This invention relates to a clamping force control device for continuously variable transmission systems including those which are electronically controlled.

For continuously variable transmission (CVT) to transmit power, a clamping force is to be applied between the belt and pulley, the magnitude of the force to be applied being a complex derivative since it is related to CVT ratio, torque transmitted and CVT belt speed.

Accordingly, a mechanism to control this clamping force is required.

Conventionally there are three types of systems

1. Mechanical system

This system works on the inclined plane principle. Here torque is transmitted through a torque ramp or torque groove, which will develop axial force as it transmits the torque. This axial force is the clamping force developed. The generated force varies according to torque transmitted but cannot vary according to speed of CVT belt.

2. Hydraulic System

In this case, hydraulic cylinders are used to generate the required force. The cylinders connected to the pulley will press the movable pulley over the belt to generate the required force.

3. Using electric motors

Here the motor is generally connected to a mechanism, which converts rotational motion into axial motion. This axial motion presses the movable pulley over the belt to generate the required force,

The hydraulic and electrical motor systems have good control over the applied force but' consume more energy. For example, for an electrical system to work, mechanical torque is to be converted into electricity through an alternator, the energy stored in a battery and taken out again to operate an electric motor. So the overall efficiency of the system is low due to a// the energy conversions. In a mechanical system we directly convert torque into axial force; so the efficiency is high but there is less control over applied force.

This invention therefore proposes a device with the efficiency as well as the control of the above mentioned systems.

According to this invention, the clamping force control device for continuously variable transmission systems, including those which are electronically controlled, comprises a torque sensing mechanism, one end of which is connected to a movable pulley, while the other end is connected to a. wheel; a spring also connected to the movable pulley: an electric motor actuator connected to means for converting the rotational movement of the motor to linear motion, the said means compressing or releasing the spring as required; a linear position sensor for precisely sensing the position of one side of the spring and thereby determining the force applied by the spring on the pulley, the said torque sensing means applying an axial load on the pulley and the said spring also applying a load on the pulley: a controller fort controlling the rotational movement of the motor.

Preferably the other end of the torque sensing mechanism is connected to the wheel through a centrifugal clutch.

Preferably the means for converting the rotational movement of the motor to linear motion will be self-locking so that the electric motor can be switched off during steady state conditions and-used only during transient conditions.

This invention will now be described with reference to the accompanying drawings which illustrate, in Figs, f to 4. by way of example, and not by way of limitation, three embodiments of this invention.

A torque sensing mechanism TSM, one end of which is connected to a movable pulley MP. while the other end is connected to a wheel W preferably through a centrifugal clutch CC. A spring SP is also connected to the movable pulley. An electric motor actuator EM is connected to means, such as a known mechanism MIL for converting the rotational movement of the motor to linear motion, the said mechanism compressing or releasing the spring as required. A linear position sensor S precisely senses the position of one side of the spring and thereby the extent of compression of the spring and thus enables the force applied by the spring on the pulley to be calculated. The said torque sensing mechanism applies an axial load FTS on the pulley and the said spring SP a/so applying a load FSP on the pulley. A controller CT controls the operation of the electric motor EM

Preferably the means for converting the rotational movement of the motor to linear motion will he sell-locking so that the electric motor can be switched off during steady state conditions and used only during transient conditions.

In the embodiments illustrated in Figs, l and 2 the clamping force; arrangement is at the driven end of the CVT transmission and are substantially the same except that the components have changed positions.

In the configurations 3 and 4 the clamping force arrangement is at the driver side of the CVT transmission and are substantially the same except that the components have changed their positions.

In Fig, 2 the torque sensing mechanism TSM is connected to movable pulley MP. The mechanism Mil is connected to the movable pulley in such a way that it can move together with the movable pulley if required and can also move axially relative to it when requited to both cases when the mechanism moves it compresses or releases the spring against a fixed support thereby producing force which is transmitted through the mechanism MM to the movable pulley. The sensor S senses the relative position of the mechanism with respect to ground and the controller CT decides whether the mechanism will move with the pulley or relative to the pulley.

In Fig. 3 the torque sensing mechanism 'TSM is connected to the engine ENG at the driver side of the transmission. A spring SP is also connected to the same pulley. An electric motor actuator EM is connected to the mechanism MH which compresses or releases the spring as required. A linear position sensor S senses the precise position of one side of the spring and thereby the extent of compression and hence the three applied by die spring on the pulley can be calculated. 'The torque sensing mechanism applies an axial load FTS on the pulley and the compressed spring applies a load FSP on the pulley. The controller CT controls the electric motor

In Fig. 4 the torque sensing mechanism YSM is connected to the engine ENG at the driver side of the transmission. "The mechanism MR is connected to the movable pulley .such that it can move together with the pulley if required mid also can move axially relative to it when required, In both cases when the said mechanism moves it compresses or releases the spring against a fixed ground thereby producing force which is transmitted through the mechanism MM to the movable pulley. The sensor S senses the relative position of the mechanism with respect to ground. The controller CT decides whether the mechanism will move with the pulley or relative to the pulley.

It will be seen from the foregoing that in the invention proposed most of the force (say 90%) is generated through a mechanical system while the remaining (say 10%) of the force is generated by the senser efficient motor or hydraulic system. Both these systems work in parallel and the force on the belt will be a summation of individual forces. Since most of the force is generated by the more efficient mechanical system, the device proposed is very efficient and since there is the electrical motor or hydraulic arrangement to give the remaining (say l()%)there is excellent control also over the net final force.

So it uses the best of both systems. All shown configurations mainly demonstrate this idea only. They have an electric motor (EM) whose rotation is converted into axial movement by a mechanism (MH). The axial movement will compress or release a spring (SP) which on compression will produce a force (FSP). The force (FSP) added with the force (FTS)produced by the torque sensing mechanism (TSM) will be the total clamping ibree acting on the bolt

The embodiments exemplify the various ways the components (Spring SP, Mechanism MIL Electric Motor EM) can be placed.

In embodiments 1 and 2, there is the clamping force arrangement at the driven end of the CVT transmission as indicated by the wheel W. Both embodiments are substantially the same except that the parts have changed positions.

In embodiments 3 and 4 there is the same clamping force arrangement on the driver side of the CVT transmission as indicated by the engine ENG, Here again the embodiments are the same except that the components have changed positions.

It will be appreciated that various other embodiments of this invention are possible without departing from the scope and ambit of this invention.

We Claim:

1. A clamping force control device for continuously variable transmission systems comprising a torque sensing mechanism, one end of which is connected to a movable pulley, while the other end is connected to a wheel; a spring also connected to the movable pulley; an electric motor actuator connected to means for converting the rotational movement of the motor to linear motion, the said means compressing or releasing the spring as required; a linear position sensor for precisely sensing the position of one side of the spring and thereby determining the force applied by the spring on the pulley, the said torque sensing means applying an axial load on the pulley and the said spring also applying a load on the pulley; a controller for controlling the operation of the motor.

2. At device as claimed in Claim 1 wherein the other end of the torque sensing mechanism is connected to the wheel through a centrifugal clutch.

3. A device as claimed in Claim f or Claim 2 wherein the means for converting the rotational movement of the motor to linear motion are self-locking such that the electric motor can be switched off during steady stale conditions and used only during transient conditions,

4. A clamping force control device for continuously variable transmission systems substantially as herein described and illustrated with reference to any one of the Pigs.1 to 4 of the accompanying drawings. This invention relates to a clamping force control device for continuously variable transmission systems including those which are electronically controlled.