POSITIVE DISPLACEMENT PUMP ASSEMBLY WITH MOVABLE END PLATE FOR ROTOR FACE CLEARANCE CONTROL |
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申请号 | US14398039 | 申请日 | 2013-04-29 | 公开(公告)号 | US20150118094A1 | 公开(公告)日 | 2015-04-30 |
申请人 | EATON CORPORATION; | 发明人 | Daniel R. Ouwenga; Brian T. Smith; | ||||
摘要 | A positive displacement pump assembly includes a rotor housing defining a rotor cavity, and an end plate configured to at least partially close one end of the rotor cavity. Rotors are supported on and fixed to rotor shafts and extend through the rotor cavity. A first pair of bearings fixing the rotor shafts to the end plate. A second pair of bearings fixes the rotor shafts to the rotor housing, preventing relative axial movement between the rotor shafts and the rotor housing. The end plate is axially movable with the rotor shafts when the rotor shafts vary in axial length due to thermal fluctuations so that changes in an axial clearance at end faces of the rotors are reduced. | ||||||
权利要求 | |||||||
说明书全文 | This application is being filed on 29 Apr. 2013, as a PCT International Patent application and claims priority to U.S. Patent Application Ser. No. 61/640,330 filed on 30 Apr. 2012, the disclosure of which is incorporated herein by reference in its entirety. The present teachings generally include a positive displacement pump assembly, such as a supercharger assembly for an engine. Positive displacement pumps can be used to add fluid pressure under certain operating conditions. A supercharger is one type of positive displacement pump that is used to boost air pressure at an engine air intake. Positive displacement air pumps typically have meshing, multi-lobed rotors within a rotor housing. Air is moved from an inlet to an outlet; clearance between the rotors and the rotor housing is designed to prevent air from following unintended paths. Air leakage around the rotor end faces is one unintended path and a cause of positive displacement air pump inefficiency. The rotors are mounted on rotor shafts. The rotors and rotor shafts may tend to expand and contract due to thermal fluctuations. The rotor housing may also tend to expand and contract, and may do so at different rates than the rotors or rotor shafts, especially if formed from a different material. One solution has been to leave a gap between the rotor face and the rotor housing at the inlet end of the housing that is sufficiently large to allow the rotor shafts and the housing to expand relative to one another. The rotor shafts are typically fixed axially to the rotor housing at one end by bearings, referred to herein as axial bearings. Needle bearings between the rotor shafts and the rotor housing on the other end allow the rotor shafts to expand and contract axially relative to the rotor housing. A positive displacement pump assembly is provided that allows axial expansion and contraction of rotors and rotor shafts relative to the housing along the length of the rotor cavity while reducing a change in axial clearance at faces of the rotors. The positive displacement pump assembly includes a rotor housing defining a rotor cavity, and an end plate configured to at least partially close one end of the rotor cavity. Rotors are fixed to and supported on rotor shafts and extend through the rotor cavity. A first pair of bearings fixes the rotor shafts axially to the end plate. A second pair of bearings fixes the rotor shafts axially to the rotor housing, preventing relative axial movement between the rotor shafts and the rotor housing. The end plate is axially movable with the rotor shafts when the rotor shafts vary in axial length due to thermal fluctuations so that changes in the axial clearance at the end faces of the rotors due to thermal fluctuations is substantially reduced. The effect of material selection and associated thermal expansion rates of the rotors, rotor shafts, and the rotor housing on the clearance is thus significantly reduced, and leakage through the clearance will thus be minimized with a corresponding increase in efficiency of the positive displacement pump assembly. The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings. Referring to the drawings, wherein like reference numbers refer to like components throughout the several views, The rotors 12, 14 and rotor shafts 16, 18 are contained within a multi-component positive displacement pump housing 20. The housing 20 includes a front cover 22, a midportion 24 that can be referred to as a rotor housing portion, and an end portion 26. The front cover 22 and the end portion 26 are fastened with bolts or otherwise secured to the midportion 24. An input shaft 28 that can be driven by an engine belt or other drive input is operatively connected to the first rotor shaft 16 through a coupling 30. A torsion spring 32 is connected at one end to the front cover 22 of the positive displacement pump housing 20 and at another end to the input shaft 28. The torsion spring 32 damps vibrations of the input shaft 28. A first timing gear 34 is mounted on and rotates with the first rotor shaft 16 and meshes with a second timing gear 36 mounted on and rotating with the second rotor shaft 18 to cause rotation of the second rotor shaft 18. The midportion 24 defines a rotor cavity 38 through which the rotor shafts 16, 18 extend and in which the rotors 12, 14 rotate. A fluid such as air is driven through the rotor cavity 38 from an inlet 39 (shown in Specifically, an end plate 44 is axially fixed for movement with the rotor shafts 16, 18 by a first pair of bearings 46A, 46B positioned between the rotor shafts 16, 18 and the end plate 44. The bearings 46A, 46B are press fit into stepped openings 50A, 50B in the end plate 44. The stepped openings 50A, 50B are best shown in A second pair of bearings 57A, 57B is positioned between the midportion 24 and the rotor shafts 16, 18 and axially fixes the rotor shafts 16, 18 to the midportion 24. The bearings 57A, 57B are referred to herein as axial bearings. The bearings 57A, 57B are press fit into stepped openings 59A, 59B of the midportion 24 near second axial ends 65A, 65B of the rotor shafts 16, 18. The bearings 57A, 57B are configured to permit the rotor shafts 16, 18 to rotate relative to the midportion 24, but fix the axial position of the rotor shafts 16, 18 relative to the midportion 24. Seals 63A, 63B are positioned around the rotor shafts 16, 18 in the stepped openings 59A, 59B between the axial bearings 57A, 57B and the rotor cavity 38. Oil can fill the stepped openings 59A, 59B around the seals 63A, 63B, and the seals 63A, 63B prevent oil leakage into the rotor cavity 38. As the temperature of the positive displacement pump assembly 10 increases, the rotors 12, 14 and rotor shafts 16, 18 and the rotor housing 20 may expand axially an amount dependent on the linear thermal expansion coefficient of the materials from which they are formed. Expansion of the rotors 12, 14, rotor shafts 16, 18 and rotor housing 20 is also dependent on a temperature gradient that may exist along the length of the rotors 12, 14 and the housing 20 due to the fact that compressed air (or other fluid) at the outlet 42 of the housing 20 is much hotter than the air (or other fluid) at the inlet 39 of the housing 20. This may cause the ends 60A, 60B of the shafts 16, 18 to move axially toward or away from the surface 54 of the end portion 26, varying the clearance 52. The width of the clearance 52 does not affect leakage of the positive displacement pump assembly 10. By reducing variations of the clearance 48, and instead allowing the width of the clearance 52 to vary freely with the thermal fluctuations, the end plate 44 can provide a high efficiency for the positive displacement pump assembly 10. In one nonlimiting example, the rotor shafts 16, 18 can be a first material, such as steel, and the rotor housing 20 can be a second material, such as an aluminum alloy. These materials have different rates of linear thermal expansion and contraction, quantified as coefficient of linear thermal expansion. For example, the coefficient of linear thermal expansion of steel may be 13×10−6 meters per meter per degree Kelvin, while that of Aluminum may be 22.2×10−6 meters per meter per degree Kelvin, and that of an Aluminum alloy somewhere therebetween. However, the end plate 44 is fixed to move axially with the rotor shafts 16, 18 and so will significantly reduce variations in the clearance 48 despite these different rates of expansion and contraction. The end plate 44 can be the same material as the rotors 12, 14 to best maintain the clearance 48. A second portion 78 of the perimeter 70 shown in The reference numbers used in the drawings and the specification along with the corresponding components are as follows:
While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims. |