Variable valve timing controller

A variable valve timing controller has a phase adjusting mechanism. The phase adjusting mechanism includes a first rotating member and second rotating member which are respectively rotate in synchronization with a driving shaft and a driven shaft of an engine, a first arm rotatably connected with the first rotating member, and a second arm rotatably connected with the second rotating member and the first arm. In the first arm, a distance between connecting points is defined as a distance L1. In the second arm, a distance between connecting points is defined as a distance L2. A ratio L1/L2 is defined within a range of 0.5 to 2.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No. 2005-018546 filed on Jan. 26, 2005, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a variable valve timing controller which changes opening and closing timing of intake valves and/or exhaust valves of an internal combustion engine according to operating condition of the engine. The opening and closing timing is referred to as valve timing, the variable valve timing controller is referred to as the VVT controller, and the internal combustion engine is referred to as an engine hereinafter.

BACKGROUND OF THE INVENTION

The VVT controller is disposed in a torque transfer system which transfers the torque of the driving shaft of the engine to the driven shaft which opens and closes at least one of an intake valve or an exhaust valve. The VVT controller adjusts the valve timing of the valves by varying a rotational phase of the driven shaft to the driving shaft.

JP-2002-227616A shows a VVT controller having a sprocket which rotates in synchronism with the driving shaft, and a rotational phase adjusting mechanism which connects levers with the driven shaft via link arms. The phase adjusting mechanism converts a movement of the link arms into a relative rotational movement of the levers to the sprocket and varies the rotational phase of the driven shaft relative to the drive shaft.

In this conventional controller, guide balls held by the operation member are slidably engaged with a groove of the sprocket. When an engine torque is varied and some forces are applied to the phase adjusting mechanism, the operation member may slide in the groove so that the rotational phase of the driven shaft unnecessarily varies relative to the driving shaft.

U.S. Pat. No. 6,883,482B2, which is published on Apr. 26, 2005 and is not a prior art to the present invention, discloses a VVT controller in which a phase adjusting mechanism has a first arm connected with a sprocket through a revolute pair and a second arm connected with the first arm and the camshaft through revolute pairs. When some forces are applied to the arms, the arms tend to be bent in its width direction, so that durability of the VVT controller is deteriorated.

SUMMARY OF THE INVENTION

The present invention is made in view of the above matters, and it is an object of the present invention to provide the VVT controller which restricts rotational-phase fluctuations of the driven shaft if the force is applied to the phase adjusting mechanism, and has a high durability.

According to a VVT controller of the present invention, a revolute pair formed by a first arm and a first rotating member is defined as a first pair, a revolute pair formed by a second arm and a second rotating member is defined as a second pair, and a revolute pair formed by the first arm and the second arm is defined as a third pair. A distance between the first pair and the third pair is defined as a distance L1, a distance between the second pair and the third pair is defined as a distance L2. A ratio L1/L2 is established within a range of 0.5 to 2.

According to another aspect of the present invention, the third pair is arranged between the first pair and the second pair.

According to the other aspect of the present invention, in at least one of the first arm and the second arm, a phantom line connecting the first pair or the second pair with the third pair exists between both outer side peripheries of the first arm and/or the second arm in width direction thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2shows a VVT controller1according to the first embodiment of the present invention. The VVT controller1is disposed in a torque transfer system which transfers the torque of a crankshaft (not shown) to a camshaft2which opens and closes at least one of an intake valve or an exhaust valve. The crankshaft is a driving shaft and the camshaft2is a driven shaft in this embodiment. The VVT controller1adjusts the valve timing of the intake valve or the exhaust valve by varying the rotational phase of the camshaft2relative to the crankshaft.

The VVT controller1has a phase adjusting mechanism10, an electric motor30, and a motion converting mechanism40.

As shown inFIGS. 1 and 2, the phase adjusting mechanism10comprises a sprocket11, an output shaft16, a first arm20, and a second arm21in order to adjust a relative rotational phase between the sprocket11and the output shaft16, that is, a relative rotational phase between the crankshaft and the camshaft. InFIGS. 1,4, and6, hatching showing cross section is omitted.

The sprocket11has a supporting portion12, an input portion13having a larger diameter than that of the supporting portion12, and a first link portion14connecting the supporting portion12with the input portion13. The supporting portion12is rotatively supported by the output shaft16around a center axis “O”. A chain belt (not shown) runs over a plurality of gear tooth13aformed on the input portion13and a plurality of gear tooth formed on the crankshaft. When the torque is transmitted from the crankshaft to the input portion13through a chain belt, the sprocket11rotates clockwise around the center axis “O”, keeping the rotational phase unchanged relative to the crankshaft. The sprocket11, which corresponds to a first rotational member, rotates in synchronism with the crankshaft.

The output shaft16, which is the driven shaft, has a fixed portion17and a second link portion18. One end of the camshaft2is concentrically coupled to the fixed portion17by a bolt, and the output shaft16rotates around the center axis “O”, keeping the rotational phase to the camshaft2. That is, the output shaft16corresponds to the second rotational member which rotates in synchronism with the camshaft2.

The first and the second arm20,21are sandwiched between a cover15and the first link portion14together with elements41,44,45,47,49of the motion converting mechanism40. The cover15is fixed to the input portion13. The first arm20is connected with the first link portion14, forming a revolute pair therebetween. The second arm21is connected with the second link portion18and the first arm20, forming revolute pairs respectively. Thereby, the output shaft16rotates in the same rotational direction as the sprocket11. The output shaft16can rotate in an advance direction X and a retard direction Y relative to the sprocket11. The first arm20and the second arm21are connected with a movable member44of the motion converting mechanism40, forming revolute pairs respectively. Thereby, in the phase adjusting mechanism10, a revolute pair22formed by the first arm20and the second arm21is connected with the movable member44, so that the motion of the revolute pair22is converted into a relative rotational motion between the sprocket11and the output shaft16.

The electric motor30is a brushless motor which includes a housing31, bearings32, a motor shaft33, and a stator34. The housing31is fixed on the engine by means of a stay35. The housing accommodates two bearings32and the stator34.

The motor shaft33is arranged on the same axis as the sprocket11and the output shaft16, and is supported by the bearings32. The motor shaft33is connected with the input shaft46of the motion converting mechanism40through a joint36, so that the motor shaft33rotates around the center axis “O” with the input shaft46. The motor shaft33has a shaft body33aand a disk-shaped rotor33b. Multiple magnets37are disposed in the rotor33bnear the outer periphery. The magnets37are made from rare-earth magnets and are disposed around the center axis “O” at regular intervals.

The stator34is located around the rotor33b, and has a core38and a coil39. The core38is formed by stacking a plurality of iron plates and protrudes toward the motor shaft33. The core38has protrusions in same pitch, and the coil39is wound on each protrusions. The stator34generates a magnetic field around the motor shaft33based on the electric current supplied to the coil39. The electric current is controlled by an electric circuit (not shown) in order to apply a torque to the motor shaft33in a delay direction Y or an advance direction X.

As shown inFIGS. 2 and 4, the motion converting mechanism40comprises a guide member41, the movable member44, a ring gear45, the input shaft46, a planetary gear47, a bearing48, and a transfer member49.

The guide member41is a circular plate having the same axis as the output shaft16, so that the guide member41can rotate around the center axis “O” in both directions X and Y relative to the sprocket11. The guide member41is provided with two ellipse guide passages42which are arranged symmetrically to each other with respect to the center axis “O”. Each guide passage42penetrates the guide member41in its thickness direction, and arranged point symmetrically by 180° with respect to the center axis “O”. Each guide passage42is inclined relative to radial direction of the guide member41and linearly extends in such a manner that a distance from the center axis “O” varies.

The movable member44is provided in each of the guide passages42. The movable member44is cylindrical-shaped and is sandwiched between the first link portion14and the transfer member49in such a manner as to be eccentric relative to the center axis “O”. One end portion of the movable member44is respectively engaged with the corresponding guide passage42, forming a revolute pair therebetween. The other end portion of the movable member44is engaged with the first and the second arm20,21, forming a revolute pair therebetween.

As shown inFIGS. 2 and 5, the ring gear45is an internal gear of which addendum circle is inside of a dedendum circle, and is coaxially fixed on inner wall of the input portion13. The ring gear45can rotates around the center axis “O” with the sprocket11.

The input shaft46is connected with the motor shaft33of the electric motor30in such a manner as to be eccentric with respect to the center axis “O”. InFIG. 5, a point “P” represents a center point of the input shaft46.

The planetary gear47is an external gear of which addendum circle is outside of a dedendum circle.

A curvature radius of the addendum circle of the planetary gear47is smaller than a curvature radius of the dedendum circle of the ring gear45. The number of teeth of the planetary gear47is fewer than that of the ring gear45by one tooth. The planetary gear47is arranged inside of the ring gear45to be engaged with the ring gear45. The planetary gear47is capable of conducting the sun-and-planet motion with the ring gear45as the sun gear. The input shaft46is engaged with an inner periphery of the planetary gear47through the bearing48, so that the motor shaft33connected with the input shaft46is capable of rotating in the directions X, Y relative to the sprocket11.

The transfer member49is a circular plate which is coaxial to the guide member41and is arranged opposite side of the arm20,21across the guide member41. The transfer member49is engaged with and fixed to the guide member41, so that the transfer member49can rotate around the center axis “O” with the guide member41in the directions X, Y relative to the sprocket11. The transfer member49is provided with a plurality of cylindrical engaging holes49awhich penetrate the transfer member49in its thickness direction. Each of the engaging holes49ais around the center axis “O” at regular intervals. The planetary gear47is provided with a plurality of engaging protrusions47awhich are arranged around the center point “P” at regular intervals to be engaged with the engaging holes49a.

When the motor shaft33does not rotate relative to the sprocket11, the planetary gear47rotates with the sprocket11and the input shaft46, engaging with the ring gear45. The engaging protrusions47apush the inner periphery of the engaging holes49atoward the rotating direction, so that the transfer member49and the guide member41rotate, keeping the rotating phase relative to the sprocket11. At this moment, each of the movable members44does not slide in the guide passages42, and rotates with the guide member41, keeping a distance from the center axis “O”.

When the motor shaft33rotates in the retard direction Y relative to the sprocket11, the planetary gear47rotates clockwise inFIG. 5relative to the input shaft46to change the engaging position with the ring gear45. Since pressing force in which the engaging protrusions47apush the inner periphery of the engaging holes49ain the rotating direction is increased, the transfer member49and the guide member41rotate in the advance direction X relative to the sprocket11. At this moment, the movable members44slide in the guide passages42in such a manner as to be apart from the center axis “O”.

When the motor shaft rotates in the advance direction X relative to the sprocket11, the planetary gear47rotates anticlockwise inFIG. 5relative to the input shaft46to change the engaging position. Since the engaging protrusions47apush the inner periphery of the engaging holes49ain the anti-direction of the rotating direction, the transfer member49and the guide member41rotate in the retard direction Y relative to the sprocket11. At this moment, the movable members44slide in the guide passages42in such a manner as to be close to the center axis “O”.

As described above, the motion converting mechanism40converts the rotating motion of the electric motor30into the sliding motion of the movable member44. The electric motor30and the motion converting mechanism40correspond to a control means which controls the movement of the revolute pair22. The revolute pair22includes the movable member44.

Referring toFIGS. 1,2,6and7, a structure of the phase adjusting mechanism10is described hereinafter.FIG. 1shows a situation where the output shaft16is most retarded relative to the sprocket11, andFIG. 6shows a situation where the output shaft16is most advanced relative to the sprocket11.

In the phase adjusting mechanism10, the first arm20is an arch-shaped plate which is respectively provided both sides across the center axis “O”. The first link portion14is a circular plate which has the same axis as the output shaft16. The first arm20is connected with the first link portion14at two positions across the center axis “O” through a first shaft member23. The first shaft member23is a cylindrical column which is eccentric to the center axis “O”. The first link portion14and the first arm20form a revolute pair24, which is referred to as a first pair24hereinafter.

The second arm21is an arch-shaped plate which is respectively provided both sides across the center axis “O”. The second link portion18comprises two plates which project in radial direction from the fixed portion17. One end of the second arm21is connected with the second link portion18through a second shaft member25. The second shaft member25is a cylindrical column which is eccentric to the center axis “O”. The second link portion18and the second arm21form a revolute pair26, which is referred to as a second pair26hereinafter. The Distances from the center axis “O” to each second pair26are equal to each other.

The other end of the first arm20and the other end of the second arm21are connected with each other through the movable member44, whereby a revolute pair22is formed. The revolute pair22is referred to as a third pair22hereinafter.

In the phase adjusting mechanism10, when the distance between the center axis “O” and the movable member44is constant, the positions of the first to third pairs24,26,22do not change. Keeping the rotational phase relative to the sprocket11, the out put shaft16rotates with the camshaft2so that the rotational phase of the camshaft2relative to the crankshaft is kept constant.

When the distance between the center axis “O” and the movable member44is made longer, for example, when the phase adjusting mechanism10is varied from a mode shown inFIG. 6to a mode shown inFIG. 1, the first arm20rotates around the first shaft member23and the movable member44relative to the fist link portion14and the second arm21. At the same time, the second arm21rotates around the second shaft member25relative to the second link portion18so that the second pair26moves in the retard direction Y. Thus, the output shaft16rotates in the retard direction Y relative to the sprocket11in order to retard the rotational phase of the camshaft22relative to the crankshaft.

When the distance between the center axis “O” and the movable member44is made shorter, for example, when the phase adjusting mechanism10is varied from the mode shown inFIG. 1to the mode shown inFIG. 6, the first arm20rotates around the first shaft member23and the movable member44relative to the fist link portion14and the second arm21. At the same time, the second arm21rotates around the second shaft member25relative to the second link portion18so that the second pair26moves in the advance direction X. Thus, the output shaft16rotates in the advance direction X relative to the sprocket11in order to advance the rotational phase of the camshaft22relative to the crankshaft.

The structure of the phase adjusting mechanism10is described in detail hereinafter.

As shown inFIG. 8, a radial line connecting the first pair24and the center axis “O” and the other radial line connecting the second pair26and the center axis “O” form an angle θ. When the position of the third pair22(the movable member44) is moved by Δr, the angle θ is increased by Δθ. The angle θ corresponds to a relative rotational phase between the sprocket11and the output shaft16. The variation amount Δθ corresponds to the variation amount of the relative rotational phase with respect to the variation amount Δr of the third pair22. Thus, according as the variation amount Δθ per unit variation amount Δr becomes smaller, the variation in the relative rotational phase between the sprocket11and the output shaft16becomes smaller.

Under such knowledge, it becomes apparent that according as the difference in length between a distance L1 and a distance L2 becomes small, the variation amount Δθ per unit variation amount Δr becomes small. The distance L1 represents a distance between the first pair24and the third pair22in the first arm20, and the distance L2 represents a distance between the second pair26and the third pair22in the second arm21. As shown inFIG. 9, in the case that the ratio between the distance L1 and the distance L2 is within 0.5–2, the variation amount Δθ is relatively small. In the present embodiment, the first arm20and the second arm21has substantially the same shape so that the ratio L1/L2 is determined as 1.

FIG. 10shows a comparative example in which the first arm20and the second arm21are arranged in such a manner that the first pair24is positioned between the second pair26and the third pair22. The force applied to the movable member44is divided along the first arm20and the second arm21. Especially, the second arm21receives a large force. According to the inventor's study, when the third pair22is positioned between the first pair24and the second pair26, the force applied to each arm20,21becomes small. In the present embodiment, as shown inFIG. 11, the third pair22is poisoned between the first pair24and the second pair26so that the force applied to the movable member44is divided along the first arm20and the second arm21, which are relatively small.

FIG. 12shows a comparative example in which the first arm20and the second arm21are respectively curved in such a manner that a space exists on a line S connecting the first and second pairs24,26with third pair22. When a force is applied to the arms20,21through the pairs24,26,22, bending stress arises in the middle portion thereof along the outer periphery20a,21a. According to the inventor's study, in the case that the arms20,21are formed in such a manner that the line S exists within the outer periphery20a,21aas shown inFIG. 13, the bending stress becomes small. In the present embodiment, the arms20,21are respectively formed in such a manner that the line S exists within the outer periphery20a,21aas shown inFIG. 14.

According to the embodiment described above, the variation amount AO is small enough relative to the unit variation amount Δr, so that even if the position of the third pair22is varied due to the torque variation of the engine, the variation in the relative rotational phase between the sprocket11and the output shaft16is well restricted.

Furthermore, the force applied to the arms20,21is reduced, so that the arms20,21have high endurance.

The ratio L1/L2 can be determined other than 1 within the range of 0.5–2. Alternatively, in the case that the ratio L1/L2 is within the range of 0.5–2, the first pair24can be positioned between the second pair26and the third pair22as shown inFIG. 15. A space can be formed on the line S.

In the case that the third pair22is positioned between the first pair24and the second pair26, the ratio L1/L2 is determined outside of the range of 0.5–2. At least one of the arms20,21can be formed in such a manner that the space is formed on the line S.

In the case that the line S is within the outer periphery20a,21a, the ratio L1/L2 is determined outside of the range of 0.5–2. The first pair24can be positioned between the second pair26and the third pair22.

The guide passage42can be arc-shaped, spiral-shaped, or polygonal curve. The number of the guide passage42, the movable member44, and the arms20,21can be changed.

The electric motor30can be a brush motor or other type brushless motor. In the motion converting mechanism40, the motor shaft33can be directly connected with the guide member41.