FUEL DELIVERY SYSTEM

Abstract: A fuel delivery system having a fuel reservoir (64) connected to a suction side (60) of a pump (10), a fuel delivery line (66) connected to an output side (62) of the pump, a number of fuel injectors (70) connected to the delivery line, and a return line (72) from the injectors to the suction side (60) of the pump. The pump has a housing (12), a pumping chamber (14) within the housing, a driver rotor (16) and a driven rotor (18) within the pumping chamber, and an input shaft (20) to the housing. The input shaft is arranged such that rotation of the input shaft effects rotation of the driver rotor (16). The driver rotor (16) is caused to rotate by the input shaft (20) via a magnetic coupling (24). The magnetic coupling is arranged to slip when a predetermined value of torque is applied across the coupling such that a maximum pressure value of about 12 bar is attained at the output side of the pump.

Description: TITLE: Fuel Delivery System TECHNICAL FIELD: The present invention relates to a fuel delivery system according to the preamble of claim 1. BACKGROUND OF THE INVENTION: In the fuel delivery system of a commercial vehicle it is known to use a rotary displacement pump driven by the transmission of the vehicle to increase the fuel pressure in the system to a level suitable for injection of the fuel into the vehicle engine. The pump has to be capable of delivering fuel at a sufficient pressure substantially immediately upon starting the engine. This implies that at high engine speeds the pressure in the fuel delivery system is greater than actually required and, as a result, a pressure relief valve is required downstream of the pump to relieve the excess pressure. Should the pressure relief valve jamb in a partially or fully closed position, there is a risk that the pressure in the fuel delivery system becomes dangerously high, possibly resulting in rupture of a seal or fuel line. A conventional rotary displacement pump comprises a housing, a pumping chamber within the housing, a driver rotor and a driven rotor within the pumping chamber, and an input shaft to the housing. The input shaft is connected to the driver rotor to thereby effect rotation of said driver rotor. To prevent leakage of the pumped liquid from the pumping chamber, it is necessary that adequate sealing means be provided between the housing and the input shaft. Due to the rotation of the input shaft, a dynamic seal must be employed. In the fuel delivery system described above, failure of the sealing means not only implies that fuel leaks out of the system, but also that the leaking fuel may migrate into the transmission and mix with the lubricant therein. A fuel pump is disclosed in U.S. Patent No. 2 779 513 which is driven by a power source via a magnetic coupling. A permanent impervious closure seals the pump from the power source, thereby reducing the risk of leakage. A spring pressed relief valve is provided downstream of the pump so that the output of the pump which is in excess of the fuel consumed by the device, such as an internal combustion engine, to be supplied thereby is permitted to escape back into the fuel tank. SUMMARY OF THE INVENTION: It is an object of the present invention to provide a fuel delivery system suitable for use in a vehicle, which system is more energy-efficient than conventional systems and at the same time is less reliant on the necessity of a functioning pressure relief valve. This object is achieved in accordance with the present invention by a fuel delivery system comprising a fuel reservoir connected to a suction side of a pump, a fuel delivery line connected to an output side of the pump, a number of fuel injectors connected to the delivery line, and a return line from the injectors to the suction side of the pump. The pump comprises a housing, a pumping chamber within the housing, a driver rotor and a driven rotor within the pumping chamber, and an input shaft to the housing, the input shaft being arranged such that rotation of said input shaft effects rotation of the driver rotor. The driver rotor is caused to rotate by the input shaft via a magnetic coupling. The magnetic coupling is arranged to slip when a predetermined value of torque is applied across the coupling such that a maximum pressure value of about 12 bar is attained at the output side of said pump. Since the magnetic coupling is only capable of transmitting a predetermined value of torque, the pressure downstream of the pump cannot exceed a predetermined value, irrespective of the rotational speed and/or torque of the input shaft. In a preferred embodiment of the invention, the system further comprises a pressure relief valve in the fuel delivery line, the pressure relief valve being arranged to reduce the pressure in the fuel delivery line to about 6 bar. Further preferred embodiments of the invention are detailed in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS: The invention will be described in greater detail in the following by way of example only and with reference to embodiments shown in the attached drawings, in which: Fig. 1 is a schematic cross-sectional view through an embodiment of a rotary displacement pump for use in the fuel delivery system according to the present invention; Fig. 2 is a schematic perspective view of a magnetic coupling used in the pump of Fig. 1, and Fig. 3 is a schematic representation of a fuel delivery system according to the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS: In the drawings, reference numeral 10 generally denotes a rotary displacement pump for use in a fuel delivery system according to the present invention. The pump comprises a housing 12 within which a pumping chamber 14 is arranged. In a conventional manner, the pumping chamber accommodates a driver rotor 16 and a driven rotor 18. In the shown embodiment, the driver rotor and the driven rotor are gear wheels, though it is to be understood that any intermeshing rotary displacement means may be employed. The pump 10 further comprises an input shaft 20 to effect rotation of the driver rotor 16. The input shaft 20 may be driven by a gear wheel 22, pulley or any other suitable means. The driver rotor 16 is caused to rotate by the input shaft 20 via a magnetic coupling, generally denoted by reference numeral 24. In accordance with the present invention, and as will be explained in greater detail below, the magnetic coupling is arranged such that when a predetermined value of torque is applied across the coupling, the coupling slips to thereby restrict the amount of torque transmission through the coupling. As is most clearly seen from Fig. 2, the magnetic coupling 24 comprises a first magnet holder assembly 26 attached to the input shaft 20, for example by a press fit, and a second magnet holder assembly 28 attached to a carrier shaft 30 carrying the driver rotor 16 (not shown in Fig. 2). Each magnet holder assembly comprises an annular magnet holder 32 made from a non-magnetic material, preferably aluminium. Each holder 32 has a peripheral wall 34. an inner wall 36 and a number of dividing walls 38. The dividing walls 38 extend radially from the inner wall 36 to the outer wall 34 to define a number of compartments 40. Each compartment is adapted to house a pair of magnets 42. In the illustrated embodiment, each holder has four dividing walls 38 to thereby form four compartments 40. It is to be understood, however, that the invention can be realized using holders having any number of a plurality of compartments. Each magnet holder assembly 26,28 further comprises a backing plate 44 of magnetic material such as steel to which each pair of magnets 42 is adhered. The first and second magnet holder assemblies 26,28 are advantageously separated by a separation wall 46 which occupies a gap 48 between the magnet holder assemblies. The separation wall is made from a non-magnetic material and hermetically separates the first magnet holder assembly 26 from said second magnet holder assembly 28, thereby acting as a stationary seal to prevent leakage of liquid from the pumping chamber 14 out of the housing past the input shaft 20. In the shown embodiment, the separation wall 46 is provided with an axially extending flange 50 which partially encloses the second magnet holder assembly 28. The separation wall and flange may be made from non-magnetic steel and are arranged to be a press fit in the housing 12. The amount of torque which can be transmitted through the magnetic coupling 24 depends i.a. on the size of the gap 48 between the first and second magnet holder assemblies. When the coupling is not rotating, the size of the gap 48 is determined by the thickness of the separation wall 46 as well as the axial extension of the input shaft 20 beyond the end face of the magnets of the first magnet holder assembly 26 and the axial extension of the carrier shaft 30 beyond the end face of the magnets of the second magnet holder assembly 28. Due to the magnetic attraction between the first and second magnet holder assemblies, the first ends 21,29 of the input shaft 20 and the carrier shaft 30 respectively will contact the separation wall 46. Since the separation wall is stationary, it is advantageous if the ends 21,29 of the input shaft and carrier shaft are rounded to thereby reduce friction during rotation of the coupling. As a result of their magnetic attraction, the first and second magnet holder assemblies 26,28 are inevitably drawn towards each other. Thus, the input shaft 20 and the carrier shaft 30 may be arranged to be axially displaceable relative each other, thereby avoiding the need for close tolerances. Accordingly, and as is schematically represented in Fig. 1, a first end stop 52 is located adjacent a second end 53 of the input shaft 20 remote from the separation wall 46 and a second end stop 54 is located adjacent a second end 55 of the carrier shaft 30 remote from the separation wall 46. The end walls are positioned such that when the first ends 21,29 of the shafts 20,30 contact the separation wall, there is free play between the end stops 52, 54 and the second ends 53,55 of the shafts. Again, for reasons of friction, it is advantageous if the second ends 53,55 of the shafts 20,30 are rounded. The rotary displacement pump 10 operates in the following manner. When the pump is stationary, attraction between the magnets of the first and second magnet holder assemblies 26,28 ensures that the first end 21 of the input shaft 20 and the first end 29 of the carrier shaft 30 contact the separation wall 46. As torque is applied to the gear wheel 22, the input shaft 20 and hence the first magnet holder assembly 26 are caused to rotate. The magnetic field between the first and second magnet holder assemblies causes the second magnet holder assembly 28 and hence the carrier shaft 30 to rotate. As a result, the driver rotor 16 is rotated and drives the driven rotor 18 to thereby pump liquid through the pumping chamber 14. When the torque across the coupling 24 reaches a certain value, the brake torque on the carrier shaft as a result of the pumping action of the driver and driven rotors becomes greater than the magnetic field strength between the first and second magnet holder assemblies. Thus, the second magnet holder assembly 28 starts to lag behind the first magnet holder assembly 26. When a certain angular amount of lag has been achieved, the actual amount being dependent on the geometry of the magnet holders 32, the magnets of the respective magnet holder assemblies begin to repel each other, thereby causing the input shaft 20 and the carrier shaft 30 to move away from each other. The extent to which the shafts may be parted depends on the location of the end stops 52 and 54. Thus, the gap 48 between the first and second magnet holder assemblies increases and the amount of torque which the coupling is capable of transmitting will be limited by the magnetic field strength attained at such separation. In this manner, it is ensured that the pumping pressure in the pumping chamber 14 never exceeds a desired level. The above-described pump is eminently suitable for use as a fuel pump in a vehicle fuel delivery system. Such a system is schematically illustrated in Fig. 3. In the drawing, the pump is denoted by reference numeral 10. The pump has a suction side 60 and an output side 62. The suction side 60 of the pump is connected to a fuel reservoir 64 and a fuel delivery line 66 is connected to the output side 62 of the pump. A fuel filter 68 is connected into the delivery line 66. Downstream of the fuel filter 68, a number of fuel injectors 70 are provided with fuel via the delivery line. In order to ensure that the fuel delivered to the injectors 70 has a substantially uniform temperature, the pump 10 is arranged to pump a greater quantity of fuel along the delivery line 66 than is required by the injectors. The surplus of fuel is returned to the suction side 60 of the pump via a return line 72. In accordance with the present invention, the magnetic coupling 24 of the pump 10 is arranged to slip when a predetermined value of torque is applied across the coupling such that a maximum pressure value of about 12 bar, preferably about 9 bar, is attained at the output side 62 of the pump. When a magnetic coupling slips, the torque transmission temporarily drops significantly. If the fuel delivery system of the present invention were to employ a pump having a magnetic coupling which restricted the output pressure of the pump to only a value which corresponds to the operating pressure of the fuel injectors, there is a risk that the pressure would temporarily drop below this value when the coupling begins to slip. This could lead to temporary interruption of the fuel delivery. Thus, to avoid this problem, and in a preferred embodiment of the invention, the fuel delivery system further comprises a pressure relief valve 73 in the fuel delivery line 66 upstream of the fuel filter 68. The pressure relief valve is arranged to reduce the pressure in the fuel delivery line to about 6 bar, i.e. the normal operating pressure for the fuel injectors. In a typical installation, the pump 10 can be arranged to pump between 2 and 8 litres/minute (1/min) of fuel at a maximum pressure of about 9 bar at the output side of the pump. As a result of the actions of the pressure relief valve 76, a pressure of about 6 bar is present in the fuel delivery line 66 downstream of the valve. Depending on the load on the engine, between about 0.5 and 1.5 1/min of fuel is injected into the engine via the injectors 70. This implies that between about 1.5 and 7.5 1/min of fuel is returned to the pump. An amount of fuel corresponding to that which has been injected into the engine is drawn from the reservoir by the pump. A one-way valve 74 between the reservoir 64 and the pump ensures that fuel in the return line 72 does not drain into the reservoir. Since the magnetic coupling in the pump 10 can be adapted to ensure that a maximum pressure of no more than 12 bar, preferably no more than 9 bar, is generated in the delivery line 66, even if the pressure relief valve were to jamb, the pressure in the delivery line will never become so high that a risk of rupture of a component of the line arises. This further implies that less power is needed to drive the pump than with conventional pumps which rely on a functioning pressure relief valve to restrict the maximum pressure in the fuel delivery system. It is to be understood that the invention is not restricted to the embodiments described above and shown in the drawings, but may be varied within the scope of the appended claims. Thus, although the pump in the system according to the present invention has been illustrated as having axially separated magnet holder assemblies, it is to be understood that a pump having radially separated magnet holder assemblies may also be employed.

Claims: CLAIMS 1. A fuel delivery system comprising: a fuel reservoir (64) connected to a suction side (60) of a pump (10); a fuel delivery line (66) connected to an output side (62) of said pump; a number of fuel injectors (70) connected to said delivery line, and a return line (72) from said number of injectors to said suction side (60) of said pump, said pump comprising: a housing (12), a pumping chamber (14) within said housing, a driver rotor (16) and a driven rotor (18) within said pumping chamber, and an input shaft (20) to said housing, said input shaft being arranged such that rotation of said input shaft effects rotation of said driver rotor (16), said driver rotor (16) being caused to rotate by said input shaft (20) via a magnetic coupling (24), characterized in that said magnetic coupling is arranged to slip when a predetermined value of torque is applied across the coupling such that a maximum pressure value of about 12 bar is attained at said output side (62) of said pump. 2. The fuel delivery system as claimed in claim 1, characterized in that said magnetic coupling is arranged to slip such that a maximum pressure of about 9 bar is attained at said output side (62) of said pump. 3. The fuel delivery system as claimed in claim 1 or claim 2, characterized in that said system further comprises a pressure relief valve in said fuel delivery line, said pressure relief valve being arranged to reduce the pressure in said fuel delivery line to about 6 bar. 4. The fuel delivery system as claimed in claim 3, characterized in that a fuel filter (68) is provided in said delivery line downstream of said pressure relief valve. 5. The fuel delivery system as claimed in any one of the preceding claims, characterized in that the magnetic coupling (24) of said pump comprises a first magnet holder assembly (26) attached to said input shaft (20) and a second magnet holder assembly (28) attached to a carrier shaft (30) carrying said driver rotor (16), each said magnet holder assembly (26,28) comprising an annular magnet holder (32), preferably of aluminium, having a peripheral wall (34), an inner wall (36) and at least three dividing walls (38) extending radially from said inner wall to said outer wall to define a number of compartments (40), each compartment being adapted to house a pair of magnets (42). 6.The fuel delivery system as claimed in claim 1, characterized in that each said magnet holder assembly (26,28) further comprises a backing plate (44) of magnetic material to which each said pair of magnets (42) is adhered.

Inventors: HAAKANSSON NILS-OLOF, LINDBLOM JAN, HAAKANSSON, NILS-OLOF, LINDBLOM, JAN
Applicants: HAAKANSSON NILS OLOF, LINDBLOM JAN, VOLVO LASTVAGNAR AB, HAAKANSSON, NILS-OLOF, LINDBLOM, JAN
Application year: 1999
Main classification: F02M59
IPC codes: F02M37, F04C15