Compression ignition engine

Abstract

In a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of an intake valve lift and an intake valve closure timing, a control system operates to temporarily lower an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation. At a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise, the effective compression ratio is risen by controlling the intake valve characteristic. After combustion of the engine has been stabilized, the intake valve characteristic is brought closer to a desired value determined based on engine operating conditions by way of closed-loop control.

Description

TECHNICAL FIELD [0001] The present invention relates to a compression ignition engine employing a variable valve operating system for at least one of intake and exhaust valves, and specifically to the improvement of a compression ignition engine control technology suited to compression ignition engines such as a four-stroke-cycle Diesel engine, a two-stroke-cycle Diesel engine, a premix compression ignition engine, and the like. BACKGROUND ART [0002] In recent years, there have been proposed and developed various engine control technologies for compression ignition engines with variable valve operating systems. Generally, a variable valve operating system, capable of variably adjusting a valve lift and valve timing of at least one of intake and exhaust valves of a reciprocating internal combustion engine depending on engine operating conditions, is widely utilized for controlling a charging efficiency, an effective compression ratio, and an amount of residual gas of the engine, ther...

AI Technical Summary

Benefits of technology

[0008] It is, therefore, in view of the previously-described disadvantages of the prior art, an object of the invention to provide a compression ignition engine, capable of avoiding the aforementioned problem that spontaneous ignition of fuel does not take place owing to a drop in cranking speed during a starting period.

Problems solved by technology

The increased work of compression leads to a drop in cranking speed, thereby resulting in an increased heat loss of the compressed air (compressed gas).

As a result of this, a compression temperature, i.e., a temperature of the compressed gas, tends to drop, thus deteriorating the engine startability.

That is to say, the effective compression ratio is controlled to a relatively low ratio, though there is a possibility that the combustion stability is still insufficient just after completion of the starting operation.

This leads to the problem of deteriorated combustion stability.

This leads to another problem of increased manufacturing costs and increased weight.

However, the decompression device itself does not have an effective-compression-ratio reducing function that reduces the effective compression ratio after completion of the starting operation.

Thus, it is difficult to realize the improved fuel economy (i.e., the reduced fuel consumption rate) during normal engine operation, by the use of the decompression device.

However, according to the system of JP1-315631, the effective compression ratio remains high during cranking, thus resulting in an undesirable drop in cranking speed.

This also leads to the problem of reduced cranking speed.

However, even after cranking operation, intake valve closure timing IVC remains retarded, thus deteriorating the engine startability or self-ignitability during start operation.

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