Abstract:
A rotary-vane vacuum pump comprises a stator and a vaned rotor, the stator partly defining an outlet chamber and including an outlet passage opening to the outlet chamber. The rotor is rotatably sealed to the stator; it has a sealing area to block the outlet passage, and, an unsealing area alignable with the outlet passage by rotation of the rotor to periodically unblock the outlet passage. The disclosed pump offers reduced resistance to lubricant oil discharge from the outlet passage, which results in lower differential pressure between inlet and outlet chambers at the end of the pumping cycle.

Description:
TECHNICAL FIELD 
     This application relates to the field of motor-vehicle engineering, and more particularly, to a vacuum pump for a motor-vehicle engine system. 
     BACKGROUND AND SUMMARY 
     A motor-vehicle engine system may include a vacuum pump to evacuate air from one or more motor-vehicle components. Such components may include a vacuum servo booster for hydraulic brakes, a throttle driver, or an actuated damper in the ventilation system of the vehicle, for example. 
     The vacuum pump of a motor-vehicle engine system is typically a rotary-vane type positive-displacement pump. International Patent Publication Number WO2007/003215A1 shows one example of this type of pump. The pump includes a single-vane rotor that rotates within a stator and divides the interior volume of the stator into non-communicating chambers. Such chambers include an inlet chamber and an outlet chamber. The stator has an inlet passage that communicates with the inlet chamber, and an outlet passage that communicates with the outlet chamber. The rotor and stator are coated with a film of lubricant oil and configured so that each rotation of the rotor increases the volume of the inlet chamber and decreases the volume of the outlet chamber. Accordingly, air is admitted through the inlet passage and expelled through the outlet passage, providing the basic function of the vacuum pump. In this pump and others like it, a discrete non-return valve may be coupled to the outlet passage to minimize the amount of air that re-enters the pump at the beginning of each pumping cycle. The non-return valve may include a flexible, spring-loaded shutter, or reed-type element. 
     During operation of the vacuum pump, the spring-loaded shutter starts to open when the pressure in the outlet chamber overcomes the restoring (closing) force of the shutter. The inventors herein have found that the limited opening extent of the shutter, together with its somewhat large restoring force, results in excessive lubricant oil pressure in the outlet chamber at the end of each pumping cycle. Under some conditions, the high pressure of the outlet chamber relative to the inlet chamber causes misalignment or rocking of the rotor. This, in turn, may cause the rotor to impact the stator, resulting in objectionable noise from the vacuum pump. 
     Accordingly, one embodiment of the present disclosure provides a rotary-vane vacuum pump comprising a stator and a vaned rotor. The stator partly defines an outlet chamber and includes an outlet passage opening to the outlet chamber. The rotor is rotatably sealed to the stator. The rotor has a sealing area to block the outlet passage, and, an unsealing area alignable with the outlet passage by rotation of the rotor to periodically unblock the outlet passage. The disclosed pump offers reduced resistance to lubricant oil discharge from the outlet passage, which results in lower differential pressure between inlet and outlet chambers at the end of the pumping cycle. Therefore, the rotor is not subjected to misalignment or rocking forces that could result in objectionable noise from the pump. 
     The summary above is provided to introduce a selected part of this disclosure in simplified form, not to identify key or essential features. The claimed subject matter, defined by the claims, is limited neither to the content of this summary nor to implementations that address the problems or disadvantages noted herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows aspects of an example motor-vehicle system in accordance with an embodiment of this disclosure. 
         FIGS. 2 ,  3 , and  4  show aspects of an example rotary-vane vacuum pump in accordance with an embodiment of this disclosure. 
         FIGS. 5 ,  6 , and  7  show aspects of other example rotary-vane vacuum pumps in accordance with embodiments of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of this disclosure will now be described by example and with reference to the illustrated embodiments listed above. Components, process steps, and other elements that may be substantially the same in one or more embodiments are identified coordinately and are described with minimal repetition. It will be noted, however, that elements identified coordinately may also differ to some degree. The drawing figures included in this disclosure are schematic and generally not drawn to scale. Rather, the various drawing scales, aspect ratios, and numbers of components shown in the figures may be purposely distorted to make certain features or relationships easier to see. 
       FIG. 1  schematically shows aspects of an example motor vehicle  10 . The motor vehicle includes an engine  12 , which provides motive force to drive the vehicle. The engine includes a plurality of valves  14 —intake and/or exhaust valves, for example—mechanically actuated via camshaft  16 . The camshaft may be driven by the crankshaft of the vehicle (not shown in  FIG. 1 ) via a belt, a chain, or other suitable componentry. In the embodiment of  FIG. 1 , the camshaft also drives vacuum pump  18 . The vacuum pump is used to evacuate air from one or more evacuable motor-vehicle components during operation of the vehicle. Such components may include a vacuum servo booster for hydraulic brakes, a throttle driver, or an actuated damper in the ventilation system of the vehicle, for example. In the embodiment of  FIG. 1 , vacuum servo booster  20  is coupled to inlet  22  of the vacuum pump. Hydraulic lines  24  conduct hydraulic fluid to hydraulic brakes  26  of the motor vehicle. 
       FIG. 2  shows aspects of an example rotary-vane vacuum pump  18  in one embodiment. The vacuum pump includes a housing, or stator,  28 . In the illustrated embodiment, the stator is assembled from opposing front and back portions ( 30  and  32 , respectively) that together enclose a cavity  34 . 
     Stator  28  presents a curved interior wall  36  that surrounds a vaned rotor  38 . In the drawings herein, the curved interior wall takes the form of a cylinder, but differently shaped curved interior walls may be used in other embodiments. As shown in  FIG. 2 , front and back sides of the rotor rotate against the front and back portions of the stator, respectively. The rotor is coupled to and driven by a shaft  40  that extends through an oil-lubricated, sealed bearing  42  in front portion  30  of the stator. In some examples, this shaft may be or be coupled to a motor-vehicle camshaft; in other examples, the shaft may be that of an electric motor driven by a battery/alternator in the motor vehicle. 
     Continuing in  FIG. 2 , rotor  38  includes a disk-shaped rotor hub  44 . As shown in the drawing, the rotor hub may rotate in bearing area  46  of back portion  32  of stator  28 . The rotor, in turn, presents a complementary sealing area  48  to match the bearing area. In other words, the sealing area of the rotor is contiguous, and disposed in face-sharing contact, with the bearing area of the stator. In other examples, the bearing area may be formed in front portion  30  of the rotor instead of, or in addition to, back portion  32 . In some embodiments, the bearing area in which the rotor rotates may be a recessed area. It may, for example, take the form of a disk-shaped detent in the front and/or back portion of the stator. In other embodiments, the rotor hub may include a recessed sealing area, and the stator may present an elevated (e.g., disk- or ring-shaped) bearing area to receive the recessed sealing area of the rotor. More generally, the stator may include any bearing area suitably shaped to receive the rotor, and the rotor may present a complementary sealing area  48  to match the bearing area. In this and other embodiments, a slidable but substantially air-tight seal between the rotor and the stator is provided by a thin film of lubricant oil at each rotor-stator interface. The friction-reducing oil enables the rotor to move relative to the stator while maintaining the seal.  FIG. 3  shows aspects of vacuum pump  18  from another perspective. The front portion  30  of stator  28  is omitted in  FIG. 3  to reveal the internal structure of the vacuum pump. As shown in the drawing, rotor hub  44  contacts, rotates against, and slidably seals to curved interior wall  36 . In addition to the rotor hub, rotor  38  includes a segmented vane  50  that slides freely along the diameter of the rotor hub. The vane has two end segments,  52 A and  52 B, separated by a spring  54 . The spring biases each end segment against the curved interior wall, causing the end segments to slide along the curved interior wall as the rotor rotates. In the embodiment of  FIG. 3 , the rotor hub supports only one vane; in other embodiments, the rotor hub may support two or more vanes. 
     Stator  28  includes an inlet passage  56  and an outlet passage  58 . The inlet passage opens to vacuum pump inlet  22 , and the outlet passage opens to the air space outside the vacuum pump. In the embodiment illustrated in  FIG. 3 , rotor hub  44 , vane  50 , and curved interior wall  36  divide the internal cavity  34  of the stator into three variable-volume chambers: an inlet chamber  60  that communicates with the inlet passage, an outlet chamber  62  that communicates with the outlet passage, and a closed chamber  64  that communicates neither with the inlet passage nor with the outlet passage. Accordingly, the inlet chamber and the outlet chamber are each partly defined by the stator, inasmuch as the curved interior wall of the stator, together with the rotor hub and vane of the rotor, define the evolving boundaries of both the inlet chamber and the outlet chamber. Because the rotational axis R of rotor  38  is offset from the central axis C of the internal cavity, the volume of the inlet chamber increases as the rotor rotates in the direction shown in  FIG. 3 , while the volume of the outlet chamber decreases. This feature provides the basic function of vacuum pump  18 , pumping air from vacuum pump inlet  22  to air space outside the vacuum pump. 
     In some vacuum pumps, the minimum inlet pressure may be limited by ingress of air through the outlet passage and into the cavity of the pump. One way to address this issue is to couple a non-return valve to the outlet passage to minimize the amount of air that re-enters the vacuum pump. One type of non-return valve may include a flexible, spring-loaded shutter, or reed-type element, with a low-clearance backstop to protect the shutter from irreversible deformation. During operation of the vacuum pump, the spring-loaded shutter starts to open when the pressure in the outlet chamber overcomes the restoring (closing) force of the shutter. The inventors herein have found, however, that the limited opening extent of the shutter, together with its somewhat large restoring force, results in excessive lubricant oil pressure in the outlet chamber at the end of each pumping cycle. Under some conditions, the high pressure of the outlet chamber relative to the inlet chamber may cause misalignment or rocking of the rotor. This, in turn, may cause the rotor to impact the stator, resulting in objectionable noise from the vacuum pump. 
     Accordingly, the present disclosure provides a non-return function at outlet passage  58  of vacuum pump  18 , but without using a reed-type non-return valve. Instead, as shown in  FIGS. 3 and 4 , the outlet passage is positioned within bearing area  46  of the stator, where it remains covered by sealing area  48  of the rotor hub over most of the rotational range of the rotor. However, rotor hub  44  also includes, in addition to sealing area  48 , two unsealing areas  66 A and  66 B. In the illustrated embodiment, the unsealing areas are arranged symmetrically on opposite sides of rotor vane  50 . Each unsealing area is alignable with the outlet passage by rotation of the rotor to periodically unblock the outlet passage during rotation of the rotor. As shown in  FIG. 3 , one unsealing area is aligned with the outlet passage when outlet chamber  62  is at its lowest volume. The outlet passage is otherwise blocked by the sealing area of the rotor—i.e., over most of the rotational range of the rotor. Over the small range of angles where an unsealing area aligns with the outlet passage, the outlet passage becomes unblocked. When the outlet passage is unblocked, air and lubricant oil are expelled from the outlet chamber with relatively little back pressure. Although the illustrated embodiment provides two unsealing areas, this disclosure is equally consistent with embodiments having only one unsealing area. 
     As shown in  FIGS. 3 and 4 , unsealing areas  66 A and  66 B may be formed as notches in sealing area  48 . In these drawings, the notches go all the way through rotor hub  44 . In some examples, each of the notches may be formed parallel to the rotational axis R of the rotor. The notches may have a rounded trapezoidal shape, as shown, or a more semicircular shape for compactness, or a more elongated, rectangular shape for less flow resistance. In this and other embodiments, outlet passage  58  may take the form of an oblong hole of substantially the same length and width as each of the notches. However, the particular geometry of the unsealing areas and outlet passages may differ in the various embodiments of this disclosure. For example, an unsealing area may include a thru-hole formed in the rotor hub, instead of a notch. One such example is shown in  FIG. 5 , with thru-holes  66 C and  66 D periodically unblocking a similarly shaped outlet passage (not shown in  FIG. 5 ). In still other embodiments, the unsealing area may include a detent extending only part-way through the rotor. Here, detent  66 E may directly face bearing area  46  presenting a concavity thereto, as shown by example in  FIG. 6 . Although the illustrated detent has a rounded trapezoidal shape, it will be appreciated that an alternatively shaped detent may be used without departing from the scope of this disclosure. In  FIG. 7 , for instance, detent  66 F has a wedge shape. In still other examples, the detent may take the form of a spherical quadrant. 
     It will be understood that the articles, systems, and methods described hereinabove are embodiments of this disclosure—non-limiting examples for which numerous variations and extensions are contemplated as well. This disclosure also includes all novel and non-obvious combinations and sub-combinations of the above articles, systems, and methods, and any and all equivalents thereof.