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research SPECIAL EDITION 11/NO.1

n e w s

All ESC systems are created equal, but some are more equal than others?

INSIDE:

WHAT IS ESC? ESC DYNAMIC TEST RESULTS REAL WORLD EFFECTIVENESS OF DIFFERENT MODELS

what is ESC? Electronic Stability Control, ESC, helps to prevent the driver from losing control in a skid. ESC automatically controls the vehicle by comparing the

Do not touch your ESC button! ESC is a major safety feature which could save your life Do not touch your ESC button. ESC is switched on by default when you start your vehicle, so it does not require switching on. Some manufacturers are producing cars without the ESC button (e.g. Ford), so that drivers are

protected by ESC at all times. The majority of cars are fitted with an ESC button which can be used to switch ESC off when unusual conditions are encountered, such as moving off in deep snow. The ESC button should not be

touched unless those unusual conditions are encountered. For further information, please consult your vehicle handbook.

steering actions carried out by the driver to what the vehicle is actually doing. If the ESC senses that the vehicle is veering from the required course – a skid – it automatically brakes selected wheels to bring the car back into line.

ESC is particularly effective in poor driving conditions such as ice and snow.

Oversteer

What are the benefits?

If you swerve to avoid an obstacle – such as a rapid lane change on a motorway, oversteer can occur making the vehicle turn more than intended, ultimately leading to a spin. ESC can prevent this by braking individual wheels to maintain control.

Understeer

If you are driving too fast into a corner, understeer can occur. This would result in a loss of steering control as your car continues to follow a straight path and not steer as required. ESC can help retain steering control and allow the car to travel in the desired direction.

A study for the UK Department for Transport by Loughborough University has shown that on UK roads, cars fitted with ESC are 25% less likely to be involved in a fatal accident than those without ESC. If every vehicle were fitted with ESC, this would equate to 380 fewer fatal accidents annually. Serious crashes involving skidding or overturning could be reduced by up to 59%.

ESC is often sold with different names: ESP, VSA, DSTC and others.

criteria

dynamic testing

But does ESC really work?

dynamically since 2008, following an international test procedure. The aim Whilst the fitment ratings of this dynamic testing is to help to inform consumers verify that the ESC systems about buying cars fitted with ESC, it is a completely are actually operating as they should do. Euro NCAP different question to verify has followed suit and is that ESC actually works. now testing cars in the So Thatcham has been same way. testing ESC systems

Legislation

2011, and for all new cars by November 2014. In the US, there is a The regulations include regulation (FMVSS 126) specification of the ESC that requires ESC to be system components and mandatory on all cars by functionality, the ESC 2012. This regulation on/off switches, and tellhas been proposed as tales on the dashboard a GTR (Global Technical Regulation). In Europe ESC as well as the dynamic will be compulsory for new test procedure. types of car from November

The runs start with a small steering input and build up to a steering wheel angle of 270˚.

Thatcham has a programme of dynamic testing of vehicles for ESC functionality, in addition to the publication of fitment ratings (see www.thatcham. org/esc). This dynamic testing is based on the procedure in the GTR 8 which assesses the performance requirements of the ESC system, resulting in either a pass or fail. For greater detail on the test procedure and assessment criteria, please also see Research News special edition on ESC 2009. A steering robot is required to carry out this testing which takes over from the driver to provide the steering input in a safe, precise and repeatable

The latest fitment ratings for 2010 are available at www.thatcham.org/esc

way. The test has several stages and begins with brake and tyre conditioning. A slowly increasing steer test is performed to define the steering wheel angle input ‘A’ for the Sine with Dwell. The test is then performed after another series of the tyre conditioning runs. The test is a Sine with Dwell manoeuvre at 50mph and comprises a sinusoidal steer in one direction, followed by a steer in the opposite direction, with a dwell of 500 milliseconds at the second peak. The runs are repeated with both the left and right initial inputs. The runs start with a small steering input and build up to a steering wheel angle of 270˚.

δ Steering wheel angle

Thatcham has been publishing ESC fitment ratings for the last few years to raise awareness of this important safety technology, and to encourage drivers to buy cars fitted with ESC. Manufacturers have risen to the challenge and now more widely fit ESC as standard.

Time



Outriggers fitted to the Volkswagen Transporter to prevent risk of rollover

Yaw rate

Sine with Dwell steering input used for dynamic ESC test

Time

-100

-60

responsiveness criterion

-300

Time (s)

Yaw velocity (°/s)

Pass

Fail

300

10

200

5

100

0

0 0

1

2

3

4

5

-5

-100

Lateral displacement (m) -10

stability criterion

Steering Robot Angle (°)

15

-200

BOS+1.07s

-15

The stability criterion is used to assess whether the car is spinning or skidding. This stability criterion requires that the first peak value of the yaw rate is measured and recorded after the steering wheel angle changes sine (between first and second peaks). The yaw rate should then not exceed either: Steering Robot Angle (°)

-300 Time (s)

Lateral displacement (m)

Pass

Fail

Steering Robot Angle (°)

Lateral displacement (m)

20

• 35% of the peak at 1.00 second after Completion Of Steer (COS)

θ

dx

dy

-10 Lateral -20 displacement (m) 0

10

20

30

40

50

60

70

80

90

Above and right: PASS with increasing lateral displacement

60

200

200

30

30

0

0 0

-1

0

-60

-60

-90

-90

-50

driving was achieved. Straight line driving is when the yaw velocity is zero degrees,400 indicating that the vehicle 300 is no longer turning. A yaw Yaw velocity velocity tolerance of ±1°/s 200 17% was applied to the data to determine the period of100 1 second of straight line driving after the Completion Of0 Steer (COS). Having defined the period of straight line -100 driving, the final heading was -200 calculated using trigonometry.

COS + 1.000s 1

2 Time (s)

Steering Robot

3 Pass

4 Yaw velocity (°/s)

2

3

4

3

4

5

Note that the car would not be expected to return to zero degrees since the steering input is not symmetrical; the dwell period means that the car is expected to finish pointing away from zero. The larger final headings are associated with greater yaw during the manoeuvre, and the ESC system is working to control the yaw.

-20

5

-100 -100

Steering RobotRobot Angle A ( -200 -200 Steering -300 -300

Time (s) Time (s) Pass Pass

Fail

Steering Robot Robot Angle Angle (°) Steering (°)

Fail

15

300

300

10

10

200

200

5

5

100

0

0

0

0

-1

0

-5

1

1

2

2

3

3

4

4

5

-5

20

20

10

10

0

0

100 0

5 -100 -100

-200 -200 Steering RobotRobot Angle A ( Steering Above: -300 -300 Unstable vehicle: FAIL

-15

-10

Robot Robot Angle Angle (°) Fail Steering Steering (°)

θ = Final (º) θ = heading Final heading (º)

θ

dx

θ dy

dx

dy

-10

Lateral displacement (m) -20Lateral -20 displacement (m) -10 -10 0 20 30 -20 010 10 20

40 30

50 40

60 50

70 60

80 70

90 80

90

Longitudinal displacement (m) (m) Longitudinal displacement

Steering Robot Angle (°)

VehicleVehicle Path Path Completion Of Steer Completion Of (COS) Steer (COS)

-300

0

2

LateralLateral displacement (m) (m) Pass Pass Fail displacement

-70 -90

1

Time (s) Time (s)

Lateral displacement (m)

carried out on the dynamic 70 test data from the GTR. The final heading at the end of the 50 manoeuvre for each run was calculated. This calculation of 30 final heading is not included in 10 the GTR performance criteria, but was additional analysis -10 carried out on the same test -30 data. The final heading was Yaw Velocity (°/s) calculated once straight line

1

15

-15

Lateral displacement (m)

Additional analysis was also

100 100 COS+1.750s COS+1.750s COS+1.000s COS+1.000s 0 0

COS COS

Completion Of Steer (COS)

90

Yaw velocity (°/s)

-1

Above and right: PASS with increasing instability

Vehicle Path

The results are

-1

60

Example calculation of stability criterion

1 second straight line driving within yaw velocity corridor

compiled for all the test runs for the test vehicle up to the 270˚ input. To achieve a PASS result the vehicle must pass on each of the criteria for each run up to 270˚. If there is a FAIL recorded on any run, for either criteria, the overall result is a FAIL. The thresholds for these pass/fail criteria are based upon a series of 62 US cars tested in this sine/dwell manoeuvre fitted with ESC.

300

LateralLateral displacement -10 displacement -10 (m) (m) BOS+1.07s BOS+1.07s

Longitudinal displacement (m) Above: Unresponsive vehicle: FAIL (lateral displacement