Vehicle control device

Abstract

Vehicle control device (10, 20, 30) for a vehicle (SV) comprising a power engine (22), an automatic transmission (24) for transmitting power generated by the power engine (22) to drive wheels of the vehicle (SV), and a friction braking device (32) for generating a friction braking force applied to the vehicle (SV), wherein the vehicle control device (10) performs control for constant speed travel to cause the vehicle (SV) to travel such that a vehicle speed, which is the speed of the vehicle (SV), corresponds to a predetermined target vehicle speed, wherein the vehicle control device (10, 20, 30) comprises: a power reduction section (10, 20) which controls the power engine (22) in the event that the vehicle speed must be reduced to correspond to the target vehicle speed,to reduce power without causing the automatic transmission (24) to change its gear ratio; a friction braking force increase section (10, 30) which, in the event that the vehicle speed must be reduced to match the target vehicle speed, even after the power has been reduced by the power reduction section (10, 20), controls the friction braking device (32) to increase the friction braking force without causing the automatic transmission (24) to change its gear ratio; and a downshifting control section (10, 20) which, upon fulfillment of a downshifting condition, which is fulfilled when a high-load friction braking condition, a condition in which the friction braking force is greater than a predetermined limit, persists for a predetermined limit time, causes the automatic transmission (24) to perform a downshifting,wherein downshifting changes the gear ratio of the automatic transmission (24) to a gear ratio that is greater than a gear ratio at a time when the downshift condition is met, wherein the downshifting implementation section (10, 20) is configured to set the determination limit time such that the determination limit time is shorter the smaller the gear ratio of the automatic transmission (24) is during a period during which the friction brake high load condition continues.

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The present invention relates to a vehicle control device for causing a vehicle to drive in such a way that the vehicle speed (the speed of the vehicle) corresponds to a predetermined target vehicle speed. Description of the state of the art

[0002] A vehicle control device that performs a constant-speed control, which is a type of cruise control, is conventionally known. The constant-speed control causes a vehicle to travel at a "target vehicle speed set by a driver".

[0003] Such a vehicle control device (hereinafter referred to as the "conventional device") calculates a target acceleration to bring the vehicle's speed into line with the target vehicle speed. The conventional device brings the vehicle's acceleration into line with the target acceleration by controlling an internal combustion engine, an automatic transmission, and a friction braking device (see Japanese patent application publication (kokai) No. 2017-56827).

[0004] In particular, in the case where a deceleration insufficient to achieve a negative target deceleration (i.e., a target deceleration) cannot be achieved by controlling the output of the internal combustion engine, the conventional device causes the friction braking device to generate a friction braking force.

[0005] To avoid “busy shifting”, which is a phenomenon in which the gear stage (gear position) of an automatic transmission changes frequently, the conventional device also performs a downshift (gear change to change the gear stage to a gear stage that has a higher gear ratio) only when the vehicle speed has increased by a predetermined amount within a predetermined period of time.

[0006] In the event that the vehicle is traveling downhill in a state where the steering is set to maintain a constant speed, the vehicle speed occasionally tends to exceed the target speed. Accordingly, in such a situation, the conventional system causes the friction braking device to generate a relatively high frictional braking force. That is, a state occurs in which a high load acts on the friction braking device (hereinafter referred to as a "friction braking high-load state").

[0007] In such a case, a situation arises in which the vehicle's speed does not increase by the predetermined amount within the predetermined time period due to friction braking force, and therefore a downshift is not performed. Since a downshift is not performed, the force used to decelerate the vehicle does not increase, particularly the braking force provided by a drive source (for example, engine braking force), and therefore the high-load friction braking state continues.In the case where the downhill road is long, the friction braking high load condition therefore continues for a long period of time, which can result in the occurrence of a phenomenon in which the temperatures of the brake pads and / or disc rotor of each wheel increase and the braking performance deteriorates (that is, the fading phenomenon (hereinafter simply referred to as “fading”)).

[0008] In cases where brake fade has degraded braking performance, the required deceleration cannot be generated by using friction braking force while maintaining a constant speed. Therefore, the driver may experience an unnatural sensation. Furthermore, if the vehicle is locked to maintain a constant speed and the driver manually applies the brakes, the braking performance may also be perceived as poor. SUMMARY OF THE INVENTION

[0009] The present invention was created to solve the problem described above. That is, one objective of the present invention is to provide a vehicle control device (hereinafter also referred to as the "device of the present invention") that, during the execution of control for driving at a constant speed, can prevent a deterioration of braking performance due to fading, while avoiding a deterioration of drivability that would otherwise occur due to frequent downshifting.

[0010] The device of the present invention is a vehicle control device ( 10 , 20 , 30 ) for a vehicle with a high-performance engine ( 22 ), an automatic transmission ( 24) for transmitting power generated by the engine to the vehicle's drive wheels, and a friction braking device ( 32 ) to generate a friction braking force applied to the vehicle, wherein the vehicle control device performs a control for driving at a constant speed to cause the vehicle to drive in such a way that a vehicle speed, which is the speed of the vehicle, corresponds to a predetermined target vehicle speed. The vehicle control device has the following features: a performance reduction period ( 10 , 20 , Step 220 , Step 245), which, in the event that the vehicle speed needs to be reduced to match the target vehicle speed, controls the power engine to reduce power without causing the automatic transmission to change its gear ratio (step 320 , Step 325 ); and a friction braking force increase section ( 10 , 30 , Step 250 , Step 260 ), which, in the event that the vehicle speed must be reduced to match the target vehicle speed, even after the power has been reduced by the power reduction section, controls the friction braking device to increase the friction braking force without causing the automatic transmission to change the gear ratio (step 320 and step 325 ).

[0011] The device of the present invention increases the braking force of the drive source by reducing the power generated by the engine without causing the automatic transmission to downshift when the vehicle speed needs to be reduced to match the target vehicle speed, for example, when the vehicle is traveling downhill. Furthermore, the device of the present invention increases the friction braking force generated by the friction braking device without causing the automatic transmission to downshift when the vehicle speed needs to be reduced. Accordingly, the occurrence of an operational shift is unlikely.

[0012] Meanwhile, in this case, for example if the downhill road is long, the high-load friction braking condition continues for a long period of time, and as a result, the temperatures of the components of the friction braking device increase, and fading may occur, which deteriorates the braking performance.

[0013] In light of the foregoing, the device of the present invention has a downshift feedthrough section ( 10 , 20 , Step 350 ) which, upon fulfillment of a downshift condition, which is fulfilled when a friction brake high-load state, which is a state in which the friction brake force is greater than a predetermined limit, continues for a predetermined determination limit time (step 335 , Step 345), causes the automatic transmission to perform a downshift, the downshift changing the gear ratio of the automatic transmission to a gear ratio greater than a gear ratio at a time when the downshift condition is met.

[0014] As a result, a downshift is performed if the high-load friction brake condition persists for the predetermined limit time, thereby increasing the drive source braking force. This, in turn, reduces the friction braking force generated by the friction brake device, thus suppressing temperature increases in the friction brake device components. Consequently, the probability of brake fade can be reduced.

[0015] In one mode of the device of the present invention, the downshifting section is configured to adjust the determination limit time such that the determination limit time is shorter the smaller the gear ratio of the automatic transmission is during a period during which the friction brake high load condition continues (step 330 ).

[0016] For example, if the gear stage is a "high-speed gear stage with a small gear ratio," and the drive source braking force is small, a situation arises where the friction braking device must generate a greater friction braking force. In such a case, the probability increases that the temperatures of the friction braking device components will rise within a short period of time, leading to brake fade.In contrast, in this mode, the time between the point at which the friction brake high-load condition occurs and the point at which a downshift is performed (i.e., the limit time) is shorter when the automatic transmission's gear stage is a high-speed gear stage, compared to the case where, for example, the automatic transmission's gear stage is a low-speed gear stage with a large gear ratio. Therefore, the probability of brake fade due to temperature increases in the friction brake components can be rapidly reduced.

[0017] In the case where a downshift is performed when the transmission stage is a low-speed gear, a jolt is likely to be generated due to a large change in the drive source braking force, which can impair drivability. Conversely, in this mode, the time between the point at which the friction brake high-load condition occurs and the point at which a downshift is performed (i.e., the determination limit time) is longer when the automatic transmission stage is a low-speed gear, compared to when the automatic transmission stage is a high-speed gear.In the case where the automatic transmission's gear stage is a low-speed gear stage, the occurrence of downshifting is therefore less likely, which can reduce the frequency with which a deterioration in drivability occurs.

[0018] In another mode of the present invention, the downshifting implementation section is configured to set the determination limit time to a first time, and to set the determination limit time to a second time that is shorter than the first time, after the downshifting has been performed, in the case where the downshifting has never been carried out during the period in which the friction brake high load condition continued (step 710 , Step 730 , Step 740 , Step 810 ).

[0019] In this mode, the determination limit time is set to the first relatively long period before the first downshift occurs within the span during which the friction braking high-load condition continues. Therefore, if the downhill stretch is relatively short, a downshift becomes less likely. Consequently, the frequency with which a deterioration in drivability occurs can be reduced.

[0020] In the event that the high-load friction brake condition persists after the first downshift has been performed within the period during which the high-load friction brake condition continued, the determination limit time is set to the second time, which is relatively short. Accordingly, in the event that the high-load friction brake condition continues even after the first downshift, for example, because the downhill road is long, second and subsequent downshifts are performed quickly. As a result, it is possible to reduce the probability of the temperatures of the friction brake components increasing and fading occurring.

[0021] To facilitate understanding of the present invention, the constituent elements of the invention that correspond to those of the embodiments of the invention described later are accompanied in the preceding description by names and / or reference numerals in parentheses, which are used in the embodiments; however, the constituent elements of the invention are not limited to those in the embodiments defined by the names and / or reference numerals. List of characters Fig. 1 is a schematic diagram of a vehicle control device according to a first embodiment; Fig. Figure 2 is a flowchart representing a routine executed by a CPU of a drive auxiliary ECU of the vehicle control device according to the first embodiment; Fig. Figure 3 is a flowchart representing another routine that is executed by the CPU of the powertrain auxiliary ECU of the vehicle control device according to the first embodiment; Fig. Figure 4 is a timing diagram to describe the operation of the vehicle control device; Fig. Figure 5 is a graph showing the relationship between brake pad temperature and brake effectiveness; Fig. Figure 6 is a flowchart representing a routine executed by a CPU of a power assist ECU of a vehicle control device according to a second modification of the first embodiment; Fig. Figure 7 is a flowchart representing a routine executed by a CPU of a powertrain ECU of a vehicle control device according to a second embodiment; and Fig. Figure 8 is a flowchart representing a routine executed by a CPU of a drive auxiliary ECU of a vehicle control device according to a first modification of the second embodiment. DESCRIPTION OF PREFERRED EXECUTION EXAMPLES

[0022] Vehicle control devices according to the embodiments of the present invention are now described. It should be noted that in the drawings of the embodiments, the same or corresponding sections are consistently identified by the same reference numerals. <Erstes Ausführungsbeispiel> < <konfiguration>>

[0023] A vehicle control device according to a first embodiment of the present invention (hereinafter also referred to as the "device of the first embodiment") is applied to a vehicle (not shown, for example, a motor vehicle). In some cases, the vehicle to which the device of the first embodiment is applied is referred to as the "own vehicle" to distinguish it from other vehicles. As in Fig. As shown in Figure 1, the device of the first embodiment has a drive auxiliary ECU. 10 , a power engine ECU 20 and a brake ECU 30 In this technical description, ECU stands for electronic control unit.

[0024] These ECUs are interconnected via a CAN (controller area network) in such a way that they can exchange data (communicate) with each other. Each ECU has a microcomputer. The microcomputer has a CPU, ROM, RAM, an interface (I / F), etc. The CPU executes various functions by carrying out instructions (programs, routines) stored in the ROM. The following description refers to the auxiliary drive ECU. 10 For simplicity, it is referred to as the "DSECU".

[0025] The DSECU is connected to the following sensors (including switches) provided in the vehicle and receives detection or output signals from the sensors. It should be noted that each sensor may be connected to a different ECU than the DSECU. In such a case, the DSECU receives the detection or output signal of each sensor from the ECU to which the sensor is connected via the CAN bus.

[0026] A radar sensor 11 is a well-known sensor that uses a radio wave in the millimeter wave band (hereinafter referred to as the "millimeter wave"). The radar sensor 11 It receives target information that specifies the distance between its own vehicle and a three-dimensional object, the relative speed of the three-dimensional object with respect to its own vehicle, the relative position (direction) of the three-dimensional object with respect to its own vehicle, etc., and outputs the target information to the DSECU.

[0027] A vehicle speed sensor 12 It detects the driving speed Vs of its own vehicle (vehicle speed) and outputs a signal representing the detected vehicle speed Vs.

[0028] An acceleration (G) sensor 13 detects the acceleration Gs of the vehicle and outputs a signal representing the detected acceleration Gs. If the acceleration Gs has a negative value, the magnitude (absolute value) of the acceleration Gs represents a deceleration.

[0029] A constant speed switch 14 is an input device operated by the driver. Signals and information described below are transmitted via the constant speed switch. 14 entered. • Request signal to start the control system for driving at a constant speed (start request signal) • Request signal to stop the control system for a journey at constant speed (stop request signal) • Target vehicle speed Vset, which is used in the control system for driving at a constant speed.

[0030] It should be noted that the control for driving at a constant speed is a type of speed control ( CC ) and automatically causes the vehicle to travel at the target vehicle speed Vset. The constant speed switch 14 It is also used to set a target intermediate vehicle time (which will be described later) to a desired time.

[0031] In the event that the control for constant speed driving is not performed, the start request signal is sent to the DSECU when the driver engages the constant speed switch. 14 It is activated in a special way. In the case where the control is for constant speed driving, the stop request signal is sent to the DSECU when the driver engages the constant speed switch. 14 operated in a special way.

[0032] The power engine ECU 20 is equipped with a variety of power machine sensors 21 It is connected and receives detection or output signals from these sensors. The force machine sensors 21 record the operating condition variables, operating control variables, etc. of an internal combustion engine 22 (Power engine), which is a drive source for the vehicle itself. The power engine sensors 21 They have an accelerator pedal actuation force sensor, a throttle valve opening sensor, an engine speed sensor, an intake air volume sensor, etc. Furthermore, the engine ECU receives 20 the current gear stage Sgear of an automatic transmission 24 .

[0033] The power engine ECU 20 is with power machine actuators 23 and the automatic transmission 24 connected. The power machine actuators 23 change the operating state of the internal combustion engine 22 , thereby changing the power output of the internal combustion engine 22 is generated. In the present embodiment, the internal combustion engine 22 A gasoline-injected, multi-cylinder engine of the spark-ignition type, it has a throttle valve for adjusting the intake air volume. The engine actuators 23 have at least one throttle valve actuator that changes the opening of the throttle valve (hereinafter referred to as the "throttle opening").

[0034] The automatic transmission 24 is a well-known multi-stage automatic transmission. The automatic transmission 24 selects one of a multitude of gears (gear stages) by using the pressure of a hydraulic oil flowing through a hydraulic circuit.

[0035] The gear stages of the automatic transmission 24 They comprise gear stages for forward motion and one gear stage for reverse motion. The gear stages for forward motion include "first gear, second gear, third gear, fourth gear, fifth gear, and sixth gear," which differ in their gear ratios. An Nth gear (N being an integer) is also referred to as the "Nth gear stage."

[0036] As is well known, the gear ratio decreases in the sequence of first, second, third, fourth, fifth, and sixth gears. The smaller the gear ratio (the higher the gear stage), the smaller the engine braking force (the deceleration force acting on the vehicle) caused by the rotational resistance of the internal combustion engine. 22 The gear ratio for reverse movement is reverse gear. First, second, and third gears can be referred to as low-speed gear ratios. Fourth, fifth, and sixth gears can be referred to as high-speed gear ratios.

[0037] The power engine ECU 20 can change the torque (power) produced by the internal combustion engine 22 is generated by the actuators of the power machines 23 drives the engine's ECU. 20 can the gear stage (gear ratio) of the automatic transmission 24 control is based on "upshift lines and downshift lines" that are preset for the vehicle speed Vs and the throttle valve opening.

[0038] That means, in the case where the gear stage is the Nth gear stage, the engine ECU changes 20 the gear stage shifts to the (N+1)th gear stage when the operating point, which is determined by the vehicle speed Vs and the throttle valve opening, exceeds an upshift line that the N -th gear stage corresponds to this. That means the engine control unit (ECU) 20 The transmission shifts up to a higher gear stage that is adjacent to the current gear stage. In the case where the transmission stage is N The -th gear stage changes the engine ECU. 20 the gear stage to the ( N -1)-th gear stage then, when the operating point determined by the vehicle speed Vs and the throttle valve opening is determined, exceeding a downshift line which the N -th gear stage corresponds to this. That means the engine control unit (ECU) 20 downshifts the gear stage to a lower gear stage that is adjacent to the current gear stage.

[0039] In this technical description, such a transmission stage control is referred to as the "normal transmission shift control".

[0040] The torque (power) produced by the internal combustion engine 22 is generated by the automatic transmission 24 the transmission is transferred to the drive wheels (not shown). Accordingly, the engine control unit (ECU) can 20 control the driving force of one's own vehicle by adjusting the power of the internal combustion engine 22 changes by changing the actuators of the power machines 23 used and the gear stage of the automatic transmission 24 controls. That is, the engine control unit (ECU). 20 can change the acceleration Gs (including negative acceleration Gs; that is, deceleration) of one's own vehicle.

[0041] The brake ECU 30 is equipped with a variety of brake sensors 31 It is connected and receives detection or output signals from these sensors. The brake sensors 31 capture parameters used to control friction braking devices (also known as "friction braking mechanisms") 32 They can be used. The brake sensors 31 They have a brake pedal actuation amount sensor and wheel speed sensors to detect the rotational speeds of the wheels, etc.

[0042] Each friction braking device 32 has a brake disc 32a , which is attached to each of the wheels, and a brake caliper 32b , which is attached to the vehicle body. The brake caliper 32b has brake pads (not shown) that are against the brake disc 32a be pressed.

[0043] The brake ECU 30 is equipped with a brake actuator 33 connected. The brake actuator 33 is provided in a hydraulic circuit that runs between a master cylinder (not shown) and the friction brake devices. 32 extends to the front and rear, left and right wheels. The brake actuator 33 is a well-known actuator that regulates the hydraulic oil pressures supplied to the respective wheel cylinders (not shown) in the brake calipers 32b are installed, and are individually adjusted for the multitude of wheels. When the corresponding brake pads are against the brake discs 32a When the wheels are pressed by applying hydraulic oil pressure to the respective wheel cylinders, friction braking forces (hydraulic braking forces) act on the wheels.

[0044] If the brake ECU 30 The brake ECU calculates a signal representing the target braking force Bfreq, which is received from the DSECU. 30 a "target brake oil pressure for each wheel" based on the target braking force Bfreq. Furthermore, the brake ECU controls 30 the brake actuator 33 such that the pressure of the hydraulic oil supplied to the wheel cylinder of each wheel matches the target brake oil pressure of each wheel. Accordingly, the brake ECU can 30 The friction braking force applied to the vehicle is to be matched with the target braking force Bfreq. For simplicity, the target braking force Bfreq and the target brake oil pressure are referred to as a "brake instruction value".

[0045] That means the brake ECU 30 can the friction braking force generated by the friction braking device 32 applied to the vehicle itself, control by operating the brake actuator 33 controls. As a result, the brake ECU can 30 to change the acceleration Gs (deceleration, which is a negative acceleration Gs) of one's own vehicle. <<Steuerung für eine Fahrt mit konstanter Geschwindigkeit> >

[0046] In the case where the vehicle's driving mode is a normal driving mode, the DSECU will change the vehicle's driving mode to a constant speed driving control mode when the start request signal is sent to the DSECU as a result of the constant speed switch being activated. 14 is sent by the driver. If the driving mode is the control mode for constant speed driving, the DSECU performs a "constant speed driving control" to automatically cause its own vehicle to drive at a constant speed, so that the vehicle speed Vs becomes equal to the target vehicle speed Vset.

[0047] More precisely, when the DSECU performs the control for a journey at a constant speed, the DSECU obtains (calculates) the vehicle speed Vs of its own vehicle based on the signal from the vehicle speed sensor. 12 The DSECU calculates a target acceleration. Ac* , to match the vehicle speed Vs with the target vehicle speed Vset by using the following expression (1). Ac* = ( Vset − Vs ) × K1 ( Vs )

[0048] In expression (1), K1(Vs) represents an acceleration increase for a journey at constant speed, set to a positive value corresponding to the vehicle speed Vs. More precisely, the increase K1(Vs) is set such that its value decreases as the vehicle speed Vs increases.

[0049] In the case where the vehicle speed deviation (Vset - Vs) on the right-hand side of expression (1) is positive, a target acceleration Ac* (>0) is calculated to accelerate the vehicle. In the case where the vehicle speed deviation (Vset - Vs If ) is negative, a target acceleration Ac* (<0) is calculated to decelerate the vehicle.

[0050] The DSECU controls the driving force of the vehicle in such a way that the actual acceleration Gs of the vehicle, as measured by the acceleration sensor, is not affected. 13 is recorded, just like the target acceleration. Ac* It is, and also controls the friction braking force when necessary. These controls will be described in detail later. It should be noted that the DSECU, in its control system for driving at a constant speed, determines the magnitude of the change in vehicle speed. Vs per unit of time, as the actual acceleration Gs can be used.

[0051] It should be noted that the DSECU performs a "constant-speed transmission shift control" as described below when the driving mode is set to constant-speed control mode. Specifically, if the throttle valve is not fully closed, the DSECU performs a transmission shift control similar to "normal transmission shift control".

[0052] In the case where the throttle valve is completely closed, the DSECU prohibits "normal transmission shift control" and determines the shift point based on the vehicle speed Vs and the vehicle speed deviation ( Vs - Vset) and the magnitude (absolute value) of the actual acceleration Gs of the vehicle itself, whether a downshift condition for constant speed driving is met or not. If the downshift condition for constant speed driving is met, the DSECU performs a downshift. For example, in the case where the magnitude of the actual acceleration Gs of the vehicle itself is greater than a downshift determination limit, the magnitude of which is in accordance with the magnitude of the vehicle speed deviation ( Vs - Vset) is determined, the downshift condition for constant speed driving is met, and a downshift is performed. In the case where the magnitude of the actual acceleration Gs If the vehicle's own speed is equal to or less than the downshift determination limit, the downshift condition for driving at a constant speed is not met, and no downshifting is performed.

[0053] The downshift determination limit is set such that its value decreases when the vehicle speed deviation ( Vs - Vset). As a result, the probability of downshifting occurring is greater the larger the magnitude of the vehicle speed deviation ( Vs - Vset); that is, the smaller the vehicle speed deviation ( Vs The lower the Vset value, the lower the probability of a downshift occurring. It should be noted that if the downshift condition for constant speed driving is not met, the transmission shift control will not perform a downshift for constant speed driving.

[0054] In the case where the driving mode of the vehicle is a control mode for driving at a constant speed, when the stop request signal is a result of actuating the constant speed switch 14 When the driver sends a signal to the DSECU, the DSECU terminates control for a constant speed drive and changes the driving mode of its own vehicle to normal driving mode.

[0055] It should be noted that when the driving mode is the normal driving mode, the power engine ECU 20 a target throttle valve opening based on vehicle speed Vs and the amount of accelerator pedal deduction detected by the accelerator pedal deduction sensor, and drives the throttle valve actuator so that the actual throttle valve opening matches the target throttle valve opening. Furthermore, if the driving mode is normal driving mode, the brake ECU also controls 30 the brake actuator 33 Based on the amount of brake pedal deduction detected by the brake pedal deduction sensor, the vehicle then accelerates with the desired Gs in accordance with the driver's input. "Overview of the operation"

[0056] In the case where the vehicle's driving mode is the control mode for constant speed driving, the DSECU calculates the target driving force Freq and the target braking force Bfreq as described below, so that the actual acceleration Gs is equal to the target acceleration. Ac* It should be noted that the target braking force Bfreq is "0" or has a negative value. The greater the absolute value (magnitude) |Bfreq| of the target braking force Bfreq, the greater the frictional braking force exerted by the friction braking devices. 32 is generated.

[0057] The DSECU transmits a signal representing the target drive force (Frequency) to the power machine ECU. 20 The power engine ECU 20 calculates a torque (power) that is produced by the internal combustion engine 22 The torque to be generated is based on the gear stage (actual gear stage) Sgear and the target drive force Freq at the time the signal representing the target drive force Freq is received. This torque is referred to as the "engine target torque Tqreq". The engine ECU 20 controls the power machine actuators 23 such that the internal combustion engine 22 generates a torque (power) that is equal to the target torque Tqreq of the power machine.

[0058] The DSECU transmits a signal representing the target braking force Bfreq to the brake ECU. 30 The brake ECU 30 controls the brake actuator 33 such that the total sum of the friction braking forces generated by the wheels becomes equal to the absolute value |Bfreq| of the target braking force Bfreq.

[0059] In the case where the actual acceleration Gs equal to or greater than the target acceleration Ac* If the vehicle is traveling downhill (for example), the DSECU first reduces the actual acceleration Gs by gradually decreasing the target drive force Freq. As a result of this reduction in target drive force Freq, the target engine torque Tqreq is reduced to zero, thus maximizing the drive source braking force. If the actual acceleration Gs is equal to or greater than the target acceleration Ac* at this point, the DSECU reduces the target brake braking force Bfreq without downshifting. That is, the DSECU increases the absolute value (magnitude) |Bfreq| of the target brake braking force Bfreq.

[0060] As a result, the friction braking force increases, and when the actual acceleration Gs becomes equal to the target acceleration Ac*, the DSECU maintains the target braking force Bfreq at that value at that time. When the vehicle, which has been traveling downhill, enters a level road, the DSECU reduces the absolute value (magnitude) |Bfreq| of the target braking force Bfreq, because the actual acceleration Gs becomes less than the target acceleration Ac*.

[0061] However, when a vehicle is traveling downhill on a long stretch of road, a situation can arise where a prolonged period is characterized by a high absolute value |Bfreq| of the target braking force Bfreq (in other words, a high-load friction braking condition where the friction braking force exceeds a predetermined limit Bth). During this time, the temperatures of the friction braking components increase. 32 and fading can occur. It should be noted that in such a situation, it is less likely that the downshift condition for constant speed driving will be met, since the magnitude of the vehicle speed deviation ( Vs The actual acceleration Gs of the vehicle are less likely to increase than the vehicle's actual acceleration (Vset). Therefore, the probability of the transmission shift control performing a downshift during constant-speed driving is low.

[0062] Given the foregoing, if a downshift condition, which will be described later, is met, the DSECU shifts the gear stage of the automatic transmission. 24 from the current Sgear gear level down by only one level (one gear). (Downshift condition)

[0063] The downshift condition is a condition that is fulfilled when the state in which the absolute value | Bfreq | of the target braking force Bfreq is greater than the predetermined limit Bth (that is, the friction brake high load state) has continued for a determination limit time tsth or longer.

[0064] When a downshift is performed when the downshift condition is met, the amount of "drive source braking force (idle deceleration, which is a deceleration caused by the drive source braking force)" acting on the vehicle increases. Therefore, even if the friction braking force is reduced, it is possible to continuously bring the actual acceleration Gs into line with the target acceleration Ac*. That is, the DSECU can reduce the absolute value |Bfreq| of the target braking force Bfreq. Since downshifting prevents the continuation of the high-load friction braking condition, brake fade can be avoided. It should be noted that if the vehicle is traveling on a short downhill stretch of road, the downshift condition is unlikely to be met.Therefore, the frequency of downshifting decreases, which can reduce the frequency with which a deterioration in the drivability of one's own vehicle occurs. "Specific operation"

[0065] The DSECU's CPU (hereinafter referred to simply as the "CPU") executes routines every time a predetermined time elapses, which are shown in flowcharts in Fig. 2 and Fig. 3 are shown.

[0066] When a predetermined time interval has arrived, the CPU accordingly starts the routine of Fig. 2 at step 200 and takes a step 205 The process continues to determine whether the vehicle's driving mode is the control mode for constant-speed driving. The vehicle's driving mode is set to normal driving mode by an initialization routine executed by the CPU when an ignition switch (not shown) is turned from Off to On. If the driving mode is normal driving mode, the CPU makes a "No" determination at step 1. 205 and proceeds directly to step 295 continue, in order to complete the current execution of the current routine.

[0067] If the driving mode is a result of actuating the constant speed switch 14 When the control mode is changed to constant speed driving, the CPU performs the following actions at step 205 A "yes" determination leads to the sequential processing of step 210 and the processing of step 215 through, which will be described later, and proceeds step by step 220 on.

[0068] Step 210 The CPU receives the vehicle speed Vs of its own vehicle and calculates the target acceleration. Ac* , by applying the vehicle speed Vs to the expression (1) described above. Step 215 The CPU receives the actual acceleration. Gs based on the signal from the accelerometer 13 .

[0069] The CPU determines at step 220 , whether the actual acceleration Gs is smaller than the target acceleration Ac* or not. In the case where the actual acceleration Gs is smaller than the target acceleration Ac* (in the case where the vehicle itself needs to be accelerated), the CPU makes a "yes" decision at step 220 and takes a step 225 to determine whether the brake target braking force Bfreq, which is at step 260 The reduction, which is described later, is negative or not. That is, the CPU determines whether a friction braking force is generated at the present time or not. It should be noted that the target braking force Bfreq is set to "0" in the previously described initialization routine.

[0070] Here, it is assumed that the target braking force Bfreq is equal to or greater than "0". In this case, the CPU makes a "no" determination at step 225 , sequentially performs the processing of step 230 to step 240 through, which will be described later, and proceeds step by step 295 continue, in order to complete the current execution according to the current routine.

[0071] Step 230 The CPU increases the target driving force Freq by a predetermined amount dFu. Step 235 The CPU transmits a signal representing the target drive force (Frequency) to the power machine ECU. 20 . Step 240 The CPU transmits a signal representing the target braking force Bfreq to the brake ECU. 30 It should be noted that in the case where the target braking force Bfreq is "0", the brake ECU 30 the brake actuator 33 does not cause it to generate a frictional braking force.

[0072] This processing is repeated when the actual acceleration Gs is less than the target acceleration Ac* and the target braking force Bfreq is equal to or greater than "0". As a result, the target driving force Freq gradually increases.

[0073] In contrast, in the case where the actual acceleration Gs is equal to or greater than the target acceleration Ac* to the point where the CPU is processing step 220 if the action is carried out (i.e., the vehicle itself needs to be decelerated), the CPU makes a "no" decision at step 220 and takes a step 245 on. At step 245 The CPU reduces the target driving force Freq by a predetermined amount dFd.

[0074] Next, the CPU proceeds step by step. 250 further and determines whether the step 245 The calculated target driving force Freq is less than a limiting driving force Fth, or not. The limiting driving force Fth is a value determined by the gear stage Sgear and the vehicle speed Vs at the current time. The limiting driving force Fth is a value that corresponds to the drive source braking force acting on the vehicle itself when the torque produced by the internal combustion engine is exceeded. 22 The value generated is set to "0" (a value corresponding to an idle delay). In other words, the vehicle's own driving force cannot be reduced if the target driving force Freq is less than the limiting driving force Fth, unless the transmission is downshifted. That is, if the target driving force Freq is less than the limiting driving force Fth, the CPU cannot increase the drive source braking force unless it downshifts the transmission, and therefore the CPU cannot increase the idle delay.

[0075] It should be noted that the CPU at step 250 the torque produced by the internal combustion engine 22 to generate (the target torque of the power machine Tqreq) on the basis of the gear stage Sgear and the target drive force Freq at the current time, and can calculate and determine whether the target torque of the power machine Tqreq is equal to or less than “0” or not.

[0076] In the case where the target driving force Freq is equal to or greater than the limit driving force Fth, the CPU makes a "no" determination at step 250 and terminates the current execution of the current routine after performing the processing steps 235 and 240 described above.

[0077] If this condition continues, the target drive force Freq will be determined by processing step 245 The force gradually decreases and becomes smaller than the limiting driving force Fth. In this case (that is, the case in which the target driving force Freq is smaller than the limiting driving force Fth), the CPU makes a "yes" determination at step 1. 250 and sequentially performs the processing of step 255 and step 260 The CPU then performs the processing steps described below. Following this, the CPU executes the previously described steps 235 and 240 and terminates the current execution of the current routine.

[0078] Step 255 The CPU sets the target driving force Freq to a value that is equal to the limiting driving force Fth. Step 260 The CPU reduces the target braking force Bfreq by a predetermined amount dBd.

[0079] As previously described, when the drive source braking force reaches the "maximum value of the drive source braking force that is available at the Sgear gear stage and the vehicle speed Vs If the "can be generated at the current time" threshold is reached, the absolute value of the target braking force Bfreq increases, thus increasing the friction braking force. At this time, downshifting by the transmission shift control for constant speed driving is not performed unless the previously described downshift condition for constant speed driving is met.

[0080] In the case where the actual acceleration Gs is equal to or greater than the target acceleration Ac* The target drive force Freq is at step 255 at the limiting driving force Fth, and the absolute value of the target braking force Bfreq is maintained at step 260 continuously increased. Therefore, the actual acceleration Gs smaller than the target acceleration Ac* In this case, the CPU makes a "yes" determination at step 220 and takes a step 225 continue. At this time, the target braking force Bfreq is less than "0". Therefore, the CPU makes a "yes" determination at step 225 and sequentially performs the processing of step 265 and step 270 the following steps are described below. The CPU then performs the processing of "Step". 235 and step 240 " through, which were previously described, and concludes the current execution of the current routine.

[0081] Step 265 The CPU increases the target braking force Bfreq by a predetermined amount dBu. Step 270 The CPU sets the target braking force Bfreq to the smaller of "0" and the value in step 265 increased target braking force Bfreq. That is, the CPU limits (protects) the target braking force Bfreq so that the target braking force Bfreq has a value equal to or less than " 0 " is.

[0082] After this point, the processing of step 265 and step 270 repeatedly, when the actual acceleration Gs is smaller than the target acceleration Ac* and the brake target braking force Bfreq is smaller than “ 0 "Accordingly, the target braking force Bfreq gradually increases (the absolute value of the target braking force Bfreq gradually decreases), while the target driving force Freq remains unchanged. If the actual acceleration Gs is less than the target acceleration Ac* after the time at which the target braking force Bfreq is reached at step 1..." 270 on " 0 " is set, the target drive force Freq is determined by processing step 230 gradually increased.

[0083] In contrast, if the actual acceleration Gs is equal to or greater than the target acceleration, as a result of the gradual increase in the target braking force Bfreq (as a result of the gradual decrease in the absolute value of the target braking force Bfreq). Ac* If this happens, the CPU makes a "no" determination at step 220 and takes a step 245 to step 260 In the case where the vehicle travels for a long period of time on a "downhill road which requires a friction braking force to maintain a constant speed", the target braking force Bfreq accordingly remains close to a certain value.

[0084] If a predetermined time signal has arrived, the CPU starts the routine of Fig. 3 of step 300 and takes a step 305 to determine whether the driving mode of the vehicle is the control mode for driving at a constant speed or not.

[0085] In the case where the driving mode is the normal driving mode, the CPU makes a "no" determination at step 305 and takes a step 310 on. At step 310 The CPU transmits a signal to the engine control unit (ECU) to allow the previously described normal transmission shift control. 20 and sets the value of a time element ts1 (which will be described later) on “ 0 "(resets the timer ts1). The CPU then proceeds to step 395 continues and ends the current execution of the current routine. It should be noted that the value of the time element ts1 is set to "0" by the initialization routine described above.

[0086] In contrast, if the driving mode is the control mode for driving at a constant speed, the CPU makes a "yes" determination at step 305 and takes a step 320 to determine whether any of the conditions 1 and condition 2 The requirements are fulfilled, which are described below. Condition 1 : the actual acceleration Gs is greater than the target acceleration Ac* (that is, the vehicle speed) Vs must be reduced). Condition 2 The target braking force Bfreq is less than 0 (Bfreq <0). In the case where none of the conditions are met. 1 and condition 2 If the condition is met, the CPU makes a "no" determination at step 320 , takes a step 322 continues to perform the previously described transmission shift control for driving at a constant speed, and terminates the current execution of the current routine.

[0087] In the case where at least one of the conditions 1 and condition 2 at the point in time when the CPU begins processing step 320 If the condition is met, the CPU makes a "yes" determination at step 1. 320 , sequentially performs the processing of step 325 and step 330 , which are described below, and proceeds step by step 335 on.

[0088] Step 325 The CPU transmits a signal to the engine control unit (ECU) to disable the previously described normal transmission shift control. 20 . Step 330 The CPU determines (sets) the determination limit time tsth based on the gear stage Sgear at the current time. More precisely, the CPU obtains the determination limit time tsth by applying the gear stage Sgear at the current time to a lookup table M1(Sgear).

[0089] According to the reference table M1 (Sgear) the limit of determination time tsth is determined as follows. In the case where the gear stage Sgear is currently second gear, the limit time tsth is set to a time corresponding to second gear. Tth2 set. In the case where the gear stage Sgear is currently in third gear, the limit time tsth is set to a time corresponding to third gear. Tth3 set. In the case where the gear stage Sgear is currently in fourth gear, the limit time tsth is set to a time corresponding to fourth gear. Tth4 set. In the case where the gear stage Sgear is currently in fifth gear, the determination limit time tsth is set to a time corresponding to fifth gear. Tth5 set. In the case where the gear stage Sgear is currently in sixth gear, the limit time tsth is set to a time corresponding to sixth gear. Tth6 set.

[0090] These corresponding times fulfill the following relational expression ( R1 The reason for this will be described later. Tth6 < Tth5 < Tth4 < Tth3 < Tth2

[0091] Next, the CPU proceeds step by step. 335 to determine whether the absolute value (magnitude | Bfreq |) of the target braking force Bfreq is greater than a limit Bth, which is set to a predetermined positive value (hereinafter simply referred to as the "limit Bth"). That is, at step 335 , whether the previously described high-load friction brake condition occurred or not.

[0092] In the case where the absolute value |Bfreq| of the target braking force Bfreq is equal to or less than the limit Bth, the CPU makes a "no" determination at step 335 and takes a step 337 further, to determine the value of the time element ts1 to set to "0" (sets the time element) ts1 back). The CPU then proceeds to step 322 The CPU then proceeds to perform the previously described transmission shift control for driving at a constant speed. Afterward, it moves to step... 395 continues and concludes the current execution of the current routine.

[0093] In contrast, if the absolute value | Bfreq | of the target braking force Bfreq is greater than the limit Bth, the CPU makes a "yes" determination at step 335 and takes a step 340 continue, to increment the value of time element ts1 by 1. The value of the time element ts1 represents the time over which the state continues in which the absolute value |Bfreq| of the target braking force Bfreq is greater than the limit Bth (that is, the previously described friction brake high load state).

[0094] Next, the CPU proceeds step by step. 345 to determine whether the value of the time element ts1 is greater than that at step 330 The CPU determines whether or not a specific determination limit time tsth has been reached. If the value of the time element ts1 is equal to or less than the determination limit time tsth, ​​the CPU makes a "no" determination at step 1. 345 , takes a step 322 The CPU then proceeds to step 1. 395 continues and concludes the current execution of the current routine.

[0095] In contrast, if the value of the time element ts1 is greater than the limit time tsth, ​​the previously described friction brake high-load condition has continued for a long period of time, and therefore it is likely that the temperature of each brake disc 32a and the temperature of each brake pad is excessively high. That is, in the state where the value of the timing element ts1 If the threshold time tsth is greater than the limit time, it is a state in which the previously described downshift condition has been met, and a state in which the probability of fading occurring is high.

[0096] Considering the previously described scenario, in the case where the value of the time element ts1 is greater than the determination limit time tsth, ​​the CPU makes a "yes" determination at step 345 and takes a step 350 continued, to issue a request to downshift the automatic transmission's gear level. 24 from the current gear stage Sgear by one stage (that is, one downshift request) to the engine control unit 20 to transmit. Upon receiving the downshift request, the engine ECU changes 20 the gear stage of the automatic transmission 24 from the current gear level Sgear to a lower gear level adjacent to the current gear level Sgear (performs a downshift). The CPU then proceeds to step 322 continues to perform the previously described transmission shift control for driving at a constant speed, and then proceeds to step 395 continue, in order to complete the current execution of the current routine.

[0097] As a result, the braking force of the drive source increases, which in turn increases the deceleration of the vehicle itself. Thus, the actual acceleration Gs becomes lower than the target acceleration. Ac* Therefore, the processing of step 265 from Fig. 2. This is carried out so that the absolute value of the target braking force Bfreq decreases. Accordingly, the temperature of each brake disc is prevented from increasing. 32a and increase the temperature of each brake pad.

[0098] Now the operation of the DSECU will be discontinued if the vehicle itself is SV driving on a downhill road, described by using an example that is in Fig. Figure 4 is shown. In this example, the vehicle itself drives SV under control for a journey at constant speed on a road section (section between point p0 and point p1 ) including a downhill road. Your own vehicle SV drives downhill from a time t1 up to a time t8. The gear stage at that time t1 is the sixth gear.

[0099] In the span between the times t1 up to a time t2 , since the vehicle SV is traveling downhill, the vehicle speed increases Vs gradually deviates from the target vehicle speed Vset despite the fact that the control is performed for a constant speed journey. This means that a speed increase amount (vehicle speed deviation) ( Vs - Vset) gradually increases, which is the difference between the target vehicle speed Vset and the vehicle speed Vs is. Accordingly, the actual acceleration Gs will be equal to or greater than the target certificate. Ac* , and therefore the DSECU reduces the target drive force Freq over time. t1 (see step 245 ).

[0100] At that time t2 The magnitude of the target driving force Freq becomes smaller than the limiting driving force Fth. That is, the driving source braking force, in the case where the transmission stage is sixth gear, reaches its maximum value. Therefore, after time t2, the DSECU gradually reduces the target braking force Bfreq from "0" (see step 1). 260 This means that the DSECU increases the magnitude (absolute value) of the target braking force Bfreq. As a result, at time t3, the magnitude of the target braking force Bfreq becomes greater than the limit Bth. This means that the previously described high-load friction braking condition occurs at time t3.

[0101] Since the magnitude (absolute value) of the target braking force Bfreq increases after time t2, the frictional braking force exerted by each frictional braking device also increases. 32 is generated. Therefore, the vehicle speed Vs approaches the target vehicle speed Vset, and the temperature of each brake disc 32a and the temperature of each brake pad gradually increases.

[0102] It is known that, as in Fig. As indicated by line a1 in Figure 5, the braking performance (brake efficiency factor) of a friction braking mechanism decreases when the temperatures of the brake pads of the friction braking mechanism increase and exceed a certain temperature (for example, approximately 200 °C). Braking performance represents the frictional braking force generated when the brake pads are pressed against the brake disc with a specific force. 32a Brake fade occurs when the temperature of each brake pad becomes equal to or greater than a certain temperature.

[0103] In cases where brake fade has impaired braking performance, sufficient deceleration cannot be generated using friction braking force while steering for a constant speed. Therefore, the driver may experience an unnatural sensation. This occurs when the driver applies the brakes after the vehicle's driving mode has changed. SV Furthermore, when the driving mode is changed to normal, the driver may feel that the braking performance is poor.

[0104] In view of the above, if the time interval ts over which the friction brake high load condition continues (time interval ts starting from time t3) becomes longer than the limit time tsth (in this case the time Tth6 corresponding to sixth gear), the DSECU performs a downshift to end the friction brake high load condition (to reduce the load on each friction brake device). 32 ).

[0105] More precisely, if the time span ts is at a time t4 the same as the time corresponding to sixth gear Tth6 When this happens, the DSECU switches the gear stage of the automatic transmission. 24 down from sixth gear (current gear stage) to fifth gear (see step 345 and step 350 Since the drive source braking force increases as a result of downshifting, the friction braking force provided by the friction braking device may also increase. 32 to be generated, reduced (see step 265 ).

[0106] After downshifting, the DSECU changes the determination limit time tsth from the time corresponding to sixth gear. Tth6 to the time Tth5 corresponding to the fifth gear, which corresponds to the fifth gear stage after downshifting.

[0107] In the Fig. The example shown in section 4 is taken at a time t5 the time period ts over which the friction brake high load condition continues, equal to or longer than the time corresponding to fifth gear Tth5 At that time t5 Therefore, the DSECU switches the gear stage of the automatic transmission. 24 downshifting from fifth gear (current gear stage) to fourth gear. As a result, the friction braking force generated by the friction braking device can be reduced. 32 The amount to be generated can be further reduced. As a result, at a certain time t6 The magnitude of the target braking force Bfreq is less than the limit Bth, and the friction brake high-load condition ends at the time t6 This prevents the temperatures of each brake disc from varying. 32a and excessively increase the temperature of each brake pad, thus preventing brake fade.

[0108] Incidentally, the device of the first embodiment sets the time TthN corresponding to the Nth cycle (N is an integer between 2 and 6) such that the previously described relation expression ( R1 ) is fulfilled (see step 330 That is, a time TthM corresponding to the M-th gear corresponds to an M-th gear stage, which is of relatively high speed (has a small gear ratio), and is shorter than a time TthL corresponding to the L-th gear, which corresponds to an L-th gear stage (M > L), which is of relatively low speed (has a large gear ratio).

[0109] The reason why the determination limit time tsth is set as described above is as follows. That is, if downshifting is performed into a gear stage with a relatively large gear ratio (for example, a low gear stage (any of the first gear up to third gear)), the increase in the drive source braking force is large. Therefore, there is a high probability that downshifting will significantly increase the idle delay. Consequently, the idle delay after downshifting becomes excessive, and the probability of an immediate upshift becomes high.

[0110] As a result, downshifting and upshifting can be repeated frequently (i.e., operational shifting can occur), and drivability can deteriorate. Accordingly, it is preferable for downshifting to a lower gear ratio to be performed carefully. Therefore, the DSECU sets the determination limit time tsth such that the lower the gear ratio (the higher the gear ratio), the longer the determination limit time tsth. ​​That is, in the case where the gear ratio is a low gear ratio, the DSECU will perform a downshift if the friction brake high-load condition persists for a relatively long period.

[0111] In the case where your own vehicle SV When driving in a high gear ratio (for example, from fourth to sixth gear), which has a relatively small gear ratio, the braking force from the drive source is small. Therefore, the frictional braking force becomes large, and this force is generated by any friction braking device. 32 This is necessary because it places a greater load on each friction braking device. 32 When applying the command, it is preferred that the downshifting be carried out as early as possible.

[0112] Therefore, the DSECU sets the determination limit time tsth such that the higher the gear ratio (the smaller the gear ratio), the shorter the determination limit time tsth. ​​This means that in the case of a high gear ratio, the DSECU will downshift if the high-load friction brake condition persists for a relatively short period. As a result, the condition in which a high load is placed on each friction brake device can be avoided. 32 The applied force is applied, terminates early, and the occurrence of fading can be avoided. Furthermore, even when downshifting to a higher gear, the idle delay does not increase significantly. Therefore, the probability of a shifting issue is very low.

[0113] It should be noted that in the example given in Fig. Figure 4 shows the friction brake high-load condition at that time. t6 ends, which is a time t7 preceding the time span from the time t3 (at which the friction brake high load condition began to occur) equal to the time corresponding to fourth gear Tth4 will be. Accordingly, the downshifting will occur at that time. t7 not carried out again.

[0114] As previously described, the device of the first embodiment can reduce the probability that the friction brake high-load condition will persist for a long period of time, while decreasing the frequency of downshifting, for example, when the vehicle SV is traveling downhill under constant-speed control. As a result, the probability of brake fade (a phenomenon in which braking performance deteriorates) can be reduced. <Erste Modifikation der Vorrichtung des ersten Ausführungsbeispiels>

[0115] A first modification of the device of the first embodiment differs from the device of the first embodiment only in that the value of the timer ts1 is changed each time a downshift is performed by processing step 355 from Fig. 3 is set to "0" (the time element ts1 (is reset). More precisely, the device's CPU proceeds to step according to this modification. 355 continued after they have completed the processing of step 350 from Fig. 3 has been carried out, and sets the value of the time element. ts1 on " 0 ". Accordingly, when downshifting is performed, the next downshift will then be performed when the friction brake high load condition continues for the limit time tsth, ​​which corresponds to the gear stage into which the downshift was performed.

[0116] This device can also reduce the probability of “fading and deterioration of drivability due to operational shifting” like the device of the first embodiment. <Zweite Modifikation der Vorrichtung des ersten Ausführungsbeispiels>

[0117] A second modification of the device of the first embodiment differs from the first modification of the device of the first embodiment only in that the determination limit time tsth is not in accordance with the gear stage Sgear of the automatic transmission. 24 at the current time, and that the determination limit time tsth is set to a fixed value Tth (fixed time Tth).

[0118] More precisely, according to this modification, the device's CPU executes the routine described in a flowchart. Fig. 6 is shown, instead of the routine that is in Fig. 3 is shown. The routine of Fig. 6 is a routine that is obtained by taking the step 330 from Fig. 3 by step 330a is replaced, and is configured to process step 355 to carry out.

[0119] If the CPU to step 330a As the process progresses, the CPU accordingly sets the determination limit time tsth to the fixed time Tth. Furthermore, the CPU sets the value of the timer ts1 to "0" (resetting the timer ts1) at step 355 each time a downshift is performed by processing a step 350 is carried out.

[0120] This device also performs a downshift if the high-load friction brake condition persists for a fixed time Tth during the execution of the control for constant-speed travel. Accordingly, the probability of the high-load friction brake condition persisting for a long period of time can be reduced. <Zweites Ausführungsbeispiel>

[0121] Next, a vehicle control device according to a second embodiment of the present invention (hereinafter referred to as the “device of the second embodiment”) will be described.

[0122] The device of the second embodiment differs from the device of the first embodiment only in the following point. • The device of the second embodiment performs the routine described in Fig. 7 is shown, instead of the routine that is in Fig. 3 is shown.

[0123] The device of the second embodiment, which performs the routine described in Fig. As shown in Figure 7, the determination limit time tsth is not set to one of several times in accordance with the gear stage Sgear at the current time (step ). 330 Instead, the device of the second embodiment changes the determination limit time tsth in accordance with whether the vehicle itself has downshifted (undergone a downshift) during a period in which the friction brake high load condition (a condition in which the absolute value | Bfreq | of the brake target braking force Bfreq is greater than the limit Bth) continues.

[0124] More precisely, in the case where the vehicle itself did not experience a downshift during the period in which the friction brake high load condition continued (a downshift was not performed), the device of the second embodiment sets the determination limit time tsth so that it is longer compared with the case where the vehicle itself did experience a downshift (a downshift was performed at least once).

[0125] Therefore, the threshold time tsth is set to a relatively long period before the first downshift occurs within the span during which the high-load friction braking condition persists. If the downhill stretch is relatively short, downshifting becomes less likely. Consequently, the frequency with which a deterioration in drivability occurs can be reduced.

[0126] Meanwhile, the high-load friction brake condition continues after the first downshift has been performed within the span during which the high-load friction brake condition persisted; the limit time tsth is set to a relatively short time. In the case where the high-load friction brake condition continues even after the first downshift, for example, because the downhill road is long, second and subsequent downshifts are accordingly performed quickly. As a result, it is possible to reduce the probability that the temperatures of the components of each friction brake device will exceed the limit. 32 increase and fading occurs.

[0127] The device of the second embodiment will now be described with a focus on this difference.

[0128] The routine that is in Fig. As shown in 7, this differs from the routine of Fig. 3 only in the following points. • Step 330 the routine that is in Fig. As shown in step 3, this is done by step 710 replaced. • Step 720 and step 730 are between step 350 and step 322 added. • Step 740 is between step 337 and step 322 added. Accordingly, the following mainly describes these different steps.

[0129] If the CPU to step 710 As the process progresses, the CPU determines (sets) the determination limit time tsth based on a shutdown execution marker. Xs More precisely, the CPU obtains the determination limit time tsth by determining the value of the shutdown execution marker. Xs applies to a lookup table Ms at the current time.

[0130] It should be noted that in the case where the value of the downshift execution marker Xs “ 1 "This indicates that a downshift has been performed at least once (one or more times) within a period during which the friction brake high-load condition (the condition in which the absolute value | Bfreq | of the target braking force Bfreq is greater than the limit Bth) continues. In the case where the value of the downshift execution mark Xs “ 0 "This indicates that a downshift has never been performed within the period during which the friction brake high-load condition (the condition in which the absolute value | Bfreq | of the target braking force Bfreq is greater than the limit Bth) continues. It should be noted that the value of the downshift execution marker Xs through the previously described initialization routine to “ 0 " is set.

[0131] According to the lookup table Ms, the determination limit time tsth is determined as follows. In the case where the value of the downshift execution marker Xs at the current time “ 0 If the vehicle has not downshifted, the determination limit time tsth is set to a time T0th corresponding to an HS absence. If the value of the downshift execution marker Xs is "1" at the current time (i.e., if the vehicle has downshifted), the determination limit time tsth for a time corresponding to "HS attendance" T1th " set. It should be noted that these corresponding times form the following relational expression ( R2 ) fulfill. T0th > T1th

[0132] The step 710 A specific determination limit time tsth is used for the determination at step 345 used. In the case where the CPU is used for step 1. 345 progresses when the value of the downshift execution marker Xs “ 0 "is, will be the "time corresponding to an HS absence" T0th ", which is a relatively long time than the determination limit time tsth. ​​As a result, the time between the occurrence of the friction brake high-load condition ("yes" determination at step 1) is determined. 335 ) and the first downshift (step 350 ) relatively long.

[0133] In the case where the value of the time element ts1 is greater than the determination limit time tsth (=T0th), the CPU makes a "yes" determination at step 345 , sequentially performs the processing of step 350 , Step 720 and step 730 through, which will be described later, and proceeds step by step 795 continue, in order to complete the current execution of the current routine.

[0134] Step 350 The CPU transmits a request to downshift the automatic transmission's gear level. 24 from the current gear stage Sgear by one stage (that is, a downshift request) to the engine control unit 20 Upon receiving the downshift request, the engine ECU changes 20 the gear stage of the automatic transmission 24 from the current gear stage Sgear to a lower gear stage adjacent to the current gear stage Sgear (performs a downshift). Step 720 : the CPU sets the value of the timer ts1 to "0" (sets the timer ts1 back). Step 730 : the CPU sets the value of the shutdown execution marker Xs to "1".

[0135] In the case where the CPU then proceeds to step 710 progresses when the value of the downshift execution marker Xs “1” is the “time corresponding to HS attendance”. T1th ", which is a relatively short time than the determination limit time tsth used. As a result, the time until the next downshift is performed within the span during which the friction brake high-load condition continues becomes short.

[0136] In the case where the value of the time element ts1 is greater than the determination limit time tsth (= T1th), the CPU makes a "yes" determination at step 345 and takes a step 350 to send the downshift request to the engine's ECU 20 to transmit. Upon receiving the downshift request, the engine ECU executes 20 A downshift is performed. As a result, if the high-load friction brake condition continues even after the first downshift, second and subsequent downshifts are carried out quickly.

[0137] Then the CPU sets the step 720 the value of the time element Ts1 to "0" (sets the time element ts1 back) and sets at step 730 the value of the downshift execution marker Xs to "1". After the processing of the step has been carried out. 322 In this state, the CPU progresses to step 795 continue, in order to complete the current execution of the current routine.

[0138] It should be noted that in the case where the absolute value | Bfreq | of the target braking force Bfreq is equal to or greater than the limit Bth at the point at which the CPU processes the step 335 performs a "no" determination at step 335 makes and then the processing of step 337 and step 740 The following steps are described below. The CPU then processes step [number missing in original text]. 322 through and proceeds step by step 795 continue, in order to complete the current execution of the current routine. Step 337 The CPU sets the value of the timer. ts1 to "0" (sets the time element ts1 back). Step 740 : the CPU sets the value of the shutdown execution marker Xs to "0".

[0139] The device described above in the second embodiment can reduce the frequency of a deterioration in drivability and can reduce the probability that the temperatures of the components of the friction braking devices will exceed acceptable levels. 32 increase and fading occurs. <Erste Modifikation des zweiten Ausführungsbeispiels>

[0140] A first modification of the device of the second embodiment differs from the device of the second embodiment only in that the determination limit time tsth is in accordance with the gear stage Sgear of the automatic transmission. 24 will be changed at the present time.

[0141] More precisely, according to this modification, the device's CPU executes the routine described in a flowchart. Fig. 8 is shown, instead of the routine that is in Fig. 7 is shown. The routine of Fig. 8 is a routine that is obtained by step 710 from Fig. 7 through step 710a will be replaced.

[0142] If the CPU to step 710a As progresses, the CPU accordingly obtains the determination limit time Tsth by determining the value of the shutdown execution marker. Xs at the current time and the gear stage Sgear at the current time each on reference tables Ms0 and Ms1 applies.

[0143] According to the reference table Ms0 The determination limit time tsth is determined as follows. In the case where the value of the downshift execution marker Xs is “0” at the current time and the gear stage Sgear is second gear at the current time, the determination limit time tsth is set to a time T0th2 corresponding to an HS absence and second gear. In the case where the value of the downshift execution marker Xs is "0" at the current time and the transmission stage Sgear is third gear at the current time, the determination limit time tsth is set to one of HS -Absence and the corresponding time T0th3 set. In the case where the value of the downshift execution marker Xs is “0” at the current time and the gear stage Sgear is fourth gear at the current time, the determination limit time tsth is set to a time T0th4 corresponding to an HS absence and fourth gear. In the case where the value of the downshift execution marker Xs is "0" at the current time and the transmission stage Sgear is fifth gear (fifth) at the current time, the determination limit time tsth is set to one of HS -Absence and the corresponding time T0th5 set.

[0144] In the case where the value of the downshift execution marker Xs is "0" at the current time and the gear stage Sgear is sixth gear at the current time, the determination limit time tsth is set to a time T0th6 corresponding to an HS absence and sixth gear. These corresponding times satisfy the following relationship expression ( R3 ). T0th6 < T0th5 < T0th4 < T0th3 < T0th2

[0145] According to the reference table Ms1 The determination limit time Tsth is determined as follows. In the case where the value of the downshift execution marker Xs is “1” at the current time and the gear stage Sgear is second gear at the current time, the determination limit time tsth is set to a time T1th2 corresponding to HS presence and second gear. In the case where the value of the downshift execution marker Xs is “1” at the current time and the gear stage Sgear is third gear at the current time, the determination limit time tsth is set to a time T1th3 corresponding to HS presence and third gear. In the case where the value of the downshift execution marker Xs is “1” at the current time and the gear stage Sgear is fourth gear at the current time, the determination limit time tsth is set to a time T1th4 corresponding to HS presence and fourth gear. In the case where the value of the downshift execution marker Xs is “1” at the current time and the gear stage Sgear is fifth gear at the current time, the determination limit time tsth is set to a time T1th5 corresponding to HS presence and fifth gear. In the case where the value of the downshift execution marker Xs is "1" at the current time and the gear stage Sgear is sixth gear (sixth) at the current time, the determination limit time tsth set on a time T1th6 corresponding to HS presence and the sixth gear. These corresponding times fulfill the following relational expression ( R4 ). T1th6 < T1th5 < T1th4 < T1th3 < T1th2

[0146] Furthermore, these corresponding times satisfy the following relationship expressions (R5a) to (R5e) T0th2 > T1th2 T0th3 > T1th3 T0th4 > T1th4 T0th5 > T1th5 T0th6 > T1th6

[0147] Then the step 710a specific determination limit time tsth for the determination at step 345 used. As a result, in the case where a downshift has never been performed and the value of the downshift execution marker Xs is "0", the time between the occurrence of the friction brake high load condition and the first execution of a downshift (step) is used. 350 ) relatively long (see the relational expressions (R5a) to (R5e)).

[0148] In the case where the value of the downshift execution marker Xs “ 1 "If this is the case, the time until the next downshift (step) will be relatively short." 350 ) is carried out in the span during which the friction brake high-load condition continues (“Yes” determination at step 335 ) (see the relational expressions ( R5a ) until ( R5e )).

[0149] Accordingly, it is possible to reduce the frequency of a deterioration in drivability and to reduce the probability that the temperature of the components of each friction braking device will change. 32 increase and fading occurs.

[0150] Additionally, the higher the gear level of the automatic transmission, the more 24 The shorter the time between the occurrence of the friction brake high load state (the "yes" determination at step 1), the smaller the gear ratio at the current time. 335 ) and the determination to perform a downshift (“yes” determination at step 345 ) (see the relational expressions ( R3 ) and (R4)).

[0151] For example, if the vehicle is traveling downhill at a constant speed under the steering system, it is possible to reduce the probability of the friction brakes remaining under high load for an extended period by decreasing the frequency of downshifts. As a result, the likelihood of brake fade can be reduced.

[0152] This device can also reduce the frequency of drivability deterioration and decrease the likelihood that the temperatures of the components will differ from those of any friction braking device. 32 This device can increase the likelihood of fading occurring and cause fading. Furthermore, it can reduce the probability of fading occurring while decreasing the frequency of downshifting. <Zweite Modifikation des zweiten Ausführungsbeispiels>

[0153] A second modification of the device of the second embodiment differs from the first modification of the device of the second embodiment only in that the processing of step 720 from Fig. 7 is not carried out. That is, in the first modification of the device of the second embodiment, the value of the timer is changed. ts1 through the processing of step 720 each time set to "0" (the time element) ts1 (is reset) when a downshift is performed. In contrast, in the second modification of the device of the second embodiment, the value of the timer is ts1 not every time through the processing of step 720 set to "0" (the time element) ts1 (is not reset) when a downshift is performed.

[0154] This device can also reduce the frequency of drivability deterioration and decrease the likelihood that the temperatures of the components will be affected by any friction braking device. 32 increase and fading occurs.

[0155] Furthermore, this device can also reduce the likelihood of fading occurring while reducing the frequency of downshifts.

[0156] The embodiments of the present invention have been described; however, the present invention is not limited to the embodiments described above, and various modifications based on the technical idea of ​​the present invention may be used.

[0157] The automatic transmission in the previously described embodiments is a multi-speed automatic transmission. However, the automatic transmission could be a CVT (continuously variable transmission). In this case, the term "downshifting" could refer to a pseudo-downshift, in which the gear ratio continuously increases (for example, a pseudo-downshift where the gear ratio continuously increases from a predetermined gear ratio by a predetermined amount).

[0158] The previously described devices of the exemplary embodiments and their modifications can have as a drive source only a motor (power engine) or a motor and an internal combustion engine. In the case where the drive source is a motor, the drive source braking force can include a regenerative braking force. In this case, the current supplied to the motor is stopped or reduced during downshifting, thereby generating or increasing a regenerative braking force.

[0159] The devices of the exemplary embodiments described above and the modifications thereof can be configured to perform a known following-drive control (vehicle-to-vehicle distance control, adaptive cruise control (ACC)) as the control for driving at a constant speed.

[0160] A following-drive vehicle-to-vehicle distance control system is a control system that causes the vehicle to follow a vehicle ahead of it, based on target information, while maintaining a predetermined distance between itself and the vehicle ahead. Following-drive vehicle-to-vehicle distance control systems are known (for example, Japanese patent application publication (kokai) No. 2014-148293, Japanese patent application publication (kokai) No. 2006-315491, Japanese patent No. 4172434, Japanese patent No. 4929777, etc.).

[0161] The basis of the vehicle-to-vehicle distance control is, for example, as follows. During the execution of the vehicle-to-vehicle distance control, a following vehicle is set based on the information provided by the radar sensor. 11 The vehicle following the received target information was tracked within a predetermined area.

[0162] Furthermore, the DSECU calculates the target acceleration Gtgt in accordance with any of the following expressions ( 2 ) and (3). In the expressions ( 2 ) and (3) Vfx(a) is the relative speed of the vehicle being followed, k1 and k2 These are predetermined positive increases (coefficients), ΔD1 is an inter-vehicle spacing deviation (ΔD1 = Dfx(a) - Dtgt), which is obtained by subtracting a "target inter-vehicle spacing Dtgt from an inter-vehicle spacing Dfx of the following vehicle". It should be noted that the target inter-vehicle spacing Dtgt is calculated by multiplying the vehicle speeds by the product of the vehicle speeds. Vs of the driver's own vehicle and a target intermediate vehicle time Ttgt is calculated, which is determined by the driver using the constant speed switch. 14 is set (Dtgt = Ttgt × Vs).

[0163] If the value (k1 × ΔD1 + k2 × Vfx(a)) is positive or “0”, the DSECU determines the target acceleration Gtgt by using the following expression (2). ka1 is a positive increase (coefficient) for acceleration and is set to a value equal to or less than "1". Gtgt ( für Beschleunigung ) = ka1 × ( k1 × Δ D1 + k2 × Vfx ( a ) )

[0164] Meanwhile, if the value (k1 × ΔD1 + k2 × Vfx(a)) is negative, the DSECU determines the target acceleration Gtgt by using the following expression (3). kd1 is an increase (coefficient) for a delay and is set to "1" in the present example. Gtgt ( für Verzögerung ) = kd1 × ( k1 × Δ D1 + k2 × Vfx ( a ) )

[0165] It should be noted that if no object is present in the area of ​​the vehicle being followed, the DSECU calculates the target acceleration Gtgt based on a target velocity SPDtgt and the vehicle speed. Vs of one's own vehicle in such a way that the vehicle speed Vs with the “target speed SPDtgt, which is in accordance with the target intermediate vehicle time Ttgt”.

[0166] The DSECU controls the power machine actuators. 23 , by controlling the power unit ECU 20 used, and controls the brake actuator 33 by modifying the brake ECU 30 If necessary, it is used so that the vehicle's acceleration Gs matches the target acceleration Gtgt. The above description is an overview of the following-vehicle distance control.

[0167] The devices of the exemplary embodiments and the devices of the modifications can be found in step 335 Use a target brake oil pressure, the cumulative value of the brake target braking force, the cumulative value of the target brake oil pressure or the like instead of the brake target braking force. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2014148293

[0160] JP 2006315491

[0160] JP 4172434

[0160] JP 4929777

[0160] < / konfiguration>

Claims

[1] Vehicle control device (10, 20, 30) for a vehicle (SV) comprising a power engine (22), an automatic transmission (24) for transmitting power generated by the power engine (22) to drive wheels of the vehicle (SV), and a friction braking device (32) for generating a friction braking force applied to the vehicle (SV), wherein the vehicle control device (10) performs control for constant speed driving to cause the vehicle (SV) to drive such that a vehicle speed, which is the speed of the vehicle (SV), corresponds to a predetermined target vehicle speed, wherein the vehicle control device (10, 20, 30) comprises: a power reduction section (10, 20) which, in the case where the vehicle speed must be reduced to match the target vehicle speed, controls the power engine (22) to reduce the power without causing the automatic transmission (24) to change its gear ratio; a friction braking force increase section (10, 30) which, in the event that the vehicle speed must be reduced to match the target vehicle speed, even after the power has been reduced by the power reduction section (10, 20), controls the friction braking device (32) to increase the friction braking force without causing the automatic transmission (24) to change the gear ratio; and a downshifting section (10, 20) which, upon fulfillment of a downshifting condition, which is fulfilled when a friction brake high load condition, which is a condition in which the friction brake force is greater than a predetermined limit, continues for a predetermined limit time, causes the automatic transmission (24) to perform a downshift, wherein the downshifting changes the transmission ratio of the automatic transmission (24) to a transmission ratio that is greater than a transmission ratio at a time when the downshifting condition is fulfilled. [2] Vehicle control device (10, 20, 30) according to claim 1, wherein the downshifting section (10, 20) is configured to adjust the determination limit time such that the determination limit time is shorter the smaller the gear ratio of the automatic transmission (24) is during a period during which the friction brake high load condition continues. [3] Vehicle control device (10, 20, 30) according to claim 1 or 2, wherein the downshifting section (10, 20) is configured to set the determination limit time to a first time in the case where downshifting has never been performed during the period during which the friction brake high load condition continues, and to set the determination limit time to a second time which is shorter than the first time after downshifting has been performed.

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