The concrete self-feeding mixer truck is composed of a car chassis and a special device for concrete mixing and transportation. The chassis of concrete mixer trucks produced in China mostly adopts the Class II general chassis provided by the vehicle manufacturer. The special mechanism of self-feeding mixing truck mainly includes power take-off, front and rear support of mixing drum, reducer, hydraulic system, mixing drum, operating mechanism, cleaning system, etc.

动力换挡变速器离合器接合时，液压油的压力克服弹簧力压紧摩擦片。随着液压油压力的升高，摩擦片与金属盘接触并逐渐压紧，使自上料搅拌车离合器将飞轮动力平稳地传递到变速器输人轴。每次换挡时，摩擦片都要与钢片发生摩擦，产生的热量由冷却液散发出去。

When the power shift transmission clutch is engaged, the pressure of hydraulic oil overcomes the spring force to compress the friction plate. With the increase of hydraulic oil pressure, the friction plate contacts with the metal plate and gradually compresses, so that the clutch of the self-feeding mixer can smoothly transfer the flywheel power to the transmission input shaft. Each time the gear is shifted, the friction plate will rub against the steel plate, and the heat generated will be dissipated by the coolant.

当摩擦片及钢片变薄时，为了使它们充分接合就需要更多的液压油，发动机须进一步加速，摩擦片在钢片上的打滑时间也随之延长，由此产生的摩擦热量也会更多，促使液压油的温度增加，当达到足以改变变速器中密封件性能的温度时，变速器就会产生内泄。

When the friction plate and steel plate become thinner, more hydraulic oil is needed to make them fully engage. The engine must be further accelerated, and the sliding time of the friction plate on the steel plate will also be extended, resulting in more friction heat, which will increase the temperature of the hydraulic oil. When the temperature is enough to change the performance of the seals in the transmission, the transmission will produce internal leakage.

而内泄又从两个方面继续引起热量的增加：高压油经损坏的密封处泄漏，使油温继续升高；由于漏油，液压泵势必要输送更多的油液来保障接合离合器时所需的压力，使自上料搅拌车离合器充分地接合，这也要求发动机继续加速，使液压泵产生更大的流量。如此恶性循环，必将导致自上料搅拌车离合器过热或烧损，直完全失效。

The internal leakage continues to cause the increase of heat from two aspects: the leakage of high-pressure oil through the damaged seal makes the oil temperature continue to rise; Due to oil leakage, the hydraulic pump is likely to transmit more oil to ensure the pressure required to engage the clutch, so that the clutch of the self-feeding mixer can be fully engaged, which also requires the engine to continue to accelerate, so that the hydraulic pump can produce greater flow. Such a vicious cycle will inevitably lead to overheating or burning of the clutch of the self-feeding mixer truck, until it completely fails.