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Title:
ELECTROMECHANICAL CLUTCH ACTUATOR
Document Type and Number:
WIPO Patent Application WO/2004/109140
Kind Code:
A1
Abstract:
This invention describes a clutch actuator based on electric motor and generator machines, intended to be used in all motor vehicles in general. Basically it is an innovative way to produce heavy forces, with small displacement, to actuate conventional vehicle's clutch spring. The said force is directly supplied by the magnetomotive force developed in the air-gap (3) of the electrical machine (1,2,3). Depending if the outside part (1) is connected to the clutch housing in permanent rotation, or if it is connected to the stationary main housing, the electrical machine will work like a generator, or as a motor, respectively. Whenever the electrical machine is turned on, closing an electric circuit, air-gap (3) torque will be developed and the central part (2) will have a small angular displacement, that is converted into linear displacement by means of two large pitch screw threads (5,6,7), to have clutch spring actuated.

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Inventors:
ALBUQUERQUE JOSE MANUEL BRAGA (PT)
Application Number:
PCT/PT2004/000010
Publication Date:
December 16, 2004
Filing Date:
June 02, 2004
Export Citation:
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Assignee:
ALBUQUERQUE JOSE MANUEL BRAGA (PT)
International Classes:
F16D27/00; F16D28/00; H02K26/00; (IPC1-7): F16D27/00
Domestic Patent References:
WO1989004927A11989-06-01
WO1999064756A11999-12-16
Foreign References:
DE19920661A12000-11-09
PT00300008W
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Claims:
CLAIMS
1. Electromechanical clutch actuator, comprising two major systems, being one electromagnetic and another mechanical: a) The electromagnetic system comprises an electrical machine (1,2, 3), aimed to create magnetomotive force in the airgap (3), composed by an outside part (1), that is a laminated piece of iron, composed by several coils (9) (electromagnets (9) ), or permanent magnets (10). The central part (2) of the said electrical machine (1, 2, 3) also is a laminated piece of iron, wire wound, composed by several coils (8), or permanent magnets (10). Between the outside part (1) and the central part (2) there is an airgap (3), where the electromechanical energy conversion takes place. These above three parts are the socalled electrical machine (1,2, 3). According to this invention the central part (2) has some angular displacement (14) that, in general, is a fraction of one complete revolution, back and forward. Thus, according to this invention, the magnetomotive force developed in the airgap (3) of the electrical machine (1,2, 3) creates electromagnetic torque over the central part (2) and that central part (2) directly actuates the mechanical system. Being the central part (2) the actuator himself. b) The said mechanical system is composed by a set of two large pitch screw threads (5,6, 7), used to convert angular displacement (14) into linear displacement (15). It is composed by three parts, being one the innermost part (5), which must be the fulcrum, attached to the gearbox main housing (22). That fulcrum (5) comprises the first large screw thread drawn in its exterior diameter and it could be left or right handed, depending on vehicle's engine sense of rotation. The outermost part (7) is rigidly attached to the central part (2) of the electrical machine (1,2, 3), by means of thermal expansion or any other means. That outermost part (7) comprises the second large screw thread drawn in its interior diameter. This outermost part (7) is the one that will receive the torque and the angular displacement (14) from the central part (2), when the electrical machine (1,2, 3) is turned on. This outermost part (7) will have a reaction force against the fulcrum housing (22), by means of a conventional axial bearing (20). The double screw thread central part (6), of the screw thread system, is positioned between the two above mentioned ones (5,7). Therefore, both counterparts of the two large screw threads must be drawn in both sides of this central part (6), exterior and interior diameter respectively. It will be this double screw central part (6) that will perform the linear displacement (15) in order to actuate the clutch spring (11) and, therefore, it must have a conventional axial bearing (21), assembled on the side facing the clutch spring (11). According to this invention, the two large screw threads drawn in the central part (6) must be opposite, which means that when one is a left screw thread the other must be a right screw thread, and viceversa, depending on vehicle's engine sense of rotation.
2. Electromechanical clutch actuator according to Claim 1, characterised in that, by means of the double large pitch screw thread system (5,6, 7), the central part (2) doesn't have any linear displacement (15) and therefore it will be permanently aligned with the outside part (1), keeping airgap (3) effective area unchanged, which is very important for the electrical machine (1,2, 3) correct work. Also, if both screw thread pitch angle are equal, the required electromagnetic torque the central part (2) must deliver, to actuate the clutch spring (11), for any given angular displacement (14) of the central part (2), will be half the value compared to the case that only one screw thread is used to convert angular (14) to linear (15) displacement.
3. Electromechanical clutch actuator according to Claim 1 and 2, characterised in that friction losses in the double pitch screw thread system (5,6, 7) can be significant if conventional trapezoidal thread screws are used. For best performance ballscrews type of screws are recommended instead of trapezoidal thread screws. A ballscrew is a screw whose thread is a sphere rolling in a helical groove cut in the screw shaft. Instead of the usual sliding friction of conventional trapezoidal screws, the new friction coefficient is rolling friction. The double pitch ballscrew thread system (5,6, 7) works exactly the same way as the double pitch screw thread system (5,6, 7) previously described, but instead of trapezoidal thread it is used ballscrew threads, just to have better efficiency in the airgap (3) energy conversion.
4. Electromechanical clutch actuator according to Claim 1,2 and 3, characterised in that the central part (2) of the electrical machine (1,2, 3) is the main actuator himself, because it has additional freedom degrees, due to the double pitch screw thread system (5,6, 7) upon whom the said central part (2) sits on.
5. Electromechanical clutch actuator according to Claim 1,2, 3 and 4, characterised in that the power required to actuate the clutch spring (11) could be supplied, in real time, by vehicle's engine mechanical angular velocity and torque, by means of having the outside part (1) of the electrical machine (1,2, 3) permanently fixed to the clutch disk housing (25) that permanently rotates. Such electrical machine (1,2, 3) is working as a generator and creating magnetomotive force in the airgap (3) when it's turned on, hence producing the electromagnetic torque required to have clutch actuation according to Claim 1. According to this Claim no brushes, or any other type of electrical rotating contacts, are needed for the said electrical generator (1, 2, 3).
6. According to Claim 5, none of the electrical energy generated by the said generator (1,2, 3) is useful. Nevertheless electricity is required and it must be proportional to the torque developed in the airgap (3). The generated electricity is to be wasted producing heat, with no particular use to drive anything. But an amount of heat, equivalent to the mechanical power needs, must be lost to have steady state magnetomotive force in the airgap (3) and clutch spring (11) actuation.
7. Electromechanical clutch actuator according to Claim 1,2, 3 and 4, characterised in that the outside part (1) of the electrical machine (1,2, 3) could be stationary, permanently fixed to the main housing (22), and the said electrical machine (1,2, 3) will work as a motor, back and forward, directly actuating the central part (2) a fraction of a turn, to have clutch spring (11) actuation. To have motor action and magnetomotive force developed in the airgap (3), the outside part (1) of the electrical motor (1,2, 3) must be supplied (23) by 2phase or 3phase AC current, or else pulsed/switched polyphase DC current. To be compatible with the small size requirements, the central part (2) also must develop its own magnetic poles, by means of AC or DC current supplied (4) to electromagnets (8), or else by its own sources of magnetic field using permanent magnets (10) instead. The central part (2) of the electrical motor (1,2, 3) directly actuates the mechanical system of Claim 1,2, 3 and 4. According to this Claim no brushes, or any other means of electrical rotating contacts, are needed for the said electrical motor (1,2, 3).
Description:
ELECTROMECHANICAL CLUTCH ACTUATOR DESCRIPTION This invention describes a clutch actuator. It relates to motor vehicle automated clutch systems and it is based on the principles of the rotary electric motor and generator machines.

It is intended to be used in all motor vehicles in general, from small automobiles to heavy- trucks, whenever shift gears are to be fully automated via automatic clutch operation with short shift time. This actuator is to be used in automated manual transmissions systems, based on conventional spur gear transmissions and dry clutches. Although the aim target is dry clutches that pushes a spring to have disk (12) release, nothing constrains the use of this same mechanism with wet clutches oil immersed, in motorbikes for instance, or else pulling the clutch spring, as the invented system is bi-directional, so that displacement and force can be easily reversed with minor axial bearing and fulcrum adjustments.

The aim of the present invention is to virtually eliminate the conventional clutch pedal actuated by vehicle's driver, in such a way that it can automatically perform the force, the displacement and the same function of a conventional clutch pedal. By means of the present invention, the vehicle's conventional clutch pedal, used to disconnect the engine rotational speed from vehicle's transmission, is actuated by magnetomotive force and fully controlled by means of the associated electromagnetic circuits. Hence, this new clutch actuator is aimed to simplify operation, increase driving comfort and improve safety. When used with computer controlled systems it can play an important role in reduction of fuel consumption and exhaust emissions.

The invention describes an electromechanical system, invented to apply force on the powerful spring (11) of conventional diaphragm clutches. The clutch spring (11) force depends on the vehicles engine rated torque and clutch design, but it's always a heavy force.

The required force to drive this new actuator is provided by the electromagnetic torque (magnetomotive force) developed within the air-gap (3), which exists between a rotary part and a stationary part of the electrical machine (1,2, 3). In order to generate the said electromagnetic torque, this invention is based on Alternating Current (AC) machines, including pulsed Direct Current (DC) machines, that could be run like a motor, or like a generator, no matter the type of machine. According to this invention it is the electromagnetic torque created in the electrical machine (1,2, 3) air-gap (3) that is useful for the clutch actuator.

According to this invention the said force can be produced by vehicle's engine torque, wasting fuel at the moment the clutch spring (11) is actuated and whenever it stays actuated.

That is the case shown in Fig. 2 and Fig. 5, where the outside part (1) of the electrical machine (1,2, 3) is coupled to vehicle's engine fly-wheel (24), being mechanical power converted onto a magnetic field that produces the said electromagnetic torque. Therefore the electrical machine (1,2, 3) is working as a generator and electrical power is given out of the system. Or else, the same said force can be produced by an external electrical power- supply, wasting vehicles battery energy, to produce the same effect of a rotating electromagnetic torque developed in the electrical machine (1, 2, 3) air-gap (3). The later is shown Fig. 6-7, where the electrical machine (1,2, 3) is working like a motor, giving mechanical power to the clutch actuation system.

No matter how electrical machine (1,2, 3) power is flowing, motor or generator. According to this invention, the important matter is the electromagnetic torque developed by the electrical machine (1, 2, 3), within its air-gap (3), because the mechanical system upon whom the central part (2) of the electrical machine (1,2, 3) sits converts the said air-gap (3) electromagnetic torque into force over the clutch spring (11). Thus, the force over the clutch spring (11) can be controlled regulating the torque developed in the air-gap (3).

The electrical machine (1,2, 3) is integrated in the mechanical system, so that the central part (2) of the electrical machine (1, 2, 3) can be regarded as a mechanical actuator, whose angular displacement (14) is a small rotation, back and forward, of the said central part (2).

Therefore, the electrical machine (1,2, 3) is directly involved in the actuation system, by means of the electromagnetic torque generated during mechanical energy conversion to electric energy, and vice-versa. The conversion occurs in the air-gap (3), between mechanical and electrical energy, and that energy conversion is the basic working mechanism of any rotary electrical machine. Motor or generator, it simply defines the sense of electrical and mechanical power flow.

The mechanical system is composed by the central part (2) of the electrical machine (1,2, 3), plus a couple of axial bearing (20,21) to support the axial load, and a double large pitch screw thread system (5,6, 7). The double pitch screw tread system (5,6, 7) is the fundamental system to convert angular displacement (14) into linear displacement (15). Also to change the amount of force transmitted both sides of the screw thread system (5,6, 7). The linear spring displacement (15) is the usual displacement required to actuate the clutch. The angular displacement (14) is the angular displacement of the central part (2) of the electrical machine (1,2, 3), rolling upon the large pitch screw thread system (5,6, 7), back and forward.

The said angular displacement (14) of the central part (2), and its associated angular speed, is not the angular motion that turns the electrical machine (1,2, 3) on. The said angular displacement (14) must be regarded as a reaction effect. It is a back and forward motion, of about half a turn, more or less, against the force of the clutch spring (11). The main angular speed, or the frequency that induces voltages and makes the electrical machine (1,2, 3) work, must be supplied by vehicle's engine rotation in the generator approach, or by an electric AC, or DC pulsed, source of electricity in the motor arrangement. Any case to create electromagnetic rotating field in the air-gap (3), no matter the source of that rotating magnetic flux.

Depending on the approach used to create electromagnetic rotating field in the air-gap (3), generator or motor, the outside part (1) of the electrical machine (1,2, 3) must be a rotating part, fixed to the rotating clutch disk housing (25), or a stationary part fixed to the main housing (22) connected to vehicle's chassis. This is the main conceptual difference between both approaches, motor or generator, and the conceptual difference between Fig. 2 plus Fig. 5 both showing a generator arrangement ; and Fig. 6-7 both showing a motor arrangement.

For the generator arrangement the electricity produced by the generator is not usable. All the electricity generated must be dissipated on convenient loads (16,17, 18), to produce heat.

The important roll of the generator itself concerns the magnetic forces induced by the energy conversion in the air-gap (3), not the electricity it self. It is the electromagnetic developed torque that is used to actuate the clutch spring (11); not the electricity generated which is to be wasted, producing heat with no use.

In the motor approach the outside part (1) of the electrical machine (1,2, 3) is permanently stopped, fixed to the main housing (22), like shown in Fig. 6-7. To create the required electromagnetic rotating field in the air-gap (3) electricity must be supplied to the motor by an external power-supply, ultimately based on vehicle's battery. The only moving part of the system is the central part (2) and that part only moves a small angular displacement (14), back and forward. Hence, the electrical machine (1,2, 3) must be a conventional motor whose rotor trends to be locked. The fact requires special kind of motors, able to rotate a little and then hold position, at any position, like stepper motors do.

Because the angular displacement (14) is small, the central part (2) of the electrical machine (1,2, 3) is herein considered a stopped part. The central part (2) is concentric with clutch axis, face on to the clutch spring (11), as shown in Fig. 2 and Fig. 5-7. The central part (2) is mounted upon two large pitch concentric screw threads (5,6, 7). This screw system, shown in Fig. 4, is intended to convert a relatively small angular displacement (14) of the central part (2) onto an even much smaller linear displacement (15) of the clutch spring (11). The transmitted forces are inversely proportional by energy conservation Law.

The double pitch screw system (5,6, 7) works like any conventional screw system. It basically screws the central part (2) over a fulcrum. Therefore, the screw pitch can control the transmitted force. Two screw threads (5, 6,7) cut by half the linear displacement (15) and doubles the force acting on the spring (11). But fundamentally, it is required to keep the central part (2) aligned with the air-gap (3). Otherwise, if a single screw is used, the axial displacement could cause such a bad air-gap (3) misalign that the fundamental electromagnetic torque would be lost. Or else the length of the machine must increase to account for the misalign, which happens to be the double axial displacement for the same angular displacement (14) of the double screw system (5,6, 7).

To turn on-off the electrical machine (1,2, 3), the central part (2), or the outside part (1), must be magnetised and demagnetised, closing or opening an electric circuit. Again it depends if the base machine is a generator, as shown in Fig. 2 and Fig. 5, or the motor approach shown in Fig. 6-7. Theoretically any rotary electrical machine (1,2, 3) that could work as a motor, or as a generator, can provide the required electromagnetic torque in the air-gap (3). It only depends on the machine size, which is the most important constrain of this invention.

Although the basic idea and the working mechanism of the invention is straightforward and simple to understand, due to the fact that electromagnetic torque changes with mechanical rotation speed, and because full controllable force upon the clutch spring (11) is required, the right description; the basic design; the physical size and the control strategy of the electrical machine (1,2, 3) could be a very difficult task. An external electronic auxiliary system is need to accurately control the electrical power, and the quality of the power flowing through the electrical machine (1,2, 3), including the design of the right load to apply on the generator's terminals. These subjects are to be covered in the detailed description of the invention.

By means of present invention, manual speed gear systems can be converted into automated transmission systems. For instance, actuated by a push button onto drivers steer wheel, or by a programmable logic control (PLC), etc. If aimed for the fastest possible response, a good design allows the clutch actuator to act in less time then the driver could normally change a manual gear. Hence, a trigger device could be connected to the conventional gearstick and all the driver has to do is shift gears, directly coupled to the manual gearbox.

DETAILED DESCRIPTION OF THE INVENTION The majority of clutch actuation system, produced Worldwide, must compress and release a spring (11). That spring, usually a diaphragm spring (11), is actuated by an axial force applied around the axis of the clutch disk, by means of an axial bearing (21), as shown in Fig. 1-2 and Fig. 5-7. The estimated force a clutch actuation system must produce could be about 800 N (80 kg) for the smallest automobiles, about 1500 N (150 kg) for large passenger cars, 2500 N (250 kg) for high performance vehicles and about 4000 N (400 kg) for heavy- trucks, or even more.

This invention describes an innovative way to produce those heavy forces, required to actuate vehicle's engine clutches produced Worldwide. According to the present invention, that force is directly supplied by magnetomotive force developed in the air-gap (3) of an electrical machine (1,2, 3). Depending if the outside part (1) of the said electrical machine (1,2, 3) is connected to the clutch housing (25) in permanent rotation, or if it is connected to the stationary main housing (22), the electrical machine (1,2, 3) will work like a generator, or as a motor, respectively. Whenever the electrical machine (1,2, 3) is turned on, by means of closing an electric circuit, electromagnetic torque will be developed in the machine air-gap (3) and we can have force applied over the clutch spring (11), to have clutch disk (12) released.

This invention comprises two major systems, being one mechanical and another electromagnetic. Fig. 1-7 shows and describes the mechanical system. The mechanical system is basically composed by a set of two large pitch screw threads (5,6, 7), used to convert angular displacement (14) into linear displacement (15).

All Fig. 1-7 herein presented are schematic drawings of a working example and must be regarded as mere schematics, not the final drawings. Fig. 1 shows the basic elements of this invention and Fig. 1 is fully integrated into Fig. 2 and Fig. 5-7. The Fig. 2 and Fig. 5-7 shows a more complete description of the innovative clutch actuation system, integrated into the conventional clutch housing, where it is aimed to be placed replacing the conventional system. The Fig. 3 shows another view of the same system. The Fig. 2 and Fig. 5 relate to the generator arrangement and Fig. 6-7 to the motor arrangement. The only conceptual difference between Fig. 2 plus Fig. 5 and Fig. 6-7 is the point where the outside part (1) of the electrical machine (1,2, 3) is connected: the clutch disk housing (25) in generator arrangement; or to the main housing (22) in the motor approach.

According to this invention the central part (2) of the electrical machine (1,2, 3) is assumed to be stopped, but in fact it does have some angular displacement (14) that could be something between 90 degrees and 360 degrees, more or less, back and forward, depending on the particular design. More angular displacement (14) will result in a poorer response time of the clutch actuation system, but it will benefits in much less rated power, that could be very useful when very high clutch actuation forces are required, or else, when a small actuation system is the aim.

When the electrical machine (1, 2,3) is energised, electromagnetic torque is created between the central part (2) and the outside part (1), via the small air-gap (3) between them. In the generator approach the electromagnetic torque causes the central part (2) to rotate in the same direction of the outside part (1) and, if bigger enough to surpass the clutch spring (11) force, it will cause the central part (2) to accelerate and have the predefined angular displacement (14). That predefined angular displacement (14) is aimed to actuate the mechanical system, producing force and compressing the clutch spring (11). In the motor approach a similar electromagnetic torque must be created, with the same sense, by electric current supplied (23) to the stationary outside part (1).

The mechanical system is based on a set of two large pitch screw threads (5,6, 7), also called double screw threads (5,6, 7), used to convert rotation into linear displacement (15), and vice- versa. Fig. 4 shows a perspective of the double screw threads (5,6, 7). Basically it is composed by three parts, being one the innermost part (5), which will be the fulcrum, attached to the main housing (22). That fulcrum (5) comprises the first large screw thread, drawn in its exterior diameter, and it could be left, or right handed, depending on the actual actuation system sense of rotation. The outermost part (7) is rigidly attached to the central part (2), by means of thermal expansion or any other means. That outermost part (7) comprises the second large screw thread, drawn in its interior diameter. This outermost part (7) is the one that will receive the torque and angular displacement (14) from the central part (2), when the electrical machine (1,2, 3) is energised.

The double screw thread central part (6) is positioned between the two above mentioned ones. Therefore, both counterparts of the two large screw threads must be drawn in both sides of this central part (6), exterior and interior diameter, respectively. It will be this double screw central part (6) that will perform the linear displacement (15) in order to actuate the clutch spring (11) and, therefore, it must have a conventional axial bearing (21) mounted on the side facing the clutch spring (11), as shown in Fig. 1-2 and Fig. 5-7.

According to this invention, the two large screw threads drawn in the central part (6) must be opposite, which means that when one is a left screw thread the other must be a right screw thread, and vice-versa, depending on the clutch actuation system sense of rotation. Fig. 1-7 assumes that vehicle's clutch actuation system rotates clockwise, when looking at Fig. 3.

Therefore, the screw thread drawn in the fulcrum (5) must be right handed, as shown in Fig. 4, because the outermost part (7), attached to the central part (2), will rotate clockwise when the electrical machine (1,2, 3) is energised clockwise. Because both screw threads must be opposite, as previously stated, the screw thread drawn in the outermost part (7) must be left handed, as shown Fig. 4.

When the electrical machine (1,2, 3) is turned on, the central part (2) will accelerate and will trend to follow the air-gap (3) electromagnetic torque, producing the desired angular displacement (14), up to the point where it must be stopped, by means of any kind of limit device, not shown. That limit device could be positioned in the main housing (22), or it could be provided by the clutch course limit itself. When the angular displacement (14) occurs, the central part (2) and the outermost part (7) of the double screw thread system (5,6, 7) will exerts a force to the right, as seen in Fig. 1-2 and Fig. 5-7, against the fulcrum housing (22), by means of the axial bearing (20).

At same time, the central part (2) attached to the outermost part (7) will exert an equal force, with opposite direction, onto the double screw central part (6) of the double screw thread system (5,6, 7), against the clutch spring (11). Therefore, according to Fig. 1-2 and Fig. 4-7, when the central part (2) has an angular displacement (14) clockwise, the double screw central part (6) of the double screw thread system (5,6, 7) will be linearly displaced (15) to the left, in order to compress and actuate the clutch spring (11). When the electrical machine (1, 2,3) is turned off, the clutch spring (11) elastic energy will provide total, or partial, position recover of the actuation system.

In order to convert angular (14) to linear displacement (15), two screw threads (5,6, 7) is required. The system won't work correctly if only one screw thread was used, because two screw threads allow that the central part (2) doesn't have to be displaced linearly.

Independently of screw threads pitch angle, only the double thread central part (6) suffers linear displacement (15) and, therefore, the central part (2) will be permanently aligned with the outside part (1), which is very important for electrical machine (1,2, 3) correct work.

Because always exist a reaction force against any displacement, the reaction force against clutch spring (11) must be sustained by an axial bearing (20), positioned between the fulcrum (5) and the outmost part (7), as shown in Fig. 1-2 and Fig. 5-7. Another important benefit of the double screw threads system (5,6, 7) is that it cut by half the displacement (15). Hence, it doubles the force acting on the spring (11).

For instance, if the clutch actuation system must produce a linear displacement (15) of about 0.01 metre, onto the clutch spring (11), and if the angular displacement (14) of the central part (2) is defined to be about 240 degrees, assuming equal pitch threads for both screw threads and a medium diameter of 0.05 metres for the double screw central part (6), then the pitch angle thread of each screw must be of about 9.6 degrees. If only one screw thread was used, instead of the double screw thread system (5,6, 7) shown in Fig. 4, then the pitch angle of the single screw thread system must be about 4.9 degrees. Therefore, when the electrical machine (1,2, 3) is turned off, the larger angle will have faster recovery response, based on clutch spring (11) elastic energy recover, then a smaller pitch angle has. Double screw thread system (5,6, 7) greatly improves recovery response time.

Based on Physical Law's, the required energy (in Joules), to mechanically actuate the clutch spring (11), could be majored by calculating the clutch spring (11) force (in N) times the clutch needed displacement (15) (in metre). On the other hand, the energy required to completely displace the central part (2), a given angular displacement (14), will be mechanically calculated as the electromagnetic torque (N-m) times the angular displacement (14) (rad) of the central part (2). Energy conservation Law states that in an ideal system, without friction losses onto the double screw threads (5,6, 7), both energies must be equal.

Hence the electromagnetic torque required to actuate the clutch spring (11) can be calculated.

In a static energy balance, if for instance the nominal clutch spring (11) force is 1500 N (150 kg) and the required displacement (15) is 0. 01m, the energy involved will be 15 Joules, plus friction losses. To be more precise in the estimation, the actual curve for the clutch spring force (11) versus displacement (15) must be followed. Here it was assumed the worse case, of maximum force all the travelled displacement (15). The double screw thread system (5,6, 7) transmits those 15 Joules of energy to the air-gap (3). The air-gap (3) mechanical energy is torque times air-gap (3) angular displacement (14), adding friction losses. Friction losses in screw threads causes resistance against motion and creates additional mechanical resistive torque, against central part (2) angular motion (14). Finally, mass inertia of the central part (2) also creates a very large and important mechanical resistance, so that a large additional amount of torque is required to accelerate the central part (2) mass inertia.

Without being too much descriptive it can be found that friction losses also are significant. So special type of screw threads might be required to reduce the size of the electrical machine (1,2, 3). For better performance ballscrew type of screws is required for the double pitch screw thread system (5,6, 7). Ballscrew threads can have friction coefficient as low as 0.01 or better and that greatly improves response time. Therefore, ballscrews are recommended instead of conventional trapezoidal thread screws. A ballscrew is a screw whose thread is a sphere rolling in a helical groove cut in the screw shaft. Instead of the usual sliding friction coefficient of conventional trapezoidal screws, the new friction coefficient is rolling friction.

The same situation occurs with ball bearings instead of sliding surfaces.

Doing the mechanical energy balance based on the given example, in terms of torque (N-m) times angular displacement (14) (rad) of the machine central part (2), it can be found that mechanical energy required in the air-gap (3) can be a value of about 30 Joules to have actuation time in 100 milliseconds (ms), which means that the power required to fully actuate the clutch spring (11) is 300 Watts (W). Basically it has been assumed the double of the energy required for the clutch spring (11) alone, which means that half the energy is consigned to mass inertia acceleration and screw threads friction losses.

That total energy of 30 Joules converted by the double screw thread system (5,6, 7) into torque, over a displacement of 240 degrees (3/2 rad), gives a torque of 6.4 N-m applied in a radius of about 0.075 m, which is the estimated air-gap (3) radius. Hence, the shear force in the air-gap (3) is a value of 85 Newtons (N). Assuming that air-gap (3) width is a value of 0.02 m, the air-gap (3) area will be 0.0094 m2, for the example given and as shown in Fig. 1-2 and Fig. 5-7, approximately. So the required air-gap (3) shear stress is 9.0 kPa (KiloPascal).

If instead of a maximum angular displacement (14) of 240 degrees only 120 degrees were considered, the new air-gap (3) shear stress will be 20.3 kPa. Therefore, the larger the angular displacement (14) the smaller will be the air-gap (3) shear stress required.

Nevertheless, the situation is not so linear, because time due to angular acceleration of the central part (2) mass inertia changes inversely with angular displacement (14). Therefore, the above values must be regarded as general values, which must be recalculated based on the actual energy and response time required.

The electrical machine (1, 2,3) must produce electromagnetic torque to balance the said required shear stress. The minimum torque the electrical machine (1, 2, 3) must produce in the air-gap (3) is the torque required to overcome clutch spring (11) force plus friction losses.

Any excess torque given by the electrical machine (1, 2,3) will make the central part (2) to accelerate, up to the end of the angular displacement (14) allowed, knocking at a mechanical stop not shown. The larger the electromagnetic torque the electrical machine (1, 2,3) can provide, the fastest will be the actuation of the clutch spring (11).

To evaluate the electrical machine (1, 2,3) capabilities a constant maximum torque value must be provided, no matter vehicle's engine speed. This is not a problem when designing the electrical machine (1,2, 3) for the motor arrangement, because vehicle's engine speed rotation is not involved in such design. But in the generator approach vehicle's engine mechanical speed dictates electrical machine (1,2, 3) induced voltage, current and torque.

Hence, the generator approach has added complexity and requires special attention.

Because the electrical machine (1,2, 3) electromagnetic torque has a radius of application (the air-gap (3) radius), the air-gap (3) shear force can be calculated and then the shear stress value also calculated (dividing the shear force by the actual air-gap (3) area). The shear tress value is a very convenient way to compare the require electrical machine (1,2, 3) capabilities with known electrical machines. Based on electrical machines data specifications and its physical dimensions, it is possible to calculate the air-gap shear stress capabilities at any frequency (or rotation speed). Usually, maximum shear stress can be regarded as a constant value for a given electrical machine and, Physically, it translates to the amount of transverse force that can be sustained between two solenoids, or magnets, by unit of air-gap (3) area, at a given air-gap (3) distance, up to the magnetic rupture point. Usually shear stress value is a little bit smaller at low speeds and almost constant at higher speeds, mostly depending on excitation field ; machine physical size and type of construction. The shear stress is proportional to current intensity and directly related to the reluctance concept.

One of the most important figures to be noticed is that the power required to have clutch actuation, in 100 ms, is 300 W for the example given, and the required electromagnetic torque developed in the air-gap (3) could be a value of about 10 N-m. On the other hand, assuming the generator arrangement, the said torque of 10 N-m must be given with the generator rotating at idle, and also at the maximum vehicle's engine speed. From the mechanical point of view, the rotation speed of the internal combustion engine usually starts at 800 RPM (84 rad/s) and could end at 7000 RPM (733 rad/s). The outside part (1) of the generator is fixed to the clutch housing (25), rotating at that same speed. Hence, the electrical frequency generated will be 13.3 Hz at idle and 116.7 Hz at maximum speed, assuming one pair of poles for the generator as a mere basis.

For the mechanical clutch actuation system it doesn't matter the vehicle's engine rotation speed. The mechanical system only requires a constant value of torque to be fast. Since it has been assumed 10 N-m for the example given, from the mechanical point of view of the external system (which is the outside part (1) of the generator), being: Power (W) = Torque (N m) x angular speed (rad/s); we find values of 838 W at idle and 7330 W at maximum speed, of maximum power involved. A figure of 7330 W is equivalent to an electrical machine of about 10 CV (10 HP), which must be a very large and heavy machine, impossible to fit in the actual clutch housing (22).

From the clutch actuation system point of view, starting from the central part (2) of the generator, only 300 W of power is required to have clutch spring (11) actuation in the said 100 ms. Since again: Power (W) = Torque (N-m) x angular speed (rad/s); for the clutch mechanical system an average angular speed of 30 rad/s will be enough to have clutch actuation in the said 100 ms. Therefore, in the generator arrangement there is a major difficulty to relate the power of 7330 W, apparently seen by the outside part (1) of the generator, with the 300 W of real power required to have clutch actuation.

One solution was presented in the previous patent PCT/PT03/00008-"Clutch Actuation system by means of a Synchronised Generator". That solution consists to supply the excitation field of the generator with variable frequency, so that the electromagnetic rotating field, seen by the air-gap (3), is composed by the sum of two different angular velocities. The first angular velocity is the mechanical angular velocity of vehicle's engine, herein symbolically denoted by com, relative to the central part (2) that is assumed to be stopped.

The second angular velocity is the result of the magnetic frequency caused by the AC current supplied to the central part (2). That electromagnetic angular velocity is herein symbolically denoted by O) e.

According to that solution, the theoretically constant power P (in Watts) the generator must deliver, is equal to the constant rated torque T (in N-m) times the differential angular velocity (wm-we) expressed in rad/s, between vehicles engine mechanical rotation mm and the generator excitation angular velocity Me. Therefore, the differential angular velocity (Mm-me) seen by the outside part (1), in respect to the air-gap (3), is aimed to be constant. On this theoretical conditions, the equation defining the theoretical working mechanism of the said solution is the following: P = T ( (Om-COe) = constant in the outside part (1).

According to the said solution, to have such type of excitation field the current supplied to the central part (2) must be AC 2-phase or 3-phase electrical current with variable frequency, from zero up to any desired frequency. Both angular velocities com and we must have the same sense of rotation and vehicles engine angular velocity tAm must be bigger then exciter electromagnetic angular velocity we, to have generator action.

This solution provided by previous patent PCT/PT03/00008 assumes the usual concept that a generator is made to produce real power, with current in phase with voltage, so that the constant differential speed (wm-ce) solves the requirement that constant real power must be produced, being the load mostly resistive. Meanwhile a new solution was developed, based on a generator's load mostly inductive.

A Physical reasoning is required to verify that mechanical power seen by the outside part (1) of the generator could be regarded as an apparent power, and only the real power required for the central part (2) of the machine is important, somehow similar to electric circuits real power concept and reactive power concept. Real power in an electric circuit dissipates heat and has voltage in phase with current. Reactive power in the electric circuit refers to current 90 degrees out of phase with voltage, that doesn't produces or dissipates any heat, nor produces any kind of work.

Apparent mechanical doesn't exist, but in this analysis it is possible and useful to imagine there is an apparent mechanical power. The real power is the power that clutch actuation system actually needs, the said 300 W. The apparent mechanical power, which is only due to apparent rotation beyond the above calculated apparent value of 30 rad/s, must be equal to generator reactive power.

At idle, the given example needs 300 W of real power and has apparent speed of 84 rad/s (13.3 Hz). Therefore, at idle the generator must dissipate 300 W of heat in a pure resistor. To have clutch actuation it is required to have an equal amount of mechanical power dissipated into heat, because if the generator doesn't produce real power dissipated in a resistor-I R2-, no torque will be developed in the air-gap (3) to have clutch actuation. That heat is to be waste and lost for the exterior, with no use. At maximum vehicle's engine speed the clutch system still needs the same amount of real power (300 W), and again only those 300 W of power must be dissipated into heat in the resistance. Nevertheless the amount of reactive power flowing through the generator must have increased 8.75 times, which is the ratio of 7000 RPM/800 RPM.

With a load conveniently calculated, current"I"flowing though the resistor can be kept almost constant, so that voltage drop-V=R-I-on the resistor"R"is almost constant and the heat dissipated in the resistor-R-12-also is almost constant. Because generator's speed changes a lot (8.75 times for the given example), open circuit terminal voltage will change proportionally, but voltage drop in the resistor is constant, and so, mostly of the current should be flowing out of phase with voltage, which means the generator should be working at a very small power factor value. That's not strange because the apparent generator volt- ampere rating must be a least 8.75 x 300 W = 2550 VA, and the clutch actuation system only needs 300 W of real power. Being terminal voltage and current constant, the total circuit impedance"Z"must increase proportional to mechanical speed increase, so that V=Z-I=Constant (more or less). The load must be inductive in nature, because inductive impedance"X"is proportional to frequency.

Because apparent mechanical power doesn't exist, what must be the actual mechanical power provided by vehicle's engine? Based on the above explanation it can be found that the mechanical power delivered to the system is the amount of 300 W required to have clutch actuation, plus an equal amount of 300 W dissipated into heat in the load resistor, which means a total of 600 W for the example given, independently of the mechanical speed.

If the generator's load is conveniently calculated, according to generator's armature inductance, the magnetic excitation field doesn't have to be feed by alternating current with variable frequency, to have electromagnetic angular speed we like in the previous solution does. The excitation field can be supplied by Direct Current (DC) and the fine control of the clutch actuation system made by means of the intensity of the said DC magnetic field. This load strategy leads to a simpler and much economic solution.

The main drawback of the last solution is the so-called"time constant"of the electric circuit.

To circulate large amounts of reactive power, the circuit must be mostly inductive in nature.

Notice the heat to be dissipated in a pure resistor is only a small amount of the total apparent power flowing through the generator. Therefore, the time constant, which is the value of inductance L (Henry) divided by the value of resistance R (Ohm), can be a value of about 20 ms (milliseconds), which means that the transient effect only disappears completely in about 100 ms, that is the same time previously assumed to have clutch actuation.

Because the generator is always rotating, the transient effect defined by the"time constant" will start by a violent surge of current and a very high torque value, if the DC excitation field is turned on suddenly at maximum intensity, or if the electric circuit of a permanent magnets generator is closed suddenly, at the rated load required to work in steady state. This fact means that response time of the generator trends to be violent and must be controlled not to have mechanical damage, before the steady state is reached tens of milliseconds later.

Therefore, a smooth creation of excitation magnetic field is required. The time the effect last is not dependent on speed, or frequency, because the"time constant"of a LR circuit, ruled by a first order differential equation, only depends on the actual values of the inductance L (Henry) and resistance R (Ohm) of the passive elements.

It was said that the fundamental requirement to apply force over the clutch spring (11) is the creation of a rotating air-gap (3) magnetic field. It is known that Alternating Current (AC), or pulsed with modulation Direct Current (DC) can create such rotating magnetic fields. Only variable current can do this without brushes. Otherwise the use of Direct Current (DC) requires brushes and sliding electric contacts, which is not a good solution, nor is required.

The DC current pulsed with modulation creates steps of DC current that mimics AC current and hence produces a rotating magnetic field. Machines that work based on pulsed DC current are called stepper machines, being a stepper motor a good solution for the motor arrangement shown in Fig. 6-7.

Basically, a rotating magnetic field is required and therefore also alternating current is required. Monophase AC current creates two rotating fields in opposite directions, which could be made unbalanced at higher speeds and could create the desired torque.

Nevertheless, monophase AC current is not a good solution. The most convenient for clutch actuation system is 2-phase AC current displaced 90 degrees, or conventional 3-phase AC current displaced 120 degrees, or more generally AC polyphase current, because those types of current can create regular torque with a well defined sense of rotation. 2-Phase AC current is the most economic and 3-phase AC current is the most studied, perfectly balanced and continuous. The use of more then 3-phases can be used, but its benefits on the clutch actuation system only are significant for the stepper motor arrangement.

Hence, the current flowing in the armature of the electrical machine (1,2, 3) must be 2-phase or 3-phase AC current, supplied in the motor arrangement, or produced in the generator approach. The other side of the electrical machine (1,2, 3) will be the usual excitation field.

Any electrical machine must have an excitation field and there are three basic types of AC machines, based on their excitation field type.

The most common is the induction machine with a squirrel cage rotor. The excitation field of this type of machines is not direct, but a rotor reaction effect, so that magnetising current must be given by the armature. Such a machine could work, but it has several drawbacks. It requires initial armature input to start working, it is slow, has low torque capabilities, and requires a very large capacitor to sustain the field. This leads to a very complicated control strategy for a poor efficiency machine, so induction machines are not recommended.

The right electrical machines (1,2, 3) for the clutch actuation system are synchronous machines, like permanent magnets (PM) machines and wound rotor external excited machines, generally speaking. Both cases, as a motor or as a generator.

In the generator arrangement, shown in Fig. 2 and Fig. 5, the basic working mechanism of this invention doesn't work without mechanical energy, supplied by vehicle's engine rotation.

Whenever vehicle's engine stops the clutch spring (11) cannot be actuated without an auxiliary system. This situation was already described in previous patent PCT/PT03/00008, and it was said that the same generator can be used as a motor, by means of reversing the phase lines of the phases of the AC current supplied to the machine. Physically this is equivalent to reverse the sense of rotation of the electromagnetic torque developed in the air- gap (3). This electrical solution solves the above said problem and clearly shows that the clutch actuation system doesn't require vehicle's engine rotation speed to work. Thus, this clutch actuation system can work in the motor arrangement as well, like shown in Fig. 6-7, being that solution obvious and straightforward.

Nevertheless, to have motor action a powerful electric power-supply is needed. Contrary to the generator mode of operation, the magnetic field required to turn the electrical machine (1,2, 3) as a motor will need to deliver the full rated power, for the same clutch response time.

Therefore, the auxiliary power-supply must deliver values like the said 300 Watts, for the example herein given. If vehicle's battery is rated 12 Volts DC, the total consumption will be about 25 Amperes DC, plus losses in the AC electronic inverters, electrical motor losses, Joule effect losses, and so on. All that could be a very heavy load for vehicle's battery. That's why the generator arrangement of Fig. 2 and Fig. 5 is usually preferable, relative to the motor arrangement shown in Fig. 6-7.

Therefore, motor action is always possible with the same electrical machine (1, 2, 3), even if constructed according to generator's arrangement shown in Fig. 2 and Fig. 5, because all electrical machines (1,2, 3) can be reversed and that's a very well know fact.

Summarising all the above said, there are four general descriptions of four similar machines that can be used with the clutch actuator herein described, being two of then arranged in the generator's mode (Fig. 2 and Fig. 5) and two arranged in the motor approach (Fig. 6-7).

A more detailed description of those four types of machines is presented below : Fig. 2 shows a generator arrangement, because the outside part (1) of the electrical machine (1,2, 3) is fixed to the clutch housing (25) and, hence, permanently rotates whenever vehicle's engine rotates. The said outside part (1) has no connections to the exterior and its internal electric circuit is closed. The said outside part (1) is where electric energy must be generated and dissipated into heat, in a convenient load (16,17, 18) as earlier explained. The heat is to be loss with no use. The said heat must be equivalent to the amount of mechanical power required to be converted (the 300 W for the given example) to have clutch spring (11) actuation.

The central part (2) of the arrangement shown Fig. 2 is the generator's excitation field, feed externally by DC or AC current. The electrical energy that must be fed to the central part (2), through the connecting wires (4), it's only a small amount of the electricity generated on the outside part (1) and it's not included in the energy conversion. Fig. 2 shows what could be called a synchronous machine. All synchronous machines require an excitation field to be externally supplied. The excitation field is the control of the generator that turns it on-off and regulates intensity of current and developed torque. When the external circuit (4) feeds current to the central part (2) a magnetic field is created, that will induce voltage and current on the outside part (1) circuit and its load (16, 17,18). Induced voltage and current circulates in the closed circuit of the outside part (1) and electromagnetic torque is created in the air- gap (3), as an opposition to mechanical motion.

The electricity generated in the outside part (1) must be Alternating Current (AC) 2-phase, or 3-phase, whose frequency at steady state will be the so-called synchronous frequency, depending on vehicle's engine mechanical rotation, com, and the central part (2) excitation field electrical frequency we. If the excitation field of the central part (2) is supplied by DC current, then oye=0 and the synchronous frequency will be equal to mm, being this a pure synchronous machine. If the same excitation field is supplied by AC current, a frequency we is created and the outside part (1) synchronous frequency will be the difference (mm-coe) When excitation field is supplied by AC current with frequency Me, the machine shown Fig. 2 can be analysed based on induction machines theory. In such case, the outside part (1) is equivalent to the wound rotor of an induction machine, and the excitation field of central part (2) is equivalent to a grid. The grid supplies the induction generator reactive energy needs, but all the power generated is dissipated in the rotor to sustain the magnetic field, because rotor impedance is based on heavy inductive and resistive loads. Inclusive the grid must supply reactive energy needs without receiving any real power, because wound rotor losses are so great that generate the said 300 W of heat in the inaccessible part of the machine that is rotating. Such induction generator produces no useful work to the exterior (grid), as it was expected from previous premises of this invention, but consumes mechanical power and creates air-gap (3) electromagnetic torque to have clutch actuation.

Fig. 3 shows schematically an example of what could be a 3-phase machine, where each phase load (16,17, 18) is represented. The said load (16,17, 18) comprises inductance and resistance. All the machine control and regulation strategy depends on the prerequisite of that load (16,17, 18) and the ground (19) electrical circuit, Delta or Wye connected. Basically the generator synchronous frequency will depend on the load (16,17, 18), fixed to the outside part (1) that permanently rotates in the case of Fig. 2. Instead of 3-phase current it can be used more economic 2-phase current, displaced 90 electrical degrees in time, meaning only two circuit windings, two loads and two compatible excitation field channels. The same is true for any electrical machine (1,2, 3) described by this patent. 2-Phase or 3-phase can always be used, with no limitations about the number of magnetic pair of poles of electrical machine (1, 2,3).

When vehicle's engine stops the arrangement shown Fig. 2 and Fig. 5 cannot actuate the clutch system anymore, because it miss mechanical power. An auxiliary system is required, as previously stated, and the same generator must work as a motor whenever the outside part (1) is stopped. This is a root problem that implies that central part (2) of the machine shown Fig. 2 must be 2-phase or 3-phase wire wound, with the same number of poles and number of phases as the outside part (1). The central part (2) must have the same type of AC current circulating in the outside part (1), so that central part (2) rotating magnetic excitation field can be linked with the outside part (1), to produce motor action. Electronic inverters, 2-phase or 3-phase, are required to feed AC current to the central part (2) to have generator or motor action, depending on frequency. When vehicle's engine is stopped, to have clutch spring (11) compressed, the sense of rotation of the air-gap (3) electromagnetic field must be reversed, by means of reversing the phase sequence of the current wires (4) that fed the central part (2).

The generator shown Fig. 2 can work as a generator to have clutch spring (11) actuation and, suddenly, it can be turned to motor action in order to help clutch spring (11) elastic recover.

This generator/motor strategy can be very helpful if a small clutch actuator is required, or if the fastest possible cycle operation is the aim. If mechanical rotation already exist, the current and phase sequence must be always supplied in the same sense of rotation. Motor action occurs if the frequency supplied to the central part (2) is above mechanical speed.

Generator action occurs if the frequency supplied to the central part (2) is below mechanical speed. Motor action always must occur with a frequency that is not much higher above mechanical speed, because of the outside part (1) load (16,17, 18) and its voltage requirements are limitations at much higher frequencies. Nevertheless, motor action can be achieved at any mechanical speed, including at very high speeds, to have fastest recover cycle.

The generator shown Fig. 2 also has the following characteristics: The outside part (1) is a laminated piece of iron, wire wound 2-phase or 3-phase, composed by several coils (9), or electromagnets (9). The central part (2) also is a laminated piece of iron, wire wound 2-phase or 3-phase, composed by several electromagnets (8). The outside part (1) is an isolated system. The central part (2) connects with an external AC or DC power-supply, by means of electric wires (4), to create excitation field or motor action as well.

Fig. 5 shows a permanent magnets (PM) synchronous generator. This is a pure synchronous machine which carries some special features, but basically it is very similar to the generator described Fig. 2 turned upside-down. The central part (2) that was the previous excitation field, in the PM generator arrangement it's generator's armature and it's terminals, where the load must be connected to dissipate heat. The outside part (1) of previous generator, in the PM generator shown Fig. 5 is the excitation field. Permanent magnets (10) create a permanent excitation field. The said permanent magnets (10) are surface mounted in the internal part of the outside part (1), as shown Fig. 5, and that outside part (1) permanently rotate attached to clutch disk housing (25). Hence, there exists a permanently rotating excitation field, caused by permanent magnets (10) in motion. On those conditions, all that is required is a load, to have electrical energy generated and electromagnetic torque developed in the air-gap (3). The PM generator shown Fig. 5 works by means of switch on-off an external load.

The central part (2) of the PM generator shown Fig. 5 is a laminated piece of iron, wire wound 2-phase or 3-phase, composed of several coils (8), or electromagnets (8). The central part (2) is generator's armature, where electricity is generated, and so the electricity generated must be send to the exterior by means of wires (4), that carries generator's terminals. The synchronous frequency of the AC current generated is dictated by mechanical rotation speed of the outside part (1) and frequency adjustments of the electricity generated is very difficult, because this is a strictly synchronous machine, with no slip.

Without a convenient load strategy, as earlier explained, the PM generator will deliver power proportional to speed. But again, the clutch actuation system only requires a constant amount of power (300 W for the example given), no matter vehicle's engine speed.

Therefore, the earlier explained load strategy is fundamental to minimise the power requirements; the heat produced to have energy conversion; and maintain constant the production of air-gap (3) electromagnetic torque, all the speed range.

Some advantages of the PM generator shown Fig. 5, relative to the wound generator shown Fig. 2, is that PM generator doesn't require external excitation field, nor power-supply, because it is autonomous. Also, the PM generator can achieve higher air-gap (3) shear stress values, due to today's strong and economic permanent magnets (10) available. So the PM generator can work fastest, with small angular displacement (14), and so it doesn't require motor action in the clutch recover cycle to be fast enough. The main disadvantage is that to have even fast recover cycle, motor action is very difficult and complex to achieve with PM generator, since the exact synchronous speed must be evaluated and provided by an external power-supply, being the control made by vector position, which is very difficult and complex to achieve accurately in such short period of time. The wound generator shown Fig. 2 is different, because it can be controlled in frequency, with some slip, which is much easier and has great tolerance margin.

When vehicle's engine stops, again the PM generator arrangement shown Fig. 5 cannot work, because there is no mechanical power. No problem exists to run a PM generator as a motor.

Basically it is a 2-phase, or 3-phase, PM synchronous motor and the arrangement shown Fig. 5 provides access to motor's armature by means of external wires (4). When vehicle's engine stops all parts are stopped and the PM motor start-up cannot be done at synchronous frequency, nor exists any preferable synchronous frequency. There are several solutions to start a synchronous machine, being the best solution for the PM machine shown Fig. 5 the strategy that will be explained later within Fig. 6-7 description for the synchronous motor.

At normal running, the PM generator shown Fig. 5 must be turned on-off by means of switching on-off an external load at PM generator's terminals (4). The said load must be mostly inductive, then resistive, as earlier stated. The total circuit impedance"Z", including windings (8) inductance and resistance of the central part (2), must increase proportional to mechanical speed increase, so that V = Z l = Constant (more or less). The total load must be inductive in nature, because inductive impedance"X"is proportional to frequency. This strategy inevitably leads to a very small resistor value, that must be accurately controlled, and which also must dissipate the said 300 W of heat for the given example. The control of the load resistor is the only control aimed for the PM generator shown Fig. 5. This resistor must start to be a very high value, near infinite, so that it is like a switch open. The circuit is open and the PM generator off.

This is a synchronous machine and all synchronous machines, if not previously synchronised, they start violently generating a surge of current and torque in the air-gap (3).

The PM generator shown Fig. 5 is not aimed to start synchronised, hence the load must be controlled not to have mechanical damage, due to the violent surge of current that occurs if steady state load is applied suddenly at once. There is always a so-called"time constant" value, of the transient effect, that takes some amount of time to disappear. That amount of time is significant compared to the actual time aimed to have clutch actuation. The load resistor could be a set of parallel transistors mounted upon heat-sink material, or any other electronic device that could work as a switch. Transistors can work as switches to build a controllable variable resistor, made by several parallel resistors for instance.

The control of the PM generator shown Fig. 5 is straightforward based on a variable resistor control. The load resistor starts to be a very high value and then, to start the PM generator, the load resistance must suddenly decrease to an initial value and, then, decrease slowly until the transient effect passes and machine reaches steady state at the right resistance value. To have more real power generated the resistor value must increase, and vice-versa.

The smaller the resistance value is, the smaller will be the torque generated in the air-gap (3). At ideally zero resistance, no torque will be developed in the air-gap (3), because no heat could be ideally dissipated, since there is no resistance.

Fig. 6-7 shows a typical motor arrangement, because the outside part (1) of the electrical machine (1,2, 3) is fixed to the main stationary housing (22). Hence this is the same situation that occurs when vehicle's engine stops. Vehicle's engine large mass inertia is like a big stationary mass that provides reaction, like the main housing (22) does. But the vehicle's engine is not involved in the motor arrangement shown Fig. 6-7 and power must be supplied, based on vehicle's battery or any other means of energy storage, to have motor action of the central part (2), back and forward, to have clutch actuation.

The electric motor (1,2, 3) arrangement must be optimised to have the fastest response time and the lower electricity consumption possible. Based on the actual state-of-the-art, having in mind that the size of the electrical machine (1,2, 3) is critical, two types of motors and designs were chosen and represented Fig. 6-7.

One of the most important figures of this invention is that the central part (2) must accelerate; then decelerate; stop; hold position; have controllable acceleration backwards; eventually hold position progressively in any situation; and finally recover to the start and the off position. All the said situations cannot be controlled by an induction motor, without complex and expensive control strategy. It is possible in a rescue situation, as previously stated in the generator machine description, since time and accuracy is not important, because vehicle's engine is stopped. But in normal conditions, an electrical machine (1, 2, 3) working as a motor requires that the said motor must be a reluctance motor, or a stepper motor, or else a synchronous motor working like a reluctance motor, without slip. The basic mechanism of the said reluctance motors is that of magnetic poles hunting magnetic poles in synchronism without slip.

Magnetic poles hunting magnetic poles is a concept which is descriptively valid for salient pole reluctance machines. In such working mechanism, the magnetic field tries to reach a minimum reluctance position. This is less apparent for smooth rotor machines like 3-phase induction machines. Reluctance is a characteristic of a magnetic field which resists to the flow of magnetic lines of force through it, that results in magnetomotive force-mmf. The said magnetomotive force is the force that generates the required air-gap (3) electromagnetic torque and the shear stress between both sides of the electrical machine (1,2, 3).

To have motor action, again the size of the machine is critical and both sides of the electrical machine (1, 2, 3), the outside part (1) and the central part (2), they must have the ability to develop strong magnetic fields, by means of electromagnets (8,9) (or coils (8,9)), or by permanent magnets (10). Simplier and basic reluctance motors, with only one part energised, cannot work without being a large machine, which is not aimed. Maximum air-gap (3) shear stress is the aim of machine construction. The two electrical motors (1,2, 3) shown Fig. 6-7 are similar and work basically the same way. Both are doubly salient poles with phase coils mounted around diametrically opposite poles of the outside part (1), and both have salient electromagnetic fields build in the central part (2), by means of electromagnets (8), or coils (8), as shown Fig. 6, or by means of permanent magnets (10) as shown Fig. 7.

That's the basic difference between the motor arrangement shown Fig. 6 and the motor arrangement shown Fig. 7. Everything else is similar for both electrical motors (1,2, 3) shown Fig. 6-7. The advantage of the use of permanent magnets (10) shown Fig. 7 is that no wires (4) are required to fed the central part (2), as shown Fig. 6. The disadvantage is the permanent magnets (10) cost, its fragility and susceptibility to heat, for instance.

Variable reluctance motor, switched reluctance motor or stepper motor are synonyms and mainly translates the evolution of the names given to the same type of the electrical machine (1,2, 3) described Fig. 6-7. Basically they are synchronous machines. Although they are in fact synchronous machines, their operation and control differs fundamentally from conventional rotating-field AC machines. Nevertheless, conventional 2-phase or 3-phase synchronous motors, operated at very low frequency, also are reluctance machines, theoretically without any steps if 3-phase or 2-phase balanced current and operation is applied.

Conventional balanced AC 3-phase (or AC 2-phase) current; or else a reluctance machine working by means of small steps-the stepper motor-, there are so many typologies that is difficult to give an overview of all possible typologies. Reluctance or stepper motors are electrical machines (1,2, 3) where both the outside part (1) (the stator) and the central part (2) (the rotor) have salient poles. The outside part (1) comprises a set of coils (9), each of which is wound on one pole. The central part (2) also comprises a set of coils (8), or permanent magnets (10), and is created from iron lamination to minimise the Eddy-current losses.

Reluctance or stepper motors differ in the number of phases wound in the outside part (1) and central part (2). Each of them has a certain number of suitable combinations between the outside part (1) and central part (2), being one of the most common the typical 3-phase motor with a 6/4 pole configuration, where the outside part (1) has 6 magnetic salient poles and the central part (2) has 4 magnetic salient poles.

The motor is excited by a sequence of current pulses applied each phase, by means of a set wires (23). The individual phases are consequently excited, forcing the central part (2) to rotate, having clutch spring (11) actuation. The current pulses need to be applied to the respective phase at the exact central part (2) position, relative to the outside part (1) excited phase. Torque production in the reluctance motors shown Fig. 6-7 is achieved by the tendency of the central part (2) to move to a position where the inductance, and hence the magnetic field energy, of the excited winding is minimised. When any pair of central part (2) poles is exactly in line with the outside part (1) poles of the selected phase, the phase is said to be in an aligned position. The said aligned position is a position of maximal inductance and no shear force is developed, nor any torque for that phase. At this point the said phase must be switched off. Otherwise, if the central part (2) past the aligned position the attractive force between the poles produces a breaking torque. Therefore the next phase must be energised so that the polar axis of the central part (2) is aligned with the outside part (1) of the selected phase. That's a position of minimal inductance of outside part (1) and so maximum air-gap (3) shear force is developed, forcing the central part (2) to rotate searching for the next aligned position of minimum energy, and so on.

The electrical motor shown Fig. 6-7 must have at least 3-phases if it is a stepper motor, so that the sense of rotation of the central part (2) could be perfectly determined, back and forward, to compress and release the clutch spring (11). The ideal current waveform is therefore a series of pulses synchronised with aligning of central part (2) poles and outside part (1) poles. By exciting (23) the poles of different phases when poles approach the appropriate poles of the other side, then an almost continuous torque production and rotation of the central part (2) is achieved, by means of small steps. The greater the number of phases, and coils (8,9), or permanent magnets (10), the smaller the steps could be made and the torque developed more continuous. The said electric motor (1,2, 3) requires position feedback for motor phase commutation. In many cases this requirement is addressed by using position sensors, like encoders, Hall sensors, etc. A power electronic inverter with a control based on feedback of the central part (2) position is a necessity.

Nevertheless, also conventional balanced AC 3-phase, or AC 2-phase current, operating conventional AC synchronous motors, can make them work like reluctance machines whose steps are negligible and producing continuous torque, without steps. AC current of very low frequency, generated by electronic inverters, using the pulse with modulation technique, are in fact sine waves made by short DC steps, but those steps can be made negligible.

Therefore, 2-phase, or 3-phase synchronous motors are those who can develop theoretically higher and best performance, concerning shear stress created by magnetomotive force over the air-gap (3) area, because theoretically no torque drop occurs, since there are no steps.

Because electrical motor (1,2, 3) size and performance is critical, 3-phase, or 2-phase, synchronous motor balanced operation, back and forward, at low, very low and also zero frequency, based on permanent magnets (10), as shown Fig. 7, is considered to be the best electrical motor (1,2, 3) for the clutch actuation system herein described. Or else, high quality grade stepper motors, 3-phase, doubled-up pole number, 5-phase, 6-phase, etc. Requiring small steps and aimed to have the smallest torque drop during successive step cycles.

Otherwise the clutch system could be slow during maximum efforts, or else a big machine (1,2, 3) is required. That's all a matter of size of the electrical machine (1, 2, 3) and its response time due to mass inertia.