This article will take an in-depth look at engine dynos.
The article will bring more detail on topics such as:
This chapter delves into the fundamentals of engine dynamometers, discussing their structure and the principles behind their operation.
An engine dynamometer is an essential device used for assessing the performance of an internal combustion engine that has been decoupled from its typical environment, such as a vehicle or generator. Its main function is to evaluate engine performance before reinstalling it for its intended purpose.
The use of engine dynamometers can pinpoint issues like overheating, signal faults, or performance inconsistencies, while also testing the quality of new constructions and repairs in a stable environment before practical application.
These dynamometers connect to the engine under evaluation through a drive or cardan shaft, and the engines, positioned on mobile carts, can be smoothly moved into the testing chamber. Typically, these dynos utilize a water brake, electric (EC), or alternating current (AC) system to administer loads.
Despite differences, engine dynos typically share vital elements: a driver or absorption unit, a mechanism for torque generation, and a system for gauging torque and rpm. Normally, the absorber comprises a rotor placed within a housing connected to the testing assembly.
Friction, hydraulic fluids, or electromagnetic forces are common means to create torque. A load cell or strain gauge, or perhaps a scale like a crane scale, often serves as the measuring device. Note: Load cells, also known as load sensors, translate perceived mechanical force into readable signals.
A coupling is a mechanical component used to link the ends of two shafts for power transmission. It connects rotating parts, allowing for small misalignments and movements. More generally, a coupling may refer to a device connecting adjacent components or structures.
Typically, couplings do not allow disconnection of shafts during operation. Torque-limiting couplings, however, are engineered to slip or disengage when the torque surpasses a set threshold. Proper selection, installation, and maintenance of couplings can significantly reduce maintenance time and expenses.
A tachometer is designed to measure an engine's speed in RPM. Mechanical and electronic tachometers operate differently. Within the engine or gearbox, a rotating element connects to the gauge via a flexible cable with a spinning shaft. This turning shaft adjusts a needle to display engine speed.
Electronic tachometers generate electrical pulses with frequencies proportional to engine speed, using a magnetic sensor near a moving engine part. Its circuitry translates these pulses into a digital display indicating the RPM.
The torque arm, part of car suspension, connects to the rear drive axle in rear-wheel-drive vehicles. It supports straight-line acceleration while stabilizing the rear axle.
Besides facilitating braking by transferring force to the brake system, this arm is utilized on engine dynamometers. Connected to a scale, it measures and displays reaction forces.
Absorbing dynamometers simulate loads exerted on the prime mover during testing. They must operate at any specified speed and load, providing the essential torque.
Contrarily, inertia dynamometers gauge power by assessing energy needed to accelerate a known mass drive roller, bypassing a variable load. Engine dynamometers employ absorption units, measuring torque and speed, typically.
The dynamometer's power absorption unit (PAU) captures energy from the prime mover, converting it to heat dissipated into air or cooled water. Regenerative dynamometers enable prime movers to power a DC motor acting as a generator, potentially feeding excess energy back into the grid via a DC/AC inverter.
Different testing demands dictate the use of constant force or constant speed control systems in absorption dynamometers.
In mechanical engineering, trunnion bearings form a part of a rotating connection, providing strength and precision due to their extensive surface contact. These concentric bearings facilitate smooth movement of critical steering components in airframes. The term also refers to wheels supporting rotating components.
A data acquisition system, indispensable in dynamometer setups, typically encompasses two units connected via an Ethernet cable: a commander and a workstation. The commander, a Windows-based desktop computer, instructs the workstation, which manages throttle control and load, collects data, and conveys it for processing and analysis.
The workstation's efficiency, and consequently the data's accuracy, hinge on its ability to measure inputs precisely during tests. Key elements include pressure transducers, which measure fluid pressures like intake manifold and oil pressure. The operator must actively monitor and adjust fluid pressures, demonstrating the workstation's ability to manage pressures effectively.
Engine dynamometers quantify an engine's RPM or flywheel torque to determine horsepower, converting the torque into electrical signals for easy interpretation. These tools facilitate independent engine and vehicle tests, widely employed in engine diagnostics, rebuilding, design, and auto manufacturing.
Select an appropriate dynamometer based on your requirements, ensuring its correct setup before beginning horsepower evaluations. Start with a well-maintained, reliable engine operating at peak capability.
Initially, warm the engine incrementally by applying light loads. Upon adequate warming, apply a full load, adjusting the RPM with the control valve as required.
With the throttle fully open, navigate between RPM test points using the brake’s load valve, documenting results. After measurements, gradually ease the throttle and brake load, returning the engine to idle, completing the initial testing.
Repeating tests is vital for refining accuracy and validating data reliability, ultimately enhancing engine performance and data assurance.
Test data can be saved for later review and adjustment considerations to optimize engine horsepower. Repeated testing may be needed for precise performance tuning.
Several aspects should influence your choice of an engine dynamometer:
Determine if you're assessing stand-alone engines or entire vehicles. For vehicles, consider whether you're working with cars, motorcycles, trucks, or varied types. Consider four-wheel or two-wheel drive dynamometers, and whether an independent or coupled axle setup suits your needs.
Decide if focusing solely on power absorption or addition of motor capability is essential. Selection should be based on horsepower range, budget, and intended test type.
Horsepower reflects torque and RPM correlations over an engine's range. Dynos are evaluated based on torque and RPM as well. Ascertain peak torque and RPM for each engine, along with maximum RPM. Consider engine type (gasoline, diesel) and application (vehicle, industrial, racing) for horsepower predictions.
Develop a testing plan or profile indicating typical horsepower at expected RPMs, plotting a "Horsepower and Torque vs RPM" power curve to identify suitable dynamometer models, each with distinct power curves.
Dynamic testing includes three primary types:
Acceleration tests push engines from lower starting to upper finishing RPM, with deceleration tests reversing the process. Sweep testing, often used to refine performance curves, manages acceleration-deceleration rates.
Steady-state tests hold engines or vehicles at fixed speeds, torques, or power levels, such as step and break-in tests.
Transient or cyclical tests vary speed and load throughout a cycle, with the dynamometer modifying loads to meet goals. Water brake systems adapt these methods but offer slower responses to load shifts, while AC dynamometers, despite inertia, efficiently model coast-down effects.
Cost consideration in dynamometers involves power absorption units besides consistent prices for data acquisition and control systems. AC types, while versatile, are costly, yet enable both energy absorption and engine propulsion for realistic assessments. Costs tie to motor size and ancillary equipment.
Eddy current units, usually water-cooled, function with limited chilled water but their power capability and size directly impact price. Typically spanning 100-500 HP, larger models exist for high-power needs.
More affordable than AC models, water brake dynamometers provide capable power management but necessitate substantial water supplies. Low-power intermittent tests only require moderate water, yet for intense sessions, advanced cooling and water extension increase total costs, aligning water brake pricing with eddy current counterparts.
While water brake absorbers may start at 500 HP, long-duration and high-power tests require factoring the cost of water supply, equaling eddy current systems in overall expenses.
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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