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Data recorders store information about your car's speed, working much in the same way as an airplane's 'black box.' (Hemera Technologies/Getty Images)
Data recorders store information about your car's speed, working much in the same way as an airplane's 'black box.' (Hemera Technologies/Getty Images)

You & Your Car

Cars equipped with 'black boxes' Add to ...

QUESTION: I read the other day about the police using data from an engine control computer to prove an individual was speeding before a crash. Big Brother is living among us! How does this work?

Michael

ANSWER: With the advent of emission regulations, vehicles were required to operate for up to 100,000 miles with no need for service, adjusting or "tuning" themselves thanks to sophisticated electronics throughout that period. These systems involve On Board Diagnostics - the ability to store information so when a problem develops, a technician can plug in and download or read various codes.

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With each of these codes lies information about the engine and vehicle speed. Here again we can thank regulations. Most vehicles have speed limiters based on the tires that came from the factory. Tires are rated for their maximum allowable, sustained speed. If the driver attempts to exceed this speed the computer will reduce fuel flow or cut ignition to one or more cylinders. This creates erratic sensor reading and generates a code which can be read later.

Some vehicles also have data recorders built into the airbag system - think of them like the "black box" referred to in airplane crashes. They can store information about conditions at and even slightly before the moment of airbag deployment - everything from speed and whether to belts were being used to steering angle and whether or not the brakes were applied. This data is not available to technicians, only to the manufacturer.

Other systems are available in the aftermarket to allow parents to monitor the driving behaviour of their children - or fleet owners to see what their drivers are doing.

 

MORE ON IDLING

QUESTION: I would like to follow up on your recent column regarding the car idling. I understand that a car that is idling consumes gas and generates emission. But frequent shutdown/ignition would damage the engine and the ignition set, too, right? I also have the impression (I read it somewhere) that a car uses more gas, relative to idling, during the ignition phase. Please correct me if I am wrong.

Hence I think it is a trade-off between protecting engine and saving a little gas (maybe environment). What do you think is the tipping point, i.e. what is maximum/optimal number of minutes under which you would recommend idling, and over which it is better to shut off the engine?

Harry

ANSWER: This is another of those areas where modern electronics come into play.

In the old days when there was a distributor, points and carburetors, starting an engine did indeed involve a richer mixture - thus more fuel used - and quite a bit of cranking to bring things to life. Modern engines have individual precise high-pressure injectors at each cylinder and sensors at various points throughout the engine reporting on everything from temperature to the point in the compression-ignition-exhaust-intake cycle of each cylinder. The result is the ability to restart the engine within a half-turn of the crankshaft with exactly the right amount of fuel and a strong spark to ensure ignition.

These vehicles are also commonly hybrids and utilize the powerful electric motor as a starter. There is no engine damage and with no fuel consumed - no emissions and improved mileage.

Mazda engineers have developed a system that uses the energy created during the cycle to help restart the engine bringing start-stop savings to non-hybrid vehicles. It uses the "kickback" characteristics that made hand-cranking engines so dangerous before the starter was developed.

Electronics ensure all pistons in a four-cylinder engine stop exactly half-way between the top and bottom of their stroke. The electronic message to start the engine results in the injection of a tiny amount of fuel into one cylinder. It is then ignited, pushing that piston down, rotating the engine slightly "backward" and the other cylinders into compression. At this precise moment, the normal ignition and injection systems come into play, starting the engine without the need for a starter.

I've driven a vehicle equipped with this system and the restart is virtually seamless, quicker than that of a hybrid start-stop system. We haven't see it here yet because the advantages do not show within the narrow confines of the laboratory testing used to generate mileage and emission numbers. In other words the advantages in real life are not evident in the lab. We will see this and other start-stop system grow in use as standards tighten.

Do I recommend you do this with your conventional engine? Only when stopping for more than 30 seconds - not at a traffic light or in other situations where a failure to start would create safety issues.

 

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