CLIAMS:1. A method of opening a clutch(18) in an electronic clutch system (10), said method comprising:
-determining a rate of change of a gear lever (12) position from an initial position (22) to an intermediated position (24);
-determining a difference between said intermediated position (24) and a threshold position (26);
- calculating a time required for the gear lever (12) to reach said threshold position (26) based on said determined rate of change of gear position and said determined difference;
- comparing said calculated time with a predefined time required by an actuator (16) to open said clutch (18) completely;
- opening said clutch (18) if said determined time is less than or equal to said predefined time.

2. The method claimed in claim (1), wherein said method comprising a step of determining an opening time required by said actuator (16) for completely opening said clutch (18), if said clutch (18) is partially opened.
3. The method claimed in claim (1), wherein said opening time is calculated from a total stroke length of said clutch (18) and a current stroke length of said clutch (18).
4. The method claimed in claim (1), wherein said actuator (16) opens said clutch (18) completely when said calculated opening time is less than or equal to said predefined time .
5. The method claimed in claim (1), wherein said threshold position (26) is a position at which a user experiences a resistance at said gear lever (12) when shifting said gear.
6. An electronic control unit (14) to open a clutch (18) in an electronic clutch system 10,
said control unit
-determines a rate of change of a gear lever (12) position from an initial position (22) to an intermediated position (24);
-determines a difference between said intermediated position and a threshold position (26);
- calculates a time required for the gear lever (12) to reach said threshold position (26) based on said determined rate of change of gear position and said determined difference;
- compares said determined time with a predefined time required by an actuator (16) to open said clutch (18) completely;
- opens said clutch (18) if said determined time is less than or equal to said predefined time.

7. The electronic control unit (14) claimed in claim (5), wherein said electronic control unit (14) calculates an opening time required by said actuator (16) for completely opening said clutch (18), if said clutch (18) is partially opened.
,TagSPECI:Field of the invention
[0001] This invention relates to a method of opening a clutch in an electronic clutch system.

Background of the invention
[0002] In the electronic clutch system the clutch is actuated by a clutch actuator. The response of the clutch actuator is comparatively slow compared to the fast user demand requests. The user’s particular shifting input is derived from the movements imposed upon, or forces exerted by the driver on the gear lever, and converted into corresponding control signals for the clutch, so that the clutching operation and shifting operation occur in a manner correspondingly matched to one another. The clutch is made to open when a slight movement of gear lever is detected.

[0003] A United States patent application 6056095 disclosing a vehicle having an automatically actuated clutch disposed in a drive train between an engine and a manually shifted transmission having a shift lever. The invention ensures that the irregularity in the manipulation of a gear selection does not result in actuations of the clutch with that of intentional shifting operations.

Brief description of the accompanying drawings
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[0005] Figure 1 illustrates an electronic clutch system according to one embodiment of the invention;
[0006] Figure 2 illustrates a flow chart of a method of opening a clutch in an electronic clutch control system according to one embodiment of the invention; and
[0007] Figure 3 illustrates a strategy of speed of the gear lever and distance between one gear position and neutral position according to one embodiment of the invention.

Detailed description of the invention
[0008] Figure 1 illustrates an electronic clutch system 10according to one embodiment of the invention. The electronic clutch system 10comprises an electronic control unit 14 to determine a rate of change of a gear lever 12 position from an initial position to an intermediated position. The electronic control unit 14 determines a difference between the intermediated position and a threshold position and calculates a time required for the gear lever 12 to reach the threshold position based on the determined rate of change of gear position and the determined difference. The electronic control unit 14 compares the determined time with a predefined time required by an actuator 16 to open the clutch 18 completely and opens the clutch 18 if the determined time is less than or equal to the predefined time.

[0009] In a two pedal electronic clutch system, the response of the actuator 16 is slow due to the mechanical and electronic constraints. (Ex: high load). For example, when the driver shifts the gear level (for instance, from any gear to a neutral) in less than 100ms, the actuator 16 takes around 150 to 200 ms as the fastest to open the clutch 18. In such cases, the clutch 18 has to be opened when a minimal movement in the gear lever 12 is detected, in order to avoid the reverse force acting on a user of the vehicle or resistance to shift the gear on a user.

[00010] Figure 2 illustrates a flowchart of a method of opening a clutch 18 in an electronic clutch system according to one embodiment of the invention.

[00011] When the user changes the gear lever 12 from one gear to the neutral, the lever is made to move in a required direction, towards the neutral gear (i.e., from the initial position 22 to towards the intermediate position 24) and the rate of change of the gear lever 12 position from the initial position 22 to the intermediate position 24 is determined in step S1.The rate of change of position is a speed of a gear level over a time period. In step S2, a difference between the intermediated position and a threshold position 26 is determined. The difference is a distance to be travelled by the gear lever 12 (from the intermediate position 24 to the threshold position 26) while moving from one gear to the neutral. The threshold position 26 is at which a user experiences a resistance at the gear lever 12 when shifting the gear. The user experiences the resistance when a torque is getting transferred from an engine to a wheel through the partially opened clutch 18 and gear lever 12 being in threshold position. A time is calculated which is required for the gear lever 12 to reach the threshold position 26 based on the determined rate of change of gear position and the determined difference in step S3. The electronic control unit 14 compares the determined time with a predefined time required by an actuator 16 to open the clutch 18 completely in step S4. In step S5, the actuator 16 opens the clutch 18 if the determined time is less than or equal to the predefined time.

[00012] Figure 3 illustrates a strategy of speed of the gear lever 12 and distance between one gear position and neutral position in a gear lever 12 according to one embodiment of the invention.

[00013] The above disclosed method is explained in detail with the example stated below.

[00014] The lever is made to move in the required direction from 80% (initial position 22) to 77% (intermediate position 24) in 100ms as shown in the figure 2. The speed at which the gear lever 12 is moved from the initial position 22 to the intermediate position 24 (from 80% to 77%) (i.e., rate of change of gear lever 12 position over time) is determined as below:
Speed = ((80 – 77)) / 100
s = 0.03% per msec
s = 30% per sec.

[00015] If the threshold position 26 is at 70% from even gear to neutral, then the difference (which is the remaining distance to be travelled by the gear lever 12 to the threshold position 26 from the intermediate position 24) is calculated as
Distance (Difference) = 77%-70%
= 7%.
[00016] The time to reach for the gear lever 12 to reach the threshold position 26 is calculated from the speed of the gear lever 12 (from the initial position to the intermediate position) and the difference to be travelled by the gear lever 12 to reach the threshold position 26 from the intermediate position.
Time = Distance/Speed
Time required for the gear lever 12 to reach the threshold position 26 = 7/0.03
Time = 233.33 ms

[00017] If the predefined time required by the actuator 16 to open the clutch 18 completely is 120ms, the above calculated time is compared with the predefined time. Since the above calculated time is more than the predefined time (233.33ms > 120ms), the clutch 18 is not opened by the actuator 16.The clutch 18 is opened completely by the actuator 16 only when the calculated time is less than or equal to the predefined time.

[00018] The electronic control unit 14 disclosed above determines an opening time required by the actuator 16 for completely opening of the clutch 18.
If the clutch 18 is partially opened, then actuator 16 opens the clutch 18 only if the determined opening time is less than or equal to the predefined time required for the actuator 16 to open clutch 18 completely. The opening time of the clutch 18 is calculated based on the total stroke length of the clutch 18 and the current stroke length of the clutch 18. The total stroke length is a predefined value (i.e., the maximum distance between the clutch plates when the clutch 18 is in completely opened state) and the current stroke length is a dynamic value (i.e., the difference between the clutch plates when the clutch 18 is in partial opened state) which is determined by the electronic control unit 14 formed due to activation of torque tracking, clutch slipping etc. The difference between the current stroke length of the clutch 18 and the total stroke length of the clutch 18 gives the remaining stroke length of the clutch 18.

[00019] Remaining stroke length of the clutch = total stroke length of the clutch – current stoke length of the clutch.

[00020] By using the comparison methods like interpolation, the opening time required for the actuator 16 to open the clutch 18 completely is calculated.

[00021] The above calculation of the opening time of the clutch 18 is explained with the example below:

[00022] Consider 120ms as the predefined time required by actuator 16 to open the clutch 18 completely with a total stroke length of clutch 18 (TSL) of 12mm.If the clutch 18 is slightly opened i.e., current stroke length of the clutch 18 (CSL) is 5mm, due to the torque tracking (transfer of the torque from the gear lever 12 to the clutch 18) then the time required to open clutch 18 completely from this position is calculated as:

[00023] Remaining Stroke Length of the clutch (RSL) = TSL-CSL
= 12 – 5
= 7mm
[00024] So the time required by the actuator 16 to open the clutch 18 completely is calculated based on Interpolation method:

[00025] For the total stroke length of 12mm, if the actuator 16 takes 120ms to open the clutch 18 completely, then for 7mm of remaining stroke length of the clutch 18, the time required for the actuator 16 to open the clutch 18 completely is calculated as below:
Opening time (Ttc) = (RSL* Predefined time)/ TSL
= (7*120)/12
=70msec
[00026] The opening time required for the actuator 16 to open the clutch 18 completely is 70msec.The calculated opening time is compared with the predefined time and the clutch 18 is opened completely when the calculated opening time is less than or equal to the calculated time. When the calculated opening time is less than the calculated time, the actuator 16 opens the clutch 18. The above mentioned calculation is dynamic and will be executed in each cycle.

[00027] With the above method disclosed, the unintentional clutch 18 open movement can be avoided by opening the clutch 18 only when the calculated time is less than or equal to the predefined time required for the actuator 16 to open the clutch 18 completely. Since the response of the actuator 16 is comparatively slow compared to fast user demand requests, the above method provides a sufficient time for the actuator 16 to respond while opening the clutch 18. By considering the speed of the gear lever 12 and current position of clutch 18 the optimum point to open the clutch 18 can be determined. This avoids early trigger of clutch 18 open conditions due to oscillation or late opening of clutch 18.

[00028] It must be understood that the embodiments explained in the above detailed description is only illustrative and does not limit the scope of this invention. The scope of this invention is limited only by the scope of the claims.