Exhaust Heat Recovery Unit (EHRU), also known as Exhaust Heat Exchanger, is a system that recovers the wasted thermal energy from the exhaust and makes use of it if possible. The heat recovery method is the main focus of EHRU. There are three common groups of EHRU. Each of them makes use of a different heat recovery mechanism: by coolant, by Stirling engine and by thermoelectric module. This paper shows patents in EHRU in recent years. It firstly explains the heat recovery mechanism of the three groups and the requirements. Then, it describes the working principle of how the thermal energy is recovered in respective invention and also shows the problems addressed by the inventors. Finally, it estimates the trend of the researches in the following years.