Patent Description:
Let us assume that a vehicle is traveling on a frozen road surface. In this assumption, a coefficient of friction between each wheel and the frozen road surface becomes extremely lower, causing the vehicle to be likely to skid. Even for a skilled driver, it may be difficult to drive a vehicle safely on such a low friction-coefficient road surface.

Autonomous vehicles, which can autonomously perform some or all driving maneuvers, have been developing recently. Whenever traveling, such an autonomous vehicle requires an improved robustness against any disturbances for the achievement of safe and security traveling. In order to satisfy the requirement, such an autonomous vehicle preferably evaluates the condition of a road surface on which the autonomous vehicle is traveling.

From this viewpoint, <CIT> discloses a road-surface condition evaluation apparatus for detecting, based on the characteristics of a resonant oscillation of, for example, a drive shaft of a vehicle, a µ-gradient of a road surface; the µ-gradient of a road surface shows the condition of the road surface.

Furthermore, <CIT> refers to an apparatus and method for detecting friction characteristics, wherein a wheel resonant system includes a vehicle body, a road surface and at least a wheel. A vibrating system generates an exciting force that contains one of the resonant frequency of said vibrating system and the frequency component in the vicinity of said resonant frequency and exciting said vibrating system by said exciting force. A vibration response detecting means detects the quantity of state of the vibration response of said vibrating system excited by said exciting force generating means, and resonant characteristics calculating means is provided for calculating the resonant characteristics of said vibrating system on the basis of the quantity of state of the exciting force generated by said exciting force generating means and the quantity of state of the vibration response detected by said vibration response detecting means.

The road-surface condition evaluation apparatus disclosed in <CIT> is configured to, when a resonant oscillation of, for example, the drive shaft occurs naturally while the vehicle is traveling on the road surface, analyze the characteristics of the resonant oscillation to thereby evaluate the µ-gradient of the road surface; the µ-gradient of the road surface shows the condition of the road surface.

Unfortunately, the road-surface condition evaluation apparatus disclosed in <CIT> merely analyzes the characteristics of the resonant oscillation that occurs naturally while the vehicle is traveling on the road surface. For this reason, it may be difficult to evaluate the condition of the road surface with high accuracy depending on the traveling state of the vehicle. Additionally, the road-surface condition evaluation apparatus disclosed in <CIT> essentially requires the occurrence of a resonance oscillation whose resonant frequency is likely to be perceptible by one or more occupants. This may result in the vehicle being uncomfortable for the one or more occupants.

It is an object of the present invention to provide evaluation apparatuses, each of which is capable of evaluating the condition of a road surface with higher accuracy.

This object is achieved by an evaluation apparatus according to claim <NUM>. Further features and advantageous modifications are shown in the dependent claims.

An evaluation apparatus according to the present invention is operative to evaluate a condition of a road surface on which a vehicle having at least one wheel is traveling. The evaluation apparatus includes an oscillation unit configured to output an oscillation command that causes the at least one wheel of the vehicle to oscillate, and an oscillation obtainer configured to obtain an oscillation of rotation of the at least one wheel in response to the output of the oscillation command. The evaluation apparatus includes an evaluation unit configured to perform an evaluation of the condition of the road surface in accordance with the oscillation command and the oscillation obtained by the oscillation obtainer, wherein the evaluation of the condition of the road surface performed by the evaluation unit includes whether the condition of the road surface is a low-friction condition or a high-friction condition. The evaluation unit is configured to calculate a reference waveform that represents a waveform of a predicted oscillation that is predicted to occur in rotation of the at least one wheel based on the oscillation command, calculate a first attenuation rate of a waveform of the oscillation obtained by the oscillation obtainer, and a second attenuation rate of the reference waveform, and compare the first attenuation rate with the second attenuation rate to accordingly determine whether the condition of the road surface is the low-friction condition or the high-friction condition.

That is, the evaluation unit of the evaluation apparatus configured set forth above performs an evaluation of the condition of the road surface in accordance with the oscillation command and the oscillation obtained by the oscillation obtainer.

The inventors of the present invention have demonstrated that an oscillation of a rotational speed of the at least one wheel based on the oscillation command for each target road surface is more likely to decay as a friction coefficient of the corresponding target road surface becomes smaller.

For this reason, if an attenuation rate of the oscillation actually obtained by the oscillation obtainer is smaller than that of the predicted oscillation predicted based on the oscillation command, it is possible to evaluate that the condition of the road surface is in a low-friction condition.

That is, the above evaluation method outputs the oscillation command to thereby cause the at least one wheel of the vehicle to oscillate. The above evaluation method uses at least one specific frequency of the oscillation of the at least one wheel, which is different from frequencies of natural oscillations that naturally occur.

This configuration therefore makes it possible to obtain an evaluation result about the road surface with higher accuracy as compared with a method of analyzing a resonant oscillation that occurs naturally as described in <CIT>.

In particular, the oscillation unit of the evaluation apparatus is configured to output the oscillation command that causes at least one frequency of the oscillation of rotation of the at least one wheel to be different from at least one resonant frequency of the vehicle. This configuration therefore makes it possible to evaluate the condition of the road surface while preventing one or more occupants of the vehicle from having feeling discomfort.

The present invention therefore offers the evaluation apparatus capable of evaluating the condition of the road surface with higher accuracy.

The following describes exemplary embodiments of the present invention with reference to the accompanying drawings. For the sake of easy understanding, in the accompanying drawings, description of like parts, to which like reference characters are assigned, are omitted or simplified to avoid redundant description.

The following describes an evaluation apparatus <NUM> according to the first embodiment.

The evaluation apparatus <NUM> is designed to be installable in a vehicle <NUM>, and is configured to evaluate the condition of a road surface on which the vehicle <NUM> is traveling. Before description of the evaluation apparatus <NUM>, the following describes the configuration of the vehicle <NUM> with reference to <FIG>.

The vehicle <NUM> according to the first embodiment is configured as an autonomous vehicle that autonomously performs all driving maneuvers required for the vehicle <NUM> to travel. The vehicle <NUM> can be configured, as another example, as a vehicle in which some or all of driving maneuvers are performed by one or more occupants. Referring to <FIG>, the vehicle <NUM> includes a body <NUM>, first pair of wheels <NUM> and a second pair of wheels <NUM>, rotary electric machines <NUM> and <NUM>, and a battery <NUM>.

The body <NUM> of the vehicle <NUM> constitutes a main part of the vehicle <NUM>.

The first pair of wheels <NUM> is a pair of front wheels mounted to a front portion of the body <NUM>, and the second pair of wheels <NUM> is a pair of rear wheels mounted to a rear portion of the body <NUM>. That is, the vehicle <NUM> has a total of four wheels <NUM> and <NUM> mounted thereto. All the wheels <NUM> and <NUM> according to the first embodiment serve as driving wheels.

The rotary electric machine <NUM> serves as an apparatus for generating, based on electrical power supplied from the battery <NUM>, drive power for rotating the wheels <NUM>, i.e., for traveling the vehicle <NUM>. The rotary electric machine <NUM> is configured as a motor-generator. The drive power generated by the rotary electric machine <NUM> is transferred through a powertrain <NUM> of the body <NUM> to each of the wheels <NUM>, and the drive power transferred to each wheel <NUM> causes the corresponding wheel <NUM> to rotate. An inverter, which is unillustrated in <FIG>, performs electrical-power transfer between the battery <NUM> and the rotary electric machine <NUM>. The rotary electric machine <NUM> according to the first embodiment serves as a first rotary electric machine.

The rotary electric machine <NUM> serves as an apparatus for generating, based on electrical power supplied from the battery <NUM>, drive power for rotating the wheels <NUM>. Like the rotary electric machine <NUM>, the rotary electric machine <NUM> is configured as a motor-generator. The drive power generated by the rotary electric machine <NUM> is transferred through a powertrain <NUM> of the body <NUM> to each of the wheels <NUM>, and the drive power transferred to each wheel <NUM> causes the corresponding wheel <NUM> to rotate. An inverter, which is unillustrated in <FIG>, performs electrical-power transfer between the battery <NUM> and the rotary electric machine <NUM>. The rotary electric machine <NUM> according to the first embodiment serves as a second rotary electric machine.

As described above, the vehicle <NUM> includes the rotary electric machine <NUM> serving as a first rotary electric machine, and the rotary electric machine <NUM> serving as a second rotary electric machine. The rotary electric machine <NUM> is configured to generate drive power for rotating at least one wheel, i.e., the wheels <NUM>, allocated for the rotary electric machine <NUM> in the four wheels of the vehicle <NUM>, and the rotary electric machine <NUM> is configured to generate drive power for rotating at least another wheel, i.e., the wheels <NUM>, allocated for the rotary electric machine <NUM> in the four wheels of the vehicle <NUM>.

The battery <NUM> consists of a storage battery, such as a lithium-ion battery, for supplying, to each of the rotary electrical machines <NUM> and <NUM>, the electrical power for driving the corresponding one of the rotary electrical machines <NUM> and <NUM>.

The vehicle <NUM>, which is configured as an autonomous vehicle, includes a steering apparatus for autonomously performing steering of the vehicle <NUM>, and a braking apparatus for autonomously braking the vehicle <NUM>; these steering and braking apparatuses are unillustrated in <FIG>.

The vehicle <NUM> includes, in addition to the evaluation apparatus <NUM>, a higher-level ECU <NUM>. Each of the evaluation apparatus <NUM> and the higher-level ECU <NUM> is configured as a computer system comprised of a CPU, a ROM, a RAM, and one or more other peripheral devices. The higher-level ECU <NUM> performs various tasks required for autonomous driving of the vehicle <NUM>. The various tasks required for autonomous driving of the vehicle <NUM> can include a task of selecting, in a plurality of available routes, a route along which the vehicle <NUM> is going to travel. The higher-level ECU <NUM> and the evaluation apparatus <NUM> are configured to communicate with one another to thereby cooperatively perform the various tasks required for autonomous driving of the vehicle <NUM>.

That is, the higher-level ECU <NUM> according to the first embodiment is configured not to perform all the tasks required for autonomous driving of the vehicle <NUM>, and therefore the evaluation apparatus <NUM> according to the first embodiment is configured to perform one or more tasks in all the tasks required for autonomous driving of the vehicle <NUM>; the one or more tasks are allocated for the evaluation apparatus <NUM>. For example, the one or more tasks allocated for the evaluation apparatus <NUM> can include a task of transmitting a control signal to each of the unillustrated steering apparatus and the unillustrated braking apparatus. The one or more tasks allocated for the evaluation apparatus <NUM> can also include a task of adjusting the drive power generated by each of the rotary electric machines <NUM> and <NUM>.

Specifically, the evaluation apparatus <NUM> according to the first embodiment serves as both an apparatus for evaluating the condition of a road surface on which the vehicle <NUM> is traveling and an apparatus for performing travel control of the vehicle <NUM>.

The above task-sharing configuration between the higher-level ECU <NUM> and the evaluation apparatus <NUM> according to the first embodiment is an example of various configurations between the higher-level ECU <NUM> and the evaluation apparatus <NUM>. For example, the evaluation apparatus <NUM> can be configured to perform only the task for evaluating the condition of a road surface on which the vehicle <NUM> is traveling, and the higher-level ECU <NUM> can be configured to perform the travel-control tasks of the vehicle <NUM>.

The evaluation apparatus <NUM> and the higher-level ECU <NUM> can be configured as a single control apparatus. How the tasks required for autonomous driving of the vehicle <NUM> are allocated for the evaluation apparatus <NUM> and the higher-level ECU <NUM> can be freely determined. Similarly, each of the evaluation apparatus <NUM> and the higher-level ECU <NUM> can include a freely selected one of various configurations.

The following describes additional components of the vehicle <NUM>.

Referring to <FIG>, the vehicle <NUM> includes MG resolvers <NUM>, wheel speed sensors <NUM>, an acceleration sensor <NUM>, and current sensors <NUM>.

Each of the MG resolvers <NUM> is configured to measure the number of revolutions per unit time of an unillustrated output shaft of the corresponding one of the rotary electric machines <NUM> and <NUM>. Specifically, the MG resolvers <NUM> are provided for the respective output shafts of the rotary electric machines <NUM> and <NUM>. That is, two MG resolvers <NUM> are installed in the vehicle <NUM>, but <FIG> schematically illustrates a single block representing the MG resolvers <NUM>.

The number of revolutions per unit time of the output shaft of the rotary electric machine <NUM> will be simply referred to as a rotational speed of the rotary electric machine <NUM>. Similarly, the number of revolutions per unit time of the output shaft of the rotary electric machine <NUM> will be simply referred to as a rotational speed of the rotary electric machine <NUM>. A signal indicative of the rotational speed of each of the rotary electric machines <NUM> and <NUM> measured by the corresponding one of the MG resolvers <NUM> is outputted therefrom to be inputted to the evaluation apparatus <NUM>.

Each of the wheel speed sensors <NUM> is configured to measure the number of revolutions per unit time of the corresponding one of the wheels <NUM> and <NUM>. Specifically, the wheel speed sensors <NUM> are provided for the respective four wheels <NUM> and <NUM>. That is, four wheel speed sensors <NUM> are installed in the vehicle <NUM>, but <FIG> schematically illustrates a single block representing the wheel speed sensors <NUM>.

The number of revolutions per unit time of each wheel <NUM> will be simply referred to as a rotational speed of the corresponding wheel <NUM>. Similarly, the number of revolutions per unit time of each wheel <NUM> will be simply referred to as a rotational speed of the corresponding wheel <NUM>. A signal indicative of the rotational speed of each of the wheels <NUM> and <NUM> measured by the corresponding one of the wheel speed sensors <NUM> is outputted therefrom to be inputted to the evaluation apparatus <NUM>.

The acceleration sensor <NUM>, which is mounted to the body <NUM>, is configured to measure values of acceleration of the vehicle <NUM>. Specifically, the acceleration sensor <NUM> is configured as a six-axis acceleration sensor capable of measuring.

Signals representing the respective values of acceleration of the vehicle <NUM> measured by the six-axis acceleration sensor <NUM> are outputted therefrom to be inputted to the evaluation apparatus <NUM>.

Each of the current sensors <NUM> is configured to measure a drive current supplied to the corresponding one of the rotary electric machines <NUM> and <NUM>. Specifically, the current sensors <NUM> are provided for the respective rotary electric machines <NUM> and <NUM>. That is, two current sensors <NUM> are installed in the vehicle <NUM>, but <FIG> schematically illustrates a single block representing the current sensors <NUM>.

A signal indicative of the drive current supplied to the rotary electric machine <NUM> measured by one of the current sensors <NUM> is outputted therefrom to be inputted to the evaluation apparatus <NUM>. Similarly, a signal indicative of the drive current supplied to the rotary electric machine <NUM> measured by the other of the current sensors <NUM> is outputted therefrom to be inputted to the evaluation apparatus <NUM>.

Next, the following describes the configuration of the evaluation apparatus <NUM> with reference to <FIG>.

Referring to <FIG>, the evaluation apparatus <NUM> includes, as block modules each representing a corresponding function, an oscillation unit <NUM>, an oscillation obtainer <NUM>, an evaluation unit <NUM>, a travel controller <NUM>, and a transmitter <NUM>.

The oscillation unit <NUM> is configured to output an oscillation command that causes rotation of each wheel <NUM> to oscillate. An oscillation of rotation of each wheel <NUM> means oscillation of the number of revolutions per unit time, i.e., the rotational speed, of a rotational shaft of the corresponding wheel <NUM>. An oscillation of the number of revolutions per unit time, i.e., the rotational speed, of the rotational shaft of each wheel <NUM> will also be referred to as a rotational-speed oscillation of the corresponding wheel <NUM>.

The oscillation unit <NUM> outputs, as the oscillation command for each wheel <NUM>, command values for the drive current to be supplied to the rotary electric machine <NUM>, so that the outputted command values for the drive current supplied to the rotary electric machine <NUM> are inputted to the inverter connected to the rotary electric machine <NUM>. That is, the oscillation command for each wheel <NUM> represents a signal, which is outputted from the oscillation unit <NUM>, for controlling the operation of the rotary electric machine <NUM>. The oscillation command for each wheel <NUM> can include any command to be outputted to any component that can cause the rotational speed of the corresponding wheel <NUM> to oscillate.

Adjustment of the drive current to be supplied to the rotary electric machine <NUM> in accordance with the oscillation command from the oscillation unit <NUM> causes the rotational speed of each wheel <NUM> to oscillate. As described later, the task of outputting the oscillation command is carried out by the oscillation unit <NUM> when the evaluation apparatus <NUM> performs an evaluation of the condition of a road surface.

The oscillation unit <NUM> is also configured to output a command that is similar to the oscillation command. That is, the command outputted from the oscillation unit <NUM> causes the rotational speed of each wheel <NUM> to oscillate.

The oscillation unit <NUM> outputs, as the command for each wheel <NUM>, command values for the drive current to be supplied to the rotary electric machine <NUM>, so that the outputted command values for the drive current supplied to the rotary electric machine <NUM> are inputted to the inverter connected to the rotary electric machine <NUM>. Adjustment of the drive current to be supplied to the rotary electric machine <NUM> in accordance with the command from the oscillation unit <NUM> causes the rotational speed of each wheel <NUM> to oscillate.

As described later, the command for each wheel <NUM> represents a signal, which is outputted from the oscillation unit <NUM> at the same timing as the oscillation command, for controlling, i.e., suppressing, a vibration of the body <NUM> due to the oscillation command. The command outputted from the oscillation unit <NUM> to the inverter connected to the rotary electric machine <NUM> will also be referred to as a vibration control command.

The oscillation obtainer <NUM> is configured to obtain information about an oscillation of rotation of each wheel <NUM>, i.e., an oscillation of the rotational speed of each wheel <NUM>, in response to the output of the oscillation command from the oscillation unit <NUM>.

For example, the oscillation obtainer <NUM> can directly obtain, as the information about an oscillation of the rotational speed of each wheel <NUM>, the waveform of the oscillation of the rotational speed of the corresponding wheel <NUM> itself. Alternatively, the oscillation obtainer <NUM> can obtain the information about an oscillation of the rotational speed of each wheel <NUM> indirectly based on the waveform of another physical quantity that correlates with the waveform of the oscillation of the rotational speed of the corresponding wheel <NUM>. The waveform of another physical quantity that correlates with the waveform of the oscillation of the rotational speed of each wheel <NUM> can include the waveform of an oscillation of the drive shaft included in the vehicle <NUM>.

The oscillation obtainer <NUM> according to the first embodiment is configured to obtain, as the waveform of an actual oscillation of the rotational speed of each wheel <NUM>, the waveform indicative of how the rotational speed of the rotary electric machine <NUM> measured by the corresponding MG resolver <NUM> changes over time.

As an example, the oscillation obtainer <NUM> can be configured to convert the waveform, which represents how the rotational speed of the rotary electric machine <NUM> measured by the corresponding MG resolver <NUM> changes over time, into another waveform that matches the waveform of an actual oscillation of the rotational speed of each wheel <NUM>, and thereafter obtain the converted waveform indicative of how the rotational speed of the rotary electric machine <NUM> measured by the corresponding MG resolver <NUM> as the waveform of an oscillation of the rotational speed of each wheel <NUM>. In this example, the oscillation obtainer <NUM> can include a transfer function that represents a correlative relationship between (i) values, i.e., input values, of the rotational speed of the rotary electric machine <NUM> measured by the corresponding MG resolver <NUM> and (ii) respective corresponding values, i.e., output values, of the rotational speed of each wheel <NUM>. That is, the oscillation obtainer <NUM> obtains, based on how the rotational speed of the rotary electric machine <NUM> changes over time, an oscillation of the rotational speed of each wheel <NUM>.

The oscillation obtainer <NUM> can obtain, directly from change of the rotational speed of each wheel <NUM> measured by the corresponding wheel speed sensor <NUM>, an oscillation of the rotational speed of the corresponding wheel <NUM>. Specifically, the oscillation obtainer <NUM> can be configured to obtain information about an oscillation of each wheel <NUM> indirectly from values measured by the corresponding MG resolver <NUM> or directly from values measured by the corresponding wheel speed sensor <NUM>.

The evaluation unit <NUM> is configured to perform an evaluation of the condition of a road surface in accordance with the oscillation command and the information about the oscillation obtained by the oscillation obtainer <NUM>. How the evaluation unit <NUM> evaluates the condition of the road surface will be described later.

The travel controller <NUM> is configured to control how the vehicle <NUM> travels on the road surface in accordance with the evaluation result, i.e., the evaluation, about the condition of the road surface obtained by the evaluation unit <NUM>. For example, the travel controller <NUM> causes the unillustrated braking apparatus to change a usual braking method to a specific braking method that prevents each wheel <NUM>, <NUM> from locking in response to evaluating that the condition of the road surface is a low-friction condition, such as a frozen condition. In this example, the travel controller <NUM> can perform a task of reducing the traveling speed of the vehicle <NUM> down to a predetermined safety speed. The travel controller <NUM> can be configured to select one of various available travel-control methods based on the evaluation result about the condition of the road surface obtained by the evaluation unit <NUM>, and perform the selected travel-control method to accordingly control how the vehicle <NUM> travels on the road surface.

A task of controlling how the vehicle <NUM> travels on the road surface, which is carried out by the travel controller <NUM>, can perform a first task of directly adjusting the traveling speed of the vehicle <NUM> or a second task of outputting information required to adjust the traveling speed of the vehicle <NUM>. As an example of the second task, the travel controller <NUM> transmits, to, for example, the higher-level ECU <NUM>, a parameter indicative of the condition of the road surface, such as a friction coefficient or a µ-gradient of the road surface.

The evaluation apparatus <NUM> can be configured to perform only the task of evaluating the condition of the road surface, and the higher-level ECU <NUM> can be configured to perform all the remaining tasks. For example, the higher-level ECU <NUM> can include at least one of the functional modules <NUM> to <NUM> of the evaluating unit <NUM> illustrated in <FIG>. In this example, the higher-level ECU <NUM> can serve as at least a part of the evaluation apparatus <NUM>. As described above, the evaluation apparatus <NUM> and the higher-level ECU <NUM> can freely share the tasks, i.e., functions, that should be implemented by at least one of the evaluation apparatus <NUM> and the higher-level ECU <NUM>. Each of the evaluation apparatus <NUM> and the higher-level ECU <NUM> can include a freely selected one of various configurations.

The transmitter <NUM> is configured to transmit, to the higher-level ECU <NUM>, the evaluation result, i.e., the evaluation, about the condition of the road surface obtained by the evaluation unit <NUM>. The transmitter <NUM> is also configured to transmit, to one or more external components, the evaluation result about the condition of the road surface obtained by the evaluation unit <NUM>. The one or more external components can include at least one external server stored in one of cloud-storages.

In this example, the at least one external server can collect, from each of the many vehicles <NUM> traveling on respective road surfaces, the evaluation result about the condition of the corresponding one of the road surfaces. Then, the at least one server can transmit, to the higher-level ECU <NUM> of each of the many vehicles <NUM>, the evaluation results about all the respective road surfaces. This enables the higher-level ECU <NUM> of each vehicle <NUM> to ascertain the conditions of the other road surfaces on which the corresponding vehicle <NUM> is not traveling. This therefore makes it possible to determine, in a plurality of available routes, a route along which each vehicle <NUM> will travel; the route does not include road surfaces that have a low-friction condition.

Next, the following describes an evaluation routine cyclically carried out by the evaluation apparatus <NUM>. One cycle of the evaluation routine will also be referred to as a control cycle.

When starting the evaluation routine, the evaluation apparatus <NUM> determines whether an evaluating request is transmitted thereto from the higher-level ECU <NUM> in step S0 <NUM>. The evaluating request transmitted from the higher-level ECU <NUM> to the evaluation apparatus <NUM> is a signal that causes the evaluation apparatus <NUM> to perform evaluating of the road surface.

Upon determination that no evaluating request is transmitted thereto from the higher-level ECU <NUM> (NO in step S01), the evaluation apparatus <NUM> terminates the evaluation routine. Otherwise, upon determination that the evaluating request is transmitted to the evaluation apparatus <NUM> from the higher-level ECU <NUM> (YES in step S01), the evaluation routine proceeds to step S02.

In step S02, the oscillation unit <NUM> starts to output the oscillation command.

<FIG> illustrates an example of how the drive current to be supplied to the rotary electric machine <NUM> changes over time based on the outputted oscillation command. As described above, the oscillation command is outputted from the oscillation unit <NUM> as command values for the drive current to be supplied to the rotary electric machine <NUM>. For this reason, the change of the drive current illustrated in <FIG> can be regarded as the waveform of the oscillation command.

The example illustrated in <FIG> shows that the oscillation command is offset positively from zero at time t1. This causes the rotary electric machine <NUM> to generate, from the time t1, substantially constant torque that causes the vehicle <NUM> to travel forward.

From time t2 after the time t1, the oscillation command outputted from the oscillation unit <NUM> causes the drive current to sinusoidally oscillate. The sinusoidal oscillation of the drive current has a predetermined amplitude that is set to maintain the torque generated from the rotary electric machine <NUM> to be higher than or equal to zero. In other words, the offset amount of the drive current, i.e., the oscillation command, is determined such that sinusoidally oscillating drive current after the time t2 is prevented from decreasing below zero.

The example illustrated in <FIG> shows that the oscillation of the drive current has continued from the time t2 to time t3. After the time t3 at which the oscillation of the drive current is stopped, the offset amount of the drive current, i.e., the oscillation command, is set to zero at time t4.

Let us assume that the oscillation command outputted from the oscillation unit <NUM> causes the torque generated by the rotary electric machine <NUM> to alternately oscillate above and below zero. In this assumption, there would be so-called "backlash" in the drive-power transfer path, i.e., torque transfer path, from the rotary electric machine <NUM> to each wheel <NUM>, resulting in an unpredictable disturbance being applied to the oscillation obtained by the oscillation obtainer <NUM>. This would reduce the accuracy of evaluating, by the evaluation unit <NUM>, the condition of the road surface.

From this viewpoint, the oscillation unit <NUM> according to the first embodiment is configured to output the oscillation command that has offset positively from zero; the positively offset oscillation command causes torque generated by the rotary electric machine <NUM> to change to be always positive. In other words, the oscillation unit <NUM> is configured to output the oscillation command that prevents the occurrence of "backlash" in the drive-power transfer path, i.e., torque transfer path, from the rotary electric machine <NUM> to each wheel <NUM>.

This configuration of the oscillation unit <NUM> enables the evaluation unit <NUM> to check the condition of the road surface with no influence from backlash.

Oscillation of the rotational speed of each wheel <NUM> within a period for which the oscillation command has been outputted from the oscillation unit <NUM> causes the body <NUM> to vibrate. For suppressing the magnitude of the vibration to a very low level to accordingly reduce any uncomfortable feeling felt by one or more occupants of the vehicle <NUM>, the oscillation unit <NUM> according to the first embodiment is configured to output the oscillation command having a predetermined peak-to-peak amplitude; the predetermined peak-to-peak amplitude of the oscillation command causes a peak-to-peak amplitude of the vibration of the acceleration applied to the body <NUM> to <NUM>.

The oscillation of the oscillation command outputted from the oscillation unit <NUM> within the range from the time t2 to the time t3 (see <FIG>) has a predetermined frequency that is set to be different from at least one resonant frequency of the vehicle <NUM>. The at least one resonant frequency of the vehicle <NUM> show the frequency of at least one resonance that can occur at a corresponding at least one portion of the vehicle <NUM>. Usually, there are resonance frequencies of the vehicle <NUM>, which show the frequencies of resonances that can occur at corresponding respective portions of the vehicle <NUM>. These resonant frequencies of the vehicle <NUM> can include a first resonant frequency of the drive shaft of the vehicle <NUM> in a torsional direction of the drive shaft, and a second resonant frequency of the body <NUM> in the pitch direction. The frequency of the oscillation based on the oscillation command is set to be different from any of the resonant frequencies of the vehicle <NUM>.

Specifically, as described above, the oscillation unit <NUM> of the first embodiment is configured to output the oscillation command that causes the frequency of the oscillation of rotation of each wheel <NUM> to be different from the resonant frequencies of the vehicle <NUM>. This configuration prevents the occurrence of resonances in the vehicle <NUM> due to the oscillation command to accordingly prevent one or more occupants of the vehicle <NUM> from having feeling discomfort.

The waveform of the signal outputted from the oscillation unit <NUM> as the oscillation command can be a sinusoidal waveform as described above, but can be set to a waveform different from the sinusoidal waveform. For example, the waveform of the signal outputted from the oscillation unit <NUM> as the oscillation command can be set to a waveform whose frequency changes over time within a predetermined range, such as a sinusoidal chirp waveform. In this example, the frequency of the oscillation command is preferably set to be different from the resonant frequencies of the vehicle <NUM>. That is, the fluctuation range of the frequency of the oscillation command is preferably set not to overlap with any of the resonant frequencies of the vehicle <NUM>.

Following the operation in step S02, the oscillation unit <NUM> starts to output the vibration control command in step S03.

<FIG> illustrates an example of how the drive current to be supplied to the rotary electric machine <NUM> changes over time based on the outputted vibration control command. As described above, the vibration control command is outputted from the oscillation unit <NUM> as command values for the drive current to be supplied to the rotary electric machine <NUM>. For this reason, the change of the drive current illustrated in <FIG> can be regarded as the waveform of the vibration control command.

The example illustrated in <FIG> shows that the vibration control command is offset negatively from zero at the time t1. This causes the rotary electric machine <NUM> to generate, from the time t1, substantially constant torque that causes the vehicle <NUM> to travel rearward.

From the time t2 after the time t1, the vibration control command outputted from the oscillation unit <NUM> causes the drive current to oscillate. The waveform of the vibration control command is set to cause the torque, to which reference character F' is assigned, generated from the rotary electric machine <NUM> to have a value represented by the following expression (<NUM>): <MAT>.

In the expression (<NUM>), F represents the torque generated from the rotary electric machine <NUM>, G<NUM>(s) represents a first transfer function between the torque F as an input to the first transfer function and torque transferred to each wheel <NUM> as an output from the first transfer function.

In the expression (<NUM>), G<NUM>(s) represents a second transfer function between the torque F' generated from the rotary electric machine <NUM> as an input to the second transfer function and torque transferred to each wheel <NUM> as an output from the second transfer function.

The expression (<NUM>) shows that the vibration control command outputted from the oscillation unit <NUM> is adjusted to cause.

For example, the oscillation unit <NUM> can be configured to obtain the torque F generated from the rotary electric machine <NUM>, obtain the torque F' generated from the rotary electric machine <NUM>, and adjust, based on the obtained torque F and torque F', the drive currents for the respective rotary electric machines <NUM> and <NUM> such that the obtained torque F and torque F' satisfy the expression (<NUM>).

Like the oscillation command, the offset amount of the drive current, i.e., the vibration control command, is determined such that oscillating drive current after the time t2 is prevented from increasing above zero. After the time t3 at which the oscillation of the drive current is stopped, the offset amount of the drive current, i.e., the vibration control command, is set to zero at the time t4. The oscillation unit <NUM> is configured to output the vibration control command that prevents the occurrence of "backlash" in the drive-power transfer path, i.e., torque transfer path, from the rotary electric machine <NUM> to each wheel <NUM>.

At the completion of the operation in step S03, the rotational speed of each wheel <NUM> is in a state of varying based on the oscillation command, and the rotational speed of each wheel <NUM> is in a state of varying based on the vibration control command. Because the variations in the rotational speed of each wheel <NUM> and the variations in the rotational speed of each wheel <NUM> cancel one another out, a vibration of the body <NUM> is more suppressed as compared with a case where no vibration control command is outputted from the oscillation unit <NUM>.

Following the operation in step S03, the evaluation apparatus <NUM> determines whether there is a relatively great vibration of the body <NUM> in step S04. More specifically, the evaluation apparatus <NUM> determines whether the peak-to-peak amplitude of a vibration of the body <NUM>, which is measured by the acceleration sensor <NUM>, is greater than <NUM> in step S04.

Upon determination that there is a relatively great vibration of the body <NUM>, i.e., the peak-to-peak amplitude of the vibration of the body <NUM>, which is measured by the acceleration sensor <NUM>, is greater than <NUM>, (YES in step S04), the evaluation apparatus <NUM> adjusts the oscillation command to thereby cause the magnitude of the vibration of the body <NUM> to be smaller in step S05. As an example of this adjustment of the oscillation command, the evaluation apparatus <NUM> can use a lowpass filter to thereby the magnitude of the vibration of the body <NUM> to be smaller in step S05. In step S05, the evaluation apparatus <NUM> uses the expression (<NUM>) to thereby adjust the vibration control command while adjusting the oscillation command.

After the operation in step S05, the evaluation routine proceeds to step S06.

Otherwise, upon determination that there is not a relatively great vibration of the body <NUM>, i.e., the peak-to-peak amplitude of the vibration of the body <NUM>, which is measured by the acceleration sensor <NUM>, is smaller than or equal to <NUM>, (NO in step S04), the evaluation routine proceeds to step S06.

In step S06, the oscillation obtainer <NUM> obtains information about the oscillation of the rotational speed of each wheel <NUM>. For example, the oscillation obtainer <NUM> according to the first embodiment obtains, as the waveform of the oscillation of the rotational speed of each wheel <NUM>, the waveform indicative of how the rotational speed of the rotary electric machine <NUM> measured by the corresponding MG resolver <NUM> changes over time. The oscillation obtainer <NUM> stores the obtained waveform of the oscillation of the rotational speed of each wheel <NUM> in an unillustrated storage device installed in the evaluation apparatus <NUM>.

Following the operation in step S06, the evaluation apparatus <NUM> obtains the waveform of the drive current supplied to the rotary electric machine <NUM> in step S07. That is, the waveform obtained in step S07 is the waveform of the drive current supplied to the rotary electric machine <NUM> within a period for which the rotational speed of each wheel <NUM> has been oscillating based on the oscillation command outputted from the oscillation unit <NUM>. The evaluation apparatus <NUM> stores the obtained waveform of the oscillation of the drive current in the unillustrated storage device installed in the evaluation apparatus <NUM>.

That is, the waveform of the drive current stored in step S07 also represents the waveform of the oscillation command outputted from the oscillation unit <NUM>.

Subsequently from the operation in step S07, the evaluation apparatus <NUM> performs a task of calculating a reference waveform in step S08. The "reference waveform" represents a waveform of an oscillation that is predicted to occur in rotation of each wheel <NUM> based on the oscillation command outputted from the oscillation unit <NUM>. For example, the evaluation unit <NUM> of the evaluation apparatus <NUM> calculates the reference waveform under a predetermined condition that a road-surface friction coefficient has a predetermined reference value. For example, the predetermined reference value of the road-surface friction coefficient can be set to an average value between a dry road surface and a wheel.

The task of calculating the reference waveform includes a first task of converting the waveform of the drive current obtained in step S07, i.e., the waveform of the oscillation command, into a variation of torque to be outputted from the rotary electric machine <NUM>. The first task for example refers to a map indicative of a correlative relationship between (i) values of drive current to be supplied to the rotary electric machine <NUM> and (ii) respective corresponding values of torque to be outputted from the rotary electric machine <NUM> to accordingly convert the waveform of the drive current obtained in step S07 into the variation of torque to be outputted from the rotary electric machine <NUM>.

The task of calculating the reference waveform additionally includes a second task of converting the converted waveform of torque of the rotary electric machine <NUM> into the waveform of change in the rotational speed of the rotary electric machine <NUM> based on a first transfer function. The first transfer function used by the second task, which has been prepared, represents a correlative relationship between (i) values of torque to be outputted from the rotary electric machine <NUM> and (ii) respective corresponding values of the rotational speed of the rotary electric machine <NUM> on the condition that the road-surface friction coefficient is set to the predetermined reference value.

That is, the evaluation apparatus <NUM> calculates, in step S08, the reference waveform as a result of converting the waveform of the drive current obtained in step S07, i.e., the waveform of the oscillation command, into the waveform of the rotational speed of the rotary electric machine <NUM> on the condition that the road-surface friction coefficient is set to the predetermined reference value.

As described later, the reference waveform calculated in step S08 is compared with the waveform obtained in step S06. For this reason, a physical quantity represented by the reference waveform, i.e., the rotational speed of the rotary electric machine <NUM> according to the first embodiment, is preferably identical to that obtained in step S06.

For example, let us assume that the oscillation obtainer <NUM> directly obtains, as the waveform of the oscillation of the rotational speed of each wheel <NUM>, the waveform indicative of how the rotational speed of the rotary electric machine <NUM> measured by the corresponding MG resolver <NUM> changes over time. In this assumption, the evaluation apparatus <NUM> preferably calculates, as the reference waveform, the waveform of the rotational speed of each wheel <NUM> in place of the waveform of the rotational speed of the rotary electric machine <NUM>. Specifically, in this assumption, the second task is modified to convert the converted waveform of torque of the rotary electric machine <NUM> into the waveform of change in the rotational speed of each wheel <NUM> based on a second transfer function. The second transfer function used by the modified second task, which has been prepared, represents a correlative relationship between (i) values of torque to be outputted from the rotary electric machine <NUM> and (ii) respective corresponding values of the rotational speed of each wheel <NUM> on the condition that the road-surface friction coefficient is set to the predetermined reference value.

Following the operation in step S08, the evaluation apparatus <NUM> performs a task of calculating both a first attenuation rate and a second attenuation rate in step S09.

The following describes the definition of an attenuation rate. <FIG> illustrates an example of a waveform showing how the rotational speed of each wheel <NUM> changes over time. The example waveform illustrated in <FIG> has a first peak-to-peak amplitude of A1 at time t11 in a selected first period, and has a second peak-to-peak amplitude of A2 at time t12 in a selected second period after the selected first period.

The attenuation rate according to the first embodiment is defined as A2/A1 or can be defined as (A2/A1)/T1; T1 represents the length of an interval between from the time t11 to the time t12. The definition of the attenuation rate of a waveform according to the first embodiment is not limited thereto. Specifically, information indicative of the degree of attenuation of a waveform over time can be used as the attenuation rate of the waveform. It is possible to sample, from a waveform, a first peak-to-peak amplitude at any time, and thereafter sample a second peak-to-peak amplitude at any time.

The first attenuation rate calculated in step S09 is an attenuation rate that is calculated set forth above from the waveform of the oscillation of the rotational speed of each wheel <NUM> obtained in step S06. That is, the first attenuation rate can be defined as a first parameter indicative of the degree of attenuation in the oscillation of the rotational speed of each wheel <NUM>. The evaluation apparatus <NUM> according to the first embodiment calculates, as the first attenuation rate, the attenuation rate of the waveform indicative of how the rotational speed of the rotary electric machine <NUM> measured by the corresponding MG resolver <NUM> changes over time.

The second attenuation rate calculated in step S09 is an attenuation rate that is calculated set forth above from the reference waveform calculated in step S08. That is, the second attenuation rate can be defined as a second parameter indicative of the degree of attenuation in the oscillation that is predicted to occur in the rotational speed of each wheel <NUM> on the condition that the road-surface friction coefficient is set to the predetermined reference value. This makes clear that, if the friction coefficient of the actual road surface on which the vehicle <NUM> is actually traveling becomes the predetermined reference value, the first attenuation rate and the second attenuation rate can be in agreement with each other.

Following the operation in step S09, the evaluation apparatus <NUM> calculates an absolute difference between the first attenuation rate and the second attenuation rate, and determines whether the absolute difference between the first attenuation rate and the second attenuation rate is greater than a friction-condition threshold in step S10.

The inventors of the present invention have demonstrated that an oscillation of the rotational speed of each wheel <NUM> based on the oscillation command for each target road surface is more likely to decay as the friction coefficient of the corresponding target road surface becomes smaller. For this reason, the first attenuation rate calculated in step S09 for each target road surface becomes greater as the friction coefficient of the corresponding target road surface with respect to the vehicle <NUM> becomes smaller, resulting in the absolute difference between the first attenuation rate and the second attenuation rate becoming greater. The friction-condition threshold is previously determined to identify whether the condition of the actual road surface on which the vehicle <NUM> is traveling is a high-friction condition or a low-friction condition.

Upon determination that the absolute difference between the first attenuation rate and the second attenuation rate is greater than the friction-condition threshold (YES in step S10), the evaluation unit <NUM> of the evaluation apparatus <NUM> determines that the actual road surface on which the vehicle <NUM> is traveling is in the low-friction condition in step S11. Then, the evaluation routine proceeds to step S13.

Otherwise, upon determination that the absolute difference between the first attenuation rate and the second attenuation rate is smaller than or equal to the friction-condition threshold (NO in step S10), the evaluation unit <NUM> of the evaluation apparatus <NUM> determines that the actual road surface on which the vehicle <NUM> is traveling is in the high-friction condition in step S12. Then, the evaluation routine proceeds to step S13.

As described above, the evaluation result about the condition of the actual road surface obtained by the evaluation unit <NUM> includes information indicative of whether the actual road surface is in the low-friction condition or the high-friction condition. Determination of whether the actual road surface is the low-friction condition or the high-friction condition is based on the oscillation command obtained in step S07 and the information about the oscillation of the rotational speed of each wheel <NUM> obtained in step S06.

In step S13, the evaluation apparatus <NUM> performs a task of calculating a slip ratio S of each wheel <NUM> of the vehicle <NUM> in accordance with the following expression (<NUM>): <MAT>.

In the expression (<NUM>), Vtire represents a relative speed of a portion of the corresponding wheel, i.e., driving wheel, <NUM> relative to the body <NUM>; the portion of each wheel <NUM> is in contact with the actual road surface. The relative speed Vtire of each wheel <NUM> can be obtained from the signal outputted from the corresponding wheel speed sensor <NUM>. In the expression (<NUM>), Vbody represents a relative speed of the body <NUM> relative to the actual road surface, i.e., the speed of the vehicle <NUM>. A value of the relative speed Vbody in a current control cycle (n) of the evaluation routine which will be referred to as a Vbody(n), can be calculated in accordance with the following expression (<NUM>): <MAT>
where:.

The relative speed of the body <NUM> Vbody for each control cycle of the evaluation routine can be calculated from the signal outputted from at least one wheel speed sensor <NUM> provided for at least one wheel in the wheels <NUM> and <NUM>; the at least one wheel is controlled to be a driven wheel.

Following the operation in step S13, the evaluation apparatus <NUM> performs a task of calculating the friction coefficient of the actual road surface, which will be referred to as a friction coefficient µ, between the actual road surface and each wheel <NUM> in accordance with the following expression (<NUM>) in step S14: <MAT>.

In the expression (<NUM>), F is identical to F on the right side of the expression (<NUM>), and G<NUM>(s) is identical to G<NUM>(s)on the right side of the expression (<NUM>). Converting a value of the drive current obtained in step S07 into a value of torque outputted from the rotary electric machine <NUM> enables a value of the torque F generated from the rotary electric machine <NUM> to be calculated.

In the expression (<NUM>), I represents the moment of inertia about the corresponding wheel <NUM> that is an oscillation target of the oscillation command outputted from the oscillation unit <NUM>. As a value of the moment of inertia I about the corresponding wheel <NUM>, a value obtained by converting the total mass of the body <NUM> into a value of the moment of inertia I about the corresponding wheel <NUM> can be used.

In the expression (<NUM>), a represents a rotational acceleration of the corresponding wheel <NUM>, which can be calculated by differentiating the rotational speed of the corresponding wheel <NUM> with respect to time. In the expression (<NUM>), R represents the radius of the corresponding wheel <NUM>.

In the expression (<NUM>), Fz represents a normal force sustained by the corresponding wheel <NUM> from the actual road surface. For example, using a known method enables the normal force Fz sustained by each wheel <NUM> from the actual road surface to calculated in accordance with predetermined parameters including, for example, (i) the height of the center of gravity of the vehicle <NUM>, (ii) the values of acceleration applied to the body <NUM> measured by the acceleration sensor <NUM>, and (iii) the wheel base of the vehicle <NUM>. A value, which is calculated by dividing the total mass of the vehicle <NUM> by the total number of wheels <NUM> and <NUM>, i.e., <NUM> according to the first embodiment, can be used as a simplified value of the normal force Fz.

Following the operation in step S14, the evaluation apparatus <NUM> performs a task of calculating a µ-gradient of the actual road surface for each wheel <NUM> in step S15. The µ-gradient of the actual road surface for each wheel <NUM> is defined as the gradient of change in the friction coefficient µ of the actual road surface with respect to change in the slip ratio S of the corresponding wheel <NUM> of the vehicle <NUM>. The µ-gradient of the actual road surface for each wheel <NUM> can be used as a parameter needed to calculate the range of lateral force that can be generated between the corresponding wheel <NUM> and the actual road surface. The calculated range of the lateral force for each wheel <NUM> can be used to calculate an assist force for the steering of the vehicle <NUM>.

The evaluation apparatus <NUM> can calculate the µ-gradient of the actual road surface for each wheel <NUM> as a function of (i) the slip ratio S of the corresponding wheel <NUM> calculated in step S13 and (ii) the friction coefficient µ calculated in step S14.

Let us assume that a value of the slip ratio S of each wheel <NUM> is a value S1, and a value of the friction coefficient µ is a value µ1. In this assumption, the evaluation apparatus <NUM> can perform a method of calculating a gradient θ of a straight line L1 that connects between the origin <NUM> of a graph illustrated in <FIG> and a coordinate point (S1, µ1) in the graph as the µ-gradient of the actual road surface for the corresponding wheel <NUM>.

The above calculation method is an example of calculation methods. As another example, the evaluation apparatus <NUM> can be configured to.

As described above, the evaluation result about the condition of the actual road surface obtained by the evaluation unit <NUM> includes information indicative of the µ-gradient of the actual road surface for each wheel <NUM>, which represents the gradient of change in the friction coefficient µ of the actual road surface with respect to change in the slip ratio S of the corresponding wheel <NUM>.

Following the operation in step S15, the transmitter <NUM> of the evaluation apparatus <NUM> performs an output of the evaluation result about the condition of the actual road surface obtained by the evaluation unit <NUM> in step S16.

Specifically, the transmitter <NUM> transmits, to each of the higher-level ECU <NUM> and at least one external server, the evaluation result about the condition of the actual road surface obtained by the evaluation unit <NUM> that include (i) the information indicative of whether the actual road surface is the low-friction condition or the high-friction condition, and (ii) the µ-gradient of the actual road surface for each wheel <NUM> calculated in step S15. The evaluation result about the condition of the actual road surface to be transmitted by the transmitter <NUM> can include other items of information, such as the friction coefficient µ between the actual road surface and each wheel <NUM> calculated in step S14.

When completing the operation in step S16, the evaluation routine illustrated in <FIG> is terminated. Thereafter, the travel controller <NUM> controls how the vehicle <NUM> travels on the actual road surface in accordance with the evaluation result about the condition of the actual road surface outputted in step S16.

As described above, the oscillation unit <NUM> of the evaluation apparatus <NUM> according to the first embodiment is configured to output the oscillation command that actively causes the rotational speed of each wheel <NUM> to oscillate. In particular, one or more frequencies of the oscillation of the rotational speed of each wheel <NUM> based on the oscillation command are different from frequencies of natural oscillations that naturally occur in the rotational speed of each wheel <NUM>.

This configuration therefore makes it possible to obtain the evaluation result about the road surface with higher accuracy as compared with a method of analyzing a resonant oscillation that occurs naturally.

Additionally, the travel controller <NUM> of the evaluation apparatus <NUM> is configured to control how the vehicle <NUM> travels in accordance with the higher-accuracy evaluation result about the condition of the road surface, making it possible to cause the vehicle <NUM> to travel with more stably.

The oscillation unit <NUM> of the evaluation apparatus <NUM> is configured to output the oscillation command that causes one or more frequencies of the oscillation of the rotational speed of each wheel <NUM> to be different from at least one resonant frequency of the vehicle <NUM>. This configuration therefore makes it possible to evaluate the condition of the actual road surface while preventing one or more occupants of the vehicle <NUM> from having feeling discomfort.

The oscillation unit <NUM> is additionally configured to output the oscillation command for controlling the operation of the rotary electric machine <NUM>, and output the vibration control command that control the operation of the rotary electric machine <NUM> to accordingly suppress a vibration of the vehicle <NUM>.

This configuration therefore makes it possible to suppress the vibration of the vehicle <NUM> more strongly as compared with a case where the oscillation unit <NUM> outputs only the oscillation command.

The first embodiment is configured to output the oscillation command that causes the rotational speed of each front wheel <NUM> to oscillate, and output the vibration control command that causes the rotational speed of each rear wheel <NUM> to oscillate.

In place of the above configuration, the first embodiment can be modified to output the oscillation command that causes the rotational speed of each rear wheel <NUM> to oscillate, and output the vibration control command that causes the rotational speed of each front wheel <NUM> to oscillate. That is, the rotary electric machine <NUM> can serve as the first rotary electric machine, and the rotary electric machine <NUM> can serve as the second rotary electric machine.

The evaluation unit <NUM> of the evaluation apparatus <NUM> is configured to calculate the reference waveform that represents a waveform of an oscillation that is predicted to occur in the rotational speed of each wheel <NUM> based on the oscillation command. The evaluation unit <NUM> is thereafter configured to compare the first attenuation rate of the waveform of the oscillation obtained by the oscillation obtainer <NUM> with the second attenuation rate of the reference waveform to accordingly determine whether the condition of the actual road surface is the low-friction condition or the high-friction condition.

This configuration performs determination of whether the actual road surface is the low-friction condition or the high-friction condition in accordance with both the first attenuation rate of the oscillation based on the oscillation command and the second attenuation rate of the reference waveform, making it possible to accurately perform determination of whether the actual road surface is the low-friction condition.

Next, the following describes the second embodiment. The second embodiment is slightly different from the first embodiment in the following points. The following therefore mainly describes the different points of the second embodiment from the first embodiment while appropriately omitting descriptions of the remaining of the second embodiment, which is identical to that of the first embodiment.

Referring to <FIG>, the vehicle <NUM> according to the second embodiment does not include the first rotary electric machine <NUM>, so that the pair of wheels <NUM> serve as a pair of driven wheels, and therefore the pair of wheels <NUM> serve as a pair of driving wheels.

The oscillation unit <NUM> according to the second embodiment is configured to output the oscillation command, which causes the rotational speed of each wheel <NUM> to oscillate without outputting the vibration control command. That is, the rotary electric machine <NUM> according to the second embodiment serves as the first rotary electric machine, and no second rotary electric machines are provided in the second embodiment.

Next, the following describes an evaluation routine illustrated in <FIG>, which is cyclically carried out by the evaluation apparatus <NUM> according the second embodiment in place of the evaluation routine illustrated in <FIG>. The following therefore describes operations in the evaluation routine illustrated in <FIG>, which are different from the operations in the evaluation routine illustrated in <FIG>.

The oscillation command according to the second embodiment is outputted from the oscillation unit <NUM> to the inverter connected to the rotary electric machine <NUM> as command values for the drive current to be supplied to the rotary electric machine <NUM>.

After the operation in step S02, the evaluation routine proceeds to step S04 without passing through the operation in step S03.

In step S05, the evaluation apparatus <NUM> adjusts only the oscillation command without adjusting the vibration control command.

The operations carried out subsequently from the operation in step S05 are identical to the operations in the evaluation routine according to the first embodiment as long as the "wheel <NUM>" should be read as "vehicle <NUM>" and the "rotary electric machine <NUM> should be read as "rotary electric machine <NUM>".

As described above, the evaluation apparatus <NUM> according to the second embodiment is capable of performing the evaluation routine for the two-wheel drive vehicle <NUM>, which is not a four-wheel drive vehicle, like the evaluation apparatus <NUM> according to the first embodiment except for the output of the vibration control command. The two-wheel drive vehicle <NUM> is not limited to a front-wheel drive vehicle according to the second embodiment, and can be configured as a rear-wheel drive vehicle.

Next, the following describes the third embodiment. The third embodiment is slightly different from the first embodiment in the following points. The following therefore mainly describes the different points of the third embodiment from the first embodiment while appropriately omitting descriptions of the remaining of the second embodiment, which is identical to that of the first embodiment.

Referring to <FIG>, the evaluation apparatus <NUM> according to the third embodiment includes a storage unit <NUM> as a functional module. For example, the storage unit <NUM> is comprised of a nonvolatile storage device, such as a hard disc or an SSD.

In the storage unit <NUM>, a three-dimensional map of a <NUM>-way correlative relationship is previously stored; the correlative relationship represents a predetermined correlative relationship among.

Each of the oscillation commands to be outputted from the oscillation unit <NUM> represents, for example, the waveform of the drive current outputted as the corresponding one of the oscillation commands.

Each of the oscillations of the rotational speed of each wheel <NUM>, which is the oscillation target of the oscillation command, based on the corresponding one of the oscillation commands represents, for example, the waveform of change of the rotational speed of the corresponding wheel <NUM>.

Each of the information items about the road-surface condition represents, for example, one of the low-friction condition and the high-friction condition.

That is, the correlative information stored in the storage unit <NUM> represents a correlative-relationship for each road surface between.

The correlative relationship has been created based on machine learning with one or more neural networks, and is stored in the storage unit <NUM>. The correlative-relationship stored in the storage device <NUM> can be updated based on additional machine learning while the vehicle <NUM> is traveling. That is, the correlative relationship, which was loaded into the storage device <NUM> during, for example, manufacturing of the vehicle <NUM>, can be used without being updated or can be updated based on machine learning after being loaded into the storage device <NUM>.

As the machine learning, the third embodiment can use one or more machine learning algorithms that include a Bayesian Network algorithm, a support-vector machine algorithm, a Gaussian Mixture Model algorithm, a decision tree algorithm, and a random forest algorithm. Additionally, as the machine learning, a supervised learning algorithm, an unsupervised learning algorithm, or a reinforcement learning algorithm can be used. At least two algorithms selected from these learning algorithms can be used as the machine learning. At least one machine learning algorithm, which is used as the machine learning, can be rewritten based on updating of the software corresponding to the at least one machine learning algorithm.

Next, the following describes an evaluation routine illustrated in <FIG>, which is cyclically carried out by the evaluation apparatus <NUM> according the third embodiment in place of the evaluation routine illustrated in <FIG>.

The operations from step S01 to step S07 in <FIG> are respectively identical to the operations from step S01 to step S07 in <FIG>.

After the operation in step S03, the evaluation routine proceeds to step S21.

In step S21, the evaluation unit <NUM> refers to the correlative relationship stored in the storage unit <NUM> using a combination of the oscillation obtained in step S06 and the waveform of the drive current obtained in step S07 to thereby retrieve, from the correlative relationship stored in the storage unit <NUM>, a corresponding evaluation result of the road-surface condition.

The oscillation obtained in step S06, i.e., the oscillation in the rotational speed of each wheel <NUM>, corresponds to the second information stored in the storage unit <NUM>, and the waveform of the drive current obtained in step S07 corresponds to the first information stored in the storage unit <NUM>.

That is, the evaluation unit <NUM> refers to the correlative relationship stored in the storage unit <NUM> using a combination of the oscillation obtained in step S06 and the waveform of the drive current obtained in step S07 to accordingly retrieve, from the correlative relationship stored in the storage unit <NUM>, one of the information items, i.e., one of the evaluation results about the road-surface condition, which correlates with the combination of the oscillation obtained in step S06 and the waveform of the drive current obtained in step S07.

A dimension and/or scale of the first information included in the correlative relationship can preferably match with those of the information obtained in step S07, and similarly a dimension and/or scale of the second information included in the correlative relationship can preferably match with those of the information obtained in step S06.

As described above, the evaluation apparatus <NUM> according to the third embodiment includes the storage unit <NUM> in which the correlative relationship is stored; the correlative relationship is correlative relationship information among.

The evaluation unit <NUM> therefore refers to the correlative relationship to thereby evaluate the condition of the actual road surface on which the vehicle <NUM> is traveling.

The above configuration of the evaluation apparatus <NUM> makes it possible to utilize machine learning based on enormous volumes of trained data items to accordingly ascertain the condition of the actual road surface more accurately.

Following the operation in step S21, the transmitter <NUM> of the evaluation apparatus <NUM> performs an output of the evaluation result about the condition of the actual road surface obtained by the evaluation unit <NUM> in step S22, which is identical to the operation in step S16 in <FIG>.

The above methods and apparatuses described in the present invention can be implemented by a dedicated computer including a memory and a processor programmed to perform one or more functions embodied by one or more computer programs.

The above methods and apparatuses described in the present invention can also be implemented by a dedicated computer including a processor comprised of one or more dedicated hardware logic circuits.

The above methods and apparatuses described in the present invention can further be implemented by at least one dedicated computer comprised of a memory, a processor programmed to perform one or more functions embodied by one or more computer programs, and one or more hardware logic circuits.

The computer programs described in the present invention can be stored in a computer-readable non-transitory storage medium as instructions executable by a computer and/or a processor.

Claim 1:
An evaluation apparatus (<NUM>) for evaluating a condition of a road surface on which a vehicle (<NUM>) having at least one wheel (<NUM>) is traveling, the evaluation apparatus comprising:
an oscillation unit (<NUM>) configured to output an oscillation command that causes the at least one wheel of the vehicle to oscillate;
an oscillation obtainer (<NUM>) configured to obtain an oscillation of rotation of the at least one wheel in response to the output of the oscillation command; and
an evaluation unit (<NUM>) configured to perform an evaluation of the condition of the road surface in accordance with the oscillation command and the oscillation obtained by the oscillation obtainer,
wherein the evaluation of the condition of the road surface performed by the evaluation unit (<NUM>) includes whether the condition of the road surface is a low-friction condition or a high-friction condition,
characterized in that the evaluation unit (<NUM>) is configured to:
calculate a reference waveform that represents a waveform of a predicted oscillation that is predicted to occur in rotation of the at least one wheel (<NUM>) based on the oscillation command;
calculate a first attenuation rate of a waveform of the oscillation obtained by the oscillation obtainer (<NUM>), and a second attenuation rate of the reference waveform; and
compare the first attenuation rate with the second attenuation rate to accordingly determine whether the condition of the road surface is the low-friction condition or the high-friction condition.