Patent Application
20090090323
The present invention relates to a variable valve opening property internal combustion engine that can change the valve opening property such as the lift of the exhaust and/or intake valves of the engine depending on the operating condition of the engine.
Some of the recently developed gasoline and diesel internal combustion engines are fitted with a valve opening property varying mechanism to improve the output and fuel economy of the engine and reduce undesired emissions from the engine. A relatively known form of valve opening property varying mechanism is provided with low speed cams and high speed cams that can be interchangeably used depending on the operating condition of the engine. More recent attempts include those capable of continuously varying the valve opening properties (such as valve lift and valve timing) to further improve the transient response of the engine and to dispense with a throttle valve. See Japanese patent laid open publication No. 2005-291011.
According to a known variable valve opening property engine, a link mechanism is used for varying the valve opening property. In such a case, to prevent uncontrolled movement of the link member, it is desired to keep the link member in contact with an associated member of the valve actuating mechanism such as a cam and a rocker arm by biasing them toward each other by using a spring. In particular, because the relative position of such two members change in response to the varying of the valve opening property, it is necessary that the spring is arranged so as to accommodate such a relative movement.
When a spring member is used for controlling the movements of mutually abutting members, the mode of deformation of the spring member changes with the rotational speed of the engine. The deformation of the spring member should be effected in a stable manner because an unstable deformation of the spring member means a higher stress in the spring member and an increased load for the valve actuating mechanism.
In view of such problems of the prior art, a primary object of the present invention is to provide a variable valve opening property internal combustion engine that can favorably prevent uncontrolled movements of mutually abutting members of a valve opening property varying mechanism.
A second object of the present invention is to provide a variable valve opening property internal combustion engine that can ensure a stable mode of deformation to a spring member for preventing uncontrolled movements of mutually abutting members of a valve opening property varying mechanism.
A third object of the present invention is to provide a variable valve opening property internal combustion engine that can minimize the stress of a spring member for preventing uncontrolled movements of mutually abutting members of a valve opening property varying mechanism.
According to the present invention, such objects can be accomplished by providing a variable valve opening property internal combustion engine, comprising: an engine valve provided in a combustion chamber at least partly defined by a cylinder head of the engine and biased in a valve closing direction by a valve spring; a rocker arm pivotally supported by the cylinder head and having an end acting upon a valve stem of the engine valve for opening the engine valve; a camshaft rotatably supported by the cylinder head and carrying a cam; a roller link including a cam engaging part configured to engage the cam and a rocker arm engaging part engaging a slipper surface of the rocker arm, and adjustably supported by the cylinder head for a guided motion of the cam engaging part; a control link for adjusting a trajectory of the guided motion of the cam engaging part; an actuator for actuating the control link; and a spring member mounted on the cylinder head to apply a biasing force to a spring engaging part of the roller link to urge the cam engaging part against the cam; wherein the spring member is oriented such that a direction of a spring force of the spring member substantially coincides with a direction of a guided movement of the spring engaging part caused by the guided motion of the cam engaging part at least in a prescribed adjusted state of the control link.
When the direction of the spring force of the spring member substantially coincides with the direction of the guided movement of the spring engaging part caused by the guided motion of the cam engaging part, the efficiency of the transmission of the spring force to the spring engaging part can be maximized, and the cam engaging part of the roller link can be most effectively biased against the corresponding cam of the camshaft. Thereby, the jumping, bouncing and other uncontrolled movement of the roller link can be avoided. Also, the mode of deformation of the spring member is highly stabilized, and the fluctuations in the stress of the spring member can be minimized. In particular, because the direction of deformation of the spring member and the direction of the movement of the spring engaging part substantially coincide with each other, the force is most effectively utilized so that the relative lateral shifting of various members can be avoided, and the friction between such parts can be minimized. Furthermore, the load acting on the valve actuating mechanism can be minimized.
In a preferred embodiment of the present invention, the cam engaging part comprises a cam roller. Typically, the rocker arm engaging part of the roller link comprises a roller shaft disposed coaxially with respect to the cam roller, and this may be conveniently used for engaging the slipper surface of the rocker arm. Preferably, the cam roller also serves as the spring engaging part.
According to a most preferred embodiment of the present invention, the prescribed adjusted state of the control link corresponds to a minimum valve lift condition. Thereby, the transmission efficiency of the spring force of the spring member can be maximized, and the mode of deformation of the spring member can be stabilized in the minimum valve lift condition.
It is possible and may be desirable to provide a pair of spring members which are directed in the directions of movement of the spring engaging part at the time of minimum valve lift condition and at the time of maximum valve lift condition, respectively. However, when only one such spring member can be installed owing to the space or layout limitations, it is desirable to direct the spring member in the direction of the movement of the spring engaging part at the time of low valve lift condition because the travel of the spring engaging part is maximized at such a time. Thereby, the lateral deformation of the spring member and the friction between mutually abutting members can be minimized.
When the spring member is oriented or directed in the direction of the movement of the spring engaging part at the time of low valve lift condition, the transmission efficiency of the spring force may be reduced at the time of high valve lift condition. However, at the time of high valve lift condition, the spring force of the valve spring which normally urges the valve in the closing direction is directed substantially in the same direction as the movement of the spring engaging part so that the reduction in the transmission efficiency of the spring force of the spring member may be compensated by the spring force of the valve spring.
The spring member preferably consists of a coil spring, but may also consist of a torsion bar. When the spring member consists of a torsion bar, the torsion bar should be arranged such that the deflection of the torsion bar may be maximized and the maximum biasing may be produced at the time of low valve lift condition.
According to a particularly preferred embodiment of the present invention, the rocker arm engaging part of the roller link comprises a roller shaft extending coaxially from an axial end of the cam roller, and this may be conveniently used for engaging the slipper surface of the rocker arm. Also, in the particularly preferred embodiment, the control link may be pivotally supported by a control link pivot shaft extending in parallel with the camshaft and supporting a control shaft located at a prescribed distance from the control ink pivot shaft and extending in parallel with the camshaft, and the roller link may be pivotally supported by the control shaft so that the guided motion of the cam engaging part may be defined by an arcuate path centered around the control shaft. Typically, the actuator comprises a rotary actuator fixedly mounted on the cylinder head, and the control link comprises a sector gear in a gearing connection with a gear mounted on an output shaft of the actuator.
Now the present invention is described in the following with reference to the appended drawings, in which:
a is a fragmentary side view of the valve opening property varying mechanism in a minimum valve lift condition;
b is a fragmentary side view of the valve opening property varying mechanism in a maximum valve lift condition;
a is a fragmentary side view corresponding to
b is a fragmentary side view corresponding to
a is a view similar to
b is a view similar to
a is a view similar to
b is a view similar to
a is a graph showing the stress of the spring member when the spring member is oriented or directed in the direction of the movement of the spring engaging part at the time of low valve lift condition; and
b is a graph showing the stress of the spring member when the spring member is oriented or directed in the direction of the movement of the spring engaging part at the time of high valve lift condition.
The illustrated engine consists of an automotive in-line four cylinder engine, and includes a cylinder head 1 defining a combustion chamber for each cylinder and fitted with a pair of exhaust valves 2 in the combustion chamber. The cylinder head 1 is also incorporated with a valve actuating mechanism essentially consisting of a camshaft 4 formed with cams 3, a rocker arm 6 interposed between the valves 2 of each cylinder and the corresponding cam 3, and a valve spring 7 normally urging each valve 2 in a closing direction. The cylinder head 1 further includes a pair of intake valves 8 for each cylinder, and, although not shown in the drawings, the valve actuating mechanism further includes a rocker arm for each cylinder and a valve spring for each intake valve, the rocker arms for the intake valves 8 being actuated by the cams of the same camshaft or the cams of an intake valve camshaft provided separately from that for the exhaust valves.
The illustrated camshaft 4 is rotatably supported by cam holders 11 mounted on the upper surface of the cylinder head 1 in the form of upright walls by using threaded bolts, and a base plate 13 is attached to the upper surfaces of the cam holders 11 so as to connect them with one another. Thus, the cam holders 11 define a valve actuating chamber for each cylinder.
This cylinder head 1 is incorporated with a valve opening property varying mechanism essentially consisting of a link mechanism actuated by a rotary actuator 14 mounted on an upper surface of the base plate 13 for controlling the opening property of each exhaust valve 2. The rotary actuator 14 may comprise an electric motor and a reduction gear unit.
As shown in
The link mechanism further comprises a roller link 22 provided for each cylinder. The roller link 22 comprises a base portion 28 rotatably supported by the control shaft 20, a pair of arms 29 extending from the base portion 28 and a cam roller 31 supported between the free ends of the arms 29 so as to be rotatable around an axial line in parallel with the control shaft 20. The cam roller 31 engages the corresponding cam 3 of the camshaft 4. A pair of roller shafts 32 extend coaxially from the cam roller 31 and project laterally from either side of the roller link 22, and engage slipper surfaces 33 of the rocker arm 6 of the corresponding cylinder (
As best illustrated in
As shown in
Thus, as the camshaft 4 turns, each cam 3 engages the corresponding cam roller 31, and the resulting pivotal movement of the roller link 22 causes the exhaust valves 2 to be actuated via the rocker arm 6. Furthermore, as the rotary actuator 14 is actuated, the gear link 21 turns around the pivot shaft 23 thereof (see
In the idling condition or at a low speed operation of the engine, it is desired that the valve lift is reduced. To accomplish this, the gear link 21 is turned in a fully counterclockwise direction as shown in
On the other hand, in a high speed and/or high load operating condition, the valve lift may be desired to be increased. In such a case, the gear link 21 is turned in a fully clockwise direction as shown in
a and 5b are vertical sectional views of the valve opening property varying mechanism. As shown in
More specifically, in the low valve lift condition (where the link angle is zero, for instance), as the cam 3 turns, the cam roller 31 turns around the control shaft 20 in the direction indicated by an arrow, and the coil spring 41 undergoes a corresponding compressing and extending movement. At this time, the biasing direction of the spring force (Fspg) of the compression coil spring 41 substantially coincides with the direction of the movement of the cam roller 31. Therefore, the compressing and extending movement is effected in a highly stable manner. Also, the transmission efficiency of the spring force of the compression coil spring 41 is maximized. In other words, the spring force of the compression coil spring 41 is most effectively utilized as the force for urging the cam roller 31 against the dam 3.
Conversely, in the high valve lift condition (where the link angle is 60 degrees, for instance), as the cam 3 turns, the cam roller 31 turns around the control shaft 20 in the direction indicated by an arrow, and the coil spring 41 undergoes a corresponding compressing and extending movement. At this time, the biasing direction of the spring force (Fspg) of the compression coil spring 41 substantially differs from the direction of the movement of the cam roller 31. Therefore, the compressing and extending movement is effected in a somewhat unstable manner. Also, the transmission efficiency of the spring force of the compression coil spring 41 is minimized. In other words, the spring force of the compression coil spring 41 is least effectively utilized as the force for urging the cam roller 31 against the dam 3.
a and 6b show a second embodiment of the present invention. The parts corresponding to those of the previous embodiment are denoted with like numerals without repeating the description of such parts. In this embodiment, the orientation of the compression coil spring 61 is altered from that of the previous embodiment. More specifically, the biasing direction of the spring force (Fspg) of the compression coil spring 61 is made to substantially coincide with the direction of the movement of the cam roller 31 in the high valve lift condition illustrated in
a and 7b show a third embodiment of the present invention. The parts corresponding to those of the previous embodiments are denoted with like numerals without repeating the description of such parts. In this embodiment, the shape of the roller link 22 and the pivot point of the roller link 22 are modified from the first embodiment. In this embodiment also, the biasing direction of the spring force (Fspg) of the compression coil spring 71 substantially coincides with the direction of the movement of the cam roller 31 in the low valve lift condition (where the link angle is zero, for instance). Therefore, in this case, the compressing and extending movement is effected in a highly stable manner, and the transmission efficiency of the spring force of the compression coil spring 71 is maximized in the low valve lift condition (where the link angle is zero, for instance).
As can be best appreciated from the embodiment illustrated in
For this reason, it is more desirable to orient the axial line of the compression coil spring 71 so as to coincide with the direction of the movement of the cam roller 31 in the low valve lift control as is the case with the embodiments illustrated in
a is a graph showing the average value and swing of the stress that is produced in the compression coil spring 41 when the compression coil spring 41 is oriented in such a manner that the biasing direction of the spring force (Fspg) of the compression coil spring 41 substantially coincides with the direction of the movement of the cam roller 31 in the low valve lift condition.
The swing of the stress in the coil spring is significantly greater in
The illustrated embodiment may be summarized as given in the following. In a variable valve opening property internal combustion engine, a control shaft is supported by a control link which is in turn is pivotally supported by a cylinder head, and a roller link is pivotally supported by the control shaft. The roller link is provided with a cam roller that engages a cam of a camshaft and a roller shaft that engages a slipper surface of a rocker arm. The arcuate movement of the cam roller centered around the control shaft varies the swing of the rocker arm and hence the valve lift in dependence on the position of the control shaft. A compression coil spring is interposed between a part of the cylinder head and a side of the cam roller facing away from the cam. The coil spring is oriented such that a direction of a spring force (Fspg) substantially coincides with a direction of a guided movement of the cam roller, preferably in a low valve lift condition.
In the foregoing description of the embodiment of the present invention, a coil spring made of steel were used for urging each cam roller against the corresponding cam, but other forms of springs such as a torsion bar and pneumatic springs may also be used, and springs made of different materials such as rubber may also be used.
Although the present invention has been described in terms of preferred embodiments thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims.
The contents of the original Japanese patent application on which the Paris Convention priority claim is made for the present application and the contents of any related prior art mentioned in the disclosure are incorporated in this application by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-262026 | Oct 2007 | JP | national |
Reference should be made to the following copending patent application(s) filed on the same day as the present application, and the contents thereof as well as the contents of any related prior art mentioned therein are hereby incorporated in this application by reference. 12/______ filed August ______, 2008 (our ref: F1360)
