Inner cam type injection pump

Abstract: In an inner cam type injection pump, the side surface of the protruding portion of each of the plungers facing the compression space is formed in a projecting shape in the area where the plunger changes from the base end side into the front end. Specific forms of the projection include a structure constituted with slanted surfaces over a plurality' of stages with different inclinations relative to the axis of the plunger, an arc form and a structure provided with a overhanging portion formed on the side surface of the protruding portion, which does not overhang the base end, projecting out from the side surface This will prevent collision at the shoulder portion of the plunger and, consequently, prevent the deformation at the shoulder portion and ensures that plungers will not have sliding failures or become seized. Even when plungers collide, the sliding of the plungers will not be affected, ensuring that plungers do not have sliding failures or become seized.

Description: The present invention relates to an inner cam, distributor type injection pump which is employed for fuel supply to an engine or the like, i.e., a fuel injection pump which employs a system in which plungers are caused to make reciprocal movement in the direction of the radius of a rotor which rotates in synchronization with the engine. Inner cam, distributor type injection pumps in the prior art include the one disclosed in Japanese Unexamined Utility Model Publication No. S62-193173. In this injection pump, an inner cam is provided around a rotor which operates in synchronization with an engine and cam surfaces formed on the inside of this inner cam cause plungers to make reciprocal movement in the direction of the radius of the rotor. In the rotor, a pump chamber and plunger cylinders which face this pump chamber are formed. Four plunger cylinders are formed on the same plane with their phases offset by 90° from one another, and the plungers that slide in the cylinders are lifted at the same time to compress the fuel inside the pump chamber. In such a structure, in which four plungers are provided on the same plane, it is necessary to minimize the dead volume inside the pump chamber in order to assure high pressure fuel and, to achieve this, it is effective to form the portions that protrude into the pump chamber by narrowing the ends of the plungers toward the pump chamber in a cone shape and to make these protruding portions project out into the pump chamber at the maximum lift positions of the plungers, as disclosed in the publication mentioned above. However, when the rotation rate of the drive shaft increases, the plungers jump from the inner cam when they are lifted to the highest position and adjacent plungers collide with each other. Since the protruding portions 7'a of the plungers 7' are formed in a cone shape, as shown in FIG. 7, the collisions occur at the shoulder portions 7'c of the plungers 7' where they change from their base portions 7'b into the protruding portions 7'a. Such collisions of the plungers 7' result in surface deformation in the colliding areas and if such deformation occurs in a shoulder portion 7'c, the clearance between the plunger 7' and the inner surface of the plunger cylinder 6 (3 ∼ 4µm) cannot be maintained. This, in turn, may result in a sliding failure of the plunger 7' or in the worst case, the plunger 7' becoming seized to the rotor 3. The object of the present invention is to provide an inner cam type injection pump in which the problems of the prior art discussed above are solved, so that even when plungers collide with each other, the sliding of the plungers is not affected and, thus, sliding failures do not occur in the plungers and they are prevented from becoming seized. The applicant of the present invention, through extensive research into means for solving the problems discussed above, has completed the present invention based upon the observation that, when the plungers are made to collide toward the front ends of their protruding portions, but not at the shoulder portions, good sliding can be maintained even if the colliding areas become deformed. Accordingly, the present invention provides an inner cam type injection pump comprising; a pump housing; a rotor supported in said pump housing and rotatable upon receiving drive torque; a compression space formed in said rotor and connecting with passages for inflow and outflow of pressurized fluid; a plurality of plunger cylinders formed in said rotor, said plunger cylinders being provided on the same plane and extending from said compression space in radial directions of said rotor; a plurality of plungers, each of which is provided in each of said plunger cylinders, capable of reciprocating slidably; and an inner cam provided in said pump housing concentric with and around said rotor, and having cam surfaces provided on the inner side thereof for making said plungers reciprocate upon rotation of said rotor; wherein each of said plungers has a base end portion sliding in contact with the inner surface of said plunger cylinder and a protruding portion provided at the end facing said compression space, the cross-section of said protruding portion becoming smaller toward the front end thereof, and a shoulder portion between the base end portion and the protruding portion, characterized in that: the plungers are all of substantially the same length and the protruding portion comprises at least two slanted surfaces, the first slanted surface further from the front end of the protruding portion having an inclination relative to the axis of the plunger which is smaller than that of the second slanted surface nearer to said front end, whereby the plungers are made to collide toward the front ends of their protruding portions, but not at the shoulder portions so that the sliding of the plungers is not substantially affected even if the colliding areas become deformed as a consequence of the collision of the plungers. In the injection pump, the protruding portion may be constituted by slanted surfaces formed over a plurality of stages with different angles of inclination relative to the axis of the plunger, or may take the form of an arc, or may be constituted by providing an overhanging portion on the side surface of the protruding portion that does not overhang the base end side, which projects out from the side surface. Alternatively, instead of forming the side surface of the protruding portion with a projection, or with a combination of such projections, the base end side of the protruding portion may be formed with an indented shape. Furthermore, the form of the protruding portion described above may be adopted in only some of the plungers in an inner cam type injection pump that includes a plurality of plunger cylinders provided on the same plane in the direction of the radius of the a rotor, a compression space provided in the rotor facing the plunger cylinders and plungers provided in each of the plunger cylinders in such a manner that they can slide freely, with a protruding portion having a cross section that becomes smaller toward the front end, formed at the end of each plunger, where it faces the compression space, in which the movement of the plungers is regulated by an inner cam provided around the rotor. In this case, it is desirable to adopt the form mentioned earlier for the protruding portion in only one of each pair of adjacent plungers. More specifically, the form should be adopted in alternate plungers among a plurality of plungers provided in the direction of the circumference. Consequently, when the rotor rotates, the plungers are lifted in the plunger cylinders to reduce the volumetric capacity of the compression space. Although the plungers jump and adjacent plungers collide with each other, since the side surface of each protruding portion has a projected form in the area where it changes from the base end side to the front end side, the plungers do not collide at the shoulder portions where they change to the protruding portions but collide at the areas toward the front end of the protruding portions. In other words, when the projected form at the side surface of each protruding portion is constituted with slanted surfaces formed over a plurality of stages, it is possible to make collision occur at the slanted surface toward the front end or in the boundary area formed at the boundary between slanted surfaces. When the projected form is constituted with an arc, it is possible to make the collision occur around the center of the side surface of the protruding portion and when the projected form is constituted of an overhanging portion provided at the side surface of the protruding portion, it is possible to make the collision occur at this overhanging portion. In all these cases, it is possible to avoid having the collision occur at the base end (shoulder portion) of the protruding portions and, as a result, deformation of the base ends of the protruding portions can be avoided. Furthermore, if the base end side of the protruding portion is formed with an indented shape, plungers will collide with each other in an area other than the area toward the base ends of the protruding portions. Thus, in this case too, deformation of the base ends of protruding portions can be prevented. Moreover, of a plurality of plungers, the irregular protruding portion described above may be formed in only some, with the other plungers being plungers of the prior art. In this case, too, deformation of the base ends of the plungers with irregular protruding portions and the adjacent plungers can be prevented. For instance, if plungers with irregular protruding portions are provided at alternate positions, advantages similar to those achieved when irregular protruding portions are formed in all the plungers, can be achieved. The above and other features of the invention and the concomitant advantages will be better understood and appreciated by persons skilled in the field to which the invention pertains in view of the following description given in conjunction with the accompanying drawings which illustrate preferred embodiments. In the drawings: FIG. 1 is a schematic cross section of the essential portion of the inner cam type injection pump according to the present invention. FIG. 2 is a cross section through a plane that includes all the plungers of the inner cam type injection pump shown in FIG. 1. FIG. 3 shows one of the plungers used in the inner cam type injection pump according to the present invention, with (A) being its side view and (B) being its perspective. FIG. 4 shows another example of the plungers used in the inner cam type injection pump according to the present invention, with (A) being its side view and (B) being its perspective. FIGS. 5A ∼ 5D show yet other examples of plungers used in the inner cam type injection pump according to the present invention. FIG. 6 is a cross section showing a state in which alternate plungers in an inner cam type injection pump have different forms. FIG. 7 is a cross section of an inner cam type injection pump of the prior art. The following is an explanation of the embodiments of the present invention in reference to the drawings. In FIG. 1, which shows the essential portion of an inner cam type distributor type fuel injection pump, a distributor type fuel injection pump 1 is provided with a rotor 3 inside pump housings 2a and 2b. This rotor 3, upon receiving drive torque from an engine (not shown), rotates in synchronization with the engine. The rotor 3 extends through a chamber 4 where fuel from a fuel tank is supplied via a feed pump. The front end of the rotor 3 is inserted into a barrel 5, which is formed at the pump housing 2b, in such a matter that it can rotate freely and a larger diameter portion 3a formed toward its base portion, where plunger cylinders 6 extending in the direction of the radius (radial direction) are formed. In this embodiment, four plunger cylinders 6 are formed over 90° intervals, for instance, on the same plane, as shown in FIG. 2, and a plunger 7 is inserted in each plunger cylinder 6 in such a manner that it can slide freely. The front end of each plunger 7 faces a compression space 8 provided at the center of the rotor 3 enclosing this space and the base end of the plungers 7 slide against the inner surface of a ring-like inner cam 11 via shoes 9 and rollers 10. The inner cam 11 is provided concentrically to and around the rotor 3 and is provided with cam surfaces 11a, the number of which corresponds to the number of cylinders in the engine. Thus, when the rotor rotates, each plunger 7 makes reciprocal movement in the direction of the radius of the rotor 3 (the radial direction) to change the volumetric capacity of the compression space 8. In other words, an inner cam 11 which is formed in correspondence to four cylinders, for instance, is provided with projected surfaces every 90° on its inside, so that the four plungers 7 travel simultaneously toward the compression space 8 to compress the compression space 8 by constricting it and they travel simultaneously away from the compression space 8 to decompress it. The rotor 3 is provided with a longitudinal hole 12 in the direction of the axis which communicates with the compression space 8, an inflow / outflow port 13 opening onto the external circumferential surface of the rotor at a position within the chamber 4, and a distribution port 15, which can communicate with a plurality of distribution passages 14 formed in the housing 2b. A sleeve 16 is externally fitted on the chamber 4 covering the inflow / outflow port 13 of the rotor 3 in such a manner that it can side freely. An intake hole 17 and a cutoff hole 18, both of which can communicate with the inflow / outflow port 13 are formed in the sleeve 16, and the timing with which the intake hole 17 or the cutoff hole 18 communicates with the inflow / outflow port 13 is adjusted by moving the sleeve 16 in the direction of the shaft axis. The four plungers 7 which make reciprocal movement in the plunger cylinders 6 are each provided with a protruding portion 7a whose cross section becomes smaller toward the front end, where it faces the compression space 8, as shown in FIGS. 3A and B. To describe the form of these plungers 7 in comparison with the form of the plungers in the prior art, as shown in FIG. 7, the plungers in the prior art have a cone shape, whereby the protruding portion 7'a protrudes out into the compression space 8 at the maximum lift position and the side surface of the protruding portion 7'a has an inclination of 45° or greater relative to the axis of the plunger, as indicated with the two-point chain line in FIG. 3A. In contrast, in each of the plungers 7 according to the present invention, a shoulder portion 7c ( the area where the base portion 7b changes into the protruding portion 7a) is formed at a position further away from the front end and the protruding portion 7a is constituted with two slanted surfaces with different angles of inclination relative to the axis of the plunger 7 ( a first slanted surface 20 and a second slanted surface 21), as indicated with the solid lines in FIGS. 2 and 3. The slanted surfaces 20 and 21 formed on the side surface of the protruding portion 7a are formed in such a manner that the first slanted surface 20 toward the base end has an inclination smaller than 45° relative to the axis of the plunger 7 and the second slanted surface 21 toward the front end has an inclination of 45° or larger. By increasing the inclination of the slanted surface toward the front end relative to the axis of the plunger 7, the side surface of the protruding portion 7a is formed in an projected shape extending from the base end side toward the front end side. As a result, when the rotor 6 rotates, the plungers 7 make reciprocal movement in the plunger cylinders 6 of the rotor 3 in correspondence to the form of the inner cam 11 and during an intake process, in which the plungers 7 move in the direction away from the compression space 8, the inflow / outflow port 13 and the intake hole 17 become aligned with each other and the fuel in the chamber 4 is taken into the compression space 8. Then, when the operation enters a force-feed process, in which the plungers 7 move toward the compression space 8, the communication between the intake hole 17 and the inflow / outflow port 13 is cut off, the distribution port 15 and one of the distribution passages 14 become aligned and compressed fuel is supplied to a delivery valve via this distribution passage 14. When the inflow / outflow port 13 and the cutoff hole 18 become aligned during the force-feed process, the compressed fuel flows out into the chamber 4 to end fuel injection. If the rotor 3 is rotating at high speed, when the plungers 7 reach the maximum lift position at the cam apex, they jump, colliding with adjacent plungers 7 and then start to travel downward due to the fuel pressure inside the compression space 8. In the prior art, this collision occurs at the shoulder portions of the plungers, i.e., in the area where they change from their base body portion 7b into the protruding portion 7a. With the plungers 7 according to the present invention, however, they collide at the slanted surfaces toward the front end ( second slanted surfaces 21) or at the boundary area between the first slanted portion 20 and the second slanted portion 21. Thus, deformation caused by collision at the shoulder portion 7c of the plungers 7 can be prevented. While the structure in which two slanted surfaces 20 and 21 with different angles of inclination are formed in the plunger 7 to form a projected shape on the side surface of the protruding portion 7a may be constituted with the two conical surfaces over two stages, as described above, it may also be constituted with slanted surfaces over two stages formed only in the area where the plungers collide with adjacent plungers, as shown in FIGS. 4A and 4B. In other words, no slanted surface is formed on the surface of that part of the base body portion 7b where collision does not occur, and which extends into the area of the compression space unmodified. Where adjacent plungers 7 collide with each other, the shoulder portion 7'c in the prior art (indicated with the two-point chain line) in each plunger is cut off with a first slanted surface 20 with its angle of inclination relative to the axis of the plunger 7 smaller than 45° formed toward the base end and a second slanted surface 21 with its angle of inclination at 45° or larger formed toward the front end separately. In such a structure, it is necessary to provide a means for ensuring that the plungers 7 do not rotate around their axes and, for this purpose, a means for preventing rotation such as that disclosed in Japanese Unexamined Utility Model Publication No. S62-193173, for instance, may be employed without presenting any problems in achieving advantages similar to those achieved in the embodiment described above. Other structures in which the side surface of the protruding portion 7a is formed projecting from the base end side toward the front end side include those shown in FIGS. 5A, 5B and 5C. In FIG. 5A, the shoulder portion 7c of the plunger 7 (where the plunger 7 changes from the base body portion 7b into the protruding portion 7a) is formed at a position further away from the front end compared to the shoulder portion 7c in the prior art, indicated with the two-point chain line, and the protruding portion 7a is constituted with three slanted surfaces (first slanted surface 22, second slanted surface 23, third slanted surface 24) with different angles of inclination relative to the axis of the plunger 7. The slanted surfaces 22, 23, and 24 formed on the side surface of the protruding portion 7a are formed in such a manner that the inclination of the first slanted surface 22 toward the base end is less than 45° relative to the axis of the plunger 7, the inclinations of the second and third slanted surfaces 23 and 24 toward the front end are at 45 or more, for instance. By making the angle of inclination relative to the axis of the plunger 7 larger for the slanted surface that is closer to the front end, the side surface the protruding portion 7a is formed projecting from the base end toward the front end. In such a structure, when the plunger 7 jumps and collides with the adjacent plungers 7, the collision will occur at the second slanted surface 23 or the third slanted surface 24, or at the boundary area between the first slanted surface 22 and the second slanted surface 23 or at the boundary area between the second slanted surface 23 and the third slanted surface 24. Thus, deformation caused by collision occurring at the shoulder portion 7c of the plunger 7 can be prevented. Also, in FIG. 5B, the shoulder portion 7c of the plunger 7 (the area where the plunger 7 changes from the base body portion 7b into the protruding portion 7a) is formed at a position further away from the front end compared to the shoulder portion 7'c in the prior art, indicated with the two-point chain line in FIG. 5B, so that the protruding portion 7a is formed in a near hemispherical shape with its cross section gradually becoming smaller toward the front end. In addition, its side surface is formed in such a manner that it has an inclination of less than 45° relative to the axis of plunger 7 toward the base end and it has an inclination of 45° or more toward the front end, achieving a smooth projecting surface extending from the base end side toward the front end side. In such a structure, too, when the plunger 7 jumps, it will collide with the adjacent plungers 7 in the area toward the front end, away from the base end of the protruding portion 7a and, as a result, deformation in the shoulder portion 7c of the plunger 7 can be prevented. Moreover, the projected form on the side surface of the protruding portion may be constituted by providing an overhanging portion 25 that does not overhang the base end side to accommodate collision on the side surface of the protruding portion 7a, as shown in FIG. 5C. To be more specific, a ring-like overhanging portion 25 is formed as part of the protruding portion 7a, which is formed in a cone shape, at approximately the middle of the protruding portion 7a, and the shoulder portion 7c of the plunger 7 (the area where the plunger 7 changes from the base body portion 7b into the protruding portion 7a) is formed at a position further away from the front end compared to the shoulder portion 7'c in the prior art, indicated with the two-point chain line. In such a structure, adjacent plungers 7 collide with each other at their overhanging portions 25 and, as a result, collision at the shoulder portions 7c of the plungers 7 is prevented and the shoulder portions 7c are not deformed. Rather than preventing a collision at the plunger shoulder portion 7c by constituting the protruding portion 7a of the plunger 7 with a projecting form, as in the structures described so far, the base end side of the protruding portion 7a, where collision is likely to occur, may be have an indented shape to avoid collision in that area. A typical example of such a structure is provided with a first slanted surface 26 formed in such a manner that the shoulder portion 7c is formed at a position further away from the front end compared to the plunger form in the prior art, indicated with the two-point chain line, and a second slanted surface 27 formed more toward the front end compared to the first slanted surface 26 with a cylindrical surface 28 connecting the two slanted surfaces. As another structural example, a circular groove may be formed in order to remove the shoulder portion 7'c of the plunger 7 in the prior art, indicated with the two-point chain line. In these structures, even when adjacent plungers 7 collide with each other, the collision will not occur at shoulder portion 7c and thus it is possible to prevent deformation of the shoulder portion 7c, as in the embodiments described earlier. FIG. 6 shows another embodiment of the present invention. The same reference numbers are assigned to identical components with their explanation omitted, and the explanation will be given only of components that are different. In this embodiment, some of the plungers 7 are constituted with any one of the plungers shown in FIGS. 3 ∼ 5 and the remaining plungers are constituted with the plungers 7' of the prior art. More specifically, it has a structure in which plungers 7, each provided with a protruding portion with conical surfaces over two stages, as shown in FIG. 3, and plungers 7' of the prior art are provided alternately in plunger cylinders 6, for instance. In this structure, when the plungers 7 and 7' jump and collide with adjacent plungers, the collision will not occur at the shoulder portion in any of the plungers 7 and 7', as shown in FIG. 6. Rather, the plunger 7' in the prior art will collide at the slanted surface (second slanted surface 21) toward the front end of the plunger 7 according to the present invention or at the boundary area between the first slanted surface 20 and the second slanted surface 21 and, as a result, deformation at the shoulder portion of each plunger is prevented. Note that, although in this embodiment, a specific structure employing the plungers shown in FIG. 3 is explained, a similar structure may be constituted by using any of the plungers 7, shown in FIG. 4 or FIG. 5 and in that case, too, collisions at the shoulder portion can be avoided in the same manner, preventing deformation at the shoulder portion of the plunger. As has been explained, according to the present invention, since the side surface formed at the protruding portion of a plunger is made to have a projecting form in the area where it changes from the base end side toward the front end side, even when plungers collide with each other, the collision will not occur at the base end (shoulder portion) of the protruding portion and, as a result, deformation of the base end is prevented, to ensure that plungers will not have sliding failures or will not become seized. The structure in which collisions do not occur at the base end of the protruding portion may be achieved by constituting the base end of the protruding portion with an indentation and in this case, too, deformation at the base end is prevented, to ensure that plungers will not have sliding failures or become seized. Moreover, in a structure in which all plungers are not formed identically, with the protruding portions of some plungers being constituted with projected side surfaces or the base ends of the protruding portions being constituted with an indented shape, collisions of the plunger provided with a regular protruding portion and an adjacent plunger are made to occur in an area away from the base end, preventing deformation of the base end of the protruding portion in the same manner, and ensuring that plungers will not have sliding failures or become seized.

Claims: An inner cam type injection pump (1) comprising; a pump housing (2a, 2b); a rotor (3) supported in said pump housing (2a, 2b) and rotatable upon receiving drive torque; a compression space (8) formed in said rotor (3) and connecting with passages for inflow and outflow of pressurized fluid; a plurality of plunger cylinders (6) formed in said rotor (3), said plunger cylinders (6) being provided on the same plane and extending from said compression space (8) in radial directions of said rotor (3); a plurality of plungers (7), each of which is provided in each of said plunger cylinders (6), capable of reciprocating slidably; and an inner cam (11) provided in said pump housing (2a, 2b) concentric with and around said rotor (3), and having cam surfaces provided on the inner side thereof for making said plungers (7) reciprocate upon rotation of said rotor (3); wherein each of said plungers (7) has a base end portion (7b) sliding in contact with the inner surface of said plunger cylinder (6) and a protruding portion (7a) provided at the end facing said compression space (8), the cross-section of said protruding portion (7a) becoming smaller toward the front end thereof, and a shoulder portion (7c) between the base end portion (7b) and the protruding portion (7a), characterized in that: the plungers (7) are all of substantially the same length and the protruding portion (7a) comprises at least two slanted surfaces (20, 21), the first slanted surface (20) further from the front end of the protruding portion (7a) having an inclination relative to the axis of the plunger (7) which is smaller than that of the second slanted surface (21) nearer to said front end, whereby the plungers (7) are made to collide toward the front ends of their protruding portions (7a), but not at the shoulder portions (7c) so that the sliding of the plungers is not substantially affected even if the colliding areas become deformed as a consequence of the collision of the plungers. An injection pump as claimed in Claim 1, characterized in that the inclination of said first slanted surface (20) is less than 45° and the inclination of said second slanted surface (21) is at least 45°. An injection pump as claimed in Claim 1 or 2, characterized in that said first and second slanted surfaces (20, 21) are curved surfaces formed circumferentially in the radial direction of said plunger (7). An injection pump as claimed in Claim 1 or 2, characterized in that said first and second slanted surfaces (20, 21) are flat surfaces with both sides symmetrically relative to the axis of said plunger (7). An injection pump as claimed in Claim 1, characterized in that said protruding portion comprises a first slanted surface (22) extending from said shoulder portion (7c) with a specific angle relative to the axis of said plunger (7), a second slanted surface (23) extending from said first slanted surface (22) with a specific angle larger than said specific angle of said first slanted surface (22), and a third surface (24) extending from said second slanted surface (23) to said front end with a specific angle larger than said specific angle of the second slanted surface (23). An injection pump as claimed in Claim 5, characterized in that the angle of said first slanted surface (22) relative to said axis is less than 45° and the angles of said second and third slanted surfaces (23, 24) relative to said axis are at least 45°. An injection pump as claimed in Claim 5 or 6, characterized in that said first, second and third slanted surfaces (22, 23, 24) are curved surfaces formed circumferentially in the radial direction of said plunger (7). An injection pump as claimed in Claim 1, characterized in that said protruding portion is formed in a substantially hemispherical shape so that slant relative to the axis of said plunger (7) increases gradually. An injection pump as claimed in Claim 1, characterized in that said protruding portion includes an overhanging portion (25) formed in a specific position between said shoulder portion (7c) and said front end. An injection pump as claimed in Claim 1, characterized in that said protruding portion includes a cylindrical portion (28) formed by projecting with a specific width between said shoulder portion (7c) and said front end. An inner cam type injection pump, characterized in that plungers having the features defined in any one of the preceding claims and plungers without such features are provided alternately in a circumferential direction of said inner cam.

Inventors: KUBO KENICHI, NAKAMURA HISASHI, KUBO, KENICHI, NAKAMURA, HISASHI
Applicants: ZEXEL CORP, ZEXEL CORPORATION
Application year: 1996
Main classification: F02M41
IPC codes: F02M41