Patent Application
20090044770
The present invention relates to hydraulic valve timing devices of internal combustion engines; more particularly, to vane-type camshaft phasers; and most particularly, to an improved compressible wiper seal for disposal in rotor vanes and/or stator lobes of a camshaft phaser.
Camshaft phasers 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 retard chambers as required to meet current or anticipated engine operating conditions.
In a typical prior art vane-type camshaft phaser, also referred to herein simply as a cam phaser, the tip of each rotor vane and stator lobe is provided with a compressible radial seal for wiping the cylindrical wall of the opposite member, such as the stator wall and/or rotor hub, to prevent leakage around the rotor between the advance and retard chambers. Therefore, wiper seals provide a dynamically seal between two hydraulic chambers, which are pressurized in an alternating fashion. Typical cam phaser wiper seals consist of two components each made out of a different material.
A first known wiper seal utilizes a two-piece construction consisting of a plastic wiper blade and backing spring disposed within the vane or lobe to load the wiper blade against the stator or rotor surface.
A second known wiper seal utilizes a two-piece seal disposed in an axially extending groove formed in the vane or lobe tip. Typically, an elastomeric spring is over-molded onto a rigid plastic wiper-shaped substrate. The elastomeric spring is molded in place onto the substrate during an elastomer insert molding process where the wiper-shaped substrate is exposed to molding pressures and temperatures. This configuration requires two separate manufacturing steps, one successive assembly step, and two different materials to provide a one-piece wiper seal subassembly, creating undesired manufacturing and subassembly costs as well as complexity.
What is needed in the art is an improved wiper seal that is of one-piece construction manufactured in a single step and that does not need to be assembled.
What is further needed in the art is an improved wiper seal that is simple and inexpensive to manufacture, is durable, and is self-actuating to urge itself continuously against a stator or rotor wall.
It is a principal object of the present invention to reduce the complexity of a wiper seal and to improve the reliability of a wiper seal in a vane-type camshaft phaser.
It is a further object of the present invention to reduce the manufacturing cost of a cam phaser wiper seal, to reduce processing steps and process cycle time, and to reduce the amount of error-proofing needed on the assembly line.
Briefly described, a wiper seal for preventing leakage of oil between advance and retard chambers formed between rotor vanes and stator lobes in a vane-type camshaft phaser in accordance with the invention combines a spring element and a wiper element in a monolithic structure and is manufactured from a single composite material by injection molding. The wiper seal is provided at the tip of each rotor vane and/or stator lobe of a vane-type camshaft phaser for varying the timing of combustion valves in an internal combustion engine. The vane-type camshaft phaser includes a rotor having a plurality of vanes disposed in a stator having a plurality of lobes, the interspersion of vanes and lobes defining a plurality of alternating valve timing advance and valve timing retard chambers with respect to the engine crankshaft. During rotation of the rotor within the stator, the tips of the vanes sweep past concave cylindrical walls of the stator, and the tips of the lobes sweep past convex cylindrical walls of the rotor hub. In the case where wipers are provided at both the stator wall and rotor hub positions, each vane and lobe tip is provided with an axially extending groove. The wiper seal in accordance with the invention is disposed in the groove for wiping the opposing wall, such as the stator wall and/or rotor hub. The wiper seal in accordance with the invention is designed as a potential drop-in replacement for existing prior art wiper seals, thereby eliminating the need for changing the design of the vane and lobe tips.
The wiper seal in accordance with the invention includes a spring element that is designed as a cantilevered arm and provides sealing pressure to the wiper element. The cantilevered arm is positioned on the back of the wiper element and comes in contact with the wiper element at a secondary contact point during installation forming an arch. The secondary contact point increases a sealing force across the face of the wiper compared to prior art wiper seals thereby providing improved reliability. The secondary contact point also distributes the sealing force across the face of the wiper evenly and prevents over-travel and over-stress of the cantilevered arm.
The wiper seal in accordance with the invention further includes a rib element that extends the back of the wiper element and that is positioned under the cantilevered arm. The rib element assists in preventing over-compression of the cantilevered arm and in preventing tangling of a plurality of wiper seals during handling and shipping.
By designing the wiper seal in accordance with the present invention as a monolithic structure manufactured from a single composite material during a single manufacturing step, the manufacturing costs and process cycle time can be reduced compared to prior art wiper seals based on elimination of plasma treatment and elastomer insert molding steps. Lower cost materials can be used in the wiper seal in accordance to the present invention compared to prior art, wiper seals due to elimination of the exposure of the material to plasma treatment and elastomer insert molding pressures and temperatures. Furthermore, it is believed that the composite material used in accordance with the present invention exhibits better wear characteristics against aluminum than material used for known prior art wiper elements.
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
Referring to
The wiper seal 30 includes a wiper element 40, a compressible spring element 50, and a rib element 60. Wiper seal 30 combines wiper element 40, spring element 50, and rib element 60 in a monolithic structure that is formed of a single material.
In a currently-preferred method of manufacturing, wiper seal 30 is formed from a plastic composite material, such as the thermoplastic compound polyphthalamide (PPA). PPA is a thermoplastic synthetic resin of the nylon family suitable for high temperature applications. PPA is a high performance polyamide having a modulus higher than 1000 kpsi (kilo pound per square inch), and inheriting good high-temperature dimensional stability. PPA is classified as engineering plastic and is commercially available from a variety of suppliers. Although, PPA is a presently preferred material, it is understood that other materials may be used. The material used to manufacture wiper seal 30 should be selected according to wear characteristics, is stress and strain capabilities, ductility, and flexibility. Since wiper seal 30 is operated at elevated temperatures, maximum dimensional stability and, therefore, minimum post-mold shrinkage, is essential. To insure that no dimensional bias is introduced by moisture, wiper seal 30 should contain less than about 0.3% moisture by weight when measured. Wiper seal 30 is preferably manufactured as a monolithic structure during a single manufacturing step, such as an injection molding process. Other manufacturing processes including multi-step manufacturing processes may be used to form wiper seal 30.
Still referring to
Spring element 50 includes a cantilevered arm 52 that extends generally vertically from inner surface 428 of wiper element 40 proximate to second end 424 and next to second tab 46. Also, cantilevered arm 52 extends axially towards first end 422 and first tab 44 of body 42 without reaching first tab 44. Even though not shown, cantilevered arm may also extend from inner surface 428 proximate to first end 422 and next to first tab 44. Cantilevered arm 52 includes a tip 54 positioned opposite from the point where arm 52 extends from body 42 of wiper element 40. Cantilevered arm 52 operates as a spring to provide sealing pressure to wiper element 40. Cantilevered arm 52 is illustrated in
In a relaxed position shown in
Rib element 60 includes a central rib 62 that extends vertically from inner surface 428 of body 42 of wiper element 40 towards cantilevered arm 52 and is axially positioned between first tab 44 and second tab 46, preferably centered between both tabs. Central rib 62 may be positioned between inner surface 428 of wiper element 40 and cantilevered arm 52 of spring element 50. Central rib 62 is enclosed by the arch formed by cantilevered arm 52 and may be in contact with the arm 52 in the installed position, as shown in
Height 66 is determined by the degree of compression of cantilevered arm 52. Central rib 62 has a width 68 that may be less or the same as width 48 of body 42. Rib element 60 assists in preventing over-compression of cantilevered arm 52. Furthermore, rib element 60 prevents tangling of a plurality of wiper seals 30 during handling and shipping.
Referring now to
Another alternate design of wiper seal 30 is illustrated in
Cantilevered arm 52 is shown in
As shown in
All wiper seals illustrated including a rib element 60, such as wiper seal 30, 310, and 320, may be manufactured without a rib element 60 and all wiper seals illustrated without rib element 60, such as wiper seal 330, 340, and 350, may be manufactured including rib element 60. Furthermore, all other shown alternative features may be applicable to any of the shown wiper seal configurations.
In some camshaft phasers, wiper seals are required on only the rotor vanes and are omitted from the stator lobes. Such phasers are fully comprehended by the present invention.
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.
