Abstract:
Fuel line arrangement for a liquefied petroleum gas fuel injection system, and method. A fuel supply line provides flow between a fuel tank and a plurality of fuel injectors, and a fuel return line returns a portion of the supply fuel to the tank. The supply line is positioned within the return line so that return fuel substantially surrounds the supply line. Liquefied petroleum gas is vaporized within the return line under certain conditions, thereby cooling supply fuel. A novel Y-connector and bushing are also disclosed.

Description:
INCORPORATION BY REFERENCE 
     Applicant&#39;s U.S. Pat. Nos. 5,291,869; 5,325,838; and 5,423,303 are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to liquefied petroleum gas fuel injection systems and more particularly to fuel line arrangements and cooling methods for such systems. 
     BACKGROUND OF THE INVENTION 
     Liquefied petroleum gas (“LPG”) fuel supply systems are known, for example as shown in applicant&#39;s U.S. Pat. Nos. 5,291,869; 5,325,838; and 5,423,303. Such systems typically include a number of specialized fuel injectors which receive fuel from a high pressure tank. A fuel rail connected in line with a series of injectors is often employed to deliver fuel to the injectors. In many systems, uninjected fuel is returned to the fuel tank. This is generally done to keep the supply fuel as cool as possible, particularly where it is intended to inject LPG in liquid rather than gaseous form. 
     In LPG systems where uninjected fuel is returned to the fuel tank, separate supply and return fuel lines are employed in the art. More than one supply line and more than one return line are also often employed, with a separate supply and return line for each bank of fuel injectors. 
     There are many problems associated with having multiple supply and return lines in LPG systems. One is that the fuel in the supply line is exposed to heat from the engine and other sources, which causes undesirable vaporization. Another problem is that all of the lines must be very strong, typically having large wall thickness and requiring reinforcement, in order to withstand the very high pressures (sometimes over 300 psi) that can occur in LPG systems. Other problems involve safety and environmental concerns. Due to the large number of hose connections and the large amount of exposed fuel line, the possibility of fuel leaks is substantially increased. 
     What has been needed is a fuel line arrangement for LPG systems, and a method, that avoid these problems. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a method of cooling supply fuel in an LPG system, and a fuel line arrangement for an LPG system, are provided. 
     In the method of the present invention, an LPG system having a plurality of fuel injectors, a fuel supply and a fuel return line, and a fuel tank, is provided. The supply and return lines are communicated with the tank, and the supply line is communicated with each of the fuel injectors. The supply line is positioned within the return line so that return fuel substantially surrounds the supply line. Under certain conditions, return fuel in the fuel return line is vaporized, thereby cooling supply fuel in the supply line. 
     In the apparatus, a fuel line arrangement for an LPG system includes a fuel supply line for connection between the fuel tank and a plurality of fuel injectors and a fuel return line for connection to the tank and for returning a portion of the supply fuel from the supply line to the tank. The supply line is positioned within the return line so that the return fuel substantially surrounds the supply line. A mechanism is provided for vaporizing LPG returning to the tank through the return line, thereby cooling supply fuel. 
     These and other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto. However, for a better understanding of the invention and its advantages, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter in which there is illustrated and described a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a schematic diagram of a system according to the present invention; 
     FIG. 2 is a cross-sectional view of a fuel line arrangement and a connection according to the present invention; 
     FIG. 3 is a cross-sectional view of a Y-connector according to the present invention; and 
     FIGS. 4A and 4B are plan and cross-sectional views, respectively, of a bushing according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, wherein like numerals designate like parts throughout the figures, a fuel supply system  10  for providing LPG to an internal combustion engine  12  is shown. 
     System  10  includes two fuel rails  14  which deliver fuel to a plurality of fuel injectors  16 . Although fuel rails are shown in the preferred embodiment, they are not necessary within the principles of the invention; for example, separate supply lines branching from a main supply line could deliver fuel to each injector in parallel. Return fuel also need not come from each of the fuel injectors as is the case in the applicant&#39;s patented system incorporated above by reference. 
     Supply fuel from tank  18  is delivered to injectors  16  via primary  20  and secondary  22  supply lines, and return fuel is delivered back to tank  18  via secondary  27  and primary  25  return lines. A Y-connector  40 , further discussed below, splits the primary lines  20 ,  25  into secondary lines  22 ,  27 . 
     The preferred fuel line arrangement is shown in FIGS. 2 and 3. Primary supply line  20  is positioned completely within primary return line  25 , as is secondary supply line  22  with respect to secondary return line  27 . Supply lines  20 ,  22  are not restrained axially within return lines  25 ,  27 , but rather are only restrained by the inner walls of return lines  25 ,  27  along the length of the lines, thereby creating a generally concentric arrangement. The annular flow area of return lines  25 ,  27  is preferably about two or more times the annular flow area of the respective supply lines  20 ,  22  along the entire length of lines, including within fittings and connectors. Lines  20 ,  22 ,  25 ,  27  are made of nylon, but a high heat transfer metal such as aluminum may be preferable. Wall thicknesses are 0.025 and 0.035 inches for primary  20  and secondary  22  supply lines respectively, and 0.180 and 0.210 inches for primary  25  and secondary  27  return lines respectively. These relatively thin wall thicknesses for supply lines is sufficient because the pressure differential across the wall is only on the order of 30-70 psi as compared to the over 300 psi differential that would occur if supply lines were not contained within return lines. Arrangements other than the concentric fuel line arrangement shown and described herein could be employed within the principles of the invention, where the supply line is positioned within the return line so that return fuel substantially surrounds the supply line. 
     The concentric fuel line arrangement can be surrounded with an appropriate insulator in high heat areas such as the engine, transmission and exhaust, in order to minimize heat absorption. The preferred insulation is closed-cell foam rubber ¼ to ¾ inch thick. 
     The return fuel surrounding supply lines  20 ,  22  vaporizes or evaporates through thermodynamic phase change processes that are fully described in the applicant&#39;s patents incorporated by reference. As the temperature of return fuel increases, or its pressure decreases, the LPG tends to vaporize from a liquid to a gaseous state. This phase change extracts heat from supply fuel through the walls of supply line hoses  20 ,  22 . Supply fuel is consequently cooled, thereby helping to maintain it in a liquid state prior to injection into the engine. 
     FIGS. 2 and 3 show the fuel line connections. Return hoses  25 ,  27  are connected to steel return fittings  26 ,  28  with steel collar  29 , as shown in FIG.  3 . 
     Return fittings  26 ,  28  are held in place by locking clips  31  bracing against retaining flanges  30 , and can be further held in place by a device that resists rotation. O-rings  32  seal against the outer surface of return fittings  26 ,  28 , and are held in place by pressed in sleeves  33 . Supply hoses  20 ,  22  extend through bushings  50  and are sealed by O-rings  54 . In the Y-connector shown in FIG. 3, the surrounding structure cast into the part holds the various components described above in place; end caps  49  additionally retain locking clips  31 . In the fuel rail connection shown in FIG. 2, an aluminum fitting  35 , connected to fuel rail  14  by threads  36 , provides the structure which primarily holds in place the various components. Supply hose adapter  38 , a plastic part press fit into fuel rail supply channel  60 , also surrounds annular body  53  of bushing  50  and O-ring  54 . Fitting  35  is sealed to fuel rail  14  via O-rings  37 . The tank connection is the same as the primary Y connection. Any other necessary connections can be the same or similar to those shown in FIGS. 2 and 3. 
     A novel aspect of the concentric fuel line connection is bushing  50 . Bushing  50 , best shown in FIGS. 4A and B, has circumferentially spaced fingers that serve two important functions. First, when supply lines  20 ,  22  are being inserted, ramped surfaces  51  guide the hose into annular body  53  to assure proper alignment and sealing. Second, the space between fingers  52  serves as a flow path for return fuel: in the Y-connector shown in FIG. 3, they permit flow between return lines  27 ,  28  and connecting return passages  46 ; and in the fuel rail connection shown in FIG. 2, they permit flow between fuel rail return channel  61  and secondary return line  27 . Bushing  50  is made of a plastic compatible with LPB, such as nylon or acetal. 
     Another novel aspect of the present invention is Y-connector  40 , which splits primary fuel lines  20 ,  25  into two secondary lines  22 ,  27 . Primary supply hose  20  communicates with secondary supply hoses  22  via supply passage  42  and two secondary supply passages  43 . Secondary return lines  27  communicate with primary return line  25  via connecting return passages  46 ; cross-connecting passage  47  also facilitates flow between connecting return passages  46 . Y-connector is cast preferably from aluminum, but could also be cast from other metals such as brass. Internal webs (not shown) in connecting return  46  passages support internal Y  48 . A connector such as  40  could be used in places other than at the fuel rails, wherever it is desirable to split a concentric fuel line arrangement into two or more concentric lines, as for example into separate lines for individual tanks or fuel injectors. 
     It should be understood that the present invention is not limited to the preferred embodiment discussed above, which is illustrative only. Changes may be made in detail, especially in matters of shape, size, arrangement of parts, and material components within the principles of the invention, to the full extent indicated by the broad general meanings of the terms in which the appended claims are expressed.