Issue 150 January 2003
Going Mobile

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Start • Life in the Slow Lane • Frame Up • Chips and Dips • Sources and PDF

I recently got a chance to peek under the hood of an advanced concept car. No, it wasn’t the souped-up, candy-apple hot rod you might find at a car show. And with a top speed of barely 80 mph, this four-door econo-box, like most of its ilk, can barely keep up with traffic.

There is one difference worth noting. Stick your nose next to the tailpipe, and you won’t smell a thing. But, do bring a hanky, because what goes into the tank of this otherwise mild-mannered Ford Focus is hydrogen, and what comes out of the tailpipe is water (see Photo 1). More than a century after the phenomenon was first described, fuel cells are poised to hit the road.

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Photo 1—Drive me to the moon? The fuel cells that powered the Apollo space program are coming to a road near you.

I had a chance to ask the Ford representative a few questions. Why does it have a radiator? Because lots of heat is generated as a byproduct of the fuel cell electrochemical reaction, not to mention the drivetrain including the 100-kW (315 V at 330 A) inverter and 65-kW (87 hp) AC induction motor. What about that 5000-psi hydrogen tank in the trunk? Arguably safer than a gas tank and indeed even 10,000 psi (thereby increasing range) appears feasible. [1] When do they go on sale? Surprisingly soon, at least for fleet or corporate buyers that can arrange for their own source of hydrogen.

For the rest of us, there is the small matter of waiting for infrastructure (i.e., hydrogen gas stations or maybe even six-packs down at the grocery store). There’s also the fact that although there’s plenty of hydrogen around and about, energy—from somewhere—must be expended to extract it.

No, the migration to fuel cell vehicles—not to mention a greater hydrogen economy—won’t happen overnight, but I think it’s only a matter of when, not if.

LITTLE INEXPENSIVE NETWORK

Whatever kind of motor is under the hood, the trend toward making cars smarter in all ways continues at a tremendous pace. I’ve covered the topic of so-called in-vehicle networks (IVNs) before (Circuit Cellar 118 and 119). You’ll recall that relatively sophisticated networks (e.g., CAN, J1850, and fancier ones on the horizon) have been adopted to act as the backbone that interconnects major subsystems such as the engine, transmission, emissions control, and diagnostic equipment (see Figure 1).

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Figure 1—With J1850 and CAN first off the line, the in-vehicle network (IVN) race is just getting started. IVNs offer digital cables as an alternative to bulky analog wires.

The fundamental premise of IVNs—replacing bulky and balky analog wiring harnesses with a few digital cables—has taken off with a vengeance. The automakers took the IVN bet, and now they want to raise the ante.

Why stop with just the engine, transmission, and so on? I know from firsthand experience that my otherwise thoroughly modern J1850-networked ’99 still has plenty of wires running hither and yon. There’s a bundle at least an inch thick just to connect the door. That’s no surprise given the myriad of switches, relays, lights, and motors that handle the windows, locks, and mirrors.

Why not just use the existing backbone J1850 or CAN bus to network the door, replacing the point-to-point analog wiring? That sounds simple enough, but in practice there are a couple of problems.

First, having never met an MCU they didn’t like, car designers are already in a network traffic jam. There’s a lot of time-sensitive traffic and not much spare bandwidth to go around. Consider a network of PCs using Ethernet. Would it make sense to run every mouse and keyboard over the network? Neither does it make sense to hang every switch, light, relay, and motor on the primary CAN or J1850 bus.

Furthermore, big-ticket IVNs are overkill for something as simple as detecting a switch closure or activating a relay. The cost and performance of the networking hardware and software vastly exceeds that which is justified by the actual work involved, as it would for an Ethernet keyboard or mouse.

What’s needed for cars is a subnetwork that offloads the main IVN and costs less to boot. Enter LIN, which stands for local interconnect network, but might as well stand for "little inexpensive network."

Founded by Motorola and a group of car manufacturers including Audi, BMW, DaimlerChrysler, Volkswagen, and Volvo, the LIN consortium has established a standard that’s freely available and well on its way to production. And although targeting the automotive biz, I think it’s likely that LIN will migrate into non-automotive applications as well. Let’s take a closer look, and you’ll see what I mean.