Brake Testing

Overview

RACELOGIC has led the way in high-accuracy brake testing for more than ten years
As advances in braking technology increase, performance improvement is narrowing. It is therefore essential that the measurement of braking distances can be carried out repeatably and with very high accuracy. Due to their high accuracy, flexibility, and ease of installation (they can be moved from vehicle to vehicle in minutes), VBOX GPS data loggers are used by every major automotive and tyre manufacturer in the world.

Conducting tests with a trigger ensures that the response time of the braking system is measured along with the performance of the tyres, brake pads, discs, and other components.

VBOX data loggers are often employed in conducting tests to various official standards, such as ECE regulation R90 and 13H, and FMVSS135.

Modern electronically controlled braking systems are extremely efficient and are very close to reaching the optimum braking distances for a given tyre and road surface. It is therefore essential that the measurement of braking distances can be carried out with very high distance accuracy.


Due to their high precision, flexibility, and ease of installation (they can be moved from vehicle to vehicle in minutes), VBOX GPS data loggers are used by almost every automotive and tyre manufacturer in the world to carry out brake distance measurements.

There are two main kinds of braking test:

Speed Window Tests
Distance travelled between two speeds is measured


Brake Trigger Tests
Distance travelled from the point the brakes are pressed to a standstill.


Conducting tests with a trigger ensures that the response time of the braking system is measured along with the performance of the tyres, brake pads, discs, and other components. However, during a trigger activated test, the car undergoes a complex change in attitude resulting in varying speeds across the body of the vehicle.

Centre of gravity corrections – or countering the 'lever-arm' effect - of testing tall vehicles with long suspension travel can be achieved with the combined use of GPS and an Inertial Measurement Unit.

How we verify brake distance accuracies

We regularly verify the brake test measurements obtained by the VBOX unit against a light barrier, laser, and RTK DGPS setup with Base Station to confirm a positional accuracy of better than 2cm.

We also captured the test on our LabSat GPS simulator, which records the raw GPS signals and the brake trigger input, and allows us to replay it through any VBOX on the bench. This gives us a repeatable reference to check against any new firmware or hardware updates, and maintains a high standard of brake testing accuracy.

System Features

Key Features
• GPS based measurement of speed and distance
• Easy to fit, simple to use
• Braking distance accuracy +/-1.8cm
• Pedal force and travel sensor inputs via analogue or CAN
• Live and logged results
• Customisable tests
• FMVSS135 and ECE13H compatible
• Measurement of longitudinal G-forces
• Centre of gravity correction by combined use of GPS and inertial systems
• Specific brake testing software available
• Multiple brake temperature logging using thermocouple inputs
• IMU integration eliminates over-shoot errors for speed to speed brake stops

Measured Parameters

• Trigger speed
• Braking distance
• Centreline deviation
• MFDD
• Result statistics
• Lateral and Longitudinal G-forces
• Brake temperatures (TC8 module required)
• Pedal force and travel sensors
• Pitch, Roll and Yaw (using the IMU04)

Live results
A laptop or tablet PC running VBOX Brake Test software can be used to monitor the measured parameters in real time, either by a serial, USB, or Bluetooth connection.

This package also allows for detailed post processing of the logged data in sync with any video footage recorded by a Video VBOX.

IMU Integration
Conducting brake tests on tall vehicles with long suspension travel can result in a speed overshoot of the velocity data, due to the measurements being taken at the high roof position of the GPS antenna. As the brakes are initially applied, there is a higher rate of change in velocity at the roof than there is at the vehicle's centre of gravity (COG).

However, the integration of an IMU04 with a suitably upgraded VBOX 3i can be used to counteract this 'lever-arm' effect by placing the IMU at the COG, which measures the vehicle pitch as it brakes. This data, when combined with that from GPS, provides a compensation for the overshoot and allows for consistent brake stop testing.


The graphs below show how point A has travelled further than point B:

In this example of a high-dynamic brake stop, the blue trace (GPS Speed) overshoots at the initial point of brake application, and then exhibits a damped oscillation as the deceleration continues. The IMU-corrected data (red trace) accurately records the brake stop from the vehicles centre of gravity.

Counteracting the lever-arm effect will also aid test engineers when conducting high-dynamic manoeuvres other than brake stops. In slip angle measurements the speed overshoot can occur if the antenna is moving through a greater arc of travel than that of the vehicle's centre of gravity as it corners. Procedures such as lane change manoeuvres can therefore benefit from IMU integration and lever-arm compensation.

Orange = Pitch measured by the IMU Blue = GPS speed Red = IIMU itegrated GPS speed
The traces between the green and red vertical lines are of a car going over a speed hump. Note how the GPS speed alters as the vehicle roof moves independently of the COG as it goes over the hump. The integrated speed logs the correct speed of the vehicle.

Dedicated Brake Test Software
VBOX Brake Test software is designed for customers who are performing multiple high dynamic brake stop tests using a VBOX 100Hz data loggers and speed sensors.

The software is able to process both live serial data and recorded VBO files in order to generate results from either brake trigger or deceleration tests. This allows customers to perform multiple brake stop tests and view the results in a useful format.

This software has been developed on conjunction with brake test engineers to reduce test track time and simplify analysis.


Video Integration
Video integration enables engineers to have a graphical representation of the test over live footage, enhancing the data for quick fault analysis and to aid presentations.

Test Procedures
VBOX systems are suitable for the following brake test applications:
• ECE regulation 13H
• ECE regulation R90
• FMVSS135 regulation
• ADR 31 regulation
• ISO 21994 standard
• ABS testing and development
• Tyre testing and development
• AMS testing

Types of Brake Tests
Trigger Activated to Standstill

A common test for evaluating the performance of braking systems is the trigger activated test to standstill. A pressure switch is added either to the face of the brake pedal, or into the hydraulic system, to detect when the brake pedal has been pressed. This signals the start of the test and it ends when the vehicle comes to a complete stop. The distance between these two points is then calculated to measure braking performance.

As this test starts when the pedal is pressed, it measures both the response of the braking system, as well as the performance of the tyre, brake pads, discs and other components.

In a trigger activated test, it is critical to accurately capture the point at which the brake pedal is pressed because the vehicle is usually traveling quite fast at this point. The VBOX 3i uses a very sophisticated method which measures this to within 25 billionth of a second!


Between Speeds

Another popular assessment of performance is the brake test between two different speeds. These speeds are usually chosen in order to eliminate the response time of the braking system, which is usually during the more linear part of the deceleration period.

These tests are useful for analysing the performance of tyres due to the consistency of braking distances recorded.


'Split mu'

This involves both sides of the vehicle running on different surfaces to determine how the braking system copes with different levels of traction. This test also allows engineers to analyse the stability of the vehicle.


Brake and turn
This comprises of the vehicle performing a brake test during a turn. This helps engineers to determine the stability of the vehicle during such a manoeuvre.

ECE R90 Brake Pad Testing
ECE R90 stipulates that all brake pads and linings manufactured and sold within the EU must comply with R90 standards. The test involves comparing the performance of replacement brake pads with those originally fitted.
To comply, the brake pads and linings must be put through speed sensitivity and cold performance equivalence tests and perform to within ±15% of the originals. Pads that have passed will have an "E" mark alongside a number denoting which authority has approved the pad (e.g. UK – 'E11').
VBOX 3i systems can be used to measure braking distances to within ±2cm accuracy. It calculates parameters such as time, position, velocity, heading, height, vertical velocity and lateral/longitudinal acceleration at 100 samples per second.
VBOX can be used in all four main procedures to satisfy ECE R90 regulations:
• Bedding (burnishing) procedure
• Performance check
• Brake tests (in accordance with Reg. 13 Annex. 4)
• Cold performance equivalence and speed sensitivity tests
In addition to viewing results in real time via a Multifunction Display or Tablet PC, all data parameters captured using a VBOX are recorded using a Compact Flash card. All data can then be viewed using the supplied VBOX Tools software in accessible formats (e.g. graphs, charts).

ABS Testing and Development
VBOX test equipment enables you to accurately capture individual wheel speed signals, from either CAN or rotary encoders, high dynamic vehicle movement, and the vehicle's straight line deviation.

Brake Assist System Testing and Development
VBOX test equipment enables you to capture pedal force and travel sensor outputs via analogue inputs at 500Hz.

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