JPH04370765A - Calculating method for vehicle speed at time of low speed - Google Patents

Abstract

PURPOSE:To obtain a calculation method which can also calculate a vehicle speed at the time of a low vehicle speed accurately. CONSTITUTION:This method consists of a step for obtaining a vehicle speed at a time when a (N-1)th pulse is generated according to a time interval T(N-1) from a time where a (N-2)th pulse is generated to a time when the (N-1)th pulse is generated out of pluses which are generated in proportion to the vehicle speed, a step for obtaining the vehicle speed at a time when an (N)th pulse is generated according to a time interval T(N) from the time where the (N-1)th pulse is generated to the time where the (N)th pulse is generated, a step for obtaining a difference between the vehicle speed at the time where the (N-1)th pulse which is obtained in this manner is generated and that at the time where the (N)th pulse is generated and a change rate of the vehicle speed at the time the (N)th pulse is generated according to the time interval T(N), and a step for calculating the vehicle speed assuming that the vehicle speed changes based on the above change rate of the vehicle according to the vehicle speed at the time when the (N)th pulse is generated.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention provides means for generating pulses proportional to the rotation, that is, vehicle speed, in a rotating member of a drive system of a vehicle, and based on the pulses generated from this pulse generating means, the vehicle speed, particularly This article relates to a method of calculating vehicle speed at low speeds.

0002

[Prior Art] Pulse generating means is provided for generating pulses proportional to the rotation of drive system rotating members such as transmission output shafts, propeller shafts, axle shafts, wheels, etc. whose rotation speed is proportional to the vehicle speed. A method of calculating the vehicle speed by counting the number of pulses from the pulse generating means and measuring the time interval between the pulses while the vehicle is running is well known. When calculating vehicle speed in this way, if the vehicle speed is calculated by measuring the time interval for each pulse, variations due to wheel slip etc. will be directly reflected in the calculated value, and the calculated vehicle speed Therefore, each time a predetermined number of pulses are counted, the time intervals of the predetermined number of pulses are averaged, and the vehicle speed is calculated based on this average time interval to eliminate the dispersion in the calculated vehicle speed. It is designed to prevent it from getting bigger.

However, this pulse generating means usually
Pulses are generated 4 to 6 times per rotation of a car tire, and 4 to 6 is used as the predetermined number, so this predetermined number of pulses is counted and the vehicle speed is calculated for the first time. This is when the vehicle speed reaches several km/h. That is, in the conventional vehicle speed calculation method described above, the vehicle speed is not calculated until the vehicle speed reaches several km/h. If the vehicle speed is simply calculated for the purpose of displaying the vehicle speed using a speedometer, there is no problem even if such a low vehicle speed is not calculated. However, for example, in the case of electrical control of the clutch opening of a hydraulic continuously variable transmission proposed by the present applicant (Japanese Patent Laid-Open No. 1-101240, etc.), it is difficult to accurately determine the vehicle speed at extremely low vehicle speeds. There may be cases where this is necessary, and in such cases, there is a problem in that conventional vehicle speed calculation methods cannot provide a sufficient response.

[0004] For this reason, the present applicant has
As disclosed in Japanese Patent Publication No. 121759, a vehicle speed calculation method that can also calculate a low vehicle speed at the time of starting has been proposed. In this method, when starting a vehicle from a stopped state, until a predetermined number of N pulses are counted, each count is based on the time interval from the first pulse to the current pulse. When the number of pulse counts reaches a predetermined number n or more, the vehicle speed is calculated from the average value of the time intervals of the n pulses each time the pulse is counted n times.

[0005]

[Problem to be Solved by the Invention] However, in both methods, the vehicle speed is calculated by considering the vehicle speed between each pulse to be constant. Therefore, the detected vehicle speed is calculated based on the assumption that the vehicle speed is constant between each pulse. It becomes step-like. When the time interval between pulses is extremely short, such as at medium-high vehicle speeds, the vehicle speed changes in extremely small steps, and there is no practical problem, but when the pulse generation interval is long, such as at low vehicle speeds. However, if the vehicle speed is assumed to be constant during this long pulse interval, there is a problem in that the error between the actual vehicle speed and the calculated vehicle speed becomes large. For this reason, for example, if the clutch opening degree control of the hydraulic continuously variable transmission is performed using the calculated vehicle speed with such an error, there is a problem that it is difficult to perform good clutch control.

[0006] It is also conceivable to use a pulse generating means that generates a large number of pulses per rotation of the wheel so as to be able to calculate the vehicle speed at low vehicle speeds, but in this case, There is a problem in that the pulse generating means conventionally used as a vehicle speed sensor cannot be used, and a new special vehicle speed sensor (pulse generating means) must be created. Furthermore, when such a special vehicle speed sensor is used, there is a problem that the time interval between pulses becomes too short at high vehicle speeds, reducing the accuracy of measuring this time and causing variations in the calculated vehicle speed. be.

In view of these problems, the present invention aims to provide a vehicle speed calculation method that can accurately calculate vehicle speed even at low vehicle speeds using a conventionally used vehicle speed sensor. purpose.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the vehicle speed calculation method of the present invention calculates the (N-2)th pulse from the (N-2)th pulse generation point among the pulses generated in proportion to the vehicle speed.
From the time interval up to the N-1)th pulse generation time (N
-1) The step of calculating the vehicle speed at the time of the th pulse generation, and the step of determining the vehicle speed at the time of the (N)th pulse generation from the time interval from the time of the (N-1)th pulse generation to the time of the (N)th pulse generation. The step of calculating the vehicle speed, the vehicle speed at the (N-1)th pulse generation time determined in this way, and the (N
) difference from the vehicle speed at the time of pulse generation, and (N-
1) Calculating the rate of change in vehicle speed at the (N)th pulse generation point from the time interval from the (N)th pulse generation point to the (N)th pulse generation point; and and calculating the vehicle speed on the assumption that the vehicle speed changes from the vehicle speed at the (N)th pulse generation point to the (N+1)th pulse generation point based on the rate of change in vehicle speed. .

[0009]

[Operation] When calculating vehicle speed using the above method,
Since the vehicle speed change between each pulse is calculated by predicting the vehicle speed change rate between the previous pulse,
The vehicle speed change between each pulse calculated in this way is close to the actual vehicle speed change. Therefore, even when the pulse generation interval is long, such as when the vehicle speed is low, the calculated vehicle speed during this long pulse interval becomes a value close to the actual vehicle speed, and accurate vehicle speed calculation is performed. Moreover, since accurate vehicle speed calculation can be performed even if the pulse interval is long, there is no need to use a special vehicle speed sensor, and a conventional vehicle speed sensor can be used as is.

Note that from the (N)th pulse generation time (
Until the time when the N+1)th pulse is generated, the vehicle speed is integrated every predetermined calculation cycle using the rate of change that is corrected by multiplying the rate of change in vehicle speed used in the previous calculation by the predicted speed coefficient Kv (<1). It is preferable to do so. In this way, the calculated vehicle speed change becomes closer to the actual vehicle speed change, and more accurate vehicle speed calculation can be performed.

[0011]

[Example] A hydraulic continuously variable transmission in which the clutch opening degree at the time of starting and stopping is controlled based on the vehicle speed calculated by the vehicle speed calculation method of the present invention will be described below as an example. . As shown in FIG. 1, this continuously variable transmission T includes a constant displacement hydraulic pump P driven by an engine E via an input shaft 1, and a variable displacement hydraulic motor M driving wheels W.
It has The hydraulic pump P and the hydraulic motor M are connected to a first oil passage La which communicates the discharge port of the pump P and the suction port of the motor M, and the suction port of the pump P and the motor M.
The two oil passages constitute a hydraulic closed circuit and are connected to the second oil passage Lb which communicates the discharge ports of the two oil passages. Note that the output shaft 2 of the hydraulic motor M is connected to the wheels W via a forward/reverse switching unit 8. Therefore, when the hydraulic pump P is driven by the engine E, the hydraulic motor M is rotationally driven by the oil pressure from the hydraulic pump P, and this rotation is transmitted to the wheels W via the output shaft 2 and the forward/reverse switching unit 8. W is driven. Here, the hydraulic motor M is, for example, a swash plate axial piston motor, and by controlling the angle of this swash plate, the gear ratio of the transmission T can be varied steplessly.

On the other hand, the discharge port of the charge pump 10 driven by the engine E connects to the hydraulic closed circuit via a charge oil passage Lg having a check valve 11 and a third oil passage Lc having a pair of check valves 3, 3. The hydraulic oil pumped up from the oil tank 15 by the charge pump 10 and regulated by the charge pressure relief valve 12 is transferred to the lower pressure of the two oil passages La and Lb by the action of the check valves 3, 3. It is supplied to the side oil passage. Further, a fourth oil passage Ld having a shuttle valve 4 to which a fifth oil passage Le having a low pressure relief valve 6 and connected to an oil tank 15 is connected is connected to the closed circuit. This shuttle valve 4 is a 2-port 3-position switching valve, and operates according to the oil pressure difference between the first and second oil passages La, Lb, and is operated in accordance with the oil pressure difference between the first and second oil passages La, Lb. The passage is connected to the fifth oil passage Le. As a result, the relief oil pressure in the oil path on the low pressure side is regulated by the low pressure relief valve 7, and an amount of hydraulic oil corresponding to the amount of oil supplied via the check valve 3 is supplied via this fifth oil path Le. It is discharged into tank 15.

[0013] A sixth oil passage Lf is also provided between the first and second oil passages La and Lb to short-circuit both oil passages. A clutch valve 5 consisting of a variable throttle valve is provided. Therefore, by controlling the throttle amount of the clutch valve 5, the amount of oil supplied from the hydraulic pump P to the hydraulic motor M is controlled.
Clutch control can be performed to control the driving force of the engine. The operation of the clutch valve 5 is controlled by a clutch servo unit 30, and the operation of the clutch servo unit 30 is controlled by a pair of solenoid valves 45 and 46 whose duty ratio is controlled in response to a signal from a controller 40. The structure and operation of this clutch servo unit 30 will be explained with reference to FIG. 2.

The clutch servo unit 30 includes a cylinder member 31, a piston member 32 fitted into the cylinder member 31 so as to be slidable left and right in the figure, and a piston member 32.
It consists of a cover member 35 that is attached to cover the cylinder chamber into which the piston member 32 is fitted, and a spring 37 that urges the piston member 32 to the left in the figure. Piston 32a of piston member 32
The above cylinder chamber is divided into two, left and right cylinder chambers 33, 3.
Port 3 is formed in both cylinder chambers 33 and 34.
Hydraulic lines 51 and 54 are connected via 6a and 36b. The hydraulic pressure in the hydraulic line 50 is supplied by the charge pump 10.
The pressure of the discharged oil is regulated by the charge pressure relief valve 12, and this is the hydraulic oil that is led through the hydraulic line 50. The hydraulic pressure of the hydraulic line 54 is the hydraulic pressure of the hydraulic line 5
Hydraulic line 5 having orifice 52a branched from 0
This is the oil pressure obtained by controlling the oil pressure of No. 2 by two solenoid valves 45 and 46 whose duty ratio is controlled. The solenoid valve 45 controls the flow rate of hydraulic oil from the hydraulic line 52 having the orifice 52a to the hydraulic line 53 according to the duty ratio. The solenoid valve 46 is connected to a hydraulic line 55 that branches from the hydraulic line 53.
and a hydraulic line 56 that communicates with the drain side via the orifice 56a, and causes hydraulic oil to flow from the hydraulic line 56 to the drain side in accordance with the duty ratio.

Therefore, the charge pressure regulated by the charge pressure relief valve 12 acts on the right cylinder chamber 32 via the hydraulic line 51, while the two solenoid valves 45, 46 are supplied from the hydraulic line 54. The pressure lower than the charge pressure created by the operation of the left cylinder chamber 33
supplied to Here, since the pressure receiving area of the right cylinder chamber 34 is smaller than the pressure receiving area of the left cylinder chamber 33, the force that the piston member 32 receives due to the hydraulic pressure in the left and right cylinder chambers 33, 34 is determined by considering the biasing force of the spring 37. The hydraulic pressure P1 in the right cylinder chamber 34 is balanced when the hydraulic pressure in the left cylinder chamber 33 is a predetermined value P2 (P1>P2) lower than this. Therefore, by controlling the hydraulic pressure supplied from the hydraulic line 54 to the left cylinder chamber 33 using the solenoid valves 45 and 46, the piston member 32 can be moved to the right, and the left cylinder chamber 33 can be moved to the right. If the hydraulic pressure supplied to the chamber 33 is controlled to be smaller than P2, the piston member 32 can be moved to the left.

This movement of the piston member 32 in the left and right direction is transmitted to the clutch valve 5 via the link mechanism 38. The clutch valve 5 includes a fixed member 5a having a first valve hole 5b, and a second valve rotatably disposed within the fixed member 5a.
It consists of a rotating member 5c having a valve hole 5d. An arm 5e connected to the rotating member 5c is connected to the link mechanism 38, and as the piston member 32 moves, the rotating member 5c is rotated. When the rotating member 5c is rotated, the degree of communication between the first and second valve holes 5b and 5d changes from fully open to fully closed. As shown in the figure, when the piston member 32 moves to the left to the maximum, the communication opening degree in the clutch valve 5 becomes fully open, and after this, the piston member 3
2. The degree of communication opening gradually changes as it is moved to the right until it is fully closed. Here, the first valve hole 5b communicates with the first oil passage La constituting the closed circuit of the continuously variable transmission T, and the second valve hole 5d communicates with the second oil passage Lb. and the second
By changing the communication opening degree of the valve holes 5b and 5d, it is possible to change the opening degree of the sixth oil passage Lf, which is a short-circuit path between the first and second oil passages La and Lb, and thereby the clutch control is performed. It will be done.

This clutch control is performed to smoothly start and stop the vehicle, and is controlled in accordance with the accelerator opening (accelerator pedal depression amount or engine throttle opening), engine speed, vehicle speed, etc. The controller 4 controls the clutch valve 5 so that the desired opening degree of the clutch valve 5 is obtained.
A duty ratio drive signal is output from 0 to the solenoid valves 45 and 46 via control wiring 45a and 46a. Therefore, the controller 40 receives the throttle opening detection signal from the engine throttle sensor 21 via the wiring 2.
1a, an engine rotation speed signal is input from the engine rotation sensor 22 via the wiring 22a, and an intake negative pressure signal is input from the engine intake negative pressure sensor 23 through the wiring 23a.
A pulse signal proportional to the vehicle speed is input from the vehicle speed sensor 24 via the wiring 24a. In addition to these signals, the controller 40 also receives a swash plate tilt angle signal of the hydraulic motor M, a shift lever position detection signal, and the like. Based on such input signals, the controller 40 determines the current state of the engine (throttle opening, rotational speed, etc.), vehicle speed, etc., and sets, for example, the clutch valve opening required at that time. , a drive signal is output to the solenoid valves 45 and 46 so as to achieve this set clutch opening degree.

Although not shown, the continuously variable transmission T also has a speed change servo unit that controls the swash plate angle of the hydraulic motor M, and the operation of this speed change servo unit is also controlled by the controller 40. . The controller 40 controls the operation of the clutch servo unit 30 and the speed change servo unit, and clutch control and speed change control as shown in FIG. 3 are performed as follows. FIG. 3 is a graph showing the relationship between engine speed and vehicle speed.
The straight line LOW is the line with the maximum gear ratio, and the straight line TOP is the line with the lowest gear ratio.

[0019] Here, control when starting from a stopped state will be taken as an example. When the vehicle is stopped, the gear ratio is LOW, and when the accelerator pedal is depressed from this state, the engine speed increases. When the engine speed increases to a certain extent, control is performed to gradually close the clutch valve 5. As a result, as shown by line a, the engine speed and vehicle speed increase. In addition, this clutch valve 5
Since the degree of opening is controlled in accordance with the vehicle speed, etc. (details of this control will be described later), it is necessary to accurately detect the vehicle speed at this time. However, the vehicle speed at this time is quite low and it is difficult to accurately detect the vehicle speed using only the vehicle speed sensor 24. Therefore, in the present invention, the vehicle speed sensor 24
The system uses a calculation method that obtains accurate vehicle speed based on pulses from the vehicle. This enables accurate vehicle speed determination even at low vehicle speeds, accurate clutch valve closing control, and smooth start.

In this way, when the clutch valve 5 is completely closed, the speed is increased until the engine speed rises to a predetermined speed while keeping the gear ratio at its maximum (line b), and then the engine speed is maintained at a constant speed. The gear ratio is controlled so that the vehicle speed remains unchanged (line c). After the gear ratio has been shifted to the minimum in this manner, when the accelerator pedal is further depressed, the vehicle speed is increased as the engine speed increases while the gear ratio remains at the minimum (lines d and h). However, the change in vehicle speed along the line a → b → c → d → h is the change when the accelerator pedal is pressed slowly and the vehicle starts slowly, and when the accelerator pedal is pressed more firmly (
For example, in the case of a sudden start where the driver is pressed deeply, for example, the line e→
It changes along f→g→h, and clutch valve closing and gear change control are performed on the high rotation side of the engine.

Operation control of the clutch servo unit 30, ie, clutch control, by the controller 40 will be explained. This control is performed as shown in the block diagram of FIG. The accelerator opening (or throttle opening) and vehicle speed are detected (blocks B2 and B3), and the corresponding target engine speed Neo and target clutch opening C are detected.
Find Lo (blocks B4, B6). Specifically, a map or table showing the target engine speed and target clutch opening is set in advance in correspondence with the accelerator opening and vehicle speed, and the target engine corresponding to the accelerator opening and vehicle speed detected from this map is set in advance. These are determined by reading the rotational speed and target clutch opening.

This target engine rotation speed Neo is compared with the actual engine rotation detected in block B1, and a target clutch correction value corresponding to the difference is determined (block B5). Note that this target clutch correction value is also set in advance in the form of a map corresponding to the difference in engine speed. Next, by correcting the target clutch opening degree using this target clutch correction value, the final target clutch opening degree is obtained, and a clutch servo unit is configured to set the actual clutch opening degree to this final target clutch opening degree. 30 operational controls are performed.

[0023] Such control is normally performed when the vehicle speed is low, and the vehicle speed detection (block B3) in the above control is likely to be inaccurate, and if this is inaccurate, smooth clutch control may not be achieved. become unable to do so. Therefore, in the present invention, the following vehicle speed calculation is performed in order to detect the vehicle speed as accurately as possible. In FIG. 5, this vehicle speed calculation is output at time t(N) (N
An example will be described in which the vehicle speed V0 is determined at a time point t0 after the )th pulse (point C in the figure).

[0024] When calculating this vehicle speed, first, (N-2
Based on the time T(N-1) from the )th pulse (two previous pulses) to the (N-1)th pulse, (N-1
The vehicle speed V(N-1) at time t(N-1) (point A in the figure) when the )th pulse is output is calculated. Note that the time T(N-1) is obtained by counting the number of timer pulses output every 10 ms, for example. Similarly, (
Based on the time T(N) from the N-1)th pulse to the (N)th pulse, the vehicle speed V(N) at the time t(N) (point B) when the (N)th pulse is output. ) is also calculated. Next, calculate the rate of change in vehicle speed (the slope of the straight line connecting points A and B) from time t (N-1) to time t (N),
From time t(N) to time t(N+) when the next pulse is output
Up to 1), the vehicle speed V0 at time t0 is calculated on the assumption that the vehicle speed changes based on the calculated vehicle speed change rate.

In the above manner, a vehicle speed close to the actual vehicle speed can be obtained even in the case of a low vehicle speed.The actual vehicle speed calculation by the controller 40 will be explained using the flowchart shown in FIG. In this flow, first, it is determined whether the vehicle speed V(n) calculated in the previous flow is 6 km/H or more (step S1). When the vehicle speed V(n) exceeds 6 km/H, the vehicle speed is calculated as before.
That is, since there is no problem in calculating the vehicle speed from the average value of the time intervals of a plurality of pulses, the vehicle speed is not calculated using this flow. Therefore, only when the vehicle speed V(n) is 6 km/H or less, the process proceeds to the next step S2, and the predicted vehicle speed increase V
A calculation of f is performed.

This predicted vehicle speed increase Vf is determined by the formula Vf={(V
(n)-V(n-1))×Kv}/CT...
(1) Calculated as follows. This flow is repeated at every predetermined calculation period (for example, 40 ms), and the predicted vehicle speed increase Vf is calculated using equation (1) at each calculation period. Therefore, in equation (1), V(n) and V(
n-1) means the vehicle speed calculated in the previous flow and the flow before the previous time, respectively, and CT is this calculation cycle. Also,
Kv is a smoothing coefficient, and is set to a value smaller than 1.0 (0.9 in this example). This means that the change in vehicle speed when the vehicle starts is generally as shown by the chain line in Figure 5.
This is based on the fact that the vehicle speed changes in an upwardly convex curved shape, and by multiplying the calculation for each calculation cycle by the smoothing coefficient Kv, the vehicle speed change becomes an upwardly convex curved shape, which is closer to the actual vehicle speed change. This is what we are trying to do. Note that the calculation using equation (1) above is a vehicle speed calculation between each pulse, and at the time each pulse is output, the current vehicle speed and vehicle speed change rate are calculated based on the previous and previous pulses. , and using these as initial values, calculation of the predicted vehicle speed increase Vf according to equation (1) is started until the next pulse is output.

Once the predicted vehicle speed increase Vf is calculated in this way, next in step S3, V(n)>V(n
-1), that is, whether or not the speed is increasing. This determination is made because the value calculated by equation (1) within the controller 40 is an absolute value. If V(n)>V(n-1), the process proceeds from step S4 to S5, and the calculated vehicle speed V of the previous flow is
(n) is stored as V(n-1), and the vehicle speed obtained by adding the predicted vehicle speed increase Vf to the calculated vehicle speed V(n) of the previous flow is stored as a new V(n). Also, V(n)≦V(n
-1), the process proceeds from step S6 to S7;
The calculated vehicle speed V(n) of the previous flow is stored as V(n-1), and the vehicle speed obtained by subtracting the predicted vehicle speed increase Vf from the calculated vehicle speed V(n) of the previous flow is stored as a new V(n). .

New V(n) calculated in this way
and V(n-1) are used to calculate the predicted vehicle speed increase Vf according to equation (1) as the vehicle speeds calculated in the previous flow and the flow before the previous flow in the next flow. Thereafter, by repeating this flow every predetermined calculation cycle, accurate vehicle speed calculation can be performed even at low speeds.

Next, the specific contents of the operation control of the clutch servo unit 30 by the controller 40, that is, the clutch control, will be explained in detail using the flowcharts shown in FIGS. 7 to 9. In addition, in these figures, the same alphabets circled mean that they are connected. In this control, first, in step S11, it is determined whether the shift lever position is one of D, S, L, and R, that is, whether it is in a position to drive the vehicle. If the shift lever position is neither of these positions, the process proceeds to step S12, and it is determined whether the shift lever position is P or N, that is, whether the shift lever position is in a neutral state. Shift lever position is D, S, L
, R, the process advances to step S15.

On the other hand, the shift lever position is D, S, L, R.
If it is neither, it must be P or N. However, since there may be cases where there is no input indicating the shift lever position (for example, when the shift position detection switch is broken), if the shift lever position is determined to be neither P nor N in step S12, The process is performed assuming that the shift lever position is in the D range. Therefore, in this case as well, step S15
This is how the failsafe works. When it is determined in step S12 that the shift lever position is P or N, step S13
At this point, the output is fixed to the N range and the current flow ends.

In step S15, it is determined whether the accelerator is off (accelerator opening is almost fully closed), and when the accelerator is off, it is determined whether or not the engine rotation Ne has abnormally decreased (step S15). S16). As long as there is no abnormal decrease, the process proceeds to step S17, where a target clutch opening degree for neutral (N) corresponding to the vehicle speed is set, and the current flow ends. This abnormal decrease in engine speed Ne occurs, for example, when driving in the wrong direction on a slope.
In such a case, there is a possibility that as the vehicle speed increases, the target clutch opening degree becomes closed, the clutch is connected, and the engine stalls. Therefore, when an abnormal decrease in engine rotation occurs, the process does not proceed to step S17, but proceeds to step S18, and control according to this step is performed.

Note that the process also proceeds to step S18 when the accelerator is on, that is, when the accelerator pedal is depressed. In step S18, it is detected whether the vehicle speed V has reached the clutch connection completion vehicle speed Vc, and if V>Vc, the process proceeds to step S19, where an output is performed to fully close the clutch opening, and the current flow is started. end. On the other hand, V≦
When Cc, clutch opening control is necessary, and the process proceeds to steps S20 and S21, where it is determined whether the brake is on and whether the accelerator is on.

[0033] When the brake is on and the accelerator is off,
That is, when the accelerator pedal is released and the brake is pressed to decelerate while driving, step S22 is performed.
- Performs control in S24. Here, since the accelerator is off, the table (or map) is searched for the target clutch opening degree CLo corresponding to the vehicle speed V. In this table, the target clutch opening CLo is set so that the clutch is closed as the vehicle speed increases, but it differs when the shift lever position is in the S or L range and when it is in the D range. Different tables are set up. This is to make the driving feel different depending on the range.In the D range, the vehicle speed at which the clutch begins to open in response to vehicle speed deceleration is set higher than in the S and L ranges, and the effectiveness of engine braking is increased. is being moderated.

In cases other than the above, that is, when the brake is on and the accelerator is on, or when the brake is off regardless of the accelerator, steps S25 to S2 are performed.
7 control is performed. In this case, a map search is performed for the target clutch opening CLo corresponding to the accelerator opening CL and the vehicle speed V. In this map, a target clutch opening CLo is set so that the clutch is closed as the vehicle speed increases, and the target clutch opening CLo is set to increase as the accelerator opening increases. There is. Even in this case, the shift lever position is S or L.
Different maps are set for range and D range. Specifically, the D range is set so that the vehicle speed corresponding to each clutch opening is lower and the accelerator opening is smaller than in the S and L ranges. As a result, the clutch engagement when starting is D
In the range, the speed is gentler than in the S and L ranges. On the other hand, in the S and L ranges, the car starts with a slightly half-clutch, and the clutch engages when the engine speed is high, resulting in a sporty start.

When the search for the target clutch opening degree CLo is completed in this manner, the process then proceeds to step S28, where the target clutch opening degree CLo is corrected based on the engine intake negative pressure Pb. This correction is for performing clutch control that matches the engine output, and is based on the difference between the target engine intake negative pressure Pbo (for example, Pbo = 600 mmHg in this example) and the actual intake negative pressure Pba. Degree C
Lo is corrected. Specifically, the smaller the engine output, that is, the larger the difference between the target engine intake negative pressure Pbo and the actual intake negative pressure Pba, the smaller the target clutch opening degree CLo.
A correction is made to reduce the value.

Next, the process proceeds to step S29, where it is determined whether the vehicle speed is extremely low, that is, whether the vehicle speed V<6 km/H. If the vehicle speed is extremely low, detailed control is required, so the control from step S30 onwards is performed. Note that the vehicle speed at this time is determined as explained in FIGS. 5 and 6. First, in step S30, a target engine rotation speed Neo corresponding to the current accelerator opening degree is searched from a table in which target engine rotation speed Ne is set corresponding to the accelerator opening degree. Then, this target engine speed Neo and the actual engine speed Nea
(step S31), and a table search is performed for the clutch opening correction coefficient eCLO corresponding to this deviation (step S32). In this table, correction coefficients are set in advance so that the clutch opening degree is corrected to reduce the above-mentioned deviation.

However, since the absolute value of the deviation is calculated, the process proceeds to step S33, and it is determined whether Neo>Nea. When Neo≦Nea, the correction coefficient eC
The target clutch opening degree CLo is corrected to the closing side (FIX side) by LO (step S34). On the other hand, Neo > Ne
a, the actual engine speed Nea is increased to bring it closer to the target engine speed Neo,
The target clutch opening CLo is corrected to the opening side (N side) using the correction coefficient eCLO (step S35).

Since the target clutch opening CLo at extremely low vehicle speeds is set in steps S30 to S35, the process then proceeds to step S38, where the difference between the actual clutch opening CLa and this target clutch opening CLo is determined. Calculate the deviation. Then, clutch opening degree control is performed so that this deviation becomes zero, that is, the actual clutch opening degree CLa is brought closer to the target clutch opening degree CLo. However, in this clutch opening degree control, the control speed is varied depending on the accelerator opening degree. For this reason, the accelerator opening degree is divided into three stages: high, medium, and low accelerator opening degrees, and in steps S39 and S40 it is determined in which stage the actual accelerator opening degree is. Then, a clutch opening control speed is set according to each stage, and control is performed based on this control speed (steps S41, S42, S43). This makes it possible to obtain a clutch control response that corresponds to the accelerator operation.

In the above, the case of extremely low vehicle speed has been explained, but when the vehicle speed increases and exceeds the extremely low vehicle speed region,
Control moves from step S29 to step S38 via steps S36 and S37. The control in step S37 is performed at the time of transition from the control at extremely stopped speed to the control at normal vehicle speed. This is to make a smooth transition when the target clutch opening degree (target clutch opening degree) is different from the target clutch opening degree set by control at normal vehicle speed (control without correction control from steps S30 to S35). Therefore, in step S36, it is determined whether the flag FSL, which is set at the time of transition from control at extreme stop speed to control at normal vehicle speed, is set (FSL=1).

If FSL=1, step S3
Proceeding to step 7, smooth control is performed. The details of this smooth control will be explained based on the flow of FIG. 10. This control is also performed every predetermined calculation cycle, and the corrected opening is set to the previous target clutch opening CLi obtained in the previous calculation (immediately after the transition, it is the target clutch opening obtained by extremely low vehicle speed control). By adding Ks, the current target clutch opening degree CLp to be set this time is calculated (step S51).

Next, the difference S between the set clutch opening CLo set in the flowcharts of FIGS. 7 to 9 and the current target clutch opening CLp is calculated (step S52), and it is determined whether this difference S is positive or not. to decide. If this difference S is negative, there is no problem in shifting to normal speed control, so the process proceeds to step S56, the flag FSL is cleared, and the process proceeds to step S60. Furthermore, it is determined whether this difference S is larger than a predetermined opening degree Ds (for example, 3 degrees). Even in the case of S≦Ds, there is no problem in shifting to normal vehicle speed control as it is, so step S56
The process proceeds to step S60, where the flag FSL is cleared (FSL=0). If S>Ds, the process advances to step S55 and sets the flag FSL (FSL=
(set to 0).

Next, calculations in steps S57 to S59 are performed. Here, a predetermined coefficient Dk (in this example, D
k=0.4) to obtain the corrected opening degree Ks. The value obtained by adding this corrected opening degree Ks to the current target clutch opening degree CLp is stored as the previous target clutch opening degree CLi, and the previous target clutch opening degree CLi is set as the set target clutch opening degree CLo. After this, step S60
Proceed to. In step S60, the set target clutch opening degree CLo is stored as the current target clutch opening degree CLp. Hereafter, this flow is repeated every predetermined calculation cycle,
A target clutch opening degree CLo is set each time.

Setting of the target clutch opening degree by this smooth control will be explained in detail with reference to FIG. 11. In addition, Figure 11
The following description will be made assuming that control at a very low vehicle speed shifts to control at a normal vehicle speed at the time point to in the graph. Immediately after the transition, the previous target clutch opening CLi is the target clutch opening obtained by extremely low vehicle speed control, which is 20 in this example.
degree. Immediately after the transition, the initial value of the corrected opening degree Ks is zero, and the current target clutch opening degree CLp at this time is equal to the previous target clutch opening degree CLi. On the other hand, the set target clutch opening degree CLo is a target clutch opening degree obtained by normal speed control, and is 30 degrees in this example. Since the difference S between the two is 10 degrees, which is larger than the predetermined opening Ds (=3 degrees), the corrected opening Ks is obtained by multiplying this difference S by a predetermined coefficient Dk (=0.4). In this example, the corrected opening degree Ks=4 degrees.

The value obtained by adding this corrected opening degree Ks (=4 degrees) to the current target clutch opening degree CLp (=20 degrees) is set as the previous target clutch opening degree CLi and the set target clutch opening degree CLo. Then, this set target clutch opening degree C
Clutch control is performed based on Lo (=24 degrees). If smooth control is not performed, the target clutch opening degree in extremely low vehicle speed control immediately before the transition is 20 degrees, and this changes rapidly to 30 degrees when transitioning to normal speed control, but with smooth control, the target clutch opening degree is 20 degrees. It only changes once in a while, resulting in a smooth transition.

Hereinafter, if the smooth control shown in FIG. 10 is repeated using the newly set target clutch openings CLi, CLp, and CLo, the target clutch opening in extremely low vehicle speed control will be reduced as shown by the solid line in FIG. The clutch opening degree can be smoothly changed to the target clutch opening degree for normal speed control. Note that when smooth control is not performed, the change in the target clutch opening degree is as shown by the dotted line in FIG. 11. Thereafter, when the process shifts to normal speed control, that is, when the process moves to step S56 and the flag FSL is cleared, control is performed that directly leads to step S38 without passing through step S37.

[0046]

[Effects of the Invention] As explained above, according to the present invention,
Vehicle speed is calculated based on pulses that are generated in proportion to vehicle speed, but in this case, the vehicle speed change between each pulse is calculated by predicting the vehicle speed change rate between the previous pulses. Therefore, the vehicle speed change between each pulse calculated in this way is close to the actual vehicle speed change. Therefore, even when the pulse generation interval is long, such as when the vehicle speed is low, the calculated vehicle speed during this long pulse interval is approximately close to the actual vehicle speed, and accurate vehicle speed calculation can be performed. Moreover, since accurate vehicle speed calculation can be performed even if the pulse interval is long, there is no need to use a special vehicle speed sensor, and a conventional vehicle speed sensor can be used as is.

[Brief explanation of drawings]

FIG. 1 is a control circuit diagram showing a hydraulic continuously variable transmission in which clutch control is performed based on a vehicle speed calculated by a vehicle speed calculation method of the present invention.

FIG. 2 is a schematic diagram showing a clutch that is subject to the clutch control and a control device thereof.

FIG. 3 is a graph showing running characteristics of the continuously variable transmission.

FIG. 4 is a block diagram showing the clutch control.

FIG. 5 is a graph explaining the vehicle speed calculation method of the present invention.

FIG. 6 is a flowchart showing a vehicle speed calculation method of the present invention.

FIG. 7 is a flowchart showing the contents of the clutch control.

FIG. 8 is a flowchart showing the details of the clutch control.

FIG. 9 is a flowchart showing the contents of the clutch control.

FIG. 10 is a flowchart showing the details of smooth control in the clutch control.

FIG. 11 is a graph explaining the smooth control.

[Explanation of symbols]

5 Clutch valve 8 Forward/forward switching unit 21 Engine throttle sensor 22 Engine rotation sensor 23 Engine intake negative pressure sensor 24 Vehicle speed sensor 30 Clutch servo unit 40 Controller 45, 46 Solenoid valve E engine P Hydraulic pump M Hydraulic motor

Claims (2)

[Claims] Claim 1: A method for calculating vehicle speed at low speed based on pulses generated in proportion to vehicle speed, the method comprising: (N
-2) Calculate the vehicle speed at the (N-1)th pulse generation from the time interval from the time the pulse occurs to the (N-1)th pulse generation, and calculate the vehicle speed at the (N-1)th pulse generation time. The vehicle speed at the (N)th pulse generation point is determined from the time interval from 1 to the (N)th pulse generation point, and
The difference between the vehicle speed at the N-1)th pulse generation time and the vehicle speed at the (N)th pulse generation time and the (N-1)
) Calculate the rate of change in vehicle speed from the (N)th pulse generation time to the (N)th pulse generation time from the time interval from the (N)th pulse generation time to the (N)th pulse generation time. Until the (N+1)th pulse generation time, the vehicle speed is calculated on the assumption that the vehicle speed changes from the vehicle speed at the (N)th pulse generation time based on the rate of change in the vehicle speed. A method for calculating vehicle speed at low speeds. 2. During the period from the (N)th pulse generation time to the (N+1)th pulse generation time,
A claim characterized in that the vehicle speed is calculated by integrating the vehicle speed using a corrected rate of change by multiplying the rate of change in the vehicle speed used in the previous calculation by a predicted speed coefficient Kv (<1) every predetermined calculation cycle. The vehicle speed calculation method described in 1.