Measuring and testing – Internal combustion engine or related engine system or... – Compression
Patent
1986-11-07
1988-12-20
Heyman, John S.
Measuring and testing
Internal combustion engine or related engine system or...
Compression
328 1, 307290, 307494, 123478, F02B 4900
Patent
active
047918098
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a circuit arrangement to detect signals indicating a change in current through a needle lift sensor of an injection nozzle in combustion engines, which is connected to a in the circuit arrangement.
In the case of combustion engines with fuel injection, injection valves are utilized, in which the valve needle, under the pressure of the fuel that is to be injected, is moved against the force of a spring for a short time and periodically. By doing so it is lifted off its valve seat. Since an optimal regulation would require knowing the exact moment of injection, as well as the duration of injection, injection valves with integrated needle lift sensors have been developed which supply an output signal depending on the location of the nozzle needle, often magnetically by means of utilizing reverberating elements.
In a commercially available injection nozzle of this type, the sensor is supplied with a constant direct voltage and when the valve is opened a change in current of approximately 10% occurs, which amounts to less than one milliampere. In conventional combustion engines the duration of the sensor pulse is approximately between 0.5 and 15 ms; the distance between them is approximately 50 and 250 ms. Because of its minor relative and absolute magnitude, it is often difficult to detect this change in current, especially due to the high level of interference prevailing in motor vehicles. Furthermore, even negligible changes in the supply current can result in changes in the current, which could be misunderstood as pulses of the needle lift sensor and it has to be taken into account that the duty factor can range from approximately 0.2 to 25%.
It is an object of the invention to create a circuit arrangement which would allow for a reliable detection of such changes in current under the conditions predominant in motor vehicles and which would require little effort.
This object can be achieved by means of a circuit arrangement of the type mentioned above, in which, according to the invention, the sensor is located at the controlled outlet of a controlled source of direct voltage and a sensing resistor is connected between the outlet of the regulating amplifier and the outlet of the source of direct voltage. In addition, the outlet of the regulating amplifier is connected to the input of an AC amplifier with a band-pass characteristics and the outlet of the AC amplifier is connected to the input of a Schmitt trigger, the output signal of which represents the changes occurring in the sensor current.
According to the invention, a circuit arrangement which is especially resistant to interference is characterized by having the sensor located at the output terminals of a controlled direct voltage source with two symmetrically-working regulating amplifiers, by connecting one sensing resistor between each of the outlets of the regulating amplifiers and the output terminals of the direct voltage source respectively, by connecting the outlets of the regulating amplifiers with the inputs of a symmetrical AC amplifier with a band-pass characteristics, and by connecting the outlet of the AC amplifier with the input of a Schmitt trigger, the output signal of which represents the changes in the sensor current.
In order to also substantially suppress the interferences caused by the grounding, it is advisable to connect a filter capacitor between the reference voltage inputs of both regulating amplifiers, each of which is connected to a pole of the reference voltage via one resistor each.
It has also proven advantageous to equip the automatic control amplifier(s) with a capacitor in the feedback path in order to achieve low-pass characteristics.
For the purpose of an increased resistance against interference it is advisable to maintain the lower boundary frequency of the AC amplifier between 5 and 10 Hz and the upper boundary frequency between 15 and 30 KHz.
Moreover, it is advisable if the regulating time constant of the controlled direct voltage source were at a value below 1 .mu.s, preferably below
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"Voltage-regulated power supply delivers constant current", Thomas E. Skopal, Electronics, Dec. 12, 1974, page 126.
Heyman John S.
Vigil Thomas R.
Voest-Alpine Friedmann Gesselschaft M.B.H.
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