GB2073816A - Ignition timing control systems - Google Patents

Abstract

The system comprises a pair of relays J1, J2 which control the connection to an ignition unit M of a respective one of two contact breakers M1, M2 thereby advancing or retarding the ignition timing in dependence on the position of the throttle. When the throttle is depressed, an earthed switch K engages a movable contact K2 to energise the relay J2 and enable one of the contact breakers M1 or M2 to be connected to the ignition unit. Similarly, if the throttle pedal is released, the other relay is energised via contact K1 to connect the other contact breaker to the ignition unit. <IMAGE>

Description

SPECIFICATION Ignition advance control The present invention relates to apparatus for ignition advance for four-stroke petrol engines with carburettors.

The demand for ignition advance in engines varies with not only the number of revolutions but also the load. Ignition advance mechanisms with centrifugal regulators have been used for several decades incorporating the ignition advance/number of revolutions characteristics required at a full load of the motor with a fractionline approximation. If the ideal characteristic were determined, which is approximated by the ignition advance mechanism with a flyweight, into a half ignition time/number of revolutions characteristic measured from the time of ignition until the top dead centre ignition, the results would show, that in practice the ignition time scarcely varies with the number of revolutions.

The purpose of an ignition advance is to obtain symmetrical combustion of the fuel in relation to the top dead centre ignition. However, the combustion time calculated from the ideal characteristic agrees with the time of combustion taking place in the motor only at a completely open state of the throttle valve and only depends on the number of revolutions to a slight extent.

When the throttle valve is partially open the socalled volumetric efficiency decreases almost linearly with the increased number of revolutions involving a change in combustion time. For a given number of revolutions, when the throttle valve is suddenly opened, i.e. when a considerable acceleration is taking place, the volumetric efficiency will suddenly increase, filling up of the cylinder improves and simultaneously the combustion time is reduced. In this case the phenomenon of detonating combustion, following partial combustion, known as "pinking" may be observed. With motors tending to pink, the high loads and sudden acceleration have been taken into account by vacuum ignition advance mechanisms but the purpose of said mechanisms has been to prevent pinking and nothing else.

However, tendency to pink is a special feature depending on the motor construction and is connected with the design of the cylinder head or the suction pipe and also the carburettor.

Recently, as the development of electronics and fuel supply through petrol injection has introduced new possibilities for increasing the efficiency of motors, attention has been paid to the demand for a load-depending ignition advance. In this case, the purpose of the ignition advance control lies in varying the angle of ignition advance with the combustion time i.e. the load. It may be that for a given number of revolutions the ideal ignition time will differ with the load. It is easier to make qualitative statements as to the ignition advance characteristic being simultaneously dependent on the number of revolutions and load, than to define it accurately. The greatest problem is in measuring the load.

The load should be defined in terms of parameters which can be measured. With a car there is a considerably loaded motor when the throttle valve of the carburettor is opened at a greater extent than the opening of the throttle valve which would be required for travelling on a plain path for a given number of revolutions and a total nominal weight. In other words each opening of the throttle valve when travelling on a horizontal path, depends on a maximum number of revolutions. When the number of revolutions is lower than that which would be expected from the opening of the throttle valve, the motor is accelerating or the vehicle is climbing a hill, i.e. the motor is highly loaded. However, when the number of revolutions just corresponds to the opening of the throttle valve or is even higher, the motor is only partially loaded or idle running is going on.The difference between the number of revolutions measured on a plain path in relation to the opening of the throttle valve and the real number of revolutions is thus characteristic of the size of the load. Accordingly, in order to be able to measure the load, the number of revolutions and opening of the throttle valve must be known, as must also a function connecting the two, which can be plotted under steady-state operational conditions.

Measuring and recording these factors can be carried out and to make frequent calculations in order to vary the ignition timing a computer must be employed.

Recently several methods have been proposed for an ignition and fuel supply system with a micro-processor control. However, these are rather expensive and although they are mostly reliable, returning to traditional ignition is almost impossible.

In order to be able to facilitate and to simplify the control of ignition other development was required.

A device is described in DE-AS 2316031 by which pre-timing of internal combustion motors may be performed. The device incorporates electronic circuit units, generating signals proportional to the number of revolutions. For generating the control signals needed for timing the ignition only the motor speed and the position of the throttle valve is used. The drawback of this system lies in that accurate timing of the ignition is only possible on a slight change of the number of revolutions of the main shaft. In the cases of increased load or a larger fluctuation of the number of revolutions accurate timing cannot be obtained.

A device according to DE-AS 2013703 has a similar design. The number of revolutions and the position of the throttle valve control signal generators with adjustable characteristics connected to a comparator, which at a predetermined ratio, in particular on the conformity of two input signals of the comparator, starts the ignition. The equipment also comprises a pulse generator to the output of which a storing and a summing circuit are connected.

Another electronic circuit is described in U.S.

Patent No. 3718126 for ignition timing. The circuit is for reducing the quantity of nitrogen oxide present in the combustion products of an internal combustion engine. Signals are generated depending on the motor characteristics, the number of revolutions, the motor temperature, the position of the transmission control.

A further development is described in U.S.

Patent No. 4005688 and U.S. Patent No.

3930474. In both patents similar systems for the control of the ignition are described, in which ignition becomes effective at a predetermined motor temperature and above said temperature retarded ignition takes place A primary coil and a secondary coil of an ignition coil are connected to an ignition plug and the current source is connected to the primary coil. A contact breaker is connected in series with the primary coil and the current source and the parallel connected contact breakers are connected in series with the primary coil and the current source in such a manner that in a predetermined position the two contact breakers should lie in a position corresponding to the angle of rotation of the main shaft.

Under the influence of the torque of the motor, heat-sensing devices emit signals proportional to the motor temperature. The ignition spark plug is built-in between the heat sensing devices and the contact breakers, which interrupt, at a predetermined discrete signal, the path of the supply current under the influence of the signal appearing on the output of the heat-sensing devices. This system requires complicated electronic circuitry; it also operates exclusively by dependence on the motor temperature.

An object of the invention is to realise a control for ignition timing which enables more advantageous combustion of the fuel, is loaddependent, and operable with conventional fuel supply and ignition systems.

According to the present invention we propose an assembly for controlling the ignition advance of a four-stroke internal combustion engine incorporating a carburettor, having throttleactuable contacts connectible via a relay for enabling an ignition advance control with an ignition mechanism.

The traditional ignition control is absolutely suitable for a highly loaded motor but at partial loadings it would be convenient to use an ignition advance/number of revolutions characteristic similar to the former one, starting from a higher basic ignition advance, which can be easily achieved by means of a second contact breaker or a magnetic relay mounted on the base plate of the first contact breaker, provided that the contact breaker cams on the distributing shaft are of even number.That means that the- cam lobe lying opposite the just operating cam lobe on the distributing shaft may be used for generating the second characteristic being parallel displaced, when onto the same base plate a second contact breaker, displaced by more than 180" in relation to the original one, will be arranged and it depends on the load, which one of the contact breakers actuates the ignition system. Accordingly, two operational states of the motor are distinguished: the accelerated uphill operation and the nonaccelerated downhill operation.

Accordingly, if we want to accelerate or wish to maintain the number of revolutions during the uphill operation, the throttle valve is to be opened more i.e. in the loaded state of the motor. For detecting the loaded state, it is sufficient to sense the depression of the throttle pedal; for this purpose either a pneumatic or a hydraulic pressure-switch may be used.

The control circuit determines the ignition advance characteristic according to the connected device for sensing the motion of the throttle pedal and the similarly connected two contact breakers or magnetic signal devices operated by means of the centrifugal regulator or by a combined regulator (centrifugal and vacuum) and between the signals thereof there is an angular difference measured in the rotation of the main shaft, which is just required by the angular difference between the desired ignition of the loaded and unloaded motor, respectively.

The equipment has been designed in such a manner, depending on the loading of the motor out of the two parallel ignition advance characteristics one characteristic is used for the control of the traditional ignition set provided with an accumulator, transistor or thyristor. One of the ignition advance characteristics starts namely from the basic ignition advance proposed by the producer, while the other one exerts its influence only at an ignition advance exceeding this value.

The first one is used by the equipment in case of high loads, e.g. with cars during a permanent hill climb or acceleration, whereas the other one is used at a partial load or in case of a forced idle running.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 shows a schematic arrangement of an ignition advance mechanism according to the invention.

A connection 1 to a throttle pedal vehicle is in direct connection with a lever actuating the throttle valve of the vehicle engine. The connection 1 can move contacts of a switch K into two extreme positions. In one of the positions the switch K establishes a connection with a movable contact K1 and in the other position the switch K establishes a connection with another movable contact K2. The switch K is mounted on a metal prism 2, which is able to move in two directions, when guided, along the horizontal; one end of said prism 2 is connected via the connection 1 to the throttle pedal and the other end is earthed. Next to i.e. in use above the metal prism 2 there is a second prism 3, preferably made of a synthetic material and the contacts K1 and K2 are each fixed to side walls of a recessed portion of the prism 3.

The prism 3 is subjected in use to a preselected, compressive force P, which can be achieved by e.g. loading with a weight or with a working cylinder and a piston. The contact K1 is connected to the input of a relay-signalling device J1 and the output thereof is connected to a current supply line. The contact K2 is connected to the input of a further relay-signalling device J2, the output of which is also connected to the current supply iine.

The relay-signalling device J1, which is essentially an electromagnetic relay, has a fixed contact 4, operable with a movable contact 5 which is connected to a movable contact 6 which establishes a connection with an earthed fixed contact 7. The relay-signalling device J2 has a movable contact 8', which forms a pair of contacts with a fixed contact 8. The contact 8 is connected to a fixed contact 9 operable with a movable, earthed contact 10, forming a further pair of contacts being co-ordinated with the relaysignalling device J 1. A movable contact 12 intruding between a pair of fixed contacts 11 of respectively contact breakers M1 and M2 mounted onto a base plate MA, is connected to an ignition unit M. The relays and the pairs of contacts constitute a control circuit V.

The operation of the system will now be described. When the throttle pedal in the vehicle is pressed, the connection 1 , to the lever actuating the throttle valve displaces the first metal prism 2 towards contact K2 so that connection is established between the switch K and the contact K2. Both the prisms move simultaneously in the same direction but the movement of the upper prism 3 is retarded by the force P; this braking effect thus allows actuation by the switch K.

When the throttle pedal forces the prism in the opposite direction, the contact of the switch K similarly establishes a connection with the other contact K1 and the contact K1 now forwards a signal to the control circuit V.

The switch K thus remains in contact with either K1 or K2 at all stages of displacement of the throttle. The relay-signalling devices J 1 and J2 function as dual-state storing units. When the contact K1 is switched to earth, due to the closing of the contact pairs, the relay-signalling device J1 operates and remains operating via its contacts 4 and 5 and the fixed contact of the relay-signalling device J2 as long as the relay-signalling device J2 is switched from the prism 2 to earth. When the relay-signalling device J1 is released, the relaysignalling device J2 operates and maintains the operated state via its own contacts 8 and 8' and normally closed contacts 9 and 10.

Accordingly, relay-signalling devices J1 and J2 respectively store the information needed for the determination of the loaded and unloaded condition of the motor. From the signals received from the contacts of the contact breakers M1 and M2 the suitable signal may be forwarded to the ignition mechanism M.

The contact breakers M1 and M2, mounted onto the base plate MA, are activated by means of the traditional automatic advance weights and a vacuum in such a manner that the angular displacement to be measured between two signals corresponds to the difference between the ignition advance in a loaded and a partially loaded condition of the motor.

Thus, the signals arrive at the relay-signalling devices J1 and J2 in the control circuit V, which controls a conventional ignition mechanism provided with an accumulator, transistor, or thyristor, as a result of the signals from the connected throttle pedal via one of the moving contacts K1 and K2.

Claims (7)

1. An assembly for controlling the ignition advance of a four-stroke internal combustion engine incorporating a carburettor, having throttle-actuable contacts connectible via a relay for enabling an ignition advance control with an ignition mechanism.

2. An assembly according to claim 1, wherein the throttle-actuable contacts are selectively contactable by a switching contact mounted on a metallic member movably connected with the throttle and the member is also connected to earth.

3. An assembly according to claim 2 wherein the throttle actuable contacts are movable with the metallic member so that movement thereof retains that contact in contact with the switching contact and the contacts and relay dependent thereon remain made.

4. An assembly according to claims 1,2 or 3, wherein there are two electromagnetic relays.

5. An assembly according to any preceding claim, wherein associated with the or each relay are two pairs of contacts and an earth and a further contact is selectively operable to the or either relay according to whether the throttle is down or up, which further contact determines whether the ignition is advanced or retarded.

6. An assembly according to claim 1 , for the automatic load-dependent control of the ignition advance of four-stroke gasoline engines with carburettors, in which the contact breakers mounted on the base plate are connected to a contact each of a pair of contacts, and the contact connected to the ignition mechanism is protruding between the contacts of said pair; to the terminal of the supply current source of the electric ignition, a relay-signalling device each has been connected and the fixed contact of the contact pair co-ordinated to the first relay-signalling device is connected to a moving contact, which again is connected to the moving contact of a further contact pair belonging to the other relaysignalling device, while the other contact of said tacs of the said contact pair has been earthed; one of the contacts of the second contact pair belonging to the second relay-signalling device is connected directly to the relay-signalling device, simultaneously the other contact is connected to one of the contacts of the contact pair belonging to the first-relay-signalling device and the other contact of the same contact pair is earthed, characterized in that the relay-signalling devices are connected to a contact each which are fixed in a known manner onto the opposite side walls of the hollow middle part of the prism guided in a horizontal direction and the contact of the switch mounted to the metal prism connected directly or indirectly to the throttle pedal of the motor intrudes between said contacts while the prism carrying the contacts is connected to a retarding mechanism in a manner known in itself.

7. An ignition advance assembly constructed and arranged as herein described with reference to and as illustrated in the drawing.