GB2113296A - Control of mixture supply to groups of internal combustion engine cylinders - Google Patents

Abstract

The inlet tracts (6) of some cylinders (2 and 3) are interconnected by a balance tube (7) to equalize pressures in the inlet tracts and valves (5) in these tracts are prevented from fully closing. The valves (5) are arranged by a suitable linkage to be responsive to the inlet manifold vacuum or to the linkage operating the main throttle of the engine to control the supply of combustible mixture to the associated cylinders (2 and 3) at higher loads. The remaining cylinders (1 and 4) have no such control valves in the associated inlet tracts so that they are capable of normal operation under all conditions. <IMAGE>

Description

SPECIFICATION Fuel economy device for multi-cylinder internal combustion engines This invention relates to improvements in fuel economy devices and is particularly concerned with a fuel economy device for multi-cylinder internal combustion engines having the performance controlled by induction throttling.

It can be argued that variation of swept volume would be an ideal method of governing the performance of an otherwise conventional automotive petrol engine. An engine is normally designed to produce a certain level of performance, under conditions of wide open throttle, commensurate with the level of road performance desired from the vehicle to which the engine is to be fitted. Except for a few designs with very low performance, the engine will spend the vast majority of its working life at performance levels below the designed maxima.

The average automotive petrol engine produces its best thermal efficiency when running at speeds of 3555% of its maximum power speed and when producing 7085% of its potential power at those speeds. Hence, it would indeed be "ideal" if, instead of throttling to a reduced power level, the swept volume could be reduced to maintain the output at 7085% of potential at the chosen speed.

Numerous mechanisms have been suggested which allow variation of piston stroke to vary swept volume but none of these can be ciassed as commercially viable. Much work has been done in recent years on another approach known as "selective cylinder disablement" in which the whole engine is considered as a combination of independent modules which may be activated or deactivated as required.

For example, it has been proposed to deactivate the valves of one or more cylinders by various means such as stoppage of the camshaft mechanism or by making the pivots of the valve rocker arms movable. The justification of valve gear disablement is said to be so that the deactivated cylinders may act as pneumatic springs, returning on the down stroke virtually all of the energy which they absorb on the upstroke.

Hence, pumping losses are minimised and fuel is not burned unproductively. However, there are problems when the deactivated cylinders are to be brought back into use. The very high revolution speed of the engine means that a complicated mechanical system has to be employed to reengage the valve gear at the correct point in the cycle. Moreover, working temperatures are not maintained in the deactivated cylinders and, when these cylinders are reactivated, some initial misfire and a step increase in output are both likely. Either of these problems will produce excessive jerks and, thus, are likely to be unacceptable.

As an alternative, is has been proposed to cut off the fuel supply to one or more cylinders while leaving the valve gear operational. This solution does not solve the problem of maintaining the deactivated cylinders at working temperatures and thus, again, initial misfire and step increase in output are likely when the deactivated cylinders are reactivated. It has been proposed to solve this problem by complicated valve and port arrangements by means of which the fuel supply is cut off to some of the cylinders and the exhaust gases from the remaining cylinders are fed into the inlet tracts of the deactivated cylinders. This has the effect of maintaining the deactivated cylinders at or near working temperatures but it calls for very complicated valve and porting arrangements for the engine.

The present invention aims to provide a fuel economy device, using the principle of selective cylinder disablement, which overcomes the disadvantages of the previously known systems and which is cheap and easy to install in an engine.

According to the invention, there is provided a fuel economy device for a multi-cyiinder internal combustion engine wherein a valve is located in the inlet tract of at least one cylinder of the engine, the or each said valve being prevented from fully closing and being arranged to be responsive to the inlet manifold pressure of the engine to control the supply of combustible mixture to the associated cylinder in response to the pressure in said inlet manifold, at least one cylinder of said engine having no such valve in the associated inlet tract so as to be capable of normal operation under all conditions.

The arrangement according to the invention sacrifices a small amount of fuel, sufficient at least to allow the or each nominally disabled cylinder to generate enough energy to overcome its own losses, so that the disablement is only partial.

The essential concept of the arrangement according to the invention is that, for a given power output, small in proportion to the potential, a given throttle opening will be required at the entry to the induction manifold. The required amount of working fluid (air and petrol) normally fed in equal proportions to all of the cylinders of the engine is, in the system according to the invention, diverted to only some of the cylinders constituting a first or primary module so that this module receives up to 7085% of its maximum capability.As the power output demanded from the engine is increased, remaining modules can be similarly activated in turn, up to the desired power output, while any redundant modules are fed only a small amount of working fluid sufficient to maintain idle running and, at the same time, to maintain the associated cylinder(s) at working temperatures. Each module may contain one or more cylinders.

Reference to fuel consumption maps suggests a lessening of constant speed fuel consumption of around 15% at performance levels up to 50% of maximum, reducing as performance increases towards maximum.

Taking the simple example of an in-line 4 cylinder engine, this can be split into two, evenfiring, two cylinder modules comprising cylinder numbers 1 and 4 in one and 2 and 3 in the other.

One pair of valves, in the form of secondary throttles, is provided to obstruct entry to the chosen secondary module so diverting flow to the primary module. Preferably, cylinders 1 and 4 are in the primary module and cylinders 2 and 3 in the secondary module.

The invention will now be further described, by way of example, with reference to the drawings, in which: Fig. 1 illustrates, diagrammatically, an inlet manifold for an internal combustion engine fitted with a fuel economy device according to the invention; Fig. 2 illustrates, diagrammatically, one embodiment of a manual mechanism for operating the secondary throttles of a fuel economy device according to the invention; Fig. 3 illustrates, diagrammatically, one embodiment of an automatic control mechanism for operating the secondary throttles of a fuel economy device according to the invention; Fig. 4 is a vertical section through a control valve suitable for incorporation in the control mechanism shown in Fig. 3; and Fig. 5 is a vertical section through an additional control valve which can be used in conjunction with the control valve shown in Fig. 4.

In the drawings, like parts are denoted by like reference numerals.

Reference wi!l first be made to Fig. 1 of the drawings which is a diagrammatic representation of the inlet manifold on an in-line 4 cylinder engine. The engine is notionally divided into a primary module consisting of cylinders 1 and 4 and a secondary module consisting of cylinders 2 and 3. A secondary throttle 5 is provided in the inlet tract 6 of each of the cylinders 2 and 3 of the secondary module and a balance tube 7 is provided which connects the two inlet tracts 6 to ensure that the pressures in the inlet tracts 6 are equal. A tapping 9 in the inlet to the primary or main throttle 8 is also provided upstream of said main throttle and further tappings 11 and 12 are provided respectively in the region of the main throttle 8 and in the inlet manifold.

The closed position of the secondary throttles is set by means of adjustable stops 13 (see Figs. 2 and 3). The position of these stops can be found by experiment but the following procedure is suggested as a possibilityl (a) Select a road cruising speed which would be typical for the vehicle under consideration (not exceeding 72% of the maximum speed) and establish the corresponding engine speed.

(b) Set the engine to run under no-load conditions (i.e. in "neutral" gear) at the engine speed derived from (a) above and observe the inlet manifold vacuum PM produced with the secondary throttles 5 held wide open.

(c) On a rolling road dynamometer, set the secondary throttles 5 wide open, then set the dynamometer load and open the main throttle 8 as required to simulate running at the cruising speed chosen in (a) above. Progressively close the secondary throttles 5 until the inlet manifold vacuum Pp downstream from the secondary throttles 5 is seen to rise to the value PM established in (b) above. The adjustable stops 13 are then adjusted to prevent further closing of the secondary throttles 5 from this position and are desirably locked in place. The balance tube 7 connecting the ports 2 and 3 ensures that there is a similarity of flow in the two ports to allow for any discrepancy in position of the secondary throttles which may be caused by errors in adjustment.

Various methods may be used to operate the secondary throttles 5 but all should follow the basic principle of diverting working fluid to the primary cylinders 1 and 4 as power output increases until they reach about 75% of their potential output, at which point opening of the secondary throttles 5 commences. The secondary throttles should reach their fully open position at, or slightly before, the point at which the primary or main throttle 8 reaches its fully open position.

Some suggested methods are described in the following with reference to the drawings.

Fig. 2 shows a control arrangement for the secondary throttles 5 which is intended for manual operation by the driver. As shown in Fig.

2, each secondary throttle 5 is mounted on a respective shaft 1 5 which extends through the associated inlet tract 6 and carries at one end a lever 1 6. One end of each lever 1 6 is arranged to bear against a respective adjustable stop 13 in the form of a screw engaged in a screw-threaded bore provided in a lug 14 mounted on the inlet manifold casing. The other end of each lever 1 6 is pivotally connected to a rod 1 7 by a ball joint 1 8.

One end of a further rod 1 9 is pivotally connected to one end of the rod 1 7 and the other end of the rod 19 is pivotally connected to one end of a lever 21 which is pivotally mounted intermediate its ends on a shaft 22 mounted on the inlet manifold casing. The other end of the lever 21 carries a pivotal mounting 23 in which a rod 24 is axially slidable. One end of the rod 24 carries an end stop 25 and the other end is pivotally connected by a ball joint 26 to a lever 27 which is mounted on the actuating shaft 28 of the main throttle 8.

The other end of the rod 1 7 is connected to one end of a coil spring 29 the other end of which is connected to the inner core 31 of a Bowden cable 32 provided with adjustment means 33. The cable 32 leads to a control lever (not shown).

Having established a cruise condition under normal operation, a driver may then operate the control lever to tension the spring 29 which in turn causes the rod 17 to move to the right as viewed in Fig. 2 and, thus, the levers 16 are caused to pivot in a clockwise direction, as viewed in Fig. 2, until they abut the respective stops 1 3. The secondary throttles 5 are then in the closed position. Fig. 2 shows the position in which the main throttle 8 is in the half-open position with the end stop 25 on the sliding rod 24 about to contact the lever 21 to cause override of the tension spring 29 and opening of the secondary throttles. This override facility provided by the main throttle is considered to be a desirable if not necessary feature for safety purposes whereby the secondary throttles are fully opened if the main throttle is opened fully.

If desired, the cable lever may be replaced by a manually operated solenoid switch.

In the embodiment shown in Fig. 3, the two levers 1 6 are pivotally connected by ball joints 18 to a rod 37 which merely extends between said ball joints. A further rod 38 is pivotally connected at one end to one of the ball joints 18 and at the other end to a further ball joint 39. The push rod 41 of a diaphragm unit 42 is also pivotally connected to the ball joint 39, said push rod 41 extending from one side of a diaphragm in the unit 42 which side is connected with the tapping 12 via a small bore pipe 43 so that this side of the diaphragm is at the pressure PM in the inlet manifold. The other'sidle of the diaphragm is in communication with atmospheric pressure PAT.A control spring (not shown) is provided in a part 44 of the casing of the diaphragm unit 42 to urge the rod 41 in a direction to open the secondary throttles, i.e. to the left in Fig. 3.

Thus, in operation, the inlet manifold pressure PM is applied to the spring side of the diaphragm while atmospheric pressure PAT is applied to the other side. Hence, if AD is the effective area of the diaphragm, the secondary throttles will settle to a position in which ADX(PATPM)=spring ratexspring deflection and should close fully at the values of PM established as described above.

In this case, the diaphragm is moved to the right, as viewed in Fig. 3, which is effective to draw the rod 41 to the right and, via the linkage formed by the rods 38 and 37 and ball joints 39 and 18, the levers 1 6 will be caused to pivot in a clockwise direction as viewed in Fig. 3 until they abut the respective stops 13. In this position, the associated secondary throttles are in the closed position.

As power output and primary throttle opening increase, the inlet manifold pressure PM will rise and will more nearly approach atmospheric until whe pressure PAT until, when the pressure M is about 10 cm Hg below atmospheric pressure PAT' the spring will have extended to cause the diaphragm to move to the left as viewed in Fig. 3 to such an extent that the linkage formed by the rods 41, 38 and 37 and ball joints 39 and 1 8 is effective to cause the levers 1 6 to pivot in an anti-clockwise direction as viewed in Fig. 3 to move the secondary throttles to the fully open position.

Given a knowledge of diaphragm area AD and inlet manifold pressure PM at the extremes of movement of the secondary throttles, a suitable design of spring may be arrived at.

This embodiment provides a gradual opening of the secondary throttles with increasing rise in the inlet manifold pressure P,. M However, if desired the control valve shown in Fig. 4 may be incorporated in the pipe 43 between the inlet manifold tapping 12 and the diaphragm unit 42.

This control valve comprises a casing formed by two parts 51 and 52 which are separated by a diaphragm 53. A pipe 54 leading from the tapping 12 is divided into two branches 55 and 56, the branch 55 leading into a chamber formed in the upper one of the casing parts 51 and 52. The upper casing part 51 also contains a coil spring 57 arranged to bear at one end on a plate 58 secured to the diaphragm 53 and at the other end on a plate 59. The plate 59 is arranged to be acted on by an adjusting screw 60 which is engaged with a screw-threaded bore 61 in the casing part 51 and extends outside said casing part whereby the tension or compression of the coil spring 57 may be readily adjusted.

The branch pipe 56 is connected to a bore 62 in the lower casing part 52 which bore terminates in a valve seat 63. A valve member 64 is arranged to seat on the valve seat 63 and is secured at its other end to the diaphragm 53. The valve member 64 passes in sealing manner through a bore in the casing part 52 and then through a chamber 65 in the said casing part 52 before seating on the valve seat 63. A bore 66 leads from the chamber 65 and is connected to the pipe 43. A further bore 67 connects a chamber 68 in the casing part 52 on the valve side of the diaphragm with atmospheric pressure PAT The design and adjustment of the spring 57 in combination with the effective area of the diaphragm 53 cause the system to remain inoperative until the inlet manifold pressure PM is below a predetermined value.This value can be adjusted by means of the adjusting screw in order to determine the point at which the secondary throttles 5 begin to close. Fig. 4 shows the condition in which the throttles 5 are fully open and the valve 64 is closed. When the pressure PM in the inlet manifold falls below said predetermined value, which value will normally be about 10 cm Hg below atmospheric pressure PAT' the diaphragm 53 will move against the action of the spring 57 and the valve member 64 will be pulled by the diaphragm away from its valve seat 63.The diaphragm in the diaphragm unit 42 will then be connected to the inlet manifold via the tapping 12, pipes 54 and 56, bore 62, chamber 65, bore 66 and pipe 43 and will be subjected to the effect of the pressure difference between PM and P,. The diaphragm will therefore move to the right as viewed in Fig. 3 and will thus be effective to move the associated throttles 5 towards the closed position. Further reduction in the pressure PM will result in further closing movement of the secondary throttles until said throttles are forced against the adjustable stops. This will normally occur below about 20 cm Hg below atmospheric pressure.

This embodiment provides a snap-action for the secondary throttles in that, until the pressure PM drops to about 10 cm Hg below atmospheric pressure PAT' no movement of the throttles 5 will take place.

Fig. 5 shows an additional control for use in conjunction with the valve in Fig. 4 in which the control valve comprises a casing formed by two parts 71 and 72 separated by a diaphragm 75.

The upper casing part 71 has a chamber 73 which is connected to a bore 76 to the tapping 11 in the region of the main throttle (see Fig. 1). A branch pipe 77 leads from the tapping 12 into a chamber 74 formed in the lower casing part 72 and a valve member 79 and spring 81 are located in this chamber on the same side of the diaphragm 75. The valve member 79 is connected to a plate 80 mounted on the diaphragm 75 and the spring 81 extends between the plate 80 and a wall of the chamber 74. In this case, the spring 81 is not provided with an adjusting screw.

The valve member 79 passes in sealing manner through a bore in said wall of the chamber 74 and extends through a chamber 82 in the casing part 72 to seat on a valve seat 83 provided at the end of a bore 84 in said casing part 72. The bore 84 is connected by a branch pipe 78 to the tapping 12. A bore 85 leads from the chamber 82 and is connected to the pipe 54.

This embodiment provides low speed idle which is equal to that obtainable without the fuel economy system according to the invention being fitted since it takes its operating signal from the tapping 11 which may take the form of a T-piece inserted in the ignition distributor vacuum advance line. These units, by suitable positioning of the pressure tapping 11 in relation to the primary or main throttle 8 do not detect a depression during closed primary throttle conditions. Hence, it will be seen that the valve shown in Fig. 5 will remain closed until the value of the pressure PD approaches that of the pressure PM and the secondary throttles will open at low speed idle but will otherwise operate as required.

A ball valve may be inserted in the small bore pipe 43 to have free flow in the secondary throttle opening direction and damped flow in the closing direction. This will have the dual effect of damping any resonances and also of maintaining the secondary throttles in a fully open condition during gear changes occurring under hard acceleration.

Servo-control and/or programmed electronic systems may alternatively and/or additionally be provided to control the secondary throttles.

To give optimum results, each module is likely to require an independent vacuum operated, ignition timing advance unit. This would mean the use of two distributors or a single distributor with two lobe cam or sensor and twin points or pickups at 900 on independent plates with two vacuum units.

It is suggested that the secondary throttles should be so arranged that the engine will operate as follows in which F.L. stands for "Full Load": (a) Idle-Secondary throttles are open enough tQ give smooth idle.

(b) Off ldle-(T1 FL) B.M.E.P. in cylinders 1 and 4 increases at nearly twice normal rate.

Cylinders 2 and 3 remain close to idle.

(c) T F.L.-Cylinders 1 and 4 run at + B.M.E.P., cylinders 2 and 3 idle.

(d) 8 F.L.-Cylinders 1 and 4 run at i B.M.E.P., cylinders 2 and 3 idle.

(e) T F. L.-Cylinders 1 and 4 run at i B.M.E.P., cylinders 2 and 3 run at T B.M.E.P.

(f) + F. L.-All cylinders run at T B.M.E.P.

(g) F.L.-All cylinders run at full load.

With the device according to the invention, no performance loss at wide open throttle openings would be caused but there would be a significant fuel saving at lower throttle openings.

The device can be installed in an engine as original equipment or fitted into existing engines as a conversion kit.

It should be noted that the invention is not restricted to the above-described embodiment but that modifications and variations may be made without departing from the scope of the invention. Further, the device is not restricted to use with 4 cylinder engines but can be used with multi-cylinder engines having any number of cylinders. It is also possible to group the cylinders in more than one secondary module, each such module being arranged to partially disable its associated cylinders at different levels of power output.

Claims (Filed on 24/11/82) 1. A fuel economy device for a multi-cylinder internal combustion engine wherein a valve is located in the inlet tract of at least one cylinder of the engine, the or each said valve being prevented from fully closing and being arranged to be responsive to the inlet manifold pressure of the engine to control the supply of combustible mixture to the associated cylinder in response to the pressure in said inlet manifold, at least one cylinder of said engine having no such control valve in the associated inlet tract so as to be capable of normal operation under all conditions.

2. A fuel economy device according to claim 1, wherein the engine has four cylinders which are divided into a primary module and a secondary module each consisting of two cylinders, a pair of said control valves being located in the inlet tracts of the cylinders of said secondary module and no said control valves being provided in the inlet tracts of the cylinders of said primary module.

3. A fuel economy device according to claim 2, wherein the engine has four cylinders arranged in line, the outer cylinders constituting the primary module and the inner cylinders constituting the secondary module, and wherein the inlet tracts of said inner cylinders are inter-connected by a balance tube to equalize the pressures in said inlet tracts.

4. A fuel economy device according to any preceding claim, wherein the or each control valve is pivotally mounted in the associated inlet tract and carries a lever, one end of said lever being arranged to bear against a stop in the

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

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. conjunction with the valve in Fig. 4 in which the control valve comprises a casing formed by two parts 71 and 72 separated by a diaphragm 75. The upper casing part 71 has a chamber 73 which is connected to a bore 76 to the tapping 11 in the region of the main throttle (see Fig. 1). A branch pipe 77 leads from the tapping 12 into a chamber 74 formed in the lower casing part 72 and a valve member 79 and spring 81 are located in this chamber on the same side of the diaphragm 75. The valve member 79 is connected to a plate 80 mounted on the diaphragm 75 and the spring 81 extends between the plate 80 and a wall of the chamber 74. In this case, the spring 81 is not provided with an adjusting screw. The valve member 79 passes in sealing manner through a bore in said wall of the chamber 74 and extends through a chamber 82 in the casing part 72 to seat on a valve seat 83 provided at the end of a bore 84 in said casing part 72. The bore 84 is connected by a branch pipe 78 to the tapping 12. A bore 85 leads from the chamber 82 and is connected to the pipe 54. This embodiment provides low speed idle which is equal to that obtainable without the fuel economy system according to the invention being fitted since it takes its operating signal from the tapping 11 which may take the form of a T-piece inserted in the ignition distributor vacuum advance line. These units, by suitable positioning of the pressure tapping 11 in relation to the primary or main throttle 8 do not detect a depression during closed primary throttle conditions. Hence, it will be seen that the valve shown in Fig. 5 will remain closed until the value of the pressure PD approaches that of the pressure PM and the secondary throttles will open at low speed idle but will otherwise operate as required. A ball valve may be inserted in the small bore pipe 43 to have free flow in the secondary throttle opening direction and damped flow in the closing direction. This will have the dual effect of damping any resonances and also of maintaining the secondary throttles in a fully open condition during gear changes occurring under hard acceleration. Servo-control and/or programmed electronic systems may alternatively and/or additionally be provided to control the secondary throttles. To give optimum results, each module is likely to require an independent vacuum operated, ignition timing advance unit. This would mean the use of two distributors or a single distributor with two lobe cam or sensor and twin points or pickups at 900 on independent plates with two vacuum units. It is suggested that the secondary throttles should be so arranged that the engine will operate as follows in which F.L. stands for "Full Load": (a) Idle-Secondary throttles are open enough tQ give smooth idle. (b) Off ldle-(T1 FL) B.M.E.P. in cylinders 1 and 4 increases at nearly twice normal rate. Cylinders 2 and 3 remain close to idle. (c) T F.L.-Cylinders 1 and 4 run at + B.M.E.P., cylinders 2 and 3 idle. (d) 8 F.L.-Cylinders 1 and 4 run at i B.M.E.P., cylinders 2 and 3 idle. (e) T F. L.-Cylinders 1 and 4 run at i B.M.E.P., cylinders 2 and 3 run at T B.M.E.P. (f) + F. L.-All cylinders run at T B.M.E.P. (g) F.L.-All cylinders run at full load. With the device according to the invention, no performance loss at wide open throttle openings would be caused but there would be a significant fuel saving at lower throttle openings. The device can be installed in an engine as original equipment or fitted into existing engines as a conversion kit. It should be noted that the invention is not restricted to the above-described embodiment but that modifications and variations may be made without departing from the scope of the invention. Further, the device is not restricted to use with 4 cylinder engines but can be used with multi-cylinder engines having any number of cylinders. It is also possible to group the cylinders in more than one secondary module, each such module being arranged to partially disable its associated cylinders at different levels of power output. Claims (Filed on 24/11/82)

1. A fuel economy device for a multi-cylinder internal combustion engine wherein a valve is located in the inlet tract of at least one cylinder of the engine, the or each said valve being prevented from fully closing and being arranged to be responsive to the inlet manifold pressure of the engine to control the supply of combustible mixture to the associated cylinder in response to the pressure in said inlet manifold, at least one cylinder of said engine having no such control valve in the associated inlet tract so as to be capable of normal operation under all conditions.

2. A fuel economy device according to claim 1, wherein the engine has four cylinders which are divided into a primary module and a secondary module each consisting of two cylinders, a pair of said control valves being located in the inlet tracts of the cylinders of said secondary module and no said control valves being provided in the inlet tracts of the cylinders of said primary module.

3. A fuel economy device according to claim 2, wherein the engine has four cylinders arranged in line, the outer cylinders constituting the primary module and the inner cylinders constituting the secondary module, and wherein the inlet tracts of said inner cylinders are inter-connected by a balance tube to equalize the pressures in said inlet tracts.

4. A fuel economy device according to any preceding claim, wherein the or each control valve is pivotally mounted in the associated inlet tract and carries a lever, one end of said lever being arranged to bear against a stop in the

partially-closed position of the associated valve and the other end af the lever being pivotally connected to a rod linked to operating means for opening and partially closing the valve(s).

5. A fuel economy device according to claim 4, wherein the rod is connected by a pivoting linkage to a shaft for actuating the main throttle of the engine.

6. A fuel economy device according to claim 4 or claim 5, wherein the operating means comprise a cable connected at one end to the rod and at the other end to a lever, resilient means being provided to bias the rod to a position in which it is effective to move the control valve(s) to the partially closed position.

7. A fuel economy device according to claim 4 or claim 5, wherein the operating means comprises a manually operated solenoid switch.

8. A fuel economy device according to claim 4, wherein the operating means comprise a second rod pivotally connected at one end to the firstmentioned rod, a third rod pivotally connected at one end to the other end of the second rod and a diaphragm unit having a push rod connected to the other end of the third rod, one side of the diaphragm being at atmospheric pressure and the other side of the diaphragm being arranged to sense the pressure in the inlet manifold of the engine.

9. A fuel economy device according to claim 8, wherein resilient means are provided to urge the push rod of the diaphragm unit in a direction to move the control valve(s), via said rod linkage, to the fully open position.

10. A fuel economy device according to claim 8 or claim 9, wherein the said other side of the diaphragm is connected to the inlet manifold by a line in which a further control valve is provided, said further control valve comprising a casing having two inlet ports in fluid communication with the interior of the inlet manifold and an outlet port in fluid communication with the said other side of the diaphragm, one of said inlet ports leading to a chamber containing a diaphragm and a spring, the spring normally acting on the diaphragm to close a valve located in a passage in the casing connecting the other inlet port to the outlet port, the diaphragm being movable, against the force of the spring, to open the valve in said passage when the pressure in the inlet manifold falls below a predetermined value.

11. A fuel economy device according to claim 10, wherein means are provided for adjusting the force of the spring acting on the diaphragm in the casing of said further control valve.

12. A fuel economy device according to claim 10 or claim 11, wherein the said one inlet port of the valve casing is connected to an outlet port of an additional control valve having three inlet ports, a first said inlet port being connected to a bore leading to a tapping in the region of the main throttle of the engine and the second and third inlet ports being in communication with the inlet manifold of said engine, wherein the first and second inlet ports lead to either side of a diaphragm located in a chamber in the casing and wherein the diaphragm is arranged to act on a valve located in a passage in the casing interconnecting the third inlet port and the outlet port, a spring being provided to act on the.diaphragm to move the valve to its open position to open said passage in the casing.

1 3. A fuel economy device according to any one of claims 10 to 12, wherein a ball valve is provided in the line leading from the said other side of the diaphragm of said diaphragm unit to said further control valve, said ball valve allowing free flow in one direction and damped flow in the other direction.

14. A fuel economy device according to any one of claims 4 to 13, wherein the or each stop is adjustable in order to adjust the partially closed position of the associated valve.

1 5. A fuel economy device for a multi-cylinder internal combustion engine substantially as described herein with reference to the drawings.