Patent Application
20130312682
The invention relates to a triple-shaft adjustment mechanism comprising a drive part that can be connected to a drive shaft in a rotationally fixed manner, a driven part that can be connected to a driven shaft in a rotationally fixed manner, and an actuator that can be connected to an adjustment shaft in a rotationally fixed manner.
Triple-shaft adjustment mechanisms are used, for example, in internal combustion engines for adjusting the phase angles, primarily for adjusting the opening and closing times of the gas-exchange valves (camshaft adjuster, phase adjuster for actuator shafts for variable valve drives). The phase adjuster is here arranged as an actuator in a triple-shaft system. Primarily, the drive power that is discharged again via the driven shaft (e.g., camshaft) is fed to the triple-shaft system via the drive shaft (timing chain sprocket). The actuator is here arranged in the flow of power as a connecting element between the drive shaft and the shaft to be driven. It allows additional mechanical power to be coupled into the shaft system or to be discharged from this system via a third shaft (adjustment shaft) superimposed on the drive power. Therefore, the movement function (phase angle) specified by the drive shaft and relative to the driven shaft can be changed.
Examples for such triple-shaft adjustment mechanisms are wobble-plate mechanisms and internal eccentric mechanisms that are described, for example, in WO 2006/018080. Included here are also the shaft mechanism known from WO 2005/080757 and the mechanisms contained in US 2007/0051332 A1 and US 2003/0226534 A1.
Different phase adjusters are known from the prior art. For example, electromechanical camshaft adjusters are described in DE 10 2004 009 128 A1, DE 10 2005 059884 A1, and DE 10 2004 038 681 A1.
From DE 102 48 351 A1, an electromechanical camshaft adjuster is known in which the adjustment motor is connected by means of a detachable coupling to the adjuster mechanism. Through a corresponding design of the coupling, the torque that can be transmitted to the adjustment shaft can be limited. This then acts as a safety coupling.
One special case of a triple-shaft adjustment mechanism is a double-shaft arrangement in adjustment drives in which the drive shaft is mounted on the housing, i.e., power is transmitted only between the adjustment shaft and driven shaft. Such a device is used to convert a drive power of an actuator fed with high speed and low load into a driven power with low speed and high load and is used, for example, in speed-reduction devices for actuator drives in the automotive field and also in industrial applications, e.g., in robots.
To protect parts in the surroundings from undesired collisions of parts in the event of control errors by the actuating system, the adjustment range or the drive range is limited by defining the rotational angle of one of the three shafts relative to a second shaft or relative to the housing. For this purpose, a mechanical stop is used as an integral part of the device. In the known prior art of the camshaft adjuster, the stop is provided between the driven shaft and the drive shaft, because the adjustment shaft usually covers an angle of more than 360°.
In such a design, the adjustment shaft not directly limited in the adjustment angle or drive angle is then braked in the case where there is contact with the stop by means of the mechanism kinematics and the stiffness of the mechanism elements, as soon as the driven side reaches the limits of the rotational angle. Here, due to the extremely high loads, mechanism parts can be so strongly deformed that they collide with each other and cause the actuator to jam. Furthermore, mechanism parts can wear out prematurely or must be overdimensioned for normal operation, in order to also survive the high loads in the case of unbraked contact with the stop.
The objective of the invention is to construct a triple-shaft adjustment mechanism such that the effects of pulse loads that occur when there is contact with the stop in the actuator are damped such that jamming or damage of the mechanism is prevented.
The solution to meeting this objective is possible with a triple-shaft adjustment mechanism according to the invention through which the mechanism parts are decoupled in the case there is contact with the stop.
A triple-shaft adjustment mechanism initially comprises, in a known way, a drive part that can be connected to a drive shaft in a rotationally fixed manner, a driven part that can be connected to a driven shaft in a rotationally fixed manner, and an actuator that can be connected to an adjustment shaft of an actuator in a rotationally fixed manner. Between two of the three shafts, usually between the drive part and the driven part, there is a first mechanical stop for defining an adjustment angle between the drive shaft and the driven shaft.
According to the invention, an overload coupling integrated in the actuator is provided between the actuator and the drive part or between the actuator and the driven part.
The following description starts from an electromechanical camshaft adjuster with a shaft mechanism as an especially preferred embodiment with a flat construction. Obviously, the solutions here could be transferred to shaft mechanisms with a pot-shaped construction and also to other mechanism designs. The invention can also be transferred to other mechanism shapes in which the actuator has spur gear teeth.
The advantages of the invention can be seen especially in that a complete decoupling is possible without an additional mechanism part. Due to the high speeds of the adjustment shaft, only small loads occur on this shaft, so that “oversnapping,” that is, snapping of the adjustment shaft, appears to be an economical and space-saving solution for a slip coupling.
In one especially preferred embodiment, the overload coupling is formed such that the actuator has spur gear teeth with elasticity in the radial direction.
The elasticity can be formed, for example, by an elastic layer or also by elastic roller bodies, wherein, e.g., hollow balls or sleeves or roller bodies made from a material with lower elastic modulus can be used as the elastic roller bodies.
The solution according to the invention is based on soft-torsion teeth of the actuator. Due to the inertia of the adjustment shaft and the electric motor, if there is contact with the stop, a so-called collision moment is produced that also causes, in addition to the tangential tooth force, a radial tooth force in the teeth parts analogous to the normal angle of attack.
In the normal case, the radial stiffness of the actuator acts against this force. According to the invention, the radial elasticity must be dimensioned so that, starting from a certain magnitude of the radial force component of the transmitted torque (e.g., the collision moment), the teeth of two corresponding gearwheels yield to each other in the radial direction. The teeth then push tangentially under a high radial tension onto the tooth heads until they are pushed back into the tooth gaps again and the adjustment shaft snaps over.
Preferred embodiments of the invention are explained below with reference to the figures.
Shown are:
The rotational direction of the spur gear 03 is shown by an arrow 05. It can be seen that the teeth heads of the spur gear 03 yield in the radial direction and slide along the teeth heads of the internal teeth 02 before they intermesh again due to the elasticity of the teeth.
Through intentional reduction of the radial stiffness of the spur gear 03, oversnapping is permissible in the teeth 02, 04 in the case of an overload and the resulting stresses of the mechanism elements are reduced. The stiffness and thus the radial tensioning in the overload case is selected so that the affected mechanism parts can survive the oversnapping, at least for a defined period of time within the required service life of the actuator. Here, the teeth and/or the bearings must also not undergo any damage that could negatively affect the function. The design for a defined period of time is permissible, because the shown operating state occurs only under limiting conditions. On the other hand, the stiffness must be sufficiently high to be able to transfer the operating moments.
The oversnapping within the teeth 02, 04 can be viewed as complete, cyclic decoupling. The decoupling is cyclic, because the teeth heads jump back into teeth gaps as soon as they have slipped past each other and the mechanism is then no longer decoupled.
Between the outer ring 07 and the teeth 09 there is an elastic layer 11 that guarantees the radial elasticity of the spur-gear teeth 09. The elastic layer 11 can be a ring produced separately or a coating made from an elastomer. Someone skilled in the art can determine the required thickness and elasticity of the elastic layer 11 with reference to the specified material and mechanism data.
It has proven advantageous with regard to noise generation that the elastic layer is dimensioned so that, when the mechanism elements are operating normally, the teeth are in tension relative to each other slightly in the radial direction.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP11/72075 | 12/7/2011 | WO | 00 | 7/23/2013 |
