Electric-Hydraulic Valves
Electric-hydraulic valves are the interface between the microcontroller and the transmission (clutches). They control oil pressure and flow to the clutches. Stability and responsiveness are major issues here.
The new designs are developed and proven by using the latest tools on the market: Rapid prototyping, solid modelling, simulations and testing increase development speed as well as built up knowledge. Prototypes are modelled using Pro Engineer to generate 3D solid models.
Dedicated valves are used for control of hydrostatic and multispeed hydrodynamic systems.
Clutches
Clutches basically consist of friction plates and separators. One part of the clutch is connected to the input, the other to the output. By pressurizing, a piston forces the plates against each other, resulting in torque transfer from input to output. The wet clutches are mainly used in off-highway applications as they can be closed under full load conditions.
The clutch is a very critical mechanical component. Not only the torque transfer (static - dynamic), but also the thermal behaviour as well as efficiency and controllability are areas where knowledge and technology are important. For this reason we have people dealing full time with clutch calculations and design. Also several teststands are dedicated to further build up knowledge.
Simulations
Simulations allow us to discover potential design-flaws in a much earlier phase than we used to do. The impact of certain (H/W) changes can be judged sooner, and examination of eigenfrequencies can already be done during the design phase. Another strength of simulations can be found in root-cause analysis, where a huge time reduction is noticed. Clearly, all of the above positively influence both development time and cost.
At this time, the use of simulations in the Controls department is mainly twofold: on one hand there is the hydraulic behaviour of the valves (functionality, vibrations, responsiveness, …), on the other, we simulate the dynamic behaviour of a complete vehicle, where the transient situation during shifts can be fully examined. For these applications, ITI-sim and Matlab/Simulink are used.
Close cooperation with other departments permanently leads to new challenges and solutions.
Microcontroller Hardware
All required hardware used by SOHPD is developed in house. The assembly is outsourced to subcontractors.
Our main goal is building robust control systems for Off-Highway equipment. Major challenges to reach this target are:
- Reliable conditioning of signals from speed sensors, throttle and brake pedal, …
- Precise control of pressure modulating valves.
- Adherence to safety standards (e.g. IEC1508) - Fault tolerance
- Severe environmental conditions (vibrations, temperature, sealing, …)
- EMC tolerant design
To validate our designs, state of the art EDA (Electronic Design Automation) software is used. Integration of layout, steered and automated routing, schematic design and documentation has become inevitable.
Software
Software can be seen as the real core of the system as it allows customizing applications and providing excellent control of different mechanical systems.
The development covers both embedded programming of 8 and 16 bit microcontrollers and development of PC-software.
The latter mainly concerns development of tools for communication with the controller (parameter-tuning, statistics, diagnostics, etc.).
In the embedded software three layers can be distinguished:
- Real time Operating Systems & BIOS
- Algorithms: developed per application type.
- Applications: adjusted to the customer's specification.
Embedded software is developed using C and PL/M-51
In-circuit emulators, debuggers, CAN analysers and logic analysers are used to develop bug free software. The software is developed per IEC 1508 and VDE 801 standards to meet the international safety requirements.
Gears, Shafts, Bearings and Houses
Duty cycle measurements in the field tell us how the transmissions are loaded for a specific machine and application (wheel loaders, telescopic boom handlers, lift trucks...). These load spectra are used to predict the life of gears and bearings.
The calculations include the total behaviour of the system (influences of gear mesh deflections, shaft deflections, bearing deformations, housings...)
The gear geometry is optimised for manufacturability and load stresses. Applying microtopology modifications is an advanced technique to optimise contact pattern and reduces transmission error (dynamic behaviour leading to noise)
Bearings are selected based on load types, life requirements and assembly possibilities. Full engineering co-operation of major bearing suppliers helps optimising the design for cost.
Material and heat treatment are selected based on the design and manufacturing requirements.
The calculations are validated by running accelerated load tests in our test lab. Failure analysis is an important part of the process used to determine the real limits of the components.
Finite Element Model
A lot of our components are too complex for an analytical stress and deformation calculation. Here FEM is used:
- Failures in the testing phase (and in the field) are prevented,
- components are designed with an optimal functionality (weight, inertia, ...)
- at the lowest production cost without loss of reliability.
The FEM-software is also able to model (non-linear) contacts. This can be used to model complete assemblies and to simulate their functionality: e.g. pressure distribution in a clutch.
Also thermal and dynamic calculations (vibrations,...) are done with FEM. In this way the dream of virtual prototyping is gradually coming closer.
CAD
Computer Aided Design
Full 3D parametric software (Pro Engineer) is used primarily to make use of its advanced possibilities:
- Rapid prototyping on complex shaped parts to reduce lead times
- Offer 3D virtual models of our products to our customers
- Automatic detail drawing creation
- 3D assemblies
- Parametric behaviour
Powerful workstations and a lot of own customisation in the software improve the efficiency.
Testing