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The wonders of the Torque Load SensorTake a peek into this electronic control window and see how technology is shaping modern farm machinery and the things you can do with itby KEITH BERGLINDPlease accept this story as a brief look into the marvelous electronic systems that are being built into our new machinery.The newest Case IH tractor, model MXU, has a transmission that is described as a 16 x 16 (speeds) Semi-powershift with Auto feature. There are a number of operating situations where up-shifts and downshifts are made by the electronic controller. The operator has the choice of being in or out of this Auto mode, just with the touch of a button. I'm not here today to promote the tractor or its transmission. I recently attended a Case IH national sales training program in the United States, and this information showed up. So, I thought readers would like a look into this electronic control window. Future owners or operators can tell us later how they benefit from all this technology. Electronics are wonderful, and it's a pleasure to see it put to better use than DVD players and cell phones. The source of the work information is the flywheel-mounted Torque Load Sensor. This is a mechanical device, with springs and arms, looking a lot like the centre of a regular clutch disc. The purpose of this device is to "measure" the amount of torque going from the engine to the transmission. From what we could see, the input and output sections have springs trying to centre the parts. As the rotational torque being transmitted increases, the two discs will move out of "centre" alignment, giving a plus or minus reading. Now, take a moment and consider the speed sensors used on vehicles and machinery. A small stationary sensor sits close to a rotating part. There is a small magnetic field, connected to the machine controller. When some part of the moving part breaks the magnetic field, the controller reads this as a pulse. The field break or pulse can be caused by a bolt head or a notch in the rotating ring. Often, a keyway on a shaft is used for shaft speed. The controller uses these pulses to time the ignition, measure speed or engage the fuel injection. In this Auto Shift transmission, the relative position of the input and output lugs will signal speed and torque load. The tractor controller will use this information to select the correct gear for the operating conditions. So, just imagine these two spring-centred discs. The two signal marks start out neutral, and the controller will be only interested in the speed. But, as the engine goes to work and loads down, the springs compress and the lugs move apart. The sensors now monitor this spreading of the lugs, as this is a direct measure of the engine torque. We can now believe that if a limit is reached, the transmission will shift to a lower gear. That would be too easy for this machine. The tractor controller has some thinking to do. What matters next is the difference between down-shifting under full load or up-shifting under low load. Automatic down-shift occurs when: (A) Engine speed falls below 1,000 rpm, or (B) The torque reaches a pre-set limit. Automatic up-shift occurs when: (A) Engine speed exceeds 2,200 rpm, or (B) Engine speed is between 1,250 and 1,500 RPM and torque allied to the drive-train is sufficiently low. Coasting: The flywheel torque device can read both + and - positions. Therefore, loaded downhill coasting can be monitored by the tractor controller.BF
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