Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1997-09-23
1999-10-26
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9017, F01L 134, F02D 1302
Patent
active
059709294
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
For specific applications such as heavy armored vehicles, high speed boats, transportable generating sets, the diesel engine market requires diesel engines with a very high power density. This means very high turbocharged engines with high b.m.e.p.(brake mean effective pressure). The present Invention brings a way to make such engines with low fuel consumption and low emissions.
2. Description of the Related Art
With given swept volume and revolution per minute, an increase of the engines output need bigger amount of air for combustion. This amount of air depends on the inlet pressure. But the increase is limited because the higher is the inlet pressure, the higher is the pressure at the end of the compression stroke and the higher is the combustion pressure. A high combustion pressure may cause mechanical stresses in most of the components of the engine like the crankshaft. In addition to that, a high combustion pressure reduces the oil film thickness of the bearings and the life span of the piston rings.
One solution for maintaining the combustion pressure at a limited high level consists of reducing the compression ratio of the engine. But a low compression ratio makes the starting difficult and sometimes impossible. This is why some low compression ratio engines have an additional external combustion chamber. That combustion chamber must be started before the engine in order to give energy to the turbocharger. The combustion chamber and the turbocharger work together in a loop around the engine. When the air given by the turbocharger reaches a sufficient pressure and temperature, the engine can be started. Thanks to such combustion chamber, some engines run at a bmep of 35 bars. But the control of the combustion chamber, the engine starting phase and the idle are very sophisticated. The combustion chamber must be "on" all the time and the fuel consumption of these engines is rather high. The present invention offers a better solution for getting an output increase with a low compression ratio.
BRIEF SUMMARY OF THE INVENTION
The main object of the Invention is to be able to build a diesel engine with a very high b.m.e.p. (brake mean effective pressure), low b.s.f.c. (brake specific fuel consumption) and low emissions. This object is attained with the combination of: between the cams themselves (at least 45.degree. measured on the crankshaft) The cam profiles and timing are chosen in such a way that the exhaust valve is closed before the inlet valve opens.
The advantages of the present invention are the following:
a) High power density:
With this invention, it becomes possible to reach very high output of an engine because the very low compression ratio permits to feed the engine with fresh air under high pressure without reaching high combustion pressure which could have induced too high stresses on mechanical parts of the engine. The hot gases from the previous cycle which are kept into the cylinder become very hot after the compression stroke and ensure the short ignition delay which is needed for a good combustion.
b) Low fuel consumption:
When the engine runs at full load, the camshaft is in the backward position. The late closing of the inlet valve gives the low compression ratio and the late opening of the exhaust valve gives to the engine a high expansion ratio which increases the overall efficiency of the engine. This is the great advantage of the asymetrical cycle. The camshaft timing makes possible to control and optimise the amount of energy which is given to the turbochargers and to use machines with high efficiency.
c) Low emissions.
The low compression ratio reduces the temperature of the air at the end of the compression stroke. Because the cams profile and the timing have been chosen in order to have no scavenging of fresh air, it remains some hot burned gases from the previous cycle. At the end of the compression stroke, there are in the combustion chamber: temperature but with low oxygen content. high oxygen content. This is the
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patent: 4703734 (1987-11-01), Aoyama et al.
patent: 5020487 (1991-06-01), Kruger
patent: 5396874 (1995-03-01), Hitomi et al.
patent: 5421308 (1995-06-01), Hitomi et al.
Lo Weilun
Tacquet Maurice
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