Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2000-03-22
2001-07-10
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090310
Reexamination Certificate
active
06257186
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for adjusting the phase angle of a camshaft of an internal combustion engine with a drive gear for driving a camshaft accommodated in a coaxial arrangement relative to the camshaft and with an electric motor for rotating the camshaft relative to the drive gear, wherein the electric motor has two concentrically arranged rotors, of which the one is connected to the camshaft and the other to the drive gear.
To obtain optimum values for fuel consumption and exhaust emissions in different areas of the internal combustion engine's operating characteristics, the valve timing must be varied in dependence of different operating parameters. An elegant manner of varying the valve timing is realized by rotating the camshaft relative to its driving gear. The camshaft of an internal combustion engine is usually driven by a sprocket wheel, which is connected to the crankshaft via a drive chain, or by a drive gear configured as a pulley, which is connected to the crankshaft via a toothed belt.
DESCRIPTION OF THE PRIOR ART
In GB 2 221 513 A a camshaft adjusting mechanism is described wherein an electric motor operates a set of link arms turning the camshaft relative to its driving gear. To this purpose an actuating element carrying the pivoted arms is shifted in axial direction. This solution however involves considerable expense and play on account of the large number of bearings.
In DE 41 10 088 C1 and DE 39 29 619 A1 adjusting mechanisms are described wherein an adjusting element is provided between a member connected to the camshaft and a member connected to the drive gear, which element has two helical threads meshing with corresponding threads of the camshaft or the drive gear. By axially displacing this adjusting element, the camshaft can be rotated relative to its drive gear. Axial displacement of the adjusting element may be obtained by actuating a hydraulic plunger which is operated in dependence of the desired adjustment. The disadvantage of this solution is that the forces required can only be attained with a large hydraulic plunger necessitating considerable constructional expense. Moreover, a comparatively large quantity of oil is required for operating the plunger, which will necessitate a suitably sized pump and thus add to the engine load. As a further drawback of this known type of mechanism, adjustment of the camshaft is possible only between two extreme positions.
An electric adjusting device also is presented in DE 41 01 676 A1, wherein an electric motor is provided for displacing the adjusting element by means of a threaded spindle. As the adjusting element rotates essentially at camshaft speed, an axial thrust bearing must be provided between the electric motor and the adjusting element, which takes up the relative movement between the non rotating and the rotating member. In the above solution, the thrust bearing is more or less permanently subject to load throughout the entire operating period, since the torsional moments acting between drive gear and camshaft will produce a force acting on the adjusting element in axial direction. For this reason the thrust bearing is a critical component which will limit the useful life of the engine. A similar solution is disclosed in DE 33 20 835 A1, wherein the same disadvantages are encountered.
In DE 36 07 256 A a mechanism is described, wherein a stepping motor is provided for adjusting the camshaft, which stepping motor being connected to both camshaft and drive gear. As the stepping motor must take up the entire driving torque for the camshaft, such a solution cannot be achieved within reasonable limits of expense.
This disadvantage is avoided in the adjusting device disclosed in DE 41 10 195 for two structural components connected in their rotating drive, in which an electric motor with a stationary stator is driving a planet carrier supporting a couple of concentric planet gears. Such a stationary electric motor however always has to run during operation, adjustment of the two structural components relative to one another being carried out by faster or slower run. To adjust such a device is complicated.
EP 0 596 860 A discloses a device for adjusting the valve opening times in which the camshaft has a hollow configuration and comprises an inner shaft. The cams are bipartite, wherein each single cam section can be turned relative to the other by a determined angle. The rotation of the two cam sections is executed by a revolving electric motor, which is supplied via slip rings. Similar solutions are disclosed in U.S. Pat. Nos. 5,417,186 and 4,770,060.
A former suggestion of the applicant, published in EP-A 0 903 471 presents an adjusting mechanism for the phase angle of a camshaft with a planetary gear set, in which the adjustment is executed by an electric motor that is supplied with current by means of slip contacts.
Adjusting the phase angle of a camshaft by means of an electric motor proved an advantageous solution in practical operation. To supply the electric motors by means of slip contacts however is the weak point of such devices.
SUMMARY OF THE INVENTION
It is an object of the present invention to avoid these drawbacks and to develop a device as described above in such a manner that slip rings, slip contacts and the like can be omitted.
It also is an object of the invention to have a first coil arrangement non rotatably linked to one of the rotors, said first coil arrangement electromagnetically interacting with a stationary coil arrangement in order to induce or to transmit the energy needed for the operation of the electric motor.
The main point of the invention is that the electric motor that occasions the adjustment of the camshaft is energized without any contact by a coil arrangement. The energy may hereby either be transmitted like in a transformer via an air core or be induced like in a generator. Since the electric motor is a rotating member, the following description will not distinguish stator and rotor of the electric motor, as this is generally the case, but will rather speak of two rotors. One of the rotors is basically connected to the camshaft, whereas the other rotor is connected to the drive gear which may be configured as a sprocket wheel or as a pulley wheel for receiving a toothed belt. Since the driving torque needed to adjust the phase angle of the camshaft is quite big, and since, on the other side, the adjusting angle is quite small, it commonly is necessary to provide a set of gears that converts a relative movement of the two rotors of some revolutions into a rotation of the camshaft relative to the drive gear of approximately 15° to 20°.
In a particularly preferred embodiment of the present invention the set of gears is composed of a rigid, circular hollow gear and of a flexible externally toothed gear, which is accommodated on a roller bearing with an elliptical inner ring that meshes with the hollow gear. Such a gear is commonly called a Harmonic-Drive. As already described above, a quite big step-up ratio is needed between the electric motor and the member it is driving, which may be achieved by such a set of gears. If for example the teeth of the hollow gear amount to 100 and the teeth of the elliptical gear amount to 98, the step-up ratio obtained is of about 1:50. Since this is achieved by a single-stage gear without using planet gear or the like, the device according to the invention may thus be of an extremely compact design.
To have a rotor directly connected to the elliptical inner ring of the roller bearing constitutes a particularly favorable solution in this connection. It is also of advantage when the internally toothed gear has entered a rigid connection with a rotor. Thanks to these measures, a simple and compact layout may be achieved.
The disadvantage of the Harmonic Drives of the art is that they only can be loaded to a limited extent because of their relatively fine teeth. Such gears are particularly sensitive to impulsive loads. In order to avoid this disadvantage, the gear may be made of the followin
Dykema Gossett PLLC
Patel Vinod D
TCG Unitech Aktiengesellschaft
Walberg Teresa
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