Branch Hydraulic Systems have designed and developed a new steering software programme for the Multidrive 6185 and Multidrive 6195, high-speed, specialist load carriers and hauliers, from UK manufacturer, Multidrive Tractors Ltd.
Branch Hydraulic Systems were selected by Multidrive Tractors Ltd following a positive, long-standing relationship with its Leeds depot and HES Tractec division. The company was tasked with providing an upgrade to the existing 4-wheel steer software system, delivering improvements to the steering performance and stability as well as reducing movement of the rear; making for a more accurate, responsive steering system, when moving at speed.
The Software Solution
The Multidrive 4-wheel steer had originally been designed using a feedback only system. In order to improve the steering and ultimately, the performance of the machine, Branch Hydraulic Systems established that adding a feed-forward would make the system more responsive.
Using the Plus+1 controller from leading hydraulic and electronic engineering specialist, Sauer Danfoss, as the central component for the new system, Branch Hydraulic Systems was able to write the Proportional Integral Derivative (PID) control; the flexibility of the Plus+1 allowed for a feed-forward component to be added into the system.
Taking the J1939 speed signal off the vehicles Control Area Network (CAN) the system starts to reduce the steering angle on the back axle as the vehicle speeds up. As the speed scaling is an important safety feature, the speed picked up from the rear prop-shaft is continuously compared to a second signal from the front prop-shaft. If any errors occur, i.e. the speeds don’t match, the system shuts down the rear steering and returns to 2-wheel steering.
With an impressive IP rating, the Plus+1 is a total machine management system for off-highway vehicles. Communicating with one another and other intelligent systems over a machine CAN data bus, the Plus+1 hardware is designed to be effective even in a stand-alone system like the Multidrive, where it communicated with the vehicle’s dashboard. Utilising the ‘tried and tested’ technology for which Sauer Danfoss is renowned, the Plus+1 is also user-programmable, making it the ideal centrepiece for the development process.
FEED-FORWARD FOR STABLE, SAFER STEERING AT HIGHER SPEEDS
In employing the feed-forward method, Branch Hydraulic Systems significantly improved the steering performance, decreasing the steering lag – a common issue when travelling at speed and, as a result, improving the machine’s stability. For safety, the rear wheel steering is automatically turned off, at around 20 mph and locked off, so if a fault occurs at speed, the rear axle doesn’t move uncontrollably.
With power steering on the front wheels, a sensor is placed on the king pin to measure the angle that the machine is turning, at low speed (less than 20 mph) the rear axle is driven to match the front, giving the Multidrive a much smaller turning circle – perfect for crop spraying and manoeuvring within the field’s tramlines. In addition, the hydraulic applied differential locks on both axles, guaranteeing maximum traction even in the toughest ground conditions.
Commenting on the software system designed by Branch Hydraulic Systems, Tony Frazier chief engineer of Multidrive Tractors Ltd said: “In 19 years of building four-wheel steer vehicles this is the best one we have ever had. The Multidrive already offered unrivalled performance and capability, when compared to a standard tractor or piece of agricultural machinery; by improving the steering software we can be confident that it will remain in a league of its own.”
“The design team at Branch Hydraulic Systems has made every effort to ensure that the project has achieved everything we set out to, tackling performance and stability but in fact they have gone beyond this, delivering a solution that exceeds expectation,” said Tony.