Steering (automobile)
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The document discusses the steering system design for a BAJA vehicle. It describes choosing a rack and pinion system for its simplicity and ease of mounting. An Ackermann steering geometry is selected to ensure the wheels pivot around the same point during turns. A customized steering mechanism will be made based on a Maruti 800 rack and pinion gear system. Key parameters like caster angle, camber, toe-in, and scrub radius are discussed. Terminology related to steering components like the steering wheel, column, rack, and linkages are defined. The Ackermann principle is explained which ensures the inner wheel turns through a larger angle during turns to prevent tire wear.
Steering (automobile)
- 1. STEERING The essentials still remaining the same, the importance of the steering mechanism cannot be compromised with. The BAJA track consisting of sharp turns and bumpy roads, the stability of the system and the response time (Feedback) are vital factors in deciding the vehicles’ run. The Worm and Sector mechanism, Rack and pinion and the Re-circulating ball mechanism were among our options to go with. But on consideration of mounting ease, simplicity in design and considering that our vehicle is of the compact category; rack and pinion was chosen over the others. The rack and pinion being a simple system; can be easily maneuverer and the defect, if any, can be spotted and taken care of. Moreover the steering wheel and other relevant apparatus are so placed in the design, for easy entering and exit of the driver. Steering Geometry: The Ackermann geometry is the easiest to implement and has been tested for BAJA vehicles all over the globe and hence it was a unanimous choice for the steering geometry. With Ackermann Steering all four wheels of the vehicle pivot around the same point making sharp turns relatively easy to accomplish. This ensures that the vehicle tires do not slip during turns that are sudden. Steering Gearbox: We shall be manufacturing a customized centred steering mechanism, the basis of which shall be derived from the rack and pinion of MARUTI 800. Direct usage of the Maruti 800 gear system is not done, mainly because of its eccentric placement of the gearbox that disrupts the C.G. balance of the vehicle The major parameters in steering design are, 1. The Caster angle has been adjusted to 3 to 5 degree as it increases directional stability and handling of the vehicle in bumpy sections. 2. The Camber should be kept negative to ensure maximum contact of tire with ground during cornering and to reduce chances of flipping over. 3. Ackermann type of steering geometry ensures consistent and smoother ride and prevents the slipping of tires during cornering. 4. We should have a scrub radius of 40-48 mm approximately. This is acceptable as it is neither a negative value nor too large of a positive value. Such a small value will leave the car slightly harder to steer at very low speeds. It is important for this value to be equal on both tires to avoid the car “pulling” to one side. We should have kept a small Toe-in in the front. This will stabilize the car while moving straight and while coming out of turns. It will smooth out the steering response, making the car very easy to drive.
- 2. Approximate specification Sl.no. property Value between 1 Caster 4-5 degree 2 Camber 1-2 degree (negative) 3 Toe In 10-12 mm 4 King-pin inclination 12-13 degree 5 Scrub radius 42-45mm 6 Lock Angle Around 38-42 degree Terminology The Steering Wheel – The Bit the driver holds on to! It also incorporates the Air Bag. Steering Column – The shaft connecting the steering wheel to the steering box or steering rack. Steering Rack – A combination of a small gear and a toothed rack. This changes the rotation of the steering wheel into a back and forth movement of the rack which in turn moves the road wheels. Steering Box – This does a similar job to the rack but needs extra linkages and rods to connect it to the road wheels. Mostly used on old cars, but still is in use on larger vehicles. Track rod/Tie rod – A rod to connect the left and right steered wheels. The steering rack is also the track rod. Track rod end – A ball joint to allow steering and suspension movement. Ball joint/Swivel joint – Part of the suspension, but these are joints which allow the steered wheels to left and right. PAS – Power assisted steering. An engine driven pump or electric motor, provides extra force to help the driver turn the steering. Tracking – toe in or toe out setting for the steered wheels.
- 3. Ackerman Principle Ackermann stated the principle that when a vehicle travels in a curved path,its wheels should describe circles around the same centre. A wheel which follows a markedly different path will slide to some extent, this would cause excessive tyre wear. The steering mechanism is designed to insure that when the vehicle turns left or right, the inner wheel is turned through a larger angle to prevent tyre wear Steering assembly in operation, as the steering linkage is shorter than the axle, the inner wheel is turned through a larger angle. Steering Shafts and Columns Nearly all steering systems use a steering column or shaft to link the driver (steering wheel) to the steering rack or gear/box. Flexible coupling isolates steering wheel from road shocks. Universal joints allow steering shaft angles to change Most steering columns are designed with a collapsible section that helps prevent forces generated in a collision being transferred to the driver. Bottom of steering column normally has a master spline where it mounts onto the steering rack-and- pinion or steering gear/box.
- 4. Basic Steering Systems Two main types of steering Linkage or Conventional type (also known as Parallelogram) Rack-and-pinion type. Linkage type uses a worm gear inside the steering gear/box, this operates the drop arm, then couples to a centre link, idler arm, track rods and the steering knuckles. Rack-and-pinion type uses track rods to couple the rack to the steering knuckles.
- 5. Rack-and-Pinion Steering Principle Part of rack contains a piston. Two fluid ports, one on each side The side with high pressure pushes the piston to the opposite side (turning the wheel).
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- 8. Steering System( we can use power steering in the car) Power Steering normally use an engine driven pump and a hydraulic system to assist steering action. Three major types of power steering systems • Integral-piston linkage system. • External power steering system. • Rack-and-pinion system
- 9. Ball Joints Ball joints are common on most steering systems and provide a controllable link to the other steering components. Ball joints allow linkage components to swivel freely. Suspension (vertical) and steering (horizontal) movements Nearly all ball joints have some form of adjustment. Most steering rack ends have adjustable ball joints and some incorporate shock dampers. Linkage Type Steering System
- 11. As compare to last year we can apply power brake in the car, but I need to study its mechanism . I need a bit time to understand it and to design it.