Group 26 - Pressure Washer

Introduction

A requirement for MAE277, taught by Erich Devendorf, the Reverse Engineering Project is designed to help students familiarize themselves with the assembly of a product. Over the course of the semester, the students will work on five gates which will showcase the ongoing analysis of their products. This project will reinforce key skills that engineers utilize everyday.

Groups 25 and 26 were assigned a pressure washer. Rather than share entire product between two groups, the product was divided into two, with group 25 analyzing the compressor and with group 26 analyzing the engine.

Gate 1: Request for Proposal

This portion of the Reverse Engineering Project is designed to help the group become familiarized with the product, a pressure washer. A general work outline for the semester will be developed and will contain the following items: a work proposal, a management proposal, and an initial product assessment.

Work Proposal
Management Proposal
Initial Product Assessment

Gate 2: Preliminary Project Review

Causes for Corrective Action
Product Dissection Plan

Gate 3

Design Revisions

• A design revision that could prove to be useful is placing the pull starter for an electrical starter. A pull starter demands much more physical activity out of its users that could lead to fatigue and muscle strain. Users that are not physically fit may not be able to start the motor at all. The amount of activity needed is also dependent on the conditions of the motor - the less maintained the motor is, the more effort is needed to start the engine. The temperature of the unit is also a factor - the colder it is, the longer it will take to for the engine to start. Replacing the pull starter with an electrical starter would allow users to start the engine without much hassle.

Using this revision would increase the cost of the pressure washer; it would, however, improve the usability of the product.

• Another design revision that would be useful is encasing the the engine in a hard plastic similar to a car engine. Since the pressure washer deals primarily with water and chemicals, rust is constantly a problem. Encasing the engine in plastic would prevent water from entering the engine, prolonging the life of the product.

Using this revision would increase the cost of the pressure washer slightly; since it would prevent rust from forming in the engine, its reliability would improve and its maintenance would decrease.

• A third revision that would be beneficial to its users would be a self-propulsion system. The product is heavy, making it unwieldy for many to move around efficiently. Using a self-propulsion system would allow users to move the washer easily and effortlessly.

Using this revision would increase the cost of the product; its usability would increase greatly, as would its functionality.

Solid Modeled Assembly

For our modeling we chose the main components of the intake/outlet valves which includes the valve itself (A), a spring (B), a push rod (C), a threaded rod (D), a connecting plate (E), an a pair of plates to secure the spring (F). We chose these components because, as a subsystem, they show quite well how a few relatively minor and simple pieces can perform a vital function well.

The CAD package we used was Autodesk Inventor. Inventor is a powerful and fairly easy to understand package, with the added benefit of having a full version trial available for students.

Top View of Valve

Front View of Valve

Side View of Valve

Engineering Analysis

During the analysis of the engine the many parts made it difficult to choose which to use. After the analysis problem, the key component of the engine that would require a lot of analysis is the Piston and Cylinder of the engine. There are many important parts that require discussion about the chosen design and testing that would need to be done to make this part work efficiently.

As an engine runs the piston moves up and down the cylinder constantly driving the camshaft and converting chemical energy into usable mechanical energy. As the gas expands in the chamber a large amount of pressure is exerted onto the piston forcing it down. Despite this large pressure none of the gas leaks around the sides of the piston thanks to the piston rings. Because of the sizable force pushing the piston down the piston rings must fit tightly against the sides of the cylinder. This tight fit causes friction along the sides of the cylinder. This is a place where some of the largest energy loss occurs.

The equation for friction ( Ff=μ*Fn ) shows that the force of the piston pushing into the wall (Fn) greatly affects the amount of friction. One way to test Fn is to measure the force needed to pull the piston out of the cylinder. Once you find the force of movement using the equation F=ma it is possible to solve and find Ff (friction force). After this data tables readily supply the coefficient of friction (μ) and it is simple to solve for Fn. As can be seen a large amount of force can be lost from the system due to friction.

Two ways in which to decrease the Ff are usually the easiest to pursue. The most obvious is to decrease the coefficient of friction by changing the material or adding oil into the system. The other way to decrease Ff is to change the Fn which can be done by decreasing the pressure of the piston rings.

The point of these tests is to bring the efficiency of the engine closer to that of a perfect engine that does not lose energy due to friction.