GB2142986A - Distribution-type fuel injection pump - Google Patents

Abstract

A chamber (48) containing a portion of the distribution rotor (14) in which pumping plungers (22, 24) reciprocate is in constant communication with the inlet side of a fuel transfer pump (64) by a fuel passage (78). Fuel delivered by the transfer pump is supplied through a passage 46' which registers with charging ports (40) in the distributor rotor (14), as the latter rotates. <IMAGE>

Description

SPECIFICATION Distributor-type fuel injection pump The present invention relates to diesel distributortype fuel injection pumps, particularly of the socalled DPA or CAV type.

A DPA or CAV injection pump includes a pair of opposing pumping plungers mounted in a distributor rotor and adapted to follow an internal cam ring by way of rollers and roller shoes. The plungers are movable toward and away from each other, permitting fuel to enter an axial pasage of the distributor rotor and forcing it to be delivered through a delivery valve into an injection line.

The prior art fuel injection pump of this kind has a disadvantage that it tends to cause unintended variation of fuel delivery and therefore cannot provide stable fuel injection characteristics. Study has revealed that this is due to the fact that the rollers tend to leave the cam surfaces at the beginning of their outward movements along the return cam lobe portions and remain out of contact with the cam surfaces, i.e., tend to effect a so-called "jumping" action immediately after having travelled over the noses of the cam lobes and remain floating preventing the internal cam ring from controlling the positions of the plungers and causing unintended variation of plunger stroke.

In accordance with the present invention, there is provided a distributor-type fuel injection pump which comprises a drive shaft, a distributor rotor drivingly coupled with the drive shaft to rotate together therewith and having an axial passage and a plurality of radial passages branching off from the axial passage to form charging ports, an internal cam ring placed around the distributor rotor, a pair of axially opposing pumping plungers mounted in the distributor rotor in a manner two be movable toward and away from each other and transversely of the distributor rotor following the internal cam ring, the pumping plungers defining therebetween a plunger chamber in communication with the axial passage and variable in volume depending upon movement of the pumping plungers, a fuel transfer pump placed around the drive shaft and drivingly coupled with same, the transfer pump having an inlet side at which fuel is drawn thereinto and an outlet side at which fuel under pressure is discharged therefrom, means for defining a pump chamber which accommodates therein part of the distributor rotortogetherwith the pumping plungers and the internal cam ring, means for defining a first fuel passage providing constant communication between the pump chamber and the inlet side of the transfer pump, and means for defining a second fuel passage through which the charging ports are communicable one after another with the outlet side of the transfer pump as the distributor rotor rotates.

This structure is quite effective for overcoming the disadvantages noted above.

It is accordingly an object of the present invention to provide an improved distributor-type fuel injection pump which is free from the disadvantages noted above.

The features and advantages of the distributortype fuel injection pump according to the present invention will become more clearly appreciated from the following description taken in conjunction with the accompanying drawings, in which: Figure 1 is a sectional view of a prior art distributor-type fuel injection pump; Figure2 is a displacement-time diagram for pumping plungers utilized in the fuel injection pump of Figure 1, in combination with a velocity-time diagram and an acceleration-time diagram for same; Figure 3 is a schematic cross-section of a novel main portion of an embodiment of the present invention; Figure 4 is a fragmentary sectional view of a timer piston and its associated parts of the embodiment of Figure 3;; Figure 5 is a displacement-time diagram for pumping plungers utilized in the embodiment of Figure 3, in combination with an acceleration-time diagram for same and a pressure-time diagram for an axial passage of a distributor rotor utilized in the embodiment of Figure 3; Figure 6 is a schematic illustration of a novel main portion of a modified embodiment of the present invention; Figure 7 is a cross-section of an actual embodiment of Figure 6; Figure 8 is a fragmentary sectional view taken along the line VIII-VIII of Figure 7; Figure 9 is a fragmentary sectional view taken along the line IX-IX of Figure 7; Figure 10 is a fragmentary sectional view taken along the line X-X of Figure 9; and Figure 11 is a fragmentary sectional view taken along the line Xl-Xl of Figure 7.

Referring to Figures 1 and 2, description is first made to a prior art fuel injection pump for a better understanding of the inventive step of the present invention.

In Figure 1, there is shown a so-called DPA or CAV distributor-type fuel injection pump which includes a drive shaft 10 which is driven through a belt drive pulley 12 by an associated engine (not shown) and is rotatable at a speed synchronous with engine rpm.

The drive shaft 10 is drivingly coupled with a distributor rotor 14 which is journalled in a cylinder barrel 16. The distributor rotor 14 is formed with two transverse plunger chambers 18 and 20 in which two pairs of opposing pumping plungers 22 and 24 are axially movably disposed, respectively. The pumping plungers 22 and 24 are arranged in contact, at the outward ends thereof and through rollers 26 and 28 and roller shoes 30 and 32, with internal cam rings 34 and 36 so as to be driven thereby to move toward and away from each other as the distributor rotor 14 rotates.The distributor rotor 14 is also formed with an axial passage 38 communicating with the plunger chambers 18 and 20 and a plurality of radial branch passages branching off from the axial passage 38 to form a plurality of charging ports 40, a rotor discharge port 42 and a plurality of relief ports 44.

The charging ports 40 and relief ports 44 are respectively provided as many as cylinders of the associated engine and arranged circumferentially of the distributor rotor 14 with an equal interval. The charging ports 40 are communicable with a fuel passage 46 which is in turn in constant communication with a pump chamber 48 and which can be closed by a solenoid valve 50 through an ignition key. The rotor discharge port 42 is communicable with outlet ports 43 which are formed in the cylinder barrel 16 as many as the associated engine cylinders and which are respectively connected to delivery valves 52 which are in turn to be connected to injection nozzles (not shown). The relief ports 44 are communicable with a cut-off port 54 which is formed in a control sleeve 56 movably mounted on the distributor rotor 14.In this connection, differing from the above description, the distributor rotor 14 may have only one relief port 44 which is communicable with a plurality of cut-off ports 54 formed in the control sleeve 56 as many as the engine cylinders.

The cut-off port 54 extends radially of the control sleeve 56 and has an end in constant communication with a control sleeve chamber 58 which is fluidly connected to the pump chamber 48 through a communication passage 60 formed in the cylinder barrel 16 and the other end with which the relief ports 44 come in registry one after another as the distributor rotor 14 rotates. Axial movement of the control sleeve 56 relative to the distributor rotor 14 is controlled by a governor mechanism 62, whereby to variably control the timing at which one of the relief ports 44 comes in registry with the cut-off port 54 to complete fuel delivery or injection.A vane type fuel transfer pump 64 revolves together with the drive shaft 10 on a common axis and has a low pressure chamber 66 fluidly connected through an inlet port 68 and through a fuel inlet valve (not shown) to a feed pump (also not shown) and a high pressure chamber 70 fluidly connected through an outlet port 72 to the pump chamber 48. The high pressure chamber 70 is also communicated with a pressure regulating chamber (not shown) having a pressure regulating valve for bypassing excess fuel back to the inlet side of the transfer pump 64 so that pressure of fuel to be transferred to the pump chamber 48, i.e., transfer pressure increases with engine rpm.

The internal cam rings 34 and 36 are operatively connected to respective timer pistons 74 and 76 so that the angular positions of the cam rings 34 and 36 are variably controlled in accordance with engine rpm.

In operation, the pumping plungers 22 and 24 are subject to centrifugal force and urged thereby against the cam surfaces. As the rollers 26 and 28 move along the return cam lobe portions toward the "valley" between the cam lobes, the plunger 22 and 24 move outward by the effect of the centrifugal force.

As the distributor rotor 14 revolves, one of the charging ports 40 comes in registry with the fuel passage 46, permitting fuel to enter the axial passage 38. By the effect of the foregoing centrifugal force, the plungers 22 and 24 are forced outward for a distance proportional to the quantity of fuel to be injected on the following stroke. As the distributor rotor 14 continues to revolve, the charging port 40 closes and the rotor discharge port 42 comes in registry with one of the outlet ports 43. The rollers 26 and 28 then come in contact with the opposing cam lobes, forcing the pumping plungers 22 and 24 inward or toward each other. Fuel trapped between the pumping plungers 22 and 24 is forced from the pump through the outlet port 43 and one of the delivery valves 52 into an injection line.Delivery continues until one of the relief ports 44 comes in registry with the cut-off port 54 formed in the control sleeve 56. When coming in registry with the cut-off port 54, the relief port 44 permits the fuel in the axial passage 38 to be discharged into the control sleeve chamber 58, whereby to complete fuel delivery or injection.

The prior art fuel injection pump of the above described kind has a disadvantage that it tends to cause unintended variation of fuel delivery and therefore cannot provide stable fuel injection characteristics. Study has revealed that this is due to the fact that the rollers tend to leave the cam surfaces at the begining of their outward movements along the return cam lobe portions and remain out of contact with the cam surfaces, i.e., tend to effect a so-called "jumping" action immediately after having travelled over the noses of the cam lobes and remain floating, preventing the internal cam ring from controlling the positions of the plungers and causing unintended variation of plunger stroke.It is further revealed that such a "jumping" action results from the fact that the forgoing centrifugal force acting on each pumping plunger 22 or 24 becomes smaller than the sum of inertia of the corresponding plunger, roller and roller shoe at a particular cyclic part of plunger displacement where the plunger begins to move along the return cam lobe portion after having been displaced maximumly inward and decelerated maximumly as seen from Figure 2. In other words, at the begining of intake stroke of the pumping plungers 22 and 24, it is only a centrifugal force that urges the plungers 22 and 24 against the cam surfaces. Such a centrifugal force tends to become insufficient for keeping the plungers 22 and 24 in contact with the cam surfaces during the initial stage of intake stroke where the plungers are nearly maximumly decelerated.

Such disadvantages and shortcomings of the prior art fuel injection pump can be overcome by the present invention which will be described hereinaftes with reference to Figures 3 to 11 in which parts and portions like or corresponding to those of the prior art fuel injection pump of Figure 1 are designated by the same reference numerals as their corresponding parts and portions. Slightly modified parts and portions are designated by like reference numerals as their corresponding parts and portions, with prime marks added.

Figures 3 and 4 show a novel main portion of a distributor type fuel injection pump according to an embodiment of the present invention.

Referring to Figure 3, the fuel injection pump of this invention comprises a vane type fuel transfer pump 64 having a low pressure chamber 66 and a high pressure chamber 70, as is conventional.

According to the present invention, the low pressure chamber 66 is communicated with a pump chamber 48 through a fuel passage 78, while the high pressure chamber 70 is adapted to be directly communicable with charging ports 40 only through a fuel passage 46'. To this end, the fuel passage 46' is formed to have an end in constant communication with the high pressure chamber 70 through an outlet port 72' and the other end with which the charging ports 40 come in registry one after another as a distributor rotor 14 revolves. The pump chamber 48 is communicated with a control sleeve chamber 58 through a communication passage 60.

With the above structure, fuel pressure in the pump chamber 48 is equal to that in the control sleeve chamber 58 and is maintained lower than transfer pressure (i.e., discharge pressure of the transfer pump 64). In this connection, it is to be noted that the prior art fuel injection pump of Figure 1 is constructed so that transfer pressure always prevails both in the pump chamber 48 and the control sleeve chamber 58.

Referring to Figure 4, the fuel injection pump of this invention also comprises a timer piston 74 which is associated at the opposed axial ends thereof with a high pressure chamber 78 and a low pressure chamber 80, as is conventional. According to the present invention, the high pressure chamber 78 is fluidly connected to the high pressure chamber 70 of the transfer pump 64 through a fuel passage 82 having a flow restriction (not shown), while the low pressure chamber 80 to the low pressure chamber 66 through a fuel passage 84. The timer piston 74 moves increasingly to the left in the drawing against a spring 86 as engine rpm increases, whereby to adjust injection timing to a proper one.

Exceptforthe above, the embodiment is substan tiallysimilartothe priorartfuel injection pump of Figure 1.

The operation will hereinafter be described with additional reference to Figure 5.

Referring to Figure 5, the relief port 44 opens at T1 and closes at T2. By the opening of the relief port 44, fuel pressure P2 in the axial passage 38 falls to become equal to PO where P0 is pump chamber pressure or control sleeve chamber pressure (i.e., fuel pressure prevailing in the pump chamber 48 or the control sleeve chamber 58). After the closure of the relief port 44, the axial passage pressure P2 further falls a little beyond the pump chamber or control chamber pressure P0 ancl thereafter rises to become equal to same. One of the charging ports 40 opens to communicate the fuel passage 46' at T3. By the opening of the charging port 40, the axial passage pressure P2 rises to become equal to transfer pressure P1.Each plunger 22 or 24 is thus subjected to a differential pressure between the transfer pressure P1 and the pump chamber pressure PO just after the opening of the charging port 40 and is kept urged against the cam surface by the differential pressure as well as the centrifugal force until the relief port 44 opens. By this, the plunger 22 or 24 is assuredly prevented from leaving the cam surface after the charging port 40 is brought into registry with the fuel passage 46', and accordingly a plunger stroke is not affected by the "jumping" action but can be precisely proportional to the quantity of fuel required for the next injection stroke.

In Figures 6 to 11, a modified embodiment of the present invention is shown. Of the Figures, Figure 6 gives a schematic illustration of a novel main portion of the modified embodiment and Figures 7 to 11 give an actual illustration of the same embodiment.

In this embodiment, a high pressure chamber 70 of a vane type fuel transfer pump 64 is adapted to be communicable with charging ports 40 through an outlet port 72', fuel passage 88, control sleeve chamber 58' and fuel passage 90. To this end, the fuel passage 88 has opposed ends in constant communication with the high pressure chamber 70 and the control sleeve chamber 58', respectively, and the fuel passage 90 has an end in constant communication with the control sleeve chamber 58' and the other end with which the charging ports 40 come in registry one after another as a distributor rotor 14 revolves.

The fuel passage 88 has at the transfer pump side end thereof a pressure regulating chamber 92 which is communicated with a low pressure chamber 66 of the transfer pump 64 through a fuel passage 94 having a fuel inlet chamber 96. A pressure regulating valve 98 is disposed in the fuel passage 94 to bypass excess fuel back to the inlet side of the transfer pump 64 and is designed so that pressure increases with engine rpm.

A high pressure chamber 70 at an axial end of a timer piston 74 is communicated with the control sleeve chamber 58' through a fuel passage 100, while a low pressure chamber 72 at the other axial end of same is communicated with a pump chamber 48 through a fuel passage 102. The pump chamber 48 is communicated with the low pressure chamber 66 of the transfer pump 64 similarly to the previous embodiment.

With the above structure, transfer pressure always prevails in the control sleeve chamber 58'. Accordingly, fuel pressure in the control sleeve chamber 58' is maintained higher than that in the pump chamber 48.

In operation, a relief port 44 opens to cause fuel pressure P2 in an axial passage 38 of the distributor rotor 14 to fall for thereby completing fuel delivery or injection. In this connection, differing from the prior art pump, the axial passage pressure P2 does not fall to become equal to pump chamber pressure PO but control sleeve chamber pressure P1. By this, each plunger 22 or 24 is urged against a cam surface by a differential pressure between the transfer pressure P1 and the pump chamber pressure P0 in addition to the centrifugal force at the begining of its outward movement as well as at the end of its inward movement. The plunger 22 or 24 is thus assuredly prevented from leaving the cam surface and can be precisely proportional to the quantity of fuel re quiredforthe next injection stroke.

Claims (7)

1. A distributor-type fuel injection pump comprising: a drive shaft; a distributor rotor drivingly coupled with said drive shaft to rotate together therewith and having an axial passage and a plurality of radial passages branching off from said axial passage to form charging ports; an internal cam ring placed around said distributor rotor; a pair of axially opposing pumping plungers mounted in said distributor rotor in a manner two be movable toward and away from each other and transversely of said distributor rotor following said internal cam ring, said pumping plungers defining therebetween a plunger chamber in communication with said axial passage and variable in volume depending upon movement of said pumping plungers;; a fuel transfer pump placed around said drive shaft and drivingly coupled with same, said transfer pump having an inlet side at which fuel is drawn thereinto and an outlet side at which fuel under pressure is discharged therefrom; means for defining a pump chamber which accommodates therein part of said distributor rotor together with said pumping plungers and said internal cam ring; means for defining a first fuel passage providing constant communication between said pump chamber and said inlet side of said transfer pump; and means for defining a second fuel passage through which said charging ports are communicable one after another with said outlet side of said transfer pump as said distributor rotor rotates.

2. A distributor-type fuel injection pump as set forth in claim 1,furthercomprising: a control sleeve mounted on said distributor rotor and having a radial cut-off port; means for defining a control sleeve chamber which accommodates therein part of said distributor rotor together with said control sleeve; and means for defining a third fuel passage providing constant communication between said pump chamber and said control sleeve chamber; in which said radial passages of said distributor rotor further form a plurality of relief ports which come in registry one after another with said cut-off port as said distributor rotor rotates; in which said control sleeve is operative to close said relief ports and axially movable on said distributor rotor to control timing at which said axial passage is brought into communication with said control sleeve chamber through one of said relief ports and said cut-off port; and in which said second fuel passage has an end in constant communication with said outlet side of said transfer pump and the other end with which said charging ports come in registry one after another as said distributor rotor rotates.

3. A distributor-type fuel injection pump as set forth in claim 1, further comprising: a control sleeve mounted on said distributor rotor and having a radial cut-off port; means for defining a control sleeve chamber which accommodates therein part of said distributor rotor together with said control sleeve; and means for defining a fourth fuel passage having an end in constant communication with said control sleeve chamber and the other end with which said charging ports come in registry one after another as said distributor rotor rotates; in which said radial passages of said distributor rotor further form a plurality of relief ports which come in registry one after another with said cut-off port as said distributor rotor rotates; in which said control sleeve is operative to close said relief ports and axially movable on said distributor rotorto control timing at which said axial passage is brought into communication with said control sleeve chamber through one of said relief ports and said cut-off port; and in which said second fuel passage providing constant communication between said outlet side of said transfer pump and said control sleeve chamber.

4. A distributor-type fuel injection pump as set forth in claim 2, further comprising: a timer piston operatively connected to said internal cam ring and associated at the opposed axial ends thereof with a high pressure chamber and a low pressure chamber; in which said high pressure chamber is communicated with said outlet side of said transfer pump, while said low pressure chamber with said inlet side.

5. A distributor-type fuel injection pump as set forth in claim 3, further comprising: a timer piston operatively connected to said internal cam ring and associated at the opposed axial ends thereof with a high pressure chamber and a low pressure chamber; in which said high pressure chamber is communicated with said control sleeve chamber, while said low pressure chamber with said pump chamber.

6. A distributor-type fuel injection pump as set forth in claim 2 or 3, further comprising: means for defining a plurality of outlet ports; in which said radial passages of said distributor rotor further form a discharge port which comes in registry with said outlet ports one after another as said distributor rotor rotates.

7. A distributor-type fuel injection pump constructed and arranged substantially as described herein with reference to Figures 3 to 5, or Figures 6 to 11 of the accompanying drawings.