on SUCCESSFUL INVENTIONS

Hitch head stabilisers

Hitch-head stabilisers have so transformed towing today, it’s hard to remember what went before. Nevertheless, it’s worth taking a look into the past so we can see these devices in their true per spective.

Most people who’ve towed a cara van will have experienced that uncomfortable feeling when the outfit becomes unstable as the ‘tail tries to wag the dog’. Instability can be a function of several variables such as loading, speed, weight ratio, side winds and so on. Although it’s true to say that a well matched, sensibly loaded outfit, driven well, should rarely experience any problems; being hit by the bow wave of a large overtaking vehicle can be very uncomfortable. Also, a sudden avoidance manoeuvre or tyre blow-out can bring about instability.

worked in a similar way to other blade stabilisers that had become common sitioned front and aft within the hitch head, they also damp pitch as well as roll and yaw. A nice feature of the Winterhoff stabiliser is that you can’t deploy the operating handle until the towball is safely inside the hitch head. In this way the chances of mis-hitching are greatly reduced. The set-back hinging arrangement also gives more room for those with tailgate-mounted spare wheels.

Shown here is a typical blade type stabiliser from British company, Bulldog Security Products. It works by using friction discs to control the movement of a blade attached to the ‘A’ frame via a special sliding shoe. I had a blade stabiliser for many years and it worked well enough but it was a bit cumbersome, and heavy to carry around at 10 kg. The blade stabiliser was not the only yaw damping device available at the time, although it was perhaps the most popular for its combination of weight, simplicity and cost.

For these reasons aftermarket stabilising devices became very popular many years ago but most had one thing in common – weight and inconvenience. Between 1968 and 1985 AL-KO produced a device known as the Exact Drive, or Bügel Stoßdämpfer (Bugle Shock-absorber) as it became known. It employed a yoke and pair of oilfilled shock absorbers to dampen the yaw movements of a trailer. Whilst undoubtedly effective, it was a cumbersome and heavy device, and this limited its success.

In the late 1980’s AL-KO and Winterhoff triggered a paradigm shift in stabiliser technology by designing friction stabilisers with the friction built into the hitch head. The idea was to grab the towball very tightly and damp out oscillations that way. It was great idea, not only for saving weight, but for the sheer convenience it offered.

In each of the two designs (AL-KO and Winterhoff) the hitch head coupling contains friction pads that grip the towball very tightly when the operating lever is deployed. Needless to say, the towball has to be perfectly dry for this to work - a significant departure from the previous situation where the towball was normally greased.

The very first such stabiliser, AL-KO’s AKS 2000, was produced as long ago as 1989, with the smaller AKS 1300 appearing in 1995. The numbers denote the MTPLM of the trailers to which they are suited. A friction pad on each side of the hitch gripped the towball and dampened out any tendency for the trailer to yaw (sway from side to side) or roll, although pitch damping was minimal.

By 2002, end user demand was such that OEMs had started to fit hitch head stabilisers as original equipment and, in 2003 AL-KO launched the AKS 2004 stabiliser which had no less than four friction pads. These enabled it to damp pitching movements as well as rolling and yaw.

In 1985 the bugle device was superseded by the AL-KO’s APS 4, which

At the same time Winterhoff was working on its own hitch head stabiliser, the WS 2000/3000. This also uses just two friction pads but, being po-

According to AL-KO at the time ‘On the AKS 2004 Comfort, four long-term friction linings enclose the towball on the right, left, rear and front with around 1.5 tons of force. There is no metallic contact whatsoever. The friction linings can be easily replaced if they are too worn.’

In 2008 AL-KO claimed their AKS 3004 hitch ‘increases the critical driving speed by around 20% (ADAC test winner).’

In 2014 BPW launched its own brand stabiliser, the iSC (Type ZKAS), based closely on Winterhoff’s device. Sadly, both these devices have recently been discontinued. (The Winterhoff Group was acquired by AL-KO’s parent DexKo in 2016, and merged with the AL-KO business unit.)

Those looking for a similar device to the Winterhoff can opt for the KS30 from brake and trailer technology specialist Knott. Launched around 2020, it too boasts single lever activation, and a setback hinging arrangement.

The major virtues of hitch head stabilisers are their simplicity in operation with instant hitching up and no need for additional, often heavy components. A dry towball is a bonus too as there’s no grease to get on your clothes. Correctly set, the friction pads have a long service life; in the case of the AL-KO models, a lifespan of 50,000 km is claimed.

Such has been the impact of the hitch head stabiliser that today virtually all new European caravans are fitted with one as original equip-

Active stabilising devices

Active stabilising devices use sensors to detect when a trailer is becoming unstable and then apply its brakes to pull the trailer back into line. In this way any tendency for oscillations to set in is quickly damped out. Active stabilisers are not intended to allow you to tow at faster speeds but will give you an extra margin of safety if, for example, you have to make a quick avoidance manoeuvre. Operating power is normally taken from the towing vehicle so it doesn’t matter if the trailer has its own power or not.

Active stabilising devices are not to be confused with add-on systems that apply the trailer’s brakes every time the tow vehicle’s brakes are operated, such as the one introduced by Dutch company IVRA in the 1990’s. Instead, they only apply the brakes when instability is detected, and have no effect at other times.

The first such device is claimed by German inventor Wolfgang Lubs, as long ago as 1986. European patent DE3600708A1 from that year describes an anti-roll device ‘…which, connected to a trailer, is intended to prevent a dangerous building up of oscillations (rolling) beyond a certain movement, in which the trailer is automatically braked independently of the tractor vehicle.’

A box clamped to the trailer’s ‘A’ frame contains a spring and tensioning motor. When swaying is detected, the spring is released, gently applying the brakes. A warning buzzer alerts the driver to the actuation. Once stability is returned the motor re-tensions the spring for further use.

The invention appeared as the LEAS universal stabiliser around 1995. Until this point the only stabilising devices for trailers were friction-based ones which worked as constant friction dampers on every movement. None of these actually applied the trailer brakes. The LEAS stabiliser was the first one to do so, but only when lateral movement was detected. Further patents followed as the device was improved. It remains on sale to this day.

In the meantime, AL-KO and BPW set about producing their own active stabilisers. These appeared as the AL-KO ATC and BPW iDC around 2008. Although similar in principle to the LEAS device these new safety devices work in a slightly different way. As soon as any instability is detected, the ATC and iDC devices use an electric motor to gently apply the trailer brakes before snaking becomes a problem.