US3212449A

US3212449A - Fuel injection system

Info

Publication number: US3212449A
Application number: US301740A
Authority: US
Inventors: John M Whalen; Jr Carl R Canfield
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1963-08-13
Filing date: 1963-08-13
Publication date: 1965-10-19
Anticipated expiration: 1982-10-19
Also published as: DE1284156B

Description

Oct. 19, 1965 J. M. WHALEN ETAL FUEL INJECTION SYSTEM 5 Sheets-Sheet 1 Filed Aug. 13, 1963 Oct. 19, 1965 WHAI-EN ETAL 3,212,449

FUEL INJECTION SYSTEM Filed Aug. 15, 1963 3 Sheets-Sheet 2 Oct. 19, 1965 J. M. WHALEN ETAL 3,212,449

FUEL INJECTION SYSTEM 3 Sheets-Sheet 3 Filed Aug. 13, 1965 I raven 2 57's:

and (hr! B. Cargz'eZd, J71 @"JM @JM g United States Patent 3,212,449 FUEL INJECTION SYSTEM John M. Whalen, Zion, and Carl R. Canfield, Jr., Decatur,

Ill., assignors to Borg-Warner Corporation, a corporation of Illinois Filed Aug. 13, 1963, Ser. No. 301,740 Claims. (Cl. 103203) This invention relates to a fuel injection system for use with internal combustion engines and more particularly to a primary supply pump and the manner in which it is connected into the fuel injection system.

One of the primary problems with fuel handling systems is vapor lock. In conventionally carbureted cars this creates problems of varying magnitude ranging from light surging to heavy surging to a complete stall of the engine. The magnitude of the problem also varies depending upon the conditions under which the car is operated, namely, hot and cold temperatures, variations in altitude and the type of fuel used. With respect to the latter, for example, there is considerable difference in the use of hot or cold fuel. By way of explanation, hot fuel is basically a cold weather fuel. It vaporizes more easily than a cold fuel. It contains more of the lighter ends of the hydrocarbons and thus, vaporizes at a lower temperature. Hot fuel vaporizes more easily at cold temperatures than cold fuel and, consequently, is used to get better starting. Conversely, cold fuel is ordinarily used in the summertime or at higher temperatures, and it is more stable at those temperatures.

In a number of fuel handling systems when vapor lock occurs the only way it can be cured is to bleed the fuel lines 'or cut off the engine and let it stand to cool off. Sometimes a cold ice pack is put on a fuel pump to condense the vapor in the fuel pump so that pumping of fuel can once again begin.

In addition to the major problem of vapor lock our fuel injection system also must be able to meet the following requirements:

(1) A minimum pressure must be maintained in the system for the required fuel flow;

(2) The capacity of the supply pump must be adequate to supply fuel at a certain minimum predetermined pressure (for example 30 psi.) even under extremely cold conditions on the order of -30 F.;

(3) Boiling fuel vapors must be digested and continuous liquid flow maintained at the pre-determined minimum pressure;

(4) Regulation of the fuel pressure to a maximum pre-determined pressure (for example, approximately 60 psi.) must be maintained for all fuel flow conditions.

To meet operating conditions of the type described above as Well as overcoming the vapor lock problem we have incorporated into our fuel injection system an improved primary fuel supply pump designed to maintain the fuel injection system relatively free of vapor and in any event to purge the pump itself of vapor when it does form. The primary function of the supply pump is to prevent vapor forming in the fuel injection system by maintaining enough pressure in the fuel injection system at all times to maintain a flow of solid fuel. With hot fuels, for example, a pressure in the system on the order of 45-50 p.s.i. may be required to prevent the liquid fuel from flashing to vapor under very hot conditions. Preventing vapor formation is extremely important in order that the pre-determined calibrated amount of solid fuel (i.e., liquid fuel substantially free of vapor) will always be supplied.

To purge itself of slight vapors We provide in com- "ice bination with the primary fuel supply pump, a motor drive which at no load drives at high speed, and accordingly vents or bleed holes associated with the pumping cavity of the pump will permit quick purging of undesirable vapors from the cavity.

A principal object of this invention is to provide a fuel injection system in which vapor lock is virtually impossible under the most extreme high temperature conditions.

A further object of this invention is to provide a fuel supply pump constructed in such a manner that it will be effective to prevent very little vapor, if any, being introduced into the fuel injection system.

Another object is to provide a primary fuel supply pump which will maintain a minimum fuel flow at a pre-determined minimum pressure to the fuel injection pump at conditions of extremely low temperature such, for example, as -30 F.

Another object is to provide a supply pump capable of purging itself of boiling fuel vapors and maintaining continuous liquid fuel flow in the fuel injection system at a pre-determined minimum pressure such, for example, as 40 p.s.i.

Another object is to provide in the fuel injection system means whereby fuel in the system is maintained continuously under pressure once it has left the fuel supply pump.

Another object is to provide a means for driving the positive displacement fuel supply pump at variable speeds in response to fuel demand by the engine while maintaining a pre-determined minimum fuel supply pressure in the system such, for example, as 40 psi.

A still further object is to provide a fuel supply pump easily adaptable for interchange of parts for use with engines of different capacities.

The foregoing and other objects and advantages of the present invention will become apparent in the following detailed description thereof when read in conjunction with the accompanying drawings wherein:

FIGURE 1 illustrates a portion of a fuel injection system showing a tank mounted primary fuel supply pump and a fuel injection pump;

FIGURE 2 is a view in cross-section of the fuel injection pump of FIGURE 1;

FIGURE 3 is an end view of the fuel supply pump of FIGURE 1 taken along line 3-3 of FIGURE 1;

FIGURE 4 is a view of the fuel supply pump partially in section taken along the line 44 of FIG- URE 3;

FIGURE 5 is an enlarged view of a portion of FIG- URE 4;

FIGURE 6 is an enlarged view of the internal gear pump of the fuel supply pump .taken along line 6-6 of FIGURE 5;

FIGURE 7 is an enlarged view of the fuel supply pump cover plate taken along line 77 of FIGURE 5 showing the inlet cavity formed in the cover plate and the vapor bleed holes;

FIGURE 8 is an enlarged sectional view of a portion of the cover plate taken along line 8-8 of FIGURE 7;

FIGURE 9 is an enlarged section view of a .portion of the cover plate taken along line'99 of FIGURE 7;

FIGURE 10 is an enlarged view in section of a part of the fuel injection pump of FIGURE 2.

Like characters of reference in the several views refer to similar parts.

Referring now to the drawings, FIGURE 1 shows a portion of the fuel injection system. T is the fuel supply tank, S is the primary fuel supply pump, M is the motor for driving the supply pump, F is the fuel injection pump and N is a fuel injection nozzle which is adapted to be inserted into the manifold or directly into the cylinder of an internal combustion engine (not shown). The fuel is sucked out of the supply tank T through a filter 11 and then through a conduit 16 into the primary fuel supply punrp S from which it is pumped through the conduit 12 into the fuel injection pump F which pumps and distributes fuel through a series of conduits 14 to a plurality of fuel injection nozzles N.

The primary fuel supply pump S is a positive displacement type pump. It comprises a pump housing 16 formed with an inlet 18 and an outlet 20, an internal gear set 22 of the gerotor type, a pressure regulator 24, and a check valve 26. As shown in the preferred embodiment, the supply pump as shown in FIGURE 4 is mounted in an opening 28 in the tank T and is secured to the tank by any suitable means, such, for example, as bolts 30 The supply pump S also comprises a driving shaft 32 which is drivingly connected to the internal gear set 22 at one end and is connected at its other end to the driving motor M.

The drive shaft 32 is supported in the pump housing 16 by means of the sleeve bearing 33. A low shaft interference, low torque stationary rotary seal member 34 is positioned at the left end of the shaft 32 as viewed in FIGURE 5. A compression spring 35 surrounding the seal member 34 is effective to keep the lip of the seal in contact with the shaft 32. This low torque seal is used because it permits the use of a relatively low torque drive motor M thereby lowering the amperage requirements necessary to drive the pump S.

A bleed hole 36 is formed in the pump housing 16 and is in communication with the pressure side of the seal 34. The bleed hole 36 is located at the left hand end of the bearing 33 as viewed in FIGURE 5, i.e., between the bearing 33 and the seal 34. Thus a low pressure area is created which induces circulation of the fuel lubricant through the bearing. The bleed hole 36 must be sufiiciently large so that no back pressure is effected on the seal 34. It has been found, for example, that a A inch diameter hole is sufficiently large for this purpose although a larger hole may be used.

The pump housing 16 is formed with a pumping cavity 37 in which the gear set 22 is positioned. The internal gear set 22 is of the gerotor type as generally described for example, in US. Patent 2,872,872 and comprises a pair of gears or rotors-inner rotor 38 and outer rotor 39which fit snugly in the pumping cavity 37.

The outer rotor 39 comprises a plurality of radially inwardly disposed teeth 40 on its inner surface. The inner rotor 38 is formed with a plurality of radially outwardly extending teeth 42 numbering one less than the number of teeth on the outer rotor. The two rotors are disposed eccentrically of each other. The inner rotor 38 is connected to the drive shaft 32 by a spline or other suitable means. The side faces of both the inner and outer rotors are in sliding engagement with the mating surface 46 of the pump housing 16 and the mating surface 48 of the pumping cavity cover plate 23. The outer periphery of the outer rotor 39 rotates on a machined surface 50 of the pumping cavity 37.

The cover plate 23 has formed on its inner surface an arcuate suction portion or inlet kidney 52 which subtends an are greater than 90 and preferably of approximately 145". This inlet kidney is in fluid communication with the conduit leading from the supply tank T. The cover plate 23 is also formed with a recess 54 so as to be in a substantially coaxial relationship with the shaft 32. A bleed hole 56 extends from the recess 54 to the outside of the cover plate. Another bleed hole 58 extends through the cover plate and is fed by the substantially rectangular recess 60 formed in the cover plate. The purpose of the bleed holes will be hereinafter more fully explained.

It is important that the opening between the gears becomes exposed to the inlet port immediately after full mesh of the gears so that the pumping cavity may begin to fill as soon as the gears start to open. This is necessary to avoid drawing a partial vacuum which would be subject to be filled with vapor a condition which we wish to avoid.

It is preferable that the inlet port as viewed in FIG- URE 6 be terminated in its arcuate extension at such a point as to allow for a two-tooth seal as seen in the upper right hand quadrant of FIGURE 6. While a one-tooth seal may be adequate with a liquid of high viscosity, it has been determined that when pumping liquid of relatively low viscosity as gasoline, for example, a two-tooth seal minimizes the loss of efficiency which may otherwise result from gasoline flowing back across the gear teeth tips.

An outlet pressure port or kidney 62 is formed in the pump housing at a point almost 180 opposite from the inlet kidney 52. In the embodiment of FIGURE 5 the outlet kidney 62 is on the opposite side of the gears from the inlet kidney 52. The pressure kidney 62 preferably subtends an arc of approximately 135 and is positioned just before the full mesh of the gears. It will be appreciated that the pump may be constructed with a pair of inlet kidneys 52 and a pair of outlet kidneys 62. In such case one of the pair of inlet kidneys would be formed as shown and the other would be formed in the pump housing in substantial axial alignment with the one in the cover plate. One of the pair of outlet kidneys would be formed as shown and the other woulld be formed in the cover plate in substantial axial alignment with the one in the pump housing.

The arcuate length of approximately 145 for the inlet kidney and the arcuate length of approximately 135 for the outlet kidney have been found particularly suited for use with gears where the inner rotor has six teeth and the outer rotor has seven teeth. Different optimum arcuate lengths probably would be used with rotors having different numbers of teeth.

Fluid communication between the pressure kidney 62 and the inlet to the pressure regulator 24 is established by means of passage 64 formed in they pump housing.

The pressure regulator assembly 24 comprises a regulator body member 66, an open end hollow needle valve 68, a cap member threadedly secured in one end of the body member 66, and a compression spring member 72. The pressure regulator assembly 24 may be secured in the bore 73 of the pump housing by a threaded arrangement 74. An O-ring seal 76 positioned in groove 78 of the regulator body member functions as a sealing member between the body member 66 and the bore 73 in which the regulator body member is fitted. The body member 66 is formed with a circumferential recess 80, a plurality of radial slots 82, and an opening 84 which serves as a seat for the tapered needle valve 68.

The needle valve 68 may be formed of a plastic material such, for example, as Delrin. The needle valve is hollow and open-ended and adapted to receive the spring 72 so that the spring 72 is effective in conjunction with the cap '70 screwed in the end of the body member 66 to bias the needle valve into a seated position on the valve seat 84. Also formed in the needle valve 68 is a plurality of openings 86 adapted to serve as fluid passages through the needle valve when the needle valve is opened. The cap 70 is formed with an axially extending opening '71 to serve as a fiuid passage to carry fluid back to the tank T from the interior of the needle valve when the latter is opened.

The pressure regulator body member 66 also has formed at the left end thereof as viewed in FIGURE 5 an axially extending opening 88 which is in communication with inlet 90 of the check valve 26.

The check valve 26 comprises a ring portion 92 which is fitted into the bore 73 of the pump housing 16, a cap member 94, a valve disc 96 and a compression spring member 98 for holding the valve disc in a closed position on the valve seat 100. The cap member 94 is formed with a plurality of openings 102 and a central opening 104 for passing fluid to the passage 106 communicating with the outlet 20.

The motor M is of the series wound type. The drive shaft 108 of the motor M is connected to the pump drive shaft 32 by means of a flexible coupling 110.

The motor M is piloted into the pump housing 16 by means of a step flange 112 which is fitted into the bore 114 of the housing 16. The step flange is also formed with an opening 116 for receiving a sleeve bearing 118 which in turn supports the motor drive shaft 108. The characteristics which make this motor M particularly advantageous for use in conjunction with this pump will be hereinafter more fully explained.

The fuel injection pump F is of the type described in co-pending application Serial No. 791,081, filed February 4, 1959 now Patent No. 3,100,449. The fuel injection pump F comprises a drive section 120 and a metering and distribution section 122. The drive section 120 comprises a casing 124, a drive shaft 126, journaled within the casing 124, a cam 128 and a plurality of rollers 130 which function as common cam followers.

In operation, rotation of the drive shaft 126 preferably at cam shaft speed, causes a pumping plunger 132 to be driven at a 1:1 ratio therewith and the cam in moving over the rollers 130 imparts a reciprocating motion to the plunger 132.

The metering and distribution section 122 comprises a casing 134, the plunger 132, a fill valve 136 and a metering portion 138. The casing 134 is fixedly attached to the casing 124 and the pumping plunger 132 is disposed within a longitudinal cylindrical bore 140. The cylindrical bore 140 is enlarged at 142 to define a pumping or compression chamber adjacent the free end of the plunger 132. The casing 134 is also formed with a plurality of radial fuel delivery ports 144 each of which is connected to a fuel injection nozzle N by means of a conduit 14.

The plunger 132 is formed with an axial central bore or fuel passage. 146 and a radial distribution port or slot 148 communicating With the bore 146 and which is adapted to be aligned successively with the ports 144 as the plunger 132 rotates. A plug 150 is threaded into the open end of the axial bore 146. The plug 150 is formed with a central bore 152 and a fuel delivery or discharge check valve 154 having a tapered head 156 to form a tight seal on the inner end of the bore 152. A pin 158 is mounted axially within the bore 146 and a spring 160 surrounding the pin 158 acts against the valve 154 tending to maintain it in a fluid sealing position.

The fill valve 136 comprises a plug 162, threaded into the pumping chamber 142, a ring-shaped sealing member 164 and a spring 166. The plug 162 is formed with an enlarged central cavity 168 and a lapped surface 170 defining a valve seat formed on the inner end of the plug 162. The sealing ring member 164 is held against the seat 170 by the spring 166.

The metering portion 138 of the fuel injection pump F comprises a plug 174 threaded into a radial bore 176 formed in an extension of the casing 134, a movable piston or shuttle and an adjustable metering stop pin and a spring member. The structure and operation of the metering portion also are described in detail in copending application Serial No. 791,081, filed February 4, 1959. The pump F also includes a cylindrical casing portion 78 formed with a relatively large cylindrical cavity which defines a fuel supply reservoir. A flexible diaphragm 182 is provided on top of the casing 178 and is held in place by an end cap 184. The reservoir 180 is in communication with the bore 152 of the plug 150 and is connected through a fuel inlet port 186 to the primary fuel supply pump S by means of conduit 12. When the pump S supplies fuel to the reservoir 180 under a pressure, for example, of 40 p.s.i., this pressure is maintained substantially constant by means of the diaphragm 182 as will be further explained.

The nozzle N should be of the spring loaded valve type, and preferably should have an opening pressure of approximately 200 p.s.i.

Operation The operation of the fuel injection system and in particular the operation of the supply pump S and its associated driving motor will now be described. In operation the primary supply pump S supplies fuel under pressure to the fuel injection pump F through the conduit 12 for eventual distribution to a series of nozzles N inserted in the internal combustion engine. Since S is a positive displacement type pump its capacity is a direct function of speed. Under normal operating conditions, for example, the motor M will drive the pumping gears or

rotors

38 and 39 to suck fuel from the supply tank T through the filter 11 and through the conduit 10 into the inlet port 52. It will be noted that the inlet port 52 subtends an arc of approximately 145 to permit adequate filling of the successive chambers formed by the intermeshing of the

rotors

38 and 39. The outlet pressure kidney 62 subtends an arc of approximately 135. As the inner rotor 38 turns clockwise as viewed in FIGURE 6 pressure is built up within the pump S, and the fuel is pumped to the outlet pressure kidney 62 and then through the passage 64, into the recess 80, through the radial slots 82, past the check valve 26 and through the passage 106 to the outlet 20 of the pump S. Fluid then passes into conduit 12 and into the fuel reservoir 180 of the fuel injection pump F by way of the inlet port 186. Fuel is then drawn into the pumping chamber 142 through the fill valve 136 on the downward or suction stroke of the pumping plunger 132.

Under certain conditions vapors may have formed in the pump S between the inlet 18 and the valve disc 96 of the check valve 26. This is especially true when the system has been shut down and has been subjected to inordinately high temperatures for a long period of time during which time the fuel tends to boil. Before the pump S can properly pump fuel, it must be purged of these undesirable vapors. It is in this area that lies one of the main contributions of the improved fuel injection system. To assist in ridding the pump of these undesirable vapors we have provided vapor bleed means comprising bleed holes 56 and 58 and recesses 54 and 60 in the cover plate 23. The port 56 is fed by the recess 54 in the cover plate. The recess 54 is positioned substantially on a coaxial relationship with the drive shaft 32. The bleed hole 58 is fed by the recess 60 in the cover plate. The recess 60 is positioned near the root radius of the teeth of the inner gear. The recess 60 is positioned substantially toward the center of the pumping cavity 37 because the centrifugal force of the revolving gears 38 and 39 tends to throw the liquid outwardly forcing the vapor to remain in the center. The two

holes

56 and 58 are made large enough to pass enough vapor to purge a virtually dry pumping cavity and begin pumping liquid fuel. They are of sufiicient size to prevent vapor lock during any condition of pump operation, but yet are small enough that pump capacity is not reduced by any substantial amount. They may be on the order of .01.02 inch in diameter. The bleed hole 58 is of primary importance and passes the major portion of the vapor from the pump cavity. The bleed hole 56 passes the remainder of the vapor but serves primarily to eliminate thrust loads on the end of the pump shaft 32 due to pressures within the pumping cavity which build up between the end of the shaft and the pump cover plate 23. The bleed hole 58 preferably should be placed reasonably close to the discharge port. This has the effect of cutting down the distance vapors must travel and consequently the purging time.

High speed of the motor, on the order, for example, of 4,0005,000 r.p.m. is effective to almost instantaneously drive all vapor in the pumping cavity through the bleed holes and to commence pumping liquid fuel. Thus, the pump is self-priming. The bleed holes 56 and 58 are vented back to the fuel supply tank T as illustrated in FIGURES 4-, 5, and 8. When the pump S is not mounted in the tank T then a conduit means must be provided between the bleed holes 56 and 58 and the tank T so that venting will still be to the tank T. Pump speed is kept at a maximum by relieving the pressure on the lip of the seal 34 so that it will not pinch the shaft 32. This is done by means of the bleed hole 36 which is in communication with the pressure side of the seal 34 and is vented into the tank T.

The pump is driven by a motor M which is of the series wound type. This type of motor was selected as the driving medium because of two important characteristics. First, a series wound motor has a high acceleration rate and the ability to vary its speed rapidly with the applied load and second, as its speed decreases its torque capacity increases. During the operation of a vehicle fuel requirements may vary from pound per hour to 160 pounds per hour or higher on some vehicles. When an engine in which the fuel injection system is used is running at lower speeds, for example, the pressure within the pump S builds up and the pressure of the liquid fuel builds up to an amount equal to the setting of the pressure regulator 24. This pressure rises causes resistance to the pump and in turn to the motor M which slows down because of its inherent speed vs. load sensitivity. As the engine calls for an increased amount of fuel, fluid resistance to the pumping action becomes less and the motor M increases in speed correspondingly to produce higher volumes of fuel at higher fuel requirements. A series wound motor is able to attain high speed very rapidly which is particularly advantageous when fuel requirements go up rapidly, such, as for example, as at full throttle kick down.

The ability of the motor M to change speeds rapidly also permits rapid elimination of any vaporized fuel which is sucked into the pumping cavity 37. If the temperature is so high, for example, that the pump is sucking vapor as well as liquid from the tank the resistance to the pump drops causing an increase in speed of the motor M which raises the capacity. Although with an increase in motor speed an increased amount of vapor may be pulled up, the total volume of liquid fuel increases. This supplements any capacity which was lost due to pumping partially vapor.

The second characteristic of a series wound motor, namely, that as the speed decreases the torque increases, is especially important during extremely cold starts, such, for example, as at 20 F. Under such cold start conditions it is necessary to free the seal 34 quickly and start pumping the required fuel immediately. Thus under such a heavy load condition the pump driving at low speed must be able to exert a substantial torque to free the seal 34. This can be done by the motor of a series wound type.

In one particular embodiment where the fuel requirements may run from 0 to 160 pounds of fuel per hour we have found that a thirteen inch ounce motor rated at 3,000 r.p.m.s will satisfy those capacity requirements. This motor size will provide not only the necessary volume and pressure for the fuel injection system in question but also has the available power for starting the supply pump S at extremely low temperatures such, for example, as -20 F. Normal current requirements for a motor of this size are 3.5 to 4.5 amperes at 12 volts.

In summary, with respect to the motor M any motor that is used must be capable of accelerating to high speeds under a no load condition and the motor should have a rising torque curve as the speed is dropped to a low speed range for conditions of excessive loading.

One of the primary requirements of a good fuel injection system is to maintain pressure throughout the system during shut down under extreme heat conditions which would tend to vaporize the fuel. When the system is kept under a certain minimum pre-determined pressure vapor formation in a tightly pressurized system will be prevented or at least kept to a very minimum. In order to maintain this pressurized system we have provided as one of the features of our novel supply pump a check valve 26 positioned at the outlet of the supply pump S just prior to fuel entering the conduit 12 which carries the fuel to the fuel injection pump F. The outlet of the supply pump S has been found to be the optimum location for the check valve 26. Thus during a restart, for example, after the system has been subjected to a heat soak condition, only the pumping cavity of the supply pump S needs to be purged of vapor before pressure can be put on the system. When the pump is shut down the spring 98 will be effective to close the valve 96 thus maintaining pressure in the conduit 12 and preventing fuel from leaking back out of the system. Thus pressure is maintained from the pump outlet to the nozzles, and preventing fuel from flowing out of the system is effective to prevent vapor from forming in the system.

Under extreme heat conditions it has been observed that the fill valve 136 in the fuel injection pump F will not function at the same low pressure that it would normally function at when running cold fuel. Therefore, it takes more pressure to open the fill valve 136 under a condition of extreme heat or as it is sometimes referred to as hot soak condition than it does on a day of normal temperature. This is due to the formation of gasoline vapor pressure on the back or underside of the valve disc 164 which thereby requires an increase of opening pressure on the fill valve 136. Under a hot soak condition we have found it necessary, for example, to maintain the equivalent of a 55 p.s.i. system supply pressure in order to open the valve 136 when the normal supply pressure in the system sought to be maintained is 40 psi. Under normal temperature conditions the down or suction stroke of the pumping plunger 140 will theoretically pull a vacuum in the pump F or at least a pressure drop will occur on the suction stroke. Under extremely hot conditions, however, the downward suction stroke of the plunger 132 will permit the boiling fuel to flash to vapor so that no decrease in pressure on the back of the valve disc 164 takes place. Thus, it becomes necessary and extremely important under hot soak conditions to maintain pressure in the system and the check valve 26 is effective to accomplish this.

The pressure regulator assembly 24 functions as a bypass to place a limit on the maximum liquid fuel pressure that may develop within the supply pump S under all fuel flow conditions. The dumping pressure of the regulator is adjusted according to the compression put on the spring 72 by the cap 70. As the pressure builds in the pump S to a value higher than the pre-determined maximum pressure, such for example, as 60 p.s.i., the needle valve 68 is displaced from its seat 84 (to the right as viewed in FIGURE 5) and liquid will flow past the valve seat 84, through the openings 86 in the needle valve, out through the open end of the needle valve, and

through the opening 71 in the cap 70 back to the tank T. In the event, of course, that the supply pump S is mounted totally outside of the tank T, which it may be, an appropriate conduit means will be connected to the outlet end of the pressure regulator assembly 24 to carry the excess fuel back into the tank T.

Our tests have indicated that this fuel injection system will function equally well at temperatures well in excess of F. and as low as -25 F. without having the engine stumble or die out.

Thus it will be apparent that we have advantageously provided an improved fuel injection system adapted to be maintained in a pressurized state at all times in order to prevent vapor lock in the system. We have accomplished this by providing an improved supply pump S driven by a motor which operates at high speed under a no load condition and is thereby effective in conjunction with vapor bleed holes in the pump to automatically purge the pump cavity of undesirable vapors. In addition, the use of this type of motor is particularly suited for use in this fuel injection system since it is also capable of exerting a high torque at low speeds which is necessary under cold start conditions to free the pump seals and commence practically instantaneous pumping of the fuel at a normal operating temperature. Another improved feature in the fuel supply pump S is the provision of a check valve at the outlet thereof which is effective to maintain a pressure in the fuel injection system when the pump S is shut down.

While a certain preferred embodiment of the invention has been specifically disclosed, it is understood that the invention is not limited thereto as other variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

We claim:

1. In a fuel injection system for supplying fuel to an internal combustion engine from a fuel supply tank, a positive displacement fuel pump for pumping fuel from the supply tank including means defining a pumping cavity including a pair of spaced apart parallel Walls, means defining an inlet passage in communication with said cavity and adapted to be connected to the supply tank, means defining an outlet passage in communication with said cavity at a point spaced from said inlet passage, an outer pumping gear disposed within said cavity, an inner pumping gear disposed within said outer gear, a drive shaft connected to said inner gear end adapted to be connected to a source of rotational effort, means defining a vapor purging passage communicating between said cavity and the exterior of said pump, said passage communicating with said cavity through one of said spaced apart parallel walls at a location adjacent said outlet passage and spaced from said drive shaft a distance substantially equal to the root radius of said inner gear.

2. The invention according to claim 1 and a rapid acceleration variable speed electric motor for driving said fuel pump and connecting with said drive shaft, said motor being effective when said fuel pump is filled with vapors to accelerate rapidly to a high speed to purge said fuel pump, of vapors and eomrnence pumping liquid fuel.

3. The invention according to claim 1 and a pressure regulator in said fuel pump for bypassing fuel back to the fuel supply tank when the pressure in the fuel pump reaches a predetermined maximum.

4. In a fuel injection system for supplying fuel to an internal combustion engine from a fuel supply tank, a

positive displacement fuel pump for pumping fuel from the supply tank including means defining a pumping cavity including a pair of spaced apart parallel walls, means defining an inlet passage in communication with said cavity and adapted to be connected to the supply tank, means defining an outlet passage in communication with said cavity at a point spaced from said inlet passage, an outer pumping gear disposed within said cavity, an inner pumping gear disposed within said outer gear, a drive shaft extending through one of said spaced parallel walls including an end disposed adjacent the other of said walls in spaced relation thereto, said shaft being connected to said inner gear and adapted to be connected to a source of rotationial effort, means defining a vapor purging passage communicating between said cavity and the exterior of said pump, said passage communicating with said cavity through one of said spaced apart parallel walls at a location adjacent said outlet passage and spaced from said drive shaft a distance substantially equal to the root radius of said inner gear, and means defining a second vapor purging passage communicating between said chamber and the exterior of said pump through said wall spaced from said drive shaft in substantial alignment with the center line of said shaft.

5. A fuel supply pump in accordance with claim 4 wherein a low torque shaft seal is positioned within said pump in surrounding relation to said drive shaft and means defining an additional vapor purging passage communicating between the seal and the exterior of said pump.

References Cited by the Examiner UNITED STATES PATENTS 2,188,848 1/40 Svenson 103-203 X 2,423,439 7/47 De Lancey 103-203 X 2,503,016 4/50 Week et al 103-203 X 2,739,538 3/56 Witchger 103-203 X 2,776,630 1/57 Fagan 103-203 2,931,314 4/60 Erikson et a1. 103-203 3,041,976 7/62 Maynard 103-87 LAURENCE V. EFNER, Primary Examiner. ROBERT M. WALKER, Examiner