Abstract:
A cruise control has a throttle controller for maintaining the speed of a vehicle at a desired speed. The cruise control can operate in a conventional cruise mode and a fuel economy cruise mode. When in the fuel economy cruise mode, the throttle is held at a fixed position as the vehicle travels within a prescribed range of speeds from the desired speed. The throttle remains fixed until an exit condition occurs or acceleration/deceleration input is supplied at which point the cruise control provides throttle adjustment at less than normal rates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     (Not applicable) 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     (Not applicable) 
     BACKGROUND OF THE INVENTION 
     The present invention relates to electronic throttle controllers for vehicles and in particular to such controllers providing automated speed control. 
     Electronic throttle controllers are well known for operating an engine throttle valve to control the rate of fuel flow to the combustion chamber of an engine. Typically, the throttle controller receives an acceleration input signal from the operator of the vehicle via an accelerator pedal. The farther the pedal is depressed, the more the throttle valve is opened, which permits more fuel to be consumed by the engine and the vehicle to travel faster. 
     Some throttle controllers can operate automatically as a “cruise control” to maintain the speed of the vehicle at a cruising speed set by the driver. The cruise control provides a convenient means for a driver to maintain vehicle speed without using foot pedals, which can be especially advantageous on long trips. Typically, such cruise controls use an input from a speedometer or engine speed sensor to monitor the cruising speed of the vehicle. Due to varying terrain, friction and wind resistance the speed controller is nearly continuously correcting for deviations from the desired speed. Consequently, the throttle is constantly fluctuating to allow more or less fuel to be consumed by the engine to maintain the set speed. 
     A problem with such cruise controls is that the continuous throttle adjustments lower the fuel economy of the engine. This is primarily due to the inefficiencies involved with non-constant burning, which include counteracting momentum losses of the moving components of the engine as well as that of the overall vehicle. 
     Most cruise controls include stored error correction algorithms that define the response time and duration of the throttle adjustments. These algorithms are commonly designed with smoothness, accuracy and responsiveness being the highest priorities. Fuel economy is typically not a factor in the design of the algorithms. 
     Yet, U.S. Pat. No. 5,944,766 discloses a cruise control having control algorithms designed to improve the fuel economy of the vehicle. When it is sensed that the vehicle is gaining momentum, the algorithms instruct the speed controller to override the normal control of the throttle and set back the throttle position to a prescribed percentage (such as 50% or 80%) of its normal position. Thus, fuel consumption is minimized during and after the vehicle travels down hill. As such, the disclosed cruise control has only limited fuel saving benefits. 
     Accordingly, there exists a need for a cruise control with improved fuel economizing benefits. 
     SUMMARY OF THE INVENTION 
     The present invention provides a vehicle cruise control with a fuel economy cruise mode that reduces the amount of fuel consumed by the vehicle. In the fuel economy cruise mode, the cruise control eliminates changes in engine throttling within a given deviation from the desired cruising speed. Moreover, the cruise control can provide initial throttle adjustment at less than normal rates during and when exiting the fuel economy cruise mode. Thus, the present invention reduces fuel costs and exhaust emissions into the environment 
     Specifically, the present invention provides a cruise control designed for use with engines having an electronically controlled throttle valve movable to regulate fuel flow to the engine. The cruise control has an electronic control module electrically coupled to the throttle for controlling the position of the throttle valve and an input device operable from within a passenger cabin of the vehicle for signaling the control module of a speed signal corresponding to a desired vehicle speed to be maintained. The control module enters a fuel economy cruise mode and fixes the position of the throttle valve when the speed set signal is received and the vehicle speed is within a prescribed error range from the desired vehicle speed for a prescribed time period. The control module maintains the fixed position of the throttle valve until an exit condition or an acceleration/deceleration input is detected. 
     In a preferred form, the control module includes an input module, a memory module and a processor electrically coupled together. The prescribed error range and time period are stored in memory. Preferably, the prescribed error range two miles per hour and the prescribed time period is 10-30 seconds. Upon detecting an exit condition (or acceleration input), the control module can provide initial or sustained speed adjustment set backs, or in other words, less than normal acceleration and deceleration. 
     In one preferred form, the cruise control can also operate in a conventional cruise mode, activated by the input device, in which the control module repositions the throttle valve at prescribed intervals to maintain the desired vehicle speed according to speed adjustment gains of cruise control algorithms. When an exit condition is detected, the speed control module repositions the throttle valve so as to limit the rate of change of vehicle speed to less than the rate of change of speed ordinarily allowed during cruise mode. Additionally, the input device can send acceleration/deceleration signals to the control module, in which case, the control module repositions the throttle valve according to algorithms having reduced speed adjustment gains from that of the cruise mode algorithms. Preferably, the reduced speed algorithms are stored in the memory module. 
     The cruise control can also include an engine speed sensor coupled to the control module for sending the control module current vehicle speed data. The control module can be electrically coupled to a transmission clutch, a brake and a battery of the vehicle. For such a vehicle, the exit conditions can include, among others, an off input signal, a low speed input, a brake input signal, a clutch activation signal, a low battery signal and combinations thereof. 
     The present invention also provides a method of reducing the fuel consumption of an vehicle having a cruise control with a control module operated by an input device mounted within a passenger cabin of the vehicle. The method includes receiving operator inputs for a desired vehicle speed and to a begin fuel economy cruise mode; verifying that the vehicle is traveling within a prescribed range of the desired vehicle speed for a prescribed time period; entering a fuel economy cruise mode and fixing the position of the throttle; checking for an exit condition and acceleration/deceleration input; and maintaining the throttle at the fixed position until either the exit condition or acceleration/deceleration input is detected. 
     The method can further include the step of reducing vehicle acceleration and deceleration input from the operator when exiting fuel economy cruise mode. Preferably, this is done by the control module processor processing speed adjustment algorithms stored in the memory module to reduce the vehicle acceleration/deceleration rate during and when exiting the fuel economy cruise mode. 
     Thus, the present invention provides a cruise control using less fuel than conventional cruise controls, thereby reducing fuel costs and exhaust emissions into the environment. During fuel economy cruise mode all engine throttling is eliminated when the vehicle is traveling withing a range of the desired speed. Moreover, the cruise control applies reduced acceleration gains when accelerating or decelerating while in the fuel economy cruise mode or when returning to the conventional manual or cruise modes. 
    
    
     A preferred embodiment of the invention is stated in the following description and illustrated in the accompanying drawings which form a part hereof. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the cruise control system of the present invention; 
     FIG. 2 is a flow chart showing a fuel economy cruise mode entry check process; 
     FIG. 3 is a flow chart showing the fuel economy cruise mode processes; 
     FIG. 4 is a flow chart showing the error checking process; and 
     FIG. 5 is a process block diagram showing the cruise control response to various driver input conditions. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the present invention provides a vehicle cruise control system having an electronic precision speed controller (PSC)  10  controlling the operation of an electronic throttle body (ETB)  12 . The PSC  10  includes an input/output (I/O) module  14 , a microprocessor  16  and a memory module  18 . These components are suitably coupled so that the PSC processor  16  can receive input signals from various vehicle components via the I/O module  14  and process them according to algorithms stored in the memory module  18  to operate the ETB  12 . Such vehicle components include a battery  20 , speed sensor  21 , accelerator pedal  22 , clutch  23 , brake  24  and operator input device  25 . The system also includes a display  27  with cruise mode  29  and fuel economy cruise mode  31  indicators that illuminate when the PSC  10  is operating in either of the cruise modes. The display  27  receives the appropriate signal from the PSC  10  via the I/O module  14 . It should be noted that the vehicle components  20 - 25  and display  27  are shown having a separate wire connection to the PSC  10 , however, they could also be connected together via a suitable vehicle bus using a suitable operating protocol, such as SCP (Standard Corporate Protocol). 
     The ETB  12  likewise includes an I/O module  26  for receiving control signals from the PSC  10  and for sending throttle feed back data to the PSC  10 . The ETB  12  also includes a servomotor  28  and a throttle valve  30 . The motor  28  is coupled to the throttle valve  30  by any suitable means, for example, a shaft and gear arrangement or a cable. The motor  28  is controlled by the PSC  10  to open and close the throttle valve  30  in response to acceleration and deceleration input from a vehicle operator received by the PSC  10 . As known in the art, the throttle valve  30  controls the amount of fuel flowing to an engine  32  and thereby its operating speed and the overall speed of the vehicle. 
     The algorithms stored in the memory module  18  include instructions for operating the ETB  12  in three modes: manual mode, cruise mode and fuel economy cruise mode, with the algorithms for each mode stored in memory locations  34 ,  36  and  38 , respectively. 
     Generally, the manual mode is the default operating condition wherein the driver controls the speed of the vehicle with the accelerator pedal and brake. In such a case, the PSC  10  operates the ETB  12  in response to accelerator pedal  22  and brake switch  24  input signals. The cruise mode is an automated engine throttle control wherein the driver inputs to the PSC  10  a cruising speed using a steering column mounted cruise control button  25 . Once the desired cruising speed is set, the driver no longer needs to use the accelerator pedal, brakes or any other device to maintain the set speed of the vehicle. The fuel economy cruise mode is a fuel saving setting of the present invention wherein the vehicle speed is maintained within an acceptable deviation from the desired cruising speed, as described below. 
     The stored fuel economy algorithms provide instructions for entering, maintaining and exiting the fuel economy cruise mode. In the preferred embodiment, the PSC  10  is ready to enter fuel economy cruise mode only upon the coexistence of three conditions. First, the PSC  10  must already be in cruise mode. Second, the driver must supply a fuel economy cruise mode input. Third, the vehicle must be traveling at a substantially constant speed for a prescribed time. One additional requirement must also be met, and that is that no cruise mode exit condition is present. 
     Thus, referring to FIG. 2, the PSC processor  16  executes a fuel economy cruise mode ready check subroutine either at periodic intervals, or preferably upon a suitable input from the vehicle operator. The subroutine begins at step  40  to check if a suitable input is received from the input device  25  indicating that the vehicle operator wishes to enter fuel economy cruise mode. This input can be a signal from a dedicated button or switch mounted within the passenger cabin or it can be the same button or switch used to initiate the cruise mode once in the cruise mode. If no such signal is received, the PSC  10  will remain in its present mode at step  42 , otherwise at step  44  the PSC  10  confirms that it is currently in the cruise mode. If not, the PSC  10  can remain in the manual mode. Preferably, however, the PSC  10  will enter the cruise mode, notifying the driver via the display  27  in which case the process continues to step  46  where the PSC processor  16  scans the inputs from the devices  20 - 25  to confirm that no cruise mode exit conditions exist. The PSC  10  enters fuel economy cruise mode if there are no exit conditions, otherwise it returns to manual mode at step  42 . 
     At step  46 , to check for an exit condition, the PSC processor  16  scans the I/O module  14  to check for the presence of a signal from the devices  20 - 25 , such as “off” input from the input device  25  in the vehicle cabin. The PSC processor  16  can also scan for an open circuit which could result when the battery is low (e.g. 8 volts or less), the brake is applied, or the clutch is depressed. The PSC  10  can also monitor engine speed using input from a suitable speed sensor  21  or a speedometer (not shown), and an exit condition can be when the vehicle slows below a prescribed minimum speed, for example 25 miles per hour. Any one of these conditions alone can constitute an exit condition. Any exit condition will cause the PSC  10  to exit the fuel economy cruise mode to return to cruise mode and possibly manual mode, depending upon the input received (such as on “off” or brake input). 
     Once in the fuel economy cruise mode, the PSC  10  performs the process of FIG.  3 . Specifically, at decision block  50 , the PSC  10  determines whether the vehicle is traveling at a sufficiently constant speed for a given time period using the subroutine of FIG. 4 Referring to FIG. 4 a prescribed maximum speed error E(max) and time constant (Tc) are stored in a suitable location in the memory module  18  are retrieved at step  52 . Also retrieved from the memory module  18  at step  52  is the driver&#39;s desired speed (DS), which is the vehicle speed when the cruise mode was entered. As an example, the stored values could be DS=55 miles per hour, E(max)=0.5 miles per hour, and Tc=30 seconds, in which case the vehicle speed would have to be within 54.5-55.5 miles per hour to enter fuel economy cruise mode. 
     At step  54 , the PSC  10  PSC processor  16  reads the value of the speed sensor  21  and sets a current speed (CS) value in the memory module  18  to the speed sensor value. Then at step  56  the PSC processor  16  computes the actual error (E) or difference between CS and DS (which is stored in the memory module  18 ). At step  58 , the PSC processor  16  compares the absolute value of E to E(max). If E is less than E(max), then at step  60  the PSC processor  16  begins a timer count. If at step  62  the value of the timer is less than Tc, the counter is incremented at step  64 . At step  66 , the PSC processor  16  updates the value of CS according to the speed sensor and the computation of step  58  is again made. This continues until E is less than E(max) for Tc in which case the vehicle is traveling within the prescribed error, or until E is greater than E(max), in which case the vehicle is not traveling at a sufficiently constant rate. 
     Referring again to FIG. 3, if the vehicle is not traveling at a sufficiently constant rate, as step  68 , the PSC  10  is returned to cruise mode using an algorithm with set back gains so as to limit the rate of change of the vehicle speed to less than the rate ordinarily allowed during the cruise mode. For example, a suitable algorithm would be that the throttle pull equals the present throttle pull plus some fraction (e.g. 40% of normal) of a cruise control error correction algorithm known in the art. The set back gain reduces power delivery requirements thereby improves fuel efficiency. Moreover, this prevents the vehicle from surging forward unexpectedly. Note that the reduced gain could be applied only for a prescribed time period after which the full value could be used. 
     On the first pass through the subroutine of FIG. 4, however, the error should be within acceptable limits because the cruise mode algorithms were making nearly constant throttle adjustments to maintain the vehicle speed at the desired speed. As such, at step  70 , the PSC  10  signals the ETB  12  to hold the throttle valve  30  at its current position. In this way, the throttle valve  30  is not being repositioned so that the engine  32  is not fluctuating speed. Rather, the engine receives a steady flow of fuel and operates at a steady speed. This greatly reduces or eliminates energy losses from the changing momentum of the moving parts of the engine and the vehicle overall. This reduction in energy losses results in greater fuel economy, thereby making the vehicle less expensive to drive and less damaging to the environment. 
     The inventors of the present invention have conducted a study of a Ford Motor Company pick-up truck model F-150 using the speed control system of the present invention. The particular truck was driven under conventional cruise control and found to have an average fuel economy of approximately 20 miles per gallon. The results of the study indicated that the truck could travel approximately 0.5 miles farther per gallon of fuel while operating in fuel economy cruise mode. The inventors believe that with additional refinement of the fuel economy algorithms, the speed control system of the present invention could provide five percent or more savings in fuel consumption when the vehicle is operated in fuel economy cruise mode. 
     Referring still to FIG. 4, the fuel economy algorithms also instruct the PSC  10  with regard to acceleration and deceleration input from the driver. At step  72 , the PSC processor  16  scans the I/O module  14  for such input. If there is no acceleration and deceleration input, at step  74  the PSC processor  16  determines if an exit condition (as described above) present. If an exit condition is present, then at step  76  the PSC  10  calls up the acceleration algorithms having set back gains, as mentioned above. At step  78 , the PSC  10  then determines whether the exit condition (or error from step  50 ) requires it to enter manual or cruise mode. The PSC  10  returns to the proper mode using the set back gains. If at step  74  no exit condition is detected, the routine checks the speed sensor for the current speed at step  80  and loops back to step  50  continuing to hold the throttle position as long as the error is acceptable and no exit condition or acceleration input is detected. 
     If an acceleration/deceleration input was detected at step  72 , then at step  82  the PSC processor  16  uses set back gains (e.g. 80% of normal) to gradually bring the vehicle to the new desired speed, and at step  84 , the PSC  10  updates the desired speed value (DS) according to the acceleration/deceleration input. The acceleration/deceleration input can be via the foot pedal or an accelerate or coast button on the cruise control stem. Similarly, a resume input, common to conventional cruise controls, could also be a suitable input. The vehicle stays in fuel economy cruise mode until an exit condition, as described above, is detected. 
     FIG. 5 illustrates the primary events (blocks  100 ,  105 ,  109  and  112 ) performed by the PSC  10  in response to input from the driver. Generally, blocks  101 - 104  represent activation of the cruise control mode, blocks  106 - 108  represent activation of the fuel economy cruise mode, blocks  110 - 111  represent acceleration and deceleration when in the fuel economy cruise mode and block  113  represents returning to the cruise control mode from the fuel economy cruise mode. 
     The block diagram of FIG. 5 assumes that the vehicle is initially being operated in manual speed control mode, when at block  100 , the vehicle driver initiates a cruise mode input to the PSC  10 , preferably via an “on” or “set speed” button of the input device  25  located on a turn signal stem or a steering wheel hub. As mentioned above, then at block  101  the PSC  10  stores in the memory module  18  as DS the current speed sensor value at the time of receiving the cruise mode input. At blocks  102  and  103 , the speed sensor  21  is monitored and the input addresses of the other vehicle components are checked in the I/O module  14  to ensure that there are no relevant signals or open circuits indicating the presence of an exit condition. Then at block  104 , the PSC processor  16  accesses the algorithms stored in the cruise mode location  34  (see FIG.  1 ). The PSC  10  uses these algorithms, which can be any cruise control algorithms well known in the art, to maintain the current speed substantially equal to the desired set speed. Generally, in the cruise mode the PSC  10  monitors the current speed of the vehicle and corrects for any deviation from the desired speed approximately every 50 milliseconds using a correction formula governing the rate and distance of throttle position adjustment. Ordinarily, such correction formulas are designed to provide for rapid acceleration and deceleration as needed to keep the vehicle traveling at the desired speed while at the same time providing a smooth change in speed so that the vehicle does not lurch forward or slow too suddenly. 
     As indicated by block  105 , when the vehicle is traveling in cruise mode, the driver may activate the fuel economy cruise mode preferably by depressing the “cruise on” or “set speed” button a second time, however, a dedicated fuel economy cruise mode switch could also be used. At block  106 , the PSC  10  verifies that the deviation from the desired speed is within the allowed error constant for the prescribed time period, as described above, and at block  107  that no exit conditions exist. Then, at block  108 , the PSC  10  holds the throttle at its current position. 
     Once in fuel economy cruise mode, at block  109 , the driver may accelerate or decelerate the vehicle by applying pressure to the gas pedal or brake pedal as well as by using an accelerate or coast switch on the input device  25  (see FIG.  1 ). In response to this input, at block  110  the PSC  10  confirms that no exit condition is present and at block  111  repositions the throttle as needed to obtain the new speed. The PSC  10  uses set back gains defined by the fuel economy algorithms. After the speed adjustment, the PSC  10  preferably resumes fuel economy cruise mode until an exit condition is detected, in which case the PSC  10  enters cruise or manual mode, until the fuel economy conditions are present so that fuel economy cruise mode is reactivated (as described above). 
     The driver can cancel the fuel economy cruise mode, at block  112 , with a suitable input, such as depressing a “cruise off” switch in which case, at block  113 , the PSC  10  returns to either cruise or manual mode. 
     Thus, the present invention provides an automated vehicle speed control using less fuel than conventional cruise controls, thereby reducing fuel costs and exhaust emissions into the environment. During fuel economy cruise mode operation all engine throttling is eliminated when the vehicle is traveling within an acceptable speed deviation from the desired speed. Moreover, the speed control system of the present invention applies reduced acceleration and deceleration gains while accelerating or deceleration in the fuel economy cruise mode or when returning to the conventional manual or cruise modes. 
     Illustrative embodiments of the invention have been described in detail for the purpose of disclosing a practical, operative structure whereby the invention may be practiced advantageously. However, the apparatus described above is intended to be illustrative only, and the novel characteristics of the invention may be incorporated in other structural forms without departing from the scope of the invention. For example, the values for the above mentioned constants are merely exemplary and other suitable values, higher or lower, could also be used. Accordingly, to apprise the public of the full scope of the invention, the following claims are made.