Protection method for an engine having a variable valve timing controller and protection apparatus for the same

The variable valve timing controller has an electric motor which rotates a phase converter. When the electric motor is locked for some reason, the over-load more than the predetermined value is applied to a motor shaft and the phase converter. In such a case, a pin connecting the motor shaft with the phase converter is sheared at a notch. Thus, a cam shaft and the phase converter were not locked, and breakage of a motor housing is prevented.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2003-59727 filed on Mar. 06, 2003, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a protection method and a protection apparatus for an engine having a variable valve timing controller. The variable valve-timing controller is referred to as a VVT controller hereinafter.

BACKGROUND OF THE INVENTION

JP-A-11-153008 shows a VVT controller which is driven by an electric motor. In this VVT controller, a sun gear of a planetary gearing is rotated by the electric motor, thereby a phase between a ring gear and a carrier is varied. The planetary gearing functions as a phase converter. The ring gear is driven by a driving shaft of an engine and the carrier is connected with a cam shaft. The ring gear is referred to an input member and the carrier is referred to an output member in this invention.

In this kind of the VVT controller equipped with the electric motor, the motor shaft and the cam shaft rotate together with keeping a mechanical connection. When the motor shaft is locked for some reasons, the cam shaft is also locked. In this situation, an over-load applied to the phase converter and the cam shaft may cause damages of the phase converter, the engine, and a motor housing. When the motor housing is broken, an engine oil may flow out.

SUMMARY OF THE INVENTION

An object of the present invention is to protect the engine from the damages described above and to prevent the engine oil from flowing out. In accordance with the object of the invention, when the motor is locked, the motor shaft is disconnected with the phase converter.

DETAILED DESCRIPTION OF EMBODIMENT

Referring to FIG.1throughFIG. 3, the first embodiment of the present invention is described hereinafter.

FIG. 1shows the VVT controller of the embodiment. The VVT controller is connected with a cam shaft1of an engine (internal combustion engine:not shown) so that an opening-closing timing of an intake valve or an exhaust valve is varied continuously during engine operation. The left side inFIG. 1is referred to the front side and the right side inFIG. 1is referred to the rear side for convenience in explaining the embodiment.

The VVT controller is comprised of a sprocket2which is correspond to an input member of the invention, a cam connecting member3which is correspond to an output member of the invention, a phase converter4for the sprocket2and the cam connecting member3, a coupling5, an electric motor6and the like. As shown inFIG. 1, the sprocket2, the cam connecting member3, the phase converter4and the coupling5are assembled integrally and disposed in a chain cover7. The electric motor6is fixed on the chain cover7by a bolt8.

The sprocket2is driven by an crankshaft through a chain and is rotatively supported by the cam connecting member3. The sprocket2rotates with the cam shaft1around a same axis.

The cam connecting member3is fixed on the front side of the cam shaft1by a bolt11in order to rotate together, and a pin12prohibits the relative rotation between the cam connecting member3and the cam shaft1.

The phase converter4is connected with the sprocket2and has a ring gear (an outer gear having gear tooth along an inner periphery)13and a sun gear (an inner gear having gear tooth along an outer periphery)14. The sun gear14engages the ring gear13and has an eccentric axis to the cam shaft1.

The ring gear13is disposed in a hollow portion formed at the front side of the sprocket2and fixed between the ring plate15and sprocket2by a screw16.

An eccentric sleeve17is connected with a center portion of the sun gear14in such a manner that the sun gear14rotates eccentrically with engaging with the ring gear13. The inner surface of the eccentric sleeve17is rotatively supported by the outer surface of the cam connecting member3.

A plurality of the cylindrical bosses18are circularly formed at the rear surface of the sun gear14. The bosses18protrude rearward and are engaged with concave portions19which are formed on the front surface of the cam connecting member3. The inner diameter of the concave portions19is larger than the outer diameter of the bosses18. A rotational force of the sun gear14is transmitted to the cam connecting member3through the bosses18with absorbing the eccentric gap.

The coupling5is comprised of a union22and a pin23, and the coupling5connects the motor shaft21and the eccentric sleeve17so that the rotational torque of the motor shaft21is transmitted to the eccentric sleeve17.

Referring toFIG. 2, a structure of the coupling5is explained. The union22is connected with the eccentric sleeve17in such a manner that the union22rotates with the eccentric sleeve17. A through hole24extends along a line which is orthogonal to the rotational axis in the union22.

The pin23is inserted into the through hole24and a motor shaft through hole25which extends along the line being orthogonal to the motor shaft21. The rotational torque of the motor shaft21is transmitted to the eccentric sleeve17through the pin23and the union22.

The union22and the eccentric sleeve17are of sliding to each other. If there is a gap between the axis of the motor shaft21and the axis of the union22, a sliding of the union22and the eccentric sleeve17absorbs the gap.

Covers26are disposed at both ends of the through hole24for preventing the broken pieces of the pin23from falling down to a chain when the pin23is sheared due to the over-load.

An electric motor6is of conventional design and is controlled by an control unit (not shown). The electric motor6of this embodiment have a motor housing31fixed on a chain cover7by a bolt8, a yoke32supported by a motor housing31, a stator33fixed in the yoke32and a rotor34rotated by an excitation. The rotor34is connected with the motor shaft21through a bearing35and a rotational force of the rotor34is derived from the motor shaft21.

When rotational speed of the electric motor6is accelerated, a rotation of the cam shaft1is advanced more than the rotation of the sprocket2. That is, the rotational speed of the sun gear14is faster than that of the sprocket2, and the cam shaft1rotates to the advance direction.

On the other hand, when the rotational speed of the electric motor6is decelerated, the rotational speed of the sun gear14is slower than that of the sprocket2, and the cam shaft1rotates to the delayed direction.

As described above, the motor shaft21of the electric motor6is rotated with the cam shaft1via the coupling5, the sun gear14of the phase converter4and the cam connecting member3. When the motor shaft21is locked, the motor shaft21is mechanically disconnected with the phase converter4to protect the engine.

The VVT controller of the first embodiment has a safety mechanism40which breaks the connection between the motor shaft21and the phase converter4when a over-load is applied to the motor shaft21and/or the phase converter4.

As shown inFIGS. 2 and 3, the safety mechanism40is comprised of a notch41formed on the surface of the pin23. The shearing force is applied to the notch41. In this embodiment, two notches41are formed. The shape of the notch41is not limited to the shape shown inFIG. 3, other shape is acceptable. The pin23is sheared at the notches41when the a certain amount of rotational load is applied. The certain amount of rotational load is determined not to damage the engine and is determined according to type of a vehicle or an engine.

While the engine is operated, the motor6is energized and the cam shaft1and the motor shaft21rotate together. When the rotor34and the motor shaft21are locked for some reason, the motor shaft21is driven by the rotational torque transmitted from the sprocket2and a rotational load lager than the predetermined value is applied. The pin23is sheared at the notches41and the motor shaft21and the phase converter are disconnected with each other. That is, the safety mechanism40is operated.

Thus, even if the electric motor6is locked, the cam shaft1and the phase converter4are not locked. The phase converter4and the engine therefore avoid the breakage. The engine torque from the sprocket2is not transmitted to the electric motor6, and the motor housing31avoid the breakage thereof. The oil leakage from the motor housing31is prevented.

A second embodiment of the present invention is described hereinafter.

FIG. 4shows the coupling5and the safety mechanism40of the second embodiment.

The safety mechanism40is disposed between the motor shaft21and the union22and is comprised of a clutch mechanism42which disconnect the motor shaft21from the union22.

As shown inFIG. 4, the clutch mechanism42is comprised of a V-shaped outer hole43on the surface of the motor shaft21, an inner hole44at inner peripheral of the union22with confronting to the outer hole43, a ball45engaging with the outer hole43and inner hole44and a spring46biasing the ball43toward the outer hole43.

A diameter of the ball43is larger than the depth of the outer hole43. The half of the ball43extends off the outer hole43and engages the inner hole44. The diameter of the inner hole44is large enough to accept the half of the ball43biased by the spring46.

When some trouble is happened in the electric motor6and the motor shaft21is locked under the operation of the engine, the motor shaft21is driven by the rotational torque through sprocket2and an over-load is applied to the phase converter4and the motor shaft21. The ball45is thereafter disengaged with the outer hole43so that the safety mechanism40is operated.

Thus, even if the electric motor6is locked, the cam shaft1and the phase converter4are not locked. The phase converter4and the engine therefore avoid the breakage. The engine torque from the sprocket2is not transmitted to the electric motor6, and the motor housing31avoid the breakage thereof. The oil leakage from the motor housing31is prevented.

In the embodiments described above, the safety mechanism40is disposed between the motor shaft21and the coupling5. The safety mechanism40can be disposed in the coupling5or between the coupling5and the phase converter4.

The axis of the motor shaft21can be offset to the axis of the cam shaft1.

Even in the VVT controller wherein the motor shaft21does not rotate with the cam shaft1, the safety mechanism40can be disposed.

The safety mechanism40can be displaced to an electric safety device. In the electric safety device, a sensor such as a rotation sensor detects the rotational speed of the electric motor6. When the sensor detects the trouble of the electric motor6, the motor shaft21and the phase converter4are disconnected each other by an actuator (not shown) actuated according to a signal from the sensor.