Engine speed control circuit for emergency vehicle

A control circuit for a vehicle electrical system which is operative when the vehicle engine is running but the vehicle is not in motion to sense vehicle storage battery voltage and, when that voltage is below a predetermined threshold, to enable an electrically controllable device to open somewhat the engine throttle raising engine speed and increasing the output of an engine driven electrical source. The control circuit finds particular utility in emergency vehicles such as ambulances and the like where that vehicle may remain at an emergency site for an extended period of time with the engine idling and with numerous electrical demands on the vehicle electrical system to increase the engine speed when those electrical demands have sufficiently exceeded the output of an engine driven alternator with the engine running at idle.

SUMMARY OF THE INVENTION 
The present invention relates generally to voltage level responsive control 
circuits and more particularly to such control circuits in a prime 
mover-voltage regulated electrical source-storage battery system where the 
control circuit monitors storage battery voltage and increases the speed 
of the prime mover in the event that the storage battery voltage becomes 
inadequate. 
An illustrative environment and one in which the present invention finds 
particular utility is an emergency vehicle such as an emergency medical 
service vehicle ambulance, fire engine, police car and the like where the 
vehicle may remain parked at an emergency site for an extended period of 
time with the vehicle engine running and with numerous electrical devices 
operating off the electrical system of the vehicle. The electrical system 
may be called upon to supply all of the normal lighting requirements of 
the vehicle as well as emergency rotating beacons, flashing lights, two 
way radio communication and other electrical demands the aggregate of 
which will exceed the output of the vehicle engine driven alternator when 
the engine is running at idle. 
Present day emergency medical service vehicles and ambulances are 
frequently built by purchasing a van or truck chassis from one of the 
major truck manufacturers and modifying that van or chassis to suit the 
particular needs as an emergency vehicle. Sometimes such modification will 
include the addition of a second alternator driven by the vehicle engine 
along with a second voltage regulator and storage battery to be charged by 
that alternator so that the system includes a parallel connected set of 
batteries as well as a parallel connected set of voltage regulated 
alternators. Even with this enhanced electrical capability the electrical 
demands on such an emergency vehicle at an emergency site frequently 
exceed the output of the alternators when the engine is idling. 
Modern day vehicles of the type frequently modified for emergency medical 
service are designed to meed certain standards imposed by federal 
regulations on the exhaust emissions of certain pollutants such as carbon 
monoxide, sulfur dioxide and oxides of nitrogen. One system for helping to 
meet these federal standards is the provision of a vacuum actuable piston 
and an electrically controllable valve arrangement for selectively 
activating that piston to hold the engine throttle control somewhat more 
open than its normal idle position at times when the vehicle is 
decelerating at engine speeds above some specified level rather than 
allowing the throttle valve to completely close at these times. The 
structure of this antipollution arrangement may take many forms but its 
essence is to hold the engine throttle at a more open position than that 
dictated by the accelerator pedal during certain portions of vehicle 
deceleration. As supplied by the manufacturer this antipollution device is 
not active when the vehicle is parked with the engine idling. 
Among the several objects of the present invention may be noted the 
utilization of the above described antipollution arrangement for an 
entirely different purpose at times when it is not performing its original 
intended purpose; the provision of a vehicle electrical system control 
circuit for enhancing the output of a voltage regulated electrical source 
such as one or more alternators when the electrical system requires such 
an enhanced output; the provision of a scheme for increasing vehicle 
engine speed while that vehicle is parked in an engine idle condition upon 
either an automatic indication that such increased speed is desired or at 
the will of the vehicle driver or operator; and the provision of an 
emergency vehicle electrical system of enhanced versatility. These as well 
as other objects and advantageous features of the present invention will 
be in part apparent and in part pointed out hereinafter. 
In general a control circuit for a vehicle includes an arrangement for 
maintaining a vehicle engine throttle control at an engine speed setting 
above normal idle at prescribed times with an arrangement for monitoring 
the vehicle storage battery voltage and, in response to that monitored 
voltage being below a predetermined threshold, increasing the throttle 
control engine speed setting thereby driving an engine driven electrical 
source at a higher speed and a correspondingly higher output to meet the 
electrical demands associated with vehicle operation. The system may also 
be placed in the increased engine speed mode by manual actuation 
regardless of battery voltage and taken out of that increased engine speed 
mode by operator actuation of a control specifically dedicated to that 
purpose as well as operator actuation of several conventional vehicle 
controls the use of which would dictate that the engine should not be 
running in an increased speed mode such as actuation of the vehicle brake 
pedal or shifting the vehicle transmission control lever from a neutral 
condition such as "park" into a drive position.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now more specifically to the drawing a somewhat conventional 
vehicle in which the present invention is to be incorporated may include a 
storage battery 13, perhaps physically configured as a pair of 
conventional vehicle storage batteries connected in parallel, along with 
one or more engine driven voltage regulated electrical sources typically 
alternators for charging the storage battery 13 and for supplying the 
electrical needs of the vehicle system. The vehicle prior to incorporation 
of the present inventive circuitry may also include a vacuum actuable 
piston arrangement 15 under the control of an electrically controlled 
valve 17 so that, when valve 17 is electrically energized, an engine 
vacuum source such as the intake manifold or base region of the carburetor 
is connected by way of line 19 to the mechanical device 15 to block or 
move a carburetor throttle control linkage so as to cause the throttle to 
be more wide open than at engine idle. As noted earlier this electrically 
controllable mechanical device for holding an engine throttle control 
somewhat more open than its normal idle position is currently employed on 
some vehicles during deceleration at engine speeds above some specified 
value for pollution control purposes. The present invention employs this 
electrically controllable mechanical device 15 and 17 for other than 
pollution control purposes. A switch 21 which is closed when the vehicle 
shift lever is in neutral or equivalently a park position (a term 
"neutral" encompasses both) and a vehicle brake light actuating switch 23 
which is closed when the operator of the vehicle applies its brakes are 
the only other conventional vehicle elements in the schematic diagram. 
Thus elements 13, 15, 17, 19, 21 and 23 may be present on a vehicle prior 
to incorporation of the present invention. 
The remaining circuitry of FIG. 1 may be physically encapsulated in an 
epoxy or similar material for moisture and mechanical protection purposes 
with a light emitting diode 73 and a pair of normally open manually 
actuable switches 25 and 27 accessible to the vehicle driver or operator 
so that he may visually determine the status of the system and, under the 
proper circumstances, change that status by depressing one of the buttons 
25 or 27 momentarily. If only such manual control of the system is desired 
the storage battery voltage monitoring circuitry enclosed within the 
dotted line 11 may be omitted. 
The circuit 11 for monitoring the voltage of storage battery 13 senses that 
voltage by the series connection of a zener diode 31, a pair of diodes 45 
and 47 which provide a small but well defined voltage drop of around 0.5 
to 0.7 volts each, and the pair of resistors 41 and 43 with this entire 
series circuit being essentially connected between the positive terminal 
of battery 13 and ground when switch 21 is closed indicating the vehicle 
transmission selector level is in a neutral or park position. So long as 
the battery voltage is above some predetermined level such as 12 volts the 
zener diode 31 is reverse biased and conducting and the corresponding 
voltage drop across resistor 41 is sufficient to forward bias the 
base-emitter circuit of transistor 29 causing transistor 29 to also be in 
a conducting state. Capacitor 39 is connected in parallel with this series 
voltage sensing circuit merely as a filter to prevent transient phenomenon 
associated with vehicle operation from providing a false battery voltage 
level indication. In some applications capacitor 75 may be added for a 
similar purpose. When the voltage of battery 13 drops below a 
predetermined level and the reverse bias voltage on zener diode 31 becomes 
insufficient to maintain that diode conducting and current flow through 
resistor 41 ceases causing transistor 29 to switch into its nonconducting 
state. So long as transistor 29 was conductive that transistor effectively 
short circuited resistor 53 precluding the application of any base drive 
to transistor 33. 
However, when transistor 29 becomes nonconductive base drive current is 
supplied to transistor 33 and that transistor now conducts and by way of 
resistor 71 and light emitting diode 73 (now lit to indicate enhanced 
engine speed) creates a voltage drop across resistor 69 forward biasing 
transistor 35 to also become conducting. Conduction by transistor 35 
completes the circuit from the positive terminal of battery 13 through the 
electrically controlled valve 17 and by way of closed switch 21 to ground 
enabling valve 17 to apply the vacuum from line 19 to the piston 
arrangement 21 increasing engine speed as desired. Once the transistors 33 
and 35 become conductive the engine speed increases as does alternator 
output, the battery voltage will likely increase to above the threshold 
determined by zener diode 31. However, it would not be desirable for the 
voltage sensing circuit to now indicate that engine speed should be 
reduced. This circuit is arranged to have a latching function so that even 
though the battery voltage does increase at enhanced engine speeds no 
reversal of the process slowing the engine speed occurs unless the 
operator should intervene. This latching function occurs because once 
transistor 35 becomes conductive, resistor 37 provides forward bias on 
transistor 33. Numerous other actions or occurrences will, however, take 
the circuit out of this latched condition disabling the control valve 17 
and allowing the engine to return to idle. 
The vehicle transmission selector lever might inadvertently be bumped from 
its neutral or park position opening the switch 21 removing the ground 
connection and immediately disabling the valve 17 as well as causing the 
several transistors to go into their nonconducting state. Preparatory to 
moving the vehicle the driver might depress the brake pedal energizing the 
vehicle brake lights by way of switch 23. Closure of switch 23 connects 
the positive terminal of battery 13 by way of diode 57 to the base of 
transistor 33 reversed biasing (due to the slight voltage drop across 
diodes 59 and 61) the base-emitter circuit of transistor 33 causing that 
transistor to become nonconductive extinguishing the indicator 73 and 
removing base drive current from transistor 35 also switching that 
transistor to a nonconducting state and disabling control valve 17. The 
driver or operator may wish to manually reduce engine speed to idle and 
this is accomplished by simply momentarily closing the switch 25 shunting 
the base-emitter circuit of transistor 33 again causing that transistor to 
become nonconductive. 
Regardless of whether the battery voltage sensing circuit 11 is present or 
not the vehicle operator may momentarily depress switch 27 inducing 
base-emitter current flow in transistor 33 from the positive battery 
terminal by way of resistor 37 and the closed contacts of switch 27 to 
ground causing transistor 33 to again become conductive inducing the 
previously described sequence of events ultimately resulting in 
energization of the control valve 17 and enhanced engine speed. 
The circuit of the schematic diagram has been successfully incorporated 
into vans supplied by the Ford Motor Company and General Motors having the 
emission control throttle opening plunger 15 and electrically controlled 
valve 17 as a part of the standard equipment and with such a van being 
modified to include a pair of parallel connected storage batteries 
schematically illustrated at 13 along with a pair of alternators each 
having its own voltage regulator. On such an installation the following is 
a complete list of the circuit components with values and an occasional 
brief comment about that component elaborating on the above discussion: 
______________________________________ 
REFER- 
ENCE NO. DESCRIPTION COMMENT 
______________________________________ 
55 1200 OHM Resistor Current limiter and 
base current for 33 
53 560 OHM Resistor Reverse bias for 33 
41 & 43 1200 OHM 1/4 Watt Resistor 
Voltage divider and 
bias 
39 150 Microfarad Capacitor 
Filter 
29 2N 4126 PNP Transistor 
31 Zener Diode 9.3 volt 
45, 47, 59 
1N 4001 Diode Drop Each 0.5-0.7 
Volt 
57, 61, 67 
1N 4001 Diode 
25 & 27 Normally open, momentary 
close push button switch 
73 red light emitting diode 
65 1N 4001 Diode 
63 0.1 Microfarad Capacitor 
Filter 
51 39 Microfarad Capacitor 
Filter 
71 270 OHM Resistor Current Limiter 
37 1200 OHM Resistor Bias 
69 560 OHM Resistor Bias 
35 2N 5190 NPN Transistor 
33 2N 4126 PNP Transistor 
75 39 Microfarad Capacitor 
Filter 
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From the foregoing it is now apparent that a novel control arrangement for 
an emergency vehicle providing enhanced engine speed and electrical 
generator output upon operator demand or upon system need has been 
disclosed meeting the objects and advantageous features set out herein 
before as well as others and that modifications as to the precise 
configuration, shapes and details may be made by those having ordinary 
skill in the art without departing from the spirit of the invention or the 
scope thereof as set out by the claims which follow.