Patent Description:
In a steering mechanism of a vehicle, electric power steering for assisting steering with a rotational force of a motor has been known.

An electric power steering device that switches between a manual steering control and an automatic steering control has been known (see, for example, International Publication No. <CIT>). In the manual steering control, the motor is driven depending on a first motor current command value calculated based on a steering torque. In the automatic steering control, the motor is driven depending on a second motor current command value that is calculated so as to bring an actual steering angle to a target steering angle.

However, the above-mentioned electric power steering device cannot provide an assist torque appropriate for a road surface condition, for example, when the assist torque is calculated only on the input side (steering wheel side).

This means that it may not be possible to properly assist the steering regardless of the road surface condition.

A further example for assisting steering is disclosed in <CIT>.

The present invention has been made in view of above, and provides, for example, a steering device and a steering unit device that can appropriately assist steering regardless of road surface conditions.

A column assist steering device according to one aspect of the invention includes: a steering member steered by an operator; a drive unit rotating for imparting an auxiliary force to the steering member; a first control unit calculating a load torque that corresponds to a reaction force from a road surface, the load torque being estimated based on a value measured in the steering member and the drive unit, the first control unit also calculating a target steering torque for the steering member based on the calculated load torque; and a second control unit calculating the auxiliary force of the drive unit to achieve the target steering torque calculated by the first control unit. The first control unit calculates a steering torque that corresponds to the reaction force based on the load torque and a vehicle speed, calculates a restoring torque that returns the steering member to its neutral position and a damping torque that controls abrupt steering of the steering member based on the vehicle speed, and calculates the target steering torque based on the calculated torques. The first control unit calculates the load torque on which an operation of compensating for a friction of a speed reducer has been performed.

With this configuration, it is possible to properly assist the steering regardless of the road surface conditions.

In the above column assist steering device, the first control unit may calculate the load torque based on a steering torque required to rotate the steering member, a steering angular velocity, which is an angular velocity of the steering member, and a drive torque, which is a torque of the drive unit.

In the above column assist steering device, the second control unit may calculate the auxiliary force of the drive unit based on the load torque, a steering torque required to rotate the steering member, a steering angular velocity, which is an angular velocity of the steering member, and a drive angular velocity, which is an angular velocity of the drive unit. In the above column assist steering device, the load torque may be a torque applied to a pitman arm. In the above column assist steering device, the second control unit may not compensate for the friction of the speed reducer.

A steering unit according to another aspect of the invention includes, a column assist steering device, a speed reducer, and a control device controlling the column assist steering device and the speed reducer. The column assist steering device includes: a steering member steered by an operator; a drive unit rotating for imparting an auxiliary force to the steering member; first control unit calculating a load torque that corresponds to a reaction force from a road surface, the load torque being estimated based on a value measured in the steering member and the drive unit, the first control unit also calculating a target steering torque for the steering member based on the calculated load torque; and a second control unit calculating the auxiliary force of the drive unit to achieve the target steering torque calculated by the first control unit. The first control unit calculates a steering torque that corresponds to the reaction force based on the load torque and a vehicle speed, calculates a restoring torque that returns the steering member to its neutral position and a damping torque that controls abrupt steering of the steering member, and calculates the target steering torque based on the calculated torques. The first control unit calculates the load torque on which an operation of compensating for a friction of a speed reducer has been performed.

According to yet another aspect of the invention, provided is a method of calculating an auxiliary force. The method is performed by a computer of a column assist steering device that includes a steering member steered by an operator and a drive unit rotating for imparting the auxiliary force to the steering member. The method includes: a first control step in which the computer calculates a load torque that corresponds to a reaction force from a road surface, the load torque being estimated based on a value measured in the steering member and the drive unit, and the computer further calculates a target steering torque for the steering member based on the calculated load torque; and a second control step in which the computer calculates the auxiliary force of the drive unit to achieve the target steering torque calculated by the first control step. In the first control step, a steering torque that corresponds to the reaction force is calculated based on the load torque and a vehicle speed, a restoring torque that returns the steering member to its neutral position and a damping torque that controls abrupt steering of the steering member are calculated based on the vehicle speed, and the target steering torque is calculated based on the calculated torques. In the first control step, the load torque on which an operation of compensating for a friction of a speed reducer has been performed is calculated. In the second control step in the above method of calculating an auxiliary force, no operation of compensating for the friction of the speed reducer may be performed.

According to still yet another aspect of the invention, provided is a program causing a computer of a column assist steering device that includes a steering member steered by an operator and a drive unit rotating for imparting the auxiliary force to the steering member, to perform; a first control step in which a load torque that corresponds to a reaction force from a road surface is calculated, the load torque being estimated based on a value measured in the steering member and the drive unit, and a target steering torque for the steering member is calculated based on the calculated load torque; and a second control step in which the auxiliary force of the drive unit is calculated to achieve the target steering torque calculated by the first control step. In the first control step, a steering torque that corresponds to the reaction force is calculated based on the load torque and a vehicle speed, a restoring torque that returns the steering member to its neutral position and a damping torque that controls abrupt steering of the steering member are calculated based on the vehicle speed, and the target steering torque is calculated based on the calculated torques. In the first control step, the load torque on which an operation of compensating for a friction of a speed reducer has been performed is calculated. In the second control step in the above program, no operation of compensating for the friction of the speed reducer may be performed.

With the above steering device or steering unit device, it is possible to properly assist the steering regardless of the road surface conditions.

The embodiments of the invention will be hereinafter described with reference to the drawings.

<FIG> illustrates a configuration example of a steering unit device <NUM> according to an embodiment of the invention. The steering unit device <NUM> is an electric power steering system mounted on a vehicle. The vehicles in the embodiment are large commercial vehicles such as buses or trucks. A speed reducer <NUM> in the electric power steering may increase friction, and an operator of the vehicle may be unable to feel road conditions and unable to maneuver the vehicle well. Particularly in large commercial vehicles, the friction of the reducer <NUM> is large, and it is desirable to configure the control to provide the operator with a steering feeling. The steering unit device <NUM> according to the embodiment is most effective when used in large commercial vehicles, but it can also be used in passenger vehicles.

The steering unit device <NUM> includes a steering wheel <NUM> (an example of a steering member), a motor <NUM> (an example of a drive unit), a speed reducer <NUM>, a pitman arm <NUM>, various sensors <NUM>, and a control unit <NUM>. A steering device is formed by the steering wheel <NUM>, the motor <NUM>, and the control unit <NUM>.

The steering wheel <NUM> is a steering wheel operated by the operator. The motor <NUM> generates an assist torque (auxiliary force) that assists steering. The steering wheel <NUM> transmits a steering torque to a steering shaft <NUM>. The steering torque is inputted to an input portion of the speed reducer <NUM>. The speed reducer <NUM> combines the inputted steering torque and the assist torque by the motor <NUM>, and transmits the combined torque to the pitman arm <NUM> and following steering mechanism. The pitman arm <NUM> is an output arm connected to the speed reducer <NUM> and rotated by the combined torque combined by the speed reducer <NUM>. As shown in <FIG>, the output portion (case or shaft) of the speed reducer <NUM> and the pitman arm <NUM> are integrally formed with each other.

A configuration example of the speed reducer <NUM> and the pitman arm <NUM> according to the embodiment will be now described with reference to <FIG> is an explanatory diagram showing a configuration example of the speed reducer <NUM> and the pitman arm <NUM>. As shown in <FIG>, a fixing member <NUM> for fixing the speed reducer to an object is provided on one surface side of the speed reducer <NUM>. On the other surface <NUM> side of the speed reducer <NUM>, a cylindrical output portion <NUM> that rotates relative to the fixing member <NUM> and outputs a rotational force is provided. The output portion <NUM> has the pitman arm <NUM> that projects in the radial direction and rotates around a central axis (z axis) in the circumferential direction. The pitman arm <NUM> is connected to, for example, the steering device and steers wheels according to a rotational movement. Since the pitman arm <NUM> is provided in the circumferential direction of the output portion <NUM>, it is possible to reduce the width of the steering unit device <NUM> along the central axis direction and reduce its size.

Referring again to <FIG>, the various sensors <NUM> include a steering sensor <NUM>, a motor sensor <NUM>, and a speed sensor <NUM> (see <FIG>). The control unit <NUM> controls the steering device and the speed reducer <NUM>. The control unit <NUM> includes a motor control unit <NUM>, a steering control unit <NUM> (an example of a second control unit), and a feeling control unit <NUM> (an example of a first control unit). The control unit <NUM> may be implemented by using, for example, an ECU (Electronic Control Unit).

These components are each implemented by executing programs (software), for example, by a hardware processor such as a CPU (central processing unit). A part or all of the components may be implemented by using hardware (including circuitry) such as an LSI (large scale integrated circuit), an ASIC (application specific integrated circuit), an FPGA (field-programmable gate array), and a GPU (graphics processing unit) or may be implemented by the combination of software and hardware. The program may be stored in advance in a storage device (not shown) such as a HDD or flash memory, or it may be stored in a removable recording medium such as a DVD or CD-ROM and installed in the HDD or flash memory when the recording medium is connected to a drive device.

The steering sensor <NUM> detects a steering torque, steering angle, and steering angular velocity of the steering wheel <NUM>. The steering angular velocity detected by the steering sensor <NUM> is specifically calculated by the CPU based on the steering angle. The motor sensor <NUM> detects a motor torque and motor angular velocity of the motor <NUM>. The motor torque detected by the motor sensor <NUM> is specifically calculated by the CPU based on a current value of the motor <NUM>. Further, the motor angular velocity detected by the motor sensor <NUM> is calculated based on the position of the motor <NUM>. The speed sensor <NUM> detects the speed of the vehicle.

The motor control unit <NUM> controls the rotation of the motor <NUM> based on control of the steering control unit <NUM>. The steering control unit <NUM> controls an output torque of the motor <NUM> based on detection result from the steering sensor <NUM>. The motor <NUM> generates the assist torque under control of the motor control unit <NUM> and the steering control unit <NUM>. As described above, the steering of the steering wheel <NUM> operated by the operator is assisted by the assist torque of the motor <NUM>. The steering control unit <NUM> performs feedback control to adjust the assist torque of the motor <NUM> to a predetermined assist torque.

In conventional methods, the calculated torque command value has been often adjusted. Whereas in the embodiment of the present invention, the control is separated into the feeling control unit <NUM> and the steering control unit <NUM>, and a predetermined steering torque is set for the steering control unit <NUM> to perform torque control.

The feeling control unit <NUM> calculates a target steering torque for assisting steering so that the steering torque of the steering wheel <NUM> becomes the predetermined steering torque irrespective of the road surface reaction force. The feeling control unit <NUM> outputs the calculated target steering torque to the steering control unit <NUM>. The steering control unit <NUM> calculates a target motor torque based on the target steering torque outputted by the feeling control unit <NUM>, and outputs the target motor torque to the motor control unit <NUM>.

<FIG> is an explanatory diagram showing an example of various information inputted to or outputted from the control unit <NUM>. The feeling control unit <NUM> will be first described. The feeling control unit <NUM> includes a first estimation unit <NUM>, a load feeling unit <NUM>, a centering unit <NUM>, and a damping unit <NUM>. The information inputted to each unit will be hereunder described.

In the figures, subscript notations of detected values are listed and described below.

The motor torque Tmot (Nm) outputted from the motor control unit <NUM>, the steering angular velocity ωsteer (rad/s), and the steering torque Tsteer (Nm) detected by the steering sensor <NUM> are inputted to the first estimation unit <NUM>. The first estimation unit <NUM> calculates an estimated load torque Tload est (Nm) based on the inputted motor torque Tmot, steering angular velocity ωsteer, and steering torque Tsteer. The calculation (operation) of the estimated load torque Tload est will be described later.

To the load feeling unit <NUM>, the estimated load torque Tload est (Nm) outputted from the first estimation unit <NUM> and the speed of the vehicle Vveh (km/h) detected by the speed sensor <NUM> are inputted. The load feeling unit <NUM> obtains a target value of the load feeling torque based on the inputted estimated load torque Tload est and the velocity Vveh. The target value of the load feeling torque is a value that conveys to the operator a sense of the force (reaction force from the road surface) acting on the tires. The load feeling torque is also a torque that depends on the vehicle speed.

A steering angle φsteer (degree) and the steering torque Tsteer (Nm) detected by the steering sensor <NUM>, and the speed Vveh (km/h) detected by the speed sensor <NUM> are inputted to the centering unit <NUM>. The centering unit <NUM> obtains a target value of a centering torque (restoring torque) based on the inputted steering angle φsteer, steering angular velocity ωsteer, and speed Vveh. The centering torque is a force that tries to return the steering wheel <NUM> to the center position.

In the embodiment, a high friction speed reducer <NUM> is used. This causes a high back-drive torque, which may prevent the steering wheel from returning to the center position easily. To address this, the centering torque is applied to control the steering wheel <NUM> so that the steering wheel <NUM> returns to the center position even if the back drive torque is applied. The centering torque is a torque that depends on the vehicle speed.

The steering angle φsteer (degree) and steering angular velocity ωsteer (rad/s) detected by the steering sensor <NUM>, and the speed Vveh (km/h) detected by the speed sensor <NUM> are inputted to the damping unit <NUM>. The damping unit <NUM> obtains a target value of a damping torque based on the inputted steering angle φsteer, steering angular velocity ωsteer, and speed Vveh. The damping torque is a force that generates a moderate amount of steering heaviness during abrupt steering. In other words, the damping torque is a torque that generates a moderate repulsive torque against the abrupt steering wheel operation, and acts as a brake for the steering wheel operation. The term "abrupt steering" means not only the operator's steering to the left or right, but also sudden return to the neutral position. The damping torque is also applied to the steering back to the neutral position. The damping torque is a torque that depends on the vehicle speed.

<FIG> and <FIG> are explanatory diagrams showing an example of torques outputted by the units <NUM> to <NUM>. In <FIG> and <FIG>, the horizontal axis indicates the steering angle φsteer (degree) of the steering wheel <NUM>, and the vertical axis indicates the target steering torque Tsteer ref. <FIG> and <FIG> also shows a load feeling output <NUM>, a centering output <NUM>, and a damping output <NUM>. In <FIG> and <FIG>, the outputs <NUM> to <NUM> at a vehicle speed of <NUM>/h are shown. The outputs <NUM> to <NUM> are prepared for each vehicle speed.

In <FIG>, the load feeling output <NUM> indicates the target value of the load feeling torque output by the load feeling unit <NUM>. The load feeling output <NUM> shows that as the steering angle of the steering wheel <NUM> increases, the load feeling torque also increases. It also shows that as the steering angle of the steering wheel <NUM> decreases, the load feeling torque also decreases. That is, it shows that the assist torque increases as the operator turns the steering wheel at a larger angle.

The centering output <NUM> shows that the centering torque is increased when the load torque is small. This is because when the load torque is small, for example, when the steering angle is small, steering is easily affected by the back drive torque. This means that the steering wheel is more easily to return to the center position when the operator turns back the steering wheel.

The damping output <NUM> shows that a large torque is outputted when the steering angle is small. That is, it indicates that when an abrupt steering is performed by the operator at the start of steering, a repulsive torque makes the steering heavy. It also shows that when returning to the center position, the repulsive torque is generated causes the steering to gently move to the center position.

<FIG> is an explanatory diagram showing torque characteristics of resistance (steering heaviness) dependent on the steering angular velocity. In <FIG>, the horizontal axis indicates the steering angular velocity, and the vertical axis indicates a coefficient related to damping. As shown in <FIG>, the coefficient related to damping increases as the steering angular velocity increases, that is, the damping torque increases. In this way, when the steering wheel <NUM> is abruptly turned, it is configured to generate an appropriate amount of steering heaviness.

<FIG> is an explanatory diagram showing torque characteristics of brake when returning to the center position through the centering torque (slow return to the center position). In <FIG>, the horizontal axis indicates the steering angle, and the vertical axis indicates a coefficient related to damping. As shown in <FIG>, the damping torque shows that as the steering angle of the steering wheel <NUM> approaches <NUM>°, the coefficient related to damping increases, i.e., it generates a force in the opposite direction to that of the centering torque.

<FIG> shows a combined output of the outputs <NUM>-<NUM> of <FIG>. In <FIG>, output <NUM> shows a detected value of the steering torque by a sensor. The value shows a result of the control. Combined output <NUM> indicates the target steering torque Tsteer ref, which is the combined output of the outputs <NUM> to <NUM>. The feeling control unit <NUM> outputs, to the steering control unit <NUM>, the target steering torque Tsteer ref obtained for the current vehicle speed.

Referring again to <FIG>, the steering control unit <NUM> will be now described. The steering control unit <NUM> includes a second estimation unit <NUM> and an assist unit <NUM>. The steering angular velocity ωsteer (rad/s) and steering torque Tsteer (Nm) detected by the steering sensor <NUM> and the motor angular velocity ωmot (rad/s) detected by the motor sensor <NUM> are inputted to the second estimation unit <NUM>.

The second estimation unit <NUM> calculates various estimated values based on the inputted steering angular velocity ωsteer, steering torque Tsteer, and motor angular velocity ωmot. The various estimated values to be calculated include a value of the estimated steering torque Toperator est pertaining to the operator and a value of the estimated load torque Tload est. The second estimation unit <NUM> outputs the various estimated values to the assist unit <NUM>. The calculation (operation) of the various estimated values is described later.

The target steering torque Tsteer ref outputted by the feeling control unit <NUM> and the various estimated values outputted by the second estimation unit <NUM> are inputted to the assist unit <NUM>. The assist unit <NUM> calculates a target motor torque Tmot ref based on the inputted target steering torque Tsteer ref and various estimated values. The assist unit <NUM> outputs the calculated target motor torque Tmot ref to the motor control unit <NUM>. The motor control unit <NUM> causes the motor <NUM> to rotate at the target motor torque Tmot ref.

Calculations performed by the steering control unit <NUM> are described. An electric portion of a physically equivalent linear model actuator reduced with two degrees of freedom may be expressed as a first-order element in a differential equation by the formula (<NUM>).

In Formula <NUM>, τcc is a current control loop, Tmot ref is the target motor torque, and Tmot is the resulting motor torque. A simplified dynamic behavior of a torque-controlled electric motor can be approximated by this formula. To describe mechanical components mathematically, the rotating masses of the systems belonging to the same degree of freedom needs to be reduced to a single mass on the motor side. The mechanical components can be represented by equations of motion expressed by Formulas <NUM> to <NUM>.

In Formula <NUM>, jsteer is inertia (moment of inertia) of the steering wheel <NUM> and bsteer is damping of the steering wheel <NUM>.

In Formula <NUM>, ctb is a linearized torsion bar stiffness of a steering column, ipnion is a gear ratio from the steering wheel to the pitman arm <NUM> (pinion gear ratio), irv,gear is a gear ratio from the motor <NUM> to the pitman arm <NUM> (gear ratio of the speed reducer <NUM>), and btb is a torsion bar damping.

In Formula <NUM>, jred is a moment of inertia converted in terms of the motor shaft, and bred is a damping converted in terms of the motor shaft.

By using the above Formulas <NUM> to <NUM>, the steering control unit <NUM> can calculate an appropriate assist torque (target motor torque Tmot ref) with which the input steering results in the target steering torque.

Here, in general, a steering torque required for the input steering differs depending on driving conditions, road surface reaction force, and other factors. The steering feeling is determined by characteristics mainly based on the steering torque. Therefore, in order to facilitate adjustment of the steering feeling, it is desired to be able to control the steering at a predetermined steering torque Tsteer. By designing a controller (Linear Quadratic Gaussian (LQG)) from the above formulas that take into account the torque applied to the pitman arm <NUM> when calculating the target motor torque Tmot ref, it is possible to realize the target steering torque Tsteer ref set for the specified steering even when the driving conditions or road surface conditions change.

The calculation of the load torque (estimated load torque Tload est) on the pitman arm <NUM> will be now described. For safety reasons, the operator usually drives while he/she feels the road surface conditions with the force returned to the steering wheel <NUM> that he/she operates. However, in the embodiment, the road surface reaction force is not transmitted to the operator due to the use of the speed reducer <NUM>. Thus, it is necessary to configure the first estimator <NUM> to estimate the load torque (reaction force from the road surface) on the pitman arm <NUM> and return it such that the drive can feel the road reaction force. The road reaction force is the load torque applied to the pitman arm <NUM>, but it is not a load directly applied by the road surface, but rather a load applied to the pitman arm <NUM> via the tires and drag rings. In typical electric power steering systems, there are no sensors to measure the road reaction force.

The estimation function of the embodiment is capable of estimating the reaction force from the road surface regardless of vehicle conditions (vehicle specifications, road surface conditions (inclination, road friction), etc.). The estimation function is implemented by an estimator (linear quadratic estimation (LQE)) designed with a Kalman filter based on Formulas <NUM> to <NUM>. The estimation by the first estimator <NUM> can accurately estimate the torque applied to the pitman arm <NUM> by compensating for the characteristics of the speed reducer <NUM>. The first estimation unit <NUM> may calculate the estimated load torque Tload est based on Formulas <NUM> to <NUM>. Since the pitman arm <NUM> is integrated with the output portion (case or shaft) of the speed reducer <NUM>, it is possible to estimate the torque accurately.

Compensation for the characteristics of the speed reducer <NUM> will be now described. The first estimation unit <NUM> compensates for the characteristics of the speed reducer <NUM> in the estimated load torque Tload est. This makes it possible to accurately estimate the torque applied to the pitman arm <NUM>.

Note that the control of the feeling control unit <NUM> compensates for the characteristics of the speed reducer <NUM>, while the control of the steering control unit <NUM> does not compensate for the characteristics of the speed reducer <NUM> in the embodiment. LQG is an equation using the load torque with the speed reducer friction as input. Therefore, the estimated Tload est is the load torque including the friction torque. As for the torque outputted from the motor <NUM>, it is necessary to instruct a motor torque corresponding to this load torque including the friction torque. That is, if the characteristics of the speed reducer <NUM> are compensated by the steering control unit <NUM>, the outputted motor torque will become insufficient. On the other hand, for the estimation performed by the load feeling unit <NUM>, it is necessary to know the more accurate load torque, i.e., the torque applied to the pitman arm <NUM> excluding the frictional torque of the speed reducer <NUM>, in order to put the external force into the steering feeling. For this reason, the control of the feeling control unit <NUM> compensates for the characteristics of the speed reducer <NUM>, while the control of the steering control unit <NUM> does not compensates for the characteristics of the speed reducer <NUM> in the embodiment.

The friction of the speed reducer <NUM> is calculated differently depending on the motor angular velocity ωmot. The friction of the speed reducer <NUM> can be obtained using the motor angular velocity ωmot and the motor torque Tmot. The detected values of the speed reducers <NUM> may be for a viscous friction coefficient (see <FIG>) for calculating the friction, and a load torque map (see <FIG>).

<FIG> is an explanatory diagram showing an example of a load torque map <NUM>. The load torque map <NUM> is a map that shows how much torque is required for the motor torque Tmot in relation to the friction of the speed reducer <NUM>. Specifically, as shown in <FIG>, the load torque map <NUM> is a map in which the horizontal axis indicates the motor torque Tmot and the vertical axis indicates a loss torque in static and dynamic friction. As shown in the load torque map <NUM>, there is a proportional relationship between the motor torque Tmot and the loss torque of the static and dynamic friction.

<FIG> is an explanatory diagram showing an example of a friction characteristic map <NUM>. The friction characteristic map <NUM> is a map that represents the friction characteristics of the speed reducer <NUM> in relation to the angular velocity of the pitman arm <NUM>. Specifically, as shown in <FIG>, the friction characteristic map <NUM> is the map in which the horizontal axis indicates the angular velocity [rpm] of the pitman arm <NUM> and the vertical axis indicates the viscous friction coefficient [Nms/rad]. As shown in the friction characteristic map <NUM>, the angular velocity of the pitman arm <NUM> is proportional to the viscous friction coefficient except for the angular velocity of the pitman arm <NUM> is at a specific angular velocity (e.g., "<NUM>"). When the angular velocity of the pitman arm <NUM> is the specific angular velocity (e.g., "<NUM>"), the viscous friction coefficient can take multiple values. The motor angular velocity ωmot can be obtained by multiplying the angular velocity of the pitman arm <NUM> by a predetermined speed ratio.

Compensation for the friction (load torque) of the speed reducer <NUM> is calculated differently depending on the states. For example, when the motor angular velocity ωmot is "<NUM>" and the friction of the speed reducer <NUM> is greater than the external load torque, an external load torque Text is used as a friction Tfr of the speed reducer <NUM>. When the motor angular velocity is "<NUM>" and the friction of the speed reducer <NUM> is less than the external load torque, the friction Tfr of the speed reducer <NUM> is calculated from the load torque map <NUM> and the viscous friction coefficient. In this case, the direction of the force is the direction of the external load torque. When the motor angular velocity is not "<NUM>", the friction Tfr of the speed reducer <NUM> is calculated from the load torque map <NUM> and the viscous friction coefficient. In this case, the direction of the force is the direction of rotation of the motor <NUM>.

Formula <NUM> expresses a formula for calculating the friction.

In Formula <NUM>, the first line represents a static friction torque when the friction torque and the external torque (without friction) are statically balanced. When the external torque is less than the static friction torque, sticking occurs at an angular velocity of "<NUM>". The second line of Formula <NUM> represents a frictional torque at the moment of breakaway when the external torque exceeds the static frictional torque. The third line represents a frictional torque calculated using the static frictional torque and the viscous friction dependent on the angular velocity. The friction characteristics in relation to the angular velocity can be obtained by using these equations.

By subtracting the friction Tfr from the estimated load torque Tload est, the first estimator <NUM> can obtain an estimated load torque Tload est that compensates for the characteristics of the speed reducer <NUM>.

As discussed above, the steering unit device <NUM> in the embodiment estimates the target steering torque Tsteer ref based on the estimated load torque Tload est corresponding to the road reaction force, and controls the rotation of the motor <NUM> to provide the estimated target steering torque Tsteer ref. This allows the motor <NUM> to rotate at the target motor torque Tmot ref that corresponds to the reaction force from the road surface. Therefore, the operator can drive with a desired steering torque regardless of the road surface conditions because the steering can be assisted with an appropriate assist torque. Consequently, the steering unit device <NUM> of the embodiment can convey the road reaction force correctly to the operator even when the friction of the speed reducer <NUM> is large, and it is possible to provide an excellent steering feel to the operator.

In the embodiment, the feeling control unit <NUM> calculates the estimated load torque Tload est based on the steering torque Tsteer and steering angular velocity ωsteer detected by the steering sensor <NUM> and the motor torque Tmot. This makes it possible to easily calculate the estimated load torque Tload est and thus easily obtain the target motor torque Tmot ref.

The steering control unit <NUM> is able to easily calculate the target motor torque Tmot ref based on the target steering torque Tsteer ref, the steering torque Tsteer, the steering angular velocity ωsteer, and the motor angular velocity ωmot.

The estimated load torque Tload est is the torque applied onto the pitman arm <NUM>. Therefore, a more accurate estimated load torque Tload est can be obtained, which allows driving with more accurate steering torque.

In the embodiment, the feeling control unit <NUM> calculates the target steering torque Tsteer ref based on the load feeling torque, centering torque, and damping torque. Thus, the steering unit device <NUM> that allows easier steering can be provided.

In the embodiment, the feeling control unit <NUM> calculates the estimated load torque Tload est, to which the compensation operation for the friction of the speed reducer <NUM> has been made. This can reduce discomfort of the steering caused by the friction of the speed reducer <NUM>.

Modification examples of the embodiment will be now described below. In each of the following modification examples, description of the same components as the above-described embodiment will not be repeated. The following modification examples and the above-described embodiment may be combined adequately.

In a modification example, the steering unit device <NUM> has an angle detection unit <NUM> (see <FIG>) that detects the rotation angle of the pitman arm <NUM>. The angle detection unit <NUM> that detects the rotation angle of the pitman arm <NUM> is disposed between the pitman arm <NUM> and the motor <NUM>. The angle detection unit <NUM> is disposed, for example, on one side of the fixed member <NUM> facing the speed reducer <NUM>.

For example, the angle detection unit <NUM> is formed to extend in an arc shape along the circumferential direction of the output portion <NUM>, viewed from the other surface <NUM> of the speed reducer <NUM> along the central axis (z-axis). The angle detection unit <NUM> is, for example, a magnetic sensor and detects the position of the output portion <NUM> of the pitman arm <NUM> in the circumferential direction based on variation in the magnetic field that changes depending on the position of the metal pitman arm <NUM>.

This configuration allows the steering unit device <NUM> to perform the control in which the detection value of the rotation angle of the pitman arm <NUM>, which has been detected by the angle detection unit <NUM>, is compared with the command signal of the rotation angle of the motor <NUM> dependent on the rotation angle of the pitman arm <NUM> and the deviation indicating the result of the comparison is set to zero.

In another modification example, the rotation angle of the pitman arm <NUM> detected by the angle detection unit <NUM> may be used instead of or in addition to the steering angle provided by the steering sensor <NUM>. The rotation angle of the pitman arm <NUM> may be corrected to be consistent with the steering angle outputted by the steering sensor <NUM>. The rotation angle of the pitman arm <NUM> may be used by the centering unit <NUM> and the damping unit <NUM> to obtain respective values.

Specifically, the centering unit <NUM> may obtain a target value of the centering torque based on the steering angle detected by the angle detection unit <NUM>, the steering torque detected by the steering sensor <NUM>, and the speed detected by the speed sensor <NUM>. The damping unit <NUM> may obtain a target value of the damping torque based on the steering angle detected by the angle detection unit <NUM>, the steering angular velocity detected by the angle detection unit <NUM>, and the speed detected by the speed sensor <NUM>.

In this way, the invention can be applied to the speed reducer <NUM> equipped with the angle detection unit <NUM>. The steering unit device <NUM> of the modification examples can also assist steering with an appropriate assist torque, so that the operator can drive with a predetermined steering torque regardless of road conditions.

In the embodiments described above, each control unit (the motor control unit <NUM>, the steering control unit <NUM>, the feeling control unit <NUM>) and the functional units in each control unit (the first estimation unit <NUM>, the load feeling unit <NUM>, the centering unit <NUM>, the damping unit <NUM>, the second estimation unit <NUM>, the assist unit <NUM>) are provided in a single computer device. However, they may be provided in other computer devices. For example, they may be provided on an external server. In addition, the number of the computer device in which these units are provided is not limited to one, but may be two or more. Specifically, for example, some of these functional units may be provided in one computer device and other functional units may be provided in other computer device(s).

Claim 1:
A column assist steering device, comprising:
a steering member (<NUM>) steered by an operator;
a drive unit (<NUM>) rotating for imparting an auxiliary force to the steering member (<NUM>);
a first control unit (<NUM>) calculating a load torque that corresponds to a reaction force from a road surface, the load torque being estimated based on a value measured in the steering member (<NUM>) and the drive unit (<NUM>), the first control unit (<NUM>) also calculating a target steering torque for the steering member (<NUM>) based on the calculated load torque; and
a second control unit (<NUM>) calculating the auxiliary force of the drive unit (<NUM>) to achieve the target steering torque calculated by the first control unit (<NUM>),
wherein the first control unit (<NUM>) calculates a steering torque that corresponds to the reaction force based on the load torque and a vehicle speed, calculates a restoring torque that returns the steering member (<NUM>) to its neutral position and a damping torque that controls abrupt steering of the steering member (<NUM>) based on the vehicle speed, and calculates the target steering torque based on the calculated torques,
characterized in that
the first control unit (<NUM>) calculates the load torque on which an operation of compensating for a friction of a speed reducer (<NUM>) has been performed.