How to Save Gas with Start/Stop Technology

DETROIT, Jan. 11, 2011 /PRNewswire/ -- How much fuel is wasted at red lights? Or while you're trapped in gridlock during your daily commute? The National Highway Traffic Safety Administration (NHTSA) estimates Americans waste about 3 billion gallons of fuel each year stuck in traffic, which amounts to billions upon billions of consumer dollars. How can we stop wasting gas and start saving money? We'll tell you how start/stop technology is one way to do just that.

As automakers race to meet increased fuel economy requirements, many are looking at start/stop systems to meet their needs. Right now, the technology can help improve fuel efficiency by approximately 3 to 5 percent. And, DENSO has future start/stop system technology that will bump that up to over 7 percent. When it comes to saving fuel, every percent counts.

How Start/Stop Systems Work

Start/stop systems stop the engine when the vehicle is idling at a stop light or in other traffic situations. This helps reduce fuel consumption and CO2 emissions. In North America, these systems are expected to proliferate the market as fuel economy regulations become more stringent. You'll see these vehicles on U.S. roads in the 2012-2013 timeframe. And you'll know it when you drive one or even when you pull up next to one at a stop.

Systems Implication

When you cut the engine in different traffic situations, imagine the implications to the engine, the starter and other under-the-hood components. Will the driver be able to quickly restart and accelerate the vehicle? Oh – and how do the air-conditioning (A/C) or heater continue to run? If the engine isn't powering these components, what is? How does it all work?

Seamless Integration

DENSO's been developing start/stop components since the 1980s. This experience, paired with the company's in-depth knowledge of powertrain and thermal management systems gives it a unique advantage to provide automakers with an overall systems approach. Meaning, DENSO understands how to seamlessly integrate start/stop components into the vehicle and can offer superior technical support that comes from decades of integration experience. Also, DENSO can offer automakers different technology solutions depending upon their specific needs and requirements.

DENSO's Start/Stop Technology Approach

DENSO has a three-level system approach to start/stop technology:

Level 1: Basic Start/Stop Technology: The Engine Stops After the Vehicle Stops

In this level, which we have already implemented in Europe, the focus is the starter technology. The Advanced Engagement (AE) Starter helps automakers achieve approximately 3 -5 percent in fuel savings. Also, it uses existing, proven technology and also allows for easy packaging for the customer.

Level 2: The Engine Stops Before the Vehicle Stops

When the engine is cut prior to the vehicle fully stopping, this "coasting time without fuel usage" bumps the overall fuel-savings potential to over 4 percent, but it requires a unique starting system that is able to restart the engine before it reaches zero rpm. That means it doesn't need to wait for the engine to completely drop from idle speed to zero rpm, like the AE starter. With a traditional starter or even longer life starter like AE, the engine rpm must be at zero in order for the starter motor to engage to restart the engine. If not, the starter and ring gear could be damaged if the engagement took place while the engine was moving.

Why is it important to have a starter that can restart the engine before reaching zero rpm? Well, most engines shut off in about a half second. But if a light changes green fast or another situation demands the immediate ability to move and accelerate the car, then waiting a half second could be a consumer annoyance.

DENSO has developed two different starters that have the capability of restarting before zero rpm. Our Tandem Solenoid Starter (TS) and Permanently Engaged Starter (PE) provide customers with two unique solutions for this problem. The starters represent two different packaging options for automakers, as well. The PE starter has been in production since 2008, and the TS starter is scheduled to go into production later this year.

Level 3: Premium System: Electrical Regeneration

Above and beyond DENSO's Level 2 system, additional gains need to come from changing the electrical system to one that is more tailored to the repeated on/off cycling of a start/stop system. To have a more efficient system a more efficient power source is needed. By supplementing the standard lead-acid battery and switching to a more efficient power source to handle the lead-acid battery's inefficient modes, we estimate this start/stop system to achieve an additional 3 percent in fuel savings, with a total potential of over 7 percent.

DENSO is now offering this system to customers as a way to effectively double the fuel savings of the basic start/stop system.

DENSO Systems Approach

An integrated start/stop system approach is more than just starter technology. There are many other products and components that can be added at any level to improve comfort and convenience (air conditioning) and powertrain performance. Many of these products better manage energy in a vehicle, which translates into fuel efficiency. Some of these products include:

Cold storage - What happens to the A/C when the car is stopped? DENSO's cold storage system will help maintain a vehicle's temperature when a vehicle with start/stop is at a stop and the air conditioning system no longer operates. The system stores a cooled substance and uses it while the engine is stopped to ensure the A/C is maintained.  

Electric Water Pump – DENSO's brushless electric water pump will help maintain a vehicle's temperature when a vehicle with start/stop is at a stop and the heater is on.

Consumer Acceptance

So is this something the U.S. driver is going to embrace or accept? Technology and execution is critical and that's where DENSO's products and experience can help make start/stop a success in the North American market.

Note: This executive perspective release was contributed by Doug Patton, Senior Vice President of Engineering at DENSO International America, Inc. Located at DENSO's North American headquarters in Southfield, Mich., Patton is responsible for overseeing operation of development facilities, testing and technical services, engineering administration and the company's product engineering.  

SOURCE DENSO International America, Inc.