The present invention relates generally to pressure switches, and more particularly to non-contact pressure switches for vehicles.
Pressure switch manifolds are used in automotive transmission applications for direct sensing of fluid pressure. Applications include hydraulic feedback gear selection, shift timing/feel control, torque converter clutch control, solenoid feedback control, solenoid fault detection, and improved idle control.
As understood herein, contacting technology, in which case hydraulic pressure deflects or moves a diaphragm or spring loaded piston to create a short circuit condition that closes the contacting switch at a predefined hydraulic pressure valve, can be used but these structures are susceptible to contamination, corrosion, and wear. Furthermore, conductive particle contamination can generate the close (short switch) condition without pressure actuation, and corrosion and wear can prevent the close with pressure actuation.
As further understood herein, non-contact switches such as those that operate using the Hall effect tend to require a moving part to travel a distance that can be too large to be accommodated in certain applications, such as in vehicle transmissions. With these critical recognitions in mind, the invention herein is provided.
A pressure switch assembly includes a sensor body juxtaposable with a fluid chamber and a piston disposed in the sensor body for reciprocal movement therein. A deflectable diaphragm is interposed between the piston and fluid chamber, with a spring urging the piston against the diaphragm. A magnet is coupled to the piston, and a Hall effect sensor defining a field threshold line outputs a signal that is affected by the position of the magnet in the sensor body. An axial midpoint of the magnet is on a first side of the field threshold line when the piston is urged by the spring to a depressurized position. On the other hand, the axial midpoint of the magnet is on a second side of the field threshold line when pressure in the chamber deflects the diaphragm to move the piston to a pressurized position.
The field threshold line may be along the axial midpoint of the Hall effect sensor. In some embodiments a portion of the magnet is above the field threshold line in the depressurized position and another portion of the magnet is below the field threshold line in the pressurized position. As pressure in the chamber moves the piston and, hence, the axial midpoint of the magnet across the field threshold line, the magnetic field at the Hall effect sensor prominently changes direction, resulting in a pronounced change in an output of the Hall effect sensor.
In another aspect, a method for sensing pressure includes moving a piston under fluid pressure to change a magnetic field in which a Hall sensor is disposed. The field changes polarity at a field threshold line of the Hall sensor at a predetermined piston position. A magnet generates the magnetic field and is coupled to the piston such that portions of the magnet remain on both sides of the field threshold line throughout an entire range of travel of the piston.
In still another aspect, a non-contact pressure switch assembly for sensing pressure in a vehicle includes a sensor body, a Hall sensor associated with the sensor body, and a piston with integrated magnet reciprocatingly disposed in the sensor body. The piston with magnet is moved under fluid pressure to change a magnetic field in which the Hall sensor is disposed. The field changes polarity at the Hall sensor at a predetermined piston position, and the magnet at all times straddles the Hall sensor in the dimension define by piston movement.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which:
The present invention overcomes the drawbacks associated with contacting switches by using a non-contacting magnetic switch. As contemplated herein, the present switch may be used but is not limited to an automotive transmission.
A piston 24 is disposed in the body 20 against the diaphragm 22 for reciprocating movement along an axis between a depressurized position, shown in
As shown, a spring 26 is trapped in compression between the piston 24 and a cover 28 that is rigidly coupled to the body 18, such that the spring 26 urges the piston 24 toward the depressurized position of
If desired, in the non-limiting implementation shown the spring 26 fits into the piston 24, which in turn may define an annular holder 31 around which the lower portion of the spring 26 is disposed as shown to radially support the spring 26. Also if desired, the cover 28 may include a central alignment dome 28a around which the upper portion of the spring 26 is disposed.
In accordance with present principles, a permanent magnet 32 having a north pole “N” and a south pole “S” can be integrated with the piston 24 as by, e.g., press fitting into a side of the piston 24. Also, a Hall sensor 34, which may be mounted on a circuit board 36 and disposed in a sealed chamber 38 that adjoins the sensor body 18, is juxtaposed with the magnet 32 as shown.
The Hall sensor 34 defines a field threshold “T”, shown in
In the depressurized configuration of
On the other hand, in the pressurized configuration of
Accordingly, it is now to be appreciated that as the pressure in the chamber 20 moves the piston 24 (and, hence, the axial midpoint of the magnet 32) across the sense threshold “T”, the magnetic field at the Hall sensor 34 prominently changes direction, resulting in a pronounced change in the output of the Hall sensor. Thus, the Hall sensor 24 changes output state at the threshold “T”, with the spring 24 being pre-loaded accordingly. With this cooperation of structure, the total axial “throw” of the piston 24 is relatively small, yet it advantageously results in a pronounced Hall sensor output change.
While the particular NON-CONTACT PRESSURE SWITCH ASSEMBLY is herein shown and described in detail, it is to be understood that the subject matter which is encompassed by the present invention is limited only by the claims.