GB2101223A - Carburettor with a starting arrangement including a throttle valve positioner - Google Patents

Abstract

The minimum throttle valve opening stop 18 is positioned by the actuator diaphragm 23 which responds to the vacuum downstream of the throttle valve 4 in the chamber 25. A valve 31 moving with the diaphragm 23 arrests withdrawal of the stop 18 by vacuum when its stem 31 contacts the bimetal strip operated cam 34 and the valve connects the chamber 25 to atmosphere. <IMAGE>

Description

SPECIFICATION Carburettor The invention relates to a carburettor for mixture-compressing internal combustion engines, with a main fuel feed system whose outlet is situated in the venturi portion of the induction pipe, an idling fuel feed system whose outlet is situated in the induction pipe at a location downstream of a driver-actuated throttle valve, itself downstream of the venturi, and a choke valve situated in the air-inlet portion of the induction pipe and actuated, by a mechanism provided for the purpose, in dependence on temperature, induction-pipe suction, air through put and engine torque.

Carburettors of this kind are intended for installation in motor vehicles of the kind which have to satisfy certain requirements in order to comply with the official regulations on the composition of the exhaust gases. Consequently the carburettor has to be of high quality in order to minimise toxic substances in the exhaust gases while nevertheless being economical in fuel consumption and giving the vehicle a good performance on the road.

For this purpose the carburettor is equipped with various systems for particular operating conditions. Among the most difficult of these are operation when the engine is cold and when it is idling. Numerous proposals have been made for solving the problems encountered under these conditions.

An important proposal has been made in the German Offenlegungsschrift 24 46 403. This describes a device for stabilising engine speed during idling after the engine has been started.

The known carburettor has an eccentrically mounted choke valve actuated by the air stream flowing through the induction pipe and influenced by a flexible member which is responsive to temperature. The carburettor also has a throttle valve controlled by a suction controller responsive to induction-pipe suction, and a device for increasing the flow of mixture when the engine is cold. The known device is characterised in that the device for increasing the flow of mixture when the engine is cold is a pivotally mounted mechanical stop connected to the temperatureresponsive member. In low ambient temperatures the stop holds the throttle valve in a more open position. When the engine warms up and reaches a certain temperature the throttle valve is released entirely and after that the throttle valve is controlled directly by the suction controller.The temperature-responsive member is a bimetal spring.

The device proposed in the German Offenlegungsschrift 24 46 403 is intended to give the throttle valve, particularly just after the engine has fired, an exactly predetermined opening position which depends on the ambient temperature at the time when the engine is started and on engine speed (induction-pipe suction). A disadvantage of this known device is that the intended precise positioning of the throttle valve persists only for a short period after the engine has fired.

Continued control of throttle-valve position by the bimetal spring is not provided and, indeed, is not possible because the choke valve is uncoupled in the opening direction. It often happens that the vehicle has to remain stationary for a considerable period after the starting of the engine, for example in a traffic jam, at traffic lights or at a railway crossing. When this happens, control of throttle-valve position can become faulty because the return movement of the mechanical stop is impeded by friction and by the pressure of the closing spring on the actuating rod when the suction controller is actuated. The impeding of the return movement of the mechanical stop has the result that with increasing warmth the idling speed of the engine increases.This effect is interrupted only when an increasing torque requirement unloads the mechanical stop so that it is free to move and is returned by the weight of the uncoupled choke, or by the bimetal spring. For this phase of operation no means are provided for adjusting the throttle valve to a predetermined minimal idling position, ie the throttle position depends only on the characteristics of the suction controller and this must necessarily be constructed to suit the requirements of a warm engine, which are different, for example in regard to toxic substances in the exhaust gases, from the requirements of a cold and idling engine.

In attempting to solve these problems the US Patent Specification 4 181 107 describes a device in which the throttle valve is controlled by a thermo-sensitive expansion element of a kind capable of delivering much greater force than a bimetal spring but which, on the other hand, involves a greater hysteresis, is fault-prone and develops deviations of zero-setting and behaviour with ageing. Furthermore, this known device has no suction control.

The intention in the present invention is therefore to provide a carburettor of the kind mentioned above but equipped with a device which makes it possible to achieve a fully automatic starting and warming-up process so that, apart from energising the starter, the driver of the vehicle does not need to do anything while the engine is warming up. Idling speed is automatically controlled to compensate for any extra load which might be applied to the engine, for example in a modern motor vehicle the engaging of a supercharger, an air-conditioning unit or the hydraulic pump of an automatic gearbox.

The problem is solved, in a carburettor according to the invention, by the combination of the following characteristics, some of which are known per se: a) Movement of the throttle valve towards its closed position is controlled, in dependence on induction-pipe suction, by a throttle valve adjustor which is pneumatically retracted by a flexible diaphragm.

b) The closing of the throttle valve is limited by a device which is responsive to engine temperature and/or to heat from a heater.

c) Moving with the flexible diaphragm in response to induction-pipe suction is a venting valve for venting the suction chamber to the atmosphere.

d) The movement of the venting valve is relative to a temperature-responsive element in the form of a bimetal spring.

e) For actuating the venting valve the bimetal spring moves a cam in dependence on temperature.

The desired effects achieved by the invention result surprisingly from the favourable interaction of the characteristics of the individual systems which, in spite of the intermeshing of their functions, has made this combination possible.

The invention has the further advantage that during warming up, after the engine has started, the engine is controlled fully automatically, even though it may be idling, and consequently the emission of toxic substances in the exhaust gases is greatly reduced. Furthermore, when an engine is operated in the cold regions of the earth it is necessary to warm the engine up to a sufficient temperature to carry the load of the auxiliary devices before the vehicle is set into motion. The invention ensures that this takes place. Hitherto a sufficient warming up has been ensured only in motor vehicles of a high price class, such as those equipped with fuel injection or whose carburettor has a thermal shunt starter. A shunt starter is costly to manufacture. The present invention provides a genuine alternative which functions in a simple manner and is less costly to manufacture and maintain.Moreover by the use of carburettor parts which have shown themselves to be reliable in practice the continued trouble-free operation of the engine is ensured.

Method of functioning Before the cooled-down engine is started, the situation is as follows: The choke valve 6 has been thrust (by a temperature responsive device which is not shown in the drawing) into its closed position. The throttle valve adjustor 1 5 has adjusted the throttle valve 4 to give the maximal idling throttle gap. The bimetal spring 37 in the throttle-valve adjustor 1 5 has rotated the facecam 34 into a position corresponding to the existing temperature of the cooled-down engine, this movement having taken place almost without frictional resistance. Now the driver can start the engine without performing any further manipulations.When the starter is energised, the suction in the induction pipe acts directly, through the maximal idling throttle gap, on the two fuel feed systems 3 and 5, because the choke valve 6 is at this time closed. When the engine fires, the choke valve 6 is rotated open by the increasing suction, with the help of the pull-down device, to give a maximal gap. The throttle-valve adjustor 15, influenced by induction-pipe suction, retracts the sliding shaft 17 so that the throttle valve 4, pulled by its spring 11, rotates towards its minimal-gap position.The face-cam 34, which is controlled by the bimetal spring 37, has a working surface contoured so that when the engine is very cold the sliding shaft 1 7 retracts only a little way before the valve stem 33 comes into contact with the face-cam 34, whereas when the engine is comparatively warm the sliding shaft 1 7 retracts through a greater distance before this happens.

When the valve stem 33 comes into contact with the face-cam 34, the venting valve 31 opens, against the influence of its spring 30, admitting atmospheric air through the venting passage 32 into the suction chamber 25, increasing the pressure on the back-surface of the diaphragm 23, and arresting the retraction of the sliding shaft 1 7.

After that, when the engine warms up, raising the temperature of the bimetal spring 37, the choke valve 6 gradually opens and the face-cam 34 is rotated by the bimetal spring 37, allowing the throttle valve 4 to rotate towards a more closed position. During this movement, the face-cam 34 is abie to rotate with little frictional resistance, because the valve stem 33 is thrust against the surface of the face-cam 34 only by the comparatively weak effect of the valve spring 30.

The bimetal spring 37 is easily able to overcome this small amount of friction. It should be observed that when the cold engine is being started the choke valve 6 should open faster than the throttle valve 4 is being closed towards its minimal idling gap position because in modern engines friction is so great that a comparatively large throttle-valve idling gap (which determines the mass-rate-of-flow of mixture to the cylinders) must be maintained for a considerable period whereas mixture-enrichment can be cut back more rapidly by opening the choke valve 6. The bimetal spring 37 has a large movement per degree of temperature change and consequently the face-cam 34 can be constructed to ensure an accurate adaptation to the operating requirements of the engine, and the bimetal spring can move continuously without suffering stresses impeding its accuracy of response. When the throttle valve approaches its minimal idling gap position, the throttle valve adjustor 1 5 can control the throttle valve position to give the engine the torque necessary for the operation of auxiliary devices by controlled venting of the suction chamber 25 (interruption of drive, and the like).

The invention will now be described in greater detail with the help of the example shown diagrammatically in the drawing.

The carburettor shown in the drawing has an induction pipe 2, a portion of which is in the form of a venturi 1 containing the outlet of a main fuel feed system 3. Downstream of the venturi 1 there is a driver-actuated throttle valve 4 and downstream of this is the outlet of an idling fuel feed system 5. The air-inlet portion of the induction pipe 2 contains a choke valve 6 which is actuated, by means provided for the purpose, in a manner known per se, in dependence on temperature, induction-pipe pressure, air throughput and engine torque. The carburettor is equipped with all the devices necessary for its good operation, although they are not all shown in the drawing.

The throttle valve 4 is fixed to a throttie-valve shaft 7 to which is also fixed a throttle lever 8 with two eyes 9, 10 to take a spring 11 and an actuator 12. The throttle lever 8 has an arm 13 equipped with a stop-nose 14 which rests in contact with the head of an adjustment screw 1 8 of a throttle-valve adjustor 1 5 which determines the throttle gap (the gap between the rim of the throttle valve and the inner wall of the induction pipe) during idling of the engine.

The throttle-valve adjustor 1 5 is screwed to a bracket 1 6 of the carburettor and has a sliding shaft 1 7 terminating in the adjustment screw 18, which is itself locked in position on the sliding shaft 17 by a locking nut 19. The shaft 17 slides back and forth in a bearing of a housing 20. A flexible diaphragm 23 retained by two diaphragm plates 21, 22 is fixed to the inner end of the sliding shaft 17. The rim of the diaphragm 23 is clamped between the housing 20 and a cover 24, the diaphragm 23 separating an atmospheric chamber 27 in the housing 20 from a suction chamber 25 in the cover 24.The suction chamber 25 communicates, through a suction line 26, with the induction pipe 2 at a location downstream of the throttle valve 4, Screwed, adjustable in position, on the sliding shaft 1 7 is a springretained nut 27 which determines the working length of a compression spring 29, whose inner end takes support against a surface of the housing 20, the spring thrusting the sliding shaft 17, with its adjustment screw 18, towards the stop nose 14. When the sliding shaft 17 is fully advanced, towards the left in the drawing, the diaphragm plate 21 rests in contact with a surface of the housing 20. Under these circumstances the adjustment screw 1 8 can be used to adjust the maximal idling throttle gap.

Penetrating through the diaphragm plates 21, 22 and fixed to them there is a venting valve 31 controlling a venting passage 32. The venting valve 31 is influenced by a spring 30 which thrusts a valve stem 33, in the interior of the suction chamber 25, towards a rotary face-cam 34. The face-cam 34 is fixed to a cam shaft 35 mounted to rotate in a bearing of the cover 24.

The face-cam 34 is rotated by a bimetal spring 37 whose inner end 38 is fixed to a rotatable cap 39 of the cover 24, its outer end being connected to the cam shaft 35. The portion of the suction chamber 25 containing the bimetal spring 37 has a heat-exchange zone 40 through which cooling water from the engine flows, or an electric heater.

41, if necessary partitioned off.

Claims (2)

Claims

1. A carburettor for mixture-compressing internal combustion engines, with a main fuel feed system whose outlet is situated in the venturi portion of the induction pipe, an idling fuel feed system whose outlet is situated in the induction pipe at a location downstream of a driver-actuated throttle valve, itself downstream of the venturi, and choke valve situated in the airinlet portion of the induction pipe and actuated, by a mechanism provided for the purpose, in dependence on temperature, induction-pipe suction, air throughput and engine torque, characterised by the combination of the following characteristics, some of which are known per se: : a) movement of the throttle valve (4) towards its closed position is controlled, in dependence on induction-pipe suction, by a throttle valve adjustor (15) which is pneumatically retracted by a flexible diaphragm (23); b) the closing of the throttle valve is limited by a device (37) which is responsive to engine temperature and/or to heat from a heater; c) moving with the flexible diaphragm (23) in response to induction-pipe suction is a venting valve (31) for venting the suction chamber (25) to the atmosphere; d) the movement of the venting valve (31) is relative to a temperature-responsive element in the form of a bimetal spring (37); e) for actuating the venting valve (31) the bimetal spring (37) moves a cam (34) in dependence on temperature.

2. A carburettor substantially as hereinbefore described with reference to the accompanying drawing.