As assistant manager of product safety for a forkliftmanufacturer, I met with zone service managers at quarterly meetings. Although lines of communication already existed between engineering and the service department, these meetings gave useful exchanges of field problems straight from the guys in the trenches.
After I finished a brief talk on product improvements, a couple of the zone guys mentioned starter motor breakage on new trucks with relatively few hours of usage. The next day, division service engineers confirmed broken starter nose castings.
'Start' at the Beginning
The engine-powered forklift design lads had seen warranty reports, but had not made changes to any of the starter system components. Our plan: identify all the forklift models, engine types and starters, and ignition switches on forklifts with broken starters. Of the two starter types used, the first used a simple spring-loaded Bendix drive, while the other used a solenoid system to engage the starter pinion on the flywheel ring gear. The breakage occurred on the solenoid-type starters.
Several broken starters and ignition switches were brought to our lab for analysis. We found badly eroded contacts at the "Start" position in the switches. The switch supplier admitted to making a change to the contact material. Stuck contacts allowed the starter to run after engine start-up causing starter breakage. The supplier then provided heavy-duty, silver-cadmium oxide contacts on several samples that were quickly lab and field-tested. However, the anticipated improvement failed to materialize. My boss, the product safety manager, pressed for and initiated a new project to solve this mystery.
After more digging, our field service guys concluded the breakage occurred when drivers attempted to re-start an already running engine they couldn't hear because of high ambient noise levels. After brainstorming and lab tests, we prepared field kits using a relay energized by the alternator output. With the engine running, normally closed relay contacts interrupted the starter solenoid circuit, blocking an attempted re-start. This fix seemed to alleviate the problem on most forklifts. However, there were still some failures and our field people and dealers objected to the difficulty of connecting to existing truck wiring.
Switch It Up
Brainstorming between engineering and our switch supplier resulted in a mechanically interlocked ignition switch once the operator cranked the engine and released the key from the "start" to the "run" position, the keyswitch locked in the "run" position.
Re-starts were blocked unless the key was moved to the "off" position to reset the interlock. This assured the engine was stopped before (re) starting could be done. After lab tests, samples went into the field. Result? We eliminated the relay, the broken starter problems seemed to disappear, and all was well. Or was it?
While resolving the broken starter crisis, design engineering's heightened awareness led their chief engineer to mention that some forklifts could start in neutral. While he had no confirmation, I quickly sent a list of transmission neutral sensing switch part numbers to our division parts group. I received a spreadsheet showing replacement switch sales by part number and month over the past year. I saw an upward spike in switch sales over the past year for one particular part number. The neutral switch supplier admitted having made product "improvements." Our lab cut open some recent switches and some from old inventory. New units had inconsistent tolerances for a ball and spring actuator, and the internal contacts stayed closed allowing start-up when the transmission was in forward or reverse.
After speedy design revisions, new parts went to the field. A field campaign followed to change out all switches of this type. This experience led me to request a procedure to automatically report unusual parts movement to design engineering. Good interdepartmental cooperation let us put these problems behind us while we gained more reliable truck operation and avoided potential accidents.
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