Achieving Flexibility in Automotive Dynamometer Applications

frozenviolet

Achieving Flexibility in Automotive Dynamometer Applications [Copy link]

This article will introduce you to the use of National Instruments products to build a flexible dynamometer test platform.
Contents:
· Introduction
· Automotive dynamometer applications
· Dynamometer technology
· Application examples
· Integrated control system
· Conclusion
· Contact method
· Appendix A – Common design parameters
· Appendix B – Relationship between torque and horsepower


Introduction

Summary
This article describes how to use National Instruments products to build a flexible dynamometer test platform.
There are many different objects for designing and verifying applications, especially when using dynamometers to test motors, engines, or vehicles. However, most dynamometer applications encounter the following challenges:
· Inconvenience of manual operation
· How to integrate control functions, measurement functions, and operator interface functions
· Limited channel expansion capabilities
· Whether it is compatible with new signals and protocols
· Whether it is compatible with third-party devices
This article will explore which tools can be used to overcome the above challenges and will introduce some solutions based on the National Instruments platform.
For automotive engineers and system integrators who build engine and chassis performance test systems, the use of the National Instruments automotive test platform based on LabVIEW software and PXI hardware can build a real-time control and measurement system platform. Unlike dedicated solutions, the automotive test platform allows users to build applications that fully meet their testing needs. In addition, another benefit is that the automotive test platform can integrate multiple National Instruments products and third-party components into a single system. Although
this article focuses on powertrain test application cases, its techniques and methods can also be applied to test the safety, durability and operating performance of other components (such as hoses, brakes, seat belts or motors).
About National Instruments
National Instruments is a leader in PC-based data acquisition and product control. By using hardware and software products produced by National Instruments, engineers and scientists can easily automate test procedures, data acquisition and analysis, and display test results in an easy-to-understand way.
NI has many customers in various industries and R&D fields. By using NI products to create various automated test and measurement systems, their respective productivity has been significantly improved, and development and maintenance costs have been greatly reduced.


Automotive Dynamometer Applications

Common applications for automotive dynamometers include:
· Vehicle inspection and maintenance
· Chassis design and verification
· Engine design and verification
· Powertrain design and verification

Design and verification testing
Design and verification testing should consider multiple goals, including:
· Measuring performance factors such as horsepower, acceleration, and mileage
· Product life cycle and durability testing
· Verifying that product designs meet exhaust emissions and safety standards and meet product specifications
· Measuring noise and vibration
In short, when testing, the ideal dynamometer test result is that the test system can continuously generate meaningful data without causing unexpected injuries to personnel or damage to the test system and the device under test. To achieve this goal, the test system must have the following three characteristics:
· Reliability - to ensure operator safety and data integrity
· Repeatability - to obtain consistent results
· Flexibility - to accommodate different models and assembly levels
Dynamometers with these characteristics can serve as the basis for an expandable and configurable automated control system to meet the needs of a variety of test applications. The following section will introduce a method for establishing such a control system using National Instruments products.


Dynamometer Technology

A dynamometer is an energy absorbing device that applies a controlled load to the object being tested. The load is applied in the form of torque (rotational force) to the engine shaft or wheels. Dynamometers
can use several braking technologies to generate controlled loads:
· Inertial - A rotating object with a large mass provides a load proportional to acceleration. Torque can be calculated from the rate of change of acceleration. Average torque can be calculated from the time required to accelerate the object to a given speed.
· Hydraulic - The load is generated by a water pump. An impeller attached to the shaft mechanically forces water through the pump. A valve placed in the output line of the pump regulates the back pressure and generates the load. · Eddy current - The load is
generated by eddy currents induced by a rotating metal disk in a magnetic field.
· AC or DC motor - The load is generated by the motor. The motor can also act as a driver to generate torque.
· Hydraulic - The load is generated using a smooth disk power element that absorbs energy through viscous shear.
Each dynamometer technology can be classified based on cost, power, speed, dynamic response, control stability, inherent inertia, and other characteristics. Eddy current dynamometers and motor dynamometers have good response and power/torque performance at high speeds, making them the preferred choice for automotive testing applications. Motor dynamometers provide the best control response, while eddy current dynamometers can handle higher power at higher speeds.
Many dynamometers have built-in sensors for measuring torque and speed, which can be used to calculate power (see Appendix B). The latest trend is to expand from measuring torque to also measure torsional vibrations generated by pistons or other mechanical components.
Some dynamometers (especially AC and DC motor dynamometers) have a "drive" capability, which means that the braking load generated can drive the shaft in the positive direction.
Operating Modes
Dynamometers can operate in two control modes, open loop and closed loop.
Open Loop Mode
In open loop mode, the dynamometer control is set to a percentage of the available dynamometer output or load. In this mode, the load generated by the dynamometer is independent of throttle position, speed, and vehicle speed. Although manual operation of the dynamometer is permitted in open loop mode, computer automation ensures reliable and repeatable test results
.
In closed-loop mode, the load is related to a feedback signal determined by the test program. For example, in constant speed mode, the user can set a speed and keep the vehicle at that speed. Increases in throttle position are offset by increases in load, preventing the vehicle from exceeding the set speed. Several speed set points can be programmed in time, allowing the operator to slowly and gradually increase the vehicle's speed within the engine's speed range while monitoring engine parameters and their relationship to torque output.
Another example of a closed-loop application is terrain simulation, where the load is changed under computer control to simulate hill driving, cornering and other driving situations.
In most cases, continuous load adjustment is not possible using manual methods, so automated control systems must be used for test applications that require closed-loop control.


Application Examples

Here are the control system requirements for two typical dynamometer applications.
Chassis
You may be familiar with chassis dynamometers, which test vehicle performance based on speed and torque measurements of rollers (the roller's function: to make the vehicle transmission contact the wheels).



Text in the image:
integrated control system, automatic driver or driver's aid, operator interface, real-time control system, torque, speed, roll dynamometer The
chassis dynamometer shown here uses a control system to automate the test program while taking measurements and recording the measured data for later analysis. In some configurations, the control system directly "drives" the vehicle through the throttle and brake actuators. In other applications, the control system guides the driver's behavior during the test.
To maximize reliability, the control system should be built using real-time software tools. Real-time software, which is easy to install, can perform automated tasks with predictable response times. Microsoft Windows and other common operating systems are not well suited for controlling high-performance dynamometer test systems because they cannot predict response times.
However, PCs are often used as operator consoles because of their graphics and networking capabilities. Also, using a separate computer prevents operator actions from affecting the response of the real-time system.
Creating the application software is one of the most difficult tasks in building an integrated control system. Most real-time software tools require staff to develop and maintain special software libraries for handling real-time input/output interfaces and for handling the interaction between the real-time system and the operator interface. Turnkey system vendors can provide solutions that they have developed, but these solutions often require proprietary hardware and non-open software tools, which are expensive and have limited development capabilities.
To facilitate future expansion, the control system should be built with software tools that are inexpensive, easy to use, and compatible with a variety of sensors and systems. In the following paragraphs we will describe how National Instruments products can achieve this goal.
Engine
Now let's look at an engine test application. In this application, the engine can be self-tested (that is, outside the vehicle) by connecting the dynamometer directly to the engine drive shaft at the flywheel. The test system controller controls the throttle position and other engine inputs. In this application, the dynamometer has its own controller, which interacts with the test system controller through a serial connection.

Mustang dynamometer example
Text in the figure:
reference data and alarms, AC drive controller, speed, torque, real-time test cell controller, coolant system, fuel meter, oil system, high-speed network, operator interface The
figure above shows a typical engine test system that uses several independent devices to simulate the fuel, coolant, oil, electrical and other vehicle systems related to the engine. These systems may have their own parameters (such as temperature, pressure and flow) that must be controlled by the test system controller. The test system also usually includes safety interlocks and other interfaces related to the equipment, which are also managed by the test system controller.
Although not shown in the figure above, the engine is usually equipped with sensors to provide information about its internal operation. In actual production, the engine also uses bar codes or embedded flash memory to provide information about itself to the test system.
The integrated control system shown in the figure above is a typical system created by the system set members using National Instruments products. It is important to note that unlike other approaches, the real-time control system and signal input/output connections are all located within the test system. In addition, network connections replace the long and heavy cables in the original test system, which reduces installation and commissioning time and improves operational reliability and noise immunity.
Transmission
The goal of transmission applications is to test the performance of transmission, differential, and other transmission components. The drive motor applies controlled torque to the component under test at the input.


Integrated Control System

In an automated dynamometer test system, the control system has the following functions: I
· Operator interface
· Data logging
· Data acquisition
· Control engine/vehicle
· Control simulated driving environment

Development Tools
The following sections introduce National Instruments tools and methods that can be used to build a test system platform.
LabVIEW Real-Time Module
You may already be using the industry-standard LabVIEW graphical programming tool, which is the basis of the LabVIEW Real-Time Module. Using built-in LabVIEW libraries, you can quickly program hardware to complete the tasks of acquiring data, executing control loops, and communicating with instruments and devices from other vendors. While acquiring data, you can also analyze it in the time domain or frequency domain and make the analysis results immediately visible to the operator.
The LabVIEW Real-Time Module makes the LabVIEW graphical programming environment easier to use, allowing users to develop and configure real-time systems without in-depth knowledge of real-time technology or non-standard computer systems. By using the LabVIEW Real-Time Module, you can offload critical tasks to a real-time processor and have the tasks execute in a deterministic environment (i.e., "non-Windows"). Although the operator interface runs on a separate computer, it can run as an integrated application when combined with the real-time software. The PC communicates with the real-time processor via a high-speed Ethernet connection.
In dynamometer applications, the operator interface is used to configure and control the real-time control system. The real-time control system takes measurements and logs data to disk, while generating outputs that control the dynamometer, engine, and other equipment. The real-time system also executes the test programs that the user programs using the operator interface.
Note that this approach of using a single integrated system is much more cost-effective than other solutions that require separate devices for certain functions.
Modular PXI and SCXI Hardware
VME has been the most common industrial computer bus for real-time systems for the past 20 years, so many dynamometer control systems are still built using VME or VXI technology. Recently, however, the next generation CompactPCI bus has begun to be rapidly adopted in industrial environments.
National Instruments contributed to the development of PXI, which allows CompactPCI to be used in measurement and control applications. The configuration shown below includes a built-in real-time processor and PXI data acquisition and signal conditioning modules. Using a variety of chassis configurations and expansion options, it is easy to build a system with more slots, making it easy to increase the number of system channels.

Low-cost options
High-performance control systems are not necessary or appropriate for all applications. National Instruments offers the following options for customers who need less functionality:
LabVIEW Real-Time running on FieldPoint modules
LabVIEW Real-Time running on PC- and PXI-based data acquisition devices
All control and acquisition programs run in a Microsoft Windows environment

If you would like to learn more about real-time controllers, data acquisition, and signal conditioning, please visit http://www.ni.com/rt, http://ni.com/measurements, and http://www.ni.com/scxi.
Signal Input/Output
When creating your own control system, you must consider all the parameters that the system will handle.

Torque Actuator
Speed/Speed l Throttle Position
Horsepower l Brake Pedal
Temperature l Transmission
Pressure Digital Input/Output
Flow Environmental Conditions
Vibration/Noise l Barometric Pressure
Exhaust l Humidity
Engine Data
l Barcode
l Flash Memory

This list is not exhaustive, but it includes most of the common parameters required in dynamometer applications.
Measurement and control input/output of these signals can be done in several ways. Two common methods are to connect the sensors and actuators directly to the test system controller or to a device that performs a specific task (such as the AC dynamometer controller in the engine test example). Data can then be sent to the control system in the form of pure voltage or current or in the form of communication protocols such as RS-232, CAN, and GPIB.
The variety of signal interfaces can cause another problem when building a control system. Although it may be easy to determine the I/O requirements of the sensors and devices you are using, it is very difficult to predict the type of parameters and number of channels you will need a year from now. Your choices will be limited by proprietary solutions, especially when it comes to selecting special sensors and third-party instruments (such as exhaust emission analyzers) and when you need to expand an existing system to add additional I/O channels.

Sensor Communication Digital I/O
Microphone CAN Bus Counting
Accelerometer RS-232 Timing
Modbus Optically Isolated
Analog Output GP1B High Speed
Voltage Setpoint RS-422/485
Current Setpoint DeviceNet Other
Waveforms Ethernet Motion Control

The above table lists the types of sensors and signals that can be measured by National Instruments PXI modules. Although you may not need all of these features now, you will have them handy when you need them in the future. Built-in GPIB, RS-232, and RS-422/485 communication modules are compatible with most third-party instruments and subsystems.
Some types of sensors and signals require conditioning before they can be connected to a control system. National Instruments SCXI modules can provide the necessary excitation, isolation, multiplexing, and other signal conditioning when using the following types of sensors and signals.

Sensor Analog Input Digital Input/Output
Thermocouple Low Voltage TTL
RTD High Voltage 240VAC
Thermistor 0-20mA
Accelerometer Frequency to Voltage Conversion
LVDT, RVDT Resistor Multiplexer
Strain Gauge Matrix Transformer
Load Analog Output
Torque Voltage
Pressure



Current Conclusion

In this article, we have explored some of the factors driving the need for flexible dynamometer testing.
We have seen how LabVIEW Real-Time combines with PXI and SCXI hardware modules to form a comprehensive control solution that is flexible enough to meet your changing needs. The PXI platform allows users to integrate a variety of National Instruments and third-party components into a single, fully customizable system.


Contact Us

This article provides a brief introduction to the dynamometer testing tools and products available from National Instruments. If you have questions or would like to discuss your specific needs, please contact us at:
6F, Commercial Building, No. 800, Quyang Road, Shanghai (200437)
Tel: (021) 65557838
Fax: (021) 65556244
Email: china.info@ni.com
Web: ni.com/china
You can also refer to
more information about setting up your dynamometer with a National Instruments-based system or selecting a system integrator.
For more information about National Instruments products. Appendix A - Summary


of Common Test Parameters Control values include: Variable Engineering Unit Equipment Throttle, Brake Position % Actuator Load or Drive Torque lb ft, N m, % Dynamometer






Direct measurements include:
Variable Engineering Units Transducer
Force lb, N Dynamometer Torque
lb ft, N m Torque meter
Speed rpm Tachometer
Flow liters/s Flow meter
Pressure psi, psig, psia Pressure sensor
Temperature °C, °F Thermocouple, RTD
Exhaust emissions ppm, % Electrochemical, infrared Vibration
g Accelerometer
Noise Pa Microphone
Calculated values include:
Variable Engineering Units Derived from
Torque ft lb, N m Force, arm
Power hp, W Torque, speed
Speed mph, km/h Drum rate, diameter
Acceleration/deceleration m/s2, ft/s2 Speed
Braking force N Speed, vehicle mass
Fuel efficiency mpg Speed/flow or distance/total
Measurement and Control Terminology
Torque and Force
Torque is "twisting force." Torque is usually measured using a dynamometer connected to the engine flywheel or to a roller driven by the wheels.
The fundamental forces that affect a vehicle under actual driving conditions are:
Driving force (torque)
Braking
force Air resistance
Gravity (on an incline)

Some test procedures require that the dynamometer simulate these forces.
Horsepower
Horsepower is a measure of the power output of an engine. Horsepower can be calculated as follows:
Horsepower = Torque (lb ft/s) x Speed / 5252
Therefore, by measuring speed and torque, the power output can be calculated.
Note: See Appendix B - Torque and Horsepower Relationship for a detailed description of torque and horsepower.

Vehicle Speed and Speed
Vehicle speed and speed are used to calculate horsepower and acceleration. For display or analysis purposes, the measured parameter value is usually plotted against speed or speed.
Temperature and Pressure
Temperature and pressure conditions have a direct effect on engine and vehicle performance. Temperature and pressure parameters can be measured at:
· Ambient (barometric pressure)
· Oil
· Coolant
· Manifold
· Fuel
· Exhaust
· Brakes and brake fluids

Fuel and fluid flow
Fuel efficiency (miles per gallon or kilometers per liter) is an important performance parameter for customer satisfaction and regulatory compliance. Fuel efficiency is calculated from fuel and vehicle speed.
Air/fuel ratio is another important value that is calculated from fuel flow and air flow.
Vehicle Control
· Vehicle and engine control values include:
· Throttle position
· Brake position
· Transmission position

Discrete digital signals
Discrete digital signals are either on/off state indicators or control connections.
Noise and Vibration
Noise and vibration are frequency domain parameters that are important in evaluating noise, vibration and harshness (NVH) design factors. . Exhaust Low
exhaust
volume is important in meeting environmental regulations. Commonly measured exhaust gases include:
· Oxygen
· Carbon dioxide
· Carbon monoxide
· Nitrogen oxides
· Methane and other hydrocarbons

Third-party gas analyzers are used in test applications that require the measurement of gaseous emissions.


Appendix B - Torque vs. HorsepowerTorque

is the twisting force produced by an engine (usually measured in pound-feet).
Torque is defined (and often calculated) as the length of the moment arm multiplied by the normal force applied to the moment arm. The moment arm is the distance from the center of a rotating shaft (such as an axle or drive shaft) to the point where the force is applied (such as the surface of a tire in contact with the ground), and the moment arm is measured in feet.Torque

= force x moment arm (lb ft)
Text in the figure: moment arm, torque, forceNote

: The metric unit of torque is Newton-meter (N m).Note

: Engine torque is not the same as wheel torque because the gearing in the drive train changes the moment arm.As we can see below, power is proportional to speed and torque. In theory, power remains constant during the transmission process, so the ratio of wheel torque to engine torque is proportional to the ratio of engine speed to wheel speed.The
term "horsepower" was first coined by James Watt, who compared his steam engine to a horse. He found that a strong horse could lift a 150-pound object 220 feet in 60 seconds. So Watt wanted to know how many horses his steam engine could replace.


Note: It is important to distinguish between pounds, which measure force, and pounds, which measure mass. One pound of mass represents one pound of vertical force (weight) in a gravitational field. In the example of the horse lifting the weight, the lifting force is against the force of gravity. Obviously, if the horse were pulling the weight along the ground, the force required to move the weight would be completely different. So the pounds discussed here refer to force, not mass or weight.
Work is the effort required to exert a force over a given distance. In Watt's example, work is the effort required to lift the 150-pound weight 220 feet.
Work = Force x Distance (lb ft)
Power is the speed at which work is performed. In Watt's example, a 1-horsepower engine could lift the 150-pound weight 220 feet in 60 seconds, while a 2-horsepower engine could do the same in 30 seconds.
Power = Work / Time (lb ft/s)
= Force x Distance / Time
Watts determine horsepower as:
1 horsepower = 150 lb x 220 ft / 60 s = 550 (lb ft/s)
Note: The metric unit of power is the watt (1 W = 1 N m/s).
1 hp = 746 WHorsepower
is related to torque as follows:
Power (lb-ft/s) = Force (lb) x Distance (ft) / Time (s)
For the wheels,
Distance = Circumference x Revolutions
= 2 P x R (Radius or moment arm in feet) x Revolutions
Therefore,
Power = Force x 2 P x moment arm x Revolutions / Time
= Torque x 2 P x Revolutions / Time
= Torque x 2 P x Speed (rpm) / 60 (s/minute)
= Torque x Speed x 2 P / 60
horsepower = Power / 550 (lb ft/s)
= Torque x Speed x 2 P / (60 x 550)
horsepower = Torque x Speed / 5252

xiumuzhai

A speed can be set and the vehicle will always travel at that speed. Increases in throttle position are counteracted by increases in load, preventing the vehicle from exceeding the set speed. Several speed set points can be programmed over time, allowing the operator to slowly and gradually increase the vehicle's speed within the engine's speed range, monitoring engine parameters and their relationship to torque output. This is pretty cool.