Pumps – Three or more cylinders arranged in parallel – radial – or... – Radial cylinders
Reexamination Certificate
1999-06-24
2001-02-06
Walberg, Teresa (Department: 3742)
Pumps
Three or more cylinders arranged in parallel, radial, or...
Radial cylinders
C417S462000, C123S447000, C123S450000
Reexamination Certificate
active
06183212
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a supply pump for fuel injection into an internal combustion engine. More particularly, the invention relates to a supply pump with pumping plungers which are retained by sliding shoes or a cage.
One type of conventional fuel supply pump has plungers which reciprocate radially in corresponding pumping bores. As each plunger moves toward a filling position, fuel is drawn into the pumping bore. As the plunger moves toward a pumping position, fuel at an elevated pressure is discharged from the pumping bore. The plungers may be internally or externally driven. In an internally driven supply pump a rotating drive member periodically actuates the radially inner end of each plunger outwardly. In this type of pump, fuel is discharged from the bore on the radial outward stroke of the plunger and drawn into the bore on the radial inward stroke of the plunger. Thus the filling position is the radially innermost plunger position and the discharge position is the radially outermost plunger position. The converse arrangement is present in an externally driven supply pump, which has pumping plungers actuated at their radially outer end (e.g., by a rotating annular cam) and therefore a radially inwardly discharge stroke and a radially outwardly filling stroke. In either pump type, the rotary motion of the drive member is converted to linear motion of the plungers for movement to the pumping position. Because the plunger is not attached to the eccentric drive or cam, a spring is used to bias the plunger back toward the filling position. In the conventional fuel supply pump, each plunger is biased and returned to its filling position by its own return spring independently of the other plungers.
Conventionally, a sliding shoe is interposed between the plunger and drive member to aid in conversion of the rotary drive member motion to linear plunger motion. The shoes must be maintained in essentially constant contact with both the drive member and the plunger end. This is usually accomplished via an independent spring bias for each shoe and a pivotable connection between the shoe and plunger. Typically, each plunger and its respective shoe is biased by the same spring. The pivotable connection between the plunger and shoe presents problems in manufacture and assembly. Conventionally, it is difficult to find a shoe material with adequate wear resistance yet still ductile enough to allow the shoe to be formed around a plunger end to capture the plunger. It is also difficult to mechanically form the sliding shoe around the plunger captured end while achieving the optimum retentive fit between these components. Finally, assembly of the sliding shoe/plunger sub-assembly into the fuel pump bore is difficult and can only be done manually.
More efficient space utilization, higher pump efficiency and improved sliding surface lubrication can be achieved by eliminating the conventional coil return springs and dynamically connecting all of the sliding shoes or all of the plungers. In particular, a pivotable connection between the plunger and the shoe and desmodromic drive of these reciprocating members by an energizing ring or retainer cage, make spring elimination and the previously mentioned benefits possible.
SUMMARY OF THE INVENTION
An object of the invention is to provide a pivotable connection between a fuel pump plunger and sliding shoe.
Another object of the invention is to provide sliding shoe and plunger components which allow a pivotable connection and are easily manufactured.
A further object of the invention is to create a pivotable connection between a fuel pump plunger and sliding shoe which will operate in cooperation with a desmodromic drive.
Yet another object of the invention is to provide a pivotable connection between the fuel pump plunger and sliding shoe which can be quickly and easily assembled within a fuel pump body.
Still another object of the invention is to provide a method of assembling a fuel pump drive sub-assembly external to the fuel pump body, and installing the drive sub-assembly into a fuel pump.
A first embodiment of the invention concerns the pivotable connection between the fuel pump plunger and the fuel pump sliding shoe. Each sliding shoe has a first face and an opposing second face and each pumping plunger includes a body with a pumping end and an opposing driven end. The sliding shoe first face engages the driven end of the plunger while the second face of the sliding shoe slidingly engages the rotating drive member. The sliding shoes are not directly attached to the drive member, although each plunger is forced toward a pumping position by the action of the rotating member against its respective shoe. Each sliding shoe and its respective pumping plunger can therefore be thought of as a sliding shoe assembly. The driven end of the plunger includes a head, which may be substantially spherically shaped. The head may be connected to the plunger by a neck, having a smaller diameter than either the plunger body or spherical head. The sliding shoe first face includes an internal wall defining a substantially spherical socket with a circular opening. The diameter of the circular opening is smaller than the maximum diameters of either the plunger head or shoe socket. In this manner, as the plunger head is moved toward the sliding shoe socket, the socket opening “flexes” to accommodate the greater diameter of the plunger head. Once the maximum diameter of the plunger head has moved past the socket opening, the opening returns to its original diameter, thereby pivotably trapping the plunger head within the socket of the sliding shoe socket. Thus, the plunger head “snaps” into the sliding shoe socket. Preferably the flexing of the socket opening is within the elastic limit for the material comprising the sliding shoe so that no permanent deformation of the socket or socket opening takes place.
In one preferred variation, the sliding shoes are each connected to a cage so that an essentially fixed spatial relationship is maintained between the shoes. It should be understood that this fixed relationship is maintained even though the sliding shoes and cage are in motion when the supply pump is in use. Thus, as one shoe and its plunger is moved toward its pumping position by the drive member, the cage couples this movement to at least one other shoe, and thereby its plunger, which is moved toward its filling position. In this fashion, the rotary motion of the drive member is converted into the reciprocating linear motion of each plunger without the need for spring biasing of either the plunger or shoes. Although the preferred implementation of the invention uses a cage to desmodromically drive the shoe assemblies, the “snap in” connection of the shoe socket and plunger head may also be advantageously employed in conventional spring biased designs.
In another variation, the sliding shoe socket includes apertures or slots in the wall which increase the flexibility of the wall. This allows the shoe to be manufactured from less resilient materials while still allowing an elastic snap fit with the plunger head; or greater flexibility to be obtained for a given material compared to a non-slotted variation.
In a further variation, the cage includes apertures which have a width less than the diameter of the plunger head. In a fashion analogous to the snap fit of the plunger head into the sliding shoe socket, the cage apertures elastically flex to allow the larger plunger head to pass through, flexing back after passage to thereby pivotably trap the plunger head to the cage. In this variation, the sliding shoe first face includes a partially spherical cavity or seat which engages, but does not necessarily capture, the plunger head. This variation allows the use of higher strength sliding shoe materials which are too brittle to flex and capture the plunger head, while still allowing desmodromic drive of the plungers.
In a different variation, the plunger head has a larger radius adjacent the neck and a smaller radius at the free e
Alix Yale & Ristas, LLP
Pwu Jeffrey
Stanadyne Automotive Corp.
Walberg Teresa
LandOfFree
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