Transit vehicle heater

A supplementary vehicle heater is provided which includes a burner, a heat exchanger, a coolant conduit connected to the heat exchanger and a coolant pump connected to the conduit. There are controls which are operatively connected to the burner and the coolant pump which operate the heater in a first mode when the engine is stopped to preheat the engine or keep the engine warm. The controls operate the heater in a second mode when the engine is running to improve heating of vehicle interior. Preferably the controls include automatic controls which engine coolant temperature. The controls cause the burner and pump to function when the engine is running and the coolant temperature is below preset temperature.

BACKGROUND OF THE INVENTION 
This invention relates to vehicle heaters of the type which use a burner as 
a source of heat and, in particular, to such a heater particularly adapted 
for use in buses and other transit vehicles. 
Conventionally vehicle interiors are heated by the engine of the vehicle. 
Hot coolant from the engine is circulated through a heat exchanger and one 
or more fans are used to circulate air heated by the heat exchanger 
through the interior of the vehicle. However, such heaters are not always 
sufficient for the heating requirements of some vehicles, such as buses 
and other transit vehicles which have a large interior volume. The need 
for another heater is increased for certain types of engines which have 
relatively low heat output such as four cycle diesel engines. 
In addition, the vehicle engines are only an adequate source of heat after 
they come fully up to operating temperature and only as long as they 
continue to operate. Accordingly an additional source of heat may be 
desirable for heating the vehicle while the engine is still cold and for 
periods of time when the engine is shut off. 
Another type of auxiliary heater is commonly employed in vehicles, 
typically large diesel powered vehicles, to preheat the engine prior to 
starting and to keep the engine warm when the vehicle is shut off. Such 
heaters make diesel powered vehicles significantly easier to start and 
reduce initial wear on various engine components including the starting 
system and moving components which initially may not receive adequate 
lubrication when the engine is cold. 
At least two types of auxiliary heaters therefore are commonly available 
for vehicles. One is an auxiliary space heater which usually burns the 
engine fuel in a burner and circulates the heat to the interior by means 
of a fluid heated in a heat exchanger adjacent the burner. The second is a 
preheater to initially warm the engine or keep the engine warm while the 
engine is shut off. Such preheaters may also include burners operating on 
the engine fuel and are typically connected to the engine cooling system 
to initially warm the coolant or keep the coolant warm. 
Auxiliary space heaters for vehicles may in fact be necessary for transit 
vehicles. On the other hand, preheaters may only be necessary in extremely 
cold climates. However, as indicated above, they may make such vehicles 
much easier to start, improve the life of the engine and other vehicle 
components and can cut emissions by allowing the engine to be shut off 
when not required. They also save fuel costs since the engine need not 
operate to provide heat. Vehicle purchasers however are often faced with 
the necessity of ordering two separate heaters in the vehicle, a preheater 
and an supplemental, fuel-fired space heater. 
Another problem with the space heaters is encountered due to the continuous 
operation of their circulating pumps. These are typically electrically 
powered. The pump and motor have a limited service life. In many prior art 
heaters the pump circulates continuously as long as the auxiliary space 
heater is in operation. Eventually the pump and/or motor fail, possibly 
requiring the vehicle to be out of service until the components can be 
replaced or repaired and increasing the overall operating costs of the 
vehicle. 
However previous attempts to prolong the life of the coolant pump by 
shutting the heater off have been unsuccessful. This has typically been 
done by shutting the heater off through external relay logic when the 
heater enters a standby sub-state after the coolant is heated to a preset 
level, typically 85.degree. C. These attempts proved to be unsuccessful 
because shutting the heater off in this way undermines the heater's 
ability to diagnose system problems through its diagnostic system, the 
heater's ability to automatically shut itself off when certain types of 
errors are encountered and the integrity of the heater data log is 
undermined by filling it with turn on and turn off events. 
The coolant pump tends to run excessively long because the auxiliary heater 
tends to have a relatively light duty cycle when the engine is running 
because the coolant is already heated by the engine. The heater tends to 
therefore remains in a standby mode or sub-state for the majority of its 
run time with the coolant pump constantly circulating the hot coolant and 
with the burner off and monitoring the coolant temperature. The duty cycle 
of the pump can approach 100% of the time. 
One problem associated with prior art preheaters is encountered with fleet 
operations where driver turn-over is high and driver training is typically 
low. Automation, in the form of a timer, can facilitate the preheating 
operation. However automation has not typically existed for a supplemental 
heater. 
Another problem associated with preheaters is that they can be 
inadvertently left on, wasting fuel, potentially draining the battery 
voltage and requiring an operator to eventually turn off the heater. 
A further problem associated with prior art auxiliary heaters is 
incompatibility with remote starting systems. 
In the absence of a suitable supplemental heater, manufacturers often have 
employed a separate electrical heater for operation when the vehicle is 
running. This undesirable because it is yet another piece of equipment to 
install and service. 
Accordingly, it is an object of the invention to provide an improved 
vehicle heater which can combine the functions of an engine preheater and 
an auxiliary space heater for the vehicle. 
It is also an object of the invention to provide an improved heater for 
vehicles which can supplement the heat provided by the conventional 
vehicle heater, but does not require continuous operation of the heater's 
own coolant circulation pump. 
It is a further object of the invention to provide an improved vehicle 
heater which is relatively light in weight compared with prior art vehicle 
heaters, particularly the total weight of a conventional engine preheater 
and a conventional auxiliary space heater. 
It is a still further object of the invention to provide an improved 
vehicle heater which is simple and rugged in construction. 
SUMMARY OF THE INVENTION 
In accordance with these objects, there is provided an auxiliary vehicle 
heater for a vehicle having an interior, an engine and a vehicle interior 
heater heated by engine coolant. The auxiliary heater includes a burner, a 
heat exchanger and a coolant pump connected to the heat exchanger. 
Controls are operatively connected to the burner and the coolant pump to 
operate the auxiliary heater in a first mode when the engine is stopped to 
preheat the engine or keep the engine warm. Controls are operatively 
connected to the burner and the coolant pump to operate the auxiliary 
heater in a second mode when the engine is running to improve heating of 
the vehicle interior. 
There is provided, according to another aspect of the invention, an 
auxiliary vehicle heater for a vehicle having an interior, an engine and a 
vehicle interior heater heated by engine coolant. The auxiliary heater 
includes a burner, a heat exchanger and a coolant pump connected to the 
heat exchanger. There are controls operatively connected to the burner and 
the coolant pump to operate the auxiliary heater when the engine is 
running to improve heating of the vehicle interior. The controls include 
automatic controls which monitor engine coolant temperature. The controls 
cause the burner and the pump to function when the engine is running and 
the coolant temperature is below a pre-set second temperature. The 
controls stop the burner and the pump functions when the engine is not 
running or when the coolant temperature is above the pre-set second 
temperature. 
Preferably the controls operate the pump for a pre-set period of time 
before operating the burner. 
There is provided, according to another aspect of the invention, a method 
of operating an auxiliary heater for a vehicle with an engine, an 
interior, and a vehicle interior heater heated by engine coolant. The 
method includes the steps of turning on the pump and the burner when the 
engine coolant temperature is below a second pre-set temperature and when 
the engine is running. The controls stop the burner and the pump when the 
engine is not running or when the coolant temperature is above the pre-set 
second temperature. 
Preferably the controls start the pump function at a set period of time 
before starting the burner. 
Auxiliary heaters and auxiliary heating methods according to the invention 
offers significant advantages over the prior art. In one mode of operation 
the coolant pump stops when the auxiliary heater has raised the coolant 
temperature to a pre-set temperature while the engine is running. The 
vehicle engine's coolant pump then takes on the task of circulating the 
coolant through the heater. The auxiliary heater assumes a standby mode or 
sub-state. However the coolant flow through the heater, as applied only by 
the engine pump, may be small compared to the flow using the pump in the 
auxiliary heater. The auxiliary heater may therefore cool down quickly 
compared to the rest of the coolant system. This may give a false 
indication to the temperature sensor which would cause the heater to start 
up and burn fuel unnecessarily. It would then cycle off almost 
immediately. To prevent this problem, the auxiliary heater according to 
the invention preferably cycles the pump on for a period of time, say 
three minutes, before the burner. This ensures that the coolant 
temperature at the heater is the same as in the rest of the system to 
avoid a false reading which turn on the burner unnecessarily. If the 
temperature is in fact above the preset level, then the pump turns off 
without igniting the burner. 
In addition, the system clock of the internal controller is preferably 
stopped while the heater is in the supplemental-standby mode or sub-state 
so as not to accumulate misleading run times since no components are 
actually running. 
The invention also can overcome the problem of providing two separate 
heaters for preheating the engine and for supplementary interior heating 
of the vehicle. This is done by sensing when the vehicle's engine is 
running and automatically transferring the heater from the preheat 
function to the supplemental function when this occurs. The supplemental 
function can be entirely automatic and transparent to the vehicle 
operator. 
Wastage of fuel is significantly reduced by utilizing a timer to turn off 
the preheat function after a preset period of time, say 90 minutes. 
The invention also overcomes problems associated with utilizing remote 
starting systems by allowing a direct interface with the radio receiver 
unit on vehicles. 
The need for a separate, electrical supplementary heater is removed by 
providing a single heater which can perform both preheating and 
supplemental heating operations with a single piece of equipment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 16, a transit vehicle 10 is shown in the form of a 
bus. The bus is provided with a conventional diesel engine 12 and a 
conventional vehicle heat exchanger 14 with fan 16 coupled to the engine 
by coolant conduits 18 and 20. The heat exchanger is used for interior 
heating of the vehicle as is well known and is commonly known as a 
"heater". The vehicle has a fuel tank 22 which in this example is 
connected to engine 12 by a fuel line 24 for supplying diesel fuel to the 
engine. 
There is also an auxiliary heater 26 which is connected to the fuel line 24 
by a second fuel line 28. The auxiliary heater 26 is also connected to the 
engine cooling system by coolant conduits 30 and 32. 
Referring to FIG. 1, this shows the heater 26 in more detail. The heater is 
generally conventional apart from the control system. The heater includes 
a burner unit 34 including a nozzle 36. Fuel is supplied to the heater 
from fuel tank 22 by means of conduits 24 and 28 as indicated by arrow 38. 
The fuel is pumped from the fuel tank by a fuel pump 40 and regulated by a 
fuel regulator 42. 
The heater also includes an air compressor 44 which supplies compressed air 
to the nozzle through conduit 46 as illustrated by arrow 48. The nozzle 
utilizes the compressed air to atomize the fuel received from the fuel 
pump and fuel regulator. The heater has an air blower 50 which provides 
combustion air for the burner. The burner unit also includes a spark 
electrode 52. A flame sensor 54 is mounted on the burner unit adjacent the 
nozzle. 
There is a combustion tube 60 on the heater surrounded by a heat exchanger 
62. Conduit 32 serves a coolant inlet and is connected to a coolant pump 
66. The coolant pump is connected to the heat exchanger via a conduit 68. 
Conduit 30 is connected to the heat exchanger and serves as a coolant 
outlet for coolant heated by the heater. There is also a temperature 
sensor 70 mounted on the heat exchanger and an overheat sensor 72. These 
components are generally conventional and therefore are not described in 
more detail. 
FIG. 2-7 are wiring diagrams of the control system for the heater 26 
showing the controls for different modes of operation. Referring first to 
FIG. 2, this the wiring diagram for the standard heat mode. This is the 
conventional mode of operation of the heater similar to the prior art. 
During this mode the heater operates in thermostatically controlled burn 
cycles in order to keep the vehicle coolant heated. It continues to run on 
demand during this mode. Each time the coolant level drops below a preset 
level, the burner is turned on until the coolant reaches a higher preset 
temperature. When it reaches this higher temperature the burner is turned 
off, but the pump continues to run. 
The components of the heater are shown on the left side of the FIG. 2 
including overheat sensor 72, compressor 44, fuel pump 28, air blower 50, 
coolant pump 66, flame sensor 54 and temperature sensor 70 also shown in 
FIG. 1. In addition there are further components including ignition coil 
80 and hour meter 82. All of these components are connected to an 
auxiliary heater controller, shown generally at 84, by a plurality of 
conductors 86 and a pin connector 88. 
The controller 84 includes a microcontroller 90 which, in this particular 
embodiment, is an NEC D78CP14G microcontroller. The microcontroller is 
programmed with software described in the flow-chart of FIG. 15a-15j. 
Attached hereto, and labelled Appendix A is the source code of the 
software. 
Controller 84 is shown in simplified form in FIG. 2-7. A plurality of 
circuit elements are represented schematically by a series of field-effect 
transistors (FET's) 92, 94, 96, 98, 100, 102 and 104. The full details of 
the circuit are shown in FIG. 17a and 17b. 
Referring back to FIG. 2, the controller has six inputs including main 
switch input 110, auxiliary input 112, auto switch input 114, temperature 
sensor input 116, flame sensor input 118 and overheat sensor input 120. 
There are six output terminals including compressor output 122, fuel pump 
output 124, spark electrode output 126, blower output 128, coolant pump 
output 130 and hour meter output 132. 
Power for the controller is supplied from vehicle battery 134 via connector 
136. 
Standard Run State 
As mentioned above, the Standard Run State is equivalent to the prior art 
operation of auxiliary vehicle heaters. The heater operates in 
thermostatically controlled burn cycles to keep the vehicle coolant 
heated. This state is primarily entered from the off state by placing a 
constant signal voltage on the main terminal 110 via a toggle switch 140 
which is manually operated by the vehicle operator or maintenance 
personnel or alternatively by a timer. The off state is resumed when the 
signal voltage is removed by opening toggle switch 140 manually. 
As described further below, the Standard Run State overrides and cancels 
the Preheat Run State. The Standard Run State is entered from the Preheat 
Run State when a constant signal voltage is placed on the main input 110. 
The Standard Run State also overrides the Supplemental Run State described 
below. The Standard Run State is entered from the Standard (Supplemental) 
Run State when the signal voltage is removed from the auto input terminal 
112. The standard run state is exited to the Standard (Supplemental) Run 
State when a constant signal voltage is placed on the auto input 114. 
The overall operation of the heater is described diagrammatically in FIG. 
8. The standard heat mode only is shown in FIG. 9. 
Preheat Run State 
FIG. 3-7 are generally the same as FIG. 2, but show the wiring diagram and 
controller during modes of operation different from the standard heat mode 
illustrated in FIG. 2. The Preheat Mode is shown in FIG. 3 and represented 
diagrammatically in FIG. 10. When the heater is operated in the Preheat 
Run State, the heater heats the coolant in the same manner as in the 
Standard Run State. However the Preheat Run State differs in that it 
includes a timer which turns the heater off when the time expires. In this 
particular example the timer has a 90 minute duration although this can be 
changed according to requirements. The timer prevents the heater from 
running indefinitely. The timer is internal to the controller 84, in 
particular the microcontroller 90 with associated software. 
The Preheat Run State is entered from the off state when a momentary signal 
voltage is placed on the auxiliary input terminal 114 by means of a push 
button 144. Alternatively the momentary voltage can be applied by means of 
a radio transmitter transmitting a signal to remote radio receiver 146. 
The Preheat Run State is exited to the off state when the 90 minute timer 
expires. The Preheat Run State may be overridden and cancelled by either 
the Supplemental or the Standard Run State. The Preheat Run State is 
exited to the Standard Run State when a constant voltage is placed to the 
main input 110. It is exited to the Supplemental Run State when a constant 
signal voltage is placed on the auto input 112. 
As described above, the purpose of the Preheat Run State is to preheat the 
engine by heating the coolant a period of time before the vehicle is 
started. This is typically useful for vehicles stored outdoors in cold 
climates. 
Supplemental Run State 
Referring to FIG. 4 and 11, the Supplemental Run State is entered from the 
off state when a constant signal voltage is placed on auto input 112. The 
preferred way of accomplishing this is illustrated in FIG. 4 where auto 
input 112 is connected to heating ventilation and air conditioning (HVAC) 
controls 17 of the vehicle. A constant voltage can be supplied to the auto 
terminal 112 only when the controls are in the heat position as 
illustrated. The HVAC controls are connected to the engine monitor 15 
which in turn is connected to the alternator 13 of the engine 12. Thus a 
constant voltage is only supplied to input 112 when the engine is running. 
In short, the Supplemental Run State is automatically entered when the 
engine is running and the HVAC controls are turned to the heat position. 
The Supplemental Run State is entered from the Preheat Run State discussed 
below, when a constant signal voltage is placed on the auto input 112 
which occurs when the engine starts. The Supplemental Run State is entered 
from the Standard (Supplemental) Run State, described below, when a 
constant signal voltage is removed from the main input 110. 
The Supplemental Run State is exited to the off state when the signal 
voltage on the auto input is removed. This occurs when the HVAC controls 
are turned to the off or air conditioning positions. The Supplemental Run 
State is also exited to the Standard (Supplemental) Run State when a 
constant signal voltage is placed on the main input terminal 110. 
The Supplemental Run State overrides and cancels the Preheat Run State. 
Standard (Supplemental) Run State 
The Standard (Supplemental) Run State is a transition mode utilized for 
automatic operation. The Standard (Supplemental) Run State is entered from 
the Supplemental Run State when a constant signal voltage is placed on the 
main input 110. It is entered from the Standard Run State when a constant 
signal voltage is placed on the auto input 112. This state is exited to 
the Supplemental Run State when the signal voltage on the main input is 
removed and is exited to the Standard Run State when the signal voltage on 
the auto input is removed. 
This state serves as a transition between the Standard and Supplemental Run 
states. Heater function in the state is identical to the Standard Run 
State. Effectively this transition allows the Standard Run State to 
override the Supplemental Run State, but not to cancel the Supplemental 
Run State. 
Off State 
Off State is entered from the Preheat Run State when the timer described 
above expires. It is entered from the Standard Run State when the signal 
voltage on the main input 110 is removed. The Off State is entered from 
the Supplemental Run State when the signal voltage on the auto input is 
removed. The Off State is exited to the Preheat Run State when a momentary 
signal voltage is placed on the auxiliary input 114. The Off State is 
exited to the Standard Run State when a constant signal voltage is placed 
on the main input 110. The Off State is exited to the Supplemental Run 
State when a constant signal voltage is placed on the auto input 112. 
FIG. 5 illustrates the Preheat State with Stop. This is similar to the 
Preheat Run State shown in FIG. 2, but includes a stop button 145 
connected to the main input 110. The Preheat automatically stops after the 
90 minute timer or it can be manually stopped by means of push button 145. 
This is also illustrated diagrammatically in FIG. 12. 
Referring to FIG. 6 and 13, these show controls for a combination of the 
Preheat and Supplemental Run States with semi-automatic operation. 
The Preheat State is entered manually by means of push button 144. When the 
vehicle is started within the 90 minute Preheat time period, the heater 
automatically transfers to the Supplemental Run State. If the vehicle is 
not started within the 90 minute period, then the heater shuts off and 
assumes the Off State. It may subsequently enter the Supplemental Run 
State when the vehicle engine is started. When the engine is turned off, 
the heater also turns off. 
FIG. 7 and 14 illustrate the controls and operation of controls for a 
combination of the Standard and Supplemental Run States with fully 
automatic operation. An external timer 141 is utilized which is connected 
to the main input 110. Auto input 112 is connected to the HVAC controls 17 
and the engine monitor 15. 
The heater is automatically started by the external timer 141. In the 
preferred embodiment this is a seven day timer that can be set for single 
days, 5, 6 and 7 days for activation twice per day. The timer will turn on 
the heater in Standard Run State where it runs for a predetermined 
duration as set by the timer. When the vehicle engine has started within 
the timer duration the heater automatically transfers to the Standard 
(Supplemental) State where operation is identical to the Standard Run 
State. The heater continues to preheat the vehicle engine. At the end of 
the timer duration, the heater automatically transfers to the Supplemental 
Run State. If the vehicle is not started within the timer duration, the 
heater shuts off. It may still enter the Supplemental Run State when the 
vehicle is started. This configuration allows the heater to perform its 
function without any driver input except for adjustment of the HVAC 
controls in some installations. 
Full Function Heat State 
In the mode, the remote radio receiver 146 and push button 144 are 
connected to the auxiliary input 114 as shown in FIG. 3. Timer 141, 
momentary push button 143, shown in FIG. 7, and toggle switch 140 are 
connected to the main input 110. The engine monitor and HVAC controls are 
connected to the auto input terminals as shown in FIG. 7. 
This configuration allows both semi-automatic or fully automatic operation 
and is convenient if the vehicle usage is not on a consistent schedule 
and/or there is not enough notice given as to the vehicle usage. The 
addition of the momentary stop push button 143 on the main input allows 
for the manual preheat mode to be manually turned off when the momentary 
switch makes contact, the heater switches to the Standard Run State. When 
the momentary switch breaks contact, the heater switches to off. 
Sub-States 
The heater runs through several sub-states as it operates. The first of 
these is Pre-check. The heater performs a system check including checking 
all components for short circuits, checking all components for open 
circuits and checking for correct input signals from sensors. If all of 
the checks are positive, then the heater enters the Ignition Sub-state and 
operates the blower to provide combustion air, the fuel pump to provide 
fuel flow, the compressor to atomize the fuel, the ignition coil to ignite 
the combustion mixture and the coolant pump to circulate the system 
coolant. When the flame sensor indicates a flame, then the heater enters 
the Run Sub-state. In the Run Sub-state the heater runs the blower to 
provide combustion air, the fuel pump to provide fuel flow, the compressor 
to atomize the fuel and the coolant pump to circulate the system coolant. 
When the temperature sensor indicates a coolant temperature of 85.degree. 
C., the heater enters a Purge Sub-state. In Purge, the heater operates the 
blower to purge exhaust gas from the combustion chamber and runs the 
coolant pump to circulate the system coolant. The heater stays in Purge 
for three minutes, then enters Standby. 
In Standby, depending upon what state the heater is in, the heater may or 
may not run the coolant pump to circulate coolant. In the Preheat and 
Standard Run States, the heater runs the coolant pump to circulate the 
system coolant, monitors the temperature of the coolant via the 
temperature sensor and checks for fault in the above devices and monitors 
switch inputs. In the Supplemental Run State, the controls monitor the 
coolant temperature via the temperature sensor and checks for faults in 
the system. It monitors switch inputs. 
The heater stays in Standby until its temperature sensor indicates a 
temperature of 65.degree. C. The heater then enters Pre-check or Pre-run. 
Pre-run is active only in the Supplemental Run State. In Pre-run, the 
coolant pump is run for three minutes. The heater then enters Pre-check. 
The controls continue to monitor the coolant temperature via the 
temperature sensor and checks for faults in the system. It monitors switch 
inputs. After three minutes, if the temperature is greater than a preset 
amount, 65.degree. C. in this case, then the heater enters Standby State. 
After the three minutes, if the temperature is less than 65.degree. C., 
then the heater enters Pre-Check. 
If a fault is found at some point in the cycle, the heater enters the Purge 
Sub-state directly and displays the error indicator on a panel. After 
Purge it continues with Pre-Check and the rest of the cycle described 
above. If a second error is found before the heater has completed a 
temperature cycle, then the heater enters Shutdown. 
In Shutdown, the heater displays any error indicators indefinitely and 
monitors switch inputs. The heater waits in this state until inputs are 
turned off. Only then will it enter the Off-state and be ready to operate 
again. In this way the heater has a built-in automatic shutoff which 
prevents it from continuously attempting to run and potentially damaging 
itself, damaging the vehicle, or creating a safety hazard. 
The heater has the ability to provide useful diagnostic information through 
its data log file maintained by the microcontroller. The heater logs its 
switched-on time, its flame time, its duty cycle and the number of cycles 
(temperature rises from 65.degree. C. to 85.degree. C. in this example). 
The heater logs its first and second temperature cycles, including 
associated times, sensor values, and system voltage. In addition it also 
logs all faults with their associated times, associated Sub-states and 
sensor values. If the heater turned off after only its first temperature 
cycle, then the second cycle information would not be recorded. The second 
cycle information is important in calculating the vehicle's coolant 
capacity and for further diagnosing system problems. 
The heater's ability to automatically shut itself off after two consecutive 
errors is an important feature. If the heater experiences two fault 
conditions before it completes a temperature cycle, then it enters the 
Shutdown state where it disables itself and waits for an operator to reset 
it by turning off all its input devices. If the heater were turned off 
after only its first temperature cycle, then it is never able to enter 
Shutdown. Instead the heater is continuously reset and the fault will 
continuously occur. The fault may be particularly hazardous such as no 
ignition spark. In this case the heater attempts to light the fuel mixture 
for one minute before declaring a fault. A second attempt allows another 
minute worth of fuel into the combustion tube before the heater enters 
Shutdown. If the heater were turned off, then it would try to light the 
fuel mixture every time the vehicle's coolant temperature cycles. This may 
be dozens of times throughout the operation of the vehicle and may result 
in more and more fuel entering the combustion chamber, possibly leading to 
a fire hazard. 
It will be understood that many of the details described above are by way 
of example only and are not intended to limit the scope of the invention 
which is to be interpreted with reference to the following claims.