Patent Application
20140366821
The present invention relates to an internal combustion engine with a camshaft phaser which uses an electric motor to vary the phase relationship between a crankshaft and a camshaft of the internal combustion engine; more particularly, to such an internal combustion engine which uses oil from the internal combustion engine to lubricate elements of the camshaft phaser; even more particularly to such an internal combustion engine which includes a drive belt for transmitting rotational motion from the crankshaft to the camshaft; and yet even more particularly to such an internal combustion engine which includes a sealing arrangement to seal the drive belt from the oil used to lubricate the camshaft phaser.
Camshaft phasers for varying the timing of combustion valves in internal combustion engines are well known. A first element, known generally as a sprocket element, is driven by a chain, belt, or gearing from the internal combustion engine's crankshaft. A second element, known generally as a camshaft plate, is mounted to the end of a camshaft of the internal combustion engine. A common type of camshaft phaser used by motor vehicle manufactures is known as a vane-type camshaft phaser. U.S. Pat. No. 7,421,989 shows a typical vane-type camshaft phaser which generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is supplied via a multiport oil control valve, in accordance with an engine control module, to either the advance or retard chambers, to change the angular position of the rotor relative to the stator, and consequently the angular position of the camshaft relative to the crankshaft, as required to meet current or anticipated engine operating conditions.
While vane-type camshaft phasers are effective and relatively inexpensive, they do suffer from drawbacks such as slow operation at low engine speeds due to low oil pressure, slow operation at low engine temperatures due to high oil viscosity, increased oil pump capacity requirement for the oil pump used to lubricate the internal combustion because the same pump is used to actuate the vane-type camshaft phaser, and the total amount of phase authority provided by vane-type camshaft phasers is limited by the amount of space between adjacent vanes and lobes and may not be sufficient to provide the desired amount of phase authority. For at least these reasons, the automotive industry is developing electrically driven camshaft phasers.
One type of electrically driven camshaft phaser being developed uses a harmonic drive gear unit, actuated by an electric motor, to change the angular position of the camshaft relative to the crankshaft. One example of such a camshaft phaser is shown in United States Patent Application Publication No. US 2012/0312258 A1 to Kimus et al. While the camshaft phaser of Kimus et al. does not use oil to actuate the camshaft phaser, oil is used for lubrication of various element of the camshaft phaser. Accordingly, oil is supplied under pressure to the camshaft phaser where the oil lubricates various elements within the camshaft phaser. After lubricating the various elements, the oil which drains out of the camshaft phaser through various interfaces is allowed to reach a drive member, such as a chain or belt, which transfers rotational motion from the crankshaft to the camshaft phaser. While this may be acceptable to some drive members, particularly chains and gears, other drive members, particularly belts, may not tolerate exposure to oil.
What is needed is an electrically driven camshaft phaser which minimizes or eliminates one of more of the shortcomings as set forth above.
Briefly described, an internal combustion includes a crankshaft rotatable about a crankshaft axis and a camshaft rotatable by the crankshaft about a camshaft axis. The internal combustion engine also includes an oil source, an engine cover, and a drive member disposed within the engine cover for transferring rotational motion from the crankshaft to the camshaft. A camshaft phaser is disposed within the engine cover for controllably varying the phase relationship between the crankshaft and the camshaft. The camshaft phaser includes an input member driven by the drive member, an output member rotatable with the camshaft, a gear drive unit connecting the input member to the output member, and an electric motor connected to the gear drive unit to impart rotation on the gear drive unit such that rotation of the gear drive unit causes relative rotation between the input member and the output member. A supply passage communicates oil from the oil source to the camshaft phaser in order to lubricate the camshaft phaser and a drain passage drains the oil from the camshaft phaser to the oil source. A sealing arrangement defines a dry zone within the engine cover to isolate the drive member from the oil used to lubricate the camshaft phaser.
This invention will be further described with reference to the accompanying drawings in which:
Referring to
Camshaft phaser 22 comprises a gear drive unit illustrated as a harmonic gear drive unit 34; a rotational actuator 36 operationally connected to harmonic gear drive unit 34; an input sprocket 38 operationally connected to harmonic gear drive unit 34 and driven by drive member 28 via crankshaft 14; an output hub 40 attached to harmonic gear drive unit 34 and mounted to an end of camshaft 18; and a bias spring 42 operationally disposed between output hub 40 and input sprocket 38. Rotational actuator 36, herein after referred to as electric motor 36, may be, for example only, a DC electric motor.
Harmonic gear drive unit 34 comprises an outer first spline 44 which may be either a circular spline or a dynamic spline as described below; an outer second spline 46 which is the opposite (dynamic or circular) of first spline 44 and is coaxially positioned adjacent first spline 44; a flexspline 48 disposed radially inwards of both first spline 44 and second 46 and having outwardly-extending gear teeth disposed for engaging inwardly-extending gear teeth on both first spline 44 and second spline 46; and a wave generator 50 disposed radially inwards of and engaging flexspline 48.
Flexspline 48 is a non-rigid ring with external teeth on a slightly smaller pitch diameter than the circular spline. Flexspline 48 is fitted over and elastically deflected by wave generator 50.
The circular spline is a rigid ring with internal teeth engaging the teeth of flexspline 48 across the major axis of wave generator 50.
The dynamic spline is a rigid ring having internal teeth of the same number as flexspline 48. The dynamic spline rotates together with flexspline 48 and serves as the output member. Either the dynamic spline or the circular spline may be identified by a chamfered corner at its outside diameter to distinguish one spline from the other. As shown, the chamfered corner has been used to identify second spline 46.
As is disclosed in the prior art, wave generator 50 is an assembly of an elliptical steel disc supporting an elliptical bearing, the combination defining a wave generator plug. A flexible bearing retainer surrounds the elliptical bearing and engages flexspline 48. Rotation of the wave generator plug causes a rotational wave to be generated in flexspline 48 (actually two waves 180° apart, corresponding to opposite ends of the major ellipse axis of the disc).
During assembly of harmonic gear drive unit 34, flexspline teeth engage both circular spline teeth and dynamic spline teeth along and near the major elliptical axis of the wave generator. The dynamic spline has the same number of teeth as the flexspline, so rotation of the wave generator causes no net rotation per revolution therebetween. However, the circular spline has slightly fewer gear teeth than does the dynamic spline, and therefore the circular spline rotates past the dynamic spline during rotation of the wave generator plug, defining a gear ratio therebetween (for example, a gear ratio of 50:1 would mean that 1 rotation of the circular spline past the dynamic spline corresponds to 50 rotations of the wave generator). Harmonic gear drive unit 34 is thus a high-ratio gear transmission; that is, the angular phase relationship between first spline 44 and second spline 46 changes by 2% for every revolution of wave generator 50.
Of course, as will be obvious to those skilled in the art, the circular spline may instead have slightly more teeth than the dynamic spline has, in which case the rotational relationships described below are reversed.
Still referring to
Output hub 40, which acts as an output member, is fastened to second spline 46 by bolts 68 and may be secured to camshaft 18 by a camshaft phaser attachment bolt 70 extending through an output hub axial bore 72 in output hub 40, and capturing a thrust washer 74 and a filter 76 recessed in output hub 40. Filter 76 is a band-type filter that may be a screen or mesh and may be made from any number of different materials that are known in the art of oil filtering. Radial run-out between housing 52 and output hub 40 is limited by a single journal bearing interface 78 between housing 52 (input hub) and output hub 40. Journal bearing interface 78 is lubricated by oil supplied to an oil groove 79 formed in either output hub 40 (shown) and/or in housing 52 (not shown). The supply of oil to oil groove 79 will be discussed in more detail later. Output hub 40 is retained within housing 52 by a back plate 80 disposed within housing 52 and by a snap ring 82 disposed in an annular groove 84 formed in housing 52. Back plate 80 includes a central back plate bore 81 extending axially therethrough to allow at least a portion of output hub 40 and/or camshaft 18 to extend through back plate 80.
Bias spring 42 is captured axially between output hub 40 and back plate 80. An inner spring tang 86 of bias spring 42 is engaged with output hub 40 while an outer spring tang 88 of bias spring 42 is engaged with back plate 80 by a pin 90 which is fixed to back plate 80. In the event of a malfunction of electric motor 36, bias spring 42 is biased to back-drive harmonic gear drive unit 34 without help from electric motor 36 to a predetermined rotational position of second spline 46. The predetermined position may be a position which allows internal combustion engine 10 to start or run, and the predetermined position may be at one of the extreme ends of the range of authority or intermediate of the phaser's extreme ends of its rotational range of authority. For example, the rotational range of travel in which bias spring 42 biases harmonic gear drive unit 34 may be limited to something short of the end stop position of the phaser's range of authority. Such an arrangement would be useful for internal combustion engines requiring an intermediate park position for idle or restart.
In order to lubricate various elements of camshaft phaser 22, oil is provided thereto under pressure from an oil source 94 of internal combustion engine 10. Oil source 94 may provide oil to camshaft phaser 22 through radial camshaft drillings 96 which communicate with a camshaft counterbore 98 which forms a camshaft annular oil passage 100 with a portion of camshaft phaser attachment bolt 70. The oil then passes from camshaft annular oil passage 100 to an output hub annular oil passage 102 formed radially between output hub axial bore 72 and a portion of camshaft phaser attachment bolt 70. Radial camshaft drillings 96, camshaft annular oil passage 100, and output hub annular oil passage 102 together define a supply passage. The oil is then filtered by passing radially through filter 76 to prevent contaminants that may be present in the oil from passing further into camshaft phaser 22. After passing through filter 76 the oil is then communicated to a tube 104 which extends generally radially outward from output hub axial bore 72 to oil groove 79 thereby allowing the oil to be communicated to oil groove 79 where the oil lubricates journal bearing interface 78. Journal bearing interface 78 allows oil to pass thereby in both an axial direction toward back plate 80 and an axial direction away from back plate 80. Oil that passes by journal bearing interface 78 in the axial direction away from back plate 80 is allowed to lubricate harmonic gear drive unit 34, bearing 60, and coupling 62 through gravity and dynamics of camshaft phaser 22 in use. In order for the oil to reach coupling 62, axial housing passages 106 may be provided through the axial end of housing 52.
Drive member 28 may not be compatible with the oil used to lubricate camshaft phaser 22, consequently, a dry zone 108 may be formed within engine cover 32. Drive member 28 is located within dry zone 108 which is substantially free of the oil used to lubricate camshaft phaser 22. Dry zone 108 is formed by a sealing arrangement which may comprise an engine cover to camshaft phaser seal 110 and an engine to camshaft phaser seal 112. The sealing arrangement may also comprise an engine cover to motor seal 114 and a back plate to housing seal 116. The sealing arrangement will be described in greater detail in the paragraphs that follow.
Referring now to
Engine to camshaft phaser seal 112 provides a seal between camshaft support 19 and back plate 80. A camshaft support bore 126, which is cylindrical, extends into camshaft support 19 in a coaxial relationship with camshaft 18. Engine to camshaft phaser seal 112 includes an engine to camshaft phaser seal supporting body 128 which is ring shaped and secured coaxially within camshaft support bore 126, for example, by a press fit. Engine to camshaft phaser seal supporting body 128 may be made of a rigid material, for example, metal or plastic. Engine to camshaft phaser seal 112 also includes an engine to camshaft phaser seal lip seal 130 which extends radially inward from engine to camshaft phaser seal supporting body 128. Engine to camshaft phaser seal lip seal 130 may be molded and bonded to engine to camshaft phaser seal supporting body 128 and may be made of an elastomeric or rubber-like material, for example only, Nitrile Butadiene Rubber (NBR), Viton®, or silicone. Engine to camshaft phaser seal 112 may also include an engine to camshaft phaser seal dust lip seal 131 which extends radially inward from engine to camshaft phaser seal supporting body 128 and may be made from the same material as engine to camshaft phaser seal lip seal 130. Engine to camshaft phaser seal dust lip seal 131 protects engine to camshaft phaser seal lip seal 130 from external contamination that may have undesirable effects on engine to camshaft phaser seal lip seal 130. Back plate 80 includes a back plate sealing body 132 for radially mating with engine to camshaft phaser seal lip seal 130. Back plate sealing body 132 is ring-shaped and extends axially away from back plate 80 into camshaft support bore 126 in a coaxial relationship with camshaft support bore 126. Back plate sealing body 132 is sized to elastically deform engine to camshaft phaser seal lip seal 130 when assembled in order to provide an oil-tight seal between back plate sealing body 132 and engine to camshaft phaser seal lip seal 130.
Engine cover 32 includes an engine cover bore 134 extending therethrough in a substantially coaxial relationship with camshaft 18. Electric motor 36 is received coaxially within engine cover bore 134 and fixed to engine cover 32 to prevent relative rotation between engine cover 32 and electric motor 36. Engine cover to motor seal 114, which may be an O-ring as shown, fits within an engine cover to motor seal groove 136 formed within the inner circumference of engine cover bore 134. Engine cover to motor seal 114 is compressed radially between engine cover to motor seal groove 136 and electric motor 36. In this way, oil that exits the end of housing 52 which is proximal to electric motor 36 is prevented from exiting engine cover 32 between the interface of engine cover 32 and electric motor 36. It should be noted that engine cover to motor seal 114 is a static seal, unlike engine cover to camshaft phaser seal 110 and engine to camshaft phaser seal 112 which are dynamic seals, since there is no relative movement between engine cover 32 and electric motor 36. Alternatively, engine cover to motor seal 114 may be arranged to interface in an axial sealing arrangement between electric motor 36 and engine cover 32.
Back plate to housing seal 116, which may be an O-ring as shown, fits within a back plate to housing seal groove 138 formed on the outer circumference of back plate 80. Back plate to housing seal 116 is compressed radially between back plate to housing seal groove 138 and housing 52. In this way, oil is prevented from entering dry zone 108 through the interface of back plate 80 and housing 52. It should be noted that back plate to housing seal 116 is a static seal, unlike engine cover to camshaft phaser seal 110 and engine to camshaft phaser seal 112 which are dynamic seals, since there is no relative movement between back plate 80 and housing 52.
In addition to engine cover to camshaft phaser seal 110, engine to camshaft phaser seal 112, engine cover to motor seal 114, and back plate to housing seal 116; the sealing arrangement may also comprise a motor to motor shaft seal 140. Motor to motor shaft seal 140 is positioned radially between electric motor 36 and motor shaft 64 to prevent oil from migrating into electric motor 36. As with engine cover to camshaft phaser seal 110 and engine to camshaft phaser seal 112, motor to motor shaft seal 140 is a dynamic seal since motor shaft 64 rotates relative to the rest of electric motor 36.
Reference will now be made to
The operation of camshaft phaser 22 will now be described with reference to
The embodiment described herein describes harmonic gear drive unit 34 as comprising outer first spline 44 which may be either a circular spline or a dynamic spline which serves as the input member; an outer second spline 46 which is the opposite (dynamic or circular) of first spline 44 and which serves as the output member and is coaxially positioned adjacent first spline 44; a flexspline 48 disposed radially inwards of both first and second splines 44, 46 and having outwardly-extending gear teeth disposed for engaging inwardly-extending gear teeth on both first and second splines 44, 46; and a wave generator 50 disposed radially inwards of and engaging flexspline 48. As described, harmonic gear drive unit 34 is a flat plate or pancake type harmonic gear drive unit as referred to in the art. However, it should now be understood that other types of harmonic gear drive units may be used in accordance with the present invention. For example, a cup type harmonic gear drive unit may be used. The cup type harmonic gear drive unit comprises a circular spline which serves as the input member; a flexspline which serves as the output member and which is disposed radially inwards of the circular spline and having outwardly-extending gear teeth disposed for engaging inwardly-extending gear teeth on the circular spline; and a wave generator disposed radially inwards of and engaging the flexspline.
While the gear drive unit of camshaft phaser 22 has been described herein as harmonic gear drive unit 34, it should now be understood that the invention encompasses camshaft phasers using any known gear drive units. Other gear drive units that may be used within the scope of this invention include, by non-limiting example, spur gear units, helical gear units, worm gear units, hypoid gear units, planetary gear units, and bevel gear units.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but rather only to the extent set forth in the claims that follow.
