Sensor Engine running. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Sensor Engine running. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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The author proposes a block that is easy to repeat, at the output of which a signal appears about the start and operation of the car engine. Installing the sensor in the engine heating control device, developed and published earlier [1], leads to an increase in the reliability of the device. The sensor can also be used as a standalone.

When trying to install this device in a VAZ 21074 car with an injection engine, there were problems with the reliability of the start.[1]. The fact is that in these car models, the output pulses from the electronic unit - the tachogenerator sensor (DTG) have an amplitude of +5 V and are compatible with TTL logic in terms of level. Moreover, a constant component of +5 V appears immediately after the ignition is turned on, even before the engine is started. This voltage, supplied to the base of the transistor VT3 of the "engine running" sensor through a resistive divider R22-R24, caused starting problems. It was necessary to develop a new sensor, free from this drawback. It is made as a separate unit and can be installed not only in the previously developed engine warm-up control device, but also on other car models, including as an autonomous unit for indicating the start and operation of the engine.

Rice. 1. Sensor circuit (click to enlarge)

The sensor circuit is shown in fig. 1. It is assembled on a common K554CA3 chip [2] and two KT315G transistors. On transistor VT1, an amplifier-inverter of DTG signals is assembled, which appear at its output in the form of a sequence of rectangular pulses from the moment the starter starts the engine. Diodes VD1, VD2 rectify these pulses. Further, the rectified voltage smoothes the capacitor C4, and in the form of an increasing positive drop, it enters the emitter follower on the transistor VT2. From the output of the emitter follower, the increasing voltage drop is fed to the R5R6C5 delay circuit. It is necessary to delay the supply of voltage to the control unit so that the counter DD5 (see article and Fig. 1 [1]) normally works out the engine start time and only then turns off. The time-delayed voltage drop is fed to the inverting input of the comparator DA1, assembled on the above K554CA3 chip.

Resistors R7-R9 form a reference voltage source. The trimmer resistor R8 sets the threshold for the comparator, thereby adjusting the delay time. With the ratings of the R5R6C5 circuit indicated in the diagram, the delay time is 1,5 s when the engine resistor R8 sets the voltage at the non-inverting input of the comparator to about +3,8 V. After this time, after starting the car engine, a voltage of about 2 V will appear at the output (pin 1) of DA8 , which through the current-limiting resistor R13 is fed to the sensor output. LED HL1 indicates that the engine is running.

Resistors, oxide capacitors and ceramic C6, low-power diodes and npn transistors of any type can be used in the sensor. The K554CA3 chip can be replaced with an analog LM311, but it has a different pinout.

The sensor is assembled on a printed circuit board made of fiberglass laminated on one side with dimensions of 112x76 mm. A drawing of the printed conductors of the board and the elements located on it are shown in fig. 2.

Sensor Engine running
Rice. 2. Drawing of printed conductors of the board and elements located on it

To interface with the above control device [1], the sensor output is connected to pin 6 of connector X1.2, and the +9 V power line and common wire are connected to pins 1 and 2 of connector X5, respectively. If autonomous operation of the sensor is expected, then the +9 V power line is connected to the vehicle's on-board network through any +9 V voltage stabilizer with a load current of at least 20 mA.

The adjustment of the assembled sensor consists in setting the necessary delay by the engine of the tuning resistor R8.

If this device is built into a car with a carburetor engine, then the resistance of the resistor R1 must be increased to 100 kOhm, and an additional low-power zener diode (not shown in Fig. 1) should be installed at its input for a voltage of about 5 V, for example, KC447A. The cathode of the zener diode is connected to the connection point of the resistor R1 with the capacitor C1, and the anode to the common wire. On the printed circuit board for the zener diode, there are two free contact pads with holes.

Literature

Natnenkov A. Engine heating control device. - Radio, 2007, No. 7, p. 38-41.
Chipinfo. K554SA3A, K554SA3B - voltage comparator with low input current. - URL: chipinfo.ru/dsheets/ic/554/ca3.html.

Author: A. Natnenkov

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