This invention is concerned with fuel delivery systems for internal combustion engines of the type which the engine is provided with an arbitrarily operable throttle in its intake duct and, upstream of this, an air flow sensing member displaced by the flow of air into the engine against a restoring force, the movements of the sensor member, in turn, actuating a fuel metering device to increase or decrease respectively the fuel flow to the engine.

According to an aspect of the invention there is provided a fuel delivery system for an internal combustion engine comprising an intake duct having an arbitrarily-operable normal throttle valve and an air flow measuring member in the intake duct displaced from the normal throttle valve, the measuring member being movable by changes in the airflow, against a restoring force, to vary the effective area of flow past the measuring member, and a fuel-flow control valve having a movable valve member the position of which is determined by the position of the airflow measuring member, characterised by means for controlling the fuel pressure drop across the fuel-flow control valve so as to be proportional to the air pressure drop across the airflow measuring member.

Embodiments of a fuel delivery system according to the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows diagramatically a fuel delivery system with its major components shown in longitudinal section:

Figure 2 shows a modified inlet pipe;

Figure 3 shows a cross section on the line III - III of Figure 2;

Figure A is a cross section of the line IV - IV of Figure 3;

Figure 5 shows a detail of Figure 3 on an enlarged scale; and

Figure 6 shows a modifictlon to Figure 3.

Referring to the Figure 1, air flowing to the engine Intake pipe 1 in the direction of the arrow passes across an air flow measuring member 2 comprising a circular plate with an extension sleeve which slides on a guide rod 3 supported by a spider 3a. The plate bears upon the end of a lever 4 fastened to a spindle 5 by a pin 6 . The airflow measuring member 2 moves within a housing 7 of circular cross section tapering outwards in the direction of the air flow. At each end, the spindle 5 is journalled in the housing and passes through its side walls. At one end, the spindle carries a lever, not shown, to which is connected a spring, also not shown, which provides a restoring force for the measuring member 2 via the lever 4.

Downstream of the airflow measuring member 2 is a conventional arbitrarily butterfly throttle R.

Upstream of the measuring member 2 there may be an air filter F.

The spindle 5 has fixed to it by a pin 10, a cam 9 which actuates a lever 13 through a cam follower roller 11 rotatably mounted on a pin 12, carried by the lever 13. At its opposite end the lever 13 is formed with a part spherical recess 14 In which the rounded end of an -adjustable fulcrum screw 15 is engaged. In between its ends the lever 13 is formed with a further recess 16 which receives one rounded end of a push rod 17 which, at Its other rounded end engages In a recess 1R in a fuel metering member 19 urged upwards by a spring 20. The metering member 19 comprises a piston at the upper end of which is an annular wall 21 through which are cut triangular slots 23A, 23B, etc. , the number of which corresponds to the number of fuel delivery nozzles and thus preferably to the number of engine cylinders. Each slot forms with a corresponding port 27A, 27B in the casing wall 24 a fuel metering orifice which varies In size according to the square of the displacement of the metering member

19. The parts 27 lead into corresponding outlets 28.

Each engine cylinder is preferably provided with an intake duct branch 6? into which, close to the engine intake port, is fitted a fuel delivery nozzle. Each nozzle comprises a body 63 screwed into the intake branch by threads 64. In the body is fixed a fuel inlet tube 65 which is connected to one of the outlets 28 and extends with reduced diameter inside the body 63 to a point close to a fuel delivery orifice 66. Surrounding a section of the body 63 is an air supply housing 67 having an internal annular recess connected by holes 68 to an air chamber inside the body 63. A tubular connection 69 allows air to enter the body from line 70 which leads to a connection tapped into the wall of the housing 7 between the air throttle R and the air flow measuring member 2.

Fuel supplied by a pump P from a tank T enters a fuel metering of a fuel pressure-regulating valve 71 chamber 72 via a port 73, leaves via port 74 and passes through line 75 to port 35 in the regulating valve 71 and so into pressure chamber 36. Fuel in the pressure chamber acts upon the lower face of diaphragm 31 which, together with an annular valve seat formed by the top edge a tubular extension 37 of the pressure chamber wall, forms a variable area valve. Fuel passing through this variable area valve enters chamber 38 via port 39 and returns via port 40 and line 41 to the fuel tank. A spring 42 acts upon the upper surface of diaphragm 31. A pin 43 which is a close sliding fit in a housing 44 bears upon the upper surface of diaphragm 31 and the lower surface of diaphragm 33. A pin 50 bears upon the lower surface of diaphragm 31 and upon the upper surface of diaphragm 32. A spring 44 having the same load as spring 42 bears upon the lower surface of diaphragm 32. The upper surface of diaphragm 32 is exposed to the pressure in chamber 38 and port 39. The lower surface of diaphragm 33 is exposed via port 45 and line 46 to the pressure in the portion of the engine air intake pipe between the air flow measuring member 2 and the throttle R. The upper surface of diaphragm 31 is exposed via port 47 and line 48 to the pressure in the engine Intake pipe between the airflow measuring member 2 and the air cleaner F.

- A -

For ease of description the pressures of fuel and air are designated below:

P-. is the pressure between the air cleaner F and the airflow measuring member.

P ₂ is the pressure between the airflow measuring member 2 and the throttle 8.

P, is the pressure of fuel at the port 40 returning fuel to the tank.

P, is the pressure of fuel In the fuel metering chamber 72 and in the pressure chamber 36.

The circular plate of the airflow measuring member together with the tapering circular cross-section of the housing 7 within which it is housed form an annular orifice which varies in size in response to variations in the rate of air flow to the engine and it is necessary, in order to maintain a predetermined ratio of air flow to fuel flow, to provide means whereby the pressure drop across the annular orifice is effective to cause a proportional pressure drop across the fuel metering orifice 27. Since the fuel is discharged in each nozzle into pressure ?2 ^a PPUed through line 70 and hole 68 to the air chamber inside the body 63, the fuel metering pressure drop is equal to P-4~^2*

It is thus necessary that ^' & _£i ~?2 ^~ ^{s e} Q ^ua ^- ^{to a} constant multiple of ^P 1 ^"P 2-

To this end the invention provides a special relationship between the effective areas of diaphragms 31, 32 and 33 and of the tubular extension 37.

For this purpose, the areas of diaphragms 32 and 33 are each less than the effective area of diaphragm 31 by an amount equal to the

area of diaphragm 31 exposed to the pressure inside the tubular extension 37.

In order to explain the action of the fuel pressure regulator valve, the areas are defined as:

A is the area within the annular seat defined by the tubular extension 37.

C x A is the area of diaphragm 31.

(C - 1) x A is the area of each of diaphragms 32 and 33.

The force exerted by each of the springs 42 and 44 is designated as

F.

The downward forces acting on the diaphragms are: ? + x A x ?■, on diaphragm 31 and (C - 1) x A x P ₃ on diaphragm 32.

The upward forces are A x P^ plus (C - 1) x A x P^ on diaphragm 31 plus (C - 1) x A x ?2 ^on diaphragm 33 plus F on diaphragm 32.

Since the variable area valve constituted by the tubular extension 37 and diaphragm 31 will open or close to maintain a condition of balance in the forces on the diaphragms, it follows that:

PA x A = P-, x C x A - P ₉ x (C - 1) x A

Then:

- P, = C x (P _j - P ₂ )

Thus, as is required, V , - P _j is directly proportional to P, - P ₂ irrespective of any variation in the value of any or all of the pressures.

The flow-resistance pressure P, in the return line 40 reacts upon only the central area of the diaphragm 31 but acts upon the whole area of the diaphragm 32. This overcomes some of the upward force of spring 44 this being the transmitted force in the pin 50, thus causing the pressure in chamber 36 to rise. Hence as the back pressure P rises, the pressure in the chamber 36 increases to compensate.

The airflow measuring member 2 under the action of its spring will endeavour to keep the pressure Pr> constant. Every position of the airflow measuring member 2 is arranged to provide a corresponding size of metering orifice for the fuel through the rotation of the spindle 5, the resulting movement of the cam 9, the deflection of the end of the lever 13 via the roller 11 and the corresponding movement of the fuel metering member 19 via the pin 17. Thus, if the shape of the cam 9 has been made to provide the correct ratio of air flow to fuel flow for all positions of the airflow measuring member, this ratio will remain correct even if frictional forces should cause the measuring member to be in an incorrect position relative to the rate of air flow.

The system as described so far will provide for operation of the engine over most of its range but it is desirable to provide special ratios of air flow to fuel flow under certain conditions including starting, cold running, and operating at or near to full load, or when supercharge .

In order to provide enrichment of the air/fuel mixture during cold running and starting of the engine, the upper side of diaphragm 33 and the lower side of diaphragm 32 are brought into effect.

A passage 81 is connected through a restrictor 82A to the chamber 82 above diaphragm 33 and, through a restrictor 83A, to a chamber 83 above diaphragm 31 and to port 47. A restrictor 86 connects a chamber 87 below the diaphragm 32 and thus a port 89, to the passage 81.

A cold-start valve has a base 90 with a cover 91. The base 90 has mounted in it a strip 92 of bi- etallic material which bends downwards with increasing temperature. The base 90 is mounted on the engine where it will increase in temperature as a result in rise in temperature of an appropriate engine heated material, for example the engine cooling water. The free end of the strip 92 carries a tapered needle 93 extending into a bore 94 to form a variable orifice. The space containing the strip 92 is connected via port 95 and line 96 to a port 97 in the engine intake pipe between the housing 7 and the throttle. The variable orifice 93,94 is connected via port 98 to the chamber 87 via a port 89 and a line 85.

In operation, when the engine is sufficiently warm, the. strip 92 bends enough to close the orifice 93,94. Then, since the same pressure is applied to the diaphragm 33 tending to urge it downwards and to diaphragm 32 tending to urge it upwards and since both diaphragms have the same effective area there is no resultant force on the diaphragms. If the engine is cold, because the orifice 93, 94 is open to some extent according to the engine temperature, the pressure in chamber 87 is reduced and there results an increased downward force on the diaphragms which causes the fuel pressure in pressure chamber 36 to rise and so, in turn, causes the ratio of air flow to fuel flow to reduce.

An extension of chamber 82 forms a bore 100 in which a spring seat 101 Is adjustable by means of a preset adjusting screw 105 with a lock nut 106. A spring 102 is inserted between the seat 101 and the diaphragm 33. The chamber 82 is connected via port 103 and line 104 to the engine intake downstream of the arbitrarily operable throttle 8. When the engine is operating at part loads with the throttle 8 nearly closed, the pressure in the intake duct 1 in the region where line 104 is connected is low. If the throttle is suddenly opened, the pressure in the intake pipe in the region where line 104 is connected and thus in the chamber 82 rises sharply and the diaphragm 33 exerts an increased downward force and so, via pin 43, diaphragm 31 is urged downards by an additional force causing the fuel pressure in pressure chamber 36 to rise to increase the fuel flow

temporarily until the pressure difference between the chambers 82 and 83 falls away as the result of restricted flow through the restrlctors.

In engines which are supercharged either by engine driven air pumps or by exhaust driven air pumps, generally known as turbochargers, it can be arranged, by a system of orifices, that whenever the pressure in the intake pipe is above atmospheric pressure a predetermined proportion of the intake pipe pressure is applied to the upper end of piston 101 to increase the fuel pressure.

In the modified inlet pipe construction shown in Figures 2 to 5, the throttle valve 208 is mounted upstream of the airflow measuring member 202. The member 20? is attached to a hollow rack 204 which is slidable on a rod 203 supported by cross pins 207,208 secured to the inlet pipe 201. The teeth 209 of the rack 204 mesh with a pinion 206 secured to a shaft 205 rotatably mounted in the inlet pipe 201. The arrangement is such that full travel of the airflow measuring member 202 and its rack 204 corresponds to about 320° of rotation of the shaft 205.

In the vicinity of the airflow measuring member 202, the internal wall of the inlet pipe 201 is divergent so as to increase the area of the annular gap between the perimeter of the member 202 and the inner wall of the pipe 201 as the member 202 moves towards the downstream cross pin 208. As shown in Figure 2, the angle of taper of the first part 210a is less than that of the remainder 210b so as to provide increased angular movement of the shaft 201 for light airflows as compared with higher rates of airflow.

As can be seen in Figure 3, the shaft 205 is coupled to an extension shaft 212 to which is secured, by a pin 213, a fuelling control cam 214.

In order to prevent the rack 204 from twisting around on the rod 203, two washers 206a and 206b are secured to the pinion 206 at opposite ends thereof and engage flat sides surfaces of the rack

204.

Referring to Figures 3 and 4, the cam 214 co-operates with a cam follower roller 215 which is rotatably mounted on a pin 216 carried by an arm 217 which in turn is pinned to a rotary element 218 of a fuel control valve having a stationary element 219 secured between two portions of a casing 210 secured to the inlet pipe member 201.

The shaft 205 is subjected to a biassing torque in the direction to move the rack 204 and airflow measuring member 202 upstream in the inlet pipe 201 i.e. to the right in Figure 2. This may be achieved for example by means of a spring, the characteristics of wh ch are determined.

A spring 221 acts between the casing 220 and the arm 217 to hold the cam follower roller 215 in contact with the cam 214.

As shown in Figure 5, the Inner, rotary element 218 of the fuelling control valve is hollow and has a D-shaped slot 222 which registers to a varying extent with a triangular slot 223 in the stationary valve element 219, thereby defining a triangular fuel metering orifice, the cross sectional area of which varies as the square of the angle through which the inner valve member 218 has been moved from its position in which the orifice is completely closed.

Referring to Figure 3, fuel delivered from the tank T by the pump P has its pressure controlled by a first pressure regulating valve 230 having an annular space 231 to which the fuel is delivered, this space being bounded on one side by a diaphragm 232. The diaphragm 232 is loaded by a spring 233 onto an annular seat around an outlet 234 leading back to the tank. The spring 233 is located in a housing 235, the interior of which is maintained by a line 236 connected to the outlet of the inlet duct 201 and the pressure which obtains in the outlet end of the inlet duct or in a plenum chamber (not shown) connected to the outlet end of the inlet pipe 201.

Fuel from the pressure regulator 230 is delivered to the interior of

the rotary valve element 218 by a passage system 237 in the inlet pipe 201 and casing 220.

The fuel leaves the metering valve 218,219 through a further passage system 238 leading to a second fuel pressure regulating valve 240 which maintains a constant reference pressure in the passage 238 and consists of an annular chamber 241, a diaphragm 242 and a loading spring 243. Fuel leaving the valve 240 through an annular seat formed on an outlet element 245 is delivered to fuel nozzles of the kind shown in Figure 1.

To increase the fuel supply when the engine is cold, particularly for cold starting, suction may be applied to a greater or lesser extent as required to the underside of the diaphragm 242 under the control of a bi-metallic element-controlled valve of the kind shown i Figure 1 but arranged to close when the normal operating temperature is attained.

To prevent vapourisation in the lines leading to the fuel delivering nozzles, a separate pressure controlling valve 240 may be provided for each nozzle adjacent thereto. To enable any air entrained with the fuel delivered to the valve 230 to return to the tank, a small bleed hole may be formed to lead from the annular chamber 231 to the outlet 234 leading back to the tank.

The effect of the rack and pinion drive 204,206 between the airflow measuring member 202 and the cam 214 Is greatly to increase the angular movement of the latter as compared with the arm 4 in Figure 1. Accordingly, it is much easier to obtain very accurate positions for the rotary valve member 218 for a given degree of accuracy in forming the surface of the cam 214, enabling fine-tuning of the relationship between the size of the orifice in the fuel valve and the airflow to be carried out.

Instead of biassing the shaft 205 by means of a spring, the modification shown in Figure 6 may be used. In this modification, the shaft 205 carries a further cam 301 which co-operates with a

push rod 302 which slides in a guide 303 and bears against one end of a lever 304 which is pivoted at 305. The other end of the lever 304 bears against a plunger 306 which slides in a ball 307 in the housing 235 with an appropriate sealing arrangement. The plunger 306 bears on the upper end of the spring 233.

With this arrangement, the angular position of the shaft 205 determines the loading on the spring 233 and thus affects the fuel pressure. The latter, in return, in conjunction with the spring 2^3 exerts a restoring force on the shaft 205 for biassing the airflow measuring member to its upstream position.