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If spring is in the air ou're sitting pretty

19th March 1983, Page 65
19th March 1983
Page 65
Page 66
Page 65, 19th March 1983 — If spring is in the air ou're sitting pretty
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Which of the following most accurately describes the problem?

Seating is at the bottom of many drivers' problems so David Wilcox has been talking about the business to lsringhausen, a German company now making greater efforts in the UK

SRINGHAUSEN

'HE EXPRESSION "dropping lff" dates back to the days of lick Turpin when the less weal

iy rode on the top f a stage coach; if they went to leep they would quite literally rop off.

At one time there was a school f thought that suggested it was good idea to keep a lorry driver qually uncomfortable in the beef that it would stop him going ) sleep. But fortunately, more .cent thinking takes a hint from ick Turpin's contemporaries rid recognises that it is the un3mfortable driver who is in reater danger.

One company that is building n this belief is lsringhausen. A erman family concern, it was stablished 60 years ago as a small spring producer. Its logo represents one of the springs used in a bicycle saddle of that era, despite the logo's similarity to that of Seddon Atkinson or Audi there are no connections.

From this background of springs, saddles and simple seats lsringhausen progressed to hgv seat manufacture in the early 1960s when it started to make seats in Germany under licence to Bostrom. This agreement ended in 1969 and Isringhausen went into the design and man ufacutre of hgv seats in its own right. These were originally marketed here under the name of Derby but this was changed to Isri about five years ago.

lsringhausen's main manufacturing plant is in Lemgo, West Germany and produces up to 18,000 seats a month, mostly for the hgv market although there are also models for buses and coaches, construction equipment, agricultural tractors and forklifts. And the company still turns out springs in all shapes and sizes.

In addition to the Lemgo manufacturing plant lsringhausen has smaller ones in the USA, Argentina, France, S. Africa and Brazil; it assembles seats in Sweden and has licensed companies in Australia, Japan and Yugoslavia.

Five years ago lsringhausen came to the United Kingdom as well and operates out of one of Milton Keynes' ubiquitous industrial units. I was surprised to find that it is not just a sales agency, nor even an assembly line; it is a miniature factory with 30 employees. There are two small (800sqm each) halls, the first houses the seat frame and suspension unit production and the second is the trimming shop.

Managing director of Isringhausen (GB) is Axel Zaiser who explained that the company felt that merely a sales office in the UK was not sufficient: "We regard the UK as an important commercial vehicle market and to serve the manufacturers here as an original equipment (OE) supplier we wanted a proper manufacturing base."

No doubt lsringhausen also believed that a higher UK content and profile would enhance its chances with our manufacturers and Axel Zaiser was at pains to point out that British companies supply most of the raw materials and components used at Milton Keynes.

One of lsringhausen's early UK OF customers was ERF and most of the continental manufacturers fit lsringhausen suspension seats in their tractive units. That is not to say lsringhausen seats are used exclusively by -these manufacturers; many practise dual-sourcing and also fit others types such as Bostrom or Bremshey.

Although one immediately thinks of suspension seats in lorries, it is static seats that still account for the majority of the hgv market and lsringhausen makes these as well. Static seats are generally fitted as standard on vehicles up to the medium weight category (16 ton gvw), a sector that easily outsells tractive units.

The use of static seats is traditionally justified on three counts; the driver does not usually stay long enough in the seat to find it uncomfortable, there may be insufficient height in the cab to fit a suspension seat and that a suspension seat is relatively too expensive for this type of vehicle.

These arguments do not always stand up so well in today's world. Modern seat suspension units are less bulky and have a lower profile than their predecessors and so they can be squeezed in more easily (Isringhausen in South America has even fitted one in an Argentinian taxi!) And in a time when commercial vehicle sales are depressed a driver's suspension seat can carry considerable showroom appeal.

As a result, many of today's middleweights such as the Ford Cargo and Bedford TL offer a driver's suspension seat as an option.

The two main lsringhausen suspension seats are the Isri 6000/515 and the Isri 6500/515. The first one is a mechanical suspension model whereas the 6500/515 uses air suspension — a principle that Isringhausen is promoting strongly as the most advanced type of suspension available.

Mechanical suspension (sometimes called hydraulic) uses torsion bar springing and hydraulic damping to isolate the driver from the jarring and vibrations transmitted from the road surface.

In addition to the usual adjustments for height, fore and aft movement, slope and back rake there is adjustment to dial in the driver's weight. Changing this weight setting means that no matter how heavy the driver is the seat can be positioned in the middle of its vertical range of travel, which is typically 100mm (4in).

The idea of air-suspension seats is not new; Bostrom, for instance, was using the principle on lorry seats in the USA during the 1960s. lsringhausen launched its air-suspension seat about 31/2 years ago, more or less the same time that Bostrom started to sell an air-suspension seat in the UK. MAN was the first European manufacturer to specify the Isringhausen model.

Suspension on an airoperated seat is achieved by tapping the vehicle's normal air supply and controlling the input and output of air by a valve.

Air suspension typically gives a better degree of isolation from low frequency vibrations but a more readily-grasped advantage is its convenience. It has a selflevelling capability so that no matter how heavy the driver is the seat automatically finds the mid-position in its vertical travel range.

This eliminates the need for manual adjustment and so is particularly useful when a lorry is to be driven by a variety of drivers. And when the driver leaves the vehicle the seat sinks to its lowest position, making reentry slightly easier; the seat takes a couple of seconds to rise up to its correct ride height.

The rubber bellows or gaiter around the base of the suspension seat have nothing to do with its air operation — mechanical suspension seats also have this to improve the appearance of the seat, keep the mechanism clean and stop stray fingers getting trapped.

lsringhausen's air-suspension seats are more expensive than the company's mechanical equivalents. For instance, the retail prices of the air-suspension models are typically f185-E200 compared with f145-E160 for the mechanical versions. For the weight conscious, air suspension adds 2kg (4Ibs 6oz).

Although the 6000/515 and 6500/515 are fitted to a wide variety of tractive units they need to be tailored for each application. It is necessary to tune the seat's suspension characteristics to those of the vehicle so that they complement one another.

Axel Zaiser told me that the main way of tailoring an air suspension seat to a particular type of unit is to use a differently rated air valve and a suitable floor mounting kit.

The density of the foam insert used in the upholstery can also be varied; Volvo for instance, specifies a slightly denser foam than most other manufacturers. Finally, the seat is trimmed with a fabric chosen by the vehicle manufacturer and arm rests (for the passenger seat), head restraints, seat belt anchorages or heating elements can all be added to the basic seat.

The result is a seat that suits and matches the particular vehicle but has the benefit of being developed and produced by a specialist manufacturer. Currently, 30-35 per cent of Isringhausen's suspension seats are air-suspension models but Axel Zaiser predicts that in five years' time this proportion will have risen to 70-80 per cent. He believes that air-suspension represents the state of the art and cannot see where significant further improvements can be made in a seat's suspension, al though even he is not party tc what Isringhausen's research and development department doing back in Germany.

Developing and testing seat: is a complex business — how dc you measure something a; subjective as comfort?

In the UK, the leading inde pendent body for this type o testing is the Institute of Sounc and Vibration, a department o the University of Southamptor which carries out research an testing on behalf of some of th( vehicle manufacturers.

A spokesman for the Institut( confirmed that much de veloprnent has gone into the iso lation from vertical vibrations ir hgv drivers' seats and agree( that air-suspension does repre sent a high degree of achieve ment in this field.

However, he added that th( inclusion of an air-suspensior seat is not a panacea; on certair road conditions even a sten seat is better, although the re verse is generally true. In till Institute's view there is stil scope for more work to be don( in the area of non-vertical vibra tion, namely fore and aft move ment such as that due to cab nod. Isringhausen's air-suspen sion seats do incorporate an iso lator to help absorb this horizon tal movement although this car be blocked out if the driver pre fers.

Another aspect emphasise( by the Institute is that an hgl driver's seat leads an arduoul life. Putting it on a test rig whet it is new gives only half the pic ture — how does it perforn when it is five years old? Thu isolation qualities of some seat; do deteriorate significantly.

Back at Isringhausen, Axe Zaiser told me that there is / surprisingly important after sales market for drivers' seats he estimated 25 per cent of till company's sales are for retros pective fitting, usually to replaci static seats.

The five-year rental agree ment with Milton Keynes De velopment Corporation for th, Isringhausen (GB) premises ex pires later this year and Axe Zaiser is looking for a new fac tory in the town with at leas double the space, so he clearl, has high expectations for the future.

He sees the total market grow ing as suspension seats becorre standard in more medium o lightweight lorries and confi dently expects UK commercia vehicle manufacturers to adop the air suspension seat as a vir tually standard fitment in trac tive units.


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