Anti-pinch window drive circuit

1. An anti-pinch window system for a power window having a fully closed position, the system comprising:

a drive circuit capable of supplying a drive current;

a reversible d-c motor operably coupled to the drive circuit electrically, the motor being mechanically coupled to the power window such that the motor is capable of raising and lowering the window;

a reference circuit operably coupled to the drive circuit such that the reference circuit is capable of detecting, without an external sensor, both a measure of the drive current and a measure of a back EMF of the motor, distinguishing normal operation of the motor during raising of the window to the fully closed position from interruption of the raising of the window by an unsafe condition based on both the measure of the drive current and the measure of the back EMF of the motor, wherein the occurrence of the unsafe condition is distinguished; and

a control circuit operably coupled to the reference circuit and the drive circuit, such that the control circuit controls the drive circuit and automatically reverses the direction of the motor in response to the occurrence of the unsafe condition.

2. The system of claim 1 , wherein the drive circuit and control circuit are integrated in an H bridge control circuit.

3. The system of claim 1 , wherein the drive circuit and control circuit are integrated into a single IC control chip.

4. The system of claim 3 , wherein the drive circuit, the control circuit and the reference circuit are mounted on a common circuit board.

5. The system of claim 1 , further comprising a spring wherein the power window compresses the spring when the window is in the fully closed position thereby affecting the measure of the drive current and the measure of the back EMF from the motor.

6. The system of claim 5 , wherein the spring is a laminated spring directly inside the rubber window seal.

7. The system of claim 1 , wherein the reference circuit comprises:

a first reference circuit capable of monitoring the measure of the drive current and comparing the measure of the drive current to a first drive current threshold value and a second drive current threshold value that is greater than the first drive current threshold value, during raising of the window, such that if the drive current suddenly exceeds the first drive current threshold value but not the second drive current threshold value during raising of the window, then the control circuit reverses the motor;

a second reference circuit operably coupled to the first reference circuit such that the second reference circuit is capable of sampling a measure of a back EMF of the motor, after the measure of the drive current is greater than both the first drive current threshold value and the second drive current threshold value; and

a comparator circuit that is operably coupled to the second reference circuit such that the measure of the back EMF is compared to a first back EMF threshold value and a second back EMF threshold value greater than the first back EMF threshold value, and the comparator is operably coupled to the control circuit such that the control circuit reverses the direction of the motor if the first back EMF threshold value is not less than the measure of the back EMF of the motor or the measure of the back EMF of the motor is not less than the second back EMF threshold voltage.

8. The system of claim 7 , wherein the first reference circuit, the second reference circuit, the comparator circuit and the control circuit are coupled such that, if the first back EMF threshold value is less than the measure of the back EMF and the measure of the back EMF is less than the second back EMF threshold value, then the measure of the drive current is compared to the second drive current threshold again after a delay period, and the control circuit reverses the direction of the motor, if the measure of the drive current is not greater than the second drive current threshold value.

9. The system of claim 8 , wherein the first reference circuit, the second reference circuit, the comparator circuit and the control circuit are coupled such that, if the measure of the drive current as measured in claim 8 is greater than the second drive current threshold, then the second reference circuit again samples the measure of the back EMF and the comparator circuit compares the measure of the back EMF to the first back EMF threshold value and the control circuit reverses the direction of the motor, if the measure of the back EMF is not less than the first back EMF threshold voltage, otherwise the control circuit stops the motor.

10. An antipinch window system for a power window having a filly closed position and a drive motor for raising and lowering the window, the system comprising:

a means for detecting, without an external sensor, a measure of a drive current and a measure of a back EMF of the drive motor;

a means for distinguishing normal operation of the motor during raising of the window to the filly closed position from an unsafe interruption of the raising of the window based on the measure of the drive current and the measure of the back EMF supplied by the means for detecting; and

a means for automatically reversing the drive motor when the unsafe interruption occurs as determined by the means for distinguishing.

11. A process of controlling a drive motor for automatically reversing the direction of a power window in response to an unsafe condition caused by an obstruction during raising of the window, the process of controlling the drive motor, comprising:

measuring the torque on the motor using a measure of the current of the drive motor without any external sensor;

monitoring the measure of the torque during raising of the window;

detecting either an occurrence of the unsafe condition or an approach of the window to a fully closed position;

distinguishing the occurrence of the unsafe condition from the approach of the window to the fully closed position based on both the measure of the torque and a measure of a back EMF of the drive motor, without an external sensor; and

reversing the direction of the drive motor automatically in response to the occurrence of the unsafe condition.

12. The process of claim 11 , wherein the step of detecting uses only the measure of the torque, and the step of distinguishing uses both the measure of the torque and the measure of the back EMF of the drive motor.

13. The process of claim 12 , wherein the step of distinguishing comprises, in sequence:

comparing the measure of the torque obtained during the step of detecting to a first torque threshold value and a second torque threshold value that is greater than the first torque threshold value, such that the occurrence of the unsafe condition is distinguished when the measure of the torque is greater than the first torque threshold value and not greater than the second torque threshold value;

acquiring a first measure of the back EMF, only if the measure of the torque obtained during the step of detecting is greater than the second torque threshold value; and

comparing the first measure of the back EMF to a first back EMF threshold value and a second back EMF threshold value, such that the occurrence of the unsafe condition is distinguished when the first back EMF threshold value is not less than the first measure of the back EMF or the first measure of the back EMF is not less than the second back EMF threshold.

14. The process of claim 13 , wherein the step of distinguishing further comprises:

waiting for a period of time, if first back EMF threshold value is less than the first measure of the back EMF and the first measure of the back EMF is less than the second back EMF threshold;

then, determining a new measure of the torque;

comparing the new measure of the torque and the second torque threshold value, such that the occurrence of the unsafe condition is distinguished when the measure of the torque is not greater than the second torque threshold value;

acquiring a second measure of the back EMF, if the new measure of the torque is greater than the second torque threshold; and

comparing the second measure of the back EMF to the first back EMF threshold value, such that the occurrence of the unsafe condition is distinguished when the second measure of the back EMF is not less than the first back EMF threshold value.

15. The process of claim 14 , further comprising:

stopping the drive motor, after the step of comparing the second measure of the back EMF, if the second measure of the back EMF is less than the first back EMF threshold value.

16. The process of claim 13 , wherein the first torque threshold value is adjusted for changes in the temperature or for changes in the average drive current during a first lowering of the window.

17. The process of claim 11 , further comprising, after the first step of detecting, a step of reducing the speed of the motor.