Parking assist system

Abstract

The objective is to provide a parking assistance device that does not cause inconvenience to the driver when parking a vehicle. [Solution] A parking assistance device comprising: a torque calculation unit that calculates the torque to be output by a drive source based on a target vehicle speed using PD control or PID control when parking a vehicle; and a torque control unit that controls the torque, wherein the torque control unit controls the drive source to output the larger of the torque calculated by the torque calculation unit and the creep torque, and when switching from the creep torque to the torque calculated by the torque calculation unit, the torque control unit controls the torque using the creep torque as a feedforward term.

Description

Technical Field

[0001] The present invention relates to a parking assistance device.

Background Art

[0002] In order to prevent misoperation between the accelerator and the brake, a technique has been developed to limit the output when the accelerator is depressed again after the accelerator is fully closed (for example, Patent Document 1, etc.).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When parking a vehicle, by reducing the vehicle speed, it is possible to avoid a collision with a structure behind the vehicle. However, if the vehicle speed is too low, the operation will be slow in response to the driver's operation, causing annoyance to the driver. In particular, it is difficult to control the vehicle speed on a road surface including a slope. Therefore, an object is to provide a parking assistance device that can prevent the driver from feeling inconvenient when parking the vehicle.

Means for Solving the Problems

[0005] The above object is achieved by a parking assistance device including a torque calculation unit that calculates torque output by a drive source by PD control or PID control based on a target vehicle speed when the vehicle is parked, and a torque control unit that controls the torque. The torque control unit controls so as to output the larger of the torque calculated by the torque calculation unit and the creep torque from the drive source. When switching from the creep torque to the torque calculated by the torque calculation unit, the torque control unit uses the creep torque as a feedforward term to control the torque. [Effects of the Invention]

[0006] This system provides a parking assistance device that minimizes inconvenience for the driver when parking a vehicle. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1(a) is a schematic diagram of the vehicle according to this embodiment. Figure 1(b) is a diagram illustrating the target vehicle speed. [Figure 2] Figure 2 is a flowchart illustrating the process in the embodiment. [Figure 3] Figure 3 is a flowchart illustrating the process in the embodiment. [Modes for carrying out the invention]

[0008] The parking assist device of this embodiment will now be described with reference to the drawings. Figure 1(a) is a schematic diagram of the vehicle 1 according to this embodiment. The vehicle 1 includes an internal combustion engine 10, an automatic transmission 11, an accelerator pedal 12, an accelerator opening sensor 14, a brake pedal 16, a vehicle speed sensor 18, a switch 19, and an ECU (Electronic Control Unit) 20 (parking assist device).

[0009] The internal combustion engine 10 is, for example, a gasoline engine or a diesel engine, which burns fuel and outputs torque. The torque is transmitted to the wheels through a shaft (not shown), causing the vehicle 1 to move. The automatic transmission 11 can automatically switch gear ratios. When parking, the shift lever is set to R.

[0010] The driver of vehicle 1 controls the speed of vehicle 1 using the accelerator pedal 12 and the brake pedal 16. When the amount of depression of the accelerator pedal 12 (accelerator opening) increases, the torque output by the internal combustion engine 10 increases. When the accelerator opening decreases, the torque decreases. The greater the torque, the higher the vehicle speed, and the less the torque, the lower the vehicle speed. When the brake pedal 16 is depressed, braking force is generated, reducing the vehicle speed.

[0011] The accelerator pedal position sensor 14 detects the accelerator pedal position. The vehicle speed sensor 18 detects the speed of vehicle 1.

[0012] Switch 19 is, for example, a button or a lever. When the driver of vehicle 1 turns on switch 19, the process shown in Figure 2 (described later) is performed. If switch 19 is off, the process shown in Figure 2 is not performed.

[0013] The ECU20 includes a processing unit such as a CPU (Central Processing Unit), and storage devices such as RAM (Random Access Memory) and ROM (Read Only Memory). The ECU20 performs various controls by executing programs stored in the ROM and other storage devices. The ECU20 obtains the braking torque from the amount the brake pedal 16 is pressed. The ECU20 obtains the vehicle speed from the vehicle speed sensor 18. The ECU20 obtains the accelerator opening from the accelerator opening sensor 14. The ECU20 sets a target value for the vehicle speed (target vehicle speed Vt).

[0014] Figure 1(b) illustrates the target vehicle speed Vt. The horizontal axis represents the accelerator pedal position. The vertical axis represents the target vehicle speed Vt when parked. As shown in Figure 1(b), the ECU 20 sets a lower limit Vll and an upper limit Vul for the target vehicle speed Vt. For example, when the accelerator pedal position is 0%, the target vehicle speed Vt is at the lower limit Vll. From 0% to A%, the target vehicle speed Vt increases in proportion to the accelerator pedal position. At an accelerator pedal position of A%, the target vehicle speed Vt reaches the upper limit Vul, and when the accelerator pedal position is A% or higher, the target vehicle speed Vt remains at Vul.

[0015] The ECU 20 controls the torque output from a drive source such as the internal combustion engine 10 based on the actual speed V of the vehicle 1 and the target vehicle speed Vt. More specifically, the ECU 20 functions as a torque calculation unit 22 and a torque control unit 24. The torque calculation unit 22 calculates the torque (controlled drive torque) of the internal combustion engine 10, for example, by PD control (Proportional-Differential Controller) or PID control (Proportional-Integral-Differential Controller). In PD control and PID control, the torque is calculated based on the difference between the target vehicle speed Vt and the actual vehicle speed V. Further details will be described later.

[0016] The torque control unit 24 controls the torque actually output by the internal combustion engine 10. Torque consists of controlled drive torque and creep torque. The controlled drive torque is calculated by the torque calculation unit 22. Creep torque is generated due to the creep phenomenon even when the accelerator pedal 12 is not pressed. The torque control unit 24 selects either the controlled drive torque or the creep torque.

[0017] Figures 2 and 3 are flowcharts illustrating the process in the embodiment, which is a process to assist in parking vehicle 1. The process continues throughout the parking process. At the start of the process, it is assumed that vehicle 1 is traveling on a flat road surface due to creep torque.

[0018] The ECU20 acquires data from vehicle 1 (step S10). This data includes vehicle speed, brake torque Tb, and accelerator opening. The ECU20 determines whether the brake torque Tb is less than or equal to the threshold Tth1 (step S12). If the determination is negative (No), it is presumed that the driver has stopped vehicle 1 and that the brake torque Tb is large. The process shown in Figure 2 ends.

[0019] If the determination in step S12 is affirmative (Yes), the vehicle 1 travels for parking. The ECU 20 calculates a target vehicle speed Vt at the time of parking based on the accelerator opening (step S14). The ECU 20 calculates the difference Vt - V between the target vehicle speed Vt and the current vehicle speed V (step S16).

[0020] The ECU 20 determines whether the absolute value of the target vehicle speed Vt is greater than or equal to the absolute value of the vehicle speed V (step S18). In the case of an affirmative determination, the torque calculation unit 22 calculates a control drive torque Tq by PID control (step S20). In the case of a negative determination, the torque calculation unit 22 calculates a control drive torque Tq by PD control (step S22).

[0021] The ECU 20 determines whether the absolute value of the control drive torque Tq is greater than or equal to the absolute value of the creep torque Tc (step S24). In the case of a negative determination, the torque control unit 24 adopts the creep torque Tc as the torque (step S26).

[0022] In the case of an affirmative determination in step S24, the torque control unit 24 determines whether the absolute value of the control drive torque Tq0 in the previous process is less than the absolute value of the creep torque Tc0 in the previous process (step S28). In the case of an affirmative determination, the torque control unit 24 latches the previous value Tc0 of the creep torque and uses it as the feed-forward term (FF term) of the PID control (step S30). After step S30, the torque control unit 24 adopts the control drive torque Tq as the torque (step S32). In the case of a negative determination in step S28, step S30 is not executed and step S32 is performed. After step S26 or S30, the process ends.

[0023] According to the embodiment, the process of FIG. 2 is performed when the vehicle 1 is parked. The torque calculation unit 22 calculates the control drive torque Tq by PD control or PID control (steps S22 and S20). The torque control unit 24 selects the larger one between the control drive torque Tq and the creep torque Tc and outputs it from the internal combustion engine 10 (steps S26 and S32). The vehicle speed V is set to about the target vehicle speed Vt, and parking can be performed without causing discomfort to the driver.

[0024] On a flat road surface, it is considered that the vehicle speed V rises to the target vehicle speed Vt by the creep torque Tc even without an accelerator operation. Therefore, the torque control unit 24 selects the creep torque Tc (step S26). Parking on a flat road can be performed at about the target vehicle speed Vt.

[0025] When the vehicle 1 moves from a flat road to an uphill road, the vehicle speed V may decrease during running by the creep torque Tc, and there is a risk that the vehicle 1 may stop. Therefore, the torque calculation unit 22 calculates the control drive torque Tq by PID control (step S20), and the torque control unit 24 selects the control drive torque Tq (step S32). By outputting a control drive torque Tq larger than the creep torque Tc, the decrease in the vehicle speed V is suppressed, and the vehicle speed V becomes about the target vehicle speed Vt. Even on an uphill road, parking can be performed without causing discomfort to the driver.

[0026] When the road surface switches from a flat road to an uphill road, there is a risk that the torque is insufficient and the vehicle 1 may stop. On the other hand, if the torque is suddenly increased, a shock may occur, which may cause discomfort to the passengers. In the embodiment, by combining PD control and PID control, the torque at the switch to the uphill road is controlled.

[0027] The control drive torque Tq is calculated by PID control or PD control (steps S20 and S22). The mathematical formula used in PID control is shown in Equation 1.

Equation

[0028] The P term is the product of the coefficient Kp and the velocity difference (Vt-V). The I term is the product of the coefficient Ki and the integral of the difference (Vt-V) with respect to time. The D term is the product of the coefficient Kd and the time derivative of the difference (Vt-V). FF stands for Feed Forward term. In PD control, the formula used is the one obtained from Mathematics 1, excluding the I and FF terms.

[0029] On flat roads, and immediately after entering an incline from a flat road, term I reduces the torque Tq. Therefore, if the vehicle speed V is less than or equal to the target speed Vt, the road surface is considered to be flat, and the torque calculation unit 22 performs PD control without including term I (step S22). When the vehicle speed V exceeds the target speed Vt, the road surface is considered to have entered an incline, and the torque calculation unit 22 calculates the controlled drive torque Tq by PID control (step S20). This prevents a decrease in the controlled drive torque Tq during the transition from a flat road to an incline and increases Tq. After entering an incline, the torque increases rapidly, enabling comfortable driving.

[0030] The FF term shown in Equation 1 is the previous value of the creep torque, Tc0. That is, the ECU20 latches the creep torque Tc0 just before entering the slope and uses it as the FF term to calculate the controlled drive torque Tq (step S30). When entering the slope, the I term is added to calculate the torque Tq, but it takes time for the I term to increase. By adding the FF term, a large Tq can be obtained immediately after entering the slope. Because the torque increases smoothly from the flat road to the slope, shocks are less likely to occur and responsiveness is improved. Parking can be done without any inconvenience.

[0031] The ECU 20 calculates the target vehicle speed Vt based, for example, on the accelerator pedal position (step S14). As shown in Figure 1(b), the ECU 20 sets a lower limit Vll and an upper limit Vul for the target vehicle speed Vt. Since the target vehicle speed Vt is at least Vll, driving is possible even with an accelerator pedal position of 0%. The target vehicle speed Vt changes in response to the driver's accelerator operation, and the vehicle speed V follows Vt. This improves responsiveness to the driver's input. Setting an upper limit Vul suppresses sudden acceleration if the driver presses the accelerator pedal 12 too hard.

[0032] In the example above, the internal combustion engine 10 is the power source for vehicle 1 and outputs torque. For example, a motor could also be the power source. The ECU 20 controls the torque output by the motor.

[0033] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. [Explanation of Symbols]

[0034] 1 Vehicle, 10 Internal combustion engine, 11 Automatic transmission, 12 Accelerator pedal, 14 Accelerator position sensor, 16 Brake pedal, 18 Vehicle speed sensor, 19 Switch, 20 ECU, 22 Torque calculation unit, 24 Torque control unit

Claims

[Claim 1] A torque calculation unit calculates the torque output by the drive source based on the target vehicle speed when the vehicle is parked, using PD control or PID control. The system comprises a torque control unit for controlling the torque, The torque control unit controls the drive source to output the larger of the torque calculated by the torque calculation unit and the creep torque. The torque control unit controls the torque when switching from the creep torque to the torque calculated by the torque calculation unit, using the creep torque as a feedforward term, in a parking assistance device.

Images