Steering System

STEERING SYSTEM

Positioning of rack and pinion

1. Placing behind the wheel center
2. Placing ahead of the wheel center

Previously we have planned to place the rack and pinion behind wheel center but then it was not leading to a favorable Ackerman percentage.

So, we have decided to place it ahead of the wheel center and was also successful in obtaining a good Ackerman percentage.

EFFECTS OF PLACING RACK AHEAD OF THE WHEEL CENTER

• The Advantage of placing rack and pinion ahead of the wheel center is that it frees up space under the engine for things like oil and headers.
• But It increases the steering effort of the driver especially during sharp turns.

[pic 1]

[pic 2]

The ackerman condition for the above figure is

 cotϕ –cotθ = c/b

Where ϕ and θ are inner and outer angles respectively

Ackerman angle (α)=Arc tan(c/2b)

Where b is wheel base and c is centre to centre knuckle distance

CALCULATIONS

Wheel base(b) = 65”

Center to center knuckle distance(c) = 45.2”

Ackermann angle(a) = arctan(c/2b)

Therefore, Ackerman angle, a=23 deg.

Placing the rack:

When viewing front from front, rack should be in line with the wheel centre in case of height.

TIE-RODS AND LINKAGES

Due to all of the changes that have been made to the suspension and spindles, the tie-rods that were used by the previous MQP no longer work for our application.  The swages from the last MQP were not large enough to handle the stresses that would be expected from a Mega ATV competition; therefore, in an effort to limit the possibility of catastrophic failure, we decided to purchase new, stronger swages.  Additionally, the swages from the previous MQP were of different length which resulted in the need to mount the steering rack off center of the frame, purchasing new swages will allow us to center the rack.  Finally, the provided swages are not compatible with the new spindle that we purchased because it uses a different size screw to mount to the steering arm of the spindle.  The different screw size would create slop in the connection between the swage and the steering arm which would drastically hurt steering performance.

Caster & Steering Axis Inclination 

While caster and steering axis inclination both offer improvements in the area of handling and stability, they would be two aspects that that we altered to get more control over the vehicle by having more accurate steering system.

Steering Column Assembly and Mounting

 The Steering Column posed multiple challenges within its design, assembly, and chassis mounting. Initially the steering rack and pinion was raised and angled in order to ensure the steering wheel would fall into the driver’s hand at a comfortable angle. Through research, raising the rack and pinion is not ideal because in significantly affects bump steer which is the amount that the tires turn about the kingpin when encountering a large road undulation. Mounting the steering rack and pinion flat in the cockpit combined with an additional universal joint (U joint) allows raising the rack and pinion to be avoided. The second U-joint caused a need for more steering column to be purchased. The second U joint was referred to as a DD U joint due to its internal bore shape looking like two “D’s” back to back. The DD U joint caused a need to manual mill flats into the steering column rod for proper fit within the bore. Set screws are located in the middle of each flat to prevent the steering column from sliding out of the DD bore. The first U joint had a misalignment maximum of 30 degrees while the second DD U joint had a maximum misalignment maximum of 50 degrees. Together a misalignment of 60 degrees was the resultant angle that the final portion of the steering column pointed. To prevent excessive wear on each U joint, each had an extra 10 degrees of play as suggested by the retailer and were mounted in parallel phase. Parallel phase is when each U joint yoke on either end of a shaft are in the same exact rotational orientation.