Circuit diagnostics switch system

A switch system comprising a detection device that operates in first and second modes and that conducts first and second currents based on the first and second modes, respectively. A control module input circuit outputs first and second voltages based on the first and second currents. The switch system further includes a control module that receives the first and second voltages and that compares the first and second voltages to first and second predetermined voltage ranges, respectively. Further, the control module detects at least one of a proper operation and a faulty operation of the switch system based on the comparison. The control module receives the first voltage when the detection device conducts the first current and receives the second voltage when the detection device conducts the second current.

FIELD OF THE INVENTION

The present invention relates to vehicle diagnostic systems, and more particularly to a switch system for detecting faults in an electrical circuit.

BACKGROUND OF THE INVENTION

Single throw switches can be used in vehicles to detect the presence of an input, such as fluid pressure. A single throw switch typically provides a single circuit connection. Single throw switches can be utilized in circuits to create an open circuit when a desired input is not detected and a closed circuit when the desired input is detected. Accordingly, a single throw switch in a closed circuit position having an open circuit fault may not be distinguishable from a single throw switch in an open circuit position. Therefore, it may be difficult to detect circuit faults in circuits utilizing single throw switches.

SUMMARY OF THE INVENTION

A switch system comprising a detection device that operates in first and second modes and that conducts first and second currents based on the first and second modes, respectively. A control module input circuit outputs first and second voltages based on the first and second currents. The switch system further includes a control module that receives the first and second voltages and that compares the first and second voltages to first and second predetermined voltage ranges, respectively. Further, the control module detects at least one of a proper operation and a faulty operation of the switch system based on the comparison. The control module receives the first voltage when the detection device conducts the first current and receives the second voltage when the detection device conducts the second current.

In other features, the control module receives a third voltage when the control module input circuit has a first electrical fault. The control module receives a fourth voltage when the control module input circuit has a second electrical fault. The control module receives a fifth voltage when the control module input circuit has a third electrical fault.

In yet another feature, proper operation includes detecting one of the first and second modes.

In still another feature, faulty operation includes detecting at least one of the first, second and third electrical faults.

In still other features, the control module detects the first mode when the first voltage is within a first predetermined voltage range. The control module detects the second mode when the second voltage is within a second predetermined voltage range.

In yet other features, the control module detects the first electrical fault when the third voltage is within a third predetermined voltage range. The control module detects the second electrical fault when the fourth voltage is within a fourth predetermined voltage range. The control module detects the third electrical fault when the fifth voltage is within a fifth predetermined voltage range.

In still other features, the detection device is a double throw switch including two resistances having ends that communicate with the control module input circuit and having an opposite ends selectable by the double throw switch based on the first and second modes. The first mode selects the first resistance and the second mode selects the second resistance.

In still other features, the detection device is a Hall-effect switch having a Hall-effect device that communicates with the control module input circuit. The Hall-effect switch conducts a current having a first strength based on the first mode and conducts the current having a second strength based on the second mode. The first mode conducts the first current having the first strength and the second mode conducts the current having the second strength.

In yet other features, the control module determines the Hall-effect switch is in the first mode when the first voltage is within a first predetermined voltage range. The control module determines the Hall-effect switch is in the second mode when the second voltage is within a second predetermined voltage range.

In still other features, the input circuit includes an analog-to-digital (A/D) converter having an input and that outputs the voltage to the control module. A voltage, stabilizing device has an end that communicates with a voltage source and has an opposite end that communicates with the input of the A/D converter. A first resistance has an end that communicates with a ground source and has an opposite end that communicates with the input of the A/D converter. A second resistance has an end that communicates with the input of the A/D converter and has an opposite end that communicates with the detection device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIG. 1, an exemplary engine system10utilizing a switch system according to the present teachings is illustrated. The engine system10includes an engine12, an intake manifold14, an exhaust manifold16, a transmission18and a torque converter20.

The engine12combusts an air and fuel mixture within cylinders (not shown) to drive pistons (not shown) that drive the transmission18through the coupling device20. Air is drawn through a throttle22and into the intake manifold14, which delivers air to the cylinders. Exhaust from the combustion process is exhausted from the cylinders and into the exhaust manifold16. The exhaust is treated in an exhaust system (not shown) and is released to atmosphere.

A fuel injector (not shown) injects fuel which is combined with the air as it is drawn into the cylinder through an intake port (not shown). The fuel injector can be an injector associated with an electronic or mechanical fuel injection system (not shown), or another system for mixing fuel with intake air. The fuel injector is controlled to provide a desired air/fuel ratio within each cylinder.

A driver input device (DID)24enables the driver to select a desired transmission operating mode. More specifically, the DID24is illustrated as a PRNDL lever26that enables a driver to shift the operating range of the transmission between park (P), reverse (R), neutral (N), drive (D) and low drive (L). The DID24can also include tap-shift inputs not shown (i.e., tap-shift up and tap-shift down) that enable a driver to command gear shifts.

The engine system10further includes a switch system28that detects the presence of fluid used to operate the transmission. Information from the switch system28is used to determine the transmission operating mode. Additionally, the switch system28can detect electrical faults that may exist in therein.

The control system28includes a DID sensor30, a switch32, a control module input circuit34and a control module36. The DID sensor30detects the position of the PRNDL lever26and communicates with the control module36. The switch32is typically located in the valve body of the transmission18and can be adapted to detect fluid pressure. The switch32can operate in two modes to detect the presence of fluid pressure that engages operating ranges of the transmission18. A first mode exists when no fluid pressure exists. When fluid pressure is detected, the switch operates in a second mode that outputs a pressure signal to the control module input circuit. The switch32can utilize metal contacts, or another type of system that conducts current.

The control module input circuit34has one end that communicates with the switch32and an opposite end that communicates with the control module36. Although the input circuit34is shown to be external from the control module36, the control module input circuit34may be integrated therein. The input circuit34outputs a voltage to the control module36based on the position of the switch32and the electrical state of the input circuit, as discussed in greater detail below. The electrical states include normal conditions and fault conditions. The normal conditions include proper operation of the switch system when the switch32operates in the first or second positions and no electrical faults exist. An electrical fault condition includes, but is not limited to, an open circuit between the switch32and the control module36, a short circuit to a ground source and a short circuit to a voltage source.

The control module36determines whether normal and/or electrical fault conditions exist based on the voltage output from the input circuit34. Specifically, the control module36is preprogrammed with voltage values that correspond to the normal conditions and the electrical fault conditions. Voltage values are received from the input circuit34and are compared to the preprogrammed voltage values. Based on the comparison, the control module36can determine whether fluid pressure and/or electrical faults exist.

Referring now toFIGS. 2A-2E, an exemplary switch system28includes a control module input circuit34′, a control module36′ and a double throw switch38. The double throw switch38includes a resistor R1and a resistor R2that is different from R1. Ends of R1and R2communicate with the control module input circuit34′. Opposite ends of R1and R2selectively communicate with a reference potential, such as ground, based on the position of the double throw switch38. When the double throw switch38is in a first mode (POSITION A), R2communicates with ground and R1is disconnected. When the double throw switch38is in a second mode (POSITION B), R2is disconnected and R1communicates with ground.

The control module input circuit34′ includes a resistor network40, a voltage stabilizing device42, such as a constant current source, and an analog-to-digital (A/D) converter44. The resistor network40includes resistors R3and R4. One end of R3communicates with ground. An opposite end of R3communicates with an input of the A/D converter44. One end of R4communicates with the input of the A/D converter44. An opposite end of R4communicates with the double throw switch38. The voltage stabilizing device42has one end that communicates with a voltage source (VS) and has an opposite end that communicates with the input of the A/D converter44. The resistor network40is designed to output different analog voltages when normal conditions and fault conditions exist, as discussed in greater detail below. The A/D converter44communicates with the resistor network40and the control module36′ and converts analog voltages into digital voltage signals. The control module36′ receives the digital voltage signal and determines a voltage value. The voltage stabilizing device42provides a constant voltage to the input circuit and prevents variances in Vsfrom varying the voltage (VOUT) output by the control module input circuit34′.

The control module36′ receives digital voltage signals from the A/D converter44based on the position of the double throw switch38and the electrical state of the circuit, as discussed in greater detail below. The position of the double throw switch38can provide two different current paths. The different current paths can be used to conduct two different currents through the input circuit34′ to produce a different VOUT. For example, POSITION A disconnects R1and connects R2to ground (FIG. 2A). Accordingly, current is conducted through R3, R4and R2and voltage is created across R3, R4and R2. The combined voltages create VOUT, which can be expressed as:

The switch system28′ can be designed to provide the predetermined voltage values that correspond to the operating modes of the double throw switch38. For example, R1and R2can be set to 185 ohms and 754 ohms, respectively. R3and R4can be set to 286 ohms and 100 ohms, respectively. Accordingly, VOUTis approximately 3 volts when the double throw switch38is in POSITION A and no circuit faults exist in the circuit with ICat 0.014 ma. When the double position switch38is in POSITION B and no circuit faults exist, VOUTis approximately 2 volts.

Additionally, the switch system28′ can output voltages that correspond to the various circuit faults stated above. For example, when a short circuit to ground exists (FIG. 2C), current is conducted through R4, but not through R1or R2. Accordingly, VOUTis approximately 1 volt. The voltage can be expressed as:

When an open circuit exists between R4and the double throw switch38(FIG. 2D), no current flows through R4. The current through R3creates VOUT. Accordingly, VOUTis approximately 4 volts and VOUTcan be expressed as:
VOUT=ICR3.   (4)

When a short circuit to a voltage source exists (FIG. 2E), VOUTis approximately 6 volts and VOUTcan be expressed as:

The control module36′ can be programmed with one or more voltage value ranges that correspond to one or more electrical states of the control module input circuit34′ described above. The voltage ranges have an upper voltage value and a lower voltage value. For example, the control module36′ can be programmed to associate a first voltage value range VNORM1to a first normal condition and a second voltage value range VOPENto an open circuit fault. The control module36′ compares VOUTto VNORM1. When VOUTis within VNORM1, the control module36′ determines that the switch system28′ is operating in the first normal condition. When VOUTis within VOPEN, the control module36′ determines that an open circuit fault exists in the switch system28′.

Referring now toFIGS. 3A-3E, an alternative exemplary switch system28″ is shown. The double throw switch38is replaced with a Hall-effect switch45having a Hall-effect device46that can conduct current having different current strengths. When the Hall-effect switch45is in a first mode (LO mode), the Hall-effect device46can conduct a low strength current through R4. A low strength current includes a current strength of 2 mA to 5 mA. When the Hall-effect switch45is in a second mode (HIGH mode), the Hall-effect device46can conduct a high strength current through R4. A high strength current includes a current strength of 12 mA to 17 mA.

The current through R4and R3creates a voltage (VOUT) that is converted to digital voltage value by the A/D converter44and is received by the control module36″. Accordingly, the value of VOUTis based on the operating mode of the Hall-effect switch45and the electrical state of the circuit and the control module36″ detects normal conditions and fault conditions in the same manner as stated above.

Referring now toFIGS. 4A and 4B, a cross-sectional illustration of an exemplary double throw switch50adapted to detect fluid pressure is shown. The double throw switch50includes a housing52having a top54and a pressure chamber56within the housing52that holds fluid58. The top54couples to a fluid pressure source (not shown) and directs fluid58to the pressure chamber56. A sealing device60is fixed to the housing52and surrounds the top54to prevent fluid58from escaping the double throw switch50.

A switch assembly62is located in the pressure chamber56. The switch assembly62includes an upper contact plate64, a lower contact plate66and a moveable current conducting device, such as a flexible membrane68. The upper and lower contact plates64,66are made of an electrically conducting material, such as metal. The upper contact plate64is located approximately in the center of the pressure chamber56and is fixed to the inner sides of the housing52. The upper contact plate64further has inlets70that allow fluid58to pass. The lower contact plate66is fixed to the bottom of the housing52. The flexible electrically conducting membrane68is located between the upper and lower contact plates64,66. The sides of the membrane68are fixed to the inner walls of the housing52. The membrane68is designed so that it communicates with the upper contact plate64when no fluid58exists in the pressure chamber56.

Resistors R1and R2are located within the walls of the housing52. One end of R1and R2communicates with the lower and upper contact plates66,64, respectively. The opposite end of R1and R2communicates with one end of a first and second terminal74,76respectively. The opposite end of the first and second terminals74,76extend to the exterior of the housing52. Although it is shown that the value of R1is different than the value of R2, it is appreciated that values of R1and R2can be equal. The double throw switch50further has a ground terminal78that has one end that communicates with the membrane68and has an opposite end that extends to the exterior of the housing52. The first and second terminals74,76typically communicate with electrical inputs from a circuit. The ground terminal78typically communicates with a ground source (ground).

Accordingly, the switch50exists in POSITION A (FIG. 4A) when the membrane68communicates with the upper contact plate64. The switch50exists in POSITION B (FIG. 4B) when fluid pressure created by the fluid58moves the membrane68downward and the membrane68communicates with the lower contact plate66.

Positions A and B can provide first and second current paths, respectively, when the switch50communicates with a circuit. Specifically, POSITION A, provides the first path where current enters the switch50through the first terminal76and flows through R2. The current continues traveling through the upper contact plate64where it communicates with the membrane68. The current flows through the membrane68where it returns to ground through the ground terminal78.

The double throw switch50operates in POSITION B when fluid58enters the switch50through the top54and is directed to the first contact plate64. Specifically, fluid58passes through the inlets70and fills the pressure chamber56. The increased fluid pressure caused by the fluid58moves the membrane68downward and into POSITION B. When operating in POSITION B, a second current path is selected and current enters the switch50through the second terminal74and flows through R1. The current continues traveling through the lower contact plate66where it communicates with the membrane68. The current flows through the membrane68and returns to ground through the ground terminal78.

Referring now toFIGS. 5A and 5B, an alternative embodiment of a double throw switch50′ adapted to detect fluid pressure is illustrated., The double throw switch50′ is similar to the double throw switch50described in detail above. Therefore like reference numerals will be used to indicate like components. The switch assembly62′ includes a moveable electrically conductive actuator plate80that is located between the upper and lower contact plates64′,66′. Electrically conductive springs82are coupled to opposite sides of the bottom of the actuator plate80. The opposite end of the springs82is coupled to the lower contact plate66′. The top of the actuator plate80is coupled to a membrane84using linking rod86. The membrane84is adapted to receive fluid58′ and to deform based on an amount of fluid pressure.

When no fluid pressure exists in the pressure chamber56′, the springs82place the switch50′ in POSITION A by forcing the top of the actuator plate80against the upper contact plate64′. When fluid58′ fills the pressure chamber56′, the switch50′ exists in POSITION B. The fluid pressure moves the membrane84downward. As a result, the switch50′ operates in POSITION B when fluid58′ fills the pressure chamber56′ and moves the membrane84downward. The bottom of the actuator plate80is forced against the lower contact plate66′. The actuator plate80moves between first and second positions to provide first and second current paths, as discussed above.

Referring now toFIG. 6, a flowchart illustrates the steps executed by the control system according to the present invention. In step600, control determines whether a transmission range has been selected. When a transmission range has not been selected, control returns to step600. Otherwise, control determines whether a short circuit to ground fault exists in step602. When VOUTis within VSHORT—GND, control determines a short circuit to ground exists in step604and control ends. Otherwise, control determines whether an open circuit fault exists in step606. When VOUTis within VOPEN, control determines an open circuit fault exists in step608and control ends. Otherwise, control determines whether a short circuit to the voltage source exists in step610. When VOUTis within VSHORT—V, control determines a short circuit to voltage exists in step612and control ends. Otherwise, control determines no faults exist in step614and control proceeds to step616.

In step616, control determines whether VOUTis within VNORM—1. When VOUTis within VNORM—1, control determines the switch32is operating in a first mode and no fluid is detected in step618and control ends. Otherwise, control determines whether VOUTis within VNORM—2in step620. When VOUTis within VNORM—2, control determines the switch32is operating a second mode and fluid is detected in step622and control ends. Otherwise, control determines a system failure in step624and control ends.

Referring now toFIG. 7, a flowchart illustrates steps executed by a double throw pressure switch adapted to detect fluid pressure according to the principles of the present invention. In step700, control determines whether the switch has received fluid. When the switch has received fluid, control proceeds to step704. Otherwise control proceeds to step702. In step702, control retains a current conducting device in a first position and selects a LO mode. In step706, control provides a first current path and control ends.

In step704, control receives a fluid and fluid pressure moves a fluid detection device downward. In step708, control moves the current conducting device to a second position and selects a HIGH mode. Control provides a second current path in step710and control ends.