In-vehicle engine control apparatus

An in-vehicle engine control apparatus, comprising:

• a drive control circuit unit comprising a plurality of switching devices for sequentially driving electromagnetic coils of fuel injectors provided for respective cylinders of a multi-cylinder engine, in order to cause electromagnetic valves of said fuel injectors to open;
• a boost control circuit unit for generating a boosted high voltage for quickly magnetizing one of the plurality of electromagnetic coils;
• and
• a calculation control circuit unit comprising a microprocessor and a program memory as principal components,
• the program memory storing a control program controlling the generation of fuel injection command signals directed to the plurality of switching devices and for determining whether a given fuel injection command signal is to be generated once or a plurality of times during each fuel cycle period of one cylinder of the multi-cylinder engine,
• the boost control circuit unit comprising an inductive device to be intermittently magnetized by a boost switching device from an in-vehicle battery when the boost switching device is closed and a high voltage capacitor to be charged to a target voltage by a plurality of inductive device discharge operations in which electromagnetic energy accumulated in the inductive device is discharged when the boost switching device is opened,
• the boost switching device comprising a slew rate selection circuit for selecting a slew rate, which is a current increase rate through said boost switching device after a close command signal is fed to said boost switching device, from among a plurality of different boost switching device slew rate values,
• the program memory further comprising a control program and reference data, the control program serving to specify a selection value of the slew rate for the slew rate selection circuit, and the reference data comprising one of a data table and an approximation equation,
• the reference data comprising numerical data of a maximum permissible engine rotational speed determined by using the selection value specified for the slew rate selection circuit as a parameter, and using a measured environmental temperature relating to an operating environment of the boost switching device detected by an environmental temperature detector as a variable,
• the maximum permissible engine rotational speed being a largest speed such that an internal temperature of the boost switching device will be equal to or less than a predetermined permissible limit temperature even when, at the measured environmental temperature, the selection value of the slew rate is applied and a continuous operation is carried out while injection is carried out for a plurality of times, said maximum permissible engine rotational speed being based on statistical data of operating experiments,
• the control program being configured to compare a value of an engine rotational speed detected by an engine rotation sensor and a value of a maximum permissible engine rotational speed corresponding to a current measured environmental temperature to thereby determine the selection value, said maximum permissible engine rotational speed being calculated through interpolation from the reference data,
• the calculation control circuit unit being configured to select the selection value of the slew rate as small as possible under a condition that the internal temperature of the boost switching device, that will correspond to a current engine rotational speed and current measured environmental temperature, is equal to or less than the predetermined permissible limit temperature, to thereby suppress the current increase rate of the boost switching device.