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Why select the horizontally opposed engine? (1)

Friday, 27 Jul 2012

An important element in the symmetrical AWD cars of Subaru is the horizontally opposed engine, i.e. power unit. Subaru mounted the horizontally opposed engine for the first time in the Subaru 1000 and over the next 40 years has refined this extremely unusual automobile power unit. Subaru selected the horizontally opposed engine because it contains a number of elements that make it ideal as the power unit for four-wheel-drive vehicles. How much did the engineers who developed the Subaru 1000 know about the potential of the horizontally opposed engine? Here, we have collected the testimony of engineers who worked on development at the time to find out why they chose the horizontally opposed engine.

Shinroku Momose, who was the automobile design leader for Subaru at the time, told designers that the engine for the FWD sedan to be newly developed could be any type so long as it satisfied the following five conditions.

  1. Since the vehicle is FWD, locate the deferential gear in the center of the car body in order to make the drive shaft operating angle as small as possible.
  2. Since the locations of pedals are decided to make driving easy for the driver, these cannot be changed.
  3. The engine height has to be low in order to keep the center of gravity down and increase the degree of flexibility in body design.
  4. Since the vehicle is FWD, the front overhang needs to be shortened.
  5. Vibration should be reduced in order to enhance the ride quality.

Mr. Motomitsu Honda, who was an engineer in the engine design department at the time, looks back as follows.
“Mr. Momose was not fussy about the type of engine. Since top priority is given to the people riding the vehicle, he presented the required dimensions and performance and said that any type of engine would suffice providing that the engine and mission met those conditions. We generated all the ideas we could think of and eventually narrowed these down to three possible plans.”