Thermal management systems for electric and hybrid vehicles

A thermal management system in an electric vehicle is usually more complex than in conventional vehicles with combustion engines. While the battery must be either cooled or heated depending on the situation, the drive axle requires constant cooling. No waste heat from the combustion engine is available for heating the passenger compartment, so energy-efficient measures, e.g. a heat pump, are used for this purpose. To transport the heat in the vehicle and to provide the required temperatures, the refrigeration circuit and the cooling circuit must interact optimally. The connection of the two circuits changes depending on the heating or cooling requirements. This results in different operating modes.

Most thermal management systems in HV vehicles are liquid-cooled, i.e. the mode of operation is similar to that of an engine cooling system. The performance and lifetime of battery cells are closely linked to the performance of the thermal management system. A leaky thermal management system inside a HV component, e.g. the HV battery, can lead to water ingress or even flooding of the component. Coolant can thus reach almost all points of an HV system via the externally sealed HV lines and connector systems. 

If an automotive professional determines that the coolant level in the HV cooling system is too low, he should first carry out a pressure drop test by means of classic pressure testing - as he knows it from conventional cooling systems. When pressurising, the manufacturer's specifications must be observed. After ten minutes, a maximum of 0.2 bar may have escaped.  If the pressure drop is within the green range, the missing coolant can simply be refilled.  

If, on the other hand, the pressure drops excessively, the specialist must assume that there is a possible leak and continue searching for a leak. The coolant should be drained according to the manufacturer's specifications. 

So even small leaks have a big effect. In order for a thermal management system to function properly, the following requirements must be met in addition to functionality and compliance with the technical data:

The thermal management system must be absolutely leak-proof 

• Coolant leakage leads to corrosion of HV components, reduced cooling and heating capacity and increased operating temperature with possible consequences: Overheating, short circuit, fire
• The following products from Autotestgeräte Leitenberger can be used for leak testing
  • Cooling system test set for high-voltage batteries (LR 150_LR_EV 1)
  • Leak test of housings and components (LTA 01)
• We also offer a solution for the localisation of a possible leak:
  • Leakage tester for battery housings (LTBG 04_LR).

The thermo management system must be filled completely and free of bubbles.

• An incompletely filled thermal management system leads to a permanently increased component operating temperature.
• Increased component temperatures lead to reduced life and performance of the electronic and electrical BE and can lead to overheating, short circuits and fire.
• The filling of thermal management systems of HV systems is very similar in process to those on cooling systems of internal combustion engines.
• Proper filling (in OEM plants and worldwide after-sales) of the HV thermal management system is therefore imperative.
• For the proper filling of a thermal management system, Autotestgeräte Leitenberger offers various solutions for every budget
  • Radiator vacuum filling device with quick coupling (KVB 01) as well as mobile electric vacuum pump with vacuum/drainage box (EV 30_230VAC_LR)
  • Evacuation, filling and testing device for cooling systems, thermal management systems of fuel cells and electric vehicles (KVBW 01_230VAC_LR)
  • Automatic evacuation, filling and testing device for cooling systems (KVBA 01)
• The following product can be used to determine the residual air in the filled cooling system
  • Residual Air Flow Meter for Cooling Systems (RLM 01_LR)

The thermo managemnt system must be protected against corrosion and frost as best as possible with a suitable coolant.

• Current coolants must do more than "just" cool. They are also important for the surface protection of components and contain various additives.
• They provide the best possible protection against corrosion and frost.
• Medium and long-term consequences of corrosion (pitting, etc.) can be coolant leakage.
• If coolant freezes, the lines and components filled with coolant, etc. can be damaged. Consequential damage: Coolant leakage.  
• Coolant leakage can lead to a permanent increase in operating temperature.
• Worst-case scenario: Overheating, short circuit, fire.
• Autotestgeräte Leitenberger offers various solutions for analysing the coolant in the thermal management system 
  • Refractometer FT 2030
  • Detailed laboratory analyses for coolant CD 01, CD 02, CD 03