A vehicle turn signal mechanism includes a lockout device in the form of an electric timer. The flashing signal is normally cancelled by a steering wheel sensor that is arranged to generate a triggering signal for an electromagnetic detent associated with a signal selector lever. The lockout device prevents the triggering signal from being generated except after the steering wheel has been retained in its straight-ahead position for a predetermined time period.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to automotive turn signals, particularly turn 
signals used on trucks of the tractor-trailer type. The invention is 
especially concerned with a control system for returning a manually 
operated signal selector to a neutral position following a turning 
maneuver. The process is sometimes referred to as self-cancellation of the 
turn signal. 
2. Description of Prior Developments 
Automotive vehicles are commonly equipped with turn signals, i.e. flashing 
lights on the front and rear ends of a vehicle that warn other motorists 
that the driver of the vehicle intends to make either a right turn or a 
left turn. To actuate the turn signal lights, the driver operates a manual 
lever located on the steering wheel. As the lever is moved from a neutral 
position to a selected operating position, the associated switches are 
opened and closed thereby supplying current to flasher devices and the 
associated turn signal lights. 
In many cases, the turn signal system is equipped with a self-cancelling 
feature which includes a mechanism for automatically returning the manual 
lever to its neutral position following a turning maneuver By thus 
returning the lever to its neutral position, the turn signal is cancelled 
so that the signal lights cease flashing thereby avoiding a false warning 
to other motorists that the driver might be contemplating another turning 
maneuver. 
The self-cancelling mechanism can include an electrical sensor associated 
with the vehicle steering wheel to detect whether the steering wheel is in 
a straight-ahead position or in a turning position. Also, an 
electrically-operated detent is provided for retaining the lever in its 
various positions. Springs may be used to bias the lever toward its 
neutral position. 
In operation of the system, when the driver returns the steering wheel to 
its straight-ahead position following a turning maneuver, the electrical 
sensor detects the change in steering wheel condition by sending a signal 
to the electrically-operated detent. The detent releases the lever which 
allows the associated springs to automatically return the lever to its 
neutral position. The detent can include an electromagnet coil and a 
detent structure operated by the coil. 
As used in automobiles, the self-cancelling feature is generally effective 
for its intended purpose. However, when the system is used on trucks of 
the tractor-trailer type, it may not be satisfactory under all 
circumstances. For example, while the driver of a tractor-trailer is in 
the process of making a left turn, he will sometimes swing the truck first 
to the right and then to the left. The initial right turn provides 
clearance for the intermediate wheels during the actual left turn. In a 
similar manner, when making a right turn, the driver will sometimes 
initially turn the vehicle to the left before making the right turn. 
Again, this is for the purpose of obtaining sufficient curbside wheel 
clearance. 
When the driver of a tractor-trailer makes two successive turns in opposite 
directions, as described above, there is a danger that the turn signal 
system will prematurely self-cancel during the turning process, i.e. 
before the turn is completed. When this occurs, the following motorist can 
misinterpret the inadvertent cancellation of the signal as an indication 
that the driver had decided not to make the turn. Confusion on the part of 
the following motorist could lead to an accident. 
The above-described premature signal cancellation action occurs because the 
driver moves the steering wheel through the straight-ahead condition 
during the process of going from one turn direction to the other turn 
direction. As the steering wheel reaches the straight-ahead condition, the 
wheel sensor sends a signal to the electromagnetic detent which 
prematurely returns the signal select lever and associated switches to the 
neutral, no-turn position. 
The present invention is directed to a control system including electrical 
circuitry for preventing premature cancellation of a turning signal, 
particularly under the above-described condition wherein the driver sets 
the signal selector lever in an operating position for a signal and then 
turns the steering wheel in two different directions during the course of 
a turning maneuver. In one form of the invention, an electrical timer is 
interposed between the steering wheel sensor and the electromagnetic 
detent. When the steering wheel is moved from one turn direction through 
the straight-ahead position to the other turn direction, the time delay 
generated by the timer prevents the cancellation signal from reaching the 
electro-magnetic detent. The timer is designed to terminate or disable the 
premature cancellation signal. 
Electrical timers have previously been employed in turn signal systems. 
However, such timers have been used primarily for cancelling the turning 
signal only when the steering wheel is moved an insufficient amount to 
effect signal cancellation, e.g., when the signal is used to change 
traffic lanes or when the wheel sensor is ineffective to produce the 
signal cancellation action. 
U.S. Pat. No. 3,308,428 to Grontkowski shows a turn signal system having a 
timer for cancelling the turn signal at a predetermined time after initial 
turn-on of the signal lights or after application of foot pressure to the 
vehicle brake, e.g., when the vehicle is brought to a stop at a traffic 
light. The timer is apparently used as an override device to effect a 
signal cancellation action in the event the wheel sensor is ineffective 
for that purpose. 
U.S. Pat. No. 4,792,785 to Yukio, et al. shows a turn signal system having 
a timer for cancelling a turn signal only when the vehicle is travelling 
at a high rate of speed. The turn signal is turned off at a predetermined 
time following initial turnon of the signal lights. The timer is only 
operative under high speed conditions. Under normal conditions, the 
steering wheel sensor controls the signal cancellation process. 
In both the Grontkowski and Yukio systems, the timer is used as an 
auxiliary device for turning off the signal, i.e. for signal cancellation. 
In the present invention, the timer is used as a device for preventing 
premature cancellation of the signal especially while the steering wheel 
is passing through a straight-ahead condition from one turn direction to 
another turn direction. 
SUMMARY OF THE INVENTION 
The invention is directed to a turn signal system that includes a first 
electrical latch set in the latched position by manual movement of the 
signal selector level to the signalling position. The system further 
includes a steering wheel position sensor that controls a second 
electrical latch. The second latch is connected to the first latch and to 
a timer so that the timer can remain in the timing mode only when the 
steering wheel is in its straight-ahead position. 
While the steering wheel is turned away from its straight-ahead position in 
either direction, the timer is inoperative or inactive. Should the 
steering wheel remain in its straight-ahead position for a predetermined 
time period, e.g., two, three or four seconds, the timer will run through 
its cycle to apply an output signal to a driver circuit for an 
electromagnet detent associated with the signal selector lever. When the 
detent is de-energized by the driver circuit, the lever is immediately 
returned to the neutral, no-turn position so that the turning signal is 
cancelled. 
The system allows the driver to move the steering wheel in two directions 
while making a turning maneuver without prematurely cancelling the turn 
signal. For example, when making a right turn, the driver can initially 
turn the steering wheel to the left to provide a wide turning arc and then 
to the right. During the course of such a turning maneuver, the steering 
wheel will move through the straight-ahead position without actuating the 
electromagnetic detent for the signal selector lever. The timer will go 
inactive since the wheel will not remain in the straight-ahead position 
for a sufficient length of time to let the timer run through its cycle. 
When the turn has been completed and the steering wheel returned to its 
straight-ahead position for a sufficient time, e.g., four seconds, the 
timer will generate an output signal to the driver circuit to disable the 
electromagnetic detent to effect a signal cancelling operation. 
In the described system, the function of the timer is to prevent 
short-duration positioning of the steering wheel in the straight-ahead 
position from producing a cancellation of the turning signal. The timer 
ensures that the turning signal will be cancelled only after the steering 
wheel has been returned to its straight-ahead position and has remained in 
such a position for a predetermined time, e.g., several seconds.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a control circuit that includes a turn signal switch 11 having 
a switch arm 13 movable between a neutral position and two different 
operating positions. In one operating position, the switch arm delivers 
battery current to flasher 15 through contact 14 to a signal lamp 17. In 
the other operating position, the switch arm delivers battery current to 
flasher 15 through contact 16 to signal lamp 21. One signal lamp will 
typically be located on the right side of the vehicle to signal a right 
turn and the other signal lamp will be located on the left side of the 
vehicle to signal a left turn. 
FIG. 2 shows some features of a manually operable selector lever 23 for 
moving switch arm 13 between a standby, neutral position and two operating 
positions. The selector lever is pivotally mounted on a pivot 24 so that 
it can move in either direction to generate a right turning signal or a 
left turning signal. Detents 25 are associated with an electromagnet 31 
for holding lever 23 in any of its three positions. 
Coil springs 29 normally bias the lever to the neutral, standby position as 
shown in FIG. 2. When the lever is manually moved to operate switch arm 13 
to a signalling position (up or down in FIG. 2), the lever rides over one 
of the detents 25 after which the detent engages the lever to hold it in 
the signal position against the bias of springs 29. 
An electromagnetic coil 31 is de-energized to retract detent pin 26, 
thereby enabling springs 29 to return the lever to its neutral, no-signal 
position. The process is sometimes referred to as signal cancellation in 
that, when the selector lever is returned to the neutral position, the 
turn signal lamps 17 or 21 are automatically extinguished. The 
electromagnetic detent structure shown in FIG. 2 is generally old in the 
art. 
Referring again to FIG. 1, a turn signal control circuit is shown to 
include a first electric latch 30 that is triggered to a latched condition 
by movement of switch arm 13 to either of its closed positions for 
respectively generating either a right turn signal or a left turn signal. 
A second latch 33 is triggered to a latched condition by a signal sent 
from steering wheel sensor 35 through line 42, when the steering wheel is 
moved from a straight-ahead position to a turning mode and back to the 
straight-ahead position. 
Steering wheel sensor 35 detects the rotated position of steering wheel 39 
so that when the steering wheel is in a straight-ahead condition the 
sensor has one type of output, and when the steering wheel is in a vehicle 
turning condition the sensor has a different type of output. The sensor 
output is directed through line 40 to a signal shaper 41 that produces a 
pulse when the signal goes from low to high. The pulse is applied through 
line 42 to latch 33. The sensor output is also directed through line 43 to 
an electric timer 45. 
Sensor 35 provides one type of output when the steering wheel is in the 
straight-ahead, no-turn condition and a different output when the steering 
wheel is turning left or right. Sensor 35 can take various forms, e.g., a 
Hall-effect switch responsive to a permanent magnet carried by the 
steering wheel, a reed switch responsive to a magnet on the steering 
wheel, or a light-emitting diode and photo transistor located on opposite 
sides of a light control shutter carried by the steering wheel or other 
structure driven by the steering wheel. U.S. Pat. No 4,275,379 to Nakano 
shows some steering wheel sensor constructions that can be used. 
Latch 33 has a control line 46 connected to timer 45 for triggering the 
timer into or out of its timing mode. When latch 33 is set in a latched 
condition by suitable input signals in lines 37 and 42, line 46 will 
enable timer 45 to time out, i.e. provide a delayed output signal in timer 
output line 48. The timer is charged through line 43. The delayed timer 
signal is applied to a driver circuit 49 that disables transistor 50 in 
circuit with the coil (electromagnet) 31 described previously in 
connection with FIG. 2. 
When transistor 50 is disabled, coil 31 is de-energized to return signal 
selector lever 23 to its neutral position as shown in FIG. 2. 
Simultaneously, switch 13 is returned to the open circuit position for 
extinguishment of the signal lamps 17 or 21. Such lamp extinguishment 
constitutes the signal cancellation event previously mentioned. 
If the driver of a tractor-trailer vehicle desires to make a right turn, 
the driver may initially turn steering wheel 39 (FIG. 1) to the left to 
achieve wheel clearance and then to the right to negotiate the turn. 
During this process, steering wheel sensor 35 generates two different 
types of signals in line 40, i.e. one signal while the wheel is in the 
left turn mode or right turn mode, and a different signal while the wheel 
is on center as it moving from the left turn mode through the 
straight-ahead condition in order to reach the right turn mode. 
With conventional turn signal systems, there is a possibility that the 
wheel sensor signal generated during this transitional motion of the 
steering wheel through its straight-ahead position will produce a 
premature cancellation of the turn signal, e.g., a cancellation of the 
signal just as the vehicle is beginning to make the right turn. The 
circuit of FIG. 1 is designed to prevent premature signal cancellation. 
Timer 45 is designed to achieve a short time delay before generating a 
triggering signal in line 48. Typically, the delay is about four seconds 
but any predetermined delay period may be used. The purpose of this delay 
is to enable the steering wheel to pass through its straight-ahead 
position without de-energizing the electromagnet detent coil 31. Thus, 
short duration alignments or positioning of the steering wheel 39 in its 
straight-ahead position are prevented from altering the condition of coil 
31. 
Coil 31 can only be de-energized when the steering wheel remains in its 
straight-ahead condition for a period longer than the time delay built 
into timer 45, e.g., four seconds in the illustrated embodiment. The 
system is designed so that coil 31 is de-energized only after the vehicle 
turn has been completed. Premature de-energization of coil 31 during the 
course of the turning maneuver is prevented by the time delay. 
Latch 33 is connected to sensor 35 and timer 45 so that when steering wheel 
39 is in its straight-ahead position, latch 33 sends an enabling signal to 
timer 45 through line 46. The timer goes into the timing mode for 
generating a signal in line 48 after the timer cycles out, e.g., after a 
four-second time delay period. If, during the time delay period, sensor 35 
senses that the steering wheel is no longer in its straight-ahead 
position, the sensor will discharge the timer without producing a coil 
de-energization signal in line 48. 
Line 48 is connected to a circuit line 53 that leads to a reset circuit 54. 
The purpose of reset circuit 54 is to reset latches 30 and 33 to their 
unlatched states at a predetermined time after de-energization of coil 31. 
Reset circuit 54 includes a time delay circuit for delaying the latch 
reset action until after de-energization of coil 31. The delay period may 
be about two seconds. The latch reset pulses are applied to the latches 
through reset line 55. 
FIG. 3 is another depiction of the FIG. 1 circuit with certain components 
thereof shown in greater detail in order to facilitate a more complete 
understanding of the invention. Similar reference numerals are applied to 
corresponding components in the two views. In FIG. 3, dashed lines are 
used to outline certain components such as latch 30, latch 33, signal 
shaper 41, timer 45, driver circuit 49 and reset circuit 54. 
As shown in FIG. 3, latch 30 includes two NOR gates 61 and 62, and a 
transistor 63. Latch 33 includes two NOR gates 65 and 66. Timer 45 
includes a comparator 67, a resistance 68 and a capacitance 69. The 
resistance and capacitance form a charging device for accumulating a 
voltage at one input of the comparator. Driver circuit 49 includes a 
comparator 71. 
In FIG. 3, the designation "REG" signifies a voltage source having a 
relatively stable nonvarying varying value, e.g., seven volts. The 
regulated voltage is applied to various circuit components as shown in 
FIG. 3. 
In order to explain the operation of the FIG. 3 circuit, there are included 
two additional Figures showing, the FIG. 3 circuit in two different 
conditions. FIG. 4 shows the circuit when the flasher lamps are operating 
to signal a turn and the steering wheel 39 is in a straight-ahead 
condition. Such a condition can occur when signal selector 23 (FIG. 2) is 
initially moved to one of its operating positions to start the flasher 
lamps 17 or 21 flashing. FIG. 5 shows the circuit when the flasher lamps 
are operating and the steering wheel 39 is in the turning mode, to the 
left or to the right. 
In the illustrated circuit, each of the NOR gates 61, 62, 65 and 66 has two 
inputs. A characteristic of the NOR gate is that when both inputs are low, 
the output is high. If either input is high, the output is low. In FIGS. 4 
and 5, the symbol H is applied at various points in the circuit to 
designate a high signal. The symbol L designates a low signal or no 
signal. 
In the circuit condition of FIG. 4, a voltage is applied through switch 
contact 14 or 16 to one input of NOR gate 61 so that the output of gate 62 
is high, whereby the transistor 63 is conductive. Circuit line 37 thereby 
feeds a low signal to one input of NOR gate 66 to enable latch 33. 
Wheel sensor 35 is a switch, whereby the signal in lines 40 and 43 is 
either high or low depending on the condition of steering wheel 39. In the 
present arrangement, when the steering wheel is in the straight-ahead 
condition, the signals in lines 40 and 43 are switched high. When the 
steering wheel is in the turning mode, the signals in lines 40 and 43 are 
switched low. 
As further shown in FIG. 4, when line 40 is switched from low to high, the 
signal shaper 41 produces a high pulse on line 42 which causes the output 
of NOR gate 66 to go high. 
The high signal in line 43 allows capacitor 69 to charge. After a delay 
period of about four seconds, depending on the selected values for 
capacitance 69 and resistance 68, a voltage is built up at input 73 of 
comparator 67 sufficient to produce a high signal in line 48, i.e. the 
voltage at input 73 is then higher than the voltage generated in line 75 
by the regulated voltage source 74. 
The high signal generated in line 48 is delivered to comparator 71 which 
disables transistor 50. The transistor is then turned off and coil 31 is 
de-energized to effect a cancellation of the turn signal by lamps 17 and 
21 (FIG. 1). The signal cancellation action involves retractive movement 
of the detent pin 26 (FIG. 2) and return motion of the signal selector 23 
to its neutral position. 
However, if during the four-second delay period, the driver of the vehicle 
turns the steering wheel to initiate a turning maneuver, a low signal is 
produced from wheel sensor 35 and drains the voltage in capacitance 69 so 
that the line 48 will not turn on. FIG. 5 represents the condition of each 
latch in its latched state. 
As previously noted, line 53 controls reset circuit 54. A high signal in 
line 53 for a predetermined period charges capacitance 77 to a value 
higher than the regulated voltage in line 78, thereby causing comparator 
79 to deliver a high signal to reset line 80. The signal is delivered to 
latches 30 and 33 via line 55, whereby the associated NOR gate inputs are 
temporarily set high. When the reset signal is dissipated, the associated 
inputs to NOR gates 62 and 66 go low in preparation for another cycle of 
the turn signal mechanism. The values for capacitance 77 and the 
associated resistance 82 are selected so that the reset signal appears at 
line 55 approximately two seconds after de-actuation of coil 31. 
A principal feature of the invention is the interaction of latches 30 and 
33 with wheel sensor 35 and timer 45, whereby the timer remains in the 
timing mode only while the steering wheel remains in its straight-ahead 
position. This ensures that, while the steering wheel is being turned 
through its straight-ahead position between a right turn mode and a left 
turn mode, the flashing signal will not be prematurely cancelled. 
Obviously, numerous modifications and variations of the present invention 
are possible in the light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.