2.2.2 Control Unit and Sensor Faults
The control unit and sensors are the “brain” and “eyes” of the intelligent control system for electronic fuel injection engines. Their faults can lead to abnormal control signals, which in turn affect the performance of the exhaust valves.
The signal transmission delay from the control unit is primarily manifested as a time difference between the CCU output signal and the actual execution action. Under normal circumstances, the time from the CCU issuing a command to the exhaust valve starting to act should be less than 50ms. When there is a signal transmission delay, this time may extend to over 100ms, causing the opening and closing moments of the exhaust valve to deviate from the design values, thereby affecting the combustion process of the engine. The causes of the delay may include control module faults, aging communication lines, and electromagnetic interference.
Sensor faults are another significant issue. The exhaust valve of the electronic fuel injection engine is typically equipped with two redundant position sensors to monitor the position and status of the exhaust valve in real-time. When a single sensor fails, the system will issue an alarm and use data from the other sensor; when both sensors fail simultaneously, the FCM (Fuel Control Module) will control the exhaust valve at fixed intervals, which may prevent the exhaust valve from optimizing adjustments based on changing operating conditions.
Common causes of sensor faults include: contamination of the sensor probe, affecting signal acquisition; loose sensor mounting, leading to unstable signals; aging or damaged cables, causing signal interruption; and damage to the electronic components of the sensor. Particularly in cases where the engine experiences significant vibration, the connection points of the sensors are prone to loosening, leading to poor contact, false signals, or signal loss.
2.3 Mechanism Study of Mechanical Structure Issues
2.3.1 Sticking of the Exhaust Valve Actuation Mechanism
The linear actuation mechanism of the exhaust valve is a key component connecting the hydraulic drive system and the valve rod, and its working state directly affects the motion accuracy and reliability of the exhaust valve. Sticking of the actuation mechanism is a significant cause of short stroke and sluggish action of the exhaust valve.
Lack of lubrication is the most common issue. The exhaust valve operates in a high-temperature environment, with the valve rod temperature reaching 300-400℃. Insufficient lubrication can increase the friction coefficient between the valve rod and the guide sleeve, and in severe cases, may lead to sintering. Under normal conditions, the oil injection amount for the guide sleeve should be about 1 liter per day to form an effective oil seal and lubrication film between the valve rod and the guide sleeve. When the oil injection amount is insufficient, the lubrication film breaks, leading to direct metal contact, causing dry friction, which not only increases motion resistance but also accelerates component wear.
Component deformation is another important factor. Long-term operation in high-temperature and high-pressure environments can cause thermal deformation of components such as the valve rod and guide sleeve of the exhaust valve. When the deformation exceeds the design allowable value, it can lead to changes in the fit clearance and even cause sticking. Particularly under frequent thermal cycling, metal materials can undergo fatigue deformation, resulting in permanent shape changes of the components.
Carbon deposits and coking can also cause sticking of the actuation mechanism. During operation, high-temperature gases can form carbon deposits on the surfaces of the valve rod and guide sleeve, which gradually accumulate, filling the fit clearance and obstructing the movement of the valve rod. At the same time, lubricating oil can undergo oxidation and polymerization reactions at high temperatures, forming lacquer films and coking, further exacerbating the sticking issue.
2.3.2 Special Issues During Cold Start
Cold start is a special operating condition for electronic fuel injection engines, where the system temperature is low and viscosity is high, leading to various issues. Delayed action of the exhaust valve during cold start is a common phenomenon, and its mechanism is quite complex.
The increase in hydraulic oil viscosity is the primary reason. When the oil temperature is below 30℃, the viscosity of the hydraulic oil can increase by 3-5 times compared to normal operating temperatures, significantly increasing flow resistance. This slows down the flow speed of hydraulic oil from the FIVA valve to the exhaust valve drive cylinder, prolonging the opening time of the exhaust valve. According to measured data, for every 10℃ decrease in oil temperature, the opening time of the exhaust valve increases by about 20-30%.
The impact of the air spring system is more pronounced during cold starts. At low temperatures, the volume of air in the air spring decreases, leading to reduced pressure, while the rubber diaphragm becomes harder and less elastic. This results in insufficient driving force when the exhaust valve closes, slowing down the closing speed. Particularly when the ambient temperature is below 0℃, moisture in the air may freeze in the pipes and valve components, causing blockages and severely affecting the normal operation of the system.
Issues with the adaptability of the control system are also a factor. During cold starts, the control system needs to adjust control parameters based on temperature changes, but if the parameters are set incorrectly, it may lead to decreased control accuracy. For example, the compressibility of hydraulic oil changes at low temperatures, requiring corresponding adjustments to the control current of the FIVA valve. If the system fails to adjust in time, control deviations may occur.