Title:
SPEED LIMITING SYSTEMS FOR INTERNAL COMBUSTION ENGINES
United States Patent 3665903
Abstract:
A speed limiting system for an internal combustion engine includes timing means for measuring the interval between successive openings of a contact breaker or other switching device which is turned on and off in timed relationship to the engine to control the production of sparks at the plugs of the engine. A thyristor is operable by the timing means when the interval between successive openings of the switch device falls below a predetermined minimum value for preventing production of sparks.


Inventors:
Harris, Paul Anthony (Walsall, EN)
Phoenix, Lancelot (Birmingham, EN)
Application Number:
05/005421
Publication Date:
05/30/1972
Filing Date:
01/23/1970
Assignee:
Joseph, Lucas
Limited (Birmingham, EN)
Primary Class:
International Classes:
F02P11/02; F02D17/04; F02P9/00; (IPC1-7): F02D11/10
Field of Search:
123/102,148E,140.3
View Patent Images:
US Patent References:
3525017ELECTRIC GOVERNOR APPARATUS1970-08-18Rosenberg et al.
3485227SWITCHING CIRCUIT1969-12-23Meyerle
3430615ELECTRONIC SPEED CONTROL DEVICE FOR AN ENGINE1969-03-04Chavis
3402327Engine overspeed protection device1968-09-17Blackburn
3363615Switching circuit1968-01-16Meyerle
3356082Spark ignition circuit1967-12-05Jukes
3182648Speed responsive switching apparatus1965-05-11Scheider et al.
Primary Examiner:
Goodridge, Laurence M.
Claims:
Having thus described our invention, what we claim as new and desire to secure by Letters Patent is

1. A speed limiting system for 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 said primary winding is connected to a D.C. source, said engine driven switching device being turned on and off in timed relationship to the engine, and a spark being produced when the switching device is turned off to break current flow in said primary winding, said system comprising a thyristor connected in a circuit across said switching device, and a timing circuit including a first timing network coupled to said switching device and a second timing network coupled to said first timing network and to the gate of said thyristor, said second timing network when energized providing gate current to said thyristor, and said first timing network being energized upon turning off said switching device and holding said second timing network de-energized for a fixed period during which a spark is produced, whereafter the first timing network is de-energized and the second timing network is energized for a fixed period of time, said thyristor preventing conduction of a further spark if said switching device is turned off during said predetermined period of time.

Description:
This invention relates to a speed limiting system for an internal combustion engine of the kind incorporating an ignition coil, the secondary winding of which is connected to the plugs of the engine in turn, and a primary winding which is connected to a D.C. source through a contact breaker or other switching device which is turned on and off in timed relationship to the engine.

A system according to the invention includes timing means for measuring the interval between successive openings of said switching device, and control means operable by said timing means when said interval falls below a predetermined minimum value for preventing production of sparks.

In the accompanying drawings,

FIG. 1 is a circuit diagram illustrating one example of the invention, and

FIG. 2 is a circuit diagram illustrating a second example of the invention.

Referring to FIG. 1, there are provided positive and negative supply lines 11,12 which in use are connected to the battery 13 of a road vehicle, the negative terminal of the battery 13 being earthed. Connected in series between the lines 11,12 is a primary winding 14 of an ignition coil 15, and a contact breaker 16 bridged by a capacitor 17. A secondary winding 18 of the ignition coil is connected through a distributor 19 to the plugs 21 of the engine in turn in the usual way.

The junction of the winding 14 and contact breaker 16 is connected to the line 12 through a resistor 22 and capacitor 23 in series, the junction of the resistor 22 and capacitor 23 being connected through a resistor 24 to the base of an NPN-transistor 25 having its emitter connected to the line 12 and its collector connected to the line 11 through a resistor 26. The collector of the transistor 25 is further connected through a capacitor 27 to the base of an NPN-transistor 28, the transistor 28 having its emitter connected to the line 12, its base connected to the line 11 through a resistor 29 and its collector connected to the line 11 through a resistor 31, and further connected through a capacitor 32 to the base of an NPN-transistor 33. The emitter of the transistor 33 is connected to the line 12, while its base is connected to the line 11 through a resistor 34, and its collector is connected to the line 11 through a resistor 35 and is further connected to the gate of a thyristor 36, the cathode of which is connected to the line 12 and the anode of which is connected through a resistor 37 to the junction of the winding 14 and contact breaker 16.

The contact breaker 16 is opened and closed in timed relationship to the engine, and when it is closed energy is stored in the winding 14. On opening of the contact breaker 16, this energy produces a spark at the appropriate plug in the usual way.

The interval between successive openings of the contact breaker 16 will be dependent on the speed of the engine, and will decrease as the speed of the engine increases. A maximum engine speed, corresponding to a minimum interval between successive openings of the contact breaker 16, is selected, and the circuit values are chosen so that no spark is produced if the interval falls below the predetermined level.

Assuming for the moment that the speed of the engine is below the predetermined value, then at the instant when the contact breaker 16 opens, the transistor 25 will be off and the transistors 28 and 33 on, so that no gate current is being supplied to the thyristor 36. When the contact breaker 16 opens, a spark is produced, and at the same time there is a current flow by way of the filter 22, 23, 24, which is arranged to filter the high frequency oscillations occuring when a spark is produced, to the base of the transistor 25, so turning the transistor 25 on. When the transistor 25 is turned on, the transistor 28 will be turned off for a period of time determined by the resistor 29 and capacitor 27, and will then turn on again. As soon as the transistor 28 turns on again, the transistor 33 is turned off for a period of time determined by the resistor 34 and capacitor 32, and while the transistor 33 is off, gate current flows in the thyristor 36 so that the thyristor is turned on. Bearing in mind the engine speed is below the predetermined value, the arrangement is such that when the transistor 33 turns on again to remove gate current from the thyristor 36 the interruptor 16 is closed, so that the interrupter 16 short-circuits the thyristor 16, which therefore turns off. The contact breaker 16 then opens again, and the cycle is repeated. However, in the event that the engine speed is above the predetermined value, the contact breaker 16 will open in an attempt to produce another spark while the transistor 33 is still off, and in these circumstances the thyristor 36 will still be conducting, so that an opening of the contact breaker 16 the circuit to the winding 14 is completed through the thyristor 36. For this reason no spark is produced, but the rise in voltage across the interrupter 16 produced by the resistor 37 is sufficient to turn the transistor 25 on again so that another timing cycle commences.

The reason for having two timing circuits 29,27 and 34,32 is to ensure that there is always a delay determined by the resistor 29 and the capacitor 27 between the opening of the contact breaker 16 and the turning on of the thyristor 36, the spark being produced during this delay. There is then an additional delay determined by resistor 34 and capacitor 32 during which the thyristor 36 stays on, and the sum of these two delays is equal to the minimum time between openings of the contact breaker 16. Either resistor 29 or 34 can if required, be variable so that the delays can be set.

In FIG. 2, which illustrates a second example of the invention, the resistor 37 is omitted, the anode of the thyristor 36 being connected directly to the junction of the winding 14 and contact breaker 16. The cathode of the thyristor 36 is connected to the line 11 instead of the line 12, and the connection from the collector of the transistor 33 to the gate of the thyristor is omitted. The resistor 35 connecting the collector of the transistor 33 to the line 11 is omitted, and is replaced by a pair of resistors 38,39 in series connecting the collector of the transistor 33 to the junction of the winding 14 and contact breaker 16, the junction of these two resistors 38,39 being connected through the cathode-anode path of a diode 41 to the line 11, and also being connected to the gate of the thyristor.

Further the resistors 26, 29, 31 and 34 are no longer connected directly to the supply line 11, but are connected to one end of a resistor 42 and to the cathode of a Zener diode 46, the anode of the Zener diode 46 being connected to earth and the other end of the resistor 42 being connected to the supply line 11. The circuit also now includes a diode 43, the anode-cathode path of the diode 43 being connected between the supply line 12 and the junction of the resistors 22,24, and a pair of resistors 44,45. The resistor 44 is connected between the supply line 12 and the base of the transistor 25 and resistor 45 is connected between the base of transistor 25 and the collector of the transistor 28.

The overall operation is not effected by these minor circuit modifications, it being appreciated that by virtue of the winding 14 the anode of the thyristor 36 will be at a considerably higher potential than the line 11 when the contact breaker 16 is open so that the thyristor 36 can still conduct event though its cathode is connected to the positive line. The circuit modification has the advantage that because the cathode of the thyristor is connected to the positive line , there is no possibility of the thyristor 36 conducting if the engine stalls.

In a modification (not shown) of the above examples of the invention, the speed limiting system is to be used with the contact breaker 16 replaced by a semi-conductor device, and in this circuit the resistor 24 of the filter 22, 23, 24 is replaced by a Zener diode.