LAPEROS® liquid crystal polymer used in power module case of new power control unit for hybrid vehicle
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.
＊1 Cruise control: A function whereby the vehicle drives at a constant speed set by the driver without having to press the accelerator.
＊2 IGBT: Acronym of insulated-gate bipolar transistor. A semiconductor switching device used to control electrical energy.
＊3 Freewheeling diode: A diode used to protect the IGBT by returning the load current that is generated through driving
The Honda hybrid system
Cited from www.hybrid-car-guide.com/kisotisiki-info/t-h-tigai.html
New power control unit (PCU)
Intelligent power module (IPM) housed inside the PCU
Gate drive board is mounted on top
Intelligent power module (IPM)
Water jacket for cooling is located in the lower part
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.
●Further heat resistance sought, together with downsizing and higher functionality
Not only are LCP materials expensive: they have their own unique difficulties when it comes to processing in the current application. Despite this, no other material was considered for this application from the outset of development other than LAPEROS S135 on account of its heat resistance that can ensure the IPM manufacturing process and its reliability.
Blistering was among the problems that occurred when other materials were used, but in the end there were no doubts as to the suitability of LAPEROS S135 for the task at hand.Adoption of LAPEROS LCP in this case was on account of its heat resistance during the flow steps of the manufacturing process but moving forward, if further advances are made in downsizing and higher functionality of PCUs, even higher heat resistance may be sought of the IPM itself.
Surmounting flow processes in a cleanroom
The IPM is a large part but the manufacturing process takes places entirely within the confines of a cleanroom because the part itself incorporates a semiconductor. Once the part is in its final form, it is encapsulated in silicone gel. Only then can it be removed from the cleanroom. Only once encapsulated can one be at ease. Carrying out flow processes within a cleanroom was a new challenge for Keihin.
Keihin installed a Class 10,000 cleanroom at its Miyagi No.2 Plant as well as a new production line incorporating a revolutionary bare chip mounting line and advanced analytical technology.
As a cutting edge, environmentally compliant product, not only can the current IPM be deployed in hybrid vehicles: it can technically be utilized in next-generation mobility headed by electric vehicles and including the highly anticipated fuel cell vehicle. In this way, it is a product that can contribute greatly to the future electrification of automobiles. As a key research result of Keihin, much is expected of the new power control unit in the future.
General properties of LAPEROS® LCP S135
|Item||Unit||Test Method||High heat
|ISO Marking Code||ISO 11469
|> LCP-GF35 <|
|Water absorption(23℃,24hrs)||％||ISO 62||0.02|
|Tensile strength||MPa||ASTM D638||155|
|Tensile elongation||％||ASTM D638||1.3|
|Flexural strength||MPa||ISO 178||220|
|Flexural modulus||MPa||ISO 178||16,000|
|Flexural strain||ISO 178||2|
|Charpy notched impact strength (23℃)||KJ/m2||ISO 179 / 1eA||12|
|Temperature of deflection under load (1.8MPa)||℃||ISO 75-1,2||340|
|Temperature of deflection under load (0.45MPa)||℃||ISO 75-1,2||340|
|Electric strength (1mmt)||kV/mm||IEC 60243-1||40|
|Electric strength（3mmt）||kV/mm||IEC 60243-1||20|
|Volume resistivity||Ω・cm||IEC 60093||2×1016|
|Relative permittivity（1KHz）||IEC 60250||3.9|
|Relative permittivity（1MHz）||IEC 60250||3.8|
|Dielectric dissipation factor（1KHz）||IEC 60250||0.01|
|Dielectric dissipation factor（1MHz）||IEC 60250||0.01|
|Tracking resistance (CTI)||V||IEC 60112||150|
（80×80×1mmt, Flow direction,Inj. pressure 60MPa）
|The yellow card File No.||E106764|