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Chapter 3: ‘Brake’ Style Dyno Setup
Brake (Absorber) Style Dyno Setup (cont.)
Open Loop systems- You control he load manually, DYNerta3 does not have control over the brake.
Closed Loop systems- You can enter an RPM/speed and have DYNertia3 vary the load to maintain that RPM
automatically i.e. the load controller unit directly controls the brake and observes the result to allow continual adjustment.
Note: Basic DYNertia3 system alone does not control the actual brake/retarder load, this must be manually controlled. It
has ‘open loop’ functionality i.e. you cannot enter an RPM and have DYNertia3 vary the load to maintain that RPM
automatically.
For ‘closed loop’ control you need the optional ‘Load Controller’ hardware unit. For closed loop control of your load
please see web site for information on the ‘Load controller’ unit (also see the ‘Load Controller’ chapter in this manual).
In Brake mode, DYNertia3 uses Torque data from the load cell and roller RPM calculate Power. The measured Torque
is corrected to engine RPM (calculated from the dyno’s included sensor and ratio information or measured directly from
the engine). If the ratios are set incorrect then the readings will be incorrect i.e. if you just use roller RPM on a chassis
dyno then Torque will be shown as it appears at the roller only and not related to engine RPM. This is called ‘Tractive
Torque’ (Torque at the tyre) and will be higher than engine Torque due to the gears multiplying effects. It is really the
Torque delivered to the road and can be used as an effective tunning tool due to the increase in Torque resolution!
Variations
As noted earlier, some brake style dyno use a hydraulic cylinder (like a vehicle ‘master cylinder’) as the ‘load cell’, by
fitting a pressure sensor into the cylinder this provides the torque output. Alternatively some very old systems use a
spring assembly to counter the brakes rotation and then measure the displacement of this with a linear potentiometer
(position sensor).
Both can be interfaced into DYNertia3!
Mechanical instability will cause poor quality data, some old friction style brake dyno’s even have shock absorbers to
dampen movement (those just mentioned with springs in their load measurement system).
It can be very difficult to allow steady rising of the RPM for a ‘run’ without a good control system for your load, friction
brake systems are particularly difficult to operate smoothly and are often best operated for brief ‘steady state’ tunning
(‘Point by Point‘ mode is ideal). Excessive Inertia in your system can also cause difficulties on low power engines i.e. the
inertia load can end up limiting the acceleration during a test and not the load absorber device.
Types of testing used with brake (retarder/absorber) style dyno’s
Two main tests can be performed with a brake style dyno, a ‘ramp run’ or a ‘steady state’ test-
A ‘steady state’ test is where the load is applied until the engine RPM reaches a desired set point (with a fixed throttle
opening) and data is then recorded and displayed at that speed.
A ‘ramp’ test is performed by adjusting the brake load to allow the engine to accelerate through the RPM range whilst
DYNertia3 graphs the Power using the load cell as a Torque input.
Load cell calibration and wiring for Brake type
Please see the chapter on ‘Load Controller’ as the wiring and calibration procedures are explained there. Open loop or
closed loop control still uses the same load cell configuration.
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