MRE crank sensor

[JohnC]

Toyota have begun using MRE (Magnetic Resistance Element) sensors in their 2007 engines. These things are like a cross between VR (mag pickup) and Hall sensors, and they're really slick because they produce a crisp square wave output regardless of RPM, like a Hall sensor, but they operate from a simple toothed gear and don't require the rare earth magnets to be embedded in the gear as a Hall does.

Seems like they'd be a perfect swap-out for VR (mag pickup) type sensors. And with their RPM independent, clean square wave output, they should offer some real improvement for stabilising timing in EFI systems.

Denso, the manufacturer, has this to say about them:

Benefits and Features (MRE Type)

• High detection accuracy
  • DENSO’s cam/crank position sensors use a unique arrangement of two pair of MREs on an IC chip, achieving high detection accuracy, including just after the engine starts. The MRE cam/crank position sensors have almost 10 times higher sensitivity than Hall element cam/crank position sensors.
  • In DENSO’s MRE cam/crank position sensor, the molded IC chip is installed inside a cylindrical magnet, which means the IC chip is positioned closer to rotor gears rotating with the cam or crank shaft, providing even higher sensitivity.
• High reliability
  • The molded IC chip and the cylindrical magnet are integrally covered with poly phenylene sulfide(PPS) resin for greater strength.
  • PPS resin has high resistance to chemical substances including fuel, engine oil and emissions

[Hammer]

does this sensor make it's own voltage like a VRS, or does it require a 5V or so reference voltage like a hall-effect?

[JohnC]

It requires a power supply, then it outputs a certain voltage depending on the value of a pullup resistor in the circuit. Here's a cut sheet for one of these devices from the Cherry Switch catalog.

[Hammer]

well I really can't read any of that, but it seems to me like it's very similar to a Hall Effect, digital signal, and requires a source voltage and all.

[JohnC]

Sorry for the quality, but yes, it's very similar to a Hall's wiring (in fact this device is 2 Hall sensors set up in a differential circuit, but it doesn't require the magnets that a single Hall does)

Here's some more information about its power requirements and output:

Current Sink Interfacing

3-Wire Sinking Interface

Sinking outputs are often used in negative logic applications, where a low signal is required

for an active state. There, sinking outputs normally have current flowing into the device output
lead when the device is active. Also called “open collector outputs,” sinking outputs are
compatible with any logic family since a wide voltage range may be used for Vcc. Furthermore,
the voltage level used to power the Hall effect assembly may differ from the pull-up resistor
to which it is attached. The external pull-up resister connected between the output and Vcc
is required for proper operation. With the resistor connected as shown, the output will be
“pulled up” to Vcc when off and (approximately) to ground when on.
Recommended pull-up resistor values are as follows:

Volts dc

5 9 12 15 24

Ohms

470 820 1.2k 1.5k 2.2k