Patent Application
20210269049
This invention relates to the by-wire control of engine and brake actuators, and more particularly to a fail-safe interface for merging and prioritizing driver and externally generated by-wire commands.
By-wire technology is increasingly being used by vehicle manufacturers as a means of electronically controlling driver-regulated functions such as powerplant and braking controls. This replaces the traditional mechanical linkages, but also importantly, it enables an alternate or supplemental control of these functions by an external computer-based control unit. “External” in this sense, simply means a control unit separate from the on-board or OEM (original equipment manufacturer) controller that is designed to carry out driver commands. Typically, the alternate or supplemental control is safety related, as in the case of automatic braking or stability control, but it can also be an autonomous driving control designed to operate the vehicle without driver input. These alternate or supplemental controls frequently command actions that are not commanded by the driver, but it is important that due deference be given to driver commands when they are present, and also to avoid abrupt transitions between driver control and external control. At the same time, it is important to address potential failure modes of the external control unit to minimize unintended overriding of a driver-generated command. Accordingly, what is needed is an improved and failure-tolerant interface for merging and prioritizing the driver and external commands in these systems.
The present invention is directed to an improved and failure-tolerant interface circuit for a by-wire vehicle control system in which driver commands and external commands developed by a control unit are merged to form failure-tolerant actuator commands that never diminish the driver commands. The external commands are passed through a fault detection circuit that filters out aberrant cyclical and constant command signals from the external control unit, and the actuator command is determined according to the higher or maximum of the driver-generated and external commands. The interface is powered by vehicle power supply, and is electro-optically isolated from the control unit that develops the external commands so that if the control unit loses power, the actuator command faithfully follows the driver command.
In general, the present invention is designed to enable a user control unit to seamlessly interface with an OEM vehicle by-wire control system, as generally depicted in the diagram of
Also depicted in
As noted above, the Interface Circuit 32 gives due deference to the driver-generated commands by developing the final commands according to the higher or maximum of the driver-generated and external commands. This also means that if By-Wire Control Unit 31 loses power, the final commands produced by Interface Circuit 32 faithfully follow the driver commands. Using braking as an example, the Interface Circuit 32 will allow the By-Wire Control Unit 31 to cause more braking than the driver braking command, but not less; put another way, the driver will always be able to cause more braking than the By-Wire Control Unit 31 is commanding (unless both are commanding maximum braking, of course). A similar philosophy is applies to the accelerator commands, or any other actuator control.
The Interface Circuit 32 is powered by a vehicle-based power supply 36 that also supplies power to the various components of the OEM system 10, as indicated by the broken outline 40. The By-Wire Control Unit 31, on the other hand, is powered by a separate or external power supply 37, as indicated by the broken outline 42. And electro-optical isolators 43, 44, 45 and 46 electrically isolate the inputs and outputs of the By-Wire Control Unit 31. These measures electrically isolate the By-Wire Control Unit 31 from the Interface Circuit 32 and the rest of the OEM control system 10 so that electrical faults in the By-Wire Control Unit 31 or its power supply 37 do not cause faulty operation of the Interface Circuit 32 and OEM control system 10.
An embodiment of the Interface Circuit 32 as applied to brake pedal position is depicted in
In general, the Interface Circuit 32 includes, for each of the complementary external brake commands, a Fault-Detection Circuit 48 or 50, an AND-gate 60 or 62 for logically combining filtered and unfiltered external commands, and a logic gate 64 or 66 for logically combining the AND-gate output with the corresponding driver brake command. In the active-high portion of the circuit, the combining logic gate 64 is an OR-gate, whereas in the active-low portion of the circuit, the combining logic gate 66 is an AND-gate. The Fault-Detection Circuits 48 and 50, in conjunction with AND-gates 60 and 62, screen the external brake commands EXT_BR_CMD-AH and EXT_BR_CMD-AL for the most common fault modes. Fault-mode commands are forced to their inactive logic level, while non-fault-mode commands are passed unaltered. The logic gates 64 and 66 form the final brake commands FINAL_BR_CMD-AH and FINAL_BR_CMD-AL as the higher the driver brake commands DR_BR_CMD-AH or DR_BR_CMD-AL and the output of the respective AND-gates 60 and 62. In other words, the final brake commands FINAL_BR_CMD-AH and FINAL_BR_CMD-AL will have a duty cycle that is the greater of the driver and screened or passed external brake commands.
The Fault-Detection Circuits 48 and 50 screen the digital external brake commands by determining if they are actively toggling high and low within a specified range or band of frequencies. In the illustrated embodiment, this functionality is implemented with the serial combination of a high-pass filter (HPF)—or alternately, a band-pass filter (BPF)—51 or 52, a demodulator (DEMOD) 53 or 54, and a threshold circuit (THRESH) 55 or 56. Their output is a logic HIGH if no fault is detected, or a logic LOW when a faulty command is detected. These faults include both constant failure modes (that is, stuck-high or stuck-low), and invalid cyclic failure modes. The logic HIGH output enables the respective AND-gate 60 or 62 to pass the unfiltered external command, whereas the logic LOW output disables/prevents the AND-gate 60 or 62 from passing the unfiltered external command. The filters 55 or 56 are designed to pass external command signals that are actively toggling within the specified range or band of frequencies, but otherwise ideally produce a zero output. The demodulators 53 and 54 can be implemented with a timing circuit that directly determines the duty cycle of the respective PWM signal, or more simply with a low-pass filter, to produce an analog voltage proportional to the duty cycle of the filter output. And the threshold circuits 55 or 56 establish an analog voltage corresponding to a minimum PWM duty cycle; if the output of the respective demodulator 53 or 54 exceeds the threshold, the threshold circuit 55 or 56 outputs a logic HIGH, but if the demodulator output is below the threshold, the threshold circuit 55 or 56 outputs a logic LOW. This, as mentioned above, is the enable/disable signal for AND-gate 60 or 62.
In the illustrated embodiment, the active-low portion of the Interface Circuit 32 includes two additional components: an input inverter 68 upstream of Fault-Detection Circuit 50 for initially converting the active-low external brake command EXT_BR_CMD-AL to an active-high signal, and a restorative inverter 70 between AND-gate 62 and OR-gate 66 for converting the filtered signal back to an active-low signal. This allows the Fault-Detection Circuit Circuits 48 and 50 to be identical, as they both operate on active-high PWM commands. Of course, the function of inverter 68 can be implemented in the By-Wire Control Unit 31 instead of the Interface Circuit 32, if desired.
An embodiment of the Interface Circuit 32 as applied to accelerator pedal position is depicted in
In general, the Interface Circuit 32 includes, for each of the complementary external accelerator commands, a Fault-Detection Circuit 72 or 74, and a Summing Junction 76 or 78 for summing the filter output with the corresponding driver accelerator command. In effect, the Interface Circuit 32 sets the final accelerator command according to the higher of the driver command and the external command. As with the embodiment of
The combination of reducing the external accelerator command by the driver command (in the By-Wire Control Unit 31), and subsequently summing the analog external and driver commands (in Summing Junctions 76 and 78) serves to set the final accelerator commands according to the higher of the external and driver accelerator commands. For example, if the driver accelerator commands correspond to 50% pedal position, but the external accelerator pedal command is 60%, the By-Wire Control Unit 31 outputs its accelerator command based on a pedal position of 60%−50%=10%, which will cause the Summing Junctions 76 and 78 of Interface Circuit 32 to increase the driver commands by amounts corresponding to 10% pedal position, and the Powertrain Actuator 18 is regulated according to the external command. On the other hand, if the external accelerator command is less than or equal to the driver command, the By-Wire Control Unit 31 outputs its actuator command based on 0% pedal position; in this case, the Summing Junctions 76 and 78 do not increase the driver accelerator command, and the Powertrain Actuator 18 is regulated according to the driver command. Of course, the subtraction function ascribed to the By-Wire Control Unit 31 could alternatively be carried out in the Interface Circuit 32, if desired.
In summary, the present invention provides an improved and fault-tolerant interface for merging and prioritizing the driver and external commands in vehicular by-wire control systems. It will be recognized that while the invention has been described in reference to the vehicle powerplant and brake controls, it is applicable to other types of actuator control as well, and that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. Accordingly, it will be appreciated that systems incorporating these and other modifications and variations still fall within the intended scope of the invention.
