7 March 2019, 11:16
Electrohydraulic steering systems for rear axles have been standard in commercial vehicles and complex construction machinery for many years.
In the case of commercial vehicles, the use of electrohydraulic auxiliary steering is primarily to ensure compliance with the legal requirements. – Without a steered rear axle the legally defined minimum turning circle, also known as “BOKraft-Kreis“ in German, cannot be maintained.
In addition to compliance with legal requirements, complex construction machines such as mobile cranes, however, have to meet very high requirements for manoeuvrability, which can only be met by electrohydraulic auxiliary steering.
Steering modes such as crab steering, manual steering intervention or automatic rear swing out suppression are standard here, as is the complete power decoupling of the rear axles from the front axle.
Figure 2 shows a 6-axle mobile crane where four axles are equipped with EHLA® auxiliary steering systems.
Simple construction machines, such as 2-axle loaders, usually have hydrostatic front axle steering (e.g. Orbitrol) and often already rear axle steering. However, this is purely hydraulically and may only be switched on manually on the construction site.
It is obvious that application possibilities and flexibility, as well as operating comfort are very limited.
World market leader MOBIL ELEKTRONIK from Langenbrettach has committed itself to providing these vehicles with the same features that are already standard in mobile cranes. Operation will be easy and convenient. The steering mode can be changed at any wheel position. The synchronization of the axles with each other, as of Ackermann, is done automatically.
The EHLA® PLUS auxiliary steering system has been in use for a long time and is well known.
Approval for Public Road Traffic and Safety
The EHLA® PLUS auxiliary steering system complies with the requirements of ECE R79 Annex 6, so that it can be approved for use on public roads. – This can also be interesting for smaller construction machines or even be an important prerequisite if these drive a lot on public roads.
The steering system constantly monitors itself. System faults are reliably detected and the driver is informed accordingly. The controllability of the vehicle is always ensured via a defined fallback level.
Assistance features of the EHLA® PLUS steering system also increase driving stability and thus driving safety.
MOBIL ELEKTRONIK has revised some components of the EHLA® PLUS steering system to make this established steering system also attractive for smaller, 2-axle vehicles.
A newly developed generation of safety steering computers is used (Figure 4).
Already the housing with IP Code IP6K9K offers advantages because it can also be mounted outside the cabin, where extreme conditions prevail due to dirt, water and salt.
Due to a completely new hardware and software architecture, a safety level up to Pl e / ASIL D can be achieved.
The hydraulic components were also carefully examined.
The result was a compact proportional hydraulic unit in which all necessary valves are integrated, resulting in less tubing, fewer components and less assembly time.
Advantages of EHLA® PLUS on the Construction Site
The main advantages of EHLA PLUS have its greatest effect where needed: On the construction site.
Many steering modes are available to manoeuvre the vehicle in different situations, such as all-wheel steering, crab steering or manual steering of the rear axle.
Another important steering mode is the automatic rear swing-out suppression, which is of great importance when driving around obstacles.
This steering mode prevents the rear of the vehicle from swinging out when manoeuvring by means of the rear axle turning later than the front axle.
This cannot be achieved with a purely hydraulic steering system.
Flexibility and Convenience
In contrast to purely hydraulic steering, the use of electronics in the form of the safety steering computer makes it possible, that the individual steering modes as well as the entire steering system can be adjusted to the respective vehicle type or to special customer requirements just by parameters. This means that regardless of wheelbases, tyre sizes and wheel loads, the components to be installed, such as steering cylinder and steering lever arm, are always the same. A clear advantage in purchasing, logistics and replacement parts management.
The steering modes can either be selected via a MOBIL ELEKTRONIK control panel (figures 5a, 5b), or alternatively via an existing terminal in the vehicle which is connected to the safety steering computer via CAN.
Further Savings of Expenses
The automatic hydraulic centering and locking of the rear axle in exact straight ahead position when driving on public roads ensures optimum directional stability with minimum tyre wear. This is an advantage that is particularly relevant for rental vehicles.
The hydraulic supply for the rear axle steered with EHLAPLUS is provided from the vehicle's power unit. The rear axle steering is hydraulically and mechanically completely decoupled from the front axle steering. In addition to driving comfort and safety advantages, this also offers cost benefits. The hydrostatic steering (Orbitrol) of the front axle can be designed correspondingly smaller with regard to the steering power to be produced.
The higher costs for the components of the steering system are more than compensated for by savings in mechanical components, shorter assembly times and, above all, by the many advantages.
With EHLAPLUS, these vehicles can be upgraded considerably, which leads to competitive advantages for the vehicle manufacturer.
MOBIL ELEKTRONIK at the Bauma 2019 in Munich
In addition to this EHLA® PLUS concept for small construction machines
MOBIL ELEKTRONIK will also be presenting further innovations and solutions at Bauma 2019.
Hall A3 / Booth 115
Source: ME MOBIL ELEKTRONIK GMBH