Excellent articlke by Alex Lidow (CEO) in the planet analog section of EETimes (6/17/2002). Unfortunately the tables cannot be cut and pasted, so I included the URL.
In brief he discusses how increasing the current use of power semis/motion motion control in automobiles can improve gas mileage (and emissions) by about 2/3.
planetanalog.com
29 June 2002
Motion control technology jumps into the driver's seat
By Alex Lidow, CEO, International Rectifier Corporation, El Segundo, Calif.
Planet Analog
June 26, 2002 (3:33 p.m. EST)
As the electronics industry and automakers develop the vehicles of the future, they must navigate through a winding road of requirements, constraints, needs, and wants. Consumers and industry alike need better fuel economy to meet European and US mandates, reduce their government's dependence on foreign imports, and improve company operating costs. Carbon emissions need to be drastically reduced to save the planet for the next generation and meet world standards. We all would jump at an opportunity to vastly improve vehicle safety, eliminating over 50,000 deaths per year in the US alone by using readily available technology. Many of us would like to improve our driving experience so that our car rides like a Rolls Royce and handles like a Ferrari at the same time. The technology to make this happen exists today; however, there is one overriding constraint that causes the high performance, fuel efficient vehicle of tomorrow to stall -- cost.
A review of today's CAFE standard mid-sized car with a turbo-charged engine achieving 27.5 MPG best illustrates the opportunities within the industry's grasp. Radical changes can be made throughout our example car's current systems to deliver a vastly improved vehicle through the application of readily available variable speed motion control. Today's automotive subsystems - acceleration, engine cooling, steering and passenger comfort - use a half-dozen belts attached a central drive shaft. The key to greater control, comfort and efficiency is to partition these subsystems with separate motors and their own electronic controls.
Today's cooling system, for example, consists of a fan and a water pump. It offers poor control of temperature and a constant drag on the engine. That drag is equal to the maximum cooling requirement. But once a variable speed fan and cooling pump drives are introduced, that drag on the engine can be removed. The system can cool only as needed; not only maintaining better temperature control, but also delivering improved fuel economy and emissions. The fan belt also is eliminated along with its associated maintenance and warranty costs.
Figure 1. Today's Typical Automobile Engine.
The turbo charger, similarly, can be replaced by an electric turbo charger that produces optimum manifold pressure at any engine RPM. This allows a further reduction in engine displacement, which in turn reduces fuel consumption and emissions in an even greater proportion. Eliminating the annoying “turbo-lag” also enhances the driving experience.
Another improvement is offered in the air conditioner compressor. It can be sized to cool the car at idle speed. Oversized compressors suck energy from the engine at all RPM. By borrowing from the lessons household air conditioner manufacturers already have learned, system energy demands can be reduced by 60-70 percent using a variable speed compressor. Again, another belt is eliminated.
Changes to the car's starter and alternator offer a significant up side. The current “dumb” diode-driven alternator is a very inefficient way to generate electricity for a car with an increasing number of gadgets, safety features, and electronic loads. By combining the generator and starter into one motor - and relocating it between the transmission and engine - more electricity can be generated at twice the efficiency. With this new starter-alternator, previously untapped energy from braking and coasting can be recovered offering the added benefit of reducing brake wear. In fact, the electric motor can be used to inject torque thus allowing a mileage-tuned internal combustion engine to work less, consuming less fuel. In addition, the heavy flywheel and a few gears in the transmission have been eliminated and a “start-stop” capability can be implemented to eradicate waste while idling. All belts are now gone.
Figure 2. Automobile Engine of Future (without belts).
Inside the valve covers, timing chains and cams are performance limiters that can be eliminated if electric valves are utilized. These new valves can be operated with the most efficient timing for all performance and temperature conditions while greatly reducing carbon emissions. With these enhancements, the motor is smaller, weighs less, and has fewer moving parts with much less friction.
Further improvements can be achieved to other systems beyond the engine compartment. Electronic fly-by-wire brakes are a reality in many vehicles. They save weight, and, if coupled with acceleration sensors, can provide an extremely responsive and linear braking which improves the driving experience as well as safety. Electronic suspension allows shock absorbers to be replaced with electronic actuators that dynamically compensate for the bumps and eliminate dangerous rollover conditions combining the handling experience found in leading sports cars with the smooth ride conditions of today's best luxury vehicles. Finally, the installation of electronic power steering (EPS) eliminates a hydraulic pump sized for worst-case conditions and creating constant drag on the engine and removes its belt. EPS only uses energy when steering and therefore saves fuel while allowing for an improved steering feel.
Figure 3. Variable Speed Motor Control Applications In an Automobile Chassis.
These improvements yield a 70% reduction in fuel consumption with an even greater improvement in emissions. They also affect some significant breakthroughs in safety, maintenance costs, and driving experience.
Table 1: Potential Fuel Savings Using Variable Speed Motor Drive Control.
The Economics
In order to make these improvements a reality in the next decade, the electronics and automotive industries must work together to integrate motion control technology without significantly adding to the price tag of tomorrow's car.
Variable speed motion has undergone radical improvements over the past few years making it more affordable that ever before; however, the vast majority of motors installed today do not have electronic controls because of historic cost barriers. These barriers can be overcome by smart re-designs that require less labor and few materials while improving the performance and reliability of the system being replaced.
Let's look at an example of an electronic power steering system. A typical electronic power steering system uses a 1.5 kW peak output variable speed motor drive. Similar motor drive topology can be used in several automotive applications. The system consists of five sub-elements, or “layers” -- digital, analog, power, thermal management, and motor. It costs $106.30.
Figure 4. Today's Variable Speed Motor Controller.
The digital layer consists of a DSP or micro controller, a few memory chips, and some interface logic. All of these functions can be integrated easily onto a monolithic ASIC. Inside this ASIC, motion control software can be embedded that enables some significant additional cost savings. Resonant control reduces the EMI and reduces the need for capacitors in the power circuit. Sensorless space-vector control eliminates need for costly position sensors.
The second layer is the analog board. Here, current sensors can be eliminated by integrating them with the MOSFETs in the power section. In addition, gate drive function can be integrated and, by wave shaping the gate drive, EMI and the required cost to remove EMI can be further reduced. Load dump protection can be eliminated by using the analog control IC to turn on the power section when a load dump is sensed. Both the analog and digital boards can be powered by a monolithic power supply IC, an advancement first pioneered for and widely used in the telecom industry.
With the improvements to the control component circuitry on the analog and digital boards, various power discrete components and ICs now can be combined onto one PC board to shrink footprint requirements and reduce assembly costs.
At the power stage, the MOSFET transistors can be improved significantly. History has shown that a 30% per year reduction in Rds(on) can be sustained by applying leading edge technology. An example is a state-of-the-art sub-micron FET with a fully self-aligned structure recently introduced to address Pentium 4 and Itanium server requirements.
To improve the power section in the assembly, the reverse battery protection relay can be replaced with a simple MOSFET. Next, the size and reliability costs of the electrolytic capacitors can be reduced by improving temperature capability to 125 degrees C. Further reductions in the size and cost of the MOSFETs can be accomplished by moving to a higher voltage system. The need for EMI filtering can be virtually eliminated by applying a technology developed for the appliance motor control market - active EMI . This requires one high speed analog IC and two MOSFETs.
Figures 5. MOSFETs provide power and control.
At the thermal management layer, power semiconductors and heat sink may be downsized by using phase-change heat sinks that can absorb transient peak loads for tens of seconds.
Lastly, the cost of the largest offender can be greatly reduced -- the motor. With more sophisticated control capability and software, less efficient motors typically selected such as DC-brushless motors can be replaced by converter-fed motors like the switched-reluctance motor. These motors are smaller, cost less, have fewer parts, are more reliable, and offer improved efficiency.
When combined with expected learning curve and volume efficiencies, these improvements yield a 60% reduction in the cost of the assembly.
Figures 6. Cost-Reduced Variable Speed Motor Controller vs. Today's Variable Speed Motor Controller.
With savings such as these, there is an economic impetus for manufacturers to consider the adoption of variable speed motion especially if that cost can be slashed by as much as an additional 60% through a variety of systematic improvements -- most of which are tried and tested in other electronic applications. The potential cost reduction opportunities are presented in Table 2.
Table 2: Potential cost-savings with motor drive control.
A high performance, fuel-efficient vehicle is within the industry's reach through the adoption of variable speed motion. Historical cost barriers are being shattered as the electronics industry teams with automotive suppliers to apply the lessons that have brought consumers highly efficient air conditioners, refrigerators, and washing machines.
The key to mass adoption of this promising technology lies in the use of a “whole-system” approach to motor control systems, where power semiconductors, thermo-mechanical systems, software and packaging are developed in unison to deliver solutions that are superior to their predecessors in economics as well as performance. |
