Vehicle Skid Control

VEHICLE SKIDDING

SUBMITTED BY:UDAY VIR SINGH RANA(80904114110) SUPREET SINGH RANA(80904114106) SURYADEEP SINGH VIRK(80904114107) AKSHAY GARG(80904114119) GARG(80904114119)

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VEHICLE SKID CONTROL 1. INTRODUCTION Vehicle skid can be defined as the loss of  traction between a vehicle’s tyres and the road surface due to the forces acting on the vehic icle le.. Mos Most skids are are caus aused by driver ver error, although only about 15% of accidents are the direct result of a vehicle skidding. Skids

occurring

in

other

accidents

are

usually the result of last minute action, by the driver, when faced with a crisis ahead rath rather er than than actu actual ally ly caus causin ing g an acci accide dent nt.. Skids can occur both in the dry and wet as well as icy conditions, however, the chances of losi osing cont ontrol and and havi vin ng an acc accid ide ent 4

VEHICLE SKID CONTROL 1. INTRODUCTION Vehicle skid can be defined as the loss of  traction between a vehicle’s tyres and the road surface due to the forces acting on the vehic icle le.. Mos Most skids are are caus aused by driver ver error, although only about 15% of accidents are the direct result of a vehicle skidding. Skids

occurring

in

other

accidents

are

usually the result of last minute action, by the driver, when faced with a crisis ahead rath rather er than than actu actual ally ly caus causin ing g an acci accide dent nt.. Skids can occur both in the dry and wet as well as icy conditions, however, the chances of losi osing cont ontrol and and havi vin ng an acc accid ide ent 4

increases by 50% in the wet. The most common type of skid we will be confronted with is when the rear end of the car slides out, causing an oversteer or when the front of the car plows toward the outside of a turn without following the curve of the turn causi causing ng an unde unders rste teer er.. Usual Usually ly,, overs overste teer er occurs as a result of going into a corner too fast or incorrectly hitting a slick area, causing the rear wheels to oversteer. A third skid called the four wheel skid can also occur, where all the four wheels lock up and the vehicle slides in the direction where the forward momentum is carrying it, with no directional control. To counter these skids and to prevent accidents from happening, Vehicle 5

Skid Control (VSC) is incorporated in the vehicle. Vehicle Skid Control (VSC) takes the safety aspects of the driver and the vehicle to the next level. It comes under the category of “Passive Technology”, which helps you to avoid a crash. Vehicle Skid Control (VSC) senses the onset of traction loss and helps the driver stay on track. This is achieved via the system's ability to reduce engine power and to control the brake actuator. VSC helps the driver maintain vehicle traction under demanding conditions by detecting and helping to correct the wheel spin. VSC uses a variety of sensor input to determine if the car is losing traction, individual

then

applies

wheels

to

6

the help

brakes

to

correct

for

discrepancies. The system will also back off  the throttle to reduce power. VSC integrates traction control to limit rear wheelspin on slippery

surfaces.

The

VSC

system

electronically monitors speed and direction, and compares the vehicle's direction of  travel with the driver's steering, acceleration and braking input. VSC can help the driver compensate for loss of lateral traction, which can cause skids and loss of vehicle control.

2. CAUSES The main causes of

skidding are

follows:

a) Harsh or sudden acceleration. b) Excessive or sudden braking. c) Coarse or jerky steering movements. 7

as

d) Oversteer and understeer. The effects of the above will be enhanced

by

speed.

Combining

these

effects with non-recognition of adverse road and weather conditions will create problems for the driver.

3. TYPES OF SKID The main types of skid that a driver could encounter on the public highway fall into three categories. 1) The front wheel skid. 2) The rear wheel skid. 3) The four wheel skid.

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3.1. The Front Wheel Skid

3.1.1.Characteristics The car tends to take a course outside of the expected course that the driver has steered (understeer). If the front tyre approaches the traction limit more rapidly, the effect is that the front of  the car takes a wider radius curve than the driver intended. The car is said to understeer.

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3.1.2. Cause Excess speed on entry to a hazard i.e. a corner or bend, or sudden braking to reduce the speed when negotiating the hazard. Both of these actions will have the effect of destabilising the vehicle making it more vulnerable to a loss of control.

3.2. The Rear Wheel Skid

3.2.1. Characteristics The rear of vehicle swings out of  line and gives the impression of trying to overtake the front (oversteer); see figure 10

2. If the rear tyres approach their traction limit more rapidly than the front, then the effect is for the rear of the car to steer a wider path than the front wheels. This rotates the car more than the driver intended and, if nothing is done, leads to the car turning a smaller radius corner. When this occurs the car is said to oversteer.

3.2.2. Cause As with the front wheel skid, excessive speed into the hazard and sudden braking or acc-eleration with a rear wheel drive vehicle, destabilising the vehicle, are the main causes of this skid.

3.3. The Four Wheel Skid

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3.3.1. Characteristics All four wheels have locked up and the vehicle is sliding in the direction that the forward momentum is carrying it, with no directional control; see figure 3. Both front and rear wheel skids, if unchecked sufficiently early, can develop into four wheel skids.

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3.3.2. Cause Harsh or sudden braking has caused the wheels to lock. A sensation of  increase in the vehicle’s speed often occurs.

Figure 1

4. UNDERSTEER AND OVERSTEER 4.1. Understeer

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As the name implies, understeer occurs when the front slip angle is greater than the rear and the car goes straighter rather than following the intended turn.  The slip angle, or yaw angle in technical terminology, is the angle between where the car is pointing and the intended path.  The yaw moment is the rate at which the yaw angle is changing. The higher the yaw moment, the more likely it is that the driver is losing control. At the same point, the front wheel may start to grip less even when the steering is turned sharply and as a result the car continues in more of a straight line than a sharp turn. Here in this case, the skid control system brakes the inside rear wheel, effectively tightening the car’s line. By applying the brakes, the

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car

slows

down

which

further

helps

stabilise it.

4.2. Oversteer Oversteer, on the other hand, occurs when the rear tyres have a greater slip angle than the front tyres and the back threatens to overtake the front, causing the vehicle to spin. In other words, if the rear tyres approach their traction limit more rapidly than the front, then the effect is for the rear of the car to steer a wider path than the front wheels. This rotates the car more than the driver intended and, if nothing is done, leads to the car turning a smaller radius corner. When this occurs the car is said to 15

oversteer. Here the skid control system brakes the outside front wheel to reduce oversteer, effectively pulling the tail back into line.

5. SKID CONTROL Stability control systems or skid control systems Dynamic

with

names

Stability

like

Control,

StabiliTrak, Stability

Management, and Vehicle Skid Control are the latest advancement in vehicle safety. Regardless of the different names, they all perform the same task – to sense the onset of traction loss and keep the driver on track. These systems are designed to deliver

transparent

intervention

the

moment the situation becomes unstable. A vehicle skid control system actually

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detects when a driver has lost some degree of control. It then automatically stabilizes the vehicle to help the driver regain control. Vehicle Skid Control (VSC) takes the safety aspects of the driver and the vehicle to a completely new level. These skid control systems are often integrated with the engine management system to cut power in even more tricky situations. This scenario is a complex system of sensors and microprocessors that continually monitor the vehicle for any signs of instability. Once detected (usually in the form of a slide or skid), the system braking

automatically to

specific

applies

selective

wheels

thereby

stabilizing the vehicle. This split-second intervention often happens so quickly that

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it is over before drivers even realize they were in danger of losing control. By gently stabilizing the car at the critical moment, control is returned to the driver with minimal fuss and alarm. Luxury cars, such as the Mercedes Benzes, BMW, Lexus, etc. now sold in India, have stability systems installed that are designed to remove oversteer or understeer.

6. COMPONENTS The Vehicle Skid Control (VSC) is made possible by the combination of different electronic and mechanical components. Some of the components are those used in Anti-lock Braking System (ABS), and an electronically controlled engine throttle, as well as a dedicated computer and sensors,

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providing information to the VSC system.  These include:

Figure 2

•

 Yaw rate sensor.

•

G-sensor.

•

Steering angle sensor.

•

Electronic throttle control.

•

Slip indicator.

•

Computer.

•

 Yaw rate sensors detect changes in the car's rotation in a left or right direction. It keeps track of the direction in which the 19

car is moving relative to which way the driver is

turning the steering wheel. When the sensors detect understeer or oversteer, a computer takes over and applies brakes or controls power to one or both the drive wheels, so that the car comes under control.

 The system is programmed to respond to a wide variety of scenarios and is so selective that it can apply only the brake on one specific wheel if that's what is needed to regain control. The G-sensor or gravity sensor determines if the car is accelerating

or

decelerating,

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cornering

and braking forces simultaneously while the car is on the move and accordingly controls the throttle. Steering angle sensor evaluates the direction and rate of change in steering wheel movement. Electronic throttle control reduces the throttle for 1/7th of a second, to control the wheel spin, when the front or rear wheels lose traction. Slip indicator alerts the driver that the tyres are about to exceed the grip limit. The central processing computer monitors the steering movement together with

either

taking

over

and

applying

brakes or controlling the power to one or both the drive wheels.

7. WORKING The heart of all these systems is a central processor that takes information 21

from a number of sensors, and then determines whether the car is in a stable or unstable state. By combining the datas from

ABS

steering

sensors

angle

(for

sensors,

wheel

speed),

yaw

sensors

(measuring the amount a car fishtails, or rotates around its vertical center axis), and lateral force sensors (measuring the amount of sideways g-force generated by the car), the central processing unit can actually detect when a vehicle is behaving in a way contrary to how the driver intends. VSC also includes a slip indicator with a warning sound and light to alert the driver that the tyres are about to exceed the grip limit. If the processor does detect instability such as a slide produced by a sudden 22

swerve,

it

automatically

applies

light

brake pressure to a select wheel (or wheels) to maintain or restore control. Here, the VSC computer uses engine throttle

control

and

individual

wheel

braking to help counteract skidding and spinning.The constantly

high-speed compares

the

computer driver's

intentions, as indicated by steering wheel, throttle and braking activity, with the car's actual motions measured by the various sensors. If they do not correlate, the VSC computer

selectively

applies

individual

wheel brakes and/or momentarily reduces engine power as necessary to help the driver regain the intended direction of  travel.

For example, if the car were

tending to continue straight rather than

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responding to the driver's right turn of the steering

wheel,

VSC

would

typically

reduce engine power and would apply the right front brake momentarily to help the car follow the intended path. Once proper vehicle attitude is restored, VSC returns to a standby state. When VSC is active, a warning beep tone and instrument panel warning light indicate that the system is functioning. In many cases, VSC reacts well before the driver is aware of a loss of  lateral traction. A VSC shutoff button deactivates VSC and electronic traction control for use. At all other times,VSC remains on and functioning. VSC differs from

Anti-lock

Braking

System

(ABS)

technology. ABS prevents vehicle wheels

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from

locking,

decreases

the

distance

required to stop and improves a driver's

control during emergency braking on wet and slippery roads whereas VSC is intended to help a driver maintain the intended direction of travel, even when the brakes are not applied. However, VSC and ABS compliment and work in close coordination with each other in stability control system, providing enhanced driver control in a broad range of situations.VSC can help provide a measure of control in real-world situations faced by even the most careful and experienced drivers. VSC senses the onset of traction loss and helps the driver stay on track. This is achieved

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via the system's ability to reduce engine power and to control the brake actuator.

8. WHEN DOES IT HELP? Like the safety systems that preceded it, Vehicle Skid Control is designed to step in when human input is incapable of  effectively controlling the vehicle. In most cases, critical situations are the result of  human error in the first place-driving too quickly, simply

inattention, panicking

in

misjudgment an

or

emergency

situation. In these situations, everyone can benefit from a safety system that occasionally helps regain vehicle stability, while never taking full control out of the driver's hands.

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After the introduction of  ABS, no safety advancement has added such a high level of driving security as VSC. When used with ABS and traction control, Vehicle Skid Control significantly increases a driver's chances of recovering from potentially dangerous situations. But no matter how advanced the safety aid, the ultimate fate of a vehicle and its occupants remains in the hands of the driver. No safety system should ever be expected to protect unconditionally. So while the latest generation of stability control systems offer drivers increased protection from both themselves and the unexpected, they can never overcome poor judgement or the laws of physics.

9. REMEDIAL MEASURES 27

In each case, the cause can be removed

by

taking

the

foot

off

the

accelerator or brake and depressing the clutch. The reasons are as follows:•

By decelerating, the vehicle’s speed is lowered, which in turn will start to reduce the magnitude of the skid.

•

Relaxation of the pressure on the brake pedal will unlock the wheels and allow the tyres to regain traction, enabling the vehicle to be steered.

•

Depressing the clutch pedal has 3 beneficial effects: (i)

The engine will not stall, enabling the vehicle to be moved quickly from the danger area.

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(ii) The link between engine (providing power) and transmission is broken; there is no drive to any of the wheels, therefore the vehicle is no longer a front, rear or four wheel drive model.

(iii) A very slippery surface can cause the drive to lock up which in turn causes the wheels to lock, keeping the vehicle in a skid situation.

10.

ADVANTAGES

DISADVANTAGES 10.1. Advantages

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AND

1)

Monitors

each

wheel

independently

maximizing the performance of the car. 2)

Increases

comfort,

both

physical

and

psychological. 3)

Improves safety aspects of the car and the driver.

4)

Helps save money long term.

5)

Enhances

the

ability

to

dodge

a

renegade object in its pathways.

10.2. Disadvantages 1)

High initial costs.

2)

Overdependence.

3)

Not perfect.

4) 5)

Repairing cost may be high.

11. CONCLUSION Driving has become more and more dangerous

with

the 30

ever

increasing

population of man and vehicles. It is estimated that 25% of all accidents are caused by driver distractions. Automotive technology is being developed everyday to make our lives on the roads much safer. Vehicle Skid Control is one such instance. Safety is the principal benefit of this technology. But no matter how advanced the safety aid, we should never forget that the ultimate fate of a vehicle and its occupants remains in the hands of the driver. No safety system should ever be expected to protect unconditionally. So while the latest generation of stability control systems offer drivers increased protection for both themselves and the

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