The core of the e-Traction^® System is formed by the highly energy efficient electric propulsion systems, such as TheWheel™ SM500/2FE and the SM350/1AL, which both are being used in the Whisper™. A number of axles and suspension designs have been produced and tested to allow the easy integration of this new technology on existing platforms. The propulsion system receives a continuous supply of Direct Current (VDC) electricity from the Lithium-ion batteries, which have been placed in temperature controlled storage compartments. These batteries are primarily recharged by the on-board by the Auxiliary Power Unit (APU), which could operate on any fuel desired by the operator. For practical reason diesel was chosen for the Company demonstrators, but a change to CNG would be relatively easy to accomplish.  These primary components: the self-propelled wheels and their axle(s), the batteries and the APU, are tightly controlled for maximum efficiency by the (patent pending) e-Traction® Energy Management System. This system translates the wishes of the operator by means of a CANopen programmable logic computer (PLC) to each component to ensure an optimal result.

Though not necessarily required as part of the e-Traction® System, the e-Mission™ Particle Eliminator is a perfect complement that is tied into the same e-Traction® Energy Management System. 

Modular Approach:

A key design feature of the e-Traction® System is the modular approach, that allows (re)placement of the key components in a relatively short amount time. The universal rear axle, for instance, is compatible with existing axles and can be exchanged for the conventional equivalent in just a number of hours. An individual TheWheel™ SM500/2FE system can be removed and replaced in about one hour. The batteries, in their air-conditioned storage compartment, can be exchanged in about 20 minutes. The APU can be replaced in its entirety by a spare identical unit in about one hour.

The philosophy behind the modular approach is both the flexibility in application but also the minimization of the amount of time a vehicle would have to be taken out of service for maintenance or repairs.

The e-Mission™ Particle Eliminator (EPE) can be retrofitted to any vehicle, provided it has sufficient space, without the need to alter the management of its fossil fuel engine. In the case of the Whisper™ the very first installation of an EPE was accomplished in less than one day.

Redundancy:

Another key benefit of the is the redundancy it affords the operator. Under normal operating conditions, The Whisper™ requires a maximum of just 1,700 Nm. Yet its two TheWheel™ SM500/2FE's combined provide 10,500 Nm, or six times the torque needed for normal operations. In the unlikely event one traction system were to malfunction, the remaining system can comfortably handle the duties for the remainder of the trip.

The batteries of the Whisper™ have been grouped to limit the possible danger in the event of inadvertent contact. The current configuration features four strings of seven Lithium-ion batteries, which are individually monitored and controlled. When deemed necessary by the operator or the e-Traction^® Energy Management System, individual batteries or entire strings can be shut-down, without noticeably affecting the vehicle's performance.

The APU normally provides the bulk of the energy being consumed by the vehicle, while the batteries primarily function as a buffer. The Whisper™ can operate more than one hour on its fully charged batteries. In case of a required shut-down of the APU the Whisper™ will usually still be able to complete its run. The wireless connection with the maintenance department will allow a decision to be made to bring to withdraw the bus from service or make the adjustment in between runs.

The unlikely malfunction of the CANopen programmable logic computer (PLC) will not render the Whisper™ immobile. A manual override has been installed that will allow the operator to move the Whisper™ forwards or backwards with a maximum speed of 10 km/h.

To obtain maximum energy efficiency Whisper™ will normally use reverse power in braking to capture the energy that otherwise would be lost to brake pad wear and heat. In so doing 70% of the energy needed to attain a certain speed is recovered under braking. A hypothetical complete loss of electronic control over one or more the traction systems could result in a dangerous situation and thus a mechanical back-up brake system has been installed, that also will become active during hard braking and/or emergency stops.

Component Choice Criteria:

To achieve optimum energy efficiency requires forethought and discipline. Maximum and nominal vehicle weight and speed are the key factors determining the e-Traction® System size needed to achieve the desired performance. An undersized system will surely disappoint and an oversized system is needlessly heavy.

1. Designing a city-bus with highway performance could be less than optimal, unless undulations on its route do indeed require that amount of available torque and energy generation.
2. Battery storage beyond a certain minimum requirement is needlessly costly, adds weight and occupies valuable space.
3. Building a vehicle with needlessly heavy materials and seldom used heavy or energy robbing components negatively impacts energy efficiency. Examples of simple but far reaching energy conservation considerations are:

• The e-Traction-Bus, without its propulsion system, axles and seats weighs only one third of the somewhat 12.5% longer equivalent tubular frame on chassis body of the Whisper™. The composite construction technique pioneered by the now defunct Fokker company is a major contributor to the energy efficiency of the limited number vehicles for which it has been used thus far.
• Many North American public transit buses customarily feature heavy, voluminous and costly automated elevators to provide unrestricted access for disabled persons. The Whisper™ uses a simply lightweight hand operated ramp to ensure to accomplish the exact same feat, but without the significant weight penalty and virtually no additional cost. The big difference is that the operator will briefly need to leave his seat to assist the disabled passenger in the rare instances that this is indeed required.
• Constructing a vehicle with heavy and costly (stainless steel) materials, which will outlast its economic lifespan by a considerable margin, causes needless energy consumption. Universally applied safety standards equate (high speed) long distance buses with (slow speed) city-buses. The added strength required to limit casualties from a high speed impact and roll-over increases the weight and energy consumption of a city-bus that rarely travels a speeds greater than 50 KMH.
• Running the traction motor continuously to keep the air-conditioner, heater, compressor and power-steering fully operational wastes needless energy. The air-conditioner of the Whisper™ is independent of the traction system and draws its energy from the batteries. The same is true for on-demand compressor and power-steering pump. The heat generated by the traction system (including the combustion engine and the generator) is recycled as part of the heating system for the passenger compartment in the winter. Frequently buses are found parked for extended periods with their combustion engines running at considerable speed.

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Last modified: June 12, 2007