Thursday, May 28, 2009

Windshield Wiper Assembly

As stated in the last entry, the wiper assembly for the Rally Fighter's was one of the components worked on with ATG out in California.

At first glance windshield wipers seem to be extremely simple with few moving parts, but this is a misconception. Beyond the technical workings of the wiper assemblies their are strict FMVSS (Federal Motor Vehicle Safety Standards) as set by the U.S. Department of Transportation.

The windshield wipers on a car use two mechanical parts to move.

First, there is a combination of an electric motor and a worm gear reduction
(shown below) which provides power to the wipers. This uses a standard electric motor which spins a worm gear. A worm gear reduction is used since it both reduces the speed of the motor and increases the torque by the same factor of about 45 . So when the wiper motor is spinning, the resulting speed after the worm gear is 45 times slower and the resulting torque 45 times greater. This high torque is necessary to move the wipers quickly and powerfully.

Second, their is a linkage (shown below) that converts the rotational output of the motor into the back-and-forth motion of the wipers. The linkage uses a cam attached to the worm gear reduction
(A cam is a mechanism that translates movement from circular to reciprocating or oscillating. An example is the camshaft of an automobile, which takes the rotational motion of the engine and translates it into the reciprocating motion necessary to operate the intake and exhaust valves of the cylinders.). As the motor and gearing spins, the cam operates a long arm by moving it back and fourth. This long arm is connected to two smaller arms which attach to the right and left wiper blades. This linkage pushes and pulls with the converted force to move the wiper blades along their path.



Check out this video of the Rally Fighter wiper assembly:




Tell us what you think!

2 comments:

pete said...

Mike, glad you brought up the wiper assy as an example of something most people would consider mundane and unexciting to work with design wise. I spent a good part of my career doing door latch design and while some may roll their eyes or laugh out loud, if that latch fails or performs poorly I can tell you for a fact that the personal, professional and financial repercussions are immense. Back in the day I sat near a good gent who was the Wiper Design Engineer on a past Chrysler product. I called him "Wiper Dude" and the name stuck to this day. He did a great job and just as an observer in meetings I learned a lot from him. Goes to show that when you put a production car on the road, there are so many assemblies and sub-assemblies that have to package and work and interact with many other systems that vehicle design and engineering is tough task. ...Good blog, Mike.

Mike Pisani said...

Pete,
Thanks as always for the comments and feedback. Unfortunately for me, I can't take the credit for this one since our intern, Alex made the post. I'm sure he's seen your comment already, but will be sure to pass along your comments if not!