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Control circuitry for multistage fans

  • US 4,426,960 A
  • Filed: 08/24/1982
  • Issued: 01/24/1984
  • Est. Priority Date: 10/09/1979
  • Status: Expired due to Term
First Claim
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1. A multistage temperature control circuit for maintaining engine manifold coolant at a selected temperature by selectively operating a plurality of cooling fans mounted to provide a flow of cooling air to said engine, said circuit comprising:

  • means to selectively energize said fans to operate to maintain the engine manifold cooling liquid below a selected temperature level;

    sensing element means immersed in the manifold coolant for providing electrical signals proportional to the coolant temperature including a thermistor probe for sensing the coolant temperature, means responsive to said signals for enabling a first of said cooling fans at a predetermined temperature;

    means for sequentially enabling additional fans as the coolant temperature increases including a differential circuit comprising a plurality of differential amplifiers means and a resistor bridge circuit, said thermistor providing a first input to each of said differential amplifiers, and said resistor bridge circuit providing selected level inputs as the second input to each of said differential amplifiers;

    time delay circuitry for sequencing the operation of the cooling fans in accordance with a predetermined delay,means for by-passing said time delay circuitry to selectively energize said fans sooner than said predetermined delay when the temperature cycles rapidly; and

    a delay circuit connected to receive an input from a first fan, said delay circuit comprising an RC network, a logic AND gate having two inputs and input, the input from said first fan causing the RC network to charge to a high level after a first period of time delay and providing a first input to said AND gate, said thermistor providing a high logic level to said AND gate, and as the temperature rises to the energizing point of a succeeding fan, the other input to the AND gate goes high to turn ON said succeeding fan as the temperature decreases, the low logic level applied to the AND gate and said succeeding fan being turned OFF due to said first fan remaining engaged to enable said succeeding fan to be reactivated without the time delay when the temperatures again rises.

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