WO2018231226A1

WO2018231226A1 - Transmission clutch control system and method of operating the same

Info

Publication number: WO2018231226A1
Application number: PCT/US2017/037515
Authority: WO
Inventors: Christopher Blair
Original assignee: Borgwarner Inc.
Priority date: 2017-06-14
Filing date: 2017-06-14
Publication date: 2018-12-20

Abstract

A clutch control system is adapted for operation with a transmission and includes a clutch coupled to the transmission. The clutch includes a housing defining a chamber that is configured to hold a fluid, and a piston disposed within the housing configured to be moved between a first position and a second position. The clutch also includes a hydraulic circuit which includes a pump and a hydraulic control module. 'The hydraulic control module includes a valve assembly defining the hydraulic circuit. The system is configured to control the flow rate of the fluid when the piston is in the first position and when the piston is between the first position and the second position, and configured to control the pressure of the chamber when the piston is in the second position.

Description

TRANSMISSION CLUTCH CONTROL SYSTEM AND

METHOD OF OPERATING THE SAME

BACKGROUND OF THE INVENTION

1 , Field of the Invention

[0001] The subject invention generally relates to a clutch control system which includes a valve assembly for controlling a fluid and a control method for controlling a clutch control system.

2. Description of the Related Art

[0002] Conventional vehicles include a transmission operabiy coupled with a clutch system. The transmission requires the typical clutch system to operate in two distinct functional regimes. The first is the high flow regime. In this regime, during vehicle operation, a fluid fills a chamber in the clutch system to stroke a piston in preparation for a clutch apply event. The second regime is a pressure regulation regime. In this regime, the clutch system is designed to control fluid pressure within the chamber to regulate the pressure during the clutch apply event.

[0003] Conventional vehicles include control systems which control fluid pressure within the chamber. The vehicles may include a hydraulic valve that uses hydraulic control pressure feedback to regulate the pressure within the chamber during the pressure regulation regime. These control systems exhibit non-optimal characteristics during the high flow regime. More specifically, the conventional control systems have a slow clutch fill time, and repeatability is also a concern. As such, there remains a need for improved control during both the high flow regime and the pressure regulation regime. Additionally, there remains a need for improved control systems that have an improved clutch fill time and repeatability with respect to the control system. SUMMARY OF THE INVENTION AND ADVANTAGES

[0004] A clutch control system is adapted for operation with a transmission and includes a clutch coupled to the transmission. The clutch includes a housing defining a chamber that is configured to hold a fluid, a clutch plate operably coupled to the transmission and disposed within the housing, and a piston disposed within the housing and configured to be moved between a first position, where the piston is disengaged from the clutch plate, and a second position, where the piston is engaged with the ciutch plate. The clutch also includes a hydraulic circuit for moving the fluid. The hydraulic circuit includes a pump and also includes a hydraulic control module defining the hydraulic circuit for controlling a pressure of the chamber and a flow rate of the fluid to the chamber. The hydraulic control module includes a valve assembly defining the hydraulic circuit. The hydraulic control module also includes a sensor disposed in the hydraulic circuit. The electronic control module is configured to control the valve assembly based on data from the sensor when the piston is in the second position. The system is configured to control the flow rate of the fluid when the piston is in the first position and when the piston is between the first position and the second position and the system is also configured to control the pressure of the chamber when the piston is in the second position.

[0005] A hydraulic control module coupled to an electronic control module defines a hydraulic circuit for controlling a clutch system which includes a housing defining a chamber that is configured to hold the fluid; a clutch plate that is operably coupled to a transmission and disposed within the housing; and a piston that is disposed within the housing and configured to be moved between a first position and a second position. The piston is disengaged from the clutch plate in the first position and the piston is engaged with the clutch plate in the second position. The hydraulic control module also includes a sensor disposed in the hydraulic circuit. The electronic control module is configured to control the valve assembly based on data from the sensor when the piston is in the second position. The hydraulic control module includes a valve assembly defining the hydraulic circuit. The system is configured to control a flow rate of the fluid when the piston is in the first position and when the piston is between the first position and the second position and the system is also configured to control a pressure of the chamber when the piston is in the second position.

[0006] A method for controlling a clutch control system includes a clutch coupled to a transmission. The clutch includes a housing defining a chamber that is configured to hold a fluid. A clutch plate is operably coupled to the transmission and disposed within the housing. A piston is disposed within the housing and configured to be moved between a first position where the piston is disengaged from the clutch plate and a second position where the piston is engaged with the clutch plate. The clutch control system further includes an electronic control module. The clutch also includes a hydraulic circuit for moving the fluid includes a pump. A hydraulic control module partially defines the hydraulic circuit and the hydraulic control module includes a valve assembly defining the hydraulic circuit. The method includes controlling the flow rate of the fluid when the piston is in the first position and when the piston is between the first position and the second position and controlling the pressure of the fluid within the chamber when said piston is in the second position.

[0007] The ability to control the system using both pressure and flow rate optimizes performance of the clutch under both high flow and pressure control regimes. This configuration, especially during the high flow regime, may also lead to improved clutch fill accuracy, improved clutch fill repeatability, and shortened clutch fill time. When used to control pressure, the system may also have the advantage of improving or eliminating pressure accuracy error associated with the conventional system. The ability to match the control method to the momentary system requirements may also have significant performance advantages over the conventional system. BRIEF DESCRIPTION OF THE DRAWINGS

)8] Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG 1. is a schematic view of a vehicle having a powertrain system:

FIG. 2 is a schematic view of a clutch assembly according to one exemplary embodiment;

FIG. 3 is a perspective view of a valve assembly;

FIG. 4 is a schematic view of the clutch assembly having a piston in a first position; and

[0013] FIG. 5 is a schematic view of the clutch assembly having the piston in a second position.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Referring now to the figures, where like numerals are used to designate like structure unless otherwise indicated, a vehicle is schematically illustrated at 10 in the figures. As illustraied in Figure 1 , the vehicle includes a powertrain system 1 1 which includes an engine 12 in rotational communication with a transmission 14. The transmission 14 may be any type of transmission including a manual, automatic, or semi-automatic transmission as known by one of ordinary skill in the art. In one exemplary embodiment, the transmission 14 is an automatic dual clutch transmission; however, it is contemplated that the transmission 14 may be any type of manual, automatic, or semi-automatic transmission. The engine 12 generates rotational torque which is selectively translated to the transmission 14 which, in turn, translates rotational torque to one or more wheels 16, generally indicated at 16. The transmission 14 is typically controlled using hydraulic fluid. To this end, the powertrain system 1 1 typically includes a hydraulic control system 20 that directs or otherwise controls fluid to the transmission 14. It should also he appreciated that the engine 12 and the transmission 14 of Figure 1 are of the type employed in a conventional "transverse front wheel drive" powertrain system. It should further be appreciated that the engine 12 and/or transmission 14 could be configured in any suitable way sufficient to generate and translate rotational torque so as to drive the vehicle, without departing from the scope of the present invention.

[0015] Referring still to the embodiment illustrated in Figure I, the vehicle also includes an electronic control module 21. The electronic control module 21 may be a TCU or other control unit as known by one of ordinary skill in the art. It is contemplated that the electronic control module 21 may be coupled to the engine 12, the transmission 14, the hydraulic control system 20, and/or any other vehicle component. The electronic control module 21 may also be configured to control any or ail features of the engine 12, the transmission 14, the hydraulic control system 20, and/or any other vehicle component. In the embodiment illustrated in Figure 1, the electronic control module is coupled to the hydraulic control system.

[0016] Referring now to the embodiment illustrated in Figure 2, in one exemplary embodiment, the hydraulic control system 20 includes a clutch control system 18. The clutch control system 18 is adapted for operation with the transmission 14 and includes at least one clutch 22 that is coupled to the transmission 14.

[0017] The clutch 22 may be any type of clutch as known by one of ordinary skill in the art including, but not limited to, a friction clutch, a wet clutch, a dry clutch, a multi-plate clutch, a dual clutch system, an electromagnetic clutch, or an electrohydraulic clutch without departing from the spirit of the invention. The clutch 22 may include a housing 24 defining a chamber 26. The housing 24 may be comprised of any material as known by one of ordinary skill in the art including but not limited to steel, aluminum, a plastic polymer, or the like. The chamber 26 may be configured to hold a fluid. The fluid may be the hydraulic fluid described above, or any other fluid as known by one of ordinary skill in the art. The chamber 26 may have a size and shape similar to the chamber 26 illustrated in Figure 2. However, it is also contemplated that the chamber 26 may be of any size and shape as desired by one of ordinary skill in the art,

[0018] Referring still to Figure 2, the clutch 22 may also include a clutch plate 28 which may be disposed within said housing 24, The clutch plate 28 may be any type of clutch plate or clutch disk that is configured to be coupled to the transmission 14 as laiown by one of ordinary skill in the art. More specifically, the clutch plate 28 may be configured to engage a portion of the transmission 14 in order to allow energy to be transferred between the engine 12 and the transmission 14.

[0019] The clutch 22 may also include a piston 30 disposed within the housing 24. The piston 30 may be a standard piston as known by one of ordinary skill in the art or may be one or more of a trunk piston, a cross head piston, a slipper piston, a deflector piston or the like without departing from the spirit of the invention. The piston 30 is configured to move between a first position 32 where the piston 30 is disengaged from the clutch plate 28, and a second position 34, where the piston 30 is engaged with the clutch plate 28. Additionally, the piston 30 may be configured to be moved by a controller, may be configured to be moved due to a pressure of the fluid in the chamber 26, or may be moved by another method as known by one of ordinary skill in the art. In one exemplary embodiment, when the chamber 26 is empty or otherwise less than full of fluid, the piston 30 remains in the first position 32. When the chamber 26 is full of fluid, the pressure of the fluid in the chamber 26 increases and moves the piston 30 from the first position 32 towards the second position 34. As the pressure of the fluid in the chamber 26 continues to increase, the piston 30 is moved to the second position 34 where the piston 30 is engaged with the clutch plate 28. In turn, when the piston 30 is engaged with the clutch plate 28, the clutch plate 28 engages a portion of the transmission 14, as described above, to allow energy transfer between the engine 12 and the transmission 14. It is additionally contemplated that the clutch 22 may also include an end plate 29 for coupling the clutch plate 28 with the transmission 14, as illustrated in the embodiment shown in Figure 2.

[0020] Additional!}', the clutch 22 may include a biasing member 36 which is configured to bias the piston 30 towards the first position 32. The biasing member 36 may be any biasing member 36 as known by one of ordinary skill in the art including but not limited to any type of spring as known by one of ordinary skill in the art. In one exemplary embodiment, the biasing member 36 may be one or more of a tension spring, a torsion spring, a compression spring, a constant spring, a variable spring, or the like.

[0021] It is additionally contemplated that when the transmission 14 is a dual clutch transmission 14, the clutch control system 18 may include two clutches 22 each having a housing 24 defining a chamber 26, a clutch plate 28, and a piston 30 such that clutch control system 18 includes two housing defining chambers, two clutch plates, and two pistons as known by one of ordinary skill in the art. Additionally, the two clutch control systems may be the same or similar as described above with respect to the single clutch control system 18 or may include different types of clutches, housings, clutch plates, and pistons as known by one of ordinary skill in the art.

[0022] Referring still to the embodiment illustrated in Figure 2, the clutch control system 18 may also include a hydraulic circuit 38 for moving the fluid. In one embodiment, the hydraulic circuit 38 is a closed-loop circuit. However, it is also contemplated that the hydraulic circuit 38 may be an open-loop circuit depending on a position of the piston 30. The hydraulic circuit 38 includes a pump 40 configured to move the fluid through the hydraulic circuit 38. The pump 40 may be any type of pump as known by one of ordinary skill in the art including but not limited to a mechanical or electrical pump. [0023] The hydraulic circuit 38 may also include a hydraulic control module 42 which defines the hydraulic circuit 38. More specifically, the hydraulic control module 42 is configured to control the pressure of the fluid in the chamber 26. Addi tionally or alternatively, the hydraulic control module 42 may also be configured to control a flow rate of the fluid to the chamber 26. It is also contemplated that the hydraulic circuit 38 may include a sensor 44 configured to provide control pressure feedback. The control pressure feedback may be controlled by the electronic control module 21 and/or the hydraulic control module 42 according to any method as known by one of ordinary skill in the art.

[0024] Referring now to the embodiment illustrated in Figure 3, the hydraulic control module 42 may also include a valve assembly 50. In one embodiment, the valve assembly 50 is disposed within and at least partially defines the hydraulic circuit 38. Moreover, the clutch control system 18, including the valve assembly 50 and/or one or more additional elements, may also be configured to control the flow rate of the fluid in at least a portion the hydraulic circuit 38. Additionally or alternatively, the clutch control system 18, including the valve assembly 50 and/or one or more additional elements, may also be configured to control the pressure of the fluid in the chamber 26. It is contemplated that the valve assembly 50 may be a hydraulic valve assembly 50 and may be similar or identical to the valve assembly 50 illustrated in Figure 2. However, it is also contemplated that the valve assembly 50 may be any valve assembly 50 as known by one of ordinary skill in the art including but not limited to a pneumatic valve or a solenoid valve without departing from the spirit of the invention.

[0025] In one exemplary embodiment, illustrated in Figure 4, the clutch control system 18 may be configured to control the flow rate of the fluid when the piston 30 is in the first position 32 and also configured to control the pressure of the fluid in the chamber 26 when the piston 30 is in the second position 34 and when the piston 30 is between the first position 32 and the second position 34. More specifically, in one exemplary embodiment, the clutch control system 18 is configured to control the flow rate of the fl id when the chamber 26 is less than full of the fluid such that the piston 30 is in the first position 32 or between the first position 32 and the second position 34. Moreover, the size of the inlet and outlets of valve assembly 50 are configured to be controlled by the electronic control module 21 based at least upon data from the sensor 44 in order to control the pressure of the fluid in the chamber 26 when the chamber 26 is full of the fluid such that the piston 30 is in the second position 34. In the embodiment described herein, the clutch control system 18 is configured to control the flow rate of the fluid when the piston 30 is anywhere between the first position 32 and the second position 34 such that the flow rate of the fluid is controlled when the piston 30 is in any position other than the first position 32 or the second position 34. As described above, any or all of the elements of the clutch control system 18 may be coupled to the electronic control module 21 and therefore used by the system 18 to control the flow rate of the fluid and/or to control the pressure of the fluid in the chamber 26. In another exemplary embodiment, the hydraulic control module 42 is configured to control the flow rate of the fluid when the piston 30 is anywhere between the first position 32 and the second position 34 such that the flow rate of the fluid is controlled when the piston 30 is in any position other than the first position 32 or the second position 34.

[0026] In one exemplary embodiment, illustrated in Figure 3, the valve assembly 50 is a flow proportional valve. The flow proportional valve may be used with a closed loop circuit in order to regulate either flow rate or pressure of the chamber depending on the needs of the system. In the embodiment illustrated in Figure 3, the valve assembly 50 includes two outlets 52 and one inlet 54. However, it is contemplated that the valve assembly 50 may have any number of outlets 52 and inlets 54 in any combination, as desired by one of ordinary skill in the art. In one exemplary embodiment the valve assembly is the valve assembly disclosed in US Patent Publication 2015/0192179 which is hereby incorporated by reference. [0027] Additionally, the valve assembly 50 may also include the sensor 44, as stated above. It is contemplated that the sensor 44 may be the same sensor 44 as described above, or may be a separate pressure sensor such that there are one or more pressure sensors in the clutch control system 18. The sensor 44 may be a pressure sensor, a torque sensor, or another type of sensor as known by one of ordinary skill in the art. The sensor 44 may be configured to determine the pressure of the fluid in the chamber 26. The sensor 44 may provide data to the electronic control module 21 in order for the system to control the pressure of the fluid in the chamber 26 by use of control pressure feedback or another method as known by one of ordinary skill in the art to determine and control the pressure of the fluid in the chamber 26. Alternatively, or additionally, the sensor 44 may be located elsewhere within the hydraulic circuit 38 including but not limited to, inside or near the chamber 26 itself. It is additionally contemplated that the sensor 44 may be a pressure sensor already being used in the vehicle 10 for a separate application. Moreover, the valve assembly 50 may also include a flow rate sensor which is configured to sense or otherwise determine the flow rate of the fluid at a specific location within the hydraulic circuit 38. Additionally, it is also contemplated that the flow rate may be calculated by other methods as known by one of ordinary skill in the art.

[0028] Referring now to the embodiment illustrated in Figures 4 and 5, in operation, when the vehicle 10 is off or otherwise not active, the chamber 26 is empty and the piston 30 is in the first position 32 such that the piston 30 is not engaging the clutch plate 28. During vehicle operation and/or a clutch apply event, the chamber 26 begins to be filled with the fluid having its flow rate controlled by the clutch control system 18. Once the chamber 26 is completely full, the piston 30 has moved from the first position 32 towards the second position 34. Once the pressure of the fluid in the chamber 26 reaches a threshold pressure, also known as the kiss point, the piston 30 is moved to the second position 34 such that the piston 30 engages the clutch 22, and more specifically, the clutch plate 28. Once the piston 30 has moved to the second position 34, the clutch control system 18 begins to control the pressure of the fluid in the chamber 26. When the piston 30 engages the clutch plate 28, the clutch plate 28 engages a portion of the transmission 14 allowing energy to be transferred between the transmission 14 and the engine 12. The clutch control system 18 is configured to control the pressure of the fluid in the chamber 26 until the chamber 26 is no longer full and the piston 30 is removed from the second position 34. As described above, it is contemplated that the clutch control system 18 may control the pressure of the fluid in the chamber 26 using the sensor 44 coupled to the electronic control module 21 which utilizes control pressure feedback. It is also contemplated that the clutch control system 18 may use another method as known by one of ordinary skill in the art to control the pressure of the fluid in the chamber 26 and/or the flow- rate of the fluid. As described above, it is contemplated that any or all elements of the clutch control system 18, including but not limited to the electronic control module 21 and the hydraulic control module 20, may be used to control the pressure of the fluid in the chamber 26 and to control the flow rate of the fluid including but not limited to the valve assembly 50, the sensor 44, the hydraulic control module 42, the pump 40, the hydraulic circuit 38, the piston 30, the clutch plate 28, or the housing 24.

[0029] It is contemplated that the pressure of the fluid in the chamber 26, as described above, may be measured, sensed, or otherwise determined as the pressure inside of the chamber 26, the pressure immediately outside the chamber 26, and/or the pressure upstream or downstream of the chamber 26 without departing from the spirit of the invention. Moreover, it is contemplated that the flow rate of the fluid, as described above may be measured, sensed, or otherwise determined as the flow rate of the fluid entering the chamber 26, the flow rate of the fluid immediately outside the chamber 26, and/or the flow rate of the fluid upstream or downstream of the chamber 26 without departing from the spirit of the invention. [0030] The clutch control system 18 that is configured to control either the flow rate of the fluid or the pressure of the fluid in the chamber 26 based on operating conditions such as the location of the piston 30 allows the clutch control system 18 to have improved characteristics in the high flow regime. More specifically, the clutch control system 18 and control method described herein may also lead to improved clutch fill accuracy, improved repeatability, and shortened clutch fill time.

[0031] By controlling the clutch control system 18 using both pressure and flow rate, optimal performance of the clutch 22 in the pressure control regimes also occurs. When the clutch control system 18 is used to control pressure, the system 18 may also have the advantage of improving or eliminating pressure accuracy error associated with the conventional system. Moreover, the ability to match the control method to the momentary system requirements may have significant performance advantages over the conventional system.

[0032] The invention has been described in an illustrative manner, and it is to be understood that the terminology_' which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described.

Claims

What is claimed is:

i . A clutch control system adapted for operation with a transmission, said clutch control system comprising:

a clutch coupled to the transmission, said clutch comprising:

a housing defining a chamber that is configured to hold a fluid; a clutch plate operably coupled to the transmission and disposed within said housing; and

a piston disposed within said housing and configured to be moved between a first position wherein said piston is disengaged from said clutch plate and a second position wherein said piston is engaged with said clutch plate;

an electronic control module; and

a hydraulic circuit for moving the fluid, said hydraulic circuit comprising:

a pump; and

a hydraulic control module defining said hydraulic circuit and coupled to said electronic control module for controlling a pressure of said chamber and a flow rate of the fluid to said chamber, said hydraulic control module comprising:

a valve assembly disposed in said hydraulic circuit, wherein said valve assembly is configured to control the flow rate of the fluid; and

a sensor disposed in said hydraulic circuit, wherein said electronic control module is configured to control said valve assembly based on data from said sensor when said piston is in said second position;

wherein said system is configured to control a flow rate of the fluid when said piston is in said first position and when said piston is between said first position and said second position, and the system is configured to control a pressure of a fluid in said chamber when said piston is in said second position.

2. The clutch control system as set forth in claim 1, wherein said valve assembly is a hydraulic valve.

3. The clutch control system as set forth in claims 1 or 2, wherein said sensor and said electronic control module use control pressure feedback to control said valve assembly.

4. The clutch control system as set forth in any one of claims 1-3, wherein said system is configured to control the flow rate of the fluid when said chamber is less than full of the fluid such that said piston is in said first position or between said first position and said second position, and said system is configured to control the pressure of said chamber when said chamber is full of the fluid such that said piston is in said second position.

5. The clutch control system as set forth in claim 3, wherein said sensor comprises one or more of a pressure sensor or a torque sensor configured to provide said control pressure feedback.

6. The clutch control system as set forth in any of claims 1-5, further comprising a second clutch coupled to the transmission, said second clutch comprising:

a second housing defining a second chamber that is configured to hold a second fluid; a second clutch plate operably coupled to the transmission and disposed within said second housing; and

a second piston disposed within said second housing and configured to be moved between a first position wherein said second piston is disengaged from said second clutch plate and a second position wherein said second piston is engaged with said second clutch plate.

7. The clutch control system as set forth in any of claims 1 -6, wherein said clutch further comprises a biasing device for biasing said piston towards said first position.

8. The clutch control system as set forth in any of claims 1-7, wherein said clutch further comprises an end plate for coupling said clutch plate with the transmission,

9. A hydraulic control module coupled to an electronic control module and defining a hydraulic circuit for controlling a clutch control system which includes a housing defining a chamber that is configured to hold the fluid; a clutch plate operably coupled to a transmission and disposed within the housing; and a piston disposed within the housing and configured to be moved between a first position wherein the piston is disengaged from the clutch plate and a second position wherein the piston is engaged with the clutch plate, said hydraulic control module comprising:

a valve assembly defining the hydraulic circuit, wherein said valve assembly is configured to control a flow rate of the fluid; and

a sensor disposed in said hydraulic circuit, wherein the electronic control module is configured to control said valve assembly based on data from said sensor when said piston is in said second position; and

wherein the hydraulic control module is configured to control a flow rate of the fluid when the piston is in the first position and when the piston is between the first position and the second position, and the system is configured to control a pressure of a fluid in the chamber when the piston is in the second position.

10. The hydraulic control module as set forth in claim 9, wherein said valve assembly is a hydraulic valve.

1 1. The hydraulic control module as set forth in claims 9 or 10, wherein said sensor and the electronic control module use control pressure feedback to control said valve assembly.

12. The hy draulic control module as set forth in any of claims 9-1 1, wherein the hydraulic control module is configured to control the flow rate of the fluid when the chamber is less than full of the fluid such that the piston is in the first position or between the first position and the second position and the clutch control system is configured to control the pressure of the chamber when the chamber is full of the fluid such that the piston is in the second position,

13. A method for controlling a clutch control system having a clutch coupled to a transmission, the clutch comprising a housing defining a chamber that is configured to hold a fluid; a clutch plate operably coupled to the transmission and disposed within the housing; an electronic control module; and a piston disposed within the housing and configured to be moved between a first position wherein the piston is disengaged from the clutch plate and a second position wherein the piston is engaged with the clutch plate; and a hydraulic circuit for moving the fluid, the hydraulic circuit having a pump, and a hydraulic control module partially defining the hydraulic circuit the hydraulic control module having a valve assembly defining the hydraulic circuit, said method comprising:

controlling the flow rate of the fluid when the piston is in the first position and when the piston is between the first position and the second position; and

controlling the pressure of the fluid in the chamber when the piston is in the second position.

14. The method as set forth in claim 13, wherein the clutch control system controls the pressure of the chamber using a pressure sensor configured to be in communication with the electronic control module for utilizing control pressure feedback.

15. The method as set forth in claims 13 or 14, wherein the clutch control system controls the flow rate of the fluid when the chamber is less than full of the fluid and the piston is in the first position or between the first and second positions, and the clutch control system controls the pressure of the chamber when the chamber is full of the fluid and the piston is in the second position.