Patent Application
20070277755
Referring now to
As illustrated in
Intake valves 2, 2 as engine valves are operative to open and close a pair of intake ports, not shown, which are formed in cylinder head 1. Each of intake valves 2, 2 has an open position in which intake valve 2 opens the intake port and a closing position in which intake valve 2 closes the intake port. Intake valves 2, 2 is slidably held in cylinder head 1 through a valve guide, not shown. Intake valve 2 is biased toward the closing position by valve spring 9. Valve spring 9 is arranged between a spring retainer fixed to the vicinity of the stem end of intake valve 2, namely, the vicinity of an upper end of intake valve 2 as shown in
Drive shaft 3 extends in a fore-and-aft direction of the engine. Drive shaft 3 has axis X and is driven by a crankshaft of the engine so as to rotate about axis X. Drive shaft 3 receives input torque from the crankshaft through a driven sprocket, not shown, that is mounted to one end portion of drive shaft 3, and a timing chain, not shown, that is wound on the driven sprocket. Drive shaft 3 has drive cam 10 which is fixedly disposed on an outer circumferential surface of drive shaft 3.
Single drive cam 10 is provided for each cylinder of the engine. Drive cam 10 is integrally formed with drive shaft 3 and rotatable about axis X of drive shaft 3 in synchronization with the crankshaft of the engine. Drive cam 10 has a generally cocoon shape in a side view as shown in
As shown in
As shown in
Each of hydraulic lash adjusters 5, 5 is of a known type. Hydraulic lash adjuster 5 includes a closed-ended cylindrical body 5a fixedly fitted to cylindrical mount hole la that is formed in cylinder head 1, and plunger 5b that is disposed in body 5a so as to be slidable in an axial direction of body 5a. Plunger 5b has a hydraulic chamber therein and a communication hole on a lower end portion of plunger 5b. The hydraulic chamber is communicated with a higher pressure chamber within body 5a through the communication hole. A check valve is disposed within the higher pressure chamber and biased to close the communication hole. When, under operation of the engine, plunger 5b is downwardly moved by the other end portion of swing arm 4, the hydraulic pressure in the hydraulic chamber is increased to open the check valve and supply the higher pressure chamber with a hydraulic pressure. At this time, plunger 5b is forced to move upwardly so that a clearance between the one end portion of swing arm 4 and the stem end of the corresponding intake valve 2 is adjusted to zero.
As seen from
Central groove 6a is formed into a generally U-shape in side view as shown in
Motion transmission mechanism 7 includes rocker arm 11 which is swingably supported on control cam 21 as explained later, roller 14 which is contacted with drive cam 10, roller shaft 17 which supports roller 14, and a pair of links 15, 15 which connect rocker arm 11 and rocker cams 6, 6.
Specifically, rocker arm 11 is bent to form a generally arcuate shape in side view as shown in
One end portion 12 of rocker arm 11 has at least a pair of support walls for supporting roller shaft 17. In this embodiment, a pair of support walls 12a, 12a are provided as shown in
As seen from
Each of link rods 15, 15 is pressed into a generally C-shape in cross-section in view of weight reduction and facilitation in forming operation. Link rod 15 has one end portion 15a which is connected with each of bifurcated end portions 13 of rocker arm 11 through pin 18 and pivotally supported at end portion 13. One end portion 15a is bifurcated as shown in
In thus-constructed motion transmission mechanism 7, roller shaft 17, rocker arm 11, link rods 15, 15 and rocker cams 6, 6 are in positive motion connection with each other. That is, rocker cams 6, 6 are forced to swing in both of a clockwise direction and a counterclockwise direction by motion transmission mechanism 7.
The control mechanism includes control shaft 20 arranged parallel to drive shaft 3, control cam 21 disposed on control shaft 20, an actuator, not shown, which operates control shaft 20 in positive and reverse rotational directions depending on an engine operating condition, and an electronic controller, not shown, which controls the actuator.
Control shaft 20 extends in the fore-and-aft direction of the engine. As seen from
Control cam 21 is disposed in a predetermined position on an outer circumferential surface of control shaft 20 and integrally formed with control shaft 20. There is provided one control cam 21 per cylinder. As shown in
The actuator may be electrically operated and may include an electric motor and a speed reducer. The actuator is so constructed as to operate control shaft 20 in the positive and reverse rotational directions and hold control shaft 20 in a predetermined rotational position thereof depending on the engine operating condition. The electric motor as the actuator may be controlled by the electronic controller.
The electronic controller is so constructed as to detect the current operating condition of the engine by calculating input signals from various sensors such as a crank angle sensor, a throttle position sensor, a water temperature sensor and an airflow meter, and control an electric current that is outputted to the electric motor on the basis of the detected engine operating condition.
As shown in
Biasing member 22 is in the form of a return spring which has a generally U-shape in plan view. As seen from
An operation of the variable valve operating apparatus of the embodiment will be explained hereinafter. A rotational force that is transmitted from the crankshaft of the engine to drive shaft 3 is transmitted to drive cam 10 to thereby rotate drive cam 10. The rotation of drive cam 10 is transmitted to roller 14 so that rocker arm 11 swings around control cam 21. Thus, the rotational motion of drive cam 10 is converted to the swing motion of rocker arm 11. The swing motion of rocker arm 11 is transmitted to rocker cams 6, 6 via respective link rods 15, 15 so that rocker cams 6, 6 swing about pins 19, 19 at boss portions 6c, 6c. Owing to the swing motion of rocker cams 6, 6, roller 4a of each of swing arms 4, 4 rolls on cam surface 6b of each of rocker cams 6, 6, namely, base-circle surface 6d and lift surface 6e. Swing arm 4 is swung about plunger 5b of hydraulic lash adjuster 5 as a fulcrum of the swing motion and operate intake valve 2 against the spring force of valve spring 9.
Next, an operation of variable lift control of the variable valve operating apparatus of the embodiment is explained with reference to
The rotational movement of control cam 21 causes rocker arm 11 to be slightly rotated in a clockwise direction as shown in
Under the small lift control, each of intake valves 2, 2 which is moved to the open position and the closed position by each of rocker cams 6, 6 has a minute peak-lift amount as indicated at L1 in
On the other hand, when the operating condition of the engine is shifted to a high-rotation and high-load range and the electronic controller has detected that the operating condition of the engine is in this range, the electronic controller performs large-lift control.
The rotational movement of control cam 21 causes rocker arm 11 to be slightly rotated in a counterclockwise direction as shown in
Under the large-lift control, each of intake valves 2, 2 has a large peak-lift amount as indicated at L2 in
Referring to
In this condition, as illustrated in
In reaction to load FS, load FC is exerted on roller 14 contacted with drive cam 10, through the contact point between an outer circumferential surface of roller 14 and an outer circumferential surface of drive cam 10. Load FC is indicated as a vector that extends from the axis of roller shaft 17 in a direction substantially opposed to the direction of load FS which extends across axis X of drive shaft 3.
A resultant of loads FS and FC is considerably small in magnitude as compared to load FS. This is because load FS and load FC act in substantially diametrically opposite directions relative to roller shaft 17 and have a same magnitude. The resultant of loads FS and FC is indicated as a vector FT in
Thus, the load that acts on control cam 21 and journals 20a, 20a of control shaft 20 is considerably small in the respective non-lift state under the small-lift control and the large-lift control, irrespective of the valve lift amount.
On the other hand, in the respective peak-lift state under the small-lift control and the large-lift control, rocker cam 6 undergoes the rotation moment that is caused by the spring force of valve spring 9. Owing to the rotation moment, a load is exerted on control cam 21 and journals 20a, 20a of control shaft 20 via rocker arm 11 and link rods 15, 15. Further, a load acts on control cam 21 and journals 20a, 20a of control shaft 20 due to the biasing force of biasing member 22, but the load is considerably small similar to the respective non-lift state under the small-lift control and the large-lift control.
As explained above, in variable valve operating apparatus 100 of this embodiment, the load that acts on control cam 21 and journals 20a, 20a of control shaft 20 due to the biasing force of biasing member 22 is considerably small in both of the non-lift state and the peak-lift state under the small-lift control and the large-lift control. This allows quick start of rotation of control shaft 20 in response to changeover of the valve lift control of engine valves 2, 2. As a result, a response to changeover of the valve lift control in this embodiment can be improved as compared to the conventional art.
Specifically, the response at the moment at which control shaft 20 starts to rotate is more likely to undergo influence in the non-lift state in which the load exerted on the bearing surface of bearing member 8 through journals 20a, 20a of control shaft 20 is small. That is, control shaft 20 can quickly start to rotate in the non-lift state in which the bearing load exerted on the bearing surface of bearing member 8 is small.
In this embodiment, the bearing load that is exerted on the bearing surface of bearing member 8 through journals 20a, 20a of control shaft 20 is remarkably reduced in the non-lift state. In contrast, a large bearing load is kept exerted on the bearing member over one cycle of the drive shaft of the conventional art as described above. In this embodiment, owing to the remarkable reduction of the bearing load, an oil film can be readily formed between the outer circumferential surface of each of journals 20a, 20a of control shaft 20 and the corresponding bearing surface of bearing member 8 and between the outer circumferential surface of control cam 21 and the corresponding inner circumferential surface of support bore 16a of rocker arm 11 under the influence of an oil pressure to be supplied.
In particular, a friction coefficient at the journal of the control shaft and the corresponding bearing portion tends to have a value close to coefficient of static friction μ0 due to a small sliding movement between the journal and the corresponding bearing portion. However, in this embodiment, a friction coefficient at journal 20a of control shaft 20 and the bearing portion of bearing member 8 has a value close to coefficient of dynamic friction μD owing to the sufficiently small bearing load and the influence of the oil pressure to be supplied.
In a case where control shaft 20 is rotated by a driving source such as an electric motor to thereby vary the valve lift characteristic, friction moment MF is expressed by the following formula: MF=(FJ′/2)×r×μD
wherein FJ′/2 represents a bearing load for control shaft 20, and r represents a radius of the bearing portion.
In this embodiment, since the value FJ′/2 is sufficiently small and the value μD is a small value close to the coefficient of dynamic friction, control shaft 20 can smoothly start to rotate. Thus, a friction moment that acts on the bearing surface of bearing member 8 which supports journals 20a, 20a of control shaft 20 is reduced to thereby allow a smooth rotational movement of control shaft 20. This serves for enhancing a response to changeover of valve lift characteristics of intake valves 2, 2.
As understood from the above explanation, since the biasing force of biasing member 22 acts on roller 14 through roller shaft 17 in such a direction as to press roller 14 against drive cam 10, the biasing force of biasing member 22 is not largely exerted on the bearing surface of support bore 16a of rocker arm 11 and the bearing surface of bearing member 8. Therefore, a friction moment that acts on the bearing surface of bearing member 8 upon rotating control shaft 20 is reduced. Accordingly, smooth and quick start of rotation of control shaft 20 can be achieved upon changing valve lift characteristics of intake valves 2, 2, thereby serving for enhancing a response to changeover of valve lift characteristics of intake valves 2, 2.
Further, in this embodiment, biasing member 22 can restrict the swing motion of rocker cams 6, 6 in a predetermined region without directly acting on rocker cams 6, 6 and can allow a stable behavior of motion transmission mechanism 7. Biasing member 22 can restrict the swing motion of rocker cams 6, 6 in the predetermined region via the positive motion connection between roller shaft 17, rocker arm 11, rocker cams 6, 6 and link rods 15, 15. With this construction, the respective parts to be positively connected with each other can be prevented from being separated from each other, and therefore, the behavior of motion transmission mechanism 7 can be stabilized.
Specifically, in this embodiment, biasing member 22 biases roller shaft 17 onto drive cam 10 to thereby restrict the motion of roller shaft 17 within a predetermined region in which roller shaft 17, rocker arm 11, link rod 15 and rocker cam 6 are in positive motion connection therebetween in both of opposite swing directions of rocker cam 6 without being separated from each other. Accordingly, the swing motion of rocker cam 6 can be restricted within the predetermined region in which rocker cam 6 is free from separation from the other parts in the positive motion connection.
Here, the positive motion connection means that roller shaft 17 is fixed to one end portion 12 of rocker arm 11, and link rod 15 is pivotally connected with the other end portion 13 of rocker arm 11 through pin 18 so as to move in both of lift-up and lift-down directions of link rod 15 and is connected with rocker cam 6 through pin 19 so as to pivot about pin 19 in the opposite swing directions of rocker cam 6. Therefore, rocker cam 6 can be positively operated in the non-lift state of variable valve operating apparatus 100 without directly undergoing the biasing force of biasing member 22. As a result, occurrence of separation of the parts to be in the positive motion connection therebetween can be suppressed and an operation of variable valve operating apparatus 100 can be always stabilized.
Further, in this embodiment, roller shaft 17 is supported between opposite support walls 12a, 12a of one end portion 12 of rocker arm 11, and opposite end portions 17a, 17b of roller shaft 17 are supported by support walls 12a, 12a. Thus, end portions 17a, 17b of roller shaft 17 can be readily and surely supported, and roller 14 can be easily assembled to rocker arm 11 through roller shaft 17.
Further, tip end portions 22c, 22c of biasing member 22 are contacted with end portions 17a, 17b of roller shaft 17 which project from support walls 12a, 12a of rocker arm 11, so that the biasing force of biasing member 22 acts on end portions 17a, 17b of roller shaft 17. Therefore, a point of action of the biasing force of biasing member 22 is located on a side of each of end portions 17a, 17b of roller shaft 17. With this construction, degree of freedom of installation of biasing member 22 can be increased.
Furthermore, in this embodiment, an attitude of rocker arm 11 can be changed by varying a rotational phase of control shaft 20, namely, a rotational position of control cam 21. This serves for readily varying valve lift characteristic of the engine valve.
Referring to
The second embodiment can have the same effects as those of the first embodiment and can further attain the following effects. With the provision of annular sleeves 30, 30 with engaging grooves 30, 30, tip end portions 22c, 22c of biasing member 22 can be stably supported in engaging grooves 30, 30 of annular sleeves 30, 30. Further, owing to rotation of annular sleeves 30, 30, resistance to slide friction between annular sleeves 30, 30 and tip end portions 22c, 22c of biasing member 22 can be reduced. As a result, the bearing load that acts on the bearing portions for control shaft 20 can be further reduced and the swing motion of rocker arm 11 can be facilitated.
Referring to
In the third embodiment, it is not necessary that the opposite end portions of roller shaft 17 outward project from support walls 12a, 12a of rocker arm 11, thereby serving for downsizing variable valve operating apparatus 300. Further, each of support walls 12a, 12a and the corresponding side face of roller 14 cooperate with each other to restrain each of annular sleeves 30, 30 from being displaced in a direction of thrust.
Referring to
Variable valve operating apparatus 400 further includes biasing member support 33 which is disposed on a boss formed on one end portion 12 of rocker arm 11. Biasing member support 33 is constructed to support biasing member 22 thereon, through which biasing member 22 biases and presses follower portion 32 against drive cam 10. In this embodiment, biasing member support 33 is in the form of a support pin press-fitted into a pin mount hole which is formed in the boss on one end portion 12. Biasing member support 33 has opposite end portions which outward project from opposite side surfaces of the boss of one end portion 12, respectively. Tip end portions 22c, 22c of biasing member 22 are directly elastically contacted with an upper portion of the outer circumferential surface of the opposite end portions of biasing member support 33 as shown in
Biasing member 22 is arranged to apply the biasing force through biasing member support 33 substantially along a line that extends across an axis of biasing member support 33 and the axis of drive cam 10, namely, axis X of drive shaft 3. Load FS that is caused by the biasing force of biasing member 22 acts on follower portion 32 through biasing member support 33 so as to press follower portion 32 against drive cam 10. Load FT′ acting on control cam 21 is considerably small, and therefore, the load that acts on control shaft 20 and bearing member 8 through journals 20a, 20a of control shaft 20 is considerably small. Accordingly, the fourth embodiment can attain the same effects as those of the first embodiment. That is, in the fourth embodiment, a friction moment acting on bearing member 8 through journals 20a, 20a can be reduced to thereby allow a smooth rotational movement of control shaft 20. As a result, a response to changeover of valve lift characteristics of intake valves 2, 2 can be enhanced.
Especially, since biasing member support 33 is disposed on or near line Q as described above, a direction of load FS that is caused by the biasing force of biasing member 22 and a direction of load FC that is caused due to reaction against load FS are substantially opposed to each other to thereby mutually cancel loads FS and FC. Therefore, the load that is exerted on control shaft 22 due to the biasing force of biasing member 22 can be considerably reduced.
Further, in the fourth embodiment, the construction of variable valve operating apparatus 400 is simplified by omitting the roller that is supported on rocker arm 11 and contacted with drive cam 10. This serves for facilitating a production process and an assembling work and suppressing increase in costs.
The present invention is not limited to the above embodiments. A coil spring can be used as the biasing member instead of the return spring. Further, the control shaft can be formed into a crank shape with the control cam which has a reduced diameter. Further, the biasing member can be constructed so as to be contacted with an end portion of the roller shaft which projects from at least one of the opposite side walls, and can bias the end portion of the roller shaft. Further, the drive cam can be formed into an eccentric-circular shape. Further, the drive cam can be rotatably supported by a rolling bearing. Furthermore, a hydraulically operated actuator can be used instead of the electrically operated actuator.
This application is based on a prior Japanese Patent Application No. 2006-153005 filed on Jun. 1, 2006. The entire contents of the Japanese Patent Application No. 2006-153005 is hereby incorporated by reference.
Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-153005 | Jun 2006 | JP | national |
