Delivery regulator for a fuel injection pump

The invention relates to an internal combustion engine injection pump provided with a regulator unit comprising a mobile valving element on which there act an actuator, elastic means, and the back-pressure of the fuel discharged by the pump on delivery interruption, in order to improve the response characteristics of the regulator unit.

With fuel injection pumps there must be associated a control device which 
regulates the fuel delivery as a function of the position of a control 
member controlled by the operator, and of the braking load applied to the 
internal combustion engine. 
This control device is commonly known as a speed governor, and is mostly 
constructed on mechanical or hydraulic principles. Certain drawbacks are 
however associated with these types of regulators. The main drawback is 
the timing delay due to the regulator frequency characteristics and the 
inertia of the injection pump control members. Moreover, complicated 
devices have to be added in order to perform other auxiliary functions 
(torque correction, maximum throughput limitation in accordance with the 
booster feed pressure, excess fuel on starting etc.). 
To obviate these drawbacks, various types of electrically or electronically 
controlled regulators have appeared in recent years, and which by acting 
on suitable actuators enable the most complicated regulation programmes to 
be fulfilled. 
In one of the known systems (Galan, U.S. Pat. No. 4,216,752), a rotating 
double valve distributor is used to discharge part of the delivery stroke 
effected by the pumping unit. This system is however costly and bulky due 
to the presence of two large electromagnets necessary to overcome the 
opposing force of an elastic return bar. 
Another known system (Mannhardt, U.S. Pat. No. 4,136,655) utilises the 
movement of an electrically controlled spool in order to deliver the fuel, 
but this does not represent true electronic regulation because the 
electrical signal does not undergo modulation, and the throughput is 
controlled by manual or automatic rotation of the spool. This system 
requires the presence of further valve means for preventing fuel delivery 
as the spool returns to its initial position. 
A further known system (Bosch, GB No. 2,034,400A) electrically determines 
the positioning of the throughput control member as normally done by 
current mechanical regulators, and has the same level of overall size and 
cost as these. 
Other systems (Lucas, GB No. 2,037,884A) directly control the opening 
timing of the injection valve by acting on the valve needle. These systems 
are however directly subjected to the high pressure necessary for 
injection, and must oppose its thrust. This requires large forces and 
consequent considerable size of the actuator solenoid. 
Finally, another system (Lucas Bryce) utilises the principle of a needle 
seal in order to discharge part of the working stroke of the pumping unit. 
However, this system is also subjected to high pressure, and must 
therefore comprise solenoids capable of considerable force. It must also 
be considered that this considerable force can quickly cause the loss of 
the perfect seal at the seat of the control needle. Finally, it should be 
noted that to ensure rapid delivery interruption in order to prevent 
injection dribbling or injector dripping, some of the aforesaid systems 
utilise the thrust obtained by robust elastic means, which must afterwards 
overcome the considerable load in returning to their initial position. 
This produces a further need for bulky high-energy control electromagnets. 
In order to obviate the influence of high pressure on the operating 
parameters of the electronic regulator device and of the relative loads, 
certain systems (FR No. 2,095,695, FR No. 2,188,065, and GB No. 2,076,561) 
appeared during the 1970's which used a cylindrical distributor provided 
with a high pressure balancing duct and connected to an electromagnet in 
order to selectively discharge the pump pressure chamber, thus determining 
the quantity of fuel delivered. 
Said systems attain the required object, but have the drawback of requiring 
robust elastic return means and thus powerful electromagnetic control 
devices in order to ensure rapid delivery interruption. The direct use of 
the electromagnet to open the discharge port and determine the cessation 
of injection, as provided by some systems, does not solve the problem 
because it requires the same thrust level in order to rapidly overcome the 
inertia resistance of the distributor. The object of the present invention 
is therefore to simply and conveniently solve the problem of effective and 
versatile electronic regulation of a fuel injection pump, using a system 
for rapidly interrupting injection which during its return to its initial 
position does not determine any thrust opposing the action of the actuator 
solenoid. 
To this end, the device uses a cylindrical shuttle mobile along its 
longitudinal axis and provided with ducts for balancing the high pressure 
in order to modify its thrust, the shuttle being disposed branching from 
the pressure chamber of a fuel injection pump, whether this be of single 
cylinder, in-line or distributor type, said shuttle being provided with 
electrical or mechanical control means which, in cooperation with elastic 
return means, move the transfer ports provided in the shuttle into a 
position corresponding with the connection duct to the injection pump, in 
order to put the pressure chamber of said pump into irregular 
communication with the low pressure chamber containing the pumping unit 
operating mechanisms. 
During the period in which the high and low pressure chambers are connected 
together, the pumped fuel is subjected to discharge during the rising 
stage of the pump piston, in order to control the injected fuel quantity, 
whereas during the piston falling stage, the fuel is fed to the pumping 
unit in order to improve its filling. 
In the basic version, delivery commencement remains constant and is 
determined by the pump pistion during its rising stroke covering one or 
more feed ducts present in the cylinder, whereas delivery termination is 
variable and is determined by the valve action of the shuttle which, by 
controlled movement from a first position to a second position, 
selectively connects the pump to discharge for the entire remaining rising 
period. 
As already stated, rapid and precise delivery interruption is necessary on 
termination of delivery in order to prevent injection dribbling or 
injector dripping, and therefore the invention is characterised by the 
presence of a back-pressure chamber fitted with a discharge jet and able 
to accelerate the movement of the shuttle valve during its opening of the 
port which connects to the pressure chamber of the fuel injection pump.

With reference to FIG. 1, the injection pump casing 1, shown in 
diagrammatic elementary form, contains a hydraulic head composed of a 
pumping element 2, a mobile regulator element or plunger 3, a 
back-pressure chamber 4, an orifice valve or orifice-disc valve 5 and a 
number of delivery valves 6 equal to the number of engine cylinders to be 
fed. 
The lower chamber 7 of the injection pump 1 is fed with fuel by a pump 8 
connected to the tank 9 and provided with an overpressure valve 10. By 
known mechanisms, not shown, the pumping element or piston 2 is driven 
with reciprocating and rotary motion to determine the fuel intake, pumping 
and distribution action in phase with the uncovering or covering of the 
feed and discharge ducts 11 and 12 and of the delivery ducts 13. The 
regulator element 3, formed as a plunger tightly slidable in a cylindrical 
housing 14 connected by the duct 12 to the injection pump pressure chamber 
15, moves longitudinally under the control of the energisation of the 
thrust solenoid 16 and the return spring 17, in order to effect a valve 
action between said pressure chamber 15 and the chamber 4 disposed 
downstream of the regulator element 3. For this purpose, the plunger 3 is 
provided in that surface facing the chamber 4, with an axial bore 18 which 
by way of a transverse bore 19 opens in a position corresponding with a 
sunken collar formed on said plunger 3. In order to prevent the thrust 
which originates from the high pressure existing in the pressure chamber 
15 during the delivery stage from preventing the movement of the regulator 
plunger 3, the connection duct 12 opens at the regulator end in the 
hydraulic thrust balancing chamber 20. 
The back-pressure chamber 4 is connected by the duct 21 and the 
orifice-disc valve 5 to the lower chamber 7 of the injection pump 1, into 
which the fuel fed by the pump 8 flows at low pressure. In order to 
illustrate the operation of the entire apparatus, it is advantageous to 
commence with the situation existing when the piston 2 is at its bottom 
dead centre. Under these conditions, the solenoid 16 is energised, and the 
regulator plunger 3 is displaced into its end position towards the 
back-pressure chamber 4. The connection between said chamber 4 and the 
pressure chamber 15 is therefore interrupted because the edge 22 of the 
plunger 3 has passed, in terms of its axial position, beyond the 
cooperating edge 23 of the balancing chamber 20, thus determining a 
sealing band of width h (see FIG. 2) between the plunger 3 and its 
cylindrical housing 14. 
In this situation, the fuel pumping stage commences when during the next 
rising stroke of the piston 2 the upper edge of said piston 2 completely 
covers the terminal section of the connection bore 11 to the low pressure 
chamber 7. The liquid compressed in the chamber 15 is then directed by the 
axial bore 24 and the distribution cavity 25 of the piston 2, towards one 
of the delivery ducts 13 and thus towards one of the injectors 26. 
The delivery stage terminates when, on de-energising the solenoid 16, the 
thrust spring 17 causes the regulator plunger 3 to move through a stroke 
equal to the width h of the annular sealing band. This is because from 
this position onwards there becomes created between the edge 23 of the 
balancing chamber 20 and the edge 22 of the plunger 3 an annular discharge 
section, the size of which increases as the regulator plunger 3 moves 
towards its rest position most distant from the chamber 4. 
Varying the instant of de-energisation of the solenoid 16 relative to the 
stroke of the piston 2 thus determines a corresponding variation in the 
quantity of fuel injected for each rising stroke of the piston 2. 
Electronic signal modulation can therefore enable the throughput programme 
most suitable for the requirements of the user to be chosen. This 
programme can comprise certain particular functions which are required at 
the present time in regulators (torque correction, supplementary feed for 
starting, etc.), and is perfectly suitable for accepting other information 
arriving from the various sensors, such as engine temperature, barometric 
pressure, booster feed pressure, etc. In order to accelerate the axial 
movement of the plunger 3 after the aforesaid discharge port has begun to 
be uncovered, and thus determine a rapid increase in the discharge 
cross-section and a consequent precise interruption of the fuel injection 
stage, the chamber 4 is provided downstream of the regulator plunger, and 
is connected to the low pressure chamber 7 by way of the orifice of the 
orifice valve 5. The volume of the chamber 4 is such that when the 
discharge port becomes uncovered, there is a rapid decompression of the 
zone subjected to high pressure, however the orifice contained in the 
valve 5 prevents the pressure in the chamber 4 falling rapidly to the low 
value existing in the chamber 7. The intermediate pressure which thus 
arises in the chamber 4 then presses against the front surface of the 
regulator plunger 3, and by supplementing the thrust of the spring 17 
determines a more rapid movement of said plunger 3, with a consequently 
more rapid increase in the high pressure discharge cross-section. During 
the first part of the falling stroke of the piston 2, the regulator 
plunger 3 remains in its rest position most distant from the back-pressure 
chamber 4, thus leaving the connection between the chamber 15 of the 
pumping element 2 and said chamber 4 open. The fuel contained in the 
injection pump chamber 7 can thus open (raise) the valve 5, overcoming the 
resistance of the weak return spring (unnumbered), to fill the pumping 
element 2 by way of the duct 21, the chamber 4, the bore 18 of the plunger 
3, the balancing chamber 20, and the duct 12. If the available time is 
short, the filling operation can be facilitated by providing in the top of 
the piston 2 suitable longitudinal cavities for connecting the chamber 15 
to the feed duct 11. Because of the piston rotation movement, these 
cavities become offset during the pumping element rising stroke, so that 
they are not connected to the duct 11. 
During the lower part of the pumping element intake stroke, the solenoid is 
again energised, and the regulator plunger overcomes the resistance of the 
thrust spring 17 to move firstly into a position closing the connection 
between the duct 12 and the back-pressure chamber 4, and finally into its 
end-of-stroke position close to said chamber 4, in order to restore the 
annular sealing band of width h between said plunger and the cylindrical 
bore 14. 
Because, as stated, the pumping piston 2 is in its intake stage, the 
plunger 3 during its return to its initial position close to the chamber 4 
encounters only the opposition of the spring 17. The necessary force and 
thus the size of the solenoid valve 16 are consequently small. 
In this manner, in accordance with the object of the invention, a system is 
provided for accelerating the opening of the discharge duct on termination 
of delivery without affecting the force required to restore the initial 
position of the mobile member. During the final part of the intake stroke 
of the piston 2, the connection between the chamber 15 and the auxiliary 
chamber 4 is interrupted, as already noted. The pumping element 2 can 
however complete the filling action through the duct 11. 
In this embodiment shown in FIG. 1, the regulator plunger 3 is driven by a 
solenoid electromagnet 16. This actuator can be replaced by equivalent 
mechanical means. Thus, a circular cam 30 (FIG. 2) or a frontal cam could 
be used connected for example to a motor 31 of the servo-controlled or 
stepping type. The cam 30 would then move the distributor in the sense of 
closing the connection bore to the pumping element chamber 15, whereas the 
spring 17, aided by the discharge back-pressure, would effect its rapid 
opening. 
A further modification of the regulator device comprises controlling the 
throughput by controlling the commencement of delivery, instead of the 
termination of delivery as described heretofore. This would thus be an 
injection system of variable delivery commencement and constant 
termination. 
One embodiment is shown in FIG. 3. The regulator plunger 3' keeps the 
connection between the pressure chamber 15 and the decompression chamber 4 
open for the entire pumping element intake period and for part of its 
rising stroke. The delivery is thus fed to discharge until the moment in 
which the cam 30 enables the plunger 3', operated by the return spring 17, 
to close the connection with the pumping element pressure chamber 15, thus 
enabling the injection stage to commence. The constant delivery 
termination is determined by the uncovering of a discharge duct by the 
pumping piston or by the attainment of the piston top dead centre. 
The use of an electronically controlled actuator system also enables fuel 
feed to be selectively excluded from one or more engine cylinders in order 
to obtain modular engine operation. In such a case, it is necessary only 
to nullify the electromechanical actuator energisation pulse corresponding 
to the determined cylinder so that all the fuel pumped during the piston 
rising stroke is discharged through the regulator valve 3, which is kept 
constantly open by the spring 17. It is apparent that throughput regulator 
devices according to the invention are applicable to any type of injection 
pump without leaving the scope of the invention. By way of example, FIG. 4 
shows the regulator device connected to the pressure chamber of a known 
distributor-type pump comprising opposing plungers 32, and FIG. 5 shows 
the same device applied to the element of an in-line injection pump. In 
these Figures, parts equivalent to those illustrated in the preceding 
Figures are given the same reference numerals. 
The plunger of the regulator element can assume different forms from those 
shown in the preceding Figures, but being substantially equivalent 
functionally, in particular with respect to the hydraulic thrusts which 
are required to act on it for correct operation. 
As shown in FIG. 6, the plunger edge can be constituted by the edge of the 
face of the piston 3, which cooperates with an edge of the chamber in 
which it moves.