Electronic throttle control

A throttle control system including a throttle body, an air intake coupled to the throttle body providing air flow to the throttle body, a fuel supply apparatus coupled to the throttle body, where the air intake and the fuel supply apparatus, in conjunction, provide a combustible fuel-air mixture, a throttle plate coupled to the throttle body, an actuator coupled to the throttle plate to move the throttle plate within the throttle body to control at least the air flow to the throttle body, and a fuzzy logic controller controlling the actuator position and speed to provide for a desired air flow.

BACKGROUND OF THE INVENTION
 The present invention relates to a throttle body and control system for a
 vehicle. More specifically the present invention relates to a control
 method and apparatus for controlling the position of a throttle plate in a
 throttle body.
 Electronic engine control has evolved from a relatively elementary control
 system employing simple switches and analog devices to a highly precise
 fuel and ignition control system employing powerful microprocessors or
 microcontrollers. The miniaturization and cost reduction of powerful
 electronics has put the power of the computer age into the hands of
 automotive engineers. Microprocessors have allowed complex programs
 involving numerous variables to be used in the control of present day
 combustion engines, leading to better engine control and performance.
 An important facet of combustion engine control is the regulation of air
 flow into a cylinder by a throttle and accordingly the quantity of fuel
 delivered into the cylinder. In a combustion engine a throttle, having a
 movable throttle plate, directly regulates the power produced by the
 combustion engine at any operating condition by regulating the air flow
 into the engine. The throttle plate is positioned to increase or decrease
 air flow into the engine. The engine acts as an air pump with the mass
 flow rate of air entering the engine varying directly with throttle plate
 angular position. Presently, there is a need in the art to precisely
 control throttle plate position in a throttle body to tightly regulate the
 flow of air and fuel into a cylinder.
 In the operation of a standard vehicle combustion engine, a driver will
 depress the accelerator pedal to generate a portion of a throttle plate
 position command that varies the throttle plate angle and accordingly
 varies the air flow into the engine. Other factors besides driver pedal
 input such as engine temperature, engine speed, exhaust gas oxygen,
 exhaust gas recirculation valve position, air flow into the engine, and
 other similar variables will also factor into the a throttle plate
 position command, but are not limited to such. A control unit coupled to a
 fuel injector, monitoring the variables cited above, will regulate the
 fuel that is mixed with the air, such that the injected fuel generally
 increases in proportion to air flow. If a carburetor is used the air flow
 through the carburetor will directly regulate the amount of fuel mixed
 with the air, with respect to the vacuum or suction formed by the air flow
 through the throttle body. For any given fuel-air mixture, the power
 produced by the combustion engine is directly proportional to the mass
 flow rate of air into the engine controlled by the throttle plate
 position.
 SUMMARY OF THE INVENTION
 The positioning and stability of the throttle plate directly effects the
 tuning or stability of the engine. Ideally, when a position command is
 given to position the throttle plate, the throttle plate will step to that
 exact position without a large amount of overshoot and undershoot and at a
 desired angular speed. In practice, control algorithms attempt to approach
 this ideal condition. Proportional, Integral, and Derivative (PID)
 algorithms are typically used in the position control of a throttle plate
 in a throttle body. The output of a typical PID controller or algorithm
 can be represented by the equation:
 Output=K.sub.p e+K.sub.I.intg.e(t)dt+K.sub.D (de/dt)
 where
 K.sub.p =the proportional gain
 K.sub.I =the integral gain
 K.sub.D =the derivative gain
 and e=the error or difference between the setpoint or position command and
 the feedback.
 In the present invention, a position command is generated using a
 combination of the operator input on the accelerator pedal and the engine
 variables cited above. This position command is processed by a PID control
 program executed on an electronic control unit that outputs a control
 command to a controller or drive controlling an electric motor. The
 controller or drive actuates the electric motor in response to the
 position command, and a position feedback sensor such as a potentiometer
 provides speed and position feedback for the electronic control unit. The
 error (the difference between the position command and the position
 feedback) is processed by the PID control program to generate a control
 command to the motor controller drive to reposition the motor in response
 to the error (if one exists). The PID gains in the PID control program and
 the scale of the error will determine the magnitude of the control command
 to the motor controller drive and thus the motor response. Higher PID
 gains (relatively determined by the response of the system) will normally
 shorten response time (again relative to the performance of the system)
 but also generate instability in the system. Lower PID gains will lengthen
 response time but minimize instability in the system.
 A single set of PID gains for a throttle control system will normally be
 determined heuristically for the throttle control system, via the tradeoff
 between response time and stability in the system. This set of PID gains
 is traditionally fixed for the entire range of movement, position, and
 feedback variable values for the control program. This single set of PID
 gains cannot be optimized for the entire performance range of a throttle
 plate positioning system. For example, the PID gains that are optimal in a
 static state to overcome static friction for the motor will not perform as
 well in a dynamic state, i.e. when the throttle plate is constantly moved
 between different positions. Inertia generated by the angular speed of the
 throttle plate will also effect the performance of the system. Large angle
 changes of the throttle plate vs. small angle changes of the throttle
 plate have different optimal PID gains. One set of PID gains will not
 provide optimal performance for all the required moves of a throttle
 plate.
 The present invention has overcome the limitations of the prior art by
 dynamically recalculating PID gains continuously during operation. A fuzzy
 supervisory control program will monitor throttle body position feedback
 and recalculate the PID gains for different error magnitudes, each
 specific state, speed, and/or position command for the throttle body, but
 is not limited to such. In this manner, optimal PID gains for every
 condition the throttle plate is involved in may be used, resulting in
 improved performance for the throttle system and engine compared to the
 prior throttle positioning systems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The following description of the present invention is merely exemplary in
 nature and is in no way intended to limit the invention or its uses.
 Moreover, the following description, while depicting a control system
 designed to operate with a throttle body, is intended to adequately teach
 one skilled in the art to make and use a control system for a variety of
 positioning systems.
 Referring to FIG. 1, a throttle body 10 is shown coupled to a cylinder head
 12 having an intake valve 14. The throttle body 10 includes an air intake
 16, a throttle plate 18, a fuel injector 20, and an intake manifold 22.
 The air intake 16 provides air flow regulated by the angular position of
 the throttle plate 18. Referring to FIG. 2, the throttle plate 18 may be
 rotated to an angular position .theta. about pivot axis 24 to control the
 air flow. If the angle .theta. is equal to zero the throttle plate 18 will
 be in a position of maximum air flow constriction if the angle .theta. is
 equal to ninety degrees the throttle plate 18 will be in a position of
 maximum air flow. Accordingly, the air flow may have varying flow rates
 when the angle .theta. is varied between 0 and 90 degrees.
 In the preferred embodiment of the present invention, the fuel injector 20
 is mounted downstream of the throttle plate 18 in the intake manifold 22
 in a multi-point configuration for each cylinder in a combustion engine.
 The fuel injector 20 will supply atomized fuel in response to a plurality
 of engine variables, including air flow in the intake manifold measured by
 air flow sensor 26, to provide a combustible fuel-air mixture. Preferably,
 the fuel injector 20 will supply fuel in proportion to the mass flow rate
 of air in the engine. The resultant air fuel mixture will enter a
 cylinder, via the intake valve 14, coupled to cylinder head 12. The timing
 of the fuel injector 20 firing corresponds to the cycle of the engine.
 FIG. 3 is a cross-sectional diagram of a throttle control apparatus 30 of
 the present invention. The throttle control apparatus 30 includes a motor
 32 coupled to a gear train 34 that is further coupled to the throttle
 plate 18 to rotate the throttle plate 18 about axis 24. A spring 38 exerts
 a torque onto the throttle plate 18. In normal operation the torque
 exerted by the motor 32, via the gear train 34, on the throttle plate 18
 is opposite and greater than the torque exerted by the spring 38. In the
 event of a failure in the motor 32 or other mechanism in the throttle
 control apparatus, the spring 38 will bias the throttle plate 18 open to
 provide air flow to the combustion engine. This "limp" mode will enable
 the operator to drive the vehicle to a service provider to resolve
 problems with the throttle control apparatus 30.
 The motor 32 is coupled to the gear train 34 to add resolution to the motor
 32 movement as seen by the throttle plate 18. While generally the gear
 ratio can be selected as to any ratio suitable as to the conditions of
 response and torque output, the gear ratio is preferably 14 to 33. The
 gear train 34 includes a large gear 40 coupled to the motor 32 and a
 smaller gear 42 coupled to the large gear 40 and the throttle plate 18. In
 alternate embodiments of the present invention, the motor 32 will directly
 drive the throttle plate 18, eliminating the gear train 34.
 The motor 32 is preferably a DC motor having a permanent magnet field and
 an armature. In one embodiment of the present invention, a pulse width
 modulated voltage is provided to the motor armature of the motor 32 to
 provide for speed and positioning of the motor 32, although any current
 waveform known in the art may be used. In alternate embodiments, AC motor,
 DC brushless motors, or vector drive or torque motor technology may be
 used in place of the DC motor.
 A feedback device 44 is mounted to the throttle pivot axis 24 to provide
 feedback for the throttle plate 18 position. In the preferred embodiment
 the feedback device is a potentiometer, providing a voltage signal. In
 alternate embodiments a rotary voltage displacement transducer (RVDT) or
 rotary encoder (absolute or incremental) may be used.
 FIG. 4 is general diagram of the control system 50 of the present invention
 including sensors 52, such as the potentiometer 44, an electronic control
 unit 54 and an actuator 56 such as the motor 32. FIG. 5 is a more detailed
 control system diagram of the present invention. Referring to FIG. 5, the
 control system receives a throttle position request command from a car
 engine controller at block 60. The throttle position command is based upon
 numerous engine variables cited previously. The position command is
 transferred to a throttle CAM block 62 which generates a motion profile
 for the movement of the throttle plate 18 with a resultant final position
 equal to the position command. The motion profile is then factored into a
 safety block 64 to ensure that the motion profile is within safety
 parameters. A fuzzy supervisory control block 66 analyzes the position
 command profile, throttle position, error magnitude, and/or other throttle
 plate 18 variables to calculate PID gains (to be discussed in more detail
 below). The PID block 68 utilize the PID gains to calculate an output
 converted by a compensation and driver protection logic block 70 into a
 command for a motor drive 72. The command for the motor drive may be an
 analog signal or a digital signal. The PID block 68 may utilize any known
 PID algorithm known in the art and initial PID gains determined
 heuristically are used as a starting point for the PID block. The motor
 drive 72 generates a pulse width modulated (PWM) signal applied to the
 armature of the motor 32 driving the throttle plate 18 in the throttle
 body 10 and feedback is provided by throttle position sensors 44. The
 motor drive 72 may comprise any known DC motor drive known in the art,
 including triac and power transistor based DC motor drives. The fuzzy
 logic block 66 continuously calculates the PID gains for the PID control
 block 68 in response to varying position commands, motion profile,
 feedback and/or similar variables. In this manner PID gains optimal for
 all positions and states of the throttle body 18 may be utilized in the
 operation of the motor 32. The calculation speed of the fuzzy logic block
 66 is only limited by the clock speed and input/output speed of the
 electronic control unit 54 and may be considered to operate at any clock
 speed possible and desired. The Fuzzy Logic Block 66 operation is detailed
 as follows: