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Anderson Home / LEAS Stabiliser Home / Features / Electronic Stabilisation
Electronic Stabilisation - LEAS Comparison |
Translated by Rotraut Anderson from an article in the November 2008 issue
of the German ‘Camping, Cars & Caravans’ magazine.
All pull on one cable - pdf version
The Electronic stabilisation equipment that acts on the brake cable and provides greater safety while driving. There are - and not just among the “Swabians” (German joke) -
contemporaries, who over many years have been annoyed,
because they paid good money for airbags without ever having used them properly. But joking aside,
investments in safety are naturally to be viewed as more than insurance - those who have it, drive more confidently. The same is true of electronic Stabilisation systems for caravans that recently have been appearing more frequently in the marketplace. It is already possible to order directly from the manufacturer, countless current caravan models fitted with such electronic aids; but it is also often possible to fit Stabilisation systems later on. For caravans with Al-Ko Chassis there is ATC, (the Al-Ko Trailer Control), for caravans with BPW-undercarriage the iDC is available, (the Intelligent Drive Control), and practically every model - regardless whether new or used- can be fitted with the LEAS, (Lub’s Electronic Trailer Stabilisation System).
Spectacular: How does the ATC react to an initiated snake?
The system combines sensory and activating elements in one
housing (here a Demo-version) and is installed behind the axle of the caravan.
All these electronic “Anti-snaking systems” (Quote BPW) are to counter possible pendulum-like swinging (snaking) of the caravan in its very beginning and to prevent by fast and targeted action a highly dangerous driving situation. Our practical test should clarify how well the various concepts function in this extreme situation and to what extent the driver is aware of it. In this, the aim cannot be a classic three-way comparison test, because apart from the universally applicable LEAS the other two systems are licensed for and can only be fitted in combination with their own respective supplier’s chassis.
ATC, iDC and LEAS cannot replace the classic friction damper stabilisation installations of the make AL-Ko or Winterhoff - and are not intended to do so. The aim is in a completely different direction: whereas the friction stabilisation systems noticeably increase the so called critical speed - that is the speed at which a trailer that has begun to swing does not stabilise by itself -and therefore gives the driver more leeway in the matter of driving stability, the electronic systems tested here are to be viewed in contrast as real emergency aids.
| Man and System:
Wolfgang Lubs,
Dr Heiko Wahl of
Al-Ko and Matthias
Müller of BPW (from left to right) prepare the caravan and
themselves for greater
driving safety. |
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Good preparation: Each caravan is
being weighed exactly before the
beginning of the test by the test crew and then loaded critically for driving.
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Could it be one more? The fifth wheel on the towing vehicle delivers exact speed data during the course of the measured drives. |
One thing is certain: All towing combinations have an individual stability limit that is reached at their critical speed, some faster than others. But as the speed increases so does the potential for disaster, the driver has to react faster, more surely and most of all correctly. The higher the speed, the less mistakes are tolerated and they mostly have more serious consequences. Since all towing combinations are to be viewed as systems physically capable of snaking and the tendency to pendulum movement is generally increased along with rising speed, only one thing helps: reduce the speed! This is the only way in which the energy capable of causing a snake situation can be removed from the caravan towing system.
The attentive and skilled driver of towing systems senses early on the beginning of a snake and takes his foot off the accelerator early on or brakes hard in a serious situation. Modern towing vehicles with ESP Installations designed for towing do manage this also, though the trailer has to shake the towing vehicle fairly strongly before the vehicle ESP initiates the required emergency braking. According to our experience that happens usually fairly well, but the decrease of speed has at times to happen rather drastically, till the trailer has again stabilised. |
All Müller or what? The vehicle technician Jürgen Müller
(Al-Ko, left) and Matthias Müller (BPW) examine the first results of the test drives.
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The thought occurs to monitor the situation in the trailer itself and, should danger arise, immediately to initiate the counter action here. The gathered developers present at our practical test agree: The starting point in the trailer is physically the right way and always better than a corresponding ESP in the towing vehicle.
Wolfgang Lubs had this idea already about 25 years ago and developed an electro-mechanical sensor, in which at the commencement of snaking of the trailer a metal ball bearing is displaced within a curved pipe and in this way delivers the signal for braking. A unit with a large spring is fixed behind the towing vehicle on the front of the A-Frame and serves as an actuator that in an emergency instantaneously releases and pulls on the brake cable. |
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Sedative: Gently but dependably the Intelligent Drive
Control of BPW stabilises the swinging towing unit.
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In contrast the versions of Al-Ko and BPW use (now affordable) full electronic sensors which, installed in the near vicinity of the axle, constantly and sensitively register the appropriate Trailer movements, especially the lateral acceleration and send it on to the interpreting electronics. If snaking is recognised, a powerful electromotor also pulls on the brake cables. ”The basic function of such a system”, according to Jürgen Müller from Trial Vehicle Technology at Al-Ko, “is relatively simple to achieve; the challenge lies in the fine tuning.”. The lie of the road, unevenness like grooves in the lane or just necessary driving manoeuvres also permit a crosswise acceleration to arise, which has nothing in common with classical slewing. In short: the art lies in being able to distinguish a disturbance from a normal situation.
But slewing is not immediately snaking. The sideways acceleration increases normally slowly but steadily when approaching critical speed, as the signal curve shows wider and wider deflections each time - the expert speaks of Amplitudes. In this situation the emergency programme (and the brake of the trailer) is to be activated quite early by still comparatively minor swinging-amplitudes. In a contrary situation, perhaps when suddenly giving way with an instant rise in the sideways acceleration in the trailer, a rapid immediate action is required. We have simulated just this situation during our practical test through an intended steering movement on a closed off test area at constant driving speed. |
Pulling Device: The iDC-centered unit with fail-safe function is screwed on to the A-frame. |
Ready for use: Only the lateral movement sensor for the iDC is fitted to the axle of the caravan.
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| The test procedure was spiced up by balancing out the nose weight of all caravans to a ridiculous 15 Kg. Nose weight is equatable to driving safety, and with that the conditions chosen by us were not always the best. In spite of that, all electronic trailer- stabilisation systems proved themselves to be markedly superior, as shown and summarised in our diagrams of the results of the various measurements. ATC and iDC show thoroughly comparable characteristics. According to the previously set values the acceleration of the sideways swings of the trailer is to be 4 m/sec2 when swinging in response to the steering impulse (red curve). As one can see, the brake acts with both already after the second half-swing. The caravan swings to the right, swings to the left and already the towing unit is being equally restrained (blue curve) and stabilised. |
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Sensor unit: The LEAS-electronic
box is to be installed as far back as
possible in the inside of the caravan. |
Old Master: LEAS has been sold internationally over 2,000 times since 1992 and provides safe driving of towing units. |
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The LEAS comes into action one-half swing later, reacts therefore only at the third swing of the pendulum. But the braking effect of the trailer occurs rather suddenly when the pre-tensioned spring acts on the brake cables. The driver should notice that quite clearly; so that the warning buzzer only frightens totally insensible natures. |
| With the iDC the registered delay in the action of the trailer brake lies somewhat under, with the ATC somewhat over 1,5 m/sec2. That corresponds entirely with subjective impressions: with the Al-Ko emergency system the braking action was more distinctly noticeable than with the iDC. That though - and the experts are united in that - is probably caused more by the respective trailer brake. The TEC, a brand new Test-vehicle, came along with “green” brakes not yet properly bedded in, while the Hymer had already a number of miles on the clock, and also profited from the non standard larger drums, designed for a higher total weight. |
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Requirements:
The sensor for the
measuring unit is installed centrally over the axle of the caravan and delivers values about sideways
acceleration and delay. |
This experience also clarifies the limits of the emergency aids: heavy, ample powered vehicles can be problematic with comparatively light and yet unstable trailers. The insensitive driver does not notice the intended gentle braking and rushes on possibly switched on the Cruise control. That could lead to a thermal overloading of the trailer brakes. In the iDC the “brake too hot function” prevents this, a monitoring algorithm, which recognises the number and length of going into action and in a borderline case deactivates the unit as a precaution. According to BPW-Müller the fail-safe-function, which has been arrived at with much use of time, protects the iDC system and in addition, should a loss of power occur (perhaps through intermittent contact) in activated condition. Al-Ko Müller considers this danger to be of a rather theoretical nature. |
Hot Iron: After a series of driving tests the respective temperatures of the brake drum were registered - LEAS around 160 degrees Celsius, ATC and iDC reached nearly 200 degrees |
Whoever may grow enthused about
electronic stabilisation systems has to know, that for additional equipping, various
variants are available according to weight classification and make (Mono-/Tandem). The cost of assembly varies according to version and is somewhat higher with LEAS (installing of acoustic alarm and wiring in the towing vehicle); a radio version is in preparation, comprehensive assembly instruction in CCC 3/08). The iDC fits into the assembly holes already present in the current chassis; in older style chassis drilling is required. The prices of the “emergency brakes” are about 600 and 650 Euro plus labour. |
Indispensable however: The constant 12v+ supply to he trailer and that is just not yet standard, because in contrast to the developers of the electronic stabilisers, the motor manufacturers and importers - at least with regard to this matter - do not yet co-operate.
Dieter S. Heinz |
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