Task:
Manual and computer-controlled function tests on mechanical and hydraulic steering gears in rack and pinion design. The following functional tests can be carried out:
- Steering torque characteristic
- Frictional torque characteristic
- Pressure-steering wheel torque characteristic
- Rack displacement force characteristic curve
- Leaking oil in the steering gear
- Pulsation tests on mechanical steering gears with DV evaluation
- Efficiency measurement for mechanical steering gears with DV evaluation
- Determining the pump characteristic curve of the servo oil pump
Solution:
Mechanical design
- Base frame with base plate and integrated T-slot rails
- Drive unit with servo motor, angle of rotation and torque detection
- Load unit via servo cylinder with force/displacement measurement
- Separate oil pump test stand
- Clamping devices
Hydraulic version
- Power unit for power steering supply
- Power unit for servo cylinder
- Servo cylinder as load unit
- Accumulator in the load circuit
- Alternative supply of the steering gear via vehicle pump
Electrical control and regulation
The electrical control system is designed as a PLC control system. The test sequence allows manual, semi-automatic and automatic operation. In automatic mode, the test sequences are controlled by the computer via opto-decoupled inputs/outputs. Furthermore, the set values for drive speed, steering travel and load force are specified and controlled by the computer. Depending on the test procedure, force or displacement control is selected for the load device.
The electrical control and regulation equipment is housed in three 19" control cabinets. The operating and display elements are ergonomically arranged in 19" front panels of the control cabinets.
Electrical measurement technology
The following transducers are installed to determine the required measurement data:
- 1 differential pressure sensor (hydraulic pressure on the steering)
- 1 Torque transducer (drive torque)
- 1 force transducer (load force on the drive side of the steering systems)
- 1 Steering angle sensor
- 1 incremental steering travel sensor
- 2 inductive displacement transducers for pressure piece and bushing clearance measurement
- 1 Flow meter
- 2 temperature sensors (hydraulic unit and steering feed)
The measuring amplifiers and matching units with the associated digital displays are installed in 19" plug-in units or 19" front panels. A computer-controllable low-pass filter is installed for each measuring amplifier signal in order to filter out interference from the measuring signal.
The filtered measurement signals are routed to A/D input channels of the computer system. The desired measured values can also be recorded via the built-in X/Y recorder.
Data acquisition and data processing system
The data acquisition and data processing system is designed as a 19" industrial computer.
The computer system is used to specify the test sequence, record the measurement signals during the test and evaluate the results after the test.
A total of 10 measurement signals are recorded and stored at 100 Hz intervals, and the target values for drive speed and load force or steering travel are also specified in the computer. The test parameters are entered by the operator with the aid of on-screen guidance on the terminal. All system processes can be logged on request.
A test program is available for the user to check the wiring or the definition of the calibration function.
The filter characteristics of the TP filters can be changed from the computer via a V24 interface (RS 232 C).
Technological test procedure
When carrying out tests with a hydraulic unit, the hydraulic unit heater must be switched on before starting the test in order to heat the ATF oil to the required temperature. In pump mode, the hydraulic circuit is brought to the set temperature by bypassing the vehicle pump.
Once the test specimen has been mounted on the corresponding clamping device and the fasteners have been connected, manual, semi-automatic or automatic mode must be selected before the test begins. In automatic mode, the required test sequences are carried out by the computer. At the end of the test procedure, the computer outputs the test data determined as a tabular/graphic report to a printer.
