Steering system is the system which provides directional change in the performance of an automobile. This system converts rotary motion of the steering wheel into angular turn of the front wheels.
Hydraulic Power steering is a system assisting the driver in turning the frontWheels. Large amount of torque is required to be applied by the driver for steering of medium and heavy vehicles. The power steering system provides automatic hydraulic assistance to the turning effort applied to the manual steering system. The power system is designed to become operative when the effort at wheel exceeds a pre determined value say 10N. The system is always so designed that in the event of the failure of the power system, the driver is able to steer the vehicle manually although with increased effort. The system usually consists of a hydraulic pump and fluid reservoir, a power-actuating mechanism such as a power cylinder, a control valveArrangement, and a series of flexible hydraulic hoses and couplings to route the Hydraulic fluid under pressure. The pump derives power from the engine and is Belt or gear driven.
2. THE DEVELOPMENT OF POWER STEERING
The use of power steering in automotive vehicles dates back to 1925, whenVickers – a Detroit pump manufacturer – developed a power steering deviceSimilar to the linkage or booster-type we know today. In 1926, the Pierce ArrowOffered power steering. Cadillac, in 1933, put power steering on its 12-cylinderModels. As larger, heavier and faster vehicles were developed, steering systems were engineered for easier vehicle control.
During the Depression years, power steering systems were temporarily shelvedby most car manufacturers. People bought fewer cars and those they did buywere fairly utilitarian, with little demand for luxury.The war years also saw a lull in the development of power steering forpassenger cars. However, this was not so for heavy-duty vehicles such as thoseused by the military. In fact, millions of heavy-duty and hard-to-steer militaryvehicles were equipped with power steering during the 1940s.
In the early ‘50s, power steering for passenger cars re-emerged when bothChrysler and General Motors introduced it as an option on full-sized models.Following an initial surge in popularity, cars with power steering were not widelyaccepted. Many drivers tried power steering and believed it dangerous – that itdidn’t allow a “feel of the road.” This negative reaction nearly disappeared asmore and more drivers were exposed to power steering-equipped cars. Today,power steering is often considered a necessity.
3. ACKERMANN STEERING GEOMETRY
Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radii.
The intention of Ackermann geometry is to avoid the need for tyres to slip sideways when following the path around a curve. The geometrical solution to this is for all wheels to have their axles arranged as radii of a circle with a common centre point. As the rear wheels are fixed, this centre point must be on a line extended from the rear axle. Intersecting the axes of the front wheels on this line as well requires that the inside front wheel is turned, when steering, through a greater angle than the outside wheel.
4. HYDRAULIC POWER STEERING SYSTEM
Power assisted rack and pinion steering is commonly found on import carsand trucks and front wheel drive vehicles.When first introduced, it was commonly found on import cars and trucks.Today, its use is widespread and can be found on both domestic and importcars and trucks, and many sport utility vehicles.It is similar to the integral system because the power cylinder and thecontrol valve are in the same housing.
In rack and pinion steering, the gear on the steering column’s end is similarto the pinion gear in the differential: cut on an angle, and meshed with asteel bar (the rack) toothed on one side. The rack is mounted parallel tothe front axle and as the steering wheel turns, it operates directly on thetie rods without the use of a pitman arm, idler or intermediate (or relay) rod.
Adding a power assist to this type of steering is quite simple. The power pistonis actually part of the rack and the rack housing acts as the cylinder. Thecontrol valve is located in the pinion housing. Rotation of the steering shaft and pinion turns the valve to direct hydraulic pressure to either endof the rack piston.
5. MAIN PARTS OF THE HYDRAULIC POWER STEERING SYSTEM
The main parts of the hydraulic power steering system are
1. Power steering pump
2. Hydraulic hoses
3. Rack and pinion Steering gearbox
5. Hydraulic fluid
There are three types of power steering pumps: vane, roller and slipper. Thevane type is the most popular.The difference between pumps used is the design of the fins that move thefluid within the pump to build pressure. All pumps use a rotor that spins insidethe pump housing. With the vane type pump, the rotor turns inside an oval orelliptical housing. The vanes, fitted to the outside diameter of the rotor, rideagainst the housing walls as the rotor turns. Power steering fluid enters theoval housing and fluid is trapped between the vanes, housing wall and rotor.
This causes a pressure increase that pumps fluid out of the housing through
the outlet chambers.In roller type pumps, the housing’s inside contour is also oval. Wide V-groovesare cut into the rotor. Steel rollers ride in these grooves and, like the vanetype, they follow the inside contour of the pump housing as centrifugal forcepushes them out at the oval’s end. The rollers trap fluid in the same way asthe vanes and when they pass the narrow portions of the body, they pressurizethe fluid and force it out through two outlets.
Also rotating in an elliptical chamber within the pump body, the rotor of theslipper type pump has several wide slots cut into it fitted with springs toppedby scrubber-type “slippers.” The springs keep the slippers in contact with the pump body walls. The whole assembly resembles a spring-loaded honespinning
As we have seen, hoses for power steering systems generally fall into threecategories: pressure lines, return lines and cylinder lines. Cylinder lines areused on all late-model rack and pinion cars.Pressure lines are often subjected to hydraulic pressures of up to 1,300 psi.
These hoses must be constructed differently from return lines, which rarelycarry more than 50 psi.The purpose of power steering hoses is to transmit power by conducting fluidunder pressure from the pump to the actuating mechanism and back to thepump. But these hoses must perform other jobs that are not so obvious. Power steering hoses also serve as reservoirs for fluid and act as sound andvibration dampers. Pressure hoses are subject to surges in pressures andpulsation from the pump. Consequently, these hoses must be slightlyexpandable to reduce or absorb fluctuations. Hoses must also withstand heat.During parking, for example, fluid temperatures often reach 300° F.
It is important to remember that power steering hoses lose their effectivenesslong before showing external signs of deterioration and leaking. In addition,hoses usually deteriorate from the inside first. High fluid temperaturesand constant flexing cause particles of the hose interior to flake off andcontaminate the system – resulting in plugged strainers, sticking controlvalves and overall erratic system behaviour
The rack-and-pinion steering gear box has a pinion, connected to the steering column. This pinion runs in mesh with a rack that is connected to the steering tie rods. This gives more direct operation.
Both the pinion and the rack teeth are helical gears. Helical gearing gives smoother and quieter operation for the driver.
Turning the steering wheel rotates the pinion, and moves the rack from side to side. Ball joints at the end of the rack locate the tie-rods and allow movement in the steering and suspension.
Mechanical advantage is gained by the reduction ratio. The value of this ratio depends on the size of the pinion.A small pinion gives light steering, but it requires many turns of the steering wheel to travel from lock, to lock.A large pinion means the number of turns of the steering column is reduced, but the steering is heavier to turn.Ratios vary, depending on the type of vehicle.
But in each case, the ratio is the same for all positions of the wheels. It is a fixed ratio.
The hydraulic reservoir is the fluid storehouse for hydraulic power steering system. The slight movement of the steering wheel actuates a valve so that the fluid under pressure from the reservoir enters on the appropriate side of the cylinder, there by applying pressure on one side of a piston to operate the steering linkage, which steers the wheel in the appropriate direction
POWER STEERING FLUIDPower Steering Hoses
This fluid is a specially formulated solution. It may be similar to automatic transmission fluid and may contain some of the same rust and corrosion inhibitors, but it is not the same. Power steering fluid is made to withstand higher temperatures. Power steering fluid must also be compatible with the rubber materials in hoses, pump seals, valves and cylinders. Blended to resist thinning at high temperatures, it usually contains a pour point depressant to maintain flow at temperatures as low as -20° F. The power steering system must be filled to the proper level with clean fluid at all times to maintain precise steering action. The biggest enemy of power steering systems is dirt and sludge in the fluid.
6. FABRICATION DETAILS OF HYDRAULIC POWER STEERING SYSTEM
1. The power steering system used in this project is extracted from DAEWOO CIELO CARS.
2. The stand and other components were procured from various sources.
3. The rough design for the project was prepared after a thorough analysis of various aspects
4. The steel angler has been cut using cutting machine from production lab according to the measured dimensions.
5. To get perfect weld joints we cut notches in the steel angler.
6. It was welded to make a rectangular frame.
7. Supporting legs were added according to the load requirement and frame design.
8. For clamping steering gear box, two steel bars were drilled using drilling machine.
9. It was welded to the top of the base frame.
10. A steering gearbox was mounted on the steel bar frame using clamps and fastened.
11. Wheel hubs were attached to the ends of the base.
12. The steering gear box on the angular is connected to the wheel hubs.
13. The wheel hubs were connected to each other with a steel bar, in order to attain parallel movement of the wheels
14. A reservoir was fixed higher rod from the base in order to acquire the easy flow of fluid.
15. The power steering pump was fixed to the base frame.
16. The steering column was fixed to a vertical load welded to the base frame.
17. All these parts were bolted and tightened.
18. All the edges were grinded to get a smooth finish.
19. All parts were given a better finish with sand paper.
20. Metallic primer was applied to get good finish and to avoid corrosion.
21. All parts were painted with appropriate color.
22. Oil was poured into the reservoir and whole system is ready to gear up a new era of mechanical efficiency.
Because of exposure to under hood heat, high fluid temperatures, ozone,flexing, abrasion, grease, oil and road salt, power steering hoses should be replaced at least every five years to ensure safe operation.When checking power steering hoses, watch for symptoms indicating the hosehas deteriorated and should be replaced:
· Hose is brittle or hard. With age, the hose loses its ability to expand andcontract properly, and cracks appear. Exposure to excess heat (which“overcures” the rubber compounds) can cause this.
· Hose is soft and spongy. A good sign that the hose has started todeteriorate inside. Oil and grease-soaked hoses are soft when squeezed,and should be replaced.
· Exterior is worn. Caused by abrasion and contact with metal parts, thiscan eventually wear a hole in the hose, causing it to burst under pressure.Remember that not all power steering hose failures can be spotted by exteriorsigns. Hose can deteriorate from the inside, causing small particles of the tube to flake off and be carried away by the fluid. These small particles can cause expensive damage to the pump, pump cylinder and other units.This composite illustration shows the many areas of deterioration that are easy to detect by an alert technician. If the hose is soft and spongy, internal Deterioration is the problem.
8. HYDRAULIC STEERING MAINTENANCE AND REPAIR
Hydraulic steering has found almost universal acceptance in modern vessels due to its relatively simple installation, smooth operation, and remarkable reliability. In fact, hydraulic steering is so reliable that driver too often thinks hydraulic steering systems are maintenance-free, and treat them accordingly. Then, when the system does malfunction, they don’t know how to repair it because they have never worked on it.
Hydraulic steering systems are either power assisted or manual and manual systems are either pressurized or non-pressurized. Most vessels over about 30 feet with autopilots have power-assisted steering, with power supplied by a hydraulic pump driven by a main engine. The power supply may also operate the anchor winch, gurdies, reels, and other deck equipment.
The steering system may be teed off that hydraulic circuit with a selector valve, or the vessel may have separate hydraulics for steering and deck machinery. Vessels without an autopilot may or may not have power steering. In either case, the system works pretty much the same way: the steering wheel drives a helm pump which forces a non-compressible fluid through lines to cylinders, where the pressure forces out a ram attached to steering linkages. In the simplest system that’s all there is to it—one helm pump actuates one cylinder, and the only additional component is a small reservoir, usually contained within the helm unit, providing a constant supply of fluid to the pump. Some makes use a separate reservoir. Most are nonpressurized, which means that the fluid is supplied to the pump solely by atmospheric pressure, assured by a vented cap in the reservoir; but a few, such as Hynautic, use a sealed reservoir in which air pressure is added via a device such as a bicycle pump.
Obviously, multiple helms, multiple rudders, and multiple cylinders on each rudder all add to the complexity, but the system is the same. If the system has power assist or an autopilot or both, the helm pump and the cylinder assembly are about the same; but between them is a set of valves and solenoids which introduce the pressurized oil from the power pump into the lines going to the cylinders.
Although this additional complexity adds to the potential for failure, in practice these systems are so well engineered that they tend to be just as reliable as the basic steering system, assuming they are sized and installed correctly.
9. STEERING DIAGNOSIS TROUBLESHOOTING STRATEGY
Ø INSPECTION PROCEDURE 1: Excessive Play of Steering Wheel
o STEP 1. Check for looseness at the steering shaft coupling section and at the steering wheel linkage.
o STEP 2. Check the steering wheel free play.
(1) With engine running (hydraulic operation), set front wheels straight ahead.
(2) Measure the play on steering wheel circumference before wheels start to move when slightly moving the steering wheel in both directions.
Limit: 30 mm (1.2 inch)
(3) If the free play exceeds the limit value, set steering wheelstraight ahead with engine stopped. Load approximately 5 N (1.1 pound) toward steering circumference and check play.Standard value (steering wheel play with engine stopped): 10 mm (0.4 inch) or less
o STEP 3. Check steering wheel play.
Verify that the steering wheel play is not excessive.
Ø INSPECTION PROCEDURE 2: Difficult Steering Wheel Operation (Insufficient Power Assist)
o STEP 1. Check the power steering belt tension.
o STEP 2. Check the belt for damage.
o STEP 3. Check the fluid level.
(1) Park the vehicle on a flat, level surface, start the engine, and then turn the steering wheel several times to raise the temperature of the fluid to approximately 50 −60C (122 −140F).
(2) With the engine running, turn the wheel all the way to the left and right several times.
(3) Check the fluid in the oil reservoir for foaming or milkiness.Check the difference of the fluid level when the engine is stopped, and while it is running. If the change of the fluid level is 5 mm (0.2 inch) or more, bleed air from the system.
o STEP 4. Check for entry of air.
o STEP 5. Check each hose for crushing or twisting.
o STEP 6. Check for oil leaks.
o STEP 7. Check the wheel alignment (camber and caster).
o STEP 8. Check the gear box rack piston seal for damage.
o STEP 9. Check for excessive tie rod end ball joint breakaway torque.
o STEP 10. Check steering wheel operation.
Ø INSPECTION PROCEDURE 3: Rattling Noise
o STEP 1. Check for proper oil pump and gear box installation.
o STEP 2. Check for interference of other parts with the steering column and power steering hoses.
o STEP 3. Check for noise from inside the oil pumpor gear box.
o STEP 4. Check for rattling noise.
Ø INSPECTION PROCEDURE 4: Shrill Noise
o STEP 1. Check for entry of air.
o STEP 2. Check for seizure in the oil pump.
Ø INSPECTION PROCEDURE 5: Squealing Noise
o STEP 1. Check the belt tension
o STEP 2. Check for seizure in the oil pump.
Ø INSPECTION PROCEDURE 6: Hissing Noise
o STEP 1. Check for entry of air.
o STEP 2. Check each hose for crushing or twisting.
o STEP 3. Check the steering gear box for damage.
Ø INSPECTION PROCEDURE 7: Droning Noise
o STEP 1. Check the oil pump or oil pump bracket installation.
o STEP 2. Check the oil pump for damage.
Ø INSPECTION PROCEDURE 8: Squeaking Noise
o STEP 1. Check for interference of the wheel and vehicle body.
o STEP 2. Check the steering gear box for damage.
Ø INSPECTION PROCEDURE 9: Vibration
o STEP 1. Check for entry of air.
o STEP 2. Check the steering gear box for damage
Ø INSPECTION PROCEDURE 10: Oil Leakage from Hose Connection
o STEP 1. Check for loosening of the flare nut.
o STEP 2. Check the insertion of the hose and theclamp installation state.
Ø INSPECTION PROCEDURE 11: Oil Leakage from Hose Assembly
o STEP 1. Check the hose for damage or clogging.
Ø INSPECTION PROCEDURE 12: Oil Leakage from Oil Reservoir
o STEP 1. Check the oil reservoir for damage.
o STEP 2. Check for overflowing.
Ø INSPECTION PROCEDURE 13: Oil Leakage from Oil Pump
o STEP 1. Check the oil pump body for damage.
o STEP 2. Check the O-ring or oil seal for damage.
Ø INSPECTION PROCEDURE 14: Oil Leakage from Gear Box
o STEP 1. Check the gear box housing for damage.
o STEP 2. Check the oil-ring or oil seal for damage.
Steering effort is considerably reduced.Foreg. A 16 ton truck can be steered as easily as a modern small car. Due to this the driver remains alert even at the end of the day.
The vehicle can be steered lock to lock with approximately one and a half steering wheel turns on either side compared to more than three turns on either side in case of manual gears. With this high degree of steering response, the driver gets excellent maneuverability even in high congested traffic.
The hydraulics of the power steering system absorbs the road shock whereas in case of manual steering, the shocks due to potholes and humps are transmitted to the steering wheel. Thus in a power steered vehicles, there is less driver fatigue.
In a manually steered vehicle, tyre familiars and maladjusted brakes often cause violent vehicle pull to either side. Since the effort required and the response is poor, the driver is often unable to avert accident. However, in case of power steering, the hydraulic resists such deviation from the course of the vehicle and whatever minor course-correction are required, can be made quickly and effortlessly. Thus power steering system Leeds to greater safety.
11. ELECTRONIC POWER STEERING
Electrically powered steering uses an electric motor to drive either the power steering hydraulic pump or the steering linkage directly. The power steering function is therefore independent of engine speed, resulting in significant energy savings.
Conventional power steering systems use an engine accessory belt to drive the pump, providing pressurized fluid that operates a piston in the power steering gear or actuator to assist the driver.
In electro-hydraulic steering, one electrically powered steering concept uses a high efficiency pump driven by an electric motor. Pump speed is regulated by an electric controller to vary pump pressure and flow, providing steering efforts tailored for different driving situations. The pump can be run at low speed or shut off to provide energy savings during straight ahead driving (which is most of the time in most world markets).
Direct electric steering uses an electric motor attached to the steering rack via a gear mechanism (no pump or fluid). A variety of motor types and gear drives is possible. A microprocessor controls steering dynamics and driver effort. Inputs include vehicle speed and steering, wheel torque, angular position and turning rate
A "steering sensor" is located on the input shaft where it enters the gearbox housing. The steering sensor is actually two sensors in one: a "torque sensor" that converts steering torque input and its direction into voltage signals, and a "rotation sensor" that converts the rotation speed and direction into voltage signals. An "interface" circuit that shares the same housing converts the signals from the torque sensor and rotation sensor into signals the control electronics can process.
Inputs from the steering sensor are digested by a microprocessor control unit that also monitors input from the vehicle's speed sensor. The sensor inputs are then compared to determine how much power assist is required according to a preprogrammed "force map" in the control unit's memory. The control unit then sends out the appropriate command to the "power unit" which then supplies the electric motor with current. The motor pushes the rack to the right or left depending on which way the voltage flows (reversing the current reverses the direction the motor spins). Increasing the current to the motor increases the amount of power assist.
The system has three operating modes: a "normal" control mode in which left or right power assist is provided in response to input from the steering torque and rotation sensor's inputs; a "return" control mode which is used to assist steering return after completing a turn; and a "damper" control mode that changes with vehicle speed to improve road feel and dampen kickback.
If the steering wheel is turned and held in the full-lock position and steering assist reaches a maximum, the control unit reduces current to the electric motor to prevent an overload situation that might damage the motor. The control unit is also designed to protect the motor against voltage surges from a faulty alternator or charging problem.
The electronic steering control unit is capable of self-diagnosing faults by monitoring the system's inputs and outputs, and the driving current of the electric motor. If a problem occurs, the control unit turns the system off by actuating a fail-safe relay in the power unit. This eliminates all power assist, causing the system to revert back to manual steering.
HYDRAULIC POWER STEERING SYSTEM
The hydraulic power steering system is very good and advance steering system in this project hydraulic power of power system of Daewoo ciello was assembled and studied.This is system is implemented in most of advanced cars. This is highly economical and more mechanical advantages.
These system would completely eliminated mechanical connection between steering wheel and steering, replacing it with purely electronics control system it would contain sensors that tell the car what the driver is doing with the wheel and have some motor it to provide the driver with feed bake on what the car is doing the output of their sensor would be used to control a motorised steering system due to simplicity. The hydraulic power steering system is most suitable for the future explanation.