Patent Grant
8459219
This invention relates to a variable valve device capable of controlling a lift and an operating angle variably and continuously.
As a variable valve device capable of controlling a lift or an operating angle of an engine valve variably and continuously, JP2002-38913A, published by the Japan Patent Office in 2002, discloses a variable valve device that is capable of controlling a lift and an operating angle of an engine shaft variably and continuously, comprising: a drive shaft that rotates synchronously with an engine and has a drive cam on an outer periphery thereof; a rocker cam that drives the engine valve to open and close; a rocker arm, one end of which is provided on an eccentric control cam to be free to rock via a first rotation fulcrum (P1) and which is linked to the drive cam and the rocker cam to be free to rotate via second and third rotation fulcrums (P2, P3), respectively, so as to transmit a driving force of the drive cam to the rocker cam through a rocking action; a link arm that links the drive cam to the rocker arm; a link rod that links the rocker cam to the rocker arm; and a control shaft that controls rotation of the eccentric control cam using an actuator, wherein the second and third rotation fulcrums (P2, P3) exist in an identical direction relative to a line linking the first rotation fulcrum (P1) to a rotation center (X) of the drive shaft.
However, in the variable valve device described above, when the operating angle of the engine valve is modified, the position of a rocker shaft is moved without taking into account lift variation in the engine valve accompanying angular variation in a straight line (an imaginary straight line of a fixed length) linking the drive shaft center (X) and the rocker shaft center (P1) and lift variation in the engine valve accompanying variation in a distance (an imaginary distance at a fixed angle) between the drive shaft center (X) and the rocker shaft center (P1), and therefore the lift of the engine valve relative to its operating angle does not take a desired value. From a state of minimum lift control to a state of maximum lift control, angular variation in the straight line linking the drive shaft center to the rocker shaft center acts in a direction for increasing the lift of the engine valve, while the distance between the drive shaft center and the rocker shaft center increases to a midway point (from a minimum operating angle to an intermediate operating angle) so as to act in the direction for increasing the lift and then (from the intermediate operating angle to a maximum operating angle) decreases so as to act in a direction for reducing the lift. At this time, in the variable valve device described above, an offset of the rocker shaft center (the offset of the rocker shaft center P1 relative to an axial center P) is inappropriate, giving rise to an undesirable operating angle variation range in which the operating angle increases but the lift decreases greatly. More specifically, the offset of the rocker shaft center is extremely small, and therefore angular variation in the straight line linking the drive shaft center to the rocker shaft center becomes excessively small, causing the action that increases the lift of the engine valve, which is produced by angular variation in the straight line linking the drive shaft center to the rocker shaft center, to become extremely small. As a result, the action that reduces the lift of the engine valve, which is produced by variation in the distance between the drive shaft center and the rocker shaft center, cannot be overridden from the intermediate operating angle to the maximum operating angle, and therefore the lift decreases greatly while the operating angle increases.
It is an object of this invention to provide a variable valve device with which a reduction in a lift of a rocker cam can be suppressed within a predetermined operating angle range.
To achieve the above object, this invention is a variable valve device including: a drive shaft that rotates in synchronization with a crankshaft of an engine; a drive cam provided on the drive shaft; a rocker cam pivotally supported on the drive shaft; an engine valve that is driven to open and close by the rocker cam; a rocker shaft disposed parallel to the drive shaft; a rocker arm pivotally supported on the rocker shaft; a first link that links the rocker arm and the drive cam; a second link that links the rocker arm and the rocker cam; and a rocker shaft position modifying section that modifies a position of the rocker shaft relative to the drive shaft to control an operating angle and a lift of the engine valve, wherein the position of the rocker shaft relative to the drive shaft is modified such that a variation of a maximum lift of the engine valve accompanying control of the operating angle within a predetermined operating angle range of the engine valve is suppressed as compared to a variation of a maximum lift of the engine valve accompanying control of the operating angle outside of the predetermined operating angle range.
The details as well as other features and advantages of this invention are described in the following description of the specification and illustrated in the attached drawings.
The variable valve device A is a mechanism that can control a lift and an operating angle of an intake valve variably and continuously. It should be noted that subsequent description relating to lift variation indicates variation of a maximum lift.
A drive shaft 1 is supported to be free to rotate on a cylinder head serving as an engine main body. The drive shaft 1 is driven by a crankshaft of the engine via a timing chain or a timing belt. A rotation direction of the drive shaft corresponds to a clockwise direction in
The drive shaft 1 comprises a drive cam 13 having a circular outer peripheral surface that is eccentric to a center of the drive shaft 1. The drive cam 13 is formed by fixing a separate disc-shaped component having an eccentric hole to an outer periphery of the drive shaft 1 by press fitting or the like. Further, a pair of rocker cams 6 provided for each cylinder are supported on the drive shaft 1 to be free to rotate (free to rock) relative to the drive shaft 1 in positions deviating in an axial direction from a position in which the drive cam 13 is fixed. When the pair of rocker cams 6 rock (perform a vertical motion) about the drive shaft 1 within a predetermined angle range, the intake valve, which is positioned below a cam nose 6a of the rocker cam 6, is pressed such that the intake valve is lifted downward. The pair of rocker cams 6 are integrated with each other via a cylindrical portion covering the outer periphery of the drive shaft 1, and therefore rock in phase.
A variable phase mechanism that varies a phase of the operating angle by varying a phase of the drive shaft relative to the crankshaft is provided on a front end of the drive shaft 1. The variable phase mechanism has a similar constitution to a typical, well-known variable phase mechanism, and includes a sprocket provided on the front end portion of the drive shaft 1 and a phase control actuator that causes the sprocket and the drive shaft 1 to rotate relative to each other within a predetermined angle range. The sprocket rotates synchronously with the crankshaft via a timing chain or a timing belt. The phase control actuator is controlled on the basis of a control signal from a control unit. Through the control of the phase control actuator, the sprocket and the drive shaft 1 are caused to rotate relative to each other, and as a result, a lift center angle is retarded and advanced. In other words, the lift is advanced or retarded without changing a lift characteristic curve. Further, this variation can be obtained continuously. Variable phase mechanisms may have various constitutions, including those employing a hydraulic actuator and those employing an electromagnetic actuator, but in this embodiment, it is assumed that a hydraulic actuator is used.
A variable valve rocker arm 3 is supported on a rocker shaft 7 to be free to rock, and includes a first arm 8 and a second arm 9 that project to an identical side of a straight line linking the center of the drive shaft 1 and a center of the rocker shaft 7. The second arm 9 projects by a larger amount than the first arm 8. Further, the variable valve rocker arm 3 is constituted by two divided members that are fastened to either side of the rocker shaft 7 by bolts 15.
A base circle surface forming an arc that is concentric with the drive shaft 1 and a cam surface that extends from the base circle surface in a predetermined curve to form the outer shape of the cam nose 6a are formed continuously on a lower surface of the rocker cam 6, and in accordance with a rocking position of the rocker cam 6, the base circle surface and cam surface come into contact with the intake valve or a valve lifter. In other words, the base circle surface serves as a base circle section in which the lift is zero, while a section in which the cam surface contacts the valve lifter in accordance with the rocking motion of the rocker cam 6 serves as a lift section in which the intake valve gradually lifts. A small ramp section is provided between the base circle section and the lift section.
A first link 4 is formed such that one end thereof is fitted rotatably to the drive cam 13 and the other end is connected to the vicinity of a tip end of the first arm 8 via a connecting pin 10.
A second link 5 is formed such that one end thereof is connected to the vicinity of a tip end of the second arm 9 via a connecting pin 11 and the other end is connected to the vicinity of an end portion of the cam nose 6a of the rocker cam 6 via a connecting pin 12. The connecting pin 10 serves as a first connection point between the rocker arm 3 and the first link 4, and the connecting pin 11 serves as a second connection point between the rocker arm 3 and the second link 5. The first connection point and second connection point are located on the same side of the straight line linking the center of the drive shaft 1 and the center of the rocker shaft 7. The second connection point (the connecting pin 12) is positioned farther from the center of the rocker shaft 7 than the first connection point (the connecting pin 10). Further, the cam nose 6a of the rocker cam 6 is provided on the same side of the straight line linking the center of the drive shaft 1 and the center of the rocker shaft 7 as the first connection point and second connection point such that the drive shaft rotates in an identical orientation to a rotation direction of the rocker cam when the engine valve is opened.
In the variable valve device A constituted as described above, when the drive shaft 1 rotates in synchronization with rotation of the crankshaft of the engine, the first link 4 is caused to move vertically by an action of the drive cam 13, and accordingly, the variable valve rocker arm 3 rocks about the rocker shaft 7. The rocking motion of the variable valve rocker arm 3 is transmitted to the rocker cam 6 via the second link 5, causing the rocker cam 6 to rock. The cam action of the rocker cam 6 causes the intake valve to perform an opening/closing operation.
A rocking angle θ (solid line A) of the rocker cam 6 is set at zero degrees at the start of valve lift, and in a direction in which the valve lift increases, or in other words the clockwise direction in
A single period of the rocking angle θ corresponds to 360 degrees in terms of the drive shaft rotation angle, and the rocking angle θ increases from drive shaft rotation angle zero degrees to 180 degrees and decreases from drive shaft rotation angle 180 degrees to 360 degrees. When the rocking angle θ reaches a maximum value, the intake valve reaches a maximum lift, and a section in which the rocking angle θ takes a positive value (drive shaft rotation angle D1 to D2) serves as the valve lift section. A phase of the rocking angular velocity deviates from the rocking angle θ by substantially 90 degrees so as to reach zero when the rocking angle θ is at the maximum value. The rocking angular acceleration reaches a minimum, or in other words a maximum rocking negative angular acceleration, when the rocking angle is at the maximum value.
In the variable valve device A constituted as described above, varying the operating angle may be considered identical to varying an initial rocking angle of the rocker cam 6. Here, the initial rocking angle denotes the rocking angle when the drive shaft rotation angle is at zero in
For example, when the operating angle (lift) is to be reduced, the initial rocking angle is reduced (shifted far to the negative side from the reference lift start rocking angle (zero)). Thus, when the rocker cam 6 rocks in accordance with rotation of the drive shaft 1, the base circle surface remains in contact with the valve lifter for a long time, thereby shortening the period of contact between the cam surface and the valve lifter. This leads to an overall reduction in the lift and a reduction in the operating angle.
When the operating angle (lift) is to be increased, on the other hand, the initial rocking angle is increased (prevented from shifting far to the negative side from the reference lift start rocking angle (zero)). In this case, in contrast to a case in which the operating angle (lift) is reduced, the period of contact between the base circle surface and the valve lifter is shortened, leading to lengthening of the period of contact between the cam surface and valve lifter, and as a result, the lift increases and the operating angle increases.
To vary the initial rocking angle in this manner, the angle of the rocker cam 6 relative to the valve lifter when compared at a constant drive shaft rotation angle (when the angle of the drive cam is constant) must be varied, and for this purpose, the position of the rocker shaft 7 is varied.
Two basic methods of varying the position of the rocker shaft 7 exist. In one method, a distance (to be referred to hereafter as an “L0 length”) between the center of the drive shaft 1 and the center of the rocker shaft 7 is varied, and in the other method, the angle of the line linking the center of the drive shaft 1 and the center of the rocker shaft 7 is varied (the entire device is tilted), or in other words, an angle (to be referred to hereafter as an “L0 angle”) formed by an arbitrary reference line passing through the center of the drive shaft 1 in
For example, when the L0 length is increased (without varying the L0 angle) in
Meanwhile, when the L0 angle is increased (in a state where the L0 length remains unchanged), the variable valve rocker arm 3, the first link 4, the second link 5, and the rocker cam 6 rotate in the clockwise direction of
As shown in
As described above, the reason why the absolute value of the rocking negative angular acceleration increases when the operating angle is increased by increasing the L0 length is that the acceleration of the intake valve increases as the operating angle is increased. When the acceleration of the intake valve increases as the operating angle is increased, the valve lift (variation) per unit rotation angle of the drive shaft 1 increases (relatively providing that other conditions do not change), and therefore the valve lift, which increases in accordance with increases in the operating angle, can be increased quickly (i.e. the lift can be increased rapidly). If the valve lift at an intermediate operating angle (a predetermined operating angle between the maximum operating angle and the minimum operating angle) cannot be obtained quickly, a reduction in charging efficiency and an increase in pumping loss may occur, leading to a reduction in engine output. However, these dangers can be eliminated by increasing the L0 length to increase the absolute value of the rocking negative angular acceleration following an increase in the operating angle, whereby the valve lift, which increases in accordance with increases in the operating angle, can be increased quickly.
Meanwhile, when the L0 angle is varied, as shown in
As shown in
When the operating angle is increased by increasing the L0 length, the maximum absolute value of the rocking negative angular acceleration increases, and when the acceleration of the intake value increases, the valve lift per unit rotation angle of the drive shaft 1 increases (relatively providing that other conditions do not change), and therefore the valve lift in the vicinity of the predetermined operating angle (an intermediate operating angle) can be increased, thereby preventing a reduction in charging efficiency and an increase in pumping loss and enabling an increase in engine output. However, a rapid increase in the valve lift is desirable only up to the predetermined operating angle (an intermediate operating angle), and if the valve lift increases too quickly in the vicinity of the maximum operating angle, the maximum lift becomes excessively large, leading to increases in mechanical loss (for example, the work required to counteract a valve spring reaction force) and a deterioration in efficiency. Therefore, from the predetermined operating angle (an intermediate operating angle) to the vicinity of the maximum operating angle, the L0 angle is increased while shortening the L0 length, thereby increasing the operating angle of the intake valve while preventing the maximum lift in the vicinity of the maximum operating angle from becoming excessively large, and as a result, problems such as an increase in mechanical loss can be eliminated. To assist understanding, a case in which the operating angle is varied by varying the L0 angle alone without changing the L0 length will now be described in further detail with reference to a specific structure (reference example).
It should be noted that
The rocker shaft 7 is disposed substantially parallel to the drive shaft 1 and further toward an engine upper side than the drive shaft 1.
Reference numerals 20 and 21 in
A sensor that detects the rotation angle of the drive shaft 1 and a sensor that detects the rotation angle of the rocker shaft 7 about the drive shaft 1 are provided, and detection values from these sensors are read to a control unit 100. On the basis of detection values from sensors that detect the operating conditions of a vehicle (for example, a crank angle sensor, an accelerator opening sensor, and so on), the control unit 100 calculates a target operating angle of the intake valve and controls driving and stoppage of the motor 27 accordingly.
In the constitution described above, the pinion gear 26 and the gear portion 24a are intermeshed, and therefore, when the motor 27 is driven, the ring member 24 rotates about the drive shaft 1. Accordingly, the ring member 23 connected thereto via the bridge member 25 moves on an arc having a distance between a rotary axis of the drive shaft 1 and a lengthwise direction axis of the rocker shaft 7 (i.e. the L0 length) as a radius.
In other words, the L0 angle can be varied while keeping the L0 length constant. It should be noted that the state shown in
With a constitution such as that of the reference example shown in
Next, a first embodiment of this invention will be described.
The control shaft 2 takes a so-called crank shape, and includes a main journal 2a supported by the cam bracket, and the rocker shaft 7, which is offset from a center of the main journal 2a. Further, the control shaft 2 is rotated within a predetermined angle range by the motor 27 provided on one end portion thereof. A power supply to the motor 27 is controlled on the basis of a control signal from the control unit 100. The motor 27 functions not only to rotate the control shaft 2 to a target angle during modification of the operating angle, but also to hold the control shaft 2 such that the angle of the control shaft 2 does not deviate from the target angle during an operation.
A sensor that detects a rotation angle of the drive shaft 1 and a sensor that detects a rotation angle of the control shaft 2 are further provided, and detection values from these sensors are read to the control unit 100.
Since the rocking shaft 7 is offset from a rotary axis of the control shaft 2 (the center of the main journal 2a), a rocking center position of the variable valve rocker arm 3 when the engine is seen from a front surface varies according to the rotation angle of the control shaft 2. Hence, when the rotation angle of the control shaft 2 is varied by the motor 27, the rocking center position of the variable valve rocker arm 3 shifts, causing the initial rocking position of the rocker cam 6, and therefore the operating angle of the intake valve, to vary.
When the L0 length and L0 angle are varied as described above, the valve lift varies. For example, the valve lift increases as the L0 length increases and decreases as the L0 angle decreases. When the L0 length is increased using this characteristic such that the valve lift increases by an amount corresponding to a reduction in the valve lift generated by a reduction in the L0 angle, the valve lift does not vary. By varying the L0 length by an amount that cancels out variation in the valve lift generated by variation in the L0 angle in this manner, variation in the maximum valve lift accompanying modification of the operation angle can be suppressed. As a result, a situation in which the valve lift in the vicinity of the maximum operating angle increases excessively such that the maximum lift becomes excessively large, leading to an increase in mechanical loss (for example, the work required to counteract a valve spring reaction force) and a deterioration in efficiency, is prevented. An “equal lift line” in
Disposal of the control shaft 2 will now be described. The control shaft 2 is disposed to satisfy the following three conditions.
A first condition is satisfied when the L0 length at the maximum operating angle is equal to or greater than the L0 length at the minimum operating angle.
A second condition is satisfied when L0 angle max−α≅α−L0 angle min, where α is an angle formed by a straight line linking the rotary axis C0 of the control shaft 2 (the center of the main journal 2a) to the center of the drive shaft 1 and a reference line, L0 angle max is the L0 angle at the maximum operating angle, and L0 angle min is the L0 angle at the minimum operating angle, and when the rotary axis C0 of the control shaft 2 is on the same side of a normal of the equal lift line in the center CRmax of the rocker shaft 7 at the maximum operating angle as the drive shaft 1.
A third condition is satisfied when an arc traced by the center of the rocker shaft 7 as it rotates about the rotary axis C0 of the control shaft 2 approaches the equal lift line in the center position CRmax of the rocker shaft 7 at the maximum operating angle in the center position CRmax of the rocker shaft 7 at the maximum operating angle.
Next, effects obtained when these conditions are satisfied will be described.
As shown in
Meanwhile, when only the L0 angle is varied (a broken line in
In this embodiment, on the other hand, the rocking negative angular acceleration at the maximum operating angle and the minimum operating angle is equal to the rocking negative angular acceleration when only the L0 angle is varied, while the rocking negative angular acceleration at an intermediate operating angle is larger than the rocking negative angular acceleration at the maximum operating angle.
The reason for this, as is evident from the locus of the center position of the rocker shaft 7 in
When the L0 length is increased, the rocking angle increases (see
As shown in
Further, as shown in
Hence, with this embodiment, the following effects can be obtained.
(1) The cam nose 6a of the rocker cam 6 projects to the second connecting portion 11 side of the straight line linking the drive shaft 1 to the rocker shaft 7, and the rocker cam 6 is connected to the second link 5 on the same side of this straight line as the cam nose 6a. The center position of the control shaft 7 moves such that as the operating angle increases, the L0 angle increases and the L0 length increases from the minimum operating angle to the predetermined operating angle and decreases from the predetermined operating angle to the maximum operating angle, and therefore the absolute value of the rocking negative angular acceleration reaches a maximum value at the intermediate operating angle. As a result, an improvement in charging efficiency and a reduction in pump loss can be achieved during a medium load operation, i.e. at an intermediate operating angle, and an excessive increase in the lift at a small operating angle can be prevented, thereby reducing variation in an intake air amount during a low load operation. Further, a situation in which the maximum lift in the vicinity of the maximum operating angle increases unnecessarily, leading to an increase in mechanical loss, can be prevented, and as a result, an input load input to the rocker shaft 7 at the maximum operating angle can be reduced.
(2) By setting the L0 length at the maximum operating angle to be equal to or greater than the L0 length at the minimum operating angle, the rocking angle of the rocker cam 6 per unit rotation angle of the drive shaft 1 can be increased beyond the rocking angle at the maximum operating angle, and as a result, the rocking negative angular acceleration in the vicinity of the maximum operating angle can be increased.
(3) The rocker shaft 7 moves along a locus that steadily approaches the equal lift line toward the maximum operating angle, and therefore the valve lift at the intermediate operating angle can be increased while suppressing the valve lift at the maximum operating angle.
(4) The rocking axis of the control shaft 2 is located on a straight line linking the rocking axis of the variable valve rocker arm 3 and the rocking axis of the rocker cam 6 when the operating angle is substantially half the maximum operating angle, and positioned on the rocking axis 1 side of the rocker cam 6 relative to the normal of the equal lift line in the rocking axis position of the rocker shaft 7 at the maximum operating angle. Therefore, an equal lift can be maintained in the vicinity of the maximum operating angle using the control shaft 2 having an eccentric rocking axis.
A second embodiment of this invention will now be described.
This embodiment is similar to the first embodiment in the arrangement of the variable valve rocker arm 3, first arm 8, second arm 9, first link 4, and second link 5 and in that the control shaft 2 is formed in a crank shape, but differs from the first embodiment in the orientation of the rocker cam 6 and the rotary axis position of the control shaft 2.
This embodiment also differs from the first embodiment in that the rocker cam 6 drives an intake valve 31 via a roller type rocker arm 30 having a roller follower 33, and a lash adjuster 32 is disposed on a fulcrum of the roller type rocker arm 30. The rotary axis position of the control shaft 2 will be described below.
The rocker cam 6 includes a cam surface that projects to the opposite side of a line linking the control shaft 2 and the rotary axis of the drive shaft 1 to a projection direction of the first and second arms, and is connected to the second link 5 on the opposite side of the rotary axis of the drive shaft 1 to the cam surface. When the drive shaft 1 rotates such that the first link 4 moves upward, the second link 5 is also pulled upward, causing the rocker cam 6 to rotate in a counter-clockwise direction of
Further, the roller type rocker arm 30 is formed such that a contact portion with the intake valve 31 and the fulcrum thereof are located below a contact portion between the roller follower 33 and the rocker cam 6. Thus, a rocking locus of the connecting pin 12 can be secured. In other words, a situation in which a connecting part between the rocker cam 6 and the second link 5 collides with the roller type rocker arm 30 when the rocker cam 6 rocks can be avoided.
As shown in
Disposal of the control shaft 2 will now be described. The control shaft 2 is disposed to satisfy the following three conditions.
A first condition is satisfied when L0 angle max−α≅α−L0 angle min, where α is the angle formed by the straight line linking the rotary axis C0 of the control shaft 2 to the drive shaft 1 and the reference line, L0 angle max is the L0 angle at the maximum operating angle, and L0 angle min is the L0 angle at the minimum operating angle, or in other words when the L0 length at the maximum operating angle is equal to or greater than the L0 length at the minimum operating angle.
A second condition is satisfied when the rotary axis C0 of the control shaft 2 is on the opposite side of the normal of the equal shift line in the center CRmax of the rocker shaft 7 at the maximum operating angle to the drive shaft 1.
A third condition is satisfied when a center position distance between the rotary axis C0 and the rocker shaft 7 is set such that the locus of the center of the rocker shaft 7 when the control shaft 2 is rotated, or in other words an arc having the rotary axis C0 of the control shaft 2 as a center and the center position distance between the rotary axis C0 and the rocker shaft 7 as a radius, approaches the equal lift line as it comes closer to the center position CRmax of the rocker shaft 7 at the maximum operating angle from the center position CRmin of the rocker shaft 7 at the minimum operating angle and the two match in the center position CRmax of the rocker shaft 7 at the maximum operating angle.
Next, the effect when all the conditions are satisfied will be described.
As shown in
The reason for this, as is evident from the locus of the center position of the rocker shaft 7 shown in
In other words, at the intermediate operating angle, the L0 angle is larger and the L0 length is shorter than at the maximum operating angle, and when the L0 angle is increased, as shown in
When the rocking negative angular acceleration of the rocker cam 6 has the characteristic described above, the valve lift is larger than that of the prior art over substantially the entire region, as shown in
In the embodiment described above, the cam nose 6a of the rocker cam 6 projects to the opposite side of the straight line linking the drive shaft 1 and the rocker shaft 7 to the second link 5, and the rocker cam 6 is connected to the second link 5 on the same side of this straight line as the cam nose 6a. When an operating angle modification mechanism is constituted to shift the position of the rocker shaft of the variable valve rocker arm along a locus on which the L0 angle decreases as the operating angle increases, the L0 length decreases from the minimum operating angle to the predetermined operating angle, and the L0 length increases from the predetermined operating angle to the maximum operating angle, similar effects to those of the first embodiment can be obtained.
A third embodiment of this invention will now be described.
In this embodiment also, the control shaft 2 is disposed to satisfy the following two conditions.
A first condition is satisfied when the angle a formed by the straight line linking the rotary axis C0 of the control shaft 2 to the drive shaft 1 and the reference line, L0 angle max, and L0 min have a relationship of L0 angle max−α≅α−L0 angle min, or in other words when the L0 length at the maximum operating angle is equal to or greater than the L0 length at the minimum operating angle.
A second condition is satisfied when the rotary axis C0 of the control shaft 2 is positioned between the normal of the equal lift line in the center CRmax of the rocker shaft 7 at the maximum operating angle and a straight line linking the center position CRmax of the rocker shaft 7 at the maximum operating angle to the rotary axis C0 and close to the normal.
Next, effects obtained when all of these conditions are satisfied will be described.
As shown in
The reason for this, as is evident from the locus of the center position of the rocker shaft 7 shown in
In other words, at the intermediate operating angle, the L0 angle and the L0 length are both larger than at the maximum operating angle. As shown in
As shown in
Hence, with this embodiment, the following effect can be obtained in addition to similar effects to those of the first and second embodiments relating to the constitution whereby the cam nose 6a of the rocker cam 6 projects to the opposite side of the straight line linking the drive shaft 1 and the rocking axis of the rocker shaft 7 to the second link 5 and the rocker cam 6 is connected to the second link 5 on the same side of this straight line as the cam nose 6a.
The control shaft 2 supported rotatably by the engine and the rocker shaft 7 offset therefrom are provided, and the distance from the drive shaft 1 to the center of the control shaft 2 is shorter than the L0 length at the minimum operating angle, and therefore the absolute value of the rocking negative angular acceleration at substantially the minimum operating angle increases. As a result, the lift at a small operating angle can be increased.
A fourth embodiment of this invention will now be described.
In this embodiment also, the control shaft 2 is disposed to satisfy the following two conditions.
A first condition is satisfied when the angle a formed by the straight line linking the rotary axis C0 of the control shaft 2 to the drive shaft 1 and the reference line, L0 angle max, and L0 min have a relationship of L0 angle max−α≅α−L0 angle min, or in other words when the L0 length at the maximum operating angle is equal to or greater than the L0 length at the minimum operating angle.
A second condition is satisfied when the rotary axis C0 of the control shaft 2 is positioned on the opposite side of the normal of the equal shift line in the center CRmax of the rocker shaft 7 at the maximum operating angle to the drive shaft 1.
When all of these conditions are satisfied, similar effects to those shown in
In the above embodiments, a variable valve device for an intake valve was described, but this invention may be applied similarly to the opening and closing of an exhaust valve.
For example, when a valve lift that is close to the valve lift at substantially the maximum operating angle is obtained at an intermediate operating angle close to the maximum operating angle, as in the first and second embodiments, an improvement in discharge efficiency during medium and high load operations and so on can be achieved. Further, when the valve lift is increased in the small operating angle region, as in the third and fourth embodiments, a reduction in a residual gas amount can be achieved during low load operations such as idle operations.
This invention is not limited to the embodiments described above, and may of course be subjected to various modifications within the scope of the technical spirit described in the claims.
In relation to the above description, Patent Application No. 2007-209706, with a filing date of Aug. 10, 2007 in Japan, Patent Application No. 2007-214529, with a filing date of Aug. 21, 2007 in Japan, Patent Application No. 2008-043126, with a filing date of Feb. 25, 2008 in Japan, and Patent Application No. 2008-047918, with a filing date of Feb. 28, 2008 in Japan, are incorporated herein by reference.
As described above, this invention is capable of suppressing variation in a maximum lift when an operating angle of a rocker cam is varied. Therefore, particularly favorable effects can be obtained when this invention is applied to a variable valve device capable of controlling a lift or an operating angle of an engine valve variably and continuously.
Exclusive properties or features encompassed by the embodiments of this invention are as claimed below.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-209706 | Aug 2007 | JP | national |
| 2007-214529 | Aug 2007 | JP | national |
| 2008-043126 | Feb 2008 | JP | national |
| 2008-047918 | Feb 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/064609 | 8/8/2008 | WO | 00 | 2/9/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/022729 | 2/19/2009 | WO | A |
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| 2006-37812 | Feb 2006 | JP |
| 2006-329022 | Dec 2006 | JP |
| 2006-329023 | Dec 2006 | JP |
| 2007-009705 | Jan 2007 | JP |
| 2007-162706 | Jun 2007 | JP |
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| Entry |
|---|
| Shinichi Takemura et al., USPTO Non-Final Office Action, U.S. Appl. No. 12/672,809, filed Mar. 15, 2012, 13 pgs. |
| U.S. Appl. No. 12/672,809, filed Feb. 9, 2010, Takemura et al. |
| Shinichi Takemura et al., USPTO Non-Final Office Action, U.S. Appl. No. 12/672,809, filed Jul. 30, 2012, (8 pgs.). |
| Shinichi Takemura et al., Final Office Action, U.S. Appl. No. 12/672,809, dated Nov. 16, 2012, (9 pgs.). |
| Shinichi Takemura et al., Notice of Allowance, U.S. Appl. No. 12/672,809, dated Apr. 22, 2013, (8 pgs.). |
| Number | Date | Country | |
|---|---|---|---|
| 20110265748 A1 | Nov 2011 | US |
