THROTTLE CONTROL SYSTEM FOR AUTOMOTIVE VEHICLE

Abstract: In a throttle control system including electrical elements or devices (3, 4A, 4B), if trouble occurs in these elements, there exists a problem in that the throttle valve (5) is further driven forcibly in spite of the fact that the throttle valve has already been fully closed or opened. To overcome the above problem, a throttle valve close-limit switch (7A) and a throttle valve open-limit switch (7) are additionally provided for the accelerator control system, in order to generate an alarm signal or a system disabling signal in the case where the difference between the target throttle opening rate and the actual throttle opening rate exceeds a predetermined value when one of the limit switches is on.

Description: The present invention relates generally to a throttle control system for an automotive vehicle by which a throttle valve opening rate is controlled via electrical or pneumatic devices in response to accelerator pedal stroke, and more specifically to a control system which outputs an alarm or a disabling signal in case where the control system is abnormal. In an automotive vehicle, when an accelerator pedal is depressed by the driver, a throttle valve disposed in a carburetor is opened to accelerate the vehicle. Conventionally, the relationship between the stroke of the accelerator pedal depressed by the driver and the opening rate of the throttle valve is fixedly predetermined in dependence upon the mechanical structure of the throttle device. For instance, in the case of a single barrel throttle device, because the throttle valve opening rate is predetermined to be roughly linear in proportion to the accelerator pedal stroke, throttle valve opening rate increases relatively abruptly with increasing accelerator pedal stroke. These accelerator pedal control characteristics are suitable for accelerating the vehicle quickly, for instance, to avert danger when the vehicle is travelling at a high speed on a highway. However, these are not suitable for repeatedly and finely driving the vehicle a little forward slowly when the vehicle is travelling at a low speed on a busy street. In contrast with this, in the case of a twin barrel throttle device, because the throttle valve opening rate is predetermined to be delayed according to the accelerator pedal stroke, throttle valve opening rate increases relatively gently with increasing accelerator pedal stroke. Therefore, the accelerator pedal control characteristics are suitable for repeatedly and finely driving the vehicle a little forward slowly when the vehicle is travelling at a low speed on a busy street. However, these are not suitable for accelerating the vehicle quickly to avert danger when the vehicle is travelling at a high speed on a highway. That is to say, in the conventional accelerator device, it is impossible to freely obtain appropriate accelerator pedal control characteristics indicative of relationship between throttle valve opening rate and accelerator pedal stroke according to driver's preference or vehicle travelling conditions. In order to overcome the above-mentioned problems, the same inventor has proposed a novel accelerator pedal control system for an automotive vehicle such that any appropriate accelerator pedal control characteristics representative of relationship between throttle valve opening rate and accelerator pedal stroke can be selected freely by driver's preference according to vehicle travelling conditions, which is described in the document EP―A―114 401 (Article 54 (3) EPC). A similar control system is known from the document "Automotive Engineering", Vol. 90, No. 6, June 1982, pages 97-99. DE-A-1-3 028 601 discloses a system and method for controlling the throttle valve of an automotive vehicle equipped with a free-wheel drive system. The control method disclosed in this document includes the features indicated in the pre-characterizing part of the claim. In such a control system, however, since there are arranged a number of electrical or pneumatic devices such as potentiometers encoders, motors, switches, sensors, etc. between the accelerator pedal and the throttle valve, there exists a problem in that the throttle valve is further driven forcibly, in spite of the fact that the throttle valve has been fully closed or opened, because these devices operate abnormally due to potentiometer looseness or aging, element failure, etc. When such trouble occurs, some elements of the system may be damaged. With these problems in mind, therefore, it is the primary object of the present invention to provide a throttle control system for an automotive vehicle which outputs an alarm signal or a system-disabling signal or a command signal to compulsorily close a throttle valve in case the throttle valve is further driven forcibly in spite of the fact that the throttle valve is fully closed or opened. To achieve this object, the invention provides a method of controlling the throttle of an automotive vehicle as described in the claim. It is generally known from FR-A-2 453 048 to provide limit switches for detecting the fully closed and fully opened positions of a throttle valve in order to prevent the throttle valve from being driven beyond its physical limits. However, this document relates to a speed control system in which the position of the throttle valve is not uniquely determined by the position of the accelerator pedal, but is adjusted in response to the vehicle speed in order to keep the speed at a preset value. In such a system, the condition that the throttle valve is driven to its physical limits is a normal operational possibility and does not represent a fault condition. Accordingly, this document could not teach the detection of a fault condition in the manner specified in the claim. DE-A1-3 109 638 discloses a throttle control circuit in which a plurality of voltage and current values occuring at different points of the circuit are sampled and a fault signal is generated when the sampled values are not compatible with each other. However, the detection of the specific fault condition considered in the present invention is not disclosed in this reference. In applicant's co-pending European patent application EP―A―121 937, a throttle control system for an automotive vehicle is described, which comprises means for detecting the accelerator pedal is at its zero-stroke position, means for detecting the throttle valve is at its initial position and outputting a corresponding signal, and means for generating an abnormality command signal if the throttle valve initial-position signal is not outputted within a predetermined time interval after the accelerator pedal has reached its zero-stroke position. The features and advantages of the throttle control system for an automotive vehicle according to the present invention will be more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate corresponding elements and in which: Fig. 1 is a schematic block diagram of a first embodiment of the throttle control system for an automotive vehicle according to the present invention; Fig. 2 is a schematic block diagram of a second embodiment of the throttle control system for an automotive vehicle according to the present invention; Fig. 3 is a pictorial illustration showing an exemplary structure for detecting accelerator pedal stroke used with the throttle control system according to the present invention; Fig. 4 is a pictorial illustration showing an exemplary structure for detecting throttle valve opening rate used with the throttle control system according to the present invention; Fig. 5 is a timing chart showing the times when the throttle close-limit switch and the throttle open-limit switch are turned on; Fig. 6 is a graphical representation showing an example of the relationship between the output voltage of the throttle valve potentiometer and the actual throttle valve opening rate, in which the solid line a represents a normal state and the dotted and dashed lines b and c represent an abnormal state; and Fig. 7 is a program control flowchart showing the control steps of the throttle control system according to the present invention. In view of the above description, reference is now made to a first embodiment of the present invention. With reference to Fig. 1, the throttle control system of the present invention comprises an accelerator pedal 1, an accelerator pedal stroke detector 2, a control signal generator 3, a throttle servodriver 4, a throttle valve 5, a throttle open-rate detector 6, a throttle open-rate limit detector 7, and an abnormality signal generator 8. The accelerator pedal stroke detector 2 detects the stroke of the accelerator pedal 1. The control signal generator 3 reads a stroke signal outputted from the accelerator pedal stroke detector 2, determines a target throttle valve opening rate by looking-up a table in which control characteristics representative of relationship between throttle valve opening rate and accelerator pedal stroke are listed and by executing necessary interpolation calculation, and outputs a target command signal to the throttle servodriver 4. The throttle servodriver 4 drives the throttle valve 5 in accordance with the target command signal ϑ T outputted from the control signal generator 3 and a feedback signal (described later). The throttle open-rate detector 6 detects the actual throttle opening-rate and outputs a feedback signal ϑ A indicative of an actual throttle opening-rate to the throttle servodriver 4. The servodriver 4 drives the throttle valve 5 so that the difference (ϑ T - ϑ A ) can be reduced to zero. The throttle open-rate limit switch 7 detects that the throttle 5 is driven to its extreme position of fully-open position or fully-closed position. The abnormality signal generator 7 receives three signals of the target command signal ϑ T generated by the control signal generator 3, the feedback signal ϑ A indicative of the actual throttle valve opening-rate generated by the throttle open-rate detector 6, and the extreme-position signal generated by the throttle open-rate limit detector 7, respectively, and outputs an abnormality command signal when the difference between the target throttle opening rate ϑ T and the actual throttle opening rate ϑ A exceeds a predetermined value when the throttle open rate limit switch 7 detects the throttle valve extreme position. This is because whenever the throttle valve is driven to its extreme position (fully-open or -closed position), the difference (ϑ T - ϑ A ) must be zero as far as the system operates normally. This abnormality command signal is usable for producing an alarm signal, a command signal to disable the entire system or another command signal to compulsorily return the throttle valve to its initial position. Fig. 2 is a schematic block diagram of a second embodiment of the throttle control system according to the present invention. In Fig. 2, the system comprises an accelerator pedal stroke potentiometer 2A, a control signal generator 3 including analog-to-digital converters 31 and 32, a microcomputer 33 and a digital-to-analog converter 34, a motor driver 4A, a motor 4B, a throttle opening rate potentiometer 6, a throttle close-limit switch 7A, a throttle open-limit switch 7B, and an alarm generator 9. The accelerator pedal stroke potentiometer 2A outputs an analog signal the voltage level of which is proportional to the stroke of the accelerator pedal. Fig. 3 is a pictorial illustration showing an example of the structure of an accelerator pedal provided with the stroke potentiometer 2A. A bracket 100 is fixed at an appropriate position to the floor 101 of a vehicle body. The middle portion of a shallow-V-shaped pedal lever 102 is pivotably supported by the bracket 100. The accelerator pedal 1 is fixed to one end of the pedal lever 102. A return spring 103 is disposed between the floor 101 and the other end of the pedal lever 102. The pedal 1 is urged by this return spring 103 to its zero-stroke position when released. The accelerator pedal stroke potentiometer 2A is disposed between the floor 101 and the pedal lever 102. This potentiometer 2A of linear sliding-contact resistance type outputs analog voltage signals indicative of accelerator pedal stroke. The control signal generator 3 receives the stroke signal from the accelerator stroke potentiometer 2A through the analog-to-digital converter 31, the feedback signal indicative of the actual throttle valve opening rate through the analog-to-digital converter 32, and two signals outputted from the throttle close-limit switch 7A and the throttle open-limit switch 7B. The microcomputer 33 determines a target throttle valve opening rate ϑ T in accordance with table look-up method and interpolation, calculates the difference between the target value ϑ T and the actual value ϑ A , and outputs a command signal through the digital-to-analog converter 34. The motor driver 4A receives the target command signal (ϑ T - ϑ A ) from the control signal generator 3, and drives the motor 4B in the direction that the difference (ϑ T - ϑ A ) between the two signals is reduced to zero. The throttle close-limit and open-limit switches 7A and 7B are turned on when the throttle valve 5 is positioned at its fully-closed and -open positions, respectively. Fig. 4 is a pictorial illustration showing an example of the structure of a throttle valve provided with the throttle limit switches 7A and 7B and the throttle potentiometer 6. The throttle valve 5 is fixed to a throttle shaft 105 pivotably supported at an appropriate position to an intake air conduit 106. The shaft 105 is directly connected to a driven shaft of the motor 4B. At the end of the throttle shaft 105, an L-shaped lever 107 is fixed. A return spring 108 is disposed to urge the throttle valve 5 to its initial position. The throttle close-limit switch 7A is disposed at such a position as to be turned on when the throttle valve is returned to its initial position, as depicted in Fig. 5. The throttle open-limit switch 7B is disposed at such a position as to be turned on when the throttle valve is shifted to its extreme open position, as also depicted in Fig. 5. The throttle potentiometer 6 is attached on the flat end of the motor 4B. This potentiometer 6 is of rotary sliding-contact resistance type. The potentiometer 6 includes a rotatable sliding contact coupled with the driven shaft 105 of the motor 4B and a circular resistance on which the sliding contact slides. Therefore, when the motor 4B rotates through an angle, since the sliding contact also slides on and along the circular resistance together with the throttle valve 5, the potentiometer 6 outputs an analog signal the voltage level of which is proportional to the angular stroke of the throttle valve 5. Further, since the lever 107 is urged by the return spring 108 in the direction that the throttle valve is closed, when current is not supplied to the motor 4B, the throttle valve 5 is fully closed by the force of the return spring 108. In the second embodiment shown in Fig. 2, the throttle valve opening rates are represented by voltages detected by the throttle potentiometer 6. Fig. 6 shows the relationship between the throttle valve opening rate (abscissa) and the throttle valve potentiometer output voltage (ordinate). In the normal state, the throttle valve potentiometer 6 is so predetermined as follows: when the throttle valve is fully closed (ϑ AC ), a voltage of V AC is outputted; when fully opened (ϑ AO ), a voltage of V AO is outputted; when moderately opened (ϑ A ), a voltage of V A is outputted, as depicted by the solid line a in Fig. 6. However, once the potentiometer 6 goes into an abnormal state due to looseness, aging, etc., the relationship between the throttle valve opening-rate and the potentiometer output voltage is shifted to either side of the line a , as depicted by the dotted and dashed lines b and c in Fig. 6. In the case where the throttle potentiometer output is shifted lower than the normal line a , as shown by the line b in Fig. 6, the system operates abnormally as follows: when a command signal to close the throttle valve to its fully-close position is outputted, since the throttle potentiometer 6 cannot output a voltage V AC but a voltage V′ AC lower than V AC the difference ΔV = V AC - V′ AC is held at a positive value in spite of the fact that the throttle valve 5 is fully closed, so that the throttle valve is kept open beyond its extreme close position. When a command signal to open the throttle valve to its fully-open position is outputted, since the throttle potentiometer 6 cannot output a voltage V AO but a voltage V′ AO lower than V AO the difference ΔV = V AO - V′ AO is also held at a positive value in spite of the fact that the throttle valve 5 is fully opened, so that the throttle valve is further driven forcibly beyond its extreme open position. In the case where the throttle potentiometer output is shifted higher than the normal line a , as shown by the line c in Fig. 6, the system operates abnormally as follows: when a common signal to close the throttle valve to its fully-closed position is outputted, since the throttle potentiometer cannot output a voltage V AC but a voltage V′ AC higher than V AC the difference ΔV = V AC - V′ AC is held at a negative value in spite of the fact that the throttle valve 5 is fully closed, so that the throttle valve is further driven forcibly beyond its extreme closed position. When a command signal to open the throttle valve to its fully-open position is outputted, since the throttle potentiometer 6 cannot output a voltage V AO but a voltage V′ AO higher than V AO the difference ΔV = V AO - V′ AO is also held at a negative value in spite of the fact that the throttle valve is fully opened, so that the throttle valve is kept ahead of its extreme open position. The object of this invention is to overcome the above-mentioned problems by forcedly resetting the difference Δϑ or ΔV to zero whenever the throttle valve is fully closed or opened. Fig. 7 is a flowchart of an example of control program used for the microcomputer 33. With reference to Fig. 7, the operation of the second embodiment of the present invention will be described hereinbelow. First, control reads the accelerator pedal stroke data outputted from the accelerator pedal stroke potentiometer 2A via the analog-to-digital converter 31 (in block 1). In response to the read pedal stroke data, control looks up a previously-stored table and performs a required interpolation calculation in order to obtain a target throttle valve opening rate ϑ T corresponding to the read accelerator pedal stroke (in block 2). Then, control reads an actual or feedbacked throttle valve opening rate ϑ A outputted from the throttle valve opening rate potentiometer 6 via the analog-to-digital converter 32 (in block 3) and calculates the difference (Δϑ = ϑ T - ϑ A ) in throttle valve opening rate between the target value ϑ T and the actual (feedback) value ϑ A (in block 4). Here, if the calculated value Δϑ is zero; that is, when the actual throttle valve opening rate ϑ A matches the target throttle valve opening rate ϑ T , the succeeding steps (blocks 5 and 6) are both "NO", control advance to the next step to output a command signal (Δϑ = 0) (in block 7). Therefore, the motor driver 4A outputs no signal, so that the motor 4B stops rotating and thus the throttle valve 5 is kept at its balanced position. If Δϑ > 0, control determines "YES" (in block 5) and then checks whether or not the throttle open limit switch 7B is ON (in block 8). If the throttle open limit switch 7B is not ON, that is, OFF, this indicates that the throttle valve 5 is not yet fully opened, control directly advances to the succeeding step (block 7) to output a command signal (Δϑ > 0) to the motor driver 4A, so that the motor 4B rotates, in a predetermined direction that the throttle valve opening rate is increased, until the difference Δϑ = ϑ T - ϑ A reaches zero. Here, if control determines "YES" (in block ϑ T this indicates that the system is abnormal, because when the throttle open-limit switch 7B is ON (i.e. throttle valve is fully open), it is impossible that the target opening rate ϑ T is greater than the actual opening rate ϑ A (i.e. Δϑ > 0) or that the throttle valve should further be opened. Such an abnormal case as described above may be produced when the output voltage of the throttle potentiometer 6 is set to an abnormal value lower than the normal value, as depicted by the dotted and dashed line b in Fig. 6. In more detail, in spite of the fact that the throttle valve 5 is fully opened, since the throttle potentiometer 6 cannot output a voltage of V AO but a voltage lower than V AO the difference Δϑ (= ϑ T - ϑ A ) is held at a positive value. Therefore, when control determines "YES" (in block 8), the difference Δϑ is forcedly reset to zero (in block 9). Control advances to the next step to output a command signal (Δϑ = 0) (in block 7). Therefore, the motor driver 4A outputs no signal, so that the motor 4B stops rotating and thus the throttle valve 5 is kept at its fully-opened position. As a result, it is possible to prevent damage of the system due to overload caused when the throttle valve is further driven excessively after having fully been opened. Similarly, if Δϑ < 0, control determines "YES" (in block 6) and then checks whether or not the throttle close limit switch 7A is ON (in block 10). If the throttle close limit switch 7A is not ON, that is, OFF, this indicates that the throttle valve 5 is not yet fully closed, control directly advances to the succeeding step (block 7) to output a command signal (Δϑ < 0) to the motor driver 4A, so that the motor 4B rotates, in a predetermined direction that the throttle valve opening rate is decreased, until the difference Δϑ = ϑ T - ϑ A reaches zero. Here, if control determines "YES" (in block 10), this indicates that the system is abnormal, because when the throttle close-limit switch 7A is ON (i.e. throttle valve is fully closed), it is impossible that the target opening rate ϑ T is smaller than the actual opening rate ϑ A (i.e. Δϑ < 0) or that the throttle valve should further be closed. Such an abnormal case as described above may be produced when the output voltage of the throttle potentiometer 6 is set to an abnormal value higher than the normal value, as depicted by the dotted and dashed line c in Fig. 6. In more detail, in spite of the fact that the throttle valve 5 is fully closed, since the throttle potentiometer 6 cannot output a voltage V AC but a voltage higher than V AC the difference Δϑ (= ϑ T - ϑ A ) is held at a negative value. Therefore, when control determines "YES" (in block 10), the difference Δϑ is forcedly reset to zero (in block 11 ). Control advances to the next step to output a command signal (Δϑ = 0) (in block 7). Therefore, the motor driver 4A outputs no signal, so that the motor 4B stops rotating and thus the throttle valve 5 is kept at its fully-closed position. As a result, it is possible to prevent damage of the system due to overload caused when the throttle valve is further driven excessively after having fully been closed. Further, in case the above-mentioned steps shown by blocks 9 and 11 are implemented, it is preferable to output an alarm signal to the alarm generator 9. In dependence upon this alarm signal, it is possible to inform the driver of the fact that there exists an abnormality in the control system. As the alarm system, a buzzer, a voice warning, an alarm light, an alarm display, etc. are used. Further, in response to this alarm signal, it is possible to cut-off the current supplied to the motor 4B, that is, to disable the motor 4B. In this case, the throttle valve 5 is forcedly returned to its initial position by the elastic force of the return spring 108. Further, in response to this alarm signal, it is possible to hold the throttle valve at its fully-opened position by actuating an appropriate latch mechanism. Further, in the above-mentioned embodiments, a resistance-type potentiometer is used as the accelerator pedal stroke potentiometer 2A or the throttle valve opening rate potentiometer 6. However, it is of course possible to use a pulse encoder which can output encoded pulse signals representative of position, in place of the potentiometer. Furthermore, in the above-mentioned embodiments, a mechanical limit switch is used as the throttle close-limit switch 7A and the throttle open-limit switch 7B. However, it is of course possible to use other switches such as a slide switch having a movable contact and a fixed contact, a pressure sensitive switch, a magnetic sensitive switch, etc. Further, in the above-mentioned embodiments, the motor 4B is used for driving the throttle valve 5. However, it is of course possible to use other hydraulic or pneumatic actuator. As described above, in the throttle control system for an automotive vehicle by which the throttle valve is controlled, by means of electrical, hydraulic or pneumatic driving system, according to the accelerator pedal stroke, in case where an abnormal state occurs such that the throttle valve is further driven forcibly in spite of the fact that the throttle valve has already been closed or opened fully, because of failure or trouble occurred in the devices or elements incorporated within the system, it is possible to detect the abnormality and prevent damage of the system due to overload applied to the system, thus improving the reliability of the system.

Claims: A method of controlling a throttle for an automotive vehicle, comprising the steps of: a) detecting an accelerator pedal stroke; b) calculating a target throttle valve opening rate ϑ T according to the detected accelerator pedal stroke; c) detecting an actual throttle valve opening rate ϑ A ; and d) driving the throttle valve in response to said target throttle valve opening rate ϑ T and said actual throttle valve opening rate ϑ A ; characterized in that the step (d) includes the following substeps: d1) calculating the difference Δϑ between the target throttle valve opening rate ϑ T and the detected actual throttle valve opening rate ϑ A ; d2) if the calculated difference Δϑ is positive, checking whether the throttle valve is fully open and generating an abnormaly command signal if the throttle valve is fully open; d3) if the calculated difference Δϑ is negative, checking whether the throttle valve is fully closed and generating the abnormality command signal if the throttle valve is fully closed; d4) setting the calculated difference Δϑ to zero if the abnormality command signal has been generated; and d5) outputting said difference Δϑ calculated in step (d1) or set in step (d4) as a control command signal for driving the throttle valve to either set the actual throttle valve opening rate ϑ A to the target throttle valve opening rate ϑ T or keep the throttle valve in the fully closed or fully open position, respectively.

Inventors: MURAKAMI, TERUKIYO
Applicants: NISSAN MOTOR CO., LTD.
Application year: 1984
Main classification: F02D11
IPC codes: B60Q9, G05G1, F02D41, F02D11, F02D9, B60K26