JPS58113547A - Speed controller for car - Google Patents

Abstract

PURPOSE:To permit correct presetting of the car speed by installing a microcomputer equipped with memories and an anlogue/digital converter which generates the pulses having the characteristics corresponding to an operating means. CONSTITUTION:The opening degree of a throttle valve 1 installed in a flow passage for feeding fuel into an internal combustion engine is varied by the degree of stepping-in an accelerating pedal 3. The pulse from a car-speed detecting means 16 is input into the interrupting input terminal iRQ of a microcomputer 15. A preset switch 34, variable resistor 35 as operating means, and an analogue/ digital converter 36 are installed, and the car speed to be set is preset and stored in a memory 23. Therefore, correct preset of the car speed to be set is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for an automobile, and more specifically, the set vehicle speed is stored in the memory of a microcomputer by operating means such as a variable resistor, regardless of the actual vehicle speed. The present invention relates to a speed control device for an automobile that controls the opening degree of a throttle valve so that the vehicle can travel at a set speed.

In such an automobile speed control device, it is necessary to store the set vehicle speed in the memory of a microcomputer with high precision using an operating means.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a speed control device for an automobile that can store a set vehicle speed in the memory of a microcomputer with high accuracy regardless of the actual vehicle speed.

FIG. 1 is a block diagram of one embodiment of the present invention. A link mechanism $2 is connected to a throttle valve l provided in a flow path for supplying fuel to an internal combustion engine of an automobile, and an accelerator pedal 3 is connected to this link mechanism 2. By depressing the accelerator pedal 3, the opening degree of the throttle valve 1 is greatly changed. The diaphragm 5 of the actuator 4 is also connected to the link machine 4$12. Electromagnetic valves 7 and 8 are connected to the working chamber 6 of the actuator 4 . The solenoid valve 7 connects the working chamber 6 to a negative pressure source such as an intake manifold when the line 9 is at a high level and is energized, and connects the working chamber 6 to the outside atmosphere when the line 9 is at the p-level. It will be communicated to. The solenoid valve 8 is connected to the line 10
When line 10 is at a high level, it is shut off, and when line 10 is at a low level, the working chamber 6 is communicated with the outside atmosphere. As the absolute value of the negative pressure in the working chamber 6 increases, the opening degree of the throttle valve 1 increases. Line 9 has AN
A signal is applied from the D game (D game) 11 via a buffer 12. Similarly, a signal is applied to the line 10 from an AND gate 13 via a buffer 14. AND game)
A signal from a microcomputer 15 realized by a one-chip semiconductor element is given to one input of 11.13.

Pulses from the vehicle speed detector 1916 for detecting the actual vehicle speed are sent to the microcomputer 15 via the buffer 17.
It is manually input to the interrupt input terminal iRQ. Vehicle speed detection means 1
6, magnetic poles 19 of the number of paddy grains (4 in this embodiment) are spaced apart in the circumferential direction of the rotary disk 18 that rotates together with the wheels.
is magnetized, and this rotation #18 is rotated by the running of the car. One terminal of the reed switch 20 which is made conductive by the magnetic force of the magnet M#19 is grounded, and the other terminal is connected to the buffer 17. In this sense, rotary disk 1
As the reed switch 8 rotates as the vehicle travels, a pulse having a frequency proportional to the actual vehicle speed is derived from the reed switch 20.

Also connected to the microcomputer 15 are a set switch 21 and a resume switch 22 for constant speed running. While the car is running, set switch 2
1, the set vehicle speed represented by the pulse from the vehicle inspection means 16 is determined by the microcomputer 1.
A duty signal is given to the AND game 11 using the set vehicle speed stored in the memory 23, and the solenoid valve 7 is duty-controlled. At this time, the level of the signal given from the microcomputer 15 to the AND gate 13 is high level, so the solenoid valve 8 receives the low level signal and is excited.
The great sword remains blocked.

In order to cancel constant speed running, the clutch switch 123,
A parking switch 24 and a brake switch 25 are provided. The clutch switch 123 is made conductive by depressing the clutch pedal, and the parking switch 2
4 becomes conductive when the handbrake is pulled, and the brake switch 25 becomes conductive when the brake pedal is depressed. Outputs from clutch switch 123 and parking switch 24 are led to line 28 via OR gates 26 and 27. The output from brake switch 25 is routed to line 28 via OR gate 27. The signal from line 28 is an AND game) 11.1
given to 3. The signal from line 28 is also provided to time constant circuit 30 from OR gate 29. The time constant circuit 30 generates a pulse having a sufficient pulse width to allow the microcomputer 15 to respond even when a pulse having a very short pulse width is derived on the line 28, and It is applied to the reset input terminal 31 of the computer 15.

The voltage applied to energize the microcomputer 15 is detected by the voltage monitoring circuit 32, and when a momentary power outage occurs, a high level signal is output to the OR gate 29 and the time constant circuit 33 given to. The time constant circuit 33 allows the microcomputer 15 to ensure that VcM+ A pulse having a pulse width equal to that of light is given to the microcomputer 15 so that it can output the light.

Memo') In order to be able to preset and store a signal representing the set vehicle speed in 23, regardless of the speed of the actual vehicle, a preset switch 34, a variable resistor 35 as an operating means, and an analog/digital converter 36 are used. and is provided. As shown in FIG.
．． A constant voltage is applied to 41. This fixed terminal 38.
39, the selection terminal 42 contacts the resistor 37 with an angular displacement. The connection position between the selection terminal 42 and the resistor 37 can be changed by manual operation. Such a variable resistor 35 is known as a so-called volume. Fixed terminals 38.39...1, and therefore line 40.
For example, a voltage of 12 volts is applied between the terminals 41 and 41.

Referring to FIG. 3, a graph showing the relationship between the output voltage from the selection terminal 42 and the set vehicle speed of the signal stored in the memory 23 is shown. The range W1 of set vehicle speeds that can be stored in the memory 23, and therefore the range W of vehicle speeds that can perform constant speed driving, is, for example, 40 to 1.
00 km, and the t range v1 of the output from the selection terminal 42 corresponding to this set vehicle speed is 4 to 10 volts.

Speeds outside this settable range Wl, i.e. 0 to 40k
m/h range W2 and 100-120 km/8! f
The range W3 is the range v2 where the output voltage of the selection terminal 42 is from 0 to 4 volts and the range ilI! from 10 to 12 volts. Corresponds to box v3. Such a range V2. In V3, in order to prevent the selection terminal 42 from being connected to the resistor 37,
The operating range of the selection terminal 42 is limited by a stopper or the like. In this way, the selection terminal 42 has an output voltage in the range v
1, it is limited only to the range of angle θ (i2 Figure 1).

In this way, the selection terminal 42 outputs the set vehicle speed 4() to
A voltage of 4 to 10 volts corresponding to 100 km/h will be derived.

4th F1! J is a block diagram of another embodiment of a variable resistor 35 according to the invention. In this embodiment, the fixed resistor 43
．． 44 and variable resistor 45, fixed terminal 146.
A voltage is applied to 47 via line 40.41. Variable resistor 45 includes terminals 48 and 49 and a selection terminal 50. The voltage derived from the selection terminal 50 of the variable resistor 45 is in the range 4 to 10 volts, similar to the previous embodiment.
1 by the action of resistors 43 and 44. FIG. 5 is a concrete diagram of the analog/digital converter 36. A voltage corresponding to the set vehicle speed is applied to the base of a transistor 52 via a line 46 from selection terminals 42 (see FIG. 2) and 50 (see FIG. 4) of the variable resistor 35. A capacitor 5 is connected in series to the transistor 52.
4, a transistor 55 for starting the analog/digital converter 36, and a semi-fixed resistor 53 are connected. In connection with the variable resistor 35, resistors 56, 57° 58 and a diode 59 are connected in series, and the anode of the diode 59 is connected to the capacitor 5 through a resistor 60.
4 and a connection point 168 between the transistor 55 and the transistor 55 .

The output from connection point 169 of capacitor 54 is given to transistor 61 for level discrimination. The output from this transistor 61 is transferred to a buffer transistor 62.
to the microcomputer 15 via line 63. Transistor 55 is provided with an activation signal via line 64. Line 46 from variable resistor 35
By changing the voltage across transistor 5
The base voltage of transistor 2 changes, which causes the voltage at the base of transistor 5 to change.
2 collector current changes.

Referring to FIG. 6, it is assumed that the activation signal shown in FIG. It's working.

Connection point 168 is approximately at the ground level via resistor 60 and diode 59. Although the collector current of transistor 52 is selected to be very small VC compared to the current flowing from the emitter to the base of transistor 61, transistor 61 is conductive and connection point 169 is equal to voltage V of line 70. Capacitor 54 is maintained in this charged state.

The transistor 62 is conductive, and a low level signal (No. 6) shown in FIG. 6(2) is derived from the line 63.

When line 64 goes low at time tl, transistor 55 becomes conductive. This allows connection point 168
becomes the voltage on line 70 +V.

Therefore, the voltage at the connection point 169 is approximately +2V.

Therefore, transistor 61 is cut off. capacitor 5
4 is discharged with a constant current corresponding to the voltage of line 46 through transistor 52, and the voltage at connection point 169 decreases over time. With transistor 61 turned off, transistor 62 is turned off and line 63 goes high.

When the transistor 61 becomes conductive at time t2, which is a time ΔT after time t1, the transistor 62 becomes conductive and the line 63 remains at the low level again. Time t
At time t3, after 2 elapses, the line 64 returns to the high level again.

The microcomputer 15 counts the time ΔT in a counter 65 by executing a program. The ceramic oscillator 66 is externally attached to the microcomputer 15, and the oscillation circuit 67 outputs the pulse shown in FIG. 6(3). The counter 65 counts the signal or frequency-divided signal from the oscillation circuit 67.

The time ΔT between times t1 and t2 corresponds to the output from the variable resistor 35 and therefore the set vehicle speed to be stored in the memory 23.

When the preset switch 34 is operated while the output vehicle pressure corresponding to the desired vehicle speed to be set is led out to the line 46 by the variable resistor 35, the microcomputer 15
As will be described later, a starting signal is derived to line 64, and as a result, from the analog/digital converter 36, a signal that becomes low level at the above-mentioned time ΔT is derived from line 63. be measured.

The set vehicle speed measured by the counter 65 in this way is
The high-speed limiter 68 and low-speed limiter 69 executed by the program e of the microcomputer 15 determine whether the set vehicle speed is within the range Wl (see FIG. 3). When the vehicle speed set by the operation of the deprivation resistor 35 is determined by the high speed limiter 68 to be within the range W3 of 100 km/hour or more, or when it is determined by the low speed limiter 69 that the vehicle speed is less than 4Q km/hour. When the vehicle speed is determined by the variable resistor 35, the vehicle speed set by the variable resistor 35 is prohibited from being stored in the memory 23. In Figure 1, high-speed limiter 6
8 and low speed limiter 69 are shown as blocks for convenience of explanation, such high speed limiter 6
8 and the low speed limiter 69 are the microfum computer 15.
The same applies to the counter 65 and the like.

Referring again to FIG. 2, assume that the variable resistor 35 is broken and the fixed terminal 39 and the resistor 37 are disconnected. In this case, line 46 is connected from selection terminal 42 to line 46.
A voltage approximately equal to zero is derived. As a result, the voltage derived from line 46 is in the range v3 (see FIG. 3) of 10 volts or more. Therefore, the fixed terminal 39 and the resistor 3
7, the set vehicle speed range corresponding to the voltage derived from the line 46 is v3 shown in FIG. 3, and is not stored in the memory 23.

Assume that the fixed terminal 38 and the resistor 37 are disconnected. In this case, line 46 will be at approximately the same voltage as line 41. Therefore, the voltage on line 46 is in the range V2 (1%, see Figure 3), which is less than 4 volts, and the range of set vehicle speeds corresponding to this voltage is as shown by W2 in Figure 3.

Therefore, when the fixed terminal 38 and the resistor 37 are disconnected, the set vehicle speed corresponding to the voltage of the line 46 is stored in the memory 23.
It is never stored in . Such a variable resistor 35
The operation in which the set vehicle speed is no longer stored in the memory 23 when a failure occurs is the same in relation to the embodiment shown in FIG.

Therefore, in the event of a failure of the variable resistor 35, the output derived from the line 46 will be in a range W2 . W3, and therefore is not preset and stored in the memory 23. Therefore, if the vehicle attempts to run at the speed set by the variable resistor 35 in the memory 23 without knowing that the variable resistor 35 has failed, there is no risk of sudden acceleration or sudden deceleration, and safe driving is possible. become.

Even when the actual vehicle speed is stored in the memory 23 as the set vehicle speed by operating the set switch 21 while the vehicle is running, the functions of the high speed limiter 68 and the low speed IJ Mitsutaro 9 are performed, and the actual vehicle speed is allowed to be set. It is stored in the memory 23 only when it is in the range w1, and is stored in the memory 23 only when it is in the range w2. When in w3, the actual vehicle speed is not stored in the memory 23 as the set vehicle speed.

In the above embodiment, the output from the variable resistor 35 is generated by the analog/digital converter 36 to generate a pulse having characteristics corresponding to the output from the variable resistor 36, and is input to the microcomputer. Configuration is simplified. In the illustrated embodiment, the level changes to low level at 0 time t2 after the time ΔTi corresponding to the set vehicle speed has elapsed from the time t1 when the analog/digital converter 36 was started. However, as another embodiment of the present invention,
Not only is the time ΔT corresponding to the set vehicle speed detected by the level change characteristics of the pulse from the line 63, but the pulse width, the time difference between the pulses, and other characteristics are changed in accordance with the set vehicle speed. However, the present invention is intended to include such a concept.

The instruction execution time of the microcomputer 15 is, for example, 3 .mu.days eQ, and the counting time interval of the counter 65 is, for example, 100 .mu.sec. When corresponding to the set 4L speed, "#iΔT is obtained by calculating the difference between the count value of the counter 65 at time t1 and the count value of the counter 65 at time t2. Therefore, times tl and t2 are the count times of the counter 65. The time ΔT cannot be measured accurately unless the time ΔT is measured as accurately as possible.

This will be explained in more detail with reference to FIG. 6A. The pulse shown in FIG. 6A shows the waveform of the pulse derived from the oscillation circuit 67. The counter 65 measures the number of rising waveforms of this pulse over time ΔT.

If the measurement start time of this time ΔT is a time tlb earlier than the pulse rising time t4, and the measurement end time is a time t2b later than the pulse rising time t5, the rising waveform of the pulse at this time ΔT Assume that, for example, A number of times are counted. This time ΔT is started at time tlaKti, which is earlier than time tlb,
If the measurement ends at time t2a, which is earlier than time t5, the number of pulse rising waveforms to be measured is A-1. Therefore, the measurement start time of time ΔT is
When tlc is later than time t4 and the measurement end time is t2c later than time t2b, the measured value of the rising waveform of the pulse is A-1. In this way, the count value by the counter 65 at the same time ΔT becomes A or A-1 depending on the counting start time tla, tlb, resulting in an error. Therefore, when assembling the present vehicle speed control device, it is not possible to accurately adjust the resistor of the semi-fixed resistor 53 of the analog/digital converter 36.

According to the invention, by connecting the variable resistor 35 prepared in advance to the lines 40, 41, 46 and adjusting and setting the semi-fixed resistor 53 so that a constant count jia A is obtained, the Time ΔT [No error occurs in the corresponding count value A. Generally, at time rlHΔT, there are approximately 1000 pulses.

In order to measure the time ΔT as accurately as possible, the microcomputer 15 performs the operation ml·/ in conjunction with the pattern 7. The process moves from step n1 to step n2, and when the preset switch 34 is operated, it is difficult to determine whether d (measurement should be started or not.) At t, when 4 measurements should be started, the counter 6 is activated in step n3.
Read Jl-number u8 of 5.

tit' h of the counter 65 in this step n3
Let 1ef be A. Next, the process moves to step n4, and the count value of the counter 65 is read again. Set #t % 1m of the counter 65 in this step n4 to E. In step 115, step n3. At step n4, it is determined whether the first counts A and B of the counter 65 read are different or identical. If it is A-B, Kini moves to step n4, and the total 'l' of the counter 65 is obtained. ! Load the clam. When it is A to B, the process moves from step n5 to step n6, measurement is started, and the line 64 is activated to convert the level to a low level to the analog/digital converter 36 (No. 4 is derived, and the process proceeds to step n7). .The execution time of each instruction in steps n3 to n6 is:
As mentioned above, it is within several times of 3 μsea, and the counter 6
This is smaller than the counting time interval of 100 μsec in No. 5.

In this way, step n4. At n5, immediately after the counting rate of the counter 65 changes from A to B, the analog/digital converter 36 is activated and the counter 65 starts counting, so the total of 2111 tuna of the time ΔT is uniquely Determined.

FIG. 8 shows the pulse waveform input from the reed switch 20 of the vehicle speed detection means 16 to the interrupt input terminal iRQ of the microcomputer 15 via the buffer 17. When the rotary disk 18 rotates once, the same number of low-level pulses as the number of magnetic poles 19 fixed to the rotary disk 18 can be obtained.

By counting only four high-level pulses and counting the time U by the counter 70, the actual vehicle speed can be detected. Reed switch 20 is magnetic &!
19, the period during which it becomes conductive and its output becomes low level is a predetermined time ΔU, for example, 3
When the vehicle speed continues for more than m sec, the vehicle speed detecting means 16
This makes it possible to prevent false detection due to chattering of the reed switch 2°.

The time required to prevent false detection due to this chattering is 3 m.
aha is an extremely long time compared to the instruction execution time of the microcomputer 15. This time is 3 ms
The microcomputer 15 performs an interrupt program operation only for ea. If other program operations are not executed, other processing speeds will be reduced. Especially counter 6
If the counting function of No. 5 is suspended for such a long period of time, a large error will occur in the measured value of the set vehicle speed that should be preset. In order to solve this problem, in the interrupt program shown in FIG.
The present invention includes a step of detecting the rising edge of the 1 signal at time t2 (see FIG. 6 (2) K), thereby making it possible to set the set vehicle speed to be preset with high precision.

Referring to FIG. 9, when the input waveform of rising edge of microcomputer 150 interrupt input terminal 1RQVc is given,
The process moves from step ml to step m2. This step I
! 12 (well, when the preset switch 34 is operated to preset the set vehicle speed by operating the variable resistor 35, the analog/digital converter 36 representing the set vehicle speed is
It is determined whether or not the signal from the microcomputer 15 is being manually inputted to the microcomputer 15 via the line 63.

If a signal is given from the analog/digital converter 36 via the line 63 after time t1 and the counter 65 is measuring the time ΔT, the process moves to step m3, and the signal on the line 63 becomes high at time 91t2. It is determined whether or not the value has changed. step m
If the signal on line 63 changes to low level at step rn4Vc, the contents of the timer are read. In step m5, it is determined whether the vehicle speed detection output applied to the interrupt input terminal iRQ remains at a low level. In the next step m6, step m1
Step m8 determines whether 3 m sec has elapsed since
This is determined from the timer contents. Still that 3m
If the sea time has not elapsed, step m2
Move to. If the preset switch 34 is not operated, the process moves from step m2 to step m6. If time t2 has not yet been reached in step m3, the process moves to step m6.

After the output from the reed switch 20 of the vehicle speed detection means 16 changes to low level in step m6, 3m5e
When it is determined that c has elapsed, the process moves to step m7, where it is determined that the reed switch 20 has been made conductive only once, and the operations m1 to m7 are thus repeated until the time ΔU (Fig. 8) has elapsed. The vehicle speed is measured and the actual speed of the vehicle is determined.

According to such an embodiment, the microcomputer 15
When the rising waveform from the vehicle speed detecting means 16 is applied to the interrupt input terminal iRQ of the vehicle speed detecting means 16, it is determined whether the signal from the vehicle speed detecting means 16 remains at a high level for a predetermined time of 3 m5ec. , to prevent false detection due to the occurrence of chattering, and if the time ΔT of the output from the analog/digital converter 36 corresponding to the preset vehicle speed is being counted during this time, the analog/digital converter 36 Since it is determined in step m3 whether or not the rising waveform derived from line 63 from line 63 has been obtained, it is possible to measure the set vehicle speed to be preset with high accuracy. Step m2. m
3. m5. For example, the execution of m5 is at most 20 μsea.
It will be done within.

In order to be able to store the set vehicle speed to be preset in the memory 23 without error, the operation shown in FIG. 10 is performed. , In step B1, it is determined whether or not the preset switch 34 has been operated.

If the preset switch 34 is not operated, the storage area in the memory 23 in which the signal representing the constant vehicle speed to be preset is stored is cleared in step 82. In step 83, the set switch 21
Alternatively, it is determined whether the resume switch 22 has been operated or not, and if the resume switch 22 has been operated, a control 1i11 operation for constant speed running is performed in step 84 in accordance with the operation of the set switch 21 or the resume switch 22.

If the set switch 21 and the resume switch 22 are not operated, the process returns to Gt1 step 111.

Is the preset switch 34 operated? Step B
1, a routine is executed starting at step 85 for the preset operation. In step 86, a signal representative of the set vehicle speed to be preset is read in response to 8% via line 63 from the analog/digital converter 36 according to the operation of the variable resistor 35 by the action of the counter 65. Let TN be the calculation result of the Nth measurement read in step B6. In step 87, for example, the immediately preceding 100ffl a
The difference (-TN - (TN-1)) from the preset vehicle speed TN-1 preset at the N-1st measurement before eQ is calculated, and this difference is calculated as a predetermined value, for example, 2, by adding it to the vehicle speed.
If it is less than the pupil corresponding to km15#, step s
9, the preset operation is stopped. Therefore, the process moves to step 810, and the last read signal '1jTN corresponding to the set vehicle speed to be set is determined as the value to be stored in the memory 23. In step all, the signal TN is stored in the memory 23, and the process starts from step s12. Step 83
Move to. When the difference obtained in step tx7 is greater than or equal to the predetermined value, the process moves from step 88 to step slO, where the last signal TN is determined as the set vehicle speed to be stored, and the memory 2 is stored in step Ell.
3, the process again moves from step 85 to step 86, derives the activation signal from line 64, creates 11 analog/digital converters 36, reads the signal corresponding to the setting wheel and description to be newly preset, The difference is determined again in step 87, and when the difference becomes less than the predetermined one shift in step +18, the process goes to step s9. ,
When it is determined that f is greater than or equal to the predetermined 11〆1 in step 88, the new data TN is temporarily stored in the memory 23 as a dazzling vehicle, and then in step 86, it is stored in the analog/digital converter. 3
6 and read the setting wheel. In this way, the reading operation of the data of the set vehicle speed to be preset is repeated until the difference between the two data of =h becomes less than t'l:1 in advance. Therefore, even if the output voltage of the variable resistor is disturbed by noise, the set vehicle speed can be reliably stored in the memory 23.

As described above, according to the present invention, the analog/digital converter is activated immediately after the count change by the microcomputer's counter mbb after the preset switch is operated, and characteristics such as the level change of the pulse are counted. , it is possible to accurately preset the set vehicle speed by detecting with high precision a pulse having characteristics corresponding to the signal from the operating line corresponding to the set vehicle speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an electric circuit diagram showing a specific configuration of the variable resistor 35, and FIG. 3 is a diagram showing the relationship between the output from the variable resistor 35 and the set vehicle speed. A graph showing the relationship, FIG. 4 is an electric circuit diagram showing the configuration of another embodiment of the variable resistor 35, FIG. 5 is a concrete electric circuit diagram of the analog/digital converter 36, and FIG. is a waveform diagram for explaining the operation of reading the set vehicle speed to be preset by the analog/digital converter 36, No. 6AB)
Figure 7 is a waveform diagram for explaining the case where a counting error occurs in the output from the analog/digital converter 36; The figure is a waveform diagram of the signal input from the vehicle speed detection means 16 to the interrupt input terminal iRQ of the microcomputer 15, and FIG. Flowchart for explaining the operation. FIG. 10 is a flowchart for explaining the operation for storing the set vehicle speed in the memory 23 when it is preset. 1...Throttle valve 2...Link mm , 3...
Accelerator pedal, 4... Actuator, 7.8...
・m magnetic valve, 15... microcomputer, 16...
・Means for bringing out the car off-road ridge, 21... Set switch, 22.
...Resume switch, 23...Memory, 24...
・Parking switch, 25...brake switch,
31), 33... Time constant circuit, 34... Preset switch, 35... Variable resistor, 36... Analog/digital transformer, 65.70... Counter, 123
...Clutch switch agent Patent attorney Kei Nishi, Part 6 WJ Figure 6A Figure 7 Figure 9

Claims (1)

[Scope of Claims] A microcomputer equipped with a memory and having a counter function, the counting time interval of which is longer than the instruction execution time; a preset switch; an operating means for deriving an electrical signal corresponding to a set vehicle speed; an analog/digital converter for generating a pulse having characteristics corresponding to an electrical signal derived from the means; a means for detecting the actual vehicle speed; and a means for automatically controlling the throttle valve so that the actual vehicle speed becomes the set vehicle speed stored in the memory. and controlling means, wherein the microcomputer starts an analog/digital converter immediately after counting by the counter function after operating a preset switch, and counts the characteristics of the pulse.