The present invention relates to a motor reverse system.

The system is particularly, but not exclusively, applicable to closure members such as motor driven doors, windows and sunroofs.

Reverse mechanisms for motor driven automobile window back-off are already known but such mechanisms can impart an unacceptable force to a trapped limb, for example, and may be susceptible to wear in the mechanism during its life affecting operation.

According to the present invention, there is provided a motor reverse system comprising means for sensing the current in the motor to which the system is in use connected, first and second means for sensing resistance to the motion of an object being driven by the motor, said first means comprising a peak current detector for determining current instantaneously drawn by the motor or switch on, comparator means for comparing the peak current detected with the actual motor current value during normal operation, a backoff circuit arranged to operate when the actual motor current equals or exceeds the peak current, said second means comprising filter means arranged to

provides two variables from the motor current one of which responds faster than the other to rates of change of motor current whereby if the motor slows and the rate of change of motor current is sufficient such that said one variable crosses said other variable, the backoff circuit operates.

In mathematical terms, the said one variable (Iinst) is less than the said other variable (Ino ) by a variable K where K = Inom - X% Iinst and the backoff circuit operates when

d Iinst > K > d Inom dt dt

The "backoff" function can be implemented in a number of ways

When the backoff circuit operates the current to the motor is reversed for a time.

In a preferred embodiment of the invention, the current in the motor is sensed by a current sensing track. This track forms in conjunction with the motor a potential divider from which a signal is fed to an amplifier. The output from the amplifier is fed directly and simultaneously to the input of the filter means and sample and hold means. In a first operating mode for an automobile window wind up mechanism, the sample and hold means store the peak stall

current on motor switch on. This may vary depending on the mechanical condition of the mechanism and the automobile battery condition. If that stored signal is subsequently reached indicating a soft obstacle, a signal to activate th backoff means and associated further circuit to back off the window by a nominal amount. The window can then only be moved by switching the normal motor switch on again (either up or down) .In a second operating mode, the other variable tracks the first mentioned variable. When a hard obstacle is encountered by the window, the slower reacting variable can no longer keep up with the other variable and the outputs from the two crossover. This is detected and the back off system activated as before. A limit switch deactivates the system as the window approaches the closed position to prevent back off as the window closes.

In order that the invention may be more clearly understood, one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 shows a circuit arrangement for measuring a window winder motor current consumption,

Figure 2 shows a block circuit diagram of an arrangement for controlling a backoff for the motor of Figure 1,

Figure 3 shows variation of current with time for the motor of Figures 1 and 2 for a first given operating condition.

Figure 4 shows variation of current with time for the motor of Figures 1 and 2 for a second given operating condition.

Figure 5 shows variation of filter outputs with time in circuit of Figure 1 for the second operating condition of Figure 4. and

Figure 6 shows a partial, closed position, view of a window to be driven by the motor of Figure 1 and 2.

Referring to Figures 1 and 2, a window winder motor 1, draws current in operation from the usual 12v battery supply 2 of the vehicle. This current is monitored using a current sensing track 3 disposed in this supply circuit. The motor 1 and track 3 create a voltage divider and the output 4 from this divider representing the current drawn by the motor forms the input to an amplifier 5.

The output from the amplifier is fed to a low pass filter 6 having a short time constant, a low pass filter 7 having a long time constant, a comparator 8 and a sample and

hold circuit 9. The outputs from the two filters 6 and 7 are fed to a second comparator 10. The first mentioned comparator also receives an input from the .sample and hold circuit 9. The outputs from comparators 8 and 10 are fed to a backoff circuit 11 which, in conjunction with a further circuit 9, controls the backoff operation of the window (not shown in Figure 2) .

The operation of the system is as follows. The voltage at the output of the amplifier 5 is used in two different ways. As the motor 1 starts up it is effectively in stall condition until it is at working speed. The output voltage on power up will be slightly lower than that at stall. This initial voltage is stored in the sample and hold circuit 9. In the first mode of operation, if the voltage at the output of the amplifier 5 rises above that at the output of the sample and hold circuit indicating a soft obstacle in the way of the window being wound up then the comparator 8 reacts by initiating the backoff circuit 11 to operate the further circuit 12 to stop and reverse the motor 1 for a preset time. As the start up current/voltage is sampled every time the window is wound up the system adjusts automatically to variations in the mechanical elements of the system caused by wear and tear and to battery condition.

Motor current I variation with time t during this operation is shown in Figure 3. As the motor runs up to

speed, current rises rapidly from point A to point B producing a start ^* up current peak B from which, during normal operation, the current falls back to level C. When the obstacle is encountered current begins to rise again until it exceeds the stored start up peak level B when the motor is reversed by reversing the current for a preset time. The reversal point is shown at D and the reverse current at E.

When the motor 1 is in reverse, the circuits which detect motor stall are deactivated. The backoff circuit an the window will not operate again until the switch controlling the window is released, and another signal is given via the motor switch (either up or down) .

The output of the amplifier 5 is also fed into the two low pass filters 6 and 7. Filter 6 is fast reacting and is used mainly to rid the input signal of high frequency noise generated by the motor 1. This signal is then reduced by a certain percentage. Filter 7 is an integrating filter which tracks the output of the filter 6 with a delay due to the longer time constant. If the level of current taken by the motor rises slowly the output from filter 7 can track the output from filter 6. If the output from filter 6 rises at a greater rate, suggesting an obstruction, the output from filter 7 cannot keep up. The output from filter 6 crosses the output from filter 7. This condition is shown

graphically in Figure 5, the output from filter 6 being referenced F6, that from filter 7 being referenced F7 and the crossover point CP. F6 and F7 are both plots against time. The plot of motor current against time for this mode of operation is shown in Figure 4. This is similar to that of Figure 3. Window wind up begins at point G, and current rises rapidly to point H. Normally winding takes place until point I when a fast rate of change indicates a hard obstacle. The current at this point is at a much lower level than that at H which is the stall position which indicates that the rate of change of current demand has increased sufficiently to activate the window back off circuit 11. Operation of this circuit 11 and further circuit 12 is as before and as before the window will not operate after backoff until the switch is released and pressed again.

Referring to Figure 6, to prevent the backoff circuit operating when the window 19 reaches the normally closed position, a limit switch 20 is disposed for operation by the window just before the window hits the end stop in the window frame 21. Operation of the switch 20 sends a signal to deactivate the input to the backoff circuitry allowing the window to close without backing off. It will be noted that the position of the switch 20 is such that no significant gap is left to allow anything to be caught in the window.

The above arrangement enables different types of obstacles to normal window closure to be catered for and also accommodates changes due to wear and tear and battery condition.

It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention. Although described in relation to a window wind up motor, the back off arrangement could be used in an circumstance where the normal operation of a motor needs to be reversed to deal with an abnormal condition such as an obstacle. The arrangement may be implemented in software as well as hardware or a combination of the two.