Vacuum pump

A vacuum pump includes a rotor and a housing, which define a vacuum chamber. Rotation of the rotor generates negative pressure in the vacuum chamber. The vacuum pump includes an oil introduction passage, which is connected to an oil pump to introduce oil into the vacuum pump, and an atmosphere communication passage, which opens in the atmosphere to introduce air into the vacuum pump. The vacuum pump further includes a valve and a spring, which serve as a communication control mechanism. The communication control mechanism provides communication between the vacuum chamber and the oil introduction passage and closes the atmosphere communication passage when the vacuum pump is driven. The communication control mechanism provides communication between the vacuum chamber and the atmosphere communication passage and closes the oil introduction passage when the vacuum pump is stopped.

BACKGROUND OF THE INVENTION

The present invention relates to a vacuum pump that generates negative pressure.

A vacuum pump has been known that includes a rotor and a housing, which accommodates and rotationally supports the rotor. Japanese Laid-Open Patent Publication No. 2008-157070 discloses an example of such a vacuum pump. The rotor of the vacuum pump is coupled to a camshaft of an internal combustion engine and thus rotates integrally with the camshaft. Rotation of the rotor changes the volume of the space in the housing and generates negative pressure.

The vacuum pump of the '070 publication includes an oil supply pipe located in the coupling section between the rotor and the camshaft. The oil supply pipe includes a first end, which is received by the rotor, and a second end, which is received by the camshaft. The rotor includes a first oil passage that communicates with the space in the housing. The camshaft includes an oil supply hole for supplying oil to the vacuum pump. The oil supply pipe connects the first oil passage to the oil supply hole of the camshaft.

The oil supply pipe can slide in the rotor and the camshaft. The end surface of the oil supply pipe that faces the rotor is in contact with a compressed return spring. The return spring constantly urges the oil supply pipe toward the camshaft. The end surface of the oil supply pipe that faces the camshaft receives pressure of the oil supplied through the oil supply hole. When the internal combustion engine is stopped and the oil pressure applied to the end surface of the camshaft is low, the urging force of the return spring holds the oil supply pipe in the first position near the camshaft. When the internal combustion engine is operated and the oil pressure applied to the end surface of the camshaft is high, the oil pressure moves the oil supply pipe against the urging force of the return spring and holds the oil supply pipe in the second position near the rotor.

The oil supply pipe includes an atmosphere communication hole that extends through the oil supply pipe in the radial direction to provide communication between the space in the oil supply pipe and the atmosphere. Movements of the oil supply pipe bring the space in the oil supply pipe into and out of communication with the atmosphere through the atmosphere communication hole. Specifically, when the internal combustion engine and the vacuum pump are stopped, the oil supply pipe is located in the first position. In this state, the space in the oil supply pipe communicates with the atmosphere through the atmosphere communication hole. That is, when the vacuum pump is stopped, the oil supply pipe provides communication between the space in the vacuum pump and the atmosphere.

When the vacuum pump is stopped, the negative pressure remaining in the space in the housing draws oil into the housing. However, when the space in the vacuum pump communicates with the atmosphere through the atmosphere communication hole as described above, air is drawn into the housing and releases the negative pressure. This reduces the amount of oil that is drawn into and remains in the vacuum pump.

When the internal combustion engine is operated and the vacuum pump is driven, the oil supply pipe is located in the second position. The section of the oil supply pipe that includes the atmosphere communication hole is located in the rotor. Thus, the atmosphere communication hole is closed, closing communication between the space in the oil supply pipe and the atmosphere.

Since the communication between the space in the housing and the atmosphere is closed when the vacuum pump is driven, air is not drawn into the housing through the atmosphere communication hole. This limits the amount of air discharged from the vacuum pump, thereby limiting air discharge noises.

When the vacuum pump of the '070 publication is stopped, the atmosphere communication hole also provides communication between the oil supply hole and the atmosphere, allowing air to flow into the oil supply hole through the atmosphere communication hole. Thus, when supply of oil is stopped, the oil in the oil supply passage tends to be discharged by its own weight. As a result, when the internal combustion engine starts again, the vacuum pump does not receive oil until the oil supply hole is filled with oil. This prevents prompt supply of oil to the vacuum pump through the oil supply hole.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a vacuum pump that limits the amount of oil drawn into a vacuum chamber when the vacuum pump is stopped, and promptly starts lubrication when the vacuum pump is actuated.

To achieve the above object, one aspect of the present invention is a vacuum pump that includes an oil introduction passage configured to be connected to an oil pump to introduce oil into the vacuum pump, an atmosphere communication passage that opens in the atmosphere to introduce air into the vacuum pump, and a communication control mechanism that provides communication between the vacuum chamber and the oil introduction passage and closes the atmosphere communication passage when the vacuum pump is driven. The communication control mechanism provides communication between the vacuum chamber and the atmosphere communication passage and closes the oil introduction passage when the vacuum pump is stopped.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIGS. 1 to 6, one embodiment of a vacuum pump according to the present invention will now be described.

As shown inFIG. 1, a vacuum pump10is located in an internal combustion engine11that includes a plurality of shaft receiving portions14in the upper section of a cylinder head12. The shaft receiving portions14support a camshaft13and each include a circular shaft receiving hole15. The camshaft13is inserted through the shaft receiving holes15and rotationally supported by the shaft receiving holes15.

The camshaft13has a first end connected to a timing pulley16, around which a timing belt17is wound. The timing belt17is also wound around a crank pulley19that is connected to a first end of a crankshaft18. Thus, when operation of the internal combustion engine11rotates the crankshaft18, the camshaft13rotates in synchronization with the crankshaft18.

A plurality of cams20, which rotates integrally with the camshaft13, is arranged on the camshaft13. When operation of the internal combustion engine11rotates the camshaft13, the cams20press down the engine valves.

An oil pump21, which is driven by the engine, is connected to a second end of the crankshaft18. When driven by rotation of the crankshaft18, the oil pump21draws the oil stored in an oil pan22and supplies the oil to various parts of the internal combustion engine11.

The vacuum pump10is located at a second end of the camshaft13. The vacuum pump10includes a rotor23and a housing24, which accommodates and rotationally supports the rotor23. The rotor23is coupled to the camshaft13and thus rotates integrally with the camshaft13. The housing24is fixed to a support wall25formed in the cylinder head12.

Referring toFIG. 2, the structure of the vacuum pump10will now be described.

As shown inFIG. 2, the housing24is tubular and includes a receptacle26and a support27, which has a smaller radial dimension than the receptacle26. The receptacle26substantially has an oval cross-section, and the support27has a circular cross-section. The support27is eccentrically arranged with respect to the receptacle26.

The rotor23is cylindrical and includes a shaft28and a sliding portion29, which has a larger radial dimension than the shaft28. The shaft28is inserted in and rotationally supported by the support27of the housing24. The sliding portion29includes a sliding groove30extending in the radial direction. A vane31is coupled to the sliding groove30such that the vane31can slide along the sliding groove30in the radial direction of the rotor23.

The vacuum pump10includes a cover32, which substantially has the same shape as the cross-section of the receptacle26of the housing24. When coupled to the housing24, the vane31and the rotor23are located inside the housing24.

As shown inFIG. 3, the rotor23and the vane31that are coupled to the housing24define clearances R1, R2and R3in the receptacle26of the housing24. The axis of the rotor23is substantially aligned with the axis of the support27. The rotor23is eccentrically arranged with respect to the receptacle26. As described above, the receptacle26substantially has an oval cross-section. As such, when the rotor23and the vane31rotate in the housing24, the vane31slides in the sliding groove30with the two ends of the vane31in contact with the receptacle26. The volumes of the clearances R1, R2and R3in the receptacle26are thus changed.

The housing24includes an inlet port33at the border between the clearance R1and clearance R2in the state shown inFIG. 3. The inlet port33provides communication between the space in the housing24and the space in the vacuum brake booster. Counterclockwise rotation of the rotor23from the state shown inFIG. 3brings the clearance R1into communication with the space in the vacuum brake booster. The rotation of the rotor23increases the volume of the clearance R1and generates negative pressure in the clearance R1accordingly. The negative pressure generated in the clearance R1draws the air in the vacuum brake booster into the clearance R1through the inlet port33. This generates negative pressure in the vacuum brake booster.

Further counterclockwise rotation of the rotor23from the state shown inFIG. 3closes communication between the clearance R2and the inlet port33. The rotation of the rotor23reduces the volume of the clearance R2and compresses the air in the clearance R2accordingly.

Further, as shown inFIG. 4, the housing24also includes a discharge port34for air. In the state shown inFIG. 3, the discharge port34is connected to the clearance R3. Thus, while the rotor23rotates counterclockwise as viewed inFIG. 3and reduces the volume of the clearance R3, the compressed air in the clearance R3is discharged through the discharge port34.

As such, rotating the rotor23allows the vacuum pump10to perform an intake phase, in which air is drawn into the clearance R1shown inFIG. 3, a compression phase, in which the drawn air is compressed in the clearance R2shown in FIG.3, and a discharge phase, in which the compressed air is discharged from the clearance R3shown inFIG. 3. These phases are repeated to generate negative pressure. That is, when the vacuum pump10is driven, the intake phase, the compression phase, and the discharge phase are repeated in the clearances R1, R2and R3, which are defined by the receptacle26of the housing24and the rotor23. Each clearance functions as a vacuum chamber that generates negative pressure.

As shown inFIG. 4, a reed valve35is located at the discharge port34. The reed valve35is a metal plate, for example, and closes the discharge port34. A stopper36is placed on the reed valve35, and the reed valve35and the stopper36are fixed to the housing24by a bolt37. The stopper36is bent so that the upper part is farther from the reed valve35. The section of the reed valve35sandwiched by the housing24and the stopper36functions as a support, and the section opposite to the support elastically deforms toward the stopper36.

When the air in one of the clearances R1, R2and R3that communicates with the discharge port34is compressed, the increased air pressure in the clearance deforms and brings the upper end of the reed valve35into contact with the stopper36. This opens the discharge port34. When the air is discharged from the clearance and the air pressure in the clearance decreases, the reed valve35returns to its original position. This closes the discharge port34. Such a structure allows for discharge of air from the housing24through the discharge port34while limiting entry of air into the housing24through the discharge port34.

As shown inFIG. 4, the shaft28of the rotor23is coupled to a cylindrical coupling38. As shown inFIG. 2, a rectangular protrusion39protrudes from the shaft28of the rotor23. The coupling38includes a groove40, which substantially has the same shape as the protrusion39. The protrusion39on the shaft28of the rotor23is inserted in and engaged with the groove40of the coupling38, thereby coupling the rotor23to the coupling38. An insertion passage41extends in the coupling38in the axial direction.

As shown inFIGS. 2 and 4, the coupling38is coupled to the camshaft13with an oil supply pipe42inserted in the coupling38. The end of the coupling38into which the oil supply pipe42is inserted includes a rectangular protrusion43. The second end of the camshaft13includes a groove44, which substantially has the same shape as the protrusion43. The protrusion43of the coupling38is inserted into and engaged with the groove44of the camshaft13, thereby coupling the coupling38to the camshaft13. The coupling38thus couples the rotor23to the camshaft13.

The camshaft13includes an oil supply hole45, which extends in the axial direction, that is, the horizontal direction as viewed inFIG. 4. The oil supply hole45is connected to the oil pump21through an oil supply passage extending through the cylinder head12and the cylinder block. The oil supply pipe42inserted in the coupling38is also inserted in the oil supply hole45of the camshaft13. An O-ring46is attached to the outer circumference of each end of the oil supply pipe42. One of the O-rings46seals the gap between the oil supply pipe42and the coupling38, and the other seals the gap between the oil supply pipe42and the camshaft13.

As shown inFIG. 5, the support27of the housing24has an inner circumferential surface47, which includes an oil supply groove49and a communication hole50. The oil supply groove49extends in the axial direction, that is, the horizontal direction as viewed inFIG. 5, and communicates with a vacuum chamber48. The communication hole50includes an open end that opens in the atmosphere and an open end that opens in the inner circumferential surface47.

The shaft28of the rotor23includes an accommodation hole52extending in the axial direction. The accommodation hole52includes an opening51connected to the insertion passage41of the coupling38. The oil supply pipe42provides communication between the insertion passage41and the oil supply hole45of the camshaft13, which is connected to the oil pump21. That is, the accommodation hole52is connected to the oil pump21through the opening51. The accommodation hole52does not extend through the rotor23in the axial direction and includes an end wall53.

The accommodation hole52is connected to a first through hole54, which extends from the accommodation hole52in the radial direction, that is, the vertical direction as viewed inFIG. 5. The first through hole54opens in the outer circumferential surface of the rotor23, providing communication between the accommodation hole52and the oil supply groove49. A section of the accommodation hole52between the first through hole54and the opening51is connected to a second through hole55, which extends in the radial direction from the accommodation hole52. The second through hole55opens in the outer circumferential surface of the rotor23, providing communication between the accommodation hole52and the communication hole50. The second through hole55and the communication hole50form an atmosphere communication passage56, which introduces air into the vacuum pump10.

Further, a section of the accommodation hole52between the second through hole55and the opening51is connected to a third through hole57, which extends in the radial direction from the accommodation hole52. The third through hole57opens in the outer circumferential surface of the rotor23, providing communication between the accommodation hole52and the oil supply groove49. As shown inFIG. 5, the first through hole54and the third through hole57extend in the same direction from the accommodation hole52. Thus, when the first through hole54provides communication between the accommodation hole52and the oil supply groove49, the third through hole57also provides communication between the accommodation hole52and the oil supply groove49. The second through hole55is positioned to provide communication between the accommodation hole52and the communication hole50when the accommodation hole52communicates with the oil supply groove49. As a result, when the second through hole55communicates with the communication hole50and the accommodation hole52, the communication hole50communicates with the oil supply groove49through the second through hole55, the accommodation hole52, and the first through hole54.

The accommodation hole52accommodates a valve58, which is slidable in the axial direction, and a compressed spring59, which is placed between the valve58and the end wall53and urges the valve58toward the opening51. An annular first stopper61is fixed in the accommodation hole52between the first through hole54and the second through hole55. The first stopper61has an insertion hole60at the center. Further, an annular second stopper63is fixed in the accommodation hole52between the third through hole57and the opening51. The second stopper63has an insertion hole62at the center. The valve58is located between the first stopper61and the second stopper63in the axial direction. The spring59is inserted through the insertion hole62of the first stopper61and connected to the valve58.

The valve58divides the accommodation hole52into a section that faces the opening51and a section that faces the end wall53. The section of the accommodation hole52between the valve58and the opening51functions as an oil introduction passage64.

The opening51of the accommodation hole52is connected to the oil pump21. Thus, when the internal combustion engine11is operated, the oil pump21draws and supplies oil to the oil introduction passage64of the accommodation hole52. The pressure of the oil supplied to the oil introduction passage64applies force to the valve58. When this force exceeds the urging force of the spring59, the valve58moves against the urging force of the spring59and into contact with the first stopper61. As shown inFIG. 5, the valve58closes the second through hole55when in contact with the first stopper61. In this state, the oil introduction passage64communicates with the third through hole57. The valve58is thus placed in a first position, where the third through hole57intermittently communicates with the oil supply groove49when the internal combustion engine11is operated and rotates the rotor23. The oil supply groove49provides communication between the oil introduction passage64and the vacuum chamber48, introducing oil into the vacuum pump10.

When the force acting on the valve58, which is generated by the pressure of the oil supplied to the oil introduction passage64, becomes less than the urging force of the spring59, the urging force of the spring59moves the valve58into contact with the second stopper63. As shown inFIG. 6, the valve58closes the third through hole57when in contact with the second stopper63. In this state, the oil introduction passage64does not communicate with any of the through holes and is closed. In addition, the section of the accommodation hole52between the valve58and the end wall53provides communication between the second through hole55and the first through hole54. This introduces air into the vacuum pump10through the atmosphere communication passage56. The valve58and the spring59form a communication control mechanism that uses oil pressure to switch between a state where the vacuum chamber48communicates with the oil introduction passage64and the atmosphere communication passage56is closed as shown inFIG. 5, and a state where the vacuum chamber48communicates with the atmosphere communication passage56and the oil introduction passage64is closed as shown inFIG. 6. In the following descriptions, the position of the valve58when in contact with the first stopper61is referred to as the first position, and the position of the valve58when in contact with the second stopper63is referred to as the second position.

Referring toFIGS. 5 and 6, the operation of the vacuum pump10will now be described.

As shown inFIG. 5, when the vacuum pump10is driven and the pressure of the oil supplied to the oil introduction passage64from the oil pump21is high, the valve58is placed in the first position and closes the second through hole55, which forms the atmosphere communication passage56with the communication hole50. In this state, the oil introduction passage64communicates with the vacuum chamber48through the third through hole57and the oil supply groove49. That is, the atmosphere communication passage56is closed, and the oil introduction passage64communicates with the vacuum chamber48. This state limits introduction of air into the vacuum chamber48through the atmosphere communication passage56while allowing supply of oil into the vacuum chamber48through the oil introduction passage64during operation of the vacuum pump10. Thus, the amount of air discharged from the vacuum pump10and air discharge noises are limited while vacuum pump10is lubricated.

In the process of stopping the vacuum pump10, the amount of oil supplied from the oil pump21decreases, lowering the oil pressure in the oil introduction passage64. When the force generated by the oil pressure in the oil introduction passage64becomes less than the urging force of the spring59, the valve58moves to the second position as shown inFIG. 6. This brings the second through hole55, which forms the atmosphere communication passage56with the communication hole50, into communication with the first through hole54through the accommodation hole52. Since the first through hole54communicates with the oil supply groove49, which communicates with the vacuum chamber48, the vacuum chamber48is brought into communication with the atmosphere communication passage56, and the oil introduction passage64is closed. In the process of stopping the vacuum pump10, the rotor23still rotates, intermittently allowing communication between the vacuum chamber48and the atmosphere communication passage56. This supplies the vacuum pump10with air and releases the negative pressure remaining in the vacuum chamber48.

When the vacuum pump10is stopped, the valve58closes the third through hole57, and the oil introduction passage64is closed. Thus, even if negative pressure still remains in the vacuum chamber48when the vacuum pump10is stopped, oil is not drawn into the vacuum chamber from the oil introduction passage64. If the rotor23is stopped in the position that provides communication between the vacuum chamber48and the atmosphere communication passage56when the vacuum pump10is stopped, air flows into the vacuum chamber48through the atmosphere communication passage56, releasing the negative pressure in the vacuum chamber48. If the rotor23is stopped in the position that closes communication between the vacuum chamber48and the atmosphere communication passage56when the vacuum pump10is stopped, air flows into the vacuum chamber48through the gap between the outer circumferential surface of the shaft28of the rotor23and the inner circumferential surface47of the support27of the housing24, releasing the negative pressure in the vacuum chamber48.

As shown inFIG. 6, when the vacuum pump10is stopped, the valve58closes the communication between the oil introduction passage64and the atmosphere communication passage56. This limits entry of air into the oil introduction passage64through the atmosphere communication passage56when the vacuum pump10is stopped. Thus, the oil remaining in the oil introduction passage64, the insertion passage41, and the oil supply hole45is less likely to be discharged by its own weight. This maintains the oil in the oil introduction passage64when the vacuum pump10is stopped. The oil remaining in the oil introduction passage64can be promptly supplied to the vacuum pump10on the next actuation of the vacuum pump10. In addition, this structure allows for prompt increase in the oil pressure in the oil introduction passage64when the vacuum pump10is actuated, allowing the oil pressure to promptly move the valve58of the communication control mechanism to the first position. This promptly starts lubrication and limits drawing of air into the vacuum chamber48through the atmosphere communication passage56, enabling prompt generation of negative pressure.

The valve58and the spring59form the communication control mechanism. Depending on the pressure of the oil supplied to the oil introduction passage64, the valve58is movable between the first position for closing the second through hole55and the second position for closing the third through hole57. This structure is simpler than a structure with an additional mechanism to operate the valve58, thus allowing reduction in the size of the vacuum pump10.

The advantages of the present embodiment will now be described.

(1) The vacuum pump10includes the communication control mechanism. When the vacuum pump10is driven, the communication control mechanism provides communication between the vacuum chamber48and the oil introduction passage64and closes the atmosphere communication passage56. When the vacuum pump10is stopped, the communication control mechanism provides communication between the vacuum chamber48and the atmosphere communication passage56and closes the oil introduction passage64. This limits drawing of oil into the vacuum pump10from the oil introduction passage64when the vacuum pump10is stopped. Further, discharge of oil from the oil introduction passage64by the weight of oil is limited when supply of oil from the oil pump21is stopped. This increases the probabilities that oil remains in the oil introduction passage64when the vacuum pump10is stopped. As a result, when the vacuum pump10is actuated again, the oil remaining in the oil introduction passage64can be promptly supplied to the vacuum pump10. As such, drawing of oil into the vacuum chamber48is limited when the vacuum pump10is stopped, and lubrication promptly starts when the vacuum pump10is actuated.

(2) The valve58and the spring59form the communication control mechanism. Depending on the pressure of the oil supplied to the oil introduction passage64, the valve58is movable between the first position for closing the second through hole55and the second position for closing the third through hole57. When the vacuum pump10is stopped, the valve58closes the oil introduction passage64. This maintains oil in the oil introduction passage64when the vacuum pump10is stopped. Thus, when oil is supplied to the oil introduction passage64through the oil pump21on the next actuation of the vacuum pump10, the oil pressure in the oil introduction passage64will promptly increase and move the valve58to the first position. Therefore, in addition to promptly starting lubrication, the structure limits drawing of air into the vacuum chamber48through the atmosphere communication passage56, achieving prompt generation of negative pressure.

The present embodiment may be modified as follows.

The first stopper61and the second stopper63in the accommodation hole52may be omitted. In this case, the valve58may be held in the first position and the second position by adjusting the compressed length and the expanded length of the spring59.

The communication control mechanism may be modified as shown inFIGS. 7 and 8.

FIG. 7shows a vacuum pump that includes a communication hole70and an oil supply hole71in the support27of the housing24. The communication hole70extends in the radial direction and includes an open end that opens in the atmosphere and an open end that opens in the inner circumferential surface47of the housing24. The oil supply hole71extends in the axial direction and communicates with the vacuum chamber48. The oil supply hole71includes a first open hole72and a second open hole73, which are separated from each other in the axial direction. The first and second open holes72and73extend in the radial direction and open in the inner circumferential surface47of the housing24.

The shaft28of the rotor23, which is supported by the support27of the housing24, includes an oil introduction hole75extending in the axial direction. The oil introduction hole75includes an opening74connected to the oil pump21. A second through hole76extends in the radial direction from the oil introduction hole75. The second through hole76opens in the outer circumferential surface of the rotor23and communicates with the second open hole73. The second through hole76, the oil introduction hole75, and the second open hole73form an oil introduction passage83. The section of the shaft28between the oil introduction hole75and the vacuum chamber48includes a first through hole77, which extends through the shaft28in the radial direction. The first through hole77provides communication between the communication hole70and the first open hole72. The first through hole77, the communication hole70, and the first open hole72form an atmosphere communication passage78.

A first solenoid valve79for closing and opening the first open hole72and a second solenoid valve80for closing and opening the second open hole73are located in the oil supply hole71. The vacuum pump10includes a controller81, which receives output signals from an ignition switch82. In response to the output signals, the controller81controls the first solenoid valve79and the second solenoid valve80. Specifically, in a period between when the ignition switch82is turned ON from OFF and when the ignition switch82is turned OFF from ON, the controller81controls the first solenoid valve79to close the first open hole72and controls the second solenoid valve80to open the second open hole73. Thus, when the internal combustion engine11is operated and the vacuum pump10is driven, the vacuum chamber48communicates with the oil introduction passage83through the oil supply hole71, and the atmosphere communication passage78is closed.

In contrast, during the period between when the ignition switch82is turned OFF from ON and when the ignition switch82is turned ON from OFF, the controller81controls the first solenoid valve79to open the first open hole72and controls the second solenoid valve80to close the second open hole73. Thus, when the internal combustion engine11and the vacuum pump10are stopped, the vacuum chamber48communicates with the atmosphere communication passage78through the oil supply hole71, and the oil introduction passage83is closed.

In the structure described above, when the vacuum pump10is driven, the first solenoid valve79, the second solenoid valve80, and the controller81provide communication between the vacuum chamber48and the oil introduction passage83and closes the atmosphere communication passage78. When the vacuum pump10is stopped, the vacuum chamber48communicates with the atmosphere communication passage78, and the oil introduction passage83is closed. The first solenoid valve79, the second solenoid valve80, and the controller81form a communication control mechanism.

FIG. 8shows a vacuum pump that includes an introduction hole90in the support27of the housing24. The introduction hole90extends in the axial direction and includes an open end that opens in the atmosphere and an open end that communicates with the vacuum chamber48. A communication hole91extends from the introduction hole90in the radial direction. The communication hole91opens in the inner circumferential surface47of the housing24.

The shaft28of the rotor23, which is supported by the support27of the housing24, includes an oil introduction hole93extending in the axial direction. The oil introduction hole93includes an opening92connected to the oil pump21. The oil introduction hole93includes a through hole94extending in the radial direction. The through hole94opens in the outer circumferential surface of the rotor23and communicates with the communication hole91. The oil introduction hole93, the through hole94, and the communication hole91form an oil introduction passage99.

A first solenoid valve95for closing and opening the communication hole91is located in the introduction hole90. A second solenoid valve96is located in the introduction hole90near the open end that opens in the atmosphere. The second solenoid valve96opens and closes communication between the introduction hole90and the atmosphere. The section of the introduction hole90between the open end that opens in the atmosphere and the area that is opened and closed by the second solenoid valve96forms an atmosphere communication passage97.

The vacuum pump10includes a controller98, which receives output signals from the ignition switch82. In response to the output signals, the controller98controls the first solenoid valve95and the second solenoid valve96. Specifically, during the period between when the ignition switch82is turned ON from OFF and when the ignition switch82is turned OFF from ON, the controller98controls the first solenoid valve95to open the communication hole91and controls the second solenoid valve96to close communication between the introduction hole90and the atmosphere. Thus, when the internal combustion engine11is operated and the vacuum pump10is driven, the vacuum chamber48communicates with the oil introduction passage99through the introduction hole90, and the atmosphere communication passage97is closed.

In contrast, during the period between when the ignition switch82is turned OFF from ON and when the ignition switch82is turned ON from OFF, the controller98controls the first solenoid valve95to close the communication hole91and controls the second solenoid valve96to provide communication between the introduction hole90and the atmosphere. Thus, when the internal combustion engine11and the vacuum pump10are stopped, the vacuum chamber48communicates with the atmosphere communication passage97, and the oil introduction passage99is closed.

In the structure described above, when the vacuum pump10is driven, the first solenoid valve95, the second solenoid valve96, and the controller98provide communication between the vacuum chamber48and the oil introduction passage99and close the atmosphere communication passage97. When the vacuum pump10is stopped, the vacuum chamber48communicates with the atmosphere communication passage97, and the oil introduction passage99is closed. The first solenoid valve95, the second solenoid valve96, and the controller98form a communication control mechanism.