Therefore, the way to improve the NVH characteristics of the whole vehicle through the clutch is to adjust the structure of the driven disc and change its performance parameters. Clutch driven disc assembly is mainly composed of friction plate, elastic elements and damping elements, and its main performance parameters include friction coefficient f, torque T (torque transmission capacity), torsional stiffness K, torsional angle θ and damping value H, etc. the relationship among them is: T=K θ + H=β Te, where Te is the maximum output torque of the engine, which is an inherent characteristic of the engine and a constant value; β is the backup coefficient of clutch, which is a constant. Generally, the value of β for passenger vehicles is 1.3 and that for commercial vehicles is 1.6.
J L Bi et al.  analyzed the torsional mode and sensitivity of power transmission system, and concluded that the torsional stiffness K and damping value H of clutch are two important performance parameters that determine the vibration reduction function of driven plate: the smaller the torsional stiffness, the smaller the resonance peak value and the smaller the resonance frequency; The larger the damping value is, the smaller the resonance peak value is, and the resonance frequency has no obvious change. Therefore, in order to attenuate the vibration transmitted by the engine as soon as possible, the torsional stiffness of the clutch driven plate should be as small as possible, and the damping value should be as large as possible. However, due to the limitation of the structure and space of the driven disc, the torsion angle θ cannot be too large and usually does not exceed 14.
Under this limitation, if the torsion is just too small, the effective torque K θ transmitted by the clutch will be too small, and the transmission efficiency of the clutch will be too low. When designing the clutch, it is generally required that K θ = (85 ~ 93) % β Te. According to the relationship between the performance parameters of the driven disc mentioned above, if the damping value is too large, the clutch will also be affected. Moreover, the larger the damping value, the slower the response of mechanical transmission, and the excessive damping value will also affect the sensitivity of automobile operation. To sum up, properly increasing the torsional angle (wide angle) to reduce the torsional stiffness and properly increasing the damping value can improve the NVH characteristics of the whole vehicle. Therefore, this paper proposes to research and develop a wide-angle and large-damping multi-stage damping clutch driven disc assembly.
The driven plate assembly of the wide-angle multi-stage damping clutch is mainly composed of front retain plate, rear retain plate, hub plate, damping spring, cushion plate, rear damping plate, front hysteresis plate and Belleville washer. The product structure is shown in Figure 4, and the real product is shown in Figure 5.
The main technical innovations of the driven disc assembly of the wide-angle large damping multi-stage damping clutch are as follows:
1) Wide-angle and low-stiffness vibration reduction technology
By increasing the torsional damping angle of the clutch without increasing the specifications and torque transmission capacity of the damper, the purpose of reducing the spring stiffness can be achieved, and then the clutch can obtain better damping performance. In view of the defect that the main damping part of the traditional clutch is limited by the stop pin (double-headed rivet) hitting the hub (as shown in Figure 6), and its rotation angle can't be enlarged due to the space limitation (generally, the rotation angle is about 7-15 degrees), it is proposed to bend the outer side of the front damping disc and change the impact limiting parts from the brake pin to the damping disc (as shown in Figure 7)
The forward torsion angle of the traditional clutch is generally 15-21 and the reverse torsion angle is generally 10-15 (as shown in Figure 8). The forward torsion angle can reach 42, and the reverse torsion angle can reach 28 (as shown in Figure 9), and the damping effect is improved by more than 1.5 times compared with that of the common clutch, and the vibration isolation rate can reach more than 65% in the engine 800rpm-4500rpm range.
2) large hysteresis vibration reduction structure technology
The torque fluctuation of the engine is consumed by increasing the clutch damping value, so as to reduce the transmission of the clutch to the pulsating torsional vibration of the engine, reduce the jitter, knocking noise and harsh noise caused by vibration in all rotating speed ranges of transmission parts such as transmission and differential during idling, acceleration and normal driving, and improve the ride comfort and shift smoothness.
The main hysteresis value of large hysteresis clutch is 25-35N.m, while that of traditional clutch is generally 8-15n.m. The Muller-BBM automobile torsional vibration/noise First Axle analysis system (as shown in Figure 10) is used for NVH test in a self-owned brand vehicle. The experimental results show that increasing the damping value of clutch driven plate can reduce the amplitude of the system and improve the NVH problem during vehicle acceleration (as shown in Figure 11)
3) New split type pre-damping structure technology
By taking advantage of the characteristic that the injection molding process is easy to realize the complex modeling of the workpiece, a new split-type pre-vibration damping structure (as shown in Figure 12) technology is proposed, which is improved on the traditional damping plate, so that it has the function of damping plate and clamping disc, and solves the shortcomings of the traditional split-type pre-vibration damping structure, such as complex structure, many parts, difficult assembly, low efficiency and high manufacturing cost. The application of the new split pre-damping structure technology can improve the production efficiency by more than 150% and reduce the manufacturing cost by more than 30%.
4) component protection buffer damping structure technology
By adding rubber buffer spring in the traditional clutch damping spring, the buffer spring is developed to absorb vibration and reduce noise when impact occurs, and protect the internal parts of the clutch so as to improve the service life of the clutch driven plate assembly.
The traditional shock absorber uses the damping spring in the shock absorber for damping and buffering, but it is completely borne by the clutch stop pin (limit rivet) when it is impacted greatly. Although it has certain damping and buffering capacity, the service life of the clutch is still affected to some extent. Adopting clutch component protection, buffer and vibration reduction structure technology, two special rubber springs are installed in a symmetrical set of main vibration reduction springs, which can absorb vibration and reduce noise when the clutch is impacted, and protect the internal components of the clutch to improve the service life of the clutch driven plate assembly. Its working principle is: after the rubber spring is installed in the damping spring, it can be seen from the clutch characteristic curve (as shown in Figure 13) that the rear section of the torsional damping characteristic curve of the clutch is an increasing curve, which is caused by the clutch torque capacity increasing when the rubber spring plays a buffering role and absorbs the impact caused by engine torque fluctuation. When driving on a flat road, the rubber spring does not work and its torque transmission capacity remains unchanged. When the engine torque fluctuates sharply on the harsh environment, the rubber spring starts to work, and its torque capacity increases by 15% instantly, thus protecting the internal components of the clutch and prolonging the fatigue service life of the clutch.
5) Multi-stage vibration reduction technology
The output power and torque of vehicle engines under different working conditions (such as idling, starting, accelerating, driving at a constant speed, etc.) have different characteristics. the traditional clutch generally only has 1-2 stages of vibration reduction (as shown in fig. 8), which can only meet the vibration reduction requirements under 1-2 working conditions. Multi-stage vibration reduction technology, innovative use of a variety of different types and stiffness of vibration spring combinations, to achieve the combination of clutch main vibration reduction and pre-vibration reduction of 3-6 stages of multi-stage vibration reduction, effectively meet the vibration reduction requirements of vehicles under various working conditions.
It can be seen from the clutch characteristic curve (as shown in fig. 8) that the main damping and pre-damping of the traditional clutch generally have only one stage each, which can't meet the damping requirements under different torques. the 200 series products transformed by this technology innovatively adopt the arc spring damping spring structure (as shown in fig. 12), and realize the two-stage pre-damping through the asymmetric design of the pre-damping disc hub, i.e. the first stage (forward 0-3, reverse 0-3) Level 2 (3-22 in the forward direction and 0-3 in the reverse direction) participates in vibration reduction and torque transmission at start-up (slightly larger output power and torque). In the main damping part, a group of rubber springs are added into the original damping springs, whose length is much smaller than that of the damping springs. When the clutch transmits torque to force the damping springs to compress to a certain length, the rubber springs start to work, absorbing the impact generated by engine torque fluctuation and transmitting torque. The main damping part (forward 22-42, anyway 8-28) is divided into two stages: the first stage (forward 22-38, reverse 8-24) participates in the vibration reduction when the vehicle runs at a constant speed (the output power and torsion are relatively stable, and the torque waveform is small); Level 2 (38-42 in the forward direction and 24-28 in the reverse direction) participates in vibration reduction and torque transmission during acceleration (the output power and torque are the largest, the torque waveform is large, and the impact on clutch components is also the largest).