JP3380582B2 - Engine valve timing control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve timing control device for an engine having a driving cam and a swing cam. 2. Description of the Related Art Various types of engine valve gears have been proposed, and other than the conventional general valve gears which open and close valves by rocking a rocker arm by a driving cam. In addition, for example, as disclosed in Japanese Patent Application Laid-Open No. 55-137306, a driving cam and a swing cam are provided,
There is also known a swing cam type valve operating device that swings the swing cam directly or indirectly via the swing lever by the drive cam to open and close a valve. On the other hand, in such a valve gear having a driving cam and an oscillating cam, the driving cam and the oscillating cam are formed in a tapered shape, and these are relatively moved in the axial direction so that the valve is moved. There is also known a valve timing control device that varies the timing (for example, Japanese Patent Publication No. 58-3).
No. 8602). [0004] In general, in an engine valve train, if the positive acceleration of the valve lift is increased, the integral of the crank angle of the valve lift at the same opening angle and even at the same valve lift. It is known that the value, that is, the time area can be increased, thereby improving the volumetric efficiency of the engine and obtaining a higher engine output. However, in a motor having a driving cam and an oscillating cam, and by making them move relative to each other in the axial direction, the valve timing is made variable, the acceleration of the valve lift is an acceleration component caused by the driving cam. Is defined as the sum of the acceleration components of the swing cam and the swing cam, so that the valve lift acceleration (synthesized acceleration) tends to change when the valve timing is variable. If it becomes smaller, the decrease in the time area causes a decrease in the engine output. Accordingly, the present invention provides an engine valve timing control device capable of suppressing a change in the acceleration of a valve lift when the valve timing is variable, and thereby suppressing a decrease in engine output particularly due to a decrease in the acceleration. It was made as an offer. In developing specific means for achieving the above object, the present inventors focused on the acceleration characteristics of a valve lift, and focused on an acceleration component due to a drive cam and an acceleration component due to a swing cam. The effect of the relationship with the components on the acceleration (synthetic acceleration) of the valve lift before and after the variable valve timing was considered. First, an oscillating cam type valve train as shown in FIGS. 3 and 4 is assumed. In FIGS. 3 and 4, reference numeral 31 denotes a tapered drive cam that is rotationally driven by an engine, 32 denotes a cam surface 32a that slides on a valve tappet 34 provided at the upper end of a stem of a valve 33, and the drive cam 3
1 is a swing cam having an arc-shaped cam follower 32b slidably contacting the first cam surface and supported by a cam support shaft 35 so as to be swingable. The swing cam 32 swings in the direction of arrow bc with the rotation of the drive cam 31 (direction of arrow a), lifts the valve 33, and opens and closes it. Further, the valve timing can be made variable by relatively moving the driving cam 31 and the swing cam 32 in the axial direction. Here, the cam lift of the swing cam 32 is (g), the cam speed is (g '), and the acceleration is (g ").
Assuming that the cam lift of the drive cam 31 is (f), the cam speed is (f ′), and the acceleration is (f ″), the acceleration (α) of the valve lift of the valve 33 is α = f ″ · g ′ + (f ') ² · g "expressed it is known as. this means that the acceleration of the valve lift of the drive cam acceleration component (f" · g')
And the acceleration component ((f ') ² · g ″) of the oscillating cam, and is liable to change under the influence of these mutual relations. Assume the following two cases as a correlation between the acceleration component by the drive cam and the acceleration component by the swing cam. In each case, the change state of the combined acceleration (α) before and after the valve timing is changed. First, as an assumed example of the first relative relationship, as shown in FIG. 5, a positive acceleration (f ″) of the driving cam 31 is used.
Does not overlap with the positive acceleration (g ₁ ″) of the swing cam 32 during the large valve lift, and the positive acceleration (f ″) of the drive cam 31 is the positive acceleration (g ₁ ) of the swing cam 32. In FIG. 5, reference numeral (g ₂ ) indicates a positive acceleration of the swing cam 32 during a small valve lift, and (g ₁ ) indicates a lift characteristic during a large valve lift. , (G ₂ ) is the lift characteristic at the time of small valve lift, θ ₁
The opening angle of the time of a large valve lift, θ ₂ is an open angle at the time of a small valve lift. FIG. 6 shows the resultant accelerations (α ₁ ) and (α ₂ ) during valve lift in such a case. In the figure, (α ₁ ) is the composite acceleration at the time of the large valve lift before the variable valve timing, and (α ₂ ) is the composite acceleration at the time of the small valve lift after the variable valve timing.
Considering FIG. 6, since the positive acceleration of the drive cam 31 and the positive acceleration before and after the change of the swing cam 32 do not overlap and do not affect each other, the combined acceleration (α ₁ ),
(Α ₂ ) hardly changes in its size. As shown in FIG. 7, a positive relative acceleration (f ″) of the drive cam 31 and a positive relative acceleration (g ₃ ″) of the swing cam 32 during a large valve lift are assumed as the second relative relationship. ) Was set to overlap. In FIG. 7, the symbol (g ₄ ″) indicates the positive acceleration of the swing cam 32 during the small valve lift, (g ₃ ) indicates the lift characteristic during the large valve lift, and (g ₄ ) indicates the lift characteristic during the small valve lift. 8 shows the resultant accelerations (α ₃ ) and (α ₄ ) during valve lift in such a case, where (α ₃ ) is a large value before the valve timing is varied. The resultant acceleration at the time of valve lift, (α ₄ ) is the resultant acceleration at the time of small valve lift after the variable valve timing.
Considering FIG. 8, since the positive acceleration of the drive cam 31 and the positive acceleration of the swing cam 32 before and after the change overlap each other, they affect each other, and as a result, the combined acceleration after the change (α ₄ ) Is smaller than the synthetic acceleration (α ₃ ) before the change. FIG. 9 shows the change over time of the valve lift in each of the above two assumed examples. Considering FIG. 9, the valve lift curve L2 in the second assumed example is narrower than the valve lift curve L1 in the first assumed example, and therefore, the valve lift time (ie, crank angle). , Ie, the time area is the second
It can be seen that the assumed example is smaller than the first assumed example, and the engine output decreases accordingly. That is, as a result of such consideration, in order to suppress the change in engine output before and after the valve timing is varied, the cam surface shapes of the driving cam 31 and the swing cam 32 are adjusted so as to obtain the valve lift characteristics as in the first assumed example. Was found to be set. Means for Solving the Problems Accordingly, the present inventors have proposed:
In view of the findings, as specific means for solving the above-described problems, in the invention described in claim 1, a drive cam having a tapered cam surface, a cam surface slidingly contacting a valve and the drive cam having A swinging cam having a cam follower slidably in contact with a cam surface, and opening and closing the valve by swinging the swinging cam by rotation of the driving cam, and a shaft between the driving cam and the swinging cam. against the valve timing control apparatus for an engine to vary the valve timing by changing a direction relative position, the Barubuta
Before and after the variable operation of the imaging
The sum of the acceleration component and the acceleration component from the swing cam
The combined acceleration of the valve lift specified as
Not, a positive acceleration component in the cam surface of the positive acceleration component and the drive cam in the cam surface of the swing cam not overlap each other in the lift process of the valve, the driving <br/> movement cam The shapes of the cam surfaces of the driving cam and the oscillating cam are set such that the positive acceleration component precedes the positive acceleration component of the oscillating cam. [0017] With [act] Such a configuration, in the first aspect of the present invention, the valve lift being defined as sum of the acceleration component due to the drive cam and the swing cam before and after the variable operation of valves timing The change in the combined acceleration of the valve lift before and after the change in the valve timing, in particular, the decrease in the acceleration is suppressed because the combined acceleration of the drive cam does not change and the acceleration by the drive cam has little effect on the acceleration by the swing cam. . Further, in the initial stage of the valve lift, the combined acceleration is defined only by the acceleration component of the driving cam, so that the acceleration state in the initial stage of the valve lift becomes smooth. [0019] [Effect of the Invention] Thus, according to the valve timing control apparatus for an engine of the present invention, the acceleration change of the valve lift at the time of variable valve timing, since the reduced change in particular is suppressed, at the time of bus Ruburifuto valve The decrease in the time area represented by the integral value of the lift time is small, so that the engine output is increased by the improvement in the volumetric efficiency of the engine, and the effect that the acceleration state at the beginning of the valve lift can be smoothed is obtained. . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. FIGS. 1 and 2 show an engine valve timing control apparatus according to an embodiment of the present invention applied to a multi-cylinder engine. In each of the figures, reference numeral 1 denotes two valves arranged per cylinder.
Each of the valves 1, 1 is normally biased in a valve closing direction by a valve spring 2, 2, and a valve tappet 3 is attached to an upper end thereof. Each valve tappet 3 of each valve 1, 1 is slidably supported by a bracket 10 fixedly arranged on a cylinder head 16, and is opened and closed by a cam mechanism P, which will be described later, attached to the bracket 10. Is done. The cam mechanism P has a first driving cam 7 and a second driving cam 8 each having a tapered cam surface for each cylinder, which are arranged adjacent to each other in the axial direction, and is arranged in the axial direction with respect to the bracket 10. It has a camshaft 6 slidably mounted. And this camshaft 6
A helical spline is formed at one end 6a, and this one end 6a is spline-coupled to a cam gear 9 which is rotatably mounted on the bracket 10 and rotated synchronously by the engine. A motor for moving the camshaft 6 in the axial direction (the direction of the arrow RL) is attached to the other end (not shown) of the camshaft 6. Moved within. On the other hand, between the camshaft 6 and the valve tappets 3, 3 of the valves 1, 1, a swing cam bearing shaft 11 is arranged in a direction parallel to the camshaft 6. . The swing cam support shaft 11 has a first
The swing cam 4 and the second swing cam 5 are connected to the camshaft 6.
Are mounted in sliding contact with both the drive cams 7, 8 and the valve tappets 3, 3 of the valves 1, 1, respectively. Each of the swing cams 4 and 5 has a cam surface 41 and 51 sliding on the top surface of the valve tappet 3 and a tapered cam follower 42 sliding on the cam surfaces 7a and 8a of the drive cams 7 and 8, respectively. 52, and spring receiving surfaces 43, 53 which are in sliding contact with the oscillating cam biasing means 20 for constantly pressing the cam followers 42, 52 against the driving cams 7, 8 with a predetermined pressing force. The moving cams 4 and 5 correspond to the driving cams 7 and 8 described above.
The valve 1, 1 is opened and closed by swinging in the direction of the arrow cd along with the rotation in the direction of the arrow a. The cam mechanism P changes the relative position of the driving cams 7, 8 and the swinging cams 4, 5 in the axial direction by moving the cam shaft 6 in the axial direction by a motor. Thus, the valve lift of the valves 1, 1 and the opening angle of the valves can be changed. Specifically, as shown in FIG. 2, when the swing cams 4 and 5 are in sliding contact with the large-diameter sides of the drive cams 7 and 8, a large lift and a large opening angle are obtained. 6 moves in the direction of the arrow R, and the swing cams 4 and 5 slidably contact the small-diameter sides of the drive cams 7 and 8, thereby providing a small lift and a small opening angle. In this case, one end 6 of the camshaft 6 is used.
Since a is a helical spline, the rotation phase of the cam gear 9 and the camshaft 6, that is, the valve timing is also changed at the same time as the valve lift is changed, and the valve lift is operated to the large lift amount side. In this case, the advance is set, and when the small lift is operated, the retard is set. In this embodiment, when setting the cam surface shapes of the drive cams 7, 8 and the swing cams 4, 5, the present invention is applied and the swing cams 4, 5 are applied.
The positive acceleration components on the cam surfaces 41 and 51 of the drive cams 7 and 8 and the positive acceleration components on the cam surfaces 7a and 8a of the drive cams 7 and 8 do not overlap each other in the valve lift process, and the positive The cam surfaces of the driving cams 7, 8 and the oscillating cams 4, 5 are set so that the acceleration component of the oscillating cams 4, 5 precedes the positive acceleration component of the oscillating cams 4, 5. With this,
The drive cams 7, 8 and the swinging cam, which are defined as the sum of the respective acceleration components by the drive cams 7, 8 and the swinging cams 4, 5 before and after the variable operation of the valve timing, do not change. The shapes of the cam surfaces of the moving cams 4 and 5 are set. Therefore, when the camshaft 6 is moved in the axial direction and the valve timing is changed, the change in the valve lift acceleration before and after the change, particularly the change to the decreasing side, is suppressed, so that the engine output does not decrease. And good output performance is maintained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a main part of a valve train of an engine provided with a valve timing control device according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view of a main part taken along the line II-II of FIG. FIG. 3 is a structural explanatory view of a general swing cam type valve train. FIG. 4 is a view taken in the direction of arrows IV-IV in FIG. 3; FIG. 5 is a cam characteristic diagram in the case of a first assumed example. 6 is an explanatory diagram of a change state of a synthetic acceleration when a valve lift is variable when the cam characteristic of FIG. 5 is adopted. FIG. 7 is a cam characteristic diagram in the case of a second assumed example. FIG. 8 is an explanatory diagram of a change in rigid acceleration when the valve lift is variable when the cam characteristic of FIG. 7 is employed. FIG. 9 is a time area characteristic diagram of a cam. [Description of Signs] 1 is a valve, 2 is a valve spring, 3 is a valve tappet, 4 is a first swing cam, 5 is a second swing cam, 6 is a cam shaft, 7 is a first drive cam, and 8 is a 2 drive cam, 9 is a cam gear, 10 is a bracket, 11 is a swing cam support shaft, 1
6 is a cylinder head, 20 is a swing cam urging means, 21 is a tappet, 22 is a spring, 23 is a mover, 24 is a solenoid coil, 41 is a cam surface, 42 is a cam follower,
43 is a spring receiving surface, 51 is a cam surface, 52 is a cam follower, 53 is a spring receiving surface, and P is a cam mechanism.

Continuation of the front page (56) References JP-A-55-148912 (JP, A) JP-A-55-151107 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01L 13 / 00 301 F01L 1/08

Claims (1)

(57) [Claim 1] A drive cam having a tapered cam surface, and an oscillating cam having a cam surface slidingly contacting a valve and a cam follower slidingly contacting the cam surface of the drive cam. The valve is opened and closed by swinging the swing cam by rotation of the drive cam, and the valve timing is made variable by changing the axial relative position of the drive cam and the swing cam. An engine valve timing control device, wherein the drive is controlled before and after the valve timing variable operation.
The acceleration component by the moving cam and the acceleration component by the swing cam
Synthetic acceleration of valve lift defined as the sum of minutes and minutes
The degree does not change, and the positive acceleration component on the cam surface of the swing cam and the positive acceleration component on the cam surface of the drive cam do not overlap each other during the valve lift process.
In, as positive acceleration component of the drive cam precedes the positive acceleration component of the swing cam, the valve timing control of the engine, characterized in that setting the shape of the cam surface of the drive cam and the swing cam apparatus.