The automobile industry is facing a major transformation. Against a backdrop of increasingly important global environmental issues, even more stringent energy conservation and exhaust gas regulations are coming into play. Automakers are developing alternative drive systems to the conventional internal combustion engine headed by hybrid vehicles and including electric vehicles and fuel cell vehicles in response to these issues. Among these, the hybrid vehicle has made most progress in being commercialized and penetrating the market. The drive train of this type of vehicle combines a gasoline engine and an electric drive motor.
Keihin Corporation is a leading auto parts manufacturer affiliated with Honda Motor. The company is a comprehensive supplier of all types of energy management systems and it was one of the first to develop drive system components for next-generation alternative drive systems that replace internal combustion engines.

Keihin announced a new type of self-developed power control unit (PCU) for controlling the generating/drive motor
of a hybrid vehicle at the Tokyo Motor Show held in October 2015 and in November of the same year, the company
commenced commercial production of the core component of the PCU: namely the intelligent power module (IPM). This IPM is installed in the Honda ODYSSEY Hybrid debuted in February 2016.
This IPM is compact and packed with high performance features. In turn it has realized downsizing and lightweighting of the PCU itself. LAPEROS^® LCP from Polyplastics is one of the enabling technologies for this high performance component. Here we talk to Mr. Shinichiro Yuta, and Mr. Hiroaki Iida from the second section of the seventh development department at Keihin’s development headquarters about this component.

Function of power control unit (PCU)、
intelligent power module (IPM)

Hybrid vehicles are powered by a combination of a gasoline engine and an electric drive motor. The role of the PCU is to control the electricity when the motor is used in drive mode.
The PCU converts the voltage of the battery into the voltage used by the drive motor for powering the vehicle and also assists with fixed speed driving via cruise control＊ 1 and assisting with motive power during acceleration. One more function is to convert the current to DC for charging the battery when a generator is employed. An additional function is to generate power during deceleration in order to effectively recover electricity. The PCU consists of a voltage up converter, an inverter for driving the electric motor and recovering electricity, and an intelligent power module.
The intelligent power module (IPM) is a composite component at the core of the PCU incorporating a semiconductor. Keihin has achieved top-class output density in its PCU through low loss realized using an IGBT＊2 and a freewheeling diode＊3, as well as employing a cooling structure with optimized heat resistance and compactness.
The IPM developed here is located almost at the center of the PCU and a sub-pump is mounted onto it using soldering. A water jacket is located at the bottom of the module to carry out the role of cooling. Further, a gate drive circuit board is mounted in the top section of the module.
The overall size of the PCU is defined by the size of this IPM case. Keihin has realized a more compact overall PCU size through technological innovation in the IPM components.

IPM case: One of the largest parts ever molded from LAPEROS (LCP)

The intelligent power module case requires heat resistance, insulation properties, solderability, adhesivity, and gel encapsulation among other functionalities. In order to achieve this, the plastic material that is used must meet several high performance requirements including high heat resistance, high breakdown strength, material strength, and high flowability and low outgassing during molding.

●Solder heat resistance

Among the required attributes, the surface temperature of the plastic becomes very hot during the IPM manufacturing process because the case itself is also soldered. For this reason, a plastic material with the required heat resistance was required. A glass fiber reinforced grade of LCP (LAPEROS S135) was selected for this reason. Adoption of this resin enabled industry-leading downsizing and high output to be realized.

●High flowability and weld strength

The IPM case molded from LAPEROS LCP featured unprecedented dimensions as a plastic molded part for this type of resin, while the required precision remained on a par with that of much smaller high precision parts such as connectors. Furthermore, copper strips called busbars are located at multiple locations throughout the IPM case and these are covered with plastic. Joining with these metal elements must be via the molding process itself and not use any adhesive. The complex molding parameters necessitated by this were derived with a significant contribution from the molder responsible for the part.
LCP molded parts have issues with weld strength and one must make certain that the weld line does not break when heat is applied during the IPM manufacturing process. Polyplastics TSC (Technical Solution Center) played a major role in this respect through supplying the flow analysis data.
In actual fact, data for large parts molded from LCP is sparse and while it was difficult to sufficiently respond to the request, tripartite exchange of data between Keihin, the molder and Polyplastics was enough to realize a part that overcame any issues with weld strength.

●Dimensional stability – issues with warpage

Another major issue was dimensional stability, particularly with regards to warpage. The IPM is mounted directly on a water jacket for cooling. In this respect, a shape must be molded whereby there are no gaps between the jacket sand the IPM in order to maximize the cooling efficiency, and thereby maximize IPM performance. Furthermore, flow analysis data and the expertise of the molder were critical in assisting in numerous aspects that realized a design that minimized warpage.

General properties of LAPEROS^® LCP S135