SOLENOID DITHER CONTROL SYSTEM AND METHOD

1 . A solenoid control method that comprises:

supplying a drive signal to a solenoid, the drive signal including:

an average current corresponding to a desired position of an armature; and

a dither current having a dither amplitude with an associated solenoid voltage variation;

varying the dither amplitude in a region insufficient to overcome static friction of the armature;

determining a linear relationship between the dither amplitude and the associated solenoid voltage variation in said region;

increasing the dither amplitude while monitoring the associated solenoid voltage variation for a deviation different from the voltage variation indicated by the linear relationship; and

upon detecting said deviation, employing a corresponding dither amplitude to maintain mobility of the armature.

2 . The method of claim 1 , wherein said drive signal is provided using PWM (pulse width modulation) at a PWM frequency.

3 . The method of claim 2 , wherein said dither frequency is less than the PWM frequency and a period of the dither current includes multiple PWM periods.

4 . The method of claim 3 , wherein said determining includes, for each of multiple dither amplitude values:

obtaining an average solenoid voltage for each PWM period in at least one period of the dither current; and

calculating said associated solenoid voltage variation based on a difference between a maximum and a minimum of the average solenoid voltages in the at least one dither period.

5 . The method of claim 2 , wherein a calculation frequency is less than the PWM frequency and a calculation period includes multiple PWM periods.

6 . The method of claim 5 , wherein said determining includes, for each of multiple dither amplitude values:

obtaining a baseline average solenoid voltage for a first calculation period;

obtaining for each PWM period in a subsequent calculation period an absolute value of a difference between the baseline average and an average solenoid voltage for that PWM period; and

calculating said associated solenoid voltage variation as an average of said absolute values.

7 . The method of claim 1 , wherein the dither current has a triangular, sine wave, trapezoidal, rectangular or saw tooth waveform.

8 . The method of claim 1 , further comprising: indicating that the armature is blocked if the dither amplitude reaches a predetermined threshold without detection of said deviation.

9 . The method of claim 1 , further comprising: repeating said varying, determining, and increasing operations each time the desired position changes.

10 . A solenoid controller that comprises:

a PWM (pulse width modulation) driver that supplies a drive signal to a solenoid, the drive signal including:

an average current corresponding to a desired position of an armature; and

a dither current having a dither amplitude with an associated solenoid voltage variation;

a processor that controls the PWM driver to supply said drive signal, the processor implementing a control method that includes:

varying the dither amplitude in a region insufficient to overcome static friction of the armature;

determining a linear relationship between the dither amplitude and the associated solenoid voltage variation in said region;

increasing the dither amplitude while monitoring the associated solenoid voltage variation for a deviation different from voltage variation indicated by the linear relationship; and

upon detecting said deviation, employing a corresponding dither amplitude to maintain mobility of the armature.

11 . The controller of claim 10 , wherein the PWM driver supplies the drive signal via a switching element that selectively couples the solenoid coil to a power supply, and wherein the controller further includes a voltage sensor to detect the solenoid voltage.

12 . The controller of claim 11 , further comprising a current sensor for the drive signal to provide closed-loop feedback control.

13 . The controller of claim 10 , wherein said average current is provided using PWM at a PWM frequency, and said dither current is provided using a dither frequency less than the PWM frequency, with each period of the dither current including multiple PWM periods.

14 . The controller of claim 13 , wherein said determining includes, for each of multiple dither amplitude values:

obtaining an average solenoid voltage for each PWM period in at least one period of the dither current; and

calculating said associated solenoid voltage variation based on a difference between a maximum and a minimum of the average solenoid voltages in the at least one period.

15 . The controller of claim 10 , wherein said average current is provided using PWM at a PWM frequency, and said dither current is provided using a dither frequency, with each period of the dither current including less than two PWM periods, and wherein the processor performs said determining using a calculation period that includes multiple voltage averaging periods.

16 . The controller of claim 15 , wherein said determining includes, for each of multiple dither amplitude values:

obtaining a baseline average solenoid voltage for a first calculation period;

obtaining for each voltage averaging period in a subsequent period an absolute value of a difference between the baseline average and an average solenoid voltage for that voltage averaging period; and

calculating said associated solenoid voltage variation as an average of said absolute values.

17 . The controller of claim 10 , wherein the dither current has a triangular, sine wave, trapezoidal, rectangular or saw tooth waveform.

18 . The controller of claim 10 , wherein the control method further includes: indicating that the armature is blocked if the dither amplitude reaches a predetermined threshold without detection of said deviation.

19 . The controller of claim 10 , wherein the control method further includes: repeating said varying, determining, and increasing operations each time the desired position changes.

20 . The controller of claim 10 , the controller being implemented as an integrated circuit module.