ELECTRONICALLY CONTROLLED SERVOMECHANISM AND METHOD FOR AUTOMOTIVE STARTING CLUTCHES BACKGROUND OF THE INVENTION The present invention relates to servomechanisms especially suited for servo operation of vehicular starting clutches, and more particularly, to an electronically controlled servomechanism system and method in which a friction device is contained and supported by a frame or housing and operated by an electromagnetic device in different modes to engage and disengage an automotive starting clutch. Several servomechanisms for vehicle drive trains have been proposed over the years utilizing various combinations of hydraulic, pneumatic and electrical components. They are complex and expensive to manufacture, particularly when involving hydraulic components. Since most vehicle engines are now under the control of an electronic management system, it has been attempted to use electric means such as solenoids and electric motors for the actuation of starting clutches. However, these components are heavy, expensive and tend to draw a large amperage. To reduce the power requirements, it has been proposed to balance the force of the starting clutch diaphragm by the force of another spring. However, the rated power of the motor and therefore of the amplifier, are relatively high, and the system has a high manufacturing cost.

It is apparent therefore, that there is a need for improvements in such servo systems and in the method to operate the same. SUMMARY OF THE INVENTION

It is the aim of the present invention to overcome the aforementioned problems and disadvantages of present servomechanism systems, to reduce their manufacturing cost and the power required for their control, as well as describe an improved method for the control of such servomechanism systems. The advantages and purpose of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purpose of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a servomechanism for operating the starting clutch in an automotive drive train having an engine with a rotatable power output, the starting clutch being adjustable between zero and maximum torque transmitting capacity, having a rotatable starting clutch input driven by the power output of the engine, and a rotatable starting clutch output. The servomechanism includes first and second relatively rotatable servomechanism components, one of the relatively rotatable servomechanism components being coupled to the power output of the engine and a releasable friction device engageable in torque transmitting relation alternately with one of the first and second servomechanism components. A torque-to-linear force conversion device is coupled to said releasable friction device to adjust the starting clutch reversibly between zero and maximum torque capacity, and the releasable friction device is controlled by an electromagnetic device in a first electromagnetic mode to reduce the torque transmitting capacity of the starting clutch to zero, and in a second electromagnetic mode to increase the torque transmitting capacity of the starting clutch to maximum.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not ! restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate alternative embodiments of the invention and together with the description, serve to explain the principles of the invention. In the drawings,

FIG. 1 is a longitudinal sectional view of a preferred embodiment of the electronically controlled servomechanism of the invention;

FIG. 2 is a fragmentary view of the servomechanism illustrated in FIG. 1, illustrating an alternate embodiment of the means to transfer the power of the servomechanism output member to a power operating body;

FIG. 3 is a fragmentary view of the servomechanism illustrated in FIG. 1, illustrating an alternate embodiment of the means to transfer the operating power of the servomechanism output member to a power operating body;

FIG. 4 is a schematic showing the working components and the control components of an automatic starting clutch system incorporating the electronically controlled servomechanism illustrated in FIG. 1;

FIG. 5 is a graph illustrating the variation of the torque Tω which accelerates the servomechanism output member illustrated in FIG. 1, plotted on ordinates against the relative time x.. FIGS. 6 and 7 are longitudinal sectional views of an alternate embodiment of the electronically controlled servomechanism of the invention integrated into a conventional automotive starting clutch system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the drawings, the reference numbers have three digits, the first digit referring to a figure number, the two others digits referring to a part number.

Illustrated schematically in FIG. 4 of the drawings are the working and the control components of a vehicle electronically controlled automatic starting clutch system incorporating the servomechanism of the invention. The electronic starting clutch actuating mechanism is part of a vehicle engine management system, which includes, for example, the control of the engine fuel injection and ignition, and therefore, various components and signals are already available since they are utilized for the engine management system. Thus, only the components which are necessary to the functioning of the electronic clutch system and applicable to the invention are explicitly illustrated.

The vehicle power train considered in this application includes an engine 460, a starting clutch 430 operated by a release yoke 431, a multi-speed gearbox 440 operated by a shift lever 441, and a propeller shaft 446 driving rotatably the vehicle ground wheels through an axle (not shown) in conventional fashion.

The working components of the electronic starting clutch actuating system include a servomechanism 400 driven by the engine 460, the servomechanism

400 actuating the release yoke 431 of the starting clutch 430 by the action of a power cable 426, for example.

The functioning components of a first exemplary embodiment of an electronically controlled servomechanism of the invention designated generally the reference numeral 100, as shown in FIG. 1 of the drawings.

The starting clutch servomechanism of the present invention includes first and second relatively rotatable servomechanism components, one of the relatively rotatable servomechanisms components being driven by the power output of the engine, a releasable friction device engageable in torque transmitting relation alternately with one of the first and second servomechanism components, and an electromagnetic device to control the friction device.

In the embodiment of Fig. 1, the servomechanism 100 includes, as one of the first and second components, an input member 104 driven continuously, directly or indirectly, by the vehicle engine 160, 460, and an electrical power supply 103 receiving the control power from a dedicated output board of a vehicle computer system 450.

The servomechanism 100 includes a housing or frame 110, in which is journaled on a common axis 120, the input member 104 and an output member 122, respectively. The housing 110 is made preferably of a material having a low relative magnetic permeability, and is held relative to the vehicle engine 160, 460 directly or indirectly, by appropriate means.

An electromagnetic device or solenoid 106 is coaxial with and nested into a breech 104 ¹ , integrated with the input member 104 in the embodiment of Fig. 1. The solenoid 106 is not rotatable with the input member. The releasable friction device is in the form of a friction plate 105, which is coaxial with and rotatably coupled to the output member 122, preferably, but not necessarily, through a Belleville spring 115 splined internally to the output member 122 and externally to the friction plate 105. The input member 104, particularly the breech 104' thereof, and the friction plate 105 are made out of material having high relative magnetic permeability, and preferably, but not necessarily, low magnetic induction losses. The Belleville spring 115 tends to force the friction plate 105 against the housing 110, to form essentially a friction brake, whereas the magnetic field generated by the

solenoid 106 tends to force the friction plate 105 against the input member 104 to form essentially a friction clutch.

The input member 104 and breech 104' is located relative to the housing 110 radially and axially, by a bearing 101, while the output member 122 is located radially and axially relatively to the housing 110 by a bearing 102. The output member 122 is additionally located radially relative to the housing 110, indirectly by a bearing 108. The solenoid 106 is secured relative to the housing 110 by bracket 109 and as indicated, does not impede rotation of the input member 104.

In the embodiment illustrated in FIG. 1 of the drawings, power, manifested by torque in the output member 122, is transmitted to linear force in a cable 126, fastened by appropriate means directly to the output member 122, such that when the output member 122 rotates, the cable 126 winds up around the surface 123. The cable 126 is preferably, but not necessarily, a composite material, having a relatively large number of fibers of high strength materials, as an example, but not limited to, Kevlar.

Illustrated in FIG. 2 of the drawings is an alternate embodiment of a torque- to-linear force device to transfer the power of the output member 222 to a power operating body, in the form of a master hydraulic piston 207, operated by a radial cam surface 223 machined on the output member 222. The master cylinder 211 is preferably, but not necessarily, machined into the housing 210. The hydraulic line is fastened to the housing 210 by a thread 213. A section perpendicular to the axis 220 through the cam surface 223 has approximately the shape of a spiral.

In FIG. 3 of the drawings, an alternate embodiment is shown to transfer the power of the output member 322 to a power operating body in the form of a shaft 326, rotatably driven by the output member 322 through the spline 316.

The electric energy for the control of the servomechanism 100 is supplied to the solenoid 106 by a pair of wires 103 to effect two modes of electromagnetic operation. When, in a first mode, a relatively high level of electric current, or "opening current", is supplied to the solenoid 106, the friction plate 105 moves axially away from the housing 110 and comes in friction engagement with the rotating input member 104, inducing a friction torque between them, and a resulting rotation of the friction plate 105. The opening current can be either direct or

alternating but in either case, is at relatively high voltage. Because the friction plate 105 is rotatably connected to the output member 122 by the Belleville spring 115, the cable 126 is pulled into the servomechanism 100. The maximum pulling speed is obtained when the input member 104 and the friction plate 105 rotate at the same speed, and the power dissipated by friction between the input member 104 and the friction plate 105 of the control clutch is therefore relatively extremely low in this case. The cable 126 pulling force capacity F _a , varies with the intensity of the magnetic field, and is relatively high in comparison to the electric power of the starting clutch opening current supplied to the solenoid 106 and to be described in more detail below, since the mechanical power supplied to the cable 126 is derived from the mechanical power supplied to the servomechanism 100 by the vehicle engine 460.

When the power supplied to the solenoid 106 is cut off, the friction plate 105 is forced against the housing 110 by the Belleville spring 115, forming essentially a brake, and the output member 122 cannot rotate anymore around the axis 120, and the cable 126 cannot unwind.

The pressure between the friction plate 105 and the housing 110 is reduced when the solenoid 106 creates a magnetic field, and the friction plate 105 starts to rotate as soon as the friction torque, resulting from the pressure between the friction plate 105 and the housing 110, falls below the torque resulting from the force F _tt . The angular acceleration ώ of the friction plate 105 is as follows: / being the equivalent moment of inertia, relative to the friction plate 105, of all the mass located between the spring like load F _a and said friction plate 105, friction plate 105 included, and r _ω , the torque accelerating the friction plate 105:

Since the acceleration ώ is relatively extremely high for the practical applications considered herein, in the order of 10 ⁴ [s ^"2 ], the rotational speed of the friction plate 105 varies enormously during its release, with the result that its control becomes problematic. However, it is possible to obtain an almost constant speed of the friction plate 105 over very short periods of time, if a sinusoidal alternating or pulsating electric current, having a high frequency equal to f _{t c} is supplied to the

solenoid 106. The pressure between the friction plate 105 and the housing 110 varies in this case periodically at a high frequency. FIG. 5 of the drawings illustrates the variation of the torque r _ω , as a function of x, a variable defined below, and as a function of the time t. The angular acceleration ώ of the friction plate 105 varies in a short time interval as follows: F _a being the external force pulling the cable 126 and r its torque arm, assuming a constant static and dynamic coefficient of friction between the friction plate 105 and the housing 110, and assuming that the pressure between the friction plate 105 and the housing 110 is canceled out when x equals to 0.5:

FriSin {πx) ft =

I with 0 < x < 1 and x = 2 tf _{t c} The small angle ω by which the friction plate 105 rotates when x varies from 0 to 1 is as follows, with the assumption that r F _a ,f _tlec and / stay constant in this interval:

ω = — ^a

4πJf, θ ² lθC

It is therefore possible to calculate the frequency f _tkc for which the average angular speed between the friction plate 105 and of the output member 122, becomes equal to Ω when x varies from 0 to 1:

F r ^ fβl c = __. ^a _

2πJø

It is therefore possible to control the average angular speed i. of the output member 122, and therefore, the rate of release of the cable 126, by supplying the solenoid 106 with an pulsating alternating electrical cunent, or "release current" or in a second mode of electromagnetic operation. i general, a release current is supplied continuously at a constant frequency f _{t c} until a controlled parameter reaches its targeted value, the average angular velocity of the friction plate 105 staying during the adjustment, constant and equal to l if r F _a is constant. The angular velocity l of the friction plate 105 can be

modified by varying the frequency f _ekc or the amperage of the release current, or both.

It should be noted that the magnetic field of the solenoid 106 attracts the friction plate 105 at a frequency which is twice the frequency/^.,, of the electrical alternating current.

If r F _a is constant, the friction plate 105 rotates at an average constant angular speed ϊ but if the load F _a applied to the cable 126 varies over its design travel, the speed Ω varies also with it. When necessary, an approximately constant value for r F _a can be obtained by varying the effective radius r of the cam surface 123 in the inverse proportion of the variation of F _a

Preferably, but not necessarily, a high friction material 114 is fastened to the friction plate 105 in order to obtain a coefficient of friction, between the friction plate 105 and the housing 110, higher than between the friction plate 105 and the input member 104. This difference in friction coefficients helps to insure that the friction plate 105 does not get in friction engagement with the input member 104 when the release current is supplied to the solenoid 106.

With reference again to Fig. 4 of the drawings, the electric components of the electronic clutch system include, the vehicle battery 457, the vehicle ignition switch 456, a computer system 450 illustrated in block diagram and composed of a power supply 452, a logic board 454 with clock, a series of input boards 453 with signal converters for processing driver and computer system 450 inputs, and a series of output boards 455 with power amplifiers to develop appropriate computer system 450 outputs, a series of sensors, all well known to one skilled in the art, are connected to the computer system 450. More specifically, the vehicle speed sensor by the electrical wiring 445, the shift lever 441 position sensor by the electrical wiring 444, the shift lever handle sensor 442 by the electrical wiring 443, the engine throttle position sensor by the electrical wiring 462, and the engine speed sensor by the electrical wiring 463. Some of the electric components are wired in a conventional manner to a common ground. The computer system 450 inputs include the engine throttle position, the gearbox shift lever position, the shift lever handle pressure, as well as engine angular

and vehicle speeds. The computer system 450 output includes the starting clutch release yoke actuation.

Assuming that the engine 460 is idling, as soon as the driver applies a force to the handle 442 of the shift lever 441 to move it from neutral to a starting speed ratio position, the sensor located between the shift lever 441 and its handle 442, is activated. This signal triggers the computer 450 to supply the opening current to the servomechanism 400, forcing the friction plate 105 against the input member 104, with the effect that the friction plate 105 rotates, and the cable 426 pulls the release yoke 431, and this, for a time length such that the starting clutch 430 is fully open. The starting clutch 430 stays open when the power supplied to the servo system 400 is cut off, since the input member 105 is forced against the housing 110 by the effect of the Belleville spring 115. When the computer 450 has confirmation of the new fully engaged position of the shift lever 441, and if the driver then opens the engine throttle to accelerate the engine 460, and as soon as, and only when, the engine 460 reaches a specific calculated angular speed or "specific speed", the computer 450 sends a release current to the servo system 400, allowing the friction plate 105 to rotate. This has the effect of releasing the cable 126 and increase progressively, the torque capacity of the starting clutch 430 as the engine speed is over said specific speed. This is repeated each time the engine speed gets over the specific speed, and until the starting clutch 430 is fully closed. The specific speed is recalculated by the computer 450 in real time during all the starting clutch 430 engagement, and varies depending on the actual throttle position, has a maximum value close to the engine maximum torque speed, and a minimum value close to the engine minimum operating speed. Therefore, the engine 460 is maintained at the calculated specific speed by modulation of the torque capacity of the starting clutch 430, with the result that the vehicle is accelerated from rest, this acceleration increasing with the opening of the engine throttle. As soon as the engine speed and the input shaft speed of the gearbox 440 are close together, release current is supplied continuously to the servo system 400 until the starting clutch 430 gets fully closed. The gearbox 430 input speed is calculated by the computer 450 utilizing the information on the speed ratio and the vehicle speed.

To perform an upshift or a downshift, as soon as the driver applies a force to the handle 442 of the shift lever 441 to move it from one speed ratio to the next, the sensor located between the shift lever 441 and its handle 442, is activated. This signal triggers the computer 450 to supply the opening current to the servo system 400. When the new speed ratio is fully engaged, the starting clutch 430 is closed progressively according to a rate defined by programs well known in the art, which take in account, among other parameters, the engine speed and the throttle position during the closing of the starting clutch. This is achieved by supplying to the servomechanism 400 a release cunent at a rate and intervals defined by the computer 450.

If, at any time, the speed of the engine gets below the minimum operating speed, the computer 450 triggers the full opening of the starting clutch 430.

FIGS. 6 and 7 of the drawings illustrate an alternate embodiment of a servomechanism 600 of the invention, FIG. 7 illustrating the interrelated working components of the servomechanism 600 integrated into a conventional starting friction clutch system 430/730. The alternate embodiment 600 is similar to the system 100 described in the other figures of the drawing, particularly FIG. 1, and parts having a similar function have the same last two digits referral numbers.

However, parts in Figs. 6 and 7, equated by reference numeral designation to parts in Fig. 1, are alike in relation to torque and not in a rotational sense. For example, in Fig. 6, a rotatably fixed housing 604" is related by reference numeral convention to the rotatably driven input member 104 of Fig. 1 and the clutch plate 610, rotatable at all times with the output of the engine 460, is equated by the convention to the fixed housing 110 in Fig. 1. The reason for this seeming inconsistency is that in Fig. 1, the linear force of the cable 126, by rotation of the output member 122, operates on the equivalent of the diaphragm spring 731 in the clutch of Fig. 7. In the embodiment of Figs. 6 and 7, however, the equivalent linear force is applied by the servomechanism 600 directly to relative axial movement between the clutch back plate 710 and the diaphragm spring 731, both of which rotate with the engine output at all times dining engine operation. In both cases, first and second relatively rotatable servomechanism components are provided by a rotatable component (104 and 610) and a rotatably fixed component (110 and

604'), and one of the first and second components (the rotatable component in the illustrated embodiment) is driven by engine output. Also in both cases the friction device or plate 105, 605 is alternately engageable with one of the first and second relatively rotatable components. The solenoid 606 is secured axially and against rotation by adequate means to the fixed housing 604 and a breech member or rotatably fixed component 604'. The back plate 610 and a diaphragm spring 631 of the starting clutch 730 rotate all times with the power or crankshaft (not shown) output of the engine 460. The servomechanism output member 622 cooperates through a cam surface 623 on a cam body to provide a torque-to-linear force converting device. Alternatively, the cam 623 is replaced by a bolt and nut system, acme or ball system. Any relative rotation between the output member 622 and the cam body 607 pulls the diaphragm spring 631 and the clutch back plate 610 apart. Between the clutch back plate 610 and the output member 622 is located a thrust bearing 602. The friction plate sub- assembly 605 is forced against the clutch back plate 610, preferably, but not necessarily, by a Belleville spring 615 secured axially to the output member 622. The Belleville spring 615 is secured rotatably to the friction plate sub-assembly 605 and to the output member 622 preferably, but not necessarily, by spline. Therefore the friction plate sub-assembly 605 rotates with the output member 622, but can move axially relatively to the output member 622, and therefore the friction plate sub-assembly 605 can be in friction engagement either against the clutch back plate 610 or the fixed breech member 604'. The input shaft 641/741 of the gearbox 440 is coaxial with the servo system 600, but is not connected to any of its parts.

The electric energy for the control of the servo system is supplied to the solenoid 606 by a pair of wires 603. When a relatively high level of electric current, or "opening current", is supplied to the solenoid 606 in a first electromagnetic mode, the friction plate sub-assembly 605 moves axially away from the clutch back plate 610 and moves into friction engagement with the fixed member 604', inducing therefore a friction torque between them, and consequently grounding the friction plate sub-assembly 605. Since the friction plate sub-assembly 605 is rotatably connected to the output member 622 by the Belleville spring 615, the thrust member 623, rotatably driven by the diaphragm 631, pulls apart the diagram 631 and

the back plate 610, releasing the pressure on the friction plates of the starting clutch system 730. The force pulling apart the diaphragm 631 and the back plate 610 varies with the torque applied by the friction plate to the output member 622, i.e. with the intensity of said magnetic field created by the solenoid 606, and is relatively high in comparison to the electric power of the opening current supplied to the solenoid 606, since the mechanical power opening the clutch system is derived from the mechanical power supplied by the clutch back plate 610, i.e. by the vehicle engine 460.

When the power supplied to the solenoid 606 is cut off, the friction plate sub-assembly 605 is forced against the back plate 610 by the Belleville spring 615, forming essentially a clutch, and the output member 622 cannot rotate anymore around the axis 620 relatively to the cam 607, keeping the starting clutch system 730 open.

Since the pressure between the friction plate sub-assembly 605 and the back plate 610 is reduced when the solenoid 606 creates a magnetic field, the friction plate sub-assembly 605 starts to rotate as soon as the friction torque, consequent to the pressure between the friction plate 605 and the back plate 610, falls below the torque generated by the cam system 607/622 consequent to the axial force applied by the diaphragm spring 631. As explained in detail above, when an alternate current having a frequency f _{t e} is supplied to the solenoid 606 in a second electromagnetic mode, the plate 605 is free to rotate relatively to the back plate 610 at a relatively slow rotational speed ϊ, function of said frequency f _ele „ engaging the starting clutch system 730 controllably.

In light of the foregoing description and accompanying drawing illustrations, it will be appreciated that as a result of the present invention, a highly effective electromechanical servo system and method to operate the same is provided by which the aforementioned objectives are completely fulfilled.

It is to be clearly understood that the present invention is not to be limited to the embodiment shown and described herein, but is susceptible to numerous changes and modifications as will be apparent to one skilled in the art. For example, the input member of the servo system 100 can be rotatably driven by a belt powered by the vehicle engine. As another example, the means transforming the rotational

movement of the output member 105 into a linear movement of a power operating body, can be any mechanism known in the art, and as non limiting examples, a power screw, or, a rocker and cam system. Similarly, any method known to one skilled in the art can be used for the method of control of the starting clutch 430, either when starting from rest, downshifting or upshifting, since the method described herein is only an example intended to illustrate the functioning of the electromechanical servomechanism object of the invention and of the method to operate the same.

It will be also appreciated that modifications and/or changes may be made in the described embodiments, without departure from the invention. Accordingly, it is to be understood that the foregoing illustrations are illustrative of prefened embodiments only, not limiting, and that the true spirit and scope of the present invention will be determined by reference to the appended claims.