 287.

In the axial portion 256 of the oil supply conduit 250 a plug 276 is arranged. The plug 276 is formed identical to the plug 176 according to the second

embodiment. Different from the second embodiment the plug 276 according to the third embodiment is arranged in the axial portion 256 of the oil supply conduit 250 in the casing 2 and not in the shaft 40. The plug 276 is substantially formed as a bushing having a central through hole 280 for allowing oil flow from the axial portion 256 to the slanted conduit 257 of the oil supply conduit 250. The plug 276 includes an inwardly tapered surface forming the first valve seat 274. The head 273 of the pintle 272 includes a tapered portion 279 which corresponds to the tapered portion of the plug 276 forming the first valve seat 274. The plug 276 further includes a collar 278 engaging a recess 281 in the casing 2 to tight fit the plug 276 into the axial portion 256 of the oil supply conduit 250.

Similar to the second embodiment, the head 273 of the pintle 272 includes a groove 277 at an outer circumferential portion thereof to allow oil to flow through the groove 277.

The functionality of the check valve 70 according to the third embodiments (FIG. 6 to 7C) is similar to the first and second embodiments (FIG. 2 to 5C). When the vacuum pump 1 is in an idle state, the biasing member 90 forces the pintle 272 against the first valve seat 274 formed by the plug 276. Since the tapered portion 279 of the head 273 engages the first valve seat 274, no oil can flow from the axial portion 256 to the slanted conduit 257 and thus no oil can flow into the cavity 4. Only oil supply from the oil supply conduit 250 to the slanted conduit 258 and thus to the oil gallery 262 for the friction bearing of the shaft 40 is allowed. When the pressure DP, which is the difference between pressure P1 and pressure P2 in the axial portion 256 rises, the pintle 272 is moved away from the first valve seat 274 into the direction of the second valve seat 287 and oil flow from the axial portion 256 to the slanted conduit 257 and thus to the cavity 4 is established. The oil flows from the axial portion through the through hole 280 in the plug 276 then between the tapered portion forming the valve seat 274 and tapered portion 279 of the head 273 through the groove 277 along the stem 271 , then between the tapered portion 275 of the stem 271 and the tapered portion of the casing forming the second valve seat 287 and into the slanted conduit 257 of the oil supply conduit 250 and finally into the cavity 4. In case the oil pressure DP rises further and exceeds a predetermined threshold, the pintle 272 is further moved into the direction of the second valve seat 287 and engages the second valve seat with the tapered portion 275 of the stem 271 and the oil flow from the axial portion 256 into the slanted conduit 257 and thus into the cavity 4 is stopped accordingly. When the check valve 70 according to the third embodiment (FIG. 6 to 7C) is in the second closed position 104 the the oil reservoir pressure may directly by applied to the oil gallery 262 and thus to the main friction bearing of the vacuum pump 1 formed between the drive shaft 40 and the casing 2 via the slanted conduit 258. This additional oil pressure on the main bearing supplements the hydro-dynamically generated bearing pressure and significantly reduces the low speed power consumption of the vacuum pump 1 , as already described above with reference to the second embodiment (FIG. 5A to 5C).

List of references

1 vacuum pump

2 casing

3 cover plate

cavity

rim

cover fixing portion

10 engine fixing portion

12 rotor

14 moveable member/vane

16 slot

18 arrow

0, 22 ends of vane

4, 26 seal of vane

8 wall

0 first bypass port

1 inlet

2 second bypass port

3 outlet

4 connector

0 shaft

2 proximal end

4 distal end

6 engagement section

0 oil supply conduit

2 arrow (direction of the oil flow in open position) 3 arrow (oil flow in closed position)

4 radial portion

6 axial portion

8 circumferential groove forming a part of an oil gallery 0 inlet of oil supply conduit

2 distal portion diameter enlarged portion tapered portion

check valve

check valve body/ball first valve seat

plug

plug body

through hole

protrusion

top end

inwardly sloped surface second valve seat surface

biasing member/spiral spring gap

first closed position open position

second closed position screw

seal

connection portion oil supply conduit radial portion

axial portion

oil passage

circumferential groove oil gallery

oil coupling

body of oil coupling engagement portion connecting portion outwardly extending collar seal 166 seal

167 seal

171 stem

172 check valve body / pintle

173 head

174 first valve seat

175 tapered portion

176 plug

177 groove

178 collar of the plug

179 tapered portion of the pintle

180 through hole

182 outlet opening

183 inwardly extending collar

187 second valve seat

250 oil supply conduit

256 axial portion

257, slanted conduit

258 slanted conduit

260 outlet

262 oil gallery

271 stem

272 check valve body / pintle

273 head

274 first valve seat

275 tapered portion of the stem

276 plug

277 groove

278 collar

279 tapered portion

280 central through hole

283 recess

287 second valve seat A rotation axis of the shaft

P1 oil pressure on the oil gallery side of the check valve

P2 oil pressure on the cavity side of the check valve

DP oil pressure acting on check valve (DP =P1 - P2)