Accent on Power Management
A small British company plays a key role in the development of GM’s hybrid pickup.
Depending on who you talk to, a “quiet revolution” is slowly seeping through the car industry.
It could be a false dawn — but most observers believe that the hybrid is here to stay. Although the concept of a hybrid is brand new, eyebrows were raised when Toyota’s gasoline-electric hybrid Prius was voted 2005 car of the in Europe on top of a similar award in the U.S. earlier in 2004.
That prompted some industry experts to suggest modestly that the hybrid breakthrough is poised to forever change the way the world’s automotive sector operates.
And the concept is relatively simple. A hybrid car draws power from energy sources using a combination of a regular internal combustion engine and an electric motor.
|GM’s hybrid pickup has the performance of its conventionally powered counterpart, with the added benefits of reduced fuel consumption and an on-board AC power source. |
The motor’s battery is recharged by electric generator powered by a gasoline engine. As the gasoline engine at optimal speed it devours fuel in a more efficient way than normal gasoline engines. Extra power to the battery comes from kinetic energy from the wheels when the vehicles slow the gasoline engine provides extra power the car when required.
The Prius success helped Toyota to be recognized as one of the front-runners in hybrid technology and, in many cases, left rival makers struggling to match their pace. Naturally environmental benefits of such a power arrangement found favor among drivers keen to minimize the impact on the planet caused by cars and their emissions.
Toyota says the Prius has 89 percent less smog-free emissions than an average new car already meets European Union guidelines the year 2012. The maker adds the car could more than a ton of CO2 emissions entering the environment each year, again compared to the standard new car.
Not surprising then that hybrid car drivers began reporting a curious sense of “guilt-free” motoring and the endorsement of Hollywood actors keen to be linked to such a relatively planet-friendly technology fueled the attraction of both the Prius in particular and hybrid technology in general.
But as the global automotive giants scramble to top the hybdrid technology tree, a relatively small British company is at the forefront in this sector.
Zytek, founded a little over 20 years ago and based in brand new headquarters in Fradley, Staffordshire, England, has developed a strong reputation within the industry for electronic control systems, high-performance engines, concept electric vehicles and has worked alongside Jaguar, including the car’s victory at the Le Mans 24-hour race in France, and has supplied Aston Martin, Rolls-Royce and Bentley.
But its most recent claim to fame is helping General Motors to deliver what is thought to be the world’s first commercial hybrid-electric truck. It’s quite a coup for the 200-plus employees of Zytek which, three years ago, became almost one-fifth owned by global communications group Motorola.
Zytek’s involvement with the GM Hybrid Pickup began at the project’s inception, with the company asked to conduct a control systems architecture study to identify the best way to manage GM’s advanced hardware design. The challenge to Zytek was to deliver the environmental benefits of a hybrid configuration while retaining all of the existing vehicle performance and driveability characteristics, including towing capability demanded by U.S. consumers.
After successfully completing the study, GM’s hybrid engineering team elected to continue working with Zytek on the complete control systems development and integration process that would ultimately deliver a vehicle to the marketplace.
|GM worked with control system and electric vehicle specialist Zytek to produce a hybrid architecture that is safe, efficient and goes almost unnoticed by the user.|
Zytek’s engineering team worked with GM to help its engineers implement the necessary changes to the base engine and transmission control system (PCM), including the definition and application of hybrid control algorithms to maximize the effective use of the electric machine and energy storage capability.
The GM Hybrid Pickup, available in the extended cab versions of the 2004 Chevrolet Silverado and GMC Sierra, is a “mild” hybrid design using a comparatively small electric machine — a 14kW ISAD (Integrated Starter- Alternator-Damper) from Continental and GM’s Vortec 5300 5.3L V-8 engine.
The hybrid’s energy storage pack and battery management electronics are stored beneath the vehicle’s rear bench seat. The GM Hybrid Pickup achieves fuel savings of 12 percent in normal use with emissions performance equivalent to the high standards set by the original vehicle.
Fuel savings come from three principal areas. The highly developed stop/start capability of the hybrid configuration permits the engine to be shut off entirely when the vehicle is at slow speeds or stationary; the fuel supply is also shut off in a wider operating envelope of vehicle deceleration with closed throttle, while EM-applied torque during engine braking recharges the batteries.
Further fuel economy is gained by sophisticated control of the conventional automatic transmission including maximizing the efficiency gains of a locked-up torque converter. For Zytek, a major challenge was ensuring that, with all the extra complexity in the drivetrain hardware and controls, the hybrid truck still drove like its conventionally powered counterpart.
For the user, the only indication that they are driving a hybrid vehicle is the zero RPM indicated on the instrument pack along with silence when the engine stops as the truck becomes stationary.
“We needed to be very careful that the vehicle didn’t recover too much energy during coast,” explains Neil Heslington, projects director at Zytek. “U.S. drivers won’t accept pronounced engine braking.”
In operation, the hybrid functionality is controlled by the Zytek-designed Hybrid Control Module (HCM). This evaluates the vehicle’s state and issues instructions to both the Powertrain Control Module (PCM) which controls the gasoline engine and transmission, and Continental’s Starter-Generator Control Module (SGCM ) which controls the ISAD and power conversion tasks.
Battery management is handled by the Energy Storage Control Module, (ESCM) also from Continental, which communicates the state-of-charge and effective state-of-health of the battery bank.
“Control system integration is vital in a successful hybrid implementation,” says Heslington. “The complex control solution needed to cover all possible usage scenarios required considerable technical effort. Energy management strategies that work effectively in all environmental conditions along with transparent driver interfaces take some developing — for example, lead acid batteries don’t always accept the desired levels of power, so systems have to work to create the optimum conditions.
“Also engine start, for example, occurs when the driver begins to lift their foot from the brake, before they touch the throttle.” The power and flexibility of the ISAD was used by GM with Zytek’s help to overcome many of the driveability and NVH issues associated with the hybrid powertrain.
Inevitably, operation of a hybrid vehicle involves many additional driveline torque reversals as the electric machine switches from motoring to generating as the vehicle acceleration changes.
The ISAD and the internal combustion engine were used intelligently during these reversals to improve the overall smoothness of the powertrain system.
The potential to generate extra electrical power offered by the electric motor used in the hybrid is put to good use elsewhere on the vehicle. In addition to the normal 12V electrical system, the 42V energy storage system supports an electro-hydraulic power steering pump and an inverter providing power for four 120V AC power points — two in the cab and two in the truck bed — which allow the user to run power tools or domestic appliances directly from the truck while in the field.
Zytek’s experience with hybrid transmission systems goes back to the mid-1990s. It engineered the revolutionary Panoz Q9 hybrid electric racing car, which campaigned successfully in the U.S. during 1998 and has built some of the world’s most efficient full-electric vehicle transmissions.
As well as Toyota and GM, manufacturers globally are increasing their focus on hybrid vehicles including Nissan and Ford who have introduced the Ford Escape Hybrid — which it says is the first vehicle to combine SUV capability with the fuel economy and low environmental impact of a full hybrid.
To further its commitment in the field Ford has formed a Sustainable Mobility and Hybrid Vehicles program group to focus on developing all Ford Motor Company hybrids and related technology in-house.
“As the hybrid market continues to grow and evolve, we will be well positioned to drive the market and fulfill our promise to help create a better world.” the company says.
While the jury remains undecided on whether the bullish optimism that hybrids will change the motoring world forever, there is no doubt that the technology is finding favor among environmentally conscious drivers and clearly focussing the attention of the world’s automakers.