hệ thống lái rack and pinion

Rack and pinion steering systems report bản tiếng anh cho chương trình tiên tiến ô tô, tài liệu tham khảo được trích dẫn cụ thể. Báo cáo bao gồm hệ thống rack and pinion, nguyên lý, cấu tạo, xu hướng phát triển trong tương lai, hệ thống lái trợ lực thủy lực và trợ lực điện,...Đây là một tài liệu tham khảo khá bổ ích cho sinh viên ô tô các chương trình.

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

SCHOOL OF TRANSPORTATION ENGINEERING

-o0o -REPORT RACK AND PINION STEERING SYSTEM

Course name: MODERN AUTOMOTIVE STRUCTURE

Course code: TE3200E

Student’s name (code): Nguyễn Hữu Khải - 20186112

Class: Automotive Engineering – Elitech K63

Table of Contents

I Introduction Error! Bookmark not defined.

II Rack and Pinion in Steering System 3

1 Construction and Working principle 4

2 Hydraulic power steering system 6

3 Advantage and Disadvantage 8

3.1 The Advantage of Rack and Pinion Steering 8

3.2 The Disadvantage of The Rack And The Pinion Steering system 9

III Applications and Future Development 10

1 Applications 10

2 Future Development 12

IV Type of Electric Power Steering system 14

1 Colums assist type 14

2 Pinion assist type 14

3 Rack assist type 15

4 Direct drive type 15

V Vehicle Dynamics 15

1 Under Steer 15

2 Over Steer 15

3 Bump Steer 16

VI References 17

I Introduction

Rack and pinion are gears and the mechanism of gear converts rotary motion into linear motion Pinion is round gear that engages teeth on linear gear rack end or axial joints which is a toothed bar used in rack-and-pinion steering systems for translating rotational motion of pinion into linear motion The combination of rack and pinion are often uses

as a part of linear actuator Over the last few decades and the current trend rack and pinion is in the vast majority of today's vehicles It's direct, compact, simple, and gives great steering feel Major application of such mechanism is used in automobile that converts the rotational movement of steering wheel into right-to-left and vice versa

motion of the tie rod

II Rack and Pinion in Steering System

Every vehicle can move with the wheels but if you want to control your vehicle smoothly and at the right direction with the highly accuracy, we have to design a steering system The steering system is designed to control the direction of the vehicle's movement Design the steering system need to focus on the following basic criteria such as:

- Simplicity (easy to design and assembly)

- Safety (for car and driver)

- Requiring minimum steer effort (Simple in operation for everyone)

- Manufacturer financial (high profits)

When a car is travelling around a corner (the red lines represent the path that the wheels follow) the inside wheels of the car follow a smaller diameter circle than the outside wheels If both the wheels were turned by the same amount, the inside wheel would scrub (effectively sliding sideways) and lessen the effectiveness of the steering This tire scrubbing, which also creates unwanted heat and wear in the tire, can be eliminated by turning the inside wheel at a greater angle than the outside one

 Some requirements of steering system:

 Gear accurate and easy to handle

 Driving comfort

 Direction stability

To have insight into the Rack and Pinion system, next sections we will discuss the construction, working principle, advantage, and disadvantage as well as the trending of development of the Rack and pinion steering system

1 Construction and Working principle

a) Construction

As the name implies, rack-and-pinion steering consists of two major components - a rack and a pinion The rack - also known as a steering rack - is a long piece of metal that

is flat on at least one side The flat side contains teeth running the length of the rack The teeth are cut perpendicular to the edges of the rack, meaning they run side by side from one end of the rack to the other The other major component, the pinion - more correctly, the pinion shaft - is a round rod that also has teeth on it, although these teeth run parallel

to the length of the shaft, not lengthwise as on the rack The pinion shaft comes into the rack at a ninety-degree angle, held in place by a collar, and the teeth on the pinion mesh with the teeth on the rack The pinion is connected directly to the steering column, so when the steering wheel is turned to the left, for instance, the pinion rotates counter-clockwise (from the driver's perspective) Simply put, the rotary motion of the pinion is changed to transverse motion by the rack The rack moves to the right, making the wheels go left The car turns left

Figure 11 Rack and Pinion mechanism

1 www.visualdictionaryonline.com

In the automotive, the pinion gear located outside the vehicle center (on the left on the left-hand drive and on the fight on the right-hand drive) and tie rod joints do not fit into the sides of the steering rack (side take-off) is the most popular arrangement compared to others (Figure 2a) The pinion used is title gear for high load resistance and smoother steering feeling In the pinion arrangement, the pinion gear is carried by bearing (Figure 2b), which also absorbs any axial forces To limit the vertical movement, which is extending the gap with rack, the self-locking nut is add at the end of pinion, automatically tighten as the gap reach to a certain limit

Figure 2 Rack and Pinion illustrator (a)2 Rack and Pinion arrangement (b)3 Rack and

Pinion Bearing

In figure 2b show arranges inside the rack guide, contact with the rack guide spring cap surface In addition, that may also use for setting the plays, and the rack guide spring cap

is tightened against it as the distance ring role in a conventional rack system, in order to keep the frictional forces between guide-bearing and gear rack as small as possible for ensuring a good response and feedback of the steering Besides, the half-round outline of the rack guide does not allow radial movement of the steering rack In addition, by changing the response to the driver, near the end of the rack, there is the change in tooth profile, which require more moment (more driver effort) as the steering wheel

2 Jörnsen Reimpell Prof.Dipl.-Ing.,Jürgen W Betzler Prof.Dr.-Ing., in The Automotive Chassis (Second Edition), 2001

3 Tcorolla Toyota Corolla Repair Manual Components <http://www.tcorolla.net/components-1253.html>

approaches the limit The tie rod axial joints bolted to the side of the steering rack and the sealing gaiters can be seen clearly To stop them from being carried along when the toe-in is set (which is done by rotating the middle part of the rod) it is necessary to loosen the lock nut between rack end and tie-rod end In addition, for prevent ingress of dirt and dust, which able to wear down working components or may be stuck in, locking the mechanism, the gasket between pinion and control valve, clamp rack boot, which is a rubber cover, and clip are used

2 Hydraulic power steering system

In the beginning, there was the only one kind of manual steering If you want to move the car to a different direction, you grab the steering wheel and put your shoulders into it We had sweated behind the wheel until the first mainstream car with power steering hit showroom in 1951 They call the first power steering unit

“Hydraulicguide”.

a) Roles of hydraulic power steering system

Figure 34 Friction coefficient vs vehicle speed A-30 and MU-30 roads Wet asphalt

Figure 3 includes the results obtained in tests conducted on A-30 and MU-30 test roads, respectively All tests were carried out in wet conditions As it can be 4

observed, the longitudinal friction coefficient decreases progressively when the tire is locked (s = 1) and the vehicle speed increases In vehicles without power steering, greater steering effort is required when the vehicle is stopped or moving at a low speed, less steering effort is required as the vehicles speed increases.

Power steering enables the driver to use about the same effort to turn the steering wheel when the vehicle is stopped or moving at a low speed as when it

is moving at higher speeds Power steering is controlled by various mechanisms that reduce the steering effort required while retaining the feeling

of being in direct control of the vehicle as with manual steering.

b) Structure and Operation theory

Compared with manual steering, the following three components are added in power steering:

- First is the vane pump, driven by the engine via a drive belt, creates the hydraulic pressure used by the power steering system.

- Second is the power cylinder a device that uses the flow of hydraulic fluid that is the power steering fluid from the vane pump to turn the front wheels Last is the control valve which regulates the direction and volume of the flow of power steering fluid to the power cylinder in accordance with the movements of the steering wheel

A hydraulic power steering system following the operation theory: (i) A constant volume of flow is fed by the pump to the hydraulic circuit which equipped with a cylinder (ii) When the steering wheel is not being turned the fluid returns from the control valve directly to the reservoir without steering assist (iii) The control valve operates when the steering wheel is turned causing the fluid to flow into one side of the power cylinder or the other moving the piston to the left or right (iv) When the steering wheel is turned in the opposite direction the control valve switches the direction of the flow of fluid so the fluid flows into the opposite side

of the power cylinder moving the piston in the opposite direction.

3 Advantage and Disadvantage

3.1 The Advantage of Rack and Pinion Steering

When comparing steering systems you really only need to think about two types standard mechanical steering and rack and pinion steering The standard mechanical steering system is either power assisted or non-power Rack and pinion is almost always power assisted There are advantages to both, but there are some significant advantages for rack and pinion that should be considered when comparing cars

a) Fewer Parts and Lighter

Rack & pinion steering gearbox is simple in construction and lighter.Reducing the number of parts in a system also reduces the weight The rack and pinion steering system weighs less than a recirculating ball gearbox, which helps improve gas mileage and easy control Rack and pinion systems are lighter because they don't require the idler arms, Pitman arms, center links, and tie rod sleeves found in conventional steering systems

Figure 45 Rack and pinion advantage

5

The size and weight of a rack and pinion system make it a better fit for front-wheel-drive applications because manufacturers can install it right next to the transverse drivetrain The rack and pinion steering system has led to more cost-effective car production, improved gas mileage, and easier vehicle handling It is certainly a revolutionary advancement in the automotive industry

b) Road Fell

Driving on wet or icy roads can be tricky A rack and pinion steering system gives you better "road feel," which makes this type of driving a little easier It gives you quicker and better feedback than a standard system

c) Economical & easy to produce

d) It is easy to operate with accuracy

e) Contact between steering rack & pinion is free from play

f) Internal damping is maintained.

g) Minimal steering elasticity, compact so mostly used in front-engine Front-wheel

h) The idler arm & intermediate rod is not needed

i) Easy to limit steering rack travel and so steering angle

3.2 The Disadvantage of The Rack And The Pinion Steering system

a) Less Durability

When installed in a four-wheel-drive vehicle, rack and pinion steering can cause problems when driving off-road While this simple system provides responsive handling

on paved roads, the greater force required to turn the wheels on drastically uneven ground can cause it to wear out much more quickly

b) Leakage

Because of the simplicity of the system, rack and pinion steering requires fewer parts to function properly However, this places a greater strain on the individual parts, and the wear can cause leakage, requiring replacement of the rack assembly

c) Vibration

Its simpler construction and reduced number of parts help rack and pinion systems provide more road feel than other steering mechanisms However, this more intimate

connection with the road can also transfer more noise and vibration to the driver and passengers

III Applications and Future Development

1 Applications

While rack and pinion steering has been used by American automakers for less than 50 years, the concept is nearly a century old in other countries

Hemmings Motor News reports that in the 1930s, BMW produced the first rack and pinion gearboxes The first American automaker to use rack and pinion steering in production was Ford, which used it for the 1974 Mustang II and 1974 Pinto While AMC adopted the system soon after for Pacer 1975, GM and Chrysler wouldn't make cars with rack and pinion steering until the 1980s In the 1970s, Arthur Ernest Bishop invented the variable rack Combined with a standard gear, his variable rack is used to improve the vehicle's handling The main steering system used is rack and pinion and almost 80% of commercial vehicles are using this type The rack and pinion steering system is rapidly becoming the most common driving style in cars, vans and SUVs This system is mainly used on light vehicles due to its simple and compact structure The steering mechanism

is small, the rack itself acts as a steering rod, so there is no need for horizontal bars like other steering mechanisms The shell of the system is made of cast iron, in the shell of the working parts of the steering mechanism including the shaft The teeth under the main steering shaft align with the rack, the housing of the steering mechanism acts as a crossbar, so it will save costs and be suitable for more compact cars Direct tooth articulation should be highly sensitive Sliding and rolling friction are small, combined with good torque transmission, so the control force on the steering wheel is light In the line of small trucks, there are many models using this gear steering system such as Thaco Tower 800 This is the main vehicle of Thaco Thaco is also a car company that uses a rack and pinion steering system mainly on small trucks Another very popular line of small trucks today that also use this steering system is the Dongben DB102 or DB X30 series This type of vehicle weighs about 800 to 1100kg and uses mechanical power Hyundai also has many trucks that use this system, typically the Hyundai H150 or 1T5 This vehicle uses a hydraulic power steering system A new line of vehicles with rack and pinion steering is the Taraco Tera 100 This vehicle uses an electric power steering

system With SUVs, appearing in many models such as Ford Eco Sport, Hyundai Kona, Both of these vehicles use electronically controlled electric power assist In addition, the rack and pinion steering system is also applied to other models such as Murati 800, wagon, alto, i10, etc In these vehicles, manufacturers aim to reduce in root bending stress and contact stress , reduce cost, increase power density and reduce weight While most consumers are familiar with rack and pinion systems for drive cars and small trucks, rack and pinion combinations have a number of applications other The rack and pinion system is used not only to help the train climb slopes, but also to provide better brake control, especially in snow and icy conditions Stairlift.com states that rack and pinion systems are standard components in most elevators Rack and pinion mechanisms are usually operated by hydraulic or electrical power An actuator is a machine that moves various components, such as a pipeline conveying system In such a system, a rack and pinion help control the valves that the system needs for its basic function In addition to the rack and pinion drive system, another system is also common used on the trucks and SUVs that are recirculating ball systems Table 1 is comparision table between these two systems

Table 16 Rack and pinion & recirculating ball system