Patent Application
20090017920
The present invention relates to vane-type camshaft phasers for varying the phase relationship between crankshafts and camshafts in internal combustion engines; more particularly, to such phasers wherein a front cover plate clamps and seals against a stator; and most particularly, to a phaser having an improved front cover plate.
Camshaft phasers, also referred to herein simply as a cam phaser, for varying the phase relationship between the crankshaft and a camshaft of an internal combustion engine are well known. A prior art vane-type phaser 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 (OCV), in accordance with an engine control module, to either the advance or the retard chambers as required to meet current or anticipated engine operating conditions. In a typical prior art vane-type camshaft phaser a front cover clamps and seals against a stator to prevent internal oil leakage across the rotor arms.
A first known front cover is made from powdered metal steel and typically requires significant secondary high-level precision machining, deburring, grinding, and cleaning. Packaging requirements necessitate the front cover geometry to have thin sections that are typically difficult to execute in powdered metal tooling. Especially a section of the cover that interfaces with a bias spring in the assembled cam phaser is prone to cracking because of its thin cross-section. Typically, powdered metal front covers are manufactured to have a thickness of about 7 mm.
A second known front cover is die cast from aluminum, requires secondary high-level precision machining, and includes a steel insert at a lock pin seat wear interface. Compared to the first known front cover, the aluminum front cover provides mass savings and is not prone to cracking at the interface with the bias spring. However, the aluminum die cast front cover must be thicker than the powdered metal steel front cover, since additional length for adequate stator bolt thread engagement into aluminum threads is needed. This additional length is not acceptable for some applications where packaging is tight. A typical minimum thickness for a die cast aluminum front cover where the threads are cut directly into the aluminum is about 9 mm. Furthermore, the aluminum front cover typically clamps against the stator by tightening the bolts in several locations thereby generating local clamp load points. These local clamp loads may cause deflection to occur in the span of the cover between the bolts. Such deflection of the front cover may reduce the effective clamp load between cover and stator and may increase localized end clearances on top of the rotor arm, which in turn may increase internal oil leakage across the rotor arms.
What is needed in the art is an improved front cover that fulfills the packaging requirements.
What is further needed in the art is an improved front cover that effectively spreads the clamp load further out, reducing cover deflection and improving the effective clamp load between cover and stator.
It is a principal object of the present invention to provide mass reduction while providing a rigid sealing surface.
It is a further object of the present invention to enable the use of aluminum for manufacturing the front cover of a cam phaser to be packaged in the tightest application by increasing the thread strength of the bolt bores.
Briefly described, a vane-type camshaft phaser in accordance with the invention for varying the timing of combustion valves in an internal combustion engine includes a rotor having a plurality of vanes disposed in a stator having a plurality of lobes and a front cover plate that clamps and seals against the stator lobes. The front cover plate in accordance with the invention is die cast from aluminum followed by precision machining. The front cover plate includes four bolt bores for receiving stator bolts and a well that receives a hardened, ground bushing functioning as a lock pin seat. Formed steel threaded inserts are press fitted into the bolt bores of the aluminum front cover plate. This adds the required strength to the stator bolt threads to enable a shorter thread engagement, which in turn enables a thinner aluminum front cover plate that may be packaged in tight applications where prior art aluminum front covers cannot be used due to their greater thickness.
The steel threaded inserts not only provide a higher stiffness but also have a flanged shape that effectively spreads the clamp load generated during the tightening of the stator bolts further out preventing local clamp load points and, consequently, reducing cover deflection over the span of the front cover plate. Reduced cover deflection results in an improved effective clamp load between cover and stator and reduced oil leakage from valve timing advance and valve timing retard chambers formed by the rotor and the stator.
Furthermore, by utilizing steel inserts having a higher strength than aluminum materials, mass savings, and consequently manufacturing costs savings, compared to prior art powdered metal front covers are achieved by enabling the use of aluminum as material for the front cover plate while fulfilling packaging requirements for tight applications. Still further, the use of steel threaded inserts in accordance with the present invention enables the design of an aluminum die cast front cover plate that has the potential to work with the currently existing envelope at current or lower costs and that enables the use of the existing bias spring.
Therefore, the addition of steel threaded inserts pressed into the aluminum die cast front cover plate in accordance with the invention solves the problem of aluminum threat strength and localized clamp loads and, therefore, overcomes the shortcomings of prior art aluminum die cast front covers.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring to
Rear cover 12 and front cover plate 20 clamp against stator lobes 24 at opposite sides. Bolts 16 extend through bores 14 included in rear cover 12 and through bores 34 positioned in stator lobes 24 and the threaded ends of bolts 16 are received in threaded inserts 202 press fitted into bores 204 of cover plate 20. A hub of a target wheel 52 passes through front cover plate 20 and is fixed to rotor 21 for rotation therewith. Target wheel 52 spins in front of a sensor creating timed pattern of high/low signals for the purpose of sensing and/or controlling the position of phaser 10. A coiled bias spring 36 is disposed in a central well 38 formed in rotor 26 and is anchored to front cover plate 20 by tang 42 for urging rotor 26 to a predetermined rest position relative to the position of the stator, for example, fully retarded at engine shutdown. A locking pin mechanism 44 is received in a longitudinal bore 46 formed in an oversize vane 28 of rotor 26. A well 206 formed in front cover plate 20 (shown in
Referring now to
Threaded inserts 202 include shaft 226, flange 228, and threaded axial bore 232. Threaded inserts 202 are in a currently preferred embodiment manufactured from steel. The shaft 226 is provided with knurls 230, a series of small ridges or grooves on the surface of shaft 226, that enable to press fit steel threaded inserts 202 into bores 204. Knurls 230 support press fitting steel threaded inserts 202 into bores 204 and, thus, the convenient subassembly of front cover plate 20, and eliminate the need to grind or otherwise extensively machine the inner surface of bores 204 to receive the inserts 202. Flange 228 horizontally extends from shaft 226 orthogonally in all directions.
While flange 228 is shown to have a “D” shape, flange 228 may have any desired shape, such as circular, rectangular, square, hexagonal etc. Threaded bore 232 extends through shaft 226 and flange 228 and receives the threaded end of bolt 16 shown in
Referring now to
By utilizing steel threaded inserts 202 as in a currently preferred embodiment the problem of aluminum thread strength found in prior art die cast aluminum front covers is solved and, consequently, a more compact (smaller thickness 220) die cast aluminum front cover plate 20 is enabled, allowing for packaging of cam phaser 10 in tighter applications where prior art aluminum front covers will not fit. By allowing for a smaller thickness 220 steel threaded inserts 202 enable a mass savings compared to prior art front covers.
Furthermore, by horizontally extending shaft 226 and, thus, diameter of bore 204, flange 228 effectively spreads a clamp load created during tightening of bolts 16 beyond the diameter of bolt 16. Consequently, utilizing steel threaded inserts 202 enables the clamp load to be evenly distributed throughout an area surrounding bore 204 preventing local load points. Thus, deflection of front cover plate 20 is reduced and the overall effective clamping load of the front cover against the stator, compared to prior art die cast aluminum front covers, is improved.
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 will have full scope defined by the language of the following claims.
