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Keihin Corporation
Performing Aerodynamic Noise Analyses to Meet Demands for Noise Reduction

As EVs and HEVs (hybrid and electric vehicles) become more common, the need for quiet and highly efficient vehicle HVAC (Heating, Ventilation, and Air Conditioning) equipment has become increasingly important. Noise reduction is critical for air-conditioning equipment and tools using fans to move air. Keihin Corporation uses SC/Tetra to conduct aerodynamic noise analyses to identify noise sources and evaluate countermeasures to reduce noise levels. Using computational tools to predict noise is extremely complex and is considered a very challenging flow simulation application.

Pic 1 Mr. Junya Washiashi, 
Engineer, Air-conditioning
System Development
Department, Air-conditioning
​ System Business Operations

Pic 2 Mr. Jun Onodera,
Assistant Engineer,
Air-conditioning System Development Department, Division 1, Air-conditioning
System Business Operations


 Keihin Corporation is one of the largest automotive component manufacturers in the world. Their business entails research and development (R&D), design, and manufacturing of engine, transmission, air-conditioning and electrical control units for motorcycles, automobile, motorsports, and general-purpose machine.

 Mr. Junya Washiashi – Engineer (pic 1), and Mr. Jun Onodera - Assistant Engineer (pic 2) from Keihin’s Air-conditioning System Development Department, Air-conditioning System Business Operations, conduct R&D on HVAC unit of automobile air-conditioning systems. An automobile air-conditioning system consists of an HVAC unit, a compressor and condenser. The function of HVAC unit is generation of warm or cool air, to maintain comfortable temperature and humidity of car cabin, and to defrost a windshield, the main components of HVAC unit (a heat exchanger unit that heats/cools the air to the desired temperature as in fig 3), and a blower unit that moves the air into the vehicle.

Fig 3 The structure of an HVAC unit, consisting of the blower unit (the cylindrical part - lower left) and the heater unit

Higher Demand for Quiet Vehicle Environment due to the Emerging Eco-friendly Cars

 As effective air-conditioning system is crucial to create a comfortable space for passengers, customer expectations are high. When climate controlled vehicles debuted, passengers were satisfied just having an air-conditioning system. But today’s customers expect low noise and vibration from the HVAC system, as well as the elimination of the odors, pollen dusts, and small particulate matter (PM2.5). The emergence of EVs and HEVs has increased the demands placed on the HVAC system. These eco-friendly cars are quiet most of the time, and generate engine noise only when necessary. This makes noise from other sources more noticeable, especially if it is not generated from the engine. As a result, the demand from vehicle manufacturers for HVAC noise reduction increases each year.

 “CAE has become more important to us because prototyping is costly. CAE allows us to evaluate device capability and determine where the noise may occur before prototyping,” says Mr. Washiashi. Filters are used to block fine particles such as pollen dusts and PM2.5, but the air flow rate requirement into the vehicle must also be maintained while also consuming minimum amount of energy. To design a device that satisfies such a requirement, Keihin engineers are always concerned about the ventilation system resistance, which is quantified as a flow rate index. Simulation is critical for calculating the flow rate index.

Extending the Simulation from the Heater Unit to the Blower Unit

 Keihin Corporation has conducted many different kinds of simulations, including fluid flow and aerodynamic noise analyses. They first started using an analysis tool to perform fluid analysis in 1999 to evaluate the flow inside a heater unit. In 2002, they used a specially customized tool to allow their design engineers to more flexibly experiment with simulating the heater unit and the tool was only designed to simulate the flow in the heater unit. In 2003 they started using SC/Tetra to simulate rotating air flow field of the blower with the drive motor.

 Keihin Corporation primarily uses SC/Tetra to analyze the air flow inside their blowers. They evaluate different design concepts and modeling techniques with the goal of identifying the best shape. One example is a transient analysis of a rotating body to visualize the air flow, predict the flow rate, and estimate the fluid noise. Recently they have taken more interest in understanding the physics within their blowers. Now they use the analysis tool to both improve blower performance and evaluate the physical phenomena to determine if there are other mechanisms for further improvements.

 Keihin Corporation also uses SC/Tetra in the early stages of concept design and development. One of their objectives is to reduce the number of prototypes they must build. They believe that evaluating designs analytically and minimizing prototype production will continue to grow in importance. However, this will be a long-term challenge to achieve.

Fig 4 Simulating the blower capability
(in terms of PQ characteristics).
​Click to enlarge.

 Another example of how Keihin Corporation uses SC/Tetra in their design is the estimation of the blower PQ (Pressure/Flow) characteristics (fig 4). Blower capability determines the performance of the overall HVAC system, and is critical for the entire design. Keihin engineers used SC/Tetra to identify the PQ characteristics at the operational voltage, based on the relationship between the blade torque calculated from analysis and the torque characteristics of the electric drive motor derived from experiments.

*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of April 30, 2011 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors.

Company Details


Keihin Corporation
Founded December 1956
Business Manufacturing of vehicle components
Representative Tsuneo Tanai, President and CEO
Location of Head Office Shinjuku-ku, Tokyo, Japan
Capital Approx. 6.9 billion JPY
​(as of March 31, 2013)



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