Fuel delivery system with pressure-controlled electric pump
The present invention is directed to electric pumps fuel delivery systems for gasoline engine and like applications, and more particularly to control of fuel line pressure at the pump output. 
     It is an object of the present invention to provide pressure control for the electric pump in a fuel delivery system which reduces energy consumption and increases pump life, which reduces pump noise, and which maintains constant pressure in the fuel delivery line to the engine. 
     A more specific object of the present invention is to provide a fuel delivery system of the described character which finds particular utility in electronic fuel injection systems and which reduces the quantity of heated fuel recirculated in such systems to the fuel tank. 
    
    
     The invention, together with additional objects, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which: 
     FIG. 1 is a schematic diagram of a fuel delivery system in accordance with one presently preferred embodiment of the invention; 
     FIG. 2 is a fragmentary schematic diagram of a modification to the fuel delivery system of FIG. 1; and 
     FIG. 3 is a longitudinal section of a fuel pump embodying pressure control in accordance with a third embodiment of the invention. 
    
    
     FIG. 1 illustrates a fuel delivery system 10 in accordance with a first embodiment of the invention as comprising a fuel pump 14 having an input coupled to a fuel supply at the gasoline tank 12 and an output for delivering fuel to an engine (not shown). An electric motor 16 is mechanically coupled to pump 14 and electrically connected to a source of power for driving pump 14. Most preferably, pump 14 and motor 16 are provided in a unitary assembly 18 such as those disclosed in applicant&#39;s U.S. Pat. Nos. 4,352,641, 4,500,270 and 4,596,519, all of which are assigned to the assignee hereof. A fuel pressure regulator 20 in the form of a pressure-sensitive electrical switch is coupled to the output of pump 14 and electrically connected to the inputs of motor 16 for selectively connecting and disconnecting motor 16 to battery 23 as a function of pump output pressure. More specifically, switch 20 includes a flat base 22 having a peripheral upstanding lip 24 which cooperates with base 22 to form a central depression or pocket 26. An inlet passage 28 extends form pocket 26 through base 22 for connection to pump 14, and an outlet passage 30 spaced from inlet passage 28 connects pocket 26 to the vehicle engine (not shown). A generally cup-shaped cap 32 has a peripheral depending lip 34 opposed to base lip 24 and cooperating therewith to capture therebetween the periphery 36 of a flexible diaphragm 38. Cap 32 extends upwardly from diaphragm 38 to form a second hollow chamber 40 separated by diaphragm 38 from the chamber formed between diaphragm 38 and base pocket 26. 
     A coil spring 42 is captured between a flanged keeper 48 and a cup 44 carried by the generally flat central portion 46 of diaphragm 38. An adjustment screw 50 is threadably received in cap 32 and engages a central depression 52 in keeper 48 for selectively adjusting the force exerted by spring 42 against central portion 46 of diaphragm 38. Cap 32 includes an aperture 54 for venting chamber 40 to atmosphere. An electrode 56 includes a cylindrical shank or stem 58 extending through an insulating sleeve 60 in base 22 coaxially with spring 42 and screw 50, and a head 62 carried by and spaced from a boss 64 on base 22 by the flange 66 on insulating sleeve 60. Electrode head 62 has a convex surface opposed to the flat central portion 46 of diaphragm 38. A PNP transistor 70 has a base connected to the shank 58 of electrode 56, and has primary current-conducting emitter and collector electrodes connected to dc supply 23 and motor 16. Base 22 and cap 32 form a housing 72 and are preferably constructed of electrically conductive material along with diaphragm 38 for connection to electrical ground through the vehicle frame. 
     In operation, diaphragm 38, which forms a first electrical contact of switch 20, is normally urged by spring 42 against head 62 of electrode 60 so as to connect the base of transistor 70 to electrical ground, and thereby feed electrical power from battery 23 to motor 16. When fuel pressure from the output of pump against the surface area of diaphragm 38 within the fuel chamber formed by pocket 26 is sufficient to overcome the force of spring 42, electrical contact between diaphragm 38 and electrode 56 is interrupted, transistor 70 is turned off, and power is removed from motor 16. Current to motor 16 is thus pulse-width modulated as a function of reference spring pressure exerted by spring 42 and engine fuel demand, as compared with the output supplied by pump 14. 
     FIG. 2 illustrates a modified embodiment 80 of pressure switch 20 (FIG. 1) in which components identical to those hereinabove described in connection with FIG. 1 are indicated by correspondingly identical reference numerals, and elements which are different from those illustrated in FIG. 1 but perform an analogous function are indicated by correspondingly identical reference numerals followed by the suffix &#34;a&#34;. In switch 80 of FIG. 2, the movable pressure-responsive contact comprises a hollow cup-shaped piston 82 having a convex head 84 axially opposed to and aligned with the convex head 62 of electrode 56, and a cylindrical skirt 86 axially slidable within a cylindrical chamber 40a in cap 32a. Cap 32a includes a passage 54a for venting chamber 40a to atmosphere, and a screw 50a is received in cap 32a for adjusting the pressure exerted by the coil spring 42a against the inside surface of piston head 84. Thus, in the embodiment of FIG. 2, fuel pressure against piston head 84 and spring 42a within the lower chamber formed by base pocket 26 urges piston 82 out of contact with electrode 56 so as to remove power from pump motor 16 (FIG. 1). Electrical contact with piston 82 is obtained through cap 72a, screw 50a and spring 42a. It will be noted in FIG. 2 that spring 42a is captured by a nub 51 on screw 50a. 
     FIG. 3 illustrates an embodiment of the invention wherein pressure switch 90 is built into the unitary housing 18 of pump 14 and motor 16. Pump 14 and motor 16 are similar to those illustrated in above-noted U.S. Pat. No. 4,352,641, to which reference may be made for details of construction. In general, motor 16 includes a permanent magnet stator 100 which surrounds a rotor 102 having windings connected to a commutator plate 104. Armature 102 is carried by a shaft 106 for rotation within housing 18, and is coupled to a vane system 108 for pumping fuel from the inlet 110 to a pressure chamber 112 which surrounds armature 102, and thence to a pump outlet (not shown) formed in the housing base 114. Spaced passages 116, 118 parallel to the axis of rotation of armature 102 and shaft 106 respectively slidably receive brushes 120, 122 for applying power to commutator 104. A first electrical terminal 124 is received in base 114 to close passage 116, and is electrically connected to brush 120 by the conductor 126. A spring 128 urges brush 120 against commutator 104. A second terminal 130 is received in base 114 and has an internal chamber 132 which slidably receives a piston 134. Piston 134 has a head 136 which is internally urged by a coil spring 138 against brush 122. Spring 138 and piston 134 thus urge brush 122 against commutator 104. An electrical conductor 140 extends from terminal 130 to piston head 136. A passage 142 in terminal 130 vents chamber 132 to atmosphere. Terminals 124, 130 are connected across a source of dc power, such as battery 23. 
     In operation, fuel pressure within output chamber 112 operates through passage 118 against piston 134 and urges piston 134 out of electrical contact with brush 122 when fuel pressure exceeds the force exerted on piston 136 by spring 138. Thus, operation of the embodiment of FIG. 3 is similar to that of the embodiment of FIG. 2, except that pressure switch 90 is in the direct current path between power source 23 and motor 16, rather than in the current control path as in the embodiments of FIGS. 1 and 2. Thus, the embodiments of FIGS. 1 and 2 possess an advantage over that of FIG. 3 in that the former conduct less electrical current through the switch contacts, and thus are less susceptible to pitting at the contacts and arcing at the motor brush.