The compressibility of the oil in the HLA high pressure oil chamber reduces the total stiffness of the valve train and reduces the critical speed at which the flyoff begins to occur. When flying off, if the HLA reaction is fast enough, the high pressure chamber will increase, not only eliminating the valve clearance, but also excessive oil filling, so that the volume of the high pressure oil chamber exceeds the original working volume, and pump-up occurs. This will make the valve close not tight, and may even cause interference between the valve and the piston. When the engine is stopped, there is always a valve in the open state. Under the continuous action of the valve spring force, the oil in the corresponding HLA high pressure chamber leaks more, and the air enters the HLA oil storage chamber or even the high pressure chamber. When the engine is restarted, since these HLAs cannot replenish the oil in time, the valve is opened and seated on the cam working section for a period of time, thereby generating a large impact noise.

The check valve in the HLA and its spring constitute a vibration system that is very sensitive to the dynamic characteristics of the valve train, which in turn affects the dynamic performance of the valve train. For example, due to the radial runout of the cam base circle, the HLA check valve may be opened before the cam is turned into the rising working section, so that the high pressure chamber is not closed when the tappet starts to move, and a small amount of oil is returned through the check valve, so the high pressure chamber pressure The rise is slower. This affects valve timing and increases valve seating noise. Engine oil mixing will reduce the HLA stiffness and deteriorate the dynamic performance of the valve train.

The design, manufacturing, and inspection techniques of the Journal of Internal Combustion Engines are complex, and only a few companies in a few countries have mastered these technologies. Many of the car engines introduced in China in the past decade or so have adopted their HLA products. Research work on HLA and HLA-enabled valve trains is also mainly carried out in these companies, including dynamics calculations, dynamic measurements and analysis, cold start and frequent start noise, and the effects of aeration in the oil on HLA.

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