Patent Description:
In recent years, Adaptive Cruise Control (hereinafter referred to as "ACC") has attracted attention as one of techniques for assisting in driving a vehicle (see, for example, PTL <NUM>). ACC is a technique for acquiring the speed of the host vehicle, the speed of the preceding vehicle relative to that of the host vehicle, the distance between the host vehicle and the preceding vehicle, and the like to control the driving system and braking system of the host vehicle so that the vehicle speed and the following distance to the preceding vehicle are kept constant. For instance, when the speed of the host vehicle is high or the following distance is small, ACC actuates a brake to decelerate the host vehicle.

Such a technique can be used for a vehicle, such as a so-called tractor head, to which a trailer can be connected to reduce the burden on the driver operating such a vehicle and improve the comfort of running. <CIT> discloses an automatic braking system (<NUM>) for a vehicle (<NUM>) includes an electronic brake system (<NUM>) capable of applying wheel brakes (<NUM>) to decelerate the vehicle and a controller.

By the way, during brake control in ACC, an ACC control section sets a target acceleration/deceleration and outputs the target acceleration/deceleration to an engine brake system, an auxiliary brake system, and a main brake system. In general, the engine brake system performs braking when the target acceleration/deceleration reaches less than or equal to a first threshold, the auxiliary brake performs braking when the target acceleration/deceleration reaches less than or equal to a second threshold (the second threshold < the first threshold), and the main brake performs braking when the target acceleration/deceleration reaches less than or equal to a third threshold (the third threshold < the second threshold). In this manner, stepwise brake control is performed according to the target acceleration/deceleration. Incidentally, an auxiliary brake is an exhaust brake or retarder brake, and a main brake is a disk brake or drum brake.

Here, the main brake, which operates in a situation where the required deceleration is high (that is, in a situation where the target deceleration is high), has a significant impact on the feeling of the people in the vehicle, such as the driver. For this reason, delicate control is required which causes no discomfort to the people in the vehicle while attaining a target deceleration. However, delicate control, which requires a large number of computations and a large-scale circuit, is disadvantageous in that it complicates the entire configuration.

An object of the present disclosure is to provide a driving assistance apparatus that can perform delicate main brake control as needed while ensuring safety with a simple configuration.

According to the invention, the object is solved by a driving assistance apparatus having the features defined in claim <NUM>. A preferred embodiment is defined in the dependent claim.

The present disclosure provides a driving assistance apparatus that can perform delicate main brake control as needed while ensuring safety with a simple configuration, by acquisition of a degree of urgency through table lookup and determination of a gradient y related to the target acceleration/deceleration by use of the degree of urgency.

One embodiment of the present disclosure will now be described in detail below with reference to the accompanying drawings.

First, a configuration of a vehicle including a driving support apparatus according to an embodiment of the present disclosure will be described.

<FIG> is an external view showing an example of the use state of a vehicle including a driving assistance apparatus according to this embodiment. <FIG> is a block diagram showing an example of the configuration of the vehicle. Here, illustration and explanation will be given focusing on the part related to the driving assistance apparatus.

As shown in <FIG>, vehicle <NUM> is a tractor head (towing vehicle) that can be connected to trailer <NUM> and trail it.

The vehicle <NUM> is provided with, for example, a series-connected six-cylinder diesel engine. The vehicle <NUM> includes vehicle body <NUM> including a power system, such as an engine and a driving wheel, and a driver's seat; hose <NUM> and cock <NUM> for supplying air for brake actuation to trailer <NUM>; and coupler lock switch <NUM> disposed at the joint to trailer <NUM>. Coupler lock switch <NUM> is an apparatus for detecting whether or not trailer <NUM> is connected to vehicle <NUM>. The trailer <NUM> includes loading section <NUM> for loading a load and trailer wheels <NUM> for supporting loading section <NUM>.

As shown in <FIG>, vehicle <NUM> includes components such as driving system <NUM> that runs vehicle <NUM>, braking system <NUM> that decelerates vehicle <NUM>, and driving assistance apparatus <NUM> that assists the driver in driving vehicle <NUM>.

Driving system <NUM> includes engine <NUM>, clutch <NUM>, transmission <NUM>, propeller shaft <NUM>, differential apparatus (differential gear) <NUM>, drive shaft <NUM>, wheels <NUM>, engine ECU <NUM>, and power transmission ECU <NUM>.

Engine ECU <NUM> and power transmission ECU <NUM> are connected to driving assistance apparatus <NUM> via an in-vehicle network, such as a Controller Area Network (CAN), and can transmit and receive necessary data and control signals to/from each other. Engine ECU <NUM> controls the output of engine <NUM> according to a drive command from driving assistance apparatus <NUM>. Power transmission ECU <NUM> controls the engagement and disengagement of clutch <NUM> and the speed change of transmission <NUM> according to a drive command from driving assistance apparatus <NUM>.

The power of engine <NUM> is transmitted to transmission <NUM> via clutch <NUM>. The power transmitted to transmission <NUM> is further transmitted to wheels <NUM> via propeller shaft <NUM>, differential apparatus <NUM>, and drive shaft <NUM>. Thus, the power of engine <NUM> is transmitted to wheels <NUM>, thereby running vehicle <NUM>.

Braking system <NUM> includes service brake <NUM>, auxiliary brakes <NUM> and <NUM>, a parking brake (not shown in the drawing), and brake ECU <NUM>.

Service brake <NUM> is generally a brake called a main brake, a friction brake, a foot brake, a foundation brake, or the like. Service brake <NUM> is, for example, a drum brake which obtains a braking force by pressing the brake lining against the inner surface of a drum rotating with wheels <NUM>.

Auxiliary brake <NUM> is a retarder (hereinafter referred to as "retarder <NUM>") that obtains a braking force by directly applying a load to the rotation of propeller shaft <NUM>, and is, for example, an electromagnetic retarder. Auxiliary brake <NUM> is an exhaust brake (hereinafter referred to as "exhaust brake <NUM>") that increases the effect of engine braking by using the rotational resistance of the engine. Providing retarder <NUM> and exhaust brake <NUM> increases the braking force and reduces the frequency of use of service brake <NUM>, thereby suppressing wear and tear of the brake lining and the like.

Brake ECU <NUM> is connected to driving assistance apparatus <NUM> via an in-vehicle network, such as a CAN, and can transmit and receive necessary data and control signals to/from each other. Brake ECU <NUM> controls the braking force of service brake <NUM> (the brake fluid pressure in the wheel cylinders of wheels <NUM>) according to a braking command from driving assistance apparatus <NUM>.

Braking operation of service brake <NUM> is controlled by driving assistance apparatus <NUM> and brake ECU <NUM>. Braking operation of retarder <NUM> and exhaust brake <NUM> is controlled, i.e., turned on/off by driving assistance apparatus <NUM>. Since the braking forces of retarder <NUM> and exhaust brake <NUM> are substantially fixed, service brake <NUM>, which can finely adjust the braking force, is suitable for accurately generating a desired braking force.

Although not shown in the drawing, the braking system also includes a service brake provided to trailer wheels <NUM> of trailer <NUM>. In other words, brake ECU <NUM> supplies air via hose <NUM> described above and thus gives trailer wheels <NUM> of trailer <NUM> a braking force caused by the frictional force.

Driving assistance apparatus <NUM> acquires various information from following distance detection section <NUM>, ACC operating section <NUM>, accelerator operation detection section <NUM>, brake operation detection section <NUM>, and vehicle speed sensor <NUM>, and controls the operations of driving system <NUM> and braking system <NUM> according to the acquired information.

In addition, driving assistance apparatus <NUM> outputs various information on running from the information output section <NUM>.

In addition, driving assistance apparatus <NUM> achieves adaptive cruise control (ACC). In other words, driving assistance apparatus <NUM> performs constant speed running control and following running control (hereinafter collectively referred to as "automatic running control") in vehicle <NUM>.

During the constant speed running control, driving system <NUM> and braking system <NUM> are operated so that, if there is no preceding vehicle within a predetermined range, the running speed of vehicle <NUM> (hereinafter referred to as "vehicle speed") approaches a predetermined target value (a value or a value range).

During the following running control, driving system <NUM> and braking system <NUM> are operated so that, if there is a preceding vehicle in the predetermined rang, the following distance falls within the predetermined target range and the relative speed approaches zero. The details of driving assistance apparatus <NUM> will be described later.

Following distance detection section <NUM> measures (detects) the following distance between vehicle <NUM> and the preceding vehicle (hereinafter simply referred to as "following distance") and outputs the measurement results to driving assistance apparatus <NUM>. For following distance detection section <NUM>, a laser radar, a millimeter wave radar, an imaging apparatus, and the like can be used alone or in combination. The above-described driving assistance apparatus <NUM> controls the operation of driving system <NUM> and braking system <NUM> during constant-speed running and following running, according to the detection results from following distance detection section <NUM>.

ACC operating section <NUM> includes a main switch for enabling ACC and an ACC setting switch for setting/canceling ACC. ACC operating section <NUM> further includes a speed setting button for setting the target value of vehicle speed, and a following distance setting button for setting the following distance. Note that these switches and buttons may be user interfaces displayed on a display with a touch panel. ACC operating section <NUM> outputs an operation signal indicating the details of the operation performed in ACC operating section <NUM> to driving assistance apparatus <NUM>. The above-described driving assistance apparatus <NUM> sets information on the automatic running control, according to an operation signal from ACC operating section <NUM> (the driver's operation through ACC operating section <NUM>).

Accelerator operation detection section <NUM> detects whether or not the accelerator pedal for accelerating the vehicle is depressed and detects the amount of depression of the accelerator pedal and outputs the detection results to driving assistance apparatus <NUM>. Driving assistance apparatus <NUM> issues drive commands based on the amount of depression of the accelerator pedal to engine ECU <NUM> and power transmission ECU <NUM>.

Brake operation detection section <NUM> detects whether or not the brake pedal for operating service brake <NUM> is depressed and detects the amount of depression of the brake pedal. Further, brake operation detection section <NUM> detects whether or not the auxiliary brake lever for operating retarder <NUM> or exhaust brake <NUM> is operated. Brake operation detection section <NUM> outputs the detection results related to the brake pedal and the auxiliary brake lever to driving assistance apparatus <NUM>. The above-described driving assistance apparatus <NUM> issues a braking command to brake ECU <NUM> based on the amount of depression of the brake pedal. In addition, driving assistance apparatus <NUM> controls the on/off operation of retarder <NUM> or exhaust brake <NUM> according to the operation of the auxiliary brake lever.

Vehicle speed sensor <NUM> is attached to, for example, propeller shaft <NUM>, detects the vehicle speed, and outputs the detection results to driving assistance apparatus <NUM>.

Information output section <NUM> includes, for example, a speaker and a display section (display), such as a so-called instrument panel or a display (not shown in the drawing) of a navigation system. Through information output section <NUM>, driving assistance apparatus <NUM> displays information on various kinds of instruments, such as a speed meter, a tachometer, a fuel gauge, a water temperature gauge, and a distance meter, and the automatic running control, and outputs an alarm sound, for example.

Although not shown in the drawing, engine ECU <NUM>, power transmission ECU <NUM>, brake ECU <NUM>, and driving assistance apparatus <NUM> each include a central processing unit (CPU), a storage medium, such as a read only memory (ROM), a working memory, such as a random access memory (RAM), and a communication circuit. In this case, for example, the functions of the components of driving assistance apparatus <NUM>, which will be described later, are implemented when the CPU executes a control program. Note that all or part of engine ECU <NUM>, power transmission ECU <NUM>, brake ECU <NUM>, and driving assistance apparatus <NUM> may be combined in one piece.

In vehicle <NUM> with such a configuration, driving assistance apparatus <NUM> enables not only the normal running according to the driver's operation but also the running under the automatic running control according to the vehicle speed, the following distance, and the like.

The configuration of driving assistance apparatus <NUM> of this embodiment will now be described.

<FIG> is a diagram showing an example of the configuration of driving assistance apparatus <NUM>.

As shown in <FIG>, driving assistance apparatus <NUM> includes information acquisition section <NUM>, ACC control section <NUM>, and table <NUM>.

Receiving information from vehicle speed distance detection section <NUM>, information acquisition section <NUM> acquires the speed of the preceding vehicle relative to that of the host vehicle and the following distance between the host vehicle and the preceding vehicle. Information acquisition section <NUM> outputs the acquired relative speed and the following distance to ACC control section <NUM>.

ACC control section <NUM> reads a degree of urgency from table <NUM>, using the relative speed and the following distance as read addresses.

Table <NUM> prestores a degree of urgency corresponding to relative speed and following distance. To be specific, table <NUM> stores a three-dimensional map in which the relative speed and the following distance are associated with the degree of urgency. A degree of urgency is, for example, a value of <NUM> to <NUM>%, and a higher value indicates a greater degree of urgency. For instance, the higher the relative speed, the greater the degree of urgency, and the smaller the following distance, the greater the degree of urgency.

ACC control section <NUM> determines the gradient of the target acceleration/deceleration, using the degree of urgency read from table <NUM>. To be specific, ACC control section <NUM> determines gradient y of the target acceleration/deceleration, using the following equation <NUM>.

Here, a and b are predetermined fixed values, and x is a degree of urgency.

ACC control section <NUM> determines the target acceleration/deceleration using gradient y obtained from equation <NUM>, and outputs the target acceleration/deceleration to brake ECU <NUM> as a control signal for controlling the brake pressure of the main brake. Thus, the brake pressure of the main brake is controlled according to the target acceleration/deceleration having gradient y shown in <FIG>.

Gradient y reflects a degree of urgency x and the brake pressure is controlled so that the brake pressure gradually increases as the degree of urgency decreases, thereby preventing the brake pressure from unnecessarily and rapidly increasing, and thus avoiding unnecessary discomfort to the people in the vehicle. For instance, if the target deceleration indicated by the dot-and-dash line in <FIG> is set although the degree of urgency is low, the brake pressure unnecessarily and rapidly increases, which may be a cause of unnecessary discomfort to the people in the vehicle. In this embodiment, this can effectively be avoided.

The operation of driving assistance apparatus <NUM> of this embodiment will now be described.

In Step ST11, information acquisition section <NUM> determines the distance and relative speed to the preceding vehicle. In the following Step ST12, ACC control section <NUM> determines the target acceleration/deceleration according to the distance and relative speed to the preceding vehicle.

When the target acceleration/deceleration is less than or equal to threshold Th1 (Step ST13; YES), ACC control section <NUM> instructs engine ECU <NUM> to actuate the engine brake, so that the engine brake is actuated (Step ST14). When the target acceleration/deceleration is less than or equal to threshold Th2 (Th2 < Th1) (Step ST15; YES), ACC control section <NUM> instructs auxiliary brakes <NUM> and <NUM> to actuate, so that the auxiliary brakes are actuated (Step ST16). When the target acceleration/deceleration is less than or equal to threshold Th3 (Th3 < Th2) (Step ST17; YES), ACC control section <NUM> instructs brake ECU <NUM> to actuate the main brake.

On the other hand, ACC control section <NUM> reads a degree of urgency x from table <NUM> in Step ST21, and calculates gradient y of the target acceleration/deceleration using a degree of urgency x in y = a × x + b in Step ST22. In Step ST23, ACC control section <NUM> generates a control signal (target acceleration/deceleration) for the main brake having gradient y shown in <FIG>, and outputs it to brake ECU <NUM>.

In Step ST18, brake ECU <NUM> actuates the main brake by controlling the brake pressure according to the control signal (target acceleration/deceleration) for the main brake generated in Step ST23.

As described above, driving assistance apparatus <NUM> according to this embodiment includes: information acquisition section <NUM> that acquires a relative speed of a preceding vehicle, and a following distance to the preceding vehicle; table <NUM> that prestores a degree of urgency corresponding to the relative speed and the following distance; and ACC control section <NUM> that reads, from table <NUM>, a degree of urgency x corresponding to the relative speed and the inter-vehicle speed acquired by information acquisition section <NUM>, determines a target acceleration/deceleration having gradient y based on the read degree of urgency x, and outputs the determined target acceleration/deceleration as a control signal (a target acceleration/deceleration) for controlling brake pressure, thereby achieving braking assistance that avoids unnecessary sudden deceleration made through the main brake, while ensuring safety.

Further, since a degree of urgency x is acquired by looking up the table and gradient y of the target acceleration/deceleration is determined using a linear function using that a degree of urgency x, gradient y based on a degree of urgency x can be determined more rapidly with a simple configuration.

Consequently, driving assistance apparatus <NUM> can be provided that can perform delicate main brake control as needed while ensuring safety with a simple configuration.

The above embodiment merely shows specific examples for implementing the present invention and the technical scope of the present invention should not be construed as being limited because of them. In other words, the present invention can be implemented in various modes without departing from the scope of the present invention as defined by the claims.

For instance, although gradient y of the target acceleration/deceleration is determined using y = a × x + b in the above-described embodiment, this is not the only way of determining gradient y and, in brief, only has to be determined using a function in which a degree of urgency x is a variable. Note that, in the above-described embodiment in which gradient y is determined using a linear function, gradient y can be instantaneously determined with a simple processing circuit.

A part of the configuration of driving assistance apparatus <NUM> described above may be physically separated from the other parts of the configuration of driving assistance apparatus <NUM>. In this case, their configurations each need to be provided with a communication section to communicate with each other.

Claim 1:
A driving assistance apparatus (<NUM>) that assists in driving a vehicle (<NUM>), the driving assistance apparatus (<NUM>) comprising:
an information acquisition section (<NUM>) that acquires a speed of a preceding vehicle relative to the vehicle (<NUM>), and a following distance between the vehicle (<NUM>) and the preceding vehicle;
a table (<NUM>) that prestores a degree of urgency corresponding to the relative speed and the following distance; and
a control section (<NUM>) that outputs a control signal for controlling a main / service brake based on the information acquired by the information acquisition section (<NUM>) and the degree of urgency stored in the table (<NUM>),
wherein, the control section (<NUM>) is configured to:
(i) determine a target acceleration/deceleration based on the distance to the preceding vehicle and the speed of the preceding vehicle relative to the vehicle (<NUM>),
(ii) calculate a gradient of the target acceleration/deceleration, using the degree of urgency read from the table (<NUM>);
(iii) generate the control signal for the main / service brake having the gradient;
(iv) actuate an engine brake when the target acceleration / deceleration is equal to or less than a first threshold;
(v) actuate an auxiliary brake (<NUM>,<NUM>) when the target acceleration/deceleration is equal to or less than a second threshold less than the first threshold; and
(vi) actuate the main / service brake (<NUM>) by controlling a brake pressure according to the control signal when the target acceleration/deceleration is equal to or less than a third threshold less than the first threshold and the second threshold.