Patent Description:
As the techniques for enhancing the steerability of vehicles, techniques for driving each of a pair of left and right driving wheels independently of each other have hitherto been studied. Examples of techniques of this kind include the technique described in Patent Document <NUM> cited below.

Patent Document <NUM> describes a vehicle steering device. In this vehicle steering device, left and right operating handles are attached to the body of a vehicle such that they can be rotated independently of each other. When the left and right operating handles are rotated in the same rotation direction as each other, a turning device is controlled according to a first rotation angle. When the left and right operating handles are rotated in opposite rotation directions to each other, the forward movement, the backward movement, and the traveling speed of a traveling device are controlled according to a second rotation angle.

For such a traveling vehicle, proportional-integral (PI) control is used to control the current flowing through a motor. Since PI control is known, a detailed description thereof is omitted. In PI control, control is performed using "proportional action" and "integral action" in combination. Examples of the technique for controlling the driving of a vehicle using PID control, which is an extension of such PI control, include the technique described in Patent Document <NUM> cited below.

Patent Document <NUM> describes a vehicle control apparatus (hereinafter referred to as "control apparatus") that uses PID control to control the currents of motors for driving the wheels of a vehicle. To enable stabilization of the behavior of the vehicle even when steering is unsteady, the control apparatus includes an integral term correction gain calculation portion that calculates an integral term correction gain for correcting the output of an integral term in the PID control, based on a steering angle calculated from a yaw rate that can be determined from the curvature of a traveling path and the vehicle speed, and a steered steering angle over which the driver performed steering. In particular, the integral term correction gain is calculated based on a derivation value obtained by determining a time derivative of the result of comparing the steering angle calculated from the yaw rate with the steered steering angle, and is configured such that the larger the derivation value is, the smaller the integral term correction gain is.

In the technique described in Patent Document <NUM>, whether an input to the operating handles is slow steering or rapid steering is determined by comparing the left and right steering angles with preset fixed first and second reference steering angles. Specifically, when the steering angle input to the operating handles is smaller than the first reference steering angle, the rotation speed of the electric motor located on the inner side of a turn is controlled to be reduced by a certain value, thus turning the vehicle inward in the turning direction. On the other hand, when the steering angle input to the operating handles falls within a range from the first reference steering angle to the second reference steering angle, the electric motor located on the inner side of a turn is stopped, and thus the vehicle can readily turn inward in the turning direction. Furthermore, when the steering angle input to the operating handles is larger than the second reference steering angle, control is performed to counter-rotate the electric motor located on the inner side of a turn, and thus the vehicle rapidly turns inward in the turning direction.

For example, when turning the vehicle on the spot by rotating the pair of left and right driving wheels in opposite directions to each other, the operation handles are operated irrespective of the movement of the vehicle body, without being subjected to any reaction force from mechanisms such as a transmission, a speed reducer, and an engine. Accordingly, there is a possibility that the turning operation will be input over-sensitively. Therefore, there is also the possibility that the speed of the vehicle cannot be appropriately controlled.

Some traveling vehicles can travel with a tight turning radius such that the vehicle is turned on the spot by rotating one of a pair of left and right motors, while stopping the other motor. At that time, the operating lever through which an operating instruction is given to the one motor receives many low speed instructions in the neighborhood of zero speed. In such a case, according to the technique described in Patent Document <NUM>, when the integral term correction gain is set based on a derivation value obtained by determining a time derivative of the result of comparing the steering angle calculated from a yaw rate with the steered steering angle, there is the possibility of the driving wheels being locked at the zero speed (including an extremely low speed), thus forming unwanted marks in the ground surface.

Therefore, there is a need for a traveling control device capable of appropriately turning a traveling vehicle.

A characteristic feature of a traveling control device according to an embodiment of the present invention, defined in claim <NUM>, lies in a traveling control device of a traveling vehicle including a traveling control unit having a pair of left and right configurations capable of respectively driving a pair of left and right driving wheels, the traveling control device including: an instruction receiving portion configured to receive an operation instruction directed to each of the pair of left and right driving wheels; a speed instruction value calculation portion configured to calculate a speed instruction value that is to be instructed to the traveling control unit, based on each of the operation instructions; an operation instruction determination portion configured to determine, based on each of the operation instructions, whether the operation instruction is an operation instruction to rotate the pair of left and right driving wheels in the same direction as each other, or an operation instruction to rotate the pair of left and right driving wheels in different directions from each other; and a speed instruction value correction portion configured to correct, if the operation instruction is an operation instruction to rotate the pair of left and right driving wheels in the same direction as each other, one of the speed instruction values calculated for the traveling control unit by the speed instruction value calculation portion, based on the other speed instruction value.

With such a characteristic feature, it is possible to reduce the turning speed, and improve the ability to travel straight ahead. Furthermore, it is possible to prevent a reduction in the maximum speed of the traveling vehicle despite the turning speed being attenuated. Therefore, with the traveling control device according to the present invention, it is possible to appropriately turn the traveling vehicle, and appropriately control the speed of the traveling vehicle.

The speed instruction value correction portion is configured to correct the larger one of the speed instruction values calculated for the traveling control unit by the speed instruction value calculation portion, based on the smaller speed instruction value.

With such a configuration, it is possible to reduce over-sensitive turning through simple calculation performed with software. Therefore, it is not necessary to separately provide any mechanism for reducing over-sensitive turning, thus making it possible to realize a traveling control device at a low cost.

It is preferable that the speed instruction value correction portion be configured to correct, if the operation instruction is an operation instruction to rotate the pair of left and right driving wheels in different directions from each other, each of the speed instruction values calculated for the traveling control unit by the speed instruction value calculation portion, based on a preset common attenuation value.

With such a configuration, it is also possible to attenuate the over-sensitive turning when rotating the traveling vehicle on the spot.

A characteristic feature of a traveling control device according to an embodiment of the present invention lies in a traveling control device of a traveling vehicle capable of driving each of a pair of left and right driving wheels, the traveling control device including: a pair of left and right motors configured respectively to drive the pair of left and right driving wheels, and a current that is passed therethrough is controlled by PI control; an instruction receiving portion configured to receive an operation instruction directed to each of the pair of left and right motors; an operation instruction determination portion configured to determine whether each of the operation instructions is an acceleration instruction or a deceleration instruction directed to the corresponding motor; a speed control portion that, if the operation instruction is an acceleration instruction, is configured to set an integral gain in the PI control to a preset first value, and is configured to set a proportional gain in the PI control to a preset second value when a rotation speed of each of the motors becomes greater than or equal to a preset first threshold, if the operation instruction is a deceleration instruction, is configured to set the integral gain to zero, and is configured to set the proportional gain to a preset third value when the rotation speed of the motor becomes less than a preset second threshold that is smaller than the first threshold; and a motor driving portion configured to drive the motors, based on the integral gain and the proportional gain set by the speed control portion.

With such a characteristic feature, if the operation instruction is a deceleration instruction, the integral gain becomes zero when a predetermined condition is satisfied. Accordingly, the designation (operation instruction) and the actual operation are separated from each other when the driving wheel is affected by a disturbance. For example, when the right driving wheel is driven at the maximum speed, and an extreme low speed instruction is input to the left driving wheel, the left driving wheel will follow the movements of the right driving wheel and the vehicle body, and be rotated by more than the instructed amount, thus being kept from forming unwanted marks in the ground surface. Therefore, with the traveling control device according to the present invention, it is possible to suppress the formation of unwanted marks in the ground surface during traveling.

It is preferable that switching of each of the integral gain and the proportional gain has a hysteresis.

With such a configuration, it is possible to prevent an erroneous operation in the neighborhood of thresholds (the first threshold and the second threshold) of the rotation speed.

It is preferable that, when a vehicle speed of the traveling vehicle is less than a preset value, if the operation instruction is a deceleration instruction, the motor driving portion is configured to drive the corresponding motor by a torque control in accordance with an output torque of the motor instead of driving the motor in accordance with the rotation speed, even when the rotation speed of the motor is less than the second threshold.

With such a configuration, for example, even in a situation where the ground surface on which the traveling vehicle travels is slippery and the driving wheels slip, it is possible to prevent slipping by using the torque control, thus making it possible to prevent formation of unwanted marks in the ground surface.

A traveling control device according to the present invention is configured to appropriately turn a traveling vehicle, and to appropriately control the speed of the traveling vehicle. Hereinafter, a traveling control device <NUM> according to the present embodiment will be described. The traveling control device <NUM> is installed in a traveling vehicle that includes a traveling control unit <NUM> that has a pair of left and right configurations capable of respectively driving a pair of left and right driving wheels <NUM> (see <FIG>).

<FIG> shows a perspective view of an electric riding lawn mower, which is an example of the traveling vehicle in which the traveling control device <NUM> according to the present embodiment is installed. <FIG> shows an electric system diagram and a power system diagram. As shown in <FIG> and <FIG>, the electric riding lawn mower includes a vehicle body <NUM> supported by caster wheels <NUM>, which are front wheels, and driving wheels <NUM>, which are rear wheels, a battery <NUM> disposed at the rear of the vehicle body <NUM>, a driver's seat <NUM> disposed forward of the battery <NUM>, a fall protection frame <NUM> provided standing upright from behind the driver's seat <NUM>, and a mower unit <NUM> suspended between the caster wheels <NUM> and the driving wheels <NUM> from the vehicle body <NUM> such that the mower unit <NUM> can be raised and lowered via an elevation link mechanism from and to the space below the vehicle body <NUM>. The driving wheels <NUM> are driven by the traveling control unit <NUM>, the operations of which are controlled by the traveling control device <NUM>, and the operations of the mower unit <NUM> are controlled by a mower control device <NUM>. Here, the caster wheels <NUM> include a left caster wheel 4a and a right caster wheel 4b, and the driving wheels <NUM> include a left driving wheel 2a and a right driving wheel 2b.

A floor plate, which is a footrest for the driver, is provided forward of the driver's seat <NUM>, and a brake pedal <NUM> protrudes from the floor plate. A left steering lever 6a and a right steering lever 6b are disposed on opposite sides of the driver's seat <NUM>. Additionally, an electric operation panel <NUM> including a switch button, a switch lever, and the like of an electric control system is provided laterally to the driver's seat <NUM>. A mower switch for starting the mower unit <NUM> is also disposed on the electric operation panel <NUM>. Note that the left steering lever 6a and the right steering lever 6b are described as a steering lever <NUM> when there is no particular need to distinguish between them.

In the present embodiment, the left driving wheel 2a and the right driving wheel 2b respectively use the rotational force from a left motor <NUM> and a right motor <NUM>, which are in-wheel motors, as their power sources. Power is supplied to the left motor <NUM> via a left power feeding portion <NUM> that is a constituent element of an inverter <NUM>, and power is supplied to the right motor <NUM> via a right power feeding portion <NUM> that is a constituent element of the inverter <NUM>. By changing the power supplied to each of the motors, it is possible to change at least one of the rotation speed and the torque. The rotation speeds (peripheral speeds) of the left driving wheel 2a and the right driving wheel 2b can be made different from each other, and the direction of the electric riding lawn mower is changed using the rotation speed difference between the left driving wheel 2a and the right driving wheel 2b.

The traveling control unit <NUM> is a functional portion that controls the traveling and the turning of the electric riding lawn mower, and, in the present embodiment, includes the left motor <NUM>, the right motor <NUM>, and the inverter <NUM> (in particular, the left power feeding portion <NUM> and the right power feeding portion <NUM>) described above. The inverter <NUM> supplies power to each of the left motor <NUM> and the right motor <NUM>. Although power that is output from the inverter <NUM> corresponds to a speed instruction value (target value) calculated by the traveling control device <NUM>, the power is modified to increase the motor output torque when the actual rotation speed (actual speed) has become smaller than the target value owing to the traveling load. On the other hand, when the actual rotation speed (actual speed) has become larger than the target value, for example, when on a downward slope or the like, the power is modified to decrease the motor output torque.

The mower unit <NUM> includes three rotary blades 131a, 131b, and 131c. The rotary blades 131a, 131b, and 131c respectively use mower motors 130a, 130b, and 130c as their driving sources. Power is supplied to the mower motors 130a, 130b, and 130c via a mower power feeding portion <NUM> that is a constituent element of the inverter <NUM>. The mower power feeding portion <NUM> is controlled by the mower control device <NUM>. The mower control device <NUM> and the traveling control device <NUM> described above together constitute a control apparatus <NUM>.

The operation amount (pivoting angle) of the left steering lever 6a is detected by a left steering angle detection sensor 80a, and the operation amount (pivoting angle) of the right steering lever 6b is detected by a right steering angle detection sensor 80b. The operating angle of the brake pedal <NUM> is detected by a brake detection sensor 80c, and operation of the mower switch is detected by a mower sensor 80d. The rotation speed of the left driving wheel 2a is detected by a left rear wheel rotation detection sensor 70a, and the rotation speed of the right driving wheel 2b is detected by a right rear wheel rotation detection sensor 70b. The rotation speeds of the mower motors 130a, 130b, and 130c are detected by rotation sensors 100a, 100b, and 100c. The detection results obtained by the sensors are transmitted to the control apparatus <NUM>, and are used by the traveling control device <NUM> and the mower control device <NUM> as needed.

In the traveling control device <NUM>, the target rotation speeds of the left driving wheel 2a and the right driving wheel 2b are calculated based on the operation amounts of the steering levers <NUM> detected by the left steering angle detection sensor 80a and the right steering angle detection sensor 80b. Furthermore, the amounts of power that are supplied to the left motor <NUM> and the right motor <NUM> are calculated from the respective target rotation speeds. Based on the power amounts, the traveling control device <NUM> drives the left motor <NUM> and the right motor <NUM>. Here, depending on the traveling conditions, the actual rotation speeds of the driving wheels <NUM> may not match the target rotation speeds that are controlled based on the operation amount of the steering levers <NUM>. In such a case, the traveling control device <NUM> uses a known feedback control to correct the above-described power amounts such that the actual rotation speeds of the driving wheels <NUM> match the target rotation speeds based on the operation amounts of the steering levers <NUM>. At this time, the traveling control device <NUM> calculates the required driving torque (hereinafter simply referred to as "required torque") requested for the left motor <NUM> and the right motor <NUM>. The required torque means the amount of torque requested for the left motor <NUM> or the right motor <NUM> in order to match the actual rotation speed to the target speed when the actual rotation speed has not reached the target rotation speed. The traveling control device <NUM> derives the required torque from the target rotation speeds of the left driving wheel 2a and the right driving wheel 2b based on the detection results obtained by the left steering angle detection sensor 80a and the right steering angle detection sensor 80b, and the actual rotation speeds of the left driving wheel 2a and the right driving wheel 2b obtained by the left rear wheel rotation detection sensor 70a and the right rear wheel rotation detection sensor 70b. Then, based on the calculated required torque, the traveling control device <NUM> corrects the power amounts.

<FIG> is a block diagram schematically showing a configuration of the traveling control device <NUM>. As shown in <FIG>, the traveling control device <NUM> includes various functional portions, namely, an instruction receiving portion <NUM>, a speed instruction value calculation portion <NUM>, an operation instruction determination portion <NUM>, a speed instruction value correction portion <NUM>, and a traveling control portion <NUM>. Each of these functional portions is constructed by hardware or software, or both hardware and software, with a CPU serving as the core member, in order to execute processes relating to the traveling and the turning of the electric riding lawn mower. Note that <FIG> also shows the left steering lever 6a, the right steering lever 6b, the traveling control unit <NUM>, the left driving wheel 2a, and the right driving wheel 2b described above, in addition to the traveling control device <NUM>.

The instruction receiving portion <NUM> receives an operation instruction directed to each of the pair of left and right driving wheels <NUM>. The pair of left and right driving wheels <NUM> are the left driving wheel 2a and the right driving wheel 2b. The operation instruction directed to each of the pair of left and right driving wheels <NUM> is an instruction including a rotation direction and a rotation speed that are requested for each of the left driving wheel 2a and the right driving wheel 2b. The operation instruction directed to the left driving wheel 2a is input through the left steering lever 6a, and the operation instruction directed to the right driving wheel 2b is input through the right steering lever 6b. The operation instruction directed to the left driving wheel 2a corresponds to a detection result obtained by the left steering angle detection sensor 80a (hereinafter, see <FIG> for all cases), and the operation instruction directed to the right driving wheel 2b corresponds to a detection result obtained by the right steering angle detection sensor 80b (hereinafter, see <FIG> for all cases). Accordingly, the instruction receiving portion <NUM> receives the operation instruction directed to the left driving wheel 2a via the left steering angle detection sensor 80a, and receives the operation instruction directed to the right driving wheel 2b via the right steering angle detection sensor 80b. The operation instructions received by the instruction receiving portion <NUM> are transmitted to the speed instruction value calculation portion <NUM> and the operation instruction determination portion <NUM>, which will be described below.

The speed instruction value calculation portion <NUM> calculates a speed instruction value that is instructed to the traveling control unit <NUM>, based on each of the operation instructions. As described above, the operation instructions are transmitted from the instruction receiving portion <NUM>. The traveling control unit <NUM> includes the inverter <NUM>, the left motor <NUM>, and the right motor <NUM>, and controls the traveling and the turning of the electric riding lawn mower. Here, an operation instruction is an instruction including a rotation direction and a rotation speed that are requested for each of the left driving wheel 2a and the right driving wheel 2b. A speed instruction value is an instruction value of the rotation speed requested for each of the left motor <NUM> and the right motor <NUM> in order for each of the left driving wheel 2a and the right driving wheel 2b to achieve the rotation direction and the rotation speed, which constitute the operation instruction. Accordingly, the speed instruction value calculation portion <NUM> calculates the respective rotation speeds of the left motor <NUM> and the right motor <NUM> that enable the left driving wheel 2a and the right driving wheel 2b to achieve the respective rotation directions and rotation speeds requested as the operation instructions. The calculation result obtained by the speed instruction value calculation portion <NUM> is transmitted to the speed instruction value correction portion <NUM>, which will be described below.

The operation instruction determination portion <NUM> determines, based on each of the operation instructions, whether the operation instruction is an operation instruction to rotate the pair of left and right driving wheels <NUM> in the same direction as each other, or an operation instruction to rotate the pair of left and right driving wheels <NUM> in different directions from each other.

Here, in the present embodiment, when the left steering lever 6a is tilted in a forward direction relative to its position in the neutral state, the left motor <NUM> is rotated such that the left driving wheel 2a causes the electric riding lawn mower to travel in the forward direction. Similarly, when the left steering lever 6a is tilted in a backward direction relative to its position in the neutral state, the left motor <NUM> is rotated such that the left driving wheel 2a causes the electric riding lawn mower to travel in the backward direction. When the right steering lever 6b is tilted in a forward direction relative to its position in the neutral state, the right motor <NUM> is rotated such that the right driving wheel 2b causes the electric riding lawn mower to travel in the forward direction. When the right steering lever 6b is tilted in a backward direction relative to its position in the neutral state, the right motor <NUM> is rotated such that the right driving wheel 2b causes the electric riding lawn mower to travel in the backward direction. The left steering lever 6a and the right steering lever 6b are configured not to rotate the left motor <NUM> and the right motor <NUM>, respectively, when the left steering lever 6a and the right steering lever 6b are in the neutral state. The left steering lever 6a and the right steering lever 6b can be tilted in different directions from each other relative to their positions in the neutral state. In this case, the electric riding lawn mower can be turned (rotated) on the spot.

The operation instructions are transmitted to the operation instruction determination portion <NUM> from the instruction receiving portion <NUM>. An operation instruction is an instruction including a rotation direction and a rotation speed requested for each of the left driving wheel 2a and the right driving wheel 2b. The operation instruction determination portion <NUM> determines whether the rotation direction requested for the left driving wheel 2a and the rotation direction requested for the right driving wheel 2b are the same rotation direction as each other, or different directions from each other. The determination result obtained by the operation instruction determination portion <NUM> is transmitted to the speed instruction value correction portion <NUM>, which will be described below.

If the operation instruction is an operation instruction to rotate the pair of left and right driving wheels <NUM> in the same direction as each other, the speed instruction value correction portion <NUM> corrects one of the speed instruction values calculated for the traveling control unit <NUM> by the speed instruction value calculation portion <NUM>, based on the other speed instruction value. Whether "the operation instruction is an operation instruction to rotate the pair of left and right driving wheels <NUM> in the same direction as each other" is specified from the determination result transmitted from the operation instruction determination portion <NUM>. "The speed instruction values calculated for the traveling control unit <NUM> by the speed instruction value calculation portion <NUM>" are the respective rotation speeds of the left motor <NUM> and the right motor <NUM> that respectively enable the left driving wheel 2a and the right driving wheel 2b to achieve the respective rotation directions and rotation speeds requested as the operation instructions, and they are transmitted from the speed instruction value calculation portion <NUM>. "One of the speed instruction values" is a speed instruction value requested for one of the left motor <NUM> and the right motor <NUM>, and "the other speed instruction value" is a speed instruction value requested for the other of the left motor <NUM> and the right motor <NUM>.

In the present embodiment, if the operation instruction is an operation instruction to rotate the pair of left and right driving wheels <NUM> in the same direction as each other, the speed instruction value correction portion <NUM> corrects the larger one of the speed instruction values calculated for the traveling control unit <NUM> by the speed instruction value calculation portion <NUM>, based on the smaller speed instruction value.

Specifically, the speed instruction value correction portion <NUM> corrects the speed instruction value in the following manner. First, a turning component is extracted from the speed instruction value requested for the left motor <NUM> and the speed instruction value requested for the right motor <NUM>. A turning component is a value obtained by subtracting the smaller one of the speed instruction values from the larger speed instruction value.

The smaller speed instruction value is directly used as the speed instruction value. For the larger speed instruction value, the sum of the smaller speed instruction value and the product of the above-described turning component and a preset attenuation value is used as the speed instruction value. The preset attenuation value is a value corresponding to a gain, and it is possible to attenuate only the turning component by setting the attenuation value to a value smaller than <NUM>.

If the operation instruction is an operation instruction to rotate the pair of left and right driving wheels <NUM> in different directions from each other, the speed instruction value correction portion <NUM> corrects each of the speed instruction values calculated for the traveling control unit <NUM> by the speed instruction value calculation portion <NUM>, based on a preset common attenuation value. Whether "the operation instruction is an operation instruction to rotate the pair of left and right driving wheels <NUM> in different directions from each other" is specified from the determination result transmitted from the operation instruction determination portion <NUM>. The "preset common attenuation value" corresponds to the above-described gain.

Thus, the speed instruction value correction portion <NUM> corrects the speed instruction value calculated by the speed instruction value calculation portion <NUM> and requested for the left motor <NUM> to the product of that speed instruction value and the above-described gain if the directions in which the left steering lever 6a and the right steering lever 6b are tilted relative to their positions in the neutral state are different from each other, and corrects the speed instruction value calculated by the speed instruction value calculation portion <NUM> and requested for the right motor <NUM> to the product of that speed instruction value and the above-described gain. The speed instruction value corrected by the instruction value correction portion <NUM> is transmitted to the traveling control portion <NUM>, which will be described below.

The traveling control portion <NUM> supplies power to the left power feeding portion <NUM> and the right power feeding portion <NUM> that are constituent elements of the inverter <NUM>, based on the speed instruction value corrected by the speed instruction value correction portion <NUM>. Accordingly, rotation of the left motor <NUM> and the right motor <NUM> is controlled, and the left driving wheel 2a and the right driving wheel 2b are rotated, thus enabling traveling and turning of the electric riding lawn mower. The traveling control portion <NUM> uses a known feedback control to control rotation of the left driving wheel 2a and the right driving wheel 2b. That is, the traveling control portion <NUM> calculates the rotation speed (torque) of the left driving wheel 2a, i.e., the rotation speed (torque) of the left motor <NUM>, based on a detection result obtained by the left steering angle detection sensor 80a, calculates the rotation speed (torque) of the right driving wheel 2b, i.e., the rotation speed (torque) of the right motor <NUM>, based on a detection result obtained by the right steering angle detection sensor 80b, and calculates the power amount based on these rotation speeds (torques). For this calculation, it is preferable to use a table or a function representing the relationship between the operation position and the rotation speed. Based on the power amount calculated in this manner and the speed instruction value corrected by the speed instruction value correction portion <NUM>, rotation of the left driving wheel 2a and the right driving wheel 2b is controlled.

When the tread of the electric riding lawn mower is smaller than the wheel base, the gain for the turning instruction increases, and the electric riding lawn mower turns excessively. However, with the traveling control device <NUM> described above, it is possible to attenuate only the turning component, and, therefore, over-sensitive turning due to the mechanism of the electric riding lawn mower can be reduced using software. Accordingly, it is possible to reduce the turning speed, and improve the ability of the electric riding lawn mower to travel straight ahead. Furthermore, it is possible to prevent attenuation of the maximum speed of the electric riding lawn mower despite the turning component being attenuated.

<FIG> is a block diagram schematically showing a configuration of the traveling control device <NUM>. As shown in <FIG>, the traveling control device <NUM> includes various functional portions, namely, motors <NUM>, an instruction receiving portion <NUM>, an operation instruction determination portion <NUM>, a speed control portion <NUM>, and a motor driving portion <NUM>. Each of these functional portions is constructed by hardware or software, or both hardware and software, with a CPU serving as the core member, in order to execute processes relating to the traveling and the turning of the electric riding lawn mower. Note that <FIG> also shows the left steering lever 6a, the right steering lever 6b, the traveling control unit <NUM>, the left driving wheel 2a, and the right driving wheel 2b described above, in addition to the traveling control device <NUM>.

The configuration of the traveling control unit <NUM> is the same as that of the traveling control unit <NUM> described above. The motors <NUM> include a pair of left and right motors. In the present embodiment, the left motor <NUM> and the right motor <NUM> described above corresponds to the pair of left and right motors. The motors <NUM> respectively drive the pair of left and right driving wheels <NUM>, and the current that is passed through each of the motors <NUM> is controlled by proportional-integral (PI) control. The pair of left and right driving wheels <NUM> are a left driving wheel 2a and a right driving wheel 2b. The left motor <NUM> drives the left driving wheel 2a, and the right motor <NUM> drives the right driving wheel 2b. PI control includes proportional action (P) in which control proportional to the difference (the current deviation) from the target value is performed (correction output is performed), and integral action (I) in which control proportional to the magnitude of the integral (cumulative value) of the difference (the previous deviation) from the target value is performed (correction output is performed). The current that is passed through each of the motors <NUM> is a current that is passed through a coil of the motor <NUM> in order to output a rotational force from the motor <NUM>. This current is controlled by PI control. Since the PI control of the current flowing through the motor <NUM> is known, the description thereof is omitted here.

The instruction receiving portion <NUM> receives an operation instruction directed to each of the pair of left and right motors <NUM>. The pair of left and right motors <NUM> are a left motor <NUM> and a right motor <NUM>. The operation instruction directed to each of the pair of left and right motors <NUM> is an instruction including a rotation direction and a rotation speed that are requested for each of the left motor <NUM> and the right motor <NUM>. The operation instruction directed to the left motor <NUM> is input through the left steering lever 6a, and the operation instruction directed to the right motor <NUM> is input through the right steering lever 6b. The operation instruction directed to the left motor <NUM> corresponds to the operation instruction directed to the left driving wheel 2a, and the operation instruction directed to the right motor <NUM> corresponds to the operation instruction directed to the right driving wheel 2b. The operation instruction directed to the left driving wheel 2a corresponds to a detection result obtained by the left steering angle detection sensor 80a (hereinafter, see <FIG> for all cases), and the operation instruction directed to the right driving wheel 2b corresponds to a detection result obtained by the right steering angle detection sensor 80b (hereinafter, see <FIG> for all cases). Accordingly, the instruction receiving portion <NUM> receives the operation instruction directed to the left driving wheel 2a via the left steering angle detection sensor 80a, and receives the operation instruction directed to the right driving wheel 2b via the right steering angle detection sensor 80b. The operation instructions received by the instruction receiving portion <NUM> are transmitted to the operation instruction determination portion <NUM>, which will be described below.

The operation instruction determination portion <NUM> determines whether each of the operation instructions is an acceleration instruction or a deceleration instruction. The operation instructions are transmitted from the instruction receiving portion <NUM> described above. An operation instruction is an instruction including a rotation direction and a rotation speed that are requested for each of the left driving wheel 2a and the right driving wheel 2b.

The operation instruction determination portion <NUM> determines that the operation instruction is an acceleration instruction if the rotation speed requested for the left driving wheel 2a is larger than the current rotation speed, and determines that the operation instruction is a deceleration instruction if the aforementioned rotation speed is smaller than the current rotation speed. Similarly, the operation instruction determination portion <NUM> determines that the operation instruction is an acceleration instruction if the rotation speed requested for the right driving wheel 2b is larger than the current rotation speed, and determines that the operation instruction is a deceleration instruction if the aforementioned rotation speed is smaller than the current rotation speed. The determination result obtained by the operation instruction determination portion <NUM> is transmitted to the speed control portion <NUM>, which will be described below.

If the operation instruction is an acceleration instruction, the speed control portion <NUM> sets, when the rotation speed of the motor <NUM> becomes greater than or equal to a preset first threshold, an integral gain in the PI control to a preset first value, and sets a proportional gain in the PI control to a preset second value. If the operation instruction is a deceleration instruction, the speed control portion <NUM> sets, when the rotation speed of the motor <NUM> becomes less than a preset second threshold that is smaller than the first threshold, the integral gain to zero, and sets the proportional gain to a preset third value. In the present embodiment, the speed control portion <NUM> sets the proportional gain to the third value that is smaller than the second value. The speed control portion <NUM> can specify whether the operation instruction is an acceleration instruction or a deceleration instruction from the determination result transmitted from the operation instruction determination portion <NUM>. The rotation speed of the motor <NUM> is the rotation speed of each of the right motor <NUM> and the left motor <NUM>. In the present embodiment, the rotation speed of the left motor <NUM> is detected by the left rear wheel rotation detection sensor 70a (see <FIG>) as the rotation speed of the left driving wheel 2a, and the rotation speed of the right motor <NUM> is detected by the right rear wheel rotation detection sensor 70b (see <FIG>) as the rotation speed of the right driving wheel 2b.

Here, the speed control portion <NUM> uses the above-described PI control to drive each of the left motor <NUM> and the right motor <NUM>. In particular, in the present embodiment, the proportional action (proportional control) in the PI control is performed as indicated by the characteristic diagram shown in <FIG>, and the integral action (integral control) in the PI control is performed as indicated by the characteristic diagram shown in <FIG>. In <FIG>, the horizontal axis represents the rotation speed, and the vertical axis represents the proportional gain. In <FIG>, the horizontal axis represents the rotation speed, and the vertical axis represents the integral gain. Although the details will be described later, v1 is the gain switching point during deceleration, and v2 is the gain switching point during acceleration in <FIG>.

If the operation instruction is an acceleration instruction, the speed control portion <NUM> sets, when the rotation speed of the motor <NUM> becomes greater than or equal to the preset first threshold (corresponding to v2 in <FIG>), a proportional gain in the PI control to the preset second value (corresponding to P2 in <FIG>), and sets an integral gain in the PI control to the preset first value (corresponding to I2 in <FIG>). This setting is performed separately for each of the left motor <NUM> and the right motor <NUM>.

If the operation instruction is a deceleration instruction, the speed control portion <NUM> sets, when the rotation speed of the motor <NUM> becomes less than the preset second threshold (corresponding to v1 in <FIG>) that is smaller than the first threshold (corresponding to v2 in <FIG>), the proportional gain to the preset third value (corresponding to P1 in <FIG>) that is smaller than the second value (corresponding to P2 in <FIG>), and sets the integral gain to zero (corresponding to I1 in <FIG>) (disables the integral action). This setting is also separately performed for each of the left motor <NUM> and the right motor <NUM>. Accordingly, by setting the integral gain to zero in the low speed range, control is performed only by the proportional control, thus permitting a steady-state speed deviation (preventing the driving wheels <NUM> from following the operation instructions (acceleration instructions)).

Here, it is preferable that switching of each of the integral gain and the proportional gain has a hysteresis, as shown in <FIG>. Such a hysteresis makes it possible to prevent an erroneous operation in the neighborhood of thresholds (the first threshold and the second threshold) of the rotation speed. The integral gain and the proportional gain set by the speed control portion <NUM> are transmitted to the motor driving portion <NUM>, which will be described below.

Referring back to <FIG>, the motor driving portion <NUM> drives the motors <NUM>, based on the integral gain and the proportional gain set by the speed control portion <NUM>. In the present embodiment, the motor driving portion <NUM> supplies power to the left power feeding portion <NUM> and the right power feeding portion <NUM> that are constituent elements of the inverter <NUM>, based on the integral gain and the proportional gain set by the speed control portion <NUM>. Accordingly, rotation of the left motor <NUM> and the right motor <NUM> is controlled, and the left driving wheel 2a and the right driving wheel 2b are rotated, thus enabling traveling and turning of the electric riding lawn mower. The motor driving portion <NUM> uses a known feedback control to control rotation of the left driving wheel 2a and the right driving wheel 2b. That is, the motor driving portion <NUM> calculates the rotation speed (torque) of the left driving wheel 2a, i.e., the rotation speed (torque) of the left motor <NUM>, based on a detection result obtained by the left steering angle detection sensor 80a, calculates the rotation speed (torque) of the right driving wheel 2b, i.e., the rotation speed (torque) of the right motor <NUM>, based on a detection result obtained by the right steering angle detection sensor 80b, and calculates the power amount based on these rotation speeds (torques). For this calculation, it is preferable to use a table or a function representing the relationship between the operation position and the rotation speed. Based on the power amount calculated in this manner, the motor driving portion <NUM> controls rotation of the left driving wheel 2a and the right driving wheel 2b.

In the above-described embodiment, an example is shown in which the steering lever <NUM> is installed on the vehicle body <NUM> of the electric riding lawn mower. However, the electric riding lawn mower may be remotely operable. In this case, it is possible to adopt a configuration in which the turning component is extracted based on the operation of the steering levers <NUM> that is performed by a remote controller through which the steering levers <NUM> are remotely operated.

In the above-described embodiment, if the operation instruction is an operation instruction to rotate the pair of left and right driving wheels <NUM> in the same direction as each other, the speed instruction value correction portion <NUM> corrects the larger one of the speed instruction values calculated for the traveling control unit <NUM> by the speed instruction value calculation portion <NUM>, based on the smaller speed instruction value. However, the speed instruction value correction portion <NUM> may be configured to correct the smaller one of the speed instruction values calculated for the traveling control unit <NUM> by the speed instruction value calculation portion <NUM>, based on the larger speed instruction value.

In the above-described embodiment, the speed instruction value correction portion <NUM> corrects the speed instruction value to the sum of the smaller one of the speed instruction values requested for the left motor <NUM> and the right motor <NUM>, and the product of the turning component extracted from two speed instruction values and the preset attenuation value. However, this is merely an example, and the speed instruction value correction portion <NUM> may be configured to perform the correction by a different method. The attenuation value may be calculated based on any of the larger one of two speed instruction values, the smaller one of two speed instruction values, and the difference between two speed instruction values. This can prevent the attenuation amount from being excessively increased or decreased, and it is therefore possible to make the traveling vehicle travel smoothly.

In the above-described embodiment, if the operation instruction is an operation instruction to rotate the pair of left and right driving wheels <NUM> in different directions from each other, the speed instruction value correction portion <NUM> corrects each of the speed instruction values calculated for the traveling control unit <NUM> by the speed instruction value calculation portion <NUM>, based on the preset common attenuation value. However, the speed instruction value correction portion <NUM> may be configured to directly use each of the speed instruction values calculated for traveling control unit <NUM> by the speed instruction value calculation portion <NUM> without correcting the speed instruction values, based on the preset common attenuation value, or may be configured to correct the speed instruction values, based on different attenuation values from each other. In such a case, for example, the speed instruction value correction portion <NUM> may be configured to correct one of the speed instruction values that has a larger absolute value, based on the speed instruction value having a smaller absolute value, or may be configured to correct one of the speed instruction values that has a smaller absolute value, based on the speed instruction value having a larger absolute value. The attenuation value may be calculated based on any of the larger one of two speed instruction values, the smaller one of two speed instruction values, and the difference between two speed instruction values. This can prevent the attenuation amount from being excessively increased or decreased, and it is therefore possible to make the traveling vehicle travel smoothly.

In the above-described embodiment, switching of each of the integral gain and the proportional gain has a hysteresis. However, it is possible to adopt a configuration in which switching of one of the integral gain and the proportional gain has a hysteresis, or a configuration in which switching of both the integral gain and the proportional gain do not have a hysteresis.

In the above-described embodiment, if the operation instruction is a deceleration instruction, the speed control portion <NUM> sets, when the rotation speed of the motor <NUM> becomes smaller than the preset second threshold that is smaller than the first threshold, the integral gain to zero, and sets the proportional gain to the preset third value, and the motor driving portion <NUM> drives the motor <NUM>, based on the integral gain and the proportional gain set by the speed control portion <NUM>. However, if the operation instruction is a deceleration instruction, the motor driving portion <NUM> may be configured to, when the speed of the traveling vehicle is less than a preset value, drive the motor <NUM> using a torque control based on the output torque of the motor <NUM> instead of driving the motor <NUM> based on the rotation speed, even when the rotation speed of the motor <NUM> is less than the second threshold. With such a configuration, for example, even in a situation where the ground surface on which the traveling vehicle travels is slippery and the driving wheels <NUM> slip, it is possible to prevent slipping by using the torque control, thus making it possible to prevent the formation of unwanted marks in the ground surface. The motor driving portion <NUM> may also be configured to set the gain in the PI control to zero, convert, into torques, the detection result obtained by the left steering angle detection sensor 80a that detects the operation amount (pivoting angle) of the left steering lever 6a and the detection result obtained by the right steering angle detection sensor 80b that detects the operation amount (pivoting angle) of the right steering lever 6b, and perform driving in accordance with a torque command. Of course, the motor driving portion <NUM> may perform driving in accordance with a current command.

In the above-described embodiment, the speed control portion <NUM> sets the proportional gain to the third value that is smaller than the second value. However, the speed control portion <NUM> may be configured to set the proportional gain to a third value that is larger than the second value, or may be configured to set the proportional gain to a third value that is the same value as the second value.

In the above-described embodiment, an electric riding lawn mower is described as an example of the traveling vehicle in which the traveling control device <NUM> is installed. However, the traveling vehicle may be a different vehicle.

Although the traveling control device <NUM> may perform both the rotation direction control of the driving wheels described with reference to <FIG> and the motor control described with reference to <FIG> and <FIG>, the traveling control device <NUM> may perform one of these controls.

Claim 1:
A traveling control device (<NUM>) of a traveling vehicle including a traveling control unit (<NUM>) having a pair of left and right configurations capable of respectively driving a pair of left and right driving wheels (<NUM>), the traveling control device comprising:
an instruction receiving portion (<NUM>) configured to receive an operation instruction directed to each of the pair of left and right driving wheels;
a speed instruction value calculation portion (<NUM>) configured to calculate a speed instruction value that is to be instructed to the traveling control unit, based on each of the operation instructions;
an operation instruction determination portion (<NUM>) configured to determine, based on each of the operation instructions, whether the operation instruction is an operation instruction to rotate the pair of left and right driving wheels in the same direction as each other, or an operation instruction to rotate the pair of left and right driving wheels in different directions from each other; and
a speed instruction value correction portion (<NUM>) configured to, if the operation instruction is an operation instruction to rotate the pair of left and right driving wheels in the same direction as each other, extract a turning component by subtracting the smaller one of the speed instruction values from the larger one of the speed instruction values, directly using the smaller one of the speed instruction values as the speed instruction value, characterised in that the larger one of the speed instruction values is corrected to a sum of (i) the smaller one of the speed instruction values and (ii) a product of the turning component and a preset attenuation value which is smaller than <NUM>.