GB2212217A

GB2212217A - An electronically-controlled carburetter idling system

Info

Publication number: GB2212217A
Application number: GB8829781A
Authority: GB
Inventors: Michael Pontoppidan
Original assignee: Solex SA
Current assignee: Solex SA
Priority date: 1987-12-23
Filing date: 1988-12-21
Publication date: 1989-07-19
Anticipated expiration: 2008-12-21
Also published as: BR8806919A; IT1235346B; GB2212217B; ES2013384A6; IT8848701A0; FR2625262B1; GB8829781D0; FR2625262A1; DE3842466A1

Description

AN iNTEMAL COMBUQTION ENGINE CARBURET'OR 22122 17 This invention relates

to Internal combustion engine carburettors of the type comprising a body formed with an intake conduit containing a throttle means controlled by the driver and an Idling duct leading into the Intake conduit downstream of the throttle means and receiving air and fuel through respective calibrated ports to form a primary air and fuel mixture.

The carburettor must be so designed that the rate of flow of primary mixture is adapted to the different engine operating phases, more particularly transient phases. The idling duct must fulfil this function from Idling operation until a main jet system comes Into operation, such system generally leading into the intake conduit at 15 the neck of a venturi situated upstream of the throttle means.

As the throttle means is opened from Its idling position the engine Is required to receive an increasing flow of mixture but its richness must be constant.

V The attempt has been made to solve this problem by leading the idling duct Into the intake conduit not only via an idling aperture situated downstream of the throttle means (the passage cross-section of the aperture being adjusted by means of an adjustable richness screw), but also by bypass or progression ports which pass from upstream to downstream of the throttle means when the latter opens from its minimum opening position corresponding to idling. The ports may be combined in the form of a single slot parallel to the intake conduit axis.

The progression ports and slots are difficult to form with precision in mass-produced carburettors. High precision is required to ensure smooth engine operation when accelerating from idling.

The object of this invention is to provide a carburettor which more satisfactorily meets practical requirements than the prior art carburettors, particularly inasmuch as it allows regular transition from idling to the starting up of the main jet circuit.

To this end, the invention proposes more particularly a carburettor of the kind hereinbefore defined, which Is characterised in that it comprises an electrically controlled valve disposed In the Idling duc t and a valve control circuit having inputs connected to pick- ups for engine operating parameters including at least the speed of rotation of the engine and excluding the exhaust gas composition; an output adapted to deliver a pulsed signal of variable cyclic ratio to said valve; and a memory for storing the value of the cyclic ratio for a plurality of combinations of said operating parameters.

In one simple embodiment, the operating parameters are the engine speed N and the butterfly valve opening angle, which can be measured from the minimum opening position corresponding to idling.

The Invention Is of particular advantage in the case of electronic carburettors and/or carburettors provided with a damping system which entails the provision of an electrically controlled valve or damper. In such cases the same electrically controlled valve can be made to perform a number of functions and use of the Invention does not appreciably complicate the carburettor.

The Invention will be more readily understood from the following description of one specific embodiment given by way of example without limiting force and the comparison with the prior art.

Referring to the drawings:

Fig, 1 Is a diagram showing the point where the idling duct leads Into a carburettor Intake conduit in accordance with a current conventional arrangement.

E" tr Fig. 2 is a diagram showing the construction of the idling duct in one embodiment of the invention.

Fig. 3 is a diagrammatic illustration of a possible law showing the variation of the cyclic opening ratio (RCO) against the speed N and the opening angle a, according to one specific embodiment.

Fig. 1 shows the bottom part of the body 11 of a carburettor in which an intake conduit 12 Is provided. A throttle means 13, In the form of a butterfly valve whose pivot 14. is connected by a linkage to an accelerator pedal, is disposed In the intake conduit 12.

The body Is formed with an Idling duct 17 which receives air and fuel through calibrated constrictions (not shown). This duct leads Into the intake conduit 12 via an aperture 16 so disposed as to be downstream of the butterfly valve 13 even when the latter is In the Idling or minimum opening position as shown in Fig. 1. Duct 17 also leads into the Intake conduit 12 via progression ports 16a so disposed as to pass successively from upstream to downstream of the edge of the butterfly valve 13 when the latter opens from Its minimum opening position.

In conventional carburettors, the passage section offered by the aperture 16 is adjustable by means of a point screw 18 having a braking spring 19.

OV-1 e The carburettor according to one embodiment of the invention illustrated diagrammatically in Fig. 2 also comprises a body 11 formed with an intake conduit 12 containing a butterfly valve 13. The Idling duct 17, which Is fed with air from the air intake 20 via a calibrated port 21 and with fuel from a cons tanIC- level tank through another calibrated port 22 In this case leads Into the Intake conduit via an aperture 16 disposed downstream of the edge of the butterfly valve Irrespective of the opening thereof. A main jet system, which 4 - is not illustrated because the invention does not affect it, leads Into the neck of a venturi 23 mounted In the intake conduit 12, via a central tube 24.

The passage of the primary mixture through the aperture 16 is controlled by an electrically controlled valve 28 comprising a shutoff member 29 displaceable between a position engaging a seat surrounding the aperture 16 and a position in which it frees the seat. A return spring (not shown) tends to bring the shut-off member into one of its end positions, generally the fully open pos i t ion. A coil 30 of the solenoid valve is provided to apply the shut-off member to its seat when it is energized.

The solenoid valve 28 Is adapted to pulsed operation with a cyclic opening ratio which varies with the value of various engine operating parameters. The energization signals for the solenoid valve 28 are provided by a circuit 31 comprising a plurality of inputs connected, In the embodiment shown, one to a pick-up 32 delivering an analog output signal proportional to the opening angle of the butterfly valve 13, the other to an engine speed pick-up 33. The latter may be fitted in the ignition system and deliver a pulse on each engine Ignition spark.

The circuit 31 may be of known general construction. It will comprise an analog/digital converter to give a digital representation of the opening angle cc and a cartographic memory formed, for example, by a programmable network to equate a cyclic opening ratio value with each value of a, N. The circuit can be designed so that the frequency of the pulses fed by the circuit 31 to the solenoid valve 28 corresponds to the frequency of the Ignition pulses delivered by the pick-up 33. However, In most cases the circuit will instead operate at a fixed rotational frequency of the order of 100 Hz.

il 11 -1 1 The circuit 31 may be provided with manual adjustment means diagrammatically represented in Fig. 2 by the input 34 and possibly comprising an adjustable resistor which changes the characteristics of the analog/digital converter disposed In the inpit connected to the a pick-up, for example.

The operation of the above-described system will be irtafaediately apparent. It may correspond to a variation of the cyclic opening ratio of the solenoid valve RCO against the speed N and the angle a of the kind shown In Fig. 3. The values of RCO are previously stored in the control circuit 31. During idling, when the engine speed Is at a minimum (e.g. 1000 rpm) and the bu-tterfly valve opening angle is zero, the cyclic opening ratio is kept at 80%. When the butterfly valve opening angle exceeds approximately 10 and continues to rise, the control circuit 31 progressively reduces the cyclic opening ratio. For a given butterfly valve opening, this cyclic ratio will also depend on the speed of the engine, thus in particular obviating any racing of the latter.

The set of curves shown in Fig. 3 can be determined by bench or road tests.

In the embodiment shown in Fig. 2, the idling duct has no manual adjustment screw. However, an additional manual-adjustment duct may be provided in addition to the duct 17.

In the particularly advantageous case of an electronically controlled carburettor, the solenoid valve 28 may also be used to perform other functions, more particularly -deceleration cut-off and damping on engine ignition cut-off.

For cut-off when the engine Is decelerating, i.e. when a = 0 and the engine speed N is greater than a given speed while the enzine is coupled to the wheels, all that is necessary is to provide the control circuit 31 with an additional Input connected to a contact 35 disposed an the gearbox to determine whether the engine Is connected to the wheels.

Damping on engine Ignition cut-off can be obtained without the use of additional pick-ups: all that is required is to hold the solenoid valve 28 closed for a given time after Ignition cut-off, which can be detected by the pick-up 33.

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Claims

C L A I M S

1. An internal combustion engine carburettor comprising a body formed w i th an intake conduit containing a throttle means controlled by the driver and an Idling duct leading into the intake conduit downstream of the throttle means and receiving air and fuel through respective calibrated ports to form a primary air and fuel mixture, characterised in that the idling duct leads into the intake conduit solely downstream of the throttle means, an electrically controlled valve is disposed In the idling duct and a valve control circuit has inputs connected to pick-ups for engine operating parameters including the speed of rotation of the engine and the degree of opening of the throttle means; an output adapted to deliver a pulsed signal of variable cyclic ratio to said valve; and a memory for storing the value of the cyclic ratio for a plurality of combinations of said operating parameters from Idling until start-up of the main jet circuit.

2. A carburettor according to claim 1, characterised in that the engine operating parameters are the speed and the butterfly valve opening angle.

3. A carburettor according to claim 1, 2 or 3, characterised in that the said valve control circuit delivers to the valve a pulsed signal at a fixed frequency, generally of about 100 Hz.

4. A carburettor according to claim 1 or 2, characterised in that provision is also made to hold the solenoid valve closed when the engine speed is greater than a given speed, when. the butterfly valve opening angle is zero and when the engine Is connected to the wheels.

5. A carburettor for an Internal combustion engine substantially as hereinbefore described with rell'erence to the accompanying drawings and as shown in Fig. 2 of those drawings.

i Published 1989 at The Patent Office. State House, 66171 High Holborn. London WC lR 4TP. Rirther copies may be obtained from The Patent Office. Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187