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[0001] The invention relates to a device for controlling the adjustment of the relative rotary position between a crankshaft and a camshaft of an internal combustion engine.
[0002] In reciprocating four-stroke piston internal combustion engines, the camshaft is driven at half the rotational speed of the crankshaft in order to operate the charge cycle valves (intake and exhaust valves). The control times of the charge cycle valves, in particular of the intake valves, influence the achievable maximum average gas pressure in the cylinders and thus the torque and its location in the usable rotational speed band as well as the power achievable at the rated rotational speed. With control times which are constant in all the operating ranges of the internal combustion engine it is not possible to fulfill the requirements for an optimum torque profile over the engine speed, a high level of power and low exhaust gas emissions, in particular in internal combustion engines with a wide speed band, for example in spark ignition engines. For this reason, the control times are varied as a function of operating parameters, in particular, the engine speed by, for example, changing the rotary position of the camshaft with respect to the crankshaft during engine operation. This is controlled or regulated as a function of operating characteristic variables, characteristic curves and/or characteristic diagrams. As it is irrelevant for the present invention whether control or regulation is carried out, below “regulate” will also be assumed mean “control” without referring to it each time.
[0003] DE 36 07 256 A1 discloses a device for the controlled adjustment of the relative rotary position of a driven machine part with respect to a driving machine part, or in particular the relative rotary position of a camshaft with respect to a crankshaft of an internal combustion engine. Here, the camshaft is driven by the crankshaft by means of a toothed belt and an externally toothed drive wheel. A servomotor is connected in each case directly, in a rotationally fixed fashion, to the camshaft via its drive shaft and on the other hand to the drive wheel via its casing so that a rotationally contollable connection of the camshaft and drive wheel is achieved by means of a holding torque which is provided by the servomotor. By activating the servomotor it is possible to change the relative rotary position of the drive wheel and the camshaft and thus of the crankshaft with respect to the camshaft. The servomotor acts like a clutch and changes only the rotary position without affecting the transmission ratio between the crankshaft to the camshaft. As the casing of the servomotor rotates with the drive wheel, the electrical power and the control signals however have to be transmitted by means of slip contacts. In addition, the mass of the servomotor increases the rotating masses of the camshaft and its drive, and thus the forces of inertia.
[0004] EP 0 254 058 A2 discloses an adjustment device for a camshaft for controlling the gas intake and exhaust valves of internal combustion engines. The camshaft is composed of a hollow external shaft and a hollow internal shaft mounted therein by means of bearings. While the control cams for some of the valves, the inlet valves or the outlet valves, are shrink-fitted onto the hollow external shaft, the cams for the other valves are rotatably mounted on the external shaft and connected for rotation with the hollow internal shaft. The adjustment device can change the relative rotary position of the internal shaft with respect to the external shaft and thus the rotary position of the exhaust valves with respect to the inlet valves over a limited rotary angle range. At the same time, the rotary positions of the external shaft and of the internal shaft change with respect to a drive wheel, which is driven by the crankshaft.
[0005] The device comprises a planetary gear mechanism in which the drive wheel serves as a planet gear carrier on which the planet gears are rotatably supported by means of planet gear bolts. The planet gears intermesh on the one hand with an annular gear, which is connected for rotation with the casing of a servomotor by means of a side plate, and on the other hand to a sun gear, which is mounted for rotation with the internal shaft. The motor shaft of the servomotor is also connected for rotation with the internal shaft, and thus to the sun gear. If the rotary position between the cams of the inlet valves and of the outlet valves is to remain unchanged while the internal combustion engine is operating, the servomotor is electrically controlled in such a way that actuating pulses which are opposed in terms of the direction of rotation are alternately applied to the servomotor. As a result, given a sufficiently high pulse frequency, a virtually rigid connection is formed between the external shaft and the internal shaft so that the planetary gear mechanism rotates locked with the servomotor and the drive wheel. In order to change the angular position, the servomotor must merely be controlled in such a way that its motor shaft is rotated. A fixed transmission ratio of the planetary gear mechanism, which does not influence the transmission ratio of the camshaft drive, determines to what degree the cams are rotated with respect to one another and in relation to the drive wheel. The servomotor may be controlled as a function of characteristic variables, which are dependent on specific operating states of the internal combustion engine. As a result, the angular position of the cams with respect to one another can be set or controlled in accordance with the engine operating conditions. Here too, the servomotor increases the mass of the inertia of the camshaft.
[0006] It is the object of the present invention to provide a device for adjusting the relative rotary position between a crankshaft and a camshaft which reduces the installation space for the drive of the camshaft, and in which the servomotor is fixed in relation to the internal combustion engine.
[0007] In a device for controlling the relative rotary positions of a crankshaft and a camshaft of an internal combustion engine, a drive wheel is connected to the camshaft by way of an angular position control mechanism including a planetary gear arrangement with an annular gear connected to, or part of, the drive wheel, a sun gear mounted on the camshaft and at least one planetary gear disposed between, and in engagement with, the annular gear and the sun gear and rotatably supported on a planetary gear carrier which is rotatable over a certain angular range by a stationary servomotor for controlling the angular positions of the camshaft relative to the crankshaft.
[0008] The step-down ratio i
[0009] The installation space can also be reduced by forming the drive wheel and the annular gear of the planetary gear mechanism in one piece. In the same way, the gear mechanism wheel for controlling the relative rotary position of the camshaft with respect to the crankshaft can be integrally formed with the planet carrier. The relative rotary position between the crankshaft and the camshaft is changed by the electric servomotor in that it rotates the gear mechanism wheel through a desired angular distance by means of its motor shaft and an output element, said distance being predefined by the control device as a function of engine operating parameters. All the transmission means, which are known from gear mechanism technology and are suitable, can be used as drive elements. A simple and expedient solution has proven to be a worm on the motor shaft of the servomotor, which intermeshes with the externally toothed gear mechanism wheel on the planet carrier. However, beveled gears or other gear mechanism elements, which result in actuating torques being transmitted with as little play as possible and a low level of noise, can also be used. It for example is possible to use obliquely toothed gear mechanism wheels, which can also be engaged together free of play with respect to one another.
[0010] The reaction torques of the planet carrier are supported on the casing by means of the servomotor. So that the position of the planet carrier is held even without a servomotor being energized, the servomotor can be equipped with a motor brake. A simple solution is provided if the servomotor adjusts the planet carrier by means of a self-locking gear mechanism, for example in that the gear mechanism wheel is formed as a gear which intermeshes with a worm on the motor shaft of the servomotor. As a result of the self-locking, the frictional forces are sufficient to hold the gear mechanism wheel, and thus the planet carrier, in position.
[0011] The actuating torques of the servomotor can be reduced in that the servomotor drives the gear mechanism wheel by means of a plurality of gear mechanism stages. In addition, it may be advantageous to load the gear mechanism wheel or a component connected thereto in the direction of a supporting torque by means of a pre-stressed spring element. When there is an actuating movement counter to the supporting force, the actuating torque is supported by the drive torque of the camshaft so that the spring element can be pre-stressed without an appreciable degree of expenditure. When adjustment is carried out in the direction of the supporting torque, counter to the drive torques, the servomotor is supported by the pre-stressed spring element so that an approximately similar actuating torque is obtained in both actuating directions.
[0012] Further advantages will become apparent from the following description of the invention on the basis of the drawing. The drawing illustrates an exemplary embodiment of the invention. The description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them to form appropriate further combinations.
[0013]
[0014]
[0015]
[0016] The device according to the invention is accommodated in a casing
[0017] An electric servomotor
[0018] The planet carrier
[0019] In order to retaine the position of the planet carrier
[0020] A corresponding, opposed, holding torque is generated at the actuating gear mechanism
[0021] The over-all step-down ratio between the crankshaft and the camshaft