Chassis Dynamometers Theory
Methods of measuring the power and the torque of the engine with chassis dynamometer
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 on our purpose and the way of using a chassis dyno, it is possible to point out three fundamental solutions - inertial measurement (during acceleration), measurement in a load mode (during acceleration) and measurement with a balance of forces (braked). The dynos produced by us can work in all of these configurations - it depends only on their option and accessories. Chassis dynamometers with the eddy current brake or brakes will be named further braked dynos. Dynamometers working at the inertial mode, and not equipped with the brake, will be named further inertial dynos. Please note that all dynos offered by us are equipped with lifts that can pick cars up from rolls, and with a brake that blocks the rolls; one should not confuse the brake of the rolls with the eddy current brake.
Inertial measurement (method of the measurement possible on both inertial and braked dynamometer)
The inertial measurement with chassis dynamometer 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 the mass of rolls, the resistance of rolling and the resistance of the driving mechanism. The 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 then used to represent the power and the torque of the engine.
The inertial measurement has a few essential advantages compared with the measurement under burdening :
- it requires a shorter time of the full load – so it is safer for the engine,
- it doesn't require any expensive system for chilling the car –a medium-sized fan is enough,
- it is more accurate – since the load cell of the brake and driving limitations of the brake and its termical characteristics are worsening the accuracy of the braked measurement during the braked measurement.
The inertial measurement also has a few disadvantages:
- very powerful turbine engines can require a big load for correct boosting up. The dynamometer with electromagnetic brake(s) doesn't have this problem - it is possible to increase the load freely, only slightly worsening the accuracy.
- The inertial dyno doesn't allow for examining the car at constant rpm.
Process of the measurement on inertial dynamometer runs as follows:
- The vehicle drives on the dyno. A lift puts the car down on the rolls. The rolls are unlocked.
- The car is placed on the axis. Then it is fastened onto the measurement stand using belts.
- The ratio of the gearbox and the drive is examined - it is possible to do it in a few ways. The information is entered into the dyno program. Fans of the airflow are turned on.
- After making sure that the temperature of the engine is already correct, the driver accelerates the car in the highest possible gear (recommended), or in another chosen gear, to the maximum rpm essential for the measurement (usually - to the so-called “cut-off”).
- The driver presses the clutch, leaving the gear turned on. The dyno slows down until it stops. The result of the measurement is presented on the screen. The tuner can analyse the obtained results (the power, the torque, resistances of the mechanisms and rolling, the power on wheels, results from the accessory equipment of the dyno, etc.) as a function of the rpm.
Measurement in the dynamic-load mode (method of measurement possible with braked dynamometer)
The measurement in this mode is similar to that of the inertial mode, with the difference that the eddy current brake simulates a larger load. The load coefficient is a percentage, set by the user in the dyno software.
The measurement in the dynamic-load mode has some important advantages over the inertial measurement:
- The user is able to individually choose the load depending on the type and power of the measured engine.
- A possibility of enlarging the measurement time.
- The possibility of an accurate burdening of powerful turbine engines, with the aim of a correct “building-up”of the boost.
The measurement process in the dynamic-load mode runs as follows:
- In the dynamic-load mode, before starting the measurement, it is necessary to set an additional load in the dynamometer software (i.e. increase the apparent inertion of the dyno by burdening the car with the eddy current brake to a degree that is not balancing its torque). This enables precise adjustment of the load to the engine power, e.g. to the correct "building-up" and maintaining of the boost.
- The procedure of the measurement itself, after determining the load coefficient, is the same as in the inertial mode.
Measurement at constant rpm (method of measurement possible with braked dynamometer)
The measurement at constant rpm consists of balancing the driving force of the car by the eddy current brake and calculating the engine power from the load cell data. The measurement time is about 10 s of the full load (for the stabilization of rpm and result reading) for each measurement point (an individual value of rpm).
Braked measurement at constant revolution rate - advantages and faults:
Because measurement of the power of the engine on the dyno with the brake (charged in the mode with balancing the driving force) is burdened by a bigger room for error, there is on the other hand the possibility to hold the car at the rotation rate which is of interest to us - it is often applied to the strenuous research on engines and driving assemblies. Companies studying new systems of steering, fuel injection systems and constructing competitive engines are buying dynos from us that are equipped with the brake. A great advantage of such a dyno is the fact that it is possible to tune the car in real time at chosen points, although it is necessary of course to consider the limitations – particularly the thermal ones. A car with a full load produces the biggest possible amount of power for the chosen rotations and consequently the heat amount. Unfortunately the engine warms up as a result of such work and it is changing its parameters (its energy conversion efficiency is decreasing), in spite of any intense chilling. No fan is able to replace an air channel with the wind around the speed of 200 km/h - after all, a car on the motorway moves in such a "channel" already. A car’s behaviour under a full load is reproducible only during several dozen seconds. And such a mode of measurement requires a good research method, effective chilling and some serious work by the tester.
The measurement process in the constant rpm mode runs as follows:
- The tester sets in the software the measurement points at which the rpm will be stabilized.
- The driver accelerates the car, pressing the accelerator pedal completely down (if the measurement is supposed to be made for full opening of the throttling valve). The dynamometer then burdens the car automatically until the revolutions are equal to the set value and the car will neither speed up neither slow down. The value of power, measured by the load cell is presented on the screen in real time. The tuner can make changes during the measurement and immediately see the result of his work on the screen.
What is our dynamometers' power & torque measurement technology offering you ?
A rapid rate of collecting information
A fundamental flaw in the solutions of dynos presently available on the market is their frequency of sampling. On graphs from dynos by many companies one can see clearly a few to a dozen or so lines, from which the shape of their characteristics is estimated. Of course, smoothing the graph with curves is also possible but can we call it a real result? Usually the power and the torque is sampled on the dyno every 0.3-1.0 sec. and the established result is de facto the average power and the average moment in this time interval. In these techniques, measuring the torque that changes violently twice (as in turbodiesels) gives two different results. It depends on how the sampling ranges overlap.
A few years ago, our company invented a new technology of the measurement of the torque which applied both to braked dynamometers and inertial dynos. This method of the measurement was intended originally for laboratory measurements of the power but it is also present in our trade offer. The method is based on TrueForce™ technology patented by us, which allows for measuring the torque completely smoothly. Considering the speed of the force changes on the dyno, the measurement is made in real time and with an unbelievable accuracy. In fact, during every second of the measurement the encoder of the dyno provides up to three thousand pieces of information about the momentary value of the torque and the power – one linearly independent measuring point is put on the graph even every 0.0003 second. The error of determining the temporal moment is smaller than 0.00001 s. Furthermore, such accuracy is offered in the standard version. The changes on plots are smooth. Why? Because the work of an engine and changes in the torque are also not violent, on account of its own high inertia. The accuracy of the measurement is so high that the plot is smooth and the line does not shake, yet an interruption of the measurement or any small disruption is mercilessly and meticulously picked up, and it is possible to point out the exact rpm of the engine at which it appeared. It is possible to observe subtle phenomena, such as temporary resonances, a slip of the wheels (position of the rolls at any time is known within the accuracy of fractions of the degree) or a minimal loss of torque at the stabilisation of the boost pressure. What's more, even single missing ignitions are lowering the torque of the engine and these too are visible, in spite of the existence of the flywheel! Additionally, the results are reproducible in many tests (of course, if we take care about keeping the engine at a constant temperature and we don't repeat the tests one after another too many times) - as far as we want. And this is entirely without any smoothing, without the averaging, without converting or using imaginary percentages and factors. No other solution offers such accuracy and precision - you must simply see it in order to fully appreciate the possibilities of the TrueForce™ system.
The very big accuracy of the measurement and the high repetitiveness
An advantage, resulting straight from our innovative method of the measurement, is the really big repetitiveness. Since rotations of the roll are measured with unusual exactitude, the measurements of the torque and the power and the positioning of points on the graph are also accurate. On account of the good bearings, high inertia and precise balancing, the accuracy of the measurement is also higher than in other, rival solutions. Moreover, the dynos are calibrated with the use of a gravitational standard of the torque, which assures the appropriate readings of absolute measured values.
The possibility of the easy upgrade and the modularity of solutions
Probably everyone who decides to spend at least a dozen thousand euros on a device such as a dyno would like to know what next, what to do and when his needs will grow.
Our solutions are entirely modular, allowing for the possibility of upgrading the inertial dyno to the braked version and equipping the test stand with external sensors: temperature, pressure or mixture composition. All necessary measurements and conditions of the building development for the given options can be provided in advance in the form of projects - so the user can check the adequacy of the room designed for the dyno besides its possible future expansion.
Popularity and reliabilty of the manufacturer
Our solution has been chosen by over 100 companies in Europe – including many well known and popular tuner and specialist enterprises. We are one of the biggest producers of dynos in Europe. The plots produced by our measurement systems can be seen everywhere - on the internet, in papers, and in the hands of those testing their cars with our modular dynamometers. Our dynos can be found in practically every European country, and the results obtained with them are consistent thanks to the calibration of the ready dynos in our factory.
Impeccable workmanship raising the prestige of the owner
Our dynos are made on steel frames, then covered with lids of riffled plate, galvanized and painted twice for protection. The rolls are made with a no-edge technique (so the welds are not visible), they are knurled, covered with technical chromium and balanced with an accuracy below 1g. Each dyno is equipped with pneumatic brake locking rolls during both the drive-in and the leaving of the measurement stand. The controlling computer is put in a professional industrial casing, as well as the driver of the eddy current brake. The whole control is put in the 19’ industrial stand or in a special desktop. And we deliver all of the necessary elements in the set. The address data of the buyer is present on the printouts and protocols - and the graph can have any logo as the background.
How to buy a dynamometer? What is the price of dynamometer?
It is worth to remember that our product line is modular. There is no need to buy whole 4wd dynamometer at once or buy it with electromagnetic brakes. You can invest small amount of money and buy main front module (one axle dynamometer) and start to work with, so dynamometer will start to pay off itself - and then, later at any moment - expand it with 4wd (second set of rollers), eddy-current brakes, additional equipment.
First you should decide which dyno will meet your expectations best, then choose the accessories and determine the possibilities of a future upgrade. Next, you must make sure that the room for the dyno is suitable for it and, based on the project delivered by us, plan its localisation, power supply, the space for the control system, and anchors permitting to secure the car. If you have already made a decision about buying the device, you order the specified version (you sign a written purchase order, binding both parties). You make an advance payment. We determine the dyno delivery time – the delays are from 2 weeks to 2 months – depending on the complexity of the order. Our specialists will bring the dyno to you in the due time – however, you must earlier prepare the foundation for it, according to our plans. The dyno is installed and initialised during one to three working days (the dyno is already calibrated in the factory). Your staff is then trained (the operating manuals for the dyno are with the device). You can start measurements…
You can choose a few ways of financing the purchase. The simplest is to pay the advance payment and then a surcharge to the full price at the installation of the dyno. It is also possible to lease a dyno.
We guarantee a correct and failure-free functioning of the modular chassis dynamometer and no faults in the mechanisms for a period of two years. After the warranty period our company offers paid inspections by the authorised staff and expansion of warranty as long, as dynamometer is inspected once per 2 years.