This article will take an in-depth look at engine dynos.
The article will bring more detail on topics such as:
This chapter will cover the concept of engine dynos, including their design and functionality.
An engine dynamometer is a tool used to evaluate an internal combustion engine that has been detached from its vehicle, ship, generator, or other equipment. Its primary purpose is to assess the engine's performance before it is reinstalled into its original application.
Engine dynamometers assist in troubleshooting by identifying issues such as engine overheating and intermittent performance or sensor faults. They also evaluate the quality of new builds, rebuilds, and repairs in a controlled setting before the engines are put into operational use.
Engine dynamometers are connected to the engine being tested via a drive or cardan shaft. The engines are placed on rolling carts, which allows them to be easily moved into the dyno chamber. Typically, engine dynamometers employ a water brake, electric (EC), or alternating current (AC) system to apply loads.
Although engine dynos vary in design, they generally share common components: an absorption unit or driver, a torque generation mechanism, and an instrument for measuring torque and rotational speed. Typically, the absorber is a rotor housed within an enclosure that is connected to the testing apparatus.
Friction, hydraulic fluid, or electromagnetic power are commonly used to generate torque. A load cell or strain gauge is commonly used as the measuring device, however it could alternatively be a weighing scale, such as a crane scale. Note: Load cells, also referred to as load sensors, convert perceived mechanical force into measured mechanical signals.
A coupling is a device used to join two shafts at their ends to transmit power between them. It connects rotating components, allowing for some misalignment and movement between the ends. More generally, a coupling can refer to a mechanical mechanism that connects the ends of adjacent pieces or objects.
Typically, couplings do not permit shafts to be disconnected while in operation. However, torque-limiting couplings are designed to slip or disengage if the torque exceeds a set limit. By selecting, installing, and maintaining couplings appropriately, it is possible to reduce both maintenance time and costs.
A tachometer is a tool for measuring an engine's rotational speed in revolutions per minute (RPM). Tachometers, both mechanical and electronic, work in different ways. A moving item in the engine or gearbox is connected to the gauge via a flexible cable with a spinning shaft. The rotating shaft inside the instrument regulates the position of a needle that indicates the engine speed.
An electronic tachometer produces electrical pulses with a frequency that correlates to engine speed, using a magnetic sensor positioned close to a moving engine component. The device's circuitry converts these pulses into a digital display, showing the engine's RPM.
The torque arm is a suspension component that connects to the rear-drive axle of a rear-wheel-drive vehicle. This arm allows the car to accelerate in a straight line while keeping the rear axle stable and unmoved.
In addition to aiding braking by transmitting force to the braking system, this arm is also utilized on an engine dynamometer. On the dyno, it connects to a scale that measures and displays the reaction forces.
An absorbing dynamometer replicates the load exerted by the prime mover under test. It must be capable of functioning at any speed and load, delivering the required torque for the test.
It is important to differentiate absorbing dynamometers from "inertia" dynamometers. Inertia dynamometers measure power by determining the energy needed to accelerate a known mass drive roller, without applying a variable load to the prime mover. All engine dynamometers are absorbing types or incorporate absorption units, and the torque and speed of an absorption dynamometer are typically measured in some manner.
The power produced by the prime mover is absorbed by the power absorption unit (PAU) of the dynamometer. This unit absorbs the power and converts it into heat, which is either released into the surrounding air or transferred to cooling water that also dissipates into the air. Regenerative dynamometers, where the prime mover drives a DC motor functioning as a generator, can produce excess DC power that may be fed back into the commercial electrical grid via a DC/AC inverter.
To accommodate different major testing requirements, absorption dynamometers can be equipped with two types of control systems: constant force and constant speed.
In mechanical engineering, this component is part of a rotating joint where a shaft, known as the trunnion, is inserted into and rotates within a full or partial cylinder. Often used in pairs, this connection provides strength and precise tolerances due to the extensive surface contact between the trunnion and the cylinder.
These are self-contained concentric bearings utilized in airframe engineering to facilitate fluid movement in critical steering components. The term is also used to describe the wheel that supports and allows rotation of a cylindrical component.
A data acquisition system is a crucial part of a dynamometer setup. It usually comprises two units: a commander and a workstation, linked via an Ethernet cable. The commander is a desktop computer running Windows-based software, which sends commands to the workstation. The workstation, equipped with a touch screen and housed in a durable industrial enclosure, executes these commands.
The workstation manages the throttle control systems and precision load, gathers the data, and transmits it to the commander for processing, storage, and analysis. The effectiveness of the workstation, and consequently the accuracy of the data acquisition system, relies on its ability to accurately measure data during dynamometer tests.
Key to these measurements are the pressure transducers, which gauge various fluid pressures including air flow in oil pressure, intake manifold, and other fluids. It is crucial for the operator to monitor and adjust different fluid pressures while the engine is running, highlighting the importance of the workstation's capability to handle various pressures effectively.
These machines measure the revolutions per minute (RPM) or torque of an engine's flywheel or crankshaft to determine its horsepower. They achieve this by converting the torque force into an electrical signal, which is then translated into a readable measurement. Dynamometers can conduct separate tests on engines and vehicles, making them extensively used in engine rebuilding, diagnostics, design, and the production of automobiles and high-performance vehicles.
To start, select the appropriate dynamometer for your specific needs and ensure it is installed correctly before using it for horsepower testing. It is advisable to begin with a well-maintained engine that is known for its reliability and can operate at peak performance.
Next, bring the engine up to its operating temperature by applying light loads intermittently during the warm-up phase. Once the engine is sufficiently warmed, you can gradually apply a full load while adjusting the RPM with the control valve as needed.
With the throttle fully open, maintain this position while adjusting the brake’s load valve to transition between the desired RPM test points. Record the results from the dynamometer. After completing each RPM measurement (allowing sufficient time for accurate readings), gradually reduce the throttle and simultaneously decrease the brake load to bring the engine back to idle. This completes the initial dyno test.
Performing multiple tests is advised as it allows for refining the process and verifying the accuracy and reliability of the collected data. This practice is crucial for enhancing the engine’s performance and ensuring the results are repeatable and valuable.
The data obtained from the dynamometer tests can be saved and reviewed later to assess whether adjustments to the engine’s horsepower are needed. Additionally, repeating the testing process may be necessary to fine-tune the engine's performance accurately.
When selecting an engine dynamometer, several factors should be taken into account:
What exactly are you testing: engines that are removed from vehicles or the entire vehicle? If it's the latter, are you working with automobiles, motorcycles, trucks, ATVs, go-karts, or a combination of these?
Do you need a dynamometer designed for four-wheel-drive vehicles, or is a two-wheel-drive dynamometer adequate? Also, consider whether you need an independent or coupled axle setup.
Are you interested in absorbing power alone, or do you need motor capability as well? The selection of a dynamometer for either engines or vehicles should be based on factors such as the horsepower range, the type of testing required, and budget considerations.
It's important to understand that horsepower is a calculation reflecting the relationship between torque and revolutions per minute (rpm) across an engine's operational range. Like engines, dynos are rated for both torque and rpm.
To select the right engine dyno, first determine the estimated peak torque for each engine to be tested, along with the rpm at which this torque is generated. Additionally, you will need to know the maximum rpm of the engines. This information is typically provided by the engine manufacturer or designer if it's a custom-built engine. Understanding the type of engines (gasoline, diesel, etc.), their size (displacement), and their applications (trucks, cars, motorcycles, industrial, snowmobiles, racing, on-road, off-road, etc.) can help in making an approximate prediction.
Consider also the type of engine testing you plan to conduct and the parameters involved. You can create a test profile or schedule based on the typical horsepower and torque ratings at the expected rpm ranges. Using this data, you can plot a graph of "Horsepower and Torque vs RPM," known as a power curve.
With this information, you can select a dynamometer that meets these specifications. Each model and series of dynamometers has distinct absorption characteristics and corresponding power curves that match their capabilities.
There are three primary types of dynamometer testing:
An acceleration or sweep test involves allowing the engine to accelerate from a designated lower "starting" rpm to a specified upper "finishing" rpm. This method can also be applied to deceleration tests, where the engine starts at a high rpm and gradually slows down to a lower speed. During these tests, the dynamometer manages the rates of acceleration and deceleration. Sweep tests are commonly used to develop an engine’s performance or power curve.
In a steady-state test, the dynamometer maintains the engine or vehicle at a constant speed, torque, or power level for a set duration. Steady-state testing includes methods such as step tests and break-in tests.
The speed and load applied to the engine or vehicle fluctuate during a transient or cyclical test. In a transient test, load points vary throughout the test cycle, whereas in a cyclical test, load values remain constant. An example of a transient test is a drive cycle, commonly used in automobile emissions testing. Conversely, a cyclical test might simulate a car traveling around a track. In both cases, the dynamometer adjusts the load on the engine to achieve the desired results.
While most dynamometers can perform all three types of testing, some are better suited for specific types. Water brake dynamometers are generally versatile, accommodating any engine and test type, but their slower response to load changes makes them less ideal for fast transient testing. AC dynamometers, with their typically high inertia, can affect performance in acceleration tests but are effective in modeling how an engine coast-down occurs when the throttle is released, unlike water brake or eddy current dynamometers.
The cost of a dynamometer is an important factor to consider. While the expense of the data acquisition and control systems is relatively consistent across different types, the focus should be on the power absorption unit. Among the three main types of dynamometers, AC dynamometers are the most versatile but also the most expensive. The advantage of a motoring dynamometer is its ability to both absorb power and drive the engine, offering a more realistic representation of vehicle performance on the road or track. The cost of a motoring dynamometer is influenced by the motor's size (horsepower rating) and the additional equipment needed for operation, such as a drive unit and regenerative device.
Eddy current dynamometers are mostly water-cooled and require only a small amount of cold water for operation, although air-cooled versions do not need water. The physical size of an eddy current absorber is directly related to its power absorption capability, which impacts its cost—the larger the unit, the higher the price. Eddy current dynos typically handle between 100 and 500 horsepower, though there are larger models available for higher power applications.
In comparison to an AC dynamometer, a water brake dynamometer is often more cost effective. At one-fourth the cost, a water brake absorber half the size of an eddy current absorber can often manage three times the horsepower. A water brake absorber, on the other hand, requires water—and sometimes a lot of it. Only a few hundred gallons of water are required for low-power, infrequent use (two or three times per week), and short-duration testing (less than one hour per day).
For high-powered engines and prolonged testing sessions, a substantial amount of water or an advanced cooling system is required, potentially increasing the total cost of the system. Water brake absorbers typically start at around 500 horsepower and can scale up, often at a lower cost compared to similar eddy current units. However, once the cost of the water supply system is factored in, the overall expense of a water brake system can become comparable to that of an eddy current dynamometer.
This chapter will explore the different types of engine dynamometers.
Engine dynamometers of this type use an electromagnetic brake to apply a load to the engine. The electromagnetic brake generates a magnetic field in a rotating disc, creating resistance. This resistance produces heat, which is then dissipated either into the air or through water cooling. For lower-power applications, electromagnetic brakes are employed for power absorption, with dynamometers rated up to 250 horsepower. They are also commonly utilized in various chassis dynamometers for vehicle testing.
Water-cooled electromagnetic (EC) engine dynamometers offer the main advantage of precise and rapid load control. The load can be adjusted from zero to 100% within milliseconds by varying the energy supplied to the coil, allowing for very accurate adjustments. However, eddy current dynamometers are typically 40 to 60% more expensive than water brake dynamometers and have a narrower dynamic range. As a result, EC dynamometers are generally selected for more specialized testing needs.
AC dynamometers have the capability to generate a load and return excess power to the electrical grid through regenerative power electronics that operate at variable frequencies. In some cases, the operator of an AC dynamometer may even receive compensation from the utility company for the power returned to the grid, depending on local regulations.
AC dynamometers excel in transient testing due to their rapid response capabilities. They can simulate dynamic forces on an engine, such as those experienced when a vehicle rolls downhill, or manage the load patterns in emissions test cycles. This technology is applied to engine dynos with power ranges from 10 HP to 5,000 HP, as well as chassis dynos that require precise transient or road load control.
A load is created on the engine or vehicle being tested using water momentum transfer with the absorbed power heating water. These types of dynamometers are ideal for engine dynamometers of a higher power with options that range from 350 to 10,000 HP. These dynos are the technology that is the most cost effective for internal combustion engines and electric motors that are large. They make use of a hydraulic brake that is capable of converting the energy produced by the engine into heat transferred to the water that flows through the dyno.
A dynamometer of this type features a stationary side (stator) and a rotating side (rotor), each equipped with cup-shaped pockets designed to transfer water between them. An automatic control valve, mounted on the dynamometer, regulates the water quantity according to the test requirements, thereby creating the necessary load on the engine.
The primary benefit of these dynos is their extensive dynamic range, allowing them to test a wide variety of engine speeds and torques with a single unit. Additionally, water brake dynos are the most cost-effective option for dynamic testing, making them ideal for a diverse array of applications, from internal combustion engines to electric motors.
This section will compare engine dynamometers with chassis dynamometers.
An engine dynamometer measures power output by determining the amount of torque required to keep an engine running at a constant speed (rpm). The dynamometer's software then calculates the horsepower using the formula: horsepower = (torque x engine speed) / 5.252. The dyno includes a control board that displays torque, water temperature, oil temperature and pressure, rpm, exhaust temperature, and air/fuel ratio through sensors connected to the engine. The operator can start and control the engine from the board using either a cable-operated lever or electronic controls, depending on the dynamometer model. Typically, the engine is stripped of its accessory drive and fitted with a header and, if required, a full exhaust system tailored to customer specifications.
Since engine dynamometers measure torque directly, they offer the most accurate representation of an engine’s power output. This makes them ideal for detailed part comparisons or fine-tuning to achieve optimal performance. Engine dynos are valued for their repeatability, controlled testing conditions, and easy access to the engine for parts swapping and tuning.
While an engine dynamometer measures power directly from the engine, a chassis dyno measures the output of an engine or more accurately the output of the drivetrain at the drive wheels of a vehicle. In the basic form of a chassis dyno, it is composed of a platform with a pair of drums or rollers, power absorption or braking system, and software that is used to calculate power output.
In a chassis dynamometer, the vehicle is positioned on rollers or drums that the drive wheels rest upon. Depending on the type of dyno, the system calculates torque either by measuring the acceleration of the rollers or using a load cell to assess the power absorbed by the rollers. This torque value is then used to compute horsepower. Many chassis dynos are also equipped to monitor parameters such as air/fuel ratios and other engine metrics.
The primary advantage of a chassis dynamometer is its ability to measure power directly at the drive wheels, reflecting real-world vehicle performance. While tuning and testing parts to observe their impact on power can be done, it is less straightforward than with an engine dynamometer. Additionally, because drivetrain power losses are factored in, a chassis dyno provides valuable insights into the efficiency of the drivetrain.
This chapter will explore the applications, advantages, and maintenance considerations of engine dynos.
The applications of engine dynos are:
Engine dynos provide numerous advantages to users. Primarily, they enable manufacturers to assess the power and performance of their engines and electric motors before these products are launched to the market. By using engine dynos, manufacturers can identify potential inefficiencies or performance problems, such as slow power acceleration or faulty brakes, that could lead to costly issues or operational problems.
By identifying and addressing these issues, manufacturers can make the necessary fine-tuning adjustments to ensure optimal performance and safety. This not only enhances the reliability of their products but also reduces the risk of costly repairs and recalls. Additionally, it allows manufacturers to assure customers of the safety and quality of their engines.
Engine dynos also contribute to the efficiency of engines, leading to better fuel economy and reduced emissions, which benefits the environment. Manufacturers can use engine dynos to ensure their engines meet EPA standards and to promote their environmental credentials.
As engine dynos continue to evolve, they are becoming increasingly automated and advanced. This ongoing development reduces human error and enhances measurement speed and accuracy. The future of engine dynamometers promises further improvements in power, safety, efficiency, and performance for many years to come.
Considerations in engine dynos maintenance are:
To boost productivity, it is essential to service the dyno according to the recommended intervals. Following the manual guide for preventive maintenance is crucial. Additionally, key personnel should receive proper training on both the use and upkeep of the equipment. For on-site support, calibration, evaluation, maintenance, and repairs, Power Test’s technical service staff should be engaged.
Maintaining high water quality is essential for extending the lifespan of a dyno.
Engine dynos can consume over 100 gallons of water per minute. Cool incoming water helps keep the dynamometer cool, allowing it to operate efficiently for longer periods. If recirculated water is used, it should be cooled via a cooling tower before being circulated through the dyno.
Engine dynos have two types of lubrication points: high-speed bearings and trunnion bearings. The lubrication system may use grease or oil depending on the dyno's age. Refer to the owner's manual for proper lubrication procedures.
Vibration sounds may be due to a loose bolt, but they can also signal more significant issues. For example, improper phasing and alignment of a driveshaft can cause vibrations that may damage the driveshaft, dyno, engine, or even pose safety risks if the driveshaft fails.
Engine dynos, also referred to as engine dynamometers, are devices that are used to test an engine’s internal combustion. They calculate the power output by measuring the magnitude of the force (torque) required to hold a spinning engine at a set speed (rpm) directly. There are different types of engine dynos offering different benefits. For example, the water brake dynamometers which provide a wide dynamic range meaning one dyno can test a wide range of engine speeds and engine torques. However, for maximum performance, the engine dyno must be regularly maintained.
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