Haulier sees the benefits
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r HE electric retarder has men in use with British :oach operators for many fears, but the haulage conrector has been less eager to idopt it.
Advantages of fitting such i system are claimed to be nainly financial with side )enefits of safety, that are lifficult to cost.
Financial benefits come from 3xtended brake lining wear, not )nly by savings in the costs of -eplacement shoes themselves put also from a reduction in the iowntime associated with 3djustments and servicing. The safety advantages come from -laving cool brakes and a full -eservoir of air when the service system is needed.
Mew installation
Recently, a new installation has been introduced onto an articulated vehicle operating out of Hinckley's Quarries, Congleton, on the edge of the Pennines. A trailer bogie, equipped with an Eaton 812 live axle at the rear, has been fitted with a unit similar to that used on British coaches.
A system of this type has been in use for about seven years in France with good effect, The initial installation is more expensive than it is when fitted to the tractive unit. But with the trailer service life lasting up to three times longer, the extra initial cost is soon offset.
Recently, I had an opportunity to see the Telma unit on the Hinckley outfit at close quarters. The outfit consists of a Volvo F86 drawing a York bulk semi-trailer fitted with a blow discharge unit, running at 32.5 tonnes (32 tons) all up weight with a payload capacity of 21. tonnes (21 tons).
Clear of muck
The unit is slung behind th rear axle of the bogie whic helps to keep the cooling fin clear of muck thrown up by th tyres. Similar systems mounte in front of the axle have bee known to clog up in snow o heavy mud and this has led t overheating.
The unit, in its present stag of development, weighs 417k (920Ib), but on later models, is hoped to reduce this figure t around 335kg (740th).
Ralph Minshull, the regular driver of this rig, took me o board where I was able t observe his technique an collect the information from thmonitors installed to measure
the operational time of the electric retarder and the normal service system.
Ralph told me he had been converted to this way of braking with drive axle mounted units; but he felt happier with the present arrangement on articulated combinations, especially in bad weather. He felt that, on hill decents, in particular, this arrangement tended to stretch the vehicle out in a straight line.
I was told that, in tests at the TRRL, on surfaces with a low coefficient of friction (p,), this combination behaved well. And due to the leading axle on the bogie being unbraked by the Telma, sufficient side forces were generated to keep the vehicle on line even if the Telma-controlled axle was allowed to reach a lock-up type situation.
Cannot lock
The Telma on its own cannot actually lock the wheels. But it is possible on very low surfaces for wheels on one side of the axle to turn slowly forward while the other side rotates rearwards resulting in a high degree of slip between tyre and road surface.
This application is best suit ed to the specialist vehicle where tractive and trailer work permanently coupled and any increase in braking stability over a tractive mounted unit comes from the lower weight transfer induced by a rear mounted device.
The Telma is operated by a hand control which has a choice of four positions: each one, in succession, brings into use a greater number of the electro magnets in the system. The performance of the retarder is, to some extent, speed depen dent. It reaches its designed maximum efficiency at 800rpm while, below 16km /h (10mph) road speed, the performance drops away rapidly.
At its most efficient the Telma is set to give a retardation of only 0.08g. This level is critical: much higher and the service brake performance might become impaired through too little use; lower, the service brake would have to be used more often dispensing with the benefits mentioned earlier.
Test results
The journey from Congleton to Stockport on the A523, a distance of 34km (21 miles), took just 50 minutes — an average speed of 40.8km /h (25.3mph).
The retarder was used 26 times for an accumulative period of 448 seconds. The service system, on the other hand, was applied only 18 times for a total of 91 seconds.
Short journey
Although the journey was short, it was sufficient to highlight some of Telma's claims. The level of deceleration needed to check the road speed of a maximum weight commercial can be kept below 0.1g for most of the time and application of the service brake, however delicately applied, usually results in a greater value than this.
If the vehicle is not being overbraked, journey times and fuel consumption returns should be improved.
Back at the quarry, I was able to chat with Phil Clause, transport manager for Hinckley Quarries.
His first experience of running vehicles with electric retarders was on rigid vehicles.
Savings
He had found that savings of downtime and replacement parts covered the cost of installation within the first year. In having the device fitted to semi-trailer he is looking, hop( fully, towards an increase i gvw when the penalty suffere in loss of payload woul become less significant.
He went on to say the feedback from units mountei on rigid and tractive units ha led him to believe that reduction in clutch wear and, ii some cases, tyre wear ar, possible.
Later, I raised these point with Tom Scharff, genera manager of Telma, who said "We have been made increas ingly aware, by operators, o the possibility. But to substan tiate the facts to our satisfac tion, we need to examine thei service records back over th( last 10 years or so, whict usually is impossible. However it is an aspect of the in-servic( operation that we are looking a and will continue to monitor."