Abstract:
A fuel system for supplying LPG fuel, the system including a fuel storage tank and a fuel transfer tank. A first pump pushes fuel to a vehicle engine from the transfer tank and excess fuel from the engine is returned to the storage tank or the transfer tank. A second pump pulls fuel from the storage tank into the transfer tank when a fluid level within the transfer tank falls below a certain level. A method of providing LPG fuel to the engine of a vehicle.

Description:
BACKGROUND 
   Motor vehicles powered by internal combustion engines are commonly used to transport and deliver goods in many places in the world. In a number of these locales, environmental and other concerns have increased the use of motor fuels considered to be alternative fuels, as compared with the more expected gasoline and diesel fuels often used. One of the more popular alternative fuels is liquefied petroleum gas or LPG. LPG is a catchall term used to describe a variety of fuels such as commercial propane, butane which have similar physical qualities of being liquid when confined at near room temperature when moderately compressed. When in liquid form, these fuels are up to two hundred and fifty times more dense as compared to their gaseous form. Thus, it is preferable for fuel systems of LPG powered vehicles store the fuel in a liquid form until the fuel is supplied by an injector into a combustion chamber of an engine, at which point the fuel may be vaporized to improve combustion. Further, when using LPG in an engine with fuel injection, provision should be made for excess fuel from the injector rail to be returned to the fuel tank. 
   While many LPG fueled vehicles are factory conversions or retrofits of vehicles designed to use more traditional fuels, such as gasoline or diesel, the location of the tanks, pumps and other equipment used for the more traditional fuels are not the most well suited for LPG fuel systems. Maintenance and repair considerations vary between the more traditional fuel systems and LPG systems. 
   Improvements to the known systems for storing liquid LPG and supplying gaseous LPG to the engine are desirable. 
   SUMMARY 
   The present invention relates generally to an LPG fuel supply system and method of supplying LPG fuel to the engine of a vehicle. 
   More specifically, the present invention relates to an LPG fuel system for use on a vehicle using LPG to fuel an internal combustion engine, including a storage tank and a transfer tank, each tank configured to contain liquid and gaseous LPG. A fuel supply pump is mounted within the transfer tank and configured to push fuel from the transfer tank through a first fitting to the engine. The system also includes a second fitting with a biased three-way connection. A first end of the three way fitting is connected to an engine fuel return line, a second end is connected to the storage tank, and a third end is connected to the transfer tank. The three-way connection is biased to permit flow of excess fuel from the engine to the storage tank until the storage tank reaches a first specified volume of liquid LPG, and then to permit flow of excess fuel from the engine into the transfer tank. 
   The transfer tank also includes a transfer pump for pulling fuel from the storage tank into the transfer tank through a third fitting on the transfer tank. The transfer pump is configured to shut off when a second specified volume of liquid LPG is in the transfer tank. 
   The present invention further relates to a fuel transfer system for a motorized vehicle with an internal combustion engine using LPG for fuel, including a transfer tank with first, second and third fittings extending through a tank wall, a fuel supply pump and a fuel transfer pump. The fuel supply pump is connected to the first fitting and configured to provide fuel through the first fitting to the engine of the vehicle. The fuel transfer pump is connected to the second fitting and configured to pull fuel from a supply tank into the transfer tank through the second fitting when the level of fuel within the transfer tank drops below a specified volume. The third fitting is connected to a fuel return line from the engine to receive excess fuel from the engine and includes a biased three-way connector. The three-way connector is biased to direct excess fuel from the engine to the supply tank until the fuel level on the supply tank reaches a specified volume and then direct the excess fuel into the transfer tank through the third fitting. 
   The present invention also relates to a method of providing LPG fuel to an engine of a motorized vehicle. The method includes providing a storage tank and a transfer tank configured to contain liquid and gaseous LPG fuel, the transfer tank including a fuel transfer pump and a fuel supply pump. The fuel supply pump is operated to push LPG to a fuel delivery system of the engine of the motor vehicle. Excess fuel from the fuel delivery system of the engine is received in a biased valve hydraulically connected with the fuel delivery system, the fuel storage tank and the fuel transfer tank. The biased valve is configured to allow excess fuel to flow from the fuel delivery system into the fuel storage tank until an amount of LPG in the fuel storage tank reaches a first specified volume of liquid LPG and then directs the excess fuel into the fuel transfer tank. The fuel transfer pump is operated to pull LPG from the storage tank into the transfer tank until an amount of LPG in the fuel transfer tank reaches a second specified volume of liquid LPG, and is then shut off. Operation of the fuel transfer pump is resumed when the amount of LPG in the fuel transfer tank drops below the second specified volume of liquid LPG. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate several aspects of the invention and together with the detailed description, serve to explain the principles of the invention. A brief description of the drawings is as follows: 
       FIG. 1  is a schematic diagram of a motor vehicle with an LPG fuel delivery system according to the present invention. 
       FIG. 2  is a schematic view of the fuel storage and transfer tanks for the LPG fuel delivery system of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to exemplary aspects of the present invention which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
   Internal combustion engines in most late model vehicles include a fuel injection delivery system as opposed to a carbureted fuel delivery system to delivery fuel from a fuel source such as an on-board fuel tank to the cylinders of the engine for combustion. Fuel injection systems generally provide pressurized fuel in a fuel rail behind one or more fuel injectors. At an appropriate time during the rotation of the engine, each of the fuel injectors is opened to allow fuel to flow into the intake manifold or into the cylinder. To promote more consistency in the amount of fuel injected at any given time, it is desirable that the fuel rail be maintained at a relatively constant pressure. To aid in this, a fuel return is provided to allow excess pressure and fuel to be bled out of the fuel rail and returned to the fuel source for reuse. Such systems are well-known in the industry. 
   Most motor vehicles powered by an internal combustion engine  16 , such as vehicle  10  of  FIG. 1 , are powered by gasoline or diesel fuel. However, it is sometimes desirable for environmental concerns, conservation, or other business reasons to provide alternative fuel sources for such vehicles. One of the known fuel sources that can be adapted for use in existing internal combustion engines is LPG. LPG, as noted above, is desirable as it transitions from gas to liquid at relatively high temperatures and low pressures. Such a transition point allows for storage of fuel in a liquid form (at much greater density than possible with gaseous LPG) and injection into an engine in gaseous form (more efficiently burned than liquid LPG). LPG is also desirable in that in contains approximately the same energy content in liquid form as does gasoline, so that LPG can be used in a gasoline engine without alteration to the electronics controlling the delivery of fuel and ignition of fuel in the cylinders. Another advantage of LPG as an alternative fuel is that gasoline engines can generally use LPG without requiring mechanical modifications, other than to the fuel storage and delivery system. 
   Conversion of existing trucks for use with LPG may be accomplished in the factory by the original manufacturer, by a third party or by the end customer. Whoever performs the conversion, it is desirable that the extent of physical modifications to the vehicle be kept to a minimum. It is desirable for a vehicle  10 , such as shown in  FIG. 1 , that an LPG storage tank  12  be mounted in a location consistent with the location of the original gas or diesel fuel tank, such as the saddle tank location shown. While it is known to utilize a single tank for storage and transfer of LPG to an engine for combustion, such an arrangement requires the storage tank be configured with fuel pumps for transferring fuel to the fuel distribution system of the engine. In conjunction with storage tank  12 , a second, or transfer tank  14  may also be mounted to vehicle  10 . If vehicle  10  included a second original fuel tank in the location where tank  14  is indicated, tank  14  may be mounted in the original tank&#39;s location. Alternatively, if vehicle  10  was not originally configured with dual tanks, one of tanks  12  or  14  may be mounted in the original tanks position with the other tank mounted in a convenient and safe location on vehicle  10 . 
   Referring now to  FIG. 2 , a schematic diagram of an LPG fuel system  100  including storage tank  12  and transfer tank  14 . Tank  12  is the primary fuel storage tank of system  100  and is configured with a fuel inlet  16  and a fuel outlet  18 . Although inlet  16  and outlet  18  are shown diagrammatically on opposite sides of tank  12 , the inlet and outlet could be located adjacent each other or in some other configuration. Inlet  16  includes a shut off valve  20  which will prevent flow of fuel into tank  12  when tank  12  is at an eighty percent capacity liquid level, as indicated by liquid level  48 . Outlet  18  of tank  12  is connected by a fuel transfer line  42  to an inlet  40  of tank  14 . 
   Tank  14  is the fuel transfer tank of system  100  and includes an engine fuel supply pump  22  connected to a fuel outlet  24 . An engine supply fuel line  26  extends from outlet  24  to a fuel rail  52  and a plurality of fuel injectors  54  connected to fuel rail  52 . An engine fuel return line  28  returns unused fuel from fuel rail  52  to a three-way valve  30 . Valve  30  directs fuel returned from fuel rail  52  to tank  12  through a second fuel return line  36  as long as valve  20  of inlet  16  permit fuel to flow into tank  12 . If liquid level  48  of tank  12  reaches the eighty percent maximum liquid capacity of tank  12 , shut off valve  20  closes and three way valve  30  directs fuel to tank  14  instead. Fuel flowing from engine fuel return line  28  through valve  30  enters tank  14  through a fuel return inlet  32 . Inlet  32  includes a shut off valve  34  which is configured to close and prevent entry of fuel into tank  14  if a liquid level  46  within tank  14  reaches an eighty percent capacity liquid level. 
   Having the normal path for fuel returning from fuel rail  52  flow into tank  12  aids the supply of liquid fuel to fuel rail  52  from tank  14 . Fuel returning from fuel rail  52  will likely have been exposed to higher-than-ambient temperatures as the fuel passed through engine supply line  26  and returned in engine fuel return line  28 , especially where lines  26  and  28  are routed within an engine compartment of vehicle  10  or adjacent other heat generating devices or components of vehicle  10 . If this higher temperature fuel were returned normally to tank  14 , the overall heat and vapor pressure within tank  14  would be elevated. This is not desirable as it is most efficient to supply cooler, denser liquid fuel to fuel rails  52 . Directing this higher temperature return fuel to tank  12  helps maintain a lower temperature in tank  14 . 
   Tank  14  also includes a fuel transfer pump  38  which is connected to and receives fuel through inlet  40  from tank  12  through transfer line  42 . Pump  38  is fluidly connected to a shut off valve  44  which will close and prevent additional liquid from entering tank  14  if liquid level  46  reaches an eighty percent capacity liquid level. Pump  38  is also connected to a calibrated orifice  50  which is submerged beneath liquid level  46 . To pull fuel from tank  12  into tank  14 , pump  38  creates a vacuum within transfer line  42 . This vacuum will begin to draw fuel from tank  12  to tank  14  but the reduction in pressure within line  42  (created by the vacuum) may tend to cause the liquid fuel to vaporize and for gaseous fuel to be transferred instead. It is much less efficient to pump the fuel in a gaseous form as opposed to pumping it in a liquid form. However, this vaporization will also draw some heat from the fuel and this reduction of temperature of the fuel will aid in the transfer of liquid as opposed to gaseous fuel. After a given time of operation, pump  38  will have drawn enough fuel from tank  12  to fill transfer line  42  with liquid fuel and provide efficient pumping of fuel between tanks  12  and  14 . 
   Calibrated orifice  50  provides an opening beneath liquid level  46  and permits pump  38  to draw liquid fuel from within tank  14  into transfer line  42  upstream of pump  38 . One of the purposes of orifice  50  is to decrease the amount of time pump  38  has to operate to begin transferring liquid as opposed to gaseous fuel from tank  12 . The amount of fuel drawn from tank  14  is determined by the size of opening of orifice  50 . The liquid fuel drawn to pump  38  from within tank  14  serves to prime pump  38  to create a better vacuum and pumping condition. The flow of liquid fuel through pump  38  from orifice  50  may also aid in keeping pump  38  cooler during operation until liquid fuel from tank  12  arrives through transfer line  42  to pump  38 . Once liquid fuel has filled transfer line  42  and liquid from tank  12  has reached pump  38 , the amount of liquid fuel draw to pump  38  through orifice  50  will be reduced. 
   Transfer pump  38  and supply pump  22  are shown mounted on opposite ends of tank  14  for clarity in  FIG. 2 . However, it may be preferable that these two pumps are mounted adjacent to each other with tank  14  so that they may be accessible through a single access port in tank  14 . Such an arrangement of pumps  22  and  38  may also include a clustering of inlets  32  and  40  with outlet  24  adjacent the pumps. These two pumps may also be enclosed with a single housing. It is preferable that both pumps  22  and  38  be mounted so that liquid level  46  is above the pumps as much as possible, so that the pumps may utilize the fuel within tank  14  to aid in cooling the pumps during operation. 
   Power needs to be supplied to each of the pumps  22  and  38  for their operation as described above. Because of the circular nature of fuel flow that the two pumps may develop when operating simultaneously (e.g., pump  22  draws fuel from tank  14  to deliver to the engine, excess fuel from the engine fuel supply is returned to tank  12  and pump  38  transfers fuel from tank  12  to maintain an appropriate level of fuel within tank  14 ), it is preferable that the two pumps be supplied with power through a common switched power source. Such a power source might be controlled by the electronic control unit (ECU) operating the timing and operation of vehicle  10 &#39;s engine. It is common for the ECU to supply power to a fuel pump supplying fuel to an engine when an ignition switch of the vehicle is turned on. For vehicle  10 , it would be preferable for the ECU to supply power to each of the pumps  22  and  38  when the ignition switch is turned on. Operation of the shut off valves  34  and  44  may cause pump  38  to stop operating while the ignition is on. However, this would be to address a temporary condition based on fuel level  46  within tank  14 . When the fuel level  46  is below eighty percent of capacity of tank  14 , pump  38  will operate to transfer fuel from tank  12  to tank  14  when the ignition is on. Pump  22  would continue to operate to provide fuel to fuel rails  52  as long as the ignition is on. Providing power to a single circuit or wiring harness powering both pumps is preferable and such a power circuit may be simpler to construct and maintain with the two pumps  22  and  38  preferably mounted within the same housing. 
   Mounting both pump  22  and pump  38  within transfer tank  14  requires that less hardware and electronics to be installed within tank  12  or attached to tank  12 . This arrangement permits easy replacement of tank  12  and utilization of standard or known LPG storage or fuel tanks as part of LPG fuel system  100 . This is advantageous as it permits interchange or use of LPG tanks between vehicle  10  and other LPG powered vehicles such as forklifts or other industrial vehicles. Many of these vehicles do not utilize a transfer tank but rather use the natural vapor pressure of LPG and a pressure regulator to provide gaseous LPG to a carburetor for combustion. Utilization of these existing tanks which may not include any fuel supply or transfer pumps  22  and  38  may reduce the cost of components required for conversion of a vehicle to operation with LPG. Known vehicles such as fork lifts and other industrial vehicles often replace an empty LPG tank with a new, fully charged tank, rather than filling the empty tank while the empty tank is mounted to the vehicle. The empty tank can then be sent to an LPG charging location and refilled with fuel while away from the vehicle. Fuel system  100  may be adapted to utilize similar removable, replaceable and/or rechargeable tanks. 
     FIG. 1  shows tanks  12  and  14  mounted in saddle positions on opposite sides of vehicle  10 . Alternatively, tanks  12  and  14  could be mounted adjacent one another on the same side of vehicle  10 , or in other locations on vehicle  10 . Tanks  12  and  14  are illustrated as generally similar in diameter and may also be generally the same overall length and volume. Alternatively, tank  12  could be a larger storage tank positioned as shown in  FIG. 1 , and tank  14  could be smaller in volume or differently shaped and positioned closer to fuel rails  52 . It is also anticipated that more than one storage tank  12  might be included in an LPG fuel system  100  so that one of the ranks  12  could be removed and replaced without halting supply of fuel to fuel rails  52  and fuel injectors  54 . 
   As shown in  FIG. 2 , the addition of a transfer tank  14  with LPG storage tank  12  for supplying LPG fuel to an engine permits storage tank  12  to only include an inlet opening  16  and an outlet opening  18 . LPG tanks are typically limited in liquid capacity to no more than eighty percent of total volume, so that fluid and gas within the tank have sufficient room to expand and contract due to differences in atmospheric temperature and pressure. A shutoff valve  20  is included adjacent inlet opening  16  of tank  12  and operates to shutoff entry of additional LPG into tank  12  once eighty percent fluid capacity of tank  12  has been reached. 
   The embodiments of the inventions disclosed herein have been discussed for the purpose of familiarizing the reader with novel aspects of the present invention. Although preferred embodiments have been shown and described, many changes, modifications, and substitutions may be made by one having skill in the art without unnecessarily departing from the spirit and scope of the present invention. Having described preferred aspects and embodiments of the present invention, modifications and equivalents of the disclosed concepts may readily occur to one skilled in the art. However, it is intended that such modifications and equivalents be included within the scope of the claims which are appended hereto.