Injection pump for diesel engines

An injection pump for a diesel engine has a pump cylinder with a pump piston slideably mounted therein. The piston has a broadened foot portion. A cam is mounted on the camshaft and a rocker arm is mounted on a pivoting axis and has a camshaft end and a pump-side end. Means are provided for holding the camshaft end of the rocker arm in substantial contact with the cam. The pump-side end of the rocker arm has contact means for contacting the piston and moving the piston in the cylinder as the rocker arm is pivoted. The contact means includes means for loosely coupling the pump-side end of the rocker arm to the foot portion of the piston.

The invention relates to an injection pump for a diesel engine with a pump 
piston, which is guided in the pump cylinder, has a broadened foot and is 
operated by means of a spring-loaded rocker arm driven by the camshaft. 
BACKGROUND OF THE INVENTION 
In the case of known injection pumps such as that described in EP-A-0 027 
441 having a camshaft drive, a linear roller tappet is provided between 
the piston of the pump and an actuating cam. The roller tappet is guided 
by means of a guide bushing and works against a compression spring, so 
that is maintains constant contact with the actuating cam. The pump 
piston, axially aligned with the guide bushing, is guided linearly in a 
pump cylinder. The linear guidance of the roller tappet is intended to 
avoid most of the lateral pressures on the pump piston. However, in 
practice, there is usually a certain amount of center offset between the 
linear guidance of the pump piston and that of the roller tappet. In 
addition, it is not possible to avoid slight lateral forces from acting on 
the pump piston, if for no other reason than that the linear guidance of 
the roller tappet also unavoidably has free motion. 
In the case of the known injection pumps of the aforementioned type, it is 
also a disadvantage that they have relatively large external dimensions. 
Accordingly, they cannot be used for all installations, particularly where 
available space is a factor. 
Furthermore, an injection pump is known from U.S. Pat. No. 1,451,228, in 
which the outer end of the piston of the pump is broadened by means of a 
screw-on head, on which an auxiliary roller acts. The auxiliary roller is 
mounted at the end of a rocker arm. Thus, the auxiliary roller makes 
reliable contact and the piston of the pump is held against it with a 
compression spring. 
With such an injection pump having no separate roller tappet with linear 
guidance, appreciable transverse forces act on the piston of the pump, 
which therefore requires a particularly long cylinder guidance. 
Also known is a driving mechanism for an injection pump, CH-A-348 289 in 
which a 3-arm rocker arm produces a positive connection between the 
camshaft and the piston of the pump. In the case of such an embodiment, 
for which the rocker arm works without spring loading, the interacting 
parts must be produced with the highest precision in the region of their 
contacting areas. As a result, manufacturing costs are particularly high. 
In addition, conventional types or engine construction do not permit the 
injection pump to be disposed directly on the camshaft. 
SUMMARY OF THE INVENTION 
With this as background, it is an object of the present invention, for an 
injection pump of the type named above, to avoid the large transverse 
forces acting on the piston of the pump and, at the same time, to simplify 
and thus reduce the cost of the construction of the piston guidance of the 
injection pump. 
It is a further object of the present invention to provide an injection 
pump of the above-mentioned type, which is simpler and therefore less 
expensive. Another object of the present invention is to reduce the number 
of individual components of such pump as much as possible and, moreover, 
to decrease the overall size. 
Pursuant to the present invention, these objects may be accomplished by 
providing such an injection pump wherein the pump-side end of the rocker 
arm interacts directly with the foot area of the pump piston and wherein 
the end of the rocker arm is formed by an auxiliary roller operating 
piston of the pump, the foot and the auxiliary roller being loosely 
connected on one another by a catch. 
With such an injection pump, constricted according to the principles of the 
present invention, there is no tappet drive for the piston of the pump and 
no associated linear guide nor the usual piston spring. Instead of an 
expensive and voluminous pump housing, there is now only the pump cylinder 
with the associated valve support. The entire pump component is now 
located in an appropriate borehole of the crankcase and is driven there by 
means of a rocker arm operated directly by the camshaft. Moreover, the 
camshaft end of the rocker arm is supported by a contacting spring, so 
that the rocker arm is always in contact with the actuating cam of the 
camshaft. The pump-side end of the rocker arm is loosely coupled by means 
of a catch with the foot end of the pump piston. Accordingly, there is no 
driving tappet for the pump piston and no group of components associated 
with the driving tappet such as the piston spring, guide bushing and the 
part of the housing surrounding these members. 
Experiments have shown that a piston pump, which is reduced to a few 
components in accordance with the present invention, having a pump piston 
coupled by means of a catch, and driven directly by a rocker arm, fully 
meets all the requirements particularly those relating to small diesel 
engines. 
A preferred embodiment of the present invention includes an auxiliary 
roller operating the piston of the pump and is provided at the pump-side 
end of the rocker arm. This auxiliary roller may preferably include an 
outer roller and an inner roller, which are tightly fitted coaxially 
inside on another so that any clearance between these rollers may be taken 
care of by a film of oil in the space between the rollers. By these means, 
the advantageous linear contact of the foot surface of the piston of the 
pump and the auxiliary roller can be maintained during the operation of 
the piston pump. 
A further feature of the present invention is the catch used for loosely 
coupling the rocker arm to the foot of the pump is fastened pivotally to 
the end of the rocker arm for installation purposes and, in the final 
installed position, grips behind a broadened foot of the piston of the 
pump with a baffle sheet in such manner, that the piston foot is 
accommodated between the baffle sheet and the auxiliary roller. In order 
to avoid friction and secondary bending, the foot is accommodated between 
the baffle sheet and the auxiliary roller with very little clearance. 
Another feature of the present invention is that the foot of the piston of 
the pump is constructed without the central projection customarily 
provided as a stop face and is replaced by corresponding broadening of the 
foot area (so called pressure sun), as a result of which an advantageous 
linear contact with the auxiliary roller is achieved.

Referring to the drawings and more particularly to FIG. 1, a rocker arm 3 
for driving an injection pump 4 cooperates with a camshaft 1 of the diesel 
engine. The camshaft 1 has a cam 2 mounted thereon. 
A crankshaft 5 is provided with a pinion gear 6 drawn in dashed lines, 
which engages with geared teeth 7, also drawn in dashed lines, to drive 
the camshaft 1. Aside from the rocker arm 3, rocker arms 8 and 9 for the 
inlet and exhaust valves, respectively, are also operated by the same cam 
2 of the camshaft 1. At its camshaft end, the rocker arm 3 has a 
counter-cam 10 for operating the injection pump 4. A compression spring 11 
is braced against the counter-cam 10 at the rocker arm 3. The compression 
spring 11 causes the counter-cam 10 to maintain constant contact with the 
cam 2 of the camshaft 1. Accordingly, the rocker arm 3 pivots about its 
engine-fast axis of rotation 12. The extension of the rocker arm 3 beyond 
the axis of rotation 12 is the pump-side end of the rocker arm which ends 
in a forked part 13 (see FIG. 2) at which an auxiliary roller 15 is 
mounted. The roller 15 has an outer roller 16 and an inner roller 17 so 
that it can rotate about a crossbolt 14. The lower end of the piston 19 of 
the pump is supported by means of broadened foot 18 on the auxiliary 
roller 15. The foot 18 is held with a small clearance of between 0.05 and 
0.1 mm between the auxiliary roller 15 and a catch 20, which is also 
mounted so that it can pivot about the transverse axis 14 and a baffle 
sheet 21 disposed on the upper side of the piston foot 18. 
The piston 19 of the pump is guided linearly in a surrounding pump cylinder 
22 having a borehole 23 for supplying fuel and a borehole 24 for a fuel 
return line. At the upper end of the piston 19 of the pump, as viewed in 
FIG. 1, the usual control curves 25 are provided, which are adjusted by a 
controller 26, shown in greater detail in the plan view of FIG. 2. 
Depending on the operating point of the engine, the piston 19 of the pump 
is pivoted about its longitudinal axis in the direction indicated by the 
double arrow 27 by means of a controller 26. The pivoting is accomplished 
by means of a push rod 28. An adjusting bolt 30 is accommodated between 
guide disks 29 and is attached to a swiveling member 31, member 31 is 
fixedly mounted on the piston 19. As the push rod is moved forward or 
backward (FIG. 2), the guide disks 29 move the adjusting bolt 30 forward 
or backward. This pivots the piston 18 in the desired direction as 
indicated by the arrows 27. 
The pump cylinder 22 is formed in the upper part as valve support with the 
valve 32, 33 and is seated in a borehole 34 of a pipe connection 35, which 
contains the fuel pressure line 36. 
The baffle sheet 21 of the catch 20 has openings 37 on one side, through 
which the piston foot 18 can be threaded, before the baffle sheet 21 is 
swiveled in the direction of the arrow 38 over the foot 18 into the 
indicated end position. 
Referring now to FIGS. 3 and 4, the catch 20 is made from a formed and 
punched metal sheet that comprises two side walls 40, 41 having bores 42, 
43 respectively, being coaxially arranged with the transverse axis 14. 
Both side walls 40, 41 are connected via the baffle sheet 21 having 
openings 37 through which the piston foot 18 of a piston 19 (shown in 
dotted lines) can be threaded. The catch 20 is pivotally supported by the 
roller 15 which goes through holes 42, 43. Thus, no additional connecting 
rod is needed to connect catch 20 to rocker arm 3.