It may seem paradoxical to consider a braking mechanism actually enabling a truck to get to its destination faster but a retarder is designed to do just that. Acting as an alternative or additional 'speed reduction force' to the service brake system (be that hydraulic or air-powered), retarders come in many different forms, using various energy sources to bring about drive axle braking.
Paul Collings takes a look at their evolution and application in the truck world.
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Retarders promote safer, more efficient trucking but driver training is needed to maximise the benefits ands that needs more focus in SA. |
The first retarder ever built was fitted to a 5km-long goods train that crossed the Rocky Mountains in the USA. The train had a GVM of 10 000 tons and was powered by a 4000 HP diesel locomotive. The transmission system of the diesel engine was developed by German industrial giant, Voith, who were tasked to develop a braking system for the massive 'iron horse' to help it safely down gradients of up to 30%. South African road transporters conducting hauls over our impressive mountain ranges will know something of the challenges these old boys faced.
The first retarder fitted by Voith to a truck happened relatively late - in 1975. Since then, retardation technology has expressed itself in a number of ways, in both trucks and busses. Today, two types of retarders are available:
Primary retarders: hydraulic systems powered by exhaust gas and housed on the engine near the cylinder head, achieving their goal by articulating valve movement; and
Secondary retarders: powered by either electromagnetic eddies or hydrodynamics (a Voith system using either oil or water between a rotor and stator).
Secondary retarders sit on the back of the gearbox and work directly on the rotational speed of the propshaft while primary retarders work on the pressure in the combustion chamber, increasing compression and thereby slowing the vehicle down via the crankshaft.
Primary retarders come in several guises, known as exhaust brakes, engine valve brakes, turbo brakes and 'jake brakes'. Secondary retarders are not quite as multifarious and comprise intarders and the electro and hydro varieties. The amazing thing is that all these retarders seem to work on different energy-related principles. Technical detailing is, however, not what we're looking at in this article. Rather we need to know what each type of retarder can do - or not do - for the trucker.
Increasing productivity, lowering down-time
A vehicle fitted with a retarder will be able to get to its destination faster because the retarder allows the vehicle to descend hills at higher controlled speeds (sticking to the 80km/h limit) safely. Assuming the driver is well trained, he will make far less use of his service brakes, which will reduce wear not only on the foundation brake components (linings, shoes etc) but also on wheel bearings and tyres. Having replacement intervals extended on these components allows for more operational up-time. In essence, retarders save money and facilitate more trips. They also improve the resale value of the vehicle.
In September 2003, Voith Turbo (Pty) Ltd (SA), in conjunction with DaimlerChrysler SA Commercial Vehicles, conducted a road test using one Actros 2648 interlink on two trips - one trip fitted with a Voith R115 retarder and the other with the secondary retarder disconnected. The test was on the N3 from Johannesburg to Durban and, says Bruce Dickson, divisional director, road division, Voith Turbo, the results were "compelling."
"The truck without a secondary retarder applied brakes 81 times compared to 37 applications on the Voith-fitted truck, which used the retarder 133 times. Gearshifts were less on the Voith-fitted truck and its absorbed foundation braking energy was reduced by 82%. It also pipped the non-Voith model to the post by 67 minutes. Add to this the fact that fuel consumption on the Voith-fitted Actros was around 1.5 litres less per 100km." Impressive selling points indeed Mr Dickson.
| Bruce Dickson with Voith Turbo's works manager, Gordon Soetwater. |
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Strengths & weaknesses
With so many different types of retarders on the market, both as OE standard fittings or as retrofits, truckers might be excused a bit of confusion as to which retarder best suits their particular application. The essential difference between the primary and secondary retarder is what drives it.
Well, for a primary retarder it's the truck engine. This means that if the pistons stop moving, the retarder fails. If the driver slips a gear, these retarders will cease to function and foundation brakes will have to save the rig. If the brakes are cold, this won't necessarily be a problem. If they're hot and the load is heavy, trouble could ensue.
Secondary retarders work off the propshaft, independent of engine speed, so as long as the wheels are rolling at sufficient speed, the retarding action will kick in when the lever is pulled in the cab or the electronic control unit activates it. As a final safety mechanism, secondary retarders are hard to beat. However, electromagnetic retarders are air-cooled which means you can't stop and leave the truck standing immediately after extensive use of the retarder or the unit runs the risk of extensive damage to the retarder due to extreme operating temperature (500 degrees centigrade)
Intarders are secondary retarders that share the same oil as the transmission system. This can be problematic when the retarder is applied for extended periods because the oil temperature can increase to levels that could harm the gearbox. By the same token, externally fitted secondary retarders, while having a separate oil sump to that of the gearbox, share the truck's water-cooling system. When the retarder is being used, the energy used to slow the rig is absorbed by the coolant (as heat) and dissipated into the atmosphere. Drivers need to maintain the engine in the optimum rpm range to achieve maximum benefit from the retarder.
Fit for the job
The leading truck manufacturers are increasingly fitting retarders as standard on both heavy and medium commercial vehicles. The retardation units form part of the comprehensive braking system, invariably electronically controlled, linked to the automatic transmission and the CANbus system. In short, much of the braking decision-making is taken away from the driver and controlled by 'smart' technology inside the cab.
This is great for the new truck buyer but what if you want to retrofit a retarder? According to Dickson, Voith retrofits around 50 truck retarders in South Africa a year. "You need to adapt the standard gearbox to accommodate the retarder. The additional costs of down time and new parts are, in the long run, amortised, recouped and the vehicle will be worth more on the used truck market," he says.
This begs the question: Which retarder for which application? Says Dickson: "Generally speaking, when you're running at low rpm and high axle ratios, like tipper operations, a secondary retarder is perfect. Similarly, long haul trucks fitted with only a secondary retarder will benefit because of the unit's ability to function better (than a primary retarder) through the drive axle variances (high, medium, low speeds)."
Bottom line: Driver training
As we all know, there's no stopping progress and hi-tech innovations that promote safer, more efficient trucking are to be welcomed. However, for these products to make sense on our roads, truck drivers have to know exactly how to use them. This, of course, takes training and not just a day's worth. Drivers need to be immersed in an ongoing programme that educates and builds capacity. The programme also needs to conduct regular evaluation of a driver's progress to fill the necessary skills gaps. Voith Turbo, along with most leading OEs, do run driver training programmes but really only scratch the surface of our national truck driver pool.
Surely the onus rests on the operator to ensure their drivers are adequately skilled to utilise these remarkable inventions to their full potential?
FleetWatch certainly believes it does but also acknowledges the lack of adequate/sufficient training facilities. In this era of drastic unemployment and the dire need for job creation, why aren't truck specialists, along with government, catering to this blindingly obvious market need?
