Chasis dynos:

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Theory

Methods of the measurement of the power and the torque of the engine

The problem of testing internal-combustion engines is quite complex. The appropriate measurement of the power and the torque demands taking into consideration a lot of factors. Depending onour purpose and the way of using chassis dyno, it is possible to point out two fundamental solutions - inertial measurement (during speeding up) and measurement with a balance of forces (braked). Dynos produced by us can work at both configurations - it depends only on their option and accessories. Dynos equipped with the electro-spin brake or brakes will be named further braked dynos. Dynos working at the inertial mode, not equipped with the brake, will be named further inertial dynos. (Attention: all dynos offered by us are equipped with lifts picking cars up from rolls together with the brake blocking rolls - one should not confuse the brake of rolls with the electro-spin brake.)

Inertial measurement (method of the measurement possible on both inertial and braked dynos)

The inertial measurement consists of accelerating the car on the dyno, then, after declutching, on waiting until a car will stop, without using the brake. The engine is burdened by: mass of rolls and resistance of rolling and resistance of the driving mechanism. A time of the measurement is about 10-30 seconds of the full load and a few minutes of free rolling on the dyno until full stop. The power and the torque are measured as functions of the acceleration of the car on rolls (the power and the torque on wheels) and of its deceleration (the power and the torque of losses). The sum of both is representing the power and the torque of the engine.

The inertial measurement has a few essential advantages compared with the measurement under burdening with balancing the driving force:

• it requires the shorter time of the full load – so it is safer for the engine
• it doesn't require expensive chilling cars systems -a decent fan is enough (you can choose from a few fans in our offer)
• it is more accurate - since the sphygmomanometer of the brake and driving limitations of the brake and it termical characteristics are worsening the accuracy of the braked measurement.
• it presents the entire characteristics of the engine as the function of rotations rather than only a few chosen points

The inertial measurement also has a few faults:

• turbine engines can require the big load for correct boosting up. If your choice is inertial dyno, we are recommending buying the version with very heavy rolls and big diameter of rolls (e.g. option: 355 mm, 180 kg/roll). Braked dyno doesn't have this problem - it is possible to increase the load freely, only slightly worsening the accuracy.
• inertial dyno doesn't allow for examining the car at constant rpm.

Process of the measurement on inertial dyno is running as follows:

• The vehicle is driving on dyno. The lift is leaving the car on rolls and it is unblocking them.
• The car is placed in the axis by delicate moving then it is fastened on dyno using belts
• Ratio of the gearbox and the drive is being examined - it is possible to do it in a few ways. The information is entered into the dyno program. Fans of the airflow are being started.
• After making sure that the temperature of the engine is already correct, the driver is accelerating the car on highest possible gear (recommended) or another chosen gear to maximum rpm essential for the measurement (usually - to so-called cut off).
• The driver presses the clutch leaving the gear turned on. The dyno is slowing down until stop. The result of the measurement is being presented on the screen. The tuner can analyse the results obtained (the power, the torque, resistances of mechanisms and rolling, the power on wheels, results of accesory equipment of the dyno etc.) depending on rotations.

On braked dyno the process of the measurement in the inert mode looks exactly the same. We can additionally set an extra fixed charge before beginning the measurement (that is to increase the feigned inertia of the dyno through burdening the car with the brake without balancing his torque). It permits to select the load appropriate to the power of the engine and to correct torque characteristics in cars with the turbine at low rotations of the engine.

Braked measurement at constant revolution rate (method of the measurement possible on braked dynos)

The braked measurement at constant revolution rate means balancing the driving force of the car with the brake and measuring the driving moment with the use of the sphygmomanometer (sensor of force, it is kind of the precise weigh). The engine is burdened by: electro-spin brake (changeable weight) and similarly as in inertial dyno - mass of rolls and resistances of rolling and resistances of the driving mechanism. A time of the measurement is about 10 seconds of the full load (for the stabilization of revolutions and reading the result) for every measuring point (at chosen revolutions rate). The power and the torque are being measured up as functions of the weight measured on the sphygmomanometer of the brake, with taking the power and the moment of losses into consideration, which are measured earlier in the inertial mode. The sum of both is representing the power and the torque.

Braked measurement at constant revolution rate - advantages and faults:

Because measurement of the power of the engine on dyno with the brake (charged in the mode with balancing the driving force) is burdened with the bigger error but instead it allows for holding the car at the one rotation rate which is of interest to us - it is often applied to the strenuous research on engines and driving teams. Companies studying new systems of steering, the fuel injection, constructing competitive engines are buying dynos equipped with the brake from us. A great advantage of such dyno is the fact that it is possible to tune the car in the real time in chosen points although it is necessary of course to realize limitations - particularly thermal ones. The car under the full load is producing biggest amount possible of the power for chosen rotations and what is following it - warm amount. Unfortunately the engine is warming up as a result of such a work and it is changing its parameters (its physical fitness is decreasing), in spite of intense chilling. No fan is able to replace an air channel with the wind about the speed c 200 km/h - well after all in such "channel" moves a car on the motorway. The car behaviour under full load is reproducible only during several dozen seconds. Such a mode of the measurement requires a good research method, effective chilling and serious work of the tester. One should not expect the accurate result at inefficient chilling or prolonged straining - at overheating the result is usually lower than actual - or it is absurd in extreme cases, because the engine control is turning into the safe mode to save the engine from overheating, so the charging up and the dose is limited and the overboost is turned off. That is why in renowned research companies, at of this kind strenuous examinations, for holding the engine in comparatively rational thermal conditions, many additional systems of chilling are applied - such as the shower of water on the exhaust arrangement, on intercooler (for turbine engines) and directly on the radiator of cooling liquid. All such systems can be provided as the option to our dyno - if you will choose as the customer a braked dyno with the electro-spin brake and you are planning to use it not as additional „generator” of the inertia but as a weight for holding the car at constant revolutions in the purpose of tuning cars in the real time.

Another problem is that choosing a few or a dozen or so points of the measurement of the power and the torque we are really not knowing the way how an engine performance is changing outside these points. De facto we are obtaining relatively little information about parameters of the engine in the function of revolutions with the cost of bi load and strain of the engine.

However the braked measurement has a few essential advantages compared with the inertial measurement

• possibility of making measurements both in the inertial mode (inertial dyno) as well as with the load increasing the inertia (inertial dyno with the feigned weight adjusted freely)
• possibility of the measurement of the power and the torque at constant revolutions - useful for tuning engines and performing the tests

Process of the measurement with balancing revolutions on braked dyno is different a little bit than in the case of the inertial measurement (however all procedures together with the inertial measurement are performed - actually only to measure resistances of rolling and of driving mechanisms). After performing the set of operations described above, having the result of the inertial measurement, we can proceed to the actual measurement:

• The program is informed of revolutions at which the torque is supposed to be measured up with the sphygmomanometer (sensor of force).
• The driver is accelerating the car pressing the accelerator pedal completely down (if the measurement is supposed to be made for full opening of the throttling valve). The dyno is straining the car automatically until revolutions are equal the set value and the car will neither speed up neither slow down. The value of power, measured by the sphygmomanometer, after taking into consideration the force of resistances at given revolution rate (measured earlier in the inertial measurement) is being presented on the screen in the real time. The tuner can change parameters of the engine during its work and to observe changes in the power of the engine.