Variable duration electric clock timer unit

A variable duration clock timer unit which may be adjustably set to energize an electrical circuit for a selected duration for each period of clock operation includes a momentary contact, normally open, switch frictionally mounted at a selected location in a concentric annular groove in a circular clock face below a rotatable clock arm driven by an electric clock motor. The clock arm is adjustable in length and has a free end in the shape of a triangle overlying the annular groove. The switch actuator may be depressed by engagement with the free end of the clock arm to close the switch for the period of time that the free end is in engagement with the switch actuator. Adjustment of the length of the clock arm changes the width of the free end portion of the clock arm engageable with the switch actuator and thus determines the duration of switch closing. The timer unit may be used to automatically control the operation of an electric defrosting circuit of a motor vehicle.

SUMMARY OF THE INVENTION 
My invention is a timer for actuating the defrosting circuit of the windows 
of a vehicle which includes a clock for setting the automatic actuation of 
the defrosting circuit and an adjustable rotatable clock arm that adjusts 
the duration of the ON period of the timer. The clock arm is of adjustable 
length with the free end of the arm shaped as a triangle. A momentary 
contact normally open switch is frictionally mounted, at a selected 
location in concentric annular groove in a circular clock face that lies 
below the clock arm and the switch is located so that the switch actuator 
may be depressed by engagement with the free end of the clock arm so as to 
close the switch for the period of time that the arm is in engagement with 
the switch actuator. Adjustment of the radial length of the clock arm 
adjusts the time period of each cycle that the arm tip is in engagement 
with the switch actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now descriptively to the drawings, in which similar reference 
characters denote similar elements throughout the several views, FIGS. 1-2 
illustrate the use of the timer 10 to control electrical defrosting 
circuitry 11 of a vehicle, with the defrosting circuitry 11 consisting of 
electrical resistance heating elements 12 mounted or embedded in a window 
panel of the vehicle, which resistance elements are heated by the passage 
of electricity. 
As shown in FIG. 2, a battery 14 is connected through a fuse 15 and a 
manual operated switch 16 to the resistance elements 12 in conventional 
fashion for manual control. 
A switch unit 20 actuated by a clock arm 30 driven by a clock motor 21 in 
timer 10 is connected in parallel to manual switch 16. The electrically 
energized clock motor 21 is connected by manual switch 18 to battery 14. 
Clock motor 21 rotates output shaft 22 which is frictionally engaged to 
clock arm 30, with clock motor 21 rotating arm 30 at the rate of one 
complete turn, in the preferred embodiment, every twenty-four hours for 
defrosting the windows of a parked car. Shorter cycle times of the timer 
10 may be obtained using alternate clock motors. Arm 30 may be manually 
rotated relative to shaft 22 to set it in position with relation to time 
indicia 25 marked on the periphery of the clock face 26. Arm 30 is formed 
of a radial member 31 telescopically joined to a pointer member 32 by 
means of a threaded bolt 34 that fastens pointer member 32 through a 
radial slot 35 in radial member 31, so as to permit adjustment of the 
radial length of the triangular tip section 37 at the free end of the 
pointer member 32. Both members 31 and 32 of arm 30 are formed of 
conductive material so that arm 30 serves as a pole of switch 20. A fixed 
wire 29 that leads from battery 14 is maintained in commutating contact 
with radial member 31 by means of a coil spring 41 mounted about shaft 22 
and which bears against a washer 42 mounted on shaft 22 and to which wire 
29 is fixed, with washer 42 bearing against the underside of the radial 
arm 31 to maintain electrical contact. 
A fixed contact unit 50 is frictionally engaged in an annular groove 51 of 
the clock face 26, with contact unit 50 comprising a metal contact 52 
fitted with a rounded external projecting surface 53 enclosed in a housing 
54 snugly engaged in groove 51. A compression spring 56 of metal biases 
contact 52 in the extended position with spring 56 electrically connected 
to a wire 57 leading to the load defrosting resistors 12 so that contact 
unit 50 serves as the fixed pole contact of switch 20. 
Pointer member 32 is formed with a triangular shaped tip section 37, 
oriented so that one point 61 of tip section 37 extends radially away from 
arm 30, with the other two points 62 of tip section 37 located at equal 
radial distances from the center of drive shaft 22. Preferably points 62 
are spaced apart by the peripheral distance that clock arm 30 rotates in a 
period of one hour. Arm 30 may be adjusted in length so that a portion of 
tip section 37 is in electrical contact with detent 52 at least once for 
every period of rotation of arm 30 and for a duration dependent upon the 
radial length of arm 30 and the consequent length of the arc between the 
adjoining sides 65 and 66 of tip section 37 at the radial distance of 
contact detent 52 from the center of drive shaft 22. 
Alternatively, contact assembly 50 may be replaced by a momentary normally 
open switch to obviate the need for conducting electricity through arm 30, 
with said switch serving as switch 20 of FIG. 2 as shown in FIG. 7. The 
poles of normally open switch 20 are connected respectively to leads 29 
and 57, with the switch frictionally positioned in groove 51 so that the 
actuator 61 of the switch is positioned to be engaged at a selected time 
by the tip section 37 of arm 30, with such engagement serving to depress 
actuator 61 of the switch to cause movable switch contact 60 to 
electrically connect both poles of the switch and electrically connect 
leads 29 and 57 for the period of such engagement. 
While the invention has been described in terms of a timer control for a 
defrosting system, the invention is suited for control of any system which 
requires electrical cylindrical control over a time period, with 
provisions to adjust the period of the controlled time over a uniform 
timed cycle. 
Since obvious changes may be made in the specific embodiment of the 
invention described herein, such modifications being within the spirit and 
scope of the invention claimed, it is indicated that all matter container 
herein is intended as illustrative and not as limiting in scope.