Patent Application
20070098586
The invention relates to a fuel pump for a vehicle and, in particular, to a spur gear pump for delivering fuel to an engine of a vehicle.
It is currently known in the art to provide a fluid pump utilizing a pair of intermeshing gears. Often referred to as a spur gear pump, the gears cooperatively engage to rotate in the same plane, the direction of rotation determining an intake side and an output side. More specifically, the intake side is provided on a side of the gears where the teeth move out of engagement with the teeth of the other gear and generally rotate outward. The rotational movement of the gear teeth in this manner provides a vacuum or suction to draw fluid into interstices or spaces between the teeth and a pump body surrounding the gears. On the output side, the fuel is deposited as the teeth of the gears open to an output port and then intermesh, the accumulation of fuel creating a pressure to force the fluid into the output port.
High-performance racing engines such as those used in sprint and drag racing cars commonly use spur gear pumps as a fuel pump. In this case, the fuel pump draws fuel from a fuel supply on the intake side and deposits the fuel under pressure on the output side for delivery downstream to the engine intake, such as an injection system.
More specifically, many high-performance racing engines use spur gear fuel pumps to deliver alcohol or nitromethane fuel to fuel injectors for the engine. The passage of the pump surrounding the spur gears is defined by a body formed of aluminum, and the gears have a small flat face at the end of each tooth. In order to minimize damage due to contact with the aluminum body, the tooth faces are positioned a short distance or gap from the surface of the body. The size of the gap is further increased by accommodating for a range of operating temperatures. As a result, the interface between the gear teeth and the pump housing provides for fuel leakage at all operating temperatures and pressures. For a new fuel pump, this leakage or bleed is typically 3-5% of the fuel captured between adjacent teeth and up to 10% for a worn pump.
This system results in a number of problems. Ideally, the provision of fuel is linear such that the volume of fuel is in direct and exact proportion to the engine speed, as measured in revolutions per minute (RPM), regardless of pressure. Generally this linearity is attempted by rotating the gears of the pump at a direct proportion to the RPM of the engine, such as by connecting the fuel pump to the engine via the serpentine belt or the cam shaft. However, the linearity is lost due to the leakage which is exacerbated as the leakage increases as pressure increases.
In addition, the operation of the fuel pump may cause cavitation or vaporization of the fuel. The tooth faces are intentionally small to minimize the ability of the edges to contact the pump body. The vacuum at the intake created by the rotation of the gears may be sufficient to vaporize the fuel or mix air thereinto. In a vapor or gas form, it is easier for the fuel to pass between the tooth faces and the pump body, further contributing to the leakage. In any event, then the tooth face profile is combined with the narrow gap, the fuel leaking through the gap experiences a significant pressure drop. When the volatile fuel experiences this pressure drop, it often quickly vaporizes and/or cavitates.
Cavitation of the fuel at the intake or within the fuel pump leads to a number of issues. In one instance, cavitation, either through vaporization or through mixing of air into the fuel, increases the volume of a molar amount of fuel. Though the pump can continue to deliver a volume of fuel between the teeth and the pump body, the molar quantity of fuel that is deliverable as a vapor or gas is significantly reduced from that which is deliverable as a liquid. Therefore, the quantity performance for the fuel pump is reduced when the volume is fully or partially vaporized fuel or air, perhaps to a point of failing to provide the requisite amount of fuel. This effect also results in the quantity of fuel delivered being unpredictable even for constant RPM conditions, the linearity of the fuel delivery with respect to the engine speed being again lost, and the fuel delivery varying with temperature (which causes expansion of the gas or vapor). As a result, the fuel delivery to the engine may be too high or too low. Beyond this, the high-pressure of the fuel over a small area on the gear teeth and pump body causes erosion on these surfaces, reducing the serviceable life of the pump and its components.
Accordingly, there has been a need for an improved fuel pump for providing fuel to an engine in linear proportion to the engine speed and with a spur gear type fuel pump.
In accordance with one aspect, a spur-gear type fuel pump is disclosed. The fuel pump includes a pair of interengaged gears rotating in a common plane within a pump body, the gear teeth defining spaces for capturing and pumping fuel through the pump. The gear teeth rotate into contact with the interior surface to capture the fuel therebetween. The gears then rotate to pump the fuel from an intake side to an output side. The contact of the teeth with the interior surface prevents or minimizes leakage from the spaces. This allows the pump to operate at high pressure, and the high pressure aids in minimizing cavitation or vaporization of the fuel.
In accordance with a further aspect, the gear teeth have a radially oriented terminal ends including an arcuate face concentrically formed with the center of rotation of the gear. The interior surface of the pump body which is contacted by the teeth is arcuate, and the interior surface is concentrically formed with the center of rotation of the gear. As the gear teeth rotate into contact with the interior surface, the arcuate faces are flush with the arcuate interior surface. This further serves to minimize leakage across the interface therebetween.
In accordance with another aspect, the gear pair includes an idler gear positioned on a roller bearing on a fixed axle, and a driven gear. The roller bearing is provided with tolerances which allow the pressure of the driven gear to shift the idler gear relative to the fixed axle or shaft. In this manner, the idler gear can balance pressure from the driven gear, which pushes the idler gear away from the driven gear, with pressure from the pump body interior surface which pushes the idler gear towards the driven gear.
In accordance with another aspect, the driven gear is secured with an axle or drive shaft for driving the driven gear. The drive shaft includes a pair of bearing assemblies on respective ends of the drive shaft. The bearing assemblies allow the drive shaft to self-align during operation.
In an additional aspect, the fuel pump includes a casing. The pump body is secured within the casing so that a portion of the pump body extends to contact an inner surface of the casing. Preferably, the pump body contacts the inner surface of the casing in the directions in which internal pressure from the rotating gears may otherwise cause the pump body to flex outwardly. In this manner, the pump body is constrained from substantially flexing, which may otherwise lead to separation between the teeth arcuate faces and the interior surface of the pump body.
A further aspect includes selecting materials to promote predictable and linear operation of the pump over a range of temperatures. In some forms, the interior surface of the pump body is formed of a hardened material with wear characteristics providing for a long life. In some forms, the gears are formed of a hardened material with similar long-life wear characteristics. In some forms, the gears and interior surface have different surface grain size to minimize gripping or locking between the gears and the interior surface. In some forms, the materials of the gears and of the interior surface may have similar or closely matched coefficients of thermal expansion so that, as the temperature of the pump increases, the gears and pump body expand in similar or closely matched amounts. In one example, the gears may be formed of hardened bearing-grade steel, and the interior surface may be formed of a hardened bronze alloy such as silicon bronze. In a further form, the pump body may be formed of a lightweight material such as aluminum or titanium, and the interior surface may be lined or covered with the hardened material such as the bronze alloy.
In another aspect, the pump gears may be rotated in either direction for operation. In this manner, the pump may be mounted in a variety of configurations and locations in an engine compartment. The pump communicates with a fuel source to receive fuel and with the engine to deliver fuel thereto, such as via a fuel injection system, and passageways are provided for the respective fuel receipt and fuel delivery. The passageways are generally identical so that the direction of the rotation of the pump gears may be selected based on which passageway is output and intake, or vice versa.
In the drawings,
Referring initially to
More specifically, the gears 26 include a driven gear 28 and an idler gear 30. Each of the gears 26 includes gear teeth 32 for cooperatively engaging with teeth 32 on the other of the gears 26 so that the engaged gears 26 rotate together in the same plane, though in opposite directions. As the driven gear 28 rotates in a first direction, the idler gear 30 rotates in the opposite direction to create a reduced-pressure suction or vacuum on one side 34 of the gears 28 at which the gears 28 dis-engage and rotate outward, and to create an increased pressure on an opposite side 36 of the gears 28 at which the gears 28 intermesh.
Each of these sides 34, 36 is positioned adjacent a port 38 in the pump body 20. One of the ports 38 is an intake port and the other is an output port, the selection of which is determined by the direction of driving the driven gear 28. In other words, the fuel pump 10 may be used so that one of the ports 38 is an intake port 38a through which fuel is received into the body 20 from a fuel source, and the other of the ports 38 is an output port 38b through which fuel is delivered to the engine (not shown) such as through an injection system (not shown). Accordingly, the driven gear 28 rotates in a direction indicated by arrow D1, and the idler gear 30 cooperatively engaged with the driven gear 28 rotates in an opposite direction indicated by arrow D2. This produces the suction on a side 34 coincident with or adjacent the intake port 38a and an increased pressure on a side 36 coincident with or adjacent the output port 38b, as shown in
The teeth 32 of the gears 26 capture fuel received on the intake side 34 between the teeth 32 and the body interior surface 22. As the teeth on one gear rotate outward and away from the teeth of the opposite gear, a quantity of fuel is captured between consecutive teeth of each gear and the interior surface 22. Representatively and with specific reference to
As shown, each of the gears 26 includes approximately ten teeth 32, though this number may range up to fifteen or more in the preferred embodiments. As can also be seen in comparing
Each of the gear teeth 32 includes a terminal end 44 for contacting the interior surface 22. As the gears 26 rotate, the teeth 32 will sequentially contact and slide against the interior surface 22 to prevent fuel bleed or leakage between the teeth 32 and the interior surface 22. By doing so, the above-described problems associated with leakage are substantially reduced or eliminated.
Additionally, this allows the fuel pump 10 to operate at a significantly greater pressure than those of the prior art. Under high pressure, a prior art pump will leak, vaporize a percentage of the fuel, and/or cavitate the fuel, thereby rendering the pump inadequate for its purpose. In a partial attempt to reduce these effects, the prior art pump is generally run at a maximum of 75-80 psi. The construction of the fuel pump 10 described herein allows for operation in the range of 400-500 psi, thus allowing for efficient fuel delivery across a wider range of pressures and temperatures and engine speeds without a loss of linearity between the speed and the volume of fuel delivered. The increased operating pressure for the fuel pump 10 also serves to minimize vaporization of the fuel on the intake side 34 due to the vacuum created. It is preferred for the fuel pump 10 to operate with a revolutions per minute speed that is approximately one-half the RPM speed of the engine. For high-performance engines, the engine RPM may be in the order of 4,000-12,000 RPM so that the pump 10 operates at 2,000-6,000 RPM. The pump 10 is also expected to operate properly at least through the temperature range of 30-200° F.
The terminal ends 44 include a radially located face 46. The face 46 is arcuately shaped with a center of curvature located with a center of rotation 48 of each gear 26. Therefore, each point along the face 46 is generally positioned at a radius 50 for the gear 26, as shown in
Each of the gears 26 is positioned on a concentric shaft. For the driven gear 28, a drive shaft 60 is provided having a socket 62 at one end for engagement with other drive components of the vehicle. For instance, the drive socket 62 may be coupled with the engine cam shaft, with the serpentine belt, or with another system for providing a speed ratio for the desired pump speed relative to the engine speed. The drive shaft 60 includes a pair of bearing assemblies 64a, 64b on respective front and rear portions 60a, 60b with the driven gear 28 positioned therebetween. The driven gear 28 includes a central opening 66 through which the drive shaft 60 is positioned, the drive shaft 60 and driven gear 28 being non-rotationally secured so that they co-rotate. The idler gear 30 includes a central opening 68 in which a bearing assembly 70 is positioned. The bearing assembly 70 is further positioned around an idler shaft 72.
As can be seen in
The idler shaft 72 is secured with the throughbores 84, 86 so that it generally remains stationary with respect to the body 20. In prior art systems, the idler gear is fixed with its shaft or axle, which itself would have a bearing assembly at each axle end in the same manner as the drive shaft 60. The prior art configuration is designed to preserve the gap size between the gear teeth and the body surface. In contrast, the present idler shaft 72 is held stationary and the idler gear 30 rotates around the single bearing assembly 70 so that the tolerances allow a small amount of shifting of the idler shaft 72. In this manner, the idler shaft 72 can balance the pressure from its cooperative engagement with the driven gear 28 with pressure against the interior surface 22 of the body 20. This allows the idler shaft 72 and idler gear 28 to self-align and to maintain contact with the interior surface 22.
During operation, the gears 26 contact the pump body 20, rear plate 78, and cover 76 to prevent fuel leakage. As discussed above, the faces 46 of the gears 26 contact the interior surface 22 to prevent leakage across their interface. Furthermore, the gears 26 each have a top surface 81 and a bottom surface 83 which respectively contact the cover 76 and the rear plate 78. In this manner, fuel movement is generally restricted to being pumped through the spaces 40 between the teeth 32 and the interior surface 22 as the gears 26 rotate. Lubrication is provided by the fuel itself.
In greater detail, the drive shaft 60 includes a thrust bearing assembly 87 so that forces exerted on the drive shaft 60 do not create excessive friction between the top and bottom surfaces 81, 83 of the driven gear 28. The thrust bearing assembly 87 is secured to a terminal rear end 60c of the drive shaft by a bolt 88 and washer 89. A thrust bearing 90 including a cage 91 having rollers is positioned between a pair of races 92a, 92b, and one of the races 92a is positioned against the washer 89 while the other race 92b is positioned against a shoulder 93 on drive shaft terminal end 60c and around a threaded bore 94 therein for receiving the bolt 88. A securing cap 95 is positioned with an annular portion 96 positioned around the bolt 88 and washer 89 so that a leading face 97 is positioned against the race 92a. As can be seen in comparing
As such, the thrust bearing 90 prevents axial loads on the drive shaft 60 from forcing the driven gear 28 into either the body cover 76 or the rear plate 78. When an axial load is directed in a push direction into the drive shaft 60, that is, along the axis from the front portion 60a towards the rear portion 60b, the drive shaft shoulder 93 presses against the thrust bearing 90 (specifically, the race 92b), which in turn presses against the securing cap 95 secured with the casing 100. When an axial load is directed in a pull direction, opposite the push direction, the bolt 88 secured with the drive shaft 60 presses against the thrust bearing 90 (specifically, the race 92a), which in turn is secured within a step (not shown) formed within the casing 100. Accordingly, the drive shaft 60 is assembled with the thrust bearing 90 through the casing rear side 100a, and the securing cap 95 is then sealed and secured with the casing rear side 100a.
A number of considerations are presented with maintaining the contact between the tooth faces 46 and the interior surface 22. In prior art fuel pumps, inadvertent contact between the gears 2 and an interior surface leads to galling or smearing of the material. That is, the gears 2 grab and lock with the interior surface, leading to rapid and excessive wear, if not failure. To minimize wear between the present gears 26 and the interior surface 22, the gears 26 are formed of a high-strength steel such as a bearing-grade material. An example of this is AISI 8640 steel. In a preferred embodiment, the interior surface 22 is formed of an alloy such as a hardened bronze alloy, one example of which is silicon bronze. This provides wear resistant characteristics and a coefficient of friction that are generally similar to or matched with the same for the steel of the gears 26.
By utilizing different materials for the gears 26 and the interior surface 22, these characteristics are also matched but have different surface structural granularity. That is, the microscopic grain size of the materials on the contact surface is mismatched. Accordingly, the materials have a lower tendency to grab and lock with each other. The faces 46 and the interior surface 22 are highly polished to further reduce any tendency to grab and lock.
In a more preferred embodiment, the body 20 is made of a lightweight material such as aluminum or titanium that is lined with the bronze alloy on the interior surface 22. It is noted that aluminum is corroded by nitromethane and alcohol fuels. Accordingly, the interior surface 22 formed of a hardened bronze alloy provides a longer life to the fuel pump 10.
The contact between the gears 26 and the interior surface 22 is maintained over a range of temperature. The described materials for the gears 26, body 20, and interior surface 22 generally provide for similar amount of expansion or contraction due to heat. Though not exactly matched, the thermal expansion coefficients combined with the bearing assemblies of the shafts 60, 72 allow differences in pressure to equilibriate so that contact between the gears 26 and the interior surface 22 is maintained.
Referring now to
It should also be noted that the pressure within the casing 100 and, in specific, the compartment 106 is maintained at the output pressure. The output side 36 of the pump body 20 is permitted to leak or is provided with a small port so that, within a brief time from pump start-up, the internal pressure within the compartment 106 is balanced with the output pressure. The pressure is thus generally balanced within the casing 100 and the pump body 20. More precisely, the pressure inside and outside the pump body 20 is generally balanced so that the rear plate 78 and front cover 76 do not bulge during high-pressure operation. Otherwise, this bulging would cause the fuel in the pump to flow around the top and bottom surfaces 81, 83 of the gears 26 and between the gears 26 and the front cover 76 and rear plate 78, leading to inefficiency and loss of performance.
In greater detail, it should be recognized that the pump body 20 has a first pressure at the intake side 34 which is lower than a pressure at the output side 36. In a prior art fuel pump, a seal such as an O-ring is located between the front cover 76 and body 20. In forms of the present fuel pump 10, the seal is omitted allowing the pressure from the intake and output sides 34, 36 to leak to the compartment 106 around the body 20 and within the casing 100. The front cover 76 and body 20 are in direct contact, such as along an interface 78a, that is not sealed such that the pressure is allowed to leak across the interface 78a (
However, the combined pressure in the compartment 106 is greater than the pressure at the intake side 34. Therefore, this combined pressure tends to force the cover 76 and body 20 together proximate the intake side 34. As this happens, the compartment combined pressure will rise as the pressure at the output side 36 imparts a greater contribution to the combined pressure, which further serves to close the intake pressure off from the compartment 106. Eventually, the pressures equilibrate with the compartment pressure generally approximately, or equal to, the pressure at the output side 36. In this manner, the pressure in the compartment 106 is substantially as high as pressure within the pump body 20, thereby substantially eliminating problems due to bulging of portions of the body 20 or the front cover 76 or rear plate 78. It should be noted that, though described for the front cover 76 and the body 20, a seal may also or may alternatively be omitted between the body and the rear plate 78 such the interface 78a may be located therebetween.
The casing cover 102 also serves to secure the drive shaft 60 and the idler shaft 72. The drive shaft 60 is permitted to rotated within and extend through a throughbore 114 in the casing cover 102. To maintain pressure within the casing compartment 106, the drive shaft 60 is sealed with the casing cover 102. A portion (not shown) of the casing cover 102 extends into the compartment 106 for receiving the bearing assembly 64a on the front portion 60a of the drive shaft 60. The idler shaft 72, which is stationary with the casing 100, is secured in the casing cover 102 with a bolt 116.
Referring now to
Each of the passageways 120, 122 communicates with a pair of openings for either receiving or delivering fuel therethrough. Each passageway 120, 122 includes a first portion 124, 126 that is generally axially aligned and parallel to the axis of rotation of the drive shafts 60, 72. A first end of each first portion 124, 126 communicates with the respective intake and output ports 38a, 38b, while a second end of each first portion 124, 126 communicates with a second portion 128,130 of the respective passageways 120, 122. Each second portion 128, 130 is oriented generally transverse or orthogonal to the first portions 124, 126 and includes respective openings for fuel communication.
In greater detail, the second portion 128 of the intake passageway 120 includes a pair of openings 132, 134, while the second portion 130 of the output passageway 122 includes a pair of openings 136, 138. This allows each of the passageways 120, 122 to be connected in fuel communication with the fuel source and with the engine, such as through the injection system, in a variety of locations within the engine compartment and with a variety of components, such as the cam shaft or serpentine belt. Additionally, it allows the operation of the pump 10 to be reversed, as noted above, depending on its mounting location and user preference.
While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.
