What is an automotive flywheel?
The flywheel (flying wheel) is a disc-shaped part with a very high rotational inertia. Its function is similar to an energy storage device. For a four-stroke engine, every four piston strokes generate power, meaning that only the power stroke does work, while the exhaust, intake, and compression strokes all consume power. Therefore, the torque output by the crankshaft varies periodically, and the crankshaft speed is unstable. To improve this situation, a flywheel is installed at the rear end of the crankshaft.
At the power output end of the crankshaft, that is, the side connected to the transmission and the working equipment. The main function of the flywheel is to store the energy and inertia outside the power stroke of the engine. For a four-stroke engine, only the power stroke absorbs the energy from the flywheel stored energy.
The flywheel has a large rotational inertia. Due to the discontinuous power generation of each cylinder in the engine, the engine speed is also variable. When the engine speed increases, the kinetic energy of the flywheel increases and stores the energy; when the engine speed decreases, the kinetic energy of the flywheel decreases and releases the energy. The flywheel can be used to reduce the speed fluctuations during engine operation.
Installed at the rear end of the engine crankshaft, with rotational inertia, its function is to store the engine energy, overcome the resistance of other components, and make the crankshaft rotate uniformly; through the clutch installed on the flywheel, connect the engine and the vehicle transmission; engage with the starter to facilitate engine starting. And it is the integration point of crankshaft position sensing and speed sensing.
During the power stroke, the energy transmitted by the engine to the crankshaft, apart from being output externally, also has a part of the energy absorbed by the flywheel, so that the crankshaft speed does not increase much. In the exhaust, intake, and compression strokes, the flywheel releases the stored energy to compensate for the work consumed by these three strokes, so that the crankshaft speed does not decrease too much.
In addition, the flywheel has the following functions: The flywheel is the active part of the friction clutch; on the rim of the flywheel, there is a flywheel ring gear for starting the engine; on the flywheel, there is also an upper stop mark for calibrating ignition timing or fuel injection timing, and adjusting valve clearance.
The main problem of car flywheel damage is manifested as engine shaking and abnormal noise, difficulty in starting, transmission imbalance during shifting, difficulty in shifting gears, and clutch slipping or incomplete disengagement.
Starting and abnormal engine operation
Difficulty in starting and abnormal noise: During starting, there is a metallic friction sound or gear impact sound. Severe cases may require multiple attempts to start. This is usually due to the wear of the flywheel ring gear, causing the starter gear to fail to mesh normally. If the wear of the ring gear exceeds 4 teeth, the flywheel usually needs to be replaced.
Shaking and abnormal noise during acceleration: During idle, the steering wheel and the vehicle body show continuous tremors. The tremors significantly reduce when the clutch pedal is depressed. This is a typical characteristic of the failure of flywheel dynamic balance. During driving, there may be metallic cracking sounds, and the abnormal noise intensifies during sudden acceleration.
Power transmission and driving performance decline
Acceleration lag and power deficiency: During acceleration, the engine speed increases but the vehicle speed does not increase rapidly, feeling like "shaking but not moving". The vehicle body shakes significantly during low-speed starting. This is due to the wear of the flywheel surface or the failure of the shock absorber spring, affecting the efficiency of power transmission.
Abnormal increase in fuel consumption and performance decline: The fuel consumption may increase by 10%-15%, the top speed may decrease by 15-20 km/h, and the climbing ability may decrease by 40%. Automatic transmission vehicles may experience shift delay or impact.
Clutch and transmission operation faults
Clutch slipping: When starting in low gear, releasing the clutch pedal causes the car not to start or has difficulty starting; during acceleration, the vehicle speed cannot increase with the engine speed, feeling powerless, and in severe cases, there may be a burnt smell or smoke. Clutch not fully disengaged and abnormal noise: When the clutch pedal is fully depressed, the power still cannot be completely cut off, resulting in difficulty in shifting gears, teething noises or inability to stop; when the pedal is depressed slightly, a continuous "clicking" sound may be heard.
Transmission transmission imbalance: manifested as stuck shifts, difficulty in shifting gears or abnormal noise during semi-engagement. The end face runout of the flywheel exceeding 0.2mm will cause the clutch to not disengage completely, thereby affecting the operation of the transmission.
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