Isn't it about time we started to think of the engine brake on a heavy vehicle as the primary braking system and the service brakes as secondary brakes? This was a question posed by the Cape Centre of the IRTE at a recent meeting - and it's a good one to ask. In this article, Dave Scott, technical correspondent for FleetWatch, takes a look at the subject of retarders and retardation and concludes that while major benefits accrue from the use of modern retardation systems, much training needs to be done to fully realise those benefits.

Since I sold my first truck in 1966, foundation brakes have remained locked into the principle of one brake per wheel. Sure there may be dual tyres for each wheel on the road but only one brake drum or disc absorbs the energy for those tyres. Contrast this with the increase in power and combination masses that have accrued over this period.

Whereas 250 horsepower engines were considered topside in the mid-sixties for around 45 tons gross combination mass (GCM), we now run close on 500 horsepower at 56 tons and more. Despite this increase, foundation brakes, poor things, have remained much the same. This all means that average speeds have increased and far more driving skill is required in using all retardation devices available to a driver.

ADE 'noise converters'
An enduring fame of Cummins diesel engines was the 'Jake Brake'. A 'Jake' had real retardation in comparison to the ADE diesel engines of the eighties that only utilised weak exhaust brake retardation.

One of the reasons that thirsty, normally aspirated ADE V10 engines were popular in the eighties was a 16-litre capacity that offered slightly better retardation than ADE V8 turbo units. Until the advent of the ADE engine valve brake (EVB), ADE engines did little to stop a truck and had the reputation of converting exhaust brake power into noise instead of retardation.

But engine technology has changed dramatically. Modern diesel engines can produce as much kW energy for retardation in maximum GCM work as they can for forward propulsion of a vehicle combination. In fact, modern cylinder-head engine retardation devices are so powerful that a driver now has the option of operating the engine brake on 2, 4 or 6 cylinders to suit road conditions and prevent jack-knife situations. The engine brake is no longer just a 'go-no-go' switch. It now incorporates the need for driver judgement and understanding.

The green-band conspiracy 
A driving technique which was heavily promoted during the ADE years was so-called 'green-band driving'. This became the standard by which drivers were judged for correct handling of vehicle power trains by narrowly setting engine r/min management into the green maximum torque band displayed on many European truck rev-counters. 

The problem with green band driving was that it did not recognise a driver's right to run an engine up to maximum rated engine speed - and maximum r/min is the point at which engine brakes and extra retardation devices become really effective.

'Green band driving' developed a driver culture of adhering to maximum torque as the only yardstick of driving efficiency. It ignored the more important issue of being able to stop a truck with the minimum use of foundation brakes and the maximum use of retardation devices. Green band driving was actually a step backwards in terms of vehicle safety.

The green band 'conspiracy' was also a major contributor leading to the failure of extra retardation devices often fitted to heavy trucks where fleet managers found an ADE exhaust brake inadequate for operational retardation.

Hydraulic retarders, such as Voith, produce excellent retardation provided they are not driven all the way downhill at maximum retardation and low engine r/min. However, drivers fearful of exceeding ADE green band parameters would overheat an hydraulic retarder because the engine was not run at maximum rated r/min during retarder operation.

Training is a must
Managing the rolling, kinetic energy of momentum produced in a vehicle, or vehicle combination, is appropriately defined by Max Boulogne of Transport Training Technologies as 'power train management'. This requires judgement far beyond foot and trailer hand control valves.

The Cape Town Centre of the Institute of Road Transport Engineers (IRTE) recently toured Cummins Diesel in Parow and members were introduced to engine electronic control module (ECM) outputs which measure power train management.

An ECM on a Cummins Signature 500 engine records brake pedal use as well as engine brake actuation with the intent of measuring driver use of brakes and retarder. This vital information becomes an important tool to ensure the effect of driver training. Does the use of the engine brake exceed that of the foot brake and is this an improving ratio? 

This leads to questions posed by the Cape Town IRTE: "Isn't it about time that we started to think of the engine brake on a heavy goods vehicle as the 'primary' braking system and the 'service' brakes as secondary brakes?" The IRTE asks further: "Do our current driver training systems empower drivers to get the best life out of their vehicles' service brakes by correct use of an engine brake or retarder?"

Key suggestions
Measuring and setting standards on how braking and retardation is being managed is just as important as measuring fuel consumption. Here are a few key suggestions:

There are also extended consequences arising from aggressive braking and driving abuse. Premature wear of foundation brakes is reflected in the tyres where flat spot wear is evident on the tread pattern. A tyre beading also cannot take continuous temperatures above 100 0C - severe braking tests have recorded temperatures up to 170 0C in the tyre beading due to heat transference from the brake drum. When a tyre beading fails, the tyre has to be scrapped. Retarders can have a positive effect on tyre life and wear. This is not to be confused with a tyre fire where a tyre catches alight beyond 200 0C and burns at a temperature of 700 0C. (See Lessons From A Burn Out).

A real problem exists in the many abused and neglected trailers fitted with braking systems that cannot match modern trucks. Serious danger lies in poorly balanced braking systems where trailer braking is weak and badly timed. Neither retarder technology nor any amount of driver training will allow for inadequate trailer brakes. Jackknifing will occur or the truck tractor's brakes will wear prematurely in taking up all the energy transferred by a trailer that cannot stop.

Driver fatigue 'benefit'
Of course, another 'hidden' benefit in the proper use of retardation devices is that they help prevent driver fatigue by transferring human effort to mechanical effort. In many overseas manufacturing plants, the use of robots has been introduced in areas of the manufacturing process which previously required intense manual effort. The idea behind this is to better utilise the human in mental tasks rather than manual tasks. The same principle applies here. Let the driver concentrate on the road and leave the manual work to the retardation system.

It is interesting to note that even passenger vehicles are entering into the realm of high-tech retardation systems. An increased acceptance of hybrid vehicles in overseas markets and other clean energy vehicles has led to a demand for advanced braking technologies that operate in concert with the drive train.

Such technology employs regenerative braking systems that convert a vehicle's kinetic energy back into electric power for storage in battery packs. Toyota Motor Company in Japan has formed a joint venture with three other major stakeholders to establish a company with an initial capital of one billion Yen dealing in braking components and complete braking systems for this technology.

Retardation systems are at the point of an exciting threshold but here, in our mixture of First and Third World conditions, we will face the challenge of trying to balance the practicality of keeping up with global developments against the increased costs such developments may bring with them.

We cannot, however, use cost as an excuse for what is essentially a critical road safety issue. We must adopt absolute First World standards for all safety critical items fitted to the rigs on our roads - and follow this with First World training for those who operate that equipment. Anything less will be a cop-out.