Case Study of autotronics

8/10/2019 Case Study of autotronics

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Case Study on Electronic Stability Control System

INTRODUCTION

A few years ago, four wheel drive was driveline selection of choice to drive on slippery roads.

Then came anti-lock brakes (ABS) which revolutionized the brake system design and

performance followed by traction control system (TCS). Electronic Stability control is the latest

innovation that is sweeping the world of handling performance of todays fine automobiles, on

more than just treacherous terrain. In fact, the Electronic stability control systems are a key

component for intelligent vehicle highway systems of future. Electronic Stability control systems

make use of both, ABS (Anti-lock Braking system) & TCS (Traction Control system) for the

dynamic stability of vehicle.

Imagine, the special snow tires, on the S-class Sedan, are doing a commendable job on the snow-

packed road as you cruise this superbly smooth 4.2 L V8 power plant at 60 Kmph, you are full of

confidence and you cannot resist pushing the accelerator pedal a little more; the speedometer

needle climbs to 80 Kmph and the tires are now desperately searching for better grip in the snow.

The rear end begins to slide slightly to the left. You instinctively try to correct the skid by

steering slightly to the left and lifting your foot off the accelerator pedal. A yellow warming light

on the instrument console flashes emphatically, as the ABS controller is activated even thoughyou could swear you didnt touch the brake pedal. Because you lifted your foot off your foot off

the accelerator pedal, the traction control system would have been activated either and in the

fraction of seconds, it makes an amazing recovery, all with less counter steering and yaw, than

you are used to. Thus a vehicle comes now under the control of the driver.

Driving the car at the physical limits of adhesion between the tires and the road is by no means

an easy task; average drivers loose their control under such situation. If the limit of adhesion is

reached, the driver caught, with surprise, often reacts in wrong manner i.e. over-steering orunder-steering. This is the much recognized weakness in driver-vehicle environment triangle.

Stability control focuses on correcting this weakness by letting the computers do the driving in

such situations.


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ELECTRONIC STABILITY CONTROL

Electronic Stability control is the direct extension of the Anti-lock Braking system and Traction

Control System (TRC). Simply, it can be defined as the real- time method of controlling the

lateral trajectory of a vehicle to arrest the growth of skid. By definition stability implies the

capacity of an object to return to equilibrium or its original position after having been displaced.

Need of ESC System:

After all what is the need of stability control in todays automobiles? Auto India states in Jan-97

issue that, An unconfirmed study informs that in spite of what police reports say, the

environment is responsible for 50 percent of all accidents, the vehicle for 31 percent & the driver

for 19 percent. Another study found that steering was involved in one out of every two accidents;

the evasive action took place just before the collision or the vehicle leaving the road. In an

emergency, most drivers can be expected to take wrong action. Educating the people to drive

better, tried over & over again is not a viable solution any more. Instead, can manufacturers think

it is better to take as much of the control as possible away from the drivers in such situations.

Smart systems incorporated within the automobiles use superfast computers to supplement the

driver-vehicle-environment triangle. The ultimate objective of stability control systems is to

increase the safety of driver & occupants at a reasonable cost.

Specific Objectives:

To improve vehicle stability & steering performance in areas of braking, coasting,

accelerating, engine drag & load changes.

To support the driver in critical dynamic situations in the lateral direction.

To improve handling behavior in limit conditions of an average driver so that driver can

concentrate on traffic conditions.

To reduce vehicle spin in panic reactions involving extreme steering maneuvers.

To improve traction & reduce stopping distances with better steer ability & stability than

afforded by conventional ABS & TCS.


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Different manufacturers give it different names. Toyota calls it as a VSC (Vehicle Stability

Control), BMW as DSC (Dynamic Stability Control), Daimler-Chrysler calls it ESP (Electronic

Stability Program), Audi (Electronic stability program), Jaguar (Dynamic stability control),

Lexus (Vehicle Skid Control), Porsche (Porsche Stability management), Volkswagen (Electronic

stability program), Volvo (Dynamic Stability traction control). Also the Mercedes offered the

stability control equipped with ABS on production models for the first time in the market.

ELECTRONIC STABILITY PROGRAM (ESP)

History of ESP:

Anton Theodor van Zanten, who worked on ESP already in his PhD thesis at Cornell University

(1973), and Armin Mueller were the project leaders at Bosch and Daimler-Benz. Teams from

both companies, about 40 engineers, moved into a common building. ESP world premiered in

1995 in the 12 cylinder Mercedes S600 as standard feature and was optional for $1200 to $1500

in other S-Class models.

Overview:

The Electronic Stability Program is a system that relies on the vehicles breaking system as a tool

for steering the vehicle. When the stability control function it shifts the priorities that govern the

brake system the basic function of the wheel brakes to decelerate and/or stop the vehicle assumes

secondary importance as ESP intervenes to keep the vehicle stable and of course regardless of

the conditions. Specific braking intervention is directed at individual wheels (such as left rear to

counter under-steer or the right front during over-steer). This automatic reaction is engineered for

improved vehicle stability, particularly during severe cornering and on low-friction road

surfaces, by helping to reduce over-steering and under-steering. For optimal implementation of

stability objectives, ESP not only initiates braking intervention but it can also intervene on the

engine side to accelerate the driven wheel. Some ESP systems include a connection to the

powertrain controller of the vehicle to enable reductions in engine torque when required.


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Consumer Benefits:

Reduced risk of skidding.

Improved steer-ability in extreme situations.

Increased traction.

Shorter stopping distances.

Improved driving stability (within physical limits)

Reduced accident risk.

Better handling.

Relieves stress on the driver.

WORKING OF STABILITY CONTROL SYSTEM

Figure 1 gives the working principle of the Electronic stability control

Figure 1: Working Principle of ESP


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Figure 2: Layout in the car MB E Class

When the car moves into a position which is determined by the yaw sensors to be outside of the

parameter set by the system, ESP will activate. For the driver, certain functions in the car will

activate. For the driver, certain functions in the car will activate which the driver has no control

over. Depending on the manufacturer of the system (Bosch, Delphi) there will functions in the

car which are linked together & will operate together to bring car back to control. If the car

begins to skid, driver will usually attempt to brake & hopefully try to drive into the direction of

the skid. In practice, this does not always happen, so the car do it itself.

The vehicle will:

Take over the accelerator & operate this independently

Apply pressure through the braking system regardless of how much pressure of the driver

applies.

Alter the steering angle (if the vehicle is equipped electronic steering wheel control e.g.BMW, VW)

During this time, it is usual to see the ESP lamp lit & can be accompanied by a continuous

pinging noise. The duration that ESP operates is variable & dependent on how quickly the car

comes back under control. The measured yaw angle by yaw sensor, it operates like gyroscope.


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Thereby monitoring the rotational angle of the car. The sensors convert movement into electrical

data current & thereby send information through the bus to the EBCM.

CASE STUDY:

Here the effects of electronic stability control interventions on rural road crashes in Australia are

considered. Simulations of real world crashes are generated using different scenarios. Jamie

Mackenzie, Robert Anderson of Centre for Automotive Safety Research Australia has conducted

this simulation of ESP for 20 Scenarios. Here we are going to consider one scenario with ESP &

without ESP.

The software used is CARSIM. The software is inputted with vehicle data, event data &

environmental data. And the scenario considered on parameters like under-steer, over-steer &

Split mu etc. Here front wheel drive vehicle model is considered. The front wheel drive vehicle

model was based upon a modern upmarket vehicle. This vehicle and thus the vehicle model is

particularly stable during cornering and showed little propensity to yaw upon a single steering

maneuver. The authors had no ability to alter this behavior as the model was provided by Bosch

Australia. The effect which ESP may have had upon the un-simulated crashes is discussed. In 10

cases a vehicle equipped with ESP involved in the same crash scenario would likely have

avoided a collision altogether. In two cases a vehicle equipped with ESP involved in the same

crash scenario would likely have reduced the severity of a collision. In two more cases, a vehicle

equipped with ESP in the same crash scenario would likely not have changed the outcome.

Lastly, in six of the cases, the results were inconclusive.

Case 1:

Crash Description

On a Thursday at approximately 5:00 pm, a car was negotiating a blind right bend at a self-

reported speed of between 60 and 65 km/h, when the driver was confronted with an oncoming

vehicle straddling the center line. The driver steered to the left to avoid a head-on collision

causing the left wheels of the vehicle to pass onto the unsealed shoulder. The driver

overcorrected to the right, narrowly missing a guide post upon re-entering the sealed

carriageway. The vehicle yawed in a clockwise direction across both lanes of the carriageway


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and across the far shoulder and the grassed verge. The left rear of the vehicle collided with a tree

2.5 meters from the edge of the carriageway. The prevailing environmental conditions at the

crash site are given in Table 1. The site diagram for the crash is shown in Figure 3.

Figure 3: Site Diagram for Case 1

Table 1: Environmental Conditions for Case 1


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Simulation Setup

The parameters used for the simulation of this case are shown in Table 2. An initial speed of 80

km/h was used, which was higher than that reported in the actual crash. This was mainly to

compensate for the front wheel drive model which was stable at lower speeds. The higher speed

caused the front wheel drive model to yaw in the same way as a less stable vehicle travelling at a

lower speed. A preview time of 0.6 seconds and maximum steer rate of 600 degrees per second

gave the driver model a surprised and panicked response to the oncoming vehicle. The driver

path for this case, shown in Figure 4, was developed based on the crash description and tire

marks at the crash scene. The driver path was designed to model the following sequence of

events: The path begins in the middle of the left lane. As the driver is confronted with the

oncoming vehicle, the path suddenly pulls to the left. The driver then panics as the vehicle

travels onto the unsealed shoulder. The path pulls suddenly back to the right and returns quickly

to the middle of the left lane.

Figure 4: Road section and profile for Case 1


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Figure 5: Simulation animation for Case 1

Simulation Results:

The simulation of the vehicle not equipped with ESP showed only a small resemblance to the

events of the actual crash. In the simulation, the vehicle veers to the left suddenly, overcorrects

upon returning to the road and then yaws in an anti-clockwise direction across both lanes. This

was quite different to the events of the actual crash in which the vehicle yawed in a clockwise

direction upon steering back onto the road. The simulation of the vehicle equipped with ESP

produces a significantly different vehicle path. As soon as the vehicle begins the emergency

maneuvers, the ESP system attempts to slow and stabilize the vehicle. Upon returning to the

road, the vehicle overshoots the middle of the left lane and crosses the centerline a small

distance. Despite this, the ESP system keeps the vehicle stable which enables it to easily return to

the middle of the left lane and continue following the road. Equipping the vehicle with ESP

enabled it to remain stable throughout the entire emergency maneuver. While the vehicle path

did show that the vehicle equipped with ESP crossed the centerline, it did not yaw at any point

and quickly re-entered the left lane. Based on this, it is likely that a vehicle equipped with ESP,

involved in the same crash scenario, would have avoided the loss of control that led to the

collision in the actual crash.


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Table 2: Simulation parameters for Case 1

ESP Interventions

The ESP interventions for this case are shown in Figure 6. There are two main points of interest,

labeled A and B. As the driver model initially steers the vehicle to the left (prior to point A), the

ESP system slightly brakes both the left side wheels. This has the double effect of pulling the

vehicle to the left more quickly and reducing the vehicle speed a little. When the driver model

steers the vehicle back to the right (point A), there is a possibility of over-steer occurring. The

ESP system brakes the front left wheel very sharply and to a lesser extent, the rear left wheel

also. This counteracts the potential oversteer situation. The driver model then steers again to

direct the vehicle back into the left lane (point B). As the eight of the vehicle shifts from one side

to the other, there is again a possibility of oversteer occurring; this time in the other direction.

The ESP system again reacts and brakes the front right wheel sharply and the rear right slightly.

As the driver model returns the vehicle to the left lane and continues down the road (past point

B), the ESP system makes its final interventions. The braking at the front right wheel is held for

a time and the rear right is braked again. This settles the vehicle back into a stable path down the

middle of the left lane.


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Figure 6:Simulation output for Case 1


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CONCLUSION

It is estimated that ESP (Electronic Stability Program) increases the cost of the car today by

almost 1200 American dollars. says Auto India. But if, history is any indication, such

innovations finally do find their way in a common mans car, after being first offered on luxury

and exotic cars. Continuous research always finds cheaper alternatives and mass production

reduces prices and consequently expands markets.

Though the system does not come cheap at present, on the other hand, the obvious benefits of the

electronic stability control system are too great to be ignored which substantially contribute to

drive safety & reduce number of accidents or limit the damage if the accident were unavoidable.

Most of the accidents which involve single car like spinouts or rollovers could be easily avoided.

Thus, the system cuts away the large part of the source of accidents & serves the mankind by

avoiding/ reducing the possible damage of human life & money.

Case Study of autotronics

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