Patent Grant
6975493
This invention relates to providing overvoltage protection for circuits and systems. For example, circuits in vehicle systems subject to overvoltage conditions resultant from load removal and the like or where integrated circuit microcontrollers are interfaced with motors via MOSFET(s) for motor position controllers such as may be employed in vehicle steering systems. Such systems may use control electronics to provide the interface between low voltage microcontrollers and the high voltage MOSFETs. The control electronics may also include motor control logic, a charge pump, MOSFET gate drives and overvoltage and overcurrent protection.
Unfortunately, many electronic systems include components that can be susceptible to voltage transients on their supply voltage. Such transients in certain circumstances may even destroy the components leading to early failure and excessive repairs. Therefore many circuits employ over voltage and/or over current protection schemes to prevent or avoid such transients or at least avoid the damage resulting from their occurrence.
A typical method to protect such electronics modules from transients and reverse voltage would be to use transient suppression devices to limit the voltage below the maximum input voltages for the devices. Unfortunately, if there were a great amount of energy in the transient pulse, the clamping devices would be very large and expensive. Moreover, reasonably sized varistors and the like would not be able to withstand the high peak currents seen during some transients. Transient voltage suppressors that can withstand the peak power are available but are large and expensive.
Therefore, it would be beneficial to provide a cost effective means of protecting circuits from over voltage transients.
Disclosed herein is a low side overvoltage protection circuit configuration comprising: a first switching device in operable communication with and disposed between a ground and a protected ground; a load in operable communication with and disposed between a voltage source and the protected ground; a control circuit configured to control the first switching device in operable communication with a transient protected voltage source. The first switching device is configured to provide electrical circuit isolation of the protected ground from the ground.
Also disclosed herein is a method for providing a low side circuit overvoltage protection comprising: detecting an overvoltage transient on a voltage source; isolating a protected ground from a circuit ground with a first switching device; and controlling the first switching device with a control circuit in operable communication with another transient protected voltage source. The control circuit is responsive to an overvoltage transient of the voltage source.
Further disclosed herein is a system for providing a low side circuit overvoltage protection comprising: a means for detecting an overvoltage transient on a voltage source; a means for isolating a protected ground from a circuit ground with a first switching device; and a means for controlling the first switching device with a control circuit in operable communication with another transient protected voltage source. The control circuit is responsive to an overvoltage transient of the voltage source.
Also disclosed herein in yet another embodiment is a vehicle steering system with a low side overvoltage protection circuit configuration comprising: a steerable wheel; a steering mechanism operably connected to the steerable wheel for transmitting a desired steering command to the steerable wheel; a steering input device in operable communication with the steering mechanism configured to generate the desired steering command; and a motor in operable communication with the steering mechanism to provide a torque and in operable communication with a transient protected voltage source. The system also includes a first switching device in operable communication with and disposed between a ground and a protected ground; a load in operable communication with and disposed between a voltage source and the protected ground, the load including the motor; and a control circuit configured to control the first switching device in operable communication with a transient protected voltage source. The first switching device is configured to provide electrical circuit isolation of the protected ground from the ground.
The present invention will now be described, by way of an example, with references to the accompanying drawings, wherein like elements are numbered alike in the several figures in which:
Referring to
Electric power steering assist is provided through the control apparatus generally designated by reference numeral 24 and includes the controller 16 and the electric motor 46. The controller 16 is powered by the vehicle power supply 10 through line 12. The controller 16 receives a vehicle speed signal 14 representative of the vehicle velocity. Steering pinion gear angle is measured through position sensor 32, which may be an optical encoding type sensor, variable resistance type sensor, or any other suitable type of position sensor, and supplies to the controller 16 a position signal 20. Motor velocity may be measured with a tachometer and transmitted to controller 16 as a motor velocity signal 21. A motor velocity denoted ωm may be measured, calculated or a combination thereof. For example, the motor velocity ωm may be calculated as the change of the motor position θ as measured by a position sensor 32 over a prescribed time interval. It will be appreciated that there are numerous well-known methodologies for performing the function of a derivative.
As the steering wheel 26 is turned, torque sensor 28 senses the torque applied to the steering wheel 26 by the vehicle operator. The torque sensor 28 may include a torsion bar (not shown) and a variable resistive-type sensor (also not shown), which outputs a variable torque signal 18 to controller 16 in relation to the amount of twist on the torsion bar. Although this is the preferable torque sensor, any other suitable torque-sensing device used with known signal processing techniques will suffice. In response to the various inputs, the controller sends a command 22 to the electric motor 46, which supplies torque assist to the steering system through worm 47 and worm gear 48, providing torque assist to the vehicle steering.
It should be noted that although the disclosed embodiments are described by way of reference to motor control for electric steering applications, it will be appreciated that such references are illustrative only and the disclosed embodiments may be applied to any instance where rotational displacement, e.g., torque sensing is desired. Moreover, the references and descriptions herein may apply to many forms of parameter sensors, including, but not limited to torque, position, speed and the like. It should also be noted that reference herein to electric machines including, but not limited to, motors, or more specifically sinusoidally excited brushless DC motors, hereafter, for brevity and simplicity, reference will be made to motors only without limitation.
In the control system 24 as depicted, the controller 16 utilizes the torque, position, and speed, and like, to compute a command(s) to deliver the required output power. Controller 16 is disposed in communication with the various systems and sensors of the motor control system. Controller 16 receives signals from each of the system sensors, quantifies the received information, and provides an output command signal(s) in response thereto, in this instance, for example, to the motor 46. Controller 16 is configured to develop the necessary voltage(s) out of inverter (not shown) such that, when applied to the motor 46, the desired torque or position is generated. Because these voltages are related to the position and speed of the motor 46 and the desired torque, the position and/or speed of the rotor and the torque applied by an operator are determined. A position encoder is connected to the steering shaft 51 to detect the angular position 0. The encoder may sense the rotary position based on optical detection, magnetic field variations, or other methodologies. Typical position sensors include potentiometers, resolvers, synchros, encoders, and the like, as well as combinations comprising at least one of the forgoing. The position encoder outputs a position signal 20 indicating the angular position of the steering shaft 51 and thereby, that of the motor 46.
Desired torque may be determined by one or more torque sensors 28 transmitting torque signals 18 indicative of an applied torque. An exemplary embodiment includes such a torque sensor 28 and the torque signal(s) 18 therefrom, as may be responsive to a compliant torsion bar, T-bar, spring, or similar apparatus (not shown) configured to provide a response indicative of the torque applied.
Optionally, a temperature sensor(s) 23 located at the torque sensor 28. Preferably the temperature sensor 23 is configured to directly measure the temperature of the sensing portion of the torque sensor 28. The temperature sensor 23 transmits a temperature signal 25 to the controller 16 to facilitate the processing prescribed herein and compensation. Typical temperature sensors include thermocouples, thermistors, thermostats, and the like, as well as combinations comprising at least one of the foregoing sensors, which when appropriately placed provide a calibratable signal proportional to the particular temperature.
The position signal 20, velocity signal 21, and a torque signal(s) 18 among others, are applied to the controller 16. The controller 16 processes all input signals to generate values corresponding to each of the signals resulting in a rotor position value, a motor speed value, and a torque value being available for the processing in the algorithms as prescribed herein. Measurement signals, such as the abovementioned are also commonly linearized, compensated, and filtered as desired or necessary to enhance the characteristics or eliminate undesirable characteristics of the acquired signal. For example, the signals may be linearized to improve processing speed, or to address a large dynamic range of the signal. In addition, frequency or time based compensation and filtering may be employed to eliminate noise or avoid undesirable spectral characteristics.
In order to perform the prescribed functions and desired processing, as well as the computations therefore (e.g., control algorithm(s), and the like), controller 16 may include, but not be limited to, a processor(s), computer(s), DSP(s), microcontrollers, memory, storage, register(s), timing, interrupt(s), communication interface(s), and input/output signal interfaces, and the like, as well as combinations comprising at least one of the foregoing. For example, controller 16 may include input signal processing and filtering to enable accurate sampling and conversion or acquisitions of such signals from communications interfaces. Additional features of controller 16 and certain processes therein are thoroughly discussed at a later point herein.
In an exemplary embodiment, the controller 16 obtains as input signals or receives signals to facilitate computing, commands for controlling a motor. Also received by the controller 16 are a variety of implementation specific parameters, signals and values for initialization and characterization of the prescribed processes and to identify various states of the processes herein.
Continuing now with
Referring to
Continuing with
Continuing with the figure, resistor 152 also denoted R1 and zener diode 154 also denoted Z1 provide an overvoltage and reverse voltage protected supply voltage to control circuit 156 in this instance a comparator also denoted IC1. IC1 will be exposed to the full overvoltage condition as presented on voltage supply Ignition 122. The combination of control circuit IC1156, resistor 158, also denoted R2, resistor 160 also denoted R3, resistor 162 also denoted R4 and zener diode 164 also denoted Z2 cooperated to form an overvoltage detection circuit.
Continuing now with a discussion of the overvoltage detection circuit and the low side overvoltage protection provided, resistor 158 (R2) and zener diode 164 (Z2) in series, form a reference voltage to the control circuit 156 (comparator IC1). In an exemplary embodiment, the breakdown voltage of zener diode 164 (Z2) is selected to be a voltage less than the normal operating voltage of voltage source Ignition 122 (for example 2.4 Volts for a voltage source of 12 volts). This voltage establishes a reference voltage for the control circuit 156. Resistor 158 (R2) is used to limit the current through zener diode 164 (Z2) and maintain power dissipation within acceptable limits. Resistor 160 (R3) and resistor 162 (R4) form a voltage divider on voltage source 122 (Ignition) to establish an overvoltage threshold (36.7 Volts on voltage source 122 (Ignition) in this example).
The control circuit 156, voltage comparator (IC1) monitors the two voltage levels formulated above. When the voltage on the non-inverting input denoted Comp_ref is above the voltage on the inverting input denoted Ign_ref in the figure, the output of control circuit 156 will be “high” or “open collector.” In this instance a voltage defined by the series combination of resistor 134 (R5) and zener diode 132 is applied as a control to switching device 130. Conversely, when the voltage on the non-inverting input to control circuit 156 (Comp_ref) is less than the voltage on the inverting input (Ign_ref), the output will be approximately ground or “low”. In this instance a low is supplied to the gate of switching device 130 (a MOSFET in this instance). When the gate of the switching device 130 is pulled to ground, the switching device 130 (MOSFET) turns off isolating the Protected Ground 142 from ground 140.
To provide protection to the Load 144 the path to ground 140 for the “Load” 144 is broken whenever the voltage source 122 (Ignition) exceeds the selected overvoltage threshold as established by zener diode 164 (Z2). It will be appreciated that the switching device 130 is selected with a voltage rating exceeding the maximum overvoltage of voltage source 122 (Ignition).
It will also be appreciated that the exemplary embodiment depicted in
In an exemplary embodiment, under normal operating conditions, switching device 170 is turned “off” by R1 maintaining the gate of switching device 170 at the ground potential or at least less than the Vgs(on) of switching device 170 (in this instance, an n-channel MOSFET). The zener voltage of zener diode 176 (Z2) controls the selected overvoltage threshold in this embodiment. The zener diode 176 (Z2) is selected to ensure that it only allows current to flow through when voltage source 122 (Ignition) exceeds the selected (36 Volts in this example). Resistor 174 (R2) limits the current through Z2 during these overvoltage conditions. Zener diode 178 (Zcontrol) is selected to limit the maximum attainable gate to source voltage of for the switching device 170. When the voltage source 122 Ignition exceeds the zener voltage of zener diode 176 (Z2), current flows producing a voltage at the gate of switching device 170 When this voltage exceeds the Vgs(on) turn on voltage of switching device 170, switching device 170 turns “on” pulling the gate of switching device 130 to ground and thereby turning switching device 130 “off.” The Protected_Ground is then isolated from ground as described above.
Once again, it will be appreciated that the switching device 130 is the only component that requires a high voltage rating to ensure it can withstand the overvoltage levels of voltage source 122 (Ignition). Advantageously, the voltage rating of switching device 170 is determined by the selected breakdown voltage of zener diode 132, which is relatively low voltage facilitating the component selection.
Yet, another advantage of the disclosed embodiments over existing options may readily be apparent from consideration thereof. One means of providing protection to the circuitry from these high transient voltages to limit or clamp the input voltage for Ignition 122 to below the maximum input voltages for the circuit components such as, the predriver and the like, would be to employ transient suppression devices including, but not limited to transorbs, varistors, zener diodes, and the like, as well as combinations including at least one of the foregoing. Unfortunately, in such a configuration, there is often a great amount of energy in a transient pulse so the requisite clamping devices would be very large and expensive. Reasonably sized varistors, for example, would not be able to withstand the high peak currents experienced during such transients. Transient voltage suppressors that could withstand the peak power generated are available, but are large and expensive.
It will be appreciated that the use of first and second or other similar nomenclature for denoting similar items is not intended to specify or imply any particular order unless otherwise stated.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4005342 | Davis | Jan 1977 | A |
| 4890020 | Bird | Dec 1989 | A |
| 6043965 | Hazelton et al. | Mar 2000 | A |
| 6154081 | Pakkala et al. | Nov 2000 | A |
| 6198350 | Zarabadi | Mar 2001 | B1 |
| 6204715 | Sellnau et al. | Mar 2001 | B1 |
| 6392266 | Robb et al. | May 2002 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20040150929 A1 | Aug 2004 | US |
