Claims:We claim:
1. An assembly (100) of an electric actuator (114) for a Continuously Variable Transmission (CVT), said CVT comprises a primary pulley (104) having a fixed sheave (102) and a movable sheave (106), said movable sheave (106) is axially displaceable, characterized in that:
a threaded shaft (122), a first end of which is coupled to said movable sheave (106), and a second end of said threaded shaft (122) is coupled to said electric actuator (114) through a flexible member (120).
2. The assembly (100) as claimed in claim 1, wherein said flexible member (120) is selected from a group comprising a belt and at least one Bowden cable.
3. The assembly (100) as claimed in claim 1, wherein said CVT comprises a mechanical actuator, namely a variator (110), and said electric actuator (114) assists said variator (110).
4. The assembly (100) as claimed in claim 3, wherein said flexible member (120) is selected from a group comprising a belt and at least one Bowden cable.
5. The assembly (100) as claimed in claim 1, wherein a drive member (118) is mounted to an actuator shaft (116) of said electric actuator (114) and a driven member (124) is mounted to said first end of said threaded shaft (122), and wherein said flexible member (120) is couples said drive member (118) and said driven member (124).
6. The assembly (100) as claimed in claim 1, wherein said movable sheave (106) is axially displaceable on rotation of said threaded shaft (122) in clockwise and anti-clockwise direction.
7. The assembly (100) as claimed in claim 1, wherein said threaded shaft (122) is directly coupled to said movable sheave (106) through a cover (126) and a displacer (130).
, Description:Field of the invention:
[0001] The present disclosure relates to an assembly of an electric actuator for a Continuously Variable Transmission (CVT), and particularly relates to the mechanism of assisting the CVT.

Background of the invention:
[0002] According to a patent literature WO16139107, a CVT gearbox having improved controllability is disclosed. The invention relates to a CVT gearbox, comprising a conical disc pair having a stationary conical disc and an axially moveable conical disc, at least one centrifugal force element that is moveably arranged in the axially moveable conical disc, a support element which is arranged on the axially moveable conical disc and which is connected to a crankshaft, wherein the centrifugal force element is arranged between the support element and a rear wall of the axially moveable conical disc, and axially displaceable inner sleeve that is connected to the axially moveable conical disc, a positioning device for adjusting a position of the axially moveable conical disc, wherein the positioning device is connected to the inner sleeve, and a control unit that is designed to actuate the positioning device in order to displace the moveable conical disc in the axial direction (X-X) by means of the inner sleeve, in order to achieve a transmission change at the conical disc pair.

Brief description of the accompanying drawings:
[0003] An embodiment of the disclosure is described with reference to the following accompanying drawings,
[0004] Fig. 1 illustrates a top cross-section view of an assembly of the electric actuator, according to an embodiment of the present invention;
[0005] Fig. 2 illustrates a top view of the assembly with ECU control, according to an embodiment of the present invention;
[0006] Fig. 3 illustrates a perspective view of the assembly with cables, according to an embodiment of the present invention., and
[0007] Fig. 4 illustrates a method executed by an Electronic Control Unit (ECU) to operate the electric actuator, according to an embodiment of the present invention.

Detailed description of the embodiments:
[0008] Fig. 1 illustrates a top cross-section view of an assembly of the electric actuator, according to an embodiment of the present invention. An assembly 100 of the electric actuator 114 for the Continuously Variable Transmission (CVT) is disclosed. The CVT comprises a primary pulley 104 and a secondary pulley (not shown) connected to each other with a belt 112, each of the pulleys comprises one fixed sheave 102 and a movable sheave 106. The primary pulley 104 is coupled to the crankshaft 108 of an engine of a vehicle. The secondary pulley is coupled to the wheels of the vehicle either directly or through a reduction unit. The electric actuator 114 is a motor which assists the CVT as known in the art. The assembly 100 is characterized by, a threaded shaft 122, a first end of which is coupled to the movable sheave 106, and a second end of the threaded shaft 122 is coupled to the electric actuator 114 through a flexible member 120.
[0009] The coupling of the threaded shaft 122 to the movable sheave 106 is made through a connecting module 132, which rests on a support element connected to the movable sheave 106. A sleeve connects the movable sheave 106 to the support element passing through the fixed sheave 102.
[0010] In accordance to another embodiment of the present invention, the assembly 100 of the electric actuator 114 is disclosed to assist a mechanical actuator, namely a variator 110 of the CVT. The variator 110 comprises plurality of roller/ centrifugal weights which mechanically actuates the CVT. The variator 110 is the main actuator and the electric actuator 114 is operated to support the variator 110 whenever required.
[0011] The threaded shaft 122 is coupled to a driven member 124 through the first end. The electric actuator 114 is coupled to a drive member 118 through an actuator shaft 116. The driven member 124 and the drive member 118 are coupled to each other through the flexible member 120.
[0012] The drive member 118 transmits the motion to the driven member 124. The rotation of the driven member 124 rotates the threaded shaft 122 and thereby axially displaces the movable sheave 106. The movement of the threaded shaft 122 adjusts the position of movable sheave 106, which aids in change in gear ratio.
[0013] The electric actuator 114 is shown coupled on the side of the fixed sheave 102. However, the same assembly 100 is possible to be adapted on the side of the movable sheave 106 based on requirement.
[0014] The electric actuator 114 comprises the electric motor such as a linear motor with Hall sensor, or a stepper motor. Both the motors are equipped with gear system to achieve desirable torque. The electric actuator 114 rotates in both Clock Wise (CW) and Counter Clock Wise (CCW) direction. A position sensor is optimally provided to determine position of displaced actuator shaft 116. A locking mechanism is provided to lock the displaced actuator shaft 116 in predetermined position.
[0015] The threaded shaft 122 passes through a cover 126 and the displacer 130. The cover 126 comprises a cavity 128 to accommodate the displacer 130 during linear motion. The threaded shaft 122 is supported by the bearings in the cover 126.
[0016] The rotary motion of the threaded shaft 122 corresponds to the axial movement of the displacer 130. The threaded shaft 122 rotates, but the displacer 130 moves forward and backward. The limit of the rotation and/or the linear motion of the displacer 130 is configurable and decided based on requirement. The rotation of the displacer 130 is blocked by means of a stopper (not shown). The displacer 130 comprises internal thread which meshes with the external threads of the threaded shaft 122. While the electric actuator 114 is rotating, the threaded shaft 122 rotates in the same axis without any linear motion. Due to the rotation of the threaded shaft 122, the displacer 130 starts moving towards the driven member 124. If the threaded shaft 122 rotates in the opposite direction, then the displacer 130 starts moving away from the driven member 124. The reference of movement is taken as driven member 124 for the sake of clear understanding and must not be understood in limiting sense.
[0017] Fig. 2 illustrates a top view of the assembly with ECU control, according to an embodiment of the present invention. The electric actuator 114 is operatively activated to rotate the threaded shaft 122. The threaded shaft 122 is internally coupled to a displacer 130 through the second end. The rotary movement of the threaded shaft 122 leads to, to-and-fro motion or back and forth motion of the displacer 130.
[0018] The flexible member 120 is at least one selected from a group comprising a cable such as a Bowden cable and a belt such as timing belt, etc.
[0019] In an embodiment, the drive member 118 and the driven member 124 are cable plates and the flexible member 120 comprises two cables. However, a single cable is possible to be used when looped around the driven member 124 and the drive member 118.
[0020] In another embodiment, the drive member 118 and the driven member 124 are pulleys, and the flexible members 120 is a belt such as but not limited to a timing belt.
[0021] In accordance to an embodiment of the present invention, an Electronic Control Unit (ECU) 200 to control the electric actuator 114 is provided. The electric actuator 114 assists the variator 110 of the CVT. The ECU 200 comprises components such as but not limited to a processor, I/O ports, a memory unit, an ADC/DAC converter and all of which interconnected with buses. The ECU 200 is configured to receive inputs 202 comprising engine speed, vehicle speed and throttle position from respective sensors. The ECU 200 then access a map from the memory element and reads a desired (CVT ratio) based on the inputs 202. The ECU 200 then computes an actual CVT Ratio from the inputs 202 and compares with the desired CVT ratio to determine an offset CVT ratio. The desired CVT ratio is derived from the map. The ECU 200 then sends control signal to operate the electric actuator 114 and assists the CVT by achieving the desired CVT ratio based on the offset CVT ratio. The rotation of the actuator shaft 116 is held at a position when the desired speed ratio of the CVT is achieved by controlling the electric actuator 114. The ECU 200 is the Engine Control Unit or a dedicated controller in communication with the Engine Control Unit. The ECU 200 holds at gear ratio by controlling the power supply to the electric actuator 114.
[0022] In another embodiment, the electric actuator 114 is controlled for a CVT without any variator 110 or mechanical actuator, i.e. the variator 110 comprising the centrifugal roller weights is not present. Only the electric actuator 114 controls the gear ratio. The primary clamping force responsible for the gear ratio change is exerted by the electrical actuator 114 equipped with a gear system to achieve desirable torque and gear ratio, rather than just assisting the variator 110. The ECU 200 is provided for a CVT operated only with the electric actuator 114. The ECU 200 directly operates the electric actuator 114 based on the inputs 202 comprising engine speed, vehicle speed and throttle position from respective sensors and other necessary sensors for the operation of the vehicle.
[0023] Fig. 3 illustrates a perspective view of the assembly with cables, according to an embodiment of the present invention. The electric actuator 114 is shown coupled to the threaded shaft 122 through the flexible member 120 comprising a first cable 302 and a second cable 304. The drive member 118 and the driven member 124 are both cable plates with a groove at the periphery to hold the cables 302 and 304.
[0024] With respect to Fig. 1 and Fig. 3, a working method for assisting the mechanically actuated CVT is provided. Based on the movement/ rotation of the actuator shaft 116 of the electric actuator 114, the flexible member 120 is moved thereby moving the threaded shaft 122. The electric actuator 114 is operated by the ECU 200 to actuate the drive member 118. When the electric actuator 114 rotates in first direction such as clockwise (CW) direction, the first cable 302 is pulled towards the electric actuator 114, hence rotating the threaded shaft 122 and thereby axially displacing the variator 110 of the CVT to desired gear ratio. When the electric actuator 114 rotates in other/opposite direction such as counter clockwise (CCW) direction, then the second cable 304 is pulled towards the electric actuator 114, tightening the flexible member 120 in both the cases. Hence, the rotation in both the directions rotates the threaded shaft 122 and thereby axially displaces the variator 110 of the CVT to desired gear ratio.
[0025] Fig. 4 illustrates a method executed by an Electronic Control Unit (ECU) to operate the electric actuator, according to an embodiment of the present invention. The method comprises a step 402 comprising receiving inputs 202 comprising engine speed, vehicle speed and throttle position from respective sensor continuously or periodically. The ECU 200 optionally detects actuator shaft 116 displacement by a position sensor. A step 404 comprises checking/ deciding based on the inputs 202, whether the actual speed ratio/ CVT ratio is equal to the desired speed ratio. The speed ratio is calculated by dividing engine speed to the vehicle speed. If the decision is true, then the step 406 is executed, which comprises the ECU 200 controlling the electric actuator 114 in such a manner that the speed ratio is held at the desired speed ratio. At the end of the step 406, the ECU 200 executes from the step 402 again. This refers to self-locking mechanism. The locking mechanism locks the displaced actuator shaft 116 in determined position. If the decision at step 404 is false, then the ECU 200 executes the step 408 comprising moving the actual speed ratio to desired speed ratio by controlling the electric actuator 114.
[0026] Once the ECU 200 assists the electric actuator 114, the ECU 200 as per the step 410, again decides whether the actual CVT ratio is greater than the desired CVT ratio. If decision is false at the step 410, the ECU 200 executes the step 412 which comprises controlling the electric actuator 114 to achieve a lower CVT ratio (example 2.3), followed by repeating the steps from step 402 onwards. If the decision at the step 410 is true, then the ECU 200 executes the step 414, which comprises controlling the electric actuator 114 to achieve a higher CVT ratio (example 0.8) followed by repeating the steps from the step 402 onwards.
[0027] In accordance to an embodiment of the present disclosure, a drive train mechanism to actively control the variator 110 of the CVT is disclosed. In particular, the flexible member 120 are used to connect the movable sheave 106 of the primary pulley 104 of the CVT to the electric actuator 114 and to control both sides of actuation. The assembly 100 of the electric actuator 114 reduces the limitation, specifically of electromechanical actuators mounted along the crankshaft 108 which adds axial load and is subjected to high vibration and heat from the engine when compared to the standard acceptable limit. The assembly 100, increases/ improves the durability and functionality of the electric actuator 114. The assembly 100 along with the electric actuator 114 is isolated from the source of vibration and heat by the placement away from the crank shaft axis or the engine. The assembly 100 provides easy, simple and good serviceability and replacement of internal components. Exposure of the electric actuator 114 to heat and vibration is reduced.
[0028] By placing away from the crankshaft 108 and the engine, the electric actuator 114 is isolated from the source of vibration & heat. The arrangement of the electric actuator 114 enables better serviceability and ease of assembly and ease of replacement of parts in case of failure. Both way actuation is possible with new mechanics. Direct connection of threaded shaft 122 or driven member 124 to the electric actuator 114 is able to achieve accurate actuation on both the direction of operation. Further, the assembly 100 is usable as a replacement for centrifugally actuated rollers.
[0029] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.