Clutches in cars are mechanical devices located between the engine and transmission. They transfer the rotational power of an engine to the transmission and on to the driven wheels. Engaging the clutch separates the engine from the transmission, disconnecting the power flow. Disengaging the clutch connects the engine to the transmission, sending power to the wheels.
Do Automatic Cars Have a Clutch?
You usually hear about clutches in relation to manual transmissions. But automatics use clutches too, just in a different way. Automatic vehicles use a torque converter instead of a manual clutch to transfer power from the engine to the transmission. Torque converters are made up of a turbine, impeller, stator, and lock-up clutch. So while it’s different from the clutch in a manual, automatics still use a clutch.
Some automatics use a dual-clutch system instead of a torque converter. Although these systems change gears automatically, they usually come with a manual mode as well. Cars with a dual-clutch transmission usually have paddle shifters on the steering wheel for manual shifting.
How Does a Clutch Work?
Clutches work by disconnecting the engine’s power from the transmission to stop the drive shaft from spinning. Without a clutch, the only way to stop the engine from spinning the wheels is to turn the car off. Clutches allow for smooth gear changes in a manual or automatic transmission.
In a manual gearbox, the clutch transfers power from the flywheel to the transmission. The clutch can be engaged and disengaged to keep the load on the engine steady while cycling through gears. This prevents excessive loads on the engine and keeps it from stalling.
Along with the flywheel, clutches consist of a clutch disc, pressure plate, release bearing, diaphragm spring, and cover. The flywheel connects to the engine through the crankshaft, spinning with it at all times. The clutch cover attaches to the flywheel and houses the clutch disc, pressure plate, and diaphragm spring. The clutch disc sits between the flywheel and the pressure plate, connected to the transmission via the input shaft.
The flywheel and clutch disc are coated with high friction material. So when pressure is exerted against the clutch disc, the frictional force causes it to spin with the flywheel. Power is transferred from the clutch disc to the input shaft that then sends the power through the transmission.
Almost all manual transmissions have a clutch pedal to engage and disengage the clutch to shift gears. The clutch pedal is on the floor to the left of the brake pedal and is operated using a hydraulic or mechanical system.
When the clutch pedal is pressed, the release bearing is forced against the diaphragm spring. This pulls the pressure plate away from the clutch disc so it can spin freely. Power is disconnected from the engine so you can make a gear change. The clutch pedal is released after the gear change, and the power flow continues.
Where manual transmissions have a clutch, most automatic transmissions use a torque converter. Torque converters connect the engine and transmission so the wheels can spin. They consist of an impeller, turbine, stator, and lock-up clutch. The torque converter attaches to the flexplate or flywheel, which connects to the engine. It uses hydraulic fluid to transfer power from the engine to the transmission.
The lock-up clutch is engaged when the turbine catches up with the impeller speed. This keeps them spinning at the same speed. When the vehicle stops, the engine and impeller are still spinning. But when the brakes are applied, the turbine is held in place so it stops spinning. Just like the clutch in a manual, this keeps the engine from stalling.
How Can You Tell If You Need a New Clutch?
There are several indicators that you may need a new clutch. Some of the symptoms of a bad clutch include grinding noises, issues getting into gear, and a noisy clutch pedal. Replacing a clutch is just part of normal car maintenance. Clutches typically last 50,000-100,000 miles but can be burned out much sooner if not used properly.
If your automatic is having issues with gear shifts or the transmission is slipping, the torque converter may be at fault. While it's possible to repair a torque converter, it's usually more cost-efficient to replace it.
Sources: Car and Driver, HowStuffWorks, Learn Engineering, Engineering Explained