The clutch is installed between the engine and the transmission. It is an assembly directly connected to the engine in the automotive driveline. The clutch is usually installed with the flywheel set of the engine crankshaft, and it is a part that cuts off and transmits power between the engine and the drive train of the car.
The clutch is located in the flywheel housing between the engine and the gearbox. The clutch assembly is fixed on the rear plane of the flywheel with screws. The output shaft of the clutch is the input shaft of the gearbox. During the running of the car, the driver can step on or release the clutch pedal as needed to temporarily separate and gradually engage the engine and the gearbox to cut off or transfer the power input by the engine to the transmission. Clutches are a common component in mechanical transmissions, which can disengage or engage the transmission system at any time. The basic requirements are: stable joint, rapid and thorough separation; easy adjustment and repair; small outline size; small quality; good abrasion resistance and sufficient heat dissipation capacity; easy operation and labor-saving, commonly used are tooth-inlay Two types of friction.
A clutch is similar to a switch. It engages or disengages the power transmission function. The active part and the driven part of the clutch mechanism can be temporarily separated, and they can be gradually engaged. In the process of transmission, relative rotation is also possible. No rigid connection can be used between the clutch’s driving and driven parts. Any type of car has a clutch device, but it’s just a different form.
There are four types of clutches: electromagnetic clutch, magnetic powder clutch, friction clutch and hydraulic clutch: Electromagnetic clutch The on and off of the coil are used to control the engagement and disengagement of the clutch. Electromagnetic clutches can be divided into: dry single-plate electromagnetic clutches, dry multi-plate electromagnetic clutches, wet multi-plate electromagnetic clutches, magnetic powder clutches, slip-type electromagnetic clutches, and the like. The working method of electromagnetic clutch can be divided into: power-on combination and power-off combination. Dry single-plate electromagnetic clutch: When the coil is energized, magnetic force is generated to engage the “armature” disc, and the clutch is in the engaged state; when the coil is de-energized, the “armature” springs back and the clutch is in the disengaged state. Dry multi-plate, wet multi-plate electromagnetic clutch: The principle is the same as above, and additional friction is added. The same volume torque is larger than the dry single-plate electromagnetic clutch. The wet multi-plate electromagnetic clutch must be cooled by oil or other coolant when working. .
Magnetic powder clutch A magnetic is placed between the driving and the driven parts. The magnetic powder is in a loose state when no power is applied, and the magnetic powder is combined when the power is turned on. The driving part and the driven part rotate at the same time. Advantages: The torque can be adjusted by adjusting the current, allowing for large slip. Disadvantages: The temperature rise is greater when the slip is large, and the relative price is high.
Slip type electromagnetic clutch: When the clutch is working, there must be a certain speed difference between the master and slave parts for torque transmission. The amount of torque depends on the strength of the magnetic field and the speed difference. The excitation current remains unchanged, and the speed decreases sharply as the torque increases; the torque remains unchanged, the excitation current decreases, and the speed decreases more severely. The slip-type electromagnetic clutch has no mechanical connection between the main and driven parts, no wear and tear, no magnetic powder leakage, and no impact. Adjusting the excitation current can change the speed and use it as a continuously variable transmission. This is its advantage. The main disadvantage of this clutch is that the eddy currents in the rotor generate heat, which is proportional to the speed difference. The efficiency at low speed is very low, the efficiency value is the main, the speed ratio of the driven shaft, that is η = n2 / n1. The mechanical transmission system suitable for high-frequency operation can combine or separate the driven part and the active part when the active part is running. When the driving member and the driven member are in a separated state, the driving member is rotated and the driven member is stationary; the driving member and the driven member are in an engaged state, and the driven member is driven to rotate. Widely used in machine tools, packaging, printing, textiles, light industry, and office equipment. Electromagnetic clutches are generally used in media where the ambient temperature is -20-50 ° C, humidity is less than 85%, and there is no danger of explosion. The coil voltage fluctuation does not exceed ± 5% of the rated voltage.
Friction clutch Friction clutches are the most widely used and have the longest history. They are basically composed of four parts: a driving part, a driven part, a pressing mechanism and an operating mechanism. The main and driven parts and the pressing mechanism are the basic structures to ensure that the clutch is in the engaged state and can transmit power, and the operating mechanism of the clutch is mainly a device that releases the clutch. During the disengagement process, when the clutch pedal is depressed, the free clearance of the clutch is first eliminated during the free stroke, and then a release clearance is generated during the working stroke, and the clutch is disengaged. During the engagement process, the clutch pedal is gradually released, and the pressure plate moves forward under the action of the compression spring. First, the separation gap is eliminated, and sufficient pressure is exerted on the working surface of the pressure plate, driven plate and flywheel; The release bearing moves backwards under the action of the return spring, creating a free play and the clutch engages.
Hydraulic clutch Hydraulic clutch fluid (usually oil) is used as the transmission medium. Compared with mechanical clutches, in addition to various changes in transmission characteristics, it also mainly absorbs vibration and shock caused by the rotation of the driving and driven shafts. The structure of the hydraulic clutch includes an input shaft with a speed-increasing gear train; a working fluid flow chamber composed of an impeller, a driven wheel, and an impeller shell; an output shaft with a driven wheel, and the driven wheel and the impeller It can be operatively combined; generally, the impeller shell and the impeller are made of a material having a small specific gravity and a large stress tolerance range to reduce centrifugal stress.
1.Ensure the car starts smoothly This is the primary function of the clutch. Before the car starts, it is natural to start the engine. When the car starts, the car gradually accelerates from a completely stationary state. If the drive train (which links the entire car) is rigidly connected to the engine, the car will suddenly move forward as soon as the transmission is in gear, but it will not start. This is because the car has a large inertia from stationary to forward, causing a large resistance torque to the engine. Under the effect of this moment of inertia resistance, the speed of the engine drops sharply below the minimum stable speed (generally 300-500RPM) in an instant, and the engine will stop working and the car will not start. Therefore, we need the help of the clutch. After the engine starts and before the car starts, the driver first depresses the clutch pedal, disengages the clutch, disengages the engine from the drive train, puts the transmission in gear, and then gradually releases the clutch pedal to gradually engage the clutch. During the engagement process, the engine’s blocked torque gradually increases, so you should gradually press the accelerator pedal at the same time, that is, gradually increase the fuel supply to the engine, so that the engine speed is always maintained at the minimum stable speed without stopping. At the same time, as the clutch’s engagement tightness gradually increases, the torque transmitted by the engine to the driving wheels via the drive train gradually increases. When the traction is sufficient to overcome the starting resistance, the car starts to move from standstill and gradually accelerates.
2. Realize smooth shifting In the process of driving a car, in order to adapt to changing driving conditions, the drive train often needs to change gears to work. To realize gear shifting of a gear type transmission, generally, a gear or other gear-shifting mechanism is shifted to push out a certain gear pair of the original gear position for transmission, and then bring the gear pair of the other gear position into operation. Before changing gears, you must depress the clutch pedal to interrupt the power transmission, so that the meshing pair of the original gear can be disengaged. At the same time, the speed of the meshing position of the meshing pair of the new gear can be gradually synchronized. Reduced to achieve smooth shifting.
3. Prevent overloading of the drive train When the car is in emergency braking, if there is no clutch, the engine will reduce the speed sharply due to the rigid connection with the drive train, so all moving parts in it will generate a large moment of inertia (its value may greatly exceed that emitted by the engine during normal operation) Maximum torque), causing the drive train to exceed its load carrying capacity and cause damage to the parts. With a clutch, this danger can be eliminated by relying on the possible relative movement between the clutch’s active and driven parts. Therefore, we need clutches to limit the maximum torque experienced by the drive train to ensure safety.