As a core component of the automotive transmission system, the clutch pressure plate diaphragm spring's failure modes directly affect the clutch's operational stability and vehicle safety. Diaphragm spring failure typically manifests as fatigue fracture, elastic force decay, and structural deformation. These failure modes are often closely related to material properties, manufacturing processes, and operating conditions.
Fatigue fracture is the most common failure mode for diaphragm springs. During clutch engagement and disengagement, the diaphragm spring is subjected to alternating loads. After prolonged use, its inner arc surface is prone to stress concentration, leading to microcracks that gradually propagate into macroscopic fractures. This fracture usually exhibits multi-source characteristics, with fatigue steps and secondary cracks visible on the fracture surface, ultimately causing spring failure. Material quality, heat treatment processes, and surface treatment conditions have a significant impact on fatigue life. For example, the presence of non-metallic inclusions or uneven surface hardness accelerates crack initiation; while quenching cracks or insufficient tempering during heat treatment reduce the material's fatigue resistance.
Elastic force decay is another typical failure mode for diaphragm springs. With prolonged use, the elastic properties of the diaphragm spring gradually degrade, manifesting as a decrease in clamping force or insufficient disengagement stroke. This phenomenon is primarily caused by material creep, stress relaxation, and wear. Under high temperature or high load conditions, the creep effect of the spring material intensifies, leading to a reduction in spring height. Frequent friction between the release finger and the release bearing can cause localized wear, affecting the spring's leverage ratio and transmission efficiency. Furthermore, if the clutch assembly's disengagement stroke exceeds its design limit, the diaphragm spring will fail prematurely due to excessive deformation.
Structural deformation is a direct manifestation of diaphragm spring failure. When the height difference between the release finger exceeds the standard or the disc spring undergoes plastic deformation, the contact pressure distribution between the pressure plate and the driven plate will be uneven, causing unstable clutch engagement, vibration, or abnormal noise. This deformation may stem from manufacturing errors, such as taper deviation in the disc spring due to the stamping process; it may also be caused by improper use, such as prolonged driving with the clutch partially engaged or abruptly releasing the clutch pedal, subjecting the spring to excessive impact loads. Additionally, if the clutch housing deforms or the flywheel end face runout exceeds the standard, additional stress will be applied to the diaphragm spring through the pressure plate, accelerating its structural damage.
To prevent diaphragm spring failure, a comprehensive approach is needed, addressing factors such as material selection, manufacturing processes, usage and maintenance, and system compatibility. Regarding materials, high-strength, high-toughness spring steel, such as 50CrV4, should be selected, with strict control over chemical composition and non-metallic inclusion content. The heat treatment process must ensure uniform quenching and sufficient tempering to achieve an ideal balance of hardness and toughness. Surface treatment can include shot peening or coating protection to improve fatigue resistance and corrosion resistance. During manufacturing, precision stamping and molding processes are necessary to ensure the dimensional accuracy of the disc spring and release finger, and online monitoring equipment should be used to control the height difference between the release finger and the spring's free height.
Regarding usage and maintenance, drivers should avoid prolonged driving with the clutch partially engaged to reduce continuous load on the spring. Smooth operation is required when starting and shifting gears to prevent impact loads caused by abruptly releasing the clutch pedal. Regular checks of the clutch fluid level and quality are necessary to ensure the hydraulic system functions properly and prevent excessive spring deformation due to release bearing jamming. At the system matching level, the backup coefficient and unit area sliding work of the clutch assembly need to be rationally designed based on the vehicle parameters to ensure that the working stress of the diaphragm spring is within a safe range. Simultaneously, the lever ratio and stroke efficiency of the release system should be optimized to prevent spring breakage caused by excessive release stroke.
Diaphragm spring failure is the result of the combined effects of materials, manufacturing processes, usage, and system matching. By selecting high-quality materials, optimizing manufacturing processes, standardizing driving operations, and implementing scientific system design, the reliability and service life of diaphragm springs can be significantly improved, ensuring the stable operation of the clutch pressure plate and even the entire transmission system.
