EP1199446A1

EP1199446A1 - Method and arrangement for operating valves in an internal combustion engine

Info

Publication number: EP1199446A1
Application number: EP00203679A
Authority: EP
Inventors: Kjell R. Johansson; Jan-Olof Carlsson
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2000-10-20
Filing date: 2000-10-20
Publication date: 2002-04-24
Anticipated expiration: 2020-10-20
Also published as: DE60034340D1; DE60034340T2; EP1199446B1

Abstract

The invention relates to a valve operating mechanism for an internal combustion engine, which engine comprises at least one intake and exhaust valve per cylinder, a main valve actuating means (1) for opening and closing each valve, and electronic control means (26) for controlling said valve actuating mechanism. An auxiliary valve actuating means (20) is provided in addition to the main valve actuating means (1), which means is arranged to act directly or indirectly a valve stem (13, 43, 56) in order to effect a decompression of the cylinder. The invention discloses a method and an arrangement for operating said valve actuating means.

Description

TECHNICAL FIELD

The invention relates to a method and a device for operating intake and exhaust valves in an internal combustion engine, particularly for camless valves, wherein a main valve actuating means is assisted by an auxiliary valve actuating means.

BACKGROUND ART

Internal combustion engines contain at least one intake and one exhaust valve for each cylinder of the engine. The intake valve allows air to flow into the combustion chamber and the exhaust valve allows the combusted air/fuel mixture to flow out of the chamber. The timing of the valves must correspond to the motion of the piston and the injection of fuel or an air/fuel mixture into the chamber. Conventional engines incorporate cams to co-ordinate the timing of the valves with the piston and the fuel injector. Apart from being subject to wear, cams are not very amenable to variations in the valve timing during the operation of the engine. Modern engines can be provided with means for adjusting the cam and the valve timing to a certain extent, but are still too limited for the type of advanced engine management needed to meet future requirements for fuel consumption and emission levels.
Hydraulically actuated valves controlled by solenoids or piezo-electric actuators as known from US-A-4 019 481, US-A-4 724 801 and US-A-5 829 396, are as a rule relatively slow and are mainly used for large compression ignition (Cl) engines. For engines operating at higher speeds, such as internal combustion (IC) engines, a hydraulic system would require large flows of hydraulic fluid, which increases power consumption. A hydraulic system is also sensitive to air trapped in the fluid, pollution, such as particles, and requires a large number of sealing surfaces.
Electromagnetic or solenoid actuated valves are also known per se. These may act directly on the valve stem or on an extension thereof. There are two main problems with this type of actuator. Firstly, the valve is usually spring loaded in one or both directions. At high engine speeds (>7000 rpm) these springs must be correspondingly stiff, in order to avoid chatter and vibrations if the valve does not follow the actuator. Secondly, the power consumption during start-up can be considerably. For actuators arranged as a linear motor, having an armature held in a central position by a pair of springs, a procedure commonly known as "swing-on" must be performed as the engine is started, in order to move the armature from its equilibrium position to the closed valve position. The procedure involves actuating the electromagnets in turn, in order to achieve an oscillating movement of the armature, until the armature can be attracted to the upper electromagnet. Although this is only necessary at start-up, the initial force needed for moving the valve against the stiff springs require relatively large electromagnets. For cold starts in sub-zero temperatures, the armature can be actuated directly by applying a very high current to the armature. Similarly, an armature arranged on a pivoting arm held by a torsion spring between two electromagnets can also be drawn directly by applying a relatively high current to one of said electromagnets. The result in all the above cases is that each valve must be fitted with a relatively bulky and heavy actuator.
A valve operating mechanism using a piezo-electric control device is known from US-A-4 593 658. In this case a stack of piezo-electric elements acts on the valve via a pivoted lever. The size of the stack and the length of the lever must be adapted to give the required valve lift. Opening an exhaust valve against the cylinder pressure on the valve will however require a great deal of power. This may limit the length of the lever, which can result in a large stack of piezo-electric elements. A further problem is related to certain material characteristics of the piezo-electric elements themselves. If subjected to a sudden blow, such as a valve stem acting on said lever during the closing of the valve, the elements may be damaged or crack, as they are quite brittle.

DISCLOSURE OF INVENTION

It is an object of the invention to provide a valve operating mechanism and a method for operating said valves for a combustion engine or like valved engine, in which the operating mechanism enables substantially full control over all parameters for each of the valves of the engine. Although the invention can be adapted to most valved engines, it is particularly suited for high revolution engines and engines with high compression, such as diesels and/or turbo- or supercharged engines.
According to the invention as stated in claims 1 and 7 a method and a device are provided for operating valves in an internal combustion engine, which engine comprises at least one intake and exhaust valve per cylinder, a main valve actuating mechanism for opening and closing each valve, and electronic control means for controlling said valve actuating mechanism. In order to assist the main valve operating mechanism an auxiliary valve actuating means is provided, which means acts directly or indirectly on the valve for initiating valve motion during the start of a valve operating cycle and/or arresting valve motion at the end of a valve operating cycle. The latter function can be used for eliminating noise from the moving parts of the auxiliary actuator as well as preventing damage to said actuator, e.g. should the valves and the actuators temporarily lose and regain contact at high engine speeds.
The initial motion performed by the auxiliary actuating means causes a decompression of the cylinder, thus reducing the required effort by the main actuating means and enables smaller electromagnets, or piezoelectric actuators, to be used. The arresting motion caused by the auxiliary actuating means causes a gradual deceleration of both the valve stem and any moving parts in the actuating means, so that their velocity is near zero as they reach their end positions. Motion can be both initiated and arrested using a piezo-electric element, which has a shorter stroke than the main actuating means and gives a substantially shorter valve lift.
The valves are preferably opened and closed using an electromagnetic main valve actuating mechanism, although other means are possible, e.g. a piezo-electric actuator. As a result of the decompression caused by the auxiliary actuating means, the size of the main actuating means can be reduced, as they will be working against a considerably lower pressure. Smaller magnets in the actuator will obviously also give weight and cost reductions. Although the auxiliary valve actuating means may be used for all valves, it is particularly suited for exhaust valves, especially exhaust valves having large opening areas, which must act against high pressures in the combustion chamber.
The main and auxiliary valve actuators are controlled by a control means comprising a microprocessor, to which data relating to the operation of said engine is fed, and which is programmed to control the position of said piezo-electric actuating means based on said data. Said control means can be a separate unit or an integrated part of the engine management system.
A sensor is used to determine the position of the piezo-electric actuating means, which position is fed back to the microprocessor.
This sensor can be a virtual sensor, wherein known characteristics and material properties of the piezo-electric elements are used to calculate an estimated position of the piezo-electric actuating means. In this case factors such as element compression under load must be taken into account. Alternatively a sensor comprising a number of threads each electrically connected to the same number of individual elements of the piezo-electric actuating means may be used. A signal proportional to the position is obtained as the piezo-electric actuating means is subjected to a compressive load, which enables calculation of the position of the actuator.
Because of the relatively limited expansion of a piezo-electric element, the auxiliary actuating means acts on the valve via an amplifying mechanical linkage, such as a lever action spring or a hydraulic amplifier. The piezo-electric element itself can be in the shape of a stack of individual elements, but is not limited to this shape.
The total valve lift caused by the main actuator means is in the region of 8-10 mm, while the valve lift caused by the auxiliary actuating means is in the range 1-2 mm. On one hand the initial valve lift need only be sufficient to enable decompression. On the other hand it must also be lifted sufficiently clear of the valve seat avoid damage to the valve, e.g. carburisation. Preferably the ratio between the valve lift caused by the auxiliary actuating means and the main valve actuating mechanism is in the range 1:10 to 1:4.
The main valve actuating mechanism comprises one or more electromagnets, which are designed to hold the valve either in its closed end position or in an intermediate position when the engine is switched off. In the latter case, the valve is immediately phased in to assume its correct position in the working cycle as the engine is started.
A valve held in an intermediate position must be spring loaded from opposite directions by two separate springs. In this case most of the work is done by the relatively stiff springs. As this is an oscillating system the choice of spring characteristics can be crucial to avoid resonance. The top of the piston may require a recess, so that it will not strike the valve if an actuator malfunctions.
Each valve may also be spring loaded by a single spring towards its closed position only. The spring required is a weak return spring, which ensures that the piston does not damage the valve if an actuator malfunctions. Said spring can be fixed at both ends, to the actuator and the valve respectivly. In this case all the work is done by the two electromagnetic actuators, without any assistance from the spring. This system will have no resonance problems, but the moving mass of the valve and armature must be decelerated at their end positions to avoid excessive noise.
The use of electromagnetic valve actuators makes it possible to eliminate the spring/-s altogether. Without any springs present the system has no problems with resonance, a small moving mass and a correspondingly short response time. However, steps must be taken to arrest the movement of the moving masses at their end positions and to avoid possible damage to the valve as described above
Each spring that can be eliminated reduces the oscillating mass of the system, which allows a reduction of actuator size or shorter response times for the valve controlled by the actuator.

BRIEF DESCRIPTION OF DRAWINGS

Particular embodiments of the invention are described below, with reference to the drawings, wherein;

Figure 1: shows a cross-section through a valve operating mechanism according to a first embodiment of the invention;
Figure 2: shows a section through a piezo-electric element provided with sensor means;
Figure 3: shows a cross-section through a valve operating mechanism according to a second embodiment of the invention;
Figure 4A: shows a cross-section through a valve operating mechanism according to a third embodiment of the invention;
Figure 4B: shows a plan view of a main valve with a hollow valve stem according to the invention;
Figure 4C: shows an enlarged sectional view of a hollow valve stem according to the invention;
Figure 5: shows a cross-section through a cylinder provided with a separate auxiliary valve, according to a fourth embodiment.
Figure 6: shows a mechanical linkage using a pivoted spring with a single auxiliary actuator.
Figure 7A: shows a perspective view of a pivoted spring used by the mechanical linkage.
Figure 7B: shows a plan view of the front region of a pivoted spring in contact with a valve stem.
Figure 8: shows a mechanical linkage using a pair of pivoted springs with separate auxiliary actuators.
Figure 9: shows a mechanical linkage using a pair of pivoted springs with a common auxiliary actuator.
Figure 10A: shows a cut-away view of an arrangement using four springs.
Figure 10B: shows the arrangement of Figure 10A provided with a single common actuator.
Figure 11: shows a plan view of an arrangement using multiple, overlapping pivoted springs.

The figures only show schematic representations of the component parts, which are not drawn to actual size for reasons of clarity.

MODES FOR CARRYING OUT THE INVENTION

Figure 1 shows a valve operating mechanism according to the invention, wherein a main valve actuating means 1 is provided for opening and closing a valve (not shown). The actuating mechanism 1 is attached to the cylinder head 2 of an internal combustion engine and comprises an upper 3 and a lower electromagnet 4. The electromagnets are rigidly connected by a spacer 5 around their circumference, which spacer 5 separates the electromagnets 3, 4 creating a gap 6 in which an armature 7 is located. The armature 7 is fixedly mounted on a central pin 8, e.g. by welding or glueing. The pin 8 is axially slidable in a pair of bushings 9, 10 mounted in openings 11, 12 through the electromagnets 3, 4. The pin 8 is in contact with a valve stem 13, which is part of an intake or exhaust valve. In operation the valve actuating means is controlled by electrical pulses from an engine management system in response to signals from a microprocessor in said system. The electrical pulses actuates the electromagnets 3, 4 in turn, in order to open the valve using the lower electromagnet 4 or close it using the upper electromagnet 3.
Due to the electric power requirements for actuating the electromagnets, the standard 12 V system for vehicles may be insufficient. The next generation of electrical systems will most probably use 42 V as standard, which voltage is better suited for this purpose. A preferred embodiment is to use a voltage converted to 100-1000 V. This is desirable in order to reduce both the current and the cross-sectional area of the wiring, which in turn reduces weight.
The embodiment of Figure 1 is provided with an upper and a lower helical spring 14, 15, which springs hold the armature 7 in an intermediate position between the electromagnets 3, 4. The lower spring 14 is mounted between an upper surface 2a of the cylinder head 2 and the lower surface of a spring retainer 17 attached to the upper section of the valve stem 13. The upper spring is mounted between the lower surface of a housing 18 for the actuator assembly and the upper surface of a spring retainer 19, which is an integral part of the central pin 8. Said housing 18 must be rigidly connected to the actuator assembly and the cylinder head 2.
Alternative embodiments may include only the lower return spring 14, in order to ensure that the valve is in its closed position when not actuated. There is also a further embodiment in which the electromagnets are used to control all movements of the valve, so that both springs become superfluous.
In order to assist the opening of the valve, the actuator assembly is provided with an auxiliary valve actuating means 20. Preferably a piezo-electric element 21 is used, which element is mounted inside, or in parallel with, the upper spring 15 between the casing 18 and the central pin 8. Because of the short stroke of the piezo-electric element 21, a lever action spring 22 is mounted between the element 21 and the pin 8. This has the effect of extending the stroke, while keeping the actuating means compact. Pulses of electric current from the engine management system also control the auxiliary valve actuating means. Such a spring will be described in detail in connection with Figures 6-11 below. Figure 1 shows the valve stem 13 in its upper position with the valve closed. In this position there is a small space between the armature 7 and the upper magnet 3. Said space is necessary in order to prevent the armature 7 from striking the upper magnet 3. At the same time the distance must be kept small, as the strength of the magnetic field of the magnet 3 is reduced as the distance increases. In order for the upper magnet 3 to hold the armature 7 securely, the space between them should not exceed a few tenths of a millimetre.
As the valve stem 13, armature 7 and pin 8 approach their upper position, their movement is decelerated using a controlled retraction of the piezo-electric element 21, creating a soft landing.
The piezo-electric element used may be a standard type element, which only require minor physical modifications to fit the application A state of the art element may be 45 mm long and have a stroke of 0,5 mm. A lever or some other type of mechanism must compensate the short stroke of such an element, since a piezo-electric element acting directly on the valve would be excessively long. Its low power consumption and relatively high expansive power outweigh the drawbacks
Instead of a piezo-electric element, actuators made from alternative materials having similar properties may be used, e.g. polymer materials with suitable electrical properties.
In operation, the piezo-electric element 21 is actuated first, making the valve open enough to cause a decompression of the cylinder pressure. To achieve this the valve lift must be not less than 1-2 mm. Once decompression has taken place the main valve actuator 1 is actuated for full opening of the valve. The full valve lift is approximately 8-10 mm, giving a ratio between partial and full valve lift of approximately 1:10 to 1:4. This ratio may of course vary, depending on the size and type of engine. Because of the decompression, the lower electromagnet 4 only has to overcome the force of the lower spring 14, as opposed to the spring force combined with a possible high pressure acting on the valve in the combustion chamber.
The auxiliary valve actuating means 20 may be used for both intake and exhaust valves. Due to the significantly different pressures in the combustion chamber when valve actuation is performed, it may only be necessary to use the auxiliary actuating means for the exhaust valves. The invention is particularly suited for exhaust valves with a large surface area, which would require large and power consuming electromagnetic actuators to open unless assisted by decompressing auxiliary actuators.
The main and auxiliary valve actuators 1, 20 are controlled by a control means comprising a microprocessor (see Fig. 2), to which data relating to the operation of said engine is fed. The control means is programmed to control the position of said piezo-electric actuating means based on said data. Said control means can be a separate unit or an integrated part of the engine management system. A sensor is required to determine the position of the piezo-electric actuating means, which position is fed back to the microprocessor.
A sensor arrangement for a piezoelectric element 21, as shown in Figure 2, comprises a number of threads 23 each electrically connected to the same number of individual elements 24 of the piezo-electric actuating means. The individual elements 24 are enclosed in a casing to form a single element 21.
When a first signal 25 is transmitted from a microprocessor 26 in the engine control system, the auxiliary actuating means 21 is actuated to partially open the valve. As each of the piezo-electric actuating elements 24 is subjected to a compressive load, a current is delivered to each of the threads 23. This current results in a signal 27 proportional to the position of the actuating means 21. The position signal 27 is transmitted to a microprocessor 26 in the engine control system, which enables the microprocessor to calculate the position of the actuator. Additional data relating to physical characteristics and material properties of the element 21 for use in said calculation is stored in the microprocessor. The position signal 27, in combination with ignition and fuel injection data 28 from a number of other sensors in the engine, enables the microprocessor 26 to perform the necessary calculations. As soon as the auxiliary actuating means 20 completes the initial valve opening, a second signal 29 is transmitted by the microprocessor to actuate the main valve actuating means 1.
Instead of using signals from all elements, it is possible to use a signal from the first individual element, indicating initial actuation of the actuator, and a signal from the last individual element, indicating that the full stroke has been completed. A microprocessor can then calculate the theoretical position of the actuator using dead reckoning, using the current supplied to the actuator and data relating to physical characteristics and material properties of the element 21.
Alternatively a virtual sensor can be used, whereby known characteristics, such as element compression under load, and data related to the material properties of the piezo-electric elements are stored in a microprocessor. This information is used to calculate an estimated position of the piezo-electric actuating means during operation of the auxiliary actuator. It is of course possible to use other types of known position sensors, such as a Hall sensor, for measuring the actual position of the actuator and/or the valve.
Depending on the design of the actuator assembly and/or the accuracy required for determining the position of the actuator, further data relating to the material properties of the linkage and valve assembly may be needed. This information, such as the coefficient of expansion of various parts, would also be stored in the microprocessor.
At the end of each reciprocating cycle of a valve, the auxiliary actuating means 20 can be used to decelerate the moving valve and central pin 8. When the armature 7 of the energised upper electromagnet 3 reaches its end position, a great deal of noise may occur if the armature 7 comes into contact with the electromagnet 3. When a position sensor indicates that the moving mass is approaching its end position, the current actuating the piezo-electric element 21 is reduced in such a way that its retracting movement absorbs the momentum of the moving mass. This is possible due to the fast response time of piezo-electric elements. As an example, a known piezo-electric element requires no more than 50 µs (10^-6 s) to execute a stroke of 0,5 mm.
This feature may also be useful at high engine speeds, should the valve stem 13 temporarily lose contact with the pin 8. As the valve stem 13 is being returned by the lower spring 14 (see Fig. 1), it will strike the pin 8 briefly when regaining contact. Apart from causing a lot of noise, such an impact may damage a piezo-electric element 21 contacting the pin 8. In order to avoid damage to the relatively brittle element 21, the element 21 itself can be used to arrest the movement of the moving mass, as described above.
A second embodiment of the above invention is shown in Figure 3. According to this embodiment the valve stem 13 extends into a recess in the lower part of the armature 7. The lower part of the armature 7 is provided with radial slots 7a which extend in the axial direction of the valve stem 13. The stem 13 is in turn provided with radial projections 7b, such as a through pin, which extend into the slots. This arrangement allows a slight axial movement of the armature 7 relative the valve stem 13. The allowed axial movement is preferably only a few tenths of a millimetre. An end section 30 extends above the armature 7 in order to contact an actuating member 31 of an amplifying mechanical linkage 22 when the valve 33 is in its closed position. The movement of said end section 30 is controlled by a guide 32. In this case the auxiliary actuating means 20 is attached to a casing 34 enclosing the upper and lower electromagnets 3, 4, whereby the actuating member 31 extends through said casing 34. The main valve actuator 1 is provided with springs to hold the valve in an intermediate inactive position. A lower spring 35 acts between the cylinder head 2 and a spring retainer 13a on the end of the valve stem 13, while an upper spring 36 acts between the casing 34 and the armature. The mechanical linkage 22 may comprise a lever action spring, as described below, or some other suitable means.
When the piezo-electric element 21 is actuated, the member 31 will act on the stem 13. The stem 13 will perform a small movement through a guide 37 and cause the valve 33 to lift a short distance from its seat 38, in order to decompress the cylinder (not shown). The channel 39 associated with the valve 33 may be either an intake or an exhaust channel, as described above. As the valve closes, the stem 13 and the end section 30 of the armature 7 approaches the upper magnet 3. The movement of the valve stem 13 will be arrested by the valve reaching its seat 38 just as the armature 7 comes into contact with the upper magnet 3. The slot and pin assembly 7a, 7b in the lower part of the armature 7 prevents the full force of the returning valve from being transmitted to the magnet 3, and the armature itself can be decelerated by the piezo-electric element 21 as described above.
According to a third embodiment of the invention, as shown in Figures 4A and 4B, a valve unit comprises a main valve 40 provided with an auxiliary valve 41. The auxiliary valve includes a central stem 42, which extends through a bore in the main valve stem 43. The central stem 42 protrudes sufficiently from the end section 44 of the main stem 43 to enable it to be actuated by the auxiliary valve actuating means 20. In this embodiment, the armature 7 is rigidly connected to the main valve stem 43. The auxiliary valve 41 is located in the lower surface 45 of the main valve 40 and can be actuated separately by the piezo-electric element 21 when the main valve 40 is in its closed position. The bore through the main valve 40 and stem 43 has an enlarged annular section 46 adjacent the main valve 40. This section 46 is connected to at least one channel 47, which exits in the upper surface 48 of the main valve 40. Figure 4B shows an embodiment with eight channels 47 extending from the enlarged section 46. The total cross-sectional area of the channels 47 must be at least equal to the area of the annular section 46. Figure 4C shows an enlarged view of the upper end of the central stem 42. The end of the stem 42 has an enlarged portion 48, so that a return spring 49 fitted between the end section 44 of the stem 42 and said portion 48. This is to ensure that the auxiliary valve 41 returns to its closed position after having been actuated. Although the spring shown in Figure 4C is a helical spring, other types of springs may be used, e.g. a belleville washer
In operation the main valve 40 is in its closed position, when the auxiliary actuating means 20 is activated. The actuating member 31 of the piezo-electric element 21 acts on the central stem 42 of the valve unit, thereby lifting the auxiliary valve 41 from its seat in the lower surface 45 of the main valve 40. This causes a decompression of the cylinder, as the pressure is released through the enlarged section 46 and the channels 47 of the main valve 40 into the intake or exhaust channel 39.
As the valve closes, the main stem 43 and the end section 44 approaches the upper magnet 3. The movement of the valve stem 43 will be arrested by the valve reaching its seat 38 just as the armature 7 comes into contact with the upper magnet 3. As described above (Fig.1), a gap of a few tenths of a millimetre is sufficient. This prevents the full force of the returning valve from being transmitted to the magnet 3. In this case the armature itself can not be decelerated by the piezo-electric element 21 as described above. Instead the entire valve assembly is arrested immediately before the enlarged portion 48 at the end of the stem contacts the mechanical linkage of the piezo-electric element 21.
A fourth embodiment is shown in Figure 5. According to this embodiment, a separate auxiliary valve actuator 50 is arranged at a suitable location adjacent the cylinder 51. The inlet and exhaust valves 52, 53 are each provided with a main valve actuator as shown in Figure 3. The auxiliary valve actuator 50 comprises a piezo-electric actuator 54, a mechanical linkage 55, an auxiliary valve stem 56 and an auxiliary valve 57. A sealing bushing 56a is provided to prevent exhaust gas from leaking out past the stem 56 of the actuator 54. When actuated, the valve 57 opens and pressure is released through a decompression channel 58 into an exhaust or intake channel 59. The valve 57 can be connected directly to the auxiliary actuator, as it is physically separated from the main valve actuator. However, a piezo-electric actuator of a different construction or shape may require a return spring for the valve. Obviously, the actuator must be located in such a way that it does not interfere with the main valves 52, 53, the piston or any other component of the engine.
Examples of mechanical linkages that can be used to amplify the relatively short stroke of a piezo-electric element are schematically shown in the Figures 6-11. A cross-section through a single lever action spring 22 can be seen in Figure 6. Said spring 22 comprises a first section 61, which is acted on by the piezo-electric element 21, and a second section 62, which acts on the valve stem 13. In order to make the spring 22 as compact as possible it has a generally U-shaped cross-section, with a semi-cylindrical section 63 joining the first and second sections 61, 62. The lever action spring 22 can be pivoted around a pivot point 64 placed in the longitudinal direction of the semi-cylindrical section 63. In this embodiment the pivot point 64 is placed in the upper region of the semi-cylindrical section 63, where it joins the first section 61 of the spring 22.
In order to achieve sufficient leverage, said first and second sections 61, 62 are of different lengths. The leverage is determined by the distance d between a first vertical plane P₁ through the axis of the pivot point 64 and a second vertical plane P₂ through the contact point 65 of the piezo-electric element 21 in relation to the distance D between said first plane P₁ and a third vertical plane P₃ through the axis of the valve stem. A suitable value for the ratio d:D can be calculated using the available stroke of the piezo-electric element 21 and the required valve lift. For instance, if said element 21 has a stroke of 0,2 mm and the required valve lift is 2 mm, the ratio d:D is 1:10 provided it is assumed that the spring 22 does not deflect.
The stiffness of the spring must be sufficient to enable it to transmit the movement of the piezo-electric element to the valve stem. At the same time the inherent characteristics of the spring, in combination with a controlled stroke by said element, allows the movement of the valve to be dampened at the end of its return stroke. In this way the noise created by the armature striking the upper electromagnet in an uncontrolled manner can be reduced.
Figure 7 shows a plan view of a single lever action spring 22, wherein the second section 62 has a generally triangular shape. The total length of the semi-circular section 63 level with the pivot point 64 plus the length of the pivot axes 64a, 64b should not exceed the length of the base of the triangular second section 62. Said second section 62 has its base parallel to the axis of the pivot point 64 and tapers to its point of contact with the valve stem 13. The area 66 of the spring overlapping the upper surface 65 of the end of the valve stem 13 must be sufficient to allow the tip of the spring to move radially across the surface 65 as the valve 13 is moved between its opened and closed positions. The dotted line 67 shows the spring 22 in its inactive position.
In some cases it may be necessary to use more than one piezo-electric actuator, e.g. when the engine is of a high compression type, or if both full and partial valve lift is to be performed by piezo-electric elements. Such an arrangement is shown in Figure 8, in which a pair of identical piezo- electrical elements 81a, 81b act on a pair of opposing springs 82a, 82b to control a valve stem 13.
A further embodiment is shown in Figure 9, in which a single actuator acts on a pair of springs. By interposing a thin plate or disc 91 between a piezo-electric element 21 and a pair of opposing lever action springs 92a, 92b, the valve stem 13 can be actuated. Said element 21 is positioned at the centre of the plate 91, directly above the end surface of the valve stem 13. The plate 91 is in turn positioned on top of the first sections 93a, 93b of the respective springs 92a, 92b. When actuated, the element 21 will act on the plate 91 and cause the springs 92a, 92b to pivot around their pivot points 94a, 94b, so that the second sections 95a, 95b of the spring will depress the valve stem 13.
In order to achieve a more stable assembly of springs and to distribute the force acting on the upper surface of the valve stem more evenly, it is possible to increase the number of lever action springs. Figures 10A and 10B shows an assembly comprising a single piezo-electric element 21 acting on four springs 101, 102, 103, 104 via a plate 105, which is placed on top of the first sections 106, 107, 108, 109 of each spring. The plate 105 is preferably made from a light and stiff material, so that it can follow the fast expanding and contracting movements of the element with little or no deflection. As the outer ends of the triangular shapes of the second sections 110, 111, 112, 113, which are in contact with the valve stem 13 (indicated in Fig. 10A), enclose an angle α of approximately 90°, there will be no interference between the springs. The mountings for the pivot axes 114, 115, 116, 117 are not shown for reasons of clarity.
If more springs are required, an arrangement as shown in Figures 10A and 10B would need springs with a smaller enclosed angle α to avoid interference. However, if said angle is reduced too much, the stiffness of the springs will also be reduced. This problem can be solved by the embodiment shown in Figure 11, wherein the springs are partially overlapping similar to a diaphragm in a photographic lens. In this case an assembly of eight springs 121, 122, 123, 124, 125, 126, 127, 128 is used. A single piezo-electric element acts on all springs via an octagonal or circular plate contacting the upper, first sections of each spring. The valve stem can then be actuated by the pivoting action of the lower, second sections of the springs, as described above.
Although the above examples show assemblies using two, four or eight springs, any number is theoretically possible. More than ten springs would not be practical, however, due to problems with interference between pivot axes and the accumulated thickness of the springs acting on the end of the valve stem.
The stroke of the piezo-electric element can also be extended by means of a hydraulic amplifying arrangement. According to a preferred embodiment, the arrangement (not shown) comprises a cylindrical body placed between the auxiliary actuator and the valve stem. Both the actuator and the cylindrical body are fixed in relation to the cylinder head and a housing in which the actuator assembly is mounted. The cylindrical body contains an axially extending annular cavity, whereby an annular piston is slidably arranged in the upper end of said cavity. The piston or a part thereof extends out through a first end surface of the cylindrical body. Said piston can be directly or indirectly attached to the piezo-electric element, so that the element can act on the piston. If the piston is not directly connected to the piezo-electric element, a return spring is provided to ensure that the piston is returned to its inactive position. Said annular cavity is connected to a central, axially extending cylindrical cavity by means of one or more substantially radial passages. In order to keep the hydraulic amplifier compact, the passage/-s are arranged to exit from the lower end of the annular cavity, to lead radially inwards and upwards, and enter the central cavity at its upper end. The central cavity contains a further slidably arranged, central piston, shaped like a cylindrical pin. The central piston extends through a second end surface at the lower end of the cylindrical body, opposite said first end surface. When the valve is in its upper, closed position, the central piston is in contact with the valve stem.
The cavities and passages enclosed by the annular and the central pistons is filled with a hydraulic medium, such as hydraulic oil, water with anti-freezing and/or anti-corrosive additives, or some other suitable fluid. In order to prevent hydraulic fluid from leaking, both pistons must be sealed around their circumference where they exit from the end surfaces of the cylindrical body. This sealing function can be achieved either by using sealing bushings, or by manufacturing the pistons and their corresponding cavity wall surfaces to very close tolerances.
In operation, a control signal to the piezo-electric element causes it to act on the annular piston. Said piston forces hydraulic fluid through the connecting passages into the central cavity, causing the fluid to act on the central piston and the valve stem in order to perform an initial opening of the valve. The amplifying ratio is proportional to the ratio between the cross-sectional areas of the annular and central cavities. A relatively short stroke by the piezo-electric element and the annular piston will therefore cause an amplified stroke for the central piston, due to the displaced volume from the annular to the central cavity.

Claims

Method for operating valves in an internal combustion engine, which engine comprises at least one intake and exhaust valve per cylinder, a main valve actuating means (1) for opening and closing each valve, and electronic control means (26) for controlling said valve actuating mechanism, characterized in that an auxiliary valve actuating means (20) is provided in addition to the main valve actuating mechanism (1), and that said auxiliary actuating means (20) is actuated before the main actuating means (1) in order to cause a decompression of the cylinder.
Method for operating valves in an internal combustion engine according to claim 1, characterized in that the auxiliary valve actuating means acts directly or indirectly on the valve for initiating and/or arresting valve motion during the start of or end of a valve operating cycle respectively.
Method for operating valves in an internal combustion engine according to claim 2, characterized in that the arresting motion performed by the auxiliary actuating means (20) causes a gradual deceleration of the valve stem (13), so that its velocity is zero or near zero as it reaches its end position.
Method for operating valves in an internal combustion engine according to claim 1 or claim 2, characterized in that the valve motion is initiated or arrested using a piezo-electric element (21).
Method for operating valves in an internal combustion engine according to any one of the above claims, characterized in that the main valve actuating mechanism (3, 4) is operated using at least one electromagnet.
Method for operating valves in an internal combustion engine according to claim 1, characterized in that the auxiliary valve actuating means is arranged in a cylinder wall of the engine and acts on a separate auxiliary valve (57).
Valve operating mechanism for an internal combustion engine, which engine comprises at least one intake and exhaust valve per cylinder, a main valve actuating means (1) for opening and closing each valve, and electronic control means (26) for controlling said valve actuating mechanism, characterized in that an auxiliary valve actuating means (20) is provided in addition to the main valve actuating means (1), which means is arranged to act on a valve (33, 40, 57) in order to effect a decompression of the cylinder before the main valve is actuated.
Valve operating mechanism for an internal combustion engine according to claim 7, characterized in that the auxiliary valve actuating means (20) is arranged to act directly on a stem (13) on the main valve (33).
Valve operating mechanism for an internal combustion engine according to claim 7, characterized in that the main valve (40) has a hollow stem (43) and the auxiliary valve actuating means (20) is arranged to act on an auxiliary valve (41) running through said stem.
Valve operating mechanism for an internal combustion engine according to claim 7, characterized in that the auxiliary valve actuating means (20) is arranged to act on a separate valve (57) arranged in a wall of the cylinder (51)
Valve operating mechanism for an internal combustion engine according to any of the claims 7-10, characterized in that the auxiliary valve actuating means (20) is a piezo-electric actuating means (21), comprising multiple individual piezo-electric elements (24).
Valve operating mechanism for an internal combustion engine according to claim according to claim 11, characterized in that said control means comprises a microprocessor (26), to which data relating to the operation of said engine is fed, and which is programmed to control the position of said piezo-electric actuating means (21) based on said data
Valve operating mechanism for an internal combustion engine according to claim 11 or 12, characterized in that a sensor is arranged to determine the position of the piezo-electric actuating means, which position is fed back to said microprocessor.
Valve operating mechanism for an internal combustion engine according to claim 13, characterized in that the sensor is a virtual sensor, whereby known characteristics and material properties are stored in the microprocessor (26) in order to calculate the position of the piezo-electric actuating means.
Valve operating mechanism for an internal combustion engine according to claim 13, characterized in that the sensor comprises a number of threads (23) each electrically connected to the same number of individual elements (24) of the piezo-electric actuating means (21), whereby a signal (27) proportional to the position is obtained as the piezo-electric actuating means (21) is subjected to a compressive load.
Valve operating mechanism for an internal combustion engine according to any one of the above claims, characterized in that the auxiliary actuating means (21) acts on the valve via an amplifying mechanical linkage (22).
Valve operating mechanism for an internal combustion engine according to claim 16, characterized in that the mechanical linkage comprises one or more U-shaped lever action springs (22; 82a,82b; 101, 102, 103, 104) each a pair of sections (61,62) of different lengths, corresponding to a predetermined amplifying ratio.
Valve operating mechanism for an internal combustion engine according to claim 17, characterized in that each spring (22) is actuated by a single auxiliary actuating means (21).
Valve operating mechanism for an internal combustion engine according to claim 17, characterized in that all springs (22; 82a,82b; 101, 102, 103, 104) are actuated by a common auxiliary actuating means (21).
Valve operating mechanism for an internal combustion engine according to claim 19, characterized in that said common actuating means (21) acts on a plate (91; 105) which is positioned in contact with all said springs (22; 82a,82b; 101, 102, 103, 104)
Valve operating mechanism for an internal combustion engine according to any one of the above claims, characterized in that the resultant valve lift caused by the auxiliary actuating means (21) is in the range 1-2 mm.
Valve operating mechanism for an internal combustion engine according to any one of the above claims, characterized in that the ratio between the valve lift caused by the auxiliary actuating means (21) and the main valve actuating means (1) is in the range 1:4 to 1:10.
Valve operating mechanism for an internal combustion engine according to any one of the above claims, characterized in that the main valve actuating mechanism (1) comprises one or more electromagnets (3, 4).
Valve operating mechanism for an internal combustion engine according to any one of the above claims, characterized in that each valve (13, 43) is spring loaded towards its closed position.
Valve operating mechanism for an internal combustion engine according to any one of the above claims, characterized in that the auxiliary actuating means is arranged to act directly or indirectly on the valve (13, 43) for initiating and/or arresting valve motion during the start of or end of a valve operating cycle respectively.