Beginners guide to load simulation on brake testing

Load simulation is the process of putting demand on a system or device and measuring its response.

It ensures your application can perform as expected in real life scenarios and is important because even though your application may pass a functional test, it doesn’t necessarily mean it can perform the same under a load.

In the case of a brake tester, we would use a load simulation system or technique to see whether the vehicle is doing what we expect under ‘loaded’ conditions.

When selecting a load simulation system, it is important to consider the right one for your brake tester and workshop environment.

When should load simulation be used for brake testing?
The short answer is, if a brake test is performed on a heavy duty vehicle, load simulation can be used in order to produce a more accurate and reliable result.

Authorised Test Facilities (ATFs) are responsible for making sure vehicles are properly loaded before the MOT starts. This normally means at least 65% of the vehicle design axle weight (DAW). This can be achieved by using a load simulation system or by arranging to load the vehicle or trailer yourself.

When loading a vehicle for a brake test:

• Place loads close to the rear axles
• If possible, use similar loads to add weight to the vehicle: this will help in placing the loads correctly, and achieve consistency between tests
• Aim to apply at least 65% – and not less than 50% – of the design axle weight to each axle

Types of load simulation systems

There are numerous types of load simulation systems and techniques that can be implemented on brake testers. Below we have highlighted three systems for in-ground brake testers, and one for mobile brake testers. All are designed to increase productivity in workshops, produce accurate and reliable brake test results, and minimise the amount of manpower used when manually having to load a vehicle with weight.

Axle load simulation (suitable for mobile brake testers)

Axle load simulation is a method which requires chains to be installed to the sides of the subframes of the brake tester – no special adaptations to the design or construction of the brake tester are necessary.

These chains are then fitted to the axle before a brake test. The load is applied to the axle of the vehicle, however the load sensing valve/function and suspension system of the vehicle will not be activated or tested. Once the test has been complete, the chains are removed before moving the vehicle.

Some features of axle load simulation include:

• Load capacity – 8,000kg (optional 16,000kg)
• Fully mounted on the installation subframes
• Can be used on in-ground brake tester versions
• Perfect for workshops with low vehicle throughput due to the relatively time-consuming process of use

Chassis load simulation (suitable for in-ground brake testers situated on over a pit)

The chassis load simulation system consists of skates rolling on rails fitted to the floor of an inspection pit. The system consists of two I-section steel beams installed on the inspection pit floor.

Skates are then connected to the I-section beams and to the chassis, via chains and special self-tensioning claws. A spring coil ensures that the hydraulic cylinder always stays vertical.

The system works by:

1. The requested load on the axle being tested is entered via the remote control and the computer-controlled system is activated
2. The brake test of the axle is conducted
3. The load application is released via the remote control
4. The vehicle is driven forward to the next axle
5. The skates stay on the chassis while the vehicle is being moved as the claws make sure the chains remain fixed to the chassis and the skates are smoothly being pulled forward rolling on the rails.
6. The requested load on the next axle is entered via the remote control – the load simulation is activated, and the brake test is conducted.

Other features that make this system perfect for an in-ground brake tester are:

• The operator can fully control the load application from his remote control unit from the vehicle cab
• Length is made to customer specification
• Can be used in a pit

Direct load simulation (suitable for in-ground brake testers)

This system works by applying the load simulation directly from top-down onto the vehicle. The system is powered by an electrical pallet truck and is therefore easily moved around by one person. The operator moves the load simulator to its position, which can either be behind – or at the side of the vehicle. Once the system has been moved into position, the load is applied to the vehicle being tested.

An advantage that this system has over the axle load simulation is that because the load is applied from top-down, it means that the load sensing valve/function, as well as the suspension system of the vehicle is activated during the test. A slight disadvantage to using system is that it requires large amounts of groundwork as its not really practical for retrofit – but would be ideal for new builds.

Please see further features below that make this system an ideal option for any in-ground brake tester:

• Can be moved into position either behind the vehicle or at the side
• Load capacity: 10,000kg (load applied directly over the axle being tested). > 10,000kg (load applied behind the axle(s) being tested)
• Fully controlled from a control panel placed at the rear of the pallet truck
• Requested load simulation is entered, ‘START’ button is pressed and the system will apply the load instantly
• The load platform can be applied to any vehicle with a suitable flat area (open flat bed) e.g. tractors where load is applied to the fifth wheel, closed box trucks, semi-trailers.
• Optional WLAN communication with the brake tester
• Allows for control of the applied load using the RBT weighing
• One man operation

Hydraulic load simulation (suitable for use with a Totalkare in-ground brake tester)

This system is built into an in-ground brake tester – it is a unique hydraulic load simulation system, which allows the operator to raise the roller bed out of the ground. This brake tester features a large range of options that allows for a customised configuration.

Each roller bed is lifted on four hydraulic cylinders and is controlled by software that has built-in safety features protecting the vehicle and operator during the brake test. Chains are attached onto a sliding rail which is concreted to the floor – these are then attached to the axle of the vehicle as shown in the image. The chains are essentially used to pull down the vehicle whilst the hydraulic bed rises – this creates a simulated load.

This system was the first rising bed load simulation to be installed in the UK, and Totalkare had the pleasure of installing this at Transam Trucking – read the full story here

Another notable chassis load simulation system is an option used for on in-ground brake testing – it consists of cassettes rolling on rails placed on the edges of the inspection pit. Each cassette has an integrated hydraulic cylinder hooked to the chassis of the vehicle via chains. This system can integrate a load simulation from 10,000 – 80,000kg.

If you require any of the products mentioned above or any further information on load simulation, please do not hesitate to contact us.