System Concept

The purpose of this project was to design and assemble an engine dynamometer to be used by the RIT Department of Mechanical Engineering and the RIT Formula SAE Racing Team. Useful engine data is recorded and processed using National Instruments hardware and software. Design emphasis was placed on sub-system compatibility, ease of operation, and overall robust design and reliability.

Engine Powertrain

The engine used for this project is a Honda CBR 600 motorcycle, which is what the RIT Formula SAE Racing Team uses for competition in the car. The engine was originally designed with four constant velocity carburetors for fuel management; one carburetor for each cylinder. The RIT Formula SAE Racing Team has modified the engine to use a computer controlled fuel injection system for many years. Through the years the system has changed along with advances in fuel injection technology.
The use of a fuel injection system over a carburetor has many advantages in the areas of tuning, performance, economy, and reliability. Integrating ignition control into the engine management system helps make the system even more flexible, allowing the engineer to coordinate ignition timing changes with fuel settings to further optimize the engine control system.
An engine cradle was built specifically for the Honda CBR 600 motorcycle engine. The cradle picks up four of the six stock mounting points on the engine and is attached to the dynamometer frame with four mounting bolts. This setup was chosen because it allows for other engines to be adapted to the dynamometer with only a new cradle necessary to fit the mounting point of the new engine.
The engine cradle bolts down to a steel plate, which has a pattern of tapped holes in it allowing for flexibility in mounting various components to the dynamometer such as exhaust brackets.
Power transfer between the Honda CBR600 engine and the DC motor is accomplished with a chain drive, similar to that used on the Honda motorcycle. The chain acts as a damper and absorbs the shock caused by fluctuations in the engine’s power strokes so not to fatigue the crankshaft. The chain drive was designed with a reduction ratio of 2.50 in order to decrease the output speed of the engine to an acceptable range for the DC motor.

DC Motor / Powertrain

The dynamometer uses a DC motor to place a mechanical load on the Formula SAE team’s CBR 600 motorcycle engine. Current power output of this engine is 76 peak HP. The dynamometer is designed with a power handling capacity of 120 HP to account for possible increases in engine power output. The motor we chose to implement was built in Germany by Siemens Automation and Drives. Siemens donated a brand new motor that we chose from their catalog. The motor has a 470 V armature and a torque rating of 795 Nm with an efficiency of 86%. The DC motor is controlled by a Dyne Systems DynLoc IV dynamometer controller. The controller manages all aspects of motor function during dynamometer operation through closed loop control using RPM and torque feedback values. The motor is trunnion mounted, which means it is suspended from the drive shafts that protrude from both ends. We specifically ordered the motor to have a shaft protruding from both ends of the motor for this purpose. This method of securing the motor leaves the motor case free to rotate and apply measurable torque to a load cell mounted on the motor’s case. This load cell then provides feedback to the Dyn-Loc controller.

Data Aquisition

The data acquisition system implemented on the dynamometer is a professional, modern system providing both Formula SAE and the Mechanical Engineering Department at RIT with the capabilities necessary for engine tuning, education, and independent research. The sensor requirements for this project were determined by soliciting faculty and Formula SAE members, as well as relying on the team’s best judgment. Parameters monitored and logged on the dynamometer are:

Cylinder Pressure
Fuel Pressure
Oil Pressure
Manifold Absolute Pressure (MAP)
Air / Fuel Ratio
Exhaust Gas Temperature
Intake Air Temperature
Radiator Inlet and Outlet Water Temperature
Radiator Inlet and Outlet Air Temperature
Oil Temperature
Mass Air Flow
Crankshaft Position and Speed

In addition to the engine parameters acquired, the essential function of the dynamometer requires measurements of:

DC Motor Speed
DC Motor Load Torque

The systems hardware requirements are supplemented by using products from National Instruments. The adaptability and excellence of these components provides the professional quality that was demanded by this project. The DAQ card that is used is a PCI-6034E which features a 200 kHz sample rate, 16 single-ended / 8 differential analog inputs and 8 digital I/O’s (DIO). This unit is connected to an SCXI-1001 chassis, which houses and powers the other input modules. The Mechanical Engineering Department was the primary source of sponsorship in this area with their donating of a full system of hardware to interface with all the necessary sensors.
Cylinder pressure measurements are made using charge type pressure transducers from PCB Piezotronics. The 112B10 combustion sensors that were selected utilize an adaptor integral to the spark plug for easy mounting to any CBR600 engine. A National Instruments SCXI-1531 Accelerometer Input Module is used along with charge amplifiers from PCB to meet the necessary signal conditioning requirements of these sensors.
Fuel and oil pressure measurements are taken using strain gage type pressure transducers from Omegadyne. The units that were selected have built in signal conditioning for a 0-10Vdc output, operate on unregulated 24Vdc, and have an accuracy of ±0.25% FS. A 0-100 psig range is used for fuel pressure while the oil pressure measurement utilizes a 0-150 psig range.
Pressure measurements in the intake manifold are made using a Bosch PSC-A MAP sensor. This is an OEM type piezoresistive strain gage transducer that provides measurements from 3 to 15 psia with a standard 0-5Vdc output.
Measurements for air/fuel ratio are sampled using a Bosch LSU-4 Lambda Sensor (Wide-band O2), which is also used by the Motec ECU for closed-loop fuel compensation. The 0-5Vdc output of this sensor is wired to a differential voltage channel of the DAQ card.
Temperature data is acquired using thermocouples from Omega. Most measurements are made using sheathed K-types with an ungrounded junction. The exception is the intake air temperature measurement, which requires a higher degree of accuracy. This measurement is made using an exposed, ungrounded junction T-type thermocouple. Signal conditioning and cold-junction compensation are handled by National Instruments hardware, mainly a TC-2095 Terminal Block and SCXI-1102 Thermocouple Input Module with multiplexing.
Mass airflow is measured using a Delphi constant temperature hot-wire anemometer. To ensure consistent data, a special pre-manifold intake system was fabricated to provide the proper flow conditions for this anemometer.
To monitor engine speed and position and to trigger the cylinder pressure measurements, an encoder from BEI Industrial Encoders was implemented. The model used is a H25 incremental optical encoder with a minimum increment of ¼° and maximum speed of 12,000 RPM.
To calculate the power output of the engine, both torque and speed of the DC motor are measured. To obtain torque, a load cell is coupled to a torque arm attached to the DC motor. The load cell used is an Interface SM-500, which features a 3mV/V output and 500 lb capacity. The load cell is connected to the dynamometer controller, which provides excitation voltage and signal conditioning. Speed measurements are made using a hall-effect type sensor and a 60-tooth gear mounted to DC motor’s output shaft. This sensor also interfaces directly with the Dyn-Loc dynamometer controller. Both torque and speed measurements are used in conjunction to control load and speed of the DC motor via Dyn-Loc Controller. The analog output from both of these sensors is coupled to the DAQ system via a BNC-2095 Terminal Block and SCXI-1104 Multiplexer Input Module to provide a graphical display of power and torque.

Closed Loop Control

Dynamometer control is performed by a Windows XP PC-based application coded in National Instruments’ LabVIEW programming language. This application accomplishes every part of a dynamometer test run except physically starting the engine. In order to do this, the GUI integrates control of the DynLoc controller, the engine throttle, clutch, and the National Instruments DAQ hardware. The GUI can operate in two main modes: manual and automatic. Automatic mode consists of two sub modes, which are regular dyno run mode and a calibration mode for the ECU.
Control of the DynLoc is accomplished through serial communication between the RS-232 ports of the DynLoc and the PC. By communicating with the DynLoc the GUI can control all aspects of the DC motor operation, including rpm or torque setpoints and the rate of change when transitioning from one setpoint to another. A simple library of LabVIEW functions was created so that a LabVIEW programmer can control the DynLoc even with no understanding of the DynLoc’s native ASCII command format. This will simplify any maintenance or upgrades that the FSAE team or ME department may wish to perform on the GUI in the future.
A single-acting pneumatic cylinder powered by shop air actuates the clutch. The GUI controls the cylinder with a DIO line which is connected to a solid state relay to step up the control voltage from 5v to 12v before being connected to a solenoid operated valve to direct airflow to the cylinder. This system disengages the clutch with the cylinder and relies on the clutch’s internal spring force to return the clutch when air pressure is removed from the cylinder.
The throttle is actuated by an electric stepper motor with 200 steps per revolution, 21 Ohms per coil and 12v input voltage. The stepper motor is controlled by an Allegro UNC5804B Unipolar Stepper Motor Driver/Translator IC, which includes integrated power transistors to drive the motor. This IC is capable of driving 1.25A per phase, well above the 0.6A per phase required by the stepper motor in use. The GUI controls the throttle by providing 2 control signals to the UNC5804B: the direction and step input controls. The direction control signal is provided by a DIO line from the 6034E card. The step input tells the UNC5804B when to move the motor; the motor is moved one step every time a falling edge occurs at the step input control. Control of this input is provided by sending pulses from a counter output on the 6034E card.
Physical controls of the clutch and throttle exist to that the engine can be controlled with no inputs from the computer if desired. Also, a separate physical emergency shutdown button is available in case the GUI loses control of the dynamometer.

Engine Cooling & Exhaust

The cooling of the internal combustion engine is achieved through methods used in all modern day vehicles. The main components include a traditional automotive radiator, water pump, and cooling fan. Rubber hoses connect the engine directly to the radiator, and the intake line takes the hot water from the engine and runs it through the radiator. After the cooled fluid exits the radiator it runs through a line that returns it back to the engine. Ball valves are included in the lines to stop the flow of water if the engine is removed. Rubber lines are used and clamped at the connections, which minimizes the time needed to remove and replace an engine. The water pump in conjunction with the thermostat controls the fluid motion through the whole system. Water is used with no anti-freeze in the system because FSAE race teams competing at events are required to use only water in their vehicle cooling systems for environmental reasons. Therefore, our dynamometer system follows those requirements to develop accurate data so that there is no difference from competition and testing.
Special consideration was given to this section to guarantee that the removal of the exhaust gases does not affect engine performance. The main components of this system include a vacuum pump, hose, nozzle, and muffler. The FSAE designed muffler is attached to the Honda engine. The engine creates a large amount of noise that is subdued mostly by the enclosed room, but the muffler reduces the noise even further. We intended to reduce the noise so that it does not distract anyone in the college of engineering when testing is conducted. Following the muffler, the exhaust gases enter a nozzle that will increase the velocity of the air from approximately 600FPM at the inlet to 1500FPM at the Plymovent connection. The nozzle is not directly connected to the muffler but instead is suspended above it.
The Plymovent has the capability of actually pulling air through the engine and affecting performance. In order to not increase the volumetric efficiency of the engine while exhausting the gases out of the room, a nozzle was designed for the end of the Plymovent hose. The nozzle increases the sir speed from 676FPM at the inlet to 1521FPM at the outlet. A series of 2 readily available HVAC increasers were used in the design. The nozzle is 4 inches on the hose side and 12 inches at the end open to ambient air.
The other end of this Nozzle attaches to the vacuum device manufactured by Plymovent. It pulls the exhaust gases from the room to the outside of the building. The Plymovent system has a hose that is retractable so it can be attached to the nozzle during testing and recoiled out of the way when not in use. Calculations were performed to determine the size of the nozzle required to bring the velocity of the exhaust gas leaving the muffler to nearly 0mph.
Finally, combustion of fuel in an engine creates harmful gases so a carbon monoxide sensor is installed in the room for precaution. The FSAE team already is in possession of one and uses it with the current system.