1. Field of the Invention
The present invention relates to a method and a control apparatus for controlling a high-pressure fuel supply pump which is configured to supply pressurized fuel to an internal combustion engine, in particular to a common rail having a plurality of fuel injectors for injecting pressurized fuel into a combustion chamber of the internal combustion engine. Specifically, the present invention relates to a method and a control apparatus for controlling a high-pressure fuel supply pump which comprises a compression chamber, a normally-open-type solenoid-actuated intake valve for delivering unpressurized fuel to the compression chamber, a movable plunger reciprocating in the compression chamber between a first plunger position, e.g. the so-called bottom dead center position, and a second plunger position, e.g. the so-called top dead center position, for pressurizing fuel in the compression chamber, and a discharge valve for discharging pressurized fuel from the compression chamber to be supplied to the internal combustion engine. The normally-open-type solenoid-actuated intake valve of the high-pressure fuel supply pump is configured to be closed or kept closed by means of magnetic force. The present invention also relates to a computer program product comprising computer program code means configured to adapt a control apparatus.
2. Description of the Related Art
In recent years, gasoline direct injection (GDI) has become increasingly popular due to its advantages for increased power (due to a lower tendency to knock) and hence higher fuel efficiency. In gasoline direct injection, low-pressure fuel is delivered from the fuel tank by means of a low-pressure fuel pump to a high-pressure pump. In a compression chamber of the high-pressure pump, the low-pressure fuel is pressurized to high pressure and delivered to a common rail comprising a plurality of injectors for being directly injected at high pressure into a combustion chamber of the internal combustion engine.
In general, the amount of high-pressure fuel supplied by the high-pressure fuel supply pump is electronically controlled by controlling a solenoid-actuated intake valve of the high-pressure fuel supply pump. There are known normally-closed-type solenoid-actuated intake valves which can be opened and/or kept open by energizing one or more solenoids of the solenoid-actuated intake valve while being biased by one or more biasing members (such as e.g. springs) into a closing direction of the solenoid-actuated intake valve. Also, there are known normally-open-type solenoid-actuated intake valves which can be closed and/or kept closed by energizing one or more solenoids of the solenoid-actuated intake valve while being biased by one or more biasing members (such as e.g. springs) into an opening direction of the solenoid-actuated intake valve, the present invention relating to the latter normally-open-type solenoid-actuated intake valves.
Regarding high-pressure fuel supply pumps comprising normally-open-type solenoid-actuated intake valves, there are known two operation concepts for controlling the normally-open-type solenoid-actuated intake valves. According to a first-type operation concept as described in DE 10 2008 054 512 A1, the periodic operation cycle of the high-pressure fuel supply pump comprises firstly an intake period in which fuel is taken in through the intake valve into the compression chamber while a movable plunger moves in the compression chamber from a second plunder position (generally ref erred to as top dead center position) to a first plunger position (generally referred to as bottom dead center position) and the solenoid-actuated intake valve opens or is kept open by means of a biasing force, e.g. by a spring, during the intake period, secondly a spill period in which fuel is spilled out of the compression chamber through the intake valve while the movable plunger moves from the first plunger position to the second plunger position and the solenoid-actuated intake valve kept open by means of the biasing force or by means of the biasing force and hydraulic force of the fuel, and thirdly a delivery period in which fuel is pressurized in the compression chamber and discharged through a discharge valve of the high-pressure fuel supply pump to be supplied to the internal combustion engine while the movable plunger moves from the first plunger position to the second plunger position and the solenoid-actuated intake valve is kept closed by means of magnetic force.
According to the first-type operation concept, the normally-open solenoid actuated intake valve is kept closed until the movable plunger reaches the top dead center position by applying a control current to the solenoid-actuated intake valve, e.g. by applying a control voltage to the solenoid actuated intake valve. Then, after shutting off the control current when the movable starts its movement backwards towards the bottom dead center position, the normally-open intake valve opens due to the biasing force acting in the opening direction (possibly in combination with a hydraulic force generated by low-pressure fuel flowing through the intake valve into the compression chamber due to the increasing volume of the compression chamber while the movable plunger is moving towards the bottom dead center position). When the normally-open intake valve reaches a fully open position of the intake valve, an impact noise is generated which, especially for lower engine speeds such as e.g. the idle condition, will even dominate the overall noise of the engine.
For reducing the impact noise, when the normally-open intake valve reaches a fully open position, it is proposed in DE 10 2008 054 512 A1 to apply another pulse of control current to the solenoid-actuated intake valve after shutting off the control current in order to reduce the speed of the intake valve during the opening movement of the intake valve.
According to an alternative second-type operation concept as described in DE 101 48 218 A1, the periodic operation cycle of the high-pressure fuel supply pump comprises firstly an intake period in which fuel is taken in through the intake valve, if the intake valve is kept open during the intake period, or through an optionally provided auxiliary valve, if the intake valve is kept closed during the intake period by applying control current to the solenoid-actuated intake valve, into the compression chamber while the movable plunger moves from the second plunger position to the first plunger position, secondly a delivery period in which fuel is pressurized in the compression chamber and discharged through the discharge valve to be supplied to the internal combustion engine while the movable plunger moves from the first plunger position to the second plunger position and the solenoid-actuated intake valve is kept closed by means of magnetic force, and thirdly a spill period in which fuel is spilled out of the compression chamber through the intake valve while the movable plunger moves from the first plunder position to the second plunger position and the solenoid-actuated intake valve opens or is kept open by means of the biasing force.
According to the second-type operation concept, the normally-open solenoid actuated intake valve is kept closed until a time when the movable plunger moves towards but has not yet reached the top dead center position by applying a control current to the solenoid-actuated intake valve, e.g. by applying a control voltage to the solenoid actuated intake valve. Then, after shutting off the control current at a time in which the movable plunger still moves towards the top dead center position, the normally-open intake valve opens due to the biasing force acting in the opening direction (possibly in combination with a hydraulic force generated by pressurized fuel in the compression chamber due to the decreasing volume of the compression chamber while the movable plunger is moving towards the top dead center position). When the normally-open intake valve reaches a fully open position of the intake valve, an impact noise is generated which especially for lower engine speeds such as e.g. the idle condition will even dominate the overall noise of the engine.
For reducing the impact noise, when the normally-open intake valve reaches a fully open position, it is proposed in DP 101 48 218 A1 to apply another pulse of control current to the solenoid-actuated intake valve after shutting off the control current in order to reduce the speed of the intake valve during the opening movement, of the intake valve.
However, the teaching of DE 10 2008 054 512 A1 and DE 101 48 218 A1 of applying another pulse of control current of the solenoid-actuated intake valve after shutting off the control current suffers from the problem that the timing and the control current value of the pulse for reducing the speed of the opening movement has to be very accurately adjusted in order to actually help to reduce the noise of the operation of the high-pressure fuel supply pump. Specifically, if the timing of the pulse is too late or the control current value is too low, the pulse will be too late or too weak to reduce the speed of the opening movement so that the intake valve will nevertheless reach the fully open position at high speed and generate a loud impact noise.
On the other band, if the timing of the pulse is too early or the control current value is too high, the pulse may have a negative effect in that the speed of the opening movement of the intake valve may not be only reduced but stopped. It is even possible that the intake valve will, due to the pulse of control current, be closed again, possibly even up to the fully closed position (thereby possibly generating a noise when reaching the fully closed position) and after shutting off the control current of the pulse, the intake valve will start again moving in the opening direction due to the biasing force (and/or force) until it reaches the fully open position without any reduction in speed, thereby again having a high impact speed and generating a loud noise. Also, the valve will in such a situation reach the fully open position at a later time at which the movable plunger may have already an even higher movement speed depending on the cam profile. Then, the valve may even reach the fully open position at an even higher impact speed than without applying the deceleration pulse and even generate a louder impact noise.
In view of this problem, it is necessary to accurately adjust the pulse to the operating conditions such as the engine speed and the temperature of the fuel as well as to individual properties of the intake valve which can vary from one high-pressure fuel pump to another high-pressure fuel supply pump due to mass production deviations. For example, in DE 10 2008 05 512 A1, it is taught to use a cumbersome closed-loop control using a pressure sensor in order to be able to individually adjust the control of the pulse in accordance with the operating conditions such as the engine speed as well as in accordance with individual properties of the intake valve.