AU456830B2 - Speed limiting systems for internal combustion engines - Google Patents

Description

I

00,35 6 This invention relates to speed limiting systems for internal

combustion engines.

A speed limiting system according to the invention is

intended for use with an internal combustion engine having an

ignition coil with a primary winding and a secondary winding,

means connecting said secondary winding to the plugs of the engine

in turn, and an engine driven switching device through which the

primary winding is connected to a d.c. source, the engine driven

switching device being turned on and off in timed relationship to

engine and a spark being produced when said switching device is

turned off to break current flow in said primary winding, said

system comprising a thyristor connected in a circuit across said

primary winding, a transistor which is coupled to the switching'

device and is turned on as a result of opening of said switching

device, means for initiating flow of gate current to the thyristo3

at a predetermined instant of time after the transistor has been

turned on, and maintaining gate current for a predetermined perio(

of time, and means for holding said transistor .on until gate

current is supplied to the thyristor, said thyristor preventing production of a further spark if said switching deVice is turned

off during said predetermined period of time, and said predetermil

instant of time being chosen so that the switching device is neve3

turned off before said predetermined period of time commences.

in many known speed limiting systems it is necessary to measi

engine speed over a number of cycles.

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The great e with such an arrangement is that because of

the delay in speed measurement the speed can continue .to increase

to a dangerous level during said delay. Using the present

invention, he engine speed is never actually measured, but

there is automatically defined at all times a time zone,

represented by said predetermined period of time, during which

no further sparks can be produced. The reason for only

starting to supply gate current to the thyristor at a

predetermined instant of time after the previous opening of

the switching device is to give the spark time to extinguish.

It will be noted that while the spark is extinguishing during

,this period, the transistov.which must conduct to start each

cycle is held on. By keeping this transistor on, the

arrangement has the important advantage that the circuit

cannot be re-triggered by signals received from the engine

driven switching device. This is of particular importance where,

as is usual, the engine driven switching device is a contact

breaker, because when a contact breaker opens, it produces an

oscillatory signal which dies away and is then followed by a

further signal at a later .point in he cycle. This further

signal appears before the supply of gate current to the thyristor

is allowed.

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above a predetermined value, corresponding to the length of

time between successive openings of the contact breaker

being below a predetermined value.

Assuming for the moment that the speed of the engine

is below the predetermined value, then the circuit operates

in a manner which is illustrated by Figure 2. In Figure 2

the first four wave forms from the top relate to the transistors

64, 74, 79 and 95 respectively, and indicate whether the

respective transistors are conducting or not conducting. The

bottom waveform illustrates the gate current supplied to

the thyristor 89. The instants at which the contact breaker

open are indicated by the numerals zero on the time scale.

When the contact breaker 55 and winding 54 is in the form of

a short burst of oscillations, and these oscillations are

smoothed by the diode 61 and capacitor 65 and then serve to

turn on the transistor 64. As the contact breaker 55 opens

the transistors 74, 79 and 85 are all on and no gate current

is supplied to the thyristor 89, but conduction of the trans-

istor 64 results in current flowing through the resistor

being diverted by way of the capacitor 72 and the collector-

emitter path of the transistor 64, so that the transistor 74

turns off as indicated in Figure 2, and remains off for a

period of time tl, which

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In the accompanying drawings,

Figure 1 is a circuit diagram lllustrang one example

of the invention, and

Figures 2 and 3 are graphs illustrating the operation

of the circuit.

Referring to Figure 1, there are provided positive

and negative supply lines 51, 52 between which the vehicle

battery 53 is connected, the line 52 conveniently being

earthed. The ignition coil of the vehicle includes a primary

winding 54 which is connected in series with a contact breaker

between the lines 51, 52, the contact breaker 55 being

bridged by a capacitor 56 in the usual way, and the secondary

winding 57 'of the ignition ooil being connected through a

distributor 58'to'the spark plugs 59 of the engine in turn.

The Junction of the winding 54 and contact breaker

is connected through a diode 61, a resistor 62 and a resistor

62 and a resistor 63 in series to the base of an n-p-n trans

istor 64, the junction of resistors 62 and 63 being connected to the line 52 through a capacitor 65, and the base of the

transistor 64 being connected to the line 52 through a resistor

66. The collector of the transistor 64 is connected through

a resistor 67 to a supply line 68 which is coupled to the

line 51 through a resistor 69 and is earthed through a Zener

diode 71. The collector of the transistor 64 is further connect-

ed to a capacitor 72 and a resistor 73 in series to the base

of an n-p-n transistor 74, the Junction of the capacitor 72

and resistor 73 being connected to the line 68 through a

resistor

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The transistor 74 has its emitter connected to the

line 52 and its collector connected through a resistor 76

to the line 68, and further connected through a capacitor

77 and a resistor 78 in series to the base of an n-p-n

transistor 79, the emitter of which is connected to the line

52. The junction of the capacitor 77 and resistor 78 is

connected to.the line 68 through a resistor 81, and the

collector of the transistor 79 is connected through a resistor

82 to the line 68, through a resistor 80 to the base of the

transistor 84 in series to the base of n-p-n transistor

The Junction of the capacitor 83 and resistor 84 is

connected to the line 68 through a resistor 86, whilst the

transistor 85 has its emitter connected to the line 52 and

its collector connected through a resistor 87 and a diode 88

in series to the line 51. The junction of the resistor 87

and diode 88 is connected to the gate of a thyristor 89, the

cathode of which is connected to the line 51 and its anode

of which is connected to the junction of the winding 54 and

contact breaker 55. The gate-anode path of the thyristor 89

is bridged by a resistor 91.

The contact breaker 55 is opened and closed in timed

relationship to the engine, and when it is closed energy is

stored in the winding 54. On opening the contact breaker

the energy stored in the winding 54 produces a spark at the appropriate plug 59 in the usual way. The interval

between successive openings of the contact breaker 55 will

dependent on the speed of the engine, and will decrease as

the speed of the engine increases. The circuit is designed

to prevent production of sparl-s when the engine speed is

g ^§.82 represents the time taken for the capacitor 72 to charge.

Preferably, a further resistor (not shown) is connected between

the collector of.the transistor 74 and the base of th~e transistor 64 so that during- the time ti the transistor 64 is held on by current flowing through this additional resistor and the resistor

76.- As soon as the capacitor 72 is charged, current flowing

through the resistor 75 turns on the transistor 74 again, and as a result a capacitor 77 which when the transistor 74 turned

off discharged throughtbe resister 76 and 78, starts to charge

again through the collector-emitter of the transistor 74, so turning off the transistor 79. As soon as the transistor 79 turns off current flows through the resistor 82 and 80 in

series to provide base current to the transistor 64, so that

the transistor 64 stays on even if no further signal is applied by way -of the diode 61.

The transistor 79 stays off until the capacitor 77

has charged, and this time period is represented in Figure 2 by t2. At the end of the period t2, the capacitor 77 is

charged, and the transistor 79 turns on again. The transistor

64 can now turn off if no base current is being received from the capacitor/6. At the same time, the capacitor 83, which

when the transistor 79 was turned off discharged through

resistor 82 and resistor 84, starts to charge through-the

collector-emitter of the transistor 79, and resistor 86 so

turning off the transistor 85. The transistor 85 remains off

for a period of time t3 during which the capacitor 83 charges,

and the n is turned on again by current flowing through the

resistors S6 and 84. During the period when the transistor 85 is

7. 456.830

3 56 m off, Cate current can be supplied to the thyristor 89. I t will of course be appreciated that by virtue of the winding 54, the

anode of the thyristor 89 will be at a considerably higher

potential than the line 51 when the contact breaker 55 is open,

so that the thrysistor 89 can still conduct even though its cathode

is connected to the positive line. This arrangement of the thyristor 89 has the advantage that because the cathode is

connected to the positive line there is no possibility of the

thyristor 89 conducting if the engine stalls.

When the contact breaker 55 opens, it produces a further

pulse sometime after the opening. This is a known feature of ignition systems, but it could cause some difficulty if the

transistor 64 were not held on for the period of time tl+t2.

The period t2 is chosen so that this additional pulse occurs

during the period t2, and since the circuit is so designed that

the transistor 64 is intended to be conducting during this period,

the additional pulse from the contact breaker has no effect.

At the end of the period t3, the circuit remains in its steady state as indicated in Figure 2 with the transistors

74,79 and 85 all conducting. The cycle then re-starts when the contact breaker 55 opens, as clearly shown in Figure 2.

Thus, when the circuit is operating with the engine speed below

the predetermined value, the thyristor 89 can be supplied with

gate current during the period of time t3, but the gate current

is inhibited before the contact breaker opens again, so that

the thyristor 89 plays no part in the operation of the circuit.

In order to understand the operation of the circuit

when the engine speed is above the predetermined value, reference

is directed to Figure 3. At the commencement of a cycle,

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andthe the transistor 64 is turned on as described above, tl+t2. However, operation is in fact identical for the period the contact with the speed above the predetermined'value, t3. It will breaker 55 will open again during -the period t3 are so chosen. be understood that the periods tl, t2 and without ignition so that the engine is not capable of overspeeding tl+t2. that the contact re-opens within a period 89 Vhen the contact breaker 55 opens, the thyristor 91 as clearly is supplied with gate current through resistor the winding 54 is seen in Figure 3, and so the current in no spark is produced. maintained by way of the thyristor, and on again and so another However, the transistor 64 is turned 74 being turned on after cycle re-commences, with the transistor tl- is of course equal to t1. a period tl- in the new cycle, where 85 is now off at the The only difference is that the transistor fact remains off until the beginning of the new cycle, and in as indicated in end of the period t3 in the previous cycle, the Figure 3. This of course does not matter, because the period t2- in the transistor 85 is on again at the end of off to perform its function of new cycle, at which point it turns It should be noted that allowing the thyristor 89 to conduct. 3 the transistor although in the arrangement shown in Figure in the first cycle, remains off until the end of the period t3 turn on before this stage. it is possible for the transistor 85 to the second cycle, the Thus, at the end of the period tl- in 85 is still off transistor 79 turns off, and if the transistor on. Because for at this stage, it will automatically turn have been shown as equal in simplicity the periods tl,t2 and t3

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is not possible for the period tl- to terminate Figures 2 and 3, it

before the period t3. However, if the time periods are not be in practice, equal, which of course they are unlikely to period t3, and so the then the period t1- can terminate before the in time. The transistor 85 will turn on again at this point because operation is of course unaffected by this feature, is that it should the important feature of the transistor 85 the first cycle or t2- be non-conducting after the period t2 in

int he second cycle. 3 It will of course be appreciated that in Figure is not shown. the third opening of the contact breaker 55 second opening If the engine continues to run too fast after the opening will of the contact breaker, then of course the next drawn in Figure occur during the period t3- and the waveforms

3 will be modified.

In a modification, one or more of the resitors periods can be set 81,86 is variable so that the three delay to suit different requirements. The circuit can also be alme form of used when the contact breaker 55 is replaced by the engine. semi-conductor device which is turned on and off by

56n The claims defining the invention areas follows i-

1. A speed limiting system for an internal combustion engine

havin. an ignition coil with a primary winding and a.secondary

winding, means connecting said secondarywinding to the plugs

of the engine in turn, and an engine driven switching device

through which the primary winding is connected to a d.c. source,

the engine driven switching device being turned on and off in

timed relationship to the engine and a spark being produced when

said switching device is turned off to break current flow in said

primary winding, said system comprising a thyristor connected in

a circuit across said primary winding, a transistor which is

coupled to the switching device; and is turned on as a result of

opening of said switching device, means for initiating flow of

gate current to thethyristor. at a predetermined instant of time

after the transistor has been turned on, and allowing gate

current for a predetermined period of time, and means for

holding said transistor on until gate current is supplied to the

thyristor, said thyristor preventing production of a further

spark if said switching device is turned off during said

predetermined period of time, and said predetermined instant

of time being chosen so that the switching device is never turned

offAbefore said predetermined period of time commences.

r1

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Claims (1)

1. 30356 m

   2. A system as claimed in claim 1 including a first capacitor

   which charges when the first-mentioned transistor is turned on,

   a second transistor which is held off while the first capacitor t charges and is then turned on again,.a farA ba4k "ir t reom *the- nd tranoi tr to tho fir-st t-sisetor, a second

   capacitor which charges when the second transistor turns on,

   a third transistor which is turned off when the second

   capacitor is charging and then turns on again, a feedback

   circuit from the third transistor to the first transistor, said feedback circuit providing the required means for holding

   the first transistor on, a third capacitor which charges when

   the third transistor turns on again, and a fourth transistor

   which is turned off while the third capacitor is charging and

   then turns on again, the fourth transistor serving when it is

   off to allow gate current to be supplied to the thyristor.

   3. A system as claimed in claim 2 including a feedback circuit from the second transistor to the first transistor for holding

   the first transistor on when the second transistor is off.

   4. A system as claimed in claim 2 or claim 3 including means

   for varying the charging rate of the first capacitor.

   A system as claimed in any one of claims 2 to 4 including means for varying the charging rate of the second capacitor.

   6. A system as claimed in any one of claims 2 to 5 including

   means for varying the charging rate of the third capacitor.

   7. A system as claimed in any one of claims 1 to 6 in which the engine driven switching device is a contact brdaker.

   30,3 5 6/11 8. A speed limiting system for an internal combustion engine comprisinp the combination-of parts arraneed and adapted to operate substantially as described with reference to the a.cconpanyina drawings.

   Dated this 22nd day of June, 1971. v MIPLUCAS (IIDUSTa:s J..I By their Pa-.ent Attorney:.

   of GRIFFIrHI, 7A3SZL RAZERH.

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   T74I I I T79

   T-i I I 0II III- SCC

   TI E T3 TI TE TIME -N FIG.?. 1 -I

   TIME 0 FIG.3.

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