GB2072753A - Electrical control of carburettor throttle stop pneumatic actuators - Google Patents

Abstract

The motor 41 positioning the minimum opening throttle stop 60 has a continuous connection 48, 49, 50 to the induction passage 1 and a connection 70, 71, 72, 73 to atmosphere controlled by a solenoid valve 75 fed with variable duty ratio pulse signals. The duty ratio is dependent on engine speed, temperature and deceleration and operation of engine accessories to provide the desired minimum throttle valve opening, e.g. to set the engine idling speed. <IMAGE>

Description

SPECIFICATION Carburetion device for intemal combustion engines The invention relates to carburetion devices for internal combustion engines of the type comprising a main fuel jetting system opening into the induction passage ofthe carburetion device upstream Df an operator controlled throttle, an idling circuit which opens into the part of the induction passage situated downstream of the throttle, a starting air flap located in the induction passage upstream of the fuel jetting system and a correction system for defining a minimum opening position of the throttle depending on the operating conditions of the engine, said cor rection system comprising stop means operatively connected to the mobile assembly of a pneumatic motor whose position depends on the pressure which prevails in a working chamber of said motor.

Such a correction system is described in French Certificate of Addition No. 2,366,456 corresponding to U.S. Patent No.4,171,686. The flap increases the fuel/air ratio of the mixture supplied to the engine, as long as the latter has not reached its normal operating temperature. The correction system prevents the throttle member from closing beyond a predetermined opening position until the depression downwstream of the throttle member exceeds a threshold and it partially opens the throttle member if the engine is loaded while idling.

Such a correction system fulfils several functions: - before the cold engine is cranked, it opens the throttle sufficiently for the depression which appears when the engine is driven by the starter motor to be transmitted to the main jetting system; - after starting the engine, it allows the throttle to close again; - if the idling engine is loaded, for example through switching on o}electrical accessories, it partially opens the throttle.

That system is satisfactory as long a fairly high idling speed is accepted, typically of about 800 RPM for a petrol engine of a passenger car. But it does not allowtoadjustthe idling speed a a ata -value with- out risk of stalling the idling engine nor is it completely satisfactory when the motor should supply the energy required for operating accessories which are found on modern passenger cars.

According to the invention, there is provided an improved device of the type hereinbefnre defined which allows a very low idling speed to be adopted (typically as low as 600 RPM approximately) and whichis nevertheless simple in construction. Such simplicity is achieved by fulfilling required functions by only one mechanical member. li The member may preferably be used for partially opening the throttle during deceleration to increase the flow of air/fuel mixture delivered to the engine to a value avoiding poor filling of the cylinders and considerable production of unburnt hydrocarbons.

According to an aspect of the invention, there is provided a device of the above-defined type in which the working chamber of the pneumatic element is connected to the part of the induction passage situated downstream of the throttle and to atmospheric pressure and in which an electromagnetic valve con trols one of the connections and is operatively associated with a control system which supplies to the electromagnetic valve opening pulses whose duty ratio depends on several operating parameters of the engine.

The duty ratio of the electric pulses can be responsive to all the required operating parameters, in par ocular: the temperature of the engine (thereby removing the need forthe usual fast idle cam); the depression which prevails downstream of the throttle; and deceleration.

According to another aspect of the invention, there ;s provided a device ofthe above-defined type in which the working chamber is connected to the part of the induction passage situated downstream of the throttle member and to the atmospheric pressure, one at least of the connections being provided by an electromagnetic valve associated with a control system having speed-detection means and which supplies to the electromagnetic valve pulses whose duty ratio is controlled to maintain the stop and the throttle in a position corresponding to a predetermined speed, when the engine is idling.

M h this regulation, which replaces the usual manual adjustment, it is possible to adopt a much lower idling speed that those currently used: if the engine is suddenly loaded, the correction system -X~3]l come into play, open the throttle further and prevent stalling of the engine.

lie control system may be analog or digital. if digital, it may incorporate a processor capable of ful filling tunotcns other than control of the carburetion device.

The invention will be better understood from the following dssonptlon of a particular embodiment of a carburetion device according to the invention. The description referstothe accompanying drawings.

Figure lisa sinnslifiedl diagram showing the device in section, the elements being in the position ocriesponding to rest condition of the engine while cold; Figure 2 is a block diagram showing one possible construction of the control system of Figure 1.

The carburetion device shown in Figure 1 cornprises a body made from several assembled parts and in which is provided an induction passage 1.

passage 1 suzzessively locates, in the flow direction he air (as shown by an arrow): an air intake 2: a starting air flap 3; a main fuel jetting system 4 belonging to a normal-operation supply circuit and opening into the throat of a venturi 5; and a throttle 6 formed by a butterfly valve mounted on a shaft 7 which passes through the wall of passage 1 and connects up with 3 linkage controlled by the driver.

The linkage (not shown) is provided with spring means for returning butterfly valve 5 to its minimum opening position.

The carburetion device further comprises an idling circuit which comprises a passage 8 for feeding a rich primary air1fuel mixture. Passage 8, the downstream pan of which has been shown, opens by an orifice 10 into induction passage 1 downstream of the edge of butterfly valves. A screw 11 locked by a spring 12 allows adjustment of the flow cross- sectional area offered by orifice 10. In the carbure tion device shown in Figure 1, passage 8 also com municates with the induction passage 1 via a by pass orifice 13 so located that its situation with respect to the edge of butterfly valve 6 changes from upstream to downstream when the latter is opened from its minimum opening position.

Starting air flap 3 belongs to the cold-start system of the carburetion device. Flap 3 is associated with a thermostatic member subjected to a temperature representative of that of the engine and to a pneumatic capsule 31 for partial opening or "crack open" of flap 3 as soon as the engine is selfoperative after start-up. The cold-start system will not be described, for it may be of any appropriate construction, for example as described in French Certificate of Addition No.2,366,456 and U.S. Patent No. 4,171,686 to which reference may be made.

The carburetion device comprises a correction system for adjusting the degree of minimum opening of throttle 6. The system comprises a single mechanical unit, formed by a corrector 40 which adjusts the minimum opening position of throttle 6.

Corrector40 comprises a case fixedly secured to the body of the carburetor, made from several assembled parts. Two of these parts 54 and 55 define a pneumatic element 41. The movable assembly of the pneumatic element is a diaphragm 42 whose peripheral part is clamped between parts 54 and 55.

The central part of the diaphragm is clamped between two cups 43 and 44 secured together by screws 45.

Diaphragm 42 separates a work chamber 47 from an atmospheric chamber 51. Work chamber 47 is permanently connected to the part of passage 1 situated downstream of butterfly valve 6 through a hole 48, a duct 49 and a calibrated restriction 50. The atmospheric pressure is established in the second chamber 51 through an orifice 52.

A return spring 56 in chamber 47 exerts on diaphragm 42 a force which opposes that created by the depression in work chamber 47 and tends to apply cup 44 against part 54 forming a stop.

Cup 44 carries a lug 57 connected by a link 58 to a lever 59 rotatable on shaft 7 of the butterfly valve. A stud 60 on lever 59 forms a butterfly valve stop representing a one-way connection with a lever 61 integral with butterfly valve 6. Stop 60 defines the minimum opening position of the butterfly valve.

The usual return spring provided in the control linkage of the butterfly valve (not shown) maintains the latter in the position determined by stop 60 when the driver exerts no opening action.

In the device of the invention illustrated in Figure 1, chamber47 is provided with a path for communication with atmospheric pressure (outside atmosphere or air intake of the carburetor) which comprises a calibrated passage 70, a chamber 71 and a channel 72 having a second calibrated orifice 73 and comprising a cross-sectional area controlled by the plunger 78 of an electromagnetically operated valve 75. Electromagnetic valve 75 comprises a coil 76 and a stationary central core 77. When the coil 76 is not energized, a spring 79 applies plunger 78 against a seat 81 and closes the flow cross-sectional area in channel 72. When coil 76 is energized, plunger78 is drawn against core 77 and opens the passage.

The correction system further comprises a control circuit 86 associated with sensors supplying electri cal input signals to the control circuit 86.

In the embodiment shown in Figure 1, the sensors comprise: - a sensor 90 for sensing a temperature representative of the operating condition of the engine, whose sensitive element is for example a thermistor delivering an analog electrical temperature signal 0; - a sensor 91 for sensing the speed of the engine, supplying an electrical signal representative of the speedn of the engine, formed for example by pulses delivered at the rotational frequency of the engine; - an indicator 92 indicating whether the air conditioning compressor is switched on, supplying an allor-nothing electrical signal; -a deceleration sensor 93 supplying a deceleration indicating signal when both the accelerator pedal is released and the speed of the engine is above a given value n,.

The control circuit 86 will generally comprise a processor, typically digital, provided for fulfilling the different functions.

Referring to Figure 2, there is shown, in simplified form, a particular embodiment of control circuit 86.

The circuit comprises an OR output gate 94 which energizes the coil 76 of the electromagnetic valve through a power amplifier (not shown). The two input terminals of the OR gate are connected to the outputs of two branches: -one which delivers a continuous signal when the speed of the engine exceeds a given threshold n, while the accelerator pedal is released, -the other which supplies electrical current square-waves of adjustable duty ratio during slow running operation.

The first branch comprises, in series with a voltage source, a switch 93a controlled by the speed of the engine and a switch 95 which is closed when the accelerator pedal is released.

The input member of the second branch is sensor 91 which delivers calibrated electric pulses at a frequency proportional to the running speed of the engine. The pulses are applied to an integrator 96 which drives one of the inputs of a differential amplifier 97. The second input of the differential amplifier 97 receives a signal representative of a reference speed.

A switch 98 connects the reference speed input terminal to the output of one or other of two circuits, depending on the operating conditions of the engine.

(a) When switch 98 is at rest (as shown in Figure 2), it connects the reference speed input of amplifier 97 to a voltage generator 99 which supplies a voltage depending on the temperature fl of the engine.

Generator 99 is programmed so as to deliver at its output a voltage representative of a speed nO which depends on the signal which it receives from temperature probe 90.

(b) When switch 92 (actuation of the compressor of the air conditioner) and a switch 101 (opened by actuation of the accelerator pedal) are closed at the same time, switch 98 is brought into a position where it connects the input of amplifier 97 to a second voltage generator 102, supplying a voltage reprepresentative of a predetermined speed n'O. For that result, switch 98 may be formed by the mobile contact of a relay whose winding is placed in series with a current source and switches 92 and 101.

The difference signal supplied by amplifier 97 is applied to the "set" time adjustment input of a monostable (single shot) flip-flop 103. The "set" input of monostable 103 receives the output signals of a clock 105, at 10 Hertz for example. The output square-waves from monostable 103 are applied to an integrator 104 for supplying a D.C. signal.

The output signal of integrator 104 is applied to one of the inputs of a switching-pulse control circuit, formed by a comparator 107 whose other input receives voltage ramps supplied by a triggered ramp generator 106 whose trip input is connected to the output of clock 105. Comparator 107 is of a type supplying an output pulse whenever the ramp voltage exceeds the voltage from integrator 104. This pulse sets a flip-flop 108 which is reset by clock 105 at the same time as ramp generator 106.

The device operates as follows: During start-up and running of the cold engine: before starting the engine while the latter is cold, the different elements of the carburetion device are in the positions shown in Figure 1. The starting air flap 3 is closed. Butterfly valve 6 is held widely open by spring 56 of the correction device 40 which maintains the mobile assembly of pneumatic element 41 in contact with part 54. The electromagnetic valve 75 is closed.

During operation of the starter motor, the engine receives a rich mixture delivered by the main jet system 4.

Immediately after start-up of the engine, pneumatic element 31 responsive to the depression which appears downstream of butterfly valve 6 partially opens air flap 3.

Atthe same time speed sensor 91 delivers pulses at a frequency representative of the engine speedn to control system 86 which, in response, supplies to electromagnetic valve 75 square-wave pulses at a duty ratio Tt. The temperature sensor 90 delivers a signal representative of the temperature 0 of the engine and system 86 will adjust the duty ratio T50 as to adjust the running speed at a value nO which depends on temperature U of the engine. A low temperature 0, for example 0 C, of the liquid of the cooling circuit of the engine, will correspond to a relatively high value of the speed of the engine, for example 1300 RPM.

As the engine gradually warms up, the duty ratio T is reduced, whereby the depression in chamber 47 increases and the degree of opening of the butterfly valve is decreased along with the idling speed n,.

The system may be arranged so that, when the engine reaches its normal operating temperature, the time length t becomes zero. The depression in chamber47 is no longer attenuated. That depression overcomes spring 56 and the butterfly throttle 6 may come back to its minimum opening position determined by a stop (not shown).

Simuitaneously, flap 3 will be broughtto its full opening position by its thermostatic system.

It can be seen that the idling speed of the engine will thus be always perfectly matched to engine temperature. Furthermore, the system does not have the well-known drawback of fast idling cams, which is to require an action on the accelerator pedal to allow release thereof.

Deceleration: During deceleration at high speed, i.e. when the engine acts as a retarder, switches 93a and 95 which form member 93 of figure 1, are closed. System 86 then continuously feeds a D.C.

control current to electromagnetic valve 75 which remains permanently open. Then the depression in chamber 47 is strongly attenuated by the air which penetrates through channel 72. Spring 56 maintains butterfly throttle valve 6 in the partially open position shown in Figure 1 and the engine receives an amount of air-fuel mixture sufficient to avoid a high content of unburnt hydrocarbons in the exhaust gases.

The calibrated orifices 70 and 73 placed in channel 72 are dimensioned to strongly attenuate the high depressions appearing during high-speed decelerations, for example exceeding 3500 RPM.

Operation of the air conditioner: When the compressor of an air conditioner is switched on, contact 92 closes. If the engine is then rotating at its normal idling speed, for example 600 RPM, the control system 86 delivers to electromagnetic valve 75 current pulses having a duty ratio which attenuates the depression in chamber 47. The butterfly valve is opened furtherto a higher idling value, for example of about 900 RPM. This higher speed allows the air conditioner to operate with a suitable dutput.

Regulation of the idling speed at normal temperature: As was mentioned above, the carburetion device of the invention makes it possible to select an idling speed at normal temperature lowerthan the speeds currently provided at the present time, for example 600 RPM instead of 800 RPM.

If the engine, running at that lower speed, is suddenly loaded, as for example by the higher resisting torque of an alternator when the electrical accessories are switched on, its speed tends to drop below speed nO. The system 86 then energizes the electromagnetic valve 75 with pulses having a duty ratio T which is no longer zero, but is small, and slightly attenuates the depression in chamber 47 so as to cause reopening of butterfly valve 6 until the engine picks up to a speed of 600 RPM. The presence of the intermediate chamber 71 provides a damping effect which avoids "pumping". Pumping is further avoided by the presence of integrators which provide damping in system 86.

The invention is not limited to the particular embodiment which has been shown and described by way of example. In particular, the system 86 may include a digital conventional processor possibly fulfilling additional functions. The sensors will then have to supply digital output signals or be connected to the sensor through AID converters.

Claims (9)

1. A carburetion device for an internal combus tion engine of the type herein before defined, wherein said work chamber of the pneumatic ele ment is connected to the part of the induction pas sage situated downstream of the throttle and to atmospheric pressure, and wherein an electromagnetic valve controls one of the connections and is operatively associated with a control system.

which feeds to the electromagnetic valve opening pulses whose duty ratio depends on several operating parameters of the engine.

2. Acarburetion device for an internal combustion engine of the type hereinbefore defined, wherein said work chamber is connected to the part of the induction passage situated downstream of the throttle and to atmospheric pressure, one at least of the connections being provided with an electromagnetic valve associated with a control circuit having speed detection means and which supplies to the elecetromagnetic valve pulses whose duty ratio is controlled to maintain the stop and the throttle in a position corresponding to a predetermined speed, when the engine is idling.

3. A device according to claim 1, wherein one of the parameters is the speed of the engine, and the control system is provided with speed detection means and delivers energizing pulses to the electromagnetic valve which have a duty ratio adjusted to maintain the stop means and the throttle in a position corresponding to a predetermined speed, when the engine is idling.

4. A device according to claim 2 or 3, wherein the control system is provided with sensor means arranged for sensing the temperature of the engine and constructed for setting said predetermined speed at a value depending on said temperature.

5. A device according to claim 1 or 2, wherein the control system is provided with a deceleration sensor and is arranged to maintain the duty ratio at a predetermined value when the sensor supplies a signal indicating that the engine is decelerating.

6. A device according to claim 2 or 3, wherein the control system is provided with a sensor indicating the switching-on of means which receives its energy from the engine, and is arranged to supply to the electromagnetic valve in response ratio pulses having a duty ratio which maintains the stop means and the throttle in a position corresponding to a predetermined speed, higher than the normal idling speed.

7. A device according to claim 1 or 2, wherein the electromagnetic valve is located to control air flow between the work chamber and atmosphere and is open when it is energized.

8. A device according to claim 7, wherein the damping means comprise a chamber and calibrated restrictions are located on the air path between the work chamber and atmosphere.

9. A device according to claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.