Start control device of compression self-ignition engine

1. A start control device including a compression self-ignition engine, fuel injection valves for injecting fuel into cylinders of the engine respectively, a piston stop position detector for detecting stop positions of pistons, and a starter motor for applying a rotational force to the engine, the engine combusting through self-ignition, the fuel injected into the cylinders by the fuel injection valves, the device automatically stopping the engine when a predetermined automatic stop condition is satisfied, and thereafter, when a predetermined restart condition is satisfied, restarting the engine by injecting the fuel while applying the rotational force to the engine, the device comprising:

a determining module for determining whether a piston of a compression-stroke-in-stop cylinder that is stopped on a compression stroke by automatically stopping is within a specific range set on a bottom dead center side of a predetermined reference stop position;

an injection control module for controlling each of the fuel injection valves to inject the fuel into the compression-stroke-in-stop cylinder first after the piston of the compression-stroke-in-stop cylinder is determined to be stopped within the specific range and the engine restart condition is satisfied; and

an in-cylinder pressure estimating module for estimating an in-cylinder pressure of the compression-stroke-in-stop cylinder at a first top dead center on the compression stroke in a restart, where the piston of the compression-stroke-in-stop cylinder reaches after the restart starts,

wherein each of the pistons is formed with a cavity in a predetermined part of its crown surface facing the fuel injection valve, the cavity being recessed with respect to other parts of the crown surface,

wherein the injection control module performs, at least as the first fuel injection to the compression-stroke-in-stop cylinder, a main injection for causing a main combustion so that a heat release rate reaches its peak after the compression TDC, and a pre-injection for causing a pre-combustion so that the heat release rate reaches its peak before the main injection starts, and

wherein the pre-injection is performed once or more at such timings that the injected fuel is kept substantially contained within the cavity of the piston, and the number of pre-injections is increased and an injection amount per single pre-injection is set less as the in-cylinder pressure at a first compression TDC is lower.

2. The device of claim 1 , wherein the in-cylinder pressure estimating module estimates the in-cylinder pressure at the first compression TDC based on the piston stop position of the compression-stroke-in-stop cylinder, an engine stop period of time that is an elapsed period of time from when the engine is completely stopped until the restart condition is satisfied, a coolant temperature of the engine, and an atmospheric pressure.

3. The device of claim 1 , wherein the injection control module changeably sets a number of pre-injections between two and five.

4. The device of claim 2 , wherein the injection control module changeably sets a number of pre-injections between two and five.

5. The device of claim 1 , wherein the compression self-ignition engine is a diesel engine of which a geometric compression ratio is set between 12:1 and below 16:1.

6. The device of claim 2 , wherein the compression self-ignition engine is a diesel engine of which a geometric compression ratio is set between 12:1 and below 16:1.

7. The device of claim 3 , wherein the compression self-ignition engine is a diesel engine of which a geometric compression ratio is set between 12:1 and below 16:1.

8. A method of controlling a start of a compression self-ignition engine, including injecting fuel into cylinders of the engine by fuel injection valves, respectively, detecting stop positions of pistons, applying a rotational force to the engine by a starter motor, combusting the engine through self-ignition, the fuel injected into the cylinders by the fuel injection valves, automatically stopping the engine when a predetermined automatic stop condition is satisfied, and thereafter, when a predetermined restart condition is satisfied, restarting the engine by injecting the fuel while applying the rotational force to the engine, the method comprising:

determining whether a piston of a compression-stroke-in-stop cylinder that is stopped on a compression stroke by automatically stopping is within a specific range set on a bottom dead center side of a predetermined reference stop position;

controlling each of the fuel injection valves to inject the fuel into the compression-stroke-in-stop cylinder first after the piston of the compression-stroke-in-stop cylinder is determined to be stopped within the specific range and the engine restart condition is satisfied; and

estimating an in-cylinder pressure of the compression-stroke-in-stop cylinder at a first top dead center on the compression stroke in a restart, where the piston of the compression-stroke-in-stop cylinder reaches after the restart starts,

wherein each of the pistons is formed with a cavity in a predetermined part of its crown surface facing the fuel injection valve, the cavity being recessed with respect to other parts of the crown surface,

wherein controlling each of the fuel injection valves to inject the fuel includes performing, at least as the first fuel injection to the compression-stroke-in-stop cylinder, a main injection for causing a main combustion so that a heat release rate reaches its peak after the compression TDC, and a pre-injection for causing a pre-combustion so that the heat release rate reaches its peak before the main injection starts, and

wherein the pre-injection is performed once or more at such timings that the injected fuel is kept substantially contained within the cavity of the piston, and a number of pre-injections is increased and an injection amount per single pre-injection is set to be less as the in-cylinder pressure at the first compression TDC is lower.