Different Types of Steering Gear Box Mechanisms

The steering gear plays a critical role in a car's steering system by serving as the central component responsible for transferring the motion of the steering wheel to the car's wheels. With the help of power steering (if available), the steering gear enhances the vehicle's handling and provides a superior steering experience with minimal effort from the driver. Different types of steering gearboxes are used in a steering system, each with unique features and advantages. In this blog, we will explore the different types of gear used in steering systems. Continue reading to learn more about the same.

Steering Gear Box: Functions

The steering gearbox serves two fundamental functions that are crucial for a car's steering system:

• It converts the rotary motion of the steering wheel into the angular turning of the front wheels. This conversion is necessary to translate the driver's steering inputs into the appropriate directional movement of the vehicle's wheels.
• The steering gearbox multiplies the driver's effort and provides a mechanical advantage, making it easier to turn the wheels and control the vehicle's direction. It is particularly crucial in larger vehicles, where the wheels may require more force to turn due to their weight and size.

Steering Ratio: What Is It?

The steering ratio determines a vehicle's ease of steering and maneuverability. It represents the number of degrees the steering wheel must turn to steer the front wheels by 1°. Steering ratios depend on the vehicle type and its intended use, ranging from approximately 24:1 with manual steering to around 14:1 with power steering assist. For instance, the steering ratio of a bike is 1:1, and on the other hand, sports cars have a ratio of 12:1.

A higher steering ratio makes it easier to turn the wheel and steer the vehicle, while a lower ratio requires more effort at the steering wheel. Quicker-ratio steering may require higher force at the steering wheel, but it can pivot the wheels faster, providing a faster steering response.

The steering gear ratio and the steering linkage ratio determine the steering ratio. In a pitman arm steering gear, the steering gear ratio depends on the angle and pitch of the worm and sector gear teeth. In contrast, the steering ratio is determined by the number of teeth on the pinion gear in a rack and pinion steering assembly. The lower the number of teeth on the pinion gear, the higher the steering ratio, while a higher number of teeth on the pinion gear results in a lower steering ratio.

Types of Steering Gear in Automobiles

The steering gearbox is a critical component of a vehicle's steering system, responsible for converting the steering wheel's rotational movement into the front wheels' turning motion. There are several types of steering gear mechanisms, each with unique features and advantages. Let's take a closer look at some of these types:

• Worm and Nut Steering Mechanism

The Worm and Nut Steering Gear Box is a type of steering gearbox that functions like a bolt and nut system. In this system, the bolt-like component is called the worm gear, which consists of external threading, while the nut-like component is called the nut and has internal threading. When the worm gear is rotated, the nut meshes, and a rotary motion is achieved. This system is also known as a re-circulating ball type of steering gear.

The nut and worm gear have sphere-shaped grooves over the threading, allowing the steel balls to fit in. The presence of these balls moves into the nut and worm gear free, similar to a bearing system, and reduces friction. It makes the steering more responsive and efficient.

The Worm and Nut Steering Gear Box is a durable and reliable steering gear system generally found in heavy-duty vehicles. Its simple design and reduced friction make it ideal for vehicles that require precise and smooth steering control, like commercial trucks and buses.

• Worm and Sector Steering Mechanism

The Worm and Sector Steering Gear Box is a type of steering gear system that uses worm and sector gear as its main components. The sector gear, which looks like a quarter portion of a circle with teeth, meshes with the worm gear to enable both gears to contact each other.

As the steering wheel and worm gear are rotated, the sector gear attached to the pitman arm shaft will slide, allowing a maximum arc of 70 degrees. This 70-degree angle represents the maximum angle that the wheel can turn. A ball-bearing system is used between the gears to allow free play. To control the backlash between the sector and worm threads, a lash adjustment screw is provided, which allows the sector to be moved closer or farther away from the worm gear.

One of the main disadvantages of this steering mechanism is that it tends to develop more friction. A new type of steering gear system, the Worm and Roller Steering Gear Box, was proposed to address this issue.

• Worm and Roller Steering Mechanism

The Worm and Roller Steering Gear Box is an improvement over the traditional Worm and Sector Steering Gear Box. In this type of steering gear system, the sliding movement seen in the Worm and Sector system is eliminated, and rolling movement is introduced through rollers.

The rollers between the worm and sector gears reduce friction, resulting in less effort from the driver to turn the steering wheel. Additionally, the hourglass shape of the rollers allows them to stay in better contact with the worm teeth, even at the worm gear's ends.

• Cam and Lever Steering Mechanism

The Cam and Lever Steering Gear Box is another type of steering gear system that utilizes a cam and a lever to transfer rotary motion into linear motion. In this system, the worm gear is replaced by a cam, and the inner end of the pitman arm shaft is fitted with a lever that contains a tapered stud.

When the cam is turned, the tapered stud engages with the cam and causes the lever to move back and forth. When the tapered stud is fixed in the lever, the cam cannot rotate. In vehicles with this type of steering gear, the stud is mounted in bearings that allow it to roll along the cam groove, reducing friction and improving the steering response.

• Rack and Pinion Steering Mechanism

The Rack and Pinion Steering Gear Box is a popular choice for small passenger vehicles that require precise steering. This gear system consists of a straight bar with teeth known as the rack and a sphere-shaped gear with teeth called the pinion. The rack is connected to the steering arms through adjustable tie rods that help maintain the appropriate angle.

When the driver turns the steering wheel, the pinion gear attached to the end of the steering shaft rotates, causing the rack to move in either left or right directions. This movement, in turn, operates the steering linkage, allowing the driver to turn the vehicle in the desired direction. The rack and pinion gear system offers responsive and accurate steering control, making it a popular choice for many drivers. 

• Recirculating Ball Steering Mechanism

Utility vehicles, trucks, and vintage cars use recirculating ball steering systems. The system's design comprises a steering box with worm gear and multiple ball bearings. The ball bearings reduce friction between the gears, making it easier to turn the steering wheel. 

Compared to other steering systems, the recirculating ball allows for a more excellent range of motion when turning the steering wheel. This feature is handy for large trucks that carry heavy loads.

• Ram-Type Steering Mechanism

The advantages of Ram-type steering gear are immense. It is a commonly used and expensive construction in steering gear systems. Its basic principle is similar to a hydraulically-steered lift or motor engine. The steering gear system consists of four hydraulic cylinders connected to the actuator disc's two arms on both sides.

These cylinders are directly coupled to electrically-driven hydraulic pumps that generate pressure through pipes. The hydraulic pressure generated by the pumps imparts motion to the hydraulic cylinders, which act on the rudder stock. The rudder stock is an indispensable part of the ship’s entire steering gear arrangement and dictates the rudder response's exact behavior.

The action of the hydraulic pump guides the sense of turning the rudder. This type of steering gear system is commonly used in large vessels requiring precision steering.

Conclusion

Every gearbox has disadvantages in usage, and new technologies and systems are often proposed to rectify and overcome these drawbacks. In traditional mechanical steering systems, the movement of components can create friction, hindering smooth and efficient turning. To address this, power steering systems were developed. These systems utilize hydraulic pressure to minimize friction, allowing for more precise and effortless steering.

To learn more about such mechanisms deployed in automobiles and machines, take up our PG Program. Talk to our experts to get guidance in choosing the right course that suits your interests.