Automotif Engine, Repair Power Steering and defenition

POWER STEERING 

Automotif Engine   In automobiles, power steering (also power assisted steering (PAS) or steering assist system) helps drivers steer by augmenting steering effort of the steering wheel.

Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver needs to provide only modest effort regardless of conditions. Power steering helps considerably when a vehicle is stopped or moving slowly. Also, power steering provides some feedback of forces acting on the front wheels to give an ongoing sense of how the wheels are interacting with the road; this is typically called "rοad feel"

Representative power steering systems for cars augment steering effort via an actuator, a hydraulic cylinder, which is part of a servo system. These systems have a direct mechanical connection between the steering wheel and the linkage that steers the wheels. This means that power-steering system failure (to augment effort) still permits the vehicle to be steered using manual effort alone.
Other power steering systems (such as those in the largest off-road construction vehicles) have no direct mechanical connection to the steering linkage; they require electrical power. 

Systems of this kind, with no mechanical connection, are sometimes called "drive by wire" or "steer by wire", by analogy with aviation's "fly-by-wire". In this context, "wire" refers to electrical cables that carry power and data, not thin-wire-rope mechanical control cables.
In other power steering systems, electric motors provide the assistance instead of hydraulic systems. As with hydraulic types, power to the actuator (motor, in this case) is controlled by the rest of the power-steering system.

Some construction vehicles have a two-part frame with a rugged hinge in the middle; this hinge allows the front and rear axles to become non-parallel to steer the vehicle. Opposing hydraulic cylinders move the halves of the frame relative to each other to steer.

History

The first power steering system on an automobile was apparently installed in 1876 by a man with the surname of Fitts, but little else is known about him. The next power steering system was put on a Columbia 5-ton truck in 1903.

Robert E. Twyford, a resident of Pittsburgh, Pennsylvania, included a mechanical power steering mechanism as part of his patent (U.S. Patent 646,477) issued on April 3, 1900 for the first four wheel drive system.

Francis W. Davis, an engineer of the truck division of Pierce-Arrow, began exploring how steering could be made easier, and in 1926 invented and demonstrated the first practical power steering system.Davis moved to General Motors and refined the hydraulic-assisted power steering system, but the automaker calculated it would be too expensive to produce.Davis then signed up with Bendix, a parts manufacturer for automakers. Military needs during World War II for easier steering on heavy vehicles boosted the need for power assistance on armored cars and tank-recovery vehicles for the British and American armies.

Chrysler Corporation introduced the first commercially available passenger car power steering system on the 1951 Chrysler Imperial under the name "Hydraguide".The Chrysler system was based on some of Davis's expired patents. General Motors introduced the 1952 Cadillac with a power steering system using the work Davis had done for the company almost twenty years earlier.

Charles F. Hammond, an American, born in Detroit, filed several patents for improvements of power steering with the Canadian Intellectual Property Office in 1958.

Most new vehicles now have power steering, owing to the trends toward front wheel drive, greater vehicle mass, and wider tires, which all increase the required steering effort. Heavier vehicles, as are common in some countries, would be extremely difficult to maneuver at low speeds, while vehicles of lighter weight may not need power assisted steering at all.

Hydraulic systems

Most power steering systems work by using a hydraulic system to multiply force applied to the steering wheel inputs to the vehicle's steered (usually front) road wheels. The hydraulic pressure typically comes from a gerotor or rotary vane pump driven by the vehicle's engine. A double-acting hydraulic cylinder applies a force to the steering gear, which in turn steers the roadwheels. The steering wheel operates valves to control flow to the cylinder. The more torque the driver applies to the steering wheel and column, the more fluid the valves allow through to the cylinder, and so the more force is applied to steer the wheels.

One design for measuring the torque applied to the steering wheel has a torque sensor – a torsion bar at the lower end of the steering column. As the steering wheel rotates, so does the steering column, as well as the upper end of the torsion bar. Since the torsion bar is relatively thin and flexible, and the bottom end usually resists being rotated, the bar will twist by an amount proportional to the applied torque. The difference in position between the opposite ends of the torsion bar controls a valve. The valve allows fluid to flow to the cylinder which provides steering assistance; the greater the "twist" of the torsion bar, the greater the force.

Since the hydraulic pumps are positive-displacement type, the flow rate they deliver is directly proportional to the speed of the engine. This means that at high engine speeds the steering would naturally operate faster than at low engine speeds. Because this would be undesirable, a restricting orifice and flow-control valve direct some of the pump's output back to the hydraulic reservoir at high engine speeds. A pressure relief valve prevents a dangerous build-up of pressure when the hydraulic cylinder's piston reaches the end of its stroke.

The steering booster is arranged so that should the booster fail, the steering will continue to work (although the wheel will feel heavier). Loss of power steering can significantly affect the handling of a vehicle. Each vehicle owner's manual gives instructions for inspection of fluid levels and regular maintenance of the power steering system.

The working liquid, also called "hydraulic fluid" or "oil", is the medium by which pressure is transmitted. Common working liquids are based on mineral oil.

Some modern systems also include an electronic control valve to reduce the hydraulic supply pressure as the vehicle's speed increases; this is variable-assist power steering. 

Hydraulic power steering（HPS） 

This is a system designed to assist the operation of the rack bar by generating oil pressure in the pump with the engine's output. Energy savings achieved by utilizing the variable capacity pump. Showa offers a large lineup of product variations applicable to cars ranging from Mini cars to large large-sized (luxuary) cars.

Rack assisted (coaxial type) : RA-EPS

This type has a hollow shaft motor arranged coaxially on the circumference of the rack bar in the power-assisting section. This system directly assists the output shaft through a ball screw, it is highly rigid and provides a smooth steering feel designed to deliver a large power output for both mid-sized and full-sized cars.

Basic Operating Principles of the EPS
The role of power steering is to assist the driver during steering wheel operations, and EPS carries out this assistance through electrical control. Within this basic operation, when the sensor detects “heaviness” as the driver turns the steering wheel, the ECU computers the volume of assistance required based upon the “heaviness information” and “car speed information” it receives, and the motor responds in accordance with the ECU as it generates the required amount of assistance power. By providing assistance volume meeting the characterastics of the vehicle electrically, enables set ups and input various information for controlling the vehicle.

Pinion assisted : PA-EPS

The power-assisting section of this system is arranged in the pinion-shaft (input-shaft) section. This is a suitable system for compact cars, from small cars using brush motors and those using brushless motors appropriate for high-grade compact cars with high performance / high output. Showa offers a large lineup of product variations

Power assist unit

This is an general-purpose power assist unit that applies PA-EPS technology into another Showa product.
This unit is applicable for providing steering power assistance in ATVs and other small vehicles.







Replacing a Bad Power Steering Pump

 

Automotif Engine     Your spouse has been complaining about the minivan being hard to steer. Time to pick up a bottle of power steering oil on the way home. After you add the fluid, though, you notice a puddle of something under the engine. Within a minute of idling, the puddle is bigger by almost exactly 1 pint of power steering fluid. An odd coincidence, indeed. Checking the pump--which is buried well under the engine--reveals a lot of wet, oily stuff in the vicinity. Out come the ramps, and the minivan goes up in the air.

Everybody Has One

If you've never had to wrestle with your steering wheel, you've never driven a vehicle made before, say, the '70s oil crisis. Except for a few late-model cars that use electrically powered steering racks, virtually all cars and trucks on the road today have power-assisted steering. The pump provides hydraulic boost to the steering gear (the mechanism that actually pivots the front wheels) to reduce the driver's turning effort at the wheel.

When this system isn't working properly, every parking maneuver can become an upper-body workout or an ear-piercing underhood concerto. (We'll get to the noise part in a minute.) At road speeds, however, everything will seem pretty normal. Rolling front tires offer negligible resistance to turning, and the power steering system is under little load. At parking-maneuver speed, you need substantial hydraulic boost to spin the steering wheel.

The leak in this pump is from rusted-through sheetmetal housing. Usual leakage mode is shaft seal or hoses.

What's the Problem?
While the trouble may stem from any number of things, including the steering gear itself, it's most likely an issue with the pump or a slow leak in its associated plumbing. Think about it. If a hose or line has a leak so big that it's reducing pressure to the steering gear, you would have known about it right away. You could have starred on the morning news as the guy who caused a 10-car pileup when the high-pressure hose burst and dumped greasy fluid all over an interstate off ramp.

No, you have a more subtle symptom. These belt-driven pumps normally wear out from a low fluid level (caused by that slow leak), contaminated or improper fluid (possibly caused by an overzealous service station jockey), or just age.

                                     

Tight quarters around belt (seen here from underneath) make the simple task of swapping the pump a big puzzle. Remove the serpentine belt first.

A Moose in Heat

A power steering system that is in trouble often informs you of the problem by screaming for help, literally. Whenever the pump gets over-loaded, it emits a high-pitched squeal that sounds something like a moose in heat. Rotate your steering wheel to its end stops for a demonstration. The noise is normal then. But if you hear that sound under any other condition, it means the pump is under load when it shouldn't be or the system has leaked enough fluid that the pump is running dry. So check the power steering fluid level first. If the noise goes away after filling the reservoir to the proper level, you have a leak somewhere. The system won't lose fluid if it's working properly. Squealing sounds? As long as you're under the vehicle, check the pump's belt for proper tension as well as wear and tear. Many engines today use a single serpentine belt to drive all the accessories. If it fails, you'll have more than just power steering trouble. So make sure the serpentine is riding the power steering pump's pulley on the straight and narrow. Some pulleys are plastic, most metal. Regardless, eye it to be sure it's running true.

Rusty bolts holding catalytic converter to manifold had to be broken off after they refused to budge. Use fresh bolts, nuts and gasket for reassembly.

Replacing the Pump 

Power steering pumps are not a DIY rebuild item. A bad pump is replaced, usually with one that's been professionally refurbished. You may be charged a deposit, commonly called a core charge, when you pick up the new pump. You'll get that back when you bring in the old pump for rebuild. Older cars' systems were happy with generic automatic transmission fluid. These days, though, check your owner's manual and the service literature for your specific vehicle at alldatadiy.com to find out exactly what fluid your car or truck manufacturer recommends. Using the wrong fluid could mean doing the whole job over again in a few months.

A flare-nut wrench does a better job of not rounding off fitting on hydraulic line than ordinary open-end

Where Is It?

The first step in replacing the pump is finding it. Don't laugh. Its exact location under the hood depends on many factors. What kind of engine is it--inline or V? Is the engine mounted transversely or longitudinally? Is the fluid reservoir mounted remotely or is it integral with the pump? The pump will be somewhere on the front of the engine with the other accessories. On the typical GM longitudinally mounted V8, for example, the power steering pump will be right behind the radiator (though not necessarily up high and within easy reach). The car seen here is a front-wheel-drive Chrysler-built minivan with a 3.3-liter V6.

A rubber low-pressure line had to be trimmed to break loose from fitting where rubber had gotten hard.

Doing the Switch

To swap out your power steering pump, you should need only basic hand tools. However, some special flare-nut wrenches and a special tool to safely remove the pulley from the pulley shaft will make the job easier. These usually can be rented--even borrowed--from the auto parts store that sells you the replacement pump.

First, remove the drive belt(s) and take a close look--replace them if they're damaged or oil-soaked. Undo the high- and low-pressure lines from the pump body (and the reservoir hose if the fluid reservoir is mounted remotely). Have a catch pan handy for the fluid that will drip. As service manuals often say, "Reverse procedure to install replacement."

Of course, life in the real world is often nothing like life as described in a shop manual. For instance, on our minivan, the pump can be removed and installed only one way--from below. That's because it's mounted all the way at the bottom of the engine and up against the firewall. Wait, it gets worse. To get the pump out, we had to unbolt the exhaust pipe from its flange and move it aside. This is about as extreme as any power steering pump replacement can get, so yours will definitely be easier.

After the new pump is in, belt reinstalled and tensioned, refill the system with the correct fluid. Then--preferably with the front wheels just off the ground and with the engine idling--rotate the steering wheel from left stop to right stop a dozen times to burp excess air from the system. Recheck the fluid level in a couple of days.

Final step: Join a health club or gym to stay in shape because your car's power steering will no longer be your mobile Bowflex machine.

A special tool will probably be necessary to press an old pump off the pulley and press a new pump on.

Top off reservoir, then bleed by turning wheel back and forth a dozen times with wheels off ground, engine idling.