ABS - ANTI BRAKE LOCKING SYSTEM

Anti-Lock Braking System (ABS)

The ABS (Anti-lock Brake System) monitors the speed of each wheel to detect locking. When it detects sudden braking, it will release braking pressure for a moment and then provide optimum braking pressure to each wheel. By repeating this process in a short period of time, it enhances steering control during sudden stops. As a result, it will also help improve the ability of stopping the vehicle.

ABS only supports the driver's control of the vehicle, and it is not a substitute for it. It is the driver's responsibility to drive at the appropriate speed depending on the condition of the road and to keep a generous distance from the car ahead of you.

Supports unexpected braking in case of emergency
Studies show that nearly half of all drivers do not step on the brake quickly and strongly enough to stop the vehicle in case of an emergency 

When Brake Assist detects an attempted panic stop, it supports drivers by strengthening the power
Brake Assist will detect attempted panic braking based on the force that is applied to the brake pedal and how fast the driver is stepping on the pedal. When the system recognizes sudden braking, it will add additional pressure to the brake.

When your foot is released during Braking Assist,braking power lessens and regulates the brakes with ease.

Traction Control (TRC)

When you are starting the vehicle or accelerating on a wet surface, you could lose control of the wheel because of wheel spin. TRC will help prevent such events from happening.

TRC continually monitors the condition between the tires and the surface of the road.When it detects wheel spin, the system applies brakes or slows down the engine to regulate spinning and help ensure proper contact of tires. This help prevent the car from becoming unstable.

There might be the cases in which the half-side of the wheel runs off or the wheels spin off on the snowy road. And also there might be the case that the current tractino control might not be working well.In those cases, Auto LSD is one of the technologies which both improve startability and runability.

Purpose

Anti-lock brake systems (ABS) - generally also referred to as anti-lock systems (ALS) - are designed to prevent the vehicle wheels from locking as a result of the service brake being applied with too much force, especially on slippery road surfaces.

The idea is to maintain cornering forces on braked wheels to ensure that

the vehicle or vehicle combination retains its drivin

g stability and manoeuvrability as far as physically possible. The available powertransmission or grip between tyres and carriageway should also be utilised as

far as possible to minimise the braking distance and maximise vehicle deceleration.

Why ABS?

Although today commercial vehicle brakes are designed to a very hightechnical standard, braking on slippery roads often results in potentially dangerous situations. During full or even partial braking on a slippery road it may no longer be possible to fully transfer the braking force onto the road due to the low coefficient of friction  (friction coefficient (k)) between the tyres and the carriageway. The braking force is excessive and the wheels lock up. Locked wheels no longer provide any grip on the

road and are almost incapable of transferring any cornering forces (steering and tracking forces).

This often has dangerous consequences:

– The vehicle becomes unsteerable

– The vehicle breaks away in spite of countersteering, and starts to swerve.

– The braking distance is significantly increased

– Tractor-trailer combinations or semitrailer trains may break away or jackknife.

Load sensing valve influence

On dry roads today’s load sensing valves (ALB) alone are often capable of preventing the wheels from locking if the vehicle is unladen; they also help the driver to effectively grade the braking process on wet road surfaces, but they are unable to prevent locking as such (no slip monitoring). In addition, they are unable to counteract any overreactions on the part of the driver, or any variances in frictional or adhesion coefficients which may apply to different sides of the vehicle, or indeed to its different axles (μ split road surfaces).

Benefits of ABS:

Only the Anti-Lock Brake System (ABS)

– guarantees stable braking characteristics on all road surfaces.

– maintains steerability and generally reduces the braking distance

– prevents vehicle combinations from jackknifing

– reduces tyre wear.

Limits of ABS

Although ABS is an effective safety device, it can not suspend the limits

defined by driving physics. Even a vehicle fitted with ABS will become uncontrollable if driven too fast around a corner. So ABS is not a licence for a maladjusted style of driving or failure to observe the correct safety distance.

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POWER STEERING

Introduction to Power Steering

                The purpose of power steering is to reduce the driver’s effort at the steering wheel

•             Almost all modern luxury cars are equipped with power steering system instead of manual steering

•             The power steering is increasingly becoming popular on light, medium and heavy vehicles also

Introduction to Power Steering

•             Power steering system is used in big cars and heavy commercial vehicles whose unladen weight is more than1 500 kg

•             It is useful while driving on rough roads at low speeds and while reversing the vehicle for parking purpose

•             The power steering mechanism employs electrical devices, compressed air and hydraulic pressure

•             The power steering system commonly take assistance of hydraulic power for their operation

•             They become operative when the manual effort exceeds about 1kgf(9.81 N)

•             The system is designed such that if power system fails, it can be operated manually

•             In this situation the driver’s effort will be more such as in manual steering

•             The ‘Power Brakes’ utilise the vacuum and hydraulic powers for their working, but the ‘Power Steering’ utilise hydraulic power only

•             Usually oils of viscosity ratings SAE 5W to 15W flow through the system at about 10 -11kgf/cm2 (1 MPa) pressure

Advantages of Power Steering

•             Lesser steering effort

•             Reduced driver’s fatigue

•             Efficient absorption of shocks

•             Better directional stability

Advantages of Power Steering

•             Higher performance

•             Higher maneuverability

•             Enhanced safety

Types of Power Steering Systems

1.            Integral type  

a.            Rotary spool valve type

b.            Reaction control valve type

2.            Semi-integral type

Ex: Trucks and other Heavy Vehicles

3.            Linkage booster type 

Ex: Rack and pinion type

4.            Speed responding type       

Principles of Power Steering

•             The Power steering is one type of hydraulic device for utilising engine power as steering effort

•             The Engine is used to drive a pump to develop fluid pressure

•             This pressure acts on the piston with in the power cylinder so that the piston assists the rack effort

•             The amount of this assistance depends on the extent of pressure acting on the piston.

•             If more steering force is required, the pressure must be raised.

•             Variation in the fluid pressure is accomplished by a control valve which is linked to the steering main shaft.

                The working principle of a power steering

(a)          Neutral (Straight-ahead ) position

(b)          Turning position can be understood in the next slide

Neutral (Straight-ahead position):

•             Fluid from the pump is sent to the control valve

•             If the control valve is in the neutral position, all the fluid will flow pass through the control valve into the relief port and back to the pump

•             At this time hardly any pressure is created and because the pressure on the cylinder piston is equal on both sides, the piston will not move in either direction

Turning  Position:

•             When the steering main shaft is turned in either direction, the control valve also moves, closing the one of the fluid passages

•             The other passage then opens wider, causing a change in fluid flow volume and at the same time, pressure is created

•             Consequently, a pressure difference occurs between both sides of the piston and piston moves in the direction of low pressure

•             Thus, the fluid in that cylinder is forced back to the pump through the control valve

Steering Gear Booster in a Typical Power Steering System

Parts:

1.Worm      2.Sector   3.Booster cylinder   4.Gear rack   5.Arm

6.Drag link  7.Distibutor slide valve   8. Pipe line

Type Power Steering System

•             A simplified diagram of a hydraulic booster is shown in the previous

•             When the steering wheel is turned, worm (1) turns sector (2) of the worm wheel and arm (5), which turns the wheel by means of drag link (6).

Type Power Steering System

•             If the resistance offered to the turn of the wheels is too high and the effort applied by the driver to the steering wheel is  too weak

•             The worm will be displaced axially (like a screw in a nut) together with distributor slide valve( 7 ) and will thus admit oil (or compressed air) into booster cylinder ( 3) through pipe line (8)

•             The piston will move in cylinder (3) and will turn the wheels via gear rack (4), a toothed sector, arm (5) and drag link (6)

•             At the same time, the worm sector will act upon the worm and will shift with together with the distributor slide valve to its initial position and stop the piston travel

•             When the steering wheel is turned in the other direction, the wheels will be turned appropriately in the same sequence

Various Power Steering Systems 

Various Power Steering Systems

Turbocharged Direct Injection VS Common Rail Diesel Injection (TDI VS CRDI)

TDI    was ( turbocharged diesel intercooler) or (turbocharged direct injection) and CRDI was ( common rail diesel injection.)

TDI ENGINE:it had 2 variants VGT(variable geometric turbo) and (non variable) normal TDI engine had a fixed turbine.

The TDI engine uses direct injection,where a fuel injector sprays atomised fuel directly into the main combustion chamber of each cylinder, rather than the pre-combustion chamber prevalent in older diesels which used indirect injection. The engine also uses forced induction by way of a turbocharger to increase the amount of air which was able to enter the engine cylinders,and most TDI engines also feature an intercooler to lower the temperature (and therefore increase the density) of the 'charged', or compressed air from the turbo, thereby increasing the amount of fuel that can be injected and combusted.

(VGTs) slightly different design to avoid turbo lag causing by low speed, usually designed to allow the effective aspect ratio (A:R) of the turbo to be altered as conditions change. This was done because optimum aspect ratio at low engine speeds was very different from that at high engine speeds. 

If the aspect ratio was too large, the turbo will fail to create boost at low speeds; if the aspect ratio was too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output.

By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum

A CRDi engine had rails that inject the fuel into the engine, which was designed to handle higher pressure than an ordinary diesel engine "thereby having results in fuller combustion and efficiency. Since the development of the diesel engine almost a century ago, the focus had been on increasing the fuel injection pressure.In CRDi, the high fuel injection pressure was generated by a supply pump storing in a reservoir the fuel under high pressure in a central container (rail) and delivering to the individual injection valves (injectors) on demand