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Article by: Fabio Squadrani, Senior Manager, Braking Systems in Applus IDIADA
Modern braking systems development is moving towards the reduction of long tests on open roads. However one of the most critical items when reducing the mileage in open road is brake wear. This work is answering to a simple question about how to simulate brake patterns in dynamometers in order to reduce the mileage of brake tests to be performed on vehicle. In this first part of this article, a set of data coming from a brake durability test was analysed. Particularly this is needed in order to define the target wear value for the brake dynamometer procedure. In the extract of the article, the brake dynamometer test procedure was laid down. Finally, this part will deal with the wear validation.
4. Wear Validation
4.1 Validation Procedure Description
As mentioned in the 2nd part of this article, test procedure is made of a combination of different temperatures profiles. Each temperature profile has been defined in order to be representative of the typical usage in a Mojacar route, adding as much as possible the effect of the limited stochastic driving style distribution in Mojacar.
For the sake of simplicity the full validation route is not reported in this paper, however the structure of the route is as follows:
The following parameters are controlled during the dyno operation:
- Cycle Description (depending on the type of section during the route)
- Cooling speed, depending on the initial vehicle speed
- Dyno mode, being it “inertia” (in case of a deceleration stop) or “drag” (for a constant speed stop)
- Initial Speed
- Final release speed
- Drag time
- Motor Control (being it “torque controlled” for drag application or “pressure controlled” for deceleration stops)
- Pressure target (for deceleration stops)
- Torque target (for drag stops)
- Initial Brake Temperature
The total number of stops to be considered is 221 per each route.
4.2 Vehicle 1 Validation
Once the cycle is been described (paragraph 4.1) and the repetition of each cycle has been defined (paragraph 3.3), a validation cycle has been run per each vehicle.
For vehicle number 1, the following correlation table is presented:
Please note that:
- Mojacar column refers to original testing on vehicle
- Dyno column refers to the test performed on dyno, using the cycle defined in paragraphs 4.1 and 3.3
- Dyno escalated column refers to the values of Dyno column multiplied by the scaling factor defined in paragraph 3.3
In the difference column it could be appreciated a overestimation of wear of about 5% for the dynamometer procedure.
It has to be noted that no validation loops have been required, due to the correct definition of repetitions of each cycles. According to previous internal experience at Applus IDIADA, the correlation would decrease if only reference laps were considere (not including any low or high temperature cycles).
4.3. Vehicle 2 Validation
The same process has been defined for the second vehicle:
5. Conclusion
After some very simple loops of correlation a robust procedure has been defined for wear correlation in Mojacar. The procedure has been defined in order to slightly overestimate the wear, which it is considered to be the right approach when selecting a metarial in the early phases of development.
In addition to this, the procedure represents a big reduction in terms of timing. A standard vehicle testing programme in Mojacar could last around 5 weeks (2 shifts driving). The dynamometer procedure which has been summarized in this study can be run in 3 to 4 days per each axle.
In order to further improve the correlation and to provide a more realistic correlation, a certain study on the effect on bedding could be performed. A real bedding lap could be defined, instead of the standard J2707 procedure. However, the correlation results are considered to be very satisfactory.
About Applus IDIADA
With over 25 years’ experience and 2,450 engineers specializing in vehicle development, Applus IDIADA is a leading engineering company providing design, testing, engineering, and homologation services to the automotive industry worldwide.
Applus IDIADA is located in California and Michigan, with further presence in 25 other countries, mainly in Europe and Asia.
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