阅读说明：本技术 制动系统上的车轮速度传感器接口的电阻性短路抗扰性 (Resistive short circuit immunity of wheel speed sensor interface on a braking system ) 是由 塞巴斯蒂安·阿巴齐乌 贝努瓦·阿尔库夫 简-克里斯托夫·帕特里克·兰斯 于 2019-07-04 设计创作，主要内容包括：用于制动系统上的车轮速度传感器接口的电阻性短路抗扰性的设备和方法。在一个实施例中,所述设备包含用于基于传送到车轮速度传感器的第一电流产生第一周期性信号的第一电路以及用于基于第二电流产生第二周期性信号的第二电路,所述第二电流中的一些或全部是从所述车轮速度传感器接收。提供电路以用于在所述第二电流的量值大于所述第一电流的量值的情况下选择所述第一周期性信号用于输出,或在所述第二电流的量值不大于所述第一电流的所述量值的情况下选择所述第二周期性信号用于输出。所述选择的第一或第二周期性信号含有和与所述车轮速度传感器相关联的车轮的速度有关的信息。(Apparatus and method for resistive short circuit immunity of a wheel speed sensor interface on a braking system. In one embodiment, the apparatus includes a first circuit for generating a first periodic signal based on a first current communicated to a wheel speed sensor and a second circuit for generating a second periodic signal based on a second current, some or all of which is received from the wheel speed sensor. Circuitry is provided for selecting the first periodic signal for output if a magnitude of the second current is greater than a magnitude of the first current, or selecting the second periodic signal for output if a magnitude of the second current is not greater than the magnitude of the first current. The selected first or second periodic signal contains information related to the speed of a wheel associated with the wheel speed sensor.)

1. A method, comprising:

transmitting a first current to a wheel speed sensor;

receiving second currents, some or all of which are received from the wheel speed sensors;

generating a first periodic signal based on the first current;

generating a second periodic signal based on the second current;

selecting the first periodic signal for output if the magnitude of the second current is greater than the magnitude of the first current;

select the second periodic signal for output if a magnitude of the second current is not greater than the magnitude of the first current;

wherein the selected first or second periodic signal comprises information related to a speed of a wheel associated with the wheel speed sensor.

2. The method of claim 1, wherein the magnitude of the second current is greater than the magnitude of the first current when the magnitude of the second current exceeds the magnitude of the first current by a predetermined amount, and wherein the magnitude of the second current is not greater than the magnitude of the first current when the magnitude of the second current does not exceed the magnitude of the first current by the predetermined amount.

3. The method of claim 1, further comprising:

generating a third current based on the first current, wherein a magnitude of the third current is proportional to the magnitude of the first current;

generating a fourth current based on the second current, wherein a magnitude of the fourth current is proportional to the magnitude of the second current;

comparing the third current to the fourth current;

wherein the act of selecting the first or second periodic signal is performed in response to comparing the third and fourth currents.

4. The method of claim 3, wherein:

wherein the first periodic signal is generated directly from the third current;

wherein the second periodic signal is generated directly from the fourth current.

5. The method of claim 1, further comprising:

setting a signal to a first state if the first current is greater than the second current, wherein the first state indicates a resistive short circuit between a first end of the wheel speed sensor and ground within a power system;

setting the signal to a second state if the second current is greater than the first current, wherein the second state indicates a resistive short circuit within the electrical system between a second terminal of the wheel speed sensor and a supply voltage.

6. The method of claim 1, wherein:

wherein the first current changes when a tooth of the rotor passes near the wheel speed sensor;

wherein the second current changes when the teeth of the rotor pass near the wheel speed sensor.

7. The method of claim 1, further comprising:

generating a first voltage based on the first current, wherein a magnitude of the first voltage is proportional to the magnitude of the first current;

generating a second voltage based on the second current, wherein a magnitude of the second voltage is proportional to the magnitude of the second current;

comparing the first and second voltages;

wherein the act of selecting the first or second periodic signal is performed in response to comparing the first and second voltages.

8. The method of claim 1, wherein:

wherein the first periodic signal is generated directly from the first voltage;

wherein the second periodic signal is generated directly from the second voltage.

9. An apparatus, comprising:

a first circuit for transmitting a first current to the wheel speed sensor;

a second circuit for receiving a second current, some or all of which may be received from the wheel speed sensor;

a first threshold detection circuit for generating a first periodic signal based on the first current;

a second threshold detection circuit for generating a second periodic signal based on the second current;

circuitry, wherein the circuitry is configured to select the first periodic signal for output if a magnitude of the second current is greater than a magnitude of the first current, wherein the circuitry is configured to select the second periodic signal for output if a magnitude of the second current is not greater than the magnitude of the first current;

wherein the selected first or second periodic signal comprises information related to a speed of a wheel associated with the wheel speed sensor.

10. A system, comprising:

a first circuit for generating a first periodic signal based on a first current delivered to a wheel speed sensor;

a second circuit for generating a second periodic signal based on second currents, some or all of which are received from the wheel speed sensor;

circuitry, wherein the circuitry is configured to select the first periodic signal for output if a magnitude of the second current is greater than a magnitude of the first current, wherein the circuitry is configured to select the second periodic signal for output if a magnitude of the second current is not greater than the magnitude of the first current;

wherein the selected first or second periodic signal comprises information related to a speed of a wheel associated with the wheel speed sensor.

Technical Field

The invention relates to an apparatus and method for resistive short circuit immunity of a wheel speed sensor interface on a braking system.

Background

A sensor is a device that detects a change in an event or quantity and provides a corresponding output signal indicative thereof. In motor vehicles, bicycles and other vehicles, wheel speed sensors are used to obtain wheel speed information for use in control systems such as anti-lock braking systems (ABS). Active wheel speed sensors are one type of wheel speed sensor that are commonly used in newer types of vehicles for a variety of reasons. Some active wheel speed sensors (hereinafter type I active wheel speed sensors) output a square wave current signal whose period is determined by the rotational speed of the associated wheel. The magnitude of the other active wheel speed sensors may vary depending on whether the wheel is rotating in the forward or reverse direction. Other types of active wheel speed sensors output pulse width modulated signals in which additional information such as the direction of rotation and magnetic field strength is decoded. The output of still other types of active wheel speed sensors is encoded with diagnostic data. The present technology will be described with reference to a type I active wheel speed sensor for use in a motor vehicle, although it should be understood that the present technology should not be limited thereto.

The wheel speed sensor interface circuit is connected between a Wheel Speed Sensor (WSS) and an ABS controller (e.g., a microcontroller). The WSS interface circuit conditions the square wave output of the WSS for subsequent processing by the ABS controller. The ABS controller monitors speed information of all wheels of the vehicle. If the speed of one wheel changes abruptly relative to the other, the ABS controller knows that one wheel begins to lose traction. The controller then takes appropriate action by applying the brakes or performing traction control.

Disclosure of Invention

According to a first aspect of the invention, there is provided a method comprising:

transmitting a first current (i.e., a battery current) to a wheel speed sensor;

receiving a second current (i.e., a ground return current), some or all of which is received from the wheel speed sensor (some of which can be from a low-side sensor shorted to the battery);

generating a first periodic signal (i.e., an output of a high-side threshold detection) based on the first current (i.e., a battery current);

generating a second periodic signal (i.e., an output of a low side threshold detection) based on the second current (i.e., a ground return current);

selecting the first periodic signal for output if the magnitude of the second current is greater than the magnitude of the first current;

select the second periodic signal for output if a magnitude of the second current is not greater than the magnitude of the first current;

wherein the selected first or second periodic signal comprises information related to a speed of a wheel associated with the wheel speed sensor.

In one or more embodiments, the magnitude of the second current is greater than the magnitude of the first current when the magnitude of the second current exceeds the magnitude of the first current by a predetermined amount, and wherein the magnitude of the second current is not greater than the magnitude of the first current when the magnitude of the second current does not exceed the magnitude of the first current by the predetermined amount.

In one or more embodiments, the method further comprises:

generating a third current (i.e., Hrep) based on the first current, wherein a magnitude of the third current is proportional to the magnitude of the first current;

generating a fourth current (i.e., Lrep) based on the second current, wherein a magnitude of the fourth current is proportional to the magnitude of the second current;

comparing the third current to the fourth current;

wherein the act of selecting the first or second periodic signal is performed in response to comparing the third and fourth currents.

In one or more embodiments, the first periodic signal is generated directly from the third current;

wherein the second periodic signal is generated directly from the fourth current.

In one or more embodiments, the method further comprises:

setting a signal to a first state if the first current is greater than the second current, wherein the first state indicates a resistive short circuit between a first end of the wheel speed sensor and ground within a power system;

setting the signal to a second state if the second current is greater than the first current, wherein the second state indicates a resistive short circuit within the electrical system between a second terminal of the wheel speed sensor and a supply voltage.

In one or more embodiments, the first current changes as the teeth of the rotor pass near the wheel speed sensor;

wherein the second current changes when the teeth of the rotor pass near the wheel speed sensor.

In one or more embodiments, the method further comprises:

generating a first voltage (i.e., Hrep) based on the first current, wherein a magnitude of the first voltage is proportional to the magnitude of the first current;

generating a second voltage (i.e., Lrep) based on the second current, wherein a magnitude of the second voltage is proportional to the magnitude of the second current;

comparing the first and second voltages;

wherein the act of selecting the first or second periodic signal is performed in response to comparing the first and second voltages.

In one or more embodiments, the first periodic signal is generated directly from the first voltage;

wherein the second periodic signal is generated directly from the second voltage.

According to a second aspect of the invention, there is provided an apparatus comprising:

a first circuit for delivering a first current (i.e., battery current) to the wheel speed sensor;

a second circuit for receiving a second current (i.e., a ground return current), some or all of which may be received from the wheel speed sensor (some of which may be from a low side sensor shorted to the battery);

a first threshold detection circuit for generating a first periodic signal (i.e., an output of a high-side threshold detection) based on the first current (i.e., a battery current);

a second threshold detection circuit for generating a second periodic signal (i.e., an output of a low side threshold detection) based on the second current (i.e., a ground return current);

circuitry, wherein the circuitry is configured to select the first periodic signal for output if a magnitude of the second current is greater than a magnitude of the first current, wherein the circuitry is configured to select the second periodic signal for output if a magnitude of the second current is not greater than the magnitude of the first current;

wherein the selected first or second periodic signal comprises information related to a speed of a wheel associated with the wheel speed sensor.

In one or more embodiments, the magnitude of the second current is greater than the magnitude of the first current when the magnitude of the second current exceeds the magnitude of the first current by a predetermined amount, and wherein the magnitude of the second current is not greater than the magnitude of the first current when the magnitude of the second current does not exceed the magnitude of the first current by the predetermined amount.

In one or more embodiments, the apparatus further comprises:

a first current monitor circuit for generating a third current (i.e., Hrep) based on the first current, wherein a magnitude of the third current is proportional to the magnitude of the first current;

a second current monitor circuit for generating a fourth current (i.e., Lrep) based on the second current, wherein a magnitude of the fourth current is proportional to the magnitude of the second current;

a comparator circuit for comparing the third current with the fourth current;

wherein the circuit selects the first or second periodic signal in response to the comparator circuit comparing the third and fourth currents.

In one or more embodiments, the first threshold detection circuit generates the first periodic signal directly from the third current;

wherein the second threshold detection circuit generates the second periodic signal directly from the fourth current.

In one or more embodiments, the comparator circuit is configured to set the signal to a first state if the first current is greater than the second current, wherein the first state indicates a resistive short circuit between the first end of the wheel speed sensor and the ground within the power system;

wherein the comparator circuit is configured to set the signal to a second state if the second current is greater than the first current, wherein the second state indicates that a resistive short circuit exists between a second terminal of the wheel speed sensor and a supply voltage within the power system.

In one or more embodiments, the apparatus further comprises:

a first current monitor circuit that generates a first voltage (i.e., Hrep) based on the first current, wherein a magnitude of the first voltage is proportional to the magnitude of the first current;

a second current monitor circuit that generates a second voltage (i.e., Lrep) based on the second current, wherein a magnitude of the second voltage is proportional to the magnitude of the second current;

wherein the comparator circuit is configured to compare the first and second voltages;

wherein the circuitry is configured to perform selecting the first or second periodic signal in response to the comparator circuitry comparing the first and second voltages.

In one or more embodiments, the first threshold detection circuit is configured to generate the first periodic signal directly from the first voltage;

wherein the second threshold detection circuit is configured to generate the second periodic signal directly from the second voltage.

According to a third aspect of the invention, there is provided a system comprising:

a first circuit for generating a first periodic signal (i.e., an output of a high-side threshold detection) based on a first current (i.e., a battery current) transmitted to the wheel speed sensor;

second circuitry for generating a second periodic signal (i.e., an output of a low side threshold detection) based on a second current (i.e., a ground return current), some or all of which is received from the wheel speed sensor;

circuitry, wherein the circuitry is configured to select the first periodic signal for output if a magnitude of the second current is greater than a magnitude of the first current, wherein the circuitry is configured to select the second periodic signal for output if a magnitude of the second current is not greater than the magnitude of the first current;

wherein the selected first or second periodic signal comprises information related to a speed of a wheel associated with the wheel speed sensor.

In one or more embodiments, the magnitude of the second current is greater than the magnitude of the first current when the magnitude of the second current exceeds the magnitude of the first current by a predetermined amount, and wherein the magnitude of the second current is not greater than the magnitude of the first current when the magnitude of the second current does not exceed the magnitude of the first current by the predetermined amount.

In one or more embodiments, the system further comprises:

a first current monitor circuit for generating a third current (i.e., Hrep) based on the first current, wherein a magnitude of the third current is proportional to the magnitude of the first current;

a second current monitor circuit for generating a fourth current (i.e., Lrep) based on the second current, wherein a magnitude of the fourth current is proportional to the magnitude of the second current;

a comparator circuit for comparing the third current with the fourth current;

wherein the circuit selects the first or second periodic signal in response to the comparator circuit comparing the third and fourth currents.

In one or more embodiments, the comparator circuit is configured to set the signal to a first state if the first current is greater than the second current, wherein the first state indicates a resistive short circuit between the first end of the wheel speed sensor and the ground within the power system;

wherein the comparator circuit is configured to set the signal to a second state if the second current is greater than the first current, wherein the second state indicates that a resistive short circuit exists between a second terminal of the wheel speed sensor and a supply voltage within the power system.

In one or more embodiments, the system further comprises:

a first current monitor circuit that generates a first voltage (i.e., Hrep) based on the first current, wherein a magnitude of the first voltage is proportional to the magnitude of the first current;

a second current monitor circuit that generates a second voltage (i.e., Lrep) based on the second current, wherein a magnitude of the second voltage is proportional to the magnitude of the second current;

wherein the comparator circuit is configured to compare the first and second voltages;

wherein the circuitry is configured to perform selecting the first or second periodic signal in response to the comparator circuitry comparing the first and second voltages.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

Drawings

The present technology may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIG. 1 illustrates an example wheel speed sensor interface circuit and operational aspects thereof.

Fig. 2 illustrates the wheel speed sensor interface circuit of fig. 1 and its operational aspects after a resistive short circuit is created.

FIG. 3 illustrates an ABS system employing a wheel speed sensor interface circuit implementing one embodiment of the present technology.

FIG. 4 illustrates the ABS system of FIG. 3 after the generation of a first type of resistive short.

FIG. 5 illustrates the ABS system of FIG. 3 after the generation of a second type of resistive short.

Fig. 6 and 7 illustrate alternative methods employed by the wheel speed sensor interface circuit of fig. 3

Fig. 8-10 are graphical representations of inputs and outputs of the wheel speed sensor interface circuits of fig. 3-5, respectively.

Fig. 11 illustrates one embodiment of a wheel speed sensor interface circuit employed in fig. 3-5.

Fig. 12 is a method employed by the wheel speed sensor interface circuit of fig. 11.

FIG. 13 illustrates one embodiment of the comparison and adjustment circuit employed in FIG. 11.

Fig. 14 shows another embodiment of the comparison and adjustment circuit employed in fig. 11.

The use of the same reference symbols in different drawings indicates similar or identical items unless otherwise noted. The figures are not necessarily to scale.

Detailed Description

Environmental factors can cause resistive shorts between the WSS terminal and ground or between the WSS terminal and a DC power supply (e.g., a battery). For example, dirt, road salt, corrosion, or water may accumulate on or near the WSS end and create a resistive short circuit. Or a motor vehicle collision may vibrate the WSS or its electrical connection and create a resistive short circuit. Resistive shorts can corrupt the wheel speed information provided to the ABS system and adversely affect the operation of the ABS system.

Disclosed are methods and apparatus for detecting and responding to temporary or permanent resistive shorts of a WSS. While some examples of the present technology will be described with reference to a WSS interface circuit employed in an ABS of a motor vehicle, it is contemplated that this is but one application that may benefit from the present technology. The present techniques may be applied to any system that requires detection and response to resistive shorts or other defects that add DC offset to the periodic signal output of the device.

Temporary or permanent resistive shorts of a WSS may adversely affect the operation of a system employing the WSS. Fig. 1 and 2 show a basic WSS interface circuit 100 for generating a wheel speed information signal WS1 based on a current IS through the WSS 102. Fig. 1 and 2 are provided merely as an aid to assist the reader in understanding the problems caused by temporary or permanent resistive shorts. The present technique should not be limited to the techniques shown in fig. 1 and 2.

The WSS102 is located proximate to a gear-shaped rotor (also referred to as a tonewheel) 104, which gear-shaped rotor 104 is in turn attached, directly or indirectly, to the wheels of a motor vehicle (not shown). Equally spaced teeth are positioned on the circumference of the rotor 104, which rotor 104 rotates at a speed that matches the rotational speed of the wheel to which it is attached. WSS102 draws sensor current IS from a voltage supply Vss provided by a battery (not shown). WSS102 draws a substantially constant current (e.g., IS ═ 14mA) as the teeth pass. Between the teeth, WSS102 draws a low and substantially constant current (e.g., IS ═ 7 mA). The square wave signal 106 in fig. 1 represents IS as the rotor 104 rotates. Each pulse of the square wave signal 106 represents a tooth passing through the WSS 102. The period of the square wave signal 106 is proportional to the wheel speed because the rotor 104 is directly or indirectly attached to the wheel. As the rotational speed of the rotor 104 increases, the frequency of the square wave signal 106 increases, thereby indicating a faster wheel speed. The period of the square wave signal 106 may be used to determine the wheel speed.

The interface circuit 110 conditions the square wave signal 106 for further processing by the ABS control module 114. The interface circuit 110 includes a comparator 112, which comparator 112 compares the sensor current IS with a predetermined threshold level. Again, the term interface circuit should not be limited to the interface circuits shown in fig. 1 and 2. Rather, the interface circuit 110 is provided merely as an aid to illustrate the problems caused by resistive shorts.

The sensor current IS passes through a resistor R to produce a voltage VR, which IS provided as one input to the comparator 112. The predetermined voltage VT is provided to another input of the comparator 112. When VR is greater than VT, the comparator 112 outputs a high voltage (e.g., 5V), and when VR is less than VT, the comparator 112 outputs a low voltage (e.g., 0V). The resistances of VT and R are carefully selected so that the output of comparator 112 IS 5V when IS IS greater than 10mA (i.e., IS > 10mA) and the output of comparator 112 IS 0V when IS IS less than 10mA (i.e., IS < 10 mA).

WS1 is the output signal of comparator 112 and is shown in fig. 1. WS1 is a square wave that switches between 5V and 0V when signal 106 switches between 7mA and 14mA, similar to signal 106. The frequency of WS1 matches the frequency of signal 106, which in turn depends on the rotational speed of rotor 104. WS1 are provided to the ABS control module 114 as wheel speed information for the wheel corresponding to the rotor 104. The ABS control module 114 generates the traction control signals C1-C4 based on the wheel speed signals WS1-WS4, respectively, received from the corresponding interface circuits.

FIG. 2 shows the WSS102 of FIG. 1 after an inadvertent resistive short RS is created between the terminals of the WSS 102. The resistive short RS may be caused, for example, by a piece of debris that inadvertently lodges itself within the system between the ends of the WSS 102. The resistive short RS delivers a direct current IRS. Those skilled in the art understand that IRS increases or shifts VR. If IRS is large enough, VR is consistently greater than VT and therefore comparator 112 generates WS1 as a substantially constant 5V signal as shown in FIG. 2. This signal does not contain speed information for the controller 114.

FIG. 3 illustrates a system including an interface circuit 300, the interface circuit 300 being capable of detecting and responding to a resistive short of a WSS, in accordance with one embodiment of the present technology. Fig. 4 and 5 show the system shown in fig. 1 after a resistive short RS is created at the WSS. For purposes of explanation only, fig. 3-5 will be described using the same WSS102 and rotor 104 employed in fig. 1 and 2.

Fig. 8-10 show graphical representations of signals generated or received by the interface circuit 300. Fig. 3 and 8 illustrate operational aspects of the interface circuit 300 when there is no resistive short at the WSS 102. Fig. 4 and 9 illustrate aspects of interface circuit 300 when a resistive short RS exists between Vss and terminal L of WSS 102. This may be referred to as a low side resistive short. Fig. 5 and 10 illustrate aspects of the interface circuit 300 when there is a resistive short RS between ground and the terminal H of the WSS 102. This may be referred to as a high side resistive short.

The interface circuit 300 delivers a high side current IH towards the WSS 102. Interface circuit 300 also transfers low-side current IL to ground. IL and IH may be equal to each other depending on whether there is a resistive short at the ends of WSS 102; if there is no resistive short, then IL and IH should be equal. Interface circuit 300 compares IH and IL, either directly or indirectly, to determine if one is greater than the other by a predetermined value X. In one embodiment, X ═ 0. In other embodiments, X is a non-zero value (e.g., 1mA, 2mA, 4mA, 10mA, etc.). Interface circuit 300 compares IH and IL to detect the presence of a resistive short at the end of WSS 102. If a resistive short is detected, the interface circuit 300 transmits a signal (i.e., Flag1) to the ABS control 304. Flag1 may identify whether a resistive short exists at the H or L terminals of WSS 102. More importantly, if it is determined that a resistive short exists, the interface circuit 300 uses the lesser of IH and IL to directly or indirectly generate the wheel speed signal WS1 for the ABS control 302. Each wheel of the motor vehicle is provided with an interface circuit and WSS similar to that shown in fig. 3-5. The additional interface circuitry transfers WS2-WS4 and Flag3-Flag4 to ABS control module 304, as shown.

The WSS102 and rotor 104 in fig. 3-5 operate in substantially the same manner as described above with respect to fig. 1 and 2. WSS102 draws sensor current IS from supply voltage Vss via interface circuit 300. IS returns to the surface via interface circuit 300. IS varies as the teeth of the rotor 104 pass the WSS 102. When any tooth passes, WSS102 draws a substantially constant current IS of 14 mA. Between the teeth, WSS102 draws a substantially constant current IS-7 mA.

Fig. 3 presents a non-resistive short. Fig. 4 and 5 each show a resistive short RS at the WSS 102. The resistive short RS in fig. 4 is between Vss and terminal L. The resistive short RS in fig. 5 is between terminal H and ground.

Since there IS no resistive short in fig. 3, IH ═ IL ═ IS. In fig. 4, a direct current IRS flows through the resistive short RS to ground together with the sensor current IS. IRS and IS flow indirectly to the surface via interface circuit 302. In fig. 4, IH ═ IS, and IL ═ IS + IRS. In fig. 5, the direct current IRS flows directly to the ground. In fig. 5, IH ═ IS + IRS, and IL ═ IS. Interface circuit 300 employs a comparator (not shown) that directly or indirectly compares the difference between IL and IH by a predetermined value X.

Fig. 6 and 7 are flow diagrams illustrating relevant aspects of alternative methods implemented by the interface circuit 300. In step 602 of FIG. 6, the difference IH-IL is compared to X, which in one embodiment is a non-zero value. In another embodiment, X is 0. If IH-IL > X, interface circuit 300 generates WS1 using IL and interface circuit 300 sets Flag1 to HSS, which indicates that there is a resistive short between terminal H and ground. If IH-IL is not greater than X, then the process continues to step 608, where interface circuit 300 generates WS1 using IH. In step 610, the difference IL-IH is compared to X. If IL-IH > X, interface circuit 300 sets Flag1 to LSS in step 612, indicating that a resistive short exists between terminals L and Vss. If IL-IH is not greater than X in step 610, Flag1 is set to NS, which indicates that there is no resistive short at WSS 102.

Fig. 7 is an alternative and potentially preferred method implemented by the interface circuit 300. In FIG. 7, interface circuit 300 compares predetermined values X and the difference between IH and IL in step 702. If IL-IH > X, interface circuit 300 generates WS1 using IH. Interface circuit 300 also sets Flag1 to LSS, which indicates that there is a resistive short between terminals L and Vss. If IL-IH is not greater than X, then the process continues to step 708 in FIG. 7 where interface circuit 300 generates WS1 using IL. In step 710, the difference IH-IL is compared to X. If IH-IL > X, then interface circuit 300 sets Flag1 to HSS in step 712, which indicates that there is a resistive short between terminal H and ground. If IH-IL is not greater than X in step 710, Flag1 is set to NS. The remaining description will assume that the interface circuit 300 implements the process shown in fig. 7.

Fig. 8-10 show graphical representations of the signals and currents described above. Fig. 8 corresponds to fig. 3, where there IS no resistive short at WSS102, and IH IL1 IS. Fig. 8 shows square wave signals 802 and 804 representing IH and IL, respectively. Each pulse of signals 802 and 804 represents a rotor tooth passing through WSS 102. As shown, there IS no resistive short and WSS102 draws IS IL IH 7mA during each pulse. Between pulses IS IH IL 7 mA. Implementing the process shown in FIG. 7, interface circuit 300 will select IL to generate WS1, which is also shown in FIG. 8. The interface circuit 300 also asserts Flag1 (i.e., no short circuit) NS according to the process shown in fig. 7.

Fig. 9 corresponds to fig. 4, in which a resistive short RS between terminal L and VSS is suddenly generated at time t ═ ts. Fig. 9 shows square wave signals 902 and 904 representing IH and IL, respectively. Initially (i.e., before time t-ts) there IS no resistive short RS, IS-IL-IH, and interface circuit 300 uses IL to generate WS 1. However, at time t ═ ts, a resistive short RS is created, and an additional current IRS is drawn directly from Vss and returned to ground via interface circuit 300. IH does not change at time t ═ ts (i.e., IH ═ IS). However, IL does change at t ═ ts in fig. 9. More specifically, IL increases IRS (i.e., IL ═ IS + IRS). Assuming IL-IH > X, interface circuit 300 switches to using IH to generate WS1, pursuant to step 704 of the process shown in FIG. 7. In addition, interface circuit 300 switches Flag1 to LSS according to step 706, thereby indicating to ABS control 302 that a resistive short exists between terminals L and Vss. As long as there is a resistive short between Vss and terminal L, interface circuit 300 will continue to assert Flag1 — LSS. Importantly, WS1 is not affected by the creation of a resistive short RS at time t ═ ts, as shown in fig. 9.

Fig. 10 corresponds to fig. 5, in which a resistive short RS between terminal H and ground is suddenly generated at time t ═ ts. Fig. 10 shows square wave signals 1002 and 1004 representing IH and IL, respectively. Initially (i.e., before time t-ts) there IS no resistive short RS, IS-IL-IH, and interface circuit 300 uses IL to generate WS 1. However, at time t ═ ts, a resistive short RS is generated, and an additional current IRS is drawn from Vss via interface circuit 300. IL does not change at time t ═ ts (i.e., IL ═ IS). However, IH increases IRS (i.e., IH IS + IRS). Assuming IH-IL > X, interface circuit 300 continues to use IL to generate WS1, but interface circuit 300 switches Flag1 to HSS, thereby indicating to ABS control 302 that a resistive short exists between terminal H and ground. Importantly, WS1 is not affected by the sudden occurrence of a resistive short RS at time t ═ ts, as shown in fig. 10.

As described above, interface circuit 300 may directly or indirectly compare IH and IL to determine whether a resistive short exists. FIG. 11 illustrates one embodiment of an interface circuit 300 in which an indirect comparison is implemented. The interface circuit 300 in fig. 11 includes a high side current monitor 1102 and a low side current monitor 1104. The high-side current monitor 1102 generates a signal Hrep that is proportional to the current IH that is passed by the high-side current monitor 1102 from the supply voltage Vss toward the WSS 102. The low-side current monitor 1104 generates a signal Lrep that is proportional to the current IL delivered to ground by the low-side current monitor 1104. Hrep and Lrep may be voltage signals representing IH and IL, respectively, or Hrep and Lrep may be current signals representing IH and IL, respectively. Hrep and LRep are provided as inputs to a compare and adjust (CC) circuit 1106. This circuit compares Hrep and Lrep to determine which is larger, which in turn determines which of the currents IH and IL is larger. CC circuit 300 selects one of signals Hrep and Lrep for use in generating WS 1. The circuit 300 also compares Hrep and Lrep to determine if a resistive short exists at the WSS102 and, if so, whether it is a high side or low side resistive short.

Fig. 12 is a flow diagram illustrating relevant aspects of a method implemented by the CC circuitry 1106. The CC circuit 1106 employs a delta comparator (not shown in fig. 12) that compares predetermined values X and the difference between Hrep and Lrep. Again, in one embodiment, X is zero, and in other embodiments, X is a non-zero current or voltage value. In step 1202, the difference Hrep-Lrep is compared to X. If Lrep-Hrep > X, then circuitry 1106 generates WS1 using Hrep as shown in step 1204, and CC circuitry 1106 sets Flag1 to LSS in step 1206, indicating that a resistive short exists between terminals L and Vss. If Lrep-Hrep is not greater than X, then the process continues to step 1208, where circuitry 1106 generates WS1 using Lrep. In step 1210, the same or a different delta comparator (not shown) compares Hrep-Lrep with X. If Hrep-Lrep > X, the CC circuit 1106 sets Flag1 to HSS in step 1212, indicating that a resistive short exists between terminal H and ground. If Hrep-Lrep is not greater than X in step 1210, Flag1 is set to NS.

It should again be noted that both Hrep and Lrep may be current signals, or both Hrep and Lrep may be voltage signals. In embodiments where Hrep and Lrep are current signals, the difference between Hrep and Lrep may be compared to X, where X is expressed as a value in milliamps (e.g., X ═ 0.5 mA). In embodiments where Hrep and Lrep are voltage signals, the difference between Hrep and Lrep may be compared to X, where X is expressed as a value in volts (e.g., X ═ 2V). Either way, the CC circuit 1106 generates the wheel speed signal WS1 based on Hrep or Lrep.

The CC circuitry 1106 may employ a delta comparator, a signal selector, and one or more threshold detectors. Fig. 13 illustrates one embodiment of a CC circuit in block diagram form 1106. Fig. 14 illustrates in a block diagram another embodiment of a CC circuit 1106. The CC circuit should not be limited to the case shown in fig. 13 or 14.

With continued reference to fig. 11 and 12, the CC circuit 1106 in fig. 13 includes a delta comparator 1302, and a pair of threshold detectors 1304 and 1306 coupled to receive HRep and Lrep from a high-side current monitor 1102 and a low-side current monitor 1104 as shown. Threshold detectors 1304 and 1306 output square wave signals WSH and WSL, respectively, based on HRep and LRep, respectively. Each of threshold detectors 1304 and 1306 compares input signals HRep and LRep, respectively, to one or more thresholds. In one embodiment, each threshold detector compares its input signal to a first threshold. If the input signal exceeds the first threshold, the threshold detector outputs 5V. When the threshold detector outputs 5V, the threshold detector compares its input signal with a second threshold value, which is smaller than the first threshold value. If the input signal falls below the second threshold, the threshold detector switches the output to 0V. When the threshold detector outputs 0V, the threshold detector again compares the input signal with the first threshold and will switch the output to 5V again when the input signal exceeds the first threshold. In this way, the threshold detector 1304 generates an output square wave signal WSH, and the threshold detector 1306 generates an output square wave signal WSL. Assuming that there is no resistive short, the frequencies of the square waves WSH and WSL should be the same as the frequencies of HRep and LRep, respectively.

The WSH and WSL square wave signals are provided as inputs to signal selector 1310. The signal selector 1310 also receives a selection signal from the delta comparator 1302. Delta comparator 1302 compares HRep and LRep according to steps 1202 or 1210 shown in fig. 12. The differential comparator 1302 asserts a select signal (e.g., the select signal is set to logic 1) when Lrep-Hrep > X. Otherwise the delta comparator 1302 deasserts the select signal. When the select signal is asserted, signal selector 1310 outputs square wave signal WSH as WS 1. Otherwise signal selector 1310 outputs square wave WSL as WS 1.

Fig. 14 shows an alternative embodiment of the CC circuit 1106. With continued reference to fig. 11-13, the embodiment shown in fig. 14 employs most of the components shown in fig. 13. However, the components are arranged differently and have different inputs. For example, signal selector 1310 receives as inputs Hrep and Lrep. When the delta comparator 1302 asserts its select signal, the signal selector 1310 selects HRep for output to the threshold detector 1304. The differential comparator 1302 asserts a select signal when Lrep-Hrep > X. Otherwise signal selector 1310 selects LRep for output to threshold detector 1304. Detector 1304 generates WS1 based on the input signal selected by signal selector 1310 in much the same manner as described above.

A first embodiment of the method includes transmitting a first current to a wheel speed sensor and receiving a second current, some or all of which is received from the wheel speed sensor. A first periodic signal is generated based on the first current. A second periodic signal is generated based on the second current. If the magnitude of the second current is greater than the magnitude of the first current, then the first periodic signal is selected for output. If the magnitude of the second current is not greater than the magnitude of the first current, then the second periodic signal is selected for output. The selected first or second periodic signal contains information related to the speed of the wheel associated with the wheel speed sensor.

The magnitude of the second current is greater than the magnitude of the first current when the magnitude of the second current exceeds the magnitude of the first current by a predetermined amount, and the magnitude of the second current is not greater than the magnitude of the first current when the magnitude of the second current does not exceed the magnitude of the first current by the predetermined amount.

The first embodiment of the method may also include generating a third current based on the first current, wherein a magnitude of the third current is proportional to a magnitude of the first current. A fourth current may be generated based on the second current, wherein a magnitude of the fourth current is proportional to a magnitude of the second current. The third current may be compared to the fourth current. The act of selecting the first or second periodic signal is performed in response to comparing the third and fourth currents.

The first periodic signal may be generated directly from the third current and the second periodic signal may be generated directly from the fourth current.

The method may also include setting the signal to a first state if the first current is greater than the second current, wherein the first state indicates a resistive short circuit between the first end of the wheel speed sensor and the ground within the power system. Setting the signal to a second state if the second current is greater than the first current, wherein the second state indicates a resistive short circuit between the second end of the wheel speed sensor and the supply voltage within the electrical system.

The first current changes when a tooth of the rotor passes near a wheel speed sensor, and the second current changes when the tooth of the rotor passes near the wheel speed sensor.

The first embodiment of the method can also include generating a first voltage based on the first current, wherein a magnitude of the first voltage is proportional to a magnitude of the first current. A second voltage may be generated based on the second current, wherein a magnitude of the second voltage is proportional to a magnitude of the second current. The first and second voltages may be compared, wherein the act of selecting the first or second periodic signal is performed in response to comparing the first and second voltages.

The first periodic signal is generated directly from a first voltage and the second periodic signal is generated directly from a second voltage.

One embodiment of an apparatus employing the present techniques may include a first circuit to transmit a first current to a wheel speed sensor, a second circuit to receive a second current, some or all of which may be received from the wheel speed sensor. A first threshold detection circuit may be included for generating a first periodic signal based on the first current. A second threshold detection circuit may be included for generating a second periodic signal based on the second current. Circuitry may be included that may select the first periodic signal for output if the magnitude of the second current is greater than the magnitude of the first current. The circuit may select the second periodic signal for output if the magnitude of the second current is not greater than the magnitude of the first current. The selected first or second periodic signal contains information related to the speed of the wheel associated with the wheel speed sensor.

The magnitude of the second current is greater than the magnitude of the first current when the magnitude of the second current exceeds the magnitude of the first current by a predetermined amount, and the magnitude of the second current is not greater than the magnitude of the first current when the magnitude of the second current does not exceed the magnitude of the first current by the predetermined amount.

The apparatus may further include a first current monitor circuit for generating a third current based on the first current, wherein a magnitude of the third current is proportional to a magnitude of the first current. The second current monitor circuit may generate a fourth current based on the second current, wherein a magnitude of the fourth current is proportional to a magnitude of the second current. The comparator circuit may compare the third current with the fourth current. The circuit selects the first or second periodic signal in response to the comparator circuit comparing the third and fourth currents.

The first threshold detection circuit generates a first periodic signal directly from the third current and the second threshold detection circuit generates a second periodic signal directly from the fourth current.

The comparator circuit of the apparatus may set the signal to a first state if the first current is greater than the second current, wherein the first state indicates a resistive short circuit between the first end of the wheel speed sensor and the ground within the power system. The comparator circuit may set the signal to a second state if the second current is greater than the first current, wherein the second state indicates a resistive short circuit between the second end of the wheel speed sensor and the supply voltage within the electrical system.

The apparatus may further include a first current monitor circuit for generating a first voltage based on the first current, wherein a magnitude of the first voltage is proportional to a magnitude of the first current. A second current monitor circuit may also be included for generating a second voltage based on the second current, wherein a magnitude of the second voltage is proportional to a magnitude of the second current. The comparator circuit may compare the first and second voltages.

The first threshold detection circuit may generate the first periodic signal directly from a first voltage, and the second threshold detection circuit may generate the second periodic signal directly from a second voltage.

A system is disclosed that includes a first circuit for generating a first periodic signal based on a first current delivered to a wheel speed sensor. The second circuit may generate a second periodic signal based on second currents, some or all of which are received from the wheel speed sensors. The circuit may select the first periodic signal for output if the magnitude of the second current is greater than the magnitude of the first current, wherein the circuit is configured to select the second periodic signal for output if the magnitude of the second current is not greater than the magnitude of the first current. The selected first or second periodic signal includes information related to a speed of a wheel associated with the wheel speed sensor.

The magnitude of the second current is greater than the magnitude of the first current when the magnitude of the second current exceeds the magnitude of the first current by a predetermined amount, and the magnitude of the second current is not greater than the magnitude of the first current when the magnitude of the second current does not exceed the magnitude of the first current by the predetermined amount.

The system may also include a first current monitor circuit for generating a third current based on the first current, wherein a magnitude of the third current is proportional to a magnitude of the first current. The second current monitor circuit may generate a fourth current based on the second current, wherein a magnitude of the fourth current is proportional to a magnitude of the second current. The comparator circuit may compare the third current with the fourth current. The circuit selects the first or second periodic signal in response to the comparator circuit comparing the third and fourth currents.

The comparator circuit may set the signal to the first state if the first current is greater than the second current. The first state indicates that a resistive short circuit exists within the electrical system between the first end of the wheel speed sensor and the ground. The comparator circuit may set the signal to the second state if the second current is greater than the first current. The second state indicates that a resistive short circuit exists within the electrical system between the second end of the wheel speed sensor and the supply voltage.

The system may include a first current monitor circuit that generates a first voltage based on a first current. The magnitude of the first voltage is proportional to the magnitude of the first current. The second current monitor circuit may generate a second voltage based on the second current. The magnitude of the second voltage is proportional to the magnitude of the second current. The comparator circuit may compare the first and second voltages. The circuit may select the first or second periodic signal in response to the comparator circuit comparing the first and second voltages.

Although the present invention has been described in connection with several embodiments, it is not intended to be limited to the specific form set forth herein. On the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be reasonably included within the scope of the invention as defined by the appended claims.