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railELUT1=3 crj 01 col by Graham Montgomerie
A refrigeration system powered by the rea axle of the trailer has been developed jointly by Transfrig, Alpine and Rubery Owen-Rockwell. As the operator has already paid for the diesel engine's power this approach has a lot going for it
FOR YEARS the 40ft fridge market has been served by the big diesel-powered refrigeration unit but recently a system has become available which takes its power from a trailer axle.
TransFrig of Cranbourne Road Gosport markets the system under the brand name of Axle-Frig and claims that the idea "marks a new era in transport refrigeration practice". To find out if the claim is justified, I went to Gosport to talk to refrigeration sales engineer Bob Fitzer.
The company does not build for stock, it builds to order only to enable the unit to be tailored to a customer's individual requirements. According to Bob Fitzer, TransFrig prides itself on making non-standard units to keep the customer happy but using a standard kit of parts to keep the TransFrig inventory down.
For fridge units designed for the 40ft van, the main competitors of TransFrig are of course Petter and Thermo-King. Although TransFrig built a couple of diesel-powered fridge units the company admitted that they could not hope to be competitive with the two giants and dropped out of the market for a rethink.
The result of the rethink was a refrigeration system driven by the rear axle of the trailer which was developed jointly by TransFrig, Alpine (part of Allied Breweries) and Rubery OwenRockwell. The first system utilised this axle drive in conjunction with a condensing unit and TransFrig Transtubes.
The Transtubes are mild steel tubes with an outside diameter of 76mm (3in) enclosing a much smaller centre tube which is filled with eutectic solutions having predetermined freezing temperatures of between —30 and —28°C (26° and —18°F).
The space between the two tubes is a partial void to take up any expansion and also contains a mixture of salt water and methylated spirits. The sealing caps are welded on with the whole assembly being then sprayed in aluminium.
The power take-off axle is produced by RO-R with the prototypes being fabricated to be replaced by a forged design for the final production unit. The gearbox is a TransFrig design and is rated to take 50 horsepower. It is rig tested at 36 and in use will absorb a maximum of 12 horsepower. The average power transmitted is in the region of four horsepower so "it's not exactly overstressed" as Bob Fitzer put it. The condensing unit is fainl standard consisting of a con pressor, a condenser and th controls. This unit also incorps rates a standby electric motr for recharging the eutectic tube although the emphasis here on "standby" as recharging continually taking place whi the trailer is moving.
The hydraulic pumpigearbc assembly weighs only 32k (70Ib) and it is the weight savir aspect of the system which stressed as one of the major al vantages. TransFrig claims th there is a 450kg (1,000lb) adval tage on the unit alone wile compared with a convention diesel powered nosemount un
hen the weight of the fuel tank id about 30 gallon of dery is eluded then the advantage beg-nes even greater.
The Axle-Frig system is avail)le for both chilled and frozen
• oduce with a wide range of D Iding temperatures. The
• anstube system is for frozen ads only but the 120 system as more universal useage by ambining the axle drive with an ectric/hydraulic nosemount Before this system was dealoped Alpine had been using quid nitrogen which was asting £5,000 per year per 401t ailar. The equivalent cost of a )nventional diesel powered lit (including depreciation) was it at around £4,000/£4,500 hich compares with the £2,000 )tal cost which Transig claims for its Axle-Frig )eration.
TransFrig also claims major wings on the maintenance side ; there are only five moving arts in the axle drive. About the ly maintenence required is to led( the oil in the gearbox. On diesel-powered fridge unit, a irly conservative estimate puts laintaining the diesel part of it : 50 per cent of the total mainteance costs.
The basic logic behind the xle-Frig layout is "why do you ed a 20-plus horsepower die)l engine to do the job?" ransFrig estimates that to iaintain the interior temperaire of a 40ft van at —26°C -15°F) when the ambient ternerature is 30°C (86°F) requires bout 6,800 BTU/h to be aborbed. (To put this into erspective this ambient temerature has occurred six times nce 1933!)
Tradition has it that a dieselowered unit is needed to cope ut TransFrig obviously disputes his by quoting a four orsepower requirement for a ompressor speed of 1,450rpm. his power requirement has to
ome from somewhere as the .ailer axle only rotates courtesy f the tractive unit which implies lat the extra drag of the pto rill show up in increased fuel
onsumption on the prime TransFrig disputes this
s well and quotes results from a ast with SPD. On a dry run, prior D the axle take-off being fitted le outfit recorded 35.7 lit/100km 7.9mpg). Immediately after Ming the Axle-Frig, exactly the ame consumption was regisered.
The gearing of the axle drive is • ased on customer estimates of he vehicle average speed. As a ule of thumb TransFrig starts vith an average of 65km/h (40mph) but, if the customer has a multi-drop operation involving a lower speed and a higher heat loss, then the pulley wheel diameter can be changed to increase the compressor speed.
When Axle-Frig was first launched, TransFrig published estimates of the likely fuel savings compared with a conventional diesel powered refrigeration unit. The assumed conditions were: an internal temperature of —20°C ( 4°F) and a running time of 60 hours per week throughout the year. TransFrig estimated that the diesel powered fridge would average about 21/4 litres per hour (about 1/2 gal) which would result in a total of 7,020 litres (1,560 gal) annually.
The initial estimate for the Axle-Frig layout was that the increase in fuel consumption of the tractive unit as a result of the permanently engaged pto would equate to 2,545 litres (560gal). In fact, as mentioned earlier, any such increase has been too small to measure so that the overall fuel savings amount to the total used by the diesel powered fridge unit.
Although obviously not without bias, Bob Fitzer summed up the company's attitude towards the axle drive when he said: "The operator has already paid a lot for the diesel engine in his vehicle. Why shouldn't he use what he's already paid for?"
As a guide to the price, a 120 system incorporating an electric standby has a list price of £5,846 but this does not include the pt-o axle as TransFrig argues that the trailer builders will be able to haggle for a better price. As such, the axle is likely to add a further £500 to the above figure. A diesel standby version is also available, as is a system with both diesel and electric.
TransFrig can play tunes with the installation to suit individual operator requirements. With the Axle-Frig 120 for example the condensing unit can be combined with the evaporator in a nosemount unit or alternatively it can be mounted separately under the trailer chassis.
There are two sides to every argument and TransFrig accepts that there are operators who have a definite preference for diesel power. Rental fleets represent a good example because they need to be capable of doing anything for any operator at short notice.
Not all the TransFrig eggs are in the axle-drive basket. The company also produces more conventional refrigeration units but again incorporating hydraulics. The smaller units work by driving a gear type hydraulic pump from a gearbox mounted pto with the units again being tailored to provide optimum cooling capacity at the average speeds encountered by the particular operator.
These hydraulic nose mount units are suitable for body lengths of between 4.6 and 7.6 (15 to 25ft) for carrying of chilled or frozen produce.
The Gosport company specialises in transport refrigeration equipment and although the vast majority of its business is for what could be termed "conventional" systems in the transportation sense there have been some odder orders to satisfy. Like the refrigerated body for a Transit designed to carry six bodies to allow the faithful to complete the pilgrimage to Mecca ...