Fuel delivery system with recirculation cooler

This invention relates generally to a fuel delivery system and more particularly to a returnless fuel delivery system.

Electric motor fuel pumps have been used to deliver fuel to engines in a wide range of applications. In some systems, the armature of the electric motor and stator are disposed downstream of a fuel pumping assembly. Fuel is drawn into the pumping assembly and discharged therefrom under pressure into a fuel pump housing such that the fuel flow through the housing is in contact with the electric motor to cool it. In some high heat applications or conditions, this fuel flow through the pump is insufficient to cool the fuel pump. Some prior marine engine fuel systems have tried to supplement the cooling of the pump by installing the pump in a fuel reservoir and then cooling the reservoir with a water jacket through which cool water is circulated.

This fuel reservoir and water jacket system is inadequate in many applications to sufficiently cool the pump. For example, with a speed controlled. fuel pump, such as when a pulse width modulated drive is used to control the operation of the pump and hence, the fuel flow rate delivered from the fuel pump. With such a pulse width modulated drive or other variably controlled fuel pump, at idle or low engine speeds there is a relatively low fuel flow rate through the pump which provides limited cooling of the pump. Excessive heating of the fuel pump can cause vapor formation in the liquid fuel, decreased efficiency of the pump and even failure of the pump in use. Further, the fuel may become heated in different applications causing excessive fuel vapor formation which can cause vapor lock. Accordingly, it is desirable to also cool the fuel in addition to the fuel pump to reduce vapor formation and the likelihood of vapor lock.

A fuel system has a fuel pump controlled and driven by a pulse width modulated drive to deliver fuel to the engine at a rate corresponding to the engine demand and a recirculation cooler or heat exchanger which receives a portion of fuel discharged from the fuel pump, cools that fuel, and then returns the cooled fuel to the inlet of the fuel pump to cool the pump as the cooled fuel flows through the pump. The recirculation cooler is preferably formed of a material of high thermal conductivity and has a coolant passage adjacent to a fuel passage to reduce the temperature of the fuel that flows through the recirculation cooler. Desirably, the cooler fuel provided by the recirculation cooler to the inlet of the fuel pump supplements the cooling of the fuel pump motor and reduces fuel vapor formation in the fuel. In one form, the recirculation cooler comprises a block having passages drilled, bored or otherwise formed therein to define the separate coolant passage and the fuel passage. In another form, the recirculation cooler has a generally cylindrical housing with a coiled tube received in the housing and defining the fuel passage with the coolant passage defined within the interior of the cylindrical housing. In either embodiment, heat from the fuel in the recirculation cooler is transferred to the recirculation cooler material and the cooling water to reduce the temperature of the fuel.

Objects, features and advantages of this invention include providing a recirculation cooler for engine fuel systems which supplements the cooling of the fuel pump, enables use of a pulse width modulated or otherwise variably controlled electric fuel pump, permits use of an electric motor fuel pump in high heat fuel system applications, reduces vapor formation in the liquid fuel, prevents vapor lock of the fuel pump, reduces the temperature of fuel discharged from the fuel pump, and is of relatively simple design, economical manufacture and assembly and in service has a long, useful life.

These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiments and best mode, appended claims and accompanying drawings in which:

FIG. 1 is a schematic view of a fuel system for a marine engine having a recirculation cooler embodying the present invention;

FIG. 2 is a perspective view of a recirculation cooler according to the present invention;

FIG. 3 is a cross-sectional view taken along line 3 — 3 of FIG. 2;

FIG. 4 is a perspective view of a modified recirculation cooler formed from two mated plates;

FIG. 5 is a top view of a bottom plate of the recirculation cooler of FIG. 4;

FIG. 6 is a cross sectional view of a recirculation cooler according to a second embodiment of the invention; and

FIG. 7 is a schematic view of a fuel system for a marine engine having a modified recirculation cooler.

Referring in more detail to the drawings, FIG. 1 illustrates a fuel system 10 for a marine internal combustion engine 12 with a low pressure pump 14 which draws fuel from a fuel tank 16 and delivers it to an inlet 18 of a high pressure fuel pump assembly 20 . The high pressure fuel pump 20 increases the pressure of fuel received therein and discharges fuel under pressure through an outlet 22 and fuel line 23 to a fuel rail 24 and associated fuel injectors 26 for delivery to the combustion chambers of the engine 12 . A recirculation cooler 28 connected across the high pressure fuel pump 20 receives a portion of the fuel discharged from the fuel pump outlet 22 during at least some fuel flow conditions. Fuel which flows through the recirculation cooler 28 is cooled and returned to the inlet 18 of the fuel pump 20 to reduce fuel vapor formation and to supplement the cooling of the fuel pump 20 .

As shown in FIG. 1, the fuel system 10 is a returnless or no-return type fuel system wherein fuel is delivered to the engine 12 at a rate generally equal to the fuel demand of the operating engine 12 . To accomplish this, the electric motor of the fuel pump 20 may be powered by a pulse width modulated drive 30 which varies the application of electrical power to the electric motor of the fuel pump 20 to vary the operating speed of the fuel pump and thus the flow rate of fuel discharged from the fuel pump 20 according to the fuel demand of the engine 12 . Desirably, the pulse width modulated drive 30 operates to maintain a constant pressure downstream of the fuel pump 20 over a wide range of fuel flow rates from the high pressure fuel pump 20 . Desirably, to provide fuel to the recirculaton cooler 28 and also to the engine 12 , the pulse width modulated drive 30 controls the fuel pump 20 to deliver fuel at a rate slightly greater than the fuel demand of the engine. The fuel in excess of the engine fuel demand may flow through the recirculation cooler without adversely affecting the performance of the operating engine 12 .

The fuel pump 20 may be of substantially any kind such as, but not limited to, a turbine or regenerative type fuel pump such as that disclosed in U.S. Pat. No. 5,257,916 or a gear rotor type fuel pump, such as that disclosed in U.S. Pat. No. 5,219,277 the disclosure of each of which is incorporated herein by reference in its entirety.

As shown in FIGS. 2 and 3, the recirculation cooler 28 is preferably fabricated by drilling various flow paths 39 in a block 40 to define in the block 40 a fuel passage 44 and a separate coolant passage 46 adjacent to the fuel passage 44 . One or more mounting lugs 48 extending from the block 40 have holes 50 through which screws may be received to connect the recirculation cooler 28 to an adjacent component of the fuel system or vehicle. Both the fuel passage 44 and the coolant passage 46 are preferably separately defined by a plurality of interconnected holes or flow paths 39 in the block 40 .

More specifically, as shown in FIG. 3, the fuel passage 44 begins at a fuel inlet 52 of the recirculation cooler 28 which is in communication with the outlet 22 of the fuel pump 20 through a conduit 53 (FIG. 1) and a first, U-shaped portion 54 of the fuel passage 44 . This first portion 54 of the fuel passage 44 in turn leads to an exterior conduit 56 which joins the first portion 54 with a second portion 58 . The second portion 58 in turn is connected to a third portion 60 of the fuel passage 44 through a second exterior conduit 62 . The third Z-shaped portion 60 of the fuel passage 44 leads to a fuel outlet 64 of the recirculation cooler 28 which is connected with the inlet 18 of the high pressure fuel pump 20 through a conduit 65 (FIG. 1 ).

The coolant passage 46 begins at a coolant inlet 66 of the recirculation cooler 28 which is in communication with a coolant source, such as water from a river, a lake, stream or other source of water when used with a marine engine, or an alternate coolant source such as a radiator for use with engines other than marine engines potentially including gases as well as liquids. A first Z-shaped portion 68 of the coolant passage 46 is connected to a second, generally U-shaped portion 70 of the coolant passage 46 by a third exterior conduit 72 . A branch 73 of the U-shaped portion 70 is preferably closed by a plug 79 . The second portion 70 of the coolant passage 46 is in turn connected to a third portion 74 through a fourth exterior conduit 76 . This third portion 74 of the coolant passage 46 leads to a coolant outlet 78 of the recirculation cooler 28 through which coolant is discharged from the recirculation cooler 28 . Various plugs 79 close off openings to the exterior of the housing.

Alternatively, the fuel passage 44 and coolant passage 46 may be defined completely within the block 39 without any external conduits. As another alternative, as shown in FIGS. 4 and 5, a recirculation cooler 28 ′ may have the fuel passage 44 and coolant passage 46 defined by grooves 80 formed in mating faces 82 , 84 of two flat plates 86 , 88 . The grooves 80 preferaby define similar fuel and coolant passages 44 , 46 as those described with reference to FIGS. 2 and 3 with the same reference numbers applied to corresponding portions of the passages. The plugs 79 are not be needed because openings to the exterior of the housing are not needed when the passages 44 , 46 are formed in the faces 82 , 84 of the plates 86 , 88 . Additionally, fluid fittings 89 such as that shown at the coolant inlet 66 may be provided at each opening to the exterior of the recirculation cooler 28 ′ to facilitate connecting the various conduits to the recirculation cooler 28 ′.

Thus, as shown, the fuel passage 44 and coolant passage 46 are completely separate from one another within the recirculation cooler 28 or 28 ′ and are relatively convoluted to provide an increase in their surface area adjacent to each other and within the recirculation cooler 28 , 28 ′. The recirculation cooler 28 , 28 ′ is preferably formed of a material having high thermal conductivity, such as copper, aluminum or stainless steel, to increase the heat transfer from the hot fuel to the material of the recirculation cooler 28 , 28 ′ and the coolant. Thus, the temperature of the fuel which enters the recirculation cooler 28 , 28 ′ is reduced before the fuel is routed back to the inlet 18 of the high pressure fuel pump 20 to provide cooler fuel to the inlet 18 of the fuel pump 20 and thereby cool the fuel pump and reduce or prevent fuel vapor formation.

A modified recirculation cooler 100 is shown in FIG. 6 . This modified recirculation cooler 100 has an outer generally cylindrical housing 102 in which is received a tubular coil 104 which communicates at one end with the outlet 22 of the fuel pump 20 and at its other end with the inlet 18 of the fuel pump to define a fuel passage 105 through the recirculation cooler 100 . A coolant passage 106 is defined between the outer housing 102 and tubular coil 104 . Coolant from a source enters the housing 102 through an inlet 108 and is discharged through an outlet 110 of the housing 102 . The coolant flows around the tubular coil 104 to cool the coil and fuel flowing through the tubular coil 104 . Thus, as with cooler 28 , the temperature of fuel which flows through the recirculation cooler 100 is reduced before being delivered to the fuel pump 20 to cool the fuel pump 20 in use and reduce or prevent fuel vapor formation.

In each embodiment of the recirculation cooler 28 , 28 ′, 100 , the fuel inlet of the recirculation cooler 28 , 28 ′, 100 is preferably directly connected to the fuel line 23 downstream of the fuel pump 20 with a restricted size orifice 111 in the conduit 53 or tubular coil 104 which limits or controls the flow rate of fuel which is bypassed from the fuel line 23 to the recirculation cooler 28 , 28 ′, 100 . Alternatively, as shown in FIG. 7, a demand fuel pressure regulator 120 may be connected between the recirculation cooler 28 , 28 ′ or 100 and the fuel pump 22 outlet to bypass fuel discharged from the fuel pump 20 in excess of the engine's fuel demand through the recirculation cooler 28 , 28 ′ or 100 . A suitable demand pressure regulator 120 is disclosed in U.S. Pat. No. 5,579,739, the disclosure of which is incorporated herein by reference in its entirety. A valve may also be disposed between the outlet 22 of the fuel pump 20 and the fuel inlet of the recirculation cooler 28 , 28 ′, 100 to prevent fuel from being bypassed through the recirculation cooler 28 , 28 ′, 100 during high fuel demand conditions of the engine 12 . During such high fuel demand conditions of the engine 12 , there is a high flow rate of fuel through the fuel pump 20 to cool the fuel pump 20 . Thus, the secondary fuel flow through the recirculation cooler 28 , 100 may not be needed to sufficiently cool the fuel pump 20 .

The recirculation cooler 28 , 28 ′, 100 supplements the cooling effect of the fuel flow through the fuel pump 20 and reduces or prevents fuel vapor formation. This is especially important in high heat applications as well as with a pulse width modulated or otherwise variably controlled fuel pump 20 at low engine speeds. At such low engine speed conditions, there is a relatively low fuel flow rate through the fuel pump 20 which is inadequate to sufficiently cool the fuel pump 20 and can cause the fuel to become heated increasing fuel vapor formation. Thus, the delivery of the cooler fuel from the recirculation cooler 28 , 28 ′, 100 to the high pressure fuel pump 20 at these low engine speeds or other high heat conditions, is essential to prevent overheating of the fuel pump 20 and to reduce fuel vapor formation.