Engine test stand

Engine test benches are used to investigate motors ( electric, hydraulic, or internal combustion machines) regardless of their normal operating environment. If it is just about the basic speed and torque parameters, from which the power can be calculated, one speaks generally of a Leistungsprüfanlage. If the measured value acquisition further expanded ( fuel consumption, exhaust, noise, vibration, temperature behavior ) the term of the test stand is in use.

For vehicles come in addition to the engine test dynamometers also used, on which the entire vehicle can be checked. Brake testers and gear test (short aggregates test benches ) are used for the testing of passive components and require an appropriate load machine.

Usage

An engine test stand can serve two purposes:

• Investigation of motor function. The above mentioned parameters are measured and documented. The aim is either to check for compliance with specified target values ​​(eg in production), or the optimization of properties such as energy consumption and environmental impact ( in development ).
• Investigation of engine durability. In this case, the motors are operated under extreme conditions to eradicate weaknesses of engine components in an over the conventional use much shorter time.

Function

Traditional engine test benches allow, stationary discontinue individual operating points of the engine to be tested, the parameters to be measured are usually registered in a speed / torque diagram. Here satisfy relatively simple load machines brakes, with which one can set the from the device under test ( engine ) torque to be applied.

The boundary conditions to be observed today make it necessary at least for the engine manufacturers, on test rigs and dynamic cycles to drive ( " drive curves " ), which approximate the realistic application conditions of the engine. Since both to rapid changes in the torque and speed, as well as a reversal in the torque direction ( thrust operation ) are necessary only electrical load on the machine can be used in this case.

Construction of a test rig

With a mounted on the chassis dynamometer facility to be tested prime mover is coupled (via drive shaft, cardan shaft, transmission, if necessary ). The picture shows a traditional, but now outdated test structure:

Load machines

The loading machine shall be so designed that it can absorb the full power of the test specimen and apply the maximum torque. They must be suitable for the maximum speed of the DUT.

Passive load machines ( brakes)

• Water eddy brakes ( torque adjustment by changing the water flow )
• Eddy current brake ( setting the torque by changing the current and hence the magnetic field )
• Hysteresis
• Powder Brakes

Allow only the two-quadrant operation, ie the specimen drives, machine brakes, the load in both directions of rotation.

Active load machines

• DC machines
• Asynchronous
• Three-phase synchronous machine

Both species occur at the test bench in the generator mode (test drives ) are used, the active load machines on the other hand also in motor mode (test driven ). The torque adjustment is made with the help of complex power electronic components. In particular, the required frequency for induction motors represent a high cost factor dar. Nevertheless, predominantly asynchronous machines are today because of their good dynamic properties and because of their robustness in use. In the past, it often took the opportunity to control DC motors using a Leonardsatzes.

Measurement methods

The rather simple measurement of the speed type is usually digitally with the help of incremental encoders, absolute encoders or resolvers. The latter are particularly used when rested until, therefore, speed 0, should be regulated. Traditionally came tachogenerators (analog) for use.

The measurement of torque is even today in many areas by means of a pivoted loading machine ( pendulum machine ). The stator is supported via a lever arm having a defined length onto a load cell. Thus, the determination of the load torque of the supporting force ( torque reaction ) is possible out. However, this method has the serious disadvantages in that the pendulum bearing friction reduces the measured torque and the high mass of the stator, such as a low-pass filter effect, and thus filters out high frequency components. The disadvantages are solved with the increasingly coming to the use of co-rotating torque measuring devices. These are arranged in the drive train between the test specimen and loading machine and are available as shaft, flange, hub, flexible coupling or flexible disk, the torque- high due to its small size, high stiffness, and depending on the measuring principle ( shear or bending) accuracy, the most widely used in test benches the automotive industry is. The transmission of the measuring signal from the rotor to the stator is carried out by telemetry or through slip rings rare.

The optional exhaust measurement technique involves sampling at various points of the exhaust system. The gas is provided through conditioned sample gas lines several analyzers for the measurement of gaseous pollutants for particles and possibly for other exhaust gas constituents.

Test rig control

The control of the test stand on a manipulation of rotational speed and torque. It is dependent on the position of the characteristic curves in the torque / speed diagram, which size preferably by changes in the load on the machine and which can be achieved through changes in the specimen. In the examination of internal combustion engines, preferably, the speed is ' step on the gas ' on the loading machine and the torque specified by the internal combustion engine ( mutual influence ). Engine test cells are mostly based resonances, which greatly complicate the measurements. This can and must be countered by appropriate measures such as flexible connecting elements made ​​of elastomer / metal - elastomer.

Other components

Further facilities include a selection of engine test benches aggregates:

• Cooling and safety devices
• Exhaust or extraction
• In developing test benches or in the engine serial testing can horizontally or vertically disposed docking systems for automated coupling of fluid and electrical lines ( fuel, oil, air, cooling water, exhaust, electrical plugs, etc. ), shorten the setup time to a minimum.
• Modern engine test benches are equipped with a computer-controlled automation system for execution of test runs and for automatic data acquisition.
• A special role is played by the crank angle synchronous measurement of the pressure in the combustion chamber ( indicating system ) in internal combustion engines.
• Special equipment is the equipment of the dynamometer as anechoic chamber ( silenced engine bench) as a climate chamber ( cold, heat ), altitude test or pivot test.

Categories of engine test benches depending on their field of application

• Research and development of engines, typically in developing centers of automotive manufacturers
• Optimization / tuning of common engines, typically in service centers or in Motorsport
• End-of- test in production lines of automobile manufacturers
• Special test rigs for jet engines

• Drive Technology