Diagnostic detection for hall effect digital gear tooth sensors and related method

• US 5,844,411 A
• Filed: 05/31/1995
• Issued: 12/01/1998
• Est. Priority Date: 05/31/1995
• Status: Expired due to Fees

• Current Assignee: Borg-Warner Automotive Incorporated (BorgWarner Incorporated)
• Original Assignee: Borg-Warner Automotive Incorporated (BorgWarner Incorporated)
• Inventors: Vogt, Carl Randall
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US08/455,049
• Time in Patent Office: 1,280 Days
• Field of Search: 324/207.2, 324/251, 324/207.21, 324/252, 324/207.12, 324/173, 324/174, 324/166, 324/207.25, 324/160, 324/537, 327/510, 327/511, 338/32 R, 338/32 H
• US Class Current: 324/537
• CPC Class Codes: B60K 23/08 for changing number of driven wheels , for switching from driving one axle to driving two or more axles B60K17/3515 takes precedence
• CPC Class Codes: G01P 21/02 of speedometers
• CPC Class Codes: G01R 31/007 using microprocessors or computers
• CPC Class Codes: G01R 33/07 Hall effect devices

Abstract

The present invention provides a diagnostic circuit for detecting fault conditions in a Hall effect digital gear tooth sensor in a vehicle'"'"'s four-wheel drive system. The diagnostic circuit includes a voltage divider circuit connected to a window comparator circuit which is interfaced with a four-wheel drive system controller. Fault conditions, normally difficult to detect in a Hall effect sensor because of the usual open collector configuration, are detected and identified depending on the type and location of the fault. In an alternate embodiment, a safety feature is added to the voltage divider circuit to indicate a fault and prevent gear shifting in the event that the supply voltage and ground wires are inadvertently reversed.

Claims

1. A device for detecting a fault condition in a Hall effect sensor circuit, said device comprising:

a Hall effect sensor (400) comprising a first terminal (410) corresponding to supply voltage (411), a second terminal (420) corresponding to ground (421), and a third terminal (430) corresponding to output (431);

a voltage divider circuit (200) being connected to said Hall effect sensor (400), said voltage divider circuit including a reference signal line corresponding to the supply voltage of said Hall effect sensor and a speed signal line corresponding to an output of said voltage divider circuit, said voltage divider circuit (200) comprising;

a series resistor (210) being connected to the output (431) of said Hall effect sensor (400);

a pull-up resistor (220) being connected to said series resistor (210) and also being connected to the supply voltage (411) of said Hall effect sensor (400); and

,

a pull-down resistor (365 &

     366) being connected between the ground (421) of said Hall effect sensor (400) and also being connected to said series and pull-up resistors (210 &

     220);

a window comparator circuit (300) being connected to said voltage divider circuit (200), said window comparator circuit (300) comparing the output voltage of said voltage divider circuit (200) and the supply voltage of said Hall effect sensor (400) and generating a fault condition signal indicating a fault condition when an output voltage of said window comparator circuit (300) rises above a predetermined upper limit or falls below a predetermined lower limit; and

,

means for indicating when said window comparator circuit (300) generates the fault condition signal, said indicating means being connected to said window comparator circuit (300).

2. The device according to claim 1 further comprising a system controller (500), said system controller (500) being interfaced between said window comparator circuit (300) and said indicating means.

3. The device according to claim 1 wherein said series resistor (210) has a value of 685Ω

, said pull-down resistor (220) has a value of 10KΩ

, and said pull-up resistor (365 &

     366) has a value of 40KΩ

.

4. The device according to claim 1 wherein said voltage divider circuit (200) further comprises;

a diode (218) being connected from the supply voltage (411) to the ground (421);

a first capacitor (215) being connected from the supply voltage (411) to the ground (421); and

,

a second capacitor (225) being connected from the output (431) to the ground (421).

5. The device according to claim 1, wherein said Hall effect sensor (400) comprises a gear tooth sensor.

7. The device according to claim 1, wherein the predetermined upper limit has a value of 4.5 vdc and the predetermined lower limit has a value of 4.0 vdc.

8. The device according to claim 4, wherein said diode (218) has a value of 250 mW, said first capacitor (215) has a value of 0.1 μ

f, and said second capacitor (225) has a value of 1.0 nf.

6. In a computer controlled four-wheel drive system for a vehicle, said four-wheel drive having a transfer case and a Hall effect gear tooth sensor circuit, a device for detecting a fault condition in said Hall effect gear tooth sensor circuit, said device comprising:

a Hall effect gear tooth sensor having a supply terminal, a ground terminal, and an output terminal, said sensor being located inside said transfer case of said four-wheel drive system;

a voltage divider circuit being connected to said sensor, said voltage divider circuit comprising;

a series resistor being connected to the output terminal of said Hall effect sensor;

a pull-up resistor being connected to said series resistor and also being connected to the supply terminal of said Hall effect sensor;

a pull-down resistor being connected to the ground terminal of said Hall effect sensor and also being connected to said series and pull-up resistors;

a diode being connected from the ground terminal to the supply terminal;

a first capacitor being connected from the ground terminal to the supply terminal;

a second capacitor being connected from the output terminal to the ground terminal;

a reference signal line corresponding to a supply voltage of said Hall effect sensor;

a speed signal line corresponding to an output of said voltage divider circuit;

means for comparing the output of said voltage divider circuit and the supply voltage of said Hall effect sensor to a predetermined upper value and a predetermined lower value and for generating a fault condition signal indicating a fault condition when an output voltage of said comparing means rises above the predetermined upper limit or falls below the predetermined lower limit, said comparing means being connected to said voltage divider circuit; and

,

means for indicating the fault condition when said comparing means generates the fault condition signal, said indicating means being connected to said comparing means.

9. The device according to claim 6, wherein the predetermined upper limit has a value of 4.5 vdc and the predetermined lower limit has a value of 0.4 vdc.