Programmable high speed valve actuator and power supply therefor

Abstract

An electromagnetic actuator is described in which a rotor comprising permanent magnet means is rotatable in a stator which is magnetisable by causing an electric current to flow through at least one winding associated with the stator. The rotor has at least two stable rest positions, each defined by spring and/or magnetic forces acting on the rotor. Spring means stores energy during part of the movement of the rotor and provides kinetic energy for accelerating the rotor during subsequent movement thereof away from rest in one position towards another. A magnetic torque is exerted on the rotor when a current flows in said at least one winding which is sufficient to overcome the force(s) holding the rotor in that rest position, to cause the rotor to rotate in a direction from that rest position towards another a rest position. The rotor is connected to a thrust member by a mechanical linkage by which the rotational movement of the rotor is converted into substantially linear movement. The linkage has a mechanical advantage which varies in a predetermined manner during the rotation of the rotor. The actuator can be used to open and close a valve of an internal combustion engine. A power supply is provided for delivering current to the actuator from a current source so as to operate the actuator in an energy efficient manner.

Description

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is an isometric view of the rotor, viewed from the crank end,

FIG. 2 is an exploded view of the rotor and one housing, viewed from the eccentric end,

FIG. 3 is an exploded view of the rotor, lever, valve and the other housing, viewed from the crank end,

FIG. 4 is a view of the eccentric end of the actuator with the housing removed, revealing the second lever and the main spring,

FIG. 5 is a sectional view through the rotor in a plane perpendicular to the rotor axis, showing the stator poles and rotor nodes,

FIG. 6 is the same view as FIG. 5 but refers to the windings,

FIG. 7 is a perspective view of the assembled actuator,

FIG. 8 is an end view of the actuator to an enlarged scale,

FIG. 9 is a cross section through the actuator shown connected to a poppet valve,

FIG. 10 is a similar view to that of FIG. 9 in which additional bearings are in included to stiffen the rotor to allow higher speeds of rotation,

FIG. 11 is a block schematic diagram showing how the current pulses are generated from various sensors and an engine management computer,

FIG. 12 is a vertical section view of a bistable actuator embodying the invention coupled to a poppet valve, viewed along the axis of rotation of the rotor but including in the view a section through the poppet valve closure and the link that connects it to a lever in the actuator,

FIG. 13 is a diagrammatic end view of the actuator of FIG. 12 along the rotor axis with a stator end removed,

FIG. 14 is a similar view to that of FIG. 13 showing the rotor close to the one rest position,

FIG. 15 is a similar view to FIG. 13 showing the rotor just leaving the one rest position,

FIG. 16 shown the rotor just approaching the other rest position,

FIG. 17 shows the rotor in the other rest position,

FIG. 18 is another cross-section showing the spiral spring and the torsion bar spring,

FIGS. 19 to 23 are diagrams of equivalent circuits of a control system according to the invention at different stages of operation,

FIG. 23 shows a plot of rotor angle against time,

FIGS. 24 to 26 shows plots of stator winding current against time to illustrate pulses generated during valve operation,

FIG. 27 shows plots of stator winding current, valve closure displacement, and energy sum against time,

FIGS. 28( a) and (b) illustrate how actuators embodying the present invention have been incorporated in an engine, and

FIG. 29 shows a plot of valve opening duration against engine speed.

Referring to FIG. 1, permanent magnets 10 and 12 are sandwiched between three ferromagnetic (typically soft iron) pole pieces 14, 16 and 18 of the rotor. This magnetic assembly is located between two non-magnetic end-caps 20, 22.

Referring to FIG. 2, the end cap 22 of the rotor locates an eccentric journal 24 from which a stub axle projects through a bearing 26 located in a housing 28. Round the eccentric journal 24 runs a hollow cylindrical tyre 30 supported by a bearing 32.

Referring to FIG. 3, the end cap of the rotor 22 has a tapered hole 34 which permits the tapered end of a crank pin 36 to be rigidly secured thereto. The cylindrical region of cylindrical crank pin 36 carries a roller 38 which is received in an arcuate slot in the first lever 40. Beyond the lever 40, the crank pin 36 carries at the outboard end a crank arm having a cylindrical stub axle section which is rotatably supported in a bearing 42 which is secured to the second housing 50. The lever 40 is secured to a stub shaft 52 which rotates within two bearings 54 and 56 and is constrained axially by two thrust rings 58 and 62. The lever 40 is connected to the stem 70 of a poppet valve via a rigid link 72.

When closed the poppet valve head 150 seats against the annular seat 152 and is opened by being pushed by the actuator downwards away from the annular seat 152. Pivoting connections between the rigid link 72 and the lever 40 and the rigid link 72 and the poppet valve stem 70 accommodate any rotational relative movement of the various parts during opening and closing movements of the actuator and valve.

Referring to FIG. 4, a second lever 80 is pushed onto the cylindrical tyre 30 by a cupped sliding bearing 82 and a spherical head pin 84. The pin 84 is located in the main spring 86 which is clamped to the housing 50 by a clamp beam 88.

Referring to FIG. 5, the rotor is rotatably located within a stator generally designated 90. The stator has eight poles 100, 102, 104, 106, 108, 110, 112, 114 which surround the rotor pole pieces 14, 16 and 18. The central rotor pole piece has two magnetic nodes 120 and 122.

Referring to FIG. 6, round each pole in the stator is a winding 130, 132, 134, 136, 138, 140, 142, 144 through which electrical current can flow to magnetise the poles facing the rotor alternately as north and south poles.

The housings 28, 50 are fixed to the engine via fixings that can allow for some lost motion to prevent any large forces developing when the valve is closed. This motion is taken up during the initial rotation of the lever 40.

When considering the requirements for an actuator for opening and closing an internal combustion engine valve, the following can be considered to be fundamental requirements, namely:

• • long stroke
  • fast action
  • slow landing speed
  • large valve opening against substantial pressure

Desirable features in addition are:

• • individual fully independent driving mechanism
  • programmable timing in both directions (variable angular ratio)
  • variable stroke

Hitherto such valves have been opened using a camshaft, and springs have been employed to close the valves. Such mechanisms suffer from the following limitations:

• • fixed angular ratio
  • fixed stroke

By employing an actuator constructed and operated in accordance with the invention, which includes energy storage in one or more springs within the actuator drive, thereby employing so-called energy recycling, the following advantages are obtained namely:

• • a valve driven actively in both directions (desmodromic valve system, no conventional strong valve closing spring is needed)
  • full flexibility in timing (both directions)
  • some flexibility in stroke including a valve kept closed throughout some engine cycles
  • fast air inflow even at slow engine speed to achieve combustion products undesirable emission substantial reduction
  • individual valve driving mechanisms (each valve has a fully independent driver so that if desired not all valves have to be opened during each engine cycle)
  • full flexibility of engine management allowing some and not all valves to be activated in all cylinders or some cylinders
  • selectable engine operational modes: four stroke or two stroke allowing to maximise output power while low emission is maintained
  • the above mentioned mode selection may apply to some or all cylinders and, in fact, a gradual transition process can be envisaged

The actuator essentially comprises a form of electric motor and can be likened to a so-called stepper motor equipped with a rotor polarised magnetically with a permanent magnet or magnets, and a multi pole circular stator. Typically the stator has at least twice as many poles as the rotor. In the bistable actuator to be described the rotor has two poles and the stator has four poles, while in the actuator which can rotate through 360° there are four poles on the rotor and eight poles on the stator. The pair of stator poles are magnetically energised by individual coils allowing full flexibility in energy management. Electric current can be delivered to the coils to drive the motor in either direction. Energy can be taken away in any position of the rotor in view of the back e.m.f. effect. To simplify the driving procedure, the coils are linked in pairs. One or more springs provide the energy recycling/storage.

In the bistable device, rotor movement is restricted to less than 180° and the rotor describes a so-called swing action. As will be described later, this arrangement has two springs acting as energy storage mechanisms and the two pole rotor has enough locking force to remain in two stable positions: one where valve is closed and the other where the valve is opened, and in this device external energy is required to change from one stable position to the other.

In the embodiment shown in FIGS. 1 to 10 movement of the rotor is not restricted and the spring mechanism allows and full 360° rotation. This is of advantage at high engine speeds since it is not necessary to stop the rotor and reverse its direction of movement at the time for which the poppet valve is open. The duration of the valve-open condition can be controlled by slowing down or speeding up the rotor during the relevant part of its rotation. This results in substantial benefit in speed and energy conservation.

During medium and slow engine speeds both types of movement (full rotation as well as swing) can be used in the case of the actuator shown in FIGS. 1 to 10, which provides an additional degree of freedom in engine management. In this configuration energy recycling is achieved using a powerful flat spring (86 in FIG. 4). The spring acts on an eccentric wheel which is attached to and rotates with the rotor and this spring does not impede full rotation of the rotor. Maximum deflection of the spring occurs at the “stationary” top position of the rotor. In this way kinetic energy is converted into potential energy and stored in the spring as the rotor comes to its top position from either direction. Therefore this configuration is equally effective in full rotation mode as well as in swing mode.

In order to deliver a pushing force strong enough to open an exhaust valve against the substantial cylinder pressure which exists at the end of a firing stroke, as well as to secure a gentle landing speed when its poppet valve a variable mechanical advantage drive transmitting mechanism is used. There are three phases during an opening cycle and three phases during a closing cycle.

The opening cycle phases are:

• 1. Initial rotor acceleration and energy accumulation phase—in which no linear movement occurs and there is no thrust. This is achieved using a caming surface which has little or no change in radius of curvature associated with this part of the rotor.
• 2. Initial opening phase—gentle linear movement, accompanied by a strong pushing force This is achieved using a modest change of curvature. In the FIGS. 1 to 10 actuator, this action is supported by the flat spring.
• 3. Fast opening to fully open phase—linked to rapid linear movement requiring only a modest pushing force and achieved by much more rapid change of curvature of the caming surface.

The closing cycle phases are:

• 1. Fast main closing phase linked to rapid linear movement and a modest pulling force on the valve closure, achieved by very sharp change in caming curvature. During this phase kinetic energy recycling starts.
• 2. Gentle landing, final closing phase, linked to deceleration of the rotor producing gentle linear movement achieved by more modest changes in caming surface curvature and the rotor now beginning to push against the flat spring.
• 3. Final slowing down of the rotor to its final rest position during which there is again no vertical movement, and no pulling force, on the valve closure. This is achieved by the constant radius caming surface and this phase allows a bounce-free valve closing sequence to be achieved. During the rotor stopping process some degree of instability can occur, but since no linear movement is transmitted during this phase any such instability is not transmitted to the valve closure.

It is important to know the instantaneous angular position of the rotor and to this end an accurate position sensor is provided. This position sensor is shown at 153 attached to a rotating part of the actuator in FIG. 7 and FIG. 8. The sensor can generate a digital or analogue format signal. An analogue technique is shown where a permanent magnet 154 is attached to two halves of an eccentric disc 155a, 155b secured to the rotor shaft, in close proximity to a Hall effect sensor 156. Such a sensor provides an absolute and accurate reading of angular position of the rotor.

Driving Strategy

The actuator shown in FIGS. 1 to 10 can be thought of as comprising a permanent magnet based stepper motor equipped with an accurate angular position sensor and in combination with an engine management system as shown in FIG. 11 can be used to implement a variety of valve opening and closing strategies. These will be described by means of examples as follows:

1. Half Cycle Movement

• • triggered by opening clock pulse, the rotor starts moving, the sensor provides continuous information about the current rotor position to secure most effective coil driving currents sequence and therefore constitute an electronic commutator, and initial movement is assisted supported by energy stored in the spring. The combined effort of electromagnetic torque and spring force is able to open a poppet valve against a substantial internal cylinder pressure.
  • as the rotor approaches the 180° position at which the valve is fully opened, the driving electric current is withdrawn and an electric braking procedure is instigated by either shorting the coils or reversing the current flow, so that the electric motor is momentarily converted into an electric generator.

The movement is completed by reversing the rotation of the rotor so that it reverts to its start position.

2. Part Cycle Movement

Here the rotor is stopped before it reaches the 180° position and then reversed, the speed of the rotor being adjusted to occupy the required overall interval of time for operating the valve.

3. Full Cycle Movement with Additional Stop

Here the rotor completes the full 360° but pauses or slows down at and near the 180° point if it is necessary to keep the valve open for longer than would be the case if the rotor continued to rotate at a constant speed.

4. Full Cycle Movement without Additional Stop

Here the full 360° rotation is performed without any pause.

Constructional Variations

The basic configuration is shown in FIG. 9 where the entire rotating assembly of rotor 157, crank 158, eccentric wheel 32 position sensor disc and magnet 153 are supported by only two bearings 26 and 42. The rotating assembly is under substantial stress caused by centrifugal forces generated during rotation of the eccentric wheel the varying spring force acting on the wheel and when opening a valve against cylinder pressure. For these reasons the rotating assembly must be as stiff as possible to resist these forces. Increasing the diameter to increase stiffness is not convenient since this results in lower angular acceleration. To reduce angular inertia the rotor should be small in diameter. To meet both conditions (low inertia and mechanical strength), four bearings are proposed as shown at 160, 161, 162, 163 in FIG. 10.

The rotor and valve driving extension are shown in FIG. 10 as being two separate parts, and rotational drive is transmitted via coupling 164.

The actuator of the invention allows a desmodromic valve operating system to be employed in an internal combustion engine.

In such a system the valve is actively driven in both directions (to open and to close) achieving minimum time for opening and closing without putting undesirably high stress on a conventional valve closing spring. In fact there is no need to have a strong valve closing spring at all and it can be replaced by very modest spring which provides just enough force to keep the already closed poppet valve in it stable closed position. In this way any potential bouncing effect is greatly reduced. This “modest” spring is only shown in one of the figures in the drawings (FIG. 13).

In FIG. 11 the following items are shown.

• R is a Rotor mechanically coupled with Position Sensor PS
• P is a Microprocessor
• PS is a position sensor which provides Position Data—it could be in analogue or digital format
• EM is an engine management computer-based unit.
• C shows the supply of Control Data from the Engine Management Unit
• D0-D7 is the digital link between microprocessor and drivers
• HI-H4 are H Bridge type bidirectional drivers
• A1 and B1 is a one pair of stator coils
• A2 and B2 is second pair of stator coils
• A3 and B3 is a third pair of stator coils, and
• A4 and B4 is a fourth pair of stator coils.

PS provides the Microprocessor P with information representing the Current Position of the rotor R. It could be a digital formal or in analogue format. The link is always to provide a constant absolute and accurate position of the rotor.

The action to open or to close a valve starts on commands received from the Engine Management Unit EM.

The Microprocessor converts this to a target and compares it with the Current Position. On that basis a specific driving strategy is selected and executed by putting appropriate Driving Data to Bi directional Bridge Drivers H1-H4. The Drivers are very low resistance switching units and they provide time direct connection between coils and a source of electric current represented by a Battery—B.

One driver typically serves one pair of coils (connected in parallel or series).

There are four modes of operation; Fast Forward, Fast Backwards, Brake, Run Free.

The Microprocessor constantly monitors the Current Position versus Target, and develops an appropriate driving strategy. In this way an intelligent brush-less commutation process is implemented and the actuator drive can be thought of as comprising an intelligent brush-less electric motor.

It should also be noted that the actuator is subject to a constantly changing load caused by rotor inertia, spring force, pressure force, valve inertia and a wide range of temperature. It is also under a rapidly changing target. Thus with changing engine speed and/or load etc., the valve may need to be partially opened or fully opened or closed. Therefore very frequent start-stop commands are in use. This is why it is necessary to employ a Microprocessor as an intelligent programmable decision making device.

FIGS. 12-17 of the drawings show a swing mode valve actuator.

In these figures, a permanent magnet 210 is sandwiched between two ferromagnetic (typically soft iron) pole pieces 212, 214. The magnet and poles are located between two end caps 220, 222 with non-magnetic shims 216, 218 sandwiched between the magnetic elements and the end caps. Together the magnet pole pieces and end caps form a rotor. End-cap 220 includes a stub axle 221 which is received in a rolling bearing 224 fitted in a housing end 225 and retained by a washer 227 and bolt 229.

A spiral spring 226 is attached at one end to the stub axle 221 and at its other end to the housing end 225.

End-cap 222 has a tapered hole 223 which permits the tapering end of a pin 228 to be rigidly secured thereto.

The cylindrical region of the pin 228 carries a roller 230 which is received in an arcuate slot or groove in a lever 234. Beyond the lever, the pin 228 is carried at the outboard end of a crank arm having a cylindrical axle section which is rotatably supported in a needle roller bearing 232 which is secured in the second housing end 250.

The lever 234 is secured to a torsion bar spring 236 and is otherwise engaged by the roller 230. The spring 236 is rotatably located at one end in a bush 238 in stator end 250 and rigidly held at its opposite end in stator end 248. Rotation of the lever 234 about the axis of the torsion bar 236, stores energy in the latter as it is twisted.

As best seen in FIG. 13 the rotor is rotatably located within a stator generally designated 266 formed by the two ends 248, 250 between which extend four poles 268, 270, 272, 274 which surround the rotor poles 212, 214 albeit with a small air gap therebetween. Around each pole is a coil 276, 278, 280, 282 respectively, through which current can flow to magnetise the poles facing the rotor alternately as North and South poles.

The lever 234 is connected to the stem 260 of a poppet valve via a rigid link 262. When closed the head 263 of the valve seats against annular valve seat 264, and is opened by being pushed downwards away from the annular seat 264. Pivoting connections between the link 262 and the lever 234 and the link and stem 260 accommodate any non-linear relative movement of the various parts during opening and closing movements of the actuator and valve closure. They can also introduce a small amount of lost motion if desired which is taken up during the initial rotational movement of the lever.

FIGS. 14 to 17 are simplified views of the actuator shown in FIG. 13, and show how movement of the rotor is related to movement of the cam-lever and poppet valve. For convenience the same reference numerals have been employed throughout FIGS. 13-17. In particular the stator coils and poles are not shown in FIG. 14 et seq.

FIG. 14 essentially corresponds to FIG. 13 in that the rotor 215 is shown in its most clockwise position, with the roller 230 in its uppermost position.

In FIG. 15 the rotor is assumed to have rotated anticlockwise through a few degrees (typically 10-15°). The radius of curvature of the lever 234 engaged by the roller 230 over that rotation of the rotor, is essentially constant and is parallel to the locus of the axis of the roller 230. Therefore during that initial movement the rotational movement of the rotor is not converted into linear movement of the link 262 or stem 260 of the poppet valve 263.

This lost motion between the rotor and the link 262 permits the rotor to accelerate in an unimpeded manner during the first part of its anticlockwise rotation. Thereafter the shape of the caming surface 235 and opposed finger 237 of the lever 234 is such that with continued anticlockwise rotation of the rotor 215 the engagement of the rotor 230 with 235 and 237 causes the lever 230 to pivot about the axis defined by the torsion bar spring 236, twisting the latter in the process, and simultaneously forcing link 262 in a downward direction. This in turn forces the valve head 263 also in a downward direction away from the valve seat 264, to open the valve.

FIG. 16 shows the rotor shortly before it reaches its fully anticlockwise position (which latter is shown in FIG. 17), and in both FIGS. 16 and 17 the valve head 263 is shown displaced clear of the seat 264.

Although only shown in FIG. 13, a helical spring 284 is shown trapped between a stop 286 attached to the valve stem 260 and the seating 264. This spring is similar to each of the springs usually found at the top of a cylinder head of an internal combustion engine, each of which holds closed one of the valves.

However since the actuator of the present invention provides a positive drive for the valve in both opening and closing directions, the spring 284 could in theory be dispensed with. Nevertheless in order to ensure reliable closing of the valve head against its seat, a compression spring which requires only a modest force to compress it may be provided as shown.

Reversing the currents supplied to the stator coils will cause the rotor to rotate clockwise and lift the valve head 263 back into contact with the seat 264, thereby to close the valve, and the rotor returns to the position shown in FIG. 14.

FIG. 18 is a cross-sectional view on the line YY in FIG. 12 and shows the spiral spring 266 clamped at his inner end to the end cap 226 of the rotor 215 by clamp 286, and at its outer end to the stator housing end 225, by clamp 288. Also visible is the torsion bar 236 which provides the pivoting axis for the lever 234 and serves also as the second spring.

A perspective view of the lever 234 and a modified torsion bar arrangement is shown in FIG. 18A. Opposite ends of the torsion bar 236 are received in bearings at opposite ends 225, 250 of the housing at (see FIG. 12). A clamp 290 clamps a second torsion bar 292 to the first bar 236 and at its outboard end is received an anchor block 294. The lever 234 is rotated by the rotor (not shown in FIG. 18A). This rotation is transmitted to the left hand end of bar 236 by flats on the bar 236 and a correspondingly shaped opening in the lever 234.

The clamp 290 prevents the bar 236 from rotating at the point where the clamp 290 engages the bar 236, but the bar 292 is able to flex as denoted by arrow 296, its flexing 292 thereby permitting continued limited rotation of lever arm 234.

When the rotor is reversed the energy stored in 292 and 236 is available to assist in rotating lever 234.

System Description

FIGS. 19 to 23 are equivalent circuits of the control system during operation, when in the ON mode, free run (i.e. electrical current “off”) mode, the Braking mode (during which electrical energy is reclaimed), and the STOP mode (used to arrest motion if overrun is detected as being likely or just to occur).

Functional design parameters set for the proposed IVA system are as follows:

• • 1. Safe, non-destructive, failure modes
  • 2. Capability of operating within a temperature range of −40° to +150° Celsius and with valve head temperatures of 700° Celsius
  • 3. Capability of operating in an oil/air mixture environment
  • 4. Capability of operating at an engine speed of up to 8000 rpm
  • 5. Capability of providing 10 mm of intake or exhaust valve lift (with a valve mass of 36 g)
  • 6. Capability of operating a 29 mm diameter poppet valve against a cylinder pressure of 6 bar
  • 7. Capability of providing a maximum seat impact velocity of 240 nm/sec (equivalent to 0.01 mm/cam deg of conventional valve train)
  • 8. Capability to shape valve opening and closing events to avoid piston clash
  • 9. Free position of valve to be closed (valve seated)
  • 10. Provision of variable valve lift from 0-10 mm
  • 11. Electrical power consumption to be similar to current mechanical valvetrain systems (allowing a 12 volt electrical system)

The actuator tested and referred to below has a four-pole rotor constructed from permanent magnets and a stator with eight coil windings arranged as four opposed pairs.

The actuator system referred to below utilises a leaf spring which is loaded and unloaded via an eccentric of the rotor shaft. Other alternative energy recovery devices which can be used include torsion bars and torsion springs. The energy stored in the spring mechanism is used to assist in the opening of the poppet valve. The loading of the spring mechanism in the latter stages of the valve event assists in reducing valve seating velocity. Both these actions reduce the energy requirement from the electrical system for the next event and hence improve system operating efficiency.

Each actuator has its own positional sensor in the form of a reluctor ring on the rotor read by a Hall effect-sensor, which is used by the control system.

System Dynamics

A complete valve event can be as a result of an actuator displacement of up to 360 degrees. As depicted in the drawings one full rotation of 360° results in a valve opening and closing sequence giving a maximum valve lift of 10 mm.

In the case of an oscillatory motion of the rotor achieved by rotating the actuator through less than 180° and then back again, the poppet valve will only be partially opened so that a lift of less than 10 mm is achieved. The reverse rotor motion closes the valve.

The rotor and mechanism thus allows fully variable poppet valve lift and duration operation, creating the potential for the development of throttleless gasoline engines.

The actuator embodiment referred to below has a maximum speed of response of 7 ms for a complete valve event. At 700 rpm, 7 ms equates to a valve open period of 296 degrees crank angle, whereas at 1000 rpm, 7 ms equates to a valve open period of just 42 degrees crank angle. Therefore where lower valve lift is required the actuator is oscillated between the home position and less than 180°, or held at a low valve lift position.

FIG. 24 shows angle versus time.

Energy is only required to change the position of the poppet valve between poles of the actuator. If no software control is provided and a large current pulse is delivered to move the rotors an overshoot can occur.

A first method of counteracting this is to redefine the position of the current pulse until the required position is achieved.

FIG. 25 shows how an iterative process achieves this.

In accordance with a preferred feature of the invention, software is adjusted to generate correcting current pulses to slow the rotor, which enables extremely low valve seating velocity to be achieved if for example satisfactory control from the mechanical mechanism cannot be achieved.

In this preferred arrangement, PWM control delivers short current pulses and utilises continual position sensing as shown in FIG. 26. This also minimises the energy required.

As shown in FIG. 26, a short current pulse maintains speed of response to open, and can be followed by one or more short pulses to slow down the rotor movement if required.

It is possible to drive the valve open within 3.5 ms but this is not required under all operating conditions, and in the interests of energy management it maybe favourable to slow the valve opening and closing rather than having a fast opening event followed by a dwell period (at the required lift) then a fast closing event. This can be achieved using PWM control with continuous sensing of the rotor (and therefore valve) position.

It is also possible to drive the rotor at a lower speed if a reduced number of stator coil pairs are employed. A valve motion response is shown in FIG. 27 based on driving four coils. It can be seen that the valve seating velocity has been reduced without affecting the overall valve opening event, demonstrating an optimum level of current usage.

The control system defines a target position to which the valve is to move during each event, itself determined by the instantaneous power required to be generated by the engine, and the control system generated current pulses ensure that the appropriate velocity of the rotor is achieved to reach each target position at the required time.

When a braking pulse is used, the actuator effectively becomes a generator and, according to another preferred feature of the invention, this energy is fed back into the electrical system powering the actuator. Management of the energy flow in this way to allows a 12-volt system to be employed.

Energy reclamation during valve actuation is demonstrated in FIG. 28.

As shown in FIGS. 29(a) and (b), the actuator has been successfully packaged into the Powertrain ‘K’ Series engine, in which the valve centres are spaced by 35 mm and the cylinder centres are spaced by 88 mm.

A testing rig demonstrated that all the functional specification requirements can be achieved, with valve events equivalent to crankshaft speeds of up to 8000 rpm in which the opening and closing of a poppet valve has been within 7 ms, with a maximum lift of 10 mm. The rig has included a simulated gas force load of 6 bar, which is representative of a normal road-going four-stroke internal combustion engine.

A valve seating velocity below 240 nm/sec has been achieved using a combination of mechanical and software control strategies.

Valve opening durations for different engine rpm's are depicted in FIG. 30.

Where shorter valve opening durations are required they are achieved by using the oscillatory mode of the actuator. This not only provides shorter valve open durations but can allow reduced valve lift if desired since the opening duration and lift can be defined by the control software.

An embodiment of the actuator described and illustrated herein can deliver 1.5 joules, and 16 such actuators operating the poppet valves of a 16 valve 4 cylinder internal combustion engine have been found to consume 1.6 kW of electrical power.

A 4 cylinder valvetrain using 16 1.5-Joule motors operating at 67 Hz (8040 rpm) and consuming 1.6 KW of electrical power compares very favourably with a mechanical valve train system. 12 volt alternators with an output of 140 Amps giving approximately 7 kW are readily available to provide the required energy.

If vehicle architecture moves towards higher voltage and lower current systems, greater alternator power will become available and the electrical power required will be less of a constraint, allowing further enhancements of the system operation.

The invention has enabled a unique, electromagnetic valve actuation system to be developed, the dimensions of which are compatible with modern, compact, gasoline and diesel engines.

Software control of the current to the actuators, linked to the engine management system and knowledge of the position of each poppet valve at each point in time in each valve event, minimises the current demand on the electrical supply, thereby allowing the system to operate in a 12 volt system.

The reduction in electrical power required has been achieved using a system in which the valve closed and open positions correspond to zero energy usage by the actuator, using power only to trigger the opening and closing of the valve, with energy storage and recovery during each valve event.

The software control combined with the actuators employed herein also enables fully variable valve operation so that each valve is opened by only the amount required for the instant mean operating parameters of the engine, dictated by load and speed, and this will be a major factor in the future development of petrol, diesel & HCCI internal combustion engines.

Claims

1. An electromagnetic actuator in which a rotor comprising permanent magnet means is rotatable in a stator which is magnetisable by causing an electric current to flow through at least one winding associated with the stator, the rotor being rotatable between stable rest positions defined by spring and/or magnetic forces acting on the rotor, wherein spring means store energy during part of the movement of the rotor and provide kinetic energy for accelerating the rotor during subsequent movement thereof away from rest in one rest position towards another, wherein a magnetic torque is exerted on the rotor when a current flows in said at least one winding which is sufficient to overcome the force(s) holding the rotor in that rest position, to cause the rotor to rotate in a direction from that rest position towards another rest position, the rotor being connected to a thrust member by a mechanical linkage by which the rotational movement of the rotor is converted into substantially linear movement, the linkage having a mechanical advantage which varies in a predetermined manner during the rotation of the rotor.

2. An actuator as claimed in claim 1 in which the rotor has only two stable rest positions, each of which is defined by magnetic and/or spring forces acting on the rotor, wherein a first spring means stores energy during movement of the rotor towards one rest position and provides kinetic energy for accelerating the rotor away from that rest position towards its other rest position, and a second spring means stores energy as the rotor rotates towards its other rest position to provide kinetic energy to provide an accelerating force on the rotor as it moves away from the said other rest position in a reverse sense back towards its first rest position.

3. An actuator as claimed in claim 1 wherein as energy is stored in spring means associated with a rest position of the rotor, the latter is as a consequence decelerated so that its rotational speed (and therefore also the linear speed of the thrust member and linkage) is progressively reduced as the rotor approaches the rest position.

4. An actuator as claimed in claim 1 wherein the mechanical advantage profile is such that near one rest position angular movement of the rotor results in substantially no linear movement of the thrust member.

5. An actuator as claimed in claim 1 wherein the stator has an even number of poles, and the rotor has an even number of nodes which are magnetised alternately North and South around the rotor by the permanent magnet means.

6. An actuator as claimed in claim 1 wherein the mechanical linkage comprises a lost motion connection between rotor and thrust member which is taken up during part of the rotation of the rotor.

7. An actuator as claimed in claim 1 wherein the rotor is prevented from rotating through more than 180° from its one rest position and the rotor movement is oscillatory between the two rest positions.

8. An actuator as claimed in claim 1 wherein the rotor can rotate through 360° from its one rest position and the electric current pulses are controlled in use to cause the rotor to pause or slow down as it rotates through the 180° position.

9. An actuator as claimed in claim 1 wherein the rotor has more than two rest positions and the electric current pulses are controlled in use to cause the rotor to oscillate between its first rest position and any one of its other rest positions.

10. An actuator as claimed in claim 1 when employed to open and close an inlet or exhaust valve of an internal combustion engine, wherein the rest position corresponding to the valve closed position is referred to as the primary rest position, and the mechanical advantage profile is selected to produce a high mechanical advantage at the rotational position of the rotor at which the valve begins to open, and after initial opening of the valve the profile is such that the mechanical advantage progressively reduces and then progressively increases again until the valve is fully open, and wherein the mechanical advantage again decreases to a minimum and increases again as the rotor rotates towards its original primary rest position, either in reverse or with continued rotation in the same sense until the rotor approaches its primary rest position and the valve is again in its original closed position, beyond which position the rotor continues to rotate without movement being transmitted to the valve due to the lost motion connection, until the rotor reaches its primary rest position.

11. An actuator as claimed in claim 1 wherein as the rotor rotates, the permanent magnet means also rotates and produces a magnetic cogging torque as the rotor nodes align with stator poles so as to define a plurality of secondary second rest positions for the rotor.

12. An actuator as claimed in claim 10 wherein the electrical current is controlled so as to cause the rotor to rotate from its primary rest position to one of the second rest positions and back again, or through the primary second rest position to return to the primary rest position while continuing to rotate in the same direction, whereby the valve can be opened partially or fully and for differing periods of time to suit different operating conditions of an engine.

13. An actuator as claimed in claim 1 when employed to open and close a valve of an internal combustion engine, wherein the thrust member is connected to the valve closure member so as to move the latter positively in both opening and closing directions, thereby obviating the need for a separate spring to hold the valve closed.

14. An actuator as claimed in claim 1 in combination with a control system for supplying pulses of electrical energy to the or each winding thereby to provide the required instantaneous electrical energy in each current pulse and/or to control the phase (i.e. timing) and/or the duration of each current pulse, in response to varying engine load, so as to generate sufficient magnetic torque at each instant during valve opening and closing to overcome the forces acting on the valve closure at each point in the engine operating cycle, and which can vary with load, crank angle and from cycle to cycle.

15. An actuator as claimed in claim 1 wherein the stator has eight spaced apart electromagnetically polarisable poles and the rotor has four spaced apart permanently magnetised nodes.

16. An actuator as claimed in claim 1 wherein the stator has four poles, arranged in two opposed pairs, and in use the rotor will normally rest partly aligned with one pair of poles, and an initial movement of the rotor is effected by a pulse of current through at least one winding linked to the stator causing the rotor to be repelled away from the partly aligned poles.

17. An actuator as claimed in claim 2 comprising: a) a stator with four circularly arranged, inwardly radially directed poles,b) a rotor that includes a pair of diametrically opposed permanent magnet poles, and which is rotatable within the four stator poles through up to 180 degrees from one rest position to another at the two extremes of its travel,c) a first spring element which stores mechanical energy as the rotor rotates into each of the two extremes of its travel,d) a pin extending laterally from, and parallel to but offset from the axis of rotation of the rotor,e) a lever linked to the pin and pivotally mounted for rotational movement about an axis also parallel to the rotor axis, for exerting thrust externally of the actuator,f) an arcuate slot in the lever in which the pin is received in which it can slide relative to the slot and also transmit rotational movement to the lever, the extent to which angular movement of the pin produces angular movement of the lever being determined by the shape of the slot,g) a second spring element which stores mechanical energy as the lever is rotated into each of the two extremes of its travel,h) at least one winding which when an electric current flows therein will create alternate North and South poles around the four stator poles,i) a housing within which the stator, winding(s), rotor, lever and springs are located, opposite ends of which provide bearings for the rotatable parts,

18. An actuator as claimed in claim 1 wherein rotor movement is braked by short-circuiting the windings, causing induced currents to flow in the windings in an opposite sense to the initiating pulse of current, so reversing the stator pole polarity and dissipating kinetic energy of the rotor and any associated linkage.

19. An actuator as claimed in claim 1 wherein braking of the rotor is achieved by reversing the current flow in the windings in order to reverse the direction of torque to decelerate the rotor.

20. An actuator as claimed in claim 1 comprising: a) a stator of eight circularly arranged, inward radially directed poles, each pole being wound with insulated conductor to produce an electromagnet means at each pole,b) a rotor that includes two pairs of diametrically opposed permanent magnet poles, with the magnetic sense alternating north-south-north-south around the rotor, so that with appropriate polling the rotor is rotatable through 360°, or first in one direction and then back in the opposite direction.c) a spring element that stores mechanical energy as the rotor rotates to a primary rest position,d) a pin, surrounded by a tubular wheel element, extending laterally from and parallel to but offset from the axis of rotation of the rotor,e) a first lever pivotally mounted about an axis parallel to the rotor axis,f) an arcuate slot in the first lever within which the wheel and pin are received in which the wheel can roll or slide relative to the slot and also transmit rotational movement to the lever with the mechanical advantage varying with the angular position of the rotor the extent to which the angular movement of the pin and wheel produces angular movement in the lever being determined by the shape of the slot,g) the first lever having a cross-pin joint for transmitting thrust externally of the actuator,h) a sleeve extending from the rotor which is in contact with a second lever,i) the second lever being formed with an arcuate contact surface so as to move the spring via a sliding spherical bearing means, such that the spring displacement is a function of the rotor angular position,j) the arcuate surface of the second lever providing for a primary rest position, such that a small angular displacement of the rotor either side of the primary rest position results in either no movement of the spring or a slight additional straining of the spring, and such that larger movements of the spring result in the spring progressively unloading until the rotor has moved substantially 180 degrees from the primary rest position, andk) a housing within which the stator, windings, rotor lever and spring are located,l) the housing providing bearing means for the rotor, the first lever and the second lever.

21. An actuator and valve combination as claimed in claim 10 wherein the valve closure member is driven positively in both directions to open and close the valve.

22. An internal combustion engine having at least one exhaust valve when fitted with an actuator as claimed in claim 1 for opening and closing the exhaust valve.

23. An internal combustion engine having a plurality of inlet and exhaust valves when fitted with a corresponding plurality of actuators, each of which is as claimed in claim 1 for independently opening and closing the valve with which it is associated.

24. A power supply for delivering electric current to an actuator, the actuator having a rotor rotatable in a stator which is magnetisable by causing an electric current to flow through at least one winding associated with the stator and being operable in use to open and close a valve associated with a cylinder of an internal combustion engine, the power supply comprising: a source of electric current,a circuit including electrically operable switch means between the source and the stator winding by which the source is connected to the stator winding,a control system responsive to a signal from a position sensor associated with the actuator indicative of the instantaneous position of the rotor and to signals from an engine management system linked to the engine,current delivery means in the control system which in use delivers current pulses to operate the switch means,a buffer electrical energy storage means which can be connected in parallel with the stator winding by operation of the switch means, to be charged or discharged as required andprogrammable computer means in at least one of the engine management system and the control system, programmed to control the operation of the current delivery means and the delivery of the operating current pulses to the switch means, whereby in use the latter is opened and closed as required, to achieve at least one of the following:

25. A power supply as claimed in claim 24 wherein the buffer storage means comprises a capacitor.

26. A power supply as claimed in claim 24 wherein the program causes the switch means to be operated so as to connect the buffer storage means, the current source and stator winding in parallel when the rotor is to be moved out of a home position.

27. A power supply as claimed in claim 24 wherein the buffer storage means is connected to the current source before the stator winding is connected, so that its charge is also available to act as a source of current for the winding as well as the battery, when the winding is connected thereacross.

28. A power supply as claimed in claim 24 wherein, when the engine management system calls for a valve which is currently closed to be opened, the program causes a short duration pulse of current to flow in the stator winding of the actuator of that valve, so as to release the rotor.

29. A power supply as claimed in claim 24 wherein, when the sensor indicates that the rotor is beginning to approach the position at which the valve is to be closed, the program operates the switch means to connect the current source and buffer storage means combination across the stator winding to produce one or more short duration pulses to slow the rotor as it approaches said position.

30. A power supply as claimed in claim 24 wherein the program arranges for the buffer storage means to be connected across the stator winding, so that a back emf generated in the stator winding by the rotation of the rotor will cause a current to flow into the buffer storage means to charge the latter, and thereby recover energy from the rotor movement and in doing so further slow down the rotor as it approaches a target position.