JP7665402B2 - Vehicle control device - Google Patents

Description

The present invention relates to a vehicle control device.

Conventionally, vehicles equipped with a variable speed limiter (ASL) have been provided. The variable speed limiter is a function that limits the increase in vehicle speed to a vehicle speed set by the user. When the variable speed limiter is activated, if the accelerator opening operated by the driver is greater than the accelerator opening limit that converges the vehicle speed to the set vehicle speed, the driving source for driving is controlled using the accelerator opening limit, thereby limiting the vehicle speed so that it does not exceed the set vehicle speed.

JP 2010-6334 A

On a downhill road, even if the throttle opening limit is set to 0, the vehicle will accelerate due to its own weight. Therefore, in order to prevent the vehicle speed from exceeding the upper limit, it may be necessary to slow down by shifting the gear ratio of the transmission that changes the power from the drive source to the lower side (low shift). On the other hand, on a flat road, if a low shift is performed to decelerate, the rotation speed of the drive source will increase unnecessarily, increasing noise vibrations (NV), and reducing usability. Therefore, in order to perform a low shift, it is necessary to distinguish between flat roads and downhill roads.

The method of determining the gradient of the road surface on which the vehicle is located from the detection signal of the G sensor is widely used, but in order to reduce costs, there is a demand to be able to distinguish between flat roads and downhill roads without using a G sensor, and if a low gear shift is performed on a downhill road, to return the gear ratio to its original value when the vehicle moves from the downhill road to a flat road.

The object of the present invention is to provide a vehicle control device that can release low gear shifting at the appropriate time without using a sensor to determine road surface gradient.

To achieve the above object, the vehicle control device of the present invention is a control device used in a vehicle equipped with a transmission that changes the driving power output by a drive source, and controls a vehicle speed limiting function that limits the vehicle speed up to a set vehicle speed. When the vehicle speed exceeds the set vehicle speed, the transmission gear ratio is shifted to the low side, and after the vehicle speed has decreased to the set vehicle speed due to the shift, the transmission gear ratio is made free when the output of the drive source becomes equal to or greater than a predetermined output.

With this configuration, when the vehicle speed exceeds the set vehicle speed, the gear ratio of the transmission may be shifted to the low side (low shift). In that case, if the vehicle speed drops to the set vehicle speed as a result of the low shift, the purpose of the low shift is achieved, and it is possible to end the low shift. However, if the vehicle is traveling downhill, the vehicle speed will accelerate and exceed the set vehicle speed immediately after the low shift is completed.

The output of the drive source when the vehicle is traveling at the set speed on a downhill road is smaller than the output of the drive source when the vehicle is traveling at the set speed on a flat road. Due to this relationship, when the vehicle speed drops to the set vehicle speed and the output of the drive source is less than a predetermined output, the gear ratio of the transmission is not free, and when the output of the drive source is equal to or greater than the predetermined output, the gear ratio of the transmission is free, so that the low gear shift can be released at an appropriate time after the vehicle moves from a downhill road to a flat road. Moreover, the low gear shift can be released at an appropriate time without using a sensor to determine the road surface gradient.

The vehicle control device may maintain the gear ratio of the transmission at the gear ratio at the time when the vehicle speed has decreased to the set vehicle speed until the output of the drive source reaches or exceeds a predetermined output.

In this configuration, the gear ratio is kept constant, so that it is possible to determine whether the output of the drive source has reached a predetermined output without any fluctuation in the output of the drive source due to fluctuations in the gear ratio. This allows for highly accurate determination, and allows low gear shifting to be released at a more appropriate time.

The specified output may be set to the output of the drive source when the vehicle is traveling on a flat road at a set vehicle speed.

In this case, when the output of the drive source reaches or exceeds a predetermined output, it can be determined that the vehicle has moved from a downhill road to a flat road, and the low gear shift can be released at an appropriate time after the vehicle has moved onto the flat road.

According to the present invention, low gear shifting can be released at the appropriate time without using a sensor to determine the road gradient.

1 is a block diagram showing a configuration of an ASL system including an EG/CVT-ECU according to an embodiment of the present invention. 10 is a flowchart showing a process for determining whether or not a low gear shift is to be performed; 13 is a flowchart showing the flow of a low shift process. 11A to 11C are diagrams illustrating an example of time variations in gear ratio, accelerator opening limit, vehicle speed, and road surface gradient when a low gear shift is performed. 13 is a flowchart showing the flow of a low shift release process. 10 is a flowchart showing another example of the low shift execution determination process.

The following describes in detail an embodiment of the present invention with reference to the attached drawings.

<ASL System>
FIG. 1 is a block diagram showing the configuration of an ASL system 1 including an EG/CVT-ECU 11 according to an embodiment of the present invention.

The ASL (Adjustable Speed Limiter) system 1 is applied to, for example, a vehicle equipped with an engine 2 as a driving source for driving, and is a system that limits the vehicle speed to a set speed (upper limit) that is arbitrarily set by the user.

The engine 2 is equipped with an electronic throttle valve 3 for adjusting the amount of air intake into the combustion chamber of the engine 2, an injector (fuel injection device) for injecting fuel into the intake air, and a spark plug for generating an electrical discharge in the combustion chamber.

The vehicle is equipped with a CVT (Continuously Variable Transmission) 4 as a transmission that changes the speed of the power from the engine 2 and outputs it to the drive wheels. The CVT 4 is a belt-type continuously variable transmission. The hydraulic circuit that supplies hydraulic pressure to each part of the CVT 4 includes a shift solenoid valve 5 that controls the hydraulic pressure supplied to the primary sheave and secondary sheave to change the gear ratio of the CVT 4.

The ASL system 1 includes an EG/CVT-ECU (Electronic Control Unit) 11 for controlling the engine 2 and the CVT 4. The vehicle is equipped with multiple ECUs, including the EG/CVT-ECU 11. Each ECU has a microcontroller unit (microcomputer), which includes, for example, a CPU, a non-volatile memory such as a flash memory, and a volatile memory such as a dynamic random access memory (DRAM). The multiple ECUs are connected to enable two-way communication using the CAN (Controller Area Network) communication protocol. Each ECU is connected to various sensors required for control, and receives detection signals from the connected sensors. In addition to the detection signals input from the various sensors, each ECU also receives information required for control from other ECUs.

Information on the accelerator opening and vehicle speed is input to the EG/CVT-ECU 11.

The vehicle is provided with an accelerator pedal that is operated by the driver's foot, and an accelerator sensor that is associated with the accelerator pedal and outputs a detection signal corresponding to the amount of accelerator pedal operation. The amount of accelerator pedal operation can be obtained from the detection signal of the accelerator sensor, and the accelerator opening, which is the ratio of the amount of operation to the maximum amount of accelerator pedal operation, can be obtained from that amount and the maximum amount of accelerator pedal operation.

The vehicle is also provided with a vehicle speed sensor that outputs a detection signal, a pulse signal synchronized with the rotation of a rotor that rotates as the vehicle travels. The vehicle speed can be calculated by determining the frequency of the detection signal from the vehicle speed sensor and applying the frequency to a conversion formula.

The vehicle is equipped with a cruise control function that maintains the vehicle speed at a set speed that is arbitrarily set by the user. The vehicle's steering column is provided with an ASL switch (SW) 12 that activates/deactivates the ASL, which limits the vehicle speed to a set speed, and a cruise control switch (SW) 13 that activates/deactivates the cruise control function and sets a set vehicle speed that is used commonly for the ASL and cruise control. Signals corresponding to the operation of the ASL switch 12 and the cruise control switch 13 are input to the EG/CVT-ECU 11.

The EG/CVT-ECU 11 essentially comprises an ASL control unit 21, an engine control unit 22, and a T/M control unit 23 as functional processing units.

When ASL operation is instructed by operation of the ASL switch 12, the ASL control unit 21 performs ASL control to limit the vehicle speed to a set vehicle speed. In order to limit the vehicle speed to the set vehicle speed, the ASL control unit 21 incorporates an ASL throttle control logic that sets the accelerator opening according to the vehicle speed and the set vehicle speed as the limited accelerator opening, and an ASL shift control logic that outputs a low shift request to shift the gear ratio of the CVT 4 to the low side.

When ASL control is being performed, the engine control unit 22 compares the driver accelerator opening, which is the accelerator opening caused by operation of the accelerator pedal, with the limited accelerator opening input from the ASL control unit 21, and acquires the smaller of them (MIN acquisition). The relationship between the accelerator opening and the opening of the electronic throttle valve 3 (throttle opening) is stored in the non-volatile memory of the EG/CVT-ECU 11, and the engine control unit 22 uses this relationship to determine a target throttle opening corresponding to the smaller of the driver accelerator opening and the limited accelerator opening. The EG/CVT-ECU 11 then controls the electronic throttle valve 3 so that the throttle opening matches the target.

The T/M control unit 23 incorporates ASL-compatible control logic. When a low-speed change request is output from the ASL control unit 21, the ASL-compatible control logic in the T/M control unit 23 sets, for example, the target gear ratio of the CVT 4 to a gear ratio that is a predetermined value higher on the low side (the side with a higher gear ratio) than the current gear ratio. The T/M control unit 23 then controls the gear change solenoid valve 5 so that the gear ratio of the CVT 4 matches the target.

<Low gear shift execution determination process>
FIG. 2 is a flowchart showing the flow of the low shift execution determination process.

When the vehicle speed exceeds a set vehicle speed, the ASL control unit 21 of the EG/CVT-ECU 11 performs the low-speed shift execution determination process shown in FIG. 2 to determine whether or not to execute a low-speed shift, which shifts the gear ratio of the CVT 4 to the low side.

In this low-speed shift execution determination process, first, it is determined whether the vehicle speed exceeds a set vehicle speed (step S11). While the vehicle speed is equal to or lower than the set vehicle speed, the process does not proceed to the next step, and it is repeatedly determined whether the vehicle speed exceeds the set vehicle speed.

If the vehicle speed exceeds the set vehicle speed (YES in step S11), the throttle opening limit is set to 0. Then, depending on the throttle opening limit setting, it is determined whether or not an instruction to fully close the electronic throttle valve 3 (throttle full closure instruction) has been output from the engine control unit 22 (step S12).

When a throttle full closure command is output (YES in step S12), it is determined whether or not the inflection point arrival estimated time has elapsed since the throttle full closure command was output (which approximately coincides with the time when the vehicle speed exceeded the set vehicle speed) (step S13). The inflection point arrival estimated time is set to the delay time from the output of the throttle full closure command until the output of the engine 2 begins to decrease due to the electronic throttle valve 3 being fully closed. The delay time is calculated by adding the throttle delay time (fixed value) according to the time constant of the motor that opens and closes the electronic throttle valve 3, and the combustion stroke delay time required from the intake stroke to the combustion stroke of the engine 2. The combustion stroke delay time depends on the engine 2 rotation speed, so it can be calculated from the engine 2 rotation speed.

Therefore, when the estimated time to reach the inflection point has elapsed since the output of the throttle fully closed command, an inflection point is reached where the output of engine 2 changes from increasing to decreasing, and when the estimated time to reach the inflection point has elapsed, the output of engine 2 has begun to decrease. Therefore, when the vehicle is traveling on a flat road, the vehicle has begun to decelerate, and the vehicle acceleration indicates a negative value. On the other hand, when the estimated time to reach the inflection point has elapsed since the output of the throttle fully closed command and the output of engine 2 has decreased, the vehicle is accelerating and the vehicle acceleration is 0 or greater, it is considered that the vehicle is traveling downhill and accelerating due to its own weight.

Therefore, when the estimated time to reach the inflection point has elapsed since the output of the throttle full closure command (YES in step S13), it is determined whether the acceleration calculated by the time derivative of the vehicle speed is 0 or greater (step S14). If the vehicle acceleration is 0 or greater (YES in step S14), a low gear shift is determined to be performed (step S15), and a low gear shift request is sent from the ASL control unit 21 to the T/M control unit 23. On the other hand, if the vehicle acceleration is less than 0 (NO in step S14), a low gear shift is not determined to be performed (step S16), and no low gear shift request is output from the ASL control unit 21.

<Low gear shift processing>
Fig. 3 is a flow chart showing the flow of low gear shift processing. Fig. 4 is a diagram showing an example of time-dependent changes in vehicle speed, gear ratio, and accelerator opening limit when a low gear shift is performed.

When it is determined in the low-speed shift execution determination process described above that a low-speed shift should be performed, the ASL control unit 21 of the EG/CVT-ECU 11 executes the low-speed shift process shown in FIG. 3 in order to perform a low-speed shift.

In the low gear shift process, it is determined whether or not a low gear shift has been decided to be performed in the low gear shift execution determination process (step S21). If a low gear shift has not been decided to be performed in the low gear shift execution determination process (NO in step S21), the low gear shift process does not proceed further.

When it is determined that a low gear shift is to be performed (YES in step S21), a low gear shift request to shift the gear ratio of the CVT 4 toward the first gear ratio is sent from the ASL control unit 21 to the T/M control unit 23. The first gear ratio is set to a gear ratio that is at least lower than the current gear ratio of the CVT 4, for example, set to the lowest gear ratio (maximum gear ratio) of the CVT 4. Then, the T/M control unit 23 that has received the low gear shift request controls the gear shift solenoid valve 5 so that the gear ratio of the CVT 4 is shifted toward the first gear ratio (step S22).

While the gear ratio of the CVT 4 is being shifted toward the first gear ratio, it is repeatedly determined whether the vehicle speed is equal to or lower than the set vehicle speed (step S23). As shown in FIG. 4, as the gear ratio of the CVT 4 increases, the vehicle speed decreases.

Then, when the vehicle speed drops to the set vehicle speed, the target gear ratio of the CVT4 is changed from the first gear ratio to the second gear ratio. The second gear ratio is set to the gear ratio at the time when the vehicle speed drops to the set vehicle speed. In other words, when the vehicle speed drops to the set vehicle speed, the second gear ratio, which is the gear ratio at that time, becomes the target gear ratio of the CVT4 thereafter. This causes the gear ratio of the CVT4 to be held at the second gear ratio (step S24).

After that, while the gear ratio of the CVT 4 is held at the second gear ratio, the ASL control unit 21 of the EG/CVT-ECU 11 sets an accelerator opening limit that converges the vehicle speed to the set vehicle speed, and the engine control unit 22 determines a target throttle opening that corresponds to the accelerator opening limit. The engine control unit 22 then controls the electronic throttle valve 3 so that the throttle opening matches the target. This maintains the vehicle speed at the set vehicle speed.

<Low gear shift release process>
FIG. 5 is a flowchart showing the flow of the low shift release process.

The low shift release process is a process for determining whether to release the low shift, which shifts the gear ratio of the CVT4 to the low side, and is performed in parallel with the low shift process.

In the low speed change release process, it is determined whether or not the process of maintaining the gear ratio of the CVT 4 at the second gear ratio has been started (step S31). If the process of maintaining the gear ratio at the second gear ratio has not been started, the low speed change release process does not proceed further.

When the process of maintaining the gear ratio at the second gear ratio is started (step S31), it is determined whether the throttle limit output from the ASL control unit 21 to the engine control unit 22 is equal to or greater than a predetermined value (step S32). The engine control unit 22 sets a target throttle opening according to the throttle limit and controls the electronic throttle valve 3 so that the throttle opening matches the target, so that the throttle limit corresponds to the output of the engine 2. Therefore, engine output equal to or greater than a predetermined output is equivalent to throttle limit being equal to or greater than a predetermined value.

While the throttle opening limit is less than the predetermined value (NO in step S32), the gear ratio is not released from being held at the second gear ratio.

When the throttle opening limit reaches or exceeds a predetermined value (YES in step S32), the state in which the gear ratio is held at the second gear ratio is released, low shifting is released, and control of the CVT 4 returns to normal shifting control (step S33).

<Action and effect>
2, it is possible to determine whether or not to perform a low gear shift on a downhill road without using a sensor for determining the road gradient. As a result, it is possible to reduce the cost of the ASL system 1, and in turn, it is possible to reduce the cost of the vehicle equipped with the ASL system 1.

In addition, in low gear shifting, the gear ratio of the CVT 4 is shifted toward a first gear ratio that is set lower than the current gear ratio, and when the vehicle speed drops to the set vehicle speed, the target gear ratio is changed from the first gear ratio to the second gear ratio. This makes it possible to prevent low gear shifting from being performed to a gear ratio higher than that required for decelerating the vehicle, and to prevent the rotation speed of the engine 2 from increasing unnecessarily. Moreover, low gear shifting allows the vehicle speed to be decelerated to the set vehicle speed.

In addition, since the gear ratio is maintained at the second gear ratio after the vehicle speed has decreased to the set vehicle speed, unnecessary fluctuations in the rotation speed of the engine 2 due to changes in the gear ratio can be suppressed.

When the gear ratio of the CVT 4 is held at the second gear ratio, a limit accelerator opening is set to converge the vehicle speed to the set vehicle speed. A target throttle opening is then set according to the limit accelerator opening, and the electronic throttle valve 3 is controlled so that the throttle opening matches the target. This maintains the vehicle speed at the set vehicle speed.

The output of engine 2 required when the vehicle is traveling downhill at the set speed is smaller than the output of engine 2 required when the vehicle is traveling on a flat road at the set speed. Therefore, the accelerator opening limit set when the vehicle is traveling downhill at the set speed is smaller than the accelerator opening limit set when the vehicle is traveling on a flat road at the set speed. From this relationship, when the accelerator opening limit is less than a predetermined value after the vehicle speed has decreased to the set vehicle speed, the low gear shift is not released, and when the accelerator opening limit is equal to or greater than the predetermined value, the low gear shift is released, so that the low gear shift can be released at an appropriate time after the vehicle moves from a downhill road to a flat road. Moreover, the low gear shift can be released at an appropriate time without using a sensor for determining the road surface gradient.

<Another Example of Low Gear Shift Implementation Determination Processing>
Fig. 6 is a flow chart showing another example of the low gear shift execution determination process Fig. 5 is a diagram showing an example of a time change in the vehicle speed when the low gear shift execution determination process shown in Fig. 6 is performed.

In order to determine whether or not to perform a low gear shift, which shifts the gear ratio of the CVT 4 to the low side, when the vehicle speed exceeds a set vehicle speed, the ASL control unit 21 of the EG/CVT-ECU 11 may perform a low gear shift execution determination process shown in FIG. 6 instead of the low gear shift execution determination process shown in FIG. 2.

In this low shift execution determination process, first, it is determined whether the vehicle speed exceeds a set vehicle speed (step S41). While the vehicle speed is equal to or lower than the set vehicle speed, the process does not proceed to the next step, and it is repeatedly determined whether the vehicle speed exceeds the set vehicle speed.

If the vehicle speed exceeds the set vehicle speed (YES in step S41), the throttle opening limit is set to 0. Then, depending on the throttle opening limit setting, it is determined whether or not an instruction to fully close the electronic throttle valve 3 (throttle full closure instruction) has been output from the engine control unit 22 (step S42).

When a throttle full closure command is output (YES in step S42), the vehicle acceleration is calculated by time-differentiating the vehicle speed at the time when the throttle full closure command is output (which approximately coincides with the time when the vehicle speed exceeds the set vehicle speed). Also, as in the case of the process shown in FIG. 2, the estimated time to reach the inflection point is calculated by adding the throttle delay time and the combustion stroke delay time.

Assuming that the output of engine 2 is the same, the acceleration of the vehicle will be greater when the vehicle is traveling downhill than when the vehicle is traveling on a flat road. The product of the vehicle acceleration at the time the throttle fully closed command is output and the estimated time to reach the inflection point is estimated as the increase in vehicle speed from the time the throttle fully closed command is output until the estimated time to reach the inflection point has elapsed (when the inflection point is reached). If a predetermined value α is set based on the increase estimated when the vehicle is traveling on a flat road, it can be estimated that the vehicle is traveling downhill if the increase in vehicle speed is equal to or greater than the predetermined value α.

Therefore, if the increase in vehicle speed from the time when the throttle fully closed command is output until the time when the estimated time to reach the inflection point has elapsed is equal to or greater than a predetermined value α, in other words, if the estimated vehicle speed obtained by adding the increase in the vehicle speed to the set vehicle speed (estimated vehicle speed when the inflection point is reached) is equal to or greater than the set vehicle speed plus the predetermined value α (YES in step S43), a low gear shift is determined to be performed (step S44), and a low gear shift request is sent from the ASL control unit 21 to the T/M control unit 23. On the other hand, if the estimated vehicle speed when the inflection point is reached is less than the set vehicle speed plus the predetermined value α (NO in step S43), a low gear shift is not determined to be performed (step S45), and no low gear shift request is output from the ASL control unit 21.

＜Effects＞
6, it is possible to determine whether to shift to low on a downhill road without using a sensor for determining the road gradient, which results in a reduction in the cost of the ASL system 1, and in turn a reduction in the cost of the vehicle equipped with the ASL system 1.

<Modification>
Although the embodiment of the present invention has been described above, the present invention can be embodied in other forms.

For example, in the above embodiment, the ASL system 1 is applied to a vehicle equipped with an engine 2 as a driving source for running, but the present invention can also be applied to electric vehicles (hybrid vehicles, electric automobiles) that use a motor as a driving source for running, as long as the vehicle is equipped with a transmission that changes the speed of the power from the driving source for running.

The transmission is not limited to a belt-type continuously variable transmission, but may be a toroidal type or other type of continuously variable transmission, or may be a stepped automatic transmission (AT). The transmission may also be a manual transmission (MT).

In addition, various design modifications can be made to the above-mentioned configuration within the scope of the claims.

2: Engine (power source)
4: CVT (transmission)
11: EG/CVT-ECU (vehicle control device)

Claims (2)

A control device is used in a vehicle equipped with a continuously variable transmission that changes the speed of a driving power output from a drive source, and performs control for a vehicle speed limiting function that limits the vehicle speed up to a set vehicle speed,
In the control for the vehicle speed limiting function,
controlling an output of the drive source to an output corresponding to a smaller one of a driver accelerator opening, which is an accelerator opening operated by a driver of the vehicle, and a limited accelerator opening, which is an accelerator opening corresponding to a vehicle speed and the set vehicle speed;
A vehicle control device that, when the gear ratio of the continuously variable transmission is shifted to the lower side in response to the vehicle speed exceeding the set vehicle speed , if the vehicle speed drops to the set vehicle speed as a result of the gear shift, sets the limit accelerator opening degree to converge the vehicle speed to the set vehicle speed, holds the gear ratio of the continuously variable transmission at the gear ratio at the time the vehicle speed dropped to the set vehicle speed until the output of the drive source becomes equal to or greater than the specified output, and frees the gear ratio of the continuously variable transmission when the output of the drive source becomes equal to or greater than the specified output. 2. The vehicle control device according to claim 1 , wherein the predetermined output is set to an output of the drive source when the vehicle runs on a flat road at the set vehicle speed.

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