In a conventional internal combustion engine of either spark ignition or compression ignition, inlet and outlet valves are provided to allow fuel and or air into each combustion chamber of the engine and to allow exhaust gases to escape after ignition. The combustion chambers are each typically provided within a separate cylinder and the valves are arranged to be opened and closed at a desired timing relative to the movement of a piston within each cylinder. Typically this is achieved by physically linking the valves to one or more camshafts or crankshafts rotating in time with the operation of the engine or the main engine crankshaft. The valves are thus actuated by the movement of the camshaft and thus open and close with a fixed relationship to the rotation of the camshaft and therefore at a fixed timing relative to the movement of each piston. In addition to the fixed timing of the valve openings, such shaft linked valve opening systems also open the valves by the same fixed amount during each cycle, known as a fixed valve lift or fixed valve opening profile. The amount of lift is determined by the size of the camshaft lobes.

A fixed opening profile does not allow for adjustment of flow through the poppet valve during opening. Furthermore, if the valve has a fixed closing portion of its opening profile, then there is a tendency for the valve to be forced hard against the portion of the cylinder head forming the valve seat during closing. This has implications for the reliability of the valve and the valve seat and for the amount of noise generated during engine operation.

There are known variants of the above technique, by which means the particular fixed relation between the crankshaft angle and the valve timing may be altered. By altering the

valve opening timing and opening profile in this manner, the power and torque output of the engine may be optimised for a particular band of engine revolutions per minute (RPM). As the valve opening timing and opening profile is matched to a particular range of RPM, the engine performs less well at lower or higher RPM. The selection of the particular valve timing and opening profile is therefore a compromise.

An alternative method of controlling the valve timing and is by use of a hydraulic or pneumatic valve actuation means without a physical link to the main crankshaft but controlled by electronic systems which monitor the rotation of the main crankshaft. In this way it is possible to actuate the valves without physical linkage to the main crankshaft. The primary difficulty with such systems has however proved to be maintaining the seals within the valve actuation means whilst at the same time allowing a fine control of the poppet valve, especially at the speeds required by this type of application.

Existing hydraulic actuation means suitable for being fitted to poppet valves such as those described above are effectively scaled down conventional hydraulic rams which operate by a sliding motion, and having a fixed maximum range of motion. These rams must be sealed in order to retain fluid and the seals must be capable of movement. Typically the seals used may be of the lip,"O"ring or cup type which must be"wet"by the retained fluid for lubrication to allow such movement. A small amount of fluid leakage is inevitable from such seals and typically becomes worse over time as wear occurs. At the pressures required to operate hydraulic systems at the speeds required in internal combustion engines, this can prove to be a major problem causing uncertain operation and potentially disastrous misoperation. For example, if the poppet valve is jammed in the open position it may be able to come into contact with the piston head in the combustion cylinder potentially causing major damage. Additionally leakage from the ram into either the inlet or exhaust tracts can lead to excessive emissions.

Similar problems can also occur if pneumatic actuation is substituted for hydraulic actuation. A further disadvantage of typical hydraulically or pneumatically actuated valves is that this type of actuation typically provides fixed opening profiles, as a ram when pressurised drives the valve the substantially the full length of its range in a particular time interval. This can be overcome to a certain extent if different portions of the ram may be pressurised, each portion having a different maximum range of movement. In this manner a number of different fixed valve opening profiles may be provided but this leads to somewhat imprecise control of the valve lift as that discrete steps of lift are used rather than a continuously variable control. The fixed opening profile additionally leads to the same problems as described in relation to fixed opening profiles of shaft actuated valves described above.

It is therefore an object of the present invention to provide an improved means of actuating valves and controlling the timing of valve opening and closing and the opening profile.

According to the present invention there is provided a valve control system for use in an internal combustion engine having a plurality of valves, the valve control system comprising a plurality of valve actuation means, each valve actuation means capable of being independently actuated to open and or close one of said plurality of valves in response to electrical control signals received from an electronic control module wherein each said valve actuation means is a bellows comprising two expansible chambers, the first chamber being pressurised to open the valve and the second chamber being pressurised to close the valve.

In this manner inlet and or exhaust valves of each combustion chamber in an internal combustion engine may be actuated individually at a desired time and with a desired lift and a

desired speed and acceleration of lift. This also avoids the necessity for a mechanical linkage between the poppet valves and the engine rotation.

Preferably the valve control system is adapted to control the actuation of inlet and exhaust poppet valves of each combustion chamber of an internal combustion engine.

Preferably said poppet valves comprise a sealing portion and a valve stem, said valve stem extending from the sealing portion and being attached to the actuation means. Relative expansion of the chambers of the bellows in the actuation means may thus be used to open and or close the attached valve.

Preferably the electronic control module is connected to sensing means adapted to sense the speed of rotation of a camshaft or crankshaft rotating within the engine and the instantaneous position of said camshaft or crankshaft. Most preferably the electronic control module monitors the rotation of said camshaft or crankshaft rotating within the engine and generates valve control signals in response to the speed of rotation and the instantaneous position of said camshaft or crankshaft. The control signals cause each individual poppet valve to be actuated at a desired timing relative to the camshaft or crankshaft rotation, with a desired maximum valve lift and a desired lift speed, and desired lift acceleration.

Preferably the control signals cause the valve to be opened and closed with a timing and with lift parameters that are optimised over the entire range of engine operating speeds" the engine speed being related to the shaft rotation. The timing and lift parameters at each particular engine speed or at a particular range of engine speeds may be optimised to give maximum power output, torque or fuel economy as desired.

The expansible chambers within each bellows are preferably connected to one another at one point or most preferably share a common dividing wall. Preferably pressurisation and thus expansion of one chamber thereby causes contraction of the other chamber, the common

dividing wall moving along with the relative expansion and contraction of the chambers. The valve stem of the poppet valve preferably extends through and is joined to the connecting point or common dividing wall of the chambers. In this manner, the valve stem and hence the whole of the poppet valve is moved by the relative expansion and contraction of the valve chambers and thus the valve may be controllably actuated.

The chamber walls are preferably comprised of an elastically deformable material. In order to facilitate rapid expansion or deflation of the chambers when required, some walls of the chamber may preferably be pleated. Use of such hydraulic bellows avoids many of the problems associated with conventional hydraulic rams.

Preferably a linear variable differential transformer (LVDT) is provided on the valve stem to monitor valve actuation. Most preferably said LVDT is connected to the electronic control module to allow fine control of valve actuation via a feedback loop.

Preferably, the sealed chambers are pressurised by hydraulic fluid however in alternative embodiments compressed air may be used. Preferably, a proportional flow valve or other similar valve is provided, adapted to direct fluid from a pressure input hydraulic line into a selected chamber and to direct hydraulic fluid from the chamber that is not selected to a fluid return line. This allows fine control of the expansion and contraction of each chamber and thus fine control over the actuation and position of the valve. In alternative embodiments, each chamber may be supplied with fluid by independent proportional valves or independent spools, which allows even finer control of valve actuation and position to be achieved.

Preferably, an initial piezo-electric actuation of the hydraulic proportional valve may be performed as a pilot stage of valve actuation. This allows the valve to respond more quickly to control signals.

If hydraulic fluid is used to pressurise the chambers the return line preferably returns hydraulic fluid to a reservoir. If compressed air is used to pressurise the chambers then the return line is preferably adapted to vent air to the external atmosphere.

In a further alternative embodiment wherein pneumatic actuation is used, one chamber may be filled with air at a known pressure and the relative expansion of the two chambers may be facilitated by pumping air into or out of the other chamber.

Embodiments of the present invention will now be described further herein, by way of example only and with reference to the accompanying drawings, in which:- Figure la is a schematic diagram of a valve control and actuation mechanism according to the present invention; Figure lb is a schematic diagram of an alternative valve control and actuation mechanism according to the present invention; Figure 2 shows an alternate bellows arrangement for the valve of figure 1; Figure 3 shows a valve opening timing diagram for a conventional valve linked to a camshaft; Figure 4 shows a typical opening profile of a conventional camshaft linked valve and an opening profile of a secondary valve having a restricted lift and duration; and Figure 5 shows an alternate opening profile for the primary and secondary valves in figure 4.

The present invention provides a valve control system allowing the opening time, duration, phase, dwell, and the closing of each inlet or outlet valve in an of each combustion

chamber in an internal combustion engine to be controlled without mechanical linkage to the engines rotation. Referring now to figure 1, a pair of intake and or exhaust poppet valves 17, 18 are provided in a cylinder head 32 of a combustion chamber of an internal combustion engine. The valves are opened and closed at selected times during the cylinder stroke cycle.

The timing of the opening and closing of the valves 17,18 and the magnitude of the displacement during opening, the'lift', of the poppet valves 17,18 is controlled to allow varying flow rates and quantities of fuel and/or air mixtures in to the combustion chamber and varying flow rates of exhaust gases out of the combustion chamber at any desired time.

The valves 17,18 are actuated hydraulically, the hydraulic fluid being supplied along hydraulic lines 21-23 and controlled by a proportional electro-hydraulic valve 4 and a flow control valve 5. Referring to poppet valve 17 for now the valve actuation means is a sealed bellows 12 comprising two expansible chambers 13,14 the chambers having one shared wall, a stem of the poppet valve projecting through the lower chamber and being connected to the shared wall. The bellows 12 are provided within a housing 11. The chambers 13,14 may be of the form shown in figure 1 with a pleated deformable side wall or alternatively may be of the form shown in figure 2a wherein the chamber walls themselves are made from an elastic material or of the form shown in figure 2b wherein the common wall is an elastic material and is fixed in position on both sides of the housing.

To open poppet valve 17, hydraulic fluid is supplied to the top chamber 13 along hydraulic line 21 and the chamber 13 thus expands. The expansion of the top chamber 13 causes the shared wall to move in a downward direction and the valve stem connected to the shared wall is also moved in a downward direction thus opening poppet valve 17. To close poppet valve 17, hydraulic fluid is supplied to the bottom chamber 14 along hydraulic line 23 and the chamber 14 thus expands. The expansion of the bottom chamber 14 causes the shared wall to move in an upward direction and the valve stem connected to the shared wall

is also moved in an upward direction. The poppet valve 17 is thus moved to the closed position. Typically when one chamber expands, hydraulic fluid is forced out of the other chamber and back along hydraulic lines 21 or 23 towards the proportional valve 4. Poppet valve 18 is operated in the same manner as poppet valve 17.

The proportional flow valve 4 controls the supply of hydraulic fluid to the valve chambers 13,14. It is operative to direct an input flow from a pressure input line 19 into either hydraulic line 21 or hydraulic line 23 as desired. Additionally, proportional valve 4 is operative to connect either hydraulic line 21 or hydraulic line 23 to a hydraulic return line 20 when desired. In this way by controlling valve 4, pressurised hydraulic fluid may be supplied alternately to the top and bottom chambers 13,14 and thus control the operation of the poppet valve. Flow control valve 5 allows the operation of poppet valve 18 to be controlled separately to poppet valve 17, by preventing the flow of hydraulic fluid when it is not desired to actuate poppet valve 18. Proportional valve 4 is a smaller and faster operating variation upon known proportional valves. Proportional valves of this type have not previously applied to use in this application, actuation of poppet valves in an internal combustion engine.

In order to pressurise the chambers 13,14 a pump 1 takes fluid from a reservoir 6 and provides a medium pressure source, which is stabilised by a pressure regulator 2 and an accumulator 3. Pressure line 19 runs from the pump 1 to feed proportional valve 4 and return line 20 allows the fluid to be returned to the reservoir 6. The proportional valve 4 is controlled electrically by the electronic control module 7 to allow the controlled opening and closing of the poppet valves 17,18 via hydraulic lines 21,23. A further flow control valve 5 is fed from hydraulic line 21 and connects to secondary poppet valve 18 to control the opening of the valve 18 via the hydraulic line 22. As there is little friction in such a system

and hence medium pressure requirement, a power steering pump (modified) may be utilised to provide hydraulic fluid power in addition to a hydraulic accumulator 3.

As an alternative to the above described system, an independent hydraulic fluid supply may be provided for each chamber, controlled by an independent spool or by an independent valve, as is shown in figure lb. Using an independent fluid supply for each chamber has the advantage that the flow to and from each sealed chamber 13, 14 may be more closely monitored and controlled. This allows the more accurate control of the position of the poppet valve 17,18.

The operation of the hydraulic system is controlled by an electronic control module 7.

The ECM 7 is connected to control valves 4,5 and to pressure regulator 2 and sends signals to valves 4,5 to control the operation of poppet valves 17, 18.

In alternative embodiments a pneumatic system may be substituted for the hydraulic system described above. A pneumatic system has the advantage that compressed air is required rather than hydraulic fluids and is therefore simpler than a hydraulic system. A hydraulic system however does allow more accurate control of the fluid flow and pressure through the valve chamber than a pneumatic system. If a pneumatic system is used, the compressed air in the chamber that is not currently being supplied with air may be vented to the atmosphere rather than being returned to a reservoir.

In each of the above embodiments, an initial piezo-electric actuation is required in order to actuate the proportional valve 4 sufficiently rapidly for use in high-speed internal combustion engines. This small mechanical movement is used as a pilot stage for the actuation of the proportional valve 4. This helps to provide fast and very precise actuation.

In order that the position and operation of poppet valves 17,18 can be monitored and controlled accurately, a linear variable differential transformer (LVDT) 15 is provided. The

LVDT 15 is sealed into the bellows to provide accurate measurement of the position and movement of the two chambers such that via a feedback loop to the ECM 7 fine control of the position of the poppet valve 17,18 can be achieved. The use of a monitoring system of this type removes the need for a mechanical linkage between the engine rotation and the poppet valve actuation.

The ECM 7 receives signals from engine sub systems via several sensors in order to determine the desired opening and closing timing and lifting profile for poppet valves 17,18.

Typically, such sensors include a crankshaft position sensor 8 and an engine RPM counter 9.

An interface is additionally provided connecting the ECM 7 to an engine management interface 10 enabling other information to be passed to the ECM 7 if required.

The flow of either hydraulic fluid or air into and out of each chamber 13,14 is controlled by ECM 7 in response to signals received from crankshaft position sensor 8, engine RPM counter 9 or engine management interface 10 to open and close each poppet valve 13,14 with a desired acceleration, speed and lift at a desired time relative to the crankshaft rotation. Other variables describing the overall opening profile of each poppet valve may also be varied for instance the relative phase between the opening and closing of each inlet and exhaust poppet valve and the magnitude or speed of the poppet valve lift. In this manner, the poppet valve timing is adapted to maximise the power and torque generated by the engine throughout the full range of engine RPM in a similar manner as is achieved with current fuel injection systems. By adjusting the poppet valve timing in this manner, emissions (HC, NOx and CO) can also be significantly reduced, fuel economy improved and engine reliability and longevity improved ; this being, in part, due to the lower engine speeds required for a given power or torque output. In alternative embodiments the valve timing may be specifically adapted to maximise engine fuel economy rather than power or torque.

Figure 3 illustrates the opening and closing timing of typical mechanically linked inlet and exhaust poppet valves in an internal combustion engine relative to the rotation of the engine as is known from the prior art. In a four-stroke internal combustion engine, two revolutions (720degrees) complete one full cycle; the camshaft runs at half engine speed and so completes one cycle in one revolution. The inlet valve opens at a° before the camshaft reaches top dead centre (TDC) and closes b° after the camshaft reaches bottom dead centre (BDC). The exhaust valve however opens c° before BDC and closes d° after TDC. If the camshaft lobes are symmetrical, the maximum lift point occurs at the mid point x°, between opening and closing. In a mechanically linked system such as this the opening and closing of the poppet valves takes place at these fixed times in every cycle and the shape of the poppet valve opening profiles is fixed. The magnitude of the maximum lift is also a fixed value.

The particular poppet valve timings, opening profile and maximum lift are selected to maximise the performance of the engine at a particular engine speed and consequently engine performance suffers at higher or lower engine speeds.

Referring now to figure 4, the top curve shows the opening profile of a camshaft linked poppet valve as described above. The poppet valve rises rapidily to the point of maximum lift in the cycle at x° and then drops rapidly back to the closed position. The lower curve illustrates a secondary valve controlled using a camshaft version of variable valve timing., This allows the opening of the valve to be restricted and the closing to take place earlier, this however allows the passage of less gas through the open valve as the area under the curve represents the total volume able to be passed by the poppet valve. Both these opening curves are however fixed to take place at a particular timing and to have the same maximum lift at all engine speeds.

Figure 5 shows two examples of opening profiles of a poppet valve controlled by the present invention. The curves can be of any shape or profile required for best results in terms

of power and/or emissions and/or fuel consumption. In particular the curves show how the maximum lift may be sustained rather than instantaneously achieved. It also shows how the shape of the opening profiles may be varied if desired. The profile further illustrates how the closing of the poppet valve is metered such that stress on the valve and noise resulting from harsh closure can be avoided. Furthermore, as the poppet valve actuation is not directly physically linked to the rotation of the crankshaft, the ECM 7 may be used to vary the initial opening and closing times at a° and b° to different times relative to the rotation of the crankshaft.

It is of course to be understood that the invention is not to be restricted to the details of the above embodiments which are described by way of example only.