Automatic engine warmer. Scheme, description

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Automatic engine warmer. 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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This device is designed to keep the engine of a diesel car warm in the cold season in the absence of its owner. Many owners of such machines have had to deal with the problem of starting a diesel engine on frosty days, which is usually associated with a rather high freezing point of common brands of diesel fuel.

Expensive car models are equipped with a special machine that allows you to easily start and warm up the diesel engine at a specified time or at specified intervals. Based on this idea, I developed a device that starts a diesel engine at predetermined intervals, lets it run for a while and turns it off. The auto-heater was made in several copies and showed reliable operation. In particular, for three winters it has been successfully operated on a Ford Transit car.

The machine is a timer with actuators operating in the following mode: a two-hour pause, after which the ignition is turned on after 6 ... 8 s, necessary to warm up the glow plugs, the starter is turned on, the engine starts; it runs for 7 or 15 minutes, after which the ignition is turned off, the engine stops and a new two-hour pause follows.

The device is mounted on a car and is powered from the on-board network with a voltage of 12 V; the current consumed during a two-hour pause is not more than 200 mA.

Most diesel engines are equipped with special glow plugs designed to heat the fuel and installed in the cylinders (one per cylinder), or one plug on the intake pipe. To start a modern diesel engine in winter, the ignition is first turned on - the fuel supply solenoid valve opens. Further, depending on the method of turning on the glow plugs, two options are possible:

1. After the ignition is switched on, voltage is supplied to the thermal contact relay for glow plug control. If the fuel temperature is too low, the relay will trip and the spark plugs will turn on. After the fuel warms up, the relay turns off the candles, i.e. after the ignition is turned on, it is necessary to pause for 2 ... 8 s until the control lamp turns off and turn on the starter.

2. The candle control relay and, thus, the candles themselves are turned on with a special button placed on the instrument panel. The relay can only be switched on after the ignition is switched on. Candles are turned off by the same relay by means of a thermocontact sensor after heating the fuel or by releasing the button. In short, after turning on the ignition, press the button and pause (the same 2 ... 8 s) until the control lamp turns off.

Now the starter is turned on, and if the engine is serviceable and correctly adjusted, after several revolutions of the crankshaft, it starts and runs at a stable speed.

To work with the automatic heater, the driver must turn on the power of the device and, in option 2, the power of the candles (close the button contacts). Everything else is done by automation. If the button is not fixed in the pressed position, you need to connect a toggle switch in parallel with its contacts and install it in a convenient place.

After turning on the power with the SA2 toggle switch (see the diagram in Fig. 1), charging of the capacitor C3 with a voltage of 5 V from the VT12VD5R24 stabilizer through the resistor R6 begins. There is a voltage of 3 V on the collector of the closed composite transistor VT4VT5, which causes all counters DD1, DD3-DD5 to be reset to zero at input R. After about 0,5 s, the capacitor will charge, the VT3VT4 composite transistor will open, allowing the counters to work.

(click to enlarge)

The master generator of minute pulses is assembled on the DD1 chip, the frequency of which is stabilized by the ZQ1 quartz resonator. These pulses are fed to the input of the frequency divider, made on the counters DD3, DD4. 2 hours after the device is turned on, a high level will appear at the output 4 of the counter DD4, opening the transistors VT7, VT8, VT10. A voltage of 12 V will go to the output of the TC (fuel valve) of the machine, which corresponds to the ignition being turned on.

A high level from output 4 of counter DD4 passes through the VD3R9 circuit and charges capacitor C4. The node, made on the elements DD2.1, DD2.2, provides a time delay of 6 s, necessary for heating the glow plugs. After a specified time, a high level from the output of the DD2.2 element through the VD2R10C5 circuit enters the base of the composite transistor VT5VT6, as a result of which it opens, opening VT9 as well. Now a voltage of 12 V appears at the output of the PC (starter relay), which corresponds to turning the key in the ignition switch to the "Starter" position.

From this moment, the starter begins to rotate the crankshaft of the engine. At the same time, charging of the capacitor C5 begins, which lasts approximately 5 ... 6 s, after which the transistors VT5, VT6, VT9 will close and turn off the starter relay. This time is enough to start a serviceable engine.

Element DD2.3 monitors the voltage in the vehicle's on-board network. Based on the level of this parameter, the node determines whether the engine has started or not. Such a knot, although it requires fine adjustment, is the simplest.

Immediately after the power is turned on, the inputs of the DD2.3 element are set to a low level (since the capacitors C6 and C7 are discharged), and the output is high. At the lower input of the element DD2.4 according to the circuit, there is a low level (since at the first moment the capacitor C8 is discharged), therefore, at the output of this element there is a high level, due to which the transistor VT11 is open and the diode VD4 is closed.

At the moment of opening the transistor VT10 (turning on the ignition), the capacitor C8 is discharged, so the output of the element DD2.4 remains low and the VD4 diode also remains closed. Next, the capacitor C8 is charged, but the DD2.4 element can only switch when its upper input is high, and the voltage across the capacitor C8 reaches 2,5 V or more. This requires a period of time of about 10 s, by the end of which the engine should already be running.

After starting the engine, the voltage in the on-board network increases to 14,5-15 V. The voltage at the input of the DD2.3 element also increases, the high level at its output is replaced by a low one, due to which the state of the DD2.4 element does not change.

If the engine does not start or starts and stops, then the voltage in the on-board network has decreased to 13,5 ... 12,5 V, depending on the degree of charge of the battery. At the same time, a high level will appear at the output of the DD2.3 element and at the upper input of the DD2.4 element according to the scheme, and a high level will also appear at the lower input of the DD2.4 element. As a result, a low level will appear at the output of the DD2.4 element, the VT11 transistor will close, and the VD4 diode will open, which, in turn, will reset the counters DD1, DD3-DD5, close the VT10 transistor and emergency ignition off. This prevents situations where the engine is not running and the ignition is on.

Simultaneously with the opening of transistors VT7, VT8, VT10, a high level from output 4 of the counter DD4 is fed to the CN input of the counter DD5 and allows the counting of minute pulses. The SA1 switch selects the number to be counted - 8 or 16. Thus, depending on the position of the SA1 switch contacts, after 8 or 16 minutes a high level will open the VT2 transistor and the counters will be reset, i.e. the ignition will be turned off and the engine will stop. The duration of the reset pulse is very short (less than 1 µs). Immediately after it, a new counting of minute pulses by counters DD3, DD4 begins, and after 2 hours all of the above processes are repeated.

Resistor R17 sets the threshold voltage of the on-board network, at which the element DD2.3 switches.

The scheme of connecting the machine to the electrical equipment of the car is shown in fig. 2 (ЗЗ - ignition lock; GB1 - battery).

Engine heater

Almost all parts of the machine are mounted on a printed circuit board placed in a plastic case. Connect the device to the car with a four-wire cable through the connector, the socket of which is installed near the ignition switch. The length of the cable must allow the machine to be placed on the front seat of the car.

Capacitor C1 - any ceramic trimmer, C2 - ceramic or mica, C10, C11 - ceramic or metal-paper, the rest - oxide K50-35. Chip K176LA7 can be replaced by K561LA7. The main requirement for transistors is a static current transfer coefficient of at least 50. KT315, KT817 transistors can be used with any letter indices. Instead of KT818V, other powerful pn-p transistors with a current transfer coefficient of at least 50 are also suitable.

Since powerful transistors VT9, VT10 operate in switching mode and at low ambient temperatures, it is enough to install them on heat sinks with an area of 5 cm2 each.

Diodes D220 are replaceable by others for a maximum current of at least 20 mA. Instead of the AL307A LED, any other is suitable, you just need to pick up the resistor R4.

To set up the machine, first temporarily connect the CP input of the counters DD3 and DD5 to the output S1 of the DD1 microcircuit, i.e., instead of minute pulses, seconds are fed to the inputs of the counters. For control, it is more convenient to use an oscilloscope, but you can get by with a conventional autometer. The switch SA1 is set to the "16 min" position.

Turning on the power (12 ... 13 V), check the presence of minute pulses at the output M of the DD1 microcircuit and second pulses at the output S1. Next, the operation of the counters DD3-DD5 is checked, for which the base of the transistor VT2 is turned off. With their proper operation, after about 2 minutes, a high level should appear at the output 4 of the DD4 counter, and after 16s, at the output 16/10 of the DD5 counter. After checking, the output of the base of the transistor VT2 is soldered in place.

Then, two signal lamps HL1 and HL2 (Fig. 3) are connected to the machine, simulating the load and indicating the moments of switching on the vehicle components (G1 - any power source for a voltage of 14 V and a current of 2 ... 3 A), and check the correct operation of the device in in general. A selection of capacitors C4 and C5 set, respectively, the operating time and the starter turn-on delay.

Engine heater

The final laboratory operation is the adjustment of the emergency ignition shutdown unit. The machine is supplied with a regulated supply voltage within 12 ... 15 V. By increasing the supply voltage from 13 V, with a tuned resistor R17, they ensure that at 14 V the DD2.3 element switches to the 0 state.

Next, the machine is installed on the car and once again check the operation in the "16 min" position of switch SA1. After turning on the power, a time delay of 2 minutes should follow, then the ignition is turned on. After 6 s, the starter is turned on, the engine starts, after another 3 ... 4 s, the ignition is turned off and the engine stops. If necessary, adjust the emergency shutdown unit. After all these operations restore the connection of the input of the counters DD3, DD5 to the output M of the counter DD1.

In conclusion - a few recommendations for the operation of the device. Those who want to repeat this design must clearly understand that before turning on the machine, it is necessary to de-energize all electrical appliances in the car, put the gearbox in neutral, apply the handbrake or put blocks under the wheels. You will have to put a hose on the exhaust pipe and bring its free end out. Neighbors in the garage need to be informed about the installation of an automatic heater on your car.

Author: A. Dubrovsky, Novopolotsk, Belarus

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