How Car Steering Systems Work
You may have a very powerful engine and a super-responsive, highly efficient transmission that transfers all this raw energy to … Continued
You may have a very powerful engine and a super-responsive, highly efficient transmission that transfers all this raw energy to your wheels, but if you don’t have a way to control the wheels and maneuver them in the direction you want to go, then you’d still end up with nothing less than a highly glorified street luge. But even a street luge has a way to allow itself to be maneuvered. That makes a vehicle without a steering system look more like a gigantic boulder rolling along, dependent on gravity to take it where it wants to go.
A car’s steering system is as important as the vehicle’s engine and transmission. While the latter two are what effectively put energy to the wheels, you need to understand that the steering system is what controls the direction of the wheels. Go right. Go left. Go straight forward or back. That is the function of the steering wheel moving the car’s wheels as energy is applied onto the wheels. It’s a complex system, really. But that is what we’re here for. We’re going to demystify this part of the car that, to put it bluntly, you’re holding onto every time you take your car for a drive.
Steering: Essential to Driving
As we have already started blabbering about in the beginning of this article, the steering wheel is a very important component of your car. It’s like the equivalent of the reins on your horse which you use to direct the steed to a particular heading or even to control it if you see an obstacle ahead of you. The steering wheel is also the equivalent of the handlebar on your grocery pushcart which you use to maneuver and navigate through the various sections of your favorite grocery or supermarket.
To put it simply, changing your car’s heading or direction will simply be impossible without the steering wheel. Without it, you will not be able to make split-second course corrections to avoid getting into a traffic collision or vehicular accident. Without it, you will also not be able to drive it into and out of your driveway or in your parking slot.
It is for this very reason that a car’s steering system is a very essential component since it basically ensures safer driving by affording you maximum control of your vehicle’s wheels. Aside from the shift stick or gear shift lever that you manipulate from time to time, your hands will always be on the steering wheel. The vibrations, slight pulling movement towards one side, and the like are experiences that you can only obtain when your hands are firmly planted on the steering wheel. These ‘experiences’ give you feedback on what your car is doing, how it is behaving on the road, and whether or not these ‘experiences’ are telltale signs of an impending mechanical or even electrical problem.
In short, the steering wheel gives you control of the car’s direction as it moves along the road.
Basic Steering Components
Regardless of the type of vehicle that you have, its steering mechanism will always include 3 to 4 basic components that can include the following.
This is the part of the steering system that everyone is very familiar with. It is what we hold and control while driving. The steering wheels of the past were unusually large in diameter, making you think they were the helm of a ship purposely built into the car. They were relatively thinner, too, and made mostly of hard plastic. Today’s steering wheels are generally padded, affording you comfort while holding onto it for extended periods. Some come with ergonomic grooves that hug the contours of your palms and fingers. Internal splines prevent the steering wheel from slipping off the steering shaft.
The size of the steering wheel is important in driving since size is inversely proportional to the effort needed to turn the wheel. This means that the larger the steering wheel diameter the lesser is the effort you will have to exert to turn it. Conversely, the smaller the diameter of the steering wheel the more that you will feel as if you’re fighting with the wheel.
The steering wheel also houses a variety of attachments such as the horn switch and the driver’s air bag system. In newer cars, the audio or music controls, paddle shifters, as well as the cruise control are also mounted here. The air bag is officially called as the supplemental inflatable restraint or SIR system. If the car figures in a frontal collision, the impact triggers the electronic impact sensors to activate the air bag squib which, in turn, ignites a flammable substance expanding the gas and deploying the bag. All of these occur in one-tenths of a second after collision.
Steering shaft and column
Collectively called the steering system, the steering column and shaft connect the steering wheel to the rest of the steering system found near or in the wheels. Most modern cars come with a telescoping steering shaft composed of two steel tubes, one of which is solid and the other hollow. The solid tube slides inside the hollow tube allowing it to collapse in the event of a collision. The steering shaft also has a steering coupler located at the bottom which serves to absorb vibrations while also allowing for slight variation occurring in the alignment between the steer gear and the shaft. Many modern cars don’t have enough clearance to facilitate a straight connection between the steering shaft and the steering gear. In such cars, universal joints are included to allow the shaft to rotate at an angle.
The steering column covers the steering shaft. You can look at the steering shaft and column as a syringe with the steering shaft being the plunger of the syringe and the steering column the barrel of the syringe. Allowing the column to freely move are ball or roller shaft bearings located at the top and bottom of the column. Some steering columns are fully adjustable to make driving a lot more comfortable. These can be tilting or telescoping steering columns, allowing for the upward and downward adjustment or the forward and backward adjustment of the steering column, respectively.
The tie rod is that part of the steering system wherein power or force coming from the steering gear is transmitted towards the steering knuckle located at each wheel. The effective transfer of this power is what makes the wheel turn. The tie rod’s length can also be adjusted to allow for the more accurate setting of the car’s alignment angle.
The function of the steering arms as well as the ball sockets of a vehicle is to transmit motion to the steering knuckles from the steering gear. The transmission of this motion occurs through the steering linkage. The steering arms serve to transform the back and forth motion produced by the steering linkage into a rotating motion to be executed by the steering knuckle. The steering arms are shaped in such a way that they facilitate the more efficient turning of the vehicle without the tires hitting any of the wheel or the steering mechanism.
Ball sockets allow for the more flexible connection between the various parts of the steering linkage. These also allow for the horizontal distribution of load or weight which is different from a ball joint which distributes load vertically, in an up and down manner. If the ball socket connects the steering linkage of your car to its steering knuckle, this is often called a tie rod end.
When these parts are taken together it is easy to understand how the whole system works.
- You turn the steering wheel.
- This turns the steering shaft inside the steering column.
- The rotational motion of the steering shaft turns the steering gear.
- The turning steering gear transmits this motion to the steering arms and the steering knuckles through the tie rod.
- The steering knuckle executes the turning of the wheel.
The Ackermann Angle
Since we’re essentially talking about how a vehicle turns whenever we think of the steering system, it is important to understand one very important geometric principle in play – the Ackermann Angle or the Ackermann Steering Geometry. The geometric principle was actually developed by Georg Lankensperger in 1817 in Munich. However, the design was never patented until about a year later by none other than Lankensperger’s agent, Rudolph Ackerman in England. Since then, the principle was known as the Ackermann Angle although it should be rightfully called the Lankensperger Angle. Actually, there is some claim that the Lankensperger discovery may have come later since there were reports that Erasmus Darwin invested a similar principle in 1758.
Well, enough of that. How is the Ackermann Angle relevant to steering systems? In case you have noticed, every time you turn your wheels, the 2 front wheels will be angled differently in relation to one another with the inside wheel (the wheel to the side where you’re turning to) having a slightly more acute angle than the outer wheel (the wheel towards the side opposite the direction you’re turning in). This is because when you turn, the wheels follow an arc which is technically a part of a circle. And whenever circles are concerned, you have the radius to think about which is the distance to the pivot.
Since the inner wheel is nearer the pivot, it has a smaller radius relative to the outer wheel. This means that the inner wheel will travel a shorter distance while the outer wheel will have to cover a longer distance. Because of this difference in turning radius and the relative distance traveled by the front wheels, the inner and outer wheels have to be pointed at slightly different angles relative to the car’s center line. This is achieved by making simple arrangements in the various components of the steering column.
The good news is that you no longer have to worry so much about the Ackermann Angle since modern car manufacturers rarely adhere to this principle in a very strict manner. This is because there are other factors that need to be considered such as the compliant and dynamic effects of suspension and steering. Of course, the principle still works as a model for the design of all steering systems.
We know that the steering system helps you point or turn your car in the direction you want to go. We also know that the steering wheel is what you will normally manipulate or turn to make the wheels turn in that direction you want to head to. Now, most modern cars will require several turns of the steering wheel to turn the wheel to its maximum deflection or angle. This is where the steering ratio comes in. It is actually the number of turns you need to make on the steering wheel to elicit a certain amount of movement in the wheels. Typically, these numbers are measured in degrees and expressed as ratio.
For example, if turning the steering wheel by about 20 degrees in either direction you are also able to elicit a corresponding 1 degree of deflection in the wheels, then you will have a steering ratio of 20:1. Modern cars usually have a steering ratio of anywhere between 12:1 and 24:1. Only Formula 1 race cars have a steering ratio of 1:1 to allow them for lightning quick precision turning with slight movements on the steering wheel.
The lock-to-lock turn of any given steering wheel can also be ascertained using the steering ratio. To compute for this, you will need the information of your vehicle’s maximum angle of wheel deflection or how far out the wheels can be turned, often measured in degrees. Let us say your vehicle has a steering ratio of 18:1 and a maximum wheel deflection of 25 degrees, then the maximum turning angle to one side is computed as 18 x 25 to give you 450 degrees. Since this is just to one side, then you have to multiply this by 2 to get a lock-to-lock angle of 900 degrees. This means that you will have to turn your steering wheel a full 2.5 times to achieve a complete lock-to-lock angle (Since a circle has 360 degrees, you need to divide 900 by 360 to get the 2.5).
You can also use the above formula for determining the wheel deflection of your vehicle, provided of course you have its lock-to-lock angle and steering ratio. Let us say you’re mulling on buying a car with a lock-to-lock turn of 3 and a steering ratio of 16:1. First, multiply 3 by 360 degrees to get 1,080 degrees. Next divide this by two to get the lock angle for one side of the vehicle. This gives you 540 degrees. You then need to divide 540 degrees by 16 from the steering ratio to give you a quotient of 33.75 degrees. This means that the car you want to buy has a maximum turning angle of 33.75 degrees.
The steering ratio affects quite a number of things in a vehicle’s handling. Here are some of them.
- Heavier vehicles typically have higher steering ratios.
- A car with power steering will have a lower steering ratio than a manual version.
- A small steering ratio requires the steering wheel to be turned less but this also requires more effort in turning the steering wheel.
- A large steering ratio requires more turns on the steering wheel but the effort of doing so is significantly lesser than one with a small steering ratio.
- A large steering ratio can also help absorb and dissipate shock from the surface of the road.
Steering ratio, ease of steering, and the overall handling of the vehicle are quite dependent on a variety of factors including the following.
- Size of the steering wheel
- Size of the gears located in the steering gear
- Angles formed by the steering linkage
- Shape and size of the steering arms
- How much weight of the vehicle is placed on its two front wheels
- Front-wheel or rear-wheel drive options
Aren’t you just amazed at how some vehicles can perform amazing turns at even the tightest spots? Conversely, there are also those vehicles that will take you several maneuvers of forward and reverse motions to get your way out of a particular spot. This has something to do with a vehicle’s turning circle. This is depicted by the circle formed by the outer wheels of the car if it makes one complete 360-degree turn on full lock.
Computing for the turning circle of any given vehicle can be heady as there really is no hard and fast rule for such a thing. Nevertheless, if you are feeling pretty good with numbers especially geometry, you can try the following formula:
- Turning radius = (track divided by 2) plus (wheelbase divide by the sine of the average steer angle)
Some vehicle manufacturers design their cars to go in very tight turning circles. The ubiquitous black London taxis typically have a turning diameter of only 8 meters, allowing them to do perfect U-turns in the tightest spots in London. The Mitsubishi Mirage has a turning circle of 9.2 meters while the Jeep Wrangler typically makes a full turn in 10.6 meters. The bigger the vehicle the wider the turning circle. This is generally speaking, of course, because there are some large vehicles that can turn exceptionally better than smaller cars.
Steering System Designs
Two of the most common steering system designs used in vehicles today are the Pitman arm and the rack and pinion. In this section of this guide on how car steering systems work, we will try to explore a little more about these two types of steering system designs.
Pitman Arm Types
The Pitman arm is a part of the steering system that converts the turning motion produced by the sector gear into back-and-forth or linear movement. Once this motion has been converted into its linear form, it is then transferred to the steering linkage.
Technically, the Pitman arm connects to the center link supported by the idler arms. The center link is also called the track rod where the tie rods are connected to. The actual mechanical linkages that involve the Pitman arm mechanism are highly varied. They can range from the compound linkages that connect the Pitman arm to the track rod via other rods or any other mechanism on one end of the system to direct linkages connecting the Pitman arm to the track rod.
Majority of the steering box mechanisms operating the Pitman arm include a dead spot, or slack, where the steering wheel need to be turned slightly even before initiating any movement to the front wheels. The dead spot or slack can be easily adjusted or tightened; unfortunately, there really is no way you can eliminate it.
Pitman arm mechanisms are especially useful in heavy machineries since they provide a huge mechanical advantage over other steering system designs. Unfortunately, because many of today’s vehicles including those in the heavy equipment industries already roll out in power steering forms, this mechanical advantage is considered moot and academic. Nevertheless, it pays to learn the 4 fundamental types of steering boxes that operate on the Pitman arm mechanisms.
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Worm and sector
The worm and sector steering box is best defined by the use of a worm gear that is attached to the end of the steering shaft. The worm gear is completely enmeshed with the sector gear. In turn, the sector gear is mounted on a shaft that crosses the steering box where it passes through the bottom of the steering box. In this section, the shaft is splined to allow the attachment of the Pitman arms.
Whenever the steering wheel is turned the steering shaft also turns which also produces the same motion in the worm gear. As the worm gear turns, the sector gear rotates or pivots on its axis. This is made possible by the latching of the worm gear teeth onto specific grooves in the sector gear. As the sector gear pivots, the cross shaft also turns, rotating the Pitman arm in the process. The resulting motion is then transferred to the steering linkages on the track rod.
Worm and roller
This type of steering box operates essentially in the same way as the worm and sector. The only difference is that the mechanism that moves the cross shaft is a roller and not a sector gear. The roller in this case is mounted to a roller bearing shaft which is then secured onto one end of the cross shaft.
Turning the worm gear will force the roller to move along the length of the roller shaft in a twisting motion. Because of the unique nature of the roller mechanism, the worm gear has to be engineered in such a way that it follows the shape of an hourglass. This helps prevent the roller from disengaging from the roller shaft.
Worm and nut
Also known as the recirculating ball, the worm and nut type of steering box is inarguably the most ubiquitous of all Pitman arm systems design. What differentiates it from the other types of Pitman systems is that the worm drive is designed to contain more turns complete with a much finer pitch. A nut is then clamped over this worm drive before filling it up with ball bearings. It is these ball bearings that loop around or cycle around the worm drive, head towards the recirculating channel located with the box or nut, before the ball bearings find their way to the worm drive again. So, it is these ball bearings that actually travel around the system of worm drive and recirculating channels.
It is the movement of the ball bearings that actually moves the nut along the worm drive. Just outside the nut is a sector gear. The interaction between the gear teeth located on the nut and the sector gear teeth is what connects the two mechanisms. Technically, the worm and nut is pretty much like the worm and sector except that there is the addition of the nut and the recirculating channels, both of which provide for a more rigid system, avoiding the slack or dead spot seen in other mechanisms. This is the reason why the worm and nut is a favorite design among those who still adhere to the Pitman arm mechanism.
Cam and lever
This type of Pitman arm design is similar to the worm and sector, the difference being the worm has been replaced by the cam and the sector is replaced by two studs located in the cam channels. Turning the cam slides the studs along the channels, forcing the cross shaft to turn.
Rack & Pinion
This steering system design operates on a very simple mechanism that directly transforms steering wheel rotation into straight line movement. The system is composed of the rack, pinion, support bearings, and related housings. Whenever the steering wheel is turned, the pinion also rotates. This also results in the turning of the rack since both rack and pinion are enmeshed. Turning the rack also turns the wheels since the rack is technically connected to the steering knuckles.
There are quite a number of advantages of the rack & pinion mechanism over the Pitman arm. First, there’s no dead spot or slack so you get a better feel of the steering response. It’s a lot easier to repair, too, since it doesn’t involve that many mechanical parts. A greater number of mechanics are also more familiar with the system, making it much easier to repair.
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Types of Steering Explained
You may have heard from race commentators saying a particular driver is having issues with understeer or oversteer. What exactly do they mean?
This type of steering occurs when your front tires lose grip of the road, sending it all the way beyond the curb instead of following the curvature of the corner. If you’ve been watching professional racing circuits, this is when the car goes outside the track, typically hitting the grass. Countering an understeer typically involves releasing the gas if you’ve got a front-wheel drive or applying the throttle if you’ve got a rear-wheel drive.
While it is easy to say that oversteer is the opposite of understeer, this type of steering occurs because of loss of traction to the rear wheels. This sends the rear of the vehicle racing towards the front such that your front end will be typically turned toward the inner side of the track. If you cannot apply a counterspin, you’d find yourself spinning, facing in the opposite direction.
This is applied just as oversteer is about to occur. This is accomplished by turning the steering wheel in the opposite direction. So if you were to turn right and are experiencing oversteer, you need to turn your steering wheel to the left to compensate, catching the oversteer. If you’ve seen professional drift racers and demonstration drivers, they always perform this maneuver to power slide and even smoke their rear tires. Counter steering is also very important among rally racers.
The steering system is an important component of any modern vehicle. It is fundamentally composed of the steering wheel, the steering shaft and column, and the steering arms, although it is not unusual to have other components into the system depending on what kind of steering system you have in place in your vehicle. The function of the steering is to make sure the turning motion performed on the steering wheel is effectively transferred to the wheels and tires of your car. As such, concepts such as steering ratios and turning circles have to be fully understood before one can truly appreciate the importance of a steering system in a vehicle. While the rack & pinion system has clearly taken over the pitman arm mechanism when it comes to the design of the steering system, it still pays to learn these mechanisms as a whole.
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