How does a Clutch SYSTEM work? A technical article by Heeltoe.
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From: Mission Viejo, CA, USA
How does a Clutch SYSTEM work? A technical article by Heeltoe.
I have learned a lot about clutches from the guys at Clutch Specialties on the subject of clutches and want to share some of my knowledge. I wrote this paper out of boredom about 2 years ago. Some of it might seem kind of elementary, but I intend to integrate basic knowledge and advanced dynamics of a clutch system in its entirety. Also, my personal theory is interjected here and there. Corrections, debate, and questions are encouraged. This is a learning environment. Learn from me, and let me learn from you!
In the following, I am referring to a Push-Type non-self-adjusting pressure plate, which is the most common. Also, I refer to solid flywheels, not dual mass flywheels.
A clutch is an assembly which engages or disengages two shafts spinning at different speeds, or at rest.
THE COMPONENTS OF A CLUTCH
There are a few main components to a clutch system; a flywheel, pressure plate, friction disc, throw-out bearing, and sometimes a pilot bearing. An internal combustion engine creates torque that is outputted by rotation of a crankshaft. A flywheel is a heavy plate that is bolted to the engine’s crankshaft, used to transmit torque to the clutch system and thus the transmission.
The pressure plate is a spring loaded cover that bolts onto the flywheel. Both the flywheel and pressure plate have complimenting machined friction surfaces that face each other. When looking at the outer face of the pressure plate, it is noticed to have a series of symmetrical “fingers” jutting towards the center creating a circular hole. These fingers are the visible parts of the diaphragm, which is actually a spring that is levered against the machined ring on the inside of the pressure plate.
A friction disc floats inside the pressure plate and flywheel assembly. The friction disc is thin plate with a ring around the outside that is made of a compound that promotes friction against the machined surfaces of the flywheel and pressure plate. It also has a hub in the center with splines on it that match up to a corresponding input shaft coming out of the transmission. The hub can either be riveted to the disc, or be suspended in a spring-loaded assembly.
A pilot bearing, which is not always present, is a bearing that fits inside the flywheel center and accepts the transmission input shaft. This bearing acts as a support for the system. Some clutches do not have a pilot bearing, but where one is applied it is required.
HOW CLUTCHES WORK
In the assembly’s resting state, the pressure plate and flywheel are clamped down on the disc with an amount of force related to the thickness and strength of the diaphragm. This at-rest state is referred to by saying the clutch is “engaged.” In a car, the engaged state of the system occurs when the clutch pedal is out. With the clutch engaged, the flywheel, pressure plate, and friction disc all spin together with the engine and turn the input shaft of the transmission.
A car’s clutch pedal is an actuator that is attached to either a cable or a hydraulic system that moves a lever on the transmission. This lever is directly connected to a special bearing called a throw-out bearing. This bearing is designed so that it can remain attached to the lever, and can be pushed against the spinning pressure plate diaphragm. When fully depressed, the throw-out bearing pushes on the pressure plate diaphragm, causing the pressure plate diaphragm will release the clamping force on the friction disc, allowing the disc to spin independently from the engine’s crankshaft. This state of the clutch is “disengaged.” In the disengaged state, the flywheel and pressure plate spin with the engine’s crankshaft at the rpm indicated on the vehicle’s tachometer. The friction disc floats inside the assembly and is not subject to the movement of the engine’s rpm.
When the engine and transmission are bolted together, the only connection between the crankshaft and the transmission input shaft is through the clamping force of the pressure plate on the disc. Note that the pressure plate and flywheel are associated with power coming from the engine, and the disc is associated with the spinning of the transmission. The disc will always spin at a rate relative to the vehicle’s speed. This is because the wheels on the car are directly connected to the transmission via the axles, and thus the disc as well. If the car is stopped, the disc will be at rest. If the car is moving at all, the disc will spin. The rpm of this spinning is dictated by the speed of the vehicle’s movement, the selected gear on the transmission, and the gearing of the transmission final drive.
The references to “engaged” are to the system being clamped together and all spinning the same speed. The references to “disengaged” are to the system being released with the disc spinning independently inside the spinning pressure plate and flywheel. Note the difference between engaging the clutch and the clutch being engaged. Engaging the clutch is distinct because it defines the action of the transition from being disengaged to being engaged. Likewise, disengaging, or releasing, the clutch defines the action of changing the clutch from an engaged state to a disengaged state.
The most important factors in analyzing clutch operation are stiffness of the diaphragm, ability for the clutch to be engaged smoothly, the sensitivity of the clutch system to inputs. The most important factors in determining clutch requirements are engine output (usually in torque), weight of the vehicle, traction of the vehicle, and desired performance of the vehicle as a whole. Weight of the assembly also plays a factor.
*end of Part 1. Part Two: The Flywheel, Coming soon!
Marcus di Sabella
Heeltoe Automotive, Mission Viejo, CA
Originally written 12/21/2004, edited 3/17/2007
Original article: http://heeltoeauto.com/httech/...60689
In the following, I am referring to a Push-Type non-self-adjusting pressure plate, which is the most common. Also, I refer to solid flywheels, not dual mass flywheels.
A clutch is an assembly which engages or disengages two shafts spinning at different speeds, or at rest.
THE COMPONENTS OF A CLUTCH
There are a few main components to a clutch system; a flywheel, pressure plate, friction disc, throw-out bearing, and sometimes a pilot bearing. An internal combustion engine creates torque that is outputted by rotation of a crankshaft. A flywheel is a heavy plate that is bolted to the engine’s crankshaft, used to transmit torque to the clutch system and thus the transmission.
The pressure plate is a spring loaded cover that bolts onto the flywheel. Both the flywheel and pressure plate have complimenting machined friction surfaces that face each other. When looking at the outer face of the pressure plate, it is noticed to have a series of symmetrical “fingers” jutting towards the center creating a circular hole. These fingers are the visible parts of the diaphragm, which is actually a spring that is levered against the machined ring on the inside of the pressure plate.
A friction disc floats inside the pressure plate and flywheel assembly. The friction disc is thin plate with a ring around the outside that is made of a compound that promotes friction against the machined surfaces of the flywheel and pressure plate. It also has a hub in the center with splines on it that match up to a corresponding input shaft coming out of the transmission. The hub can either be riveted to the disc, or be suspended in a spring-loaded assembly.
A pilot bearing, which is not always present, is a bearing that fits inside the flywheel center and accepts the transmission input shaft. This bearing acts as a support for the system. Some clutches do not have a pilot bearing, but where one is applied it is required.
HOW CLUTCHES WORK
In the assembly’s resting state, the pressure plate and flywheel are clamped down on the disc with an amount of force related to the thickness and strength of the diaphragm. This at-rest state is referred to by saying the clutch is “engaged.” In a car, the engaged state of the system occurs when the clutch pedal is out. With the clutch engaged, the flywheel, pressure plate, and friction disc all spin together with the engine and turn the input shaft of the transmission.
A car’s clutch pedal is an actuator that is attached to either a cable or a hydraulic system that moves a lever on the transmission. This lever is directly connected to a special bearing called a throw-out bearing. This bearing is designed so that it can remain attached to the lever, and can be pushed against the spinning pressure plate diaphragm. When fully depressed, the throw-out bearing pushes on the pressure plate diaphragm, causing the pressure plate diaphragm will release the clamping force on the friction disc, allowing the disc to spin independently from the engine’s crankshaft. This state of the clutch is “disengaged.” In the disengaged state, the flywheel and pressure plate spin with the engine’s crankshaft at the rpm indicated on the vehicle’s tachometer. The friction disc floats inside the assembly and is not subject to the movement of the engine’s rpm.
When the engine and transmission are bolted together, the only connection between the crankshaft and the transmission input shaft is through the clamping force of the pressure plate on the disc. Note that the pressure plate and flywheel are associated with power coming from the engine, and the disc is associated with the spinning of the transmission. The disc will always spin at a rate relative to the vehicle’s speed. This is because the wheels on the car are directly connected to the transmission via the axles, and thus the disc as well. If the car is stopped, the disc will be at rest. If the car is moving at all, the disc will spin. The rpm of this spinning is dictated by the speed of the vehicle’s movement, the selected gear on the transmission, and the gearing of the transmission final drive.
The references to “engaged” are to the system being clamped together and all spinning the same speed. The references to “disengaged” are to the system being released with the disc spinning independently inside the spinning pressure plate and flywheel. Note the difference between engaging the clutch and the clutch being engaged. Engaging the clutch is distinct because it defines the action of the transition from being disengaged to being engaged. Likewise, disengaging, or releasing, the clutch defines the action of changing the clutch from an engaged state to a disengaged state.
The most important factors in analyzing clutch operation are stiffness of the diaphragm, ability for the clutch to be engaged smoothly, the sensitivity of the clutch system to inputs. The most important factors in determining clutch requirements are engine output (usually in torque), weight of the vehicle, traction of the vehicle, and desired performance of the vehicle as a whole. Weight of the assembly also plays a factor.
*end of Part 1. Part Two: The Flywheel, Coming soon!
Marcus di Sabella
Heeltoe Automotive, Mission Viejo, CA
Originally written 12/21/2004, edited 3/17/2007
Original article: http://heeltoeauto.com/httech/...60689
Joined: Jul 2006
Posts: 212
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From: Columbus, GA, USA
Re: How does a Clutch SYSTEM work? A technical article by Heeltoe. (MrHeeltoe)
Nicely done. My family has been in the clutch business for 50+ years and I found your write-up a good read. Looking forward to Part II.
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Joined: Aug 2003
Posts: 3,429
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From: Mission Viejo, CA, USA
Re: How does a Clutch SYSTEM work? A technical article by Heeltoe. (FarinaMotorsports)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by FarinaMotorsports »</TD></TR><TR><TD CLASS="quote">Nicely done. My family has been in the clutch business for 50+ years and I found your write-up a good read. Looking forward to Part II.</TD></TR></TABLE>
Thanks! I am going to get more in-depth! Should be interesting
Thanks! I am going to get more in-depth! Should be interesting
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