Hybrid Systems

ISE specializes in production of "series" hybrid-electric drive systems, where the engine is completely decoupled from the driveline and is used only to generate electrical power. This type of hybrid architecture is especially attractive for large vehicles that perform large amounts of stop-and-go driving, such as urban transit buses and delivery trucks. Conventional buses and trucks of this type are highly inefficient and produce high levels of toxic emissions because they have large (typically diesel) engines that are constantly ramping up and down - the least efficient way to operate a power source. In the ISE series hybrid system, a smaller engine is mated to a generator and operated at a constant, efficient speed and power output level. When vehicle power requirements temporarily increase - such as during acceleration or hill-climbing - additional power is drawn from an onboard energy storage system comprised of batteries or ultracapacitors (a new type of energy storage device). When vehicle power requirements are low, the energy storage system is recharged. Not only is engine efficiency increased, but the vehicle is able to recapture energy whenever it slows down through a process called "regenerative braking."

In ISE's series hybrid drive system, the APU and energy storage systems work in harmony to supply power to the motive drive system. During braking, the motive drive system recaptures energy and sends it back into the energy storage system - a process that can increase overall vehicle energy efficiency by 25% or more. The ThunderCAN operating system constantly monitors vehicle power needs and the status of all of the vehicle's components, assuring that these power needs are met in the most efficient way possible, and provides early warning of any potential problems with vehicle components. This flexible, integrated operating system uses a proprietary network-based architecture based on the automotive Computer Area Network ("CAN") data standard that is essential to the effective utilization of Siemens and other leading components in heavy-duty vehicles, and that ISE believes is the most advanced and versatile means of power and control for heavy duty vehicles.

The other type of drive system is referred to as “parallel” hybrid technology.  In a parallel hybrid system, the engine is still used to mechanically drive the wheels, but drives the wheels through an electric motor (or motor set) instead of a transmission.  In this configuration, the electric motor(s) provide a mechanical "assist" to the engine and can drive the vehicle independently of the engine under certain conditions.  However, the engine remains the dominant source of mechanical power to the wheels under most circumstances.  The principal advantage of parallel systems is in the cases where vehicles operate for extended periods at constant speed, with minimal changes in power requirements.  Certain types of parallel systems can be produced more cheaply than series systems.  As a result, parallel systems seem to be emerging as the favored technology for low value vehicles such as passenger cars and light delivery trucks that do more highway driving and for whom the additional costs of a series system is prohibitive.  A recent study by the U.S. Department of Transportation confirms that the series hybrid system is the most “energy efficient system when the vehicle is operated in stop and go mode.”

The main obstacle to the adoption of series hybrid drive systems has been the technological complexity of managing the interaction of the three separate power sources in such a system: the engine-generator, energy storage system, and the electric drive motor (which acts as a generator during regenerative braking). This problem is particularly challenging in heavy-duty buses and trucks, where the power levels to be managed are significantly higher than in smaller vehicles such as passenger cars. ISE's proprietary control system uses a network architecture similar to an Ethernet computer network to monitor and control all of the hybrid system components. Each major hybrid component is controlled by a microcomputer that acts as a "gateway" to the overall network, which uses an ISE-developed operating system that uses standard automotive industry Controller Area Network (CAN) protocols. This gives the ISE hybrid architecture greater flexibility and upgrade potential than competing architectures, as any engine or other component using CAN-based controls can be plugged into the ISE system with a minimum of new development. The ISE "ThunderCAN" operating system has shown itself to be as robust and reliable as it is flexible, making ISE's hybrid-electric drive system one of the first to be purchased on a large scale by a major U.S. transit bus manufacturer or transit agency.

ISE has built several key innovations into its control system and hybrid architecture that further improve the performance of the overall system. For example, ISE has developed an engine "idle-stop" capability that automatically stops the engine-generator subsystem when the vehicle comes to a stop or sees its power consumption decline for an extended period. The idle-stop capability is enabled by an ISE-developed control algorithm and a suite of electrically-driven accessories that power the vehicle's power steering, braking, and air conditioning accessories using electric motors and compressors. Conventional accessories, which rely on engine-driven belts, require the engine to be operated all the time, and are notoriously inefficient and prone to mechanical failure. ISE hybrid systems using deep-cycle battery packs enable large buses and trucks to drive ten miles or more in an "all-electric" mode, on battery power alone - producing zero emissions and almost no noise.