Improved driveability and mass reduction was Queen’s Formula Racing’s focus for this year’s steering assembly. Mechanical Engineering students, Thomas McMullan and Sean Young, were responsible for the design of the steering system that will feature for QFR at Formula Student UK in July.

Using steering geometries to reduce the steering weight, reducing the system’s mass and relocating the steering rack were all key aspects of QFR18’s steering system design.

“From driver feedback, the steering on last year’s car was found to be too heavy,” explained Thomas.

“To reduce the effort required to rotate the steering wheel, the distance between the kingpin axis and steering mounting point on the upright was increased.”

In addition to optimising the steering geometries, a higher rack speed was specified when ordering the Titan steering rack. This will decrease the amount of rotation required at the steering wheel to ensure lock to lock can be achieved in 180 degrees of rotation of the steering wheel.

“We optimised the steering column and the tie-rods to minimise the mass of each component,” said Sean.

“120 g per tie rod was reduced and the mass of the steering column was reduced by 95 g by optimising the wall thickness and improved material selection.”

Further calculations were carried out to analyse the potential mass reduction for the steering rack. These calculations demonstrated the potential of gun drilling the rack bar and removing excess material from the steering rack housing.  A feasibility study for the use of composites in the steering system was also completed to help future steering designers.

Overall, the total mass saving for the new system was 679 g, a significant reduction of over 22% when compared to QFR17.

Mounting the steering rack this year posed a challenge. QFR17 utilised the rack as a structural member of the chassis which meant the rack had to be disassembled before it could be removed from the chassis. To enable steering torque reduction and bump steer elimination the rack was positioned in an area which did not permit the use of a typical C-Clamp style bracket.

Instead a split collar clamp was used to constrain rotation of the rack whilst using a tab placed on the nearest chassis member to constrain the other degrees of freedom within the assembly in a clevis type arrangement. FEA was then used to optimise the stiffness and mass of the bracket to evaluate the stresses and deflections in critical locations. The solution provides minimal deflection under simulated max loads whilst maintaining the desired position of the rack, whilst remaining removable for repair/maintenance.

WhatsApp Image 2018-03-26 at 08.53.32

2 comments

  1. 2 Questions: 1) You have chosen trailing steering (rack behind the kingpin axis). Was this because of packaging issues or a need to add some compliance understeer to the car ? Pushing on the tierod with the highest load generates buckling compliance instead of pulling on it (as with leading steering: tierods ahead of the spindle). 2) You are running your steering intermediate shaft in a CV configuration (yokes aligned). Had you considered running a phase angle in the shaft to run a pseudo-variable ratio effect to lower the steering effort on- or off- center ? Nice job. Just wondering…

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    1. Hi Bill, thanks for your questions. The steering is actually in front of the kingpin axis. The change in steering rack location was mainly due to packaging, however, one of the main goals of steering this year has been to reduce steering weight and improve driver feel.

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