Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2002-07-15
2004-02-03
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090150, C464S160000, C251S012000
Reexamination Certificate
active
06684834
ABSTRACT:
BACKGROUND
This invention pertains to a device to change the timing of gas exchange valves in an internal combustion engine, and it is particularly advantageous to implement in rotating piston positioning devices with a lightweight design that are used to adjust the angle that a camshaft is rotated relative to a crankshaft.
A device to change the timing of gas exchange valves in an internal combustion engine is known from DE 196 23 818 A1, with this device defining a class and being designed as a rotating piston positioning device to adjust the angle that a camshaft is rotated relative to a crankshaft, with the device having a lightweight design, and being located at the drive end of a camshaft that is held in the cylinder head of the internal combustion engine. In principle, this device, also identified as a tilting-vane positioner, is designed as a hydraulic actuator that can be controlled in response to various operating parameters of the internal combustion engine, and is formed essentially of a drive member that is driven by a crankshaft of the internal combustion engine and a driven member that is fixed to the camshaft of the internal combustion engine. The drive member is made up of a drive pulley that contains at least two hydraulic working chambers formed within a hollow cylindrical lightweight metal stator with at least two intermediate radial walls, including two ferrous metal sidewalls. In contrast to this, the driven member in this device is provided in the form of a vane wheel formed in its entirety of a lightweight metal bolted axially to the camshaft by means of a central fastening screw. The vanes of this vane wheel extend radially into the working chambers of the drive pulley and divide each of the chambers into two opposing hydraulic pressure chambers. The drive member rotates external to the driven member, i.e. on the end of the camshaft and on the head of the central fastening screw. It transfers force to the driven member by means of the hydraulic pressure chambers formed within the device in such a way that by selectively or simultaneously charging these pressure chambers with a pressure medium, the driven member is rotated relative to, or fixed with respect to, the drive member. Consequently, the camshaft is rotated relative to the crankshaft.
However, a disadvantage to this known device is that the driven member, which is made of a lightweight metal, must be bolted to the camshaft with a high torque from the central fastening screw so as to transfer the drive torque effected by the crankshaft of the internal combustion engine through the drive member to the driven member and effectively to the camshaft. However, in a driven member made of a lightweight metal or a plastic, high torques lead to detrimental compressive deformations and high stresses, mainly in the conical zone of force at the fastening screw, such that the driven member can only be bolted to the camshaft using low torques to avoid these compressive deformations and stresses. Thus, the driven member is only suitable for transferring small drive torques or chain forces to the camshaft. Transfer of higher drive torques or chain forces to the camshaft is only possible by increasing the friction between the driven member and the camshaft with the help of expensive coatings or surface treatments, or by using additional shape-locking elements at the contact surfaces, which are expensive as well. Even if the driven member is bolted with a higher torque to the camshaft so as to transfer high drive torques, the larger radial and axial play between the drive member and the driven member in the device, which are necessary due to the compressive deformations and the high stress, have the disadvantage that in addition to the increased danger of seizing, and thus the possibility of failure of the device, increased leakage of pressure medium occurs within the device that negatively influences the positioning speed and its ability to hold its angle. Moreover, a general disadvantage of the known device designed as a tilting-vane positioner is that the hole pattern for the pressure medium channels feeding the pressure chambers of the device, said pattern to be incorporated into the device's driven member, which for the most part is designed as a one-piece tilting vane wheel, is technically complicated to manufacture, relatively speaking. Also, it is relatively difficult to brace by hand against the torque applied to the fastening screw when installing the driven member onto the camshaft.
SUMMARY
It is therefore the object of this invention to provide a device to change the timing of gas exchange valves in an internal combustion engine, in particular a rotating piston positioning device to adjust the angle that a camshaft is rotated relative to a crankshaft, with the device having a driven member made of a lightweight metal or a plastic and that can be bolted to the camshaft using a central fastening screw, and the driven member being provided such that the frictional lock between it and the camshaft is increased so as to transfer higher drive torques to the camshaft without resulting in compressive deformations and high stresses or having to implement expensive measures, and wherein said driven member is characterized by a simplified means of manufacturing the pressure medium channels that feed the pressure chambers of the device and is characterized by a simple way to brace against the torque applied to the fastening screw.
According to the invention, this object is met by a device in which the conical zone of force from the fastening screw to the driven member is designed into a special collar made of a compression-resistant material on which the driven member can be locked axially, radially and circumferentially by means of shape-locking or by friction, and through which the driven member can be bolted to the camshaft without deforming.
A useful further development of the device according to the invention is for the collar positioned within the driven member to preferably be made of a steel material or similar high strength material, and at the same time for it to be a prefabricated pressure medium distributor containing the pressure medium channels leading from the pressure medium feed and discharge ports of the device to their associated pressure chambers. However, it is also possible to use the collar positioned within the driven member for the exclusive purpose of preventing compressive deformations and stresses and to allocate the function of pressure medium distribution to the camshaft and to the device.
Another feature of the device according to the invention is that the collar has ends that extend beyond the axial width of the device and that its exterior surface beyond the driven member forms the external radial bearing of the drive member. Using steel covers as side walls for the driven member, one of which can at the same time be designed as a chain pulley or a belt pulley, each cover having a center hole that fits over the collar, higher bearing forces can be withstood by the radial bearings. At the same time, it is no longer possible for thermally caused changes to occur in the bearing play between the drive member and the driven member, thanks to the materials being the same. Moreover, it is advantageous to, at the same time, design the extended ends of the collar to have a means at one end to brace against the torque applied to the fastening screw and a means at the other end to center the device on the camshaft. This enables the transfer of higher drive forces from the crankshaft to the camshaft by means of the driven member by increasing the torque on the fastening screw, as well as enables the exact positioning of the device on the camshaft. However, an alternative option here is to design the collar without extended ends and to form the external radial bearing of the driven member by the exterior surfaces of the head of the fastening screw and the end of the camshaft, for example.
One preferred embodiment of the device according to the invention is further characterized in that t
Chang Ching
INA-Schaeffler KG
Volpe and Koenig P.C.
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