Overflow valve for distributor-type fuel injection pumps

An overflow valve is provided in a distributor-type fuel injection pump, for returning excess fuel from the suction chamber of the pump to a lower pressure zone in the pump. The valve comprises a passage communicating with the suction chamber, a check valve arranged within the passage and operable in response to the suction chamber pressure for closing and opening the same passage, and throttle forming means formed by the passage and the check valve. The valve body of the check valve has a pressure-applying surface on which the suction chamber pressure acts in the valve-opening direction, and which assumes a larger surface area when the valve is in an open position than when it is in a closed position. The check valve is closed at the start of the engine to increase the suction chamber pressure so that the timing device of the fuel injection pump acts to advance the fuel injection timing.

BACKGROUND OF THE INVENTION 
This invention relates to an overflow valve for use in a distributor-type 
fuel injection pump. 
Internal combustion engines, particularly Diesel engines with divided 
combustion chambers have some difficulties in starting at low 
temperatures. As a starting aid, a glow plug has conventionally been used, 
which preheats the intake air. Besides such starting aid, the timing 
device of the fuel injection pump is adapted to advance the fuel injection 
timing at the start of the engine, to thereby improve the startability of 
the engine as well as reduce emission of hydrocarbons from the engine. A 
timing device provided in a distributor-type fuel injection pump is 
generally designed to be controlled by fuel pressure within the suction 
chamber of the fuel injection pump. However, according to such a timing 
device, at the start of the engine, the rotational speed of the engine is 
so low that the suction chamber pressure is not yet increased to a level 
sufficient for the timing device to obtain a required advance in the fuel 
injection timing. That is, the suction chamber is supplied with fuel 
pumped by a feed pump which is driven by the engine, and therefore the 
suction chamber pressure varies in proportion to the rotational speed of 
the engine so that the timing device responsive to the suction chamber 
pressure eventually operates in response to the rotational speed of the 
engine. Therefore, it is necessary to control the fuel injection timing 
for improvement of the startability of the engine so as to advance same 
independently of the rotational speed of the engine upon and immediately 
after the start of the engine. 
To comply with such requirement, a timing device has been proposed by 
Japanese Provisional Utility Model Publication No. 55-49078, which is 
adapted to advance the fuel injection timing at the start of an internal 
combustion engine. According to this proposed timing device, an auxiliary 
piston is arranged on an extension of the axis of the timer piston of the 
timing device for urging contact therewith by the force of an auxiliary 
spring. One end of the auxiliary piston cooperates with an opposed end of 
the timer piston to define a pressure chamber supplied with fuel having 
pressure variable as a function of the rotational speed of the engine from 
the suction chamber of a fuel injection pump associated with the timing 
device. When the pressure of fuel supplied into the pressure chamber is 
low at the start of the engine, the auxiliary spring urgingly biases the 
timer piston in the injection timing-advancing direction, to thereby 
obtain an advance in the injection timing. Then, as the pressure within 
the suction chamber increases with an increase in the engine rotational 
speed, the auxiliary piston is moved by correspondingly increased pressure 
within the pressure chamber against the force of the auxiliary spring, 
accompanied by movement of the timer piston in the injection 
timing-retarding direction by the force of a timer spring urging same 
toward the auxiliary piston, to retard the fuel injection timing. After 
this, as the engine rotational speed further rises to cause a further 
corresponding increase in the suction chamber pressure, correspondingly 
increased pressure within the pressure chamber causes movement of the 
auxiliary piston to its most receded position while compressing the 
auxiliary spring, and thereafter a further increase in the engine 
rotational speed causes movement of the timer piston in the injection 
timing-advancing direction against the force of the timer spring, whereby 
injection timing control is effected in response to the varying engine 
rotational speed. 
However, the above proposed timing device is inevitably large in size and 
complicated in structure due to the structural disadvantage that the timer 
piston is directly driven by the auxiliary piston arranged in line 
therewith to obtain an initial starting advance in the injection timing, 
requiring a large mounting space and a large manufacturing cost. 
As another measure for obtaining an initial starting advance in the 
injection timing, if the setting pressure of a pressure-regulating valve 
for regulating the pressure of fuel supplied into the suction chamber is 
set at a larger value than a usual value, an advance can be obtained in 
the injection timing at the start of the engine. However, according to 
this another measure, the timing device is kept in the injection 
timing-advancing position even after the starting condition of the engine 
is over, and then the injection timing cannot be controlled to best values 
appropriate to the rotational speed of the engine. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an overflow valve for use in a 
distributor-type fuel injection pump, which is adapted to cause a 
substantial increase in the suction chamber pressure at the start of the 
engine so as to improve the startability of the engine, etc., thereby 
making it unnecessary to use starting injection timing-advancing means 
mounted on the timing device. 
It is a further object of the invention to provide an overflow valve 
provided with the above-mentioned starting injection timing-advancing 
function, for use in a distributor-type fuel injection pump, which is 
simple in structure and low in manufacturing cost. 
It is another object of the invention to provide a distributor-type fuel 
injection pump which is equipped with an overlfow valve provided with the 
above-mentioned starting injection timing-advancing function. 
According to the invention, there is provided an overflow valve for use in 
a distributor-type fuel injection pump for an internal combustion engine, 
having a suction chamber filled with fuel variable in pressure as a 
function of the rotational speed of the engine, and a timing device 
operable in response to the pressure of the fuel within the suction 
chamber for advancing the fuel injection timing of the fuel injection pump 
with an increase in the pressure of the fuel within the suction chamber. 
The overflow valve serves to return excess fuel from the suction chamber 
to a zone under lower pressure of the fuel injection pump, and comprises: 
a passage having one end communicating with the suction chamber and 
another end communicating with the above lower pressure zone; a check 
valve arranged within the above passage and responsive to the pressure of 
the fuel within the suction chamber for closing and opening the same 
passage; and means for forming a throttle in the above passage when the 
check valve is in an open position. The check valve has a valve body 
having a pressure-applying surface area on which the pressure of the fuel 
within the suction chamber acts in a direction of opening the check valve, 
and which assumes a first surface area when the check valve is in a closed 
position, and a second surface area larger than the first surface area 
when it is in an open position. 
The above and other objects, features and advantages of the invention will 
be more apparent from the ensuing detailed description taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION 
Details of the invention will now be described with reference to the 
drawings. 
Referring first to FIG. 1, there is illustrated a distributor-type fuel 
injection pump provided with an overflow valve according to an embodiment 
of the invention. The fuel injection pump 1 is provided with a supply 
pump, not shown, incorporated therein and disposed to be driven by a drive 
shaft 3 which is in turn driven by an engine, not shown, to rotate at 
speeds as a function of the rotational speed of the engine. The supply 
pump is operable to pump fuel out of a fuel tank, not shown, and supplies 
the pumped fuel into a suction chamber 4 defined within the housing 2 of 
the fuel injection pump 1. Therefore, the pressure within the suction 
chamber 4 is variable as a function of the rotational speed of the engine. 
An overflow valve 5, details of which will be described later, is mounted 
on a ceiling wall 2a of the housing 2, to return excessive part of the 
fuel within the suction chamber 4 to the fuel tank. 
A plunger 20 has an end portion slidably received within a plunger barrel, 
not shown, mounted within the housing 2 and carries a cam plate 21 secured 
to the other end thereof. The cam plate 21 has a camming end face kept in 
urging contact with rollers 22a carried by a roller holder 22 slightly 
rotatably fitted on an end of the drive shaft 3, by the force of a plunger 
spring, not shown. The other end of the plunger 20 is coupled to the above 
end of the drive shaft 3 by means of a driving disc, not shown, interposed 
therebetween. Thus, the plunger 20 is rotatable about its own axis in 
unison with the drive shaft 3, with simultaneous axial reciprocating 
motions due to the rolling engagement of the rollers 22a with the cam 
plate 21, to thereby compress fuel introduced into a pump working chamber, 
not shown, from the suction chamber 4, at predetermined angular positions 
thereof, and successively deliver same to fuel injection valves, not 
shown, of the engine. 
A regulating collar 22 is slidably fitted on the plunger 20, connected to a 
control lever 26 through a tensioning lever 24 and a governor spring 25, 
and engaged by an end face of a sliding sleeve 31 of a centrifugal 
governor 30 through a starting lever 27. The centrifugal governor 30 has a 
toothed gear 32 meshing with another toothed gear, not shown, rigidly 
fitted on the drive shaft 3 to be rotatatively driven thereby. The sliding 
sleeve 31 is axially slidably fitted on a governor shaft 33 supported by 
the toothed gear 32 and has an end face disposed in urging contact with 
the starting lever 27 and the other end face urgedly engaged by a pair of 
flyweights 34 which are mounted on the toothed gear 32 for rotation in 
unison therewith and are radially expandable in response to its own 
centrifugal force produced during their rotation. Thus, the sliding sleeve 
31 is axially movable by the flyweights 34 radially displaced as a 
function of the rotational speed of the engine, to thereby control the 
position of the regulating collar 22 relative to the plunger 20 through 
the action of the starting lever 27. The regulating collar 22 is also 
controlled in position in response to the angular position of the control 
lever 26 through the actions of the governor spring 25 and the tensioning 
lever 24. Thus, the quantities of fuel supplied to the fuel injection 
valves are controlled. 
As shown in FIG. 2, a timing device 40 is arranged beneath the roller 
holder 22 in the housing 2. In the timing device 40, a timer piston 41 is 
coupled to a lower portion of the roller holder 22 by means of a coupling 
rod 42. The timer piston 41 is formed therein with a hole 41a in which the 
coupling rod 42 is pivotally engaged, as well as an orifice passage 41c 
communicating at one end with the hole 41a and terminating at the other 
end in an end face 41b of the timer piston 41. A pressure chamber 43 is 
defined between the above end face 41b of the piston and an opposed 
internal surface of the housing 2. Thus, pressurized fuel within the 
suction chamber 4 is introduced into the pressure chamber 43 through the 
hole 41a and the orifice passage 41c. A returning timer spring 44 is 
interposed tautly between the other end face 41d of the timer piston 41 
and an opposed internal surface of the housing 2, and urges the timer 
piston 41 in the rightward direction as viewed in FIG. 2. 
The timer piston 41 is moved leftward or rightward in FIG. 2 in response to 
the difference between the fuel pressure within the pressure chamber 43 
transmitted from the suction chamber 4 through the orifice passage 41c and 
the urging force of the timer spring 44, to cause rotation of the roller 
holder 22 in an injection timing-advancing direction indicated by the 
arrow A in FIG. 2 or in the opposite injection timing-retarding direction 
indicated by the arrow B in the same figure. When the roller holder 22 is 
rotated in the direction of the arrow A, the timing of starting the fuel 
delivery by the plunger 20 to the fuel injection valves is advanced, 
whereas if the roller holder 22 is rotated in the direction of the arrow 
B, the same timing is retarted. 
The overflow valve 5 is constructed as shown in FIG. 3. A holder 6 of the 
overflow valve 5 has a bottom portion 6a in the form of an annular flange, 
which is rigidly joined to the outer surface of the ceiling wall 2a of the 
housing 2 by means of fastening bolts 14. The holder 6 is formed along its 
axis with a valve bore 6c having a circular cross section and opening in 
an upper end face 6b of the holder 6 which is closed by a cap 7 threadedly 
fitted in the valve bore 6c. Movably arranged within the closed valve bore 
6c is a ball 8 in a manner spaced from the inner peripheral surface of the 
valve bore 6c by a small clearance. A coil spring 9 is interposed between 
the ball 8 and a lower end face 7a of the cap 7 and urges the ball toward 
a bottom surface 6c' of the valve bore 6c. The holder 6 has its lower 
portion 6d formed along its axis with a small bore 6e having a 
predetermined inner diameter much smaller than that of the valve bore 6c 
and disposed in concentricity with the valve bore 6c, as well as a hole 6f 
having a larger inner diameter, continuing from the small bore 6e in 
concentricity therewith and opening in a lower end face of the bottom 
portion 6a. The hole 6 f is aligned with a through hole 21b formed through 
the ceiling wall 2a of the housing 2 and thus communicates with the 
suction chamber 4 within the housing 2 through the hole 21b. Formed in the 
peripheral wall portion of the holder 6 at a predetermined location is a 
through hole 6g as an overflow passage, in which is fitted an end of a 
connection pipe 11 leading to a lower pressure zone in the pump 1, for 
instance the fuel tank. The cap 7 has an extension 7b with a smaller 
diameter from the lower end face 7a, around which is fitted the coil 
spring 9. 
The ball 8 is disposed within the valve bore 6c in such a manner that its 
outer surface defines an annular space 13 as a throttle passage in 
cooperation with the inner peripheral surface of the valve bore 6c. The 
outer diameter of the ball 8 is set at a value much larger than the inner 
diameter of the small bore 6e. The spring 9 has one end disposed in urging 
contact with the ball 8 and the other end with a shim 12 with a 
preselected thickness fitted on the extension 7b of the cap 7 in urging 
contact with the lower end face 7a of the cap 7, urging the ball 8 with a 
certain force against an opposed open end 6e' of the small bore 6e. In the 
illustrated state, the ball 8 is seated on the open end 6e' of the small 
bore 6e to close same. Thus, the ball 8 and the spring 9 cooperatively 
form a check valve. The outer diameter of the ball 8, the inner diameter 
of the open end 6e' of the small bore 6e, the clearance of the throttle 
passage 13 between the inner peripheral surface of the valve bore 6c and 
the outer surface of the ball 8, and the urging force or setting load of 
the spring 9 are set at such respective values as to obtain a suction 
chamber pressure characteristic required for achieving an optimum 
injection timing characteristic relative to the rotational speed of the 
engine. For instance, the inner diameter of the open end 6e' of the small 
bore 6e and the setting load of the spring 9 are set at such respective 
values that the check valve can be kept closed within a low engine speed 
range from 0-400 rpm. 
With the above described arrangement, when the engine is at rest, the 
pressure P within the suction chamber 4 assumes a value of zero, wherein 
the ball 8 is positioned in urging contact with the bottom face 6c' of the 
valve bore 6c, closing the open end 6e' of the small bore 6e by the force 
of the spring 9. The setting pressure of the pressure regulating valve 
previously referred to, which is mounted within the housing 2 for 
regulating the pressure of fuel pumped into the suction chamber 4 by the 
supply pump, is set at a certain value larger than that of a pressure 
regulating valve used in a conventional distributor-type fuel injection 
pump without an overflow valve according to the present invention. 
When the engine rotational speed is within a low speed range, e.g. 0-400 
rpm at the start of the engine, the check valve is kept closed wherein the 
ball 8 is in the above-mentioned seated position closing the small bore 
6e. On this occasion, there occurs no overflow of fuel from the suction 
chamber 4 so that the fuel pressure P within the suction chamber 4 
abruptly increases at a large rate as the engine rotational speed Np 
increases, as indicated by the curved line Ia in FIG. 5. In the closed 
position of the check valve, the ball 8 has a pressure-applying surface 
area S1 represented by .pi.d.sup.2/4. The ball 8 is kept closing the small 
bore 6e by the spring 9 until the suction chamber pressure P exceeds a 
predetermined valve opening pressure Pa preset by the spring 9 and the 
shim 10. 
Thereafter, as the engine rotational speed further increases so that the 
suction chamber pressure P correspondingly increases to exceed the 
predetermined valve opening pressure Pa, the ball 8 is urgedly displaced 
by the increased suction chamber pressure P against the force of the 
spring 9, and can be even brought into contact with the tip of the 
extension 7b, as shown in FIG. 4. Then, the small bore 6e is opened to 
allow part of the pressurized fuel within the suction chamber 4 to be 
drained through the small holes 6f, 6e, the annular throttle passage 13, 
the hole 6g, and the interior of the connection pipe 11 into the fuel 
tank. As a result, the suction chamber pressure P drops along the curved 
line Ib by an amount .DELTA.P in FIG. 5. On this occasion, the ball 8 has 
an increased pressure-applying surface area S2 represented by .pi.D.sup.2 
/4 (&gt;S1). Due to the increased pressure-applying surface area, the ball 8 
does not drop or drops through a very small stroke even if the suction 
chamber pressure P drops along the broken line in FIG. 5 so that the ball 
8 will never close the small bore 6e so long as the engine continues its 
operation, thereby always allowing suitable overflow of fuel from the 
suction chamber. After the suction chamber pressure P has dropped along 
the curved line Ib in FIG. 5, the suction chamber pressure P increases 
with a further increase in the engine rotational speed along the straight 
line Ic in FIG. 5 in accordance with a predetermined suction chamber 
pressure characteristic adapted to the operating characteristics of an 
engine applied, during normal operation. 
Since the overflow valve 5 according to the invention is thus adapted to 
make the overflow amount zero only at the start of the engine, while 
always allowing suitable overflow amounts when the engine is operating in 
other operating conditions, the suction chamber pressure can be elevated 
up to a required level so as to obtain a required advance in the fuel 
injection timing at the start of the engine, and can be controlled to 
proper values as a function of the rotational speed of the engine after 
the engine has shifted into normal operating conditions after the start 
thereof. Therefore, the engine can have improved startabilty, and during 
normal operation of the engine after the start, an optimum injection 
timing characteristic is available to thereby improve the output 
characteristics, emission characteristics, etc. of the engine. 
The sloping degree of the straight line Ic of the characteristic curved 
line I in FIG. 5 is determined by the cross-sectional area of the throttle 
passage 13 formed by the clearance between the inner peripheral surface of 
the valve bore 6c and the outer surface of the ball 8. Further, the drop 
amount .DELTA.P of the suction chamber pressure in FIG. 5 upon opening of 
the check valve is a function of the overflow amount, that is, it 
increases as the overflow amount increases. 
While a preferred embodiment of the invention has been described, 
variations thereto will occur to those skilled in the art within the scope 
of the present inventive concepts which are delineated by the following 
claims.