Recirculating gear pump for vehicle heater

A fuel delivery apparatus for an auxiliary vehicle heater includes a burner with a fuel nozzle. A fuel pump has an intake port and a discharge port. There is a first fuel conduit connected to the intake port. A second fuel conduit connects the discharge port to the nozzle. A third fuel conduit extends between the discharge port and the intake port. A pressure release relief valve is operatively disposed along the third conduit. Fuel from the discharge port is recirculated back to the intake port when pressure of fuel supplied to the nozzle through the second conduit exceeds a preset amount. Preferably the fuel nozzle is an air aspirated fuel nozzle and the fuel pump is a gear pump. The third conduit may be internal to the fuel pump.

BACKGROUND OF THE INVENTION 
This invention relates to auxiliary vehicle heaters and, in particular, to 
gear pumps used in conjunction therewith. 
Auxiliary vehicle heaters are heaters which are independent of the 
conventional heaters used in vehicles which are actually heat exchangers 
transferring heat from the engine coolant. Auxiliary vehicle heaters are 
usually powered by fuel drawn from the conventional fuel tank of the 
vehicle. These heaters have a fuel nozzle associated with a burner and a 
combustion chamber. A fuel pump conventionally draws the fuel from the 
fuel tank and supplies it to a nozzle of the burner. 
In conventional units, fuel is supplied at a relatively high pressure to 
the nozzle. The pumps are designed so they have the capacity to initially 
suck the air and lift the fuel from the fuel tank. This requires a 
relatively high displacement pump. The priming operation requires 8 to 10 
times the capacity of pump needed to deliver fuel during normal heater 
operation. Excess fuel from the fuel pump is returned to the vehicle fuel 
tank by a fuel return line. Such a fuel return line is disadvantageous for 
a number of reasons, chiefly the hazard of fuel spillage should the return 
line be damaged. Also the incorporation of the return line increases the 
costs and complexity of an auxiliary heater installation. 
High pressure fuel systems are, by their nature, prone to fuel leaks 
through the shaft seal of the pump, through the relief seal, solenoid seal 
and nozzle seal. Fuel cannot be recirculated within the fuel pump of high 
pressure fuels systems because of the detrimental effects of large 
pressure changes. Thus high pressure systems require a fuel return line 
and draw as much as ten times the fuel required by the burner. They 
require a large supply line and an additional pressurized return line and 
associated systems. These relatively complicated installations therefore 
have a potential for fuel leaks. 
Accordingly, there is a need for of fuel supply system for auxiliary 
vehicle heaters which overcomes these disadvantages. 
It is therefore an object of the invention to provide an improved fuel 
delivery system for auxiliary vehicle heaters which significantly reduces 
the risks of fuel spillage associated with conventional high pressure 
systems. 
It is another object of the invention to provide an improved fuel delivery 
system for auxiliary vehicle heaters which eliminates the high flow rates 
associated with prior art units. 
It is further object of the invention to provide an improved fuel delivery 
system which eliminates the need for a fuel return line extending from the 
pump to the fuel tank of vehicle. 
It is also an object of the invention to provide an improved fuel delivery 
system for auxiliary vehicle heaters which is simpler and more robust than 
conventional high pressure systems. 
SUMMARY OF THE INVENTION 
According to the invention there is provided a fuel delivery apparatus for 
an auxiliary vehicle heater with a burner having a fuel nozzle. The fuel 
pump has an intake port and a discharge port. A first fuel conduit is 
connected to the intake port. A second fuel conduit connects the discharge 
port to the nozzle. This may be via a regulator. A third fuel conduit 
extends between the discharge port and the intake port. The pressure 
relief valve is operatively disposed along the third conduit. Fuel from 
the discharge port is recirculated back to the intake port when the 
pressure of fuel supplied to the nozzle through the second conduit exceeds 
a preset amount. 
In a preferred embodiment of the invention, the fuel pump has a body, the 
third fuel conduit and the pressure relief valve being within the body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to drawings, and first to FIG. 1, this shows an auxiliary vehicle 
heater 10 including a burner 12, with an aluminum body in this example, 
and a fuel pump 14 in a fuel delivery unit 15 having a body 16. The burner 
has a body 18 with an internal combustion chamber 20 and fuel nozzle 22. 
In this example, the fuel nozzle is an air aspirated nozzle shown in 
better detail in FIG. 5. The nozzle has a distributor 100, an orifice disk 
102, a nozzle body 104 and an adapter 106. There is a screw pin 108 with 
an O ring 110. The nozzle has an air inlet 114. There is also an oil 
inlet, or fuel inlet 116. There is an associated flame shield 21, flame 
sensor 23 and electrode 25 shown in FIG. 2. 
The fuel pump has an intake port 24 which is connected to a first fuel 
conduit 26 which, in turn, is connected to a fuel tank 30 of a vehicle 
where the heater is installed as seen in FIG. 1. The pump also has a 
discharger port 32. A pair of gears 40 and 42, shown in FIG. 1, 3d and 3e, 
are rotatable within a close fitting chamber 44. The ports communicate 
with the chamber. Gear 40 is connected to a powered shaft 48, while gear 
42 is connected to an idler shaft 50. In this particular example the shaft 
48 is coupled to an electric motor although other means could be employed 
for powering the pump. 
In the conventional manner, as the gears rotate, they draw fuel from the 
tank 30, through fuel line 27, elbow 29, shown in FIG. 2, 3a and 3b, 
through the first conduit 24 and port 26 into the chamber 44. The fuel is 
pressurized by the gears and discharged from the chamber through port 32 
shown in FIG. 1. 
Fuel discharged from the chamber 44 is fed to the nozzle 22 by a second 
fuel conduit 51 including a portion 52 within body 16 of the unit 15. 
Third fuel conduit 54 extends between the discharge port 32 and the intake 
port 24. In this particular example the conduit 54 is internal to the body 
16 of the unit 15. A pressure relief valve 60 is operatively disposed 
along the third conduit. The valve includes a body 61, a poppet 62 and a 
coil spring 64. There is also an O-ring 66 which serves as a seat for 
poppet 62. Spring 64 biases the poppet towards O-ring 66, thus preventing 
a flow of liquid through the conduit 54. There is also a pressure 
regulator 200, a zero pressure regulator in this example, connected 
between nozzle 22 and solenoid 202. The pressure regulator is similar to 
those conventionally used in chain saws. 
Operation of the pump and heater starts when the pump is primed. During 
priming the poppet 62 is seated against the O-ring 66. The poppet is held 
in this position by the spring 64. A priming vacuum, approximately equal 
to the relief valve setting, but also dependent on part clearances, is 
reached. After the fuel pump 14 is primed, fuel for combustion flows to 
the nozzle 22 through conduit 51, fuel regulator 200 and solenoid 202. 
After the set fuel pressure is reached, spring 64 is deflected and poppet 
62 moves away from the O-ring 66. Excess fuel flows past the poppet 64 and 
back to the inlet side of the pump through conduit 54. 
Overheating of the fuel is prevented by using an air aspirated fuel nozzle 
and lowering the fuel pressure so that overheating does not occur. The 
system operates at a very low pressure, about 9 psi in this example, and 
is completely contained within the body of the fuel pump. 
The fuel is recirculated within the body of the gear pump, thus eliminating 
the return line to the fuel tank and high fuel flow rates. Only the fuel 
being burned is drawn by the fuel pump. Since there is no fuel return line 
from the tank and the supply line is a suction line, there is no potential 
for fuel leaks between the fuel tank and the air. 
It will be recognized by someone skilled in the art that many of the 
details describedabove 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.