Camshaft phaser

A camshaft phaser includes a stator having an inner wall with lobes extending radially inward and a stator flange extending radially outward, the stator flange having a plurality of apertures; a rotor coaxially disposed within the stator, the rotor having vanes interspersed with the lobes defining alternating advance chambers and retard chambers; a plurality of compression limiters extending through the apertures; a front cover which closes one end of the advance and retard chambers; a back cover which closes the other end of the advance and retard chambers; and a plurality of fasteners which extend through the apertures such that the fasteners apply a clamping load which clamps the stator between the front cover and the back cover such that the clamping load is transmitted through the compression limiters.

TECHNICAL FIELD OF INVENTION

The present invention relates to a camshaft phaser which selectively varies the phase relationship between a crankshaft and a camshaft of an internal combustion engine; more particularly to such a camshaft phaser which includes a stator having a plurality of inwardly extending lobes and a rotor having a plurality of outwardly extending vanes that are interspersed with the lobes to define advance and retard chambers; and still even more particularly to such a camshaft phaser which includes compression limiters which carry a clamping force between a back cover and a front cover which close off the advance and retard chambers.

BACKGROUND OF INVENTION

A typical vane-type camshaft phaser for changing the phase relationship between a crankshaft and a camshaft of an internal combustion engine 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. A back cover and a front cover are used to close off respective sides of the advance chambers and the retard chambers such that fasteners are used to clamp the stator between the front cover and the back cover. Engine oil is selectively supplied to either the advance or retard chambers and vacated from the other of the advance and retard chambers by an oil control valve in order to rotate the rotor within the stator and thereby change the phase relationship between an engine camshaft and an engine crankshaft.

German patent application publication number DE 102010010205 A1 to Gautier, hereinafter referred to as Gautier, shows an example of a camshaft phaser as previously described. Gautier teaches that a toothed pulley is spaced radially outward from the stator such that the toothed pulley is integrally formed with the back cover. The stator is clamped between the back cover and the front cover by a plurality of cover bolts which extend through apertures formed in each of the lobes of the stator in order to seal the advance and retard chambers between the back cover and the front cover. However, the stator of Gautier includes five lobes spaced substantially equally around the stator. Consequently, five equally spaced cover bolts provide a clamping force to clamp the stator between the back cover and the front cover. While five equally spaced cover bolts may be sufficient to clamp the stator between the back cover and the front cover, some camshaft phasers have stators with fewer lobes or with lobes that are not equally spaced. Consequently, cover bolts that pass through apertures in the lobes may not provide an adequate clamping force to provide a proper seal between the back cover and the stator and between the front cover in all stator designs. Furthermore, some camshaft phasers have stators with lobes that are not sufficiently large to accommodate cover bolts passing therethrough.

EP patent application publication EP 2058478 A1 to Sluka et al., hereinafter referred to as Sluka et al., shows another example of a camshaft phaser as previously described. Sluka et al. teaches a stator having an inner stator wall from which three lobes extend radially inward. The stator also includes an outer stator wall formed integrally therewith which is spaced radially outward from the outer stator wall such that the outer stator wall includes pulley teeth on the outer circumference thereof. The stator also includes a front cover formed integrally therewith which closes off one side of the advance chambers and the retard chambers. A back cover is clamped to the stator using cover bolts in order to close off the other side of the advance chambers and the retard chambers. A plurality of ribs extend radially between the inner stator wall and the out stator wall such that three of the ribs are sufficiently large to accommodate apertures for receiving cover bolts which clamp the front cover to the stator. The ribs extend axially the same distance as the inner stator wall; consequently, the ribs carry a clamping force from the cover bolts. While the stator of Sluka et al. allows the placement of the cover bolts to be independent of the location of the lobes of the stator, the ribs which receive cover bolts can be difficult to form in stators that are made using powder metal process. Furthermore, the ribs add weight to the stator which goes against the desire to minimize weight in order to maximize fuel efficiency of motor vehicles.

What is needed is camshaft phaser which minimizes or eliminates one or more the shortcomings as set forth above.

SUMMARY OF THE INVENTION

A camshaft phaser is provided for use with an internal combustion engine for controllably varying the phase relationship between a crankshaft and a camshaft in the internal combustion engine. The camshaft phaser includes a stator extending along an axis and having an inner stator wall, the inner stator wall including a plurality of lobes extending radially inward therefrom and a stator flange extending radially outward therefrom, the stator flange having a plurality of stator flange apertures extending therethrough. A rotor is coaxially disposed within the stator, the rotor having a plurality of vanes interspersed with the plurality of lobes defining a plurality of alternating advance chambers and retard chambers extending axially from a back end to a front end. The camshaft phaser also includes a plurality of compression limiters, each one of the plurality of compression limiters extending through a respective one of the plurality of stator flange apertures. A front cover closes the front end of the plurality of advance chambers and the plurality of retard chambers and a back cover closes the back end of the plurality of advance chambers and the plurality of retard chambers. The camshaft phaser also includes a plurality of fasteners, each one of the plurality of fasteners extending through a respective one of the plurality of stator flange apertures such that the plurality of fasteners apply a clamping load which clamps the stator between the front cover and the back cover such that the clamping load is transmitted through the plurality of compression limiters.

Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.

DETAILED DESCRIPTION OF INVENTION

In accordance with a preferred embodiment of this invention and referring toFIGS. 1-3, an internal combustion engine10is shown which includes a camshaft phaser12. Internal combustion engine10also includes a camshaft14which is rotatable about an axis16based on rotational input from a crankshaft (not shown) and a drive belt (not shown) driven by a plurality of reciprocating pistons (not shown). As camshaft14is rotated, it imparts valve lifting and closing motion to intake and/or exhaust valves (not shown) as is well known in the internal combustion engine art. Camshaft phaser12allows the timing between the crankshaft and camshaft14to be varied. In this way, opening and closing of the intake and/or exhaust valves can be advanced or retarded in order to achieve desired engine performance.

Camshaft phaser12generally includes a stator18, a rotor20disposed coaxially within stator18, a back cover22closing off one end of stator18, a front cover24closing off the other end of stator18, a camshaft phaser attachment bolt25for attaching camshaft phaser12to camshaft14, and a valve spool26which directs oil to control the rotational position of stator18relative to rotor20. The various elements of camshaft phaser12will be described in greater detail in the paragraphs that follow.

Stator18is generally cylindrical and includes an inner stator wall28which is annular in shape and centered about axis16. A plurality of lobes30extend radially inward from inner stator wall28, thereby defining a plurality of radial chambers32. In the embodiment shown, there are three lobes30defining three radial chambers32, however, it is to be understood that a different number of lobes30may be provided to define radial chambers32equal in quantity to the number of lobes30. The back axial face of inner stator wall28may include a stator back O-ring groove28awhich is annular in shape. The purpose of stator back O-ring groove28awill be described in greater detail late. Stator18also includes a stator flange34which extends radially outward from inner stator wall28such that stator flange34is centered about axis16and is annular in shape. Stator flange34includes a plurality of stator flange apertures36which extend therethrough in the same direction as axis16. Stator flange apertures36are preferably circular and are preferably equally spaced around stator flange34. While five stator flange apertures36have been illustrated (although not all labeled), it should be understood that a greater or lesser number of stator flange apertures36may be provided. It is important to note that inner stator wall28has a thickness in the axial direction, i.e. in the direction of axis16, that is greater than stator flange34as can best be seen inFIG. 3. Stator18also includes an outer stator wall38which extends radially outward from stator flange34such that outer stator wall38radially surrounds stator flange34. It is important to note that outer stator wall38has a thickness in the axial direction, i.e. in the direction of axis16, that is greater than stator flange34as can best be seen inFIG. 3. Consequently, an annular recess39is defined radially between inner stator wall28and outer stator wall38. The outer circumference of outer stator wall38includes a plurality of pulley teeth40which extend radially outward from therefrom. In this way, stator18, via pulley teeth40, is configured to engage complementary teeth of the drive belt (not shown) which transmits rotational motion from the crankshaft of internal combustion engine10to stator18. As shown, outer stator wall38is offset axially in the direction toward front cover24compared to inner stator wall28. However, outer stator wall38may alternatively be aligned with inner stator wall28or offset axially in the direction toward back cover22compared to inner stator wall28as may be required for pulley teeth40to mate appropriately with the drive belt.

Rotor20includes a central hub42with a plurality of vanes44extending radially outward therefrom and a central through bore46extending axially therethrough. The number of vanes44is equal to the number of radial chambers32provided in stator18. Rotor20is coaxially disposed within stator18such that each vane44divides each radial chamber32into advance chambers48and retard chambers50such that advance chambers48extend axially from a back end48ato a front end48band such that retard chambers50extend from a back end50ato a front end50b. The radial tips of lobes30are mateable with central hub42in order to separate radial chambers32from each other. Each of the radial tips of vanes44may include one of a plurality of wiper seals52to substantially seal adjacent advance chambers48and retard chambers50from each other. While not shown, each of the radial tips of lobes30may similarly include a wiper seal52.

Back cover22is sealingly secured, using fasteners illustrated as cover bolts54, to the axial end of stator18that is proximal to camshaft14. Tightening of cover bolts54prevents relative rotation between back cover22and stator18. Furthermore, a back O-ring56is located within stator back O-ring groove28aand is compressed between stator18and back cover22in order to aid in sealing the interface between stator18and back cover22. Back cover22includes a back cover central bore58extending coaxially therethrough. The end of camshaft14is received coaxially within back cover central bore58such that camshaft14is allowed to rotate relative to back cover22.

Similarly, front cover24is sealingly secured, using cover bolts54, to the axial end of stator18that is opposite back cover22. Cover bolts54pass through stator18and threadably engage front cover24, thereby clamping stator18between back cover22and front cover24to prevent relative rotation between stator18, back cover22, and front cover24. In this way, advance chambers48and retard chambers50are defined axially between back cover22and front cover24. Furthermore, front cover24includes a front cover O-ring groove24ain the face of front cover24which faces toward stator18such that front cover O-ring groove24ais annular in shape. A front O-ring60is located within front cover O-ring groove24asuch that front O-ring60is compressed between stator18and front cover24in order to aid in sealing the interface between stator18and back cover22.

In order to prevent distortion of either or both of back cover22and front cover24, due to the clamping load applied by cover bolts54, which could compromise the seal between back cover22and stator18and between front cover24and stator18, compression limiters62are provided. More specifically, compression limiters62extend from back cover22to front cover24by passing through stator flange apertures36. It should be noted that compression limiters62are partially located within annular recess39radially between inner stator wall28and outer stator wall38. Consequently, when cover bolts54are tightened, a clamp load is applied through compression limiters62. As shown, compression limiters62are preferably tubes which each define a compression limiter passage62aextending therethrough such that a respective cover bolt54passes through compression limiter passage62a. Compression limiters62are most preferably cylindrical tubes. Compression limiters62are preferably sized to interface with stator flange apertures36such that compression limiters62are prevented from moving relative to stator18in a direction across axis16, i.e. in a direction across a plane that is perpendicular to axis16. Consequently, compression limiters62may interface with stator flange apertures36in a slip fit relationship or in an interference fit relationship.

Camshaft phaser12is attached to camshaft14with camshaft phaser attachment bolt25which extends coaxially through central through bore46of rotor20and threadably engages camshaft14, thereby clamping rotor20securely to camshaft14. In this way, relative rotation between stator18and rotor20results in a change in phase or timing between the crankshaft of internal combustion engine10and camshaft14.

Oil is selectively supplied to advance chambers48and vented from retard chambers50in order to cause relative rotation between stator18and rotor20which results in advancing the timing of camshaft14relative to the crankshaft of internal combustion engine10. Conversely, oil is selectively supplied to retard chambers50and vented from advance chambers48in order to cause relative rotation between stator18and rotor20which results in retarding the timing of camshaft14relative to the crankshaft of internal combustion engine10. Advance oil passages64may be provided in rotor20for supplying and venting oil from advance chambers48while retard oil passages66may be provided in rotor20for supplying and venting oil from retard chambers50. Supplying and venting of oil to and from advance chambers48and retard chambers50may be controlled by a multi-way oil control valve, illustrated herein as valve spool26together with camshaft phaser attachment bolt25. Valve spool26is disposed within a valve bore68of camshaft phaser attachment bolt25such that valve spool26is displaced along axis16by an actuator70and a valve spring72. Movement of valve spool26opens and closes passages between an oil supply (not shown) which is typically the lubrication system for internal combustion engine10, a drain (not shown), advance oil passages64, and retard oil passages66in appropriate combinations to either advance rotor20relative to stator18, retard rotor20relative to stator18, or hold the position of rotor20relative to stator18. More specifically, valve spool26can be positioned to 1) supply oil to advance chambers48while simultaneously draining oil from retard chambers50in order to advance rotor20relative to stator18, 2) supply oil to retard chambers50while simultaneously draining oil from advance chambers48in order to retard rotor20relative to stator18, or 3) maintain the volume of oil in advance chambers48and retard chambers50in order to hold the position of rotor20relative to stator18. Various arrangements are well known in the art for supplying and venting oil in camshaft phasers, and consequently further details will not be discussed herein. However, further details are provided in United States Patent Application Publication No. US 2012/0255509 A1 to Lichti et al. which is incorporated herein by reference in its entirety. Alternatively, the multi-way oil control valve may be located external to camshaft phaser12as is known in the art, for example as shown in United States Patent Application Publication No. US 2010/0288215 A1 to Takemura et al. which is incorporated herein by reference in its entirety. In this way, rotor20rotates within stator18between a maximum advance position and a maximum retard position as determined by the space available for vanes44to move within radial chambers32.

By utilizing compression limiters62which pass through stator flange apertures36, stator18can be designed to place cover bolts54in appropriate quantity and locations in order to achieve an adequate clamp load on back cover22and front cover24to maintain sealing between back cover22and stator18and between front cover24and stator18. Utilizing compression limiters62which pass through stator flange apertures36also allows stator18to be made lighter in weight compared to stators that utilize radially extending ribs between the inner stator wall and the outer stator wall. In fact, the Inventors have realized a 25% reduction in weight of stator18with compression limiters62compared to a design which utilizes radially extending ribs between the inner stator wall and the outer stator wall. Furthermore, stator18with stator flange apertures36is more favorable to manufacturing stator18using powder medal process and stator18can also accommodate error proofing, i.e. Poka Yoke, features which could not be accommodated at all, or could not be accommodated without adding significant weight, in stator designs having radially extending ribs between the inner stator wall and the outer stator wall.

It should be noted that camshaft phaser12has been described herein in simplified form, and may include additional features that are known in the camshaft phaser art, such as, by way of non-limiting example only, a bias spring which biases rotor20to a predetermined position relative to stator18and one or more lock pins which mechanically lock rotor20in a predetermined position relative to stator18. Further features that may be used in camshaft phaser12are described in U.S. Pat. No. 8,056,519 to Cuatt et al. which is hereby incorporated herein by reference in its entirety.

While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited.