Abstract:
A throttle control apparatus and method is disclosed in a vehicle having a throttle valve with a default position intermediate a fully-closed position and a fully-open position, and a spring mechanism coupled to the throttle valve that creates torque to move the throttle valve toward the default position in the absence of other torque. The throttle control apparatus includes an actuator for generating torque to open and close the throttle valve in response to a control signal, wherein the actuator is attached to the throttle valve by a mechanical coupling having lash. The throttle control apparatus also includes a processor in communication with the actuator, the processor generating the control signal based upon a command signal. The processor executes a stored program including a portion to compare a new value of the command signal with a prior value of the command signal, and to generate the control signal as a function of the deviation between the new and prior values of the command signal.

Description:
FIELD OF THE INVENTION 
     The present invention relates to electronically controlled throttles for vehicle engines. In particular, the present invention relates to the controlling of throttles that are spring biased towards a fast-idle default position. 
     BACKGROUND OF THE INVENTION 
     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 vehicle, to the throttle valve. 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 throttle actuator (typically an electric motor) for actuating the throttle valve. 
     While electronic control without mechanical linkages allows for the introduction of a variety of desirable control features, electronic control also makes the operation of the throttle dependent upon the throttle signals to the throttle controller, which controls the throttle actuator. These throttle signals may pick up errors due to noise or otherwise. Those errors can have undesirable effects on the control of the throttle, as discussed below. 
     As shown in FIG. 1 (Prior Art), a typical throttle includes a conduit, through which air (or an air-fuel mixture) flows, and a rotatable throttle plate that in part determines the flow rate based on its position within the conduit. In between a closed position, in which the throttle plate prevents nearly all flow through the conduit, and a wide-open position, in which the throttle plate allows a maximum flow rate, there is typically a default position for the throttle plate. The default position is a position of the throttle plate in which a relatively small flow rate is allowed (i.e., where the throttle plate is closer to closed than open). 
     Under normal operating conditions, the position of the throttle plate is positioned by the throttle actuator (i.e., electric motor). The throttle actuator is typically coupled to the throttle plate by a pair of gears in between which exists lash. (In other cases, the throttle actuator and throttle plate can be coupled by other linking elements that also have lash, such as a belt.) However, the throttle plate is also coupled to a spring mechanism which biases the throttle plate towards the default position. If for some reason the throttle actuator is unable to control the position of the throttle plate (i.e., the throttle actuator produces no output torque), the spring mechanism moves the throttle plate to the default position. Because there is a small amount of flow through the conduit in the default position, the vehicle remains (at least partly) operational when this occurs. 
     Although the spring mechanism is necessary for allowing partial operation of the vehicle when the throttle actuator is malfunctioning, the spring mechanism complicates the electronic control of the throttle. Proper control of the throttle under normal operating conditions (i.e., when the throttle actuator is properly operating) requires that the throttle actuator compensate for (i.e., counteract) the torque of the spring mechanism. Typically, this compensation is effected by the introduction, into the throttle signals, of a feedforward component. 
     Generation of the proper feedforward component when the throttle plate is near the default position is difficult, however, for two reasons. As shown in FIG. 2 (Prior Art), the torque provided by the spring mechanism changes in a discontinuous manner when the throttle plate crosses over the default position. Additionally, because the spring mechanism biases the throttle plate in opposite directions when the throttle plate is on opposite sides of the default position, the gears coupling the throttle plate and the throttle actuator experience a relative shift due to the gear lash as the throttle plate moves through the default position. 
     Because of the interaction of the spring mechanism, the gear lash and the feedforward component, exact control of the positioning of the throttle plate near the default position is difficult, and undesirable fluctuation of the throttle plate can occur near the default position. This particularly becomes a problem if noise (i.e., duty cycle variation) occurs within the throttle command signal when the throttle plate is at or very close to the default position, such that the throttle signals are effectively commanding the throttle plate to shift back and forth across the default position. Under these circumstances, the throttle plate can experience rapid, undesirable fluctuation that can result in annoying rattling of the throttle plate. 
     SUMMARY OF THE INVENTION 
     The present inventor has recognized that the rapid fluctuation and rattling of the throttle plate is caused by the operation of the feedforward component of the throttle control signal while the throttle plate is positioned near the default position, at which there are discontinuities due to operation of the spring mechanism and the gear lash. Thus, the rapid fluctuation and rattling of the throttle plate can be reduced by modifying the throttle control signal. 
     The present invention therefore relates to a throttle control apparatus in a vehicle having a throttle valve with a default position intermediate a fully-closed position and a fully-open position, and a spring mechanism coupled to the throttle valve that creates torque to move the throttle valve toward the default position in the absence of other torque. The throttle control apparatus includes an actuator for generating torque to open and close the throttle valve in response to a control signal, wherein the actuator is attached to the throttle valve by a mechanical coupling having lash. The throttle control apparatus further includes a processor in communication with the actuator. The processor generates the control signal based upon a command signal. The processor executes a stored program including a portion to compare a new value of the command signal with a prior value of the command signal, and to generate the control signal as a function of the deviation between the new and prior values of the command signal. 
     The present invention additionally relates to a throttle control method in a vehicle having a throttle valve with a default position intermediate a fully-closed position and a fully-open position, and a spring mechanism coupled to the throttle valve that creates torque to move the throttle valve toward the default position in the absence of other torque. The throttle control method includes receiving a command signal at a processor, comparing a new value of the command signal with a prior value of the command signal at the processor, and generating a control signal at the processor, wherein the control signal is a function of the deviation between the new and prior values of the command signal. The throttle control method further includes providing the control signal to an actuator that is attached to the throttle valve, with lash existing between the actuator and the throttle valve, and generating torque at the actuator to open and close the throttle valve in response to the control signal. 
     The present invention further relates to a vehicle comprising a throttle valve with a default position intermediate a fully-closed position and a fully-open position. The vehicle includes a restoring means coupled to the throttle valve for creating torque to move the throttle valve toward the default position in the absence of other torque, a torquing means attached to the throttle valve for generating torque to open and close the throttle valve in response to a control signal, wherein lash exists between the torquing means and the throttle valve, and a processing means, which is in communication with the torquing means. The processing means executes a stored program to compare a new value of a command signal with a prior value of the command signal, and to generate the control signal at the processor, wherein the control signal is a function of the deviation between the new and prior values of the command signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is cross-sectional views of a throttle including a throttle plate within a conduit, in which the throttle plate is shown to be in closed, wide-open and default positions (Prior Art); 
     FIG. 2 is a graph of spring torque versus throttle plate position (throttle angle) for a spring mechanism that biases the throttle plate of FIG. 1 toward the default position (Prior Art); 
     FIG. 3 is a perspective view of an exemplary vehicle having (in phantom) an engine, a throttle assembly, and an electronic throttle control system in accordance with the present invention; 
     FIG. 4 is a block diagram of an exemplary throttle assembly and electronic throttle control system in accordance with the present invention; 
     FIG. 5 is a flow chart showing exemplary steps of a first computer algorithm that may be employed in accordance with the present invention; and 
     FIG. 6 is a flow chart showing exemplary steps of a second computer algorithm that may be employed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 3, a vehicle having an engine  12 , a throttle assembly  14 , and an electronic throttle control system  16  is shown. Vehicle  10  may be any one of a variety of types of vehicles having internal combustion engines or other types of engines that employ throttles, including automobiles, trucks, busses, construction vehicles, agricultural vehicles, and other vehicles or stationary power units. 
     Turning to FIG. 4, elements of an exemplary throttle assembly  20  and an exemplary electronic throttle control system  30  are shown. Throttle assembly  20  includes a conduit (e.g., a tube, pipe or other channel)  22  through which air or an airfuel mixture is to flow. Positioned within conduit  22  is a throttle plate (or simply throttle)  24 , which is elliptical in shape and rotates within conduit  22  (which is cylindrical). Throttle plate  24  is capable of rotating to a fully-closed position, a fully-open position and a variety of other positions including a default position. In alternate embodiments, conduit  22  may take on any number of different shapes; in such cases, throttle plate  24  also takes on a corresponding shape such that the throttle plate may, when rotated to a closed position, completely close off (or nearly completely close off) the conduit. 
     Electronic throttle control system  30  includes a powertrain control module (PCM)  32  that is coupled to an electronic throttle unit (ETU)  34 . PCM  32  receives an operator input signal  37  from a pedal position sensor  36 , which indicates the angular deflection of an accelerator pedal  38  as actuated by the vehicle driver. PCM  32  provides a throttle command signal  40  on a first channel  42  and also on a second channel  44  to ETU  34 . Throttle command signal  40  is generated based upon operator input signal  37  and indicates a desired throttle position. First and second channels  42 ,  44  can be provided on separate conductors, so as to reduce the chance of loss of both signals from a conductor break, or can be time or frequency multiplexed on a single conductor. In alternate embodiments, throttle command signal  40  is provided from PCM  32  to ETU  34  via only a single channel. Also, in alternate embodiments, PCM  32  provides throttle command signal  40  based on information other than (or in addition to) operator input signal  37  (e.g., the throttle command signal can be completely generated by a computer in an automatic mode of control). 
     Based upon throttle command signal  40 , ETU  34  provides an output signal (typically a voltage signal)  46  to a throttle actuator  48 , for example, an electric motor. Throttle actuator  48  is coupled to throttle plate  24  by a first rotating shaft  52  and a second rotating shaft  53 , which in turn are coupled by a first gear  55  and a second gear  57 . Gear lash exists between first and second gears  55 ,  57 . Consequently, when the driving gear (that gear which is at a particular time delivering torque to the other gear) switches direction, it does not engage the other gear immediately upon switching direction, but instead must rotate a certain distance before engaging the other gear. In alternate embodiments, throttle actuator  48  can be coupled to throttle plate  24  by other elements that also have lash, such as a belt. 
     Output signal  46  is based upon (or even equivalent to) throttle command signal  40 , and is provided to cause throttle actuator  48  to rotate throttle plate  24  to the desired throttle position. Also coupled to throttle plate  24  are one or more sensors  51  for generating a throttle position signal  50  indicative of actual throttle position, and providing the throttle position signal to ETU  34  via first feedback channel  54  and a redundant feedback channel  56 . The information in throttle position signal  50  provided via first and redundant feedback channels  54 ,  56  is used by ETU  34  for closed loop control of throttle plate  24  by adjusting output signal  46 . Feedback channels  54 ,  56  can be provided on separate conductors, so as to reduce the chance of loss of both signals from a conductor break, or can be time or frequency multiplexed on a single conductor. 
     Each of the PCM  32  and ETU  34  preferably is (or includes) a microcontroller or other computer processor having memory. The memory of PCM  32  includes a computer program for generating throttle command signal  40  indicative of the commanded throttle position based upon operator input signal  37 . The memory of ETU  34  includes a computer program for monitoring and controlling the operation of throttle plate  24  in response to throttle command signal  40 . Specifically, ETU  34  monitors the difference between the actual throttle position as indicated by throttle position signal  50  and the commanded throttle position as indicated by throttle command signal  40 . Based upon the difference between the actual throttle position and the commanded throttle position, ETU  34  then sets output signal  46  to cause throttle plate  24  to adjust towards the commanded throttle position. In alternate embodiments, PCM  32  and ETU  34  can be combined into a single control unit, which performs the functions of the PCM and ETU. Further, in alternate embodiments, PCM  32  and ETU  34  (or the combined controller) are hard-wired rather than microcontroller-based. 
     Further as shown in FIG. 4, a spring mechanism  59  is coupled to throttle plate  24 . Spring mechanism  59 , which is coupled directly with second gear  57  (and not directly with first gear  55 ), biases throttle plate  24  towards the default position. To compensate for the torque of spring mechanism  59 , output signal  46  (provided by ETU  34 ) includes a feedforward component. The torque provided by spring mechanism  59  experiences a change in direction and a discontinuity as throttle plate  24  crosses over the default position. Consequently, the feedforward component of output signal  46  also experiences a change in direction and a discontinuity as throttle plate  24  passes through the default position. Because of the lash between first and second gears  55 ,  57 , the gears can experience a slight relative rotation with respect to one another as they rotate when throttle plate  24  crosses over the default position, both as a result of the spring mechanism  59  and the feedforward component of output signal  46 . Consequently, if noise exists on throttle command signal  40  and then is transferred onto output signal  46  while throttle plate  24  is at or near the default position, the throttle plate can experience rapid fluctuation and produce rattling (or other undesirable sounds). 
     Turning to FIG. 5, a flow chart  100  showing exemplary steps of a computer algorithm for filtering undesirable noise from throttle command signal  40  is provided. By implementing these steps on ETU  34 , undesirable noise from throttle command signal  40  can be removed so that output signal  46  is free of the noise and consequently throttle plate  24  does not experience rapid fluctuation or rattling near the default position. Upon starting, the flow chart begins with step  110 , in which a new value of the commanded throttle position (TP_command_unsmoothed) is obtained at ETU  34  (in the form of throttle command signal  40 , from PCM  32 ). Next, at step  120 , a determination is made as to whether this is the first time that the algorithm has been run (i.e., whether this is the first cycle through the algorithm). This can be the case either because the processing has just been turned on (i.e., the vehicle was just started), or because a vehicle fault condition has just been corrected. If so, the algorithm proceeds to step  160 , such that the new value of the commanded throttle position is used to determine output signal  46 . In this case, throttle command signal  40  is not filtered (since there is no basis for determining that the throttle command signal is faulty). 
     If this is not the first cycle through step  120  of the algorithm, the algorithm proceeds to step  115 . Step  115  determines whether a prior value of the commanded throttle position (TP_command, i.e., the value previously received before the new value) commanded throttle plate  24  to move outside the region immediately surrounding the default position. If so, there is no need to filter throttle command signal  40  (since the rapid fluctuation and rattling of throttle plate  24  only occur due to the interaction of the lash with the operation of spring mechanism  59  and the feedforward component of output signal  46  while the throttle plate is at the default position) and so the algorithm proceeds directly to step  160 . Again, at step  160 , the new value of the commanded throttle position is used to determine output signal  46  (i.e., throttle command signal  40  remains unchanged). 
     However, if the prior value of the commanded throttle position directed throttle plate  24  to move to a position within the particular range around the default position, filtering of any noise from throttle command signal  40  becomes important for precluding undesirable fluctuation and rattling of the throttle plate. The algorithm thus proceeds to step  130 , where the absolute value of the difference between the new value of the commanded throttle position (T_command_unsmoothed) and the prior value of the commanded throttle position (TP_command) is calculated. Then the algorithm proceeds to step  140 , which determines whether the absolute value of the difference between the two values is smaller than a threshold. If the difference is smaller than a threshold, this indicates that the change in the commanded throttle position was likely due to noise. Such a change could lead to undesirable fluctuation and rattling of throttle plate  24 , and therefore should be filtered from the commanded throttle position. Hence, the algorithm advances to step  150 , which maintains the prior value of the commanded throttle position constant instead of updating the commanded throttle position to equal the new value of the commanded throttle position. The change in throttle command signal  40  is filtered from the signal before it is used to generate output signal  46 . 
     If, however, at step  140 , the difference is found out not to be smaller than the threshold, the algorithm proceeds to step  160 . In step  160 , the new value of the commanded throttle position is substituted for the prior value of the commanded throttle position and no filtering is performed. After performing either step  150  or step  160 , the algorithm has determined the latest commanded throttle position and therefore proceeds to step  170 , in which this commanded throttle position is utilized by ETU  34  as the basis for determining output signal  46 . The algorithm then returns to step  110  to read a new value of the commanded throttle position, unless performance of the algorithm is ended. 
     Referring to FIG. 6, a second flow chart  200  is provided showing exemplary steps of a second computer algorithm that may be performed by ETU  34  to filter throttle command signal  40 . Flow chart  200  is identical to flow chart  100  except insofar as it does not include a step paralleling step  115  of flow chart  100 . Otherwise, steps  210  through  270  each correspond respectively with steps  110  through  170  of flow chart  100 . Because flow chart  200  lacks a step paralleling step  115  of flow chart  100 , the algorithm of flow chart  200  does not limit the filtering process to times when the throttle command signal  40  is commanding throttle plate  24  to a position near the default position of the throttle plate. Instead, the algorithm filters throttle command signal  40  at all times regardless of the current position of throttle plate  24 . 
     The algorithms of flow charts  100 ,  200  are meant to be exemplary. The particular algorithms of flow charts  100 ,  200  of FIGS. 5 and 6, respectively, can be modified to operate differently under different circumstances. Each of the algorithms has several characteristic parameters than can be adjusted. For example, the period of each algorithm is typically 4 milliseconds (i.e., a new value of the commanded throttle position will be obtained every 4 milliseconds). However, the period/frequency of operation can be speeded-up or slowed-down to correspond with the rapidity of change of throttle command signal  40 . Also, the noise threshold of steps  140 ,  240  typically are set to 0.075% or at least ¾ of a tenth of a degree. Changes in the commanded throttle position that are less than this amount will be filtered from throttle command signal  40  when the filter is operating. Use of this threshold is consistent with allowing control of the position of throttle plate  24  to within {fraction (1/10)} of a degree. However, other thresholds can be used to allow greater or lesser tolerance of small changes in the commanded throttle position. With respect to step  115  of flow chart  100 , the range about the default position can also be set to a variety of levels. 
     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. For example, other algorithms may be used to filter or otherwise process a throttle command signal to remove noise and consequently reduce undesired throttle fluctuations or rattling. Some of these algorithms employ more complicated tests to provide filtering only when certain patterns of changes occur in the commanded throttle position, or under circumstances where throttle rattling is likely to occur for an extended period of time. Also, multiple algorithms may be used at different times in the system as throttle operation changes over time, or in response to different operational conditions of the vehicle. In order to apprise the public of the various embodiments that may fall within the scope of the invention,