Patent Description:
Driving control apparatuses for vehicles having automatic braking functions, for example, driving control apparatuses having full speed range ACC functions, decelerate a vehicle to a stop by operating automatic braking when the vehicle approaches a vehicle ahead that decelerated to a stop or when a vehicle ahead as a target of following cruise has decelerated to a stop. In order to suppress swing back (pitching vibration) at the time of such deceleration and stop, control to temporarily reduce brake pressure immediately before stopping is known (for example, Patent Literature <NUM>).

[Patent Literature <NUM>] discloses that a vehicle speed control system comprises a low-speed progress control system (LSP) which is operable to cause a vehicle to operate at a target speed value by controlling an amount of brake torque applied by a braking system and an amount of drive torque applied by a powertrain to one or more wheels. The LSP control detects, via sensors, a leading wheel step event in which a leading wheel, e.g. front wheels, encounters an obstacle such as a boulder which presents an abrupt increase in surface gradient. After detection of the obstacle the LSP control applies brake torque against drive torque in anticipation of a trailing wheel step event, e.g. rear wheels encounter the obstacle. The LSP control maintains the brake torque at least until the trailing wheel/s has travelled a sufficient distance to reach a location at which the leading wheel/s experienced the leading wheel step event.

[Patent Literature <NUM>] discloses a vehicle having a controller for controlling an engine and a braking system to decelerate the vehicle based on a detected forward object and an adaptive cruise control mode being active. The controller controls the braking system to apply a braking torque to brake the vehicle to a full stop and hold a vehicle stationary in an absence of powertrain torque based on a current road grade, and auto-stop the engine based on distance to the object falling below a first predefined threshold and vehicle speed falling below a second predefined threshold with the mode being active.

A vehicle equipped with an AMT type automatic transmission can improve sensation when the vehicle decelerates and stops by disengaging a clutch and disconnecting an engine from a drive shaft side when the vehicle decelerates and stops by an automatic brake. However, when this control and the above-mentioned pitching suppression control were used together on an uphill road, it was recognized that there was a tendency to feel a slight backward movement at a stop position until a braking force increased after brake pressure reduction.

The present invention has been made in view of the above-described circumstances, and an object is to provide a driving control apparatus for a vehicle that can provide the same deceleration-and-stop-time sensation as on a flat road, even on an uphill road.

In order to solve the above-described problems, there is provided a driving control apparatus as set out in independent claim <NUM>. Advantageous developments are defined in the dependent claims <NUM> to <NUM>.

In the driving control apparatus for a vehicle according to the present invention, as described above, since the predetermined torque request is made to the engine in addition to the pitching suppression control of increasing pressure after temporarily reducing pressure of the braking force when a road surface gradient equal to or greater than the predetermined threshold value is detected when the vehicle decelerates and stops according to a vehicle ahead, the same deceleration-and-stop sensation as on a flat road can be provided without the sensation of a slight backward movement, even on an uphill road.

In <FIG>, a vehicle <NUM> includes an internal combustion engine <NUM> and an AMT type automatic transmission <NUM> in a torque transmission path from the engine <NUM> to drive wheels (<NUM>), and also includes an engine controller <NUM> as engine control means for making a torque request to the engine <NUM>, and an AMT controller <NUM> that controls a gear shifting operation of the automatic transmission <NUM> to a gear stage determined based on an engine speed and the torque request, and a clutch opening/closing operation linked thereto.

The vehicle <NUM> includes a brake system that includes a brake control apparatus <NUM> (including a brake controller and a brake actuator (hydraulic actuator)) capable of individually controlling the braking force of brakes <NUM> of left and right front wheels <NUM> and brakes <NUM> of left and right rear wheels <NUM>, a brake pedal <NUM>, a hydraulic pressure sensor <NUM>, wheel speed sensors <NUM> of the left and right front wheels <NUM> and wheel speed sensors <NUM> of the left and right rear wheels <NUM>, and forms an ABS/vehicle behavior stabilization apparatus.

The vehicle <NUM> further includes vehicle ahead detection means <NUM> that forms an ACC system together with an ACC controller <NUM>. One or more detection means, such as a millimeter wave radar, stereo camera, or LiDAR, that have a function for detecting the presence of a vehicle ahead or an object (obstacle or structure) in front of the vehicle and can measure a relative distance between the vehicle ahead or obstacle and the vehicle can be used for the vehicle ahead detection means <NUM>.

The ACC controller <NUM> is configured to issue an acceleration/deceleration command to the engine controller <NUM> and the brake control apparatus <NUM> instead of the driver's accelerator/brake operation on the basis of a vehicle speed calculated from detection information of the vehicle ahead detection means <NUM> and detection values of the wheel speed sensors <NUM> and <NUM>, and perform full speed range adaptive cruise control (constant speed cruise/following cruise control/deceleration stop and restart control).

That is, the brake control apparatus <NUM> (brake controller) that has received the deceleration command from the ACC controller <NUM> controls the vehicle speed by issuing a braking request (hydraulic request) to a brake actuator and controlling the braking force of the brakes <NUM> and <NUM>. The engine controller <NUM> that has received the acceleration/deceleration command as a torque request to the engine <NUM> from the ACC controller <NUM>, controls actuator output (degree of throttle opening), thereby controls the torque of the engine <NUM>, and controls the vehicle speed.

By the above-described control of the ACC controller <NUM>, the vehicle <NUM> performs constant speed cruise while maintaining a set vehicle speed when there is no vehicle ahead, and when catching up with a vehicle ahead, performs following cruise to the vehicle ahead while maintaining an inter-vehicle distance corresponding to a predetermined inter-vehicle time (time gap = inter-vehicle distance / vehicle speed) according to the speed of the vehicle ahead. Furthermore, when the vehicle ahead decelerates and stops while the vehicle <NUM> is performing following cruise or the vehicle <NUM> approaches the vehicle ahead that has decelerated and stopped, the vehicle <NUM> decelerates and stops while ensuring the predetermined inter-vehicle distance, and when the vehicle ahead starts within a predetermined time, restarts accordingly and continues the following cruise.

The engine controller <NUM>, AMT controller <NUM>, brake controller of the brake control apparatus <NUM>, and ACC controller <NUM> described above each include a microcomputer (MCU) composed of a ROM for storing a control program, setting data or the like, a RAM for temporarily storing arithmetic processing results, a CPU for performing arithmetic processing, a communication interface (I/F), and the like, and are connected with each other intercommunicatively together with the vehicle ahead detection means <NUM> and a sensor group including a gradient sensor <NUM> described below via an on-vehicle network (such as a CAN).

The vehicle <NUM> according to the embodiment of the present invention includes a gradient sensor <NUM> as gradient detection means for detecting a road surface gradient. As the gradient sensor <NUM>, a gradient sensor for detecting a gradient in the front-rear direction of the vehicle <NUM> on the basis of gravitational acceleration, an acceleration sensor, a multi-axis inertia sensor, or the like can be used.

The driving control system according to the present invention is characterized by deceleration stop control in an ACC function performed by the ACC controller <NUM>, and performs deceleration stop control in consideration of the road surface gradient detected by the gradient sensor <NUM> in addition to the detection information of the vehicle ahead detection means <NUM>. Hereinafter, improved deceleration stop control will be described with reference to <FIG>.

First, as shown in <FIG>, when the vehicle ahead <NUM> decelerates and stops while the vehicle is performing following cruise at a predetermined set inter-vehicle time Xg to a vehicle ahead <NUM> detected by the vehicle ahead detection means <NUM>, or the vehicle approaches the vehicle ahead <NUM> that decelerates and stops, the ACC controller <NUM> issues a deceleration command.

As shown in <FIG>, a brake hydraulic pressure rises due to a braking request and a braking force starts to act; on the other hand, at the same time as a torque request to the engine <NUM> becomes zero, a clutch of the automatic transmission <NUM> is disengaged, a drive torque transmitted to a drive shaft becomes zero, and the vehicle <NUM> starts decelerating at a predetermined deceleration according to the braking request (<FIG>, step <NUM>).

After that, as shown in <FIG>, in a case of a sloped road about which a road surface gradient equal to or greater than a predetermined threshold value (for example, <NUM>%) is detected by the gradient sensor <NUM> (YES in step <NUM> in <FIG>) immediately before the vehicle <NUM> stops while ensuring an inter-vehicle distance Xd from the vehicle ahead <NUM>, a required value of creep torque (torque that makes the vehicle <NUM> stand still against the road surface gradient) that compensates for the road surface gradient is calculated.

Next, a torque request is issued to the engine <NUM> on the basis of the required value (<FIG>, step <NUM>) when the vehicle <NUM> reaches a first vehicle speed Va (for example, <NUM>/h) immediately before stopping (point a in <FIG> and YES in step <NUM> in <FIG>), and at the same time, a fastening force is applied to the clutch of the automatic transmission <NUM>, and the torque begins to be transmitted to the drive shaft.

Although the torque transmission starts together with such a torque request and clutch fastening, the braking force of the brakes further decelerates the vehicle <NUM>, and when a second vehicle speed Vb (for example, <NUM>/h) is reached (point b in <FIG> and YES in step <NUM> in <FIG>), a brake pressure is temporarily reduced (point b in <FIG> and step <NUM> in <FIG>).

By the increase in the drive torque and the reduction in the brake pressure, the deceleration of the vehicle <NUM> is mitigated; when the vehicle <NUM> reaches a third speed Vc (for example, <NUM>/h) regarded as substantially a stopped state (point c in <FIG> and YES in step <NUM> in <FIG>), the brake pressure is increased (step <NUM> in <FIG>); and even after the vehicle <NUM> completely stops (YES in step <NUM>) and the increase in the brake pressure is completed, the brake pressure is maintained (step <NUM>). In the elapse of a predetermined time after stopping, the torque request becomes zero, and at the same time, the clutch of the automatic transmission <NUM> is disengaged (step <NUM> in <FIG>).

On the other hand, in a case of a flat road for which the road surface gradient detected by the gradient sensor <NUM> is less than the predetermined threshold value (for example, <NUM>%) (NO in step <NUM> in <FIG>) immediately before the vehicle <NUM> stops while ensuring the predetermined inter-vehicle distance Xd from the vehicle ahead <NUM>, the brake pressure is temporarily reduced (step <NUM> in <FIG>) when the predetermined vehicle speed Vd (for example, <NUM>/h) is reached (YES in step <NUM> in <FIG>); then when the vehicle <NUM> reaches the third speed Vc (for example, <NUM>/h) regarded as substantially a stopped state (YES in step <NUM> in <FIG>), the brake pressure is increased (step <NUM> in <FIG>), and the vehicle <NUM> is completely stopped (steps <NUM>-<NUM>).

In <FIG>, in each step <NUM>, <NUM> or <NUM> in the case in which it is determined there is a gradient in step <NUM> or in each step <NUM> or <NUM> in the case in which it is determined there is no gradient, when the deceleration command from the ACC controller <NUM> is stopped due to start of the vehicle ahead <NUM> or the like, the deceleration stop control ends at that time point, and the operation returns to ACC control. When the vehicle ahead <NUM> starts after deceleration stop, depression of the accelerator pedal or a predetermined button operation makes the operation return to the ACC control.

After the torque request according to the road surface gradient is issued in step <NUM> in <FIG> and the clutch of the automatic transmission <NUM> is fastened (for example, point b' in <FIG>), as shown in <FIG>, when the brake pedal <NUM> is depressed by the driver, and a brake pedal ON signal is detected (step <NUM>), the torque request immediately becomes zero in order to avoid engine stall, and at the same time, the clutch of the automatic transmission <NUM> is disengaged (step <NUM>).

In this case, it is determined that control by the ACC controller <NUM> is overridden by the driver's brake pedal operation, and the driver may be notified of ACC cancellation by an HMI apparatus and the shift to manual operation may be performed or the ACC control may be continued by the specified button operation or accelerator pedal operation, as described above.

As detailed above, in the driving control system according to the present invention, since the predetermined torque request is made in parallel with the control of increasing pressure after temporarily reducing pressure of the braking force when a road surface gradient equal to or greater than the predetermined threshold value is detected when the vehicle <NUM> reaches the first vehicle speed Va based on which the vehicle <NUM> is determined to be immediately before stopping, the vehicle <NUM> can stop in a state in which torque is applied in the uphill direction while suppressing pitching at the time of decelerating and stopping, and the same deceleration-and-stop sensation as on a flat road can be provided without sensation of a slight backward movement, even on an uphill road.

In particular, by starting the control of increasing pressure after temporarily reducing pressure of the braking force at a second time point when the vehicle reaches the second vehicle speed Vb that is slower than the first vehicle speed Va after the predetermined torque request at a first time point when the vehicle reaches the first vehicle speed Va based on which the vehicle is determined to be immediately before stopping, the vehicle can be stopped in a state in which the torque is reliably applied before the temporary reduction in the braking force.

Although the vehicle <NUM> equipped with the AMT type automatic transmission <NUM> performs fastening processing of the clutch at the same time as the torque request, a fastening force is applied to the clutch immediately before the braking force is increased and a time to generate a driving force (creep torque) is very short, and so the load on the clutch is small and there is no effect on the clutch due to heat generation.

A torque request when a road surface gradient equal to or greater than the predetermined threshold value is detected is preferably a torque request corresponding to a torque for making the vehicle stand still against the road surface gradient. However, it is not necessary to be a request value to strictly balance, a compensation torque request value is set according to the road surface gradient within a range in which the torque request is not excessive. For example, the compensation torque is set to be greater in proportion to the road surface gradient, and it is advantageous to prepare a compensation torque request value corresponding to the road surface gradient as a lookup table.

It is also possible to obtain acceleration of the vehicle <NUM> and slip ratios of the wheels from wheel speeds detected by the wheel speed sensors <NUM> and <NUM>, estimate a road surface friction coefficient (road surface µ), and switch the compensation torque request value (lookup table) according to the road surface state.

In the above embodiment, in the vehicle <NUM> equipped with the AMT type automatic transmission <NUM> in the torque transmission path from the engine <NUM> to the drive wheels (<NUM>), the clutch of the automatic transmission <NUM> is disengaged at the same time as the torque request becomes zero, and the clutch is fastened at the same time as the torque request. However, the present invention can also be implemented in a vehicle equipped with another type of automatic transmission, such as a CTV type, which is weaker than a force to balance the gradient.

Claim 1:
A driving control apparatus (<NUM>) for a vehicle (<NUM>) comprising: engine control means (<NUM>) for controlling an engine (<NUM>) according to a torque request, brake control means (<NUM>) for controlling a braking force of a break according to a braking request, gradient detection means (<NUM>) for detecting a road surface gradient, and vehicle ahead detection means (<NUM>) for detecting a vehicle ahead (<NUM>),
the driving control apparatus (<NUM>) having a function for decelerating and stopping with maintaining a predetermined inter-vehicle distance when the vehicle ahead (<NUM>) detected by the vehicle ahead detection means (<NUM>) decelerates to a stop, and being characterized in that it is configured to perform pitching suppression control of increasing pressure after temporarily reducing pressure of the braking force immediately before the vehicle (<NUM>) stops,
wherein the driving control apparatus (<NUM>) is further configured to make a predetermined torque request in parallel with the pitching suppression control in a case in which a road surface gradient equal to or greater than a predetermined threshold value is detected by the gradient detection means (<NUM>) when the vehicle (<NUM>) reaches a first vehicle speed (Va) based on which the vehicle (<NUM>) is determined to be immediately before stopping.