The present invention relates to an engine, particularly an automotive engine having an automated manual transmission system and intake system therefor. The engine is particularly suitable for use in two/three or four wheeled vehicles.

Engines require an intake system which admits fuel and air as a charge to the engine as demanded, as required, by an operator of the engine for combustion in a cylinder of the engine. Various types of intake system are available and intake system design varies dependent on considerations including whether the engine is fuel injected or carburetted; and the nature of the fuel being combusted in the engine whether gaseous fuel or liquid fuel, or a mixture of both.
Engines are connected to a transmission system. Though combustion of the air fuel charge drives a crankshaft and provides motive force for the vehicle, this motive force must be controlled to meet the vehicle operating conditions. To this end, motive force from the crankshaft is managed by a transmission system, typically having a plurality of gears, each gear providing controlled motive force to wheels of the vehicle. Manual, automated manual and automatic transmissions, such as continuously variable transmissions, are available for use in two/three or four wheeled vehicles.

A significant consideration for a vehicle is driveability or rideability. That is, the engine and transmission should work so that the vehicle is operated in a smooth and comfortable manner. Shocks and vibrations during engine operation should be minimised. Currently, a problem exists with rideability during gear shift phase with engines having automated manual transmissions. Jerkiness may be experienced at this time. The jerkiness results from undesired engine torque during the gear shift. Undesired torque results from undesired fuelling given when the engine is undergoing a gear shift. Further, such undesired fuelling reduces fuel ecopomy.

Engines with manual transmissions are not affected by jerkiness to the same extent. For manual transmission engines, the rider typically closes the throttle position partially or fully during the gear shift phase so that excessive fuelling and consequential jerkiness is avoided. In an automated manual transmission, the objective is to operate the vehicle, particularly a motorcycle, with respect to a particular control strategy without need of the operator closing the throttle during gear shift. The control strategy is aimed at optimising engine and vehicle operation. Various attempts have been made in the past to reduce or prevent the problem of jerkiness while gear shifting.

Some prior art suggests controlling fuelling through sophisticated fuel injection methodology. As the required automatic fuel control system is sophisticated, it is relatively costly and complex.
US5079969A (1992) and JP07034916 (1993) disclose use of carburetted fuel systems in which air/fuel supply is controlled while gear shifting.

US5079969 teaches connection of carburetor to throttle as well to actuators by employing a junction box. The carburetor (and the air fuel supply) is controlled by actuators; themselves controlled by the control unit, while gear shifting.

JP 07-034916 discloses a carburetor fuelling system for an engine with a manual transmission system. The carburetor throttle valve is controlled by a controller by sensing inputs from clutch lever position, gear shifter position and throttle position. Again this is a sophisticated, costly and complex arrangement.

The above noted systems also require space and this is at a premium in some vehicles, especially small motorcycles used for urban commuting.

It is an object of the present invention to provide an engine having an automated manual transmission that provides a less complex and less costly system for controlling fuelling during a gear shift phase while also providing better rideability/driveability during that phase.

With this object in view, the present invention provides an engine having an automated manual transmission system with a plurality of gears comprising:

an intake system including an intake manifold and a carburetor for metering fuel to be mixed with air to form a fuel air mixture for admission to the engipe;

a throttle operating mechanism;

a cylinder head having a combustion chamber for combustion of the fuel air mixture; and

a control unit; wherein said carburetor is of constant velocity (CV) type and a restriction element is provided in said intake manifold, said restriction element being operable by said control unit to control admission of fuel air mixture to said combustion chamber during a gear shift phase. The restriction element manages torque, particularly by interrupting it, during the gear shift phase such that jerkiness experienced with current automated manual transmission engines is avoided. At the same time, fuel economy is improved since fuel is not unnecessarily delivered to, and exhausted from, the engine during a gear shift phase. Excessive fuelling is avoided.

The particular form of carburetor for use in the engine, typically a liquid fuelled engine though a gas fuelled or dual fuelled engine is not excluded, is a constant velocity, also known as constant vacuum (CV) type of carburetor. On CV carburetors, the throttle cable actuates a butterfly valve and, as the throttle is opened, the air pressure difference between the sealed vacuum chamber above the slide (piston) and inside the carburetor venturi forces the slide (located in front of the butterfly valve) to move up and down.

The CV type carburetor offers improved driveability over other types of carburetor. Air/fuel supply to the engine by CV type carburetor is influenced by throttle position, set by rider in the case of a motorcycle engine, and opening/closing of carburetor piston which depends upon engine manifold vacuum in contrast with other carburetors (for example Non CV type carburetors) in which operation is influenced only by throttle position (as the carburetor piston movement is directly controlled by throttle position). In a Non CV type carburetor, the reliance on throttle position change by operator following a gear shift may lead to either a jerky situation or excessive air fuel supply to an engine, having an automated manual transmission, leading to higher emissions since rider setting of throttle position results in insufficiently precise control.
Therefore, in the case of a CV carburetor, when the restriction element is actuated, engine vacuum is not experienced by the carburetor. Hence the carburetor piston (which controls the flow of fuel) consequently and automatically moves towards idle position and reduces supply of fuel irrespective of any manually set throttle position. As soon as the restriction element is deactivated, engine vacuum is again experienced by the carburetor and the carburetor piston automatically lifts to supply fuel proportional to engine vacuum. Thus the engine should attain its required speed without jerks or driveability problems being experienced during a, gear shift phase.

The said restriction element is any engine compatible device that controls, with the CV carburetor, fuel air flow (also referred to as "mixture" flow) to the engine during a gear shift phase. Operation of the restriction element by the control unit, which may be an engine control unit or transmission control unit, is independent of operation of the throttle and throttle position which is controlled by the rider controlled throttle mechanism. Restriction element operation is not intended to be influenced by the operator's control of the throttle.

The restriction element may take the form of a valve or flap which is operated to control the flow of fuel to the engine during a gear shift.

Such control may be achieved by controlling the angular movement of the valve or flap in the intake manifold. This angular movement could be between zero degrees (normal operation) and maximum 90 degrees (complete stoppage of fuel air mixture flow to the engine). This angular movement is hereinafter referred to in the specification and claims as "stroke". The period for controlling fuel mixture flow to the engine may range from a few hundred milliseconds to about a second, a very short duration as per a predefined control strategy for engine operation, particularly a gear shift strategy.

To minimise lag, and to meet required fuelling control period, the restriction element conveniently in the form of a flap having peripheral geometry (typically circular or oval) matching that of the intake manifold - is actuated by an actuating device, for example using a solenoid switch or stepper motor. A solenoid switch is an ON/OFF type switch with fixed stroke whilst a stepper motor can be controlled to have variable stroke. The stepper motor is actuated by the control unit to control fuel supply (in an air/fuel mixture form) to the engine, for example as above ipdicated to idle fuelling, when a gear shift is required. Such actuation of the restriction element and solenoid switch or stepper motor is done irrespective of throttle position adopted by the engine operator during a gear shift phase.

When gear shifting is predicted or demanded by the control unit with respect to a predefined engine operating strategy, the control unit activates the actuating device (for example a stepper motor) to actuate the restriction element fpr a stroke and duration corresponding to the particular gear being shifted to control air fuel mixture flow to the engine. Stroke and duration of actuation of the restriction element is controlled by the control unit, allowing for adaptive control over air fuel mixture flow to the engine. Duration and stroke may be adjusted to the duration of specific gear shifts for the automated manual transmission of the engine. When the restriction element is activated, engine vacuum experienced by the carburetor is correspondingly reduced and the carburetor piston automatically moves towards idle position with fuel supply being reduced for the gear shift. This occurs irrespective of throttle position set by the rider, where the engine is a motorcycle engine.

Then, at an appropriate time - possibly when a gear shift is completed - the control unit deactivates the restriction element, engine vacuum experienced by the carburetor is restored and the carburetor piston automatically lifts to supply fuel to the engine in quantity proportional to the engine vacuum. In this way, the engine attains required speed, after a gear shift, without jerks or driveability problems being experienced.

The restriction element is located in the intake manifold of the engine at a position to reduce lag in re-establishing required fuelling following a gear shift phase. The position is so selected or optimised such that once the restriction element is deactivated it does not affect, or has a minimal affect on, driveability by producing jerks or other issues such as high hydrocarbon emissions. Such issues like jerks could be caused either by less supply of air fuel mixture to the engine; or due to supply of excessively rich air fuel mixture to the engine. Excessively rich air fuel mixtures also often lead to undesirably high hydrocarbon emission levels. The fuelling during a gear shift phase is controlled to avoid such situations.

The cylinder head includes ignition means, preferably a plurality of ignition means, in the form of spark plugs. Ignition timing may also be controlled by an engine control unit to reduce jerkiness during a gear shift.

In another embodiment, which could also include other features as described above, the engine may be a gas fuelled engine using a fuel such as CNG pr LPG. In such case, the function of fuel metering is performed by a gaseous fuel supply means typically comprising a gas regulator, mixer unit and CV type carburetor. The gas regulator consists of a diaphragm valve which operates on pressure differential principle by sensing and applying the engine vacuum to control the gas flqw. Further, the mixer unit mixes the air and gas in a venturi construction and the fjow of said gas-air mixture to the engine is controlled by the CV type carburetor which is having a throttle mechanism operated by the rider. It will be understood that the engine could also be dual fuelled, typically using CNG or LPG as primary fuel and petrol (other liquid fuel).

One embodiment of engine in accordance with the present invention will now be described with reference to the following figures in which:

Numeral Description
1 Butterfly throttle
1a Butterfly throttle shaft
2 Carburettor piston or slide throttle
3 Vacuum chamber
5 Membrane
7 Needle valve
8 Main Jet
9 Spring
10 Engine intake system
12 Carburetor
14 Intake Manifold
15 Intake port
17 Cylinder head
19 Bowl
20 Flap
21 Adjuster screw
22 Solenoid switch
22a Plunger
23 Spring
24 Linkage
25 Screw
30 Air filter
40 Flap/Solenoid assembly
42 Rotatable shaft
44 Bracket throttle
49 Mounting plate
50 Throttle pulley
51 Throttle cable
114 Intake Manifold
120 Flap
122 Stepper motor
123 Coupler
125 Seal
126 Sealing bush
127 Screw
128 Stepper motor shaft
142 Flap shaftRegulator
150 Throttle chamber
151 Regulator
152 Mixer unit
153 Low pressure hose
154 Intake pipe

Fig. 1 is a schematic side view of the intake system of an engine in accordance with one embodiment of the present invention.

Fig. 2 is another schematic side section view of the intake system of Fig. 1.

Fig. 3 is a schematic view of the restriction element/actuating device assembly for the intake system of Figs. 1 and 2.

Fig. 4 is a schematic side section view of the restriction element/actuating device assembly for the intake system of Figs. 1 and 2 and taken along section line B-B of Fig. 3.

Fig. 5 is a schematic side section view of the restriction element/actuating device of Fig. 4 taken along section line C-C of Fig. 4.

Fig. 6 is another schematic side section view of the restriction element/actuating device assembly of Fig. 4.

Fig. 7 is a schematic side section view of the carburetor used in the intake system of Figs. 1 and 2.

Fig. 8 is another schematic view of the carburetor used in the intake system of Figs. 1 and 2.

Fig. 9a is a schematic side view of an alternative embodiment for the restriction element/actuating device illustrating fully open stroke positions of restriction element for use in the engine of Figs. 1 and 2.

Fig. 9b is a schematic section view restriction element taken along section line A-A of the fig. 9a

Fig. 9c is a schematic side view of an alternative embodiment for the restriction element/actuating device illustrating fully closed stroke positions of restriction element for use in the intake system of Figs. 1 and 2.

Fig. 9d is a schematic section view restriction element taken along section line A-Aofthefig. 9c

Fig. 9e is a schematic side view of an alternative embodiment for the restriction element/actuating device illustrating partly open stroke positions of restriction element for use in the intake system of Figs. 1 and 2.

Fig. 9f is a schematic section view restriction element taken along section line A-A of the fig. 9e

Fig 10 illustrates a schematic view of intake system with gaseous fuel supply system for a gaseous fuelled engine according to another embodiment of the invention.

Fig 11 illustrates another schematic view of intake system with gaseous fuel supply system for a gaseous fuelled engine according to another embodiment of the invention.

Referring to Figs. 1 and 2, there is shown an engine intake system 10 for a motorcycle engine. The engine is a four stroke single cylinder engine having an automated manual transmission system having a plurality of gearing ratios as described in the Applicant's co-pending Indian Patent Application No. 3470/CHE/2011, the contents of which are hereby incorporated herein by reference. This automated manual transmission system excludes synchromesh devices to simplify the transmission system and reduce bulk and cost. In particular, the transmission system is of constant gear mesh type with dog type shifting arrangements which may be referred to as a clash mesh shifting type system or gearbox.

Engine intake system 10 comprises an intake manifold 14 which dr$ws air fuel mixture into the engine for combustion. At one end of intake manifold 14 is carburetor 12 for metering the air/flow mixture to the engine. Air filter 30 is provided upstream of carburetor 12 for filtering particulates from intake air. The other end of intake manifold 14 is connected to an intake port 15 formed in a cylinder head 17 of the engine. Two or more intake ports 15 may be provided for the engine.

As the engine is liquid fuelled, using gasoline fuel, a carburetor 12 is located upstream of intake manifold 14. Carburetor 12 is of constant velocity (CV) type carburetor 12 and is operated under control of a throttle mechanism (50, 51 as shown in Fig. 8) having throttle position as set by the rider of the motorcycle though it will be appreciated that operation of carburetor 12 is also influenced by engine vacuum. Further description of carburetor 12 is made with reference to Fig. 7 below. In accordance with these parameters, the liquid fuel is mixed with air in CV carburetor 12.

In such manner, intake manifold 14 provides a charge of fuel and air to the engine. The fuel air charge is combusted in the engine following ignition by an ignition means, however a plurality of ignition means could be employed to promote fuel economy and to reduce hydrocarbon and CO emissions.

Intake manifold 14 additionally includes a restriction element in the form of a metal flap or butterfly valve 20 having peripheral geometry (here circular) matching to the internal geometry of the intake manifold 14 allowing the flap 20 to rotate through an angular movement of 90 degrees to completely close the intake manifold when required by the electronic control unit. The flap 20 is in open state, allowing fuel air charge to be delivered to engine, through intake manifold 14, other than when a gear shift phase is occurring. During a gear shift phase, the flap 20 is activated to control fuel air flow through intake manifold 14 to the engine, here to a closed position though flap 20 may be controlled, through a stroke, to move to an angle intermediate 0 and 90 degrees.
Flap 20 is located in the intake manifold 14 in a position comparatively proximate to intake port 15 in this embodiment. However, flap 20 location is optimised to minimise lag in re-establishing required fuelling to the particular engine during a gear shift phase. That is, when a gear shift phase or event is. complete, engine operating stability requires rapid but smooth re-establishment of the flow of fuel air charge to the engine. Further, this assists in better fuel efficiency.
Operation of flap 20 is controlled by the control unit during a gear shift phase. To this end, flap 20 may conveniently be controlled by a transmission control unit which also controls the gear shift process in accordance with a pre-defined strategy. However, the engine control unit could equally well perform this duty. As fuel air flow to the engine may be shut off for a period of a few hundred milliseconds to about a second, a solenoid switch 22 is advantageously adopted as actuating device for electronically operating the flap 20 between the open and closed position (as illustrated in Figs 5 and 6 to reduce fuel air flow to the engine to a controlled amount corresponding to the particular gear shift). The flap 20 and solenoid switch 22, as conveniently shown in detail view in Figs. 3 to 6, together forming an assembly 40 are accommodated within the structure of intake manifold 14 providing dustproofing and waterproofing for both components.

The control unit here actuates the solenoid switch 22 to completely close the flap 20 (stroke 90 degrees) and intake manifold 14 when a gear shift phase is initiated for the automated manual transmission system of the engine. Solenoid switch 22 is connected through plunger 22a and linkage 24 (itself connected to plunger 22a by screw 25) to a rotatable shaft 42. Rotatable shaft 42 is held in required alignment by spring 23 and is connected to bracket throttle 44, in perpendicular direction, to control the end position of flap 20 in closed condition through adjuster screw 21. Access to flap/solenoid switch assembly 40 is through mounting plate 49 which can be removed for servicing of parts. In operation of solenoid switch 22, force from the movement of the plunger 22a is transmitted through linkage 24 and rotatable shaft to rotate flap 20 (connected to rotatable shaft 42 by two screws) to position as required by the control unit: open when np gear shift phase in process, closed when a gear shift is occurring. The flap 20 is shown open in Figs. 3 to 6.

The control unit maintains the flap 20 in closed position, reducjng fuel air mixture flow, for duration of the gear shift phase. This duration may, ag alluded to above, be predetermined for the control unit. However, the control unit mpy allow for adaptive control over switching of solenoid switch 22 and duration of flap 20 closed position (and fuel air shutoff duration), adjusting the duration to the duration of specific gear shifts for the automated manual transmission system of the engine. The transmission system has known gearing ratios and so the specific gear shifts 1-2, 2-3, 3-4, 4-5 and the reverse order of these gears are known for the engine. Gear shift duration for each of these shifts is likely to differ, particularly with the clash mesh gearbox. The control unit may controls duration of flap 20 angular movement to closed or other position dependent on the actual gear shift required Ijy the pre¬defined engine operating strategy.

The control unit may also generally control stroke of flap 20, flap 20 does not necessarily always have to be closed (i.e stroke of 90 degrees).

The engine therefore has a clash mesh gearbox. If gears clash on engagement, duration of a gear shift phase may be increased over a situation where smoother engagement is possible. So, gear shift phase duration and the duration for which flap 20 must be maintained closed, is likely to be variable and the control unit may allow for this.

Engine gear shift strategy is controlled by the control unit. There is no rider involvement in setting of gear shifts. Indeed, as the automated manual transmission system implements gear shifts significantly faster than a human mediated gear shift, rider involvement - even if possible - would not be effective. However, the motorcycle rider still has control over throttle position during normal running condition and when the gear shifting is not planned. To avoid this compromising effective gear shift strategy, the control unit determines gear shift phase timing and controls fuel air charge flow through intake manifold 14, by closing flap 20, independently of throttle position set by the motorcycle rider. The control unit does not alter throttle position during a gear shift phase.

As described above, driveability is enhanced by use of CV carburetor 12 as shown in Fig. 7. CV carburetor 12 operation is influenced by throttle position and engine manifold vacuum. To that end, CV carburetor 12 includes two throttles, butterfly throttle 1 (mounted on butterfly throttle shaft 1a) which is linked to rider throttle control through throttle cable 51 and pulley 50 mounted on rotatable shaft 42 and vacuum slide throttle 2, position of which is regulated by engine vacuum when the flap 20 is actuated, here such that vacuum on engine side is not experienced by the CV carburetor 12. On closing of flap 20, the carburetor piston 2 (which controls the flow of fuel) goes towards idle condition (by automatically moving to idle position) and reduces supply of fuel to idle quantity, this quantity of fuel being admitted through the idle jet. As soon as the flap 20 is deactivated after the gear shift, engine vacuum (which affects the pressure in vacuum chamber 3) again acfs, through membrane 5 of carburetor 12, and the carburetor piston 2 automatically lifts to supply fuel proportional to engine vacuum from bowl 19 through main jet 8 dependent on position of carburetor needle valve 7. Position of needle valve 7 is also set in accordance with throttle 1 position as sensed by a throttle position sensor. Thus the engine attains its required speed without jerks or driveability problems being experienced following a gear shift.
This concept is applicable only when a CV type carburetor device or similar fuel metering devices are employed. In other types of carburetor, a control unit and complicated cabling mechanism would be required to achieve the same function.

Referring to Figs. 9a, to 9f, in a further variation, the solenoid switch 22 actuating device may be replaced with a stepper motor 122. In this case, stepper motor 122 has a shaft 128 which is inserted into a coupler 123 and tightened with a screw 127, this coupler 123 being connected to flap shaft 142 to form an assembly of the three parts. The flap shaft 142 is connected to a restriction element in the form of flap 120. The stepper motor shaft 128 is inserted into the coupler 123 and tightened with a screw 127. Sealing and fixing arrangements are provided at both sides (i.e. sealing bush 126 at flap shaft side and seal 125 at stepper motor shaft 128 side). The control unit actuates the stepper motor 122 to rotate the flap 20 through the stepper motor shaft 128-coupler 123 flap shaft 142 assembly to close intake manifold 114 for a predefined stroke and duration during gear shift phase to prevent air/fuel mixture from entering the engine through intake port(s) 15. Once the gear shift phase is completed the control unit actuates stepper motor 12 in reverse direction to rotate flap 120 through the stepper motor shaft 128,-coupler 123, flap shaft 142 assembly again allowing air/fuel mixture to enter the engine through intake port(s) 15. Figs 9a to 9f show how the stepper motor 122 allows control over flap 120 movement to fully open, fully closed and partly closed positions. The partly closed position is illustrative and not limiting. Stepper motor 122 could allow stroke of flap 120 to be controlled anywhere in the range 0 to 90 degrees though fixed positions allows an easier stroke control strategy and use of a less expensive stepper motor 122.
Referring to figs. 10 and 11, when the engine operates on gaseous fuel, the intake system comprises a CNG/LPG cylinder ( not shown), a regulator 151, a mixer unit 152, a pressure hose pipe 153, an air filter 30,a carburetor 12 The gas from CNG/LPG cylinder flows into regulator through intake pipe 154.The said regulator delivers the gas to mixer unit 152 through a hose pipe

153.The mixer unit has a venturi construction. The said mixer unit mixes the air and gas which is then fed to engine cylinder head 17 through the carburetor 12 , a CV type carburetor and intake manifold 14. In this case the said CV type carburetor is not performing the function of mixing of fuel and air (which is performed by the said mixer unit 152), however the said CV carburetor is used to automatically close and open piston 2 jn the flow passage and housing a throttle mechanism 50, 51. However, in place of a CV type carburetor for performing the above said functions, a throttle chamber 150 having a butterfly valve equivalent to butterfly throttle 1 and a piston moving up and down in a flow passage controlled by engine vacuum and spring, equivalent to CV carburetor piston 2 and spring 9 can be employed. The said intake manifold is provided with flap 20. During gear shift phase, control unit actuates the stepper motor 122 to activate the flap 20 in intake manifold 14 for a predefined stroke. With this action, the engine vacuum experienced by regulator 151 reduces, resulting into reduction of flow of gaseous fuel from regulator 151, thus reducing the torque output of engine irrespective of position throttle mechanism of carburettor operated by rider. As soon as the flap 20 is deactivated, engine vacuum is sensed again, through the throttle chamber 150, mixer 152 and low pressure hose 153 resulting in regaining the of flow of gaseous fuel from regulator 151 to cylinder head 17 through low pressure hose 153, mixer 152 and throttle chamber 150.

The engine can be dual fuelled i.e. working on gaseous fuel supply or gasoline (petrol) supply. The selection of mode of fuel is controlled by rider. A selector switch of known technology could be adapted to perform this function. Necessary tuning of carburettor, venturi of mixer unit may be done for proper workability for operating the intake system for both type of fuel supply. Rather, the tuning may be done appropriate to primary fuel supply system.

Modifications and variations to the engine disclosed in the present specification may be apparent to the skilled reader. Such modifications and variations are deemed within the scope of the present invention.

WE CLAIM:

1. An engine having an automated manual transmission system with a plurality of gears comprising:

an intake system including an intake manifold and a carburetor for metering fuel to be mixed with air to form a fuel air mixture for admission to the engine;

a throttle operating mechanism;

a cylinder head having a combustion chamber for combustion of the fuel air mixture; and
a control unit; wherein said carburetor is of constant velocity type and a restriction element is provided in said intake manifold, said restriction element being operable by said control unit to control admission of fuel air mixture to said combustion chamber during a gear shift phase.

2. An engine having an automated manual transmission system with a plurality of gears comprising:

an intake system including an intake manifold with a gaseous fuel supply means for metering gaseous fuel, a carburetor, a mixer unit to mix gaseous fuel with air to form a fuel air mixture for admission to tjie engine;

a throttle operating mechanism;

a cylinder head having a combustion chamber for combustion of the fuel air mixture; and
a control unit; wherein said carburetor is of constant velocity type and a restriction element is provided in said intake manifold, said restriction element being operable by said control unit to control admission of fuel air mixture to said combustion chamber during a gear shift phase.

3. An engine as claimed in claim 1 or 2 wherein operation of the restriction element by the control unit is independent of operation of the throttle and throttle position which is controlled by the rider controlled throttle mechanism.

4. An engine as claimed in any one of the preceding claims wherein said restriction element takes the form of a valve or flap which is operated to control the flow of fuel air mixture to the engine during a gear shift.

5. An engine as claimed in claim 4 wherein a period for controlling fuel air mixture flow by said restriction element ranges from a few hundred milliseconds to about a second.

6. An engine as claimed in any one of the preceding claims wherein said restriction element is actuated by an actuating device.

7. An engine as claimed in claim 6 wherein said actuating device is a solenoid switch or stepper motor.

8. An engine as claimed in claim 7 wherein said control unit actuates the solenoid switch or stepper motor to control fuel air mixture flow for a pre¬determined duration during the gear shift phase.

9. An engine as claimed in claim 8 wherein said pre-determin^d duration corresponds with the period of the gear shift phase.

10. An engine as claimed in claim 9 wherein said control unit allows for adaptive control over duration of fuel control, adjusting the duration to the duration of specific gear shifts for the automated manual transmission system of the engine.

11. An engine as claimed in any one of the preceding claims wherein a stroke of the restriction element and its duration of activation is alsq controlled during said gear shift phase.

12. An engine as claimed in any one of the preceding claims wherein said restriction element is located in the intake manifold of the engine at optimum location to reduce lag in re-establishing required fuelling to the engine following a gear shift phase.
13. An engine as claimed in any one of the preceding claims wherein ignition timing is controlled by the control unit in a gear shift phase to reduce jerkiness during said gear shift.

14. An engine claimed in claim 2 to 13 comprising:

an intake system including an intake manifold with a gaseous fuel supply means for metering gaseous fuel, a throttle chamber, a mixer unit to mix gaseous fuel with air to form a fuel air mixture for admission to the engine;

a throttle operating mechanism;

a cylinder head having a combustion chamber for combustion of the fuel air mixture; and
a control unit; wherein said throttle chamber comprising a butterfly valve and a piston in flow passage; movement of said piston is controlled by engine vacuum and said butterfly valve is used to control the air fuel mixture flpw into the intake manifold and a restriction element is provided in said intake manifold, said restriction element being operable by said control unit to control admission of fuel air mixture to said combustion chamber during a gear shift phase.

15. An engine as claimed in any one of the preceding claims wherein said engine is a dual fuelled engine.

16. A vehicle comprising an engine as claimed in any one of thq preceding claims.