Text: Wolfgang Tschakert and Peter Büttner
Rolling on where others fear to tread – BPW’s hydraulic drive axle AGRO Drive digs deep when the going gets tough. The hydrostatic drive system keeps trailers and agricultural machinery on the move.
The Fendt tractor needs to mobilise all of its power resources to plough through the heavy ground with an outfit weighing almost 40 tonnes. Even then, the heavy beast and its trailer suddenly cease to make any headway. Despite permanent all-wheel drive and highly specialised off-road tyres, the powerful tractor is unable to transfer its enormous torque to the ground. The rolling resistance beneath the broad low-pressure tyres of the heavy liquid manure tanker in tow simply becomes too great. Serious crop damage is just a short step away – by continuing its journey, the tractor would sink further into the ground and leave deep tracks.
Farm vehicles regularly reach their limits on soft, loosely packed ground and on slopes, but Peter Lindner, BPW’s head of agricultural sales in Germany, now has some good news for such situations. “To make it easier to pull away on these surfaces and prevent immobilisation, we have developed a hydraulic drive axle for agricultural trailers,” he explains. The BPW AGRO Drive is the solution that makes a key difference – it keeps outfits moving even in the most inhospitable conditions. At the push of a button, the tractor driver can deliver the additional thrust required to propel the outfit forwards or backwards at the critical moment.
The principle is simple – AGRO Drive distributes the available power to an additional axle. Its positioning directly underneath the load distributes the weight well and enables the drive to overcome the rolling resistance and propel the outfit forward. “Since the drive provides assistance only on demand, none of the available power is diverted unless it is needed. This solution conserves precious energy resources,” insists Lindner.
Bigger and heavier
Ample traction is absolutely vital, especially when cultivating the land. Whenever it is lacking, even the most sophisticated implements become ineffective. And even high-performance 4WD tractors can quickly be brought to their knees when towing heavy machinery, as rigorous testing in the field by BPW’s engineers has demonstrated. The problem is that the tractor’s drive axles often lack the downward force required to convert the high engine torque into forward motion on wet and heavy ground. In addition, towed farm machinery and implements are likely to continue becoming bigger and heavier. Both of these factors call for additional drive power.
Demand for the solution certainly exists. Just last autumn numerous agricultural contractors suffered the painful experience of being unable to work their fields because of wet conditions. Likewise in view of amended fertilizer regulations, which will prompt the application of much larger quantities of liquid manure and fermentation residues during brief periods in the springtime, the AGRO Drive offers tremendous benefits. For one thing, it finally eliminates the costly downtimes incurred while farmers await the ideal ground conditions. According to Peter Lindner, “Contracts will no longer be awarded to the lowest bidders, but to the contractors who have the ability to work the fields in question.”
BPW developed the new product in response to many users calling for drive axles in order to increase their working flexibility. “Although we were entering completely new territory, it perfectly matched our strategy of offering a truly comprehensive range of agricultural products, especially for exceptional user needs, within our portfolio of running gear and drive solutions for commercial vehicles,” comments Lindner. The requirements to be satisfied in order to operate a trailer’s axle drive are very modest. Farmers simply need a tractor with a hydraulic system, which is the norm these days in any case.
The auxiliary drive in the trailer’s front axle delivers additional traction in difficult terrain.
Two travel and working speeds
Measured against other hydraulic drives, the crucial difference of the BPW AGRO Drive lies in its two-stage power output. The first speed stage delivers the maximum torque – for situations demanding the greatest possible propulsive force. With this stage engaged, the tractor-trailer outfit can travel and work at speeds up to 6 km/h. In the second stage, selectively disabling alternate cylinders reduces the torque and raises the outfit’s travel speed to 10–13 km/h. The axle’s maximum power output stands at 37,000 Newton metres with a hydraulic supply rated at 400 bar, but tractors delivering a working pressure of 200 bar are nonetheless capable of operating the axle. The drive system starts to freewheel at the latest when the travel speed reaches 15 km/h.
Mátyás Andrási, design chief of BPW-Hungária, operates the AGRO Drive system from a terminal in the tractor cockpit.
A further advantage of the innovative AGRO Drive system is the small number of its components. Thanks to its well-conceived design, moreover, the drive axle does not impose any special demands on repair shops. Maintenance work can be performed and brake pads renewed without the hydraulic motor being removed. Thanks to the BPW brake system, the brake drum is simply pulled off the end of the axle. The drive axle can be installed in trailers with leaf spring, air or hydraulic suspension. The maximum axle load up to a travel speed of 40 km/h is an impressive 13,500 kg. The system is operated from a small terminal in the tractor cockpit. The driver is presented with buttons that accurately control pressure, travel direction, speed, and freewheeling. He can easily monitor the entire system simply by glancing at the display.
In addition, an interface is provided as standard to allow the simple connection of a tyre pressure control system. This enables the driver, while operating the outfit, to adjust the inflation of the trailer’s modern low-pressure tyres to suit extreme ground conditions. Speed, rotational direction and ABS sensors can also be integrated in the axle to capture useful information for other applications. Another advantage of the drive system is the small additional weight of the hydraulic axle. The AGRO Drive adds a mass of only around 350 kilograms.
The acquisition of a drive axle can certainly make good business sense as well, especially if it avoids the need to purchase a more powerful tractor. Trailers equipped with AGRO Drive axles can be towed by relatively lightly powered machines.
BPW brought together all of its running gear expertise in the production of the axle. The development work involved its sales, application consulting and design teams, and manufacturing takes place in its plant in Hungary. Here the company has established a centre of excellence for agricultural running gear systems, which also accommodates a testing facility with a brake tester and servo-hydraulic test rig. The drive system is just one of many new developments spearheading the current expansion of BPW’s agricultural product portfolio.
Another example is provided by an innovative weighing system to upgrade the running gear computer AGRO Hub, which already gives agricultural customers an exact overview of their trailers’ running gear mileage. By way of a sensor, both the daily and the total mileage are calculated in hours and kilometres. Thanks to the integration of additional axle load sensors, vehicle operators can now capture and store the trailer weight as well. “The sensors measure the weight of a trailer with a tolerance of around two percent. Given that many of our agricultural customers issue invoices for their work based on weight these days, our new weighing system represents an especially efficient solution,” explains Peter Lindner. Analysing the data, typically as represented in a histogram, allows vehicle capacity utilisation to be quickly and easily documented. The data can be transmitted wirelessly to Android smartphones by the BPW AGRO app and, thanks to a recent development, to the display in the vehicle by way of an ISOBUS communication channel.
Another milestone has been passed with the addition of nine-tonne axles to the range in order to cater for lighter trailers. But BPW has enlarged its axle offering at the top end of the heavy segment as well. “We aspire to supply appropriate and efficient solutions for all applications,” insists Mátyás Andrási, the design chief of BPW-Hungária. The company is certainly moving in the right direction.
Agricultural products from the BPW centre of excellence
The AGRO Drive axle is manufactured by BPW-Hungária Kft. at the Szombathely facility in the northwest of Hungary. This wholly owned subsidiary of BPW Bergische Achsen KG serves as the centre of excellence for agricultural vehicles and machinery within BPW Group. The product portfolio extends from dead axle stub assemblies and single axles to complete tridem running gears with frames including suspension and fitted brake systems. These high-quality and technically sophisticated axles and running gear systems are produced by a labour force of more than 1,500 people in Hungary. The agricultural products are marketed through BPW Group’s global network.