Frequently Asked Questions

1. WHAT IS THE FUNDAMENTAL DIFFERENCE BETWEEN THE ISE-SIEMENS AND ALLISON SYSTEMS?

The ISE Siemens system is a series hybrid system, where the conventional internal combustion engine is totally disconnected from the wheels and is used only to generate electricity. Electric motors drive the wheels, without any mechanical assistance from the engine.

The Allison system is a parallel hybrid system, where the conventional internal combustion engine is still connected to the wheels. In the Allison configuration, an electric drive unit (EDU) takes the place of the transmission. The EDU contains a motor that supplies torque to augment the engine and that also acts as a generator to recapture regenerative braking energy.

In both the ISE-Siemens and Allison systems, an energy storage system is used to store energy recaptured during regenerative braking, and to release this energy when surge power is required. This capability allows, in both cases, use of a smaller engine than in a conventional drive system and helps allow the engine to be operated at a more optimal speed. The ISE-Siemens system offers batteries or ultracapacitors, while the Allison system offers just batteries.

2. WHICH IS BETTER - SERIES OR PARALLEL HYBRID TECHNOLOGY?

ISE believes its system is a better choice for any heavy-duty vehicle that operates on an urban route or spends a large percentage of its time idling or in stop-and-go conditions. Series systems such as the ISE-Siemens system are expected to be more efficient when vehicles perform lots of stop-and-go driving, because decoupling the engine from the wheels allows the engine to be run at extremely low speeds and power output levels when the vehicle is moving very slowly or idling. In fact, in series hybrid systems where the accessories (power steering, power braking, and air conditioning) are run electrically, the engine can be turned off completely when the vehicle is gliding, braking, or stopped, resulting in zero fuel consumption or emissions during these periods. ISE has developed an engine "idle-stop" control algorithm to take full advantage of this capability; a central computer automatically turns the engine off every time the vehicle stops or power consumption is reduced below a given level for more than a few seconds.

Prior to recent experience, parallel systems like the Allison system were expected to fare better during sustained high speed driving, because the internal combustion engine can mechanically drive the axle directly. In the series system, the engine has to convert its energy to electrical power via a generator and then back to mechanical power via the drive motors, which was thought to be less efficient in steady-state operation. However, recent experience with ISE series hybrid and Allison parallel hybrid buses in New Jersey suggests that parallel drive may not be as advantageous as previously thought. These buses are both operating on high speed commuter bus routes that were expected to favor Allison's parallel hybrid system, but the buses using ISE's series hybrid drive system have consistently exhibited better fuel economy than the Allison bus, both in absolute terms and relative to the conventional buses operating on each route. Since ISE's latest control software updates were made in early December 2003, three ISE series hybrid buses have averaged nearly a 25% improvement in fuel economy over conventional buses operating on the same route, while four Allison parallel hybrid buses gave averaged only about a 12% improvement over conventional buses on their route. In absolute terms, the ISE hybrid buses have averaged 5.8 miles per gallon over this period, while the Allison hybrid buses are getting 4.9 mpg. The Allison bus is about 10% heavier than the ISE bus, but even after normalizing for this difference the ISE performance is better. In addition, the third ISE bus in this series averaged better than 8 miles per gallon while being driven cross-country from San Diego to New Jersey in May 2004. ISE attributes its advantage to the efficiency of its electrically-driven accessories and superior battery and vehicle control technology, which more than offset the savings the Allison system offers for locomotion when the vehicle is operating at constant speed.

Another advantage of the ISE-Siemens architecture is that series systems can be converted to fuel cell based systems more easily, because the engine in a series system performs exactly the same function as a fuel cell - electricity generation. In the parallel system, where the engine is still relied on to supply torque to the wheels, a fuel cell power plant would not work, because these types of power plants can only generate electricity and are not designed to supply mechanical torque. In addition, lighter weight engines such as the Ford V10 gasoline engine can be uses in series hybrid systems because they are not relied upon to supply torque to the vehicle's wheels. For large buses and trucks, the Allison system depends on diesel engines because the engine in its system must still provide torque to the wheels. This has allowed ISE to develop ultra-clean hybrid systems that use gasoline and hydrogen-burning engines, whereas Allison cannot use these types of power plants in its system.

For the above reasons, it is the opinion of ISE that the ISE-Siemens series hybrid system is generally a better choice for vehicles used primarily for urban stop and go driving, and that there may even be a large number of higher speed vehicles that can benefit from the ISE series technology. There may be a class of trucks that spend enough time in constant-speed driving to favor a parallel hybrid drive system such as Allison's, but Allison would probably have to develop electrically-driven accessories and emulate other features of the ISE series hybrid system to match the ISE-Siemens advantage. Why bother, when you can buy the ISE-Siemens system today at the same or lower price than the Allison system?

3. HOW ARE DRIVE SYSTEMS PURCHASED?

ISE offers a fully integrated "ThunderVolt®" hybrid-electric drive system based on Siemens ELFA components. Siemens ELFA components constitute the core elements of the ISE series hybrid drive system: drive motors, motor controllers (inverters), and generators. ISE adds three major elements to the Siemens components: (1) ultracapacitors and/or batteries for energy storage, (2) electrically-driven accessories, and (3) an advanced control system. Siemens has endorsed ISE's integrated system by executing an agreement with ISE in August 2002 establishing ISE as Siemens' distributor and "preferred integrator" of ELFA products in the U.S.

The Allison drive system is a parallel hybrid drive system that can be purchased in its entirety, with the exception of the engine and integration hardware, from Allison or one of Allison's distributors. Like ISE, Allison buys its battery packs and some of its other components from outside suppliers, and packages the entire system into an assembly that can be installed by anyone familiar with the electrical, mechanical, and other interfaces among the components, and between the components and the vehicle.

ISE and Allison each offer integration support to vehicle manufacturers to help them learn how to install and operate their respective drive systems. ISE has also performed complete installations of the Allison system into three different bus models and is available to support OEMs who cannot or do not want to obtain this support from Allison. However, ISE's main focus is on selling and supporting the Siemens-based series hybrid drive system, which ISE believes is a better choice for most urban transit buses.

4. WHY DOES ISE BELIEVE THE SIEMENS-BASED SYSTEM IS BETTER FOR URBAN TRANSIT BUSES?

As indicated above under Item #2, series hybrid systems are more efficient than parallel systems, especially in stop-and-go driving cycles. This is because in the series system, the reliance on the engine solely for the production of electricity allows for use of smaller, lighter, more efficiently operated engines than in the parallel system. The data from New Jersey show that even on relatively high-speed bus routes, the ISE-Siemens drive system provides more than twice the fuel economy benefit as the Allison system. Based on its own testing of buses on more localized routes, ISE believes its advantage over the Allison system will be even greater for vehicles that perform more stop-and-go driving, such as buses on inner city urban routes. Whereas ISE's system is improving fuel economy by 25% in New Jersey, it expects a fuel economy benefit of 50-100% for urban transit buses.

Series hybrid systems also produce lower levels of harmful emissions such as nitrous oxide (NOx), for the same reasons that fuel ecomomy is improved (i.e., the engine is smaller and operated more efficiently). In addition, ISE believes that its ThunderVolt® hybrid drive system, based on Siemens ELFA components, has other specific advantages over the Allison parallel hybrid system. These include the following:

• The Siemens ELFA components have a much longer and more proven track record than their counterparts in the Allison system, and have demonstrated very high reliability. ELFA components have been installed into more than 700 buses in Europe and have logged more than 30 million miles of real world use - more than all other heavy-duty vehicle hybrid-electric drive systems combined. ELFA motors and inverters have shown extremely long mean times between failures. By comparison, Allison's motors and inverters are still in the prototype phase, have undergone fundamental design changes as recently as 2002, and are just now entering regular production.

• The standard energy storage system offered by ISE utilizes ultracapacitors, which can store and release energy more efficiently than the nickel metal hydride batteries used by Allison. This enables vehicles to take greater advantage of regenerative braking energy while reducing the weight of the energy storage system. Ultracapacitors are also expected to last longer than batteries - at least five years and possibly as long as 10-12 years. This expectation is based on cycle testing performed by Maxwell Technologies, manufacturer of the ultracapacitors used by ISE, and is backed by a five-year warranty. ISE also offers nickel sodium chloride "ZEBRA" batteries as an option for vehicles that require large amounts of total energy to be stored on board. These batteries have a higher energy density than the nickel metal hydride batteries used by Allison and can therefore meet a given energy storage requirement with less onboard weight. The ZEBRA batteries are recommended when vehicles need to spend long periods idling with their accessories running or when there is a need to drive the vehicle for long distances with the engine stopped, such as through a tunnel. Note: Allison claims to have a "HUSH" mode where engine use is curtailed to reduce noise and emissions, but this is a limited capability operating mode where the engine still has to run at least at idle to keep the vehicle's accessories functional, and which can only be sustained for relatively brief intervals. When ZEBRA batteries are used, ISE's more "battery-dominant" hybrid system enables vehicles to drive for as many as twenty miles with the engine completely stopped. This gives operators the option of turning off the APU when operating in environmentally or noise sensitive areas, and allows extended off grid capability in trolley bus applications

• The combination of ISE's electrically-driven accessories, ultracapacitor, and deep-cycle battery technology also improve the overall operating efficiency of all of ISE's hybrid configurations. In configurations using ZEBRA batteries, the availability of two completely independent sources of deep-cycle energy also provides redundancy in case either the APU power source or the energy storage system fails.

• ISE's Siemens-based system is more flexible than the Allison system. ISE offers variants of the ELFA-based series drive system using engines fueled by gasoline, propane, natural gas, and hydrogen fuel. In addition, ISE offers alternative auxiliary power unit (APU) options not offered by Allison, including fuel cells. In fact, ISE offers an "ICE-to-Fuel Cell" evolutionary hybrid drive system that can be converted to a fuel cell-based drive system merely by replacing the internal combustion engine (ICE)-based APU with a fuel cell-based APU and replacing the system's fuel system with hydrogen-based system. ISE has already integrated and deployed a fuel cell bus using its basic ELFA hybrid technology, which was operated with 90%+ reliability at several California transit agencies in 2002 and 2003.

ISE has improved the packaging of its integrated drive system to make it as simple to install as the Allison drive system. Part of the appeal of the Allison system is that the Allison drive unit looks a lot like a standard transmission, making vehicle manufacturers feel that it is a relatively simple installation. To match this appeal, ISE has developed an Integrated Drive Unit (IDU) package that integrates most of the components of its ELFA-based drive system into a package with a similar shape and dimensions to standard vehicle transmissions, and that can be installed in the same space claim usually occupied by the transmission. ISE series drive systems using this new IDU packaging, which were first demonstrated in late 2003, actually have fewer separately mounted components than the Allison system.

5. WHAT IS THE COST DIFFERENCE?

The entire ThunderVolt® package of components comprising ISE's ELFA-based series hybrid drive system are available for prices starting at $169,000, and in quantity, the total system price is expected to decline to less than $150,000. Allison does not publicly release pricing for its system but ISE believes the ThunderVolt® prices compare favorably. One consideration that should not be overlooked is that Allison's quoted price frequently excludes the cost of the engine, which Allison typically requires its bus manufacturer customers to purchase on their own, whereas ISE's standard price includes the engine. ISE's price also includes electrically-driven accessories, which are not included in the Allison system, and which eliminate the need for the bus manufacturer to separately purchase components such as air conditioning compressors, as well as providing enhanced capability. The time required to install the Allison and ISE-Siemens systems into typical transit buses is estimated by ISE to be approximately equal. When Allison's prices are "normalized" to include these items, ISE believes its prices are lower, or at worst in the same general range.