U.S. patent number 3,867,918 [Application Number 05/311,638] was granted by the patent office on 1975-02-25 for fuel supply systems for internal combustion engines.
This patent grant is currently assigned to C.A.V. Limited. Invention is credited to Anthony John Adey, Geoffrey Albert Kenyon Brunt, Christopher Robin Jones, Malcolm Williams.
United States Patent |
3,867,918 |
Williams , et al. |
February 25, 1975 |
FUEL SUPPLY SYSTEMS FOR INTERNAL COMBUSTION ENGINES
Abstract
An electronic governor, particularly for a diesel engine has a
summing amplifier receiving signals representing the output of the
pumps supplying fuel to the engine, engine speed, and engine
demand. The summing amplifier serves to produce an output for
operating the pump in accordance with predetermined engine current
characteristics. A second summing amplifier may be used to override
the first summing amplifier to limit maximum fuel. Alternatively,
the first summing amplifier may compare demanded fuel supply with
actual fuel supply, in which case the second amplifier sets the
maximum speed.
Inventors: |
Williams; Malcolm (Solihull,
EN), Brunt; Geoffrey Albert Kenyon (Glastonbury,
EN), Jones; Christopher Robin (Alcester,
EN), Adey; Anthony John (Slough, EN) |
Assignee: |
C.A.V. Limited (Birmingham,
EN)
|
Family
ID: |
27257248 |
Appl.
No.: |
05/311,638 |
Filed: |
December 4, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Mar 12, 1971 [GB] |
|
|
56188/71 |
Apr 4, 1972 [GB] |
|
|
15353/72 |
Apr 4, 1972 [GB] |
|
|
15364/72 |
|
Current U.S.
Class: |
123/357; 123/497;
290/40R |
Current CPC
Class: |
F02D
41/407 (20130101); F02D 2200/703 (20130101); F02D
2250/18 (20130101); Y02T 10/40 (20130101); F02B
3/06 (20130101); F02D 2200/0406 (20130101) |
Current International
Class: |
F02D
41/40 (20060101); F02B 3/00 (20060101); F02B
3/06 (20060101); F02m 039/00 (); F02b 003/00 () |
Field of
Search: |
;123/32EA,102,139E
;60/39.28 ;290/40,51 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Cox; Ronald B.
Attorney, Agent or Firm: Holman & Stern
Claims
We claim:
1. A fuel supply system for an engine, comprising in combination a
pump for supplying fuel to the engine, pump control means for
controlling the output of the pump, a first summing amplifier to
which are fed electrical signals representing the demanded and
actual values of pump output, the first summing amplifier comparing
the signals and producing an output for controlling the pump
control means, a second summing amplifier to which are fed
electrical signals representing engine speed, pump output, and a
reference, and a discriminator coupling the first and second
summing amplifiers to the pump control means, the output from the
discriminator at any given instant being the output from the
summing amplifier which demands the least fuel, so that the second
summing amplifier limits the maximum speed of the engine but varies
the maximum speed of the engine in accordance with the pump output,
said summing amplifiers each having a feedback path incorporating a
resistor, and each of said feedback paths being taken from the
input to the pump control means.
2. A system as claimed in claim 1. including means for limiting the
maximum output of the pump.
3. A system as claimed in claim 2, in which said means acts by
restricting the demand signal to a predetermined level.
4. A system as claimed in claim 1, in which the discriminator
comprises a pair of diodes through which the outputs of the
amplifiers are fed to the pump control means, whereby at any given
moment one of the diodes will be conducting and will reverse bias
the other diode.
5. A system as claimed in claim 1 in which the maximum output of
the pump is controlled, but the system includes circuit means
having a first state and a second state, said circuit means when in
its second state increasing the maximum output of the pump, said
circuit means being driven to its second state when the engine
speed is below cranking speed and being driven to its first state
when the engine speed is above a datum speed, the datum speed being
in excess of the cranking speed.
6. A system as claimed in claim 5, in which the datum speed at
which excess pump output is terminated is set by a bistable circuit
forming part of said circuit menas and the cranking speed at which
excess pump output is permitted again is set by a control circuit
which until the engine speed falls to cranking speed holds the
bistable circuit in a state to prevent excess pump output.
7. A system as claimed in claim 6, in which said control circuit
becomes operative when the engine speed is above cranking speed,
and when operative is capable of holding the bistable circuit in a
state to prevent excess pump output, but not of driving the
bistable circuit to a state to prevent excess pump output.
8. A system as claimed in claim 5, in which the circuit means
incorporates a bistable circuit switching to the first state at
said datum speed, and by virtue of its own differential switching
back to the second state at the cranking speed.
9. A system as claimed in claim 6, in which the engine drives a
vehicle and an accelerator pedal is provided for setting said
demand signal, said circuit means being driven to its second state
only when the engine speed is below cranking speed and the
accelerator pedal is depressed beyond a predetermined position, and
the circuit means being driven to its first state when either the
engine speed is above the datum speed, or the pedal is not
depressed beyond said predetermined position.
10. A system as claimed in claim 11, in which excess pump output is
permitted only if the engine temperature is below a predetermined
value.
11. A system as claimed in claim 1, including means for maintaining
said circuit means in its first state between the datum and
cranking speeds even if the supply to the circuit means becomes
momentarily disconnected between the datum and cranking speeds.
12. A system as claimed in claim 11, in which said means includes a
capacitor.
13. A system as claimed in claim 1, in which the engine has an air
intake manifold and the maximum pump output is controlled but is
modified in accordance with the pressure of the air in said intake
manifold.
14. A system as claimed in claim 1, in which the first and second
summing amplifiers are each operational amplifiers having an
inverting input and a non-inverting input, and the signals fed to
the summing amplifiers representing the demanded and actual values
of pump output, engine speed and said reference are in the form of
currents fed to the inverting input of the appropriate summing
amplifier.
15. A system as claimed in claim 14 in which the feedback network
of the amplifier includes a capacitor for modifying the d.c. gain
of the amplifier.
16. A fuel injection system for a diesel engine, comprising in
combination a pump for supplying fuel to the engine, an
electromechanical actuator coupled to the pump to control the pump
output, a drive circuit for controlling the electromechanical
actuator, first, second and third transducers producing
respectively output voltages representing engine speed, pump output
and throttle position, a first operational amplifier connected as a
summing amplifier and having its inverting input connected through
resistors to the second and third transducers, said first amplifier
producing an output representing the difference between the actual
and demanded pump outputs, a second operational amplifier connected
as a summing amplifier and having its inverting input connected
through resistors to the first and second transducers, and a
discriminator coupling the amplifier producing the greater output
to the drive circuit, the arrangement being such that until a
predetermined engine speed is attained, the discriminator couples
the first amplifier to the drive circuit, but when said
predetermined engine speed is reached, the discriminator couples
the second amplifier to the drive circuit to limit the maximum
engine speed, the maximum engine speed being varied with pump
output by the second amplifier.
17. A system as claimed in claim 16, in which the discriminator
comprises a pair of diodes, one coupling each of the amplifiers to
the drive circuit, and the resistive feedback paths of the two
amplifiers are taken from the input to the drive circuit.
18. A fuel supply system for an engine as claimed in claim 1, a
transistor which receives an input representing engine speed and
conducts at a predetermined engine speed, and circuit means
selectively connectible to said transistor so as alternatively to
increase or decrease the maximum pump output when the transistor
conducts.
19. A system as claimed in claim 18 in which the maximum pump
output is modified above a predetermined engine speed.
20. A fuel supply system for an engine as claimed in claim 1,
comprising means associated with said first summing amplifier for
limiting the maximum pump output, and a control network to which an
electrical signal dependent on engine speed is applied, said
control network including a transistor which is turned on at a
predetermined engine speed and when conductive modifies the input
to the first summing amplifier to modify the maximum pump
output.
21. A fuel system as claimed in claim 1, for a compression-ignition
engine, in which each feedback circuit includes a capacitor in
series with said resistor.
Description
This invention relates to fuel supply systems for engines. The
invention is praticularly, but not exclusively, concerned with fuel
injection systems for diesel engines.
In one aspect, the invention resides in a fuel supply system for an
engine, comprising in combination a pump for supplying fuel to the
engine, pump control means for determining the output of the pump,
means for producing a first electrical signal representing the pump
output, means for producing a second electrical signal representing
engine speed, means for producing a demand signal representing the
required engine speed, and a summing amplifier to which the three
signals are applied, the summing amplifier comparting the three
signals and controlling the pump control means.
In another aspect, the invention resides in a fuel supply system
for an engine, comprising in combination a pump for supplying fuel
to the engine, pump control means for determining the output of the
pump, a first summing amplifier to which are fed electrical signals
representing the demanded and actual values of a parameter of the
system, the first summing amplifier comparing the signals and
producing an output for controlling the pump control means, a
second summing amplifier to which are fed electrical signals
representing a further system parameter and a reference, and a
discriminator coupling the first and second summing amplifiers to
the pump control means, the output from the discriminator at any
given instant being the output from the summing amplifier which
demands the least fuel, so that the second summing amplifier limits
the maximum value of said further system parameter.
In another aspect, the invention resides in a fuel supply system
for an engine, comprising in combination a pump supplying fuel to
the engine, an actuator for controlling the output of the pump, a
first transducer for measuring the engine speed, a second
transducer for measuring demand, a third transducer for measuring
the output of the pump, a control circuit operable in accordance
with the outputs from the transducers for controlling the actuator,
said control circuit restricting the output of the pump to a
predetermined maximum value, and a control network which receives
an input from the first transducers and provides an input to the
control circuit for a range of engine speeds so that the maximum
pump output is modified for said range of speeds.
In another aspect, the invention resides in a fuel supply system
for an engine, comprising in combination a pump for supplying fuel
to the engine, an actuator for controlling the output of the pump,
a control circuit for comparing at least two engine parameters and
providing an output for controlling the actuator and so regulating
the output of the pump, said control circuit incorporating means
for restricting the maximum pump output, and the system including
circuit means having a first state and a second state, said circuit
means when in its second state increasing the maximum pump output,
said circuit means being driven to its second state when the engine
speed is below cranking speed and being driven to its first state
when the engine speed is above a datum speed, the datum speed being
in excess of the cranking speed.
In another aspect, the invention resides in a fuel supply system
for an engine, comprising in combination first, second and third
transducers producing output voltages representing respectively
rate of supply of fuel to the engine, engine speed and demand, the
outputs from the transducers being fed to the inverting terminals
of one or more summing amplifiers which form part of a control
circuit for determining the rate of supply of fuel to the engine in
accordance with the required characteristics of the system, the
system further including one or more current sources operable under
selected system conditions to modify a characteristic of the system
by altering the current flowing to an inverting terminal of one of
the summing amplifiers.
In the accompanying drawings,
FIG. 1 is a circuit diagram, partly in block form, illustrating one
example of the invention,
FIGS. 2 to 4 are graphs illustrating the outputs of three
transducers used in FIG. 1,
FIG. 5 represents a fuel-speed characteristic for an engine to be
controlled by the arrangement of FIG. 1,
FIG. 6 is a view similar to FIG. 1 of a second example of the
invention,
FIG. 6a is a fragmentary view illustrating a minor modification of
FIG. 6.
FIG. 7 is a view similar to FIG. 5 but showing the characteristic
obtained by FIG. 6,
FIG. 8 is a circuit diagram showing an excess fuel control
circuit,
FIG. 9 is a circuit diagram illustrating another form of excess
fuel control circuit,
FIG. 10 is a circuit diagram illustrating one form of torque
control circuit,
FIG. 11 is a graph showing the fuel-speed relationship obtained
with the circuit shown in FIG. 10,
FIG. 12 is a circuit diagram illustrating another form of torque
control circuit,
FIG. 13 is a circuit diagram illustrating a third form of torque
control circuit,
FIG. 14 is a graph illustrating the characteristics obtained with
the circuit of FIG. 13, and
FIG. 15 is a circuit diagram showing a modification of the
arrangement shown in FIG. 1.
All the examples described relate to a fuel injection system for a
diesel engine driving a road vehicle, so that demand is set by an
accelerator pedal. However, the arrangements shown can be used with
other engines, and the engine employed need not drive a road
vehicle, in which case the demand is of course set in some other
way.
Referring first to FIG. 1, a fuel pump 11 supplies fuel to the
cylinders of an engine 12 in turn, the fuel pump being driven in a
conventional manner, with the timing of injection controlled in the
usual way. The driving of the fuel pump forms no part of the
present invention and is not therefore described. Moreover, the
type of pump used is not critical, but in the example shown the
pump is a conventional in-line pump having a control rod 14 the
axial position of which determines the rate of supply of fuel to
the engine 12 by the pump 11. The axial position of the control rod
14 is controlled by an electro-mechanical actuator 13 to determine
the pump output.
The system further includes three transducers 15, 16 and 17. The
transducer 15 produces an output in the form of a voltage shown in
FIG. 2, the magnitude of the voltage being dependent on the
rotational speed of the engine. The transducer 16 produces an
output voltage shown in FIG. 3 the voltage being dependent on the
rate of supply of fuel to the engine, (i.e., the pump output). For
this purpose the transducer 16 conveniently senses the axial
position of the control rod 14 as indicated by the dotted line. The
transducer 17 produces a voltage representing demand. Typically,
the transducer 17 is controlled by the accelerator pedal of the
vehicle which is driven by the engine, and in the particular
example being described, the engine is controlled by an all-speed
governor, so that the output from the transducer 17 is a voltage
representing demanded engine speed. The form of this voltage is
shown in FIG. 4, and it should be noted that the slope of this
output is opposite to the slopes of the outputs from the
transducers 15, 16.
The outputs from the transducers 15, 16 and 17 are all applied, by
way of resistors 15a, 16a, 17a converting the signals to current
signals, to the inverting terminal of an operational amplifier 18
connected as a summing amplifier, whilst the output from the
transducer 16 is also connected through a resistor 16b to the
inverting terminal of an operational amplifier 19 connected as a
summing amplifier. The amplifiers 18 and 19 are powered by positive
and negative supply terminals 21, 22 and have their non-inverting
terminals connected to a terminal 23 which is at a reference
potential intermediate the potentials of the terminals 21, 22. The
output from the amplifier 18 is fed through a diode 24 to a drive
circuit 25 which incorporates a power amplifier and which serves to
control the electro-mechanical actuator 13. Similarly, the output
terminal of the amplifier 19 is connected to the drive circuit 25
through a diode 26. The diodes 24 and 26 together constitute a
discriminator, which ensures that only the amplifier 18, 19
producing the more positive output is coupled to the drive circuit
25 at any given instant. Thus, if the amplifier 18 is producing the
more positive output, then the diode 26 is reverse biased, and if
the amplifier 19 is producing the more positive output, the diode
24 is reverse biased. FIG. 1 also shows the feedback resistors 27,
28 associated with the amplifiers 18, 19 respectively, and it will
be noted that the feedback circuit for each amplifier is taken from
the input terminal of the drive circuit 25. By virtue of this
arrangement, the effect of the forward voltage drop across the
diodes 24 and 26 is reduced by a factor dependent upon the
amplifier open-loop gain, and so the temperature characteristics of
the diodes become negligible when considering the temperature
characteristics of the system. Also, there is a very sharp
changeover from control by one amplifier to control by the other
amplifier.
There are various other controls in FIG. 1, the purpose of which
will be described later. However, the basic operation is as
follows. Neglecting for the moment the input to the inverting
terminal of the amplifier 18 from the transducer 16, then the
amplifier 18 receives a current input representing demanded speed,
and a current input representing actual speed. These inputs are of
opposite polarity as seen in FIGS. 2 and 4. If the actual speed is
less than the demanded speed, then the amplifier 18 produces an
output which is fed to the drive circuit 25, and causes the pump
output to increase so that the engine speed increases. As the
demanded and actual signals approach one another, the output from
the amplifier 18 becomes such that the drive circuit 25 produces
just sufficient current to keep the control rod 14 in the position
it has assumed. This simple explanation, however, ignores the input
from the transducer 16, which modifies the operation to provide the
required engine characteristics in a manner to be explained in more
detail later. It will be seen that by virtue of the input from the
transducer 16, the amplifier 18 will in fact compare the demanded
speed and the actual speed, and change the rate of supply of fuel
until these two parameters have a relative value which is
determined by the pump output.
The amplifier 19 receives a signal by way of the resistor 16b
representing pump output and also receives a reference current from
a reference source 20. If the pump output exceeds a predetermined
value, then the amplifier 19 produces a positive output which is
more positive than the output of the amplifier 18, so that the
diode 24 ceases to conduct as previously explained, and the
amplifier 19 produces an output to the drive circuit 25. It should
be noted that a larger positive output from the amplifier 19 than
from the amplifier 18 is in fact a demand for less fuel, that is to
say there is an inverting stage between the amplifier and pump.
When the amplifier 19 is producing an output, the system operates
in the same way as when the amplifier 18 is producing an output to
reduce the output of the amplifier 19 to a value such that the
output from the drive circuit 25 keeps the control rod 14 in the
position it has assumed. The system will stay in this condition
until the amplifier 18 demands less fuel than the maximum set by
the amplifier 19. When the amplifier 18 demands less fuel, it
produces a greater positive output than the amplifier 19, and so
takes over the operation.
Referring now to FIG. 5, the way in which the governor is designed
and operates can be seen from the graph of pump output against
speed. This graph also shows the effect of a number of controls not
yet mentioned in relation to FIG. 1. The line 40 is set by the
amplifier 18 by virtue of the way in which the comparison of actual
and demanded speeds is modified in accordance with the input from
the transducer 16. The line 40 in the drawings represents 50
percent demand, and is one of a family of curves stretching from 0
percent demand to 100 percent demand. The extremes of this curve,
that is to say no demand and full demand, are indicated at 38 and
43. The curve 38 is set by a current source 31 providing an input
to the inverting terminal of the amplifier 18, to ensure that the
engine speed varies with pump output in the manner indicated by the
curve 38 even when the demand is zero. The maximum speed is set by
a control 29 shown in FIG. 1 and which acts by limiting the maximum
demand from the transducer 17.
The line 35 is the maximum fuel line which is set by the amplifier
19 as previously explained. This line has a portion 36 which is set
by a circuit known as a torque control circuit 32. This torque
control circuit 32 modifies the maximum permitted fuel under
certain conditions of engine speed, as will be explained in more
detail later. Also, there is shown in FIG. 5 a curve 37 which is
under the control of an excess fuel control 33 shown in FIG. 1. In
certain circumstances when an attempt is made to start the engine
the control 33 allows a substantially increased pump output as
indicated by the curve 37. There is also a control 34 in FIG. 1
which modifies the maximum permitted fuel in accordance with air
density or air pressure or air temperature or any combination of
these three parameters. The control 34, when operative modifies the
input current to the amplifier 19, and so changes the position of
the lines 35, 36 on the vertical axis, that is to say it lifts both
lines up and down dependent upon air conditions. The reason for
this is that basically the maximum fuel line 35, 36 is set to
prevent excess pollution as a result of the engine receiving too
much fuel. The maximum amount of fuel that the engine can burn
depends on the amount of air entering the engine, which is
dependent on the three air parameters mentioned above. In a
turbo-charged engine it is often sufficient to measure the air
pressure, and operate the control 34 in accordance with the air
pressure.
The boundary line 39 is a function of the engine, not the governor,
and represents the no-load fuel requirements of the engine under
different demands, so that the points 41 and 42 are the no-load
engine speeds at zero and full demand, (i.e.) with the pedal
released and fully depressed respectively.
FIG. 5 explains how the engine will behave in any circumstances.
Suppose that the pedal has been set to demand 50 percent,
corresponding to the line 40 shown in FIG. 5. The exact position on
the line 40 at any given instant will depend upon the load on the
engine, and so for this given setting of the pedal, the engine
speed can vary within the limits set by the lines 35 and 40. The
slope of the line 40 is, as previously explained, a result of the
input to the amplifier 18 from the transducer 16. Assuming that the
engine is operating at a particular point on the line 40, then if
the vehicle starts to go up an incline, the load will increase, and
so for a given position of the pedal the operating point will move
up the line 40, so that the speed is reduced. If the load becomes
sufficiently great, the line 35 will be reached, and no further
increase in pump output will be permitted. At this point, the speed
falls rapidly. If the load decreases, then the operating point
moves down the line 40 with the corresponding increase in speed. If
the load decreases to zero, the line 39 is reached.
If the demand is changed, then assuming for the sake of argument
that it changes from 50 percent demand to 100 percent demand, the
pump output will increase as rapidly as the pump will allow until
the line 35 is reached, and the engine will then move along the
lines 35, 36 onto the maximum demand line 43, and will assume a
position on the line 43 which is dependent upon the load.
If the demand is reduced, then assuming the demand is reduced from
50 to 0 percent, the operating point will move vertically downwards
until the fuel supply is zero. The speed then decreases until the
line 38 is reached, after which the operating point moves up the
line 38, finishing at a point on the line 38 determined by the load
on the engine.
Turning now to FIG. 6, there is shown a second example in which the
governor is a two-speed governor, that is to say a governor in
which the demand signal is a fuel signal which is compared with the
actual fuel, the pump output then being modified to provide the
desired fuel output. In FIG. 6, the amplifier 18 receives a signal
from the transducer 16 by way of the resistor 16a, this signal
representing actual fuel. A signal representing demanded fuel is
fed by way of the resistor 17a to the amplifier 18, but it will be
noted that there is no speed term set to the amplifier 18 from the
transducer 15. The characteristics of the system are shown in FIG.
7. The line 40a is one of a family of horizontally extending lines
which are set by the governor, and can be taken to represent the 50
percent demand line. When the pedal sets a demand of 50 percent,
the amplifier 18 sets the required fuel level. The operating point
on the line 40a will of course then depend on the load on the
engine.
The amplifier 19 overrides the amplifier 18 in FIG. 6 in a similar
manner to the arrangement in FIG. 1, except that the amplifier 19
now receives a signal by way of the resistor 15a representing
speed, and also a reference current from a source 20a indicating
the maximum engine speed. The amplifier 19 sets the maximum speed
of the engine, which is indicated by the line 43 in FIG. 7. It will
be noted that the line 43 has a slope, that is to say the maximum
permitted speed varies with pump output. This slope is obtained by
feeding to the amplifier 19 a signal representing pump output, this
signal being fed by way of the resistor 16b.
The maximum pump output, that is to say the line 35 in FIG. 7, is
set by a control 29a which limits the maximum demand, in much the
same way as the control 29 limits the maximum speed in FIG. 1. The
torque control circuit, which provides the required slope 36 in
FIG. 7, could act directly on the input to the amplifier 18, but
preferably it serves as shown to act on the control 29a the torque
control circuit being shown at 32.
The excess fuel line 37 is obtained by a current source 33 acting
on the amplifier 18. Finally, the minimum engine speed, indicated
by the line 38, is set by a current source 31a, which is similar to
the current source 31 except that because the current source 31a
acts on the amplifier 18, which does not receive a speed term, the
current source 31a must receive a speed term as indicated by its
connection to the transducer 15. The dotted line in FIG. 6
indicates that when the source 31a is operative, it modifies the
output of the transducer 32 to keep the line 35 in its correct
position.
Referring now to FIG. 8, there is illustrated one example of an
excess fuel control to produce the line 37 in FIG. 5 or FIG. 7. The
terminals 21, 22 and 23 are used in the circuit, the terminal 23
being at a potential intermediate the terminals 21 and 22, and
ideally being halfway between the potentials of the terminals 21
and 22. FIG. 8 also shows a transducer 15.sup.1. The transducer 15
in FIG. 1 produces a d.c. voltage representing engine speed as
shown in FIG. 2, but in practice this is accomplished by producing
an a.c. voltage at a frequency representing engine speed, and
feeding this a.c. voltage to a frequency to voltage converter to
produce the required d.c. voltage output. The transducer 15.sup.1
in FIG. 8 represents the part of the transducer 15 which produces
an alternating voltage at a frequency dependent on engine
speed.
The output from the transducer 15.sup.1 is fed to the base of an
n-p-n transistor 51 by way of a series circuit including a resistor
52, a capacitor 53 and a diode 54. The junction of the capacitor 53
and diode 54 is connected through a diode 55 to the terminal 23,
and the base of the transistor 51 is connected to the terminal 23
through a resistor 56 and a capacitor 57 in parallel, the
transistor 51 has its collector connected to the terminal 21 and
its emitter connected through a resistor 58 to the terminal 23, the
emitter and collector of the transistor 51 being interconnected
through a capacitor 59, and the emitter being further connected to
the base of an n-p-n transistor 61 having its collector connected
through a resistor 62 to the terminal 21. A further n-p-n
transistor 63 has its collector connected through a resistor 64 to
the terminal 21, and the emitters of the transistors 61, 63 are
connected through a resistor 65 to the terminal 22. The base of the
transistor 63 is connected to the collector of the transistor 61,
and the collector of the transistor 63 is connected through a
resistor 66 to the base of a p-n-p transistor 67, the emitter of
which is connected to the terminal 21 and the collector of which is
connected through a resistor 68 to the terminal 23, and through a
pre-set resistor 69 to an output terminal 69a which is connected to
the summing terminal of the amplifier 19 if the arrangement is used
with FIG. 1, or to the summing terminal of the amplifier 18 if the
arrangement is used with FIG. 6.
The base of the transistor 61 is further connected to the collector
of a p-n-p transistor 71. The base of the transistor 71 is
connected through a resistor 70 to a transducer 17.sup.1, and its
emitter is connected to the junction of a pair of resistors 72, 73
connected in series between the terminals 21, 23. The transducer
17.sup.1, is the transducer 17 plus a constant voltage bias causing
the transducer to produce a positive output increasing with pedal
movement from zero to a maximum.
While an attempt is made to start the engine, the engine speed will
be low. The diode pump circuit 52 to 57 produces across the
capacitor 57 a voltage dependent upon the speed of the engine, and
the transistor 51 acts as an emitter follower to apply this voltage
to the base of the transistor 61. While the engine speed is low
then the transistor 61 is off, and the transistor 63 is on. The
transistor 63 provides base current to the transistor 67 which
conducts to provide an input to the summing junction of the
amplifier 19 or 18, so that the amplifier 19 or 18 permits excess
fuel to be supplied to the engine 12, the amount of the excess
being determined by the resistor 69. When the datum speed is
reached, however, the transistor 61 turns on, turning off the
transistors 63 and 67 so that the amplifier 19 or 18 again controls
the maximum fuel as previously explained with reference to FIGS. 1
and 6.
When the engine speed is decreasing, it is important not to provide
excess fuel between the datum speed and the cranking speed of the
engine. The bistable circuit constituted by the transistors 61 and
63 will of course have a differential, that is to say it will
switch from a first state to a second state at one voltage, but
only revert to the first state at a lower voltage. The design of
the bistable circuit is such that although the transistor 61 turns
on at the datum speed, it does not turn off again until the engine
speed falls below cranking speed, so that excess fuel is not
provided while the engine speed is reducing from the datum speed to
the cranking speed.
A minor difficulty with the arrangement thus far described is that
if, while the engine speed is reducing from the datum speed to the
cranking speed, the supply to the terminals 21, 22, 23 is
momentarily cut-off and then re-established, the transistor 61
turns off and stays off so that excess fuel would be provided
between the datum and cranking speeds. The capacitor 59 prevents
this possibility by ensuring that every time the supply is
connected, the transistor 61 turns on and remains on for a period
of time while the capacitor 59 charges.
The above description ignores the transistor 71, which is
particularly desirable when the engine is used to drive a road
vehicle. In these circumstances, the transistor 71 ensures that
excess fuel is not available unless the accelerator pedal of the
vehicle is depressed beyond a predetermined position before an
attempt is made to crank the engine, and is left in that position
while the engine is being cranked. The arrangement is such that
unless the pedal is depressed sufficiently the transistor 71 is on.
Whenever the transistor 71 is on, it provides base current for the
transistor 61, holding the transistor 61 conductive so that the
transistors 63 and 67 are off and excess fuel cannot be
provided.
In a modification, excess fuel is only permitted if the engine
temperature is below a predetermined value. Alternatively, both the
pedal and the temperature may be sensed, so that excess fuel is
only provided if the pedal is depressed beyond the predetermined
position and the engine temperature is below the predetermined
temperature.
Referring now to FIG. 9, there is shown a second form of excess
fuel circuit. The circuit receives an input from the transducer 15,
as distinct from the transducer 15.sup.1 in FIG. 8, and provides an
output in the form of a current to a terminal 95a which can be
connected to the amplifier 19 or the amplifier 18 depending upon
whether the arrangement is to be used with the example of FIG. 1 or
the example of FIG. 6.
Referring to FIG. 9, the transducer 15 provides an input by way of
resistor 81 to the base of an n-p-n transistor 82 having its
collector connected through resistors 83, 80 in series to the
terminal 21, and its collector-base junctions interconnected
through a capacitor 84. The emitter of the transistor 82 and the
emitter of a further n-p-n transistor 85 are connected through a
resistor 87 to the terminal 23, and the base of the transistor 85
is connected to the junction of a pair of resistors 105, 106
connected in series between the terminals 21, 23. The collector of
the transistor 85 is connected to the terminal 21 through a
resistor 86.
The junction of the resistors 80, 83 is connected to the base of a
p-n-p transistor 79 having its emitter connected to the terminal 21
and its collector connected to the junction of a pair of resistors
78, 77 which are connected in series between the lines 21, 23.
The circuit further includes a pair of p-n-p transistors 89, 92
having their emitters connected to the terminal 21 through a
resistor 93, and their collectors connected to the terminal 23
through resistors 91, 94 respectively. The collector of the
transistor 89 is connected to the terminal 21 through a resistor 96
and a resistor 97 in series, and the junction of the resistors 96,
97 is connected to the base of the transistor 92, which has its
collector connected through a pre-set resistor 95 to the terminal
95a. The transistor 89 receives an input at its base by way of a
diode 88 from the collector of the transistor 79, further inputs by
way of diodes 103, 104 from controls 101, 102, and a fourth input
by way of a diode 98 from the junction of a pair of resistors 107,
108 connected between the output of the transducer 15 and the
terminal 23.
The transistors 89, 92 constitute a bistable circuit having a first
state in which the transistor 89 conducts and a second state in
which the transistor 92 conducts. In the second state, a signal is
fed by way of resistor 95 to the summing terminal of the amplifier
19 or 18 to increase the maximum fuel limit during starting.
Ignoring for the moment the diode 88, the bistable circuit is
driven to its second state only when it receives no input through
any of the diodes 98, 103, 104. The control 101 is sensitive to the
position of the accelerator pedal, and the control 102 is sensitive
to the engine temperature. The source 101 produces no signal only
when the accelerator pedal is depressed beyond a predetermined
position, and the source 102 produces no signal only when the
engine temperature is low. The resistors 96, 97 are adjusted so
that there is no signal by way of the diode 98 only when the engine
speed is below a datum speed. Thus, if the engine speed is below a
datum speed, the engine is cold and the accelerator pedal is full
depressed, then the transistor 89 switches on and excess fuel is
permitted. If the engine speed is above the datum speed, or the
accelerator pedal is not depressed, or the engine temperature is
above a predetermined value, then the transistor 89 is turned on
and the transistor 92 is off so that no excess fuel is
permitted.
With the arrangement so far described, it will be possible for
excess fuel to be provided between datum and cranking speeds as the
engine speed is reducing. The purpose of the diode 88 is to prevent
this occurrence. The amplifier 85, 82 controls the conduction of
the transistor 79. At low engine speeds, the output voltage of the
transducer 15 is high (see FIG. 2) and so the transistors 82, 79
are on and the diode 88 is reverse biased. At cranking speed, the
transistor 85 conducts sufficiently to reduce the conduction level
of the transistor 82, 79 so that the diode 88 is no longer reverse
biased.
When the diode 88 is conducting, it provides an input to the
bistable circuit which ensures that once the bistable circuit is in
its first state, it cannot be driven to its second state, until the
diode 88 stops conducting. Thus, assuming that excess fuel has not
been permitted when the diode 88 conducts, then the bistable
circuit will be in its first state and will stay in its first state
until the diode 88 ceases to conduct. However, if when the diode 88
conducts the bistable circuit is already in its second state, so
that excess fuel is being provided the diode 88 will not switch the
circuit back to its first state, but when the datum speed is
reached and the circuit is switched back to its first state, the
diode 88 holds it in the first state until cranking speed is
reached, and the diode 88 is reverse biased.
Referring now to FIG. 10, there is shown one form of torque control
circuit for modifying the maximum fuel characteristics in
accordance with speed. Connected in series between the terminals
21, 22 are a pre-set resistor 111, a pair of diodes 112, 113 and a
resistor 114. The junction of the resistor 111 and diode 112 is
connected to the base of a n-p-n transistor 115, the emitter of
which is connected through a resistor 116 to a transducer 15",
which is the transducer 15 with a constant negative bias so that
the output is zero at zero speed and then increases negatively. The
transducer 15" also provides an input by way of a resistor 117 to
the emitter of a p-n-p transistor 118, the collector of which is
connected to the terminal 22 through a resistor 119 and the diode
120 in series. The terminals 21, 22 are bridged by a series circuit
including a resistor 121, diodes 122, 123 and a resistor 124, and
the junction of the diode 123 and resistor 124 is connected to the
base of the transistor 118. The collector of the transistor 118 is
also connected to the base of an n-p-n transistor 125, the emitter
of which is connected through a resistor 126 to the terminal 22.
The collectors of the transistors 115, 125 are connected to a
terminal 130 which in the case of FIG. 1 is connected to the
summing input of the amplifier 19, but in the case of FIG. 6 is
arranged to modify the control 29a as previously explained.
The arrangement of FIG. 10 is designed to give maximum fuel against
speed characteristic of the form shown in FIG. 11. It will be seen
that this curve differs from FIGS. 5 and 7 in that as well as the
parts 35, 36 of the curve, there is a portion 36a at low speeds
where the maximum fuel is also reduced. In order to understand the
operation of FIG. 10, it is convenient to consider a situation
where the speed of the engine lies between the values indicated by
the points 131 and 132 in FIG. 11. The transducer 15" produces an
output in the form of a voltage which decreases relative to the
terminal 23 with engine speed. Thus, when the engine speed is low,
the output from the transducer 15 is relatively low negative and
the output will increase negatively passing through a first known
value when the engine speed is at the point 131, and then passing
through a second known value when the engine speed is at the point
132. The base potential of the transistor 115 is set by the series
circuit 111, 112, 113, 114 at the second known value, and the base
potential of the transducer 118 is set by the series circuit 121,
122, 123, 124 at the first known value. Thus, on the portion of the
curve indicated at 35, that is to say between the two engine speeds
represented by the points 131 and 132, neither the transistor 115
or the transistor 118 will be conductive. In these circumstances,
the maximum fuel available is indicated by the portion 35 of the
curve in FIG. 11.
Imagine now a situation in which the engine speed increases to the
point 132 shown in FIG. 11. As the engine speed increases, the
output voltage of the transducer 15" increases negatively until at
a speed indicated by the point 132, the emitter potential of the
transistor 115 is less than its base potential, and so the
transistor 115 starts to conduct and takes from the regulator a
collector current dependent on speed, so that the maximum fuel is
reduced in the manner indicated by the portion 36 of the curve in
FIG. 11.
Consider now the situation where the engine speed falls to the
point indicated by 131 in FIG. 11. With falling engine speed, the
output voltage of the transducer 15" reduces negatively until at
the point 131, the emitter potential of the transistor 118 becomes
greater than its base potential, so that the transistor 118
conducts. Current flowing through the transistor 118 turns on the
transistor 125, which removes current from the terminal 130 and it
will be seen that the curve will follow the portion 36a shown in
FIG. 11 as the speed reduces still further.
It will be appreciated that in effect the transistors 115 and 118
and their associated components are acting as pre-set and
temperature stable Zener diodes sensing the speeds indicated by the
points 132 and 131 and then providing the required shaping of the
curve.
It will of course be appreciated that the example described can be
modified in a number of ways. For example, depending on the type of
engine employed modification of the maximum fuel may only be
required below the speed indicated by the point 131, or above the
speed indicated by the point 132. Also, the curves 36a and 36 in
the example both indicate decreasing maximum fuel, but in some
cases increasing maximum fuel may be desired for one or both
portions of the curve. Such an arrangement can readily be achieved
using the circuit described with minor modifications. Thus, as
shown in FIG. 12, the circuit can be modified so that the
transistor 115 is a p-n-p transistor with its base connected to the
junction of the diode 113 and the resistor 114. In similar fashion,
if it is desired that the portion 36 of the curve represents an
increasing maximum fuel, then as shown in FIG. 12 the transistor
118 is replaced by an n-p-n transistor having its base connected to
the junction of the resistor 121 and the diode 122 and its
collector connected to the terminal 21 through the diode 120 and
resistor 119. In this case, the transistor 125 is a p-n-p
transistor with its emitter connected through the resistor 126 to
the terminal 21 and its collector connected, together with the
collector of the transistor 115, to the amplifier 19. It will be
noted that the polarities are such that FIG. 12 requires an input
from the transducer 15, not the transducer 15".
In both FIGS. 10 and 12, modification of the maximum fuel is
effected in a linear manner, but clearly non-linear modification of
the fuel is possible using a suitable control circuit.
Referring to FIG. 13, which shows another form of torque control
circuit, the output from the transducer 15 is fed through a
resistor 131 and a pre-set resistor 130 in series to the terminal
22, the junction of the resistors 131, 132 being connected to the
base of an n-p-n transistor 133 and its collector connected to the
terminal 21 and its emitter connected through a resistor 134 to the
terminal 22. The emitter of the transistor 133 is further connected
through a pre-set resistor 135 to the emitter of an n-p-n
transistor 136, the base of which is connected through a detachable
link 137 to the terminal 23, and through another detachable link
138 to an output terminal 160 for connection to the summing
terminal of the regulator in the same way as the terminal 130 in
FIGS. 10 and 12. The collector of the transistor 136 is connected
through a detachable link 140 to the base of a p-n-p transistor
139, and is also connected to the terminal 21 through a resistor
141 and a diode 142 in series. The transistor 139 has its collector
connected to the output terminal 160 and its emitter connected to
the terminal 21 through a detachable link 143 and a resistor 144 in
series.
The transducer 15 also provides an output which is coupled to the
terminal 22 through a resistor 145 and a pre-set resistor 146 in
series, the junction of the resistors 145, 146 being connected to
the base of a p-n-p transistor 147. The transistor 147 has its
collector connected to the terminal 22 through a resistor 148 and
its emitter connected through a resistor 149 to the collector of a
p-n-p transistor 151 having its emitter connected through a pre-set
resistor 152 to the terminal 21. The base of the transistor 151 is
connected through a resistor 153 and a diode 154 in series to the
terminal 21, and is further connected through a resistor 155 to the
terminal 23. The collector of the transistor 151 is further
connected through a resistor 156 to the emitter of a p-n-p
transistor 157 having its base connected to the junction of a pair
of resistors 158, 159 connected in series between the terminals 21,
22 and its collector connected through a resistor 161 and a diode
162 in series to the terminal 22. The collector of the transistor
157 is also connected to the base of an n-p-n transistor 163, the
collector of which is connected to the output terminal 160 and the
emitter of which is connected through a pre-set resistor 164 to the
collector of the transistor 147.
The transistors 133, 136, 139 and their associated components are
designed to give the required fuel shaping above the speed
indicated by the point 132 in FIG. 14. Assume for the moment that
the upwardly inclined line is required in the characteristics, then
the link 138 is removed from the circuit. As long as the engine
speed is below the point 132 in FIG. 14, the output from the
transducer 15 is sufficient to hold the transistor 133 on, and so
the transistor 136 is off. However, at the point 132, conduction of
the transistor 133 decreases sufficiently for the transistor 136 to
turn on and provide base current to the transistor 139, which turns
on to provide current to the terminal 160. As the speed increases
further, the transistor 133 conducts less, and the transistors 136,
139 conduct more to provide the desired characteristic.
Assume now that the downwardly inclined dotted line is required,
then the links 137, 140, 143 are removed from the circuit. The
transistor 133 still behaves in the same way, but at the point 132
base-emitter current flows in the transistor 136 by way of the link
138, drawing current from the terminal 160. As conduction of the
transistor 133 decreases further, more current is drawn through the
base-emitter of the transistor 136, although of course the
transistor 136 does not conduct in its collector since the link 140
is removed. It will be seen that a downwardly inclined
characteristic is now obtained. In both arrangements, the resistors
130, 135 set the desired slopes of the dotted lines and the point
132.
Turning now to the other half of the circuit, the transistors 147,
157 constitute a long tail pair having a constant current source in
the tail, this constant current source being constituted by the
transistor 151. At speeds above the point 131 in FIG. 14, the
transistor 147 is conducting a substantial current, and the
transistor 157 is conducting very little current so that the
transistor 163 is off. As the speed reduces and the point 131 is
reached, then the conduction of the transistor 147 reduces to a
point at which the correspondingly increased conduction of the
transistor 157 is such that the transistor 163 is not on, but is
about to come on. At this stage, the transistors 147, 157 are
conducting equally. Any further reduction in speed reduces the
conduction of the transistor 147 further, and the transistor 157
increases its conduction, turning on the transistor 163, which
removes current from the terminal 160. The resistor 164 sets the
slope of the curve at speeds lower than the point 131, and two
possible slopes are shown in FIG. 14, one nearly vertical, and one
at a small angle to the horizontal. It will be noted that the
nearly vertical sloped curve strikes a horizontal curve, which
represents the minimum permitted value of the maximum fuel which is
set by the circuit. This line corresponds to complete switch-off of
the transistor 147. It will be clear that this limit will only be
reached if the slope is sufficiently steep for the fuel to be
decreased sufficiently before the speed reduces to zero. The point
131 is set by the resistor 136.
By reversing the two parts of FIG. 13, and making minor polarity
attention the low speed dotted lines and the high speed dotted
lines of FIG. 14 can be interchanged.
Referring now to FIG. 15, the arrangement shown operates in a
similar manner to the arrangement of FIG. 1, but the parts are
arranged differently. In FIG. 1, the amplifier 18 is responsive to
the three basic system parameters, and also to two subsidiary
controls from controls 29, 31. In FIG. 15, the controls 29, 31 do
not influence the amplifier 18. However, associated with the
amplifier 18 is an amplifier 184 which receives signals from the
transducer 16 by way of a resistor 16c, from the transducer 15 by
way of a resistor 15b, and from the control 31. The outputs from
the amplifiers 18, 184 are fed through a pair of diodes 182, 187 to
the diode 24, and the junction of the diodes 24, 182, 187 is
connected to the terminal 21 through a resistor 181.
The control 29 now provides an input to the summing junction of an
amplifier 185, which also receives an input by way of a resistor
16d from the transducer 16 and by way of a resistor 15c from the
transducer 15.
The amplifier 19 is the same as in FIG. 1 except for the control
33, which now provides an input to an amplifier 186 which also
receives an input by way of a resistor 16e from the transducer 16.
The outputs from the amplifiers 19, 186 are fed by way of diodes
192, 191 to the diode 26, and the junction of the diodes 26, 191,
192 is connected to the terminal 21 through a resistor 189.
Moreover, although none of the feedback connections to the five
amplifiers are shown in FIG. 15, these connections are all taken
from the input to the drive circuit 25, for the reasons previously
explained.
The arrangement is such that at any given instant only one of the
diodes 24, 188, 26 can be conducting. Moreover, if the diode 24 is
operative, then either the amplifier 18 or the amplifier 184 is
operative by virtue of the diodes 182, 187. Similarly, if the diode
26 is operative, then either the amplifier 19 or the amplifier 186
is operative, by virtue of the diodes 192, 191.
Assuming that the diode 24 is conducting, then the amplifier 18
operates in the manner described with reference to FIG. 1. However,
if at any time the amplifier 18 demands a speed less than the
minimum speed set by the regulator, then the amplifier 184 produces
an output, reverse biasing the diode 182 so that the output by way
of the diode 24 is controlled by the amplifier 184.
If at any time a speed greater than the maximum engine speed is
demanded, then the amplifier 185 produces an output, reverse
biasing the diodes 24, 26 and controlling the engine.
The amplifier 19 operates in the manner described with reference to
FIG. 1, except that excess fuel is provided by way of the amplifier
186. When excess fuel is demanded, then the amplifier 186 produces
an output reverse biasing the diode 192.
It will readily be appreciated that the various components can be
re-arranged in a number of different ways. In particular, the
arrangement of FIG. 15 can readily be adapted to operate as a
two-speed governor simply by omitting connection through the
resistor 15a. In such an arrangement, the transducer 17 would of
course demand fuel, not speed.
In all the examples shown, the transducer 15 conveniently comprises
an a.c. generator driven by the engine and producing an output at a
frequency proportional to engine speed, this output being fed to a
diode pump circuit which produces an output voltage dependant upon
engine speed. The transducer 16 can be in the form of a transformer
having an oscillator coupled to its primary winding, and means
whereby the position of the control rod 14 determines the coupling
between the primary and secondary windings. Detection means is then
incorporated in the transducer to measure the amplitude of the
signal in the secondary winding, and so produce an output voltage
representing the position of the rod 14. A similar arrangement can
be used in connection with a demand transducer, where the coupling
is varied by the pedal position.
In some cases, it may be desirable to include a capacitor in the
resistive feedback circuit of one or more of the amplifiers shown
in FIG. 6a, so as to increase or otherwise modify the d.c. gain of
the amplifier and so improve stability.
* * * * *