Patent Publication Number: US-7223199-B2

Title: Transmission system

Description:
This invention relates to a transmission system and in particular to a continuously variable transmission for continuously varying a drive ratio of the transmission between a minimum value and a maximum value. The invention has particular application to systems including more than one drive motor and, in particular, to both series and parallel hybrid vehicles including an internal combustion engine and an electric propulsion motor for powering the vehicle. 
   The invention provides a transmission system including: 
   a dual sunwheel system having a first sunwheel and a second sunwheel, the first sunwheel providing output rotary power when the transmission system is operating; 
   a planet system including a first planet gear and a second planet gear coupled to the first planet gear, the first planet gear meshing with the first sun gear and the second planet gear meshing with the second sun gear; 
   a cage for carrying the planet system; 
   input means for receiving input power from an input power source and supplying the input power to the dual sunwheel system to cause the dual sunwheel system to supply rotary power at the first sunwheel; and 
   control means for controlling the dual sunwheel system so as to set the drive ratio of the transmission by causing the first sunwheel to advance or regress relative to the input means by displacing momentum back and forth between the first sunwheel which provides the output rotary power and the control means. 
   In one embodiment of the invention the input means comprises a shaft coupled to the second sunwheel so that rotation of the second sunwheel causes rotation of the planet system to in turn rotate the first sunwheel. 
   In this embodiment of the invention the control means comprises the cage of the sunwheel and cage speed control means for rotating the cage to cause the first sunwheel to advance or regress relative to the second sunwheel and change the drive ratio of the transmission. 
   In other embodiments of the invention the input means comprises the planet cage of the dual sunwheel system and the control means includes a control shaft coupled to the second sunwheel for rotating the second sunwheel to cause the first sunwheel to advance or regress relative to the cage to change the drive ratio of the output relative to the cage. 
   In this embodiment of the invention the input to the cage may be from a single power supply coupled directly to the cage. 
   However, in other embodiments a dual power supply system may be utilised. In this embodiment the cage of the sunwheel system is coupled to an epicyclic planet system, the epicyclic planet system having a first input for input of power and a second input for input of power, the epicyclic planet system being connected to the cage of the dual sunwheel system to thereby rotate the cage to provide the input rotatory power into the dual sunwheel system. 
   The epicyclic planet system includes an epicyclic sunwheel, an orbit gear and at least one said epicyclic planet gear, the said epicyclic planet gear being carried by the cage of the dual sunwheel system, a first input shaft connected to the epicyclic sunwheel and a second input shaft connected to the orbit gear so that when either or both of the first or second input shafts is rotated the epicyclic planet gear orbits about the epicyclic sunwheel to thereby rotate the cage of the dual sunwheel system and provide input rotary power into the dual sunwheel system. 
   The provision of the epicyclic planet system in this embodiment of the invention provides a decoupling of the two input power supplies so that each can remain connected into the system and each can operate independently of the other or jointly with the other without interfering with the operation of the other power supply. 
   In general, transmission systems for hybrid vehicles or other environments in which more than one input supply is used, require an uncoupling of one of the power supplies at some stage when the other of the power supplies is driving the system. This uncoupling is usually performed by a clutch, mechanical dog or other device. The need to provide this uncoupling can result in waste of energy and also additional mechanical components which are required in the system. 
   It would therefore be desirable to provide a transmission system in which the inputs can be decoupled, that is they remain in driving contact with the transmission but each is able to drive independently of the other without effecting the operation of the other. 
   This aspect of the invention relates to a transmission system which has a plurality of input power supplies. 
   This aspect of the invention provides a transmission system including: 
   an epicyclic planet system having an orbit gear, a sunwheel and at least one planet gear between the sunwheel and the orbit gear, the orbit gear receiving input rotary power from a first power source and the sunwheel receiving input rotary power from a second power source; 
   a dual sunwheel system having a first sunwheel and a second sunwheel, the first sunwheel being coupled to an output shaft; 
   the dual sunwheel system further having a planet system including a first planet gear in mesh with the first sunwheel and the second planet gear in mesh with the second sunwheel, the first and second planet gears being coupled together, the planet system being supported in a cage, the cage also carrying the at least one planet gear of the epicyclic planet system so that when input rotary power is input from the first or second source to the orbit gear or the sunwheel of the epicyclic planet system the planet gear of the epicyclic system orbits about the sunwheel of the epicyclic planet system to rotate the cage and thereby supply rotary power to the planet system and to the first sunwheel to drive the output; and 
   a control means coupled to the second sunwheel for controlling the rotary speed of the second sunwheel which in turn rotates the planet system via the second planet gear to cause the first sunwheel to advance or regress relative to the cage to thereby change the drive ratio of the transmission. 
   Preferably the control means includes: 
   a control circuit having at least a first sensor and a second sensor for providing respective signals indicative of the rotary speed of any two of the cage, the second sunwheel and the output, and processing circuitry for receiving the signals and for producing a control signal; and 
   a control mechanism for driving or impeding rotary motion of the second sunwheel dependant on the control signal. 
   In one embodiment of the invention, the first and second sensors sense the speed of the cage and the output respectively. However, in another embodiment, the sensors detect the speed of the cage and the second sunwheel, and the speed of the second sunwheel is used as an indicative speed of the output. 
   In one embodiment of the invention the control mechanism comprises an electric motor. However, in another embodiment of the invention the control mechanism comprises a magnetic powder brake or clutch. 
   In yet in further embodiments the control mechanism may comprise a mechanical or hydraulic variable drive. 
   In embodiments where the electric motor is utilised, the motor uses energy to control the control shaft. That energy is returned to the system as momentum or drive. When the control motor is impeding rotation of the control shaft so as to control the drive ratio of the transmission energy is extracted from the system in the form of electrical power which, can be used to power other electric components or to recharge batteries. 
   If mechanical or hydraulic control systems are utilised those systems may not be as efficient as embodiments in which an electric motor is used. In these embodiments some energy may be put back into the system and some energy will be lost. 
   Preferably the processing circuitry includes: 
   means for setting a predetermined ratio between the first and second signals and for producing an initial control signal indicative of a variation from the set ratio; 
   means for producing the control signal in the form of a variable pulse signal having a duty cycle indicative of the magnitude of the initial control signal; and 
   switch means for receiving the variable pulse signal, the switch means being coupled in a power supply to the control mechanism so that the control mechanism is powered by switching the switching means on by the variable pulse signal so that the control means is powered on in pulse fashion with a duty cycle dependant on the duty cycle of the control signal so the control shaft is driven to increase rotary speed when the control mechanism is powered and impedes rotation on the control shaft when the control mechanism is not powered is set in accordance with the duty cycle of the control signal. 
   In embodiments where the control mechanism is a motor the motor speed is dependant on whether the motor is being driven, that is powered, or is not being driven. The faster the control shaft is moving, the higher gear the transmission is in (that is the lower the gear ratio). If the motor is switched on and powered it can supply drive to the control shaft to increase its speed thereby reducing the gear ratio. If the motor is not powered then the control shaft can slow down thereby increasing the gear ratio. Thus by continually comparing the initial control signal with a predetermined value such as 0 volts, the motor can be switched on or off to either increase the speed of the control shaft or allow the control shaft to slow so as to produce an initial control signal which is indicative of 0 volts or 0 error voltage from the preset level. When 0 volts is produced the controls shaft is rotating at the required speed to provide the required drive ratio and therefore the motor need not be operated. Thus, the motor is continually switched on or off to attempt to achieve an initial control voltage of that 0 voltage. In embodiments where a magnetic clutch or brake is utilised the amount of progressive braking supplied by the clutch is also proportional to the pulse width of the control signal so that the speed of the second sunwheel can be increased or decreased by the magnetic brake or clutch. 
   Preferably the switching means comprises at least one transistor which is provided in series with the control mechanism so that when the transistor is switched on power is able to flow through the control mechanism to activate the control mechanism to increase the rotational speed of the second sunwheel. 
   In one embodiment the control mechanism is a motor, and a second transistor is arranged in parallel with the motor so that when the first transistor is switched off, the second transistor is switched on and current is able to flow through the second transistor and to a load so that in environments in which the motor is running at a speed higher than the input power to the motor the motor can generate electricity and supply that electricity to the load and impede the rotation of the control shaft. 
   In some embodiments of the invention the load may comprise a battery for supplying power to an electric propulsion motor in a hybrid power supply system so that the motor can recharge the batteries depending upon the operating conditions of the motor. 
   Preferably the control circuity includes current sensing means for sensing current supply to the motor and, in the event of over supply of current, switching off the switching means so that current cannot flow through the motor and the motor is de-energised. 
   Preferably the control circuitry also includes a reverse gear signal indicating means for providing a reverse signal when the transmission system is placed in reverse for preventing the switching means from switching on so as to maintain the motor in a switched off condition when the vehicle is in reverse gear. 
   The invention may also be said to reside in a transmission system including: 
   a dual sunwheel system including a first sunwheel provided on an output shaft for supplying output rotary power; 
   a second sunwheel; 
   a control shaft coupled to the second sunwheel; 
   a planet system having at least a first planet gear in mesh with the first sunwheel and a second planet gear in mesh with the second sunwheel; 
   a cage for carrying the planet system; 
   input rotary power supply means for supplying input rotary power to the cage; and 
   control means for controlling the speed of rotation of the control shaft to control the speed of rotation of the second sunwheel to set the drive ratio of the transmission. 
   Preferably the control means comprises a control motor for controlling rotation of the control shaft. 
   In another embodiment of the invention the control means comprises a first magnetic powder clutch having a first component including a coil and a second component including a brake element, the first component being coupled to either the cage or the control shaft, and the second component being coupled to the other of the cage or the control shaft so the component which is coupled to the cage rotates with the cage upon supply of input rotary power to the transmission system, and control power supply means for supplying a control signal to enable energisation of the coil to cause the magnetic clutch to activate so as to progressively lock the component having the coil to the component having the brake element so that rotation is transmitted from the component coupled to the cage to the component coupled to the control shaft to thereby make the control shaft rotate in accordance with the control signal supplied to the coil. 
   In this embodiment of the invention a second magnetic powder clutch of the same structure as the first magnetic clutch is also provided, the second magnetic clutch having its first component fixed stationary and its second component coupled to the control shaft so that when a control signal is supplied to energise the second magnetic clutch the second magnetic clutch can completely lock-up to prevent rotation of the control shaft to thereby cause the control shaft to remain stationary and thereby place the transmission system into reverse gear. 
   In accordance with this embodiment of the invention in order to provide precise ratio control of the transmission both the first and second magnetic clutches can be controlled with control signals from a controller to precisely adjust the speed of rotation of the control shaft to precisely set the drive ratio of the transmission. 
   Preferably the first magnetic clutch has the first component including the coil coupled to the cage for rotation with the cage, the first component including a slip ring for engaging a ring fixed stationary in the transmission system so control signals can be supplied via the fixed ring to the slip ring and to the coil in the first component. 
   In one embodiment of the invention the planet system comprises the first planet gear and the second planet gear fixed integral with the first planet gear, the integral first and second planet gears being mounted on a shaft fixed to the cage. 
   In other embodiments the planet system comprises the first planet gear in mesh with the first sunwheel, the second planet gear being separate from the first planet gear and in mesh with the second sunwheel, and the first and second planet gears being coupled by an idler gear in mesh with both the first and second planet gears. 
   In a still further embodiment the planet system comprises the first planet gear in mesh with the first sunwheel, and the second planet gear being in mesh with the second sunwheel and being coupled in the first planet gear by being in mesh with the first planet gear. 
   In a still further embodiment of the invention the planet system comprises the first planet gear in mesh with the first sunwheel, the second planet gear in mesh with the second sunwheel, and an idler planet gear fixed onto the second planet gear for rotation with the second planet gear and the idler gear being in mesh with the first planet gear to thereby couple the first planet gear to the second planet gear. 
   A still further aspect of the invention may be said to reside in a transmission system including: 
   a dual sunwheel system including a first sunwheel provided on an output shaft for supplying output rotary power, a second sunwheel, a planet system having at least a first planet gear in mesh with the first sunwheel and a second planet gear in mesh with the second sunwheel, the first and second planet gears being coupled together, a cage for carrying the planet system; 
   input rotary power supply means for supplying input rotary power to the dual sunwheel system; 
   a first magnetic powdered clutch having a first component including a coil and a second component including a brake element, the first component being coupled to the dual sunwheel system for controlling the drive ratio of the transmission system or an input drive control, and the second component being coupled to the other of the dual sunwheel system or the input drive control; 
   a second magnetic powdered clutch having a first component including a coil and a second component including a brake element, the first component being coupled to either the dual sunwheel system or being held fixed stationary, and the second component being coupled to the other of the dual sunwheel system or fixed stationary; and 
   power supply means for supplying power to the first and second magnetic powder clutches to control the dual sunwheel system to thereby set the drive ratio of the transmission system. 
   According to this aspect of the invention by controlling the first magnetic clutch preliminary or primary control over the dual sunwheel system is obtained in order to set the drive ratio of the transmission and precise control an more rapid adjustment to a particular ratio can be set by activating the second magnetic clutch which can quickly correct for any over adjustment produced by the first magnetic clutch to thereby set the drive ratio of the transmission system accurately and quickly in response to the environment in which the transmission is operating. 
   In the preferred embodiment of the invention the input drive control comprises the input rotary power supply means so that the input rotary power into the transmission drives the first or second component of the first magnetic clutch so that when the clutch is activated the degree of slippage between the first and second component is changed to cause the other of the first or second component to move with a particular degree of slippage with respect to the first component so as to control the dual sunwheel system to set the drive ratio of the transmission, and wherein additional control is effected by operating the second magnetic clutch so as to cause the first or second component of the second magnetic clutch to further control the dual sunwheel system to set the drive ratio of the transmission. 
   Preferably the first component or second component of the first and second magnetic clutches is connected to the second sunwheel of the dual sunwheel system for controlling the drive ratio of the transmission. 
   Preferably the second sunwheel includes a control shaft and the first or second component of the magnetic clutches is connected to the control shaft. 
   Preferably the second component of the first and second magnetic clutches is connected to the control shaft. 
   Preferably the first component of the first magnetic clutch is connected to the cage for carrying the planet system so that when the cage rotates, the first component of the first magnetic clutch rotates with the cage, and when the first magnetic clutch is operated to produce the desired degree of slippage between the first and second components the second component is caused to rotate in accordance with a degree of slippage of the first magnetic clutch. 
   The invention also provides a controller for controlling a ratio control device for setting a drive ratio of a transmission system, said controller including: 
   sensor means for providing first and second speed signals indicative of the rotary speed of any two of the input power supply into the transmission system, the rotary speed of a ratio control member which sets the drive ratio of the transmission, and the output shaft; 
   ratio adjusting means for setting an adjustment ratio and for providing an output signal if the ratio of first and second speed signals differs from the adjustment ratio; 
   control signal generating means for generating a control signal dependant on the output signal; and 
   switching means for receiving the control signal and for controlling the ratio control device to cause the control device to drive the ratio control member to thereby set the drive ratio of the transmission. 
   Preferably the sensor means provides first and second speed signals indicative of the input power supply and the output shaft. 
   However, in other embodiments, the sensor means for providing the first and second speed signals can provide speed signals of the input and the ratio control member, with the speed of the ratio control member being used as an indicative speed of the output shaft. 
   Preferably the ratio adjusting means comprises a voltage divider pot for receiving the first and second speed signals and outputting the output signal if the ratio of the voltage of the first signal to the voltage of the second signal is different to the ratio set by the voltage divider. 
   Preferably the control signal generating means includes a pair of operational amplifiers, the amplifiers each receiving a saw tooth wave signal and an offset signal, the offset signals being of different magnitude and the output of the operational amplifiers being a variable pulse width signal, set in accordance with the magnitude of the output signal, which provides said control signal. 
   Preferably the operational amplifiers are coupled to the switching means for controlling the switching means to enable the switching means to switch power supply to the control device so that the control device is operated in accordance with the duty cycle of the variable pulse width signal supplied to the switching means. 
   In one embodiment of the invention the switching means comprises a first transistor connected in series with the control device so the each time the transistor is switched on for a period set by the duty cycle of the control signal the motor is powered on for periods set the duty cycle of the control signal. 
   In the embodiment which includes a control device in the form of a motor, a second switching transistor is also provided for enabling the motor to generate electricity in some operational conditions of the transmission system and supply the generated electricity to a load. In this embodiment the first transistor is switched off when the second transistor is switched on so that motor is connected to the load for supply of the electricity to the load and cause the rotation of the control shaft to be impeded to rotate the motor in a state of constant speed regardless of changing momentum condition in the transmission system. 
   In some embodiments of the invention the load may be a battery and the supply of electricity can be used to recharge the battery. 
   Preferably the controller also includes an overcurrent sensing means for sensing the supply of overcurrent to the motor and for causing the motor to be switched off to prevent damage to the motor. 
   Preferably the motor is caused to be switched off by the supply of a signal which prevents the first transistor from switching on to enable power to be supplied through the motor to operate the motor. 
   Preferably the controller also includes a reverse signal generator for providing a signal when the transmission system is placed in reverse gear for preventing switching on of the first transistor to also prevent the motor from being energised by the supply of power to the motor. 
   Preferably the sensors comprise sensing circuitry which provides a first voltage signal which is a voltage signal proportional to the speed of the input and a second voltage signal which is proportional to the speed of the control member. 
   In one embodiment of the invention the sensor may include chopper wheels connected to the input and the control member, and photo-interrupters for generating pulses when the chopper wheels rotate with the input and the control member, the pulses producing frequency signals which are converted into voltage signals proportional to the frequency and therefore proportional to the rotary speed of the input and the control member. 
   The invention may also be said to reside in a transmission system including: 
   a first sunwheel; 
   an output connected to the first sunwheel for providing output rotary power; 
   a control sunwheel; 
   a planet system including a planet cage having first and second planet gears, the first planet gear meshing with the first sunwheel and the second planet gear meshing with the control sunwheel; 
   input supply means for supplying input to the planet cage so that rotary power is transmitted from the cage via the first and second planet gears to the first sunwheel and therefore to the output; 
   a controller for:
         (a) receiving signals indicative of the rotary speed of at least any two of the output, the control sunwheel and the input supply means, and for producing control signals based on the said at least any two of the speeds of the output, the control sunwheel and the input supply means, to enable a change in drive ratio in a forward direction of the transmission; and   (b) producing a locking signal when reverse motion of the transmission is required;       

   a first progressive control device for receiving the control signals from the controller to speed up or slow down the control sunwheel between a stationary condition of the sunwheel and a first rotary speed of the sunwheel to change the drive ratio of the transmission; and 
   a second control device for receiving the locking signal from the controller for locking the sunwheel to the input to increase the speed of rotation of the control sunwheel to a speed above the first speed to thereby place the transmission into reverse. 
   Preferably the first control device comprises a magnetic powder clutch. 
   Preferably the second control device comprises a cone clutch. 
   Preferably the sunwheel is provided on a control shaft and the control shaft carries a gear which meshes with a gear coupled to an output of the first device and also with a gear coupled to an output of the second control device. 
   Preferably the controller includes a processor for receiving signals indicative of the speed of the input supply means and the speed of the output, switching means connected to the processor for receiving output signals from the processor to switch the switching means on and off to produce control signals for application to the first progressive control device for actuating the first progressive control device to speed up or slow down the control sunwheel. 
   Preferably the control signals comprise: 
   a DC pulse signal for actuating the first progressive control device to lock the first progressive control device to the control sunwheel; 
   a variable AC frequency signal for controlling the first progressive control device to adjust the speed of the control sunwheel to a speed less than the said first speed; and 
   a variable pulse width AC signal for actuating the first progressive control device to enable the control device to control the speed of the control sunwheel from the said certain speed to the first speed. 
   Preferably the controller includes means for producing a transition AC/DC signal for transition of the control signal from the DC pulse signal to the AC variable frequency signal. 
   The invention may also be said to reside in a transmission system including: 
   a first sunwheel; 
   an output connected to the first sunwheel for providing output rotary power; 
   a control sunwheel; 
   a planet system including a planet cage having first and second planet gears, the first gear meshing with the first sunwheel and the second planet gear meshing with the control sunwheel; 
   input supply means for supplying input rotary power to the planet cage so the rotary power is transmitted from the cage via the first and second planet gears to the first sunwheel and therefore to the output; 
   a controller including speed indicating means for providing signals indicative of the rotary speed of at least any two of the output, the control sunwheel and the input supply means, and for generating a control signal for controlling the drive ratio of the transmission system; and 
   a control mechanism for receiving the control signal and for controlling the control sunwheel in accordance with the control signal to thereby adjust the drive ratio of the transmission. 
   In one embodiment the control device includes a first progressive control device for receiving the control signal from the controller to speed up or slow down the control sunwheel to change the drive ratio of the transmission. 
   In this embodiment the control device may also include a second control device, the controller also being for generating a locking signal indicative of the requirement for reverse gear, the second control device being for receiving the locking signal and for causing the second control device to lock the control sunwheel to the input to increase the speed of rotation of the control sunwheel to a speed above the first speed to thereby place the transmission into reverse gear. 
   Preferably the first control device comprises a magnetic powder clutch. 
   In one embodiment of the invention the control sunwheel is connected to a control shaft which comprises a first control shaft portion and a second separate control shaft portion, the first and second control shaft portions being coupled together by gears, the control mechanism being mounted on the second control shaft portion. 
   In one embodiment of the invention the control device is mounted for rotation and is coupled to control shaft drive means for rotating the control mechanism. 
   Preferably the control shaft drive means comprises a gear system which transmits drive from the input to the control device. 
   Preferably the gear system comprises a ring gear coupled to the cage, a pinion gear meshing with the ring gear, a shaft coupled to the pinion gear, a second pinion gear on the shaft, a second ring gear having internal and external teeth, the second pinion meshing with the internal teeth, and the external teeth meshing with a gear coupled to the control device for rotating the control device. 
   Preferably the control device comprises a magnetic powder clutch having an outer housing portion coupled to the further gear, and an inner section mounted on the second portion of the control shaft, so that when the input is driven, the outer housing of the powder clutch is rotated by the gear system and when the powder clutch is activated, the inner section and second portion of the control shaft is controlled in rotation, dependent on the control signal supplied to the powder clutch to in turn control the rotation of the first portion of the control shaft and therefore the control sunwheel, to set the drive ratio of the transmission. 
   In a still further embodiment of the invention the second portion of the control shaft includes a variable centroid system having moveable masses which, upon rotation of the second portion of the control shaft, move rotary outwardly to slow down rotation of the second portion of the control shaft and therefore the first portion of the control shaft. 
   In a still further embodiment the control device includes a first variator having a toroidal gear track having gear teeth which change in pitch from an inner diameter portion to an outer diameter portion, the first variator being coupled to a variator drive mechanism for rotating the first variator, a second variator having a toroidal track having gear teeth which change in pitch from an inner diameter portion to an outer diameter portion, the second variator being connected to the control shaft, a pitch transfer gear in mesh with the gear teeth of the first variator and the gear teeth of the second variator, means for rotating the pitch transfer gear so that the gear can engage at any portion along the variable pitch of the toroidal track of the first variator and the toroidal track of the second variator to thereby set a drive ratio between the first and second variators, and a driver for setting the orientation of the pitch transfer gear. 
   Preferably the variator drive system comprises a gear system for transmitting drive from the input cage to the first variator. 
   Preferably the control shaft comprises a first control shaft portion and a second control shaft portion, a pair of gears for coupling the first control shaft portion to the second control shaft portion, the first variator being rotatable relative to the second control shaft portion and the second variator being mounted on the second control shaft portion for rotating the second control shaft portion so that the second control shaft portion and therefore the first control shaft portion is controlled in rotation, dependent on the gear ratio set by the pitch transfer gear. 
   Preferably the orientation of the pitch transfer gear is set by a stepper motor and the stepper motor receives the control signal to activate the stepper motor to rotate the stepper motor to in turn change the position of the pitch transfer gear to control the rotation of the control shaft and therefore the control sunwheel. 

   
     Preferred embodiments of the invention will be described, by way of example, with reference to the accompanying drawing in which: 
       FIG. 1  is a schematic diagram of a transmission system according to a first embodiment of the invention; 
       FIG. 2  is a schematic diagram of a transmission system according to a second embodiment of the invention; 
       FIG. 3  is a cross-sectional view through part of the transmission system of  FIG. 1 ; 
       FIG. 4  is a schematic view of a modified form of the system shown in  FIG. 2 ; 
       FIG. 5  is a cross-sectional view through part of the embodiment of  FIG. 4 ; 
       FIG. 6  is a cross-sectional view of a transmission system according to a still further embodiment of the invention; 
       FIGS. 7 ,  8  and  9  are views showing various dual sunwheel systems which are used in the embodiments of the invention; 
       FIG. 10  is a circuit diagram forming part of a control system used in the preferred embodiments of the invention; 
       FIG. 11  is a further circuit diagram showing the remainder of the control system used in the preferred embodiment of the invention; 
       FIG. 12  is a diagram showing an operational amplifier used in the circuit of  FIG. 11  and used to illustrate operation of that circuit; 
       FIG. 13  shows how pulse width control is performed by the circuit of  FIG. 11  in order to control the drive ratio of the transmissions according to the preferred embodiments of the invention; 
       FIGS. 14 ,  15 ,  16 ,  17 ,  18  and  19  are diagrams showing signals created and used in the circuit of  FIG. 11  to facilitate explanation of the manner in which the circuit operates; 
       FIG. 20  is a circuit diagram similar to  FIG. 19 , showing a further embodiment of the invention; 
       FIG. 21  is a graph which explains the control of the control shaft and the manner in which momentum is switched to displace momentum from one part of the transmission to another part of the transmission; 
       FIG. 22  is a cross-sectional view of a still further embodiment of the invention which operates in accordance with the principles described with reference to  FIG. 21 ; 
       FIG. 23  is a perspective view of the embodiment of  FIG. 22  with some of the parts removed for ease of illustration; 
       FIG. 24  is a block circuit diagram of a second controller according to another embodiment of the invention which has particular application to the embodiment of  FIGS. 22 and 23 ; 
       FIG. 25  is a diagram of a further section of the controller according to the second embodiment; 
       FIGS. 26 ,  27 ,  28 ,  29  and  30  are wave form diagrams which will be used to explain the embodiment of  FIGS. 24 and 25 ; 
       FIG. 31  is a simplified circuit diagram of part of the circuit of  FIG. 25  used to facilitate explanation of the wave form diagrams of  FIGS. 26 to 30 ; 
       FIG. 32  is a graph illustrating the transmitted torque v 1/impedance of a powder clutch used in the embodiment of  FIGS. 22 and 23 , also used to explain the operation of  FIGS. 26 to 31 ; 
       FIG. 33  shows a further embodiment which is a modification to the embodiment described with reference to  FIG. 22 ; 
       FIG. 34  shows a still further modification to the embodiment of  FIG. 33 ; 
       FIG. 35  is still a further embodiment of the invention which shows a different modification to the embodiment of  FIG. 22 ; and 
       FIG. 36  is a perspective view of the embodiment of  FIG. 35  from the exterior of the transmission casing. 
   

   With reference to  FIG. 1  a transmission system for a hybrid drive for a motor vehicle is disclosed. The hybrid drive of the motor vehicle includes an internal combustion engine  12  and an electric propulsion motor  14 . One of the other motors  12  or  14  or both of the motors  12  or  14  can be used to provide power to drive a vehicle. 
   The transmission system of this embodiment of the invention includes an epicyclic planet system  16  and a dual sunwheel transmission  18 . The dual sunwheel transmission  18  drives an output  20 . 
   The internal combustion motor  12  and the electric propulsion motor  14  provide first and second inputs into the epicyclic planet system  16 . The input from the motor  12  is via a first input shaft  22  into the epicyclic planet system  16  and the input from the electric propulsion motor  14  is via a belt  24  to a second shaft  26  of the epicyclic planet system  16 . The input shafts  22  and  26  will be described in more detail with reference to  FIG. 3 . 
   In the embodiment shown in  FIG. 1  the drive from the propulsion motor  14  is via the belt  24 . However, in production embodiments the electric propulsion motor  14  can be directly mounted on the shaft  26  so that it surrounds the shaft  26  and drives the shaft  26  directly without the need of a belt  24  to transmit the drive. 
   The transmission system of  FIG. 1  also includes a control motor  28  which controls rotation of a control shaft  30  of the dual sunwheel system  18 . Drive is transmitted from the control motor  28  to the shaft  30  via a belt  32 . However, once again, the control motor  28  can be mounted directly on the shaft  30  so that drive is transmitted directly to the shaft  30  without the need for a belt  32 . 
   In the embodiment of  FIG. 1  drive from either the motor  12  or the motor  14 , or drive from both the motors  12  and  14  is input into the epicyclic planet system  16  which in turn drives the dual sunwheel system  18 . Output power is supplied from the sunwheel system  18  to the shaft  20  to provide output propulsion. The drive ratio of the transmission is controlled by rotating the control shaft  30  relative to the input into the dual sunwheel transmission  18  by appropriate control of the control motor  28  as will be described in more detail hereinafter. 
   The coupling of the internal combustion motor  12  and electric propulsion motor  14  to the dual sunwheel system  18  via the epicyclic planet system  16  provides a decoupled connection of the two motors into the transmission which means that each can function independently except that they are part of the same planetary system and will alter the ratio at which power is input into the transmission. That is, if one motor shuts down the other is asked to supply sufficient power to drive the whole system and is able to do this because the decoupling causes a higher ratio for the motor left driving. Thus, the decoupling of the system by the epicyclic planet system enables both motors to be always connected to the system and either one or the other or both are able to provide drive without the need to disconnect one motor from the system such as by a clutch, dog or other mechanical device which would therefore uncouple one of the motors from the system when it is not required to drive. 
   In the embodiment of  FIG. 1  the control motor  28  is controlled to control the control shaft  30  to set the drive ratio of the transmission. However, in some operating conditions the control motor  28  can also act as a generator to supply electricity. This supply of electricity can be used to recharge batteries (not shown) which power the electric propulsion motor  14 . 
     FIG. 2  shows a transmission system according to a second embodiment of the invention. In this embodiment only a single drive motor such as an internal combustion motor  12  is utilised. The internal combustion motor  12  is connected to an input shaft  27  coupled to a planet case  42  (see  FIG. 5 ) the sunwheel transmission system  18 , and the sunwheel system has a control shaft  30  which is controlled by a control motor  28  via a belt  32  in the same manner as the previous embodiment. Once again, output power is supplied to output shaft  20  for driving a vehicle or other machine. 
     FIG. 3  is cross-sectional view through the transmission system used in the embodiment of  FIG. 1 . With reference to  FIG. 3  input shaft  22  from motor  12  is connected to a sunwheel  35  of the epicyclic planet system  16 . The second input shaft  26  is connected to planet cage  36  of the system  16 . Planet cage  36  carries an orbit gear  38  which has internal teeth  40 . A plurality of planet gears  38  (only one shown) mesh with teeth  39  of the sunwheel  35  and also teeth  40  of the gear  38 . The planet gears  38  are journalled on shafts  40  which are fixed to a planet cage  42  of the dual sunwheel system  18 . 
   As shown in  FIG. 3  the shaft  26  is concentric with the shaft  22  and in order to provide relative rotation between the shaft  22  bearings or bushes  44  are provided between the shaft  22  and  26 . The shaft  26  may also be mounted on an external bearing  45 . Planet cage  36  of the epicyclic system  16  is mounted on the planet cage  42  via bearing  49 . The cage  42  of the dual sunwheel system  18  is mounted on a stub end  50  of input shaft  22  via a bearing  53 . 
   Thus, when input drive is supplied to either the input shaft  22  or the input shaft  26  or both the input shafts  22  and  26  that drive is transmitted to planet cage  42  of the dual sunwheel system  18  via, in the case of the shaft  26 , the planet cage  36 , the gear  37 , the planet gear  38  and the shaft  40  which connects to the planet cage  42  to therefore drive the planet cage  42 , and in the case of the input shaft  22  via the sunwheel  35 , the planet gear  38  and therefore the shaft  40  to drive the planet cage  42 . That is, in both arrangements the orbiting of the planet gears  38  about the sunwheel  35  will carry with them the cage  42  so that the cage  42  is rotated about the longitudinal axis of the input shaft  22  and  26 . 
   The cage  42  carries a plurality of planet systems  60 . In the embodiments shown in  FIG. 3  the planet systems  60  are in the form of a planet cluster having a first planet gear  62  and a smaller planet gear  64  formed integral with the planet gear  62 . The integral cluster  60  is mounted on a shaft  66  which is fixed in the planet cage  42 . In other embodiments, as will be described with reference to  FIGS. 7 to 9  the planet system  60  can take forms other than an integral planet cluster of the type shown in  FIG. 3 . 
   The dual sunwheel system  18  includes a first sunwheel  70  and a second sunwheel  80 . The second sunwheel  80  is formed integral with the control shaft  30 . The first sunwheel  70  is formed on the output shaft  20 . The first sunwheel  70  has teeth  72  which are in mesh with teeth  68  on the planet gear  62  and the second sunwheel  80  has teeth  82  which are in mesh with teeth  69  on the second planet gear  64 . 
   As is shown in  FIG. 3  the cage  42  is mounted onto the control shaft  30  by a bearing  88  and the cage  42  has a bearing  90  which mount onto a casing (not shown) of the transmission. As seen in  FIG. 3  the control shaft  30  is mounted onto the output shaft  20  via bearings or bushes  81  so as to allow for relative rotation between the shafts  20  and  30 . 
   When the planet cage  42  is rotated due to input power supply to the shafts  22  and  26  the planet cluster  60  is carried with the cage  42 . Because of the meshing of the gear  62  with the sunwheel  70  drive is transmitted to the sunwheel  70  to rotate the sunwheel  70  and therefore rotate the output shaft  20  to provide output rotary power from the transmission. In order to control the drive ratio of the transmission the control shaft  30  is controlled by the control motor  28  described with reference to  FIG. 1  so as to rotate the control shaft  30  at a predetermined speed relative to the input cage  42 . By changing the speed of rotation of the control shaft  30  relative to the input cage  42  the speed of rotation of the sunwheel  80  is also changed relative to the cage  42 . Because of the meshing of the sunwheel  80  with the planet gear  64  and integral coupling of the planet gear  64  with the gear  62  a change in relative speed of the sunwheel  80  will cause the planet cluster  60  to advance or regress relative to the cage  42  thereby causing the speed of the sunwheel  70  to advance or regress to thereby change the speed of the sunwheel relative to the cage  42  and change the speed of the output shaft  20  relative to the input shafts  22  and/or  26 . 
   In order to control the drive ratio of the transmission the speed of rotation of the input cage  42  relative to the control shaft  30  or output  20  needs to be known so that the control shaft  30  can be controlled relative to the speed of the input cage  42  and output shaft  20  to set the drive ratio. In order to provide data for the relative control of the shaft  30  with respect to the input cage  42 , the input cage  42 , output shaft  20 , and the control shaft  30  carry a slotted chopper wheel  90 . The wheel  90  rotate with the cage  42 , shaft  20  or the shaft  30  as the case may be and each of the wheel  90  has a photo-interrupter  92  associated with it. As each slot (not shown) in the wheels  92  pass through the respective photo-interrupter  92  a light pulse is detected within the photo-interrupter  92  to provide data relating to the speed of rotation of the shafts  20 , 30  and also the input cage  42 . 
   In other embodiments rather than use a chopper wheel and optocoupler, other devices for providing data relating to the speed of rotation of the shafts  20  or  30  and the cage  42  can be used such as encoders and the like. 
   The manner in which the speed of the control shaft  30  and input cage  42  is monitored and used to control the drive ratio of the transmission will be described in more detail with reference to  FIGS. 10 and 11 . 
   In the embodiment of  FIG. 3 , if the control shaft  30  is rotating at the same speed as the input cage  42  then drive ratio set by the transmission is 1:1. If the control shaft  30  is rotating at speed slower than the input cage  42  then the drive ratio will drop from 1:1 down towards neutral depending on the speed differential between the control shaft  30  and the input cage  42 . If the control shaft is completely stopped the output shaft  20  will be caused to turn in the reverse direction thereby providing a reverse gear. If the speed of the control shaft is greater than the input cage  42  then the drive ratio will go into overdrive. 
   Thus, by controlling the speed of the control shaft  30  via the control motor  28  the drive ratio of the system can be set. 
     FIG. 4  is a view of a modified form of the second embodiment described with reference to  FIG. 2 . In this embodiment rather than utilise control motor  28  in order to control the drive ratio of the transmission the drive ratio is controlled by a magnetic clutch or brake system  110 . The magnetic clutch or brake system  110  provides a progressive braking force to the control shaft  30  to adjust its speed. Such clutches are known and therefore need not be described in detail. 
   In this embodiment of the invention a second magnetic clutch  120  which can be identical to the first clutch is mounted on a shaft  122  which is coupled to the control shaft  30  by a belt  124 . The purpose of the second clutch  120  is to provide a reverse gear. This system incorporates electric ratio control system  124  for supplying power to the clutch  110  to cause the progressive braking so that the shaft  30  is driven at the prescribed speed and an electronic reverse control  126  which provides power to the clutch  120  to provide the reverse gear function. 
   As explained-with reference to  FIG. 2  this embodiment of the invention includes a single drive motor such as an IC motor  12 . 
     FIG. 5  is a cross-sectional view through the transmission system of  FIG. 4 . Input supply is provided from the motor  12  to the input shaft  22  which is coupled to first planet cage  42 . Planet cluster  60  is mounted in cage  42  and, as in the earlier embodiment, planet gear  62  meshes with the sunwheel  70  which is fixed onto the output shaft  20 . Second sunwheel  80  is mounted on the control shaft  30  as in the earlier embodiment and, in this embodiment the output shaft  20  can extend through the control shaft  30  simply so that output power can be taken from either end of the transmission shown in  FIG. 5 . 
   As in the earlier embodiment planet cluster  60  is fixed to the cage  42  and the first planet gear  62  meshes with the sunwheel  70  and the second planet gear  64  meshes with the sunwheel  80 . The first magnetic clutch  110  has a housing  120  which includes a sleeve section  123  which is fixed to cage  42 . The housing  120  is mounted on bearings  126  for rotation relative to the control shaft  30 . The housing  120  carries coil  128  which is connected to a slip ring  127 . The slip ring  127  is provided adjacent ring  128  mounted in block  129  which is fixed to casing  150  in which the transmission is mounted. A bearing  130  is provided between the sleeve  123  and the casing  129  to provide for relative rotation of the sleeve  123  relative to the block  129 . Electric current for controlling the coil  128  is supplied by wires  134  into ring  128  and then into slip ring  127  which rotates relative to ring  128  and slides on the ring  128  so power can be transmitted from the fixed ring  128  to the slip ring  127  and then into the coil  128 . A brake element  130  is provided within the housing  120  and fixed to the control shaft  30 . Cavity  132  between the brake element  130  and the coil  128  is filled with a non-permanently magnetisable material such as ferromagnetic material. When current is supplied to the coil  128  the ferromagnetic material progressively provides an impedance to the brake element  130  to thereby control the speed of rotation of the control shaft  30  relative to the input cage  42 . 
   Thus, in this embodiment of the invention drive is transmitted from the input shaft  27  to the cage  42 , the planet cluster  60  and then to the sunwheel  70 . Because the housing  120  of the magnetic clutch  110  is fixed to the cage  42  the housing  120  is rotated with the cage  42 . If no current is supplied to coil  128  the cage  120  is able rotate freely relative to the brake element  130  and therefore no control over the output  30  is supplied by the magnetic clutch  110 . Thus, the output shaft  20  is driven with the input cage  42  via the input shaft  27  because of the transmission of drive from the cage  42  through the planet cluster  60  to the first sunwheel  70  which is fixed onto the output shaft  20 . 
   If the magnetic clutch  110  is controlled so that the coil  128  is effectively locked onto the brake element  130  so that the brake element  130  rotates with the housing  120 , the control shaft  30  is therefore rotated at the same speed as the input cage  42  and the drive ratio of the transmission is set at 1:1. Once again, if the control shaft rotates at a lower speed the drive ratio can change from 1:1 down to neutral depending on the relative speed differential. Neutral is achieved when the control shaft  30  is rotating quite slowly just before it stops. In order to stop the control shaft  30  so as to provide the reverse gear the second magnetic clutch  120  is energised to completely stop the control shaft  30  from rotating. In the embodiment of  FIG. 5  the second magnetic clutch  130  is shown mounted directly on the control shaft  30  beside the first clutch  110  rather than being connected via the belt  124  shown in  FIG. 4 . Coil  141  of the second clutch  120  is mounted within the casing  150  and a brake element  142  of the second clutch  120  is fixed onto the control shaft  30  in the same manner as the brake element  130 . Thus, when the coil  141  is fully energised to completely lock the brake element  142  to the coil  141  the shaft  30  is prevented from rotating because the coil  141  is fixed onto the casing  150 . Once the shaft  30  is prevented from rotating the output shaft  20  is caused to rotate backwards by the drive transmitted from the cage  42  to the planet cluster  60  to the sunwheel  70  and therefore to the output shaft  20  thereby providing reverse gear. Thus, reverse gear is simply provided by controlling the second clutch  120  via the control  126  to cause the magnetic clutch  120  to provide full braking and therefore full coupling of the coil  141  to the brake element  142  so no rotation can occur between the element  142  and the coil  141  because the coil  141  is held fixed in the casing  150  the control shaft  30  is therefore completely stopped and held stationary. When it is no longer required to place the transmission into reverse the power to the coil  141  is stopped thereby releasing the braking effect of the second clutch  120  so that the control shaft  30  can then rotate under the influence of the control signals applied to the first magnetic clutch  110 . 
   As in the earlier embodiment, if the control shaft  30  is controlled so that it rotates faster than the input cage the transmission goes into overdrive. 
   Although in the embodiment described above the second magnetic clutch  120  is used only for completely stopping the control shaft  30  to provide reverse gear, the second magnetic clutch  120  can also be used in combination with the first magnetic clutch  110  so as to provide precise control over the ratio set in the transmission. This can be achieved by controlling the magnetic clutches  110  and  120  to provide the braking previously described without fully locking the magnetic clutch  120  to stop the control shaft. The second magnetic clutch  120 , apart from providing reverse gear, can also thereby provide some additional control over movement of the control shaft  30  that precise ratios can be set if desired. 
   The ability to use the second magnetic clutch  120  to assist in setting and controlling the drive ratio of the transmission in the embodiment described above is quite important because the effective “dynamic range” of the first magnetic clutch between fully locked on condition and fully released condition is relatively short. Therefore, it can be difficult to precisely set the drive ratio of the transmission or control the drive ratio of the transmission with only the first magnetic clutch operating. Using the second magnetic clutch provides a rapid means of correcting any error in the drive ratio which is set by the first magnetic clutch by quickly switching the second magnetic clutch on to provide an impedance or slight braking of the control shaft  30  in response to any over correction or adjustment of the control shaft, and therefore over correction or adjustment of the drive ratio of the transmission, which is set upon operation of the first magnetic clutch  110 . Thus, by using the first and second magnetic clutches in combination the drive ratio of the transmission can be more quickly and accurately adjusted and set in accordance with the driving conditions which the transmission is experiencing and the drive ratio which is actually required or set by an operator. 
   The control of the magnetic clutches is substantially identical to the control of the control motor  28  in the earlier embodiment and generally the same control circuit to be described with reference to  FIGS. 10 and 11  can be utilised. The magnetic clutches  110  and  120  are controlled by varying the duty cycle or pulse width of a signal supplied to the clutches so as to cause the gradual and progressive braking of the clutches to provide the required speed control over the shaft  30 . For example, if no signal is applied to the coils of these clutches, in other words a signal having 0 duty cycle is applied, then the brake elements  130  and  142  are able to rotate freely. If a signal having a 100% duty cycle is supplied to the coils  128  and  141  the brake elements  130  and  142  are caused to lock fixed to the coils so that the brake elements cannot move relative to the coils and, in the case of the clutch  110  the brake element  130  and therefore the control shaft  30  will rotate with the coil  128  and therefore the cage  120  and input cage  42 , and in the case of the clutch  120  the brake element  142  would remain stationary since the coil  141  is fixed stationary. If a signal having a duty cycle somewhere between 0 and 100% is supplied to the coils  128  and  141  then a partial braking effect is provided which, in the case of the clutch  120  will cause the brake element  130  to be dragged around with the coil  128  and housing  120  with a prescribed degree of slippage which is proportional to the duty cycle of the signals supplied. Thus, by varying the duty cycle the speed of rotation of the control shaft  30  relative to the input cage  42  can be set so as to set the speed of the control shaft  30  to set the drive ratio of the transmission. 
   As can be seen in  FIG. 5  the second clutch  120  is mounted on bearings  145  to allow for rotation of the control shaft and the brake element  142  relative to the coil  141  and the casing  150  when no power is supplied to the coil  141 . 
   As in the earlier embodiments the control shaft  30  is mounted onto the output shaft  20  by bearings  147 . The input shaft  27  is also mounted on the output shaft  20  via bearings  148  to provide relative rotation between the output shaft  20  and the input  27 . 
   In the embodiment of  FIG. 5  the output shaft  20  is shown extending completely through the transmission. However, the output shaft need not extend any further than the first sunwheel  70  and the input  27  could be mounted on a lay shaft or otherwise journalled for rotation if desired. The arrangement shown in  FIG. 5 , as previously mentioned, simply provides configuration in which output power can be taken from either end of the transmission as is required. 
     FIG. 6  shows a still further embodiment of the invention. In this embodiment input rotary power is supplied by input shaft  170  to sunwheel  172  of the dual sunwheel system  18 . Second sunwheel  174  is connected to output shaft  20 . Cage  176  supports a plurality of planet systems  60  which, in this embodiment comprise a first planet gear  162  which is in mesh with the sunwheel  172  and a second planet gear  178  which is in mesh with the sunwheel  174 . The gear  178  is formed separate from the gear  162  and meshes with the gear  162 . The gears  162  and  178  are supported on separate shafts journalled in the planet cage  176 . 
   Planet cage  176  carries a control gear  179  which is integral with the cage  176  or fixed onto the cage  176 . 
   In this embodiment of the invention the input rotary power is supplied from a motor (not shown) to the input shaft  172  which rotates the sunwheel  172 . Drive is transmitted to the planet gear  162  and then to the planet gear  178  which in turn, rotates the sunwheel  174 . Rotation of the sunwheel  174  drives the output  20 . In order to change the drive ratio of the transmission the cage  174  is caused to advance or regress relative to the sunwheel  172  by supplying drive to the gear  179 . Advancing or regressing the cage  176  will cause the planet cluster  60  to advance or regress the sunwheel  174  thereby changing the drive ratio of the shaft  20  relative to the shaft  170 . 
   The gear  179  is controlled to in turn control the rotation of the cage  176  by a control motor  28  which is the same as that previously described. The control system of this embodiment is shown in dotted lines and can include a lay shaft  191  connected to the motor  128 . The lay shaft  191  carries a transfer gear  191   a  which is in mesh with the gear  179  so that by controlling the motor  28  the gear  191   a  is rotated to rotate the gear  179  and the cage  176 . 
   In other arrangements the control may be preformed by a magnetic clutch  110  shown in dotted lines in  FIG. 6  which is the same as that described with reference to  FIG. 5 . In this embodiment the magnetic clutch is connected to the input shaft  170  and also to the cage  176  via the stem portion  182  of the cage  176 . As in the earlier embodiment, the coil can be mounted onto the shaft  170  and the brake element onto the stem  182  so that, depending on the signal supplied to the clutch  110  the stem  182  and the cage  176  is caused to rotate at a speed which is either identical to the input shaft speed or a described ratio with respect to the input shaft speed depending on the signal which is supplied to the clutch  110 . 
   The embodiment of  FIG. 6  has particular application to controlling the speed of machines which include one or more rollers and which are coupled to the output shaft  20  so as to enable at least one of those rollers to rotate at a precise drive ratio to other rollers. This, in turn, requires the machine to be able to control the drive ratio of the output shaft  20  very precisely so that the drive ratio between various rollers in the machine can be set. Thus, in this embodiment of the invention only forward rotation of the output shaft  20  is required and a reverse is never needed. 
   As shown in  FIG. 6  the cage  176  is supported on bearings  180  by the stem portion  182 . A casing  190  is arranged around the transmission and includes cover plates  192  and  196  which are either bolted to or fixed integral to the casing  190  and which mount on bearings  197 . As also shown the cage  176  is mounted onto the output shaft  20  via bearing  199  to provide for relative rotation between the cage  176  and the output shaft  20 . 
   Although in  FIG. 6  the transmission has been described primarily with the shaft  170  acting as the input and which is driven by motor  110  and ratio control being achieved by controlling the cage  176 , this transmission can be considered as a duel input system in which drive through both of the input shaft  170  and cage  176  power the transmission. In this case, the speed of the transmission is controlled by driving the cage  176 , while the motor  110  which drives the shaft  170  is used as a tension sensing device and will modify the ratios produced by the control of the cage  176 . 
   In this embodiment the motor  28  which controls the cage  176  can be a simple three phase motor and the nature of the control can be by way of the motor controller of the three phase motor. 
   The gear box of  FIG. 6  is designed to perform very slow changes in ratio and to operate under constant load. The speed of the transmission is controlled by the motor  28  and the uncontrolled motor  110  simply senses the tension on the output shaft  20  through the process of what is known as slip in the motor  110 . 
   Although the embodiment of  FIG. 6  has been described in terms of the input power supply being introduced into the shaft  170 , which in other embodiments is described as the control shaft, and control being performed by manipulation of the cage  176 , the control is nevertheless performed by relative speed variation between the cage  176  and the shaft  170 . Thus, for all intents and purposes, this embodiment could still be regarded as the same as the earlier embodiments in which input drive is provided into the cage  176  and control is provided by rotation of the shaft  170 . 
     FIGS. 7 to 9  show first different embodiments of planet cluster system  60  which can be utilised in the preferred embodiments of the invention.  FIG. 7  shows a configuration similar to that shown in  FIG. 3  except in this embodiment the first sunwheel is larger than the second sunwheel  80  and the first planet gear  62  of the cluster  60  is smaller than the second planet gear  64 . This form of planet cluster  60  and sunwheel configuration can be used in systems; 
   in which no reverse gear is required. In this system the output ratio is equal to 
           1     (     1   -     (       A   /   B     ×     C   /   D       )               
with control shaft stationary;
 
   the control gear ratio is 
           1     (     1   -     (       B   /   A     ×     D   /   C       )               
with stationary (Neutral);
 
   where A, B, C are the number of teeth on the sunwheel  80 , second planet gear  64 , first planet gear  62  and first planet gear  70  respectively. 
     FIG. 8  shows a system in which very high or very precise ratios are required. In this embodiment the first and second planet gear  62  and  64  are separated from one and other and mesh with an idler gear  200 . The drive ratio can be determined in accordance with the equation referred to above and the idler gear  200  need not be considered. 
     FIG. 9  shows an arrangement in which the planet gear  64  carries a integral gear  201  which in turn meshes with the gear  62 . The gear  201  is smaller than the gear  64 . In this embodiment overdrive gear ratios can be provided and the control shaft  30  can turn in the same direction as the input. 
   The drive ratio is set by the following equation, in which A, B, C and D have the same meaning as described above. 
                   R   ⁢           ⁢   output     =     1     (     1   -     (       A   /   B     ×     C   /   D       )                         R   ⁢           ⁢   control     =     1     (     1   -     (       B   /   A     ×     D   /   C       )                       
when in neutral
 
     FIGS. 10 and 11  show control circuitry for monitoring the speed of the input cage  42 , the output shaft  20 , and the control shaft  30 . As previously explained the control shaft  30  and the input cage  42  are provided with a chopper wheel  90  which has a plurality of slots and which with the respective cage  42  or control shaft  30 . 
   In order to provide the control, any two of the speed of the input cage  42 , the output shaft  20  or the control shaft  30  needs to be measured. If the speed of any two of the input cage  42 , the output shaft  20  and the control shaft  30  is known, the speed of the remaining one of the input cage  42 , the output shaft  20  and the control shaft  30  can be determined. This is because the speed of all of these components are interrelated by a function which is dependent on the number of teeth on the gears in the planetary system and on the sunwheels. Thus, for any particular speed of two of the input cage  42 , the output shaft  20  and the control shaft  30 , the speed of the remaining one of the input cage  42 , the output shaft  20  and the control shaft  30  can be calculated. This relationship can be seen in  FIG. 21 , which will be described in more detail hereinafter by the trace T in that figure. As is apparent from the figure, the X axis is the speed of the control shaft  30  and the Y axis is the ratio of the input speed to the output speed. Thus, by measuring, for example, the speed of the control shaft, an indirect measure of the speed of the output shaft is also provided. Thus, the speed of the control shaft in fact provides an indication of the speed of the output shaft. In other words, by determining the ratio of the transmission (ie. the ratio of the input to the output, which is the Y axis in  FIG. 21 ), and by determining where that ratio intersects the trace T, the control shaft speed can be determined from the X axis. In order to obtain a measure of the output speed from the control shaft speed, if the input shaft speed is known, the reverse can happen. This could be done mathematically if the mathematical function represented by the trace T is known, or a simple look-up table of input to output ratios with corresponding control shaft speeds could be provided in the processing circuitry so the processor can simply select the unknown speed from the table if the other two speeds are provided. 
   In the embodiment of  FIG. 10 , and also in the embodiment of  FIGS. 24 and 25 , the actual measured speed is the speed of the input  42  and the output  20  (and the corresponding input and output in the embodiment described with reference to  FIGS. 24 and 25 ). However, the speed of the input cage  42  and the control shaft  30  could also be used with the control shaft speed being used as a proportional indication of the speed of the output shaft. Thus, only two of the three parameters referred to above need be measured, although, if desired, all three of the parameters could be measured and utilised. 
     FIG. 10  shows how the rotary speed of the input cage  42  or the output shaft  20  is measured. Each of the chopper wheels  90  is provided with a photo-interrupter  92  which includes a light emitting diode  301  and a light sensitive transistor  302 . The chopper wheel  90  is disposed between the diode  301  and transistor  302  so each time a slot of the chopper wheel  90  interposes between the diode  301  and transistor  302  light is able to be transmitted from the diode to the transistor to cause the transistor  302  to conduct. 
   As is shown in  FIG. 10  the diode  301  is connected to a 12 volt source of voltage via resistor  303  and the transistor  302  is connected to a 9 volt source of voltage via transistor  304 . A buffer  305  is connected between the resistor  304  and the transistor  302  so that the buffer  305  receives a pulse each time one of the slots in the wheel  90  causes the transistor  302  to change state from a conducting condition to a non-conducting condition. The buffer  305  has an output line  306  which connects to a diode  307 . The output line  306  is connected to 9 volt voltage source via resistor  308  and a second buffer  309  is connected to the diode  307  by line  310 . Resistor  311  connects between the 9 volt voltage source and line  310  between the diode  307  and the buffer  309 . 
   The buffer  305  is also connected via resistor  312  to the 9 volt voltage source and via compacitor  313  to ground to provide power and conventional control to the operation of the buffer  305 . The buffer  305  acts to condition the pulse received on line  314  into a square wave pulse and diode  307  and resistor  311  convert the square wave output pulse received on line  306  from the buffer  305  to a series of spikes by removing the high or positive component of the square wave pulses to thereby leave the low or negative component to producing a series of spikes of a particular frequency on line  310  which are received by the second buffer  309 . The buffer  309  is connected to resistor  316  and also compacitor  317  which set a time delay in the buffer  309  so each pulse output from the buffer  309  is time delayed by a particular amount set by the value of the resistor  316  and compacitor  317 . The output from the buffer  309  is provided on line  320  via resistor  321  to operation amplifier  322 . The operational amplifier  322  receives the pulses from the buffer  309  and produces an output voltage which is proportional to the frequency of the pulses of for example, between 0 and 8.5 volts. A meter  323  can be connected in parallel with the operational amplifier  322  simply for providing an indication of the nature of the signal output from the operational amplifier  322 . 
   The circuit showing  FIG. 10  is therefore a circuit which converts frequency to voltage to thereby obtain a voltage signal which is proportional to the rotary speed of the chopper wheel  90  and therefore the respective input cage  42  or output shaft  20 . 
   The circuit showing  FIG. 10  may include additional compacitors  325  and resistor  326  which act to provide required signal conditioning and filtering. 
   Thus, the circuit shown in  FIG. 10  produces a DC voltage at output  340  between, for example, 0 volts and 8.5 volts, which is proportional to the speed of rotation of the output shaft  20  or the input cage  42  as the case may be. 
   With reference to  FIG. 11 , the output  340  which relates to the input cage  42  is supplied on line  340 ′ in  FIG. 11  and the output from the circuit which is associated with the output shaft  20  appears on line  340 ″ in  FIG. 11 . Line  340 ″ is connected directly to a pot  350 . The line  340 ′ is connected to an invertor  351  which inverts the voltage signal on line  340 ′ so that, for example, if a 5 volt signal appears on line  340 ′ the output  352  of the invertor  351  is −5 volts, The invertor  351  has a resistor  353  connector to one of its inputs merely to stop offset errors and assist proper operation of the invertor  351 . The invertor  351  may also be provided with a trim-pot circuit  353  which can change the nature of the inversion of the invertor  351  should that be desired or necessary. For example, if something other than the inverted signal is required at output  352  then the trim-pot circuit  353  can be adjusted to, for example, in the case of a five volt signal on line  340 ′ provided a 4 volt signal on line  352  should that be required or necessary. This type of alternation of the signal could be used if it is desired to, for example, sense the speed of the control shaft, rather than the output shaft and by appropriate setting of the pot, convert the voltage value to a voltage representative of the output shaft speed in accordance with the functional relationship described with reference to  FIG. 21  or from an appropriate look-up table. 
   Alternatively, the trim-pot circuit  353  can be adjusted to ensure that the signal on line  352  is of the same magnitude but of opposite plurality to that on line  340 ′ should that be necessary. 
   The trim-pot  350  has a wiper arm  355  which is connected to line  357 . The line  357  connects to ground via a capacitor  358  which removes high speed erroneous signals which may be generated from the pot  350 . 
   The pot  350  provides the ratio transmission control function and would act as an input in order to change the drive ratio of the transmission. For example, the pot  351  could be under the control of gear shift or other device in order to provide gear changes within a vehicle within which the transmission is installed. 
   As will be explained in more detail hereinafter by changing the wiper  355  the output from the wiper  355  on line  357  will change which will cause a change to the drive ratio of the transmission. If we assume, for example, that the input cage  42  and the output shaft  20  are rotating at the same speed then the same voltage signals are applied on lines  340 ″ and  340 ′. If the wiper  355  is set at its mid point then the signals applied to the pot  350  cancel each other out because the signal on line  340 ′ has been inverted by the invertor  351 . Thus, if the wiper  355  is at its mid point 0 volts appear at line  357 . By changing the position of the wiper the drive ratio can be set because of the different voltage ratio set by the pot  350 . For example, the wiper  355  can be moved by the gear change (not shown) so that in order to produce the 0 volts at the wiper  355  the signal on line  340 ″ must, for example, be higher than the signal on line  340 ′, indicative of the fact that the output shaft is travelling at a different speed to the input thereby producing a particular ratio which is set by the driver by manipulation of the gear shift. 
   Line  357  is connected to the non inverting input of a first operational amplifier  360  and a second operational amplifier  362 . The inverting input of the operational amplifier  360  is connected via line  363  to a motor pre-set pot  364 . The inverting input of the amplifier  362  is connected to a generator pre-set pot  366  via line  367 . The lines  363  and  367  are connected by line  368  which includes capacitors  370 . A saw tooth signal input  371  is connected to a pot  372  which in turn has a wiper  373  connected to buffer  374  which has an output  375  which connects between the capacitors  370 . A saw tooth signal is supplied to the line  371  from a saw tooth wave generator (not shown) and the pot  372  acts as a loop gain in order to set the frequency or size of the saw tooth wave which is supplied by the buffer  374  to the output  375 . The capacitors  370  isolate the DC voltage received on lines  364  and  367  and allow the saw tooth signal to be supplied to the inverting inputs of the operational amplifiers  360  and  362 . 
   The pots  364  and  366  are set to shift the voltage on the inverting inputs of the operational amplifiers  360  and  362  away from 0 volts by different amounts so that field effect transistors  380  and  382  will be switched on and off at different times and cannot be switched on together as will be explained in more detail hereinafter for the reasons which will also be explained in more detail hereinafter. 
   The offset set by the pot  366  is a slight positive voltage above 0 volts and the offset which is set by the pot  364  is a slight negative voltage of the same magnitude below 0 volts. 
   The operational amplifiers  360  and  362  therefore receive on their non inverting inputs the voltage signals supplied by the wiper  355 . If we assume that the voltage signal is positive voltage indicating that the control shaft  30  is relating at a higher speed than is required, as set by the gear shift and the position of the wiper  355 , a high output will appear on line  385  and  386  from the operational amplifiers  362  and  360 . The signal on lines  385  and  386  is inverted by invertors  387  and  388  so that a low signal is supplied to buffers  390  and  392 . The invertors  387  and  388  are provided to clean up the edge of the signals received from the amplifiers  362  and  360  and the invertors also act to assist in conditioning of the signal because they basically ignore small voltage changes and only switch large voltage changes. The signal which is supplied to the buffer  390  or  392  from the invertors  387  or  388  appears on output lines  395  from the buffers and is used to control the transistors  380  and  382  to either place the motor  28  into a driving condition where it can drive the control shaft  30  (to speed it up) or in a generator condition in which the motor actually generates power to supply to a load  410  and impedes the control shaft  30 . The actual inversion of the signal from the operational amplifiers  362  and  360  is not required and if the signal is not inverted (and otherwise conditioned for supply to the buffers  390  and  392 ) the high signal from amplifiers  360  and  362  could simply be input to the inverting inputs of the buffers  390  and  392  so that output from the buffers on line  395  and  396  is low. 
   Resistors  398  and capacitors  399  provide signal conditioning and stop stray signals from the power supply from upsetting operation of the operational amplifiers  360  an  362 . 
   The field effect transistor  380  is a P channel transistor and the field effect transistor  382  is an N channel transistor. Transistor  380  has its gate connected to the 12 volt voltage supply whereas the transistor  382  has its gate connected to ground. 
   A load  410  is connected between the transistors  380  and  382 . Control motor  28  for controlling the speed of the control shaft  30  is connected between the 12 volt supply and a point between the load  410  and the transistor  382 . 
   The transistor  382  forms a motor control transistor for driving the motor and the transistor  380  forms a generating control transistor for allowing the motor  28  to provide generated electric power to the load  410 . 
   A meter  422  may be connected in series with the motor for measuring the current through the motor and shunt resistors  423  are connected across the motor  422  to enable the voltage signal to be read from the meter  422 . 
   The voltage across the motor  422  is also supplied at point  424  to a current shut off circuit  444  at point  445 . 
   When the output from the operational amplifiers  385  is high indicating that the output shaft  20  is rotating at higher speed than required and therefore that the transmission is in a higher gear than required the transistor  380  is turned on by the low signal on line  395  and the transistor  382  is turned off by the low signal on line  397 . Thus, power is not supplied to the motor  28  and the spinning of the motor  28  because it is connected to the control shaft  30  causes the motor  28  to actually generate electricity which is supplied to the load  410 . Since the motor is no longer powered it impedes the control shaft  30  to reduce the speed of the control shaft  30  until the output shaft  20  is at the required speed to produce the 0 volts at the wiper  355 . 
   If the motor  28  is running faster than is required because of the speed of the control shaft  30 , which may be the case during regenerative braking situations or if the vehicle is suddenly under less load, for example, if it begins to travel downhill, the motor  28  can therefore generate power and supply the power to load  410  for either recharging batteries or for any other use of electrical power which may be required by the vehicle or system in which the transmission is installed. 
   If the input speed into the transmission is too high so that the signal on line  340 ′ is of higher magnitude than the signal on line  340 ″ then a negative voltage will appear at wiper  355  which is supplied to the amplifiers  360  and  362 . This will produce a high signal at the transistors  380  and  382  which will cause the transistor  380  to switch off and the transistor  382  to switch on. When the transistor  382  is switched on power is able to flow from the supply voltage source through the motor  28  and the transistor  382  to thereby drive the motor  28 . By driving the motor  28  the motor will speed up the control shaft  30  so as to adjust the drive ratio of the transmission. This form of adjustment continues to happen depending on the position of the wiper  355  and therefore the gear in which the transmission is set so as to produce a  0  voltage at the wiper  355 . When 0 volts appears at the wiper  355  the transistors  380  and  382  are effectively switched off so that the motor  28  is not driven, nor does it generate because the rotation speed of the control shaft  30  is correct and the transmission is therefore in the correct drive ratio. Thus, the circuit shown in  FIG. 11  continually attempts to bring the voltage at the wiper  355  to 0 and the rotational speed at the control shaft  30  is therefore set depending on the position of the wiper  355  to set the drive ratio of the transmission. 
   The manner in which the motor is switched on and switched off will be described in more detail hereinafter. 
   The diodes  381  prevent any transient during switching on and off of the motor  28  from being supplied to the transistors  380  and  382  and will result in any such transient voltage merely being conducted to the power supply to prevent damage to the transistors  380  and  382 . 
   When the voltage of the wiper  355  is 0 or very close to 0 volts then the transistors  380  and  382  will toggle on and off causing the motor  28  to continuously switch between a powered condition when the transistor  382  is on and power is supplied through the motor  28 , to a generating condition when the transistor  380  is on and power is effectively switch off to the motor  28 . 
   At extreme positive or negative voltages at the wiper  355  the motor  28  can either be switched on to drive all the time or switched off completely so it is fully generative. When the motor is switched on all the time the control signal has a duty cycle of 100% and when the motor is switched off all the time the control signal has a duty cycle of 0%. 
   At voltages in between the extreme voltage and 0 voltage, some degree of switching on and off of the motor  28  takes place in accordance with the duty cycle or pulse width of the signals which apply to the transistors  380  and  382  as will be explained in more detail hereinafter. 
   As previously explained, the generator preset pot  366  and the motor preset pot  364  are set so that the inverting inputs of the operational amplifiers  362  and  360  are set differently. The result of this is that the two transistors  380  and  382  can never be switched on at the same time and that there is a delay between the time that one of the transistors is switched off and the other is switched on so they do not conduct at the same time. If the transistors  380  and  382  conduct at the same time then supply of power completely bypasses the motor  28  and may damage the transistors  380  and  382  or simply heat up the load  410  and possibly damage it. The overlap or underlap of the on and off signals supplied to the transistors  380  and  382  from the buffers  390  and  392  is therefore set by adjusting the pots  366  and  372  to ensure that the voltage shift on the inverting inputs of the preamplifiers  360  and  362 , from 0 volts, is different. 
   As previously mentioned, over current sensing circuit  444  connects to point  424  which provides a signal indicative of the current through the motor  28 . If the current is too large, which value is set by pot  450 , a signal is supplied to transistor  452  which causes the transistor to switch on thereby supplying a voltage signal to invertor  453 . This signal is supplied to invertor  453  and then to buffer  392  to switch the buffer off so that transistor  382  cannot be switched on thereby preventing the flow of current through the motor  28  and preventing damage to the motor  28  in the case of an over supply 
   The buffer  392  is also switched off to prevent the motor  28  from being driven when it is desired to place the vehicle in reverse gear. When the vehicle is placed in reverse gear (which is done by causing the output shaft  20  to become stationary thereby requiring-the motor  28  to not drive the control shaft  30 ), a signal from a reverse switch associated with the gear shift is supplied via resistor  460  to invertor  462 . The invertor  462  is connected to invertor  453  via diode  465  so that the invertor  453  supplies the signal to the buffer  392  to switch off the transistor  382  and maintain the transistor in the switched off condition until the signal supplied through resistor  460  is removed (indicative of the vehicle being taken out of reverse gear). 
   As previously described, the signal supplied to the inverting input of the amplifiers  360  and  362  is a saw tooth signal which is superimposed on the DC signal supplied from the pots  364  and  366 . 
   As is shown in  FIGS. 12 and 13  the triangular wave is supplied to the operational amplifier  362  at the inverting input on line  367  and the DC voltage from the pot  350  is supplied to the non inverting input on line  357 . The output from the operational amplifier  362  is therefore in the form of a pulse width signal which is defined by the intersection of the DC signal  490  shown in  FIG. 13  and which is supplied on line  357  and the triangular wave  492  which is supplied on line  367 . As the signal  490  increases or decreases then the effective pulse width defined by the portion of the signal  390  which intersects the triangular wave and labelled  500  in  FIG. 13  will increase or decrease in length thereby changing the effective pulse width of the signal output from the operational amplifier  362 . Thus, the transistors  380  and  382  are controlled variable pulse width signals which are set by the triangular wave  492  and the level of the DC voltage on line  357  to provide pulse width control of the motor  28  so that the motor  28  is switch on and off in accordance with the pulse width of the signals supplied to the transistors on lines  395 . Therefore, the motor  28  is controlled in accordance with a variable pulse width signal which is proportional to the voltage at the wiper  355  of the pot  350 . 
   Because the pots  364  and  366  are set differently, as has been previously explained, the operational amplifiers  362  effectively switch at different points on the triangular wave because of the different 0 voltage offset, set by those pots  364  and  366 . If an extreme error occurs between the required speed of the output shaft  20  and the required speed of the input cage  42  a larger extreme voltage error signal at wiper  355  will be produced. In these situations only the motor operational amplifier  360  will change at this extreme level thereby switching motor  28  on to control the speed of the control shaft  30  to adjust the drive ratio of the transmission to that which is required. If the error voltage signal at the wiper  355  is very small indicative of very small changes then the transistors  380  and  382  will effectively switch on and off relatively quickly causing the motor to switch on and off rapidly to maintain the speed of the control shaft  30  so that drive ratio of the transmission is held at the required ratio. 
   Thus, when the vehicle including the transmission according to the present invention is initially started the motor  28  rotates the control shaft  30  slowly so as to maintain the vehicle in neutral. This can be don by ensuring that the vehicle can only be started with a gear stick in neutral as in the case of a convention automatic transmission so that as soon as the transmission system is powered the control circuitry of  FIG. 11  appropriately sets the speed of the control shaft  30  to provide neutral gear. However, in general, because the vehicle is stationary and there is no load on the control shaft  30  the dual sunwheel system  18  will tend to merely go into neutral gear by rotating the sunwheel  80  and therefore the control shaft  30  because the output shaft  20  is stationary. In order to increase the speed of the vehicle the gear shift is manipulated to cause the wiper  355  to move to change the voltage division ratio set in the pot  350 . The nature of the change of the wiper  355  is to make the voltage signal on the wiper  355  negative. This negative voltage is applied to the operational amplifiers  360  and  362 , the invertors  388  and  387  and the buffers  392  and  390  which, in this case, results in a low signal being applied to the transistors  380  and  382 . This switches the transistor  382  on to cause the motor  28  to be driven so that motor rotates the control shaft  30  to increase the speed of the control shaft  30 . As the speed of the control shaft  30  increases the transmission is driven down in ratio (or up in gear to a higher gear) towards 1:1 ratio so that the speed of the vehicle increases. This will continue to happen until the voltage signal on the lines  340 ″ and  340 ′ cause a 0 voltage output at the wiper  355 . If the gear shift continues to move into a higher gear then the same process occurs to further reduce the gear ratio of the transmission or place the transmission to a higher gear thereby making the vehicle travel faster. Similarly, if it is desired to increase the drive ratio or place a transmission into a lower gear then the wiper  355  is adjusted by manipulation of the gear stick or automatic transmission so that the divided voltage at the pot  350  is positive at the wiper  355 . This causes the transistor  380  to be turned on as previously explained and the transistor  382  to be turned off so that the motor no longer drives the control shaft  30  so that the control shaft  30  will slow thereby placing the transmission into a lower gear. This will continue to happen again until the voltage of the wiper  355  is 0. 
     FIGS. 14 to 19  show how the pulse width control of the motor  28  takes place and also how the transistors  380  and  382  are prevented from turning on at the same time. 
     FIGS. 14  an  15  are pulsed diagrams showing the signals supplied to the transistors  380  and  382  respectively. 
   As can be seen the saw tooth signal  490  has been lifted up above 0 volts by the offset voltage supplied by the voltage supplied by the pot  366  and the saw tooth wave  490  in  FIG. 15  has been moved downwardly by the negative offset voltage set by pot  364 . In  FIGS. 14 and 15  VO is the voltage supplied at the wiper  355  and for the sake of comparison in  FIGS. 14 and 15  we will assume that voltage is 0 volts. The saw tooth signal  490  shown in  FIGS. 14 and 15  has the frequency of say 3.6 KHz suitable frequency other than that could be used if desired. Since 0 volts are produced at the wiper  355  the transmission system is in the right drive ratio and the control shaft  30  is rotating at the right speed to maintain that drive ratio. As can be seen from  FIGS. 14 and 15 , prior to time t 1  transistor  380  is on because a low signal is supplied to that transistor and transistor  382  is off because a low signal is applied to that transistor. Thus, no power is supplied to the motor  28  and it is not driven. Rotation of the motor  28  by virtue of its connection with the control shaft  30  causes the motor  28  to generate and supply electricity to the load  410  via the transistor  380 . At time t 1  the voltage of the saw tooth wave crosses 0 volts and becomes positive and therefore the high voltage is supplied to the transistor  380  which causes the transistor  380  to switch off. At time t 1  the transistor  382  is also off because the voltage applied to that transistor is still low. At time t 2  the saw tooth voltage applied to the comparative  360  switches from negative to positive and shown in  FIG. 15  and transistor  382  receives a high signal thereby switching the transistor on. It will be apparent from the graphs in  FIGS. 14 and 15  that between times t 1  and t 2  both transistors  380  and  382  are switched off and therefore the transistor  382  cannot be switched on before the transistor  380  is off. The time t 2 −t 1  is the delay between switching off the transistor  380  and switching on the transistor  382 . The transistor  382  remains switched on until time t 3  while the saw tooth wave voltage is positive and shown in  FIG. 15 . At time t 3  the saw tooth wave voltage  490  in  FIG. 15  again goes negative thereby switching off the transistor  382 . It should be noted that at this time the saw tooth wave voltage  490  in  FIG. 14  and which is applied to the transistor  380  is still positive thereby maintaining the transistor  380  off. At time t 4  the voltage of the saw tooth wave in  FIG. 490  goes negative thereby switching the transistor  380  on. It should be noted that between the times t 3  and t 4  both transistors are switched off again preventing one transistor from being switched on while the other is already on. The transistor  380  remains for the time period between times t 4  and t 5 . The transistor  382  is switched off for that entire time period. At time t 5  the transistor  380  is switched off as the saw tooth wave  490  goes positive in  FIG. 14 . At this time the transistor  382  is still switched off because of the voltage of the saw tooth wave at that time is still negative. At time t 6  the transistor  382  is switched on. Thus, it would be appreciated that between times t 5  and t 6  both transistors are switched off. The transistor  382  is switched on from period t 6  to t 7  while the transistor  380  is maintained off for that entire period. Thus, the delay between switching one transistor on after the other transistor goes off is set by the different offset voltages which are supplied to the amplifiers  360  and  362  and which is defined by the time differences t 2 −t 1 , t 4 −t 3 , t 6 −t 5  etc shown in  FIGS. 14  and  15 . Thus, one transistor is always required to switch off before the other can be switched on. 
   The graphs is  FIGS. 14 and 15  show that when the voltage at the wiper  355  is 0 volts or very close to 0 volts the transistors  380  and  382  toggle on and off with a duty cycle which is set by the time (t 3 −t 2 )÷(t 6 −t 3 ) in the case of the transistor  382  and time (t 4 −t 1 )÷(t 5 −t 4 ) in the case of the transistor  380 . The toggling on and off of the transistors causes the motor  28  to be driven in short bursts by pules of power supplied while the transistor  382  is switched on with those pules of power being determined by the duty cycle referred to above. Thus, the motor is driven slightly to drive the control shaft  30  then switch off so that the control shaft is impeded and so on with a frequency of 3.6 KHz and a duty cycle of the on time to the off time which is determined as mentioned above and which is dependant on the voltage VO at the wiper  355 . Thus, during this toggling on an toggling off the control shaft is driven slightly then slowed whilst the motor generates through the load  410 , then driven to maintain the 0 volts at the wiper  355  and maintain the control shaft travelling at the required speed to set the drive ratio regardless of the momentum changes within the transmission. 
     FIGS. 16 and 17  show an extreme condition of the voltage at the wiper  355 . If we assume that the speed of control shaft  30  is extremely high and producing a high positive voltage at the wiper  355  of VO shown in  FIGS. 16 and 17  which is greater than the amplitude of the saw tooth voltage  490  then a continuous high voltage is output from the amplifiers  360  and  362  which results in a low signal being applied to the transistors  380  and  382 . This switches the transistor  380  permanently on and the transistor  382  permanently off so that the motor is not driven and is in the generative state where it supplies electricity through the load  410  and transistor  380 . This impedes the control shaft  30  to slow the control shaft the control shaft will be continuously impeded until the voltage VO at the wiper  355  reduces so that it again overlaps the saw wave signal  490  at which stage the toggling effect described above will again begin to commence with a duty cycle dependant on the position of where the voltage VO overlaps the saw tooth wave  490 . 
   At the opposite extreme where the signal on line  340 ′ is much higher than a signal on the line  340 ″ indicating that input is travelling much faster than the control shaft (for the required gear ratio) a negative voltage is produced at the wiper  355  of amplitude greater than the saw tooth wave amplitude as shown by voltage VO′ in  FIGS. 16 and 17 . The opposite effect takes place because the low voltage VO will produce a high at the transistor  380  therefore turning the transistor  380  off and a low voltage at the transistor  382  thereby turning the transistor  382  on. Thus, the motor is powered by electric current supplied from the power supply through the motor, through the transistor  382  and to the other terminal of the power supply so the motor  28  is driven to speed up the control shaft  30  to change the drive ratio of the transmission. As the voltage VO′ rises from its extreme negative value towards 0 volts and overlaps the saw tooth signal  490  the toggling effect again beings to commence with transistors  380  and  382  being switched on and off with a duty cycle which is set by the position at which the voltage VO′ overlaps the saw tooth wave signal  490 . 
     FIGS. 18 and 19  show situations where the voltage VO is somewhere between 0 volts and the extreme conditions shown in  FIGS. 16 and 17  and positive in magnitude. The transistor  382  is continuously off and the transistor  380  is switched on but with a duty cycle which is very high in terms of percentage of the on time to the off time, for example, 90% or thereabouts as shown in  FIG. 18 . At the other extreme when the voltage VO is negative of the same magnitude the opposite will occur and the transistor  380  will be switched off for most of the time if not all of the time and the motor  28  will be powered periodically with a duty cycle dependant on the time the transistor  382  is switched on compared to the time when it is switched off. In this case the duty cycle might also be 90%. 
   Thus, it will be apparent that when the voltage is around about 0 at the wiper  355  the transistors  380  and  382  toggle on and off continuously. If the voltages are at an extreme the motor  28  is either held on or completely off so as the control shaft  30  is adjusted to the required speed by either being driven by the motor  28  or by being impeded by the motor  28 . The most usual situations where the voltage is not extreme but just above or below 0 volts there will be a switching on and off of the motor  28  with a duty cycle depending on the value of the voltage at the wiper  355  to cause the motor  28  to be switched on and speed up the control shaft or switched off and slow down the control shaft in proportion to the duty cycle of the switching on and switching off of the motor  28 . The larger the duty cycle of the signal which switches on the transistor  382  the faster the motor  28  will rotate to bring the speed of control shaft  30  up to the required operating speed to place the transmission in the required drive ratio. Conversely, the greater the duty cycle of the transistor  380  the more the impeding of the control shaft to slow the control shaft and the more electricity is generated by the motor  28  to supply to the load  410 . 
   It will be apparent from the graphs of  FIGS. 14 to 19  that whenever the voltage at the wiper  355  changes state from a negative to a positive voltage then this change is applied to the transistors  380  and  382 . However, the transistor which is switched on will be switched off always before the other transistor is switched on thereby ensuring that the transistors  380  and  382  are not switched on at the same time. Normally when the transmission is holding the ratio set by the wiper  355  there will be slight fluctuations and the voltage at the wiper  355  will probably go up and down from the 0 voltage state slightly thereby causing the transistors  380  and  382  to be continually switching on and off to cause the motor  28  to be driven or stopped to ensure that the control shaft catches up or reduces speed to produce the 0 volt output at the wiper  355 . 
   As previously mentioned, the drive ratio can be set manually be adjusting the wiper  355  of the pot  350  by effectively coupling the wiper  355  through a gear shift stick. In other embodiments the adjustment could be automatic and the wiper  355  can be adjusted in position dependant on various parameters which are sensed by computer control of a vehicle or engine. Such parameters may include the conventionally sensed parameters including vehicle speed, inlet manifold pressure, load, engine speed etc. Information relating to all of the parameters can be input to a processor which, from a look-up table, can select an appropriate drive ratio for the operating conditions of the engine and in accordance with the selected ratio can adjust the position of the wiper  355  so as to cause the motor  28  to control the shaft  30  to bring the transmission to that drive ratio. 
   As previously described, the magnetic powder clutches  110  and  120  can be controlled by the same circuit as described with reference to  FIGS. 11 and 14  to  19 .  FIG. 20  shows an embodiment of the circuit modified to control the clutches  110  and  120 . In this embodiment, the clutch  110  is coupled between the 12 volt power supply and the other side of the load  410  that is in parallel with the transistor  380  and the load  410  and the second magnetic clutch  120  is connected in parallel with the transistor  382  in the load  410  as shown. When the transistor  382  is on the clutch  110  is operated in accordance with the duty cycle of the switching on of the transistor  382  in the same manner as previously described so that the clutch  110  causes drive to be transmitted to the shaft  30  to speed up the shaft  30 . When the transistor  380  is switched on power is suppled to the clutch  120  to cause the clutch  120  to stop the control shaft  30  if the clutch  120  is fully locked up. If the control shaft  30  is being adjusted also by the clutch  120  then the clutch  120  can be switched on and off dependant on the duty cycle of switching on and off the transistor  380  so that the clutch  120  perform correction control of the speed of the control shaft  30  to set the desired drive ratio. 
   Other embodiments of the control circuitry may also be used and these embodiments include merely coupling the transistors  380  and  382  respectively and independently t the magnetic clutches  110  and  120 . In this embodiment the transistors  380  can be of the same type at the inputs to the operational amplifier  362  are simply reversed. 
   Furthermore, in the magnetic clutch embodiments the circuitry for detecting the speed of the output shaft and input and supplying the signal on lines  340 ′ and  340 ″ may use a magnetic sensor rather than a photo-interrupter in order to provide the signal data. The magnetic sensor may include a Hall effect type device or other magnetic sensor which provides an output pulse every time a magnetic on the rotating component passes the sensor. 
   In still further embodiments in which precise control of ratio is not required an AC motor can be used as the motor  28  and the AC motor controlled by the conventional AC motor controller. This embodiment has particular applications to situations where a drive ratio needs to be set and then not further adjusted such as is the case with some industrial machinery. By simply controlling the electronic controller to drive the AC motor the speed of the control shaft  30  can be set to the required speed either by visual inspection or speed measurement. 
   The specific process used in the transmissions previously described, and which will be described with reference to  FIGS. 22 and 23 , is to rapidly displace the momentum of the system back and forth, from the output means, ie sunwheel  70 , to the control shaft (ie. sunwheel  80 ) so as to maintain a predetermined ratio. Change in ratio is achieved by biasing a momentum gate openings to create a new momentum distribution, and then to stabilise it by precisely sensing angular velocity of the input, the output and the control shaft and opening and closing the gate in response to a feedback system. For precise operation it is important to open and close the gate rapidly, 3 kHz is an appropriate speed. It is the nature of these double sunwheel machines, that they will try to respond to external load and speed conditions and alter the transmission ratio. The control process must in general oppose this except where the ratio achieved fits in with the designed ratio control program. This is shown in  FIG. 21 . 
   The momentum gate and the manner in which it is biased is achieved, in the preferred embodiments, by controlling the electric motors and magnetic clutches as previously described in order for them to control rotation of the control shaft and therefore the control sunwheel (such as the sunwheel  80 ) to enable momentum to be displaced back and forth from the output to the sunwheel  80  and the control shaft  20  so the momentum is displaced from the output to the control shaft  20  and stored in the clutches or motor, which can be returned to the output via the control shaft  20 , the planet system  60  and the output sunwheel  70 . 
   If an uncontrolled transmission of this kind is operating unloaded at position (r 1 ,ω 1 ), as shown in  FIG. 21 , experiences a load opposing the rotation of the output shaft, momentum will be displaced onto the control shaft by causing it to rotate faster. This will result in the ratio changing and the transmission operation moving to the right along the curve towards the neutral position, shown in  FIG. 21 , to be located at the asymptote of the hyperbola, which function describes the relationship between the transmission ratio and the angular velocity of the control shaft. This situation will continue until a new momentum situation on the control shaft (due to its mass and new angular velocity), is able to stabilise at some new position (r 2 ,ω 2 ) in  FIG. 21 . Further, loading will of course cause still further movement to the right, until neutral is reached at the asymptote. 
   If a momentum gate is fitted to the control shaft, the above process can only occur while the gate is open. If the gate is closed, momentum is prevented from being displaced onto the control shaft to speed it up and the ratio will remain at the position (r 1 ,ω 1 ) if the gate is opened and closed to a program that will maintain such a state as the output load varies. 
   The above describes a very simple gate system operating on the positive part or forward part of the ratio function. Such a gate may be referred to as a positive gate created by a mechanical impedance. A gate can also be made operable on the negative or reverse part of the ratio function. This is referred to as a negative gate. 
   A simple positive gate operating on its own is only able to open and close the gate in one direction, that is to either displace momentum from the control shaft onto the output means, or to prevent any displacement. A more sophisticated gate combines a positive and negative gate and is able to close the gate completely, or to open it in either direction. 
   There are at least three mechanism means of achieving the above.
     1. To alter the angular velocity of the control shaft by slowing it down by a mechanism impedance or some kind of a brake, or speeding it up, so that   

   
     
       
         
           
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       2. To alter the moment of inertia of the control shaft so that 
     
  
   
     
       
         
           
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       3. To alter both the moment of inertia and the angular rotation of the control shaft so that 
     
  
   
     
       
         
           
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   It should be noted that in situation 2 above, to oppose momentum displacement onto the control shaft (close the gate) without altering the rotation of the control shaft, the device used to alter the moment of inertia must be controlled by some other method. 
   In order for a gate to open in both directions, it must be able to apply torque directly to the control shaft, or alternatively use some other method of directly transferring momentum to the shaft or else altering the moment of inertia to increase the angular velocity of the shaft. One way of doing this is to use an electric motor which can be switched rapidly to either drive the control shaft motion or to impede it by acting as a generator. 
   A second method of creating a gate which will open in both directions can include a second switchable brake or clutch operating upon the negative side of the function. Energy must be taken from the input to speed up the control shaft across the asymptote and cause reverse operation. A ratio control program will then rapidly switch both the positive and the negative gate on and off to achieve the same thing as an electric motor described previously. 
     FIGS. 22 and 23  show a still further embodiment of the invention which operates in accordance with the above description and the principles described with reference to  FIG. 21 . 
   The transmission shown in  FIGS. 22 and 23  has an output shaft  600  which carries an output sunwheel  602 . An input flange  604  is mounted about the shaft  600  on bearings  605  and is coupled to planet cage  606 . Input rotary power may be supplied from a motor or other suitable source (not shown) to the flange  604  to rotate the flange  604  and therefore the cage  606 . 
   The cage  606  supports a planet system  607  which comprises a transfer gear  608  which has a first gear portion  609  which meshes with sunwheel  602  and a second portion  610  which meshes with planet gear  611 . The planet gear  611  mesh with control sunwheel  612  which is provided on control shaft  614 . 
   In the embodiment described, the transfer gear  608  is elongated so that the portions  609  and  610  are merely an extension of one another. However, in other embodiments the portion  610  could be provided on a reduced diameter portion so as to provide a different ratio to the portion  609 . 
   As previously described, the planet system  607  can take many different forms, including all of the forms described with reference to  FIGS. 7 to 9 . 
   The control shaft  614  is mounted in bearings  617  which, together with bearing  619 , support the cage  606  for rotation. Thus, rotation of the cage  606  will carry the planet system  607  so that rotation is imparted to the output sunwheel  602  and therefore to the output shaft  600 . 
   The cage  606  has a reduced diameter portion  620  which carries a gear  622 . The gear  622  meshes with a gear  623  provided on a cone clutch  624 . Cone clutches are well known and therefore need not be described in detail herein. Suffice it to say that the cone clutch  624  has a first portion  625  which has a conical surface  626 . The portion  625  carries the gear  623  which meshes with the gear  622  as shown in  FIG. 22 . The clutch has a second portion  628  which has a matching conical surface  629  which can move in the direction of double-headed arrow A in  FIG. 22  so as to cause the clutch to engage or disengage. A screw thread mechanism  630  controls the movement of the portion  628  in the direction of double-headed arrow A to cause the clutch to engage or disengage and the screw mechanism  628  is operated by a lever  631  which is pushed into and out of the plane of the paper in  FIG. 22  by a solenoid  632 . The solenoid  632  is controlled by a control section which will be described hereinafter. 
   The portion  628  also carries a gear  633  which meshes with gear  634  fixed onto the control shaft  614 . 
   A magnetic powder clutch  640  (which is the same as the powder clutched as previously described) is connected to a gear  641  which also meshes with the gear  634 . In this embodiment of the invention, the control shaft which controls the rotation of the control sunwheel  612  is provided in two parts rather than as a single shaft. The two parts comprise the shaft  614  and shaft  639  which is in effect a lay shaft provided through the magnetic powder clutch and which has its rotation controlled by the powder clutch  640 . Thus, rotation of the lay shaft  639 , or in other words, the second part of the control shaft, rotates the first part of the control shaft  614  on which the control sunwheel  612  is mounted by virtue of the engagement of the shafts  614  and  639  by the gears  634  and  641 . 
   Thus, in order to change the ratio of the transmission, current is supplied to the powder clutch  640  in the manner previously described. This causes the powder clutch to progressively engage in the manner previously described so that the meshing of the gear  641  with the gear  634  progressively slows down the speed of the control shaft  614 . Referring to  FIG. 21  for example, assuming that the speed of the control shaft was initial S 1  and the transmission is in a relatively low gear or high ratio, slowing down of the control shaft will cause the gear ratio to move down the trace T in  FIG. 21  to decrease the ratio or place the transmission into a higher gear. When the control shaft  614  is completely stopped by complete locking of the powder clutch  640 , the gear ratio will be in an overdrive ratio on the graph shown in  FIG. 21  at ratio 0′ which is the lowest ratio the transmission is designed to provide. It should be noted that because the powder clutch  640  will simply stop the shaft  614 , but will not rotate it backwards, the transmission will not go into a gear ratio lower than 0′ and represented by the dotted trace T′ in  FIG. 21  because this requires a reverse rotation of the transmission to move the speed to the left of the origin (or zero speed) of the axis shown in  FIG. 21  and marked 0,0. It should be further noted that if it is desired to rotate the shaft  614  backwards a motor, as described in earlier embodiments, could be used to further increase the overdrive ratio of the transmission. 
   Thus, by appropriate control of the current supplied to the clutch  614 , as is described previously, the drive ratio can be adjusted along the trace T between a very high gear ratio approaching the asymptote As down to the maximum overdrive ratio 0′ which is established when the control shaft  614  is completely stopped. 
   In order to place the transmission into reverse gear, the cone clutch  624  is utilised. As is apparent from  FIG. 21 , when the transmission is in neutral the trace T is approaching the asymptote As or, in other words, the transmission is in extremely high ratio in which the input is obviously rotating but the output shaft  600  is stationary. In order to provide reverse gear which is shown by the trace R in  FIG. 21 , it is necessary to increase the speed of the control shaft  614  to a speed greater than the speed at where the asymptote As crosses the X axis of the graph in  FIG. 21 . This is achieved by supplying power to the solenoid  632  which activates the lever  631  to thereby rotate the screw mechanism  630  so that the cone clutch  624  engages by forcing the portion  628  to the left in  FIG. 22 , so the surfaces  626  and  629  fully engage to lock the clutch. Since the clutch is coupled to the input via the cage  606  (and in particular by the meshing of the gear  622  with the gear  623 ) the clutch is rotated so that the gear  633  rotates the gear  634  to increase the speed of the gear  634  and therefore the shaft  614 . This drives the speed to the right in  FIG. 21  so that the speed crosses the asymptote As and places the transmission into reverse gear as shown by trace R. As also shown by trace R, as the speed is forced across the asymptote As, the transmission will initially go into a very high ratio where the trace R approaches the asymptote but will then smoothly move to a gear ratio on the trace R which is set by the gear ratio provided between the gears  622 ,  623  and  633  and  634 . This effectively locks the control shaft  614  to the input  619  and the gear ratio can be provided to be a relatively low reverse gear ratio so the vehicle will move in reverse at a speed which is dependent on the input speed provided by the input cage  606  and the gear ratio between the above-mentioned gears. 
   As in the earlier embodiments, in order to control the cone clutch  624  and the powder clutch  640 , the speed of rotation of the output, the input and the control shaft are sensed. This may be provided by speed sensors  651  on output shaft  600 , sensor:  652  on cage  606  and sensor  652  on the control shaft  614 . By detecting these speeds and processing the speeds, an appropriate output signal can be supplied to the magnetic powder clutch  640  to progressively lock the clutch  640  to provide the desired forward gear ratio, or to release the clutch  614  completely and lock the clutch  624  to provide reverse gear. 
   It should be noted that in other embodiments, different forms of cone clutch  624  can be provided. The above embodiment utilises a cone clutch which is mechanically controlled by a screw mechanism  626 . However, the clutch could be controlled by hydraulic control systems or magnetic control systems as is well known. 
   The manner in which momentum is displaced back and forth from the control shaft and the output shaft will be explained. In general, input rotary power is supplied through the flange  604  to the planet cage  606  and via the planet gear system  607  to the output sunwheel  602 . If a load is supplied to the output shaft  600 , the planet system  607  will immediately attempt to transfer the momentum into the control sunwheel  612 . This will try to turn the gear  634  and the therefore the gear  641  and the lay shaft  639  on which the gear  641  is mounted, which is within the powder clutch  640 . Thus, the momentum will now attempt to reside in the control shaft  614  and the rotary part (ie. the lay shaft  639 ) of the powder clutch  640 . If the powder clutch  640  is switched completely off, the momentum will therefore be displaced from the output shaft  600  to the control shaft  614  and the lay shaft  639 . However, if the magnetic powder clutch  640  is activated by supply of current, then the shaft  639  is stopped from freely rotating and momentum is forced back via the meshing gears  641  and  634 , the control shaft  614  and the control gear  614  through the planet system  607 , and back to the sunwheel  602  and output shaft  600 . How much the momentum is transferred back will determine the drive ratio of the transmission. Thus, by controlling the clutch  640  and the amount of progressive braking provided by the clutch  640 , the drive ratio of the transmission can be controlled by providing control over the speed of the control shaft  614  and therefore the control sunwheel  612 . This process is a rapid performance of a displacement of momentum back and forth between the output shaft  600  and the control shaft  614  and powder clutch  640  and the stability of the ratio will depend on accurately switching on and off the clutch  640 , which effectively opens and closes the momentum gate to control the displacement of momentum from the output shaft  600  to the control shaft  614  and lay shaft  639 . 
   In a sophisticated application of the transmission of  FIGS. 21 and 22 , the cone clutch  624  can also be switched on and off so as to displace momentum from the output shaft  600  to the control shaft  614 . This is advantageous because, in some instances when the transmission is in overrun (for example when a drive takes his or her foot off the accelerator), momentum will not want to be displaced from the output shaft  600  to the powder clutch  640 . By switching the cone clutch  624  on, the momentum is forced to be displaced from the output shaft  600  to the control shaft  614 . The second advantage is that this process would make the displacement of the momentum occur much faster and stabilise the ratios much more quickly. 
   In still further applications, the control shaft  614  may include a section  660  shown in dotted lines, which carries a variable centroid system  662 , for example the moving mass system, similar to that disclosed in our co-pending International Application No. PCT/AU00/00603, the contents of which are incorporated into this specification by this reference. The system  662  will assist the clutch  640  to manage the momentum displacement process without large use of energy by the magnetic clutch  640 . 
     FIGS. 24 to 32  show a further embodiment of a controller which can be used in the preferred embodiments of the invention. The controller of these Figures has particular application to the embodiment of  FIGS. 22 and 23 . However, this controller could also be used with the earlier embodiments and the controller described with reference to  FIGS. 10 to 20  could also be used with the embodiment of  FIGS. 22 and 23 . 
   With reference to  FIG. 24 , the controller has a pair of field effect transistors  700  and  701  which are connected in parallel with one another. Power is supplied to the field effect transistors from a battery  703 . A diode  704  is provided to protect the circuitry should a battery of a higher voltage than required be used or the battery connected in reverse polarity. A fuse  705  is connected between the diode  704  and the battery so that should the voltage supplied by the battery be too high or the battery connected in reverse polarity, the fuse  705  will burn out to thereby shut off power supplied to the circuitry shown in  FIG. 24 . 
   Capacitor  706  smooths the voltage supply to the transistors  700  and  701 . The transistors  700  and  701  have an output  707  which provides a locking signal to solenoid  632  described with reference to  FIG. 22  and which controls the cone clutch  624 . The transistors  700  and  701  are also connected to a diode  708  and a capacitor  709  is connected in parallel with the transistors  700  and  701 . The diode  708  and the diode  708   a  ensure that the voltage at the output  707  cannot go significantly higher than the voltage V+ supplied by the battery  703  or below the voltage V−. Typically, the battery  703  is a 12V battery and the voltage V+ is 12V and V− is 0 volts. 
   The transistors  700  and  701  receive an input on line  710  from a port  751  of a microprocessor  750  shown in  FIG. 25  and which will be described in more detail hereinafter. Thus, in other words, the port  751  of the processor  750  is connected to line  710  shown in  FIG. 24 . As also shown in  FIG. 24 , the line  710  connects via line  711  to the transistor  701  so that both of the transistors  700  and  701  are switched on by the signal on line  710 . 
   When the signal is received from the microprocessor  750  on line  751 , the transistors  700  and  701  are therefore switched on to supply a voltage at output  707  which activates the solenoid  632  ( FIG. 22 ) so as to lock the cone clutch  624  so that a control shaft  614  is connected to input cage  606  to thereby place the transmission of  FIG. 22  into reverse gear in the manner previously described. 
   The circuit in  FIG. 24  also includes a pair of high side driver circuits  720  (only one shown). The pair of high side driver-circuits  720  are identical and therefore only one is shown in  FIG. 24 . The other driver operates in the same manner, as will be apparent from the following description. The voltage applied to circuit  720  is stabilised by capacitor  709 . 
   The driver  720  receives control signals from the microprocessor  750  so that outputs are supplied on lines  721  and  722  to control field effect transistors  723  and  724 . The other driver (not shown) provides output signals in the same fashion to control another pair of field effect transistors which are identical to those shown in  FIG. 24  (and indicated by reference numeral  723 ′ and  724 ′ in  FIG. 31 ). 
   Turning now to  FIG. 25 , processor  750  receives signals on line  753  from sensor  652  shown in  FIG. 22 , indicative of the speed of rotation of the input. The line  754  receives signals from the sensor  651  indicative of the speed of the output shaft  600 . A third input on line  756  may also be provided which provides a signal indicative of the speed of the control shaft  614  if desired, and which would come from the sensor  652  shown in  FIG. 22 . 
   The processor  750  also receives a signal on line  757  from a reverse switch circuit  758  which is closed when a driver wishes to place the transmission into reverse. This happens automatically by actuation of a vehicle reverse gear switch indicative of the fact that reverse gear is required. The reverse switch circuit  758  includes a diode  759  and the capacitor  758  which stop interference from spurious signals so that a false signal will not be provided on line  757 . Thus, when the driver places the vehicle into reverse, the reverse switch circuit  758  is closed and a reverse signal provided on line  757  to the processor  750 . The processor then determines from other inputs which are received into the processor  750 , whether it is appropriate to place the vehicle into reverse gear. These other signals will include speed of the vehicle at the output shaft, etc. so that if the processor  750  determines that the vehicle should not be placed into reverse gear, such as if the vehicle is travelling at high speed in forward direction, then the processor will not output the locking signal on line  751 . However, if the processor  750  determines that reverse gear is appropriate, then a switching signal is applied on line  751  to the line  710  to switch on the transistors  700  and  701  as previously describes, so that the locking signal is provided from output  707  to the solenoid  632  to place the transmission into reverse gear. 
   If reverse gear has been selected either erroneously or inappropriately and the processor  750  decides that a signal will not be output on line  751 , the processor  750  can output a signal on line  765  to transistor  766  to switch the transistor on so that current flows through coil  767  to activate a light or alarm shown by reference  768  to indicate erroneous selection of reverse gear. The alarm  768  can also be used to indicate other alarm conditions if required. 
   The processor  750  also receives an input from pot  760  via line  761  which is indicative of throttle position of the vehicle. The processor  750  may also receive an input indicative of front wheel speed on line  762  and vacuum condition of the engine on line  763 . 
   The processor  750  may also receive signals from an input circuit  770  which can be used to change parameters within the processor  750  to effectively reprogram the processor  750  to operate in accordance with modified protocols or algorithms as is required. This circuitry can be used in initial set-up or alternatively for servicing or other requirements by authorised personnel. This circuitry has no bearing on the actual function of the device and therefore will not be described in any further detail. 
   The processor  750  outputs signals on lines  780 ,  781 ,  782  and  783 . The line  780  connects with line  730  of driver  720  and the line  781  connects with line  731  of the driver  720 . 
   The lines  782  and  783  connect to the other driver which is not shown on lines corresponding to lines  731  and  730 . 
   The output lines  721  and  722  of the driver  720  are connected to the field effect transistors  723  and  724  as previously described so as to switch on and off the transistors  723  and  724  dependent on whether the signal on lines  721  or  722  is high or low. When the transistor  723  is switched on, the transistor can conduct to provide a voltage at output  740 . When transistor  724  is switched on, the voltage at line  754  is effectively connected to ground and is therefore zero volts. 
   Diodes  741  and capacitors  742  protect the transistors  723  and  724  and prevent the voltage across the transistors from increasing above or below a predetermined voltage to prevent damage to the transistors  723  and  724 . 
   Capacitors  743  and  744  stabilise the voltage supplied to the transistors  723  and  724 . 
   Voltage V+is also connected to line  745  via diode  746 . The line  745  includes capacitor  747  and is connected to output  740  via line  748  which connects to the driver  720 . The reason for this is to ensure that the voltage available on line  721  will be above the voltage at output  740  to ensure that the transistor  723  is maintained switched on because in order to hold the transistor  723  on, the voltage on line  721  must be above the voltage at output  740 . Thus, as soon as the transistor switches on, the capacitor  747  is able to charge up and its discharge will enable voltage to be supplied to the driver  720  together with the voltage V+ from the battery for output on line  721  to maintain the transistor  723  switched on by supplying a voltage on line  721  which is above the voltage at output  740 . 
   The output  740  and the corresponding output from the other driver  720  which is not shown are connected across the powder clutch  640  shown in  FIG. 22 .  FIG. 31  is a simplified diagram illustrating this connection. 
   The switches shown in this diagram represent the transistors  723  and  724 . The switches  723 ′ and  724 ′ are the field effect transistors associated with the driver which is not shown in  FIG. 24 . 
   Thus, it can be seen that by closing the switch  723  and the switch  724 ′, current is supplied through the powder clutch  640 . Similarly, by closing the switches  723 ′ and  724 , reverse polarity power can also be supplied through the powder clutch  640 . 
     FIGS. 26 to 31  show wave forms which are output on the lines  721  and  722  to control the transistors  723  and  724  (and also the transistors  723 ′ and  724 ′). These wave forms are selected by the processor  750  based on the inputs receives on the lines  753  and  754  which are indicative of the speed of the input and output (or control shaft) in the transmission, the throttle position  760  and other engine operating data to thereby set the drive ratio of the transmission. The processor, from those inputs, produces outputs on lines  780  to  783  which are provided to the driver  720  (and the driver which is not shown) to cause those drivers to output signal on their respective lines  721  and  722  to switch on the transistors  723  and  724  for the required time period to produce the required pulses. 
     FIG. 26  shows a wave form which will cause the powder clutch  640  to lock so that the lay shaft  639  is held stationary and fixed to the casing  640   a  to thereby stop the control shaft  614  and place the control shaft  614  into a stationary condition. This occurs by outputting DC pulses of a particular duty cycle (which may, for example, be 25% on) to switch transistors  723  and  724 ′ on to activate the clutch  640  into the locked position. 
   In order to control the clutch  640  so that some movement of the lay shaft  639  is allowed to thereby control the rotation of the shaft  640 , the transistors  723 ,  724 ,  723 ′ and  724 ′ are controlled by an AC frequency control rather than simply by changing the duty cycle of the pulses as in the control system of the earlier embodiment. In order to produce the frequency control, the switching of the transistors first goes through a DC to AC transition which is best illustrated in  FIGS. 27 to 30 . 
   This occurs by controlling the transistors so that pulse P 1  is effectively shortened in time duration and a negative pulse P 2  of a very short duration is produced ( FIG. 27 ). It should be noted that the pulses are separated in time, in other words, there is a time delay between the pulse P 1  and P 2 . This is achieved by switching on the transistors  723  and  724 ′ to produce the pulse P 3  and then switching off those transistors. After a time delay, the same transistors are switched on for a shorter duration to produce the shorter time duration pulse P 1 . Those transistors are then switched off and, after a delay, the transistors  723 ′ and  724  are switched on for a short time period to create the negative pulse P 2 . 
   As shown in  FIG. 28 , the time of switching on the transistor  723  and  724 ′ increases so that the pulse P 2  increases in duration. It should be noted that the pulse width of the pulses P 1  and P 3  also change. 
   As shown by  FIG. 29 , the pulse width of the pulse P 3  and P 1  further change as the pulse width of the pulse P 2  increases and this continues to occur until the pulse P 1  is effectively zero, thereby just leaving the pulses P 3  and P 2  as is shown in  FIG. 30 . This effectively provides an AC signal with the pulses P 2  and P 3  being the same duration. 
   Although the conversion from AC to DC has been shown in only four steps in  FIGS. 27 to 30 , obviously additional steps will be used. As is apparent from the drawings, as the pulse P 1  decreases in duration, the pulse P 3  increases in duration as does the pulse P 2  until the situation in  FIG. 30  is produced where the signals are of the same duration. 
   Once the DC to AC conversion has taken place, the control over the clutch  640  now occurs by frequency control by varying the time between time T 1  and time T 2  in  FIG. 30 , whilst maintaining the pulse width of the pulses P 2  and P 3  and the delay times ΔT 1  and AT 2  in the same ratio as shown in  FIG. 30 . Thus, each of these durations, including the durations of the pulses P 2  and P 3 , will decrease so the time from T 1  to T 3 , which is the time of the leading edge of the next pulse P 3  in the cycle, decreases. In  FIG. 30  the effective wavelength is  48  milliseconds. As that time period decreases, the frequency increases to thereby control the powder clutch  640  to alter the amount of rotation of the lay shaft  639 , which the powder clutch  640  allows, to in turn control the speed of the control shaft  614 . This form of frequency control can be used to allow the powder clutch  640  to control the speed of the control shaft  614  up to a certain speed. 
   In order to further speed up the control shaft, the duty cycle of the pulses P 3  and P 2  is altered so as to change the on time and off time of those pulses whilst maintaining the frequency constant to provide AC pulse to control the clutch  640  to provide complete opening of the clutch  640  and therefore freeing the control shaft  614  completely for rotation without any impedance up to speed S 1  in  FIG. 23 . 
   For convenient data processing within the processor  250 , the nature of the signals which are output to the driver  720  on the lines  780  to  783  to in turn set the time period for which the transistors  723  and  724 , etc. are switched on, is divided into intervals of 0 to 255, which conveniently corresponds to 8 bits of data. By considering the information which is received from the speed sensors  651  and  652 , the pot  760 , vacuum signal on line  763  and possible front wheel speed  762 , the processor  750  can determine from those numbers the appropriate output to supply to the drivers on the lines  780  to  783  to control the transistors  723 ,  724 ,  723 ′ and  724 ′ to in turn control the clutch  640  in the appropriate manner. For example, and with reference to  FIG. 32 , number  255  produces the DC pulses which completely lock the clutch  640  and stop the control shaft  614 . Numbers  254  down to  223  can produce the DC to AC conversion in  32  steps by gradually decreases the pulse width P 1 , increasing the pulse width P 3  and producing the increasing pulse width P 2  so as to eventually produce the AC signal shown in  FIG. 30 . Numbers  223  down to number  31  can produce the frequency control by changing the time period T 3 −T 1  to thereby produce the changing frequency so as to perform the control over the clutch  640  which will change the degree of allowed rotation of the shaft  614  up to the certain speed of the control shaft  614 . As is shown by the torque curve N in  FIG. 32 , the change in pulse width of the signal with constant frequency can occur from numbers 31 down to 0 to bring the speed of the control shaft to a speed S 1 . The pulse width AC control is desired because to bring the speed to the speed S 1 , the powder clutch can no longer follow the torque curve which would produce simply by frequency control. 
     FIG. 33  shows a modification to the embodiment of  FIGS. 22 and 23 . In  FIG. 22  the outer housing  640   a  of the powder clutch  640  is fixed to the casing of the transmission and held stationary. In the modified embodiment of  FIG. 33 , the casing  640   a  is coupled to the input, as will be explained below, so that the casing  640   a  can rotate. This assists the powder clutch  640 , maintaining the required control over the control shaft  614  so that it is not necessary for the powder clutch  640  to work as hard as in the embodiment of  FIG. 22 . This embodiment of the invention allows the powder clutch to operate in the region of the graph in  FIG. 21  between the speeds S 1  shown in  FIG. 21  and S 2  which is the speed of the control shaft which will produce the 1 to 1 ratio. Since the powder clutch is operating only in this part of the curve of  FIG. 21 , it is more easy to control the powder clutch so that the powder clutch operates satisfactorily to maintain the control of the speed of the control shaft  614  to produce the drive ratios between the speeds S 1  and S 2  in  FIG. 21 . Again, in this embodiment, when it is desired to place the transmission into reverse gear, the cone clutch previously described locks the input to the control shaft to increase the speed of the control shaft above the speed S 1  in  FIG. 21  to place the transmission into reverse gear. 
   It should be noted that only the modified part of  FIG. 22  is shown in  FIG. 33  and like reference numerals indicate like parts to those previously described. 
   In  FIG. 33  the lay shaft  639 , control shaft  614  and a shaft  901  connected to the cone clutch  624  are journaled in casing  900  of the transmission. The planet cage  600  is shown schematically and carries ring gear  902  which has internal teeth which mesh with pinion  903  supported on shaft  904 . The other end of the shaft  904  carries a pinion  905  which meshes with internal teeth on a ring gear  907  which is journaled on the end of the control shaft  614 . 
   The control shaft  614  carries gear  634  which meshes with gear  633  connected to the cone clutch  624  and the gear  641  on the lay shaft  639  as previously described. 
   The ring gear  907  also has external teeth which mesh with the gear  623  of the cone clutch  624  and a gear  907  provided on sleeve  908  which connects to outer casing  640   a  of the powder clutch  640 . 
   Thus, when the input cage  606  rotates, the pinion  903  is rotated to, in turn, rotate pinion  905  which rotates gear  907 . Rotation of gear  907  is imparted to gear  909  which rotates the outer casing  640   a  of the powder clutch. In other words, the outer casing  640   a  of the powder clutch is coupled to the cage  606 . 
   Depending on the control signals which are applied to the powder clutch  640 , this attempts to slow down the speed of the control shaft  614  towards the speed of the planet cage  606 . Thus, when the powder clutch is fully locked so that the shaft  639  is effectively fixed to the outer casing  640   a , the cage  606  is coupled to the control shaft  614  and the control shaft  614  will rotate at a speed relative to the input cage  606  dependent on the gear ratio between the gears  902 ,  903 ,  905 ,  907 ,  907 ,  909  and  641  and  634 . These gear ratios can be chosen to set the lowest gear ratio or highest speed of the transmission and may for example be 1 to 1 as described above, or could move the transmission into overdrive if the gear ratio between these gears is such that it results in the control shaft  614  rotating at a speed below the speed S 2  shown in  FIG. 21 . 
   When it is desired to place the vehicle into reverse gear, the powder clutch  640  is completely released which allows the control shaft  614  to speed up as shown by trace T towards neutral. In other words, the gear ratio increases and the transmission goes into low gear approaching neutral. In order to place the transmission into reverse gear, the control shaft  614  needs to be increased in speed beyond the speed S 1  as previously disclosed, and this is done in the same way as previously described by activating the cone clutch  624  so that the gear  623  is locked onto the shaft  901  by the cone clutch  624  so that drive is transmitted from the cage  606  via the gear  907  to the gear  623 , to the shaft  901  and then to the gear  633  and the gear  634 . The drive ratio between these gears is such that the speed of the control shaft  614  will increase in speed, thereby moving the velocity of the control shaft to the right in  FIG. 21  and thereby placing the transmission into reverse gear in the same manner as previously described. 
   It will be noted that since the outer casing  640   a  of the powder clutch  640  is able to rotate in this embodiment, powder is supplied to the clutch  640  via a slip ring which is the same as the slip ring  127 ,  128  described with reference to  FIG. 5 . 
     FIG. 34  shows a still further modification in which the variable centroid system  662  described with reference to  FIG. 23  is provided on the lay shaft  639 . This system operates as disclosed in the aforementioned International application and functions to take further load from the powder clutch  640  to further facilitate the control the powder clutch  640  has over the control shaft  614 . As the lay shaft increases in speed, the moveable masses  920  (only one shown) move radially outwardly against the bias of springs  921  so as to slow down the rotation of the shaft  639  to maintain the control over the control shaft  614 . Thus, the combined operation of the powder clutch  640  and the system  622  has the effect of slowing down the control shaft  614  to change the drive ratio from neutral towards 1 to 1 and overdrive ratio as previously described. In this embodiment, not all of the work to control the control shaft  614  to change the drive ratio from neutral towards 1 to 1 and overdrive therefore needs to be performed by the powder clutch  640  and the system  622  supplements the operation of the powder clutch  640 . 
     FIGS. 35 and 36  show a still further embodiment in which the control over the control shaft  614  is performed by a toroidal pitch transfer gear system  950 . This gear system is described more fully in our co-pending Australian Provisional Patent Application No. PR3303 the contents of which are incorporated into this specification by this reference. Thus, in this embodiment, the cone clutch and powder clutch are completely removed and the pitch system  950  is controlled by one or more servo-motors  998  which, in turn, are controlled by control signals received by a controller  999  indicative of the speed of any two of the input, the output or the control shaft in the same manner as previously described. 
   In this embodiment, the sleeve  908  connects to a first toroidal track variator  960 . The variator  960  rotates with the gear  909  and sleeve  908  and carries a toroidal track  961  having gear teeth which change in pitch from an inner diameter portion  962  to an outer diameter portion  963 . A second pitch variator  965  is fixed onto the lay shaft  639  and also includes a toroidal track  966  which forms a track pair with the track  961 . The track  966  also has toroidal teeth which change in pitch from inner diameter  967  to outer diameter  968  as is described in more detail in the aforesaid provisional application. 
   A pair of pitch transfer wheels  980  and  981  are mounted between the tracks  961  and  966  and are arranged on rotatable shafts  985 . Each of the pitch transfer wheels  980  and  981  comprises two pitch gears having a different number of teeth so that the teeth are slightly out of phase with one another. The two gears are able to move relative to one another so as to transfer drive from the variator  960  to the variator  965 , as is clearly described in the aforesaid Australian provisional patent application. As clearly shown in  FIG. 36 , the pitch transfer wheels  980  and  981  are arranged in cut-outs or slots  987  in the shafts  985  and are journaled on pivot pins  989  so that the pitch transfer wheels  981  can rotate on the pins  989  to transmit drive from the variator  960  to the variator  965 . 
   As is best shown in  FIG. 36 , the shafts  985  (only one shown) are supported between plates  986  which are shown in  FIG. 36 . At one end the shafts have lugs  991  which are provided with elongated slots  992 . The slots  992  each receive a pin  993  located on block  994  which is connected to a screw threaded shaft  995 . The screw threaded shaft passes through a screw threaded nut  996  and is rotated by the servo-motor(s)  998  so that the shaft  994  is driven back and forward in the direction of arrow X rotate the shafts  985 , which in turn rotates the pitch transfer gear  981  in the directions of double-headed arrow M in  FIG. 35 . This changes the drive ratio between the variator  960  and the variator  965  depending on the rotated position of the shafts  985  and therefore the location of the pitch transfer gears  981  with respect to the toroidal tracks  961  and  966 . Thus, the drive transmitted from the. cage  606  via the gear  902 , pinion  905 , gear  907 , gear  909 , sleeve  908  and then from the variator  960  to the variator  985  is altered dependent on the orientation of the pitch transfer gears  981 . Thus, the drive transmitted to the shaft  614  is altered in accordance with the orientation of those pitch transfer gears to thereby control the rotary speed of the shaft  614  to in turn control the drive ratio of the transmission. 
   If the drive ratio between the variators  960  and  965  is high, the shaft  614  is therefore slowed down by the drive ratio to thereby place the transmission into a higher gear, or in other words speed up the transmission. If the drive ratio between the variator  960  and  965  is decreased, the control shaft  614  is able to increase in speed thereby bringing the transmission down towards neutral. If it is desired to place the transmission into reverse gear, the drive ratio between the variator  960  and  965  can be designed so that the speed of the shaft  614  can be further increased, thereby placing the drive ratio into reverse as previously described. 
   Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.