A/C compressor clutch power management

1. A method of controlling an electric power input to a compressor clutch that selectively drives an A/C compressor in a vehicle HVAC system, the method comprising the steps of:

(a) determining, with a controller, a first electric power level needed to cause the compressor clutch to move to a full engagement position from a compressor clutch non-engagement position;

(b) applying the first electric power level, via a voltage controller, to the compressor clutch to cause the compressor clutch to move to the full engagement position;

(c) determining, with the controller, a second electric power level, which is lower than the first electric power level, needed to maintain the compressor clutch in the full engagement position; and

(d) applying the second electric power level, via the voltage controller, to the compressor clutch to maintain the compressor clutch in the full engagement position.

2. The method of claim 1 including steps:

(e) calculating, with the controller, an estimated compressor torque;

(f) determining, with the controller, a third electric power level needed to maintain the compressor clutch in the full engagement position based on the estimated compressor torque; and

(g) applying the third electric power level, via the voltage controller, to the compressor clutch to maintain the compressor clutch in the full engagement position.

3. The method of claim 1 including steps:

(e) calculating, with the controller, an estimated compressor cycling rate;

(f) determining, with the controller, a third electric power level needed to maintain the compressor clutch in the full engagement position based on the estimated compressor cycling rate; and

(g) applying the third electric power level, via the voltage controller, to the compressor clutch to maintain the compressor clutch in the full engagement position.

4. The method of claim 1 including steps:

(e) calculating, with the controller, an estimated compressor cycling rate and an estimated compressor torque;

(f) determining, with the controller, a third electric power level needed to maintain the compressor clutch in the full engagement position based on the estimated compressor cycling rate and the estimated compressor torque; and

(g) applying the third electric power level, via the voltage controller, to the compressor clutch to maintain the compressor clutch in the full engagement position.

5. The method of claim 1 wherein step (a) is further defined by calculating an estimated compressor torque on compressor clutch engagement, and determining the first electric power level based on the estimated compressor torque.

6. The method of claim 1 wherein step (c) is further defined by waiting for a predetermined time after the compressor clutch moves into the full engagement position before determining the second electric power level.

7. The method of claim 1 wherein the first electric power level and the second electric power level are based on a ramped curve relating a clutch voltage to a compressor torque.

8. The method of claim 1 wherein the first electric power level and the second electric power level are based on a stepped curve relating a clutch voltage to a compressor torque.

9. The method of claim 1 wherein steps (b) and (d) are further defined by the voltage controller being an A/C clutch voltage controller receiving signals from an HVAC comfort control module and an engine control unit, which define the controller, and directing a voltage to the compressor clutch.

10. A vehicle HVAC system comprising:

an A/C compressor;

a compressor clutch configured to selectively engage the NC compressor with a source of driving torque;

an HVAC comfort control module;

an engine control unit; and

an A/C clutch voltage controller configured to receive inputs from the HVAC comfort and control module and the engine control unit, and direct a zero voltage to the compressor clutch for clutch disengagement and a plurality of voltages to the compressor clutch for obtaining and maintaining clutch full engagement based on vehicle operating conditions.

11. The vehicle HVAC system of claim 10 wherein the plurality of voltages directed to the compressor clutch for obtaining and maintaining clutch full engagement are based on a compressor torque.

12. The vehicle HVAC system of claim 10 wherein the plurality of voltages directed to the compressor clutch for obtaining and maintaining clutch full engagement are based on a compressor cycling rate.