What is a Transmission Dynamometer?
This article is the third in a series of three articles highlighting the basics of dynamometer testing. In the first article, "What is an Engine Dynamometer?" we reviewed the principle components of the water brake engine dynamometer (dyno) and how they work. In the second article, "What is a Chassis Dynamometer?" we reviewed the principle components of chassis dynos.
A transmission dynamometer is a service tool that allows the operator to safely place a controlled load on a transmission once it has been removed from the vehicle. With the use of a dynamometer, a vehicle's transmission and differential as well as transmission components such as the valve body and torque converter can be properly operated throughout a transmission's power and speed range. Assembly deficiencies may be detected before the transmission is reinstalled and an actual evaluation of a transmission's operating condition may be performed. The dynamometer is the final quality test before a transmission is put into service. Construction
The main component of a transmission dynamometer system is the transmission test stand. The transmission test stand consists of the stand, a prime mover (electric or hydrostatic), and an absorption unit.
Transmission dynamometers use a variety of power sources as prime movers, but hydrostatic drives and electric motor drives are two common ones used. Hydrostatic drives use an electric motor or combustion engine to power a hydraulic pump which powers the hydrostatic drive unit. These systems provide excellent torque capability and are ideal for locations that do not have the power source for a large electric motor to be used as a prime mover to drive the transmission directly. Electric motors as a prime mover are typically quieter and more compact than a hydrostatic drive, but require an adequate electrical power source. Absorption units were discussed in our previous articles, "What is an Engine Dynamometer?" and "What is a Chassis Dynamometer?" As in a chassis dyno, most transmission dynamometers are equipped with eddy current absorption units. An eddy current absorber uses electrical current to produce a load. Eddy current dynamometers require an electrically conductive core, shaft or disc, moving across a magnetic field to produce resistance to movement. Available in both air cooled and liquid cooled applications, eddy current chassis dynamometers provide quick response rates. The housing of an eddy current absorber is restrained by a torque arm within the chassis dynamometer assembly that is connected to a load cell.
In all cases, the absorption unit is restrained using a torque arm that is connected to a load cell. The load cell measures the force with which the stators are trying to rotate.
In addition to measuring the torque capabilities of the transmission being tested, tranny dynamometers also use the load created by the absorption unit to cause the transmission to shift as it would when placed in a vehicle. The combination of the input speed from the transmission test stand's prime mover and the load from the absorption unit simulates the conditions the transmission would encounter when in operation. This results in a transmission running through a complete series of up shifts and down shifts as speed and load are applied. Operation
A transmission is mounted to the transmission test stand and is coupled to the load absorption unit via a guarded drive shaft. The transmission then performs a series of tests that often mimics the operating conditions the transmission would face during its intended use. During a test, the transmission will operate at numerous speeds under varying loads which will result in automatic shifting. Manual shifts can also be performed by an operator, or through an automated test depending on the control system supplied with the trans dyno.
Transmission dynamometers are capable of performing the following tests:
- Check shift points (automatic transmission test)
- Set shift points (automatic transmission test)
- Full and closed throttle upshift and downshift test (loaded or unloaded)
- Downshift inhibitor test
- Measure output torque (stall test)
- Locate shaft seal leaks
- Identify clutch leakage
- Check noise/vibration
- Detect mechanical binding
- Check main, clutch and converter pressure
- Monitor converter flow and temperature
- Determine converter inlet and outlet pressure
What makes up a Transmission Dynamometer System?
The transmission test stand itself is only one component of a complete transmission dynamometer system. A typical dynamometer system consists of a transmission test stand, a manual/electric shift console, and a data acquisition and control system.
Shift Console
Shift consoles, such as AIDCO Test Systems ESC, provide a variety of shifting capabilities when used in conjunction with a transmission test stand. Top-panel mounted diagnostic plugs simplify reprogramming of the corresponding TCM/ECU (if provided) and allow for quick diagnosis when troubleshooting the transmission during a test. A convenient main harness connects the console to the transmission.
Data Acquisition and Control Systems
A typical dynamometer controller contains the dyno system's pressure and temperature sensors. The sensors are housed inside an industrial cabinet and are supplied with quick disconnects. Information is collected from the sensors and in many cases a TCU/ECM and combined with power measurements, speed measurements, and torque measurements from the dynamometer and sent to the dynamometer system's computer.
The computer in a data acquisition and dyno control system connects with the dynamometer controller and the dynamometer and performs all of the embedded control functions. It is also the location where new tests are run and reports are generated, printed, and stored.
For more than 30 years, Power Test has been an industry leader in the design, manufacture, and implementation of dynamometers and dyno control systems. Power Test has provided dynos and data acquisition and dynamometer control systems to manufacturers, rebuilding facilities, and distributors worldwide, with products in over 75 countries on six continents.