A CONSTANT SPEED CRUISE CONTROL SYSTEM OF DUTY RATIO CONTROL TYPE AND A LEADING ANGLE CONTROL METHOD THEREOF

Abstract: A constant speed cruise control system of duty ratio con­ trol type for approximating an actual tarveling car speed to a stored target car speed, by on/off control of a control valve (10,89a) of an actuator (ACT,102,89,155) to adjust the throttle valve opening degree by an output duty ratio D obtained from a control line (70) having a gradient showing a conversion characteristic of car speed and duty ratio. The system has a controller (ECU) in which a set duty ratio SD corresponding to the target car speed is calculated as SD = SD1 + (DM - SD1)/n and the output duty ratio D is calculated as D = G × ΔV + SD where G: gradient of control line ΔV: car speed deviation DM: integrating element responding quickly to duty ratio change SD1: integrating element responding slowly to duty ratio change n: constant and the controller (ECU) corrects to integrate the set duty ratio SD in a direction of approximating the output duty ratio D.

Description: The present invention relates to a constant speed cruise control system of duty ratio control type for approximating an actual traveling car speed to a stored target car speed, by on/off control of a control valve of an actuator to adjust the throttle valve opening degree by an output duty ratio D obtained from a control line having a gradient showing a conversion characteristic of car speed and duty ratio. Such a constant speed cruise control system of duty ratio control type is known from EP-A-OO51000. An automotive constant speed cruise control system known as Auto-Drive or automatic speed control is intended to control the car speed constantly, once a desired car speed is preset, without having to step on the accelerator pedal, and in the known system, the coil for the control valve of a pressure type actuator to drive the accelerator link, using an engine negative pressure (e.g. an intake manifold negative pressure, a vacuum pump negative pressure or the like) as driving source, is driven by a pulse signal of duty ratio corresponding to the difference between the detected traveling car speed (detected car speed) and the car speed preset by the driver (target car speed). The constant speed cruise control system of duty ratio control type is to control constant speed traveling by determining a set duty ratio which is a duty ratio necessary for traveling at constant speed at a target car speed (preset car speed), and delivering by adding or subtracting a duty ratio corresponding to the difference between the target car speed and traveling car speed to or form the set duty ratio. However, the required duty ratio varies with the characteristics of the actuator, throttle drive system or engine, road surface gradient, engine load of air conditioner, vehicle load of speed change gear or other conditions, and if the set duty ratio is fixed, there occurs a car speed deviation corresponding to the difference from the required duty ratio. In one of the conventional examples of such constant speed cruise control system, the controller or ECU (electronic control unit) detects the traveling car speed by the signal from a car speed sensor having a reed switch which is turned on/off by the magnet rotating in proportion to the rotation of the vehicle drive shaft. When the preset switch is turned on, the ECU stored the traveling car speed, and after it is turned off, it controls the duty ratio of the control valve of the actuator ACT. A negative pressure is introduced when the control valve is turned on, which raises pressure generating by the diaphragm linked to the throttle valve SL. When turned off, the atmosphere is introduced to lowered pressure generating by the diaphragm. During this control period, the release valve is turned on, and the atmosphere is cut off. When a cancellation signal (clutch switch; or in A/T car, neutral start switch, parking switch, or brake switch) is fed, both the control valve and the release valve are turned off, and the atmosphere is led in from both to stop the control swiftly. When a resume switch is turned on after cancellation, traveling control is restored at the car speed stored previously. A microcomputer is used in the ECU, of which processing is described below. The output duty ratio D for on/off control of the control valve is determined depending on the difference between the target car speed VM stored in the memory and the traveling car speed Vn. To be precise, it is not the traveling car speed Vn, but a skip car speed VS adding a car speed variation component (differentiation component) is used. This is for compensating in advance the action delay of the actuator, or the loss time due to hysteresis or play of the throttle valve or drive system in an leading direction. Therefore, the skip car speed VS is determined in the following equation. where Vn: present car speed V n-1 : previous car speed K: proportional constant Incidentally, the output duty ratio D may be also determined as follows. where SD: set duty ratio VM: target car speed (stored car speed) VB: control speed width In the above equation, VM-VS is a car speed deviation ▵V, and the control speed width VB is an inverse number of control gain (gradient of control line) G, so that equation (2) may be rewritten as follows. In the prior art, meanwhile, since the criterion value of the duty ratio necessary for constant speed traveling is fixed as a set duty ratio, a car speed deviation occurs due to fluctuations in the actuator system or vehicle load variations: For example, as shown in FIG. 1, if the set duty ratio SD corresponding to the stored car speed VM(e.g. 80 km/h) is 40% and the required duty ratio D is 55%, the control criterion initially located at point A converges at point B along with the decline of the car speed due to lack of duty ratio. Since the required duty ratio at point B is also nearly 55% (to be precise, there is a car speed coefficient of about 0.1%/km/h for the required duty ratio as indicated by chain-line 28, but it may be almost ignored in this example), when the control speed width VB is, for example, 20 km/h, a deviation of occurs, and the car is controlled at 77 km/h at point B. Accordingly, such vehicle cruises at a constant speed as shown in Fig. 2, with the traveling speeds varying with road loads. This phenomenon will be described in further details. The prior control system of the constant speed cruise control can be roughly represented as shown in Fig. 3 if its non-linear element is disregarded. Fig. 4 depicts this control system in terms of its relationships with the target car speed. Suppose cruising is maintained with an actual car speed in complete agreement with the target value under a particular condition, and that the target speed varies stepwise by a factor of B. Another way of saying this is that to the target car speed V(S) is given at B/S, and the target value X(S) transmitted to the feedback system tracks the variation path and converges into V(S) as depicted in Fig. 5. On the contrary, the actual car speed Y(S) varies as in Fig. 5. The final value of the deviation Z(S) between X(S) and Y(S) is given by: This indicates that under a given condition there is only one-actual car speed, if any, which comes in perfect agreement with the target value, and that under different conditions a deviation unavoidably occurs between them. Fig. 6 shows the control system in terms of its relationships with road loads. Here again, let us assume that cruising is continued with the target car speed and the actual value being in complete harmony with each other. Also assume that load changes stepwise by C at time t1. Expressed in other terms, a load U(S) is given at C/S. F(S) (the car speed corresponding to the load variation) signalled to the feedback system traces the path illustrated in Fig. 7, and Y(S) varies therewith. This indicates variations in load induces changes in actual car speed without any change of the target value, i.e., the actual car speed varies with changing road gradient without varying the target car speed. If A is made larger to give a smaller deviation regardless of stability, it becomes possible to decrease q (t)t → ∞. This leads to an inevitable reduction of q (t)t → ∞ and hence a smaller deviation due to changes in target car speed can be attained, but the variations in car speed due to load changes become greater. As noted previously, the fixed set duty ratio system of the prior art inevitably was involved in the creation of car speed deviation. Such car speed deviation may be rendered to zero when the control criterion is corrected from point A to point C in Fig. 1. However, if the corrected speed is too low, deviation convergence takes much time, while if the corrected speed is too high, stability could be impaired due to excessive correction. Incidentally, since constant speed traveling control starts by pressing a set switch while traveling to store the traveling speed at that time as a target car speed, sudden duty ratio fluctuations occur right after this setting. Accordingly, if the same control as in the subsequent constant speed traveling is done, the change of SD is too fast, and a car speed hunting in FIG.8 may linger on. In equation (2), meanwhile, the control speed width VB denotes a range of car speed for varying the output duty ratio D linearly in a range of 0 to 100%, and its inverse number is the gain. The set duty ratio SD is the duty ratio corresponding to the target car speed VM, and ideally it is the control center. The leading angle control describe above obtains a skip car speed (leading angle car speed) VS by adding the differential value (acceleration) ▵V of the traveling car speed Vn, in which if Vn changes, VS varies as shown in FIG. 9, so that the change in Vn may be fed back to the output duty ratio D in advance. However, if the car speed changes suddenly due to abrupt variations of the road surface or shift-down of an automatic car, a sufficient controllability (response) is hard to obtain, partly because of the effects of car speed filter (integrating filter). Accordingly, one of the objects of the invention is to nullify car speed deviation during a constant speed traveling. Another object of the invention is to enhance traveling stability. Further object of the invention is to prevent hunting right after setting. Another object of the invention is to make a car speed change small even if a sudden change of a car speed occurs when a road gradient changes suddenly or the like. According to the present invention, constant speed cruise control system according to the preamble of claim 1 is characterized in that there is provided a controller, in which a set duty ratio SD corresponding to the target car speed is calculated as and the output duty ratio D is calculated as where G: gradient of control line ▵V: car speed deviation DM: integrating element responding quickly to duty ratio change SD1: integrating element responding slowly to duty ratio change n: constant and the controller correcting to integrate the set duty ratio SD in a direction approximating the output duty ratio D. Thus, accordingly, if change of set duty ratio is required due to road surface variations or the like, the dynamic gain may be increased by the movement of element DM, and the element SD1 is moved while suppressing the car speed deviation, so that the car speed deviation may be nullified while arresting the car speed variations. In a second preferred embodiment, the elements DM and SD1 are calculated as In this control system, however, when the entire car speed region is controlled at a constant control gain, the gain of the entire control system becomes high in the low speed traveling region where the vehicle gain is high, accordingly hunting is likely to occur, while in the high speed traveling region where the vehicle gain is low, the gain of the entire control system is low, accordingly the response becomes inferior. This may be avoided by varying the gain of the entire control system, but in the generally employed method of varying the static control gain, the stability is impaired. Accordingly, the gain of the entire control system is preferably changed by varying the dynamic control gain derived from the response. In a third preferred embodiment, the controller therefor changes over the value of n depending on the traveling car speed, and corrects to integrate the set duty ratio SD in a direction of approximating the output duty ratio D. In another fourth preferred embodiment, the controller changes over the value of K, depending on the traveling car speed, and integrates and corrects the set duty ratio SD in a direction of approximating the output duty ratio D. In this way, since the dynamic control gain is varied depending on the car speed, the traveling stability in high speed region is enhanced, and the response to car speed changes in low speed traveling region is enhanced, too. The controller, furthermore, quickly changes DM and SD1 when the car speed acceleration ▵Vn exceeds a certain value in correction formula where A, B: constants in the unit of dury ratio(%)/ acceleration and integrates and corrects the set duty ratio SD in a direction of approaching the output duty ratio D. In this cruise control system, incidentally, the duty ratio is calculated mainly at the intermediate point of an integrating element 1 (DM) responding quickly to duty ratio change and an integrating element 2 (SD1) responding slowly to duty ratio change, and it is intended to respond by a quick movement of integrating element against road surface fluctuations or other variations, but if the change of DM is too quick in an ordinary traveling state, the gain becomes too large, which may affect car speed hunting, so that too fast movement is not allowed. Accordingly, where a quick response against sudden changes are required, the control is delayed in this state, and the overshoot or undershoot of car speed may be too large. Hence, in this invention, when the car speed acceleration ▵Vn exceeds a certain value, a value proportional to the acceleration is subtracted from each integrating element to give a quick response against a sudden change, thereby preventing delay of control. Specifically, A·▵Vn is subtracted from DM, and B·▵Vn in subtracted from SD1, where A, B are constants in the unit of duty ratio(%)/acceleration. Thus, when movement of set duty ratio is required due to road surface changes or the like, the dynamic gain is preferably increased by the movement of element DM, and the element SD1 is moved while suppressing the car speed deviation, so that it is possible to nullify the car speed deviation while controlling the variations of car speed. If the acceleration exceeds a certain value, the values of DM, SD1 are changed in proportion to the acceleration, so that a car speed deviation can be held small even if the road gradient changes suddenly, so that a stable control may be ensured. Accordingly, in a preferred sixth embodiment, the controller determines a difference ▵D between the integrating element SD1 or the set duty ratio SD and the output duty ratio D, changing β corresponding to the magnitude of the difference ▵D, and correcting to integrate the integrating element SD1 in a direction of approximating the output duty ratio D. In another preferred seventh embodiment, the integrating element SD1 is changed within a range between an upper limit value and a lower limit value. In yet another preferred eighth embodiment, the integrating element DM is changed within a range between an upper limit value and a lower limit value. Right after setting a target car speed, since the previous state is not known, it may too large if the value of correction term β is changed corresponding to the value of ▵D as mentioned above. So, in another nineth preferred embodiment, for a specified time after setting (for example, 14 seconds), the value of β is limited to a certain value so that the integrating speed may be moderate. By varying this value in various car speed regions, the speed is optimized considering the difference in the vehicle gain. Thus, hunting right after setting a target car speed may be prevented in a constant speed cruise control system of duty ratio control type for integrating and correcting the set duty ratio SD. According to a tenth preferred embodiment, the controller integrates and corrects the set duty ratio SD in a direction of approximating an output duty ratio D, by determining the difference ▵D between a set duty ratio SD corresponding to a desired target car speed and an output duty ratio D, and moving the control line parallel at an integrating speed corresponding to the magnitude of this ▵D. Since the set duty ratio SD is not fixed, when it is corrected, it is possible to run constantly at a target car speed by theoretically nullifying the car speed deviation. At this time, when the correcting speed is varied depending on the magnitude of difference ▵D between output duty ratio D and set duty ratio SD, the car speed deviation may be quickly eliminated in a range not to spoil the stability. Thus, in the constant speed cruise control system of duty ratio control type, since the basic duty ratio value is integrated and corrected by varying the speed depending on the difference from the output duty ratio, the car speed deviation can be eliminated at a pratically sufficient speed without sacrificing the stability. In another eleventh preferred embodiment, the integrating speed is limited by fixing γ at a certain value for a specified time after setting the target car speed. In a further twelveth preferred embodiment, the value γ is selected for differentiated values in car speed regions. In order to keep the car speed deviation always at minimum range, it is necessary to correct the set duty ratio SD continuously without limitation. However, for instance, when the descending suddenly after gradually increasing the set duty ratio SD to climb up a steep slope (for example, when climbing up a hill), the set duty ratio SD decreases, and at this time, a large car speed overshoot occurs due to the delay of ECU and delay of actuator line. To the contrary, when moving from downslope to upslope, the relation is reverse, but a large car speed undershoot occurs according to the same principle. Hence, to prevent such phenomena, the range of integrating correction preferably is limited. Thus, in a constant speed cruise control system of duty ratio control type, since the basic duty ratio is integrated and corrected by varying the speed depending on the difference from the output duty ratio D, the car speed deviation may be eliminated at a practically sufficient speed without sacrificing the stability. At the same time, since the range of integrating correction is limited, overshoot or undershoot of car speed due to sudden changes of road surface conditions may be decreased. The invention also relates to a leading angle control method of the constant speed traveling control system of duty ratio control type for approximating an actual traveling car speed to a stored target car speed, by determining the acceleration by differentiating the traveling car speed obtained from car speed signal, calculating the leading angle car speed by adding the acceleration to the traveling car speed, and on/off controlling the control valve of an actuator for adjusting the opening degree of throttle valve by the output duty ratio obtained from the conversion characteristic between the leading angle car speed and duty ratio, in which a correction duty ratio is added to the output duty ratio if the acceleration exceeds a certain value. Such a method is known from Fr-A-2409385. According to the invention this known method is characterized in that the correction duty ratio is increased in proportion to the acceleration Accordingly, this offers the advantage that if sudden car speed changes should occur, a large correction is applied to the duty ratio depending on the acceleration, and the subsequent car speed changes (overshoot, etc.) may be reduced, so that the stability of constant speed control may be enhanced. In a preferred embodiment, the specified value is not zero. In another preferred embodiment, the specified value is zero. It is also an important characteristic of this invention to apply a correction duty ratio increasing together with the passing of the time to the output duty ratio if the acceleration exceeds a specified value. Thus, if sudden car speed changes should occur, a large correction is temporarily applied to the duty ratio, and the subsequent car speed changes (overshoot, etc.) may be reduced, so that the stability of constant speed control bay be enhanced. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantage of the invention will become more apparent upon a reading of the following detailed specification and drawings, in which: FIG. 1 is a drawing showing the relation between car speed and output duty ratio D in duty ratio control of the prior art; FIG. 2 is a drawing to explain the operation of the prior art shown in FIG. 1; FIG. 3 is a block diagram of a constant speed cruise control system in the prior art; FIG. 4 is a block diagram of that in FIG. 3, arranged regarding a target car speed; FIG. 5 is a drawing showing a relation between a target car speed and true car speed; FIG. 6 is a block diagram showing the block diagram of FIG. 3, arranged regarding load; FIG. 7 is a drawing showing change of a car speed in connection to the load; FIG. 8 is a graph showing a relation between the time transition of car speed and duty ratio in the prior art; FIG. 9 is a drawing showing the car speed changes with the passing of the time in other prior art; FIG. 10 is a block diagram showing one of the embodiments of this invention; FIG. 11 is a block diagram to explain the processing operation of a processing circuit 188 in FIG. 10; FIG. 12 is a drawing showing the relation between car speed and duty ratio to explain the principle of this invention; FIG. 13 is a drawing to explain the operation of the embodiment of this invention; FIG. 14 is a flow chart to explain the operation of this invention; FIG. 15 is a drawing to show the relation between car speed and duty ratio accompanying the passing of the time in an embodiment of this invention; FIG. 16 is a drawing to explain the dynamic control gain conforming to this invention; FIG. 17 is a drawing to explain the operation of an embodiment following the concept of this invention; FIG. 18 is a drawing to explain the operation of the embodiment of this invention in contrast to the prior art; FIG. 19 is a waveform diagram to explain the operation of the abovementioned embodiment; FIG. 20 is a flow chart to explain the operation of other embodiment of this invention; FIG. 21 is a block diagram to show a control line of an embodiment of the invention; FIG. 22 is a block diagram to show another function of the control line in FIG. 21; FIG. 23 is a graph to show change of a deviation z(t); FIG. 24 is a block diagram to show still another function of the control line in FIG 22; FIG. 25 is a graph to show changes of calculated value y(t). FIG. 26 is a block diagram of a further different embodiment of this invention; FIG. 27 is a general block diagram of this invention including the constitution shown in FIG. 26; FIG. 28 is a flow chart to explain the output duty ratio calculation and output processing in the embodiment shown in FIG. 26 and FIG. 27; FIG. 29 is a flow chart to explain the averaging processing action of output duty ratio of the embodiment shown in FIG. 26 through FIG. 28; FIG. 30 is a drawing to explain the operation of the embodiment shown in FIG. 26 through FIG. 29; FIG. 31 is a block diagram showing part of a different embodiment of this invention; FIG. 32 is a drawing to explain the operation of the embodiment shown in FIG. 31; FIG. 33 is a drawing to show the characteristic of leading angle control following this invention; FIG. 34 (A) is a drawing to show the changes in the car speed, duty ratio and throttle valve opening degree with the passing of the time in a further different embodiment of this invention; FIG. 34 (B) is a time transition diagram of car speed, duty ratio and throttle valve opening degree according to the two-step differentiating method conforming to this invention; FIG. 34 (C) is a time transition diagram of car speed, duty ratio and throttle valve opening degree according to the one-step differentiating method; FIG. 34 (D) is a time transition diagram of car speed, duty ratio and throttle valve opening degree conforming to the two-step differentiating control method; FIG. 35 is a drawing to explain the car speed signal processing in an embodiment of this invention; FIG. 36 is a flow chart to explain the operation of an embodiment of this invention; FIG. 37 is a flow chart to explain the operation of a different embodiment of this invention; FIG. 38 is a block diagram of a further different embodiment of this invention; FIG. 39 is a drawing showing the operation of the embodiment shown in FIG. 38 in comparison with that of the prior art; FIG. 40 is a flow chart to explain the operation of a different embodiment of this invention; FIG. 41 is a flow chart to explain the operation of another embodiment of this invention; FIG. 42 is a flow chart to explain the operation of a still different embodiment of this invention; FIG. 43 is a view to explain the action in the prior art shown in FIG. 13; and FIG. 44 is a flow chart to explain the operation of a still further different embodiment of this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, preferred embodiments of the invention are described below. FIG. 10 is a system block diagram showing an example of a constant speed traveling control system following the aspect of this invention, in which a controller or ECU 6 (electronic control unit) detects the traveling car speed by the signal from a car speed sensor 6 having a reed switch 4 which is turned on or off by a magnet 2 rotating in proportion to the rotation of the vehicle drive shaft. The ECU 6 stored the traveling car speed when a preset switch 8 is turned on, and, after it is turned off, contorls the duty ratio of a control valve 10 of an actuator ACT. A pressure is lowered when the control valve 10 is turned on to increase the pressure generating by a diaphragm 12 linked to a throttle valve SL. When the control valve 10 is turned off, the atmosphere is introduced, and the pressure generating by the diaphragm 12 is weakened. In this control period, a release valve 14 is turned on to shut off the atmosphere. When a cancellation signal (clutch switch 15; in A/T car, neutral start switch, parking switch 16 or brake switch 18) is fed, both control valve 10 and release valve 14 are turned off, and the atmosphere is led in from the both sides to stop the control swiftly. When a resume switch 20 is turned on after cancellation, the traveling control by the previously stored car speed is restored. A microcomputer is used in the ECU, and processing in this unit is shown in a block diagram in FIG. 11. The output duty ratio D for on/off control of the control valve is determined by the difference between the target car speed VM stored in the memory and the traveling car speed Vn, but precisely it is not Vn itself, but a skip car speed VS is used, which is its sum with the car speed change component (differential component) in a differentiation circuit 22 added up in an adder 24. This is intended to compensate for the loss time due to lag of action of actuator ACT or hysteresis or play in the throttle valve SL or drive system, in a leading direction. Therefore, the skip car speed VS is obtained in the following equation. where Vn: present car speed V n-1 : previous car speed K: proportional constant And the output duty ratio D is determined as follows. where G: gain SD₀: set duty ratio ▵V: car speed deviation (= VM - VS) In this preferred embodiment, this set duty ratio SD is variable, and can be expressed as: DM is a high-speed integrating element which will quickly respond to changes in duty ratio (which can also be called as changes in car speed), thereby reducting the set deviation. It operates on the principle that as illustrated in Fig. 12 (a), the control line is made to rotate at high speeds so that the deviation is decreased. On the contrary, SD1 is a low-speed integrating element which will respond slowly to changes in duty ratio and decrease the set deviation. Its operation strategy is to shift the control line parallel in the direction of decreasing the deviation as indicated in Fig. 12 (b). For both DM and SD1, the initial value is equivalent to SD₀ in Eq. 2, and traces the path against the changes in duty ratio D as shown in Fig. 13. The figure (a) is an illustration of the operations when there is a drop in the speed of a cap moving from a level to a uphill road (the duty ratio increased), while the figure (d) illustrates the operation including a downhill. As shown in the figure (a), when duty ratio D varies with varying car speeds, both DM and SD1 initiate changes. But since DM responds more quickly of the two, DM first follow up. SD1 later starts changing, so that the overall SD1 changes like a dashed line, and then merges with duty ratio D. This is because SD shifts from SD₀ to D = A, where the equation 6 becomes stabilized when ▵V = 0, and SD = A. Using the equations 5 and 6, the output duty ratio D can be expressed as: FIG. 14 is a flow chart showing an embodiment of this invention, and it corresponds to the block diagram in FIG. 18. In this embodiment, a high speed integrating element DM is changed in proportion to the difference from the duty ratio D. That is, at step s16, supposing when the present element DM(i) is changed by α from the previous DM (i-1) , if this α is, for example, the difference between the present duty ratio D(i) and the previous element DM (i-1) is applied, and the correcting speed is varied (where K is a constant). By contrast, a low speed integrating element SD1 is, using a variable β which is smaller than α, expressed, at step s37, as follows and when this β is a fixed value, the correcting speed is constant. For example, it is assumed: In this way, when DM, SD1 at each point are determined, they are put into equation (13), and SD is calculated at steps s47, s48, or by putting into equation (12), the duty ratio D is calculated. At step s49, a duty ratio D(i) is output, by which the actuator is controlled, so that constant speed cruising is effected at duty ratio D(i). The calculation cycle at steps s2 to s49 is, for example, 50 msec/1 cycle. What is mentioned before is a basic construction of this embodiment, which further controls corresponding to various driving conditions. For a specified time (for example 12 sec) after the set switch is on, processing is at steps s3 to s4 just after a setting which will be mentioned later. After 12 seconds passing, processing is performed, passing steps s3, s23. At step S23, duty ratio deviation ▵D is determined by a difference between a set duty ratio SD (its initial value is SD₀) and output duty ratio D, and depending on the size of this ▵D, β is determined so that SD is corrected at step s24 to s36. In this method, as shown in FIG. 1, the control diagram is moved parallel from the solid line (including points A, B) to the broken line (including point C), and thereafter the car speed at car speed deviation of zero around point C. In this embodiment, as shown in steps S25 to S36, by dividing into several steps by the size of the difference ΔD (=SD-D) between the set duty ratio and output duty ratio D, integrating correction speeds are set individually. The setting method is based on the following three basic rules. [1] No correction is made where the ▵D is very small (for example, ±1%). This is a kind of dead zone, and it is intended to keep stable by not making unnecessary correction while traveling stably. [2] The correction speed is faster when the absolute value of ▵D is greater. That is, when the ▵D is great (the car speed deviation is large), the correction speed is raised to decrease the car speed deviation as quickly as possible, and when the car speed deviation becomes small, the correction speed is lowered to prevent excessive correction. [3] If the absolute value of ▵D is the same, the correction speed is varied between the increasing direction and the decreasing direction. For example, when the ▵D is over 20%, the correction speed (the SD decreasing direction) is extremely enlarged to decrease car speed overshoot when changing from upslope to downslope, thereby keeping the speed increase state to a minimum. Meanwhile, discriminating by the difference ▵D of duty ratio as in this embodiment is same as discriminating by the magnitude of car speed deviation, but to be more precise it is different from the point that the output duty ratio D is discriminated by the sum of the skip car speed VS and control speed width VB (which is a value to express the gain of ECU, electronic control unit), and as compared with the method of discriminating merely by the magnitude of car speed deviation, it is excellent in two points, that is: (I) a transient control amount is taken into consideration, and (II) it is discriminated by a duty ratio which directly influences the actual actuator line operation. While, within 12 seconds, β is automatically determined in the quantitative relation of D, SD and car speed region. That is, in a low speed region of 60 km/h or less, at steps s5, s7, s8, β = ±0.04%/sec, in which the plus sign refers to the case of D > SD, and the minus sing represents the case of D ≦αµρ¨ SD. On the other hand, in a high speed region exceeding 60 km/h, at steps s6, s9, s10, it is only β = ±0.2%/sec, and β is determined regardless of the magnitude of D - SD. At this time, β is intended to keep the integrating correction speed at a moderate constant value. FIG. 15 is a diagram to explain the operation of this invention. By controlling the correction speed of SD1 at a moderate constant speed until passing time T after setting, variations of other factors accompanying the duty ratio change may be arrested, so that hunting as shown in FIG. 8 may be prevented. At the time of determining β, ▵D may be defined not by SD-D, but by SD1-D. According to the abovementioned, when β is determined, SD1 is calculated based on the equation (1) at step s37. However, in advance of that, at steps s11 to s15, a correction term of DM is determined corresponding to a car speed, the DM being calculated based on the equation (9), (10), that is when it is less than 60 km/h, the DM is calculated with [1] having K = 512 at step s12, or when 100 km/h or more, DM is calculated with [3] having K = 64 at step s13, s14, and in the intervening zone, the DM is calculated with [2] having K = 128 at step s14. When the value of K is varied in this way, the dynamic control gain changes as shown in FIG. 21, so that the gain of the entire control system can be changed along with the variation of the vehicle gain. FIG. 17 is an operational waveform diagram, in which the broken line denotes the characteristic omitting steps s11 to s15 in FIG. 14, and the solid line represents the characteristic with steps a11 to s15 in FIG. 19. Meanwhile it is also possible to control more delicately by dividing the preset car speed into smaller sections than in this embodiment. Next, the processing represented by steps s17, s18; s38, s39 is described hereinbelow. The processing performs quick changing DM and SD1 to make car speed change small when car speed acceleration is large, for example when passing from upslope to downslope. That is if the acceleration ▵Vn exceeds, for example, 1.25 km/h/sec, 4·▵Vn is subtracted from DM at step s18, and ▵Vn from SD1 at s38. As a result, both DM and SD1 change suddenly. However, since the ▵Vn takes the plus sign when accelerating, and the minus sign when decelerating, when the duty is lowered, both DM and SD1 decrease, when it is raised, both values increase. FIG.18 explains this operation. More specifically, FIG. 18 (A) shows the basic system of FIG. 14, that is, the constitution without steps s17, s18; s38, s39, while FIG. 18 (B) relates to an improved method including steps s17, s18; s38, s39. The duty ratio change in FIG. 18 (B) is steeper than in FIG. 18 (A) , which means that the car speed change may be suppressed to a small extent if the road surface gradiemt changes suddenly. Thus, the processings at steps s19 to s22 and steps s40 to s43 are performed after the processing at steps s17, s18; s38, s39. This step limits the integrating range, which define the range of parallel movement of control line in FIG. 1. Generally, when the duty ratio is under 20% or over 80%, the pressure generating by the actuator is saturated at 0 and maximum, respectively, and it is meaningless to correct the set duty ratio up to these ranges. And if the correction range is slightly limited further, there may be slight effects on a steep slope, but it is a practically safe level. Accordingly, by limiting the set duty ratio correcting range, the car speed fluctuations due to sudden slope changes are restricted. Two setting methods of limiting range of set duty ratio are considered as follows. (1) In the duty ratio type Auto Drive Unit, an average required duty ratio is set as initial set duty ratio (SD₀). Based on this SD₀, upper limit A1 and lower limit B1 are set. For example: (2) That limits are defined by the absolute value of duty ratio. For example: Both (1) and (2) may be established by the one-side limit only. For example: At steps s19 to s22, the value of DM is limited by use of an upper and lower limit values A1 and B1. At steps s40 to s43, the value of SD1 is limited by use of an upper and lower limit values C and E which can be obtained in a same manner. After the processings at steps s40 to s43, those at steps of s44 to s46 are performed. According to the result of a car speed discrimination (60km/h or not?) at step s44, the value of n is changed as n=2 (60km/h or more) at step s45, and as n=4 (less than 60km/h) at step s46. The value of n is a value for use at step s47 to calculate SD. The value of n is arbitrary, but at n = 1, the control line in FIG. 12 (A) stand upright, and the gain becomes maximum. Then as the value of n increases, the gradient of control line becomes moderate (the gain decreases). Therefore, in FIG. 14, at 60 km/h or higher when the vehicle gain begins to drop, the dynamic control gain G1 is raised as n = 2 at step s45, and at less than 60 km/h when the vehicle gain begins to go up, the dynamic control gain G1 is lowered as n = 4 at step s46. FIG. 19 is a operational waveform diagram, in which the broken line denotes the characteristic omitting steps s44 to s46 in FIG. 14, and the solid line represents the characteristic with steps s44 to s46 in FIG.14 . In this embodiment, meanwhile, only an example of varying the dynamic control gain G1 in a low speed traveling region (for example, less than 60 km/h) is shown, but it is also possible to vary the dynamic control gain G1 (to decrease the value of n) also in a high speed traveling region (for example, over 100 km/h). Or more delicate control is possible by dividing the preset car speed into smaller sections. In accordance with SD1, DM and n obtained hereabove, at step s47, set duty ratio SD is calculated, next, at step s48, output duty ratio D being calculated. A control signal corresponding to the duty ratio D is output to the actuator at step s49. FIG. 20 shows a different embodiment of this invention inwhich the set duty ratio SD is corrected directly by β at steps s24 to s36 of FIG. 14 without using DM and SD1. Steps s1 to s10 in FIG. 14 correspond to steps ℓ1 to ℓ10, and stpes ℓ3a, ℓ3b, ℓ21 to ℓ31 correspond to steps n23 to n36. The value β in FIG. 14 is rewritten as γ in FIG. 20. What is of note is that the value of SD is directly corrected depending on ▵D (= SD - D) by γ as and when ▵D is large, SD is correctly promptly. This value of SD is cotrolled in a range between upper limit A2 and lower limit B2 at steps ℓ12 to ℓ15. As this ▵D increases, the value of γ is set larger. In a further different embodiment of this invention, instead of equation (50a) above, SDi may be corrected as shown in equation (53a). The other constitution is same as in the preceding embodiments. A brief description will be given of the principle wherein car speed deviation does not occur, in the aforestated embodiment. The improved control system of the constant speed cruise control is roughly as depicted in Fig. 21 if its non-linear element is disregarded. Fig. 22 is an illustration of this control system in relation to the target car speed. Suppose that cruising is maintained with an actual car speed in complete agreement with the target value under a given condition, and also that the target value varies stepwise by B at a given time t1. Another way of saying this is that the target car speed V(S) is given at B/S, and the target value X(S) transmitted to the feedback system tracks the variation path and converges to V(S) as depicted in Fig. 23. On the contrary, an actual car speed Y(Y) varies as in Fig. 23, but the final value of the deviation Z(S) between X(S) and Y(S) is given by: This denotes that, whatever the target value, an actual car speed comes to merge with the target speed. Fig. 24 describes the relationships between the control system and road load. Here again, let us assume that cruising is kept up with the target car speed and the actual one being in complete harmony with each other. Also assume that load changes stepwise by C'at a given time t2. Expressed in other terms, a load U(S) is given at C/S, and F(S) (the car speed variation corresponding to load changes) signalled to the feedback system varies as shown in Fig. 25, with the attendant change of Y(S). What is noteworthy here is the fact that the car speed F(t) corresponding to load is rendered to zero at t → ∞. This can be seen from the fact that the final value of F(S) becomes zero as a result of the calculation using the following equation: Also of note is that the final value of Q(S), a deviation between F(S) and Y(S), becomes zero. This is to be recognized by the fact that the final value of Q(S) is given by the following formula and becomes zero. The above two findings denote that with the latest improvement, cruising speed is not affected by loads on a steady basis, and that as mentioned previously, the control system is constructed so that cruising is maintained with an actual car speed kept in agreement with the target value. FIG. 26 is another embodiment according to the invention, and this invention presents a constant speed cruise control system comprising an output duty ratio calculating means 101 for calculating the output duty ratio D corresponding to the difference between a detected traveling car speed and a preset car speed based on the control car speed width for calculation of output duty ratio calculation and a set duty ratio, and a driving means 103 for driving a coil 102a for control valve in an actuator 102 for driving a throttle valve operating on a driving source of engine negative pressure by generating a pulse signal possessing a duty ratio corresponding to an output duty ratio calculated in this output duty ratio calculating means 101, in which are also contained an average calculating means 104 to determine the average of output duty ratios calculated by the output duty ratio calculating means 101, and a set duty ratio correcting means 105 for obtaining a set duty ratio for calculation of output duty ratio of output duty ratio calculating means 101 by correcting a set duty ratio (fixed value) predetermined according to the average of output duty ratios calculated by the average calculating means 104. If the predetermined set duty ratio is improper, the actual car speed contains the target car speed and stationary deviation, but at this time, a difference depending on the stationary deviation occurs between the average of output duty ratios and the set duty ratio, and the set duty ratio to be applied to the output duty ratio calculating means 101 is corrected in a direction to decrease the stationary deviation by the set duty ratio correcting means 105, so that the stationary deviation is controlled small. According to this invention, if the predetermined set duty ratio is improper, the set duty ratio for calculation of output duty ratio is corrected by the output duty ratio calculating means in a direction to decrease the stationary deviation by the set duty ratio correcting means, so that the stationary deviation may be reduced, and moreover since it is not necessary to vary the control speed width, the stability is not sacrificed. FIG. 27 is a block diagram of essential parts showing concretely the system of FIG. 26. In this drawing, numeral 80 is a reed switch for detection of traveling speed of an automobile, and 81 is a permanent magnet which is rotated being driven by a speed meter cable. The reed switch 80 is turned on and off by the rotation of the permanent magnet 81, and generates a pulse signal having a frequency proportional to the car speed. This pulse signal is applied to a frequency-voltage converter (F/V converter) 82 to be converted into a DC voltage possessing a level proportional to the car speed. The output voltage of the F/V converter 82 is held in a memory circuit 84 when an analog switch 82 is turned on. The set voltage held in the memory circuit 84 is fed into a differential amplifier 85, where the difference from the output voltage from the F/V converter 82, that is, the traveling car speed is obtained. This difference signal is converted into a digital value in an A/D converter 86, and is fed into the input port of microcomputer 87. The microcomputer 87 is to generate a pulse signal possessing an output duty ratio depending on the difference signal, and the pulse signal, while an AND circuit 96 is opened, passes through this AND circuit 96 and is applied to a control valve coil 89i of an actuator 89 through an amplifier 90. The actuator 89 comprises a control valve 89a and a release valve 89b, and the control valve 89a is opened or closed by the control valve coil 89i which is excited by the output of the amplifier 90. Then, as the control valve coil 89i is energized, the atmospheric pressure from port 89c is cut off, and an intake pipe negative pressure from port 89d is led into a chamber 89e, and when the energization is cut off, the negative pressure from the port 89d is cut off, and the atmospheric pressure from the port 89c is led into the chamber 89e. The release valve 89b is opened and closed by a release valve coil 89j which is driven by the output of a self-holding circuit 92 through an amplifier 91, and when energized, it cuts off the atmospheric pressure from port 89f, and when energization is turned off, it introduces this atmospheric pressure into the chamber 89e. As the pressure in the chamber 89e is controlled in this way, a diaphragm 89g moves, so that a rod 89h which is linked to an accelerator link (not shown) is moved in the axial direction, thereby controlling the opening degree of a throttle valve SL. There is an AND circuit 95 which receives the output of preset switch 8 and the output of high speed limit circuit 94, and by the output of this AND circuit 95, the analog switch 83 is closed, and the self-holding circuit 92 is preset. As the self-holding circuit 92 is preset, another AND circuit 96 is opened, and the release valve coil 89j is energized through the amplifier 91, so that traveling control is enabled. The high speed limit circuit 94 is designed to close the AND circuit 95 when receiving a chime signal telling that the speed has exceeded, for example, 100 km/h, so as to prevent the storing operation of set car speed. A cancellation switch 98 is a switch to reset the self-holding circuit 92, and when reset, the self-holding circuit 92 stops energization through the amplifier 91. A resume switch 97 is intended to resume the constant speed traveling control once interrupted by the cancellation switch 98, and when it is pressed, constant speed traveling control is effected on the basis of the previous set car speed as the target. Meanwhile, a low speed limit circuit 99 is intended to force to reset the self-holding circuit 92 when the car speed drops below, for example, 30 km/h. FIG. 28 is a flow chart showing an example of calculation and output processing of output duty ratio executed by the microcomputer 87, and FIG. 29 is a flow chart showing an example of averating processing of output duty ratio executed by the micorcomputer 87, of which operation is described below. Meanwhile, FIG. 26 is a block diagram of microcomputer 87. The microcomputer executes steps S2 to S4 for calculation of duty ratio shown in FIG. 28 in a specified period, for example, at every 50 msec (S1). In this processing, first the difference between the output of the A/D converter 16, that is, the detected car speed XN and the target car speed XA stored in the memory circuit 84 (the car speed difference) is read (S1), and the present output duty ratio DU is calculated in the following equation (S3). however, 0 ≦αµρ¨ D ≦αµρ¨ 100 where VB is a control speed width, and SD is a set duty ratio for calculation of output duty ratio, and this SD is variable in this invention. The steps s2 to s3 correspond to the output duty ratio calculating means 101. The microcomputer 87, after calculating the present output duty ratio D at step S3, delivers a pulse signal possessing a duty ratio equal to that duty ratio to the AND circuit 96 through output port (S4). At the time, the microcomputer 87, by executing the processing shown in FIG. 29 at every, for example, 50 msec, is always correcting the set duty ratio SD used in calculation of output duty ratio. That is, every time the correction period comes around, the mean. Dmean of a new output duty ratio is calculated in the following equation from the mean Dmean of the previous output duty ratio and the output duty ratio D at that time (S10). where M is an averaging coefficient (a normalizing coefficient), and is, for example, 7. This step s10 corresponds to the mean calculation means 104 in FIG 26. The microcomputer 87 calculates the mean Dmean of output duty ratio, and also claculates the set duty ratio SD for calculating a new output duty ratio in the following equation (24) (S11). where SD₀ is a value determined in the designing state, corresponding to the conventional set duty ratio, and is a fixed value preliminarily stored in the read only memory of microcomputer 87. Incidentally, K is a constant for substantially determining the variable width of set duty ratio SD for calculation of output duty ratio, and it is set at, for example, about 2. This step s 11 corresponds to the set duty ratio correcting means 105 in FIG. 26. In this embodiment, since the set duty ratio SD for calculation of output duty ratio is corrected on the basis of mean Dmean of output duty ratio in every specified period as shown above, if, for example as shown in FIG. 30, there is a speed deviation of ▵XN in the control by the initial fixed set duty ratio SD₀, the output duty ratio D is corrected toward the Dmean depending on the difference between SD₀ and the mean Dmean of output duty ratio at that time, and the characteristic curve of car speed difference to output duty ratio is revised, for example, from the solid line to the virtual line shown in the same diagram, so that the stationary deviation is decreased as ▵XN1. In a system where plural fixed set duty ratios are set at every target car speed, they may be individually corrected. FIG. 31 is a block diagram showing a calculation part of leading angle car speed, in which numeral 150 is a car speed signal processing part, 152 is a preset switch, 153 is a set car speed memory unit, 154 is an output processing part, 155 is an actuator, 156 is a primary differentiator, and 157 is a secondary differentiator. In this embodiment, the input car speed f(t) is differentiated in the differentiator 156, and is multiplied by a coefficient K1 in a coefficient multiplier 160, while it is further differentiated in the differentiator 157 and multiplied by another coefficient K2 in a coefficient multiplier 162. Therefore, the leading angle car speed g(t) obtained by adding them up in an adder 158 is as follows. The third term of the right side of the above equation is the portion not found in the conventional system, and it is part B shown in FIG. 32 (A). This part B is effective to cancel and nullify the overcompensating part A due to the second term of the right side of the above equation. FIG. 33 is an leading angle characteristic drawing of this invention, assuming K1 = 1.8, K2 = 1.8 x 0.6, in which the leading phase has been extended up to 180°. Accordingly, a sufficient phase leading time can be maintained up to a high frequency region. The operational waveform diagram of this case is shown in FIG. 34 (A), in which the car speed is increased from 40 km/h at 5 km/h increments at high gain. As clear from the figure, the absolute quantity of hunting is small, and the difference is converged in a short time. Meanwhile, to alleviate the duty ratio variations, the moving average of the high order differential term may be taken. That is, the leading angle car speed calculation in the microcomputer is performed as where VSn: leading angle car speed VRn: traveling car speed at measuring point K1: coefficient of primary differential term K2: coefficient of secondary differential term and for example, employing the two-time moving average method, by setting the third term of the right side of the above equation is set as so that the duty ratio variations can be lessened. In this case, supposing the calculation cycle as 50 msec, it approximately follows that K1 = 36, K2 = 216. The above explanation relates to the basic action with the coefficient K2 of the secondary differential term being constant, and in this invention, this coefficient K2 is further varied depending on the set car speed. An example is shown in FIG. 33 (B). This diagram shows the characteristic of lowering the coefficient K2 gradually from the initial value of TK2 if the set car speed (VM) exceeds a specified value (in this example, 40 km/h). In this case, K2 is, assuming TK2 = 1.08 sec², expressed as follows and K2 is 0 at VM = 124km/h. Besides, other methods are possible, such as the method of lowering the value of K2 in steps, for example, in two steps, that is K2 = TK2 in a low speed region under VM = 80 km/h, and K2 0 in a high speed region over it. FIG. 34 (B) refers to a case of constant speed traveling in a high speed region with the value of K2 in equation (25) being fixed. If there is disturbance in the car speed signal in such a case, the duty ratio changes significantly. The change of this duty ratio is larger than in the conventional case shown in FIG. 34 (C), which indicates the shortcoming of adding a secondary differential term. However, when K2 is set smaller in high speed region, the effect of the secondary differential term is lowered, and the variation width of duty ratio becomes narrow as shown in FIG. 34 (D), so that the stability of control is maintained. Fig. 35 is a schematic drawing showing how the car speed sensing portion works, wherein ℓ of the following equation 29 and m of the equation 30 are both set at 4 and the time synchronizing timing at 50 msec. where, T*: the time filtered by the equation 29, X*: the car speed filtered by the equation 30, and Vn: the traveling car speed at n. The processing operation in this preferred embodiment is done by the processing circuit 188 in Fig. 10. The pulse cycle Ti* can be determined from the step r1 to r9 in the flowchart in Fig. 36. Each pulse of car speed signals is used as an interruption signal. The process is interrupted (at step r1) every time the rise of an edge of the car speed signal pulse is sensed, and the interruption time is read and the time data previously read and stored are shifted one by one (step r2, r3, r4, r5 and r6). Expressed in other words, the processing circuit 188 in Fig. 15, which is comprised of a central processing unit (CPU), a timer connected to the CPU through a bus line, a random access memory (RAM), a read only memory (ROM) and other devices, reads the interruption time into the CPU register in response to the clock pulse from the timer each time interruption conditions are set out (at step r1). The last fith to preceding time data (interruption time) stored in each address from N+ 4th to Nth in the RAM is rotated one after another; the time data most recently picked up is stored in the Nth address as the latest time, thereby performing processes r2 through r6. The pulse cycle Ti is calculated (step 7) by deducting the last fifth time data registered in the N + 4th address of RAM from the last one stored in the Nth address. Using the preceding pulse cycle filtered value T * / i -1 and the latest cycle value Ti, the latest filtered pulse synchronization value T * / i -1 is computed (step r8) with the equation 22 (ℓ = 4), and stored into the specified address. This filtered pulse synchronization value Ti is determined and updated at each rising of a car speed pulse signal, maintaining the latest pulse cycle filtered value Ti in a specified address of RAM. At the completion of computation of pulse cycle filtered values, this interruption process is put to an end and the main process is resumed (step r9). The car speed filtered value Xn* is determined using the step P1 and P2 in the flowchart of Fig. 37. This process indicates detailed car speed calculation strategies (step S2), performed each 5 msec. Here, the car speed Xn is calculated (step P1) by reading out the latest pulse cycle filtered value Ti* from a given address of RAM, and applying an appropriate coefficient to an inverse number of the Ti*. Then, using the preceding car speed filtered value X * / n -1 and the latest car speed Xn, the latest car speed filtered value Xn * is determined by the equation 30 (m = 4) (Step P3), and put into RAM. All this done, the next process is proceeded to. In this preferred embodiment, a primary integrating filter is cited as an example, but this filtered value calculation is applicable to a secondary or other filters. As described on the previous pages, in this car speed sensing scheme, pulse cycle Ti in a give number (4 in this embodiment) is determined by synchronizing with each pulse of pulse signals from a car speed sensor 6, the value is filtered by the equation 22 to calculate pulse cycle filtered value Ti*, which is converted at each specified interval into an invert number to determine car speed Xn. Then, the value is filtered with the equation 30 to determine car speed filtered value Xn* and introduced as cruising car speed Vn. Accordingly, disturbance of pulse signals caused by the car speed sensor 6, and also traveling car speeds with less low-frequency modulation can be obtained. For this reason, the traveling car speed Vn is always a true representation of actual car speeds, thereby leading to improved driving stability. More specifically, the pulse cycle calculation procedure in which pulse-to-pulse cycle Ti in synchronism with pulse is also a traveling distance interval synchronization measurement. In this procedure, moreover, time cycle measure ment is carried out at a specified interval to give car speed Xn. Consequently, in the pulse cycle and time synchronization measurements, a modulation waveform and a modulation frequency differ with regard to the same input, thus giving no constant modulation operation. In addition, for pulse synchronization measurement and time synchronization measurement, respectively, appropriate integrating filters are provided to give traveling car speed Vn showing less modulation characteristics. Fig. 38 is a block diagram showing the processing strategies of other embodiments of this invention. The car speed signal from the car speed sensor is deprived of noise by passing the same through a car speed filter 184 according to the previously described method, giving a car speed Vn. A set switch 8 is a switch used to set a target car speed VM. The set switch 8 is turned on to read a car speed Vn at that time into a memory 190. The throttle valve is controlled depending on the difference between the target car speed VM and the car speed Vn. In this perferred embodiment, to compensate for the operation delay of an actuator, and the control lag due to hysterisis and play of the throttle and drivetrain, the skipped car speed VS, where a derivative component ▵V processing the car speed Vn with a derivation means 192 is added to the car speed VM, is employed. And, the difference signal between the target car speed VM and the skipped car speed VS (VM - VS) is provided to a duty conversion means 194 used to determine the duty for controlling said actuator. Said derivative component ▵V from the derivation means 192 is given also to a determination means 168 and a correction means 170. Using the correction means 170, corrected values K1 and K2 are determined according to the derivative component ▵V or vehicle acceleration. When using the determination means 168, the derivative component ▵V or vehicle acceleration is higher than a specified value (during acceleration conditions) or lower (during deceleration conditions), a swtich 172 is thrown on, to give the corrected values K1 and K2 to a duty ratio conversion means 194. The duty ratio conversion means 194 is also provided with a control gain VB for duty ratio control and determines a duty ratio D. Fig. 39 is a graph shwoing the operation of this preferred embodiment. The control using the conventional system is as indicated by (G). For instance, in combined use with an automatic transmission, when a vehicle is moving from a level to a uphill road, the duty ratio increases with decreasing speed, but if a small gear ratio is selected, the car speed decreases due to lack of tractive force. When the difference between the target and actual car speeds reaches the specified value, the gear is shifted down. When this occurs, the traction increases and the car accelerates, but at the time of the shiftdown occuring the duty ratio has become considerably large, and it takes time to reduce the duty ratio to the required value. Hence, the car speed shoots over. In this preferred embodiment, considering that when acceleration (deceleration) is massive, the actual duty ratio is greatly varied from the required duty ratio, the control delay is compensated to prevent overshoot by applying a large correction duty ratio temporarily. Fig. 40 shows an embodiment of the microprocessor-based processing scheme of that indicated in Fig. 38. In this example, a duty ratio D is determined by the following formula: where, FD: correction duty ratio during acceleration conditions FU: corredction duty ratio during deceleration conditions At step q1, a car speed signal is fed from the car speed sensor, and at step q2, a car speed Vn is determined by the filtering method described above. At step q3, an acceleration ▵V is determined from the difference between the car speed previously determined, V n-1 and the latest one, Vn. Step q4 is a step provided to determine whether an acceleration is beyond the specified value (1.25 km/h/sec), and when an acceleration is beyond the specified value, the correction duty ratio, FD, is increased in proportion to the acceleration ▵D (FD ← FD + K1·▵D: K1 = 4) . In this preferred embodiment, the processing cycle is 50 msec; for instance, when the acceleration is 1.25 km/h/sec, ▵V is 0.0625 km/h, and hence, the correction amount becomes FD ← FD + 4x0.0625 = FD = 0.25 . Steps q6 and q7 are provided to set a upper limit γ1 on the correction duty ratio FD, and in this preferred embodiment, the upper limit γ1 of the correction duty ratio FD is set at 20%. When the acceleration is within the specified value (1.25 km/h/sec), the correction duty ratio FD is decreased at step q8 (FD ← FD - β₂:β₂ = 5) . This decrease in correction duty ratio FD should be done quickly, because when the acceleration is within the specified value (1.25 km/h/sec), the correction duty ratio FD has no longer become necessary, and thus it is advantageous, for control purposes, to refrain from making a correction with the correction duty ratio FD. Steps q9 and q10 are provided to set a lower limit on the correction duty ratio FD to prevent FD from dropping below zero or making an inverse correction. Steps q1 to q17 are steps designed to determine a correction duty ratio FU during deceleration, in contrast with the steps q4 to q10. A step q11 is a step used to determined whether an acceleration is below the specified value (-1.25 km/h/sec) (or a deceleration is above the value). If an acceleration is below the specified value, a correction duty ratio FU is increased at step q12 depending on the acceleration (FU ← FU + K2·▵V:K2 = 4) . Steps q13 and q14 are given to set an upper limite γ2 on the correction duty ratio FU, and in this embodiment, the limit γ2 is set at 10%. When an acceleration is out of the specified value (-1.25 km/h/sec), the correction duty ratio FD is decreased at step q15 (FU ← FU - β₄:β₄ = 5) . The decrease in the correction duty ratio FU should be as quick as in the case of the correction duty ratio FD. Steps q16 and q17 are designed to set a lower limit on the correction duty ratio FU, thereby preventing the correction duty ratio FU from dropping below 0 or making an inverse correction. Step q18 is a step used to determine a skipped car speed VS, performing operations of a car speed Vn and its derivative component ▵V. Then, at step q13, a duty ratio D is determined from the aforestated various values in accordance with the equation. At step q20, a duty ratio 20 is put out, and is used to control the actuator (step q21). In sum, the forgoing process consists of determining an output duty ratio D by the following equation, and of varying correction duty ratios FD and FU as follows with the calculation cycle of a microprocessor us a unit of change: 1. If ▵V ≧ α1, then FD ← FD + K1·▵V 2. If V < α1, then FD ← FD - β2 However, 0 ≦αµρ¨ FD ≦αµρ¨ γ1 3. If ▵V ≦αµρ¨ - α2, then FU ← FU + K2·▵V 4. If ▵V > -α2, FU ← FU - β4 when However, 0 ≦αµρ¨ FU ≦αµρ¨ γ² The cases 1 and 3 above refer to the time of compensation, and the cases 2 and 4 represent the resetting time. The resetting constants β2 and β4, and the limiting constants γ1 and γ2 are constant, while the compensation terms K1·▵V and K2·▵V are variables including an acceleration ▵V (K1 and K2 are constants), and are used to change FD and FU in proportion to an acceleration ▵V. In this preferred embodiment, α1 = α2 = 1.25 km/h/ sec, K1 = K2 = 4, β2 = β4 = 5%, γ1 = 20%, and γ² = 10% In this embodiment, the correction duty ratios for acceleration and deceleration are separately processed depending on their characteristics to permit more accurate control. Fig. 41 is another example of the other microprocessor-based processing schemes. Here, a duty ratio D is determined by: Unique features of this embodiment are found in a process 178, where the remaining steps, U1 to U3 and U11 to U14 are identical to q1 to q3 and q18 to q21 in Fig. 40, hence they are left unmentioned here. Step U4 is a step used to determine whether an acceleration is plus or minus, i.e., whether the vehicle is being accelerated or decelerated. If it is being accelerated, a correction duty ratio is obtained at step US (F ← F + K1·▵V : K1 = 4) , and the correction duty ratio F is restricted within its upper limite (γ1 = 20) at steps U6 and U7. If the car is being decelerated, a correction duty ratio F is obtained at step U8 (F ← F + K2·▵V: K2 = 4) , and the duty ratio F is restricted within its upper limit (γ2 = -10) at steps 9 and 10. To sum up, this processing procedure consists of computing an output duty ratio from the following equation, and of changing a correction duty ratio F in accordance with an acceleration ▵V in the following manner: 1. If ▵V ≧ 0, then F ← F + K1·▵V 2. If ▵V < 0, then F ← F + K2·▵V However, - γ 2 ≦αµρ¨ F ≦αµρ¨ γ2 In this embodiment, K1 = K2 = 4, γ1 = 20, γ2 = 10. In this embodiment, a control scheme is simple enough to achieve with a short program, thus allowing curtailed memory capacity. Furthermore, Fig. 42 shows another example of the microprocessor-based processing strategies. A duty ratio D is determined by: The operations in this preferred embodiment, ω1 to ω4, ω5 to ω11, and ω13 to ω21 are not mentioned here since they are identical to q1 to q4, q5 to q11 and q13 to q21 in Fig. 40. Difference between this embodiment and that in Fig. 40 lies in the fact that in the latter correction duty ratios FD and FU are increased or decreased in response to acceleration, while inthis embodiment they are increased or decreased with time. Experessed in other words, if an acceleration is beyond the specified value α1 (α1 = 1.25 km/h/ sec), a correction duty ratio FD is increased in a given amount at step ω5 (FD ← FD + β1 :β1 = 0.25) . If an acceleration is lower than the specified value α2 (α2 = -1.25 km/h/sec), a correction duty ratio FU is increased in a specified amount at ω2 (FU ← FU + β3:β3 = 0.25) . In sum, the forgoing process consists of determining an output duty ratio D by the following equation, and of changing correction duty ratios FD and FU as follows in proportion to time. Supposing the calculation cycle of a microprocessor to be a unit of change: 1. If ▵V ≧ α1, then FD ← FD + β1 2. If ▵V < α1, then FD ← FD - β2 However, 0 ≦αµρ¨ FD ≦αµρ¨ γ1 3. If ▵V ≦αµρ¨ - α2, then FU ← FU + β3 4. If ▵V > - α2, then FU ← FU - β4 However, 0 ≦αµρ¨ FU ≦αµρ¨ γ2 The cases 1 and 3 above refer to the time of compensation, and the cases 2 and 4 represent the resetting time. The increasing and decreasing constants β1 to β4 and the limiting constants γ1 and γ2 are constant, and resetting is rapidly performed with β1 < β2 and β3 < β4. In this example, α1 = α2 = 1.25 km/h/sec, β1 = β3 = 0.25%, β2 = β4 = 5%, γ1 = 20%, and γ2 = 10%. The calculation cycle is 50 msec, so that duty ratio correction is carried out at a rate of 5% (= 0.25% x 20), and its resetting is performed at its twentyfold rate. In this embodiment, there is no need to determine correction duty ratios FU and FD in proportion to car speeds, thereby achieving a shorter program and smaller memory capacity. Different correction duty ratios FD and FU are applied during acceleration and deceleration conditions, and thus control can be maintained so that it suits their respective characteristics. Although detailed descriptions are omitted, in the preferred embodiment in Fig. 41, the correction amount of a correction duty ratio F can be kept constant, i.e., F ← F + β1 at step U5 and F ← F + β2 at step U8. In the examples of Figs. 41 and 42, processing is repeated at specified intervals, hence the longer the time required for correction becomes, the greater a correction duty ratio is. As a result, quicker speeds are achieved at which a car speed converges to the target car speed. This invention further relates to a car speed signal processing circuit of a constant speed traveling device for integrating and processing a car speed signal from the car speed sensor, and using its output in the setting of target car speed and detection of traveling car speed, in which setting is prohibited for a specified time when a car speed change exceeding a specified value occurs in the car speed signal. In this constitution, as shown in FIG.34(B), if the output of the integrating filter changes suddenly in response to input abnormality, the target car speed cannot be set (the memory is cleared) if the preset switch is pressed for a specified time including its converging time (for example, 3 seconds), so that constant speed traveling control at unexpected car speed V' can be securely prohibited although it is impossible to transfer to a constant speed traveling at a car speed V expected by the driver. This method is simpler in processing than the method of removing the noise N2 by the integrating filter in the previous stage (in which prediction is difficult). FIG. 44 is a flow chart showing a processing thereof, in which the calculation cycle is 50 msec. The car speed filter 184 shown in FIG. 38 is the integrating filter, and advancing from step z1 to z3, the difference VR₀ - VR1 of two momentary values of the integrated output is compared with a specified value, and abnormal portion N2 in FIG. 43 is detected. In this case, VR₀ is the present calculated value, and VR1 is the previous calculated value. The car speed filter 184 may be placed somewhere between the buffer 186 and processing circuit 188 in FIG. 10. In this embodiment, the criterion is the acceleration of 1 km/h per 50 msec, therefore, 20 km/h/sec (generally, the limit is about 4 km/h/sec). If a speed change exceeding this standard is detected, the prohibit timer in the processing circuit 188 is set at step z6 to prohibit control in this period, and the prohibition is canceled at steps z7, z9. It means that, if the preset switch 8 in FIG. 10 or FIG. 38 is pressed, data is not stored in the memory 190 or processing circuit 188 (that is, it is cleared). This prohibition of control continues until the prohibit timer expires (for example, 3 seconds), and thereafter the prohibit timer is cleared, and the control mode is set at step z8. As a result, set signal processing is enabled, and when the preset switch 8 is pressed, the output of the car speed filter 184 at that time is stored in the memory 190 and processing circuit 188, and the constant speed traveling control using that output as the target car speed is started at steps z10, z11.

Claims: A constant speed cruise control system of duty ratio control type for approximating an actual tarveling car speed to a stored target car speed, by on/off control of a control valve (10,89a) of an actuator (ACT,102,89,155) to adjust the throttle valve (SL) opening degree by an output duty ratio D obtained from a control line (70) having a gradient showing a conversion characteristic of car speed and duty ratio, characterized in that there is provided a controller (ECU) in which a set duty ratio SD corresponding to the target car speed is calculated as SD = SD1 + (DM - SD1)/n and the output duty ratio D is calculated as D = G x ▵V + SD where G: gradient of control line ▵V: car speed deviation DM: integrating element responding quickly to duty ratio change SD1: integrating element responding slowly to duty ratio change n: constant and the controller (ECU) correcting to integrate the set duty ratio SD in a direction of approximating the output duty ratio D. A constant speed cruise control system of duty ratio control type as claim in claim 1, wherein the controller (ECU) performs calculation in which the integrating element SD1 is calculated as SD1 = SD1 + β and the integrating element DM is calculated as DM = DM + (D - DM)/K where β: constant K: constant A constant speed cruise control system of duty ratio control type as claimed in claim 1, wherein the controller (ECU) changes over the value of n depending on the traveling car speed, and corrects to integrate the set duty ratio SD in a direction of approximating the output duty ratio D. A constant speed cruise control system of duty ratio control type as claimed in claim 2, wherein the controller (ECU) changes over the value of K, depending on the traveling car speed, and corrects to integrate the set duty ratio SD in a direction of approximating the output duty ratio D. A constant speed cruise control system of duty ratio control type as claimed in claim 1, wherein the controller (ECU) quickly changes DM and SD1 when the car speed acceleration ▵Vn exceeds a certain value in correction formulas DM ← DM - A · ▵Vn SD1 ← SD1 - B · ▵Vn where A, B: constants in the units of duty ratio (%)/acceleration, and corrects to integrate the set duty ratio SD in a direction of approximating the output duty ratio D. A constant speed cruise control system of duty ratio control type as claimed in claim 2, wherein the controller (ECU) determines a difference ▵D between the integrating element SD1 and the output duty ratio D, changing β corresponding to the magnitude of the difference ▵D, and correcting to integrate the integrating element SD1 in a direction of approximating the output duty ratio D. A constant speed cruise control system of duty ratio control type as claimed in claim 1, wherein the integrating element SD1 is changed within a range between an upper limit value (C) and a lower limit value (E). A constant speed cruise control system of duty ratio control type as claimed in claim 1, wherein the integrating element DM is changed within a range between an upper limit value (A1) and a lower limit value (B1). A constant speed cruise control system of duty ratio control type as claimed in claim 1, wherein the set duty ratio SD is changed within a range between an upper limit value and a lower limit value. A constant speed cruise control system of duty ratio control type as claimed in claim 2, wherein the controller (ECU) determines a difference ▵D between the set duty ratio SD corresponding to the target car speed and the output duty ratio D, changing β corrresponding to the magnitude of the difference ▵D, and correcting to integrate the set duty ratio SD in a direction of approximating the output duty ratio D. A constant speed cruise control system of duty ratio control type as claimed in claim 2, wherein the controller (ECU) limites the integrating speed by fixing a correction term β of the set duty ratio SD into values differentiated from one another in car speed regions for a specified time after setting the target car speed. A constant speed cruise control system of duty ratio control type as claimed in claim 1, wherein is determined a leading angle car speed advanced in phase from an input car speed by treating the input car speed in a leading angle, the lower order differential term and higher order differential term of the input car speed being determined, the leading angle car speed by adding the product of each differential term and respective coefficient to the input car speed being calculated, and the coefficient of highter order differential term being set smaller in a higher speed region of preset car speed than in a lower speed region. A constant speed cruise control system of duty ratio control type as claimed in claim 1, wherein the system comprising: a car speed sensor (6) for outputting a pulse train having a frequency corresponding to a car speed, means for measuring a time of a specified number of consecutive the pulses in response to the pulses corresponding to a car speed, means for outputting the time measured at a specified time interval, means for outputting as a car speed a value obtained by calculating a inverse number of the time measured in response to an output from the means for outputting the time measured. A constant speed cruise control system according to claim 1, characterized in that the controller (ECU) is correcting to integrate the set duty ratio SD in a direction of approximating the output duty ratio D, by determining the difference ▵D between the set duty ratio SD and the output duty ratio D, and moving the control line parallel at an integrating speed corresponding to the magnitude of the difference D. A constant speed cruise control system of duty ratio control type as claimed in claim 14, wherein the controller (ECU) performs calculation in which the set duty ratio SD is calculated as SD = SD + γ and the output duty ratio D is calculated as D = G x ▵V + SD where G: gradient of control line ▵V: car speed deviation γ: constant A constant speed cruise control system of duty ratio control type as claimed in claim 14, wherein the set duty ratio SD is changed within a range between an upper limit value and a lower limit value. A constant speed cruise control system of duty ratio control type as claimed in claim 15, wherein the integrating speed is limited by fixing γ at a certain value for a specified time after setting the target car speed. A constant speed cruise control system of duty ratio control type as claimed in claim 17, wherein the value γ is selected for differentiated values in car speed regions. A constant speed cruise control system of duty ratio control type as claimed in claim 14, wherein the controller quickly changes the set duty ratio SD when the car speed ▵Vn exceed a specified value. A leading angle control method of a constant speed cruise control system of duty ratio control type for approximating an actual traveling car speed to a stored target car speed by determining a acceleration by differentiating the traveling car speed obtained from a car speed signal, calculating a leading angle car speed by adding the acceleration to the traveling car speed, and on/off control of a control valve (10,89a) of an actuator (ACT,102,89,155) to adjust a throttle valve opening degree by the output duty ratio obtained from a conversion characteristic between the leading angle car speed and a duty ratio, wherein a correction duty ratio is added to the output duty ratio when the acceleration exceeds a specified value, characterized in that the correction duty ratio is increased in proportion to the acceleration. A leading angle control method of a constant speed cruise control system of duty ratio control type as claimed in claim 20, wherein the specified value is unequal to zero. A leading angle control method of a constant speed cruise control system of duty ratio control type as claimed in claim 20, wherein the specified value is zero. A leading angle control method of a constant speed cruise control system of duty ratio control type as claimed in claim 20, wherein the correction duty ratio is increased together with passing of the time.

Inventors: HITOTSUYA, MASAKI C/O FUJITSU TEN LTD., MASUDA, JIRO C/O FUJITSU TEN LTD., MIYAZAKI, AKIRA C/O FUJITSU TEN LTD., NAGASAKA, MASUMI TOYOTA JIDOSHA KABUSHIKI KAISHA, TACHIBANA, TAKESHI TOYOTA JIDOSHA KABUSHIKI KAISHA, TAKAHASHI, JUNJI C/O FUJITSU TEN LTD., TAKAHASHI, MINORU C/O FUJITSU TEN LTD., TERATANI, TATSUO TOYOTA JIDOSHA KABUSHIKI KAISHA, YAMASAKI, HIROFUMI C/O FUJITSU TEN LTD.
Applicants: FUJITSU TEN, LTD., TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1986
Main classification: B60K31
IPC codes: B60K31