Motorbike On-Road Brake Test

Author(s):
V. Arunachalam - Soliton Automation Private Limited

Industry:
Automotive

Products:
LabVIEW

The Challenge:
Developing a data acquisition (DAQ) system for on-road motorbike brake testing that gives real-time data to the rider/tester during the trials about stopping distance, brake temperature, and more.

The Solution:
Using LabVIEW software and NI hardware, as well as a rugged FieldWorks computer, signal conditioning hardware, and an input/output device to develop the on-road DAQ system.

Introduction
Our customer, a tier-one supplier to large motorbike manufacturers in India, wanted an on-road data acquisition system to test motorbike front disk brakes. The brakes were to be tested by measuring stopping distance during various road trials. The most straightforward way to determine stopping distance is to bring the motorbike to the required speed before reaching a certain predetermined marked point, and then to apply the brake from that point until the motorbike stops. Using a tape measure or a more sophisticated distance-measuring instrument, we can determine the stopping distance. This is a tedious and time -consuming process and not practical during long trials over different terrain. Additionally, in this method, other parameters relating to braking, such as the brake-pad temperature and hydraulic pressure, cannot be obtained.

We designed the on-road brake test system to measure the braking distance of a motorbike under different road conditions in real time. This data is used offline to compute the performance parameters of the disc brake as per the customer’s specifications.

System Description
The on-road brake test system is designed to acquire real-time road test data. The test required a dedicated onboard computer to run the system and acquire the test data. A laptop computer was considered and excluded, as it was not rugged enough to withstand the rigors of field test conditions. We developed a test system based on a small form factor rugged FieldWorks computer, with National Instruments data acquisition card, signal conditioning modules, and application software written in LabVIEW 6i.
The following sensors are used in the data acquisition system:

• Rotation encoder - for rotational displacement and the wheel speed
• Thermocouple - for pad temperature during braking
• Pressure sensor - for the brake hydraulic line pressure
• Accelerometer - for the instantaneous acceleration of the vehicle

For user inputs and display, a small-sized integrated keyboard and LCD display was interfaced with the FieldWorks computer through the RS-232 port because the FieldWorks 2200 model does not include an integrated display. Using this display, the motorbike rider can send commands, set parameters, and receive feedback from the system, such as the braking distance. The motorbike’s 12 V battery powers the computer, the user-interface kit, and the signal conditioning modules. The conditioned signals from the transducers connect to National Instruments PCMCIA multipurpose high-speed data acquisition card installed in the FieldWorks computer. Three analog input channels and two counter/timers from the DAQ card are used for the data acquisition.

The encoder and the accelerometer are both used to acquire the data used in calculating the braking distance. Two complementary and independent methods are used to calculate the stopping distance. The first method uses the pulses per revolution (ppr) output of the encoder to measure both the speed and the displacement. The accelerometer data is used as supplementary data. The braking distance is obtained by using the initial speed of the motorbike and integrating the acceleration value twice. Because this accelerometer data is not as accurate as the encoder data, it is used only when a wheel lock is detected.

The data acquired by the various sensors is stored in the onboard computer. At the end of the test, the onboard computer can be connected to an Ethernet network and the data can be downloaded on to another PC for offline analysis. A software application was developed for the offline data review and analysis, shown below. This application includes a review module that can be used to review the test data and view graphs that plot various parameters against time, such as pressure, acceleration, speed, and brake-pad temperature.

Operation
The encoder used in this system gives an output of 1,000 ppr. The encoder shaft connects to the front wheel of the motorbike. The encoder output connects to the two counters of the DAQ card. We measure the duration between the encoder pulses to obtain the instantaneous speed of the vehicle and another counts the number of pulses, which is translated into displacement.

We need reference signals to start and stop the counters during braking. The start signal is obtained from the pressure sensor, which is mounted on the disk brake hydraulic cylinder. The pressure signal is a trigger to start counting the pulses. Zero speed is the stop signal to stop counting the pulses. A low cut-off speed is used to detect the zero speed condition. The figure below shows a schematic that depicts this basic scheme used for measuring braking distance.

With the user interface kit and integrated LCD display and keyboard, the user can enter various speeds at which to start braking, and the LabVIEW application monitors the motorbike speed and gives a signal to start braking at the desired speed range. When the bike comes to a stop, the display immediately shows the braking distance. During the braking, the brake -pad temperature and acceleration are also acquired using the high-speed data acquisition card.

Conclusion
The on-road brake test system we developed can measure braking distance to an accuracy of 1% over a distance of 30 m. The system also handled wheel-lock conditions by using the accelerometer data during these periods. The small form factor of the NI PCMCIA data acquisition cards and the FieldWorks 2000 embedded computer made it easy to mount it on the motorbike. The whole system was rugged enough to handle accidental falls during testing. With user interface, the user can set up different tests during the road trials and also see the results without having to connect a laptop to the embedded computer. We plan to make the system more user friendly by interfacing a microphone to one of the DAQ channels, so the rider can record comments during the tests.

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