Variable valve timing for four-stroke engines

Details Variable valve timing for four-stroke engines Variable valve timing for four-stroke engines

1983-08-30

1986-02-25

Cline, William R.

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

123 9027, F01L 134

Patent

active

045721181

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns a mechanism for internal combustion engines that makes it possible to vary the opening and lift time of intake and exhaust valves. Mechanical valve gears equipped with such adjustments have already been patented, although none has actually been put into application due to certain major limitations.
In most of these mechanisms, movement is produced by a pitman rod system. The resulting disadvantages are illustrated by the schematic representation of FIG. 1, which is a variant of the prior art. Variable opening of the valve (6), for which the spring (7) causes the return movement, is obtained by using all or part of a static cam profile (5) that is positioned for just this purpose. The roller (4), activated by the short connecting rod (1) of the crankshaft (2), which is subjected to back-and-fourth movement along the profile of the static cam (5), communicates this motion to the lever (3), thus actuating the valve (6). While the distance of reciprocal movement remains constant, the length of the active portion of the profile of the static cam (5) varies in inverse proportion to that of the neutral portion. The laws of valve (6) opening and closing are approximately symmetrical.
Here, the static cam (5) is set in the position corresponding to the longest valve (6) opening and lift time. The solid line in the drawing shows the short connecting rod (1), lever (3), roller (4), valve (6), and spring (7) in the position of maximum valve (6) lift; the broken line indicates the positions at beginning of opening and end of closing of the valve (6).
The valve (6) stroke is greater than 150.degree. which, for a fourstroke engine in which the shaft (2) is turning at half-speed, represents a cam angle greater than 300 CD (CD=camshaft degrees, at engine output).
Valve (6) opening times of such long duration, only used in sports car engines, could bring about the following adjustments, given as an illustration: the crankshaft (2) travel range is active.
Considering also the limitations created by the profile of the static cam (5), both camshaft (2) travel range and the corresponding distance of alternating movement are too great. The resulting bulkiness explains why the system is incompatible with modern, compact engines.
A German prior art patent concerns a mechanism with an alternating cam moved by a rotating cam; adjustment consists of placing the main camshaft out of center in such a way as to cause relative rotation of the alternating cam with respect to the lever that actuates the valve. Adjustment by the main out-of-center camshaft precludes the use of a single camshaft for both intake and exhaust, and the resulting mechanism is far too bulky.
The present invention makes it possible to avoid these drawbacks by using a valve actuation device built according to the principle of a kinematic chain with two cams; the main cam, in fixed-axis rotation, communicates the invariable primary reciprocating movement to a reciprocating/pivoting arm, based on which the appropriate system makes it possible to use all or part of the profile of the secondary valve lift cam, which can be static, reciprocating, or rocking, depending on the manner in which the invention is realized. The invariable back-and-forth laws in reciprocating movement can be perfectly symmetrical or very distinct; the result is that the valve opening and lift phase are symmetrical or asymmetrical, respectively. For very brief valve opening times, it is preferable to limit valve lift distance in order to avoid considerable efforts on the parts. With sufficient valve opening time, however, it is possible to maintain a long valve stroke or modify it very gradually, increasing the travel range.
The present invention offers the widest possible choice for the law of primary alternating movement; the entire minimized travel range is used by the second valve lift cam during the greatest valve opening time. This advantage is possible due to the neutral portion of the reciprocating movement, corresponding to the neutral portion of the main c

REFERENCES:
patent: 1444857 (1923-02-01), Taub

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