Abstract:
A throttle control system employs redundant throttle signals in which faults may be detected so that control may continue using a non-faulted channel when one channel fails. Rehabilitation of the failed channel may occur when the fault condition ends, and changes in throttle setting based on that rehabilitation, are phased in gradually to prevent abrupt changes in vehicle operation. In this way, high availability and reliability are obtained.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     The present invention relates to electronically controlled throttles for vehicle engines and in particular to a high reliability throttle controller using redundant throttle signals. 
     A throttle controls the flow of air, or air and fuel, inducted into an internal combustion engine, and thereby controls the power produced by the engine. Engine power defines the speed of the engine or vehicle to which it is attached, under a given load condition, and thus, reliable control of the throttle setting is important. 
     In prior art mechanical systems, a direct mechanical linkage controlled the throttle, typically in the form of a cable running from the accelerator pedal, operable by the user of the automobile, to the throttle valve. Absent tension on the cable from the pedal, the throttle valve would revert to an idle opening under the influence of a biasing spring. The idle opening provides sufficient inducted air and gas to permit low speed operation of the engine under no- or low-load conditions. 
     Although mechanical linkages are simple and intuitive, they are not readily adapted to electronic control of an engine such as may be desired in sophisticated emissions reduction systems or for features such as automatic vehicle speed control. For these purposes, the mechanical linkage may be replaced with electrical wiring carrying throttle signals from a position sensor associated with the accelerator pedal to a throttle controller operating a motor actuating the throttle valve. The throttle signal may be monitored for loss or faults to provide greater reliability to the system. 
     It is desirable that any faults in the throttle signal be minimized to avoid disabling the vehicle unnecessarily. One method of reducing such faults is by using redundant throttle signals conveyed through separate control channels. If one channel fails, the non-faulted channel may be used to provide continued control to the engine. If both channels fail, the throttle is moved to a safe state. 
     Such systems may nevertheless be subject to conditions, such as intense electromagnetic interference, which can cause faults in both channels disabling them and causing a loss of availability of the throttle control. 
     BRIEF SUMMARY OF THE INVENTION 
     The present inventors have recognized that under certain circumstances, a faulted control channel may be rehabilitated once the fault is gone to provide substantially increased availability. Such rehabilitation creates a possibility of a sudden change in throttle plate position if the rehabilitated channel provides a throttle setting different from that currently in effect. This problem is addressed by a procedure which smoothly changes from one throttle setting to another in a “ramping” when a control channel is rehabilitated, thus preventing abrupt changes in engine power. 
     Specifically, the present invention provides a throttle control for a vehicle engine where the throttle control has an input for receiving a first and second redundant throttle signal providing throttle settings. A fault detection circuit communicates with the inputs to detect a fault, if any, in at least one of the first and second redundant throttle signals. A throttle signal processor receives information from the fault detector and the inputs and operates to (1) in the absence of a fault in at least one of the first and second throttle signals, to provide a normal throttle setting determined from the throttle settings of at least one of the first and second throttle signals, and (2) upon recovery from the fault of at least one of the first and second throttle signals, to produce a throttle command gradually transitioning between a fault throttle setting used during a fault of at least one of the first and second throttle signals and the normal throttle setting. 
     Thus it is a first object of the invention to permit the rehabilitation of faulted inputs in the throttle signals without creating an abrupt transition in vehicle power or speed. The gradual transition between the fault throttle setting and the normal throttle setting allows reaction and compensation by the operator of the vehicle. 
     Upon a fault of the first and second throttle signals, the fault throttle setting may produce an output signal adjusting the throttle to a setting within the idle range of the engine. 
     Thus it is another object of the invention to provide for operation of the vehicle but at a reduced capacity in the event of a complete failure of the throttle signals. 
     Alternatively, the fault throttle setting may be determined from a throttle setting of the non-faulted one of the first and second throttle signals when only one of the first and second throttle signals has failed. 
     Thus it is another object of the invention to provide for continued operation during a failure of one signal yet with the gradual recovery described above when the signal is rehabilitated. 
     Alternatively or in addition, the fault throttle setting may be used when the first and second throttle signals deviate in value by an amount greater than a predetermined deviation amount and the fault throttle setting may be determined from the first and second throttle signals associated with the lower throttle setting. 
     Thus it is another object of the invention to detect possible faults indicated by deviation in the values of the throttle signals and to adopt the more conservative throttle signal as the fault throttle setting. 
     The fault throttle setting may be produced only when the fault condition exceeds a predetermined time. 
     Thus it is another object of the invention to allow continued throttle operation for extremely short, intermittent fault situations. 
     The throttle setting when neither the first nor second throttle signal is faulted may be based on a preferred one and only one of the first and second throttle signals. 
     Thus it is another object of the invention to provide a simple method of converting redundant throttle signals into a single throttle setting. 
     The throttle signals may be a series of pulses whose widths represent throttle settings. The fault detection circuit may indicate a fault when either the frequency of the pulses or their width exceeds a predefined range. 
     Thus it is another object of the invention to provide a redundant fault detection system such that provides good assurance that when no fault is detected, that the signal may be rehabilitated for use in controlling the throttle. 
     The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessary represent the full scope of the invention, however, and reference must be made to the claims herein for interpreting the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic state block diagram showing the communication of redundant throttle signals from a power train control module to an electronic throttle unit which provides a closed loop feedback control of an electronically controlled throttle actuator; 
     FIG. 2 is a graphical representation of a pulse width modulation of the redundant throttle signals to encode the throttle setting in the duty cycle of the pulses and showing a duty cycle window and frequency window used to detect faults of the throttle signals; 
     FIG. 3 is a schematic representation of the electronic throttle unit of FIG. 1 showing edge detection circuitry used for monitoring faults in the throttle signals and showing a microcontroller executing the fault detection program and a throttle signal processing program of the preferred embodiment of the present invention; 
     FIG. 4 is a state diagram of the throttle signal processing program of FIG. 3 showing its operation under various fault conditions; and 
     FIG. 5 is a graph of redundant throttle signals versus time showing various fault conditions and the throttle setting produced using the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a throttle control system  10  includes an accelerator pedal  12  attached to a pedal position sensor  14  such as may indicate the angular deflection of the accelerator pedal  12  as actuated by the vehicle driver. 
     The pedal position sensor  14  provides a signal to the power train control module  16  which encodes the signal from the pedal position sensor  14  into a redundant first throttle signal  18  on a first channel, and second signal  20  on a second channel for transmission to an electronic throttle unit (ETU)  22 . The channels may be separate conductors, so as to reduce the chance of loss of both signals from a conductor break, or may be time or frequency multiplexed signals on a single conductor. 
     The ETU  22  provides an output signal, indicating a throttle setting  24 , to a throttle actuator  26 , for example, an electric motor providing a rotating shaft  29  attached to a throttle valve  31  within the throttle body  32 . The actuator  26  and/or throttle  32  may include sensors generating position feedback signal  28  and a redundant position feedback signal  30  indicating throttle valve position that may be used by the ETU for closed loop control of the throttle according to the throttle setting  24 . 
     Referring now to FIG. 2, the throttle signals  18  and  20  may be pulse-width modulated (PWM) to produce a series of pulses  34  having pulse widths  38  and occurring at a regular frequency or period  36 . The desired throttle setting  24  may be encoded in the pulse widths  38  which may vary within a pulse termination window  40  after a rising edge of the pulse  34  to indicate a full range of operation of the throttle valve  31 . The frequency of the pulses  34  may vary within a pulse repetition rate window  42  conveying no throttle information but used for fault detection as will be described. 
     Referring to FIG. 3, the ETU  22  may include a microcontroller  44  holding a memory  46  including a fault detection program  48  and a throttle signal processing program  50  both which will be described. The microcontroller  44  may communicate with input/output circuitry  52  providing the signal indicating the throttle setting  24  and receiving the feedback signals  28  and  30  as described above with respect to FIG.  1 . 
     The microcontroller  44  may also receive the throttle signals  18  and  20  at onboard inputs  54 . The throttle signals  18  and  20  may also be received by edge detectors  56  detecting rising or falling edges of the pulses  34  to provide an interrupt input  58  causing execution of the fault detection program  48  as an interrupt service routine upon each rising edge. Generally, as shown in FIG. 2, the fault detection program  48  determines if there is a falling edge of the pulse  34  within pulse termination window  40  and then a subsequent rising edge within pulse repetition rate window  42 . If either of these conditions is not met, for a predetermined period of time or number of pulses  34 , a fault condition is associated with the given throttle signal  18  or  20 . The particular throttle signal  18  or  20  associated with the fault may be deduced through an actual reading of the inputs  54 . 
     Referring now to FIGS. 4 and 5, the throttle signal processing program responds to indications of faults on throttle signals  18  and  20  according to a state diagram executed by the throttle signal processing program  50 . In this diagram, throttle signal  18  is designated as CHANNEL  1  and throttle signal  20  is designated as CHANNEL  2 . 
     At an initialization of state block  60 , the fault conditions of the throttle signals  18  and  20  are checked. If CHANNEL  1  is faulted but CHANNEL  2  is good, the program proceeds to state block  62  as indicated by state transition arrow  61  and CHANNEL  2  only is used to determine throttle setting. Generally this involves simply a conversion of the pulse width  38  into an angular position of the throttle according to a standard conversion for the particular actuator  26 . 
     Conversely if CHANNEL  1  is good and CHANNEL  2  is faulted, the program proceeds to state block  64  as indicated by state transition arrow  63  and the CHANNEL  1  signal is used only. 
     More typically, CHANNEL  1  will be good and CHANNEL  2  will be good and the program will proceed to state block  66  as indicated by state transition arrow  65  where both channels are good and CHANNEL  1  is used for control of the throttle. Once at state block  66 , should CHANNEL  1  fault, the program proceeds to state block  62  as indicated by state transition arrow  71 . Conversely, once at state block  66 , should CHANNEL  2  fault, the program proceeds to state block  64  as indicated by state transition arrow  76 . 
     The present invention allows for rehabilitation of the CHANNELS and return from state blocks  62  (via state transition arrow  75 ) or state block  64  (via state transition arrow  78 ) if the fault conditions in the respective CHANNELS  1  or CHANNEL  2  should disappear. Rehabilitation is instantaneous with the disappearance of the fault, in contrast to the fault condition which requires a predetermined time interval of a fault condition. 
     Referring to FIG. 5, the program  50  may be at state block  66  during period  68  shown in FIG. 5 during which both CHANNELS vary but nevertheless track each other. Throttle setting  24  then tracks throttle signal  18  of CHANNEL  1 . 
     During subsequent period  70 , CHANNEL  1  may fail as indicated by the break in the line indicating signal  18 , causing the throttle setting  24  to drop to follow the second throttle signal  20  per state block  62  and state transition arrow  71 . 
     During next period  74 , throttle signal  18  may be restored for example if the failure was intermittent, and the program will proceed back to state block  66  per state transition arrow  75  increasing the availability of the channels during throttle operation. 
     Referring to FIGS. 4 and 5 at interval  80 , the CHANNEL  1  and  2  signals may begin to deviate from each other by more than a predetermined amount A and the program  50  may move from state block  66  to state block  82  per state transition arrow  84 . In this state, the throttle setting  24  tracks the CHANNEL with the lower throttle signal thus ensuring a conservative operation of the vehicle. 
     If CHANNEL  2  or the lower channel should then fault during interval  94 , then as indicated by state transition arrow  86 , the throttle setting  24  will drop to a high idle level  89 . High idle level is set so that the engine will remain running and will permit driving the vehicle at a very low speed of around  5  miles per hour to a service center. This high idle condition is shown by state block  88  and this transition is indicated by state transition arrow  86 . 
     If at state block  88 , one or both of the CHANNELS stops being faulted as shown in interval  95 , then as indicated by state transition arrow  90 , the program  50  proceeds to the ramp up state  92  in which the throttle setting  24  ramps upward either to (1) the lower of the two throttle signals of state block  82  as shown by state transition arrow  97 , (2) to the CHANNEL  2  value per state block  62  if CHANNEL  2  recovers as indicated by state transition arrow  96  or (3) to the CHANNEL  1  value of state block  64  if CHANNEL  1  recovers as indicated by state transition arrow  98 . If the fault returns during the ramping process, the state block  88  is returned to, but with the same smooth ramping between the last throttle setting (which may have been arrived at during an incomplete ramping) and the high idle state  89 . 
     Importantly however, the transition is not immediate but follows a smooth ramp  102  taking from approximately 0.5 to 2 seconds to complete indicated by interval  95 . This time is set to allow the operator of the vehicle to react to the change in throttle setting if it is undesired. For example, if during throttle failure, the user has pressed the accelerator pedal to the full downward position, this ramping allows the user to release the accelerator pedal as the speed ramps upward. The ramping prevents the user from being surprised by an abrupt transition in throttle setting upward or downward. 
     From state block  92 , and during interval  106 , the rehabilitation of CHANNEL  2  may thus cause program  50  to move to state block  82  per state transition arrow  96 , with the throttle setting  24  returning to CHANNEL  2  control. If CHANNEL  1  is then rehabilitated, the program  50  may move to state block  66  via state transition arrow  104 . 
     If as shown in interval  108 , both CHANNELS fail together, the throttle setting  24  drops to the high idle level  89  following a transition from state block  66  to  88  along state transition arrow  110 . 
     Again, when one or both CHANNELS are restored, the program  50  proceeds via state transition arrow  90  to the state block  92  and a ramp-up interval occurs during interval  112  when the fault value returns to the normal throttle setting in this case of CHANNEL  1  along either state transition arrow  98  and then along state transition arrow  78  to state block  66  or along state transition arrow  96  and then along state transition arrow  75  to state block  66 . 
     The above description has been that of a preferred embodiment of the present invention, it will occur to those that practice the art that many modifications may be made without departing from the spirit and scope of the invention. In order to apprise the public of the various embodiments that may fall within the scope of the invention, the following claims are made.