Wake-up circuit in an electric steering system

Patent metadata

Field	Value
Publication number	US-9434407-B2
Application number	US-201414455982-A
Country	US
Kind code	B2
Filing date	Aug 11, 2014
Priority date	May 14, 2010
Publication date	Sep 6, 2016
Grant date	Sep 6, 2016

Abstract

In one aspect, a wake-up circuit is provided for triggering a determination of an absolute rotational position of a rotatable shaft of a motor in an electric power steering system of a vehicle. The wake-up circuit includes a plurality of inputs coupled to separate phases of the motor. A voltage boosting circuit is operable to increase a back electromotive force (EMF) voltage induced on one or more of the inputs by rotation of the rotatable shaft of the motor and produce at least one voltage-boosted back EMF voltage. A comparator circuit is operable to compare the at least one voltage-boosted back EMF voltage to a reference voltage and trigger a monitoring system to perform the determination of the absolute rotational position of the rotatable shaft of the motor in the electric power steering system based on a result of the compare during an ignition off state of the vehicle.

First claim

What is claimed is:

1. A wake-up circuit for triggering a determination of an absolute rotational position of a rotatable shaft of a motor in an electric power steering system of a vehicle, the wake-up circuit comprising:
a plurality of inputs coupled to separate phases of the motor;
a voltage boosting circuit operable to increase a back electromotive force (EMF) voltage induced on one or more of the inputs by rotation of the rotatable shaft of the motor and produce at least one voltage-boosted back EMF voltage, the voltage boosting circuit comprising at least one capacitor in-line with each of the inputs and a blocking diode positioned between pairs of the inputs to prevent the at least one capacitor in-line with each of the inputs from discharging into the phases of the motor; and
a comparator circuit operable to compare the at least one voltage-boosted back EMF voltage to a reference voltage and trigger a monitoring system to perform the determination of the absolute rotational position of the rotatable shaft of the motor in the electric power steering system of the vehicle based on a result of the compare during an ignition off state of the vehicle.

2. The wake-up circuit of claim 1 , wherein the voltage boosting circuit charges the at least one capacitor on a first cycle polarity of each of the inputs and effectively doubles the back EMF voltage on a second cycle polarity opposite the first cycle polarity to produce the at least one voltage-boosted back EMF voltage.

3. The wake-up circuit of claim 1 , further comprising a full-wave rectifier circuit, wherein the at least one capacitor on each of the inputs of the voltage boosting circuit is positioned between a diode pair of the full-wave rectifier circuit for each of the inputs.

4. The wake-up circuit of claim 3 , wherein a first diode of the diode pair establishes a ground reference for one of the phases of the motor, and a second diode of the diode pair establishes an instantaneous forward voltage for the comparator circuit.

5. A wake-up circuit for triggering a determination of an absolute rotational position of a rotatable shaft of a motor in an electric power steering system of a vehicle, the wake-up circuit comprising:
a plurality of inputs coupled to separate phases of the motor;
a voltage boosting circuit operable to increase a back electromotive force (EMF) voltage induced on one or more of the inputs by rotation of the rotatable shaft of the motor and produce at least one voltage-boosted back EMF voltage;
a scaling and protection circuit comprising a voltage divider circuit and a voltage clamp; and
a comparator circuit operable to compare the at least one voltage-boosted back EMF voltage to a reference voltage and trigger a monitoring system to perform the determination of the absolute rotational position of the rotatable shaft of the motor in the electric power steering system of the vehicle based on a result of the compare during an ignition off state of the vehicle.

6. The wake-up circuit of claim 5 , wherein the scaling and protection circuit further comprises at least one current limiting resistor positioned between the voltage divider circuit and the voltage clamp, and a comparator input voltage indicative of the at least one voltage-boosted back EMF voltage is established between the at least one current limiting resistor and the voltage clamp.

7. A system for determining an absolute rotational position of a rotatable shaft of a motor in an electric power steering system of a vehicle, the system comprising:
a wake-up circuit comprising a voltage boosting circuit and a comparator circuit, the voltage boosting circuit operable to increase a back electromotive force (EMF) voltage induced on one or more inputs by rotation of the rotatable shaft of the motor and produce at least one voltage-boosted back EMF voltage, the voltage boosting circuit comprises at least one capacitor in-line with each of the inputs and positioned between a diode pair of a full-wave rectifier circuit for each of the inputs, the comparator circuit operable to compare the at least one voltage-boosted back EMF voltage to a reference voltage and output a control signal based on a result of the compare during an ignition off state of the vehicle; and
a monitoring system comprising a microprocessor and first and second position sensors operable to generate signals indicative of a relative rotational position of the rotatable shaft, the microprocessor configured to activate in response to the control signal and determine a current absolute position value indicating a current absolute rotational position of the rotatable shaft based on a previously stored absolute position value and an amount of relative rotation of the rotatable shaft based on the signals from the first and second position sensors.

8. The system of claim 7 , wherein the voltage boosting circuit charges the at least one capacitor on a first cycle polarity of each of the inputs and effectively doubles the back EMF voltage on a second cycle polarity opposite the first cycle polarity to produce the at least one voltage-boosted back EMF voltage.

9. The system of claim 7 , wherein a first diode of the diode pair establishes a ground reference for one phase of the motor, and a second diode of the diode pair establishes an instantaneous forward voltage for the comparator circuit.

10. The system of claim 7 , wherein the wake-up circuit further comprises a blocking diode positioned between pairs of the inputs to prevent the at least one capacitor in-line with each of the inputs from discharging into phases of the motor.

11. The system of claim 7 , wherein the wake-up circuit further comprises a scaling and protection circuit comprising a voltage divider circuit and a voltage clamp.

12. The system of claim 11 , wherein the scaling and protection circuit further comprises at least one current limiting resistor positioned between the voltage divider circuit and the voltage clamp, and a comparator input voltage indicative of the at least one voltage-boosted back EMF voltage is established between the at least one current limiting resistor and the voltage clamp.

13. A method for triggering a determination of an absolute rotational position of a rotatable shaft of a motor in an electric power steering system of a vehicle, the method comprising:
increasing a back electromotive force (EMF) voltage induced on one or more inputs from separate phases of the motor by rotation of the rotatable shaft to produce at least one voltage-boosted back EMF voltage, the increasing performed by a voltage boosting circuit comprising at least one capacitor in-line with each of the inputs that charges the at least one capacitor on a first cycle polarity of each of the inputs and effectively doubling the back EMF voltage on a second cycle polarity opposite the first cycle polarity to produce the at least one voltage-boosted back EMF voltage;
comparing the at least one voltage-boosted back EMF voltage to a reference voltage; and
triggering a monitoring system to perform the determination of the absolute rotational position of the rotatable shaft of the motor in the electric power steering system of the vehicle based on a result of the comparing during an ignition off state of the vehicle.

14. The method of claim 13 , wherein the at least one capacitor on each of the inputs is positioned between a diode pair of a full-wave rectifier circuit for each of the inputs.

15. The method of claim 13 , further comprising preventing the at least one capacitor in-line with each of the inputs from discharging into the phases of the motor.

Assignees

• Steering Solutions Ip Holding

Inventors

• Amin Ishtiaque
• Bright Philip G
• Fisher Paul M

Classifications

• B62D15/0235

  by measuring or deriving directly at the electric power steering motor · CPC title

• B62D5/0481 Primary

  monitoring the steering system, e.g. failures · CPC title

• B62D15/021

  Determination of steering angle · CPC title

• H02P6/182

  using back-emf in windings · CPC title