It is known that the temperature mode of the motor vehicle depend strongly on many of its characteristics. As insufficiently warmed the engine overheated is a source of additional problems.
Now the drivers that have to drive on the streets of big cities, are increasingly get into the situation where for a long time you can only move walking speed, and then, in General, no longer stand. In the summer in such "traffic jams" the engine of the machine is usually quickly overheats and requires downtime for cooling.
About how to make life easier for yourself and the vehicle in such cases, says the author of this article.
A sad joke: a motorist who dropped out to go on a domestic machine, the difficulties of not experiencing disadvantage. Really, he's always at hand their wide range - from a cold start in cold weather before, no matter how paradoxically, running, hot engine in hot weather. I propose to discuss some features of the overheating of the engine.
On most modern cars put an electric fan, equipped with simple Electromechanical automation (see scheme in Fig. 1). The node connected to the clamp 15/1 ignition switch. Note that terminal marking the electrical system complies with international, which also made all leading domestic car manufacturers.
The sensor on the motor M1 fan thermal switch is SF1, mounted usually on the radiator. If the temperature of the car engine increases, but has not yet reached the upper threshold (99&No. 176;C for car Vase and 92 - AZLK), contacts SF1 will be open, and the motor is de-energized.
Once the engine has warmed up to the upper temperature threshold, contacts sensor SF1 closes, will relay contacts K1 and K1.1 will include the motor M1 of the fan. Will begin an intensive cooling of antifreeze in the cooling system.
When the engine temperature falls below the lower temperature threshold (94&No. 176;for vehicles With Vase and 87&No. 176;C - AZLK), contacts SF1 will open and the fan will again be de-energized. Thus set temperature operating conditions of the engine. Described automatic cooling system works quite satisfactorily during movement and even in the Parking lot if the weather is moderately hot. However, once you get into a traffic jam on a hot summer day, will have to ensure that car fan works without turning off and the engine temperature dangerously is growing.
In such circumstances, attempts at least for a short time, stop the engine, to cool him, most likely will not lead to the desired result, but even on the contrary. After all when the ignition is fully de-energized and the fan, a heat radiating engine will create under the hood real "sauna", the carburetor and the fuel pump will quickly become overheated, as this may cause a again to start the engine you probably will not succeed.
How can that be?
To some extent alleviate the situation by applying automatic electronic switch of the fan. It is connected to the host automation as shown in the diagram Fig. 2.
The automation node, regardless of whether it is connected to the electronic switch advisable to modify by typing two protective diode VD1 and VD2. These diodes will greatly reduce the electroerosion contacts K1.1 relay K1 and thermocontact sensor SF1, respectively.
The fan switch (see diagram in Fig. 3) only works when overheated engine. In nominal same temperature conditions, work fan controls described above node of automation, which is fed with clip 15/1 ignition switch. Voltage of 12 V in this clip is present in only two (four) the provisions of ignition "Ignition" and "start".
The same switch is powered by a clip 30, i.e. actually from positive output rechargeable batteries. Capacitors C1, C2 and diode VD4 decrease pulsation the supply voltage. Diode VD4, together with the diode VD1 and protect low-voltage part of the device from incorrect supply voltage is connected in reverse polarity.
The voltage from the ignition switch from its clip 15/1 - arrives at the shaper, assembled on the element DD1.1, the resistors R1, R2, capacitor C3 and Zener diode VD2. This shaper suppresses high-frequency ripple voltage, so and impulse noise high voltage.
In addition, the switch has three shaper intervals. First of them, consisting of a capacitor C4, a resistor element R4 and DD1.2, forms single low level pulse duration of about 100 MS. Second - on the element DD1.3 and differentiating circuit C5R8 - produces the interval a duration of about 1 MS. Finally, the third time interval with duration of 60 form elements DD2.3, DD2.4 and differentiating circuit C6R9.
When the ignition is switched to the inputs of the element DD1.1 the applied voltage is high level, then the output of this element is low. Therefore, the capacitors C4-C6 is discharged and the input elements DD1.2, DD1.3 and the lower circuit on the inputs elements DD2.3, DD2.4 operates a low level.
The high level from the output of the element DD1.2 holds closed the transistor VT1. RS-flip-flop assembled elements DD2.1, DD2.2, may be in any the state, at its inputs - high level. The output elements DD2.3, DD2.4, in parallel, there will be high level, so the transistor VT2 is closed, relay switch K1 is de-energized, the contacts K1.1 open (Fig. 3 they are not shown).
After turning off the ignition at the input element DD1.1 appears a low level at the output is high. An output current flowing through the relatively low impedance resistor R3, begin charging the capacitors C4-Sat. Opens the transistor VT1, and through the diode VD3 and the circuit of the thermistor current begins to flow, as defined the resistance of the resistor R6 and the thermistor.
It is necessary to consider two cases: the first - the engine is cold, the resistance the circuit of the thermistor is high, the second the engine is hot, the resistance is small.
When the engine is cold the ignition is turned off the output element DD1.3 in 1 MS appears low. Since the resistance of the thermistor large, level the voltage on the resistor element R7 DD1.4 determines how high. Thus, and the lower circuit on the input of the flip-flop will be low. Therefore, the output both elements are single voltage.
The lower circuit on the input elements DD2.3, DD2.4 for 1 min (while charging the capacitor C6) there is also high level. Therefore, the output of these items will be low level and the transistor VT2 will open.
But after 1 MS the low level at the output of the element DD1.3 will be changed to high. It sets the trigger at the lower entrance to the state 0 and the closing transistor VT2. In a time of 1 MS, the relay will not be actuated because its the performance is in the range of 7...10 MS.
After about 100 MS to charge the capacitor C4, closes the transistor VT1 and the input element DD1.4 is again set low trigger condition is not going to change. In a minute to charge the capacitor C6 and the lower input elements DD2.3, DD2.4 high level changes to low. The switch go into a stationary the state in which it can remain indefinitely.
If you switch off the ignition when the engine is hot, the output element DD1.3, as in the first case, there will be low level, and the output element DD1.4 - high because the resistance of the thermistor is decreased and the voltage at the resistor element R7 DD1.4 now defines as a low level.
As a result, the trigger will immediately switch top entry in state 1, After 1 MS, and at the upper input of flip-flop appears high level, not changing trigger status. It will take 100 MS - closes the transistor VT1 . Thus the voltage across the resistor R7 is reduced to almost zero (low level), and a trigger remains in a single state. So for 1 min transistor VT2 will be is open and the relay K1 is turned on. So does the fan, the cooling fluid in the radiator of the vehicle and providing ventilation in the engine compartment.
At the end of minute exposure, the fan is turned off and the switch will go back in a stationary state. This mode of operation allows in appropriate cases to give the engine some stock thermal stability. After switching on the ignition and start the engine fan starts to operate the existing site automation with contact sensor SF1.
Duration the length of time during which a fan after actuation of the switch, you can change the selection of the resistor R9. More than the resistance of this resistor, the longer it will run the fan. Required the duration should be determined experimentally. Excessive exposure results in the unnecessary loss of heat, electricity, fuel, resource blower motor. However, if a "hot" engine start up gives you too much trouble, consider these costs can be justified.
The same can be said about the temperature threshold of the switch. The value of this threshold is best determined empirically based on specific the conditions and characteristics of your car's engine. So, if a hot engine runs poorly, the threshold should choose a fairly low - about 80°C, and sometimes even 60°C. the Threshold set by the selection of resistor R6; more the high threshold corresponds to less resistance.
Note here that the focus on the car thermometer should not be because it too big error. It is better to use a homemade thermometer, described in [1].
In the switch, you can use the IC series C, K, K ( better not C to apply, as they require a more stable voltage). Elements DD1.3, DD1.4, DD2.1, DD2.2 permissible to substitute one trigger (two in one the casing) KTM or TM, KTM.
Transistor CTE (VT1) to replace CTG or CTG, and the transistor CTG (VT2)-CTG.
Diodes VD1 and VD4 can be practically any compact silicon, and VD3 and VD5 - any of a series KD, KD, KD, KD, KD, KD. Zener diode VD2 fit on any low-voltage stabilization from 8 to 15 In (at if you can do without it). Oxide capacitors - series K52, K53, IT; the other is ceramic. Relay K2 - 111.3747, 112.3747, 113.3747, 113.3747-10 or any other suitable number, for example, described in[2].
Literature
Author: B. Bannikov, Moscow