Putting the Brakes on Accidents

Recent media attention surrounding heavy vehicle accidents across Australia is forcing industry regulators to set their considerable sights on closer scrutiny of company driven maintenance programs.

According to the NTARC (National Truck Accident Research Centre), 25 per cent of all accidents are caused by speed, 12.1 per cent through fire losses and mechanical failure, with fatigue coming in third at 11.9 per cent. Each of these top three causes are shining a light on contributory brake issues.

With the recently released 2013 major accident report by the NTARC stating brake problems can result in tyre fires and explosions, recommendations are being made that brake and tyre maintenance become a priority.

Coupled with the recent woes of one of Australia’s largest transport companies being issued with multiple defect notices for brake, wheel and suspension faults, the major impact on company earnings and reputations cannot be ignored. Neither can the
cause.

The equipment

Regular brake testing allows the operator to keep an auditable record of testing. In the event a vehicle is involved in an accident, the risk of legal action can be reduced if accurate testing information is readily available. Also, regular testing can minimise vehicle downtime in the workshop, reduce brake lining and component wear and can assist in decreasing tyre wear, saving businesses time and money.

As with any product, there are multiple types of brake testers available. The three main contenders are decelerometers, plate testers and roller testers.

The most common and cost effective piece of test equipment is the decelerometer. Usually found strapped to the passenger seat of the vehicle being tested, it measures and records the inertial force of the vehicle as it decelerates from a pre-determined speed to a stop. Service brake speed is generally around 30 km/h with the park or emergency brake speed being 15 km/h.

What they don’t do is provide information pertaining to individual wheel performance. This type of testing will also not show hidden faults like drag and cracked or warped brake drums or discs, as it doesn’t weigh the vehicle. Motion is also a factor, with the vehicle required to be moving for the testing to be conducted, there is potential safety issues due to the possibility of the operator getting distracted.

The second type of testing is called plate testing. It measures the inertial deceleration force of a vehicle being driven at a pre-determined speed. The unit is installed in a static position on the ground and the vehicle is driven onto it. Brakes are then applied when the wheels are on the skid plates, allowing the reading of sideways movement of the vehicle wheel under braking as well.

Last of the options is roller brake testing, where trucks are driven onto a set of rollers which are covered in a plastic medium infused with friction material. When tested the wheels are turned by the constant speed of the roller, keeping the vehicle static during the test.

Roller brake testing measures deceleration by means of torque force produced by the decelerations of the wheel against the rollers. This method produces the most consistent results across all axles. It is possible to test one wheel at a time, review efficiency of service, and test parking and emergency brakes.

Roller brake testers can be configured for air pressure testing, ovality (warped or cracked discs/drums), bind (rolling resistance) and in some makes you can accurately test time lag, which can help reduce the likelihood of ‘jack-knifing’. One of the more impressive services  this style of testing provides is the ability to match prime movers to trailers, maximising vehicle balance and efficiency.

There are also a number of options to enhance the system including speedo checking, play detectors, emission testers, headlight aimers and noise meters. These accessories give this unit the added advantage of being able, in some cases, to form the basis of a complete vehicle test lane.

While the roller brake tester sounds like the darling of the three, it does have some dirty laundry to air. Due to the powerful drive systems, it needs three phase power to operate and safety rules must be strictly adhered to. The weight of the mobile units (1.2 tonne) can be inhibitive. While installation can also present some challenges, with the in-ground units requiring some civil work to get the job done.

The bottom line

When it comes to operation, roller brake testers will measure the torque reaction generated by the vehicle brakes against a roller turned by a motor, while the plate brake testers have strain gauges attached to a plate supported on bearings, and measure the forces required to hold the plate when the truck brakes. Decelerometers are placed in the vehicle and have a pendulum (more recently, airbag type accelerators) which moves when a vehicle is braked, the amount of ‘swing’ on the pendulum is measured to indicate deceleration during braking.

Roller brake and plate brake testers testers use the same braking surfaces, ensuring accurate comparative tests. However, the decelerometer tests on road so the braking surface can vary  depending on conditions. While roller brake testers test all vehicles at a consistent test speed, both the decelerometer and plate brake testers tend to test at variable test speeds.

Roller brake testers can test the entire range of every brake fitted to the vehicle, from zero to full braking, or wheel lock, consistently and repeatedly, without the influence of momentum or weight transfer. The plate brake testers and decelerometers cannot test the entire range of a vehicles brake successfully.

Decelerometers cannot test individual axles, plate brake testers can compare the balance of brakes across individual axles, while roller brake testers are able to consistently and repeatedly compare the balance of the brakes across individual axles.

Roller brake testers are able to achieve consistent and repeatable results for brake tests on individual wheels to full brake effort or wheel lock up, while plate brake testers and decelerometers normally do not brake to full capacity, as this would be too dangerous. The brakes are tested to try to exceed a pre-defined deceleration and if this figure is exceeded, then the brakes are deemed to be ‘good enough’.

The roller brake testers are compact but require sufficient room at each side of the brake tester for the vehicle. Plate brake testers are the most space greedy, with a large area required for the plates and a suitable amount of room required for acceleration and deceleration including a safe overrun area. The decelerometer is the most space friendly, with no installation required for the vehicle mounted unit.

To give meaningful loading results with the all three of the testers, the vehicle needs to be loaded to more than 60 per cent of its carrying capacity, or in the case of the rolling brake tester, a simulated load applied.

The facts

Driver fatigue, mechanical failure and speed dominate as the main causes of heavy vehicle accidents, costing lives and billions of dollars across Australia every year. Safety and maintenance are being brought into focus through critical media attention, which will send a ripple out across the entire industry.

It is safe to say that with the introduction of the National Heavy Vehicle Regulator and a review of the NHVAS, a greater focus on a national standard for vehicle maintenance and inspection cannot be far behind. Will you be ready?

Freewheeling braking New culture in RMS

Author: Tim Giles

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