DE69123829T2 - Method for controlling a throttle valve in an internal combustion engine of a vehicle - Google Patents

Description

The present invention relates to a throttle valve control system and in particular to an electronic throttle valve control system for the internal combustion engine of a motor vehicle according to the preamble of claim 1 (see document EP-A-0393930)

It is known, for example, from US Patent No. 4,831,985 to provide for a vehicle an electronic throttle control system of the type comprising a throttle body and a rotatable throttle valve mounted within the throttle body for controlling the supply of fuel and/or air to the engine of the vehicle.

The system includes means for detecting the actual position of the throttle valve and for providing a signal indicative thereof, means for providing a signal indicative of a desired position of the throttle valve and means for comparing the signals indicative of the actual position and the desired position of the throttle valve and for providing a control signal to a throttle valve actuator means for adjusting the throttle valve position accordingly.

Such a prior art throttle valve control system has the problem that the friction and stiction associated with the throttle valve, as shown in Figure 1, increases at small throttle valve openings due to the differential pressure generated by the throttling effect of the throttle valve, which on the one hand leads to the behavior of the control system becoming inadequate and on the other hand causes the actuator means to oscillate.

The object of the present invention is to improve the behavior of the control system at small throttle openings.

According to the invention, a throttle control system is provided for an engine of a vehicle, having a throttle valve rotatably mounted in an intake port of the engine, the control system comprising:

a throttle sensing means for supplying a signal indicating the rotational position of the throttle valve, an input means for supplying a signal indicating a desired rotational position of the throttle valve, an actuator means for changing the angular position of the throttle valve between a closed position and an open position; and a control means for supplying a control signal D to the actuator means to change the angular position of the throttle valve, the control means comprising:

a comparator means for comparing the signals received from the detecting means and the input means and generating an error signal E and a control means for processing the error signal E received from the comparator means and providing an output signal O, the control signal D being calculated by multiplying the output signal O by a system total gain factor K, characterized in that the control means contains a gain factor control means for varying the system total gain factor K, which is operable such that when a signal received by the gain factor control means from the detecting means indicates that the throttle valve is in or near the closed position within a predetermined range, the system total gain factor K is increased with respect to the system total gain factor K used for throttle valve openings above the predetermined range, so that within the predetermined range the control signal D for a certain magnitude of error signal E is larger than at throttle valve openings above the predetermined range.

This has the advantage that the control signal sent to the actuator is increased at small throttle valve openings in order to compensate for the increased static friction and the increased friction.

The predetermined range may be throttle valve openings in the range of 0 to 10 degrees from the throttle valve closed position.

When the throttle valve is within the predetermined range, the overall system gain factor may advantageously be increased by a factor of up to 3 times beyond the predetermined range relative to the overall system gain factor used.

The overall system gain is preferably constant over the predetermined range and increases linearly within the predetermined range as the throttle is closed.

The control signal 'D' to the actuator can be

D = K * (k₁ E + k₂ Edt + k₃ dE/dt)

where k₁, k₂, k₂ are control system constants.

The control means may be a central processing unit (CPU) having at least one read-only memory (ROM) location and one random access memory (RAM) location, the overall system gain factor being digitally stored in the form of a look-up table in the or one of the read-only memory (ROM) locations.

The input device can be an input device that can be operated by the driver in the form of a potentiometer attached to an accelerator pedal of the vehicle.

The input device could also be a control unit for the idle speed of the engine.

The input means can be switched between a potentiometer attached to an accelerator pedal of the vehicle and a control unit for the idle speed of the engine.

The invention will now be described by way of example with reference to the accompanying drawing, of which:

Figure 1 is a graph of friction and stiction plotted against throttle opening for a rotary throttle valve;

Figure 2 is a graph of the system gain factor plotted against the percentage throttle opening for a control system according to a first aspect of a first embodiment of the invention;

Figure 3 is a graph of throttle position versus time showing the performance obtained from a control system according to the prior art and the performance obtained from a control system according to the first aspect of the first embodiment of the invention;

Figure 4 is a block diagram of a throttle control system according to the first embodiment of the invention;

Figure 5 is a block diagram of a throttle control system according to a second embodiment of the invention;

Figure 6a is a graph of accelerator pedal position versus time for a prior art throttle control system;

Figure 6b is a graph of the signal sent to an engine controller over time for a prior art throttle control system;

Figure 6c is a graph of motor current versus time for a prior art throttle control system;

Figure 6d is a graph of throttle position versus time for a prior art throttle control system;

Figure 7a is a graph of accelerator pedal position versus time for a throttle control system according to a second aspect of the first embodiment of the invention;

Figure 7b is a graph of the signal sent to an engine driver over time for a throttle control system according to the second aspect of the first embodiment of the invention;

Figure 7c is a graph of motor current plotted over time for a throttle control system according to the second aspect of the first embodiment of the invention;

Figure 7d is a graph of throttle position versus time for a throttle control system according to the second aspect of the first embodiment of the invention.

With particular reference to Figure 4, there is shown an internal combustion engine 11 of a motor vehicle (not shown), the engine 11 having an intake manifold 12 defining an intake tract 13 in which a disk-shaped throttle valve 14 is rotatably mounted.

The disk-shaped throttle valve 14 can be rotated approximately 90 degrees from a closed position where it covers the intake passage 13 to an open position where it offers little resistance to the flow of fluid through the intake passage 13. The throttle valve opening is conveniently measured in degrees of rotation from the closed position or in percent open, so 10 percent open is approximately equal to a 9 degree rotation from the closed position.

The throttle valve 14 is rotated by an actuator means in the form of an electric motor 15 which is connected to a spindle 8 of the throttle valve 14, the spindle 8 being supported by two simple bearings 9.

At the other end of the spindle 8 to the electric motor 15 a throttle valve detection device in the form of a rotary potentiometer 30 is connected.

A control means 21 is connected to the motor 15, the potentiometer 30 and also to an input means in the form of a position sensor 31 connected to an accelerator pedal 16 of the motor vehicle. The accelerator pedal 16 is rotatably connected to a part of the body 10 of the motor vehicle via pivoting means (not shown).

The control means 21 comprise a proportional integral-derivative (PID) controller 22, a motor drive power amplifying device 23, a gain control device 24, a step input device 25, a comparator 26 and a Switching means 28.

The control means 21 is essentially a central unit to which a number of read-write memory locations (RAM) and read-only memory locations (ROM) are assigned in order to form a microcomputer.

The comparator 26 is designed to receive a signal 'P' indicating the position of the throttle valve 14 from the potentiometer 30 and a signal 'I' from the position sensor 31 and to carry out the calculation E = (I-P) where:

E is a signal indicating the difference between a desired throttle position indicated by signal 'I' and 'P' is a signal indicating the actual throttle position.

According to a first aspect of the invention, the signal 'E' is fed to the PID controller 22, which, according to the general transfer function

Output signal 'O' = k₁E + k₂ Edt + k₃ dE/dt

operates, the output signal 'O' being supplied to the gain control device 24.

The gain control device 24 includes a read only memory (ROM) storing a look-up table of the gain factor ‘K’ versus throttle position ‘P’, a portion of which is shown in graphic form in Figure 2.

The gain control device 24 receives a signal indicative of the actual throttle position which is used to address the correct part of the look-up table. The gain control device 24 takes the signal 'O' and factors it by the gain factor 'k' from the look-up table so that a control signal 'd' is sent via the switching means 28 to the motor driver 23.

Therefore 'd' = K * 0 or

d = K (k₁E + k₂Edt + k₃dE/dt)

where E = I - P,

k₁, k₂ and k₃ are system constants and

K = total system gain factor

The motor control 23 changes the signal ‘d’ received from the gain control 24 into a control current ‘D’, which is sent to the motor 15.

The graph of Figure 2 shows a relative system gain where the normal gain is 1.0 and a maximum relative gain of 3.0 is used when the throttle position is sensed to be in or near the closed position, where the actual signal ratio between 'O' and 'D' could be any suitable value. For example, for throttle openings of 10 degrees and above, K could be 50, which would give a maximum circuit gain of 150.

If the signal 'P' indicates that the opening of the throttle valve 14 is less than 2 degrees and the error signal 'E' is positive, then according to a second aspect of the invention the control means 21 actuates the change-over switch 28 by turning on the step input device 25 and bypassing the comparator 26.

The step input device 25 generates a predetermined control signal ‘e’ which is stored in digital form in a read-only memory to the motor driver 23.

The predetermined control signal 'e' is several times larger than the error signal 'E' that would be present due to such a small throttle opening, and is large enough to provide the motor 15 with a control signal 'D' that is below, but close to, the signal level required to overcome the stiction associated with the control valve A.

The operation of the throttle control system can be best understood by reference to Figures 3, 6 and 7.

First, consider Figure 3 and assume that at time 0.0 the accelerator pedal 16 is immediately moved to a position indicating a 2.5% open throttle target position.

In the case of a prior art throttle control system, the throttle valve 14 will tend to oscillate because the integrator portion of the PID controller will integrate the small error signal 'E' until the drive 'D' to the motor 15 is sufficient to overcome the existing stiction. The throttle valve 14 will then overshoot the set position and remain too wide open until the integrator has dropped sufficiently that the motor 15 can force the throttle valve 14 to close.

In the case of the control means 21 according to the invention, the amount of run-out and the frequency response of the throttle system is increased by the increase in the system gain introduced by the gain control device 24 in a predetermined range of 0 to 10 degrees from the closed position.

The control signal D sent to the engine 15 for small throttle openings is larger than would normally be the case due to the action of the gain control device 24, causing the integrator portion of the PID controller 22 to rise and fall more quickly.

The fact that the friction on the spindle 8 increases at small throttle openings due to the increased load from the throttle valve 14 prevents the throttle valve control system from becoming unstable even though the system gain is up to three times what can normally be used for the control system to operate satisfactorily.

At very small throttle openings of less than 2 degrees, the system performance is further improved by bypassing the comparator 26 and switching on the step input device 25, as can be understood with reference to Figures 6 and 7. Figures 6a - d show the behavior of a prior art throttle control system without a step input device or gain control. In Figure 6a it is shown that at time zero the driver requests a small throttle opening by means of the accelerator pedal. Due to the low speed at which the integrator part of the PID controller operates, as shown in Figure 6d there is no movement of the throttle and therefore at time T1 the driver requests a larger throttle opening, which results in the engine suddenly overcoming the friction associated with the throttle valve 14 and opening the throttle valve 14 rapidly, causing it to overshoot the throttle target opening.

Figures 7a-d show the response to a driver requesting a small throttle opening in a control system in which a step input device 25 forms part of the control means.

The step input device 25, which detects a small throttle opening and a small accelerator pedal 16, actuates the switch 28 to allow a step input of the size 'e' to the motor control 23.

As soon as it is detected that the position of the accelerator pedal 16 has moved by a predetermined amount, and the signal 'd' exceeds the signal 'e', the step input device 25 is blocked by means of the switch 28 so that the normal error signal 'd' can reach the motor control 23.

The effect of the step input device 25 is to send a short current pulse to the motor 15 which is large enough to overcome the static friction.

Figure 7d shows the response to a step input from the accelerator pedal 16 as shown in Figure 7a.

When comparing Figures 6d and 6d, the improvement in system behavior compared to a state-of-the-art throttle control system becomes clearly visible.

Referring to Figure 5, a second embodiment of the invention is now shown, which in many ways respects similar to the first embodiment just described.

Figure 5 shows an internal combustion engine 111 of a (not shown) motor vehicle, the engine 111 having an intake manifold 112 defining an intake tract 113 in which a disk-shaped throttle valve 114 is rotatably mounted.

The disk-shaped throttle valve 114 can be rotated approximately 90 degrees from a closed position in which it covers the intake passage 13 to an open position where it offers little resistance to the flow of fluid through the intake passage.

The throttle valve opening is conveniently measured from the closed position in degrees of rotation or in percent open.

The throttle valve 114 is rotated by an actuator means in the form of an electric motor 115 which is connected to a spindle 108 of the throttle valve 114, the spindle 108 being supported by two simple bearings 109.

At the other end of the spindle 108 to the motor 115, a throttle valve detection device in the form of a rotary potentiometer 130 is connected.

A control means 121 is connected to the motor 115, the potentiometer 130 and also to an input means in the form of a position sensor 131 connected to an accelerator pedal 116 of the motor vehicle or to an engine control unit 117 of the motor vehicle.

A change-over switch in the form of an accelerator switch 127 connected to the accelerator pedal 116 in a manner not shown is provided to select the required respective input means.

The accelerator pedal 116 is pivotally connected to a part of the body 110 of the motor vehicle via pivot means (not shown).

The control means 121 comprises a three-element proportional-integral-derivative controller (PID) 122, a motor drive power amplifying device 123, a gain control device 124, and a comparator 126.

The control means 121 is essentially a central unit to which a number of read-write memories and read-only memories are assigned in order to form a microcomputer.

The comparator 126 is designed to receive a signal 'P' indicating the throttle valve position from the potentiometer 130 and a signal 'I' from the position sensor 131 and to calculate

E = (I - P) or E = ('I₂' - P), where

E is a signal indicating the difference between a desired throttle position indicated by signal ‘I or I2’ depending on the position of the throttle switch 127; and ‘P’ is a signal indicating the actual throttle position.

The signal E is fed from the comparator 126 into the PID controller 122, which according to the general transfer function

Output signal 'O' = k₁E + k₂ Edt + k₃ dE/dt

operates, the output signal 'O' being supplied to the gain control device 124. The gain control device 124 includes a read-only memory in which a look-up table of the gain factor K plotted against the throttle position P is stored.

The operation of the gain control device 124 is such that the control signal ‘d’ sent to the motor driver is equal to K x O, or in other words

d = K (k₁e + k₂Edt + k₃dE/dt)

where E = (I - P) or

(I₂ - P) depending on the position of switch 127.

k₁, k₂ and k₃ are system constants and

K = total system gain factor

The signal P is provided to the gain control device 124 to determine the required actual gain factor from the look-up table. If the signal P indicates that the throttle position is less than 10 degrees open, then the value of the gain factor K is increased by an amount depending on its value stored in the look-up table. The control signal d is therefore proportionally larger at throttle valve 14 openings less than 10 degrees than it would be at throttle valve openings greater than 10 degrees open.

The motor controller 123 receives the signal ‘d’ and converts it into a current output signal ‘D’ of correct polarity.

Under normal driving conditions, the accelerator switch 127 is in the position shown in Figure 5, but when the driver removes his foot completely from the accelerator pedal 116, the accelerator switch 127 is moved to the opposite position such that the comparator 126 now receives the signal I₂ from the electronic control unit 117 instead of the signal I from the position sensor 131 connected to the accelerator pedal 116.

The engine control unit 117 now acts as an idle speed control device, receiving an indication of the actual engine speed from a speed transducer 129 and adjusting the signal I2 to maintain a substantially constant, predetermined engine idle speed.

Therefore, when the driver takes his foot off the accelerator pedal 16, when the actual engine speed is above the predetermined idle speed, the signal 12 will be such as to cause the control means to send a signal 'D' forcing the throttle valve 114 to close.

As soon as a driver of the motor vehicle moves the accelerator pedal 116, the accelerator pedal switch 127 is actuated to reconnect the output I of the position sensor 131 to the comparator 126. The control means 121 now acts via the motor 115 and the detection means 130 as a closed throttle control system, wherein each movement of the accelerator pedal 116 is mimicked by the throttle valve 114.

Claims (9)

1. Throttle valve control system for an engine (11, 111) of a vehicle, with a throttle valve (14, 114) rotatably mounted in an intake channel (13, 113) of the engine, the control system comprising: a throttle valve detecting means (30, 130) for providing a signal indicative of the rotational position of the throttle valve (14, 114); an input means (31, 131) for supplying a signal indicating a desired rotational position of the throttle valve; an actuator means (15, 115) for changing the angular position of the throttle valve (14, 114) between a closed position and an open position; and a control means (21, 121) for supplying a control signal D to the actuator means (15, 115) to change the angular position of the throttle valve (14, 114), wherein the control means (21, 121) comprises: a comparison means (26, 126) for comparing the signals received from the detection means (30, 130) and the input means (31, 131) and generating an error signal E; and a control means (22, 122) for processing the error signal E received from the comparator means (26, 126) and providing an output signal O, the control signal D being calculated by multiplying the output signal O by a total system gain factor K, characterized in that the control means (21, 121) includes a gain control means (24, 124) for varying the total system gain factor K, which is operable such that when a signal received by the gain control means (24, 124) from the detection means (30, 130) indicates that the throttle valve (14, 114) is in or near the closed position within a predetermined range, the total system gain factor K is adjusted with respect to the total system gain factor used for throttle valve openings above the predetermined range. K is increased so that within the predetermined range the control signal D is greater than for a certain magnitude of error signal E at throttle valve openings above the predetermined range. 2. Control system according to claim 1, wherein the predetermined range is openings of the throttle valve in the range of 0 to 10 degrees from the throttle valve closed position. 3. A control system according to claim 1 or claim 2, wherein, when the throttle is within the predetermined range, the overall system gain factor K is increased relative to the overall system gain factor K used by a factor of up to 3 times over the predetermined range. 4. Control system according to one of claims 1 to 3, in which the overall system gain factor K is constant over the predetermined range and increases linearly within the predetermined range when the throttle valve (14, 114) is closed. 5. Control system according to claim 1, wherein the control signal D to the actuator means is equal to D = K * (k₁ E + k₂ Edt + k₃ dE/dt) where k₁, k₂, k₂ are control system constants. 6. Control system according to one of the preceding claims, in which the control means (21, 121) is a central processing unit (CPU) with at least one read-only memory location (ROM) and at least one random access memory location (RAM), the overall system gain factor K being digitally stored in the form of a look-up table in the or one of the read-only (ROM) memory locations. 7. Control system according to one of the preceding claims, in which the input means is an input means operable by the driver in the form of a potentiometer (31, 131) attached to an accelerator pedal (16, 116) of the vehicle. 8. Control system according to one of claims 1 to 6, wherein the input means is a control unit (117) for the idle speed of the engine. 9. Control system according to one of claims 1 to 6, in which the input means is switchable between a potentiometer (131) attached to an accelerator pedal (116) and a control unit (117) for the idle speed of the engine.