Vehicle control devices

Abstract

The present invention provides a vehicle control device. When vehicle speed control is executed in response to a fault in a steer-by-wire steering system, the device prevents a vehicle from accelerating after a speed reduction caused by a braking operation by a vehicle operator. When a fault in the steering system is detected, speed limit control limits the vehicle's travel speed to below an upper speed limit. The speed limit control is configured to: set a target deceleration for the vehicle based on the limited travel speed; execute deceleration control so that the vehicle's actual deceleration approaches the target deceleration; and limit the actual deceleration during the deceleration control to prevent it from shifting toward acceleration.

Description

Technical Field

[0001] The present invention relates to a control device for controlling a steer-by-wire type steering system provided in a vehicle. Background Art

[0002] In a steer-by-wire steering system, a steering wheel operated by a driver and a rack that steers the wheels are mechanically separated from each other. The steering angle of the steering wheel is detected by a steering angle sensor, and the wheels are steered according to the steering angle by a steering actuator.

[0003] In steer-by-wire steering systems, redundancy is provided to improve reliability. However, if redundancy is lost due to a fault in the system, steering may become difficult if the system continues to be used in this situation. Therefore, in abnormal situations that cause or may cause loss of redundancy, it is necessary to quickly move the vehicle to a safe location, such as the roadside.

[0004] Conventionally, a technology for controlling a vehicle in the event of a steer-by-wire steering system failure has been known to reduce power consumption by limiting the vehicle's travel speed in the event of a generator failure. This ensures that the steering system has sufficient power for the vehicle operator to maneuver the vehicle to a safe position. For example, see JP5013312B.

[0005] When limiting a vehicle's speed as a countermeasure for a malfunction in a steer-by-wire steering system, if the vehicle speed is limited to a certain upper speed limit and the driver applies the brakes, the braking operation temporarily decelerates the vehicle, but the vehicle may subsequently accelerate toward the upper speed limit. For example, if the upper speed limit is set at 15 km / h and the driver's braking operation reduces the vehicle speed to 10 km / h, there is room for acceleration back to 15 km / h. However, such vehicle acceleration is undesirable as part of emergency control, and the driver may experience some discomfort due to such acceleration. Summary of the Invention

[0006] In view of such problems in the prior art, the main object of the present invention is to provide a vehicle control device that, when performing vehicle speed control in response to a fault in a steer-by-wire steering system, prevents the vehicle from accelerating after a speed reduction caused by a braking operation by a vehicle operator.

[0007] To achieve such an object, the present invention provides a vehicle control device, which is configured to be installed on a vehicle provided with a steering system, the steering system including: an operating member, which is configured to be operated by a driver; a steering member, which is mechanically separated from the operating member and configured to steer a wheel; and a steering actuator, which is powered by electricity supplied from an on-board power supply and configured to actuate the steering member according to an input from the operating member, wherein the vehicle control device is configured to perform speed limit control to limit the driving speed of the vehicle to below an upper limit speed when a fault in the steering system is detected, and the speed limit control is configured to: set a target deceleration of the vehicle according to the limited driving speed, perform deceleration control so that the actual deceleration of the vehicle becomes close to or near the target deceleration, and limit the actual deceleration in the deceleration control to prevent it from changing to the acceleration side.

[0008] Therefore, when a malfunction occurs in a steering system in which the operating member and the steering member are mechanically separated, as in the case of a steer-by-wire type steering system, and vehicle speed limit control is executed, the resulting deceleration control limits the actual deceleration of the vehicle so as not to be on the acceleration side. Therefore, when the driver performs a braking operation and then stops the braking operation, the vehicle is prevented from accelerating after the braking operation is stopped.

[0009] Preferably, the deceleration control is performed as feedback control including an integral term, and when the feedback control is started, the target deceleration for the feedback control is set to an initial value of the integral term.

[0010] Thereby, the time period required for the actual deceleration to converge to the target deceleration is shortened when feedback control is started, thereby improving responsiveness.

[0011] Preferably, the deceleration control is performed as feedback control including an integral term, and the integral term is prevented from changing to an acceleration side in the feedback control.

[0012] This suppresses the accumulation of the integral term in the feedback control, shortening the time period required for the actual deceleration to converge to the target deceleration and improving responsiveness. In this case, by setting the lower limit of the integral term in the feedback control close to the target deceleration, the integral term is prevented from shifting toward the acceleration side.

[0013] Preferably, the deceleration control is performed as feedback control including an integral term, and when the deceleration of the vehicle caused by the driver's braking operation becomes greater than the target deceleration, the target deceleration for the feedback control is set as an initial value of the integral term.

[0014] Thereby, accumulation of the integral term in the feedback control is suppressed, so that when transitioning from the control operated by the driver to the feedback control, a time period required for the actual deceleration to converge to the target deceleration is shortened.

[0015] The present invention thus provides a vehicle control apparatus that, when executing vehicle speed control in response to a failure in a steer-by-wire type steering system, prevents the vehicle from accelerating after a speed reduction caused by a braking operation by a vehicle operator. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of a vehicle equipped with a control device according to an embodiment of the present invention;

[0017] Figure 2 is a flow chart illustrating the operating mode of the control device;

[0018] Figures 3A to 3C is a graph illustrating an operating mode of the control device;

[0019] Figure 4 is a block diagram of the control device;

[0020] Figure 5A and Figure 5B is a graph illustrating an operating mode of the control device;

[0021] Figure 6A and Figure 6B is a graph illustrating another mode of operation of the control device; and

[0022] Figure 7A and Figure 7B is a graph showing yet another operating mode of the control device. DETAILED DESCRIPTION

[0023] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

[0024] Figure 1 1 is a schematic diagram of a vehicle 1 equipped with a steering system 11 according to an embodiment of the present invention. The vehicle 1 is composed of a four-wheeled vehicle having four wheels 4 supported by a vehicle body 2 via corresponding suspension devices 3.

[0025] Vehicle 1 includes a power plant 5 that drives wheels 4, and a transmission 6 that allows the mode of transmitting driving force from power plant 5 to wheels 4 to be changed. Power plant 5 is at least one of an internal combustion engine and an electric motor, and the driving force and braking force (engine braking) of power plant 5 are transmitted to wheels 4. Power plant 5 is controlled based on the driver's accelerator pedal operation. Furthermore, transmission 6 is controlled based on the driver's gear shift operation.

[0026] The vehicle 1 is provided with a steer-by-wire steering system 11 that steers the wheels 4. The steering system 11 includes a rack 12 (steering member), a steering wheel 13 (operating member), a steering angle sensor 14, a rotation angle sensor 15, a steering actuator 16 (steering device), a reaction force actuator 17 (reaction device), and a steering torque sensor 18. The steering system 11 is a non-axial steer-by-wire steering system in which the rack 12 and the steering wheel 13 are not mechanically connected or disconnected from each other.

[0027] The driver operates the steering wheel 13. A steering angle sensor 14 detects the steering angle of the steering wheel 13. A rotation angle sensor 15 typically detects the rotation angle of the wheels 4 by displacing the rack 12. A steering actuator 16 pushes and pulls the rack 12 to steer the wheels 4. A reaction force actuator 17 applies a reaction force to the steering wheel 13 to counteract the driver's operating force. A steering torque sensor 18 detects the steering torque applied to the steering shaft 19.

[0028] The vehicle 1 is also equipped with a control unit 21 (ECU), a vehicle speed sensor 22 (driving condition detection means, vehicle speed detection means), and an acceleration sensor 23 for detecting the vehicle's longitudinal deceleration. The control unit 21 includes a processor, memory, and the like, and controls the operation of the steering actuator 16, the reaction force actuator 17, and the like based on detection results from sensors such as the steering angle sensor 14, the rotation angle sensor 15, the steering torque sensor 18, the vehicle speed sensor 22, and the acceleration sensor 23.

[0029] The vehicle 1 is also provided with a power supply system 31 that supplies electric power to the steering system 11, the control unit 21, etc. This power supply system 31 includes a battery 32 (electricity storage device), a generator 33, and the like.

[0030] Furthermore, the vehicle 1 is provided with a brake system (brake device) (not shown in the drawings) that applies brakes to the wheels 4. This brake system is controlled according to the driver's brake operation.

[0031] The steering system 11 incorporates system redundancy to enhance reliability. For example, the steering actuator 16 (steering device) can have redundancy comprised of two systems. Furthermore, the reaction force actuator 17 (reaction force device) can also have redundancy comprised of two systems. Furthermore, the control unit 21 can have redundancy comprised of two systems. Furthermore, the power supply system 31 can have redundancy comprised of two systems.

[0032] Next, we will refer to Figure 2 Discuss the control actions of vehicle systems, Figure 2 is a flowchart showing the operation procedure of the control unit 21 in such a vehicle system.

[0033] When using a steer-by-wire steering system 11, there is a possibility that the steering system 11 may not operate properly while the vehicle is traveling due to a fault in the steering system 11 itself or in the power supply system 31 that supplies power to the steering system 11. Therefore, in this embodiment, vehicle speed limit control is implemented to ensure a safe state by limiting the vehicle speed so that steering operations do not become difficult for the vehicle operator. More specifically, in this embodiment, vehicle speed limit control can be implemented in three different modes: escape vehicle speed limit control, mandatory vehicle speed limit control, and maximum speed limit control.

[0034] like Figure 2 As shown, when the vehicle system is activated, the control unit 21 first determines whether any fault is detected that would make it difficult to continue the steering operation (step ST1). Faults in the vehicle system may include loss of redundancy in the steering system 11, reduced output of the steering actuator 16, and the generator 33 being unable to supply sufficient power to the steering actuator (failure of the power generation function).

[0035] If any failure that would make it difficult to continue the steering operation is detected (ST1: YES), the control unit 21 determines whether the power generation function is lost (step ST2).

[0036] Here, if the power generation function is not lost, or in other words, if the redundancy of the steering system 11 is lost or the output of the steering actuator 16 is insufficient (ST2: No), the escape vehicle speed limit control is executed (step ST3). This escape vehicle speed limit control is continued until the ignition is turned on again.

[0037] On the other hand, if the power generation function is lost (ST2: YES), the compulsory vehicle speed limit control is executed (step ST4). The compulsory vehicle speed limit control is continued until the ignition is turned on again.

[0038] If there is no fault that makes it difficult to continue the steering operation (ST1: NO), it is determined whether there is insufficient available power for achieving and maintaining a safe state or a state in which the vehicle is traveling at a safe speed that allows the vehicle to stop immediately (step ST5). More specifically, it is determined whether the output of the battery 32 is insufficient due to deterioration or low temperature.

[0039] If the amount of available electric power is insufficient to achieve and maintain a safe state (ST5: YES), maximum speed limit control is executed (step ST6).

[0040] On the other hand, if the amount of power required to achieve and maintain the safe state is insufficient (ST5: NO), the vehicle speed limit control (escape vehicle speed limit control, compulsory vehicle speed limit control, and maximum speed limit control) is not executed, and normal control is maintained (step ST7).

[0041] Next, the vehicle speed limit control executed by the control unit 21 will be described below. Figures 3A to 3C An overview of the vehicle speed limit control executed by the control unit 21 is shown.

[0042] The control unit 21 executes the vehicle speed limit control in one of three different modes (escape vehicle speed limit control, mandatory vehicle speed limit control, and maximum speed limit control) depending on the nature of the vehicle system failure.

[0043] Figure 3A This example shows an escape mode for vehicle speed limit control executed when a fault exists that makes continued steering operation difficult, but the generator 33 is able to supply sufficient power (not when the power generation function is lost). In other words, this mode is executed when redundancy in the steering system 11 is lost or when the output of the steering actuator 16 is insufficient.

[0044] The escape vehicle speed limit control sequentially transitions from the first speed limit state to the third speed limit state (voluntary escape state, forced deceleration state and safe speed maintenance state).

[0045] In the voluntary escape state, when the vehicle is restricted from driving at inappropriately high speeds by setting a fixed upper speed limit, the driver is allowed to voluntarily or actively escape from the current state. More specifically, the upper speed limit is set to the higher of the vehicle speed when the fault is detected and the speed limit of the road on which the vehicle is traveling, and the vehicle is prevented from traveling at a speed higher than the upper speed limit. The vehicle can be accelerated and decelerated relatively freely, and lane changes can be made as long as the upper speed limit is not exceeded. Therefore, the vehicle driver is able to move the vehicle to a safe position with the help of steering operations. The voluntary escape state can be maintained for a certain period of time, which can allow the driver to move the vehicle to a safe place. Therefore, the driver is given a certain degree of freedom when operating the vehicle. If the vehicle does not stop or reach a safe position within the specified time period, forced deceleration is initiated.

[0046] In the forced deceleration state, the vehicle is forcibly decelerated to a safe speed by gradually reducing the upper speed limit. More specifically, the upper speed limit is gradually reduced from the initial speed (or the upper speed limit in the voluntary escape state) to a predetermined safe speed. This safe speed is selected as a speed at which the vehicle can be quickly and safely stopped by the driver's braking operation without requiring steering. The upper speed limit in the forced deceleration state is selected as the speed at which the vehicle travels when the driver does not operate the accelerator or brake pedals. Preferably, the vehicle's deceleration in this state should be low enough to allow the driver to calmly perform steering operations. For example, deceleration can be achieved solely by the braking force of the power unit 5. In addition to the braking force of the engine brake, this braking force may also include regenerative and / or friction braking. Due to this control action, the vehicle can be decelerated to a safe speed within a predetermined period of time without the driver having to apply the brakes. In the forced deceleration state, if the vehicle speed approaches the upper speed limit, acceleration by the driver's accelerator pedal is prohibited, but deceleration by the driver's brake pedal is permitted.

[0047] In the safe speed maintenance state, the upper speed limit is set to the safe speed, and the vehicle speed is limited to the upper speed limit. This control action allows the driver to drive the vehicle at a speed lower than the safe speed until reaching a suitable safe position, and then apply the brakes at the appropriate time to stop the vehicle. Therefore, even if steering suddenly fails or becomes difficult, the driver can safely stop the vehicle by applying the brake pedal.

[0048] In the escape vehicle speed limit control, the driver is prompted to execute an escape maneuver, or in other words, to move the vehicle to a safe location, such as a curb, without undue delay. Specifically, in the forced deceleration state, the driver is prompted to execute forced deceleration through a visual display or audio output. Due to the high level of urgency and to ensure the vehicle is properly decelerated, the driver may be repeatedly warned to slow down. Furthermore, in the safe speed maintenance state, visual displays or audio outputs may be used to encourage the driver to stop the vehicle in a safe location. In this case, as the level of urgency decreases, the warnings may be issued intermittently.

[0049] When there is a steering fault that will make it difficult to continue driving the vehicle, perform Figure 3B Forcible vehicle speed limit control shown in ; for example, when the generator 33 becomes unable to supply electric power (power generation function loss state).

[0050] The mandatory vehicle speed limit control sequentially transitions from the first speed limit state to the third speed limit state (mandatory deceleration state, safe speed maintenance state and vehicle stop and hold state). Figure 3A ), there is no voluntary escape state, and deceleration begins immediately in the forced deceleration state.

[0051] The forced deceleration state and the safe speed maintenance state are similar to escaping the vehicle speed limit control (see Figure 3A It should be noted that in the forced deceleration state, the speed of the own vehicle becomes the initial speed when the fault is detected.

[0052] In the vehicle stop hold state, the vehicle is forcibly stopped by a speed limiting action that gradually reduces the upper speed limit. This control action may include prompting the driver to brake the vehicle to stop it. Once the vehicle is stopped, the EPB (Electric Parking Brake) and / or the park position of the transmission 6 are used to maintain the vehicle stationary. Due to this control action, the vehicle can be decelerated to a complete stop and reliably maintained at a standstill while the available power allows this operation.

[0053] Furthermore, during mandatory vehicle speed limit control, the driver is informed that the vehicle speed will be limited due to the loss of power generation. Specifically, during vehicle stop-holding, as in mandatory deceleration, the driver can be notified of intervention in vehicle stopping measures through visual displays on the display, voice output, and other means, similar to mandatory deceleration. In this case, due to the high level of urgency, continuous warnings can be provided.

[0054] Figure 3C The maximum speed limit control shown in is executed in the following situation: when there is no fault that will cause difficulty in steering operation in any foreseeable future, and the power supply is insufficient to achieve a safe state or maintain a safe state.

[0055] In maximum speed limit control, a maximum speed (upper speed limit) is set based on the vehicle's power conditions (available power and power consumption), and the vehicle speed is controlled to remain below the predetermined maximum speed. More specifically, assuming constant power consumption, the maximum speed decreases as available power decreases, and increases as available power increases. This control ensures that sufficient power is maintained to achieve and maintain a safe state, allowing the vehicle to be safely stopped.

[0056] In the maximum speed limit control, it may be arranged to inform the driver of the vehicle speed being limited due to a reduction in available electric power by visual and / or audible warnings.

[0057] The feedback control performed by the control unit 21 will be described below. Figure 4 is a block diagram showing an outline of feedback control performed by the control unit 21 .

[0058] In the vehicle speed limit control, the control unit 21 sets a target deceleration based on the restricted vehicle speed, and performs feedback control (deceleration control) so that the actual deceleration approaches or comes close to the target deceleration.

[0059] The subtractor 41 in the control unit 21 subtracts the actual deceleration from the target deceleration. The actual deceleration can be obtained by the acceleration sensor 23 (see Figure 1 ) etc. The integral term gain processing unit 42 calculates the integral term (I term) by integrating the difference between the target deceleration output from the subtractor 41 and the actual deceleration and multiplying the result by a gain. The adder 43 adds the deviation in the deceleration output from the integral term gain processing unit 42 to the requested braking force or the previous feedback deceleration (manipulation amount) to calculate the current feedback deceleration.

[0060] The F / B control execution determination unit 44 determines whether feedback control can be performed. The F / B control execution switching unit 45 switches between the first input and the second input based on the determination result of the F / B control execution determination unit 44. More specifically, when feedback control is to be performed, the first input, or the feedback deceleration output from the adder 43, is selected, while when feedback control is not to be performed, the second input, or the braking force requested by the driver's brake operation, is selected.

[0061] The initial value of the integral term is set in integral term initial value setting unit 46. In this embodiment, the target deceleration is set as the initial value of the integral term. Integral term initialization determination unit 47 determines whether the integral term is to be initialized. In this embodiment, the integral term is initialized when feedback control is initiated. Furthermore, when the deceleration due to the driver's braking operation becomes greater than the target deceleration, the integral term is determined to be initialized. Based on the determination result of integral term initialization determination unit 47, integral term initial value switching unit 48 switches between a first input and a second input. More specifically, when the integral term is to be initialized, the first input, or in other words, the initial value of the integral term (target deceleration) output from integral term initial value setting unit 46, is selected. Conversely, when the integral term is not to be initialized, the second input, or the feedback deceleration output from F / B control execution switching unit 45 or the braking force requested by the driver's braking operation, is selected.

[0062] Integral term upper limit value setting unit 49 sets the integral term upper limit value. Upper limit processing unit 50 executes processing for limiting deceleration based on the integral term upper limit value output from integral term upper limit value setting unit 49. Integral term lower limit value setting unit 51 sets the integral term lower limit value. In this embodiment, the integral term lower limit value is set to a value close to or near the target deceleration to limit the shift of the integral term toward acceleration due to the driver's braking operation. Lower limit processing unit 52 executes processing for limiting deceleration based on the integral term lower limit value output from integral term lower limit value setting unit 51 and outputs the requested braking force.

[0063] Next, we will refer to Figure 5A 、 Figure 5B 、 Figure 6A 、 Figure 6B 、 Figure 7A and Figure 7B The control actions performed by the control unit 21 are described below. Figure 5A 、 Figure 5B 、 Figure 6A 、 Figure 6B 、 Figure 7A and Figure 7B A graph illustrating control actions performed by the control unit 21 is shown. Figure 6A and Figure 7A and Figure 5A same.

[0064] like Figure 5A As shown in FIG, when the vehicle speed limit control is started, the control unit 21 prohibits acceleration and keeps the accelerator operation signal off to gradually reduce the vehicle speed from the initial speed to a safe speed. If the driver operates the brake pedal during this process, the vehicle speed ratio is further reduced only by the normal vehicle speed limit control.

[0065] Figure 5B The example shown in shows a case where neither control for initializing the integral term nor control for limiting the integral term is executed at the start of feedback control. In this case, because the initial value of the integral term is set to 0 at the start of feedback control, it takes some time for the integral term to accumulate, extending the time required for the actual deceleration to converge to the target deceleration, resulting in impaired responsiveness. Furthermore, when switching between driver-operated control and feedback control, a certain amount of time is required to offset the accumulation of the integral term, resulting in impaired responsiveness.

[0066] exist Figure 6B In the example shown in , the initial value of the integral term is controlled at the start of feedback control. More specifically, at the start of feedback control, the initial value of the integral term is set to the target deceleration (e.g., -0.1 m / s 2). This shortens the time period required for the actual deceleration to converge to the target deceleration at the start of feedback control, resulting in improved responsiveness. Figure 6B In the example shown in , a control action is performed to limit the integral term. Here, the control action is performed to limit the lower limit of the integral term. More specifically, the lower limit of the integral term is set close to or near the target deceleration, thereby limiting the time it takes for the integral term to shift toward acceleration due to the driver's braking operation. As a result, the accumulation of the integral term is suppressed, shortening the time required for the actual deceleration to converge to the target deceleration. This results in improved responsiveness when switching between driver-operated control and feedback control.

[0067] exist Figure 7B In the example shown in Figure 6B In the example shown, the initial value of the integral term is controlled at the start of feedback control. Figure 7B In the example shown in , with Figure 6B Similar to the example shown in , control is executed to limit the shift of the integral term toward acceleration. More specifically, when the deceleration due to the driver's braking operation becomes greater than the target deceleration, the integral term is set to the target deceleration. In other words, a determination is made as to whether the deceleration due to the driver's braking operation has become greater than the target deceleration, and if or when this determination result or determination flag is on, the integral term is set to the target deceleration. As a result, the accumulation of the integral term is suppressed, shortening the time required for the actual deceleration to converge to the target deceleration when switching between driver-operated control and feedback control, resulting in improved responsiveness.

[0068] The description of a specific embodiment is completed here, but the present invention is not limited to this specific embodiment and can be widely modified without departing from the scope of this information. In addition, the specific configuration, arrangement, quantity, angle, process, etc. of each component and part can be appropriately changed within the scope of the present invention. On the other hand, all the constituent elements shown in the above-mentioned embodiment are not essential in nature and can be appropriately selected and replaced. The contents of any reference cited in this disclosure will be incorporated into this application by reference. In addition, the present invention can be used not only when a steer-by-wire steering system fails, but also when the system performance is reduced due to the overheat protection of the steering system, or when an abnormality of redundancy loss occurs in a brake-by-wire braking system or autonomous driving.

Claims

1. A vehicle control device configured to be mounted on a vehicle provided with a steering system, the steering system comprising: an operating member configured to be operated by a driver; a steering member mechanically separated from the operating member and configured to steer the wheels; and a steering actuator powered by electric power supplied from an on-vehicle power supply and configured to actuate the steering member according to an input from the operating member, wherein The vehicle control device is configured to execute speed limit control to limit the traveling speed of the vehicle to below an upper speed limit when a failure in the steering system is detected, and The speed limit control is configured to set a target deceleration of the vehicle according to the limited traveling speed, and perform feedback control so that the actual deceleration of the vehicle becomes close to the target deceleration. The feedback control includes an integral term calculated by integrating a difference between the target deceleration and the actual deceleration, and When the deceleration of the vehicle becomes larger than the target deceleration due to the driver's braking operation, the integral term is set to the target deceleration.

2. The vehicle control device according to claim 1, wherein: When the feedback control is started, the target deceleration for the feedback control is set as an initial value of the integral term.

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