Internal-combustion engines – Engine speed regulator – Having condition responsive means with engine being part of...
Patent
1997-06-23
1998-09-15
Miller, Carl S.
Internal-combustion engines
Engine speed regulator
Having condition responsive means with engine being part of...
73119A, 123372, F02D 3100
Patent
active
058064877
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a fuel injection pump unit, comprising a fuel injection pump wherein a control rod is displaced by an actuator and its position monitored by a position pickup, and a control unit which calculates an injection rate, from which injection rate a signal representative of a desired position of the element determining the injection rate is determined using stored characteristic values, and a control signal for the actuator is generated by a position controller by comparing the desired control rod position signal with an actual position signal furnished by the position pickup, stop means limiting the course of the control rod. The stored characteristic values give the correlation of injection rate (usually mm.sup.3 per stroke) and course of the control rod as a function of engine parameters (for instance engine revs) usually, but not necessarily as a characteristic mapping.
From DE 38 30 534 C, a process for readjusting a group of unit injectors actuated from a common control rod is known, whereby for correcting the measurement errors of the position pickup, two fixed stop means which are a known distance apart are struck and the corresponding pickup signals are used for correcting subsequently measured values. In this way, the position controller always compares the desired course of the control rod determined from the characteristic mapping with corrected, thus correct, actual values of the course of the control rod, in order to elaborate the output signal for the control rod. The characteristic mapping itself, instrumental to calculating the desired course of the control rod from the desired injection rate, remains completely unaffected thereby.
Further, from DE 30 11 595 A a correction circuit for a fuel metering system with drift compensation is known, where the correlation between injection rate and the position of the control rod in an operating point is corrected so as to make the signal equal to the original (before drift occurred) desired value signal correlating with this operating point. To this end, the original feedback signal is in this case adjusted to a certain injection rate. The expenditure is, however, considerable: The correlation is modified during operation with speed-control in the idling operating point until the position controller reaches the value correlating with the actual operating point; this requires an additional adjusting device. This method is time-consuming and requires either an elaborate pickup or the superposition of an additional error signal.
This gives a fairly accurate feedback signal, but the injection-pump-related accuracy of the desired value for each individual pump (differing from other individuals due to manufacturing tolerances), is at least equally important for accurate positioning of the control rod. These inaccuracies are not taken account of. Only an accurate feedback signal together with an accurate desired value safeguard accurate control of the injection rate. Modern diesel engines require highest accuracy of the injection rate for each individual cylinder. Foremost, this is in order to keep the air/fuel ratio and therewith toxic emissions within a very narrow range and in order to fully exploit the maximal rated performance, in case of individual injection pumps the maximal rated performance of each cylinder. As minimizing emissions of NOX requires measures contradictory with those required for minimizing the emission of particles, and as the optimal trade-off is restricted to a very narrow range of air/fuel ratios, the importance of accurate adjustment of the injection rate for minimizing emissions cannot be exaggerated. Minimizing emissions often requires also an accurate control of exhaust gas recirculation (EGR).
The accuracy of the desired value of the position of the element which determines the injection rate depends on the identity of the characteristic map of the injection pump with its actual individual pumping behavior, which not only depends on speed, but also on counter-pressure, thus fue
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Miller Carl S.
Steyr-Daimler-Puch Aktiengesellschaft
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