2003 Honda FCX -- Powertrain
The FCX powertrain-an unwavering dedication to cleanliness, performance, and efficiency
System combines a fuel cell stack and ultra-capacitor with an onboard high-pressure hydrogen tank
A fuel cell vehicle is powered by an electric motor running on electricity generated by a fuel cell stack using hydrogen as its energy source. There are a number of methods for creating such a powertrain. The principal methods for supplying the hydrogen include those in which it is stored directly onboard the vehicle and those in which a reformer is used to convert methanol or gasoline into hydrogen. There are also various methods for storing hydrogen onboard the vehicle. In terms of power supply, some systems use power output from the fuel cell stack alone to drive the motor, while others supplement the FC stack output with an assist device using a battery or capacitor. After considering a variety of factors, such as energy efficiency during power generation and driving, overall system weight, and packaging efficiency, Honda decided to equip the FCX with a system that combines a fuel cell stack and ultra-capacitor with an onboard high-pressure hydrogen tank.
Components laid out for efficient use of overall vehicle space
The powertrain of a fuel cell vehicle has more components than a gasoline-powered vehicle does, and they weigh more and take up more space. On the other hand, components apart from the drive mechanism can be laid out freely, and their positioning has a significant effect on the car's performance. For the FCX, Honda developed a custom platform for optimum positioning of the various components, while making each one as compact and lightweight as possible. Starting with the FC stack, which is the heaviest component, power-generating equipment was centrally located under the floor, while the hydrogen tank was tucked beneath the rear seat and the ultra-capacitor installed behind the rear seat. This layout significantly contributes to comfort and performance by ensuring plenty of cabin space while at the same time achieving a low center of gravity and the optimum front-rear weight distribution for a front-wheel-drive vehicle.
Main powertrain components
- Fuel cell stack - PEFC (polymer electrolyte fuel cell) electrical generation device. Lightweight, compact, with a maximum output of 78kW.
- High-pressure hydrogen supply system - Equipped with two tanks. Can be filled with up to 156.6L of hydrogen at approximately 5,000 PSI (350 atmospheres).
- Air supply system - An air pump with a high-voltage electric drive motor supplies the FC stack with air at the appropriate pressure and flow rate.
- Humidification system - The recycled-water-recovery (fully independent) humidification system recycles water vapor generated in the FC stack for use in hydrogen and air humidification.
- Fuel cell cooling system - Equipped with one fuel cell system radiator (large) specially developed for use in fuel cell vehicles and two drive train radiators (small), for improved cooling performance.
- Honda ultra-capacitor - Delivers instantaneous high-output assist during startup and acceleration, while also efficiently recovering energy generated during braking.
- Combines high responsiveness with high efficiency.
- Powertrain - Composed of a drive motor, transmission, and drive shaft. The newly developed drive motor combines high efficiency with high output and torque (maximum output: 80 horsepower (60kW); maximum torque: 201 lb.-ft. (272Nm).
- PCU (power control unit) - Controls electrical systems, including FC stack output, capacitor output, drive motor output, air pump, and cooling pump.
Differences between a fuel cell vehicle and an EV (electric vehicle)
Fuel cell vehicles and EVs have two things in common: in both, electricity powers an electric motor to drive the vehicle, and output of CO2 and other harmful emissions is zero. But in terms of practicality, the difference between the two types of automobile is very significant.
An EV stores electricity in a battery, which once depleted must be recharged before the vehicle can be driven again. Considering recharging time and other limitations EVs are most effectively used for use within a predetermined area, such as commuting short distances to and from work. A fuel cell vehicle, on the other hand, employs a system using an onboard fuel cell stack to generate its own electricity, enabling it to travel comparatively long distances when fueled with a large volume of high-pressure hydrogen. Because fueling takes only three minutes, the fuel cell vehicle delivers convenience on par with that of a gasoline-powered car.
A vehicle with no CO2 or exhaust gas emissions: The fuel cell stack achieves the ultimate in clean performance
Electricity made from hydrogen and oxygen-the only emission is water
The FCX's fuel cell stack is a PEFC (polymer electrolyte fuel cell) electrical generation device that employs an electrochemical reaction between hydrogen and oxygen to directly convert chemical energy into electrical energy. This can be viewed as the reverse of the principle of electrolysis, in which an electrical current is used to separate water into hydrogen and oxygen. We have created a clean-running system that is capable of continuous electrical generation when supplied with hydrogen and oxygen, simultaneously generating electricity and water, with no CO2 or other harmful emissions whatsoever.
How electricity is generated
- When hydrogen is delivered to the hydrogen pole it is ionized by a catalytic reaction with the platinum electrode, emitting electrons. This produces a DC electrical current.
- After emitting the electrons, the hydrogen ions pass through an ion exchange membrane, where they bond with oxygen ions from oxygen delivered to the oxygen pole and the previously emitted electrons arriving via an external circuit.
- This reaction creates a DC electrical current, generating electricity. Water is generated at the oxygen pole as a byproduct.
- Because the ion exchange membrane must always be kept moist, both the hydrogen and the oxygen supplies need to be humidified. To accomplish this, the water vapor generated in the fuel cell stack is recycled, providing the water necessary for humidification.
- Structure of the fuel cell stack
- The ion exchange membrane is composed of an extremely thin polymer layer (PEM, or proton exchange membrane, which exchanges positive ions). This membrane is sandwiched between two electrodes (the hydrogen pole and the oxygen pole), which in turn are sandwiched between separators on each side to compose one cell.
- These cells are stacked, and when the electricity generated by each cell is combined, a large voltage is produced.
- The FCX employs a compact, lightweight fuel cell stack manufactured by Ballard Power Systems, which outputs 78kW of power. Honda is also conducting research on its own fuel cell stack.
A 5,000 PSI high-pressure hydrogen tank provides ample storage capacity resulting in a vehicle range of 160 miles*
Because the hydrogen used as fuel has a low energy density per volume, as much hydrogen as possible must be available to ensure a practical vehicle range. At the same time packaging considerations dictate that as little storage space as possible must be taken up by the fuel tanks.
The FCX utilizes a high-pressure hydrogen tank with a three-layer construction composed of an aluminum liner, carbon fiber, and glass fiber, for superior strength and corrosion resistance, to achieve a filling capacity of up to 5000 PSI. Two of these tanks are employed to secure a 3.75Kg fueling capacity. This large capacity plus improved fuel consumption results in a vehicle range of 160 miles*. Fueling time at a high-pressure fueling station is only three minutes, for a level of convenience comparable to that of a gasoline-powered vehicle.
*EPA - estimated vehicle range.
Honda's testing procedures have been officially adopted in the U.S. for measuring fuel consumption in fuel cell vehicles.
At Honda, we feel that a fuel cell car should not only be zero emissions/zero CO2 , but also energy-efficient. That's why, in addition to developing a fuel cell vehicle, we have also independently researched our own procedure for measuring fuel consumption. Since there was no standardized testing procedure for measuring fuel consumption in fuel cell vehicles as there is with gasoline-powered vehicles, we investigated a number of procedures and settled on the weight-based method-a measurement of the distance the vehicle can run on one kilogram of hydrogen-as being the most accurate. (Unit of measurement: miles/kg-H2) This method is not influenced by the temperature or pressure of the gas, there are no calculation measurement errors, and the measurement equipment itself is inexpensive, consisting of scales and piping. This weight-based method is now used by the American SAE (Society of Automotive Engineers). The method has also been certified by the US EPA (Environmental Protection Agency) and adopted as their official fuel consumption testing procedure. We also pursued a fuel consumption testing procedure for use with dual electric power sources, as with the combined fuel cell stack and capacitor.
Honda's own originally developed ultra-capacitor - output and efficiency surpassing that of batteries
More powerful drive assistance, more efficient energy recovery during braking
Honda has independently developed a new high-performance ultra-capacitor (electric dual layer capacitor) to serve as a supplementary power source to the FCX's main power source - the fuel cell stack-for more powerful performance under various driving conditions.
The new ultra-capacitor combines the electrical storage capacity needed for high output and high responsiveness with solid reliability. It stores the energy produced during deceleration and braking and provides powerful drive assist during startup, acceleration and at other times when an extra boost is required. The ultra-capacitor's internal resistance is lower than that of a battery, and moreover, because it stores and discharges electricity in response to voltage fluctuations in the fuel cell stack, it doesn't require a converter for voltage regulation as in a battery system, so it delivers higher output. The result is improved drive-power performance and higher system efficiency.
Outstanding charging and discharge functionality
In order to improve electrical storage capacity, a new high-performance activated-carbon electrode was used, and electrode wrapped-element construction employed to achieve high-density electrode packing right out to the case. This results in energy efficiency 7-10% higher than that of a nickel-hydride battery, the difference increasing with output. The capacitor achieves an energy density of 3.9Wh/kg (at a 2.7-1.35V discharge) and an output density of over 1,500W/kg. Its charging and discharge functionality is among the highest in the world for a capacitor.
(Values based on Honda in-house testing)
A combined fuel cell stack and ultra-capacitor deliver powerful, responsive performance and outstanding fuel efficiency
The fuel stack acts as the main electrical power source, aided by the powerful assist function of the ultra-capacitor during startup, acceleration, and other times when a large boost is required. In the low to mid speed ranges, the FCX delivers powerful, torquey acceleration response that can surpass that of a gasoline-powered vehicle. During deceleration, energy is recovered and stored in the ultra-capacitor. Electricity from the fuel cell stack is also stored there at this stage. And during idling, an auto idle stop system cuts the power to the motor to reduce fuel consumption.
Energy management is optimized by the PCU (Power Control Unit) for efficient power use and waste-energy recovery. As a result, the FCX achieves an energy efficiency of 45%-twice that of a gasoline-powered vehicle and 1.5 times that of a hybrid car. The FCX also attains fuel economy greater than that of a hybrid vehicle; another area in which it displays superb practical driving performance.
(Values based on Honda in-house testing)
Outstanding performance on startup and acceleration
The drive motor responds instantaneously to the driver's operation of the accelerator, providing the combined powerful output of the fuel cell stack and ultra-capacitor to make startup and acceleration nimble and torquey compared to gasoline-powered cars, hybrids, and electric vehicles. The result is off-the-line performance comparable to that of a high-performance mid-sized gasoline-powered vehicle.
Outstanding energy efficiency, high revs and high output make the newly developed drive motor faster off the line
Energy loss reduction technology and a heat-management design, for high efficiency over a wide range and expanded power band
The drive motor for the FCX is a further development and refinement of the high-performance technology Honda developed for the EV-Plus electric vehicle. First, reluctance torque combined with a low-loss magnetic circuit and full-range, full-digital vector control were applied to secure high efficiency over a broad output range, along with an expanded power band. Then heat generation in the rotor was also controlled to expand the power band in the high-rev range.
Rotor heat generation control technology
To respond to increased magnetic flux variations in the rotor due to reluctance torque, magnetic partitioning was employed to greatly suppress the occurrence of eddy currents. Newly developed high heat-resistant magnets and a magnetic circuit configuration appropriate for high output further achieved a high demagnetization suppression effect. The result is an expanded high-output range at high revs, and the securing of continuous-rated maximum output.
Noise-reduction measures in the powertrain enhance the fuel cell vehicle's already outstanding quietness
Powered by an electric motor, the fuel cell vehicle offers outstanding quietness, with none of the vibration or exhaust noises associated with the engine of a gasoline-powered car. In addition, the FCX further reduces intake noise and noise and vibration in the air pump, to achieve even quieter, more comfortable driving.
Powertrain noise-reduction measures
- Muffled resonator chamber and unitized intake module - A compact, module-type resonator chamber suppresses intake noise radiation over a broad frequency band.
- Double floating mounts - The air pump and the air pump motor are secured to the motor and transmission with rubber mounts, which in turn are secured to the sub-frame with rubber mounts as well, resulting in a two-stage reduction of air pump rotational vibration to the body.
A lightweight, compact motor and transmission with unitized construction-single-speed, fixed reduction ratio utilizes the motor's output characteristics to maximum effect
The simple, high-efficiency transmission transmits power to the differential through a two-stage reduction from main (primary) to counter (secondary) to final. Built for high revs and high output, the unit has also been made more lightweight and compact. This allows the FCX to offer distinctively smooth, powerful performance, while at the same time offering the packaging merit of permitting a large radiator to be installed, contributing to improved cooling performance.
Instruments with an advanced design for superb visibility and a firm grasp of energy management conditions
Energy management conditions are presented in an easy-to-understand display, showing variations in fuel stack output under different driving conditions, ultra-capacitor assist output and recharging status, and more. Along with the hydrogen fuel gauge, there is also a Distance to Empty gauge that indicates remaining vehicle range in response to fuel consumption. The lower center portion of the display includes odometer, tripmeter, and a multi-information display that can be changed to display various changes to vehicle status.