Working for a major lift truck manufacturer, I got a job assignment that a young engineer usually only dreams about. While our staff hustled to prepare new forklift models to be introduced at a dealer show, our company finalized purchase of a manufacturer of engine-powered golf cars and an in-development electric car. My new task included development of controls, cabling and wiring for the new electric golf car.
Dropping everything, I traveled to GE's semiconductor division at Auburn, NY for a briefing on a compact solid-state dc motor control for the new golf car. As an EE with power semiconductor experience, I relished this task. I met engineers I admired such as Bill Gutzwiler and Neville Mapham.
I then traveled to the newly-acquired golf car plant. With dawn-to-dusk efforts, the cars were made ready for the big show. There, the new forklifts were well received, but the golf cars and utility vehicles were such big hits that a forklift dealer who owned a well-appointed New Jersey golf course ordered a small fleet of electric golf cars.
Scene of the Crime
Since production tooling was not ready, ten cars were hand-built to meet this order. The course owner reported quiet, smooth, efficient operation, and all seemed good in life. Within two weeks, this happy state was rudely cut short when that same dealer/golf course owner reported a disastrous brake failure on a new golf car.
We learned that an "Outfit" Capo playing the front nine made his shot over a hill to the edge of a water hazard. He descended the hill in his golf car while his bodyguards followed in another car. The brakes didn't seem to slow the car's dash down the hill right into the water hazard up to the seat cushions. While the chieftain was in water up to his derriere, his growls and threats involving kneecaps and other body parts left the golf course owner up to his tail in alligators.
The Investigation
Because of a potential product liability problem on this new product, my boss, the Chief of Development Engineering, and I rushed to the golf course to solve the mystery. There, we inspected the dried out, cleaned up car. The brake pedal, linkage and brake operation were OK. With my boss riding shotgun, I drove to the hill and down toward the water hazard. Pressing the brake pedal gave only intermittent and anemic braking. Already alert to a possible problem, I gently steered to approach the water's edge at a tangent. On level ground the brakes brought us to a stop. The tire tracks did not reveal any signs that the brakes ever locked up. We had the car towed back to the maintenance shed for a closer look.
The brake pedal and linkage again checked OK. The single disc brake acted on the pinion shaft, and was correctly adjusted with no oil or other materials on it. After pondering what failure mode caused loss of brakes on the hill, my boss and I concluded that the brake locked up the ring and pinion while the differential gears let the wheels turn. Since neither wheel had locked up, we suspected a broken axle or damaged differential. Pulling the rear wheels and hubs, we found the driver's side axle-hub key had sheared.
The Smoking Gun
We surmised that friction between the hub and axle allowed us to drive and stop on level ground. However, stopping on the hill required increased brake torque. With the pinion held stationary, the differential gears allowed the wheel with the good key to turn normally while the axle with the sheared key intermittently held or spun backwards inside the left hub, resulting in poor to no braking. We suspected the key had sheared just prior to, or during the "good fella's" critical descent.
Once home, we reported that the single brake system was not safe, and management stopped sales of the electric vehicles. Only 15 electric units had been built and all were recalled. Once converted to a drive axle with brakes at each wheel, similar to the engine-powered units, sales resumed. There were no further brake problems. Oh, and what of the "outfit" chieftain? A free course membership and his choice of new golf clubs from the pro shop calmed his rage quite well.
To view a diagram of the cart's powertrain, go to http://rbi.ims.ca/4911-510.
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