Note: Descriptions are shown in the official language in which they were submitted.
I lB1~29
The invention relates to apparatus for
maintaining a diesel engine at a ready-to-start
temperature. The invention is particularly,
although not exclusively, applicable to large
diesel engines of the kind which are used in
trucks, earth moving vehicles, and military vehicles.
It is well known that it is difficult to
start many types of diesel engines in cold weather
and, so far as the applicant is aware, no
satisfactory apparatus is currently available which
will maintain a large diesel engine at a ready-to-
start temperature without drawin~ heavily on a
battery or requiring an external power source.
Apparatus is known which is operable to periodically
start and run internaI combustion engines of the
kind including spark plugs,ignition coils and
associated electrical equipment and carburettors,
but such apparatus cannot be satisfactorily used
with a diesel engine.
It is therefore an object of the invention
to provide apparatus which will satisfactorily
periodically start and run a diesel engine,
especially a large diesel engine, without draining
a battery or requiring an external power source.
According to the present invention,
apparatus for maintaining a diesel engine at a
ready-to-start temperature comprises means
responsive to the falling of the engine block
temperature to a predetermined low value to actuate
the starter for a predetermined period of time and
to actuate the fuel supply means, means responsive
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to the attainment of a predetermined oil pressure
corresponding to an engine running condition to
de-actuate the starter and continue the actuation
of the fuel supply means to continue running of
the diesel engine, and means responsive to the
raising of the engine block temperature to a
predetermined high value to de-actuate the fuel
supply means and thereby stop the diesel engine.
Thus, as soon as the engine block
temperature has fallen to a predetermined low
value, for example about 90F. (~2C.), the
engine is started and runs until the engine block
temperature has increased to a predetermined high
value, for example about 150F. (65C.), at which
time the engine is stopped. When the predetermined
low engine block temperature is sensed, the
starter is actuated for up to a predetermined
maximum period of time, for example about 7(seven)
seconds, and engine starting is sensed by the
attainment of a predetermined oil pressure. Thus,
the diesel engine is satisfactorily`maintained at
a ready-to-start temperature.
The apparatus may also include means
responsive to the end of the predetermined period
of time to increase the speed of the engine if
the engine has started. Thus, initial start-up
of the engine may cause the engine to run at an
idling speed, with the engine speed being increased
to an appropriate higher value at the end of the
predetermined period of time. Means may also be
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provided to obtain a higher than normal idling
speed ~rom the commencement of engine rl~nning.
The apparatus may also include means
responsive to failure of the diesel engine to
start during the predetermined period of time to
indicate the failure after the predetermined
period of time. Thus, if the engine fails to
start at the end of a single attempt, this failure
is indicated. The apparatus may also include
means responsibe to failure of the engine to
start during the predetermined period of time
to prevent a further start attempt being made.
The failure of the engine to start at the
predetermined low engine block temperature almost
certainly means that some fault requiring
attention has developed, and in such a case the
apparatus does not make further start attempts
which may cause further damage.
The means responsive to the falling of
the diesel engine block temperature and to the
raising of the engine block temperature may
comprise an electrical resistor whose resistance
varies in accordance with engine block temperature.
The means responsible to the falling of
the engine block temperature to the predetermined
low value and the means responsive to the
raising of the engine-block temperature to the
predetermined high value may comprise electrical
means operated by the falling of the engine block
temperature to the predetermined low value to
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actuate the starter and the fuel supply means
and to hold the electrical means in its operated
state un-til the engine block temperature has
risen to the predetermined high value.
Such electrical means may comprise relay
means actuated by the attainment of the
predetermined voltage corresponding to the
predetermined low engine block temperature to
cause the actuation of the starter and the fuel
supply means for the predetermined period of time,
the relay means also actuating a holding circuit to
maintain a relay operating voltage until the engine
block temperature has risen to the predetermined
high value.
One embodiment o the invention will now
be described by way of example, with reference to
/ the accompanying drawing, which shows an electrical
circuit diagram of apparatus for maintaining a
large diesel engine at a ready-to-start temperature.
Referring to the drawing, apparatus is
provided for maintaining a liquid-cooled diesel
engine 12 at a ready-to-start temperature, the
diesel engine 12 being of the kind which has a
negative ground electrical circuit. The apparatus
comprises an operational amplifier 14 with 8
terminals numbered 1 to 8. Terminal 6 is
connected through resistors R7 and R8 to a voltage
supply line 16 which is connected through diode D3
and an on/off switch 17 to the positive terminal
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` I ~61929
of the battery 18 of the engine 12. The
~unction of resistors R7 and R8 is connected
to the base of a transistor Tl whose emitter
is connected to voltage supply line 16 and
whose collector is conne~ted through resistor
R9 to one end of the coil of a relay Yl. ~
diode D2 is connected across the ends of the
reIay coil, and the other end of the relay coil
is connected to ground. Terminal 7 of amplifier
14 is connected directly to voltage supply line 16.
Terminal 2 of amplifier 14 i5 connected
through line 20 to an engine block tempexature
sensor 22 which comprises a thermistor with a
negative temperature coefficient which senses
the temperature of the engine block of the diesel
engine. Thus, as the engine block temperature
falls, the electrical resistance o~ the sensor 22
increases. Terminal 2 is also connected through
resistor R10 to voltage supply line 16. Terminal
3 is connected to the junction of resistors R5 and
R6 connected between voltage supply line 16 and
gxound. Terminal 4 is connected to ground, and
terminals 1, 5 and ~ are not used.
Relay Yl has two normally open contacts
24, 26, a normally closed contact 28~ and two-way
contact 29. Contact 24 is connected between
voltage supply lines 16 and resistor R12 which is
connected to engine block temperature sensor
line 20. Contact 26 is connected between voltage
supply line 16 and a line 30 through a resistor
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~ 16~
to a failed start indicator 31, which will be
described in more detail later. Contact 28
is connected to line 34 which is connected to
the junction between resistor R4 and one end of
the coil of relay Y3, resistor R4 being
connected to voltage supply line 16, and the
other end of the coil of relay Y3 being
connected to ground. Normally, contact 28
connectsline 34 to ground but, when relay Yl
is energized, contact 28 disconnects line 34
from ground. Line 34 is also connected to line
36 which is connected to an oil pressure
switch 38 in the lubricating oil circuit of the
engine. When the oil pressure in engine 12 is
below a predetermined value, the pressure switch
38 connects line 34 and 36 to ground. When the
oil pressure rises above the predetermined value,
the oil pressure switch 38 disconnects lines 34
and 36 from ground.
An electronic timer 40 has eight
terminals numbered 1 to 8. Terminal 8 is
connected through resistor R16 and line 42
to normally closed contact ~4 of override
switch 73 which is connected to line 16. Terminal
2 is connected through resistor Rl to line 16 and
also through line 21 to the normally open terminal
of contact 29 of relay Yl. Capacitor Cl is
connected between the common terminal of contact
29 and ground. Resistor R17 is connected between
the normally closed terminal of contact 29 and
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1 161~2g
ground. Terminal 8 is also connected through
capacitor C4 to ground.
Terminal 6 and 7 are connected through
resistor R2 to line 16 and through capacitor C3
to ground. Terminal 3 is connected through
resistor R3 to the base of transistor T2 with a
diode Dl being connected between terminal 3 and
ground. The collector of transistor T2 is
connected to line 16 and the emitter is connected
to one end of relay coil Y2. The othar end of
coil Y2 is connected to ground. Terminal 1 is
connected to ground, and terminal 5 is connected
through capacitor C2 to ground. Terminal 4 is
connected by line 44 to a transmission and hood
detector switch 46 which will be described in
more detail later.
Relay Y2 has two contacts 48, 50 and
relay Y3 has two contacts 52, 54. Normally open
contact 48 is connected between the positive
terminal of battery 18 and line 56 which is
connected to the common terminal of two-way
contact 54 and to failed start indicator 32.
Two--way contact S0 has a common terminal connected
through ~ine 62 to the positive terminal of
battery 18 and normally connects llne 62 through
line 64 to a throttle up solenoid 66 in the
diesel engine 12. The function of the throttle
up solenoid 66 will be explained later. The
open terminal of contact 50 is connected by line
68 to the open terminals of contacts 52 and 54
g
and by line 58 to fuel control solenoid 60 which
controls fuel supply to the diesel engine 12.
Normally open contact 52 has its common
terminal connected to line 62 and, when closed,
connects voltage supply line 62 through line 58
to the fuel control solenoid 60. Two-way contact
54 normally connects line 56 through line 70 to
the engine starter 72, and when relay Y3 is
energized contact 54 connects line 56 to line 58
instead of to line 70.
As previously mentioned, line 64 is
connected to a throttle-up solenoid 66, and
throttle-up solenoid 66 is connected to the oil
pressure switch 38 which, when the oil pressure
is at the engine running value, connects the
throttle up solenoid 66 to ground to complete
the circuit therethrough.
The operation of the circuit as 50 far
described will now be explained, assuming that
the diesel engine-12 is installed in a truck or
other diesel po,wered vehicle which has been driven
to a location where the ambienk temperature is
less than 40F (4C.). While the diesel engine
12 is running, the temperature of the engine
block will be at least 150F (65C). When the
operator switches off the engine, the operator
also closes the main switch 17 of the readiness-
maintaining circuit. Owing to the relatively
high temperature of the engine block, the engine
block sensor 22 has a low resistance and the
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amplifier 14 does not produce a sufficient voltage
at the base of transistor T1 to effect conduction
; thereof. As the temperature of the engine block
falls, the resistance of the engine block
temperature sensor 22 increases and thereby causes
the voltage at terminal 2 of the amplifier 14 to
increase.
When the temperature of the engine block
has fallen to ~0F (27C), the voltage at terminal
2 of amplifier 14 has risen to a value such that
the voltage on the base of transistor Tl causes
transistor Tl to conduct, thereby energizi~g relay
Yl. Thus, contact 24 connects resistor R12 between
voltage supply line 16 and terminal 2 of amplifier
14, thereby putting resistor R12 in parallel with
resistor R10, and thus raising the voltage at
terminal 2 to a higher value. As will be more
clearly apparent later, this means that the voltage
at terminal 2 will not fall to a value causing
transistor Tl to cease conduction until the engine
block temperature sensor 22 has sensed a temperature
considerably higher than that which originally
caused the amplifier 14 to effect conduction by
transistor Tl. In this embodiment, the arrangement
is such that the conduction of transistor Tl will
not cease until the engine block temperature
reaches 155 F (68 C).
Energi~ation of relay Yl also causes
contact 26 to connect voltage supply line 16 to
line 30, to resistor R13 and the failed start
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indicator 31. Also, contact 28 ope~ns, and contact
29 connects terminal 2 of amplifier to capacitor
Cl instead of to resistor R17, thereby actuating
timer 40 with resultant conduction of transistor
5 T2 and energization of relay Y2.
13nergization of relay Y2 causes contact
48 to connect line 56 to the positive terminal of
battery 18, and thereby supply voltage throuyh
line 70 to the starter 72. Energization of relay
10 Y2 also causes contact 50 to connect voltage
supply line 62 to line 68 instead of to the throttle
up solenoid line 64. The consequent voltage supply
line 68 thus supplies voltage to line 58 to cause
operation o fuel control solenoid 60. Thus,
15 the starter 72 is operated and :Euel is supplied to
the engine by operation of the fuel control
solenoid 60. If the engine 12 starts within the
operating period of the timer, i.e. within 7(seven)
seconds, the oil pressure in the engine will
20 increase to a value sufficient to actuate the oil
pressure switch 38, with the result that line 36
is disconnected from ground, thereby causing relay
Y3 to be energized from the voltage supply line 16
through resistor R4. Actuation of the oil pressure
25 switch 38 also connects throttle up solenoid 66 to
ground.
Energization of relay Y3 causes contact
52 to connect voltage supply line 62 through line
58 to the fuel control solenoid 60, thereby
30 maintaining the supply of fuel to the engine
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12, and causes contact 54 to disconnect starter
line 70 from voltage supply line 68, thereby
discontinuing operation of the starter 72. The
engine therefore now runs at a speed set by the
fuel control solenoid 60, for example an idling
speed of 600-800 rpm. and, at the end of the 7(seven)
second time period, the timer 40 de-energizes
relay Y2. Contact 48 opens, and contact 50
connects supply line 62 to throttle up solenoid 66
instead of to line 68. Since oil pressure switch
38 has already been actuated, throttle up solenoid
66 is then actuated to cause the engine 12 to
operate at a higher speed, for example 900 to
1000 rpm.
Thus, the engine will now run at the
higher speed until the engine temperature reaches
155F., at which time the resistance of the engine
~lock temperature sensor 22 will have fallen to
a predetermined low value which causes the voltage
at terminal 2 of amplifier 14 to fall to a value
to cause transistor Tl to cease conduction. Relay
Yl is then de-energized so that contact 28 grounds
line 34 to de-en,orgize relay Y3. De-energization
of relay Y3 causes contact 52 to remove voltage
from the fuel control solenoid 60, and the engine
therefore stops. De-energization of relay Yl also
causes contacts 24 and 26 to open, and de-
energization of relay Y3 also causes contact 54 to
re-connect line 56 to starter line 70.
The engine then remains stopped until
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the engine block temperature again falls below
~0F (27C), whereupon the previously described
sequence re occurs. Thus, the engine is maintained
at a ready-to-start temperature, being started
whenever the engine block temperature falls below
80F (27C), with each engine running stage being
continued until the engine block temperature has
reached 155F (68 C).
If the engine did not start within the
7(seven) second period of operation of the timer
40, relay Y3 will not have been energized by
engine oil pressure, and relay Y2 will be de-
energized at the end o~ the 7(seven) second time
period. Since the engine block temperature does
not rise, amplifier 14 will keep relay Yl energized
with the result that timer 40 will not be re-
activated. Thus, if the engine does not start within
the 7(seven) second time period, no further starts
are attempted.
In addition, the trouble light indicator
31 is provided to indicate such an occurrence. The
trouble light indicator 31 is a light emitting
diode whose cathode is connected via line 80 to line
56. The anode of indicator light 32 is connected
through resistor R13 to line 30. If the engine
fails to start, opening of contact 48 by de-
energization of relay Y2 isolates line 56 from the
positive terminal of battery 18. A circuit is
therefore conducted from line 30 through indicator
light 31 and line70 to ground, thereby activating
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:
.
indicator light 31.
It was previously mentioned that a
transmission and hood de~ector switch 46 is
connected to terminal 4 of timer 40. The switch
46 has two normally open switch contacts, one of
which is connected to the gear selector of the
engine and the other of which is connected to the
hood of the vehicle, such that the respective
switch unit closes if the transmission is engaged
or if the hood i5 raised to connect line 44 to
yround, thereby preventing operation of the
electronic timer 40.
In the circumstances, the dirver may wish
to keep the engine running at idling speed
continuously. In this case, after closing the main
on/off switch 17, the over-ride switch 73 is
operated. The override switch 73 has two sets of
contacts 74, 76. Normally closed contact 74
normally connects line 16 to line 42, but when
override switch 73 is operated, contact 74 isolates
line 42 and connects line 16 through resistor Rl9
to an override indicator light 79. Normally open
contact 76 connects the positive terminal of
battery 18 through resistor Rll to the engine
block temperature sensor line to cause the
voltage at terminal 2 of amplifier 1~ to increase
sufficiently to cause transistor Tl to conduct,
continuously with resultant energization of relay
Yl, thereby permitting continuous engine operation
to a pre-set higher temperature in the 185F to
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..
to 200F range (85 C to 93C).
An advantage of the override feature
` is that the engine bIock temperature sensor 22
automatically shuts off the engine while running
; 5 with the override switch 32 engaged, if the
engine block temperature rises above a pre-set
value as a result of overheating, by causing
transistor Tl to cease conduction with resultan-t
de-energization of relays Yl and Y3. Such over-
heating could occur for example if the coolant
is lost or its circulating pump fails.
To indicate when main switch 17 is closed,
indicator light 86 is connected to voltage supply
line 16 and to ground through resistor R15.
The majority of the components of the
described circuit can be provided as a very
compact linear integrated circuit, and the
complete circuit may be readily fitted to a diesel
engine. The described embodiment is adapted for
use with a diesel engine with a negative ground
electrical circuit. A person skilled in the art
will readily appreciate that the circuit can with
appropriate changes be easily adapted for use
with a diesel engine with a positive ground
electrical circuit. It w-ill also be readily apparent
that the invention is applicable to a li~uid-cooled
or an air-cooled diesel engine.
Other examples and embodiments of the
invention will be readily apparent to a person
skilled in the art, the soope of the invention being
defined in the appended claims.
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