Research plan 2008-2010

Task 1: Extension of operational range of the drive systems

The application range of the conventional one-motor hydrostatic transmission is limited by the corner power - maximum torque multiplied by the maximum speed - and the maximum useful torque conversion range. The overall efficiency is also limited. Through combining hydrostatic transmission and planetary gears into a CVT gear, the system corner power, torque conversion range, and efficiency can be improved.

The research activities will start with studying and comparing the different kinds of CVT solutions. There are two main principles in CVT, which are speed or torque summation methods. The dimensioning, and also a first-hand behaviour study, of CVT will be performed by means of mathematical modelling. The mathematical model will also predict the efficiency of the gear. The next step is to make a CVT gear according to the previous results. The real behaviour study will be performed on a test bench and a mobile machine.The research methods used are literature study, modelling, simulation, and measurements.

Expected results: solution to extend the operational range of drive systems

Task 2: Position, force and velocity control of modular vehicle

The usability of the mobile machine means that the machine has to be well handled, also under demanding load and earth surface conditions. On the other hand, legislation is bringing in new restrictions regarding damage caused to the earth’s surface. One sub-objective is to design the control of the drive of a mobile machine so that the demands are fulfilled. One principle of the velocity control of a hydrostatic drive is shown in the figure above. In this principle the whole drive chain is under upper level control. The individual subsystems have their own control. The same principle is also adopted for working activities.

Because of the environment in which these mobile machines are working, the traction control of the driving wheels is also essential. The next stage will be the ESP of the machine. This is also an important research area from the environmental point of view. The controllability and usability of hydraulic control valves will be increased by making the properties of the control valves programmable. The different operating curves of the valves will be programmed for separate operators.

The research activities for the first 3 years are:

  • to produce steady-state and dynamic models of actuators and their control, including valves
  • to study the control of the whole power transmission chain (prime mover, transmission, actuators, load)
  • to test the developed power transmission systems in a mobile machine with measurements
  • to study the traction control and electronic stability possibilities with mobile machines
  • to develop and test the traction control of the machines
  • to develop the programmability of the control valves

The results of this task will be used in Task 8.1 (Multi-wheel system control).

Expected results: position and velocity control of drives and working activities

Task 3: Use of digital hydraulics in mobile machines

In fluid power the independent control of two or more flows with one valve is difficult. This problem is a key one in cylinder applications. If the independent control of each control edge is possible, efficient, flexible, and also programmable control is achievable. This can be carried out by means of digital hydraulics. This also means the intelligent control of digital valves.

The digital hydraulics used will be studied in boom and drive applications. The objectives of this research work are the efficiency, flexibility, reliability, and high performance of work activities. The demands of valves in these applications will first be studied. The main problem and research activity is the appropriate control of valves. The properties of the digital valves will also be studied. The Academy of Finland is supporting this research field with a Research Fellow post for Dr. Matti Linjama.

Expected results: actuators controlled by digital hydraulics

Task 4: Self-learning and tuning modules

The main purpose of this task is to develop the self-learning facilities of the modules. The main activities are the data-collecting procedure of the system and the use of these data in an appropriate way to tune the control of the activities. This property can also be used for self-diagnostic purposes.

The second part of this task is to develop a procedure in which the properties of the valves and actuators used are tested. By means of this procedure the differences between units are taken into account and the parameters of individual units are stored in the memory of the controllers. This property is essential for compensating the differences between valve and actuator properties.

Expected results: self-learning and tuning facilities of the machine

Task 5: Transmission of data between modules

The main purpose of this task is to research the data transmission possibilities between modules. The transmission can be carried out by wired or wireless connections, preferably using standard protocols (for instance Flexray and CAN buses). One key issue is, of course, the reliability of the transmission system. Telemetric sensors and the use of these will also be studied. The results of this task will be used in Task 6.4 (Distributed use MEMS sensors, methods to use internal sensors for indirect sensing of terrain quality or for obstacle probing) and vice versa.

Expected results: data transmission procedure