The present invention relates generally to diagnostics of a materials handling vehicle, and, more particularly, to utilizing a traction model to perform diagnostics.
Forklifts and other types of industrial vehicles are expected to operate under a variety of different conditions. Further, such vehicles typically include a number of different functional systems such as a traction system to control a travelling speed of the vehicle and a steering system to control a direction in which the vehicle travels.
For diagnostic purposes, it may be beneficial to monitor different attributes of one or more of the different functional systems while the vehicle is being operated.
One aspect of the present invention relates to a method that includes receiving, by a traction application executing on a vehicle control module of a vehicle, a traction speed control input to control a traction wheel of the vehicle; and based on the traction speed control input, determining, by the traction application, a first setpoint value of a control attribute related to the traction wheel. The method also includes receiving, by a first diagnostic supervisor: a) a measured value of the control attribute related to the traction wheel, and b) the first setpoint value from the traction application; wherein the first diagnostic supervisor comprises a first model of a traction system of the vehicle. Based on the first setpoint value and the first model, the first diagnostic supervisor calculates a first virtual value of the control attribute related to the traction wheel; and determines a first operating condition of the traction system of the vehicle based on the first virtual value and the measured value of the control attribute related to the traction wheel. The traction system can include a traction control module and a traction motor and the traction application can transmit the first setpoint value to the traction control module.
Also, the method can include generating, by the traction application, a second setpoint value of the control attribute related to the traction wheel. There can also be a second diagnostic supervisor which receives a) the second setpoint value, from the traction application, and b) the measured value of the control attribute related to the traction wheel, from the traction control module; wherein the second diagnostic supervisor comprises a second model of the traction system of the vehicle. Based on at least the second setpoint value and the second model, the second diagnostic supervisor can calculate a second virtual value of the control attribute related to the traction wheel; and determine a second operating condition of the traction system of the vehicle based on the second virtual value and the measured value of the control attribute.
In particular, the control attribute related to the traction wheel can be one of a speed of the traction wheel, or a speed of a traction motor coupled with the traction wheel of the vehicle.
In accordance with another aspect, a steering application executing on the vehicle control module can receive: a) a steering control input to control a steered wheel of the vehicle; b) a measured value of a control attribute related to the steered wheel; and c) the measured value of the control attribute related to the traction wheel of the vehicle. Based on the steering control input, the measured value of the control attribute related to the steered wheel and the measured value of the control attribute related to the traction wheel, the steering application can determine a setpoint value of the control attribute related to the steered wheel. Also, based on the steering control input, the measured value of the control attribute related to the steered wheel and the measured value of the control attribute related to the traction wheel, the steering application can determine a target steering angle. Additionally, the steering application can calculate a wheel angle command based on the steering control input.
In addition to the steps described above, the steering application, can determine a traction speed limit based on the wheel angle command; and that the measured value of the control attribute related to the traction wheel of the vehicle is less than the traction speed limit. Afterwards, the steering application can set the setpoint value of the control attribute related to the steered wheel to equal the wheel angle command; and set the target steering angle to equal: a) the wheel angle command, when the wheel angle command is greater than the measured value of the control attribute related to the steered wheel, and b) the measured value of the control attribute related to the steered wheel, when the wheel angle command is less than or equal to the measured value of the control attribute related to the steered wheel.
Alternatively, the steering application can determine a) a traction speed limit based on the wheel angle command; b) a wheel angle limit based on the measured value of the control attribute related to the traction wheel; and c) that the measured value of the control attribute related to the traction wheel of the vehicle is more than or equal to the traction speed limit. Afterwards, the steering application can set the target steering angle to equal the wheel angle command; and set the setpoint value of the control attribute related to the steered wheel to equal one of: a) the wheel angle limit, when the wheel angle limit is between the measured value of the control attribute related to the steered wheel and the wheel angle command; b) the measured value of the control attribute related to the steered wheel, when the wheel angle limit is: i) not between the measured value of the control attribute related to the steered wheel and the wheel angle command; and ii) closer to the measured value of the control attribute related to the steered wheel than to the wheel angle command and c) the wheel angle command, when the wheel angle limit is: i) not between the measured value of the control attribute related to the steered wheel and the wheel angle command; and ii) closer to the wheel angle command than to the measured value of the control attribute related to the steered wheel.
Yet another aspect relates to the traction application generating a second setpoint value of the control attribute related to the traction wheel, based on the first setpoint value; and a second diagnostic supervisor which receives a) the second setpoint value, from the traction application, and b) the measured value of the control attribute related to the traction wheel, from the traction control module; wherein the second diagnostic supervisor comprises a second model of the traction system of the vehicle. Based on the second setpoint value, a vehicle battery voltage, the measured value of the control attribute related to the traction wheel and the second model, the second diagnostic supervisor can calculate a second virtual value of the control attribute related to the traction wheel; and determine, based on the second virtual value and the measured value of the control attribute related to the traction wheel, a second operating condition of the traction system of the vehicle.
Another aspect of the present invention relates to a system that includes a first controller comprising: a first memory storing code executable by the first controller; and a first input configured to receive a traction speed control input to control a traction wheel of the vehicle. The executable code includes a traction application configured to, based on the traction speed control input, determine a first setpoint value of a control attribute related to the traction wheel. The executable code also includes a first diagnostic supervisor configured to receive a measured value of the control attribute related to the traction wheel, and the first setpoint value, from the traction application; wherein the first diagnostic supervisor comprises a first model of a traction system of the vehicle. The first diagnostic supervisor is also configured to calculate, based on the first setpoint value and the first model, a first virtual value of the control attribute related to the traction wheel; and determine, based on the first virtual value and the measured value of the control attribute related to the traction wheel, a first operating condition of the traction system of the vehicle.
Yet another aspect of the present invention relates to a method that includes receiving, by a steering application executing on a vehicle control module a steering control input to control a steered wheel of a vehicle; and based on the steering control input, determining, by the steering application a traction threshold value associated with a traction control attribute related to a traction wheel of the vehicle. The method also includes receiving by a first diagnostic supervisor executing on the vehicle control module a) a measured value of the traction control attribute; and b) the traction threshold value. When the measured value of the traction control attribute exceeds the traction threshold value, the first diagnostic supervisor repeatedly calculates a respective difference between the traction threshold value and the measured value of the traction control attribute; to generate a set comprising a plurality of the respective differences. Based on the plurality of respective differences, the first diagnostic supervisor can determine a first operating condition of a traction system of the vehicle. In particular, the first diagnostic supervisor, for each respective difference, can determine if the difference is greater than a difference threshold; and when the difference is greater than the difference threshold, incrementing a first counter value; and when the difference is less than or equal to the difference threshold, resetting the first counter to a first initial value. The method can also include determining a fault condition of the traction system has occurred when the first counter value is greater than a first counter threshold. The traction threshold value can, for example, include a traction speed limit.
In a particular embodiment, the first counter threshold and the difference threshold are based on response characteristics of the traction system to at least one operational input received by the vehicle.
Also, the method can include, for each respective difference: a) determining if the difference is greater than a difference threshold; and when the difference is greater than the difference threshold, incrementing a first counter value, and when the difference is less than or equal to the difference threshold, resetting the first counter to a first initial value; and b) determining if the difference is greater than an immediately preceding difference in the set of respective differences; and when the difference is greater than the immediately preceding difference, incrementing a second counter value; when the difference is less than or equal to the immediately preceding difference, resetting the second counter value to a second initial value. Thus, the method can include determining a fault condition of the traction system has occurred when either the first counter value is greater than a first counter threshold or the second counter value is greater than a second counter threshold.
In one particular embodiment, the first counter threshold, the second counter threshold and the difference threshold are based on response characteristics of the traction system to at least one operational input received by the vehicle.
As one alternative, the method can include, for each respective difference: a) determining if the difference is greater than a first difference threshold; when the difference is greater than the first difference threshold, incrementing a first counter value; and when the difference is less than or equal to the first difference threshold, resetting the first counter to a first initial value; and b) determining if the difference is greater than a second difference threshold; when the difference is greater than the second difference threshold, incrementing a second counter value; and when the difference is less than or equal to the second difference threshold, resetting the second counter to a second initial value. In particular, the method can include determining a fault condition of the traction system has occurred when either the first counter value is greater than a first counter threshold or the second counter value is greater than a second counter threshold.
Furthermore, the first counter threshold, the second counter threshold, the first difference threshold, and the second difference threshold are based on response characteristics of the traction system to at least one operational input received by the vehicle.
One further aspect of the present invention relates to a vehicle control system that includes a controller that has: a) a first input configured to receive a steering control input to control a steered wheel of a vehicle; b) a second input configured to receive a measured value of a traction control attribute related to a traction wheel of the vehicle; c) a third input configured to receive a traction speed control input to control the traction wheel of the vehicle; and d) a memory coupled with the controller and storing code executable by the controller. The executable code can include a steering application configured to receive a steering control input to control a steered wheel of a vehicle; and determine, based on the steering control input, a traction threshold value associated with a traction control attribute related to a traction wheel of the vehicle. The executable code can also include a diagnostic supervisor configured to a) receive a measured value of the traction control attribute, and the traction threshold value; b) repeatedly calculate, when the measured value of the traction control attribute exceeds the traction threshold value, and a respective difference between the traction threshold value and the measured value of the traction control attribute, to generate a set comprising a plurality of the respective differences; and c) determine, based on the plurality of respective differences, a first operating condition of a traction system of the vehicle.
Still a further aspect of the present invention relates to a method that includes iteratively performing the following steps: a) receiving, by a steering application executing on a vehicle control module a steering control input to control a steered wheel of a vehicle; a measured value of a steering control attribute related to the steered wheel; and a measured value of a traction control attribute related to a traction wheel of the vehicle; b) based on the steering control input, the measured value of the steering control attribute and the measured value of the traction control attribute, determining, by the steering application a first setpoint value of the steering control attribute related to the steered wheel and a target steering angle of the steered wheel of the vehicle; c) receiving, by a traction application executing on the vehicle control module of the vehicle, a traction speed control input to control the traction wheel of the vehicle, and the target steering angle, from the steering application; and d) based on the traction speed control input and the target steering angle, determining, by the traction application a second setpoint value of the traction control attribute.
In particular, the steering control attribute can include a steered wheel angle or an angular velocity of a steering motor coupled with the steered wheel of the vehicle. The traction control attribute can, for example, be one of a speed of the traction wheel or a speed of a traction motor coupled with the traction wheel of the vehicle.
The method can also include the steering application calculating a wheel angle command based on the steering control input, determining a traction speed limit based on the wheel angle command, and determining that the measured value of the traction control attribute related to the traction wheel of the vehicle is less than the traction speed limit. The steering application can then set the first setpoint value to equal the wheel angle command; and set the target steering angle to equal a) the wheel angle command, when the wheel angle command is greater than the measured value of the steering control attribute, and b) the measured value of the steering control attribute, when the wheel angle command is less than or equal to the measured value of the first control attribute.
Alternatively, the method can include the steering application determining: a) a traction speed limit based on the wheel angle command; b) a wheel angle limit based on the measured value of the traction control attribute related to the traction wheel; and c) that the measured value of the traction control attribute related to the traction wheel of the vehicle is more than or equal to the traction speed limit. The steering application can then set the target steering angle to equal the wheel angle command; and set the first setpoint value to equal one of: a) the wheel angle limit, when the wheel angle limit is between the measured value of the steering control attribute and the wheel angle command; b) the measured value of the steering control attribute, when the wheel angle limit is i) not between the measured value of the steering control attribute and the wheel angle command; and ii) closer to the measured value of the steering control attribute than to the wheel angle command, and c) the wheel angle command, when the wheel angle limit is i) not between the measured value of the steering control attribute and the wheel angle command; and ii) closer to the wheel angle command than to the measured value of the steering control attribute.
A further aspect of the present invention relates to a system that includes a controller which comprises: a) a first input configured to receive a steering control input to control a steered wheel of a vehicle; b) a second input configured to receive a measured value of a steering control attribute related to the steered wheel; c) a third input configured to receive a measured value of a traction control attribute related to a traction wheel of the vehicle; and d) a fourth input configured to receive a traction speed control input to control the traction wheel of the vehicle. The controller also includes a memory coupled with the controller and storing code executable by the controller. The executable code can include a steering application and a traction application that iteratively perform: a) based on the steering control input, the measured value of the steering control attribute and the measured value of the traction control attribute, determining, by the steering application a first setpoint value of a steering control attribute related to the steered wheel of the vehicle and a target steering angle of the steered wheel of the vehicle; b) receiving, by the traction application a traction speed control input to control the traction wheel of the vehicle, and the target steering angle, from the steering application; and c) based on the traction speed control input and the target steering angle, determining, by the traction application a second setpoint value of the traction control attribute.
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.
Referring now to
The vehicle 10 includes a main body or power unit 12, which includes a frame 14 defining a main structural component of the vehicle 10 and which houses a battery 15. The vehicle 10 further comprises a pair of fork-side support wheels 16 coupled to first and second outriggers 18, a driven and steered wheel 20 mounted near a first corner at a rear 12A of the power unit 12, and a caster wheel (not shown) mounted to a second corner at the rear 12A of the power unit 12. The wheels 16, 20 allow the vehicle 10 to move across a floor surface.
An operator's compartment 22 is located within the power unit 12 for receiving an operator driving the vehicle 10. A tiller knob 24 is provided within the operator's compartment 22 for controlling steering of the vehicle 10. The speed and direction of movement (forward or reverse) of the vehicle 10 are controlled by the operator via a multi-function control handle 26 provided adjacent to an operator seat 28, which control handle 26 may control one or more other vehicle functions as will be appreciated by those having ordinary skill in the art. The vehicle 10 further includes an overhead guard 30 including a vertical support structure 32 affixed to the vehicle frame 14.
A load handling assembly 40 of the vehicle 10 includes, generally, a mast assembly 42 and a carriage assembly 44, which is movable vertically along the mast assembly 42. The mast assembly 42 is positioned between the outriggers 18 and includes a fixed mast member 46 affixed to the frame 14, and nested first and second movable mast members 48, 50. It is noted that the mast assembly 42 may include additional or fewer movable mast members than the two shown in
The vehicle 10 of
In the illustrated embodiment, the VCM 200 includes one or more processors or microcontrollers 216, input/output hardware 218, network interface hardware 220, a data storage component 222, and a memory component 202. The data storage component 222 and the memory component 202 may each be configured as volatile and/or nonvolatile memory and as such, may include random access memory (including SRAM, DRAM, and/or other types of RAM), flash memory, secure digital (SD) memory, registers, compact discs (CD), digital versatile discs (DVD), and/or other types of non-transitory computer-readable mediums. Any stored information that is intended to be available after the vehicle 10 is shutdown and restarted may beneficially be stored in non-volatile memory. Also, depending on the particular embodiment, the non-transitory computer-readable medium, mentioned above, may reside within the VCM 200 and/or external to the VCM 200.
Additionally, the memory component 202 may store software or applications that can be executed (i.e., using executable code) by the one or more processors or microcontrollers 216. Thus the memory component 202 may store an operating application or logic 204, a traction application or logic 208, a steering application or logic 206, a hoist application or logic 210, and accessory application(s) or logic 212. The operating logic 204 may include an operating system and other software such as, for example, diagnostic-related applications for managing components of the VCM 200. The traction application or logic 208 may be configured with one or more algorithms and parameters for facilitating optimal traction control for the vehicle 10. The steering application or logic 206 may be configured with one or more algorithms and parameters for facilitating optimal steering control of the vehicle 10. The hoist application or logic 210 may include one or more algorithms and parameters for facilitating optimal hoist control of the vehicle 10, which acts as the primary load handling assembly system used to raise and lower the movable assembly 47 of the vehicle 10. Additionally, the accessory application or logic 212 may include one or more algorithms and parameters for providing control of accessories of the vehicle 10 such as an auxiliary load handling assembly system, which performs additional tasks such as tilt and sideshift of the carriage assembly 44. A local communication interface 214 is also included in
The one or more processors or microcontrollers 216 may include any processing component operable to receive and execute instructions (such as from the data storage component 222 and/or the memory component 202). The processors or microcontrollers 216 may comprise any kind of a device which receives input data, processes that data through computer instructions, and generates output data. Such a processor can be a microcontroller, a hand-held device, laptop or notebook computer, desktop computer, microcomputer, digital signal processor (DSP), mainframe, server, cell phone, personal digital assistant, other programmable computer devices, or any combination thereof. Such processors can also be implemented using programmable logic devices such as field programmable gate arrays (FPGAs) or, alternatively, realized as application specific integrated circuits (ASICs) or similar devices. The term “processor” is also intended to encompass a combination of two or more of the above recited devices, e.g., two or more microcontrollers.
The input/output hardware 218 may include and/or be configured to interface with a monitor, positioning system, keyboard, touch screen, mouse, printer, image capture device, microphone, speaker, gyroscope, compass, and/or other device for receiving, sending, and/or presenting data. The network interface hardware 220 may include and/or be configured for communicating with any wired or wireless networking hardware, including an antenna, a modem, LAN port, wireless fidelity (Wi-Fi) card, WiMax card, mobile communications hardware, and/or other hardware for communicating with other networks and/or devices. From this connection, communication may be facilitated between the VCM 200 and other computing devices including other components coupled with a CAN bus or similar network on the vehicle 10.
It should be understood that the components illustrated in
It also should be understood that the VCM 200 may communicate with various sensors and other control circuitry of the vehicle 10 to coordinate the various conditions of manual operation and automatic operation of the vehicle 10.
In the description below, the following terms are used and are intended to convey the following definitions:
steering control input: sensor output signal values from the operator steering mechanism.
Wheel_Angle_Cmd: a value generated by the steering application and is a transformation of a digitized value of the steering control input into units that reflect an angle/angular velocity value.
Wheel_Angle_Target, or target steering angle θT: based on the operator's input, this is a value generated by the steering application and provided to the traction application in order to calculate a second Trx_Speed_Limit2. Depending on the current operation of a vehicle its value can be one of either the Wheel_Angle_Cmd or a Wheel_Angle.
Wheel_Angle_Limit: a highest allowable steered wheel angle, generated by the steering application based on the measured value of the traction wheel/motor speed and can be used to modify the Wheel_Angle_Setpoint in order to stay within a desired Wheel Angle-to-Traction Speed relationship.
Wheel_Angle_Setpoint, or steering setpoint ω1 or θ1: a value generated by the steering application, based on the operator's input, but modified based on traction speed, this is the input sent to the steering control module to effect a change in the steered wheel angle/angular velocity.
Steering feedback (ω2 or θ2), or Wheel_Angle: a measured value of the steered wheel angle/angular velocity, generated by the steering control module.
traction speed control input: a value received from a sensor/actuator that the operator manipulates.
Trx_Speed_Cmd: a value generated by the traction application and is a transformation of the digitized voltage reading of the traction speed control input into units that reflect a speed.
First Trx_Speed_Limit1: a highest allowable traction wheel/motor speed for a particular wheel angle value, based on a desired wheel angle-to-traction speed relationship such as defined by the graph in
Second Trx_Speed_Limit2: The second Trx_Speed_Limit2 is generated by the traction application and uses Wheel_Angle_Target as the particular wheel angle value, see
traction speed setting ω4: a value generated by the traction application, based on the operator's input, but modified based on the Trx_Speed_Limit2; this velocity value will eventually be converted to a torque value by the traction application.
traction setpoint, θ1: a torque value based on the traction speed setting and the current speed of the vehicle, and is generated by the traction application.
Trx_Speed, or speed feedback, ω3: is a measured value of the traction wheel/motor speed, generated by the traction control module.
Referring to
In
The steering application 206 additionally produces the target steering angle θT or Wheel_Angle_Target which is provided to the traction application 208. As discussed below, with respect to
The TCM 258 monitors the traction motor 264 and provides a traction feedback speed ω3 to the traction application 208, the steering application 206 and the two diagnostic supervisors 250, 252. Since the steering setpoint (θ1 or ω1) is partly dependent on the actual traction wheel or motor speed, i.e., speed feedback ω3, the diagnostic supervisors 250, 252 can verify that the actual traction speed ω3 is responding correctly to the traction setpoint τ1. The traction speed, or speed feedback, ω3 could also be converted to an actual linear speed of the vehicle 10 by the traction application 208. If, for example, the speed feedback ω3 was an angular speed of the traction motor 264, then the traction application 208 could scale that value to an actual linear speed, v3, of the vehicle 10 based on a) a gearing ratio between the traction motor 264 and the driven wheel 20 and b) the circumference of the driven wheel 20. Alternatively, if the speed feedback ω3 was an angular speed of the driven wheel 20, then the traction application 208 could scale that value to an actual linear speed, v3, of the vehicle 10 based on the circumference of the driven wheel 20. The linear speed of the vehicle equals the linear speed of the driven wheel 20, presuming there is no slip at the driven wheel. As explained more fully below, the traction application 208 can provide the value of the actual linear speed, or linear speed feedback, v3 to the diagnostic supervisors 250, 252 in some embodiments. Providing the linear speed feedback v3 to the diagnostic supervisors 250, 252 could be performed as an alternative to, or in addition to, the TCM 258 providing the speed feedback ω3, as shown in
The first simulation model 254 is configured to compute a virtual response ω5 of the vehicle speed, i.e., traction wheel speed or traction motor speed, under various conditions while under control of the traction control module (TCM) 258 via the traction setpoint τ1. In instances where the linear speed feedback v3, rather than the angular speed feedback ω3, is provided to the first diagnostic supervisor 250, the virtual response ω5 (whether it represents a traction wheel speed or a traction motor speed) can also be scaled to a virtual linear speed response v5 by the first diagnostic supervisor 250. The traction setpoint τ1 is determined by the traction application 208 using a Trx_Speed_Cmd which is generated by the traction application 208 and is based on a traction speed control input or traction speed control input signal 260 received from an operator controlled traction speed control input sensor 262, such as the multi-function control handle 26 of the vehicle 10, and the target steering angle θT output from the steering application 206. The traction setpoint τ1 is output from the traction application 208 to the TCM 258 as a torque value which results in a corresponding speed of a traction motor 264 under the control of the TCM 258.
Based on the virtual response ω5 provided by the first model 254 and the speed feedback ω3 from the TCM 258, the first diagnostic supervisor 250 can perform a correlation computation to determine the degree of similarity of the predicted, or virtual, traction speed ω5 to the actual traction speed ω3. Alternatively, the first diagnostic supervisor 250 can perform a correlation computation to determine the degree of similarity of the predicted, or virtual, linear speed v5 of the driven wheel and vehicle to the actual linear speed v3. The first diagnostic supervisor 250 executes so as to provide the first model 254 with the setpoint τ1 value, a present voltage of the vehicle battery 15, and the speed feedback ω3 value as inputs in order to generate, or calculate, the virtual response ω5 as an output. The first model 254 is designed to accurately reflect or predict the behavior of the traction system, which traction system includes the traction control module 258, the traction motor 264 and a load that represents a reactive force of the traction or driven wheel 20 of the vehicle 10 whose speed is being changed by the traction motor 264. Hence, the virtual response ω5 should closely reflect the intended or desired speed of the traction wheel 20 or the traction motor 264 which is a result of the setpoint τ1 and other vehicle operating conditions being provided to the traction control module 258 of the presently operated vehicle. If the virtual response ω5 and the actual speed of the traction wheel 20 or the traction motor 264 differ significantly, then this is an indication that there may be a problem with the traction control module 258, the traction motor 264, and/or the determination of the setpoint values, τ1 or ω4.
Accordingly, the first diagnostic supervisor 250 can compare the feedback value ω3 with the virtual response cos. As explained below, the first model 254 can be an empirically-based model that produces a predicted result based on the operating conditions of the vehicle 10. The virtual response ω5 can be compared to the measured, or feedback, value ω3 for verification of proper operation of the vehicle's traction system. If the comparison indicates that the two values differ by more than a predetermined threshold, then the first diagnostic supervisor 250 can generate a fault signal, indicating a fault condition is occurring. The VCM 200 can, in response to the fault signal, stop movement of the vehicle 10.
The second simulation model 256 is configured to compute a virtual response ω6 of the traction motor or driven wheel speed under various conditions while under control of the traction control module (TCM) 258 via a traction setpoint τ1. A traction speed setting or setpoint ω4 is determined by the traction application 208 using the input signal 260 received from the operator controlled traction speed control input sensor 262 and the target steering angle θT output from the steering application 206. The traction speed setting ω4 is also used by the traction application 208 along with a current or actual traction speed ω3 or Trx_Speed to calculate the traction setpoint τ1, as discussed below, which results in a corresponding speed of a traction motor 264 under the control of the TCM 258. The second model 256 can be a virtual traction system comprising the TCM 258, the traction motor 264, and a load that represents a reactive force of the traction wheel of the vehicle 10 whose speed is being changed by the traction motor 264.
While one example type of model is described in more detail below, the second model 256 can be of any type that simulates the behavior of the isolated traction system such that the model provides a predicted result of how the control attribute of the traction system should react, i.e., what its speed should equal, if the traction control module 258 is provided with a particular setpoint τ1 (or equivalently ω4).
The second diagnostic supervisor 252 executes so as to provide the model 256 with the traction speed setpoint ω4 value as an input in order to generate, or calculate, the virtual response ω6 as an output. Assuming that the model 256 accurately reflects the behavior of the isolated traction system, the virtual response ω6 should closely reflect the actual speed of the traction wheel 20 or the traction motor 264 (i.e., the speed feedback ω3) which is a result of the traction speed setpoint ω4 being used to calculate the setpoint τ1 that is provided to the traction control module 258 of the presently operated vehicle, presuming the traction system is operating properly.
Accordingly, the second diagnostic supervisor 252 can compare the feedback value ω3 with the virtual response ω6. As mentioned, the second model 256 is essentially a virtual traction system that produces a simulated response (i.e., the virtual response ω6) of the vehicle's traction system. The virtual response ω6 can be compared to the measured, or feedback, value ω3 for verification of proper operation of the vehicle's traction system. If the comparison indicates that the two values differ by more than a predetermined threshold, then the second diagnostic supervisor 252 can generate a fault signal, indicating a fault condition is occurring. The VCM 200 can, in response to the fault signal, stop movement of the vehicle. As described above with respect to the virtual response ω5, the output of the second model 256, i.e., the virtual response ω6, can be converted to a virtual linear speed response v6 for comparison to the actual linear speed v3 of the vehicle 20, when appropriate.
One of ordinary skill will recognize that the first model 254 and the second model 256 may be different types of models, as described above, or they can be the same type of model. In either case, a redundant diagnostic system is provided that monitors the operating conditions of the traction system of the vehicle 10. While the description below focuses on the second diagnostic supervisor 252 and the second model 256, similar techniques can be utilized with the first diagnostic supervisor 250 and the first model 254.
In step 302, the steering application 206, which is executing on the vehicle control module, receives a steering control input signal 278 to control a steered wheel of a vehicle and a measured, feedback value θ2, ω2 of a first control attribute related to the steered wheel, such as a steered wheel angle or a steering motor angular velocity. The steering application also receives a measured, feedback value ω3 of a second control attribute related to a traction wheel of the vehicle, such as a traction wheel speed or a traction motor speed.
Then, based on the steering control input signal, the measured value of the first control attribute and the measured value of the second control attribute, the steering application determines, in step 304, a first setpoint value θ1, ω1 of the first control attribute related to the steered wheel, and a target steering angle θT of the steered wheel.
In step 306, the traction application 208, which is executing on the vehicle control module, receives a traction speed control input signal 260 to control the traction wheel of the vehicle, the measured value ω3 of the second control attribute and the target steering angle θT, from the steering application. Based on the traction speed control input signal, the measured value ω3 of the second control attribute, and the target steering angle, the traction application determines, in step 308, a second setpoint value τ1 or ω4 of the second control attribute.
There is also a first diagnostic supervisor 250 executing on the VCM and it receives, in step 310, the measured value ω3 of the second control attribute, and the second setpoint value (τ1 or ω4); wherein the first diagnostic supervisor comprises a first model 254 of the traction system of the vehicle.
In step 312, based on the second setpoint value and the first model, the first diagnostic supervisor calculates a first virtual value ω5 or ω6 of the second control attribute related to the traction wheel and, in step 314, based on the first virtual value and the measured value of the second control attribute, the first diagnostic supervisor determines a first operating condition of the traction system of the vehicle.
In step 316 the traction application can generate a third setpoint value (ω4 or τ1) of the second control attribute. A second diagnostic supervisor 252 may also be executing on the VCM and receives, in step 318, the third setpoint value and the measured value ω3 of the second control attribute; wherein the second diagnostic supervisor comprises a second model 256 of the traction system of the vehicle.
In step 320, based on the third setpoint value and the second model, the second diagnostic supervisor calculates a second virtual value ω6 or ω5 of the second control attribute and, in step 322, based on the second virtual value and the measured value of the second control attribute, determines a second operating condition of the traction system of the vehicle.
As mentioned earlier, the steering application 206 and the traction application 208 operate in conjunction with one another to control a steered wheel angle and traction speed of the vehicle 10. A steering control input sensor 276 associated with a steering wheel or tiller knob can generate a steering control input signal 276 that varies according to an operator's manipulation of the apparatus. This signal can then be converted to a digital value which can be scaled and adjusted to represent a value that has units appropriate for either a steered wheel angle (e.g., units of degrees) or an angular velocity of the steering motor (e.g., units of RPM). For instance, such a value can be referred to as a Wheel_Angle_Cmd and represents the operator's desired wheel position or steering motor angular velocity. One priority of a steering system comprising the steering control input sensor 276, the steering application 206, the SCM 272, the steering motor 274 and the steered wheel 20 is to position the steered wheel to the desired operator setting indicated by the Wheel_Angle_Cmd. Because the Wheel_Angle can be adjusted very quickly by the steering system, this rapid positional change may produce operator instability. Therefore, it is desirable that the steering application 206 produces control that will achieve the Wheel_Angle_Cmd as quickly as possible and without significant delay while also, in appropriate circumstances, reducing the traction speed so as to achieve a desired Wheel Angle-to-Traction Speed relationship (one example of which is depicted in
Even though the operator's input may result in a Wheel_Angle_Cmd indicating that the operator desires the steered wheel to have an angle x, the steering system can position the steered wheel per the operator command as quickly as possible without operator perceived delay, but in order to maintain operator stability, the steering application 206 of the VCM 200 may not immediately issue the new command x to the SCM 272 based on the traction wheel/motor speed feedback or Trx_Speed but rather in smooth incremental changes as the traction speed reduces. For instance, while a vehicle is traveling relatively fast, there may be a greater likelihood that a sharp steering change can cause control or stability issues as compared to when the vehicle is traveling relatively slowly. Accordingly, a current measured value of the traction speed or Trx_Speed of the vehicle can be used to determine a maximum allowable angle to which the steered wheel can be changed so as to stay within a desired Wheel Angle-to-Traction Speed relationship maintaining operator stability, such as shown in
Also, the Wheel_Angle_Target can be used by the traction application 208 to determine a maximum allowable traction speed at which the vehicle can be traveling at a wheel angle equal to the Wheel_Angle_Target so as to maintain a desired Wheel Angle-to-Traction Speed relationship, such as shown in
An example control algorithm, or process, for the steering application 206 of the VCM 200, is illustrated in
In
Referring to
The steering application 206 can also receive the measured steered wheel angle θ2 of the steered wheel 20 or the measured angular velocity ω2 of the steering motor 274, i.e., a measured Wheel_Angle, that has a value indicative of the present angle of the vehicle's steered wheel or angular velocity of the steering motor. In step 406, a determination is made as to whether the vehicle's current traction speed, Trx_Speed, is less than the first Trx_Speed_Limit1. If it is not, then the traction speed of the vehicle is reduced by the traction application 208 while the steering application 206 adjusts the Wheel_Angle to equal the Wheel_Angle_Cmd. As shown by block 410 of
Returning to step 406, if the vehicle's traction speed, however, is below the first Trx_Speed_Limit1, then the traction wheel or motor speed or the Trx_Speed requires no reduction to meet the Wheel Angle-to-Traction Speed relation, such as illustrated in
According to an example algorithm depicted in
Referring back to
The Trx_Speed_Cmd reflects a vehicle speed that the operator desires to reach. In step 454, the traction application 208 may use the second Trx_Speed_Limit2 to reduce the Trx_Speed_Cmd in order to calculate an allowable Trx_Speed Setting, ω4.
For example, a lookup table 720 constructed from a graph 724 in
When the Trx_Speed is equal to or greater than the first Trx_Speed_Limit1 in step 406 in
The traction setpoint may be a traction speed setpoint ω4 defined by the Trx_Speed Setting ω4, or the traction setpoint may be a traction setpoint τ1 that can be calculated based on the Trx_Speed Setting and a current Trx_Speed of the vehicle. As one example and as known to those skilled in the prior art, a proportional-integral-derivative (PID) controller can be used that receives, as an input, a difference value between the Trx_Speed Setting and the Trx_Speed and calculates, as output, the traction setpoint τ1. Thus, in step 456, the traction application 208 calculates the traction setpoint τ1 which the TCM 258 will use to control operation of the traction motor 264. The traction setpoint τ1 is calculated so as to control the traction motor speed, e.g., to reduce the Trx_Speed of the vehicle when the Trx_Speed is equal to or greater than the first Trx_Speed_Limit1 in step 406 in
In step 472, the steering application also determines a value of the target steering angle θT. Independent of the logical flow of the steering application, the traction application executes in order to determine a second, traction setpoint (i.e., τ1 or ω4). In particular, in step 474, the traction application receives the target steering angle θT and a traction speed control input. In step 476, the traction application uses the Wheel_Angle_Target or target steering angle θT and the graph of
The logical flow of the flowchart of
The steered wheel 20 of at least some vehicles can be turned in a complete circle (i.e., 360 degrees) from a position pointing straight ahead (i.e., 0 degrees) to a position pointing straight behind (i.e., 180 degrees). Also, the steered wheel 20 can also be turned to the right and turned to the left. Therefore, the steered wheel 20 can be located in any one of first, second, third and fourth quadrants 810, 811, 812, and 813 shown in
Regardless of which quadrant 810, 811, 812, 813 the Wheel_Angle_Cmd value is actually in, it can be measured as shown in
With respect to the table 710 of
Additionally, the flowcharts of
Correlation example of a diagnostic comparison:
Because of the way microcontrollers and other digital hardware of the vehicle handle signals and values of signals, the feedback value ω3, for example, can be an array of values that results from a continuous signal being sampled at a periodic rate (e.g., every 10 ms). Similarly, the second model 256 can be provided with the respective setpoint or traction speed setting ω4 every 10 ms (for example) so that a new virtual value ω6 is calculated every 10 ms. While it would be possible to compare each individual feedback value ω3 with a single, corresponding virtual value ω6, that comparison may not accurately reveal whether or not the traction system of the vehicle is malfunctioning. However, comparing the last predefined number, e.g., 100, feedback values ω3 with the predefined number, e.g., 100, of most recently generated virtual values ω6 would likely provide a much more accurate indication of whether or not the vehicle's traction system is malfunctioning. Thus, the virtual value ω6 can comprise a first array of individually valued elements and the measured value ω3 can comprise a second array of corresponding individually valued elements so that the similarity between the measured value ω3 and the virtual value ω6 is determined based on a computed correlation between the first array and the second array.
In general, the more samples of feedback values ω3 and the more calculations of the virtual values ω6 that are used for a comparison to one another, the more accurate of a result will be produced. However, accumulating more samples of these values reflect a longer time period which might allow a malfunction to occur for an extended period of time before that condition is detected. Accordingly, there is typically some operational upper limit to the amount of time used to collect values before a comparison is made between the feedback value ω3 and the virtual value ω6. For example, there may be operational constraints that require detection and/or mitigating action be initiated within, for example, 100 ms of a malfunction occurring. Or for instance, there may be a maximum allowable deviation between the setpoint ω4 and the actual speed ω3 to keep the system under proper control which would potentially decrease or increase the diagnostic evaluation time.
If the sample period of the feedback value ω3 is 10 ms, then 10 samples can be collected and used for the comparison between the feedback value ω3 and the virtual value ω6 using a 10 ms response time. The 10 samples of the feedback value ω3 can be considered a first random variable, X, comprising an array of 10 actual responses (e.g., x1-x10) to 10 input values (i.e., setpoint values ω4) and the virtual value ω6 can be considered a second random variable, Y, comprising 10 simulated model responses (e.g., y1-y10) to those same 10 input values. One measure of similarity of two random variables is known as a correlation coefficient, P. The correlation coefficient of two variables, sometimes simply called their correlation, is the covariance of the two variables divided by the product of their individual standard deviations. It is a normalized measurement of how the two variables are linearly related. However, one of ordinary skill will recognize that there are many other techniques for measuring similarity between two arrays of values.
Using well understood techniques, the respective average,
C
xy= 1/10(Σi=110((xi−
which allows the correlation coefficient to be calculated according to:
When two variables or signals exactly correlate P=1 and for exactly uncorrelated signals, P=0. Thus, a predetermined threshold value can be identified which is used to determine that when the P value is below that threshold, the feedback value ω3 and the virtual value ω6 are not similar to one another. In the example where 10 samples are used to calculate P, then a value for P of around 0.5 to around 0.8 likely indicates that the feedback value ω3 and the virtual value ω6 are similar enough that a traction system malfunction is unlikely. If a P value is calculated below 0.5, then a malfunction of the traction system of the vehicle is likely occurring. Because of unexpected noise or other anomalies, the occurrence of a single P value below that threshold may occasionally occur even in the absence of a malfunction. Thus, the second diagnostic supervisor 252 may increment a counter each time a P value is calculated below the predetermined threshold and decrement the counter each time a P value is calculated above the predetermined threshold. If the value of that counter ever reaches a maximum allowable number (e.g., 5), then the second diagnostic supervisor 252 can alert the VCM 200 that a fault condition has occurred.
Independent of the second diagnostic supervisor 252, the first diagnostic supervisor 250 can also calculate how similar the virtual value ω5 from the first model 254 is to the feedback value ω3. While the first diagnostic supervisor 250 could employ a model 254 different than the second model 256, a different sampling period, or a different similarity measurement technique, the first diagnostic supervisor 250 may also be configured substantially similar to the second diagnostic supervisor 252 so that it operates in almost an identical way. Thus, the first model 254 and the second model 256 may both be the same model and a similar correlation coefficient and counter can be used by the first diagnostic supervisor 250 to generate its own diagnostic signal alerting the VCM 200 of a fault condition of the vehicle's traction system. In order to utilize the above correlation technique, the diagnostic traction model can generate the required simulated response sequence. There are various ways to model or simulate systems similar to the isolated traction system of the vehicle described above. Any of these known modeling techniques may be used without departing from the scope of the present invention. However, one example type of model that can be used for either the model 254 or 256 is a transfer function model calculated based on observed responses of an actual isolated traction system to a plurality of different operating conditions.
Generally, a transfer function (and analogous terms “system function” and “network function”) refers to a mathematical representation to describe a relationship between the inputs and outputs of a system. In particular, the relationship is described using a ratio of polynomials where the roots of the denominator polynomial are referred to as the system poles and the roots of the numerator polynomial are referred to as the system zeros.
A transfer function for a system can be developed by providing the system with well-defined input values and collecting the resulting output values. For example, an isolated vehicle traction system as described above that includes a controller, a traction motor, and a load on the motor can be provided with input values and then observed in order to measure the resulting output.
In
The output signal 1404 can include a number of characteristic attributes. The point 1406 corresponds to when the output signal 1404 first shows a response to the step input 1402; the point 1408 corresponds to when the output signal 1404 reaches the value 1403; the point 1410 corresponds to the peak value 1411 of the output signal 1404; and the point 1412 corresponds to when the output signal 1404 settles (i.e., reaches steady state) at the desired traction wheel or traction motor speed value 1403. These different points help define a delay time td between points 405 and 406, a peak time tpk between points 1405 and 1410, a settling time tset between points 1405 and 1412, and a rise time tr between points 1406 and 1408. The output signal 1404 also includes an overshoot value related to the steady state value 1403 and the peak value 1411. The output signal's overshoot is typically referred to as “percentage overshoot” and calculated according to:
The oscillating portion of the output signal 1404 before it settles to its steady state value includes an oscillating period T that defines a natural frequency fn (i.e., 1/τ) which, in terms of radians, is ωn=2πfn. Also, a damping coefficient ζ can be calculated according to:
The input signal 1402 can be considered a time-based continuous signal x(t) and the output signal 1404 can also be considered a time-based signal u(t) such that the Laplace transform of each signal is X(s) and U(s). The transfer function, H(s) for the isolated traction system is therefore generically defined as U(s)=H(s)X(s). More specifically, a system that produces the output signal 1404 of
As described above, however, the microcontrollers and diagnostic supervisors operate with discrete time-sampled values and not with continuous signals. Thus, the transfer function H(s) can be transformed into a discrete transfer function H(z) by a variety of different methods. One method, known as a bilinear transfer transforms H(s) to H(z) by making the substitution of:
where
ts is the sampling time (e.g., 10 ms) used to measure values of the input and output signals.
There are, however, automated methods for calculating a discrete transfer function that are available as alternatives to the methods just described. For example, MATLAB includes a function “c2d” that automates this process. If, for example, the input signal 1402 and the output signal 1404 reveal an initial transfer function of:
then the commands:
will first define the continuous transfer function “h” and transform it to a discrete transform function “hd” using a sampling time of “0.01” seconds. The MATLAB command “hd=” will print out the discrete transform function as:
This transfer function H(z) can be used by the first and second diagnostic supervisors 250, 252 to produce virtual values for the control attribute related to the traction wheel or traction motor of the vehicle. In particular, when a setpoint value is received by a diagnostic supervisor (250, 252) it is transformed by the transfer function H(z) to a virtual value. Thus, a stream of discrete samples of the setpoint value (e.g., traction speed setting or setpoint ω4) produces a corresponding stream of virtual values (e.g., ω6). These virtual values can then be compared with the feedback values ω3 to determine an operating condition of the traction system of the vehicle.
In particular, if “k” is used as an index to refer to a particular sample x[k] in the stream of discrete samples of the setpoint value ω4, then a corresponding virtual value y[k] (i.e., ω6) can be calculated according to the above transfer function using:
where, for this particular example transfer function:
MATLAB also provides tools to fine-tune this initial transfer function H(z). For example, the transfer function H(z) can be modeled in SIMULINK which includes an OPTIMIZATION TOOLBOX. The OPTIMIZATION TOOLBOX includes a tool for model parameter estimation. In the example transfer function H(z) above, the numerator coefficients are [0.01187 0.06408 0.009721] and the denominator coefficients are [1 −1.655 0.7408]. The parameter estimation function of the OPTIMZATION TOOLBOX can be provided with a set of input data, a set of output data and the transfer function. For example, the parameter estimation tool can be provided with data representing the input signal 1402, the output signal 1404 and the transfer function H(z). The parameter estimation function will use the input data and the transfer function H(z) to calculate a simulated set of output data. Based on a comparison between the actual output signal 1404 and the simulated output data, the parameter estimation function will fine-tune the numerator and denominator coefficients to more closely match the simulated data to the actual output data signal 1404.
To further refine the transfer function H(z), other actual input and output data can be provided to the parameter estimation function of the SIMULINK OPTIMIZATION TOOLBOX. For example, a sinusoidal input and its resulting output can be provided and a ramp input and its resulting output can be provided. As a result, a transfer function H(z) can be developed that is calculated based on observed responses of a vehicle traction system to a plurality of different operating conditions.
A second type of model that may be used by one or both of the diagnostic supervisors 250, 252 is an empirically-based model that includes the lookup table depicted in
The inputs to the lookup table 600 are the operating vehicle battery voltage, a motor speed feedback value ω3, and a traction command or traction setpoint τ1 value. The output of the lookup table 600 is an applied torque value. The battery voltage can be measured in volts and range between a voltage (e.g., 32V) below a nominal battery voltage (e.g., 36V) of a vehicle to a voltage (e.g., 40V) above that nominal voltage. The speed feedback value can be either a speed of the traction motor (e.g., RPMs) or the speed of the traction wheel (e.g., m/sec) and range from 0% of a maximum speed to 100% of the maximum speed. The traction command or traction setpoint, as well as the applied torque value, can be a torque value measured in Nm and range from 0 to an amount that will stall the traction motor. The applied torque value is an amount of modeled torque realized by the traction motor that is applied to the traction wheel/load under a particular set of battery voltage, speed, and traction setpoint values.
As mentioned above, the collected or modeled data can be arranged in a three-dimensional lookup table 600 of
In summary, the traction system models described herein can be represented as a transfer function (TF), a lookup table, or a 5, 7 parameter model (ParModel). In any case, the model represents an input to output relationship where the inputs are values such as, for example, the traction setpoint τ1, battery voltage, and a current traction speed while the output is a virtual, or expected, traction speed value. Thus, in general, any one of the three traction model implementations discussed above may be selected when evaluating a current operating condition of the truck. Input values appropriate for the selected model are first determined. For example, for the first model 254, the traction setpoint τ1, the operating vehicle battery voltage, and the motor speed feedback value ω3 may be used as inputs. For the second model 256, the traction speed setting ω4 from the traction application 208 can be used as the input to a transfer function. Regardless of the model implementation selected, the output of the model is a virtual response (e.g., ω5 or ω6) that can be compared with the speed feedback value ω3 to determine if the traction system of the vehicle is in a fault condition.
In step 908, this “torque applied” value is then used to determine an expected, or virtual, speed that would result if applied by the traction motor to the traction wheel of a vehicle in which the VCM 200 is incorporated. In particular and in accordance with one embodiment of the present invention, the operation of such a vehicle can be modeled by the equation:
where:
The above equation forms part of the first model 254 in a first embodiment and can be solved for speed ω5 in order to determine an expected, or virtual value, of rotational speed of the traction motor or traction wheel that is expected to result if the “torque applied” value from the lookup table (or traction model) were applied to the traction wheel.
The above equation is in terms of torques and angular velocities but could also be converted to an equivalent equation in terms of linear velocities and linearly-applied forces. The conversion of a torque to a linearly applied force can be accomplished by scaling the torque value based on a) a gear ratio between the traction motor and the traction, or driven, wheel and b) a diameter of the traction, or driven, wheel.
Hence, in accordance with another embodiment of the present invention, the operation of the vehicle in which the VCM is incorporated can be modeled by an equation scaled from the above torque-based equation (e.g., Nm) to a linear-based force equation
such that:
F
applied=Acc·m+v5B+Fload
which can be solved for a linear vehicle speed “v5” resulting from an applied force and the value “v5” is the virtual linear speed calculated by the first diagnostic supervisor 250 in
In the above equation, which forms part of the first model 254 in a second embodiment:
Thus, in step 910, the virtual value ω5 or virtual linear speed value v5, can be compared with an actual vehicle speed ω3, or actual linear speed v3, so that an operating condition of the vehicle can be determined in step 912.
In another example, one or more diagnostic comparisons can be performed by a model that utilizes timing constraints and signal thresholds for comparison to the actual response from the TCM 258. Such a model, for example, is depicted in
In step 1018 a determination is made whether the present iteration Trx_Speed Err[i] value is greater than or equal to the previous iteration's Trx_Speed Err[i−1]. If this condition is true, then the Trx_Speed is greater than the Trx_Speed_Limit1 and, furthermore, diverging from the Trx_Speed_Limit1. A “No Response” counter can be associated with this condition such that whenever the determination in step 1018 is true, the “No Response” counter is incremented in step 1020. If either the determination in step 1012 or the determination in step 1018 is not true, then the “No Response” counter is set to, or remains at, “0” in step 1022.
In step 1024, a determination is made whether or not the Trx_Speed Err[i] is greater than a second, larger “difference threshold” amount such as, for example, 0.8 m/s. A “Large Error” counter can be associated with this condition and incremented, in step 1026, when the determination in step 1024 is true. When the determination in step 1024 is not true, then the “Large Error” counter can be set to, or remain at, “0” in step 1028.
Each of the “Above Command”, “No Response”, and “Large Error” counters can have an associated counter limit, or “counter threshold” that is reflective of how long each of the three conditions described above are allowed to exist before the diagnostic supervisor determines that the vehicle's traction system is likely in a fault condition. Thus, after each of the three counters are adjusted during a current iteration of the method of
For example, the “Above Command” counter threshold may be 300 and if, as assumed above, the flowchart of
In step 1030 a determination is made whether any of the three counters exceed their respective counter threshold. If the determination in step 1030 is true, then a status flag is set, in step 1032, to a first value (e.g., “1”). If the determination in step 1030 indicates that all three counters are at or below their respective counter threshold, then the status flag is set, in step 1034, to a second value (e.g., “0”). If the status flag is set to the first value, then the diagnostic supervisor may determine that the operating condition of the vehicle traction system is in a fault condition. If the status flag is set to the second value, then the diagnostic supervisor may determine that the operating condition of the vehicle traction system is not in a fault condition.
The predetermined values such as 0.1 m/s in step 1012, 0.8 m/s in step 1024 and the counter thresholds in step 1030 can be based on the actual response 1002 of an operating vehicle to an operator's input.
Analysis of the different signals of
One example malfunction that might lead to the “Above Command” counter reaching 300 is if communication between the traction application 208 and the TCM 258 is not occurring. As explained above with respect to
A second time period time2 represents a period of time in which the response signal 1002 is greater than the Trx_Speed_Limit1 by the example threshold amount of 0.1 m/s and is increasing. These conditions exist when step 1018 in
As mentioned, the response signal 1002 of
Thus, the values 0.1 m/s and 0.8 m/s for the “Above Command” and “Large Error” determination, respectively, are based on a vehicle's traction system response to an operator's input. For example, the actual response signal 1002 can be tested and observed for a statistically significant number of examples (e.g., one or more examples) to determine that it typically settles within about 0.1 m/s of the Trx_Speed_Limit1 for a particular vehicle's traction system. Also, analysis of those examples of the response signal 1002 may reveal that while overshoot is very likely to occur, overshoot that exceeded 0.8 m/s rarely happened and could empirically be linked to a traction system failure. Similarly, the threshold values for the counters (e.g., 300, 170, 50) are also based on the actual response of a vehicle's traction system to an operator's input. One of ordinary skill will recognize that these values are provided by way of example and other specific values would be appropriate for different and varying vehicles. The “300” can be used in conjunction with a processing loop speed (e.g., every 10 ms) so that the threshold corresponds to a time period. If, for example, an operating condition is tested every 10 ms and a “true” result increments a counter, then that counter reaching 300 corresponds to the operating condition being “true” for the previous 3 seconds. Thus, instead of any of the conditions tested in steps 1012, 1018 or 1024 immediately resulting in a determination of a fault condition, the threshold values represent how long a respective one of the conditions may last before a fault condition is determined. Analysis of a statistically significant number of examples (e.g., one or more examples) of actual response signal 1002 can reveal that the time taken for the signal 1002 to settle within 0.1 m/s of the Trx_Speed_Limit1 rarely if ever exceeds 3 seconds. One of ordinary skill will recognize that these values are provided by way of example and other specific values would be appropriate for different and varying vehicles.
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
This application is related to and claims the benefit of provisional patent application entitled “Model Based Diagnostics Based on Traction Model,” Application Ser. No. 62/205,092, filed Aug. 14, 2015, the disclosure of which is incorporated by reference herein in their entirety.
Number | Date | Country | |
---|---|---|---|
62205092 | Aug 2015 | US |