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Hybrid and EV cooling system service

Wednesday, May 1, 2019 - 07:00
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Cooling systems! Could there be a more boring topic? That is exactly what I would be thinking if I were reading this article right now, but I would be wrong. Hybrid and electric vehicle cooling systems are anything but boring. They will challenge you, frustrate you and make you yearn for the good old days before all of this started. Unless you have had no internet access, you have probably read that the entire automotive industry is moving towards the electrification of their vehicle lineup. It is time to get the proper training and tools to service these complex cooling systems.

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Figure 1 - Refilling the high voltage battery cooling system using a vacuum fill procedure on a 2017 Chevrolet Bolt EV

Two years ago, our automotive technology department received a grant to develop and provide hybrid and electric vehicle training to teachers of automotive programs at high schools and other colleges in our state. The purpose of the training was to help prepare the next generation of service professionals for jobs in the electrified automotive industry of today and tomorrow. We purchased three new electrified vehicles for this training: A Hybrid-Electric vehicle (HEV), a Plug-In Hybrid-Electric Vehicle (PHEV), and a Battery Electric Vehicle (BEV).

As part of the curriculum development process, I began exploring the technology of each of these vehicles. My exploration included completely removing, disassembling all of the high voltage components and documenting these efforts on video for my students. One technology I had not thought much about is their cooling systems. As you will see, some of these cooling systems are very complex with multiple coolant loops, switching valves, one-way valves, chillers, heaters, pumps and dozens of hoses. PHEVs have the most complex systems, followed by HEVs and then BEVs.

All of these cooling systems require special procedures for diagnostics, service, maintenance and repair. For this article, we will concentrate on the liquid cooling systems; however, some hybrid and electric vehicles use air cooling for some of their components.

Hybrid-Electric Vehicle (HEV) Cooling Systems

The first vehicle I explored for our training project was a 2017 Toyota Prius HEV. We picked the Prius for training purposes because it has been the top selling hybrid in the U.S.A. for the last 18 years. Any HEV will have a complex cooling system due to the fact that an Internal Combustion Engine (ICE) is still involved in propelling the vehicle. The Prius is a series-parallel hybrid; this hybrid type has the most complex cooling system when compared to series hybrids and parallel hybrids. The Prius has 5 coolant loops as shown in Figure 1.

Figure 2 - The 2017 Toyota Prius has a two-section radiator, 5 cooling loops, 16 major components, 20 coolant hoses, and 2 electric coolant pumps!

Prius Internal Combustion Engine (ICE) Cooling

The 2016-2019 Prius has four parallel coolant loops that are connected to the upper section of the radiator just for the ICE. This cooling system has 11 major components and 14 coolant hoses!

  1. ICE Cooling Loop 1, for ICE Cooling
  2. ICE Cooling Loop 2, for Expansion and Air Bleeding Loop:
  3. ICE Cooling Loop 3, for Exhaust Gas Recirculation (EGR) Cooling and Throttle Deicing Loop
  4. ICE Cooling Loop 4, for Exhaust Heat Recovery for Fast Warm Up Loop

Prius Power Electronics (PE) and Transaxle Cooling

There is a single coolant loop connected to the lower section of the radiator for the high voltage electronics and transaxle. This cooling system has 5 major parts and 6 coolant hoses.

  1. Power Electronics and Transaxle Cooling Loop
Figure 3 - The 5 coolant loops of the 2016-2019 Toyota Prius HEV

Prius High Voltage (HV) Battery Cooling/Heating

The HV battery on the Prius is air cooled/heated with a single cooling fan pulling in air from the passenger compartment and pushing it out the one-way pressure relief vents in the rear quarter panels.

Plug-In Hybrid-Electric Vehicle (PHEV) Cooling Systems

The second vehicle I explored for our training project was a 2018 Chevrolet Volt PHEV. We picked the Volt for training purposes because it has the longest range (53 miles (85.3 km)) of any PHEV sold in the U.S.A. As you may know, GM recently stopped production of the Volt and has made a commitment to move to a Battery Electric Vehicle (BEV) lineup.

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