Distributor injection pump for internal combustion engines

A distributor injection pump for internal combustion engines includes a high pressure pump for generating fuel injection pressure, a slide valve for defining fuel amounts to be injected and a piezoelectric adjustment member which actuates via a control chamber filled with fuel the slide of the slide valve. To prevent fomation of bubbles in the control chamber a rinsing conduit is provided, connected to the control chamber to rinse the latter. The rinsing conduit includes one portion connected to a fuel supply line and the other portion connected to a fuel return line leading to a fuel container.

BACKGROUND OF THE INVENTION 
The present invention relates to a distributor injection pump for internal 
combusticn engines, particularly diesel motors. 
Known distributor injection pumps of the type under consideration have a 
hydraulic control chamber which is subdivided by an adjustment piston, 
actuated by an adjustment member, into two portions which are continually 
hydraulically pressurized. The adjustment piston has two throttle gaps 
through which both pressure chambers are in connection with each other and 
with an initial hydraulic pressure. A slide valve normally provided in 
such a pump has two control chambers arranged at two end faces of the 
control slide, which chambers are connected with one of the two 
aforementioned portions of the hydraulic control chamber. If an exiting 
voltage is applied to the piezoelectric adjustment member the latter 
expands and displaces the adjustment piston. Pressure rises in one 
pressure chamber in a sudden manner and decreases in the other pressure 
chamber, also in the sudden fashion. Pressure in the control chambers 
changes in the same manner. The control slide is adjusted by the 
difference in pressures and the valve opens. If the exiting voltage is no 
longer applied to the adjustment member the adjustment member is displaced 
in the opposite direction. Pressure ratios in the pressure chamber 
portions and thus in the control chambers interchange, and the control 
slide is again brought to the open position. 
The avoidance of the formation of gas bubbles in the pressure medium 
(diesel oil) of the hydraulic control chamber filled with fuel is obtained 
by that the pressure chambers are continually hydraulically prestressed. 
Due to a double-side acting adjustment piston, as opposed to one-side 
operating pistons, there is no danger that gas would drag in the pressure 
medium through the guidance gap. In order to overcome the problem of the 
length change of the piezoelectric adjustment member due to temperature 
fluctuations and various volume expansions of the pressure medium in the 
hydraulic control chamber the portions of the pressure chamber are 
connected to each other by a throttle gap; a hydraulic translation ratio 
of the cross-section of the piston to the cross-section of the control 
slide is greater than the ratio between the path of the control slide and 
the path of the piston, and the adjustment path of the control slide is 
limited by adjustable mechanical stops. 
As studies have shown, despite such construction expenses and extremely 
quick strokes of the control slide and piezoelectric adjustment member 
over a longer period of time, the occurence of gas bubbles in the pressure 
medium of the hydraulic control chamber can not be totally avoided as 
desired. Gas bubbles in the hydraulic control chamber cause not only 
changes in the length of the piezoelectric adjustment member due to 
temperature fluctuations but also to an undesired adjustment of the 
injection start and/or end and thereby amounts of fuel being injected. 
Thus the distributor injection pump does not operate optimally. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved distributor 
injection pump for internal combustion engines. 
This and other objects of the present invention are attained by a 
distributor injection pump for internal combustion engines, especially for 
diesel motors, comprising a high pressure pump alternatively operated in a 
suction phase for a fuel suction and a high pressure phase for generating 
a fuel injection pressure; a distributor for a series connection of the 
high pressure pump with aplurality of injection valves; a slide valve for 
determining an amount of fuel being injected, said slide valve having an 
inlet and an outlet and a control slide; a piezoelectric adjustment 
member; a control chamber provided between said adjustment member and said 
control slide for a hydraulic translation of an adjustment path of said 
adjustment member into displacement of said control slide; a housing; a 
fuel supply line; a fuel return line; and a rinsing conduit, said rinsing 
conduit including a first conduit portion connectable with said fuel 
supply line and opening into said control chamber and a second conduit 
portion connectable with said fuel return line, wherein a connection of 
said rinsing conduit with said fuel supply line and said fuel return line 
is established during the suction phase of the high pressure pump through 
said distributor. 
The distributor may include a distributor shaft rotating with said high 
pressure pump and having a periphery, said housing having openings 
arranged at and opening towards the periphery of said shaft, a first 
opening being in connection with said fuel supply line, a second opening 
being in connection with said first conduit portion, a third opening being 
in connection with said second conduit portion and a fourth opening being 
in connection with said fuel return line, said distributor shaft being 
formed at said periphery with at least two control grooves, respectively 
corresponding to and cooperating with said openings, and wherein in at 
least one of rotation positions of said distributor shaft one of said 
control grooves is connected to said first and said second openings and 
the other of said control grooves is connected to said third and said 
fourth openings. 
The advantage of the distributor injection pump of the invention resides 
not only in supressing the formation of gas bubbles to a much higher 
degree than known pumps of the foregoing type but also that the 
distributor injection pump can be substantially simpler in construction 
and thus less expensive. In place of high-priced double piston-slide 
valves a simple slide valve with a restoring spring can be used. An 
additional adjusting piston for generating two portions of the pressure 
chamber can be omitted. 
Due to a continual rinsing or scavenging of the hydraulic control chamber 
during each suction phase of the high pressure pump the latter can be 
bubble-free. 
Four openings may be arranged at said periphery pairwise, and a distance 
between said pairwise arranged openings, respectively, is selected so that 
upon rotation of said shaft a connection between said third and said 
fourth openings is temporarily interupted before the connection between 
said first and said second openings. 
If now, in accordance with the scavenging or rinsing of the hydraulic 
control chamber, the separation of the first conduit portion of the 
rinsing conduit from the fuel return line would temporarily take place 
before the separation of the second portion of the rinsing conduit from 
the fuel supply line, the control pressure built-up would be always 
reliably at the same pressure level, and the time of reversal movement of 
the control slide in the slide valve would be stable. 
Inasmuch as the control chamber is rinsed up or scavenged in each suction 
phase pressure compensation in the pressure medium is also obtained. The 
control pressure for the control slide in the slide valve builds up with 
each new energizing of the piezoelectric adjustment member. Thus changes 
in length of the piezoelectric adjustment member due to temperature 
fluctuations are completely compensated for and can not be unfavorably 
affect amounts of fuel being injected. 
The number of said control grooves may correspond to the number of said 
injection valves, said control grooves being spaced at said periphery by 
an equal rotation angle and each extending circumferentially of said shaft 
at the same rotation angle. 
Throttle means may be provided in the pump. 
The throttle means may be formed in said second conduit portion or in the 
fuel return line. 
The pump may further include a plate spring which limits said control 
chamber, said piezoelectric adjustment member being centrally secured to 
said spring. 
Due to the provision of the plate spring a favorable translation ratio of 
the adjustment path of the piezoelectric adjustment member to the path of 
displacement of the control slide is obtained. The plate spring serves as 
a prestressing spring of the adjustment member and replaces a customary 
sheet spring. The plate spring in contrast to a sheet spring is massive 
and friction-free and makes short switching periods possible. This spring 
also serves as a control chamber limitation and replaces a limiting piston 
connected to the adjustment member as utilized up till now. The plate 
spring is inexpensive and leackage-free. 
A pressure-limiting valve may be provided, which is in connection with said 
inlet. 
The control slide of said slide valve may be spring-loaded and connects 
said inlet and said outlet with each other in a non-controlled 
non-operative position and separates said inlet and said outlet from each 
other in a controlled operative position, said inlet being connected to 
said fuel supply line and said outlet being connected to said high 
pressure pump. 
The rotation movement of said distributor shaft and a control of said 
piezoelectric adjustment member are adjusted to each other so that a 
reversal of said control slide takes place only when said rinsing conduit 
is separated from said fuel supply line and said fuel return line. 
The novel features which are considered ad characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drawing illustrates the principle of the distributor injection pump 
which can be designed of any suitable embodiment. The distributor 
injection pump of the invention has a housing 10 which is shown as a 
portion in cross-section. The distributor injection pump is connected via 
a fuel supply line 11 with a fuel supply pump 12 and via a fuel return 
line 13 with a fuel container 14. The fuel supply pump 12 is connected in 
the known manner via a filter 15 with container 14. The distributor 
injection pump is connected via injection conduits with four injection 
valves of which only one injection conduit 16 and one injection valve 17 
are shown. 
A high pressure pump 18 and a distributor 19 are accommodated in the 
housing block 10. Both are illustrated in the drawing schematically. The 
distributor and the high pressure pump of this type have been known and 
disclosed, for example in EP-OS No. 0074550. 
The high pressure pump 18 has a pair of pistons of which only one piston 20 
is shown. Each piston 20 is supported by means of a compression spring 23 
against a roller pair 21 which is pressed against an inner cam surface of 
a cam ring 22 positioned in the housing block 10. Ring 22 together with 
roller pair 21 are shown as turned by 90.degree. in the plane of the 
drawing. Each piston 20 is guided in a radial bore 24 of a rotating body 
which is formed of one piece with a distributor shaft 25 of the 
distributor 19. Radial bores for two pistons are arranged diametrically 
opposite. 
The driven distributor shaft 25 is positioned in a bore 26 of the housing 
block 10 and has a central passage 27 which at the one side is in 
connection with a pressure chamber 28 of the high pressure pump 18 and at 
the other side with a distributor radial bore 29. Four injection channels 
are arranged as a star around the distributor shaft 25 in the plane of the 
distributor bore 29 in the housing block 10. Only one such injection 
channel 30 is shown in the drawing. The injection conduit 16 leading to 
the injection valve 17 is connected to the injection channel 30. During 
the rotation of the distributor shaft 25 the injection channel 30 becomes 
connected via the distributor bore 29 with the pressure chamber 28 of the 
high pressure pump 18, and a dosed amount of injected fuel is supplied to 
the respective injection valve 17. 
The pressure chamber 28 of the high pressure pump 18 is further connected 
via a slide valve 31 to the fuel supply 11. The slide valve 31 is 
integrated in the housing block 10. The slide valve has a valve inlet 32, 
a valve outlet 33 and a control slide 34 which, at the one side, is loaded 
with a restoring spring 35 and, at the other side limits a control chamber 
36, and is displaceable by a control pressure generated in chamber 36 
against the force of the restoring spring 35. The valve inlet 32 and the 
valve outlet 33 are connected to each other in the ground or inoperative 
position of the control slide 34 and are separated from each other in the 
controlled operative position. The valve inlet 32 is connected with the 
fuel supply line 11 while the valve outlet 33 is connected to the pressure 
chamber 28 of the high pressure pump. Furthermore, the inlet of a pressure 
limiting valve 37 also accommodated in the housing block 10 is connected 
to the valve inlet 32 while the outlet of the pressure limiting valve 37 
is connected to the fuel return line 13. 
The slide valve 31 is controlled by a piezoelectric adjustment or control 
member 39 which is comprised in the known manner of a piezo-stack 40, the 
restoring position of which is effected by a plate spring 43. The 
piezo-stack received in an inner chamber 42 formed in the housing block 10 
is supported against the bottom wall of the chamber 42 at one side, and is 
connected to the plate spring 43 centrally thereof at the other side. 
Spring 43 has a disc-shaped rim which is supported against an annular 
shoulder 44 of the inner chamber 42. The plate spring 43 limits a 
hydraulic control chamber 38 filled with fuel. Control chamber 38 is in 
connection with the control chamber 36 of the slide valve 31. 
An exiting voltage can be applied to the piezo-stack 40 via an connection 
conduit 45 whereby the length of the piezo-stack would be increased. 
The change in the length of the piezo-stack 40 and also an adjusting path 
of the piezoelectric control or adjustment member 39 is hydraulically 
translated via the hydraulic control chamber 38 into a displacement of the 
control slide 34 in the slide valve 31. The connection between the 
hydraulic control chamber 38 and control chamber 36 of the slide valve 31 
is identified in the drawing by a connection conduit 46. 
The distributor shaft 25 of the distributor 19 has, at the distance from 
the distributor bore 29, control grooves 47 which are spaced from each 
other at the circumference of the shaft by the same angle and which extend 
circumferentially over the same distance. The number of control grooves 47 
corresponds to the number of the injection valves 17 available, however 
with the provision of only one injection valve 17 two control grooves 47 
must be provided are provided. 
Four openings 48-51 are provided in the housing block 10 against the 
distributor shaft as in the same cross-sectional planes in which the 
control grooves 47 are formed. The openings or bore mouths 48-51 are 
formed pairwise. Each pair, namely pair of openings 48, 49 or pair of 
openings 50, 51 can be connected via the control grooves 47 and also 
substantially at the same time. By the respective selection of the 
distance between the openings 48, 49 on the one hand, and openings 50, 51, 
on the other hand, from each other, the connection between the opening 50 
and opening 51, upon the rotation of the distributor shaft 25 is 
temporarily established before the connection between opening 48 and 
opening 49 is interrupted. The opening 48 is in connection with the fuel 
supply line 11 through a bore or conduit 52, and opening 51 is in 
connection with the fuel return line 13 through a bore or conduit 53 in 
the housing block 10. A throttle 54 is provided in the bore 53. 
Openings 49 and 50 form the beginning and the end respectively, of a 
rinsing conduit 55 for the hydraulic control chamber 38 from which a bore, 
forming a first portion 56 of the rinsing conduit leads from the opening 
49 to the hydraulic control chamber 38, and a second bore, forming a 
second portion 57 of the rinsing conduit leads from the hydraulic control 
chamber 38 to the opening 50. 
The arrangement of control grooves 47 on the distributor shaft 25 as well 
as the arrangement of the cam ring 22 in the housing block 10 for the 
pistons 20 of the high pressure pump 18 are made relative to each other 
such that the connection of openings 48-51 via the control grooves 47 is 
always established then when the high pressure pump 18 is in its fuel 
suction phase and piston 20 is radially moved in the outward direction. 
Additionally, the control of the piezoelectric adjustment member is 
adjusted through the connection conduit 45 to the rotational movement of 
the distributor shaft so that the reversal of the control slide 34 in the 
slide valve 31 takes place only when the rinsing conduit 55 is separated 
from the fuel supply line 11 and fuel return line 13. This separation of 
the rinsing conduit 55 takes place at the time when the control grooves 47 
interrupt the connection between the pairwise openings 48, 49 and 50, 51. 
The mode of operation of the distributor injection pump of the invention is 
as follows: 
When the piezoelectric control or adjustment member 39 is non-energized the 
slide valve 31 takes the position shown in the drawing, which position is 
a non-operative position in which the valve inlet 32 and the valve outlet 
33 are connected to each other. In the exact rotation position of the 
rotatable distributor shaft 25 shown in the drawing, openings 48-51 are 
connected to each other through control grooves 47. Piston 20 of the high 
pressure pump 18 has already passed its outermost radial position so that 
the pressure chamber 28 and the open slide valve 31 are filled with fuel 
through the fuel supply line 11 and open slide valve 31 and thereby the 
fuel suction phase of the high pressure pump 18 has already ended. The 
rinsing conduit 55 becomes connected through the control grooves 47 with 
the fuel supply line 11 and the fuel return line 13, and the fuel required 
by the supply pump flows through the hydraulic control chamber 38 and 
passes via the throttle 54 and fuel return line 13 again into the supply 
container 14. The hydraulic control chamber 38 is thereby rinsed with fuel 
during the suction phase of the high pressure pump 18. 
As the distributor shaft 25 rotates further the connection between openings 
50 and 51 is first interrupted and later the connection between openings 
48 and 49 is also temporarily interrupted. An energizing voltage in form 
of direct voltage pulses is applied to the piezoelectric control member 
39, the duration of this voltage corresponding to the duration of 
injection. The piezo-stack 40 expands and displaces fluid volumes via the 
plate spring 43 acting as a diaphragm so that when the rinsing conduit 55 
is closed by the connection conduit 46, the displacement of the control 
slide 34 in the slide valve 31 is effected in the direction of the valve 
closing. When the slide valve 31 is closed the pressure limiting valve 37 
is also separated from the pressure chamber 28 of the high pressure pump 
18. An injection pressure is formed by the piston 20 of the pump 18 
sliding radially inwardly in the radial bore 24 and the injection valve 17 
connected to the pressure chamber 28 by the distributor bore 29 injects 
fuel due to that pressure. 
The application of direct voltage pulses is ended with the end of fuel 
injection. The piezo-stack 40 assumes under the action of the plate spring 
43 its initial length. Under pressure is established in the hydraulic 
control chamber 38, which underpressure together with the force of the 
restoring spring 35 moves the control slide 34 in the slide valve 31 in 
the direction of opening. When the slide valve 31 is open the pressure 
chamber 28 of the high pressure pump 18 is connected to the pressure 
limiting valve 37 and thereby pressure in the pressure chamber 28 is 
reduced in a sudden manner. The injection process is thereby ended. 
Upon a further rotation of the distributor shaft 25, piston 20 of the high 
pressure pump 18 moves again in the radial bore 24 radially outwardly. 
Thereby fuel is sucked through the open slide valve 31 into the pressure 
chamber 28. The connection to the injection valve 17 is interrupted, and 
the control grooves 47 again establish, via the connection of openings 
48-51, the connection of the rinsing conduit 55 to the fuel supply line 11 
and the fuel return line 13. The hydraulic control chamber 38 is again 
rinsed. 
As the distributor shaft 25 further rotates the above described process is 
repeated. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
distributor injection pumps differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
distributor injection pump for internal combustion engines, it is not 
intended to be limited to the details shown, since various modifications 
and structural changes may be made without departing in any way from the 
spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.