CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. JP2018-114371 filed on Jun. 15, 2018, incorporated by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a braking control apparatus for a combination vehicle that includes a tractor vehicle and a trailer vehicle coupled thereto.

2. Description of the Related Art

A combination vehicle comprises a tractor vehicle and a trailer vehicle. The trailer vehicle is coupled to the tractor vehicle pivotally about a hitch point relative to the tractor vehicle as viewed from above by a coupling device. Wheels of the trailer vehicle are non-steered driven wheels, and braking forces of those wheels are controlled by a braking control apparatus that controls braking forces of wheels of the tractor vehicle.

In a combination vehicle, it is known that behavior of a tractor vehicle is stabilized by applying a braking force or braking forces to a wheel or wheels of the tractor vehicle when the behavior of the tractor vehicle becomes unstable. For example, in Japanese Patent Application Laid-open Publication No. 2011-68248, a braking control apparatus is described which is configured to estimate a lateral force acting on a hitch point and, when the behavior of the trailer vehicle is unstable and the lateral force is high, apply braking forces to the wheels of a trailer vehicle such that a yaw moment is generated which causes a force in the direction opposite to the lateral force to act on the hitch point.

In a combination vehicle as well, a tractor vehicle may be in a spin state or a drift-out state in a situation where the vehicle turns while running on a traveling path having a road surface with a low coefficient of friction. Therefore, also in a combination vehicle, it is known to perform behavior control that stabilizes the turning behavior of the tractor vehicle when the turning behavior of the tractor vehicle deteriorates. For example, it has been known that when the tractor vehicle is in a spin state, spin suppression control is performed to apply a braking force to a turning outer front wheel, and when the tractor vehicle is in a drift-out state, drift-out suppression control is performed to apply braking forces to left and right rear wheels.

When a braking force is applied to a predetermined wheel of the tractor vehicle by behavior control in a situation where a combination vehicle turns, the tractor vehicle is decelerated, so that an acting force resulting from a difference in deceleration between the tractor vehicle and the trailer vehicle is exerted on the trailer vehicle from the tractor vehicle via a hitch point. As a result, the tractor vehicle receives a reaction force of the acting force from the trailer vehicle, and the reaction force pushes a rear end of the tractor vehicle diagonally forward and increases a yaw rate of the tractor vehicle, so that a hitch angle may become excessive. Notably, the braking control apparatus described in the Laid-open Publication described above cannot prevent a hitch angle of a combination vehicle from becoming excessive.

SUMMARY

The present disclosure provides a braking control apparatus for a combination vehicle which is improved to reduce, compared to the prior art, the possibility of a hitch angle of the combination vehicle becoming excessive in a situation where a braking force or braking forces is applied to a wheel or wheels of a tractor vehicle by behavior control and turning behavior of the tractor vehicle is stabilized.

According to the present disclosure, a braking control apparatus for a combination vehicle is provided which includes a tractor vehicle and a trailer vehicle coupled to the tractor vehicle by a coupling device pivotally relative to the tractor vehicle as viewed from above, the braking control apparatus comprising a braking device that applies braking forces to wheels of the tractor vehicle and wheels of the trailer vehicle, and a control unit that controls the braking device, and the control unit being configured to perform behavior control for stabilizing turning behavior of the tractor vehicle by applying a braking force or braking forces to a predetermined wheel or wheels of the tractor vehicle when the turning behavior of the tractor vehicle is not stable.

The control unit is configured to control the braking device such that when a braking force or braking forces is applied to a predetermined wheel or wheels by the behavior control, braking forces according to a force that the tractor vehicle acts on the trailer vehicle through the coupling device due to the application of the braking force or braking forces to the predetermined wheel or wheels are applied to the wheels of the trailer vehicle.

During turning of a combination vehicle, when a braking force or braking forces is applied to a predetermined wheel or wheels of a tractor vehicle by behavior control, the tractor vehicle decelerates relative to a trailer vehicle, so that the tractor vehicle exerts an acting force on the trailer vehicle through a coupling device. As a result, the trailer vehicle applies a reaction force of the acting force to the tractor vehicle through the coupling device, and the reaction force pushes a rear end of the tractor vehicle diagonally forward toward the turning outside, so that it generates a yaw moment in the direction to promote turning of the tractor vehicle, and the hitch angle of the combination vehicle is increased. Therefore, by reducing the force with which the trailer vehicle presses the rear end of the tractor vehicle diagonally forward, it is possible to reduce the possibility that the hitch angle of the combination vehicle increases and becomes excessive.

According to the above configuration, when a braking force or braking forces is applied to a predetermined wheel or wheels by behavior control, braking forces according to a force that the tractor vehicle acts on the tractor vehicle through the coupling device due to the application of the braking force or braking forces to the predetermined wheel or wheels are applied to the wheels of the trailer vehicle. Consequently, a difference in deceleration between the tractor vehicle and the trailer vehicle is smaller than when braking forces are not applied to the wheels of the trailer vehicle, and an acting force exerted by the tractor vehicle on the trailer vehicle through the coupling device and a reaction force thereof are reduced. Therefore, a yaw moment generated in the direction to promote turning of the tractor vehicle by the reaction force is also reduced, so that the possibility that a hitch angle of the combination vehicle increases and becomes excessive can be reduced.

In one aspect of the present disclosure, the control unit is configured to estimate a force acting in the front-rear direction of the trailer vehicle through the coupling device due to the application of a braking force or braking forces to the predetermined wheel or wheels and control the braking device such that a sum of braking forces applied to the wheels of the trailer vehicle is less than or equal to the force acting in the front-rear direction.

When a sum of braking forces applied to the wheels of the trailer vehicle exceeds a force acting in the front-rear direction, the trailer vehicle exerts a force to decelerate the tractor vehicle through the coupling device. Therefore, there is a possibility that the hitch angle of the combination vehicle may be reduced and become too small, and there is also a possibility that stabilization of the turning behavior of the tractor vehicle may not be properly performed due to excessive deceleration of the tractor vehicle.

According to the above aspect, a force acting in the front-rear direction of the trailer vehicle through the coupling device due to the application of a braking force or braking forces to the predetermined wheel or wheels is estimated, and the braking device is controlled such that a sum of braking forces applied to the wheels of the trailer vehicle is less than or equal to the force acting in the front-rear direction. Therefore, while avoiding that turning behavior of the tractor vehicle is not stabilized appropriately due to excessive deceleration of the tractor vehicle, it is possible to reduce the possibility that a hitch angle of the combination vehicle becomes excessive.

In particular, if the braking device is controlled such that the sum of the braking forces applied to the wheels of the trailer vehicle is the same as the force acting in the front-rear direction between the tractor vehicle and the trailer vehicle through the coupling device, the force acting in the front-rear direction is zero. Therefore, it is possible to prevent the hitch angle of the combination vehicle from increasing and becoming excessive without inhibiting the stabilization of the turning behavior of the tractor vehicle by the behavior control.

In another aspect of the present disclosure, the control unit is configured to calculate a hitch angle of the combination vehicle, calculate a yaw moment acting around a center of gravity of the tractor vehicle due to the application of a braking force or braking forces to the predetermined wheel or wheels, and calculate a force acting in the front-rear direction based on the hitch angle and the yaw moment.

According to the above aspect, a hitch angle of the combination vehicle is calculated, a yaw moment acting around the center of gravity of the tractor vehicle due to the application of the braking force or braking forces to the predetermined wheel or wheels is calculated, and a force acting in the front-rear direction of the trailer vehicle is calculated based on the hitch angle and the yaw moment.

Consequently, for example, a force acting in the front-rear direction of the trailer vehicle can be calculated more accurately than when a force acting in the front-rear direction of the trailer vehicle is calculated as a component of the braking force or braking forces applied to the predetermined wheel or wheels. Therefore, braking forces applied to the wheels of the trailer vehicle can be appropriately controlled, and the possibility of the hitch angle becoming excessive can be appropriately reduced.

In another aspect of the present disclosure, the control unit is configured to calculate a yaw moment based on a braking force or braking forces of the predetermined wheel or wheels and lateral forces of the wheels of the tractor vehicle when the braking force or braking forces is applied to the predetermined wheel or wheels.

According to the above aspect, a yaw moment is calculated based on a braking force or braking forces of the predetermined wheel or wheels and lateral forces of the wheels of the tractor vehicle when the braking force or braking forces is applied to the predetermined wheel or wheels. Therefore, as compared to where a yaw moment is calculated without considering lateral forces of the wheels of the tractor vehicle, a force acting in the front-rear direction of the trailer vehicle can be more accurately calculated and the possibility of the hitch angle becoming excessive can be more appropriately reduced.

In another aspect of the present disclosure, the trailer vehicle has left and right wheels, and the same braking forces are applied to the left and right wheels.

According to the above aspect, the same braking forces are applied to the left and right wheels of the trailer vehicle. Consequently, no yaw moment is given to the trailer vehicle by the braking forces applied to the left and right wheels of the trailer vehicle. Therefore, it is possible to prevent that a yaw moment to be given to the tractor vehicle by the behavior control is adversely affected by applying braking forces to the wheels of the trailer vehicle and the behavior control is not appropriately performed.

Other objects, other features and attendant advantages of the present disclosure will be readily understood from the description of the embodiments of the present disclosure described with reference to the following drawings.

