Coolant management for a reheating process for operating a cooling system for a motor vehicle, cooling system, and motor vehicle having such a cooling system
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Solution Overview
Problem
Refrigeration systems with heat pump functions in vehicles face issues with refrigerant management during reheating, leading to overheating and reduced comfort due to temperature inhomogeneity and lubrication problems caused by insufficient refrigerant in the low-pressure side, especially during small excess heat conditions.
Innovation Solution
A reheating method that adjusts operating settings by increasing load absorption in the refrigeration system by measuring and lowering the target temperature of supply air after the evaporator, increasing the proportion of recirculated air, integrating additional evaporators, and adjusting air flow through the heating register and external heat exchanger to ensure sufficient refrigerant availability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the reheating expansion valve is opened to reduce heating output surplus, then the heating output is reduced, but refrigerant shortage occurs on the low-pressure side leading to overheated refrigerant
Solution Approach 1:
The control unit continuously monitors the state of refrigerant in the external heat exchanger and adjusts the expansion valve position accordingly. When refrigerant shortage is detected on the low-pressure side, the control unit increases the opening of the reheating expansion valve to allow more refrigerant flow, preventing overheated refrigerant conditions while maintaining heating output control.
Solution Approach 2:
The system uses the refrigerant's own phase change characteristics and flow dynamics to self-regulate. By monitoring pressure and temperature differentials across the external heat exchanger, the system automatically adjusts refrigerant distribution without external intervention, ensuring sufficient refrigerant reaches the evaporator while maintaining desired heating output.
2Power
If the reheating expansion valve is closed to increase heating output, then the heating output is increased, but temperature inhomogeneity and discomfort occur due to refrigerant shortage
Solution Approach 1:
The control unit monitors temperature distribution and refrigerant flow conditions in real-time. When temperature inhomogeneity is detected indicating refrigerant shortage, the system adjusts the expansion valve to increase refrigerant flow to the evaporator, ensuring uniform temperature distribution and comfortable interior conditions while maintaining the desired heating output level.
Solution Approach 2:
The system dynamically changes operating parameters including expansion valve opening degree, refrigerant flow rate, and pressure differential to optimize both heating output and temperature uniformity. By adjusting these parameters based on real-time conditions, the system achieves high heating output without compromising interior comfort or causing temperature inhomogeneity.
3Loss of energy
If the refrigerant is almost entirely in liquid form in the external heat exchanger, then heat transfer efficiency is high, but oil deposits occur in the refrigerant reservoir causing lubrication problems
Solution Approach 1:
The system controls the refrigerant's phase state by adjusting operating parameters such as pressure, temperature, and expansion valve opening. By maintaining the refrigerant in a gaseous or two-phase state rather than entirely liquid in the external heat exchanger, the system ensures proper oil circulation to the compressor while still achieving efficient heat transfer through controlled condensation in appropriate sections of the system.
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
This approach ensures sufficient refrigerant is available, reducing temperature inhomogeneity and lubrication issues, thereby enhancing interior comfort and reducing power consumption by increasing the refrigerant's gaseous state at the external heat exchanger, allowing for more efficient reheating operations.
Implementation Method 1
The heating register is a heat source in which heat stored in the refrigerant is transferred to another medium, such as air
Implementation Method 2
the air cooled and dehumidified by the evaporator
Implementation Method 3
a refrigerant compressor that is connectable or connected to a primary line and a secondary line
Implementation Method 4
at least one afterheating expansion valve arranged between the heating register and the external heat exchanger
Data Source
Figure 1
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Figure 3
AI summary
The invention relates to a reheating process (500) for operating a cooling system (10) having a heat pump function for a motor vehicle, wherein the cooling system (10) comprises: a coolant compressor (12) which is or can be connected to a primary line (14) and a secondary line (16); an external heat exchanger (18) which is arranged in the primary line (14); an evaporator (22) which is arranged in the primary line (14); a heating coil (26) which is arranged in the secondary line (16); and at least one reheating expansion valve (AE4) which is arranged in the secondary line (16) between the heating coil (26) and the external heat exchanger (18). The reheating process comprises the following steps: determining (S503) a heat differential value (H dif) by comparing a heat dissipation actual value (H act) at the heating coil (26) with a heat dissipation target value (H tar); and adapting (S507) at least one operating setting of the cooling system (10) such that the load capacity in the cooling system (10) is increased if the heat differential value (H dif) is greater than 0 and smaller than a heat differential threshold value (H dif tv). The invention also relates to a cooling system for carrying out the reheating process, and to a motor vehicle having such a cooling system.