Vehicle AC Inverter Overheat Control Without Pressure Buildup
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Solution Overview
Problem
Existing vehicle air conditioning systems face challenges in protecting the motor drive unit from overheating, especially when the electric compressor is at rest or when the refrigerant flow is forced, leading to potential damage and loss of refrigerating cycle function due to inadequate cooling and excessive pressure.
Innovation Solution
An air conditioning system with an electric compressor and motor drive unit that operates in a protection-against-overheat mode, where the air conditioning control unit manages the rotational speed of the electric motor to ensure cooling by the refrigerant, and includes features like temperature and pressure detection to prevent damage and maintain cycle functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the rotational speed of the electric motor is increased to increase the flow rate of refrigerant for cooling the motor drive unit, then the cooling effect of the motor drive unit is improved, but the torque and current of the electric motor increase excessively causing the temperature inside the motor drive unit to rise and the cooling effect to be lost
Solution Approach 1:
The control unit continuously monitors the temperature of the motor drive unit and adjusts the rotational speed of the electric motor based on real-time temperature feedback. When the temperature exceeds a predetermined threshold, the control unit increases the rotational speed to enhance cooling; when the temperature is within the normal range, the control unit reduces the rotational speed to prevent excessive torque and current increase, thereby maintaining an optimal balance between cooling effectiveness and energy efficiency.
2Temperature
If the rotational speed of the electric motor is increased to cool the motor drive unit, then the cooling effect is improved, but the pressure at the refrigerant inlet of the condenser increases excessively potentially damaging the refrigerant flow path
Solution Approach 1:
The control unit monitors the temperature of the motor drive unit and adjusts the motor's rotational speed accordingly. By increasing speed only when temperature exceeds the threshold, the system avoids excessive pressure buildup in the refrigerant flow path that would occur with continuous high-speed operation, thereby preventing potential damage while still providing effective cooling when needed.
Solution Approach 2:
The system dynamically changes the operational parameters (rotational speed) of the electric motor based on the thermal state of the motor drive unit. Instead of maintaining a constant high rotational speed, the system adjusts the speed parameter adaptively, increasing it only when cooling is required and reducing it when the temperature is acceptable, thus avoiding harmful pressure effects.
3Temperature
If the flow rate of refrigerant to the evaporator is increased to cool the motor drive unit, then the cooling effect is improved, but the evaporator is cooled excessively causing condensed water to freeze and the refrigerating cycle to fail
Solution Approach 1:
The control unit uses temperature feedback from the motor drive unit to regulate the refrigerant flow rate through the evaporator. By adjusting the flow rate dynamically based on actual cooling needs, the system avoids excessive cooling that would cause condensed water to freeze and maintain the reliability of the refrigerating cycle while still providing sufficient cooling protection for the motor drive unit.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively protects the motor drive unit and maintains refrigerating cycle function by ensuring proper cooling and preventing excessive pressure, even when the compressor is at rest or refrigerant flow is minimal, thereby preventing overheating and system failure.
Implementation Method 1
the motor drive unit is arranged at a position at which heat exchange can be effected with the refrigerant at the suction side of the electric compressor
Implementation Method 2
a compression mechanism (5) that sucks and compresses a refrigerant
Data Source
AI summary
An inverter 6 that drives an electric motor 4 of the electric compressor 3 operates in a protection-against-overheat mode, in which the electric motor is driven at a rotational speed for protection against heat different from a rotational speed specifying value from an air conditioning control unit 20, in order to ensure the flow rate of the refrigerant and cool the inverter itself when the temperature detected by an inverter temperature sensor 22g exceeds a predetermined value. At this time, if the refrigerant pressure increases or the evaporator discharge temperature falls, the air conditioning control unit stops the protection-against-overheat mode operation of the inverter and directs the inverter to forcedly stop the electric motor. Due to this, an excessive increase in the refrigerant pressure and evaporator freezeing can be prevented, and thus the function of the refrigerating cycle can be protected.