Governor for internal combustion engine

A speed governor for engine includes a variation removing circuit responsive to an engine rotational speed signal indicative of the rotational speed of a diesel engine to remove a periodical variation component of the signal due to the pulsation of the output torque which the diesel engine generates, from the signal. The period of the variation to be removed by the variation removing circuit changes with the change of the rotational speed of the engine. The variation removing circuit may be formed of a sample-and-hold circuit or a variable characteristic filter of which the suppression frequency is variable.

BACKGROUND OF THE INVENTION 
This invention relates to governors for internal combustion engine and 
particularly to a governor for an engine having a fuel injection pump, 
such as a diesel engine. 
The governor for a diesel engine adjusts the amount of injected fuel to be 
supplied to the diesel engine thereby controlling the rotational speed of 
engine. 
Various types of governor are classified in accordance with their mechanism 
such as mechanical or electronic, but these governors perform the same 
function, namely, to supply sufficient fuel to the engine for a desired 
engine speed. To perform this function, the desired engine speed furnished 
to the governor and the actual speed of the diesel engine are compared to 
produce a speed deviation from which an amount of injected fuel necessary 
for the actual engine speed to follow the desired speed in accordance with 
a predetermined relationship is determined by control and calculation such 
as proportion, integration and differentiation. The fuel adjusting 
plunger, or rack of the fuel injection pump is then regulated by a signal 
indicative of this determined amount of injected fuel. 
In the diesel engine, at each fuel injection timing an amount of fuel 
corresponding to the rack position of the fuel pump at the fuel injection 
timing at each cylinder is injected into corresponding cylinders and 
consumed to generate an output torque. However in a case where the fuel 
pump rack is operated by a governor, the control of engine speed is 
actually made by only the rack position of the fuel pump at the fuel 
injection timing at each cylinder. As a result, the variation of the rack 
position of the fuel pump between timings is not taken into consideration 
in the control of the engine speed. 
Also, in the diesel engine, since the output torque is generated by the 
explosion of intermittently injected fuel, thus torque pulsates in 
accordance with the number of explosions. That is, when the diesel engine 
of Z cylinders rotates at a rotation speed N (rpm), the output torque 
pulsates at the period of 60/N.multidot.Z (sec.) for a two-stroke engine, 
or at the period of 120/N.multidot.Z (sec.) for a four-stroke engine. As a 
result, the engine speed pulsates at the same period. 
The conventional governor of a diesel engine is not intended to control the 
periodical variation of engine speed due to the pulsation of the output 
torque generated by the diesel engine itself. Moreover, however the amount 
of injected fuel is adjusted by the governor, the output torque of the 
diesel engine cannot be prevented from pulsating. 
In addition, even if the governor controls the rack of the fuel pump in 
response to the periodical change of engine speed due to the pulsation of 
the output torque, it repeats only useless operation of the rack because 
the operation at a time other than the fuel injection timing is useless. 
Therefore, it is desired that the governor of diesel engine should not be 
affected by the periodical variation of engine speed due to the pulsation 
of the output torque generated from the diesel engine itself. In the 
conventional governor, however, any countermeasure effective against that 
problem is not made yet. 
A governor may be proposed in which a mechanical or electrical low-pass 
filter for the engine-speed signal is provided so that the governor does 
not respond to the periodical speed variation due to the pulsation of the 
output torque generated from the diesel engine itself. 
In such a governor, however, since the period of the engine-speed variation 
is changed in proportion to the rotational speed, the cut-off frequency of 
the low-pass filter must be decreased to remove the engine speed variation 
in the low engine speed range. Therefore, this governor arrangement 
suffers a deterioriation in its control ability at various engine speeds 
by the effect of phase lag in the low-pass filter, and as a result the 
control of the engine speed is apt to be unstable. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide a governor for an 
internal combustion engine capable of eliminating periodical variations of 
engine speed so that fuel injection control can be achieved to provide 
stable control of rotational speed. 
To accomplish this objective a variation removing, over a wide range of 
engine speeds, circuit is provided for accurately removing the periodical 
variation of the detected signal of engine speed due to the pulsation of 
the output torque generated by the internal combustion engine itself. 
According to one aspect of this invention, there is provided a governor for 
an internal combustion engine comprising engine speed detecting means for 
detecting the rotational speed of the engine and for producing an engine 
speed signal indicative of the engine speed, a variation removing circuit 
responsive to the engine speed signal from the detecting means for 
removing periodical variation components of the speed signal, engine speed 
presetting means for producing an engine speed setting signal indicative 
of a desired rotational speed of the engine, and means for calculating an 
amount of injected fuel to be supplied to the engine on the basis of the 
output signals from the variation removing circuit and from the engine 
speed presetting means and supplying a fuel signal indicative of the 
calculated amount of injected fuel to a fuel injection pump provided in 
the engine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the whole basic arrangement of a governor of the invention. 
Referring to FIG. 1, there are shown a speed regulating unit 101, a diesel 
engine 102, a fuel injection pump 100 of the diesel engine 102, a driving 
shaft 103 connected to the crank shaft (not shown) of the diesel engine 
102, and a marine propeller mounted to the driving shaft 103. 
At least an engine speed detector 105 is provided at the driving shaft 103, 
and thus an engine speed signal therefrom is supplied via a line L 105 to 
the speed regulating unit 101. 
The speed regulating unit 101 determines an amount of injected fuel 
necessary for the engine to reach a desired rotational speed on the basis 
of an engine speed set signal from an engine speed presetting device 111 
and the engine speed signal, and supplies a fuel signal indicative of the 
amount of injected fuel via line L 113 to the fuel injection pump 100, 
thereby controlling the position of the rack (not shown) for adjusting the 
amount of injected fuel within the fuel injection pump 100. 
The speed regulating unit 101 includes the engine speed presetting device 
111 for presetting the rotational speed of the diesel engine 102, a 
subtracter 112, a control calculation device 113 for calculating a 
necessary amount of fuel on the basis of the output from the subtractor 
112 and producing an output signal corresponding to the amount of fuel, 
and a variation removing circuit 500 for removing the periodically varying 
component within the engine speed signal which the engine speed detector 
105 produces, over a wide range of engine rotational speed. This variation 
removing circuit 500 features this invention. According to the governor of 
this invention, since the engine speed signal which the engine speed 
detector 105 generates is supplied through the variation removing circuit 
500 to the subtracter 112, the control calculation device 113 is able to 
always calculate correct amount of injected fuel over a wide range of 
engine rotational speed. The fuel signal from the control calculation 
device 113 is fed via the line L 113 to the fuel injection pump 100 of the 
diesel engine 102. 
An embodiment of this invention will hereinafter be described with 
reference to FIG. 2. FIG. 2 shows the whole arrangement of a first 
embodiment of this invention. In FIG. 2, like elements corresponding to 
those in FIG. 1 are identified by the same reference numerals. Referring 
to FIG. 2, there are shown the engine speed detector 105 and a crank angle 
detector 106 provided on the driving shaft 103. The engine speed signal 
and crank angle signal therefrom are supplied via the line L 105 and a 
line L 106 to the speed regulating unit 101. 
The speed regulating unit 101 determines an amount of injected fuel 
necessary for the engine to reach a preset rotational speed on the basis 
of the engine speed set signal from the engine speed presetting device 
111, the engine speed signal and the crank angle signal, and supplies the 
fuel signal through the line L 113 to the fuel pump 100, thereby 
controlling the position of the rack (not shown) of the fuel pump. 
In FIG. 2, the variation removing circuit 500 comprises a sample-and-hold 
circuit 114 and a synchronizing signal generator 115. That is, the speed 
regulating unit 101 comprises the engine speed presetting device 111, the 
synchronizing signal generator 115, the sample-and-hold circuit 114, the 
subtractor 112 and the control calculation device 113. These elements 
function as follows. 
The synchronizing signal generator 115 is responsive to the crank angle 
signal from the crank angle detector 106 to produce a timing signal at 
intervals of 360.degree./Z (Z is the number of cylinders) for crank 
angles, 0.degree. to 360.degree.. This timing signal is supplied through 
the line L 115 to the sample-and-hold circuit 114. 
The sample-and-hold circuit 114 is supplied with the timing signal from the 
synchronizing signal generator 115 via the line L 115 and with the engine 
speed signal from the engine speed detector 105 via the line L 105. Thus, 
this sample-and-hold circuit samples the engine speed signal when the 
timing signal is received and holds the sampled rotational-speed signal 
until the next timing signal is received. This held rotational-speed 
signal is supplied through a line L 114 to the subtractor 112. 
The subtracter 112 acts to calculate the difference between the engine 
speed preset signal from the engine speed presetting device 111 via the 
line L 111 and the rotational speed signal which is held in the 
sample-and-hold circuit 114 and supplied therefrom via the line L 114, and 
to supply the deviation signal via the line L 112 to the control 
calculation device 113. 
The control calculation device 113 is responsive to the rotational-speed 
deviation signal fed via the line L 112 from the subtracter 112 to 
calculate a fuel signal by the control calculation such as proportion, 
integration and differentiation. This fuel signal is indicative of an 
amount of injected fuel to be fed to the diesel engine 102, and supplied 
via the line L 113 to the fuel injection pump 100 to control the rack (not 
shown) of the fuel injection pump 100. 
The engine rotational speed of the diesel engine 102 is periodically 
changed due to the pulsation of the output torque which the diesel engine 
102 itself generates, and therefore the engine speed signal detected by 
the engine speed detector 105 shows the periodic variation as indicated by 
a curve a in FIG. 3. 
On the other hand, the sample-and-hold circuit 114 samples the engine speed 
signal in response to the sampling signal which is produced from the 
synchronizing signal generator 115 in synchronism with the variation 
period of the rotational speed, and holds and produces the sampled 
rotational speed signal until the next timing signal is received by the 
sample-and-hold circuit. 
Therefore, the held and produced rotational speed signal from the 
sample-and-hold circuit 114 is as indicated by a stepped broken-line b in 
FIG. 3. That is, the periodic variation due to the pulsation of the output 
torque generated by the diesel engine 102 itself is removed from the 
detected engine speed signal, so that an averaged rotational speed signal 
is produced from the sample-and-hold circuit. 
Thus, the subtracter 112 and the control calculation device 113 make 
calculation on the basis of the signal fed via the line L 114 from the 
sample-and-hold circuit 114, and thereby control only the averaged 
rotational speed without response to the variation of the rotational speed 
due to the pulsation of the output torque generated from the diesel engine 
102 itself. 
A second embodiment of this invention will be described with reference to 
FIGS. 4 and 5. 
In FIG. 4, like elements corresponding to those of FIG. 2 are identified by 
the same reference numerals. 
The engine speed detector 105 is provided on the driving shaft 103, and 
this engine speed detector 105 produces a pulse signal at intervals of a 
constant rotational angle, or at every constant crank angle and supplies 
it via the line L 105. 
As shown in FIG. 4, the variation removing circuit 500 comprises a 
sample-and-hold circuit 214 and a synchronizing signal generator 215. In 
other words, a speed regulating unit 201 comprises an engine speed 
presetting device 211, the synchronizing signal generator 215, the 
sample-and-hold circuit 214, a subtracter 212, and an control calculation 
device 213. These elements function as follows. 
The sunchronizing signal generator 215 the construction of which will be 
described later is responsive to the pulse signal from the engine speed 
detector 105 via a line L 150b to produce a timing signal and supply it 
via a line L 215. In the speed regulating unit 201, the timing signal is 
formed from the engine speed signal. 
The sample-and-hold circuit 214 the construction of which will be described 
later receives the pulse signal from the engine speed detector 105 via the 
line L 105a and supplied a digitized engine speed signal via a line L 214. 
The subtracter 212 calculates the difference between a engine speed set 
signal fed via a line L 211 from the engine speed presetting device 211 
and the digitized engine speed signal fed via the line L 214 from the 
sampleand-hold circuit 214 and supplies it via a line L 212 as an engine 
rotational speed deviation signal. 
The control calculation device 213 is supplied with the engine rotational 
speed deviation signal from the subtracter 212 via the line L 212, and 
determines an amount of injected fuel to be fed to the diesel engine 102 
by the control calculation such as proportion, integration and 
differentiation. The fuel signal is supplied via the line L 113 to the 
fuel injection pump 100, controlling the rack position (not shown) of the 
fuel injection pump 100. 
The sunchronizing signal generator 215 as shown in FIG. 5 comprises a first 
counter 215a for integrating the pulse signal fed via the line 105b and a 
timer circuit 215b which is responsive to an overflow signal from the 
first counter 215a to produce a pulse signal of a constant duration 
.DELTA.T as a timing signal. 
The first counter 215a is designed to produce for the synchronization with 
the timing signal the overflow signal at the pulse count 
[360.degree./Z/.DELTA..theta.] corresponding to the crank angle 
316.degree./Z (Z is the number of cylinders) plus 1, where .DELTA..theta. 
is the crank angle corresponding to the pulse signal from the engine speed 
detector 105 and the bracket [X] indicates the maximum integer not 
exceeding a number X. 
The sample-and-hold circuit 214 comprises an AND gate 214a for controlling 
the pulse signal from the engine speed detector 105 via the line L 105a to 
pass therethrough in response to the timing signal of constant time 
duration .DELTA.T, a second counter 214b for integrating the pulse signal 
from the AND gate 214a, a register circuit 214c for holding the integrated 
digital signal from the second counter 214b, and a control circuit 214d 
for generating a transfer signal to the register circuit 214c and a reset 
signal to the second counter 214b in response to the timing signal of a 
constant width fed via the line L 215 from the timer circuit 215b. 
Thus, the synchronizing signal generating circuit 215 supplies the timing 
signal of a constant duration .DELTA.T via the line L 215 to the 
sample-and-hold circuit 214 at intervals of crank angle, 360.degree./Z. 
The AND gate 214a of the sample-and-hold circuit 214 opens while this 
timing signal is being supplied thereto, permitting the engine speed 
signal to pass therethrough, and the second counter 214b thereof 
integrates the engine spaced signal. 
When the timing signal is stopped from being supplied after the lapse of 
the constant time .DELTA.T, the AND gate 214 closes and the second counter 
214b stops its integrating operation. The integrated value, count of the 
second counter 214b is the number of pulses occuring during the constant 
time .DELTA.T, or the average rotationalspeed of engine in the time 
.DELTA.T. Also, as soon as the timing signal is stopped, the control 
circuit 214d supplies the transfer signal to the register circuit 214c and 
the integrated value from the second counter 214b is transferred to the 
register circuit 214c. That is, the timing signal in the speed regulating 
unit 201 shown in FIG. 4 is the gate signal for controlling the AND gate 
214. 
Then, the control circuit 214d supplies the reset signal to the second 
counter 214b, thus resetting it. 
As a result, the register circuit 214c holds the rotational speed signal of 
engine integrated and digitized in the second counter 214b. This engine 
speed signal is updated at each timing signal. 
Moreover, in this embodiment, since the timing signal is synchronized with 
the period of the variation of engine speed due to the pulsation of the 
output torque of the diesel engine 102, the digital engine speed signal 
held in the register circuit 214c includes no periodical variation of 
engine speed due to the output torque of the diesel engine 102. 
The governor according to this invention is not limited to the second 
embodiment, but can be constructed to include various types of 
synchronizing signal generator and sample-and-hold circuit depending on 
the type of the engine speed detector to be used. 
Third and fourth embodiments of this invention will be described with 
reference to FIGS. 6 and 7. 
FIG. 6 shows the whole arrangement of a third embodiment of this invention. 
In FIG. 6, like elements corresponding to those of FIGS. 1, 2 or 4 are 
identified by the same reference numerals. 
The engine speed detector 105 is provided on the driving shaft 103, and the 
engine speed signal is fed therefrom via the line L 105 to a speed 
regulating unit 301. 
The speed regulating unit 301 determines an amount of injected fuel 
necessary for the engine to reach a preset rotational speed on the basis 
of a engine speed set signal from a engine speed presetting device 311 and 
the engine speed signal, and supplies the fuel signal via the line L 113 
to the fuel injection pump 100, thereby controlling the rack position (not 
shown) of the fuel injection pump 100. 
In FIG. 6, the variation removing circuit 500 is formed of a variable 
characteristic filter 314. That is, the speed regulating unit 301 
comprises the engine speed presetting device 311 for presetting a engine 
speed of the diesel engine 102, the variable characteristic filter 314, a 
subtracter 312, and a control calculation device 313. These elements are 
operated as follows. 
The variable characteristic filter 314 receives the engine speed signal fed 
from the engine speed detector 105 via the line L 105, eliminates the 
variation of the rotational speed of engine due to the pulsation of the 
output torque of the diesel engine 102 and supplies a filtered engine 
speed signal corresponding to the average rotational speed, via a line L 
314 to the subtracter 312. 
The engine speed presetting device 311 supplies the engine speed set signal 
via a line L 311a to the subtracter 312. 
The subtracter 312 receives the engine speed set signal from the engine 
speed presetting device 311 and the filtered engine speed signal from the 
variable characteristic filter 314, calculates the difference therebetween 
as a rotational-speed deviation signal and supplies it via a line L 312 to 
the control calculation device 313. 
The control calculation device 313 receives the rotational-speed deviation 
signal from the subtracter 312, and produces a fuel signal necessary for 
the average rotational speed of the diesel engine 102 to follow the preset 
value from the engine speed presetting device 311, by the known control 
calculation such as proportion, integration and differentiation of the 
rotational speed deviation signal. This fuel signal is supplied via the 
line L 113 to the fuel injection pump 100, controlling the rack position 
(not shown) of the fuel injection pump 100 for injecting a necessary 
amount of fuel. 
The variable characteristic filter 314 is a band-eliminating filter which 
receives the engine speed set signal fed from the engine speed presetting 
device 311 via the line L 311b and eliminates a signal component of a band 
including the engine speed variation frequency f.sub.c corresponding to 
this engine speed set signal. 
In other words, the rotational speed variation frequency f.sub.c is 
selected to be 
EQU f.sub.c =N.sub.s .multidot.Z/60 (Hz) 
for two-stroke diesel engine, or to be 
EQU F.sub.c =N.sub.s .multidot.Z/120 (Hz) 
for four-stroke diesel engine. Thus, the elimination band of the variable 
characteristic filter 314 changes in accordance with the change of the 
engine speed set signal from the engine speed presetting device 311. Here, 
N.sub.s represents the set engine speed (rpm), and Z the number of 
cylinders. 
Since the rotational speed of engine follows the rotational speed set by 
the engine speed presetting device 311, the engine speed varying component 
included in the engine speed signal can be eliminated by the variable 
characteristic filter corresponding to the speed variation frequency 
f.sub.c for the engine speed set signal. 
FIG. 7 shows the whole arrangement of the fourth embodiment of this 
invention. In FIG. 7, like elements corresponding to those in FIGS. 1, 2, 
4 or 6 are identified by the same reference numerals. 
The engine speed detector 105 is provided on the driving shaft 103, and the 
engine speed signal is supplied via the line L 105 to a speed regulating 
unit 401. 
The speed regulating unit 401 comprises an engine speed presetting device 
411 for presetting the rotational speed of the diesel engine 102, a 
variable characteristic filter 414, a subtractor 412, a function generator 
415, and a control calculation device 413. These elements are operated as 
follows. 
The variable characteristic filter 414 receives the engine speed signal fed 
from the engine speed detector 105 via the line L 105, eliminates the 
variation of the engine speed due to the pulsation of the output torque of 
the diesel engine by means which will be described later, and supplies a 
filtered engine speed signal corresponding to the average engine speed to 
the subtracter 412 via a line L 414. 
The engine speed presetting device 411 supplies the engine speed set signal 
to the subtracter 412 via a line L 411. 
The subtracter 412 receives the engine speed set signal from the engine 
speed presetting device 411 and the filtered engine speed signal from the 
variable characteristic filter 414, and calculates the difference 
therebetween to produce an engine speed deviation signal. This engine 
speed deviation signal is supplied via a line L 412 to the function 
generator 415. 
The function generator 415 receives the engine speed deviation signal from 
the subtractor 412 adn supplies an output signal, for example as shown in 
FIG. 8, via a line L 415. That is, the function generator 415 provides a 
low gain for small engine speed deviation signal and a normal gain for 
larger engine speed deviation signal. 
Therefore, for the variation amplitude of the periodical variation due to 
the pulsation of the output torque of the diesel engine itself, the 
function generator provides a low gain to reduce the amount of operation 
of the fuel pump, while for a large speed deviation due to the change of 
engine speed set value, great change of load and so on, the function 
generator shows such a response that it were not connected in the signal 
path, thus the engine speed being caused to follow the preset engine 
speed. 
The control calculation device 413 produces a fuel signal for the amount of 
injected fuel necessary for the average engine speed of diesel engine 102 
to follow the preset value from the engine speed presetting device 411 by 
the known control calculation such as proportion, integration and 
differentiation of the output signal from the function generator 415 via a 
line L 415. This fuel signal is supplied via the line L 113 to the fuel 
injection pump 100, controlling the rack position of the fuel injection 
pump 100. 
The variable characteristic filter 414 in this embodiment is a 
band-elimination filter which receives the engine speed signal fed via the 
line L 105b, and eliminates the signal component of the band including at 
its center the speed variation period, 1/f.sub.c assumed as shown in FIG. 
9 on the basis of the previously given equation, this speed variation 
being caused by the pulsation of the output torque of the diesel engine. 
Thus, the elimination band of the variable characteristic filter 414 is 
changed with the change of the average speed of the diesel engine. 
The average engine speed necessary in the variable characteristic filter 
414 may be the average of the engine speed in a predetermined time, the 
speed signal filtered out by another filter incorporated in the variable 
characteristic filter 414, or the filtered engine speed from the variable 
characteristic filter 414. 
The governor for internal combustion engine according to this invention is 
not limited to the above first to fourth embodiments but can take various 
modifications and variations in accordance with the conditions in which 
the respective elements or devices are operated. 
For example, although the pulsation of the output torque is great in the 
diesel engine, it also exists within cycle in the gasoline engine. Thus, 
it is obvious that this invention can be applied to the gasoline engine 
thereby making more accurate speed regulation control. 
According to the governor of the invention, since the variation removing 
circuit is provided, the periodical variation of engine speed due to the 
output torque which the internal combusion engine itself generates can be 
removed and thus the average engine speed necessary for driving the load 
can be stably controlled. In addition, since the useless operation of the 
rack of the fuel pump can be removed, it is possible to reduce the 
mechanical damage and wear thereof. 
Moreover, according to the third and fourth embodiments of this invention, 
since the speed variation frequency due to the pulsation of the output 
torque of the engine itself is assumed on the basis of a preset engine 
speed and the band including at its center the assumed frequency can be 
eliminated by the variable characteristic filter which forms the variation 
removing circuit, the governor is prevented from unnecessarily responding 
to the variation of engine speed, and the adverse effect of phase lag 
caused by the insertion of the low-pass filter can be minimized by 
removing the band matched with the operating condition of the engine by 
the variable characteristic filter. 
Furthermore, it is possible to eliminate the engine speed variation not 
only due to the pulsation of the output torque of engine itself, but also 
due to the torsional vibration of the driving shaft which is caused by the 
relation between the pulsation of the output torque and the load.