JP4682641B2 - Vehicle traction control device - Google Patents

Description

  The present invention relates to a vehicle slip state acquisition device applied to an all-wheel drive vehicle in which the driving force of a drive source is transmitted to all wheels, and a vehicle traction control device and antiskid using the slip state acquisition device. The present invention relates to a control device. In the present specification, the vehicle body acceleration in the longitudinal direction of the vehicle body takes a positive value when the vehicle is in a driving state (acceleration state), and takes a negative value when the vehicle is in a braking state (deceleration state). To do.

  Conventionally, when the degree of slip in the acceleration direction (hereinafter simply referred to as “acceleration slip”) generated in the wheels when the vehicle is in a driving state exceeds a predetermined acceleration slip threshold, 2. Description of the Related Art A traction control device that determines that an occurrence has occurred and starts / executes traction control is widely known. In the traction control, for example, a predetermined braking force is applied to the wheel. Thereby, the acceleration slip of the said wheel is suppressed and the traction of the wheel can be maintained favorable.

  Further, when the vehicle is in a braking state and the degree of slip in the deceleration direction generated on the wheels (hereinafter simply referred to as “deceleration slip”) exceeds a predetermined deceleration slip threshold, deceleration slip occurs. There is also widely known an ABS control device that determines that the vehicle is in operation and starts and executes anti-skid control (hereinafter also referred to as “ABS control”). In the ABS control, the braking force applied to the wheel is reduced / adjusted. Thereby, the deceleration slip of the said wheel is suppressed and the increase in braking distance can be suppressed.

  In order to accurately start and execute such traction control or ABS control, it is necessary to accurately estimate the degree of acceleration slip or deceleration slip. In general, the degree of acceleration slip can be represented by, for example, a value obtained by subtracting the vehicle body speed of the vehicle from the wheel speed (hereinafter referred to as “acceleration slip amount”). It can be represented by a value obtained by subtracting the wheel speed from the speed (hereinafter referred to as “deceleration slip amount”). Therefore, in order to accurately estimate the degree of acceleration slip or deceleration slip, it is necessary to accurately estimate the vehicle body speed of the vehicle.

In general, vehicle body speed can be estimated based on each wheel speed. However, when the vehicle is excessively driven in the all-wheel drive vehicle, acceleration slip may occur simultaneously on all the wheels. In this case, it is very difficult to accurately estimate the vehicle body speed from the wheel speeds. For this reason, a technique for estimating the vehicle body speed of the vehicle by detecting the vehicle body acceleration in the longitudinal direction of the vehicle body by a longitudinal acceleration sensor and integrating the detected vehicle body acceleration (hereinafter referred to as “vehicle body acceleration detection value”) over time. Is known (see, for example, Patent Document 1).
JP-A-2-306865

  By the way, in general, an error may occur in the output characteristics of the acceleration sensor, and the magnitude and direction of the error varies to some extent for each individual. Therefore, depending on the individual, the case where the detected value of the vehicle body acceleration becomes larger or smaller than the true vehicle body acceleration may occur. When the vehicle acceleration detection value is smaller than the true vehicle acceleration, the vehicle speed obtained by integrating the vehicle acceleration detection value over time is estimated to be smaller than the true vehicle speed, so the acceleration slip amount is calculated to be larger. .

  Therefore, when the vehicle body speed is estimated based on the vehicle body acceleration detection value itself, the acceleration slip amount easily reaches the acceleration slip threshold. Therefore, it is determined that acceleration slip is occurring at an early stage where it should not be determined that acceleration slip is occurring, and as a result, traction control is started at an early stage where traction control should not be started. Malfunctions can occur.

  In order to prevent the occurrence of such a malfunction related to traction control, Patent Document 1 discloses a value obtained by adding a predetermined value (positive value) to a vehicle body acceleration detection value (hereinafter referred to as “vehicle body acceleration raising value”). The technique of estimating the vehicle body speed of a vehicle by time integrating is described. As a result, the vehicle body acceleration raising value can always be calculated to a value greater than or equal to the true vehicle body acceleration, and therefore the vehicle body speed can always be estimated to be a value greater than or equal to the true vehicle body speed. As a result, the acceleration slip amount is calculated to be small, and the occurrence of malfunction related to the traction control can be prevented.

  In the following, in order to prevent the occurrence of malfunction related to traction control, a case will be considered in which the vehicle body speed is estimated based on the vehicle body acceleration raising value for all-wheel drive vehicles. In this case, as described above, since the acceleration slip amount is calculated to be small, the acceleration slip amount tends to hardly reach the acceleration slip threshold value.

  Even in this case, if the wheel speed of all the wheels (accordingly, the acceleration slip amount) suddenly increases, for example, when the driver depresses the accelerator pedal greatly, the acceleration slip amount of all the wheels immediately starts the acceleration slip. The threshold can be reached. As a result, it can be immediately determined that the acceleration slip has occurred for all the wheels, and the traction control can be immediately started for all the wheels.

  On the other hand, even if the driver is stepping on the accelerator pedal slightly while driving on a road surface with a relatively low road surface friction coefficient (hereinafter referred to as “low μ road surface”), an acceleration slip occurs on all wheels simultaneously. obtain. In this case, the increasing speed of the wheel speed of all the wheels (accordingly, the acceleration slip amount) is very small. Furthermore, as described above, the acceleration slip amount is calculated to be smaller due to the estimation of the vehicle body speed based on the vehicle body acceleration increase value.

  As a result, the time when the acceleration slip amount reaches the acceleration slip threshold value may be greatly delayed, or the acceleration slip amount may not reach the acceleration slip threshold value. In other words, the timing at which it is determined that the acceleration slip has occurred is greatly delayed (that is, the timing at which the traction control is started is greatly delayed), or it cannot be determined that the acceleration slip has occurred (that is, , Traction control cannot be started).

  On the other hand, since it is difficult for wheel traction to occur during such low μ road surface travel, it is particularly required that traction control be started and executed at an appropriate timing. From the above, when an all-wheel drive vehicle is in a driving state, it cannot be determined that acceleration slip is occurring at an appropriate timing (particularly during low μ road traveling) (therefore, traction control is started). There is a problem that may not be possible).

  The above problem also occurs in the case of deceleration slip (and hence ABS control). That is, when the vehicle body acceleration detection value becomes larger than the true vehicle body acceleration due to the variation in the output characteristics of the acceleration sensor described above, the vehicle body speed obtained by time integration of the vehicle body acceleration detection value is estimated to be larger than the true vehicle body speed. Therefore, the deceleration slip amount is calculated to be large.

  Therefore, when the vehicle body speed is estimated based on the vehicle body acceleration detection value itself, the deceleration slip amount easily reaches the deceleration slip threshold value. Therefore, it is determined that deceleration slip is occurring at an early stage where it should not be determined that deceleration slip is occurring, and as a result, ABS control is started at an early stage where ABS control should not be started. Malfunctions can occur.

  In order to prevent the occurrence of such malfunction related to ABS control, a value obtained by subtracting a predetermined value (positive value) from the vehicle body acceleration detection value (hereinafter referred to as “vehicle body acceleration lowering value”) is integrated over time. A technique for estimating the vehicle body speed of the vehicle by doing so is also known. As a result, the vehicle body acceleration bulk reduction value can always be calculated to a value less than or equal to the true vehicle body acceleration, and therefore the vehicle body speed can always be estimated to a value that is less than or equal to the true vehicle body speed. As a result, the deceleration slip amount is calculated to be small, and the occurrence of malfunction related to the ABS control can be prevented.

  Hereinafter, in order to prevent malfunctions related to ABS control, a case where the vehicle body speed is estimated based on the vehicle body acceleration bulk reduction value for all-wheel drive vehicles will be considered. In this case, as described above, since the deceleration slip amount is calculated to be small, the deceleration slip amount tends to hardly reach the deceleration slip threshold value.

  Even in this case, when the wheel speed of all the wheels rapidly decreases (therefore, the deceleration slip amount increases rapidly) due to the driver depressing the brake pedal greatly, the deceleration slip amount of all the wheels is reduced. The deceleration slip threshold can be reached immediately. As a result, it can be immediately determined that deceleration slip has occurred for all wheels, and ABS control can be immediately started for all wheels.

  On the other hand, even when the vehicle is traveling on the low-μ road surface and the driver slightly depresses the brake pedal, deceleration slips can occur simultaneously on all the wheels. This tendency is particularly likely to occur in all-wheel drive vehicles. In this case, the reduction speed of the wheel speeds of all the wheels (accordingly, the increase speed of the deceleration slip amount) is very small. Further, as described above, the deceleration slip amount is calculated to be smaller due to the estimation of the vehicle body speed based on the vehicle body acceleration reduction value.

  As a result, the time when the deceleration slip amount reaches the deceleration slip threshold value may be greatly delayed or the deceleration slip amount may not reach the deceleration slip threshold value. In other words, the timing at which it is determined that deceleration slip has occurred is greatly delayed (that is, the timing at which ABS control is started is greatly delayed), or it cannot be determined that deceleration slip has occurred (that is, , ABS control cannot be started).

  On the other hand, since the braking distance is particularly likely to increase during traveling on a low μ road surface, it is particularly required that the ABS control be started and executed at an appropriate timing. From the above, when the all-wheel drive vehicle is in a braking state, it cannot be determined that deceleration slip is occurring at an appropriate timing (particularly during low μ road traveling) (therefore, ABS control is started). There is a problem that may not be possible).

  From the above, in order to cope with such a problem, in an all-wheel drive vehicle, regardless of whether the vehicle is in a driving state or in a braking state (especially when traveling on a low μ road surface), the slip state of the wheel is determined. A more appropriate acquisition is desired.

  The present invention has been made to cope with such a demand, and an object of the present invention is to provide a slip state acquisition device for a vehicle that can more appropriately acquire a slip state of a wheel in an all-wheel drive vehicle, and its An object of the present invention is to provide a vehicle traction control device and an anti-skid control device using a slip state acquisition device.

  An apparatus for acquiring a slip state of a vehicle according to the present invention includes all wheel speed sensors that output a signal that represents a vehicle wheel speed and a longitudinal acceleration sensor that outputs a signal that represents a vehicle body longitudinal acceleration of the vehicle. Applies to driving vehicles.

  The vehicle slip state acquisition device according to the present invention is characterized in that first vehicle body acceleration acquisition means for acquiring vehicle body longitudinal acceleration based on the output of the wheel speed sensor, and vehicle body based on the output of the longitudinal acceleration sensor. Based on a comparison result between second vehicle body acceleration acquisition means for acquiring vehicle body acceleration in the front-rear direction and vehicle body acceleration based on the acquired wheel speed sensor output and vehicle body acceleration based on the acquired front-rear acceleration sensor output. A slip state acquisition means for acquiring the slip state of the wheel is provided.

  Here, the first vehicle body acceleration acquisition means, for example, when the vehicle is in a driving state, the vehicle brakes a value obtained by time differentiation of the minimum value of the wheel speeds of all the wheels obtained from the wheel speed sensor output. In the state, a value obtained by time-differentiating the maximum value of the wheel speeds of all the wheels obtained from the wheel speed sensor output is acquired as “vehicle acceleration based on wheel speed sensor output”.

  Further, the second vehicle body acceleration acquisition means, for example, when the vehicle is in a driving state, obtains a value obtained by adding a predetermined value to the vehicle body acceleration detection value corresponding to the longitudinal acceleration sensor output (that is, the vehicle body acceleration raising value). When the vehicle is in a braking state, a value obtained by subtracting a predetermined value from the vehicle body acceleration detection value (that is, the vehicle body acceleration reduction value) is acquired as “vehicle body acceleration based on the longitudinal acceleration sensor output”. Note that the second vehicle body acceleration acquisition means may always acquire the vehicle body acceleration detection value itself as “vehicle body acceleration based on the longitudinal acceleration sensor output”.

  For example, when the acceleration slip amount of a certain wheel increases when the vehicle is in a driving state, the increasing gradient of the wheel speed of the wheel (and thus the time differential value of the wheel speed (positive value)) It means that it is larger than the increasing gradient (hence, the vehicle body acceleration (positive value)). In other words, when the acceleration slip amount of a certain wheel increases when the vehicle is in a driving state, the “vehicle acceleration based on wheel speed sensor output (positive value)” becomes “vehicle acceleration based on longitudinal acceleration sensor output (positive Tend to be larger than

  Similarly, when the vehicle is in a braking state, an increase in the deceleration slip amount of a certain wheel means that the decreasing gradient of the wheel speed of the wheel (and hence the time differential value (negative value) of the wheel speed) is the vehicle speed. It means that it is smaller than the decrease gradient (hence, vehicle body acceleration (negative value)). In other words, when the deceleration slip amount of a certain wheel increases when the vehicle is in a braking state, “vehicle acceleration based on wheel speed sensor output (negative value)” becomes “vehicle acceleration based on longitudinal acceleration sensor output (negative Tends to be smaller (absolute value becomes larger).

  Therefore, based on such a viewpoint, the slip state of the wheel can be appropriately acquired based on a comparison result between “vehicle body acceleration based on wheel speed sensor output” and “vehicle body acceleration based on longitudinal acceleration sensor output”.

  More specifically, when the vehicle is in a driving state, the slip state acquisition means calculates a vehicle body acceleration (positive value) based on the acquired wheel speed sensor output as the acquired longitudinal acceleration sensor output. It is configured to determine that slip in the acceleration direction has occurred on the wheel on condition that the acceleration is greater than a vehicle body acceleration (positive value) based thereon.

  As described above, when the vehicle is in a driving state, the “vehicle acceleration based on the longitudinal acceleration sensor output” may be set to the vehicle acceleration increase value from the viewpoint of preventing the occurrence of malfunction related to traction control. Many. In this case, the “vehicle acceleration based on the longitudinal acceleration sensor output” can be a value greater than or equal to the true vehicle acceleration.

  That is, when the vehicle is in a driving state, the condition that “the vehicle body acceleration based on the wheel speed sensor output” is larger than “the vehicle body acceleration based on the longitudinal acceleration sensor output” is surely increased in the acceleration slip amount. Means that Therefore, when such a condition is satisfied, it can be determined that an acceleration slip has occurred without waiting for the acceleration slip amount to reach the acceleration slip threshold. In other words, it can be determined that the acceleration slip has occurred at an earlier time and at an appropriate time than the conventional device described above.

  The vehicle slip state acquisition device according to the present invention is applied to a vehicle including an accelerator operation amount corresponding value sensor that acquires a value corresponding to the accelerator operation amount of the vehicle. On condition that the vehicle body acceleration based on the speed sensor output is larger than the vehicle body acceleration based on the longitudinal acceleration sensor output, and the acquired accelerator operation amount correspondence value is greater than zero and smaller than a predetermined value. It is preferable to be configured to determine that a slip in the acceleration direction has occurred on the wheel. Here, the accelerator operation amount corresponding value is, for example, the accelerator operation amount itself, the throttle valve opening, and the like.

  As described above, in the conventional apparatus that determines that the acceleration slip has occurred when the acceleration slip amount reaches the acceleration slip threshold, the above-mentioned “all the operation is performed by a slight accelerator operation during low μ road surface travel”. In the case where the phenomenon that the acceleration slip amount of the wheel gradually increases occurs, a problem such as a large delay in the timing for determining that the acceleration slip has occurred can particularly occur.

  On the other hand, even if the above-mentioned “phenomenon in which the acceleration slip amount gradually increases” occurs, the “vehicle body acceleration based on the wheel speed sensor output” described above is “the vehicle body acceleration based on the longitudinal acceleration sensor output”. The condition that “acceleration” is greater than “acceleration” can be established immediately after the occurrence of the phenomenon. In other words, if the accelerator operation amount is a small value and the “vehicle acceleration based on the wheel speed sensor output” is larger than the “vehicle acceleration based on the longitudinal acceleration sensor output”, the “acceleration slip amount is moderate. This means that a phenomenon that increases rapidly is occurring.

  Therefore, when configured as described above, in the case where the “phenomenon in which the acceleration slip amount gradually increases” occurs, without waiting for the acceleration slip amount to reach the acceleration slip threshold, It can be determined that an acceleration slip has occurred at an appropriate time.

  Moreover, in the slip state acquisition device for a vehicle according to the present invention, the slip state acquisition unit is configured to generate a slip in the acceleration direction on the wheel when the condition continues to be established for a predetermined time. Suitably configured to determine.

  According to this, the above-described “vehicle acceleration based on the wheel speed sensor output” is larger than “vehicle acceleration based on the longitudinal acceleration sensor output” (and the accelerator operation amount corresponding value is larger than zero and smaller than the predetermined value). It is determined that the acceleration slip is generated only when the above condition continues to be established stably over a predetermined time. Therefore, it is possible to suppress the occurrence of a situation in which it is erroneously determined that the acceleration slip has occurred when the acceleration slip has not occurred.

  Further, the vehicle traction control device according to the present invention using any of the above-described vehicle slip state acquisition devices according to the present invention includes a wheel speed sensor that outputs a signal representing the wheel speed of the vehicle, and the vehicle body of the vehicle. The present invention is applied to an all-wheel drive vehicle including a longitudinal acceleration sensor that outputs a signal representing vehicle acceleration in the longitudinal direction.

  The vehicle traction control device according to the present invention includes an estimated vehicle body speed acquisition means for acquiring an estimated vehicle body speed of the vehicle based on at least the output of the longitudinal acceleration sensor, and the wheel speed based on the output of the wheel speed sensor. Traction that starts / executes traction control when a value based on a value obtained by subtracting the acquired estimated vehicle body speed (that is, acceleration slip amount) exceeds a predetermined threshold (that is, the acceleration slip threshold). Control means, and the traction control means, when it is determined by the vehicle slip state acquisition device according to the present invention that slip in the acceleration direction has occurred in the wheel, the acceleration slip threshold value. Is configured to be small.

  Here, for example, when the vehicle is in a driving state, the estimated vehicle body speed acquisition means integrates the vehicle body acceleration increase value over time, and when the vehicle is in a braking state, The estimated vehicle body speed is obtained by time-integrating the acceleration reduction value.

  The estimated vehicle body speed acquisition means may further acquire the estimated vehicle body speed based on the wheel speed sensor output. In this case, for example, when the vehicle is in a driving state, the estimated vehicle body speed is obtained by time-integrating the minimum value of the wheel speeds of all the wheels obtained from the wheel speed sensor output and the vehicle body acceleration raising value. When the vehicle is in a braking state, the maximum value of the wheel speeds of all the wheels obtained from the wheel speed sensor output and the above-mentioned vehicle body acceleration bulk reduction are set. It is set to the larger of the values obtained by integrating the values over time.

  According to this, when it is determined that the slip in the acceleration direction has occurred on the wheel by the vehicle slip state acquisition device according to the present invention described above (that is, when traction control should be started), Since the acceleration slip threshold is reduced, traction control is easily started. That is, particularly when the above-mentioned “phenomenon in which the acceleration slip amount of all wheels gradually increases due to a slight accelerator operation during low μ road traveling” occurs, the traction control compared to the conventional device. However, it is easier to start at an appropriate time. The case where the vehicle is in the driving state has been described above.

  On the other hand, when the vehicle is in a braking state, the slip state acquisition means determines that “the vehicle body acceleration based on the wheel speed sensor output (negative value)” is greater than “the vehicle body acceleration based on the longitudinal acceleration sensor output (negative value)”. Is smaller (has a larger absolute value), it is determined that a slip in the deceleration direction has occurred on the wheel.

  As described above, when the vehicle is in a deceleration state, the “vehicle acceleration based on the longitudinal acceleration sensor output” may be set to the vehicle acceleration pull-down value from the viewpoint of preventing malfunctions related to the ABS control. Many. In this case, the “vehicle acceleration based on the longitudinal acceleration sensor output” can be a value equal to or less than the true vehicle acceleration.

  That is, when the vehicle is in a braking state, if the condition that “vehicle acceleration based on wheel speed sensor output” is smaller than “vehicle acceleration based on longitudinal acceleration sensor output” is satisfied, the amount of deceleration slip increases reliably. Means that Therefore, when such a condition is satisfied, it can be determined that deceleration slip is occurring without waiting for the deceleration slip amount to reach the deceleration slip threshold. In other words, it can be determined that deceleration slip is occurring at an earlier time and at an appropriate time than the conventional device described above.

  The vehicle slip state acquisition device according to the present invention is applied to a vehicle including a brake operation amount corresponding value sensor that acquires a value corresponding to an operation amount of a brake operation member of the vehicle, and the slip state acquisition means is , “Vehicle acceleration based on wheel speed sensor output” is smaller than “vehicle acceleration based on longitudinal acceleration sensor output”, and the obtained operation amount corresponding value of the brake operation member is larger than zero and smaller than a predetermined value. On the condition, it is preferable that the wheel is configured to determine that a slip in the deceleration direction has occurred. Here, the operation amount corresponding value of the brake operation member is, for example, an operation stroke of a brake operation member (for example, a brake pedal), an operation force of the brake operation member, a master cylinder hydraulic pressure, or the like.

  As described above, in the conventional device that determines that the deceleration slip has occurred when the deceleration slip amount reaches the deceleration slip threshold, the above-described “by a slight brake pedal operation during low μ road traveling” In the case where the phenomenon that the deceleration slip amount of all wheels gradually increases occurs, there may be a problem that the timing for determining that the deceleration slip is occurring is greatly delayed.

  On the other hand, even when the above-mentioned “phenomenon in which the deceleration slip amount gradually increases” occurs, the “vehicle body acceleration (negative value) based on the wheel speed sensor output” described above becomes “longitudinal acceleration”. The condition that the vehicle body acceleration based on the sensor output (negative value) becomes smaller can be satisfied immediately after the occurrence of the phenomenon. In other words, the fact that the brake pedal operation amount is a small value and the “vehicle acceleration based on the wheel speed sensor output” is smaller than the “vehicle acceleration based on the longitudinal acceleration sensor output” means that the “deceleration slip amount” is This means that a "slowly increasing phenomenon" has occurred.

  Therefore, when configured as described above, when the “phenomenon in which the deceleration slip amount gradually increases” occurs, without waiting for the deceleration slip amount to reach the deceleration slip threshold, It can be determined that deceleration slip is occurring at an appropriate time.

  In the slip state acquisition device for a vehicle according to the present invention, the slip state acquisition unit is configured to generate a slip in the deceleration direction on the wheel when the condition continues to be established for a predetermined time. Suitably configured to determine.

  According to this, the above-described “vehicle acceleration based on the wheel speed sensor output (negative value)” is smaller than “vehicle acceleration based on the longitudinal acceleration sensor output (negative value)” (and the operation amount of the brake operation member). It is determined that the deceleration slip has occurred only when the condition that the corresponding value is greater than zero and smaller than the predetermined value continues to be established stably over a predetermined time. Therefore, it is possible to suppress the occurrence of a situation in which it is erroneously determined that the deceleration slip has occurred when the deceleration slip has not occurred.

  The vehicle ABS control apparatus according to the present invention using any one of the above-described vehicle slip state acquisition apparatuses according to the present invention includes a wheel speed sensor that outputs a signal representing the wheel speed of the vehicle, and the vehicle body of the vehicle. The present invention is applied to an all-wheel drive vehicle including a longitudinal acceleration sensor that outputs a signal representing vehicle acceleration in the longitudinal direction.

  The ABS control apparatus for a vehicle according to the present invention includes an estimated vehicle body speed acquisition means for acquiring an estimated vehicle body speed of the vehicle based on at least the output of the longitudinal acceleration sensor, and the wheel speed sensor based on the acquired estimated vehicle body speed. ABS that starts and executes ABS control when a value based on a value obtained by subtracting the wheel speed based on the output of (i.e., deceleration slip amount) exceeds a predetermined threshold (that is, the deceleration slip threshold). Control means, and the ABS control means, when it is determined by the vehicle slip state acquisition device according to the present invention that a slip in the deceleration direction has occurred on the wheel, the deceleration slip threshold value. Is configured to be small.

  According to this, when it is determined by the vehicle slip state acquisition device according to the present invention described above that the wheel is slipping in the deceleration direction (that is, when ABS control is to be started), Since the deceleration slip threshold value is reduced, the ABS control is easily started. That is, particularly in the case where the above-described “phenomenon in which the deceleration slip amount of all wheels gradually increases due to slight brake pedal operation during low μ road traveling” occurs, the ABS is higher than that of the conventional device. Control is easily started earlier and at an appropriate time.

  Hereinafter, embodiments of a vehicle traction control device and an ABS control device including a vehicle slip state acquisition device according to the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a schematic configuration of a vehicle equipped with a traction control device 10 including a slip state acquisition device according to a first embodiment of the present invention. This vehicle is a four-wheel drive type vehicle in which all four wheels are drive wheels.

  The motion control device 10 generates a driving force and transmits the driving force to the driving wheels FL, FR, RL, and RR, and a braking force generated by brake fluid pressure on the wheels. The brake fluid pressure control device 30, the sensor unit 40 including various sensors, and the electric control device 50 are included.

  The driving force transmission mechanism unit 20 controls the opening degree TA of an engine 21 that generates driving force and the throttle valve TH that is disposed in the intake pipe 21a of the engine 21 and that makes the opening cross-sectional area of the intake passage variable. A throttle valve actuator 22 composed of a DC motor, a fuel injection device 23 including an injector for injecting fuel near an intake port (not shown) of the engine 21, and a transmission 24 having an input shaft connected to the output shaft of the engine 21 are provided.

  The driving force transmission mechanism unit 20 appropriately distributes the driving force transmitted from the output shaft of the transmission 24 and transfers the allocated driving force to the front wheel side propeller shaft 25 and the rear wheel side propeller shaft 26, respectively. 27, a front wheel side differential 28 that appropriately distributes the front wheel side driving force transmitted from the front wheel side propeller shaft 25, and transmits the distributed front wheel side driving force to the front wheels FL and FR, respectively, and a rear wheel side propeller shaft 26 A rear wheel differential 29 is provided that appropriately distributes the transmitted rear wheel driving force and transmits the rear wheel driving force distributed to the rear wheels RR and RL, respectively.

  As shown in FIG. 2 showing a schematic configuration, the brake fluid pressure control device 30 includes a brake fluid pressure generating unit 32 that generates a brake fluid pressure corresponding to the operating force of the brake pedal BP, and wheels RR, FL, FR, RR brake hydraulic pressure adjusting unit 33, FL brake hydraulic pressure adjusting unit 34, FR brake hydraulic pressure adjusting unit 35, each of which can adjust the brake hydraulic pressure supplied to the wheel cylinders Wrr, Wfl, Wfr, Wrl arranged in RL, An RL brake fluid pressure adjustment unit 36 and a return brake fluid supply unit 37 are included.

  The brake fluid pressure generating unit 32 includes a vacuum booster VB that responds when the brake pedal BP is operated, and a master cylinder MC that is connected to the vacuum booster VB. The vacuum booster VB uses the air pressure (negative pressure) in the intake pipe of the engine 21 to assist the operating force of the brake pedal BP at a predetermined rate and transmit the assisted operating force to the master cylinder MC. ing.

  The master cylinder MC has two output ports including a first port and a second port. The master cylinder MC receives the supply of brake fluid from the reservoir RS and responds to the assisted operating force by the first master. The cylinder hydraulic pressure Pm is generated from the first port, and the second master cylinder hydraulic pressure Pm corresponding to the assisted operating force, which is substantially the same hydraulic pressure as the first master cylinder hydraulic pressure, is generated. It is generated from the second port.

  Since the configurations and operations of the master cylinder MC and the vacuum booster VB are well known, a detailed description thereof will be omitted here. In this way, the master cylinder MC and the vacuum booster VB (brake hydraulic pressure generating means) generate the first master cylinder hydraulic pressure and the second master cylinder hydraulic pressure according to the operating force of the brake pedal BP, respectively. ing.

  A normally open linear solenoid valve PC1 is interposed between the first port of the master cylinder MC and each of the upstream portion of the RR brake hydraulic pressure adjusting unit 33 and the upstream portion of the FL brake hydraulic pressure adjusting unit 34. . Similarly, a normally open linear solenoid valve PC2 is interposed between the second port of the master cylinder MC and each of the upstream part of the FR brake fluid pressure adjusting part 35 and the upstream part of the RL brake fluid pressure adjusting part 36. Has been. Details of the normally open linear solenoid valves PC1 and PC2 will be described later.

  The RR brake fluid pressure adjusting unit 33 includes a pressure-increasing valve PUrr that is a 2-port 2-position switching type normally-open electromagnetic on-off valve and a pressure-reducing valve PDrr that is a 2-port 2-position switching-type normally-closed electromagnetic on-off valve. Yes. The pressure increasing valve PUrr can communicate or block the upstream portion of the RR brake fluid pressure adjusting unit 33 and a wheel cylinder Wrr described later. The pressure reducing valve PDrr is configured to communicate or block the wheel cylinder Wrr and the reservoir RS1. As a result, the brake fluid pressure (wheel cylinder fluid pressure Pwrr) in the wheel cylinder Wrr can be increased, held and reduced by controlling the pressure increasing valve PUrr and the pressure reducing valve PDrr.

  In addition, a check valve CV1 that allows only one-way flow of the brake fluid from the wheel cylinder Wrr side to the upstream portion of the RR brake fluid pressure adjusting unit 33 is disposed in parallel with the pressure increasing valve PUrr. When the operated brake pedal BP is released, the wheel cylinder hydraulic pressure Pwrr is rapidly reduced.

  Similarly, the FL brake hydraulic pressure adjusting unit 34, the FR brake hydraulic pressure adjusting unit 35, and the RL brake hydraulic pressure adjusting unit 36 are respectively a pressure increasing valve PUfl and a pressure reducing valve PDfl, a pressure increasing valve PUfr and a pressure reducing valve PDfr, a pressure increasing valve PUrl, and The pressure reducing valve PDrl is configured to control the brake pressure in the wheel cylinder Wfl, the wheel cylinder Wfr, and the wheel cylinder Wrl (wheel cylinder hydraulic pressure Pwfl, Pwfr, Pwrl) by controlling the pressure increasing valve and the pressure reducing valve. The pressure can be increased, held and reduced. In addition, check valves CV2, CV3, and CV4 that can achieve the same function as the check valve CV1 are arranged in parallel on the pressure increasing valves PUfl, PUfr, and PUrl, respectively.

  The reflux brake fluid supply unit 37 includes a DC motor MT and two hydraulic pumps (gear pumps) HP1 and HP2 that are simultaneously driven by the motor MT. The hydraulic pump HP1 pumps up the brake fluid in the reservoir RS1 returned from the pressure reducing valves PDrr, PDfl, and the brake fluid pumped up through the check valve CV8 adjusts the RR brake fluid pressure adjusting unit 33 and the FL brake fluid pressure. It supplies to the upstream part of the part 34. FIG.

  Similarly, the hydraulic pump HP2 pumps up the brake fluid in the reservoir RS2 that has been refluxed from the pressure reducing valves PDfr and PDrl, and the pumped brake fluid through the check valve CV11 and the FR brake fluid pressure adjusting unit 35 and the RL brake. The hydraulic pressure adjusting unit 36 is supplied to the upstream portion. In order to reduce the pulsation of the discharge pressure of the hydraulic pumps HP1 and HP2, a hydraulic circuit between the check valve CV8 and the normally open linear solenoid valve PC1 and between the check valve CV11 and the normally open linear solenoid valve PC2 are used. These hydraulic circuits are provided with dampers DM1 and DM2, respectively.

  Next, the normally open linear solenoid valve PC1 will be described. An opening force based on a biasing force from a coil spring (not shown) is constantly acting on the valve body of the normally open linear electromagnetic valve PC1, and the upstream portion of the RR brake hydraulic pressure adjusting portion 33 and the FL brake hydraulic pressure adjustment are applied. Force in the opening direction based on a differential pressure (hereinafter sometimes simply referred to as “actual differential pressure”) obtained by subtracting the first master cylinder hydraulic pressure Pm from the pressure upstream of the section 34, and a normally open linear A force in the closing direction is applied based on the attractive force that increases in proportion to the energization current to the solenoid valve PC1 (and hence the command current Id).

  As a result, as shown in FIG. 3, the command differential pressure ΔPd corresponding to the suction force is determined so as to increase in proportion to the command current Id. Here, I0 is a current value corresponding to the urging force of the coil spring. The normally open linear solenoid valve PC1 is closed when the command differential pressure ΔPd is larger than the actual differential pressure, and the first port of the master cylinder MC, the upstream portion of the RR brake hydraulic pressure adjusting unit 33, and the FL The communication with the upstream portion of the brake fluid pressure adjusting unit 34 is blocked. On the other hand, the normally open linear solenoid valve PC1 opens when the command differential pressure ΔPd is smaller than the actual differential pressure, and opens the first port of the master cylinder MC, the upstream portion of the RR brake fluid pressure adjusting unit 33, and the FL brake fluid. The upstream part of the pressure adjustment part 34 is connected.

  As a result, the brake fluid upstream of the RR brake fluid pressure adjusting unit 33 (supplied from the fluid pressure pump HP1) and the upstream portion of the FL brake fluid pressure adjusting unit 34 is supplied to the master cylinder via the normally open linear solenoid valve PC1. By flowing to the first port side of the MC, the real differential pressure can be adjusted to coincide with the command differential pressure ΔPd. The brake fluid that has flowed into the first port side of the master cylinder MC is returned to the reservoir RS1.

  In other words, when the motor MT (and hence the hydraulic pumps HP1 and HP2) is driven, the actual differential pressure (allowable maximum value) is controlled according to the command current Id to the normally open linear solenoid valve PC1. To get. At this time, the upstream pressure of the RR brake hydraulic pressure adjusting unit 33 and the upstream pressure of the FL brake hydraulic pressure adjusting unit 34 add the actual differential pressure (and thus the command differential pressure ΔPd) to the first master cylinder hydraulic pressure Pm. (Pm + ΔPd).

  On the other hand, when the normally open linear solenoid valve PC1 is brought into a non-excited state (that is, when the command current Id is set to “0”), the normally open linear solenoid valve PC1 is kept open by the biasing force of the coil spring. ing. At this time, the actual differential pressure becomes “0”, and the upstream pressure of the RR brake hydraulic pressure adjusting unit 33 and the upstream pressure of the FL brake hydraulic pressure adjusting unit 34 become equal to the first master cylinder hydraulic pressure Pm.

  The normally open linear solenoid valve PC2 has the same configuration and operation as that of the normally open linear solenoid valve PC1. Therefore, when the motor MT (and hence the hydraulic pumps HP1 and HP2) is driven, the upstream portion of the FR brake hydraulic pressure adjusting unit 35 and the RL brake according to the command current Id to the normally open linear solenoid valve PC2. The pressure upstream of the hydraulic pressure adjustment unit 36 is a value obtained by adding the command differential pressure ΔPd to the second master cylinder hydraulic pressure Pm (Pm + ΔPd). On the other hand, when the normally open linear solenoid valve PC2 is in a non-excited state, the upstream pressure of the FR brake hydraulic pressure adjusting unit 35 and the upstream pressure of the RL brake hydraulic pressure adjusting unit 36 become equal to the second master cylinder hydraulic pressure Pm. .

  In addition, the normally open linear solenoid valve PC1 has a one-way direction of the brake fluid from the first port of the master cylinder MC to the upstream portion of the RR brake fluid pressure adjusting portion 33 and the upstream portion of the FL brake fluid pressure adjusting portion 34. A check valve CV5 that allows only the flow of is arranged in parallel. Thus, even when the actual differential pressure is controlled according to the command current Id to the normally open linear solenoid valve PC1, the first master cylinder hydraulic pressure Pm is changed to the RR brake hydraulic pressure by operating the brake pedal BP. When the pressure is higher than the pressure at the upstream portion of the adjusting portion 33 and the upstream portion of the FL brake fluid pressure adjusting portion 34, the brake fluid pressure corresponding to the operating force of the brake pedal BP (that is, the first master cylinder fluid pressure). Pm) itself can be supplied to the wheel cylinders Wrr and Wfl. Further, the normally open linear solenoid valve PC2 is also provided with a check valve CV6 that can achieve the same function as the check valve CV5.

  With the configuration described above, the brake hydraulic pressure control device 30 includes two hydraulic circuits, a system related to the right rear wheel RR and the left front wheel FL, and a system related to the left rear wheel RL and the right front wheel FR. Has been. The brake hydraulic pressure control device 30 can supply the brake hydraulic pressure (that is, master cylinder hydraulic pressure Pm) corresponding to the operating force of the brake pedal BP to the wheel cylinders W ** when all the solenoid valves are in the non-excited state. It is like that.

In addition, “**” appended to the end of various variables etc. “fl” added to the end of the various variables etc. to indicate which of the various wheels FR, etc. , “Fr”, etc., for example, the wheel cylinder W ** is a wheel cylinder Wfl for the left front wheel,
A wheel cylinder Wfr for the right front wheel, a wheel cylinder Wrl for the left rear wheel, and a wheel cylinder Wrr for the right rear wheel are comprehensively shown.

  On the other hand, in this state, when the motor MT (accordingly, the hydraulic pumps HP1 and HP2) are driven and the normally open linear solenoid valves PC1 and PC2 are respectively excited with the command current Id, the command current Id is higher than the master cylinder hydraulic pressure Pm. The brake hydraulic pressure higher by the command differential pressure ΔPd determined in accordance with the pressure can be supplied to the wheel cylinders W **.

  In addition, the brake hydraulic pressure control device 30 can individually adjust the wheel cylinder hydraulic pressure Pw ** by controlling the pressure increasing valve PU ** and the pressure reducing valve PD **. That is, the brake fluid pressure control device 30 can individually adjust the braking force applied to each wheel regardless of the operation of the brake pedal BP by the driver. As a result, the brake hydraulic pressure control device 30 can achieve traction control as will be described later by an instruction from the electric control device 50 described later.

  Referring to FIG. 1 again, the sensor unit 40 includes electromagnetic pickup type wheel speed sensors 41fl, 41fr, 41rl, and 41rr that output signals having frequencies according to the wheel speeds of the wheels FL, FR, RL, and RR, respectively. An accelerator opening sensor 42 (accelerator operation amount corresponding value sensor) that detects the operation amount of the accelerator pedal AP operated by the driver and outputs a signal indicating the operation amount Accp (accelerator operation amount corresponding value) of the accelerator pedal AP. And (first) master cylinder hydraulic pressure sensor 43 (brake operation amount corresponding value sensor which detects master cylinder hydraulic pressure and outputs a signal indicating master cylinder hydraulic pressure Pm (operation amount corresponding value of brake operation member). 2) and a longitudinal acceleration sensor 44 that detects a vehicle body acceleration in the longitudinal direction of the vehicle body and outputs a signal indicating the vehicle body acceleration detection value Gx.

  The vehicle body acceleration detection value Gx is set to take a positive value when the vehicle (moving forward) is in an acceleration state, and takes a negative value when the vehicle (moving forward) is in a deceleration state. .

  The electrical control device 50 includes a CPU 51 connected to each other by a bus, a routine (program) executed by the CPU 51, a table (lookup table, map), a ROM 52 in which constants are stored in advance, and the CPU 51 temporarily stores data as necessary. The microcomputer includes a RAM 53 that stores data, a backup RAM 54 that stores data while the power is on, and retains the stored data while the power is shut off, and an interface 55 including an AD converter. The interface 55 is connected to the sensors 41 to 44 and supplies signals from the sensors 41 to 44 to the CPU 51, and in response to instructions from the CPU 51, the electromagnetic valves and the motor MT of the brake hydraulic pressure control device 30. Drive signals are sent to the throttle valve actuator 22 and the fuel injection device 23.

  Thus, in principle, the throttle valve actuator 22 drives the throttle valve TH so that the opening degree TA of the throttle valve TH becomes an opening degree corresponding to the operation amount Accp of the accelerator pedal AP, and the fuel injection device 23. Injects an amount of fuel necessary to obtain a predetermined target air-fuel ratio (for example, theoretical air-fuel ratio) with respect to the in-cylinder intake air amount that is the amount of air sucked into the cylinder (inside the cylinder). It has become.

(Outline of traction control)
Next, an outline of traction control executed by the traction control device 10 according to the first embodiment of the present invention having the above configuration (hereinafter also referred to as “this device”) will be described. The traction control is a control for preventing the occurrence of excessive acceleration slip of the wheels in order to efficiently generate the traction when the vehicle is in a driving state.

  Specifically, this device calculates the acceleration slip amount S ** individually for each wheel, and applies a predetermined brake to be described later to a wheel whose acceleration slip amount S ** is equal to or greater than the acceleration slip threshold Sth. A braking force based on the hydraulic pressure is applied (that is, traction control is started / executed). The acceleration slip threshold Sth is basically set to a value equal to a predetermined basic acceleration slip threshold Sthbase (a constant value), but is set to another value only in a specific case as described later. The Here, the acceleration slip amount S ** is calculated according to the following equation (1).

S ** = Vw ** − Vrefacc (1)

  In the above equation (1), Vw ** is a wheel speed acquired as described later based on the output of the wheel speed sensor 41 **. Vrefacc is an estimated vehicle body speed in the longitudinal direction of the vehicle body for traction control, and is calculated according to the following equation (2).

Vrefacc = min (Vwmin, Vgup) (2)

  In the above equation (2), Vwmin is the minimum value (minimum wheel speed) of the wheel speeds Vw **. Vgup is a time integral value (vehicle speed based on the raised value) of the vehicle body acceleration raised value Gup, which is a value obtained by adding a positive constant α1 to the detected vehicle acceleration value Gx detected by the longitudinal acceleration sensor 44. That is, the estimated vehicle speed Vrefacc for traction control is set to the smaller value of the minimum wheel speed Vwmin and the vehicle speed Vgup based on the raised value.

  Here, the constant α1 is set to a value for always making the vehicle body acceleration raised value Gup equal to or greater than the true vehicle body acceleration even when the individual variation in the output characteristics of the longitudinal acceleration sensor 44 is taken into consideration. Therefore, the vehicle body speed Vgup based on the raised value is always maintained at a value equal to or higher than the true vehicle body speed Vreal.

  The reason why the estimated vehicle speed Vrefacc for traction control is calculated according to the above equation (2) is as follows. That is, when the vehicle is in a relatively gentle acceleration state (specifically, when the degree of acceleration slip of the wheel corresponding to the minimum wheel speed Vwmin is small), the true vehicle speed Vreal is a value close to the minimum wheel speed Vwmin. Tend to be. As a result, the minimum wheel speed Vwmin becomes smaller than the vehicle body speed Vgup based on the raised value. Therefore, according to the above equation (2), when the vehicle is in a relatively gentle acceleration state, the estimated vehicle speed Vrefacc for traction control is set to a value equal to the minimum wheel speed Vwmin. Can be calculated with high accuracy.

  On the other hand, when the vehicle is in a relatively rapid acceleration state (specifically, when the degree of acceleration slip of all four wheels is large (thus, when the degree of acceleration slip of the wheel corresponding to the minimum wheel speed Vwmin is large)). ) When the minimum wheel speed Vwmin largely deviates from the true vehicle speed Vreal, the vehicle speed Vgup based on the raised value may be smaller than the minimum wheel speed Vwmin.

  In such a case, according to the above equation (2), the estimated vehicle speed Vrefacc for traction control is equal to the vehicle speed Vgup based on the raised value that is closer to the true vehicle speed Vreal than the minimum wheel speed Vwmin. Can be calculated to a value. Therefore, according to the above formula (2), when the vehicle is in a relatively rapid acceleration state, the estimated vehicle body speed Vrefacc for traction control is always calculated to be equal to the minimum wheel speed Vwmin. The speed Vrefacc can be calculated with high accuracy.

  Furthermore, as described above, the vehicle body speed Vgup based on the raising value is always maintained at a value equal to or higher than the true vehicle speed Vreal. In this case, the acceleration slip amount S calculated according to the above equation (1) is used. ** will be calculated smaller. As a result, according to the above equation (2), when the vehicle is in a relatively abrupt acceleration state, the malfunction as described above “the traction control is started at an early stage where the traction control should not be started”. Can be prevented. The above is the reason why the estimated vehicle speed Vrefacc for traction control is calculated according to the above equation (2).

(Reduced acceleration slip threshold)
As described above, in principle, the traction control is started / executed for a wheel whose acceleration slip amount S ** is equal to or greater than the acceleration slip threshold Sth (= basic acceleration slip threshold Sthbase). . However, when the acceleration slip threshold value Sth is always set to the basic acceleration slip threshold value Sthbase (a constant value) as described above, the acceleration slip amount of all the wheels is reduced by the slight accelerator operation during the low μ road running. When the “slowly increasing phenomenon” occurs, there may be a problem that the timing at which the traction control is started is greatly delayed (or the traction control is not started). Hereinafter, this will be described with reference to FIG.

  FIG. 4A shows a case where the vehicle is traveling on a low μ road surface and the driver slightly depresses the accelerator pedal AP (accelerator pedal operation amount Accp <small value Accpref is satisfied) at time t1. Of the actual vehicle speed Vreal, the vehicle speed Vgup based on the raised value, the minimum wheel speed Vwmin, and the estimated vehicle speed Vrefacc for traction control It is the time chart which showed the example. As described above, the vehicle body speed Vgup based on the raising value is always calculated to be equal to or higher than the true vehicle body speed Vreal.

  In this example, after time t1, the wheel speed Vw ** (and hence the minimum wheel speed Vwmin) of all wheels gradually deviates from the true vehicle speed Vreal toward the larger side. As a result, the minimum wheel speed Vwmin is smaller than the vehicle body speed Vgup based on the raised value before the time t1 to the time t2, and the vehicle body speed Vgup based on the raised value is later than the minimum wheel speed Vwmin after the time t2. It is getting smaller.

  Accordingly, as shown by the thick solid line, the estimated vehicle speed Vrefacc for traction control is set to a value equal to the minimum wheel speed Vwmin from before time t1 to time t2, and based on the raised value after time t2. It is set to a value equal to the vehicle speed Vgup. As a result, the acceleration slip amount S ** of all the wheels calculated according to the above equation (1) is maintained at substantially “0” from before time t1 to time t2, and gradually increases after time t2. Go.

  Here, in this example, the true acceleration slip amount (that is, the value obtained by subtracting the true vehicle speed Vreal from the wheel speed Vw **) is the acceleration slip threshold Sth (= basic acceleration slip threshold at time t3). Sthbase). In other words, the traction control should be started at time t3.

  On the other hand, the acceleration slip amount S ** of all wheels calculated according to the above equation (1) is due to the fact that the vehicle body speed Vgup based on the raising value is calculated to a value equal to or higher than the true vehicle body speed Vreal. Since it is calculated to be smaller than the true acceleration slip amount, the acceleration slip threshold Sth (= basic acceleration slip threshold Sthbase) is reached at time t4 after time t3. Therefore, if the acceleration slip threshold value Sth is always set to the basic acceleration slip threshold value Sthbase (a constant value), the traction control is actually started at time t4.

  Here, in this example, a case where the vehicle is traveling on a low μ road surface and the driver slightly depresses the accelerator pedal AP is shown. Therefore, the wheel speeds Vw ** of all the wheels (therefore, the minimum wheels). The speed at which the speed Vwmin) increases (that is, the speed at which the wheel speed ** deviates from the true vehicle speed Vreal) is very small. Therefore, the time t4 is a time point that is greatly delayed from the time t3, and as a result, the timing at which the traction control is started is greatly delayed.

  In this way, when the acceleration slip threshold Sth is always set to the basic acceleration slip threshold Sthbase (a constant value), “the acceleration slip amount of all wheels gradually increases due to a slight accelerator operation during low μ road travel. In the case where the phenomenon of “going” occurs, there arises a problem that the timing at which the traction control is started is greatly delayed.

  As one method for dealing with this problem, it is determined that “a phenomenon in which the acceleration slip amount of all the wheels gradually increases due to a slight accelerator operation during low μ road traveling” occurs. If it is determined that the same phenomenon has occurred (thus, if it is determined that an acceleration slip has occurred), it is conceivable to reduce the acceleration slip threshold Sth. Hereinafter, a method of determining that the “phenomenon in which the acceleration slip amount of all the wheels gradually increases due to a slight accelerator operation during low μ road traveling” has occurred will be described.

  When the vehicle is in a driving state, the acceleration slip amount S ** of a certain wheel increases when the wheel speed Vw ** (= Vwmin) of the wheel increases (that is, Vwmin in FIG. This means that the slope of the line shown (positive value) is larger than the increasing slope of the true vehicle speed Vreal (that is, the slope of the line showing Vreal (positive value) in FIG. 4A). In other words, when the acceleration slip amount S ** of a certain wheel increases when the vehicle is in a driving state, the time differential value of the minimum wheel speed Vwmin (hereinafter referred to as “vehicle acceleration DVwmin based on wheel speed sensor output”). Is greater than the true vehicle acceleration.

  On the other hand, as described above, the vehicle body acceleration raising value Gup is always set to a value greater than or equal to the true vehicle body acceleration. From the above, when the vehicle is in a driving state, the “vehicle acceleration DVwmin based on the wheel speed sensor output” is based on the vehicle body acceleration raised value Gup (hereinafter also referred to as “vehicle acceleration Gup based on the longitudinal acceleration sensor output”). If this condition is satisfied, it means that the acceleration slip amount S ** is surely increased.

  Further, it can be determined that the driver slightly depresses the accelerator pedal AP because “0 <accelerator pedal operation amount Accp <the above-described minute value Accpref” is satisfied. From the above, the phenomenon that “the acceleration slip amount of all wheels gradually increases due to slight accelerator operation while driving on a low μ road surface” has occurred is “0 <Accp <Accpref” and “DVwmin> Gup Can be determined by satisfying the two conditions.

  Furthermore, in order to more reliably and accurately determine that the above phenomenon has occurred, the determination condition is that the above two conditions are continuously satisfied over a certain period of time. It is considered preferable to add.

  In view of the above, when the above two conditions are continuously satisfied for a predetermined time T1 or more, the present device indicates that “the acceleration slip amount of all the wheels is moderated by a slight accelerator operation during low μ road running”. It is determined that the phenomenon of “increasing speed” has occurred (accelerated slip has occurred). And this apparatus is the value obtained by subtracting the value β1 (positive constant) from the basic acceleration slip threshold Sthbase only while it is determined that the above phenomenon occurs. Change to (Sthbase-β1). Hereinafter, this will be described with reference to FIG.

  FIG. 4 (b) shows the same situation as FIG. 4 (a) described above (that is, from the time t1, “the acceleration slip amount of all the wheels is moderated by a slight accelerator operation (0 <Accp <Accpref) while traveling on a low μ road surface”. Example of changes in true vehicle speed Vreal, vehicle speed Vgup based on raising value, minimum wheel speed Vwmin, and estimated vehicle speed Vrefacc for traction control It is the time chart shown.

  In this example, “the vehicle body acceleration DVwmin based on the wheel speed sensor output” (that is, the slope of the line indicating the minimum wheel speed Vwmin) is “from time t1 before the start of acceleration slip of all wheels to time t5”. It is smaller than the “vehicle acceleration Gup based on the longitudinal acceleration sensor output” (that is, the slope of the line indicating the vehicle velocity Vgup based on the raising value), and is larger than the “vehicle acceleration Gup based on the longitudinal acceleration sensor output” after time t5. ing.

  Therefore, in this case, the present apparatus determines that “low μ” at time t6 when two conditions “0 <Accp <Accpref” and “DVwmin> Gup” are continuously satisfied over the predetermined time T1. It is determined that “a phenomenon in which the acceleration slip amount of all the wheels gradually increases due to a slight accelerator operation while traveling on the road surface” has occurred (acceleration slip has occurred).

  Then, after time t6, the present apparatus changes the acceleration slip threshold Sth from the basic acceleration slip threshold Sthbase to a value (Sthbase-β1). As a result, the acceleration slip amount S ** of all the wheels can reach the acceleration slip threshold (Sthbase-β1) at time t7, which is substantially the same time as time t3 in FIG. Therefore, the present apparatus starts the traction control at the time t7 that is substantially the same time as the time t3 that is “the time when the traction control should be started”.

  As described above, when “a phenomenon in which the acceleration slip amount of all the wheels gradually increases due to slight accelerator operation during low μ road traveling” has occurred, the acceleration slip threshold Sth is reduced. Thus, the traction control can be started at an appropriate time. The outline of the traction control and the reduction of the acceleration slip threshold have been described above.

(Actual operation)
Next, FIGS. 5 to 8 are flowcharts showing routines executed by the CPU 51 of the electric control device 50 for the actual operation of the traction control device 10 according to the first embodiment of the present invention configured as described above. The description will be given with reference.

  The CPU 51 repeatedly executes the routine for calculating the wheel speed and the like shown in FIG. 5 every elapse of a predetermined time (execution interval time Δt, for example, 6 msec). Therefore, when the predetermined timing is reached, the CPU 51 starts the process from step 500, proceeds to step 505, and calculates the wheel speed (the speed of the outer periphery of the wheel **) Vw ** at the current time of the wheel **. Specifically, the CPU 51 calculates the wheel speed Vw ** based on the fluctuation frequency of the output value of the wheel speed sensor 41 **.

  Next, the CPU 51 proceeds to step 510, sets the minimum wheel speed (current value) Vwmin to the minimum value of the calculated wheel speed Vw **, and in step 515, the minimum wheel speed Vwmin and the minimum Based on the wheel speed previous value Vwminb and the formula described in step 515, the time differential value of the minimum wheel speed Vwmin, “vehicle acceleration DVwmin based on wheel speed sensor output” is calculated. Here, the minimum wheel speed previous value Vwminb is a value set in step 540, which will be described later, during the previous execution of this routine. This step 515 corresponds to first vehicle body acceleration acquisition means.

  Subsequently, the CPU 51 proceeds to step 520 and adds the positive constant α1 to the vehicle body acceleration detection value Gx detected by the longitudinal acceleration sensor 44 to obtain a vehicle body acceleration raised value (ie, “vehicle body acceleration based on the longitudinal acceleration sensor output). Gup "). This step 520 corresponds to second vehicle body acceleration acquisition means.

  Next, the CPU 51 proceeds to step 525, and adds “Gup · Δt” to the value of Vgup at that time, thereby adding the “uplifting value” which is the time integral value of “vehicle acceleration Gup based on the longitudinal acceleration sensor output”. Based vehicle speed Vgup ".

  Next, the CPU 51 proceeds to step 530 to set the estimated vehicle speed Vrefacc for traction control to the smaller value of the minimum wheel speed Vwmin and the “vehicle speed Vgup based on the raised value”.

  Then, the CPU 51 proceeds to step 535 to calculate the acceleration slip amount S ** for each wheel by subtracting the estimated vehicle body speed Vrefacc from the wheel speed **, and then at step 540, the minimum wheel speed previous value Vwminb is calculated. The minimum wheel speed (current value) Vwmin is set, and the routine proceeds to step 595 to end the present routine tentatively. Thereafter, the CPU 51 sequentially updates the various values by repeatedly executing this routine every time the execution interval time Δt elapses.

  Further, the CPU 51 repeatedly executes a routine for determining all-wheel acceleration slip on the low μ road and selecting a threshold shown in FIG. 6 every elapse of a predetermined time (for example, 6 msec). Therefore, when the predetermined timing is reached, the CPU 51 starts the process from step 600 and proceeds to step 605, where the current accelerator operation amount Accp obtained from the accelerator opening sensor 42 is greater than “0” and the minute value Accpref. If the determination is “Yes”, the process proceeds to step 610.

  When the CPU 51 proceeds to step 610, the “vehicle acceleration DVwmin based on wheel speed sensor output” calculated in the previous step 515 is calculated as “vehicle acceleration Gup based on the longitudinal acceleration sensor output” calculated in the previous step 520. It is determined whether it is larger than "." When the CPU 51 determines “Yes” at step 610 (that is, when both the conditions at steps 605 and 610 are satisfied. Therefore, “the acceleration slip amount of all the wheels is reduced by a slight accelerator operation during low μ road running”. If a “slowly increasing phenomenon” has occurred), the process proceeds to step 615. Here, steps 605 and 610 correspond to slip state acquisition means.

  Assuming that “a phenomenon in which the acceleration slip amount of all the wheels gradually increases due to a slight accelerator operation during low μ road traveling” has not occurred, the CPU 51 determines in any of steps 605 and 610 as “ It determines with "No", progresses to step 630, and the value of the counter N is cleared to "0". The CPU 51 proceeds to step 635, sets the acceleration slip threshold Sth to the basic acceleration slip threshold Sthbase, proceeds to step 695, and once ends this routine. Thereafter, unless the phenomenon that “the acceleration slip amount of all wheels gradually increases due to slight accelerator operation during low μ road running” has occurred, the acceleration slip threshold Sth is equal to the basic acceleration slip threshold. The value is maintained at Sthbase.

  On the other hand, assuming that “a phenomenon in which the acceleration slip amount of all the wheels gradually increases due to a slight accelerator operation during low μ road traveling” occurs from this state, the CPU 51 proceeds to Steps 605 and 610. Both are determined as “Yes”, and the process proceeds to step 615 to increment the value of the counter N (currently “0”) by “1”. That is, the value of the counter N represents a duration time in which it is determined that a “phenomenon in which the acceleration slip amount of all the wheels gradually increases due to a slight accelerator operation during low μ road traveling” has occurred.

  Next, the CPU 51 proceeds to step 620 and determines whether or not the value of the counter N has reached a determination reference value N1 corresponding to the predetermined time T1 (see FIG. 4B). At present, the value of the counter N is smaller than the determination reference value N1, so the CPU 51 determines “No” in step 620 and proceeds to step 635 described above. Therefore, thereafter, the acceleration slip threshold Sth is set to the basic value until the value of the counter N reaches the determination reference value N1 (that is, until the predetermined time T1 elapses in a state where the phenomenon occurs). The acceleration slip threshold Sthbase is maintained.

  Assuming that the predetermined time T1 has elapsed with the above phenomenon occurring, the CPU 51 makes a “Yes” determination when proceeding to step 620 and proceeds to step 625, where the acceleration slip threshold Sth is reached. Is set to the value “Sthbase−β1”, and this routine is terminated once. Thereafter, the acceleration slip threshold Sth is maintained at the value “Sthbase−β1” as long as the above phenomenon continues (and therefore N ≧ N1 holds). As described above, the acceleration slip threshold Sth is sequentially selected as one of the basic acceleration slip threshold Sthbase and the value (Sthbase−β1).

  Further, the CPU 51 repeatedly executes the routine for performing the traction control start / end determination shown in FIG. 7 for each wheel every elapse of a predetermined time (for example, 6 msec). Therefore, when the predetermined timing is reached, the CPU 51 starts processing from step 700 and proceeds to step 705 to determine whether or not the value of the flag TRC ** is “0”. Here, the flag TRC ** indicates that the traction control is being executed for the wheel ** when the value is “1”, and the traction control is not being executed for the wheel ** when the value is “0”. It shows that.

  Assuming that the traction control is not being executed for the wheel ** and the traction control start condition described later is not satisfied, the CPU 51 determines “Yes” in step 705, and proceeds to step 710. The acceleration slip amount S ** for the wheel ** calculated in the previous step 535 is greater than or equal to the acceleration slip threshold Sth set in either of the previous steps 625 and 635, and the accelerator. It is determined whether or not the operation amount Accp is larger than “0” (that is, whether or not the traction control start condition is satisfied). Here, “No” is determined and the routine proceeds to step 795 to temporarily execute this routine. finish. Thereafter, the value of the flag TRC ** is maintained at “0” unless the traction control start condition is satisfied for the wheel **.

  On the other hand, assuming that the traction control start condition is satisfied for the wheel ** from this state, the CPU 51 determines “Yes” when it proceeds to step 710 and proceeds to step 715, and the value of the flag TRC ** Is changed from “0” to “1” and the routine proceeds to step 795 to end the present routine tentatively.

  Thereafter, since the value of the flag TRC ** is “1”, the CPU 51 determines “No” when proceeding to Step 705 and proceeds to Step 720, and the traction control end condition for the wheel ** is satisfied. It is determined whether it is established. Here, the traction control end condition is, for example, that when the accelerator operation amount Accp becomes “0”, the acceleration slip amount S ** is less than a predetermined end reference value smaller than the acceleration slip threshold Sth. It is established when.

  Since the present time is immediately after the traction control start condition is satisfied for the wheel **, the traction control end condition is not satisfied for the wheel **. Accordingly, when the CPU 51 proceeds to step 720, it determines “No”, proceeds to step 795, and once ends this routine. Thereafter, the value of the flag TRC ** is maintained at “1” unless the traction control end condition is satisfied for the wheel **.

  On the other hand, assuming that the traction control end condition is satisfied for the wheel ** from this state, the CPU 51 determines “Yes” when the process proceeds to step 720 and proceeds to step 725, and the value of the flag TRC ** Is changed from “1” to “0” again.

  Thereafter, since the value of the flag TRC ** is “0”, when the CPU 51 proceeds to step 705, it determines “Yes” again and proceeds to step 710, and the traction control start condition for the wheel ** is reached. Whether or not is satisfied is monitored again. In this way, the value of the flag TRC ** is sequentially selected as either “0” or “1” for each wheel.

  Furthermore, the CPU 51 repeatedly executes a routine for executing the traction control shown in FIG. 8 every elapse of a predetermined time (for example, 6 msec). Accordingly, when the predetermined timing is reached, the CPU 51 starts processing from step 800 and proceeds to step 805 to determine whether or not the flag TRC ** is “0” for all wheels (that is, traction control for all wheels). If it is determined whether or not it is not being executed), and if it is determined to be “Yes”, the process proceeds to step 825, and all the solenoid valves of the brake fluid pressure control device 30 (see FIG. 2) are set in a non-excited state. An instruction is given to put the motor MT in a non-driven state, and the routine immediately proceeds to step 895 to end this routine once.

  On the other hand, if the CPU 51 makes a “No” determination at step 805, it proceeds to step 810 and is based on the acceleration slip amount S ** calculated at the previous step 535 and the table described in step 810. The target hydraulic pressure Pwt ** is determined for each wheel. As a result, for a wheel ** in which the acceleration slip amount S ** is greater than the acceleration slip threshold Sth, the target hydraulic pressure Pwt ** is set to a larger value as the acceleration slip amount S ** increases, and the acceleration slip amount The target hydraulic pressure Pwt ** is set to “0” for the wheel ** where S ** is equal to or less than the acceleration slip threshold Sth.

  Subsequently, the CPU 51 proceeds to step 815, and the electromagnetic valve and motor MT of the brake hydraulic pressure control device 30 are set so that the wheel cylinder hydraulic pressure Pw ** of the wheel ** becomes the set target hydraulic pressure Pwt **. The control instruction is performed. Thereby, the traction control based on the application of the braking force by the brake fluid pressure is achieved.

  Subsequently, the CPU 51 proceeds to step 820 and gives an instruction to reduce the output of the engine 21 by an amount corresponding to the maximum value of the acceleration slip amount S **. Thereby, when the said maximum value is not "0", the engine output reduction control based on traction control is performed. Then, the CPU 51 proceeds to step 895 to end this routine once. In this way, traction control based on the application of braking force by brake fluid pressure and engine output reduction control based on traction control are executed for each wheel.

  As described above, according to the traction control device according to the first embodiment of the present invention, the traction control is executed when the acceleration slip amount S ** of the wheel ** becomes equal to or greater than the acceleration slip threshold Sth. To do. Here, in principle, the acceleration slip threshold Sth is set to a basic acceleration slip threshold Sthbase (a constant value). On the other hand, “0 <accelerator operation amount Accp <minor value Accpref” and “vehicle acceleration DVwmin based on wheel speed sensor output (that is, slope of a line indicating the minimum wheel speed Vwmin in FIG. 4)> vehicle body based on longitudinal acceleration sensor output When the two conditions “acceleration Gup (that is, the slope of the line indicating the vehicle speed Vgup based on the raised value in FIG. 4)” continue to be satisfied for a predetermined time T1, “a slight accelerator during low μ road running” It is determined that the phenomenon that the acceleration slip amount S ** of all wheels gradually increases due to operation ”(acceleration slip has occurred), and the acceleration slip threshold Sth is determined as the basic acceleration slip. The threshold value Sthbase is changed to a value (Sthbase−β1) obtained by subtracting the value β1 (positive constant).

  As a result, when "a phenomenon in which the acceleration slip amount of all the wheels gradually increases due to a slight accelerator operation during low μ road running" has occurred, the acceleration slip threshold Sth is reduced, Traction control can be initiated at an appropriate time.

  The present invention is not limited to the first embodiment, and various modifications can be employed within the scope of the present invention. For example, in the first embodiment, the time differential value DVwmin of the minimum wheel speed Vwmin is adopted as the “vehicle body acceleration based on the wheel speed sensor output”, but the second smallest value among the wheel speeds Vw **. The time differential value may be used.

  In the first embodiment, the vehicle body acceleration raising value Gup (= vehicle body acceleration detection value Gx + positive constant α1) is adopted as the “vehicle body acceleration based on the longitudinal acceleration sensor output”. The value Gx itself may be adopted.

  Further, in the first embodiment, acceleration slip occurs when “a phenomenon in which the acceleration slip amount S ** of all wheels gradually increases due to slight accelerator operation during low μ road traveling” occurs. The amount by which the threshold value Sth is reduced is constant at the value β1 (positive constant), but may be variable according to the degree of acceleration slip. For example, a value (DVwmin−Gup) (> 0) obtained by subtracting “vehicle acceleration Gup based on longitudinal acceleration sensor output” from “vehicle acceleration DVwmin based on wheel speed sensor output” as the degree of acceleration slip is adopted (DVwmin). It is preferable to increase the value β1 as -Gup) increases.

  Further, in the first embodiment, the traction control is performed when “a phenomenon in which the acceleration slip amount S ** of all the wheels gradually increases due to a slight accelerator operation during low μ road traveling” occurs. Although the acceleration slip threshold value Sth is reduced in order to facilitate the start, the value α1 (> 0) may be reduced instead of or in addition to this. When the value α1 is decreased, the vehicle body acceleration raising value Gup is reduced. Therefore, the vehicle body speed Vgup (accordingly, the estimated vehicle body speed Vrefacc) based on the raising value is reduced and the acceleration slip amount S ** (= Vw ** − Vrefacc ) Is calculated larger (see FIG. 4). As a result, the traction control start condition is easily established and the traction control is easily started.

(Second Embodiment)
Next, an ABS control apparatus according to the second embodiment of the present invention will be described. The second embodiment is different from the first embodiment only in that ABS control is executed instead of traction control. Therefore, the following description will focus on such differences.

(Outline of ABS control)
An outline of the ABS control executed by the ABS control apparatus (hereinafter also referred to as “this apparatus”) according to the second embodiment of the present invention will be described. ABS control is control that prevents the occurrence of excessive deceleration slip of a wheel in order to suppress an increase in braking distance when the vehicle is in a braking state.

  Specifically, this device calculates the deceleration slip amount L ** individually for each wheel, and reduces the brake fluid pressure for the wheel whose deceleration slip amount L ** is equal to or greater than the deceleration slip threshold Lth. Make adjustments (ie, start / execute ABS control). The deceleration slip threshold Lth is basically set to a value equal to a predetermined basic deceleration slip threshold Lthbase (a constant value), but is set to another value only in a specific case as will be described later. The Here, the deceleration slip amount L ** is calculated according to the following equation (3).

L ** = Vrefdec−Vw ** (3)

  In the above equation (3), Vrefdec is an estimated vehicle body speed in the vehicle longitudinal direction for ABS control, and is calculated according to the following equation (4).

Vrefdec = max (Vwmax, Vgdown) (4)

  In the above equation (4), Vwmax is the maximum value (maximum wheel speed) of the wheel speeds Vw **. Vgdown is a time integral value (vehicle speed based on the lowering value) of the vehicle body acceleration raising value Gdown, which is a value obtained by subtracting a positive constant α2 from the detected vehicle acceleration value Gx corresponding to the output of the longitudinal acceleration sensor 44. That is, the estimated vehicle speed Vrefdec for ABS control is set to a larger value of the maximum wheel speed Vwmax and the vehicle speed Vgdown based on the lowering value.

  Here, the constant α2 is set to a value for always setting the vehicle body acceleration lowering value Gdown to a value equal to or less than the true vehicle body acceleration even when the individual variation in the output characteristics of the longitudinal acceleration sensor 44 is taken into consideration. Accordingly, the vehicle body speed Vgdown based on the above-described lowering value is always maintained at a value equal to or lower than the true vehicle body speed Vreal.

  The reason why the estimated vehicle speed Vrefdec for ABS control is calculated according to the above equation (4) is as follows. That is, when the vehicle is in a relatively gentle deceleration state (specifically, when the degree of deceleration slip of the wheel corresponding to the maximum wheel speed Vwmax is small), the true vehicle speed Vreal is a value close to the maximum wheel speed Vwmax. Tend to be. As a result, the maximum wheel speed Vwmax becomes larger than the vehicle body speed Vgdown based on the reduction value. Therefore, according to the above equation (4), when the vehicle is in a relatively gentle deceleration state, the estimated vehicle speed Vrefdec for ABS control is set to a value equal to the maximum wheel speed Vwmax. Can be calculated with high accuracy.

  On the other hand, when the vehicle is in a relatively rapid deceleration state (specifically, when the degree of deceleration slip of all four wheels is large (thus, when the degree of deceleration slip of the wheel corresponding to the maximum wheel speed Vwmax is large)) ) When the maximum wheel speed Vwmax greatly deviates from the true vehicle speed Vreal to the smaller side, the vehicle body speed Vgdown based on the bulk reduction value may become larger than the maximum wheel speed Vwmax.

  In such a case, according to the above equation (4), the estimated vehicle speed Vrefdec for ABS control is equal to the vehicle body speed Vgdown based on the lowering value that is closer to the true vehicle speed Vreal than the maximum wheel speed Vwmax. Can be calculated to a value. Therefore, according to the above equation (4), when the vehicle is in a relatively rapid deceleration state, the estimated body speed Vrefdec for ABS control is always calculated to be equal to the maximum wheel speed Vwmax. The speed Vrefdec can be calculated with high accuracy.

  Furthermore, as described above, the vehicle body speed Vgdown based on the above-described lowering value is always maintained at a value equal to or lower than the true vehicle body speed Vreal. In this case, the deceleration slip amount L calculated according to the above equation (3) ** will be calculated smaller. As a result, according to the above equation (4), when the vehicle is in a relatively abrupt deceleration state, the malfunction “ABS control is started at an early stage where ABS control should not be started” as described above. Can be prevented. The above is the reason why the estimated vehicle speed Vrefdec for ABS control is calculated according to the above equation (4).

(Deceleration slip threshold reduction)
As described above, the ABS control is basically started and executed for a wheel whose deceleration slip amount L ** is equal to or greater than the deceleration slip threshold Lth (= basic deceleration slip threshold Lthbase). . However, when the deceleration slip threshold Lth is always set to the basic deceleration slip threshold Lthbase (a constant value) as described above, the above-mentioned “deceleration slip amount of all the wheels by a slight brake pedal operation during low μ road surface travel” In the case where the phenomenon of “slowly increasing” occurs, there may occur a problem that the timing at which the ABS control is started is greatly delayed (or the ABS control is not started). Hereinafter, this will be described with reference to FIG.

  FIG. 9A shows a case where the vehicle is traveling on a low μ road surface and the driver slightly depresses the brake pedal BP (when master cylinder hydraulic pressure Pm <small value Pmref is satisfied) at time t1. The change in the true vehicle speed Vreal, the vehicle speed Vgdown based on the lowering value, the maximum wheel speed Vwmax, and the estimated vehicle speed Vrefdec for ABS control when deceleration slips start to occur on all wheels (four wheels) simultaneously It is the time chart which showed the example. As described above, the vehicle body speed Vgdown based on the lowering value is always calculated to a value equal to or lower than the true vehicle body speed Vreal.

  This example shows a case where the wheel speed Vw ** of all the wheels (and hence the maximum wheel speed Vwmax) gradually deviates from the true vehicle speed Vreal toward the smaller side after time t1. As a result, the maximum wheel speed Vwmax is larger than the vehicle body speed Vgdown based on the lowering value before the time t1 to the time t2, and the vehicle body speed Vgdown based on the lowering value is higher than the maximum wheel speed Vwmax after the time t2. It is getting bigger.

  Therefore, as indicated by a thick solid line, the estimated vehicle speed Vrefdec for ABS control is set to a value equal to the maximum wheel speed Vwmax from before time t1 to time t2, and based on the lowering value after time t2. It is set to a value equal to the vehicle speed Vgdown. As a result, the deceleration slip amount L ** of all the wheels calculated according to the above equation (3) is maintained at substantially “0” from time t1 to time t2, and gradually increases after time t2. Go.

  Here, in this example, the true deceleration slip amount (that is, the value obtained by subtracting the wheel speed Vw ** from the true vehicle speed Vreal) is the deceleration slip threshold Lth (= basic deceleration slip threshold at time t3). Lthbase). That is, the ABS control should be started at time t3.

  On the other hand, the deceleration slip amount L ** of all wheels calculated according to the above equation (3) is due to the fact that the vehicle speed Vgdown based on the lowering value is calculated to a value less than or equal to the true vehicle speed Vreal. Since it is calculated to be smaller than the true deceleration slip amount, the deceleration slip threshold Lth (= basic deceleration slip threshold Lthbase) is reached at time t4 after time t3. Therefore, if the deceleration slip threshold Lth is always set to the basic deceleration slip threshold Lthbase (a constant value), the ABS control is actually started at time t4.

  Here, in this example, a case where the vehicle is traveling on a low μ road surface and the driver slightly depresses the brake pedal BP is shown. Therefore, the wheel speeds Vw ** of all the wheels (therefore, the maximum wheels) The speed of reduction of the speed Vwmax (that is, the speed at which the wheel speed ** deviates from the true vehicle speed Vreal) is very small. Therefore, the time t4 is a time that is greatly delayed from the time t3, and as a result, the timing at which the ABS control is started is greatly delayed.

  In this way, when the deceleration slip threshold Lth is always set to the basic deceleration slip threshold Lthbase (a constant value), “the deceleration slip amount of all wheels gradually increases due to a slight brake pedal operation during low μ road surface travel. In the case where the phenomenon of “doing” occurs, there arises a problem that the timing at which the ABS control is started is greatly delayed.

  One way to deal with this problem is to determine that a phenomenon occurs in which “the deceleration slip amount of all wheels slowly increases due to slight brake pedal operation while driving on a low μ road surface”. If it is determined that the same phenomenon has occurred (thus, if it is determined that deceleration slip has occurred), it is conceivable to decrease the deceleration slip threshold Lth. Hereinafter, a method of determining that the “phenomenon in which the deceleration slip amount of all the wheels gradually increases due to a slight brake pedal operation during low μ road running” will be described.

  When the vehicle is in a braking state, the deceleration slip amount L ** of a certain wheel increases when the wheel speed Vw ** (= Vwmax) of the wheel increases (that is, Vwmax in FIG. The slope of the line shown (negative value)) is smaller than the increasing slope of the true vehicle speed Vreal (that is, the slope of the line showing Vreal (negative value) in FIG. 9A) (the absolute value is large). Means that. In other words, when the deceleration slip amount L ** of a certain wheel increases when the vehicle is in a braking state, the time differential value of the maximum wheel speed Vwmax (hereinafter referred to as “vehicle acceleration DVwmax based on wheel speed sensor output”). Is smaller than the true vehicle acceleration (absolute value is larger).

  On the other hand, as described above, the vehicle body acceleration lowering value Gdown is always set to a value equal to or less than the true vehicle body acceleration. From the above, when the vehicle is in a braking state, “vehicle acceleration DVwmax based on wheel speed sensor output” is referred to as a vehicle acceleration bulk reduction value Gdown (hereinafter also referred to as “vehicle acceleration Gdown based on longitudinal acceleration sensor output”). If the condition that the speed is smaller (the absolute value is larger) is satisfied, it means that the deceleration slip amount L ** is surely increased.

  Further, it can be determined that “0 <master cylinder hydraulic pressure Pm <the above-described minute value Pmref” holds that the driver has depressed the brake pedal BP slightly. From the above, the fact that “a phenomenon in which the deceleration slip amount of all wheels gradually increases due to slight brake pedal operation while driving on a low μ road surface” has occurred is that “0 <Pm <Pmref” and “DVwmax < It can be determined when two conditions of “Gdown” are satisfied.

  Furthermore, in order to more reliably and accurately determine that the above phenomenon has occurred, the determination condition is that the above two conditions are continuously satisfied over a certain period of time. It is considered preferable to add.

  In view of the above, when the above two conditions are continuously satisfied for a predetermined time T2 or more, this device indicates that “the deceleration slip amount of all the wheels is reduced by a slight brake pedal operation during low μ road travel”. It is determined that “a slowly increasing phenomenon” has occurred (deceleration slip has occurred). And this apparatus is the value obtained by subtracting the value β2 (positive constant) from the basic deceleration slip threshold Lthbase only while it is determined that the above phenomenon has occurred. Change to (Lthbase-β2). Hereinafter, this will be described with reference to FIG.

  FIG. 9 (b) shows the same situation as FIG. 9 (a) described above (that is, from the time t1, the deceleration slip amount of all the wheels is reduced by a slight brake pedal operation (0 <Pm <Pmref) during low μ road running. Example of changes in true body speed Vreal, body speed Vgdown based on bulk reduction value, maximum wheel speed Vwmax, and estimated body speed Vrefdec for ABS control in a situation where “a slowly increasing phenomenon” starts to occur) It is the time chart which showed.

  In this example, “the vehicle body acceleration DVwmax based on the wheel speed sensor output” (that is, the slope of the line indicating the maximum wheel speed Vwmax) is “from time t1 before the start of deceleration slip of all wheels to time t5”. It is larger than the “vehicle acceleration Gdown based on the longitudinal acceleration sensor output” (that is, the slope of the line indicating the vehicle velocity Vgdown based on the lowering value), and smaller than the “vehicle acceleration Gdown based on the longitudinal acceleration sensor output” after time t5. ing.

  Accordingly, in this case, the present apparatus determines that “low μ” at time t6 when the two conditions “0 <Pm <Pmref” and “DVwmax <Gdown” are continuously satisfied over the predetermined time T2. It is determined that “a phenomenon in which the deceleration slip amount of all the wheels gradually increases due to a slight brake pedal operation while traveling on the road surface” has occurred (deceleration slip has occurred).

  The apparatus changes the deceleration slip threshold Lth from the basic deceleration slip threshold Lthbase to a value (Lthbase−β2) after time t6. As a result, the deceleration slip amount L ** of all the wheels can reach the deceleration slip threshold (Lthbase-β2) at time t7, which is substantially the same time as time t3 in FIG. Therefore, the present apparatus starts the ABS control at time t7 which is substantially the same time as time t3 which is “the time when ABS control should be started originally”.

  As described above, when “a phenomenon in which the deceleration slip amount of all wheels gradually increases due to slight brake pedal operation while driving on a low μ road surface” has occurred, the deceleration slip threshold Lth is reduced. Thus, the ABS control can be started at an appropriate time. The outline of the ABS control and the reduction of the deceleration slip threshold have been described above.

(Actual operation of the second embodiment)
The actual operation of the ABS control device according to the second embodiment will be described below. The CPU 51 of this apparatus replaces the routines shown in FIGS. 5 to 8 executed by the CPU 51 of the first embodiment with predetermined routines shown in the flowcharts of FIGS. 10 to 13 corresponding to FIGS. Repeatedly for each passage of time.

  Here, steps 1005 to 1040 of the routine shown in FIG. 10 correspond to steps 505 to 540 of the routine shown in FIG. Therefore, a detailed description of the routine of FIG. 10 is omitted. Various values are successively updated by repeatedly executing the routine of FIG.

  Further, steps 1105 to 1135 of the routine shown in FIG. 11 correspond to steps 605 to 635 of the routine shown in FIG. Therefore, detailed description of the routine of FIG. 11 is also omitted. By repeatedly executing the routine of FIG. 11, the deceleration slip threshold Lth is sequentially selected as one of the basic deceleration slip threshold Lthbase and the value (Lthbase−β2).

  The value M1 in step 1120 is a determination reference value corresponding to the predetermined time T2 (see FIG. 9B). Further, the value of the counter M is a counter representing a duration in which it is determined that “a phenomenon in which the deceleration slip amount of all the wheels gradually increases due to slight brake pedal operation during low μ road traveling” has occurred. It is.

  Also, steps 1205 to 1225 (except for step 1217) of the routine shown in FIG. 12 correspond to steps 705 to 725 of the routine shown in FIG. Accordingly, detailed description of the routine of FIG. 12 is also omitted. By repeatedly executing the routine of FIG. 12, the value of the flag ABS ** is sequentially selected as one of “0” and “1” for each wheel. The flag ABS ** indicates that the ABS control is being executed for the wheel ** when the value is "1", and the ABS control is not being executed for the wheel ** when the value is "0". .

  The condition described in step 1210 is an ABS control start condition. Further, the ABS control end condition in Step 1220 is satisfied, for example, when the master cylinder hydraulic pressure Pm becomes “0”, when a predetermined time elapses after the ABS control starts, or the like. In addition, T ** in Step 1217 is an elapsed time from the ABS control start time for the wheel **, and when the ABS control start condition is satisfied for the wheel ** ("Yes" is determined in Step 1210). It is cleared to “0” at the time).

  Further, the CPU 51 of this apparatus repeatedly executes a routine for executing the ABS control shown in FIG. 13 for each wheel every elapse of a predetermined time (for example, 6 msec). Accordingly, when the predetermined timing is reached, the CPU 51 starts processing from step 1300 and proceeds to step 1305 to determine whether or not the flag ABS ** is “1” (that is, ABS control is being executed for the wheel **). If it is determined as “No”, the process immediately proceeds to step 1395 to end the present routine tentatively. In this case, ABS control is not executed for the wheel **.

  On the other hand, if “Yes” is determined, the CPU 51 proceeds to step 1310 to appropriately set the pressure increasing valve PU ** and pressure reducing valve PD ** according to the elapsed time T ** from the ABS control start time for the wheel **. The opening / closing control is performed, and the pressure increase / hold / reduction control is performed as described in Step 1310 on the wheel cylinder hydraulic pressure Pw ** for the wheel **. This achieves ABS control for the wheel **.

  As described above, according to the ABS control device of the second embodiment of the present invention, the ABS control is executed when the deceleration slip amount L ** of the wheel ** becomes equal to or greater than the deceleration slip threshold Lth. To do. Here, the deceleration slip threshold Lth is basically set to a basic deceleration slip threshold Lthbase (a constant value). On the other hand, “0 <master cylinder hydraulic pressure Pm <small value Pmref” and “vehicle body acceleration DVwmax based on wheel speed sensor output (ie, the slope of the line indicating the maximum wheel speed Vwmax in FIG. 9 (negative value)) <front and back When two conditions of the vehicle body acceleration Gdown based on the acceleration sensor output (that is, the slope of the line indicating the vehicle body speed Vgdown based on the lowering value in FIG. 9 (negative value)) continue to be satisfied for a predetermined time T2. , "Phenomenon that deceleration slip amount L ** of all wheels slowly increases due to slight brake pedal operation while driving on low μ road surface" has occurred (deceleration slip is occurring) The deceleration slip threshold Lth is changed to a value (Lthbase−β2) obtained by subtracting the value β2 (positive constant) from the basic deceleration slip threshold Lthbase.

  As a result, when the phenomenon that “the deceleration slip amount of all wheels gradually increases due to slight brake pedal operation during low μ road running” occurs, the deceleration slip threshold Lth is reduced. ABS control can be initiated at an appropriate time.

  The present invention is not limited to the second embodiment, and various modifications can be adopted within the scope of the present invention. For example, in the second embodiment, the time differential value DVwmax of the maximum wheel speed Vwmax is adopted as the “vehicle body acceleration based on the wheel speed sensor output”, but the second largest value among the wheel speeds Vw **. The time differential value may be used.

  Further, in the second embodiment, the “vehicle acceleration based on the longitudinal acceleration sensor output” employs the vehicle acceleration bulk reduction value Gdown (= vehicle acceleration detection value Gx−positive constant α2) (FIG. 10). The vehicle body acceleration detection value Gx itself may be adopted.

  Further, in the second embodiment, the deceleration slip occurs in the case where “a phenomenon in which the deceleration slip amount L ** of all the wheels gradually increases due to a slight brake pedal operation while traveling on a low μ road surface” occurs. The amount by which the threshold value Lth is reduced is constant at the value β2 (positive constant), but may be variable according to the degree of deceleration slip. For example, a value obtained by subtracting “vehicle acceleration Gdown based on longitudinal acceleration sensor output” (DVwmax−Gdown) (<0) from “vehicle acceleration DVwmax based on wheel speed sensor output” as a degree of deceleration slip is adopted (DVwmax It is preferable to increase the value β2 as the value of (−Gdown) decreases (the absolute value increases).

  In the second embodiment, the ABS control is performed in the case where “a phenomenon in which the deceleration slip amount L ** of all the wheels gradually increases due to a slight brake pedal operation while traveling on a low μ road surface” occurs. The deceleration slip threshold value Lth is reduced to make it easier to start, but the value α2 (> 0) may be reduced instead of or in addition to this. If the value α2 is decreased, the vehicle body acceleration lowering value Gdown increases, so that the vehicle body speed Vgdown (and hence the estimated vehicle body speed Vrefdec) based on the lowering value increases and the deceleration slip amount L ** (= Vrefdec−Vw **). ) Is calculated larger (see FIG. 9). As a result, the ABS control start condition is easily established and the ABS control is easily started.

  Furthermore, it is preferable that both the traction control device according to the first embodiment and the ABS control device according to the second embodiment are provided. In this case, the CPU of the electric control device is configured to execute the routines of FIGS. 10 to 13 in addition to the routines of FIGS.

1 is a schematic configuration diagram of a vehicle equipped with a traction control device according to a first embodiment of the present invention. It is a schematic block diagram of the brake fluid pressure control apparatus shown in FIG. It is the graph which showed the relationship between the command electric current and command differential pressure about the normally open linear solenoid valve shown in FIG. FIG. 4 (a) shows that the acceleration slip threshold is not reduced when "a phenomenon in which the acceleration slip amount of all wheels gradually increases due to a slight accelerator operation during low-μ road surface travel" occurs. It is a figure for demonstrating that the start time of traction control is overdue. FIG. 4B is a diagram for explaining the effect obtained by reducing the acceleration slip threshold in the same situation as FIG. 3 is a flowchart showing a routine for calculating wheel speed and the like executed by a CPU shown in FIG. 1. 2 is a flowchart showing a routine for performing all-wheel acceleration slip determination on a low μ road and selection of an acceleration slip threshold executed by a CPU shown in FIG. 1. FIG. 3 is a flowchart showing a routine for performing start / end determination of traction control executed by a CPU shown in FIG. 1. FIG. It is the flowchart which showed the routine for performing traction control which CPU shown in FIG. 1 performs. FIG. 9 (a) shows that the deceleration slip threshold is reduced when "a phenomenon in which the deceleration slip amount of all wheels gradually increases due to slight brake pedal operation during low-μ road surface travel" occurs. It is a figure for demonstrating that the start time of ABS control will be delayed if it is not carried out. FIG. 9B is a diagram for explaining the effect obtained by reducing the deceleration slip threshold in the same situation as FIG. 9A. It is the flowchart which showed the routine for calculating the wheel speed etc. which CPU of the ABS control apparatus which concerns on 2nd Embodiment performs. It is the flowchart which showed the routine for performing the low-micro road all-wheels deceleration slip determination and selection of the deceleration slip threshold value which CPU of the ABS control apparatus which concerns on 2nd Embodiment performs. It is the flowchart which showed the routine for performing the start / end determination of the ABS control which CPU of the ABS control apparatus which concerns on 2nd Embodiment performs. It is the flowchart which showed the routine for performing ABS control which CPU of the ABS control device which concerns on 2nd Embodiment performs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vehicle traction control device, 30 ... Brake hydraulic pressure control device, 41 ** ... Wheel speed sensor, 42 ... Accelerator opening sensor, 43 ... Master cylinder hydraulic pressure sensor, 44 ... Longitudinal acceleration sensor, 50 ... Electric control Device, 51 ... CPU

Claims (4)

A wheel speed sensor that outputs a signal representing the wheel speed of the vehicle;
A longitudinal acceleration sensor that outputs a signal representing vehicle acceleration in the longitudinal direction of the vehicle;
An accelerator operation amount corresponding value sensor for acquiring a value corresponding to the accelerator operation amount of the vehicle;
A vehicle traction control device applied to an all-wheel drive vehicle in which the driving force of the drive source is transmitted to all wheels,
First vehicle body acceleration acquisition means for acquiring a first vehicle body acceleration in the longitudinal direction of the vehicle body based on the output of the wheel speed sensor;
Second vehicle body acceleration acquisition means for acquiring second vehicle body acceleration in the vehicle longitudinal direction based on the output of the longitudinal acceleration sensor;
Estimated vehicle body speed acquisition means for acquiring an estimated vehicle body speed of the vehicle based on at least the output of the longitudinal acceleration sensor;
Acceleration slip amount acquisition means for acquiring an acceleration slip amount by subtracting the acquired estimated vehicle body speed from a wheel speed acquired based on an output of the wheel speed sensor;
A specific condition is established that the acquired first vehicle body acceleration is greater than the acquired second vehicle body acceleration, and the acquired accelerator operation amount corresponding value is greater than zero and less than a predetermined value. Determination means for determining whether or not,
When it is determined that the specific condition is not satisfied, traction control is started / executed based on the acquired acceleration slip amount being equal to or greater than a reference threshold, and the specific condition is satisfied Traction control means for starting and executing the traction control based on the acquired acceleration slip amount being equal to or greater than a threshold value smaller than the reference threshold value when it is determined that
Vehicle traction control device comprising:   The traction control device for a vehicle according to claim 1,
  The estimated vehicle body speed acquisition means includes
  A vehicle traction control device configured to acquire an estimated vehicle body speed based on a vehicle body acceleration raising value obtained by adding a reference addition value in an acceleration direction to a detection value based on an output of the longitudinal acceleration sensor. A wheel speed sensor that outputs a signal representing the wheel speed of the vehicle;
A longitudinal acceleration sensor that outputs a signal representing vehicle acceleration in the longitudinal direction of the vehicle;
An accelerator operation amount corresponding value sensor for acquiring a value corresponding to the accelerator operation amount of the vehicle;
A vehicle traction control device applied to an all-wheel drive vehicle in which the driving force of the drive source is transmitted to all wheels,
First vehicle body acceleration acquisition means for acquiring a first vehicle body acceleration in the longitudinal direction of the vehicle body based on the output of the wheel speed sensor;
Second vehicle body acceleration acquisition means for acquiring second vehicle body acceleration in the vehicle longitudinal direction based on the output of the longitudinal acceleration sensor;
A specific condition is established that the acquired first vehicle body acceleration is greater than the acquired second vehicle body acceleration, and the acquired accelerator operation amount corresponding value is greater than zero and less than a predetermined value. Determination means for determining whether or not,
When it is determined that the specific condition is not satisfied, an estimated vehicle body speed of the vehicle is acquired based on a value obtained by adding a reference addition value in the acceleration direction to a detection value based on the output of the longitudinal acceleration sensor, Estimated vehicle speed acquisition means for acquiring the estimated vehicle speed of the vehicle based on a value obtained by adding an added value in the acceleration direction smaller than the reference added value to the detected value when it is determined that the specific condition is satisfied When,
Acceleration slip amount acquisition means for acquiring an acceleration slip amount by subtracting the acquired estimated vehicle body speed from a wheel speed acquired based on an output of the wheel speed sensor;
Traction control means for starting and executing traction control based on the acquired acceleration slip amount being equal to or greater than a reference threshold;
Vehicle traction control device comprising:   In the traction control device for a vehicle according to any one of claims 1 to 3,
  The determination means includes
  A vehicle traction control device configured to determine that the specific condition is satisfied based on the specific condition continuing to be satisfied for a predetermined time.

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