GB1583769A

GB1583769A - Internal combustion engine carburatio systems

Info

Publication number: GB1583769A
Application number: GB1914977A
Authority: GB
Original assignee: Societe Industrielle de Brevets et dEtudes SIBE
Current assignee: Societe Industrielle de Brevets et dEtudes SIBE
Priority date: 1976-05-14
Filing date: 1977-05-06
Publication date: 1981-02-04
Also published as: DE2721774C2; GB1583770A; FR2351269B1; AU2516777A; IT1078128B; AU514616B2; FR2351269A1; DE2721774A1

Description

(54) IMPROVEMENTS IN OR RELATING TO INTERNAL COMBUSTION ENGINE CARBURATION SYSTEMS (71) We, SOCIETY INDUSTRELLE DE BRE VETS ET D'ETUDES S.I.B.E., a French Body Corporate of 3 Villa Bergerat, 92200 Neuillysur-Seine, France, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to internal combustion engine carburation systems of the kind comprising a main fuel circuit and at least one second "idling" or transfer circuit for supplying the engine with air-fuel mixture at a rate ensuring proper operation of the engine at low speed and low load.

To ensure that the flow rate and richness of the air-fuel mixture supplied to the engine by the idling circuit are the minumum necessary for steady engine operation, a corrective closed loop system can be provided, comprising a solenoid valve actuated in response to signals provided by means for detecting variations in the time length of successive engine operating cycles, and metering the amount of fuel supplied through the idling circuit.

Such a system ensures steady operation of the engine but only during idling, since a comparison between the lengths of successive periods of the engine cycle is not fully significant except at low engine running speeds, at which instability may occur in operation.

While the system has some effect at partial engine loads (when the idling circuit continues to supply an appreciable part of the fuel to the engine), it fails to have a corrective effect under other operating conditions, more particularly when nearly all the fuel is supplied to the intake pipe by the main fuel circuit.

In another prior art carburation device (U.S. Patent No. 3 986 352), there is provided an electronic control circuitry which provides closed loop control when practical and open loop operation under predetermined operating conditions of the engine (idling, wide open throttle operation and engine warm-up. Then, the engine is run rich. No attempt is consequently made to minimize fuel consumption and pollution during idling, while that type of operation is quite important for vehicles operated in large cities.

The invention is intended to provide a carburation device comprising an improved corrective system, inter alia for delivering an approp riate supply of air-fuel mixture to the engine under all operating conditions while maintaining fuel consumption at a minimum level.

The specification of our co-pending Appli cation No. 7941225 disclosed and claims a carburation system for an internal combustior engine comprising at least one fuel circuit for supplying the engine with air-fuel mixture at a flow rate ensuring proper operation of the engine and a corrective system which com prises, in a fuel supply to the fuel circuit an electrically operated valve and closed loop regulation means for delivering electric actuating pulses to said valve, the ratio between the time length of the pulses and the time period between successive pulses being controlled in response to the composition of the exhaust gases of the engine associated with the carburation system, and means for opening the closed loop upon occurrence of predetermined operating conditions, and memory means for storing the value of said ratio at opening of the closed loop and for adjusting the ratio between the time length of the pulses and the time period between successive pulses at a value which is in proportion to said stored value immediately after said opening.

According to the present invention, there is provided a carburation system for an internal combustion engine comprising a main fuel circuit, at least one second circuit for supplying the engine with air-fuel mixture at a flow rate ensuring proper operation of the engine at low speed and low load, and a closed loop corrective system which comprises a first solenoid valve disposed in a fuel supply to the first circuit, a second solenoid valve disposed in a fuel supply to the second circuit, and means for delivering electric actuating pulses to said valves, the ratio between the time length of the pulses and the time period, between successive pulses being controlled in response to at least one engine operating parameter.

In one embodiment of the invention, the solenoid valves in both carburettor fuel circuits receive the same electric pulses; in another embodiment, the valves receive pulses produced by different means responsive to different engine operating parameters.

The valves may be located on the only path along which fuel is supplied by the circuits or may by-pass restrictions in such circuits. The valves can be energized by pulses at fixed or variable frequency.

The invention will be better understood from the following description of embodiments given by way of non-limitative examples. The description refers to the drawings, in which: Figure 1 is a simplified vertical cross-section of a downdraught carburettor according to the invention Figure 2 is a block diagram of a modified embodiment of the electronic circuit controlling the solenoid valve of the main fuel circuit; Figure 3 is a simplified representation of part of the circuitry in the block diagram of Figure 2.

Referring to Figure 1, there is shown a carburettor comprising an intake passage 1 having a main throttle means or butterfly 2 controlled by the driver via a linkage (not shown). Passage 1 has an air inlet 3, usually provided with an air filter (not shown). The carburettor comprises a starting device which is not shown since it is not directly connected with the invention.

The main fuel circuit of the carburettor is supplied with fuel from a float chamber 4 via one or more main calibrated nozzles or calibrated orifices. In Figure 1, there are provided two main nozzles 5a, 5b disposed in parallel.

Air for the fuel emulsion is provided by a calibrated orifice 6 which takes air from inlet 3 via a duct 7. The air and fuel mix in a well 8 into which a conventional emulsion tube 9 projects, the tube having the calibrated orifice 6 at its top. A rich primary mixture is formed inside tube 9 and flows out through duct 10 which opens at the throat 11 of a venturi 12.

The second circuit (idling and progression circuit) opens into intake passage 1 via ports 13, 14 and 14a. Port 13 is permanently downstream of the edge of the main throttle means 2, whereas apertures 14, 14a successively move from upstream to downstream of the edge when means 2 opens from its minimum opening position, which is adjusted by an abutment (not shown).

Apertures 13, 14, 14a are supplied with fuel through a channel 15 and a duct 16 whose inlet is connected either to well 8 (as shown by continuous lines in the drawing) or directly to the float chamber (as shown by broken lines).

In the first case, the fuel supplies to the main circuit and the second circuit are not completely independent, since the duct 16 supplying fuel to the idling circuit takes the fuel from well 8 upstream of the main nozzles 5a, 5b. However, since the flow cross-sectional area controlling the flow rate in the second circuit is small compared with that of nozzles 5a and 5b, the interaction between the two circuits is very limited and usually acceptable.

If it is desired to make the circuits completely independent, the system represented by broken lines can be adopted.

Fuel is supplied to the second circuit by an idling nozzle 17 having a calibrated flow crosssection and located at the inlet of duct 16. The air for forming the air fuel emulsion, which is subsequently introduced into the intake passage 1 via aperture 13, 14 and 14a is supplied through an air intake 18 having a calibrated cross-section. A screw 19 is provided for adjusting the amount of air-fuel mixture supplied by the idling circuit through aperture 13 downstream of butterfly 2.

In the embodiment of Figure 1, the main nozzle 5b and the idling nozzle 17 are controlled by solenoid valves 20, 21 respectively.

It will be assumed hereinafter that when valve 20 or 21 is energized, it closes the corresponding nozzle Sb or 17 (a reversed control system being also acceptable). The frequency of the actuations ofjets Sb and 17 and the time for which they are maintained in closed or actuated condition are determined by electric pulses from control means. The control means shown in Figure 1 comprise an electronic circuit 22 which delivers pulses at a rate which may be either fixed or variable (but is sufficiently high to avoid unsteady operation-, the ratio between the pulse length and period being determined by the valve of one or more signals representing one or more respective engine operating parameters detected by one or more probes such as probe 23.

In the embodiment illustrated, the electronic device 22 comprises a single probe 23 which provides e.g. a signal representing a physical or chemical property of the engine exhaust gases.

Device 22 can e.g. have a construction similar to that of the corresponding device described in French Patent specification 2 228 158.

Alternatively, use can be made of a system adapted to receive a number of input signals representing engine operating parameters, some signals being representative of variation in the fuel supply rate, resulting in a closed looped system (example of such parameters are the difference between the duration of successive engine cycles, the temperature of the exhaust gases, etc), whereas other parameters are independent (e.g. the ambient temperature or pressure). Alternatively, device 22 can be designed so that one of the signals has an overriding action under given engine conditions, e.g. idling, whereas another signal preponderates when the engine conditions are different e.g. maximum speed or deceleration.

In addition, different signals representing different parameters can be selected to control the main and the second circuit. For example, device 22 and the connections between it and valves 20, 21 can be adapted so that valve 21, which controls the second circuit, receives electric pulses having a length-to-period ratio determined by instabilities in engine operation, whereas solenoid valve 20, which controls the main circuit, receives electric pulses having a ratio determined by a probe detecting the characteristics of the engine exhaust gases.

The actuating means can be designed so that they control the richness and operate under "closed loop" conditions only under particular operating conditions of the engine.

The actuating means can for instance be designed to hold valves 20, 21 permanently open when the engine is under full load; for that purpose a pneumatically controlled contractor may be located between the output of device 22 and the input of valves 20 and 21, the contractor being connected to a suitable place along the intake pipe 1.

Referring to Figure 1, there is shown a contactor 24 comprising a pneumatic element connected by a pipe 26 to the throat 11 of venturi 12. The movable diaphragm of the pneumatic element carries a movable contact 27 and a return spring biases contact 27 against a fixed contact 28 to close a circuit between the output of device 22 and the solenoid valves 20, 21.

When the dpression at throat 11 of venturi 12 becomes sufficiently high to overcome the force of the retum spring, the diaphragm of the pneumatic element moves and separates the electric contacts 27 and 28, thus cutting off the electric power supply to the valves. Nozzles Sb and 17 are then permanently open, so that the fuel supply cannot be controlled by reduction of the flow cross-section and the system operates under open loop conditions.

A substantially equivalent result can be obtained by replacing contact or 24 with contactor 25; then connections A and B of contactor 25 are substituted for connections A and B of contactor 24. Contactor 25 comprises a pneumatic element which is connected by a pipe 29 to pipe 1 downstream of butterfly 2.

The depression transmitted by pipe 29 tends to close contacts 30,31 of contactor 25 against the action of a return spring. During idling and low load, a considerable depression prevails downstream of butterfly 2 (which is then in its minimum opening position or in a partial opening position) and contactor 25 is closed. Under full load, on the other hand, butterfly 2 is completely open, the depression transmitted by pipe 29 to the pneumatic element of contactor 25 decreases and the return spring opens contacts 30, 31. This avoids any reduction in richness under full load, i.e. when maximum torque is required.

The invention can be modified in numerous ways. More particularly, a single main nozzle can be used (i.e. by eliminating jet So) or more than two jets can be provided, one jet being permanently open and the others being actuated by solenoid valves, if advisable in dependence on different parameters. Each solenoid valve can have a seat which is distinct from the nozzle and disposed upstream or downstream thereof.

Referring now to Figure 2, there is shown the block diagram of a system adapted to fulfill several functions: - under normal operating conditions, it constitutes a closed loop system which controls air-fuel ratio for maintaining an acceptable exhaust gas composition; -under full load conditions, it constitutes an open loop system providing the air-fuel mixture enrichment necessary for obtaining maximum torque from the engine; -under acceleration conditions and while the engine is cold, it provides a fuel enrichment which is adjusted responsive to the rate of flow of fuel which was delivered to the engine immediately before acceleration begins.

For that purpose, the system illustrated in block form on figure 2 comprises several circuits which will be described in succession.

A regulation circuit 35 for closed loop control has an input connected to an oxygen probe 23 located in the exhaust gas flow of the engine and which delivers an input signal to circuit 35.

A circuit 36 for modulated enrichment under acceleration conditions has its input connected to the output of circuit 35. The outputs of circuits 35 and 36 are connected to respective analog inputs of a selection circuit 37. A control input of circuit 37 receives a logic or binary signal which has a first predetermined level (which may be considered as a binary 1) if a temperature threshold circuit 39 indicates a temperature lower than a predetermined value and if simultaneously a micro-switch 41 indicative of acceleration conditions is closed and receives a signal at a second level (a binary zero) if either one or neither condition is fulfilled. For that purpose, circuit 39 and a circuit 42 responsive to closure of switch 41 have their outputs connected to respective inputs of an AND gate 38 whose putput is connected to the control input of 37.Circuit 37 is so constructed that if a binary one is received on the control input, the signal from circuit 35 is passed to the output; if a binary zero is received, the signal from 36 is passed to the output. Circuit 37 may consist of a pair of analog gates.

The signal delivered from the output of circuit 37 is amplified at 48 and then fed to the solenoid valve 20.

Last, a circuit 43 is provided for opening the control loop when a micro switch 44 is open to indicate full load operation of the engine.

Referring now to figure 3, an embodiment of the circuits referred to above will be described with more details.

The input element of the regulation circuit 35 is a probe 23 which is typically a resistor associated with a voltage source for delivering to an amplifier 45 a signal representative of the oxygen content in the exhaust gases. The oxygen probe is typically a probe comprising a body of electrolyte in solid form (ZrO2 doped with yttrium oxide) and platinum electrodes.

When the amount of free oxygen in the exhaust gases decreases the voltage delivered by the probe increases, all the more since residual oxygen is used for oxidizing carbon monoxide on the surface of the probe with platinum operating as a catalyst.

The analog output voltage from 23 is ampli fied at 45 and applied to a first input of a differential amplifier whose other input receives a reference voltage. The switch 44 which closes responsive to the degree of vacuum which prevails in passage 1 under full load operation is located on a line from the first input to ground.

The output signal of amplifier 46, in the form of square pulses whose time length depends on the oxygen content of the exhaust gas, is applied to a first input of a second differential amplifier 47 via a normally closed movable contact 48 of a relay 49. The input is also connected to ground via a storage capacitor 50 and is connected by a diode 5 1 to the midpoint of a resistive voltage divider.

The other input of amplifier 47 receives a saw tooth signal from a circuit comprising an oscillator 72 and a triggered ramp generator 73 of conventional type.

Tlie circuit 36 for temporary enrichment includes a differential amplifier 52 whose two inputs are connected to the output of amplifier 47 via two different branches. The first branch comprises a single shot multivibrator 53 which delivers a short pulse responsive to the trailing edge of each output pulse from amplifier 47 and a switching transistor 54. As long as transistor 54 is cut off, a current source 55 loads a capacitor 56. When transistor 54 is conducting. it unloads 56 to ground.

The second branch comprises an invertor 57 and a switching transistor 58. When the transistor 58 is cut off, a capacitor 59 is loaded by a current generator 60 and the voltage at the corresponding input of differential amplifier 52 increases.

The amplifier 48 receives an input signal from 35 via the rest contact of a switch 62 (actuated at the same tine as switch 48) as long as coil 49 is not energized. It receives an input signal from 36 when 49 is energized.

The coil of relay is located in a circuit in series relation with the contact 64 of a first, temperature responsive relay which constitutes circuit 39 with a differential amplifier and with the contact 65 of the second acceleration responsive relay 42. The coil of that relay is energized upon closure of a contact connected to the movable wall of a pneumatic element (fig.

2). A first chamber of the pneumatic element is connected to the induction passage 1 and the other chamber is connected to the first chamber by a restricted orifice; at rest, a return spring maintains contact 41 in open condition.

Operation of the device is as follows.

During closed loop operation (as illustrated in Figure 3), the square pulses delivered by amplifier 46 are directed to the storage capacitor 50 which unloads through the output impedance of amplifier 46 when the latter is blocked.

The differential amplifier 47 operates as a comparator and delivers a positive output pulse as long as the value of the saw tooth voltage is lower than the voltage across the electrodes of capacitor 50.

As long as contact 62 is in rest condition, the pulses from the output of amplifier 47 are directed to solenoid valve 20 and retain it in closed condition during short time durations at a rate which is determined by oscillator 72.

If the level of the voltage peaks from probe 23 increases due to insufficient contents of oxygen at the exhaust, the voltage across capacitor 50 increases, the output pulses from 47 are longer and the time periods of closure of valve 20 increase.

Under fill load operation, switch 24 is closed and energizes its associated relay whose contact 44 grounds the inputs of amplifier 46.

Amplifier 47 remains blocked, the voltage across 50 decreases until a value which is determined by diode 51 and the associated voltage divider: the length of the pulses directed to valve 20 decreases to a value which provides the enrichment necessary to satisfactory full load operation.

During acceleration while the engine is cold, contact 64 is closed and switch 65 remains closed until pressure balance has been achieved across the diaphragm of pneumatic motor 67 by airflow across restricted orifice 68 (Figure 2).

Simultaneous closure of contacts 64 and 65 results in opening of contact 48. From that time on, the voltage across 50 will remain constant and will retain, at least temporarily, the last value before opening of 48. Consequently. there appears at the output of amplifier 47 square pulses of constant length.

During the positive square pulses of constant duration delivered by amplifier 47 and inverted by 57, transistor 58 is blocked and capacitor 59 is loaded under a constant current.

At the end of said constant duration, there occurs simultaneously: - delivery of a short pulse by 53 which results in 54 becoming conductive and almost instantaneously reducing to zero the voltage across capacitor 56, which loads progressively again immediately after the end of the short pulse, - switching of 58 to conduction state, thereby unloading 59 and maintaining it in unloaded condition until a new positive square pulse increases.

The values of the components are so selected that the voltage of 59 increases with time at a faster rate than that of 56; as soon as they are equal, the output of amplifier 52 becomes zero and solenoid valve 20 opens.

Due to the memory effect of capacitor 50, the opening time of solenoid valve is increased with respect to the opening time before acceleration by an amount which is in direct relation with that opening time before acceleration.

WHAT WE CLAIM IS: 1.A carburation system for an internal combustion engine comprising a main fuel circuit, at least one second circuit for supplying the engine with air-fuel mixture at a flow rate ensuring proper operation of the engine at low speed and low load, and a closed loop corrective system which comprises a first solenoid valve disposed in a fuel supply to the first circuit, a second solenoid valve disposed in a fuel supply to the second circuit, and means for delivering electric actuating pulses to said valves, the ratio between the time length of the pulses and the time period, between successive pulses being controlled in response to at least one engine operating parameter.

2. A system according to claim 1, characterized in that the means for delivering pulses actuate the two valves in dependence on the same engine operating parameter.

3. A system according to claim 1, characterised in that said means actuate the first valve in dependence on a first operating parameter, such as a physical or chemical property of the engine exhaust gases, and the second valve in dependence on a second operating parameter such as the difference between the time lengths of successive engine cycles.

4. A system according to claim 1, 2 or 3 characterised in that the main circuit is supplied with fuel via a plurality of calibrated orifices, one of which is permanently open, at least one other orifice being controlled by the solenoid valve of said main circuit.

5. A system according to any of Claims 1 to 4, characterised in that said means further comprise a contactor disposed in the circuit for supplying electric pulses to at least one of the solenoid valves, the contactor being auto magically actuated in dependence on the engine operating conditions so as to hold at least one of the solenoid valves permanently open under predetermined engine conditions.

6. A system according to Claim 5, characterised in that the contactor is a movable wall carrying a movable contact and limiting a chamber connected to the intake passage.

7. A carburation system according to Claim 1 or 2, wherein said engine operating parameter is the composition of the exhaust gases of the engine, further comprising means for opening the closed loop which is responsive to said composition of the exhaust gases upon occurrence of predetermined operating conditions.

8. A carburation system according to Claim 7, wherein the predetermined operating condition is either acceleration of an engine associated with the carburation system while said engine is at a temperature lower than a predetermined value or operation of an engine associated with the carburettor under full load.

9. A carburation system according to claim 7 or 8 further comprising memory means for storing the value of said ratio at opening of the closed loop and for adjusting the ratio between the time length of the pulses and the time period between successive pulses at a value which is in proportion to said stored value immediately after said opening.

10. A carburation system according to Claim 9, wherein said memory means consists of a capacitor which is loaded under a voltage in direct proportion with said ratio.

11. A carburation system as claimed in Claim 1 as hereinbefore described with reference to, and as shown in, the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

equal, the output of amplifier 52 becomes zero and solenoid valve 20 opens.

Due to the memory effect of capacitor 50, the opening time of solenoid valve is increased with respect to the opening time before acceleration by an amount which is in direct relation with that opening time before acceleration.

WHAT WE CLAIM IS: 1.A carburation system for an internal combustion engine comprising a main fuel circuit, at least one second circuit for supplying the engine with air-fuel mixture at a flow rate ensuring proper operation of the engine at low speed and low load, and a closed loop corrective system which comprises a first solenoid valve disposed in a fuel supply to the first circuit, a second solenoid valve disposed in a fuel supply to the second circuit, and means for delivering electric actuating pulses to said valves, the ratio between the time length of the pulses and the time period, between successive pulses being controlled in response to at least one engine operating parameter.
2. A system according to claim 1, characterized in that the means for delivering pulses actuate the two valves in dependence on the same engine operating parameter.
3. A system according to claim 1, characterised in that said means actuate the first valve in dependence on a first operating parameter, such as a physical or chemical property of the engine exhaust gases, and the second valve in dependence on a second operating parameter such as the difference between the time lengths of successive engine cycles.
4. A system according to claim 1, 2 or 3 characterised in that the main circuit is supplied with fuel via a plurality of calibrated orifices, one of which is permanently open, at least one other orifice being controlled by the solenoid valve of said main circuit.
5. A system according to any of Claims 1 to 4, characterised in that said means further comprise a contactor disposed in the circuit for supplying electric pulses to at least one of the solenoid valves, the contactor being auto magically actuated in dependence on the engine operating conditions so as to hold at least one of the solenoid valves permanently open under predetermined engine conditions.
6. A system according to Claim 5, characterised in that the contactor is a movable wall carrying a movable contact and limiting a chamber connected to the intake passage.
7. A carburation system according to Claim 1 or 2, wherein said engine operating parameter is the composition of the exhaust gases of the engine, further comprising means for opening the closed loop which is responsive to said composition of the exhaust gases upon occurrence of predetermined operating conditions.
8. A carburation system according to Claim 7, wherein the predetermined operating condition is either acceleration of an engine associated with the carburation system while said engine is at a temperature lower than a predetermined value or operation of an engine associated with the carburettor under full load.
9. A carburation system according to claim 7 or 8 further comprising memory means for storing the value of said ratio at opening of the closed loop and for adjusting the ratio between the time length of the pulses and the time period between successive pulses at a value which is in proportion to said stored value immediately after said opening.
10. A carburation system according to Claim 9, wherein said memory means consists of a capacitor which is loaded under a voltage in direct proportion with said ratio.
11. A carburation system as claimed in Claim 1 as hereinbefore described with reference to, and as shown in, the accompanying drawings.