Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1995-12-22
1997-02-18
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9039, 123568, F01L 1300, F02M 2507
Patent
active
056032927
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a valve mechanism in an internal combustion engine, comprising at least one intake valve and at least one exhaust valve in each cylinder and, for each cylinder, at least two rocker arms journalled on a rocker arm shaft for operating the valves.
There are great potential gains to be achieved by reducing the harmful substances in diesel exhaust by recirculation of exhaust, without adversely affecting engine efficiency or soot level as much as with other methods.
Recycling exhaust which has first been cooled is an effective step, especially at high load, but the required cooling power will be quite high and a cooling device will be required which can provide half the cooling power of the engine intercooler. Since the exhaust is polluted and hot, there will, however, be practical problems with such a system. Returning exhaust without cooling has positive effects primarily when engine load is low but not quite as positive when the engine load is high.
Conventional systems for exhaust return comprise shutter and valve devices in the exhaust and intake systems. When using such systems in turbo-charged engines, there will, however, be problems due to the fact that the pressure is higher on the intake side than on the exhaust side. Thus, some form of pump device is needed to get the exhaust to the pressure side of the turbo compressor. Alternatively, one could lead the exhaust to the suction side of the turbo compressor prior to the intercooler, but this is not practical, since hot dirty exhaust would soon destroy the intercooler.
The purpose of the present invention is, starting from a conventional valve mechanism of the type described by way of introduction, to achieve an arrangement, by means of which exhaust can be returned to the intake air without requiring an extra shutter and valve system on the exhaust and intake side.
This is achieved according to the invention by means of a valve mechanism which has transmission means which are arranged to selectively open the exhaust valve during the engine intake stroke to draw exhaust into the cylinder during the intake stroke.
Such an arrangement avoids condicting the exhaust to the intake side and eliminates problems with soiling and deposits. The invention utilizes the fact that, even in a supercharged engine, the pressure in the cylinder after the initial intake stroke during the intake cycle, is lower than the exhaust pressure, due to the pressure drop over the intake valve. This eliminates the need for an extra pumping device for exhaust return.
According to a preferred embodiment of the valve mechanism according to the invention, the transmission means comprise a second shaft rotatably journalled parallel to the rocker arm shaft and having first and second pivot arms, non-rotatably joined to said shaft, the first of which interacts with the intake rocker arm to convert its rocking motion to a rotary movement of the second shaft, and the second of which interacts with the exhaust rocker aim to convert the rotary movement of the second shaft into a rocking movement of the exhaust rocker arm. One of said surfaces is made as a cam surface, so that the lifting of the exhaust valve during the intake stroke is variable from no lift at all in a predetermined axial position of the second shaft to maximum lift after a certain displacement of the second shaft from said predetermined position.
By varying the length of the open time for the exhaust valve during the intake stroke it is possible to regulate the mount of recirculated exhaust and determine the percentage of exhaust in the Combustion air. Since the opening of the exhaust valve is effected individually in each cylinder and can be rapidly controlled, the mixing-in of exhaust will be well defined and can be varied as a function of engine work load or rpm for example. It is not affected by residual gases in the intake manifold for example as in conventional systems. Each axial position of the second shaft and thus of the second pivot arm will thus define a given lifting height and ti
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AB Volvo
Lo Weilun
LandOfFree
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