The Hindu Business Line : ‘Honey, I shrunk the test time’

Nothing is constant in life — least of all customer expectations. Hence organisations across the globe look to constantly assess changing consumer needs and tastes, and launch products accordingly.

Take, for instance, the cell-phone or pen. Companies making these products come up with new launches or upgrades ever so often. The product life-cycle for such gadgets has come down drastically — from several years earlier to a few months now.

In the case of vehicles, the life of a model is relatively longer.

While the product life-cycle of a passenger car is between 18 and 24 months, for a commercial vehicle, it is four to five years. While manufacturers no doubt want to bring out new products in good succession to keep sales healthy, the challenge is to come up with new designs without compromising on the safety of the vehicle’s occupants and other road users.

And this safety is ensured through standard procedures that are also time-consuming.

While the regulations require automobile manufactures to test new vehicles for one to two million km cumulatively by a set of ten or 15 vehicles, the tough reality is that this consumes enormous time. Vehicle manufacturers are squeezed between shortening product life-cycle and increasing statutory requirements.

But what if product testing time could be reduced, without compromising on road safety?

This is where electronics and software come in, promising manufacturers a two-in-one combo – faster innovation with no dip in safety standards.

One such instance is the testing lab at Ashok Leyland’s Technical Centre in Vellivoyalchavadi, about 30 km north of Chennai. The ‘Six Poster Road Simulator’ gains significance on two counts — first it is the only one of its kind in the country to test fully laden truck or bus with three axles, in other words, six wheels. Second, it recently received accreditation from the National Accreditation Board for Calibration & Testing Laboratories, for mechanical testing.

Here, typically, new product development comprises four stages — concept, verification, component validation and vehicle validation. The most time-consuming process is vehicle validation to assess end-of-life of the vehicle. The Six Poster Road Simulator validates the structure of the vehicle, which is like bones for the human body.

Saving on time, stress

Six poster simulation test in progress

In the conventional method, the structural validation is done under real conditions — for instance, if a vehicle is designed for coal mines, it will be tested in the coal mines for about two lakh km. This will take about two years and consume more than one lakh litres of diesel and about 4,000 man-days.

Hence, manufacturers seek to simulate the test conditions. This test is conducted on the ‘proving ground’ with artificially created road conditions featuring Belgian Pave (randomly distributed stones to represent terrain), Corrugation (bumps arranged perpendicular to the vehicle travel), Herring bone (concrete bumps profiled like bones of the Herring fish) Setts (randomly spaced stones) and Pothole (wide and varied potholes).

Here the testing time ratio between proving ground and actual field test is 1:70. This implies that if the vehicle continuously runs on the proving ground for three months, it is as good as having run it for two years in the field test.

However, even the three months of simulated testing can put tremendous pressure on the driver testing the vehicle — he absorbs all the shocks, as it were.

This is where the Six Poster Road Simulator steps in. Using it, manufacturers can reduce the actual testing time to 15 days. The testing time ratio between simulator and actual field test is 1:420, helping vehicle manufacturers to save on time in new product development.

How the simulation is done

Let’s visualise how all this happens: Strain gauges, accelerometer and string potentiometer are mounted on the vehicle at vantage instrumentation points. (An Instrumentation point is that which gives you a good indication of conditions – the reason why a stethoscope is placed on the patient’s chest for the best diagnostic possibility) When the vehicle is ‘running’ in the field, the vibrations sensed by these gadgets are transformed into electrical pulses. These are subsequently correlated with mathematical algorithms and retrieved in the form of digital data.

The accelerometer measures vibration in milliseconds while the string potentiometer measures relative displacement (difference in movement) in millimetre. The strain gauges assess micro strains experienced by the vehicle parts. Vehicles that are usually tested here have 12 to 24 instrumentation points, depending upon the model and design configuration of the vehicle and data flows along 60 channels for a six-wheeled vehicle. Since only 1,024 data samples can be retrieved per second along one channel, the testing unit is provided with ten channels considering the volume of information flow from one wheel of the vehicle. The total data per cycle is about 5 gigabyte in size.

Data generation and reading

Initially the vehicle is tested in actual road conditions for a day or two and on the proving ground for a few hours. The signals generated from these drives are fed into the remote parameter control software of MTS — the manufacturer of Six Poster Road Simulator.

All this data is transferred in digitised form to a computer to be analysed and edited as per the requirement. Since the test systems have mechanical fixtures, hydraulics and test specimen, there will be some mismatch between the actual transfer of data and the time of actuation in the testing machine. Therefore it is necessary to perform iterations until a suitable drive signal is achieved. After deriving the compatible drive signals for a cycle, the data is fed into the controller to execute the durability test.

Experience IT

Then, we move to the next thing. The vehicle is placed on Six Poster Road Simulator — which is nothing but six actuating posts where the wheels are mounted. These actuators perform based on the inputs they receive from the controller. Continuous inputs from the controller simulate actual road conditions.

If you sit inside the cabin with eyes closed, you feel you are driving the vehicle on the road and hitting every pothole on it.

All the measuring gadgets do their job — they give you data on the testing, and the endurance limits. This will help the manufacturers to come up with the right product at the first instance itself.

To give you an idea of the instrumentation at work in the simulation, let’s take a look at the hydraulic unit. This pumps 2,400 litres of hydraulic fluid per minute at about 3,000 psi (pounds per square inch) pressure to actuate the six posts in the testing machine. (Compare this to the 30 psi that your car tyre should have.) The high-pressure is required to make the six-poster move up and down rapidly, thereby simulating actual road conditions. This pressure can cut a one-inch-thick steel plate at one go.

Insight from data

Tests conduced using the Simulator can be repeated for any number of cycles as the data captured is available. The same data can be used for testing different models in the same track sample, thereby eliminating the first few stages in the test schedule. Over time, the lab will have catalogued field track data for several road stretches in the country and, to a large extent, can eventually eliminate field tests for new models.

This testing methodology gives designers the details of conditions of the vehicle in digital form. Based on the end application it helps them reduce design time drastically.

Usually the laboratory conducts tests in un-laden, laden and overload conditions. The simulator can test multi-axle vehicles of up to 60 tonnes and on a wide variety of road surfaces.

Since the Six Poster Road Simulator generates a lot of vibration, the technical centre decided to have seismic blocks. The simulator is erected on a 1,500-tonne concrete block supported by 24 piles of 16 meter deep with eight-inch steel bed plates.

tmurrali@thehindu.co.in

Related Stories:
Ashok Leyland to develop new range of trucks by 2012
Ashok Leyland develops new CNG engine for buses
Ashok Leyland to invest Rs 70 cr on R&D units

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