GB2037885A - Pneumatically Controlled Device for the Indirect Injection of Fuel Into Internal Combustion Engines - Google Patents

Abstract

The device comprises a pneumatic sensor 5 responsive to induction manifold pressure, connected to a stem 20 of a needle valve fuel injector 21 by means of a mechanical linkage primary adjustable resilient means 11, 16 act on the linkage 10, 12, 20 for adjusting the rate of valve opening with respect to change of manifold pressure; and an adjustable means 23 acts on the linkage for adjusting the bias tending to keep the valve closed when there is no pressure depression in the manifold. The sensor may be a barometric capsule and the device mounted directly in the induction passage. <IMAGE>

Description

SPECIFICATION Pneumatically Controlled Device for the Indirect Injection of Fuel into Internal Combustion Engines The present invention concerns an automatic device for the indirect injection of fuel into internal combustion engines. More particularly it relates to a device that utilizes a pneumatic signal produced in the induction manifold of the engine for the dosing of the fuel, without requiring its transduction or its transformation into a signal of another nature, and which does not suffer from troubles such as load drops and/or harmful turbulence in the air-flow sucked in by the engine.

The indirect injection technique (with electronic, mechanical or pneumatic control) for introducing fuel into an internal combustion engine has been widely used for a long time. With respect to the use of a suctiontype or injectiontype carburettor, the technique in general offers advantages in fuel consumption, air pollution and ready intervention, particularly when electronic control is used. However, in practice there are greater difficulties in installation and maintenance and the installed equipment has a shorter operational life.

More particularly, electronically controlled indirect injection uses complicated and expensive equipment, and requires highly specialized personnelfor its installation, setting-up and maintenance. The indirect electronically controlled injection apparatus is dependent on the electrical system of the vehicle, and if this is not operating efficiently the engine may not start.

Moreover, electronic injection at a constant fuel flow rate requires the fuel to be at a controlled pressure. It also requires the injector nozzles to be grouped in a well defined number for each type of engine, and the control signals for the injectors to be short in order not to create complications of concentration and mixing.

Last but not least, the electronic components used are sensitive to temperature and the whole equipment consists of specially selected components set by the manufacturer, so that any upsetting of the calibration due to wear and ageing, makes it necessary to replace the whole electronic control module.

Mechanically controlled injection, in contrast to feeding fuel through a suction-type carburettor which causes a varying pressure in the induction manifold, regulates the fuel feed by exploiting as an independent variable the position of the accelerator. According to a known embodiment, the accelerator position controls directly the quantity of fuel introduced into the engine, on which depends the quantity of air required and, possibly, a variable pressure condition in the induction manifold, a pressure condition that is not at all exploited for the purposes of the adjustment.

According to another known embodiment, the mechanical injection controls the indirect ,injection causing an intentional drop in load localized in the induction manifold whose pressure head, varying with the number of revs of the engine, operates a transmission lever which positions a slide valve gear in the fuel circuit thereby regulating its flow rate.

This known embodiment, which exploits the loss of load in the inducted air circuit in order to obtain a metered flow rate, is commonly defined as mechanical-pneumatic injection.

Now, since all the indirect injection systems in internal combustion engines operating the "Otto" cycle raise the overall performance of the engine principally by improving the volumetric efficiency of the engine, it follows that the overall performance of the engine will be greater the closer the pressure of the inducted air approaches atmospheric pressure, that is reduced losses in load will occur.

Thus, an object of this invention is of providing a device with pneumatic control for the indirect injection of fuel into internal combustion engines which uses a pneumatic signal produced in the induction manifold of the engine itself, a signal that will be used directly, that is without the transduction into a signal of another character, and above all without introducing into the system troubles such as casual or intentional drops in load in the flow of sucked-in air.

The invention provides a device responsive to induction manifold pressure for indirect injection of fuel into an internal combustion engine, which comprises a pneumatic sensor responsive to induction manifold pressure, connected to a stem of a needle valve fuel injector by means of a mechanical linkage; primary adjustable resilient means acting on the linkage for adjusting the rate of valve opening with respect to change of manifold pressure; and secondary adjustable resilient means acting on the linkage for adjusting the bias tending to keep the valve closed when there is no pressure depression in the manifold, and thus for adjusting the fuel/air ratio over all engine speeds.

Thus, the invention may provide a pneumatically controlled indirect injection device of extreme constructional simplicity and of limited overall size, of easy adjustment and maintenance, suited for being used for the contemporaneous injection into a plurality of cylinders or for a single cylinder, as well as for groups of cylinders, depending on the characteristics and type of engine to be fed.

A further feature of this invention is that of providing a device that possesses a high efficiency, is independent from the electric installation of the vehicle and is structurally of such design as to allow its realization in metal, or entirely or partially in plastics material, with obvious economical as well as production advantages.

The pneumatic sensor may be a deformable membrane or a barometric capsule or other mechanical pressure sensor.

The mechanical linkage may comprise a rod attached at one end to the sensor and at the other end to a crank connected to the valve stem.

More particularly, the primary resilient means associated with the membrane and with the linkage, may consist of two springs of which one is preloaded and placed between the membrane and a body, while the other is placed coaxially to the former between the crank gear support and the body and is provided with adjusting or calibrating means. These springs preload. the membrane in such a way as to relate the variable air pressure in the manifold to the correct positioning of the deformable membrane, and thus the valve.

Moreover, the secondary resilient means associated with crank, may consist of springs or the like suited for resiliently supporting the crank, and which is adjustable through a screwhandwheel to the exact point of rest (with the engine off) of the crank and, consequently, the closing load of the injector. This closing load is of opposite sign to the load caused by the suction of the engine to which the needle valve of the injector is subjected as the injector opens.

The invention will now be described in further detail with reference to the attached drawings which represent a preferred but not exclusive practical embodiment and are given for purely indicative and not limiting purposes, wherein: Figure 1 represents a schematic view of a pneumatically controlled device for indirect injection of fuel into an internal combustion engine according to this invention; while Figure 2 represents a schematic view of the device of Figure 1, inserted into the induction circuit of the engine.

The device consists of a box-like supporting body 1 made of plastics material or of metal, suitable for being mounted onto the induction manifold 2 of a standard engine 3 near the inlet valve 4 (Figure 2).

To this supporting box-like body 1 is rigidly attached a bell-shaped body 5, closed at its fore end by a lid 6. Between annular edges 7 and 8 of the lid 6 and of the bell 5 respectively is held a membrane 9 attached at its center to a transmission bar 10. Coaxially with this transmission bar 10 is mounted a coil spring 11, which is compressed between the membrane and the wall of body 1. The free end of the transmission bar 10 is hinged at point 1 3 to a pivoting element 12, which consists of a plate hinged at 14 to a bracket 15 on the body 1.

Coaxially to the spring 10 is mounted a second spring 16 which is guided by the shank 17 of an adjustable screw 1 8. By operating screw 1 8 the membrane 9 may be pre-loaded in such a way as to connect the variable pressure of manifold 2 with the position of the membrane itself when the engine is running, whatever be the rest position.

Thus, for each running speed of the engine there is a corresponding equilibrium pressure between the net force exerted by the springs and the opposite force exerted in the direction of arrow A by the air pressure on the membrane.

Onto the pivoting element 12, by the use of a coil spring 20a there is hinged at 1 9 the stem 20 of the needle valve of a conventional pin injector indicated generically with numeral 21 in Figure 2.

The upper part of the pivoting element 12 is shaped as a rack 22 which meshes with a worm screw 23 that can be operated by handwheel 24.

By acting on said handwheel, small angular displacements of element 12 around the hinge point 14 are achieved with consequent small displacements of the stem 20 of the needle valve.

Thus, the operating of handwheel 24 allows the preload on the closed needle valve to be altered.

This load tends to keep the injector closed.

The regulation of the initial opening load of the injector has, in this case, the function of regulating the composition of the exhaust gas. In fact, the initial load on the needle valve controls the opening of this needle valve, thereby producing either an enrichment or impoverishment of the fuel-air mixture at all engine speeds and, thus, a corresponding variation in composition of the exhaust gas. In Figure 1, numeral 25 indicates the fuel inlet, while arrow A indicates the direction and sense of the air pressure that acts on membrane 9.

In Figure 2 there is schematically represented the engine induction system of an internal combustion engine whose manifold is associated with an indirect injection device of this invention.

In Figure 2, 26 indicates the fuel tank, 27 a filter and 28 indicates a feed pump for sending fuel through inlet 25 into injector 21. An overpressure valve 29 serves for the recyciing into the tank of excess of fuel. A choking device 30 between the pump and the injector, compensates for any variations in the flow rate of the pump itself.

Within the manifold 2 is inserted a conventional butterfly valve 31, operated by the accelerator pedal and a corresponding screw 32 for adjustment of the engine idling speed.

Moreover, an additional injector 33 is provided for enriching the fuel mixture in order to facilitate starting of the engine at low temperatures.

The indirect injection device of this invention is inserted into the circuit of Fig. 2 near inlet valve 4 and is globally indicated as 34. The variable pressure in manifold 2 is monitored at 35 by means of a branch line 36 connected to the chamber in which is located the yielding wall formed by the membrane 9. In this way the pneumatic signal tapped at point 35 from the manifold controls the flow rate of the fuel through injector 21.

From what has been described above, it is clear that: the tapping or picking up of the pneumatic signal does not disturb the flow rate of the air in the manifold, since it is a static tapping and therefore does not interfere with any variable of the air flow; there is essentially no consumption of power by the pneumatic injection, in contrast to mechanical injection wherein the additional loss in load makes the flow rate worse and lowers the density of the air; the force that acts on the dosing device is simply proportional to the pressure depression in the suction duct; the density of the inducted air in this pneumatic system is greater than that of the air in a mechanical-pneumatic system.

the pneumatic signal is drawn off and used directly, that is without the necessity of being converted into other types of signals, and therefore offers a considerable advantage with regard to the constructional simplicity of the injection device; finally, the flow rate of the fuel is instantaneously adjustable proportionally to the demand, that is, the instantaneous fuel flow rate is proportional to the pressure depression caused and may thus superimpose itself on the suction without creating any unbalance.

Moreover, the above described pneumatic device may be used for simultaneously feeding all the cylinders of the engine, or it may be used singly, that is so that each single cylinder has its own injection device.

The device may be made of plastics material with obvious advantages from the economic point of view as well as that of weight and durability.

Obviously, in the practical realization of the invention as herein described there may be introduced structurally and functionally equivalent modifications and variants such as for instance barometric capsules or Bourdon tubes in place of the membrane, without thereby falling outside the protective scope of the invention itself.

Claims (10)

Claims

1. Device responsive to induction manifold pressure for indirect injection of fuel into an internal combustion engine, which comprises a pneumatic sensor responsive to induction manifold pressure, connected to a stem of a needle valve fuel injector by means of a mechanical linkage; primary adjustable resilient means acting on the linkage for adjusting the rate of valve opening with respect to change of manifold pressure; and secondary adjustable resilient means acting on the linkage for adjusting the bias tending to keep the valve closed when there is no pressure depression in the manifold, and thus for adjusting the fuel/air ratio over all engine speeds.

2. Device according to claim 1, wherein the pneumatic sensor is a deformable membrane or a barometric capsule.

3. Device according to either preceding claim, wherein the mechanical linkage comprises a rod attached at one end of the sensor and at the other end to a crank connected to the valve stem.

4. Device according to claim 3, wherein the primary resilient means comprises a first spring operative between the sensor and a body of the device whereon the crank is mounted, and a second spring operative coaxially to the first spring between the body and the crank and being provided with tension adjusting means.

5. Device according to claim 3 or 4, wherein the secondary resilient means comprises a spring tending to close the valve and means for adjusting the spring tension by varying the crank position when there is no pressure depression in the manifold.

6. Device according to any preceding claim constructed substantially of plastics material.

7. Device according to any preceding claim, which comprises at least two fuel injectors controlled by the sensor.

8. Device responsive to induction manifold pressure for indirect injection of fuel substantially as described with reference to and as shown in the drawings.

9. The combination of an induction manifold and at least one device according to any of preceding claims, wherein the sensor is connected to the manifold downstream of a butterfly valve controlling air flow in the manifold.

10. The combination of claim 9 substantially as described with reference to and as shown in Figure 2 of the drawings.