Power Window Pulldown Circuit

Abstract

Power window apparatus for opening and closing a window in accordance with the setting of a selectively operable switch. Upon placement of the switch in a window opening setting a window drive motor connected to the window is placed in a first energized condition so as to open the window. Upon placement of the switch in a window-closing setting power is supplied through a transistor to the motor so as to place the motor in a second energized condition and close the window. Should the motor be stalled by the window being closed on an obstacle the window travel is reversed by the resultant decrease in the voltage across the motor armature causing a bias network to both turn off the transistor and place the motor in the first energized condition. A limit switch that is responsive to the window position is provided to prevent the armature voltage from effecting reversal of the window when the window is substantially closed so as to allow the motor to seal the window. A time delay network is provided for preventing voltage transients generated upon starting the motor from effecting reversal of the window travel during a predetermined time.

Description

This invention relates to power window apparatus and, more particularly, to power window apparatus for use in motor vehicles.

Many diverse types of power window systems have heretofore been employed to operate the windows of motor vehicles. Though these systems are of various designs their functions are basically similar inasmuch as most of them raise and lower vehicle windows in accordance with the setting of a selectively operable switch that is manipulated by a vehicle occupant. In addition, some of these prior art power window systems are designed to have a provision for reserving the direction of window travel when the window is being closed on an object that is positioned so as to obstruct the window. It is this latter type of power window system to which the present invention relates.

While many of the power window systems presently in commercial usage and heretofore proposed are capable of carrying out their assigned functions admirably, the continuing interest of vehicle owners and occupants in convenience features such as power window systems in their motor vehicles provides considerable incentive for the development of an economical and reliable power window design which may be adopted for widespread consumer usage. The present invention is proposed as a means of fulfilling this widespread need.

Accordingly, it is now proposed to open a window by direct energization of a reversible window drive motor and to close the window by energizing the window drive motor through a transistor. Should the motor be stalled and its armature voltage reduced by the window striking an obstacle while it is closing, the direction in which the motor drives the window is reversed by biasing the transistor to its nonconductive condition and energizing the motor through the transistor bias circuitry. A limit switch that is responsive to the position of the window is provided for preventing the bias circuitry from turning off the transistor and effecting reversal of the motor when the window is substantially closed so as to allow the motor to stall while tightly sealing the window closed. In addition, a time delay network is provided for preventing the bias circuitry from turning off the transistor and effecting the reversal of the motor for a predetermined time after the motor begins to close the window so as to prevent voltage transients generated upon starting the motor from effecting reversal of the motor during the predetermined time.

Other advantages and features of the subject invention will become apparent from the following description and accompanying drawing, which schematically illustrates power window apparatus incorporating the principles of the subject invention.

As is shown in the drawing, a window 10, which is portrayed as a vehicle window that includes a window frame 12 and a windowpane 14, is opened and closed by a motor 16 which includes first and second selectively energizable field windings 18 and 20 and an armature 22 that is drivably connected to the window 10 through a suitable drive mechanism 24. Though the drive mechanism 24 may be of any suitable type, as is apparent to those versed in the art, it is presented in the drawing for purposes of illustration as including a gear 26 driven by the armature 22 and a rack 28 driven by the gear 26 and connected to the windowpane 14. A control circuit 30 is provided for controlling the energization of the windings 18 and 20 so that when the first winding 18 is energized the motor 16 opens the window 10 and when the second winding 20 is energized the motor 16 closes the window 10.

The control circuit 30 is powered by a suitable power source, such as a vehicle battery 32 of a conventional design, that is in series circuit with a vehicle ignition switch 34, which is preferably of a conventional design that precludes operation of the control circuit 30 and the window 10 when the vehicle ignition is turned off. Upon closure of the ignition switch 34 the battery 32 is connected to a switch arm 36 of a selectively operable switch 38 of the well-known and presently widely used type in which the switch arm 36 is normally spring-biased by a spring mechanism (not shown) to the neutral center position illustrated in the drawing. When it is desired to open the window 10 a vehicle operator manually places the switch 38 in a window opening setting by engaging a first contact 40 with the switch arm 36. To close the window the vehicle operator places the switch 38 in a window closing setting by engaging a second contact 42 with the switch arm 36.

Upon placement of the switch 38 in the window opening setting the battery 32 is connected through the switch 38 and a lead 44 to the motor 16 so as to energize the first winding 18 through the armature 22. The motor 16 is thus placed in a first energized condition and opens the window 10.

When the switch 38 is placed in the window closing setting the battery 32 is connected through the switch 38 to the emitter terminal 46 of a PNP-power-transistor 48 which has its collector terminal 50 collected through a lead 52 to the second winding 20 of the motor 16. Accordingly, when the switch 38 is placed in the window closing setting and the transistor 48 is biased so as to be in a conductive condition the second winding 20 is energized by the battery 32 through a current path which includes the switch 38, the transistor 48, and the armature 22 so as to close the window 10.

The bias network 54 is provided to assure that the transistor 48 is normally biased to its conductive condition when the switch 38 is placed in the window-closing setting. The bias network 54 includes a resistor 56 and a diode 58 series connected between the base terminal 60 of the transistor 48 and ground. In addition, the bias network 54 includes a silicon-controlled rectifier (SCR) 62 connected between the emitter and base terminals 46 and 60 of the transistor 48. Since power is only supplied by the battery 32 to the SCR 62 when the switch 38 is in the window-closing setting the SCR 62 is nonconductive upon placement of the switch 38 in the window-closing setting and remains nonconductive until a voltage signal greater than a certain value is applied to the gate terminal 64 of the SCR 62.

Upon placement of the switch 38 in the window-closing setting the voltage at the base terminal 60 of the transistor 48 thus falls below the voltage at the emitter terminal 46, the precise voltage lever being determined by the reverse leakage characteristics of the diode 58, and the forward biased base-emitter junction of the transistor 48 causes the transistor 48 to assume its conductive condition. By properly selecting the diode 58 to have appropriate reverse leakage characteristics the base terminal 60 of the transistor 48 is held at a relatively high-voltage but is nevertheless at sufficiently low a voltage to keep the transistor 48 fully conductive. For example, in a typical installation in which the battery 32 is a 12 -volt battery the base terminal 60 of the transistor 48 may be held at about a 9-volt potential when the transistor 48 is conductive. Accordingly, a relatively small increase in voltage at the base 60 of the transistor 48 will suffice to turn off the transistor 48. The diode 58 thus helps protect the transistor 48 against large voltage excursions which may be generated when switching the windings 18 and 20, as will subsequently become apparent to persons versed in the art.

The conductivity of the SCR 62 is controlled in accordance with the voltage across the armature 22 of the motor 16 so that when the window 10 is closed on an obstacle the resultant stalling of the motor 16 and decrease in the armature 22 voltage causes the generation of a voltage signal that switches the SCR 62 to its conductive state. When the SCR 62 is conductive it reverses the motor 16 and opens the window 10 by biasing the transistor 48 to its nonconductive condition and energizing the first winding 18, as will subsequently be explained. To this end the voltage across the armature 22 is monitored by a voltage-monitoring network 66 which includes an NPN-transistor 68, a coupling resistor 70, and suitable biasing resistors 72 and 74. When the voltage-monitoring network 66 has detected that the motor 16 is stalled, it causes a control network 76 to generate and transmit to the gate terminal 64 of the SCR 62 a voltage signal of sufficient magnitude to switch the SCR 62 to its conductive condition.

The control network 76 includes a unijunction transistor 78, a charging resistor 80, a charging capacitor 82, a discharge resistor 83, a coupling resistor 84, and a second SCR 86. Power for operating the control network 76 is provided by the battery 32 through the switch 38, a lead 88, and the second SCR 86 when the switch 38 is placed in the window-closing setting and the second SCR 86 is conductive. The control network 76 in turn provides the energization for the voltage-monitoring network 66 through the transistor 68. However, it is desirable that the supply of power to the control network 76 and the voltage-monitoring network 66 be interrupted so as to prevent the switching of the SCR 62 at certain times, most notably when the motor 16 stall while sealing the window 10 closed and when voltage transients generated by starting the motor 16 may inadvertently cause switching of the SCR 62.

Accordingly, a normally closed limit switch 90 that is positioned so as to be responsive to the window 10 position is connected in series with the second SCR 86 so as to interrupt power to the control network 76, and hence preclude the control network 76 from generating the requisite voltage signal to switch the SCR 62, when the window is substantially closed. The motor 16 is thus allowed to stall when the window 10 is substantially closed so as to tightly seal the window 10 in its closed position.

Voltage transients which may be generated upon starting the motor 16 are prevented from inadvertently switching the SCR 62 by a time delay network 92, which includes a resistor 94, a timing capacitor 95, and a discharge diode 96. The time delay network 92 is supplied power by the battery 32 through the lead 88 and controls the voltage applied to the gate terminal 97 of the second SCR 86. Upon placement of the switch 38 in the window-closing setting the capacitor 95 is charged through the resistor 94. Since the capacitor 95 does not have an initial charge the second SCR 86 is held nonconductive for a predetermined time after the switch 38 is placed in the window-closing setting, the time being determined by the time constant of the time delay network 92. By properly selecting the values of the resistor 94 and the capacitor 95 the second SCR 86 is kept turned off until after the voltage transients generated by starting the motor 16 have died out. After the predetermined time has elapsed the charge on the capacitor 95 is sufficient to turn on the second SCR 86, which becomes conductive and discharges the capacitor 95 through the diode 96. Since the second SCR 86 must be conductive to supply power to the control network 76 the time delay network 92 thus prevents these voltage transients from switching the SCR 62 during the predetermined time.

After the predetermined time has elapsed stalling of the motor 16 when closing the window 10 decreases the armature 22 voltage below the certain level that is indicative of the motor 16 being stalled. Assuming that the window 10 is open sufficiently that the control network 76 is not disabled by the limit switch 90, the voltage-monitoring network 66 detects the low armature 22 voltage and the control network 76 generates a voltage signal which exceeds the predetermined value so as to switch the SCR 62 from its nonconductive to its conductive condition. When the SCR 62 is in a conductive state the voltage on the cathode 98 on the SCR 62 deenergizes the second winding 20 by turning off the transistor 48 and energizes the first winding 18 through a diode 99, as will be explained in the following operational description.

A vehicle occupant may operate the aforedescribed apparatus merely by changing the setting of the switch 38. When the vehicle operator wishes to open the window 10, he places the switch 38 in the window-opening setting by engaging the contact 40 with the switch arm 36. The battery 32 is then connected in series circuit through the switch 38 and the lead 44 with the first winding 18 and the armature 22. Accordingly, the motor 16 is placed in a first energized condition in which it opens the window 10 until either the window 10 is fully open or the switch 38 is removed from the window-opening setting.

When a vehicle occupant desires to close the window 10 he places the switch 38 in the window closing setting by engaging the second contact 42 with the switch arm 36. The full voltage of the battery 32 is then applied through the switch 38 to the emitter of the transistor 48 and, through the lead 88, to both of the SCR's 62 and 86 and the time delay network 92. Since the timing capacitor 95 is not initially charged, the gate terminal 97 of the second SCR 86 is initially at ground potential when the switch 38 is placed in the window-closing setting. The second SCR 86 is thus initially held in its nonconductive condition and the control network 76 is precluded from applying a voltage signal to the gate terminal 64 of the SCR 62 that would switch the SCR 62 to its conductive condition. The SCR 62 therefore initially remains nonconductive so as to bias the transistor 48 to its conductive condition. Accordingly, as soon as the switch 38 is placed in the window-closing setting, the second winding 20 is energized through the transistor 48 and the armature 22 so as to cause the motor 16 to close the window 10.

At a predetermined time after the switch 38 is placed in the window-closing setting, the time being determined by appropriate selection of the resistor 94 and the timing capacitor 95, the voltage across the capacitor 95 is sufficient to turn on the second SCR 86. When the second SCR 86 is turned on it discharges the capacitor 95 through the diode 96 and allows the passage of a current from the lead 88 through the second SCR 86, the normally closed limit switch 90, the coupling resistor 84, the resistor 80, and the capacitor 82. This current tends to charge the capacitor 82 to a level sufficient to turn on the unijunction transistor 78 but the voltage-monitoring network 66 continuously drains the charge from the capacitor 82, keeping the unijunction transistor 78 nonconductive.

As persons versed in the art will appreciate, the voltage across the armature 22 is proportional to the speed of the motor 16. Accordingly, when the motor 16 is closing the window 10 the lead 44 and the first winding 18 are substantially at the potential of the voltage across the armature 22. The armature 22 voltage is thus sensed by the voltage-monitoring network 66 through the first winding 18 and the coupling resistor 70, which applies the armature voltage to the base terminal of the transistor 68. By properly biasing the transistor 68 with the resistors 72 and 74 the voltage which is applied from the armature 22 to the base terminal of the transistor 68 when the window 10 is being closed is sufficient to turn on the transistor 68, which drains the charge from the capacitor 82 so as to prevent the turning on of the unijunction transistor 78. Accordingly, the unijunction transistor 78 normally remains nonconductive and the voltage on the gate terminal 64 of the SCR 62 is insufficient to turn on the SCR 62.

However, should the window 10 be closed upon an obstacle which stalls the motor 16 the resultant decrease in the armature 22 speed causes a corresponding decrease in the voltage across the armature 22. When the armature 22 voltage has fallen below a certain level the potential applied to the base terminal of the transistor 68 is insufficient to maintain the transistor 68 conductive. Accordingly, the voltage-monitoring network senses that the motor 16 is stalled by the turning off of the transistor 68 and allows the capacitor 82 to accumulate a charge sufficient to turn on the unijunction transistor 78. When the unijunction transistor 78 is turned on some of the power being supplied through the second SCR 86 is diverted through the unijunction transistor 78, so as to generate a large voltage signal across the discharge resistor 83. The voltage signal is applied to the gate terminal 64 of the SCR 62 and is of sufficient magnitude to switch the SCR 62 to its conductive condition. Due to the inherent latching characteristic of SCR's such as the SCR 62 the SCR 62 remains conductive so long as its supply of energy from the battery 32 through the switch 38 remains uninterrupted.

Upon switching the SCR 62 to its conductive condition substantially the same potential is applied through the SCR 62 to the base terminal 60 of the transistor 48 as is applied to the emitter terminal 46 of the transistor 48. The voltage across the emitter-base junction of the transistor 48 is thus insufficient to maintain the transistor 48 conductive so that it is switched to its nonconductive condition, causing the resultant deenergization of the second winding 20. Subsequent closure of the window 10 by the motor 16 after the motor 16 is stalled is thus precluded by switching the transistor 48 to its nonconductive condition.

When the SCR 62 is switched to its conductive state, it also supplies a large current through the diode 99 and the lead 44 to the first winding 18, causing the energization of the first winding 18 through the armature 22. Since the second winding 20 is deenergized simultaneously with the energization of the first winding 18 through the bias network 54, the direction in which the motor 16 drives the window 10 is reversed so as to open the window 10 as soon as its closure on an obstacle has been detected by the voltage-monitoring network 66. Furthermore, the latching of the SCR 62 in its conductive condition causes the first winding 18 to remain energized through the bias network 54 and the diode 99 so long as power is supplied to the SCR 62 by holding the switch 38 in the window-closing setting. The window 10 will therefore be opened either until it is fully opened or the vehicle operator releases the switch 38.

Should the window 10 not encounter an obstacle while being closed the motor 16 does not stall but rather drives the window 10 to its fully closed position. When the window 10 is substantially closed it opens the limit switch 90. Since power is only supplied to the control network 76 through the limit switch 90, opening of the limit switch 90 prevents the control network 76 from effecting reversal of the motor 16 by switching the SCR 62. The motor 16 is thus allowed to stall while tightly sealing the window 10 closed.

While the foregoing description and the drawing are directed toward the preferred embodiment of the present invention, persons versed in the art will appreciate that various modifications in the subject apparatus may be made without departing from the spirit of the invention.

Claims

I claim as my invention:

1. Apparatus for opening and closing a window comprising, in combination, a power source, a reversible electric motor having an armature drivably coupled to the window for opening and closing the window, a selectively operable switch having at least window-opening and window-closing settings, the selectively operable switch connecting the motor and the power source in series circuit when placed in the window-opening setting effective to place the motor in a first energized condition so as to open the window, a power switch having conductive and nonconductive conditions connected in series circuit with the power source and the motor by the selectively operable switch when the selectively operable switch is in the window-closing setting, biasing means for normally biasing the power switch to its conductive condition effective to place the motor in a second energized condition so as to close the window when the selectively operable switch is in the window-closing setting, means for monitoring the voltage across the motor armature when the motor is in the second energized condition and for controlling the biasing means in accordance with the monitored voltage effective to place the power switch in its nonconductive condition when the monitored voltage has fallen below a predetermined level indicative of the motor being stalled and effective to maintain the power switch in its nonconductive condition until the selectively operable switch is removed from the window-closing setting, and means responsive to the biasing means for effecting energization of the motor through the biasing means so as to place the motor in the first energized condition so long as the biasing means maintains the power switch in its nonconductive condition whereby stalling of the motor while the window is being closed effects reversal of the window travel.

2. Apparatus for opening and closing a window comprising, in combination, a power source, a reversible electric motor having an armature drivably coupled to the window for opening and closing the window, a selectively operable switch having at least window-opening and window-closing settings, the selectively operable switch connecting the motor and the power source in series circuit when placed in the window-opening setting effective to place the motor in a first energized condition so as to open the window, a power switch having conductive and nonconductive conditions connected in series circuit with the power source and the motor by the selectively operable switch when the selectively operable switch is in the window-closing setting, biasing means for normally biasing the power switch to its conductive condition effective to place the motor in a second energized condition so as to close the window when the selectively operable switch is in the window-closing setting, means for monitoring the voltage across the motor armature when the motor is in the second energized condition and for controlling the biasing means in accordance with the monitored voltage effective to place the power switch in its nonconductive condition when the monitored voltage has fallen below a predetermined level indicative of the motor being stalled and to maintain the power switch in its nonconductive condition until the selectively operable switch is removed from the window closing setting, means responsive to the biasing means effective to energize the motor through the biasing means so as to place the motor in the first energized condition so long as the biasing means maintains the power switch in its nonconductive condition whereby stalling of the motor while the window is being closed effects reversal of the window travel, and means responsive to the window position effective to prevent the biasing means from placing the power switch in its nonconductive condition when the window is substantially closed, thereby allowing the motor to seal the window closed and preventing the stalling of the motor while sealing the window closed from effecting reversal of the window travel.

3. Apparatus for opening and closing a window comprising, in combination, a power source, a reversible electric motor having an armature drivably coupled to the window for opening and closing the window, a selectively operable switch having at least window-opening and window-closing settings, the selectively operable switch connecting the motor and the power source in series circuit when placed in the window-opening setting effective to place the motor in a first energized condition so as to open the window, a power switch having conductive and nonconductive conditions connected in series circuit with the power source and the motor by the selectively operable switch when the selectively operable switch is in the window-closing setting, biasing means for normally biasing the power switch to its conductive condition effective to place the motor in a second energized condition so as to close the window when the selectively operable switch is in the window-closing setting, means for monitoring the voltage across the motor armature when the motor is in the second energized condition and for controlling the biasing means in accordance with the monitored voltage effective to place the power switch in its nonconductive condition when the monitored voltage has fallen below a predetermined level indicative of the motor being stalled and to maintain the power switch in its nonconductive condition until the selectively operable switch is removed from the window-closing setting, means responsive to the biasing means effective to energize the motor through the biasing means so as to place the motor in the first energized condition so long as the biasing means maintains the power switch in its nonconductive condition whereby stalling of the motor while the window is being closed effects reversal of the window travel, and time delay means for preventing the biasing means from being controlled in accordance with the monitored armature voltage for a predetermined time after the selectively operable switch is placed in the window-closing setting so as to prevent reversal of the window travel during the predetermined time, thereby preventing voltage transients generated upon starting the motor from effecting reversal of the window travel during the predetermined time.

4. Apparatus for opening and closing a window comprising, in combination, a power source, a motor having first and second selectively energizable field windings and an armature drivably coupled to the window for opening and closing the window in accordance with the energization of the windings, a transistor having conductive and nonconductive conditions, a selectively operable switch having a window-opening setting in which the switch connects the power source in series circuit with the first winding effective to open the window and a window-closing setting in which the switch connects the power source in series circuit with the transistor and the second winding, a bias network for controlling the conductivity of the transistor, the transistor normally being biased to its conductive condition by the biasing network so as to effect energization of the second winding by the power source when the switch is placed in the window-closing setting, and means for deenergizing the second winding and energizing the first winding when the voltage across the armature has fallen below a certain predetermined level indicative of the motor being stalled due to the window encountering an obstacle while closing, said means including monitoring means for detecting stalling of the motor when the window is being closed by monitoring the voltage across the armature, means for controlling the biasing of the transistor by the bias network in accordance with the monitored voltage whereby the bias network maintains the transistor in its conductive condition until the voltage across the armature has fallen below the certain level and thereafter maintains the transistor in its nonconductive condition by changing the bias applied to the transistor, means for energizing the first winding so long as the bias network maintains the transistor nonconductive, thereby reversing the window travel, means responsive to the window position for preventing the bias network from biasing the transistor to its nonconductive condition when the window is substantially closed so as to allow the motor to stall while sealing the window closed without effecting reversal of the window travel, and time delay means for preventing the bias network from biasing the transistor to its nonconductive condition for a predetermined time after the switch is placed in the window-closing setting so as to prevent voltage transients generated upon starting the motor from effecting a change in the energization of the windings during the predetermined time.

5. Apparatus for opening and closing a window comprising, in combination, a motor having first and second selectively operable field windings and an armature drivably connected to the window effective to open the window when the first winding is energized and close the window when the second winding is energized, a power source, a transistor having conductive and nonconductive conditions, a window-controlling switch having at least a window-opening setting in which the switch connects the power source to the motor effective to energize the first winding so as to open the window and a window-closing setting in which the switch connects the power source to the motor through the transistor effective when the transistor is conductive to energize the second winding so as to close the window, a bias network for controlling the conductivity of the transistor, the bias network including a controlled rectifier responsive to a voltage signal and effective upon placement of the switch in the window-closing setting to bias the transistor to its conductive condition when the voltage signal is below a certain value and to bias the transistor to its nonconductive condition when the voltage signal is above the certain value, the controlled rectifier keeping the transistor biased to its nonconductive condition until the switch is removed from the window-closing setting, means for coupling the controlled rectifier to the motor effective to energize the first winding whenever the controlled rectifier biases the transistor to its nonconductive condition, thereby reversing the direction in which the motor drives the window, a voltage-monitoring network for monitoring the voltage across the armature when the second winding is energized so as to detect stalling of the motor, the monitored armature voltage falling below a certain level when the motor is stalled, a control network responsive to the voltage-monitoring network for generating the voltage signal in accordance with the monitored armature voltage, the voltage signal being below the certain value when the motor is not stalled and above the certain value when the motor is stalled, thereby reversing the direction in which the motor drives the window upon stalling of the motor, a limit switch responsive to the window position for preventing the control network from generating the voltage signal when the window is substantially closed, thereby allowing the motor to stall while sealing the window without effecting reversal of the window travel, and a time delay network for preventing the control network from generating the voltage signal for a predetermined time after the window-controlling switch is placed in the window-closing setting so as to prevent voltage transients caused by starting the motor from effecting reversal of the motor during the predetermined time.

6. Apparatus for opening and closing a window comprising, in combination, a reversible electric motor having first and second selectively energizable field windings and an armature drivably connected to the window effective to open the window when the first winding is energized and close the window when the second winding is energized, a power source, a transistor having a control terminal and conductive and nonconductive conditions, a selectively operable switch having at least a window-opening setting in which the switch connects the power source to the motor effective to energize the first winding so as to open the window and a window-closing setting in which the switch connects the power source to the motor through the transistor effective to energize the second winding so as to close the window when the transistor is in its conductive condition, a bias network for controlling the conductivity of the transistor for controlling the voltage applied to the control terminal of the transistor, the bias network including a controlled rectifier having anode and cathode terminals connected between the switch and the control terminal of the transistor and a gate terminal so as to bias the transistor to its conductive condition when the controlled rectifier is nonconductive and to its nonconductive condition when the controlled rectifier is conductive, the controlled rectifier normally being nonconductive and being latched in its conductive state upon application of a voltage signal larger than a certain value to the gate terminal, a diode connected between the control terminal of the transistor and the motor for effecting energization of the first winding by the power source through the controlled rectifier and the diode when the controlled rectifier is in its conductive state, thereby reversing the direction in which the motor drives the window when the voltage signal exceeds the certain value, a voltage-monitoring network for detecting stalling of the motor by monitoring the voltage across the armature, the armature voltage falling below a predetermined level when the motor is stalled, a control network responsive to the voltage-monitoring network for generating the voltage signal in accordance with the voltage across the armature, the voltage signal being below the certain value when the motor is not stalled and above the certain value when the motor is stalled, stalling of the motor when the window is being closed thereby effecting reversal of the direction in which the motor drives the window, a limit switch that is responsive to the window position effective to prevent the control network from generating a voltage signal greater than the certain value when the window is substantially closed so as to prevent stalling of the motor when sealing the window closed from effecting reversal of the direction in which the motor drives the window, and a time delay network for preventing the control network from generating a voltage signal greater than the certain value for a predetermined time after the selectively operable switch is placed in the window-closing setting so as to prevent voltage transients generated by starting the motor from effecting reversal of the direction in which the motor drives the window during the predetermined time.