In most instances, new products that improve hybrid or diesel powertrain designs are quite different from those for spark ignition (SI) engines. For hybrids, the high voltages and high power requirements for a driving motor, as well as the power conversion and special considerations for today's nickel-metal hydride batteries, demand different electrical/electronic components than conventional SI engine vehicles. A key design aspect is heat removal to keep electrical and electronic components within their safe operating area. With increasing hybrid vehicle experience and growing hybrid vehicle applications, developments are occurring to reduce component size, power consumption, weight and, of course, cost. Here are three examples.
DC POWER RELAY
Omron Electronic Components G9E series of dc power relays switch up to 200A at 400V dc. The SPST-NO contact relays use a sealed, gas-filled construction that produces a cooler arc during switching. The cooler arc means a reduced contact gap and a 70 percent reduction in overall size compared to contactors, as well as a 50 percent reduction in noise. Measuring 36 x 73 x 67.2 mm, the G9EA model handles up to 60A at 400V dc or 100A at 120V dc. Other versions with slightly different dimensions include the G9EC that switches up to 200A at 400V dc and the G9EB that switches up to 25A at 250V dc. Units are available with coil operating voltages of 12, 24, 48, 60 and 100V dc.
BATTERY COOLING SYSTEM
With most hybrid vehicle traction batteries mounted inside the passenger compartment, a traditional cooling system employs forced cabin air for cooling. Using air cooled by the rear air conditioning system, as well as cabin air to cool the battery, DENSO Corp.'s battery cooling system provides comparable cooling performance with only half of the air flow required by previous models. The reduced noise level (approximately 30 percent lower) was required for passenger comfort in the Lexus LS600h and the Lexus LS600hL. In addition to the batteries, other system components such as the system main relay and the current sensor are typically cooled by the battery cooling system.
HYBRID POWER CONTROL UNIT
DENSO Corp. developed a Power Control Unit (PCU) that includes the boost converter and two inverters for the main traction motors of hybrid vehicles. Used initially on the Lexus LS600h and LS600hL, the dc-dc converter boosts the 288V battery voltage to 650V. Compared to the company's conventional technology, the new PCU produces approximately 60 percent higher output power per unit volume. Cooling relies on a new structure that sandwiches the heat generating power devices between two heat sinks and in layers between stacked cooling tubes. Soldering both sides of the power devices to the heat sinks reduced the thickness of each power device, as well as the stress on the solder joints to ensure high reliability. By changing the number of stacked power devices and cooling tubes, the PCU's design can easily be revised to handle different output voltages in other hybrid systems.