How Does the Electronic Expansion Valve (EEV) Work?
May 19, 2025
The electronic expansion valve (EEV) is essential parts of vehicle refrigeration systems. Refrigeration performance and energy efficiency are much improved by changing the refrigerant flow in compliance with a designated program.
Main Components of EEV
1. Controller
A microcontroller forms the heart of the controller. Based on sensor data, it conducts exact computations and control.
2. Actuator
The actuator modulates the valve opening in response to controller signals, therefore regulating refrigerant flow.
3. Sensors
Important information including pressure and temperature is gathered by sensors. For instance, real-time monitoring of refrigerant status is provided via temperature and pressure sensors placed at the evaporator output.
Types of Electronic Expansion Valves
From the working mode perspective, EEVs are divided into:
1. Electromagnetic EEV
Motivated by coil's produced magnetic force. Before electricity is turned on, the needle valve is totally open. Magnetic force closes the valve opening when powered. As control voltage rises, the valve opening lowers, therefore limiting refrigerant flow. This kind demands constant power throughout operation yet has a basic construction and quick response. 2. Electric EEV
Divided into two types: direct-drive and gear-reduction, both driven by a stepper motor.
Direct-drive type:
Driven directly from a pulse stepper motor, the needle valve Control pulses given to the stator coils rotate the rotor—made of permanent magnets. The needle valve is moved up or down by a threaded mechanism to change flow during this revolution.
Gear-reduction type:
Has a set of reducing gears. The torque of the stepper motor flows via the gears to the needle valve. With varying sized valves and adjustable ranges, the gears increase torque, therefore facilitating easier operation.
Three Primary Functions of EEV
1. Throttling and Pressure Mitigation
The refrigerant coming out of the condenser is a high-pressure, medium-temperature liquid. It becomes a low-temperature, low-pressure liquid following throttling by the EEV before passing into the evaporator. Reduced pressure in the evaporator helps the refrigerant to evaporate, therefore absorbing heat and producing a cooling effect. 2. Superheat Regulation
The EEV regulates the superheat of refrigerant vapour by monitoring the temperature at the evaporator outlet.
Insufficient superheat may result in liquid refrigerant returning to the compressor, posing a risk of damage.
Excessive superheat results in inefficient evaporator utilisation and diminished system performance.
3. Regulation of Refrigerant Flow
By tracking the temperature at the evaporator output, the EEV controls the superheat of refrigerant vapour.
Insufficient superheat could cause liquid refrigerant to return to the compressor, therefore increasing the danger of damage.
Too high superheat causes poor evaporator efficiency and reduced system performance.
Applications for Electronic Expansion Values (EEVs)
1. Bus air conditioning system
Traditional throttling components—such as capillary tubes and thermal expansion valves—can no longer satisfy the comfort and energy efficiency criteria of heat pump air conditioning systems in pure electric buses running under significant temperature fluctuations.
The Electronic Expansion Valve (EEV) presents great sensitivity, steady and exact control, and a broad adjustment range as a new kind of throttling control component. Modern HVAC systems find great application for these benefits.The EEV can modify the superheat setpoint to exactly control the valve opening during system running. This enables the system to adjust to variations in compressor speed and refrigerant circulation requirements of both heat exchangers (evaporator and condenser), therefore guaranteeing effective performance over a range of working circumstances.
2. BTMS—battery thermal management system
Running EVs with electric motors and batteries generates a lot of heat from their components. Keeping appropriate operating temperature and heat dissipation depends on a good thermal management system.
The Electronic Expansion Valve (EEV) is indispensable in this process by managing refrigerant flow. This ensures that the battery and motor remain within their prescribed temperature range, thereby increasing the motor's dependability and performance and extending the battery's driving range.
