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Smooth on the rou

3rd July 1997, Page 17
3rd July 1997
Page 17
Page 17, 3rd July 1997 — Smooth on the rou
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Which of the following most accurately describes the problem?

by Dan Gilkes • The ability to carry a load across rough terrain often results in a poor on-road ride, low travel speeds and an increase in noise and vibrations in the cab. Much of this is due to the fact that many all-wheeldrive trucks are based on modified on-road chassis with a drive/steer front axle, raised suspension, lower differential ratios and a transfer box to transmit power to both ends of the vehicle. But there are always compromises between true off-road ability and the demands of the highway.

Timoney Technology of Navan, County Meath in the Republic of Ireland has taken a slightly different approach to the problem with a no-compromise approach which it calls the high mobility truck I-1MT420. If it looks vaguely familiar it's because Timoney buys in the FL cab from Volvo. The Swedish manufacturer also donates the 420hp, 12-litre engine and a fully automatic Powertronic transmission from its off-road articulated dump truck.

Timoney's expertise comes into play lower down on the truck: the company has developed a rigid chassis with fully independent suspension on every axle.

The axles have a central differential housing with in-board mounted, air-actuated disc brakes (for other applications the brakes can be fitted at the hubs).

The box-section chassis rails mount direct to the axle housing to form a rigid structure. There are no cross braces other than the housing. Drive shafts run down to the hubs which are attached to lower wishbones. These, in turn, are suspended by long-travel coil springs.

Depending on the specification, the suspension can be built with single or double coil springs or hydro-pneumatic struts. Timoney has also developed an on-road version for fire appliances which uses torsion bar suspension.

The modular system means that the same axle is used throughout, but the steering mechanism is locked out on the rear two axles. The axles can also be used on a 4x4, 6x6 or even a 10x10 truck.

Driving impressions

Commercial Motor tried the truck on very rough bog roads around the company's head office. The 420hp engine provides plenty of get up and go for a truck laden to 32 tonnes and Volvo's Powertronic transmission is a revelation, changing up and down with a smooth action that is certainly not present on Volvo's own dump trucks.

The rigid chassis has very little flex on the rough, with the independent suspension soaking up the bumps as if they weren't there. The wheels have far greater travel than with a rigid live axle—up to 500mm of movement is possible--and there's more ground clearance as the differential housing can be mounted higher.

The HMT420 lives up to its high-mobility title. It's happy to run at surprisingly high speeds across terrible surfaces.

One of Timoney's engineers was following us in a Toyota Hiace van: we left him wallowing on the heavily rutted and potholed road. The HMT420 also has superb hill-climbing abilities, with the Powertronic transmission making downchanges while maintaining tractive effort on the steepest of climbs. The truck is currently being shown to prospective military buyers but it has obvious applications on (or off) civvy street. If there is a fly in the ointment it's possible problems with meeting demand.

The suspension system has also been incorporated on military vehicles as far afield as the US and Australia. Earlier this year AM General was awarded a contract for the US Marine Corps for five prototype vehicles using the Timoney suspension—phase two of this order could take production up to 11,500 vehicles.

Obviously this is too big for Timoney's 70-strong workforce, which is why the firm is forming partnerships with truck manufacturers.

Timoney has 6x6 and 4x4 I-IMTs waiting in the wings and the company is looking at a vehicle which could finally challenge the dominance of the Unimog in the utility sector.

If they runs as well on the rough as the HMT420, Unimog had better prepare for some serious competition.

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