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LAPEROS® LCP has been used for the power module case in hybrid vehicles from Honda.

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LAPEROS<sup>®</sup> LCP has been used for
the power module case in
hybrid vehicles from Honda.

We interviewed the staff members of Keihin Corporation, which was responsible for the design and development of the new power control unit (PCU) and intelligent power module (IPM), a product that succeeded in realizing top class power density.

From left: Managers Shinichiro Tomota and Hiroaki Iida, 2nd Section, 7th Development Department, Development Division, Keihin Corporation

Against a background of increasingly important global environmental problems, there is demand for automobiles with higher energy-saving performance and reduced exhaust gas. In response to these issues, vehicles such as hybrid vehicles, electric vehicles, and fuel cell vehicles are being developed going forward. Specifically, hybrid vehicles (which use two power sources: a gasoline engine and a drive motor) were the first to be commercialized, and have now been widely popularized. Keihin Corporation is the largest manufacturer of automobile parts related to Honda Motor Co., Ltd. It was one of the first companies to begin developing next-generation drive system components to manage various kinds of energy.

What is PCU/IPM?

New Power Control Unit (PCU)

IPM inside PCU
A gate drive board is placed on the top

Hybrid cars use a gasoline engine and a drive motor as power sources. PCU is used to control the electric power necessary in order to use the motor as a power source. PCU plays the following roles.

  1. Convert the voltage supplied from the battery into voltage to drive the motor.
  2. Convert the electric power generated by the generator into DC voltage to charge the battery.

PCU consists of parts such as a boosting converter, an inverter for motor driving and regeneration, and IPM. IPM is a composite semiconductor part that forms the core component of the PCU. Keihin has realized semiconductor power devices to control electrical energy that have low loss, high heat resistance, and more compact sizes by developing optimal cooling structures. This has allowed the device to achieve top-class power density as PCU.

The new IPM we have developed is located in the center of PCU and has a water jacket under the power module for cooling. The overall size of the PCU is determined by the size of this IPM case. Technical innovation in the IPM components made it possible to reduce the size of PCU wholly.

LCP Realize Top-Class Size Reduction and High Output

A power module case produced using LAPEROS® LCP

The functions required for IPM cases include heat resistance, electrical insulation, solder bondability, and adhesive properties. To achieve these, the resin materials must have high-level properties, including high heat resistance, dielectric breakdown strength, mechanical strength and flowability during molding, and also low outgassing.

In particular, resin materials that can withstand the high temperature generated in soldering processes including IPM cases in the production processes of IPM are required for heat resistance. After investigation, it was decided to use Polyplastics LAPEROS® LCP-grade resin containing glass fiber. This material made it possible to achieve a compact size and a high output that are in the top class in the industry.

Two Issues Overcome Using Flow Analysis Technology from Polyplastics

IPM cases are large for items molded by LCP, but they are required to have the same level of high precision as the conventional ultra-small precision components. In general, LCP has a rapid solidification speed as well as high anisotropy, so there is a tendency for the strength of welded parts* to become weaker. This caused concern about the welded parts cracking when the temperature rises during the IPM production processes. The other issue is warping. IPM is used on top of the water jacket for cooling. IPM cases must be molded to the shape that fits closely to the top of the water jacket with no gaps because cooling efficiency significantly affects IPM performance. It was critical to design a profile that would not warp. The flow analysis by Polyplastics Technical Solution Center (TSC) played a major role here. The analysis was repeated multiple times with various different conditions, and the data obtained was also shared with the molding processing company. These efforts made it possible to overcome the two issues of weld strength and warping.

* The parts where the flows of the molten resin intersect inside the mold

Functions Required of IPM Cases and Functions Required of Resins

Prospects for Extension to
Next-Generation Mobility and Fuel Cell Vehicles

The newly developed Power Control Unit (PCU)/Intelligent Power Module (IPM) has advanced environmental performance, so it can also be used on electric vehicles and fuel cell vehicles in addition to hybrid vehicles. There are high expectations for this product's ability to contribute greatly to promoting the use of electric motors in vehicles in the future.

As the Best Partner in Development

Yoshiyuki Yokote
Manager, Unit 1, Japan Sales Headquarters, Global Sales and Marketing Division Polyplastics Co., Ltd.

We first worked on developing a large precision component for our LCP. After appropriately understanding the needs of the customer (as it says in our "Polyplastics- Way"), we fully utilized the technical support structures we have at our TSC. The decisive factor in this development was that we were able to obtain and supply materials data covering multiple items and flow analysis using CAE*. We hope that our products and technical expertise will continue to be used for automobile components that are developed based on environmental awareness.

* Computer-Aided Engineering (computer support for design)

Keihin Corporation

As a manufacturer developing systems that manage various sources of energy, Keihin Corporation was one of the first to develop products that support the advances in gasoline engines and products for the drive systems that serve as an alternative to the internal combustion engine. These products will be key devices in the future and will be used in vehicles such as hybrid vehicles, electric vehicles, and fuel cell vehicles.