Note: Descriptions are shown in the official language in which they were submitted.
C~
1 ENGINE R.P.M. CONTROL SYSTEM FOR SNOWMOBILE
The present invention relates to a safety control system for
a vehicle and more specifically relates to a safety control
system for preventing a vehicle from "running away" in the event
that its throttle sticks and for preventing the vehicle engine
from overspeeding in the event that the load is suddenly removed
from the engine as might be occassioned by a drive train element
breaking while the engine is under load with the vehicle operating
at or near full throttle.
While the problems solved by the present invention may occur
with a large number of vehicles they seem to occur more frequently
with snowmobiles due to the latter being operated in an environ-
ment which contributes to stuck throttles and due to the use of
drive trains which can fail in various ways resulting in the load
being suddenly removed from the engine.
Previous attempts of solving the problem of runaway has been
to provide the snowmobile with a normally open switch connected
to the ignition system such that the ignition will be grounded
out whenever the switch is released. This has no~ proved satis-
factory however since an operator may inadvertently release theswitch resulting in the engine of the snowmobile stopping when it
is not intended or desired that it do so.
Summary of the Invention
According to the present invention, there is provided a
novel vehicle engine control.
An object of the invention is to provide an engine control
means for preventing vehicle "runaway" during starting without
inhibiting the normal operation of the vehicle.
More specifically, it is an obj~ct of the invention to
provide an engine R.P.M. limiting control which operates to limit
the R.P.M. of the engine below drive engagement speed during
starting and which is selectively operable for limiting the R.P.M.
1- ~
- -
3`~
l of this engine ~ust below its maximum designed operational speed.
These and othe~ objects will become apparent from a reading
o~ the ensuing description together with the appended drawings.
Brief Description of the Drawings
Fig. 1 is a perspective view of a snowmobile embodying the
present invention.
Fig. 2 is a diagram of the engine R.P.M. limiting control
circuitry.
Description of the Preferred Embodiment
_
Referring now to Fig. 1, therein is shown a snowmobile lO
including a frame 12 having a pair of skiis 14 attached thereto
adjacent the forward end thereof and a traction drive track 16
suspended beneath a rearward portion thereof. Mounted on the
forward end of the frame 12 is an internal combustion engine 18.
Provided for driving the track 16 from the engine 18 is a variable
speed drive 20 including a variable speed primary drive pulley 22
connected to an output shaft of the engine, a variable speed
secondary drive pulley 24 connected to a countershaft and a drive
belt 26 trained about the pulleys 22 and 24. The pulleys 22 and
24 are respectively speed and torque responsive and no torque
will be transmitted therebetween until the engine speed reaches a
predetermined engagement speed. A typical idle speed for a
snowmobile engine might be in the neighborhood of 2,000 R.P.M.
with the engagement speed being about 3,000 R.P.M. and top design-
ed speed being 6,500 R.P.M.
The speed of the engine is controlled by means of a throttle
control including a lever 28 mounted on a right handle bar 30 of
the snowmobile and coupled to a throttle assembly 32 by means of
a sheathed cable 34. The lever 28 is mounted in a conventional
manner, not specifically shown, whereby it is operative to open
throttle valving in increasing amounts in accordance with increas-
ing movement of a trigger portion of the lever 28 from a released
-- 2 --
l position spaced away from the handle bar 30 to a fully depressed
position against the har.dle bar. Under normal circumstances, one
or more r~turn springs 36 forming part of the throttle assembly
32 will act to retain the throttle valving to an "idle" position
when the trigger portion of the lever 28 is released. However,
if the sheathed cable 34 should bind or some other malfunction
occur which prevents the throttle valving from so returning to
its "idle" position upon the operator releasing the throttle
control lever 28, then the valving will remain at whatever
position to which it has been actuated to thus present a hazard
in the event that the engine is to be started or an operator is
thrown from the snowmobile lO with the throttle in a stuck open
position.
Referring to Fig. 2, therein is shown an electrical engine
R.P.M. control system 40 for eliminating or at least reducing the
hazard just mentioned and for also reducing the possibility of
engine or drive component damage as might occur as a result of a
load suddenly being removed from the engine when the latter is
operating at or near full throttle.
Specifically, the system 40 includes an ignition circuit
comprising an alternator 42 which is driven by the engine 18 in a
conventional manner for providing power through a lead 44 for
firing a spark plug 46 in correspondence with the closing of a
set of ignition points 48. Connected to the lead 44 is a lead
50, which contains a silicon controlled rectifier or SCR 52 that
is switched, in accordance to an unsafe condition sensed by the
remainder of the system 40, to connect the lead 50 to a ground
lead 54 to ground out the ignition to maintain the engine speed
at a safe value. ~-
Forming an impor~ant part of the system 40 are a pair of
identical integrated timing circuits which are indicated by the
boxes 56 and 58. The circuits 56 and 58 may take many forms
3 --
, . . . .
. .
hDW~Y~ ~hP C~ S ~hDS~ 2S~ h~ p~ r~ .y simila~ t~
ones su})~lied as part No. MC 14~ hy Motorola S~miconduct~:~
Products Inc. Each of the circuits 56 and 58 include a ground
pin lr a trigger pin 2, an output pin 3, a reset pin 4, a control
voltage pin 5, a threshold voltage pin 6, a ~ischarge volta~e pin
7, and a supply voltage pin 8. The supply voltage for driving
the circuits 56 and 58 is provided by the alternator 42, which is
connected to a power supply lead 60. Connected in series in the
lead 60 is a rectifier diode 62 and a resistor 64. A lead 66
containing a capacitor 68 connects a junction 70, located between
the diode 62 and resistor 64 with the ground lead 54 while a lead
72 containing a Zener regulator diode 74 is connected to the lead
60, after the resistor 64, and to the ground lead 54. Thus, as
employed in the circuit, the diode 62, resistor 64, capacitor 68
and Zener diode 74 cooperate to provide a d.c. voltage equal to
the reverse breakdown voltage of the Zener diode 74 to power the
timing circuits 56 and 58. Accordingly, the power supply line 60
is connected to the supply voltage pins 8 of the circuits S6 and
58 respectively by leads 75 and 76 while the circuits 56 and 58
are respectively grounded by leads 77 and 78 connected between
the ground pins 1 of the circuits and the ground lead 54. A lead
: 80 is coupled to the supply line 60 ahead of the rectifier diode
62 and conveys an alternating voltage to the base of a txansistor
82 which results in the latter being turned on and off at a
frequency equal to that o~ the voltage and thus at a frequency
which corresponds to the engine R.P.M. A lead 84 is connected
between the lead 80 and ground and contains a Zener diode 86
- which regulates the voltage in the lead 80 such that it is never
negative nor exceeds the reverse breakdown voltage of the Zener
diode 86.
The threshold and discharge voltage pins 6 and 7, respec-
tively, of the timing circuit 56 are connected in parallel to a
,
~ t~
1 lead of the timing circuit 56 are connected in parallel to a lead
90 which is connected to an emitter 92 of the transistor 82.
Thus, when the voltage in the lead 80 switches on the transistor
82, the latter conducts to connect the pins 6 and 7 to ground
such as to cause a capacitor 94 to discharge, the capacitor 94
being located in a lead 96 connected between the power supply
lead 60 and ground lead 54 and joined to the lead 90 at 98.
Connected in the lead 96 in series with the capacitor 94 is a
resistor 100. When the capacitor 94 discharges and the transistor
82 switches off during the negative excursion of the voltage in
line 80, the voltage at the pins 6 and 7 builds at a rate deter-
mined by the time constant of the resistor 100 and capacitor 94,
this time constant being designed to be less than the frequency
of the voltage produced when the engine R.P.M. is at a value for
effecting drive engagement speed but above idle speed. For
example, if the engine idles at 2,000 R.P.M. and the drive 20
engages when the engine reaches 3,000 R.P.M., the time constant
may be selected to correspond to a voltage frequency produced
when the engine is operating between 2,400-2,500 R.P.M. Accord-
20 ingly, if the engine is designed according to the example givenand is operating at some speed below 2,400 R.P.M. the frequency
at which the transistor 82 is turned on and off will be suffici-
ently low to permit the voltage in the lead 90 to attain a value
greater than the threshold voltage of the timing circuit 56
during the time that the transistor 82 is turned off. The circuit
56 is designed such that during the time that the voltage at pin
6 is building from 0 to the threshold value the output voltage ~t
pin 3 will be high, this voltage becoming low upon the threshold
value of the circuit being reached. Thus, during slow R.P .M.
30 operation of the engine 18, the output voltage at pin 3 will
change states at a frequency corresponding to the R.P.M. value.
_ 5 _
.: '' . - ' ` " '~ . :
, ~ : ' . . . - :
- . :
1 OI1 the other hand, should the speed of the engine 18 increase
to a value above 2,400-2,500 R.P.M., the frequency at which the
transistor 82 is turned on and off will be too high to permit the
voltage in the lead 92 to ever attain a value greater than the
threshold voltage of the circuit 56 during the time that the
transistor 82 is turned off and the voltage at the output pin 3
will remain high.
The output pin 3 of the timing circuit 56 is connected by
means of a lead 102, to the base of a transistor 104 having its
10 emitter 106 connected, by means of a lead 108, to the threshold
and discharge pins 6 and 7 of the timing circuit 58. A lead 110,
which is connected between the power supply lead 60 and ground
lead 54, joins the lead 108 at 112 and connected in series in the
lead 110 is a resistor 114 and capacitor 116. Anytime that the
output voltage at the pin 3 is high, the transistor 104 is turned
on to discharge the capacitor 116 to ground and anytime output
voltage at the pin 3 is low, the transistor 104 is turned off and
the voltage in the lead 108 builds at a rate determined by the
time constant of the resistor 114 and the capacitor 116. This
time constant is somewhat greater than that of the resistor 100
and capacitor 94 but still corresponds to an engine R.P.M. fre-
quency below drive engagement speed, it being noted that the
purpose of the circuit S8 is to give stability to the system to
ensure that transient voltages do not efect unwanted control of
the engine.
Thus, when the engine R.P.M. is below engagement speed and
below that speed for producing a voltage having a frequency equal
to the time constant of the resistor 100 and capacitor 94 and the
output voltage at pin 3 changes from high to low at this fre-
30 quency, and consequently the transistor 104 will be turned on andoff at this frequency. The time constant of the resistor 114 and
capacitor 116 is sufficiently long that the threshold voltage of - -
, . . . . ~: - . :
, , ~ ' " '
1 the circult 58 is never reached and the voltage at the output pin
3 thereof remains high. However, if the R.P.M. of the snowmobile
engine is equal to the preset critical limit of the circuit 56
such as to effect a constantly high output voltage at the pin 3
thereof, the transistor 104 will be constantly turned off permit
ting the voltage at the pins 6 and 7 to go high resulting in the
circuit 58 effecting a low voltage at its output pin.
The output pin 3 of the circuit 58 is connected, by means of
a lead 118, to the base of a transistor 120 having its collector
connected to the power supply lead 60 by a lead 122 and having
its emitter 124 connected to ground by a lead 126. Connected
between the lead 122 and the gate of the SCR 52 is a lead 128.
Whenever the output voltage at the pin 3 of the timing circuit 58
is high the transistor 120 is on and the gate voltage o the SCR
52 is low so that the latter is off. However, when the voltage
at the output pin of the timing circuit 58 is low, the transistor
is off and the gate voltage of the SCR 52 is high enough to gate
the SCR 52 on to ground out the ignition to limit the snowmobile
engine speed to a value below the critical speed.
Provided for permitting the engine to run at speeds in
excess of engagement speed is circuitry including a resistor 130
connected in series with the resistor 100 by means of a lead 132
having one end connected to the power supply lead 60 and the
other end connected to the lead 96. A normally open switch 134
is located in the lead 132 between the resistor 130 and power
supply lead 60. The switch 134 would be located at a location
convenient for actuation by the operator whenever he desired to
operate the snowmobile engine at speeds above drive engagement
speed. Such operation of the switch 134 changes the time constant
30 to a value equal to the product of the resistances of the resis- ~ -
tor~ 100 and 134 divided by their sum and multiplied by the
capacitance of the capacitor 94. Thus the time constant is
-- 7 --
.. . ~
. .
1 shortened such as to requ-re increased engine R.P.M. to effect
turning on of the SCR 52. Thus a high speed limit is provided
and it is selected to be just slightly below the maximum design
speed o~ the engine 18 and/or drive 20. Thus, in the event that
the drive belt 26 breaks or some other part of the traction drive
20 fails such as to remove the load from the engine 18 when the
latter is being operated at or near full throttle, the engine
ignition will be controlled to limit the speed of the engine
below the maximum design speed.
10Should the operator be thrown from the snowmobile 10, the
switch 134 will immediately open to automatically re-establish
the lower speed limit whereby the engine ignition is controlled
such as to lower the engine speed below that for effecting drive
engagement.
~, - 8 ~
,
. .
