Electronic throttle control system

Abstract: A closed-loop controller implemented by an engine control microprocessor for adjusting the position of the intake throttle 12 of an engine 10. Sensing means 18,22,46, typically shared with other engine control mechanisms, develop electrical signal values indicating intake air pressure and temperature as well as the pressure within the intake manifold 16. A programmed microcontroller 29,50 responsive to these signal values, and to a value indicating a desired rate of air flow into the engine, produces a further value representing a desired throttle position. A comparator 60 is used to produce an error signal indicating the extent to which the measured actual air flow rate value deviates from the desired flow rate value. Finally, a closed-loop feedback control mechanism 56,70 jointly responsive to this error signal and to the desired throttle position value operates a mechanism which controls the throttle position, thereby maintaining a close correspondence between the actual and desired air flow rates.

Description: This invention relates to electronic engine control systems and more particularly to a system for controlling the position of a throttle valve in an internal combustion engine to achieve a desired air flow rate into the engine's intake manifold. It is already known from US Patent 4 563 989 to provide an idling regulation system for an internal combustion engine in which the idling is governed by means of two superimposed closed control loops. An inner control loop regulates air throughput from the air intake tube to the engine to a predetermined set-point value which is formed by an outer control loop that regulates the rpm of the engine to the desired value. The present invention takes the form of an electronic system for controlling the position of a throttle valve employed to control the flow of intake air from an air intake into the intake manifold of an internal combustion engine as defined in claim 1, said system comprising, in combination, means adapted to produce an intake air pressure signal (B) having a value indicative of the air pressure at said air intake, means adapted to produce a manifold air pressure signal (M) having a value indicative of the air pressure within said intake manifold, means adapted to produce a temperature signal (T) having a value indicative of the temperature of the air flowing into said air intake, means adapted to produce a desired air flow signal (D) having a value indicative of a desired rate of air flow, processing means adapted to produce, from said intake air pressure signal (B), said manifold air pressure signal (M), said temperature signal (T) and said desired air flow signal (D), a throttle area input value being indicative of a desired effective throttle valve area for the value of the desired rate of air flow (D) means adapted to produce a pressure drop signal (VAC) from the intake air pressure signal (B) and the manifold air pressure signal (M), means adapted to produce a desired throttle angle value from the throttle area input value and a value of the pressure drop signal (VAC), means adapted to produce an actual air flow signal (A) indicative of the actual rate of air flow into said air intake, feedback controller means adapted to respond to said desired air flow signal (D) and said actual air flow signal (A) to produce an error feedback signal indicative of the extent to which said actual and said desired rates of air flow differ, and positioning means responsive to a comparison of the error feedback signal and the desired throttle angle value to adjust the position of said throttle valve such that said actual rate of air flow more nearly matches said desired rate of air flow. The invention will now be described further, by way of example, with reference to the accompanying drawings in which the single figure is a block schematic diagram of an electronic throttle control system which embodies the present invention. The description which follows will begin with a general discussion of the embodiment shown in Fig. 1, followed by a more detailed description of the theory which underlies the signal processing steps employed. As seen in Figure 1, an internal combustion engine illustrated by the single cylinder indicated generally at 10 includes a throttle valve 12 positioned between an air intake 14 and an intake manifold 16. A sensor 18 produces an output signal quantity M on line 20 which indicates the pressure within the intake manifold 16. Similarly, a sensor 22 produces an output signal quantity B on line 24 which indicates the barometric pressure at the air intake 14. As will be understood by those skilled in the art, the airflow and pressure values may be indirectly measured or inferred based on other measured values, particularly engine speed. A comparator 26 having its inputs connected to lines 20 and 24 produces an output signal quantity VAC on line 28 representing the pressure drop across the throttle 12. The quantities B and M are also used as index values to identify a particular predetermined value F in a two-dimensional lookup table 29. Each of stored values of F in table 29 have a predetermined functional relationship to the ratio between the intake barometric pressure indicated by the quantity B and the manifold pressure indicated by the quantity M. The lookup value F from table 29 is supplied via line 30 to one input of a multiplier 32, the second input of which receives the quantity B via line 24. Multiplier 32 produces an output quantity K = F * B on line 34 which is delivered to one input of a divider 36. The second input to divider 36 is connected to receive a quantity D from an external source 40. The source 40 typically produces the desired air flow rate quantity D based on the vehicle's accelerator position set by the driver, and/or on values produced by cruise control, anti-skid, or other mechanisms. The divider 39 delivers a quotient value (D/K) over line 42 to one input of a second multiplier 44. The second input of multiplier 44 is connected to receive a value indicative of the square root of the intake air temperature produced the combination of a temperature sensor 46 and a square-root circuit 48 which indicates the desired rate of air flow to the engine. The output from multiplier 44 is a supplied as a first indexing input to a second two-dimensional lookup table 50, the second indexing input being the quantity VAC supplied via line 28 from the comparator 26. As discussed in more detail later, the first indexing input value, (D*Sqrt(T))/K, is indicative of the desired effective throttle valve area for a particular desired flow rate D, a given intake air temperature T, and a given relationship between the barometric and manifold pressures B and M. The lookup table 50 stores values which indicate the desired throttle angle Θ given a particular effective throttle area (from multiplier 44) and a given pressure drop value VAC from comparator 26. Table 50 delivers the resulting desired throttle angle value Θ via line 54 to a comparator 56. A comparator 60 is connected to an airmeter 64 which senses the actual instantaneous air flow rate into the engine. Comparator 40 subtracts this actual rate value from the desired rate quantity D from source 40 to produce an instantaneous flow rate error value E on line 66. The instantaneous error quantity E is then processed by a conventional proportional-integral-differential or "PID" feedback controller 70 which generates an error feedback signal : the first being proportional to the instantaneous error value E, the second being related to the integral (weighted average) of the instantaneous value, and the third being related to the derivative (rate of change) of the instantaneous value. While a PID controller of the type indicated at 70 could be used by itself to directly control throttle position based on the instantaneous error signal E, substantially improved performance is achieved by allowing the controller to work in combination with the mechanism contemplated by the invention for separately producing the desired throttle angle Θ. The inclusion of this added mechanism allows the controller 70 to be tuned mainly for improved transient response and steady state noise rejection, since the production of a desired throttle angle frees the controller from the need to provide the steady state component of the output control signal. The control mechanism shown in Fig. 1 is preferably implemented, to the extent possible, using the same processor that provides other engine control functions, such as fuel delivery rate control. The processing required to implement the disclosed comparisons, divisions, multiplications and table-lookup operations may be readily accomplished by suitably programming the existing engine control microprocessor and by storing the information forming the lookup tables 29 and 50 in available read-only memory. THROTTLE FLOW MODEL The theoretical foundation for the present invention is found in known mathematical models which describe the effect of a throttle plate on the flow of air into the manifold plenum. The air flow rate is a known function of the manifold pressure P m , the air temperature at the inlet T in , and the atmospheric pressure P a . Theoretical analysis of the flow of an ideal gas under steady, one dimensional, frictionless, compressible, adiabatic flow yields the following expression for the mass flow rate through the throttle body: dMa dt = C d A th P a 1 R * T inlet Φ where, for non-choked flow: Φ = 2γ γ-1 ( P m P a ) 2 γ - ( P m P a ) γ+1 γ for P m P a > ( 2 γ+1 ) γ γ-1 and where, for choked flow: Φ = γ ( 2 γ+1 ) γ+1 2(γ-1) for Pm P a ≤ ( 2 γ+1 ) γ γ-1 In the foregoing expressions, R is the specific gas constant and 8 is the ratio of specific heats and is equal to approximately 1.4 for an air charge. The product of C d and A th makes up the effective flow area with C d being a discharge coefficient typically determined by a regressed equation of several flow and geometric parameters, and with A th being the geometric flow area of the throttle. The theoretical basis for these relationships, and as well as related methods of modelling the flow rate through physical throttle systems, is described in more detail in published literature, including "Internal Combustion Engine Fundamentals" by J. B. Heywood (McGraw Hill, 1988); "Simulation of the Breathing Processes and Air-Fuel Distribution Characteristics of Three-Valve, Stratified Charge Engines" by J. M. Novak,SAE 770881 ( Society of Automotive Engineers , September, 1977); and "Analysis and Digital Simulation of Carburetor Metering" by D. L Harrington and J. A. Bolt, SAE Paper 700082, SAE Transactions, Vol. 79 (1970). If the mass flow rate given by equation 1 is measured in lbm/minute (kg/min), the throttle area A st in square inches (cm 2 ), P a in inches-Hg (Pascal), and T inlet in degrees C, equation (1) can be reduced through the use of a units conversion factor CF to: dMa dt = C d A th P a Φ T inlet * CF where CF = 22.87891298 lbm * °K inches 2 * inches-Hg * min ≈ 0,475·10 -3 Kg· °K cm 2 ·Pascal·min The quantity Φ described in equation 3 may multiplied by P a and by CF to form a quantity K where CF*Φ is determined as a function f of the pressure ratio (P a / P m ), where the values of the function f are stored in the lookup table 29 shown in fig. 1. Accordingly, the value K may be expressed as follows: K = CF * P a * f( P a P m From equation 4, it may be seen that the product of Cd and Ath, which expresses the effective flow area of the throttle, is then given by the relation: C d A th = MAF desired * T inlet K This effective flow area value may then be used, along with a value indicating the pressure drop across the throttle valve, to access a set of corresponding throttle position values stored in the lookup table 50, each stored position value specifying the throttle angle needed to provide the indicated effective flow area at a given pressure drop across a given physical throttle geometry.

Claims: An electronic system for controlling the position of a throttle valve (12) employed to control the flow of intake air from an air intake (14) into the intake manifold (16) of an internal combustion engine (10), said system comprising, in combination, means (22) adapted to produce an intake air pressure signal (B) having a value indicative of the air pressure at said air intake (14), means (18) adapted to produce a manifold air pressure signal (M) having a value indicative of the air pressure within said intake manifold (16), means (46) adapted to produce a temperature signal (T) having a value indicative of the temperature of the air flowing into said air intake (14), means (40) adapted to produce a desired air flow signal (D) having a value (D) indicative of a desired rate of air flow, means (64) adapted to produce an actual air flow signal (A) indicative of the actual rate of air flow into said air intake, and feedback controller means (60,70) adapted to respond to said desired air flow signal (D) and said actual air flow signal (A) to produce an error feedback signal indicative of the extent to which said actual and said desired rates of air flow differ, characterised in that the system further comprises; processing means (29,32,36,44) adapted to produce, from said intake air pressure signal (B), said manifold air pressure signal (M), said temperature signal (T) and said desired air flow signal (D), a throttle area input value (D*Sqrt(T)/(K) being indicative of a desired effective throttle valve area for the value of the desired rate of air flow (D), means (26) adapted to produce a pressure drop signal (VAC) from the intake air pressure signal (B) and the manifold air pressure signal (M), means (50) adapted to produce a desired throttle angle value (Θ) from the throttle area input value (D*Sqrt (T)/K) and a value (VAC) of the pressure drop signal, and positioning means (56,70) responsive to a comparison of the error feedback signal and the desired throttle angle value (Θ) to adjust the position of said throttle valve (12) such that said actual rate of air flow more nearly matches said desired rate of air flow. An electronic system as claimed in claim 1, wherein said means (50) adapted to produce a desired throttle angle value (Θ) from the throttle area signal and the pressure drop signal (VAC), comprises means (50) storing a plurality of predetermined throttle position values in a lookup table, each of said lookup values being designated by the throttle area signal and the pressure drop signal (VAC). An electronic system as claimed in claim 2, wherein said means (29,32,36,44) adapted to produce said throttle area signal is effective to generate a quantity proportional to the quotient of (1) the value of said desired air flow signal (D) times the square root of the value of said temperature signal (T), divided by (2) a value (K) functionally relating the air intake pressure signal (B) and the manifold air pressure signal (M).

Inventors: PALLETT TOBIAS, PALLETT, TOBIAS
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S.A., FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1996
Main classification: F02D11
IPC codes: F02D11, F02D41