A Variable Pressure Multi-Pressure Rail System Design for Agricultural Applications

Abstract

This paper presents a solution for reducing energy loss in the hydraulic control system of agricultural tractors and their implements. The solution is referred to as a multi-pressure rail (MPR) and provides power to the hydraulic functions following a pressure control logic, as opposed to the traditional flow control logic typical of hydraulic systems used in off-road vehicles. The proposed hydraulic control system allows for elimination of redundant flow control valves in the state-of-the-art system, which cause excessive throttling losses leading to poor overall energy efficiency. Related work on MPR technology targets construction vehicles, where the MPR solution can allow energy recovery during overrunning loads and better engine management. This paper alternatively addresses the case of agricultural applications where functions mostly operate under resistive load conditions with slow dynamics, which offers an opportunity to target throttle losses. For this purpose, the paper introduces a variable pressure control strategy to handle the instantaneous pressure at each rail. To develop both the controller and the hydraulic system architecture, a stationary test rig is conceived and used to validate a numerical simulation model of the MPR system and its control strategy. Particular focus is given to the dynamic behavior of the system during the switches of a function between different pressure rails, which needs to ensure reduced oscillations of the flow provided to each hydraulic function. Once validated, the simulation model is used to predict the energy savings of the MPR solution in an actual application: a 435 hp hydraulic tractor powering a 16-row planter, for which operating features during typical drive cycles were available to the authors. The results show up to 59% total power reduction at the pump shaft, corresponding to 89.8% system efficiency gain.

Fundamentals of Hydraulic Transformers

“…The main reason, why hydraulic transformers are generally not used, is that there are hardly any hydraulic transformers that have reached the market [7][8][9][10][11]. The market is still waiting for a winning design.…”

A pressure control method for increasing the energy efficiency of the hydraulic system powering agricultural implements

“…30 The latter one was formulated and implemented by the authors on the same reference vehicles showing an efficiency increase by 89%. 31 An important drawback of these solutions pertains to vehicle compatibility, in the sense that an implement using a circuit different than an LS one cannot interface with a conventional LS tractor and vice versa, which can severely hamper commerciality. Therefore, there is high merit for investigating solutions specifically conceived to address the low efficiency of the tractor-implement system based on the LS architecture as in Figure 1.…”