Patent Description:
In an electric travelling vehicle according to Patent Document <NUM>, the travel driving system that rotates drive wheels using an electric motor is provided with an electromagnetic brake, and upon the electric motor being driven in response to a manual operation performed using an accelerator, the electromagnetic brake simultaneously cancels braking on the travel driving system. Also, upon an operation performed using the accelerator being stopped, the electromagnetic brake simultaneously activates braking on the travel driving system. This electric travelling vehicle is also provided with a manual switch that is used to activate or cancel braking performed by the electromagnetic brake. That is, in this electric travelling vehicle, starting of power supply to the electromagnetic brake (brake cancellation) and stopping of power supply to the electromagnetic brake (brake activation) are triggered by a manual operation, and are performed simultaneously with this operation.

The electromagnetic brake that is provided on a motor shaft of the electric motor of the electric travelling vehicle, or on a transmission shaft coupled to the motor shaft, is an electromagnetic power-off brake that is provided with a brake spring that presses an armature against a brake disk using a biasing spring force, and an electromagnetic coil that releases the armature from the brake disk using an electromagnetic force. An electromagnetic power-off brake is in a braking state when the coil of the electromagnetic brake is not excited, due to a spring or the like, and is in a released state when the coil of the electromagnetic brake is excited. Therefore, an electromagnetic power-off brake requires excitation the entire time the vehicle travels, and there is an issue of high power consumption. Since the capacity of an on-board battery is limited, power consumption is a significant issue for an electric travelling vehicle. In addition, a premature braking action performed by an electromagnetic power-off brake places an unnecessary load on the electric motor and the brake shaft.

In a grass mower, the driver's seat is located in an upper portion of a travelling machine body, and a mower unit is located in a lower portion of the travelling machine body. Therefore, it is difficult for the driver sitting on the driver's seat to check the driving state of the mower unit. Thus, technology for avoiding issues by using a detection signal from a sensor that monitors the driving state of the mower unit has been proposed. For example, in an electric lawn mower according to Patent Document <NUM>, a load applied to a mower motor that rotates cutter blades is calculated, and the travel speed is reduced when the load exceeds a threshold value. Also, an electric lawn mower according to Patent Document <NUM> is provided with: a mower motor that rotates cutter blades; a thermostat that detects the temperature of the motor; a cooling flow path that cools the mower motor; and a cover that opens and closes the cooling flow path, and when the temperature of the motor rises, the cover is opened and the mower motor is cooled by cooling air that flows in via the cooling flow path. Thus, the mower motor is prevented from overheating. <CIT> deals with control systems and methods for electric drive utility vehicles. <CIT> deals with a backlash reduction control device for an electric vehicle.

One objective of the present invention is to provide an electric travelling vehicle that appropriately performs excitation control on an electromagnetic power-off brake according the travel state, and performs brake control under which unnecessary and non-urgent excitation is avoided.

An electric travelling vehicle according to one embodiment of the present invention is defined in claim <NUM>, and includes: a vehicle body; a power device that includes an electric motor that is driven by being excited, and an electromagnetic power-off brake; a drive wheel configured to be driven by power from the power device; a steering operation part configured to be displaced to a forward travel position, a neutral position, and a rearward travel position from one to another by a manual operation; a motor controller configured to control the electric motor based on displacement of the steering operation part; a brake controller configured to bring the electromagnetic power-off brake into a released state or a braking state; and a travel state detector configured to detect a travelling state that is accompanied with the released state, a stopped state that is accompanied with the braking state, and a transit stopped state that is accompanied with the braking state and is a transit state between the stopped state and the travelling state,
wherein a transition from the travelling state to the transit stopped state occurs on a condition that, in the travelling state, the steering operation part has been returned to the neutral position and a predetermined period of time has elapsed upon a rotational speed of the electric motor decreasing to a very low rotational speed, and a transition from the transit stopped state to the stopped state and a transition from the stopped state to the transit stopped state occur upon a manual operation being performed.

In conventional electric travelling vehicles, control is performed in order to selectively create: a travelling state in which an electromagnetic power-off brake (hereinafter abbreviated as an electromagnetic brake, except in specific cases) is excited and brought into a released state and an electric motor is excited so that a vehicle body travels; and a stopped state in which excitation of an electromagnetic clutch is stopped and the electromagnetic clutch is brought into a braking state and excitation of the electric motor is stopped so that the vehicle body is stopped. With the above-described configuration according to the present invention, a control state called a transit stopped state is set between a travelling state and a stopped state. Thus, a transit stopped state occurs before a transition from a travelling state to a stopped state occurs, and the electromagnetic brake and the electric motor are controlled based on individual conditions so that the timing of controlling the electromagnetic brake and the timing of controlling the electric motor can be optimized. For example, in the process of control in which the driver returns the steering operation part to the neutral position to reduce the number of rotations of the electric motor (the vehicle speed) to zero to stop the vehicle body that is travelling, the electromagnetic brake and the electric motor are not simultaneously controlled. Instead, excitation of the electromagnetic brake continues until a predetermined period of time has elapsed upon the rotational speed of the electric motor decreasing to a very low rotational speed (e.g. within the range from <NUM> rpm to several ten rpm), and excitation of the electromagnetic brake is only stopped upon the predetermined period of time (e.g. approximately <NUM> seconds to <NUM> seconds) elapsing, so that the electromagnetic brake performs braking. This control is automatically performed, and thus a transition from a travelling state to a transit stopped state is complete. As a result of control automatically being performed on the electric motor and the electromagnetic brake, the vehicle body transitions from a travelling state to a transit stopped state, and the vehicle body is temporarily stopped. In this automatic control performed on the electric motor and the electromagnetic brake to temporarily stop the vehicle body, both power saving and safety are considered in a balanced manner. Also, a transition from this transit stopped state to a stopped state in which the vehicle is reliably stopped occurs on the condition that a manual operation is performed. Therefore, the driver has the intention of fully stopping the vehicle body when bringing the vehicle body into a stopped state.

After the driver returns the steering operation part to the neutral position to reduce the vehicle body speed, and the control state transitions from a travelling state to a transit stopped state, when the driver wishes to set the vehicle body in motion again, the driver operates the steering operation part in a forward travel direction or a rearward travel direction from the neutral position. As a result, the control state transitions from a transit stopped state to a travelling state. Also in this process of control from a transit stopped state to a travelling state, it is preferable that both power saving and safety are considered in a balanced manner when the electromagnetic brake and the electric motor are controlled. For example, in a preferred embodiment of the present invention, a transition from the transit stopped state to the travelling state occurs at least on a condition that, in the transit stopped state, a predetermined period of time (e.g. <NUM> seconds) has elapsed upon the steering operation part being deviated from the neutral position.

In the embodiment of the present invention as defined in claim <NUM>, the electric travelling vehicle includes a brake operation part of a manual operation type, and the brake operation part is configured to be switchable to a first position to make a request to bring the power-off brake into the released state, and to a second position to make a request to bring the power-off brake into the braking state. Using this brake operation part, the driver can manually bring the electromagnetic brake into a release state or a braking state according to the driver's own will, to stop the vehicle body in an emergency or reliably stop the vehicle body, for example. Furthermore, according to this embodiment of the invention, a transition from the transit stopped state to the stopped state occurs at least on a condition that, in the transit stopped state, the brake operation part has been switched to the second position (braking), and a transition from the stopped state to the transit stopped state occurs at least on a condition that, in the stopped state, the brake operation part has been switched to the first position (brake releasing). With the former configuration, the driver can convey an intention to stop the vehicle body to the control system, by operating the brake operation part in such a manner. Considering the driver's intention to stop the vehicle body, the control system brings the vehicle body from the transit stopped state to the stopped state. With the latter configuration, the driver can convey an intention to start running the vehicle body to the control system, by operating the brake operation part in such a manner. Considering the driver's intention to stop the vehicle body, the control system brings the vehicle body from the stopped state to the transit stopped state.

It is possible to perform more appropriate control on the electric motor and the electromagnetic brake by providing various conditions for detecting the travel state. Therefore, according to one preferred embodiment of the present invention, the travel state detector detects the travelling state on a condition that the steering operation part has deviated from the neutral position, the electromagnetic power-off brake is in the released state, the electric motor is in an excited state, and the brake operation part is at the first position. Furthermore, the travel state detector detects the stopped state on a condition that the steering operation part is at the neutral position, the electromagnetic power-off brake is in the braking state, the electric motor is in an unexcited state, and the brake operation part is at the second position. Furthermore, the travel state detector detects the transit stopped state on a condition that the steering operation part is at the neutral position, the electromagnetic power-off brake is in the braking state, the electric motor is in an unexcited state, and the brake operation part is at the first position.

With such a configuration of the present invention, it is possible to prevent the driver from forgetting to operate the brake operation part. In addition, it is possible to save power consumption by automatically stopping excitation of the electromagnetic brake and the travel motor when the vehicle body is temporarily stopped. It is also possible to prevent the electric motor from slightly moving due to a torque loss by activating the electromagnetic brake before activating the electric motor.

The brake operation part of a manual operation type is used by the driver to bring the vehicle body into an emergency stopped state through a braking operation. It is preferable that the above-described transition control is applied to such a transition to an emergency stopped state as well. Therefore, in a preferred embodiment of the present invention, when the brake operation part is switched from the first position to the second position in the travelling state, the power-off brake enters the braking state and a transition from the travelling state to an emergency stopped state in which the vehicle body is stopped occurs when a predetermined period of time (e.g. within the range of <NUM> seconds to <NUM> seconds) has elapsed upon a no-rotation instruction being output to the electric motor. With this configuration, when the vehicle body is travelling, it is possible to sufficiently decelerate the vehicle body before the electromagnetic brake enters the braking state, and thus it is possible to reduce the amount of work involved in braking.

A grass mower according to one example of the present disclosure that is not claimed per se includes: a mower unit that includes a rotation shaft to which a cutter blade is attached, a mower motor, and a mower power transmission mechanism that establishes a power transmission path through which power from the mower motor is transmitted to the cutter blade; a mower motor controller configured to control the mower motor; a mower drive state detector configured to detect a drive state of the mower motor; and a mower abnormality detector configured to detect an abnormality in the power transmission path based on a detection signal from the mower drive state detector.

With this configuration, an abnormality in the power transmission path is detected based on a detection signal from the mower drive state detector that detects the drive state of the mower motor. Typically, a motor control system has the function of detecting the drive state of the motor in order to appropriately drive the motor and protect the motor. Examples of the motor drive state to be detected include the number of rotations of the motor, the temperature of the motor, a current flowing through the motor, and load on the motor. If an abnormality occurs in the power transmission path through which power output from the mower motor is transmitted to the cutter blade to rotate the cutter blade, the abnormality also affects the mower motor connected to the power transmission path, which results in a change in the drive state of the motor. The mower abnormality detector detects an abnormality in the power transmission path, i.e. an abnormality in the mower power transmission mechanism, based on such a change in the drive state of the motor. Examples of abnormalities in the power transmission path include disengagement between the rotation shaft and the cutter blade, and disengagement of a belt if the mower power transmission mechanism employs a belt power transmission mechanism.

According to one example of the present disclosure that is not claimed per se, the mower motor controller forcibly stops the mower motor upon the mower motor abnormality detector detecting an abnormality. If power is continuously supplied even after an abnormality has occurred in the power transmission path, the abnormality may become more significant or cause a secondary problem. Therefore, it is appropriate to forcibly stop the mower motor to stop power supply.

One example of the present disclosure that is not claimed per se includes a manual operation part configured to provide the mower motor controller with a drive instruction that is an instruction to drive the mower motor and a stop instruction that is an instruction to stop the mower motor from driving, and when the mower motor is to be recovered from a forcibly stopped state, the stop instruction and the drive instruction that is subsequent to the stop instruction are required to be provided from the manual operation part. With this configuration, if the mower motor is forcibly stopped while the mower motor is driven according to an instruction provided through an operation performed using the manual operation part, the mower motor will not be recovered from the forcibly stopped state or rotate, unless a stop instruction that is an instruction to stop the mower motor from driving is provided through an operation performed on the manual operation part. Thus, it is possible to avoid an issue such as unexpected rotation of the mower motor during the task of eliminating an abnormality in the power transmission path.

In one example of the present disclosure that is not claimed per se, the mower motor is supplied with power via an inverter, the mower drive state detector is a current detector that is built into the inverter and is configured to detect a current value of the mower motor, and the mower abnormality detector detects an abnormality in the mower unit upon the current value falling below a predetermined value while the mower unit is driving. Current detection is essential for motor control performed by an inverter. Therefore, in terms of costs, it is preferable that the mower abnormality detector uses the result of detection received from the current detector built into the inverter. For example, in a case where the current value of the mower motor is more than <NUM> amperes when the mower motor is performing work under a load, and is approximately one third thereof when the mower motor is under no load, if power transmission is blocked due to disengagement of the power transmission belt or the like, the current value of the mower motor will be several amperes. If the cutter blade and the rotation shaft slip, the current value will be several tens of amperes when the mower motor is performing work, and is approximately one half thereof under no load. Based on such a phenomenon, the mower abnormality detector can detect an issue in the power transmission path.

Based on the specifications of the grass mower, the current value of the mower motor when the mower motor is performing work under a load, the current value (the rated value) of the mower motor under no load, and the current value (or the amount of a drop from the rated value) when a power transmission failure has occurred in the power transmission path for the mower unit can be checked in advance through experiments. Therefore, according to one simple example of the present disclosure that is not claimed per se, the mower abnormality detector detects, as an abnormality in the power transmission path, a power transmission failure in the mower power transmission mechanism or an attachment failure in which the cutter blade and the rotation shaft are improperly attached to each other, upon the current value falling below the predetermined value while the mower unit is driving. This configuration is advantageous in terms of costs because an abnormality in the power transmission path can be detected by simply performing a threshold value determination on the current value. Of course, in order to more accurately detect an abnormality in the power transmission path, it is preferable that the mower abnormality detector has the function of detecting an abnormality in the power transmission path based on changes over time in the detection signals from the mower drive state detector, i.e. fluctuations in the detection signals.

Furthermore, the mower abnormality detector may be configured to calculate the probability of occurrence of an abnormality, using a detection signal from the mower drive state detector other than the current detection signal, or various detection signals including the current detection signal, and to detect an abnormality when the probability of occurrence of an abnormality exceeds a predetermined value.

The second example is not claimed per se and is present for illustration purposes only.

The following describes one specific embodiment of an electric travelling vehicle according to the present invention with reference to the drawings. The electric travelling vehicle according to the present embodiment is an electric grass mower. In the present specification, "front" means forward in the front-rear direction (the travel direction) of the vehicle body, and "rear" means rearward in the front-rear direction (the travel direction) of the vehicle body. Also, a left-right direction or a lateral direction means a direction that is orthogonal to the front-rear direction of the vehicle body and is transverse to the machine body (the width direction of the machine body). "Upper" and "lower" indicate a positional relationship in a perpendicular direction (a vertical direction), and show a relationship with respect to a height above ground.

<FIG> is a side view of the electric grass mower, and <FIG> is a plan view schematically showing a control system and a power system of the electric grass mower.

This grass mower is provided with: front wheels <NUM> that include a left front wheel 1a and a right front wheel 1b that are of a caster type and can freely rotate; drive wheels <NUM> that include a left rear wheel 2a and a right rear wheel 2b; a vehicle body <NUM> that is supported by the front wheels <NUM> and the drive wheels <NUM>; a battery <NUM> that is located in a rear portion of the vehicle body <NUM>; a driver's seat <NUM> that is located forward of the battery <NUM>; and a rollover protection frame <NUM> that is located rearward of the driver's seat <NUM> and stands upright. A mower unit <NUM> is suspended from the vehicle body <NUM> in a space below the vehicle body <NUM>, between the front wheels <NUM> and the drive wheels <NUM>, such that the mower unit <NUM> can be lifted and lowered by a lifting/lowering linkage mechanism <NUM>.

A floor plate, on which the driver's feet can be placed, is provided forward of the driver's seat <NUM>. Steering operation parts <NUM> that include a left steering lever 15a and a right steering lever 15b are respectively provided on the left and right sides of the driver's seat <NUM>, each steering lever being swingable about a horizontal swing axis that extends in a direction that transverses the machine body <NUM>. A brake operation part <NUM> of a manual operation type is provided on the left side of the driver's seat <NUM>.

As shown in <FIG>, a left motor <NUM> and a right motor <NUM>, which are electric motors <NUM> that supply a rotational force to the left rear wheel 2a and the right rear wheel 2b, are provided. The rotational speeds of the left motor <NUM> and the right motor <NUM> are individually changed according to the amount of power supplied thereto via an inverter drive module <NUM>. Therefore, the rotational speeds of the left rear wheel 2a and the right rear wheel 2b can be set different from each other, and the grass mower can turn using the difference between the speeds of the left and right rear wheels.

To transmit power between the electric motors <NUM> and the drive wheels <NUM>, transmissions <NUM> for travel are provided. Electromagnetic brakes <NUM>, which are electromagnetic power-off brakes, are interposed between the electric motors <NUM> and the transmissions <NUM> to brake power transmission from the electric motors <NUM> to the transmissions <NUM>. As shown in <FIG>, in the present embodiment, the output shafts of the electric motors <NUM> function as rotation shafts <NUM> of the electromagnetic brakes <NUM>, and the rotation shafts <NUM> are coupled to input shafts 24a of the transmissions <NUM>. Power input to the input shafts 24a of the transmissions <NUM> is transmitted to rear axles 24b, which are output shafts of the transmissions <NUM>, via gear power transmission mechanisms. That is, the electric motors <NUM>, the electromagnetic brakes <NUM>, and the transmissions <NUM> constitute a power device that transmits power to the drive wheels <NUM>. If wheel motors or the like are employed, it is possible to omit the transmissions <NUM>.

Each electromagnetic brake <NUM> includes a fixed core <NUM>, an armature <NUM>, a holding plate <NUM>, and a brake disk <NUM>. The fixed core <NUM> is fixed to a brake housing <NUM>, and includes an electromagnetic coil <NUM> and a brake spring <NUM> that are arranged coaxially with the rotation shaft <NUM>. The brake disk <NUM> is a circular disk that has a boss portion that is coupled to the rotation shaft <NUM> so as not to be rotatable relative to the rotation shaft <NUM>. A friction portion is formed on each side of the brake disk <NUM>. The armature <NUM> is a ring plate that is disposed coaxially with the rotation shaft <NUM> and is movable in the axial direction. When the electromagnetic coil <NUM> is not excited, the armature <NUM> is pressed against the brake disk <NUM> due to the biasing spring force of the brake spring <NUM>, and when the electromagnetic coil <NUM> is excited, the armature <NUM> is released from the brake disk <NUM> due to an electromagnetic force that is greater than the biasing spring force.

The holding plate <NUM> is a ring plate that is disposed coaxially with the rotation shaft <NUM>, and is fixed to the fixed core <NUM> by coupling rods <NUM> that are distributed at three positions in a circumferential direction. The coupling rods <NUM> also function as guide rods for the armature <NUM> that moves in the axial direction, and as rods for preventing the armature <NUM> from rotating.

Therefore, the coupling rods <NUM> are fitted into recesses that are provided in the outer periphery of the armature <NUM>.

As shown in <FIG>, the mower unit <NUM> is of a side discharge type provided with three cutter blades (blades), and includes a mower deck 3a and three rotary cutter blades <NUM>. A blade drive mechanism <NUM> that rotates the cutter blades <NUM> includes a cutter blade motor <NUM>, which is an electric actuator, and a cutter blade power transmission mechanism <NUM> that transmits power from the cutter blade motor <NUM> to the cutter blades <NUM>. The cutter blade motor <NUM> is also supplied with power by the inverter drive module <NUM>.

Grass that has been cut by the cutter blades <NUM> as a result of the grass mower travelling while rotating the cutter blades <NUM> is transported by wind generated by wind stirring blades of the cutter blades <NUM> and baffle plates, to a lateral end side on which a discharge port is located, through the inside of the mower deck 3a, and is discharged from the discharge port located on the lateral end side, laterally outward of the mower deck 3a.

As shown in <FIG>, a control unit <NUM> excites the electric motors <NUM>, the cutter blade motor <NUM>, and the electromagnetic brakes <NUM> based on detection signals from sensors and switches. Therefore, a left steering position detection sensor 80a that detects a swing position (a forward travel position, a neutral position, or a rearward travel position) of the left steering lever 15a, a right steering position detection sensor 80b that detects a swing position (a forward travel position, a neutral position, or a rearward travel position) of the right steering lever 15b, rotation sensors <NUM> that respectively detect rotations of the left motor <NUM> and the right motor <NUM>, a brake sensor <NUM> that detects an operation position of the brake operation part <NUM>, and so on are provided.

The control unit <NUM> is connected to the left steering position detection sensor 80a, the right steering position detection sensor 80b, the rotation sensors <NUM>, the brake sensor <NUM>, and so on. The control unit <NUM> supplies brake excitation currents, which excite the electromagnetic brakes <NUM>, to the electromagnetic brakes <NUM> via a driver (not shown).

The inverter drive module <NUM> outputs drive currents respectively to the left motor <NUM>, the right motor <NUM>, and the cutter blade motor <NUM> to excite and rotate them, based on control target signals from the control unit <NUM>.

Next, control functional units related to the electric motors <NUM>, the electromagnetic brakes <NUM>, and the brake operation part <NUM> will be described with reference to the functional blocks shown in <FIG>. The control unit <NUM> includes a motor controller <NUM>, a brake controller <NUM>, and a travel state detector <NUM>.

The motor controller <NUM> generates target control signals for controlling the left motor <NUM> and the right motor <NUM>, based on detection signals from the left steering position detection sensor 80a and the right steering position detection sensor 80b that respectively detect displacement of the left steering lever 15a and displacement of the right steering lever 15b. Furthermore, the motor controller <NUM> generates a target control signal for controlling the cutter blade motor <NUM>. Target control signals are supplied to the inverter drive module <NUM>. The inverter drive module <NUM> includes an inverter drive signal generator <NUM> and an inverter circuit <NUM>. The inverter drive signal generator <NUM> generates inverter drive signals based on the target control signals. The inverter circuit <NUM> generates motor excitation currents (drive currents) that are supplied to the left motor <NUM>, the right motor <NUM>, and the cutter blade motor <NUM>, based on the inverter drive signals.

The brake controller <NUM> controls excitation currents to bring the electromagnetic brakes <NUM> into a released state (excited) or a braking state (not excited). The brake operation part <NUM> is switchable to a first position (releasing) to make a request to bring the electromagnetic brakes <NUM> into a released state, and to a second position (braking) to make a request to bring the electromagnetic brakes <NUM> into a braking state. The brake operation part <NUM> at the first position or the second position is detected by the brake sensor <NUM>, and a detection signal thus generated is transmitted to the control unit <NUM>.

The travel state detector <NUM> detects various control states such as a travelling state, a transit stopped state, a stopped state, and emergency stopped states (an emergency stopped state A and an emergency stopped state B have been set in the present embodiment) of the vehicle body <NUM>. A transit stopped state is a state between a stopped state and a travelling state. When transitioning from a stopped state to a travelling state and when transitioning from a travelling state to a stopped state, the vehicle body <NUM> necessarily undergoes a transit stopped state.

When specific conditions are satisfied in each of the control states detected by the travel state detector <NUM>, the control unit <NUM> controls transition to another control state. Next, transition to each of the control states, which, in the present embodiment, occurs when specific conditions are satisfied, will be described with reference to <FIG>.

First, the control states in the present embodiment are defined as follows.

The brake operation part <NUM> is at the first position (releasing), the steering operation parts <NUM> have deviated from the neutral positions, the electromagnetic brakes <NUM> are in a released state (excited), and the electric motors <NUM> are in an excited state (rotated).

The brake operation part <NUM> is at the first position, the steering operation parts <NUM> are at the neutral positions, the electromagnetic brakes <NUM> are in a braking state (not excited), and the electric motors <NUM> are in an unexcited state (not rotated).

The brake operation part <NUM> is at the second position (braking), the steering operation parts <NUM> are at the neutral positions, the electromagnetic brakes <NUM> are in a braking state (not excited), and the electric motors <NUM> are in an unexcited state (not rotated).

The brake operation part <NUM> is at the second position, the steering operation parts <NUM> have deviated from the neutral positions, the electromagnetic brakes <NUM> are in a braking state (not excited), and the electric motors <NUM> are in an unexcited state (not rotated).

The brake operation part <NUM> is at the first position, the steering operation parts <NUM> are at the neutral positions, the electromagnetic brakes <NUM> are in a braking state (not excited), and the electric motors <NUM> are in an unexcited state (not rotated). This state functions as a transit state for returning to a normal travelling or stopped state from an emergency stopped state A.

Conditions for a transition from each state to a specified state are as follows.

A condition that, in the travelling state, the steering operation parts <NUM> have been returned to the neutral positions (in the present embodiment, each of the left steering lever 15a and the right steering lever 15b may be located within the range of plus or minus <NUM>% from the neutral position thereof), and a predetermined period of time has elapsed upon the rotational speed of each of the electric motors <NUM> decreasing to a very low rotational speed <Condition a>. The very low rotational speed is, for example, no greater than <NUM> rpm, and may be positive, negative, or zero. The predetermined period of time is, for example, one second. Upon <Condition a> being satisfied, excitation of the electromagnetic brakes <NUM> is stopped, and the electromagnetic brakes <NUM> enter a braking state.

A condition that, in the transit stopped state, a predetermined period of time has elapsed upon at least one of the steering operation parts <NUM> deviating from the neutral position thereof <Condition b>. This predetermined period of time is, for example, <NUM> milliseconds. Upon <Condition b> being satisfied, excitation of the electromagnetic brakes <NUM> is started, and the electromagnetic brakes <NUM> enter a released state.

A condition that, in the transit stopped state, the brake operation part <NUM> has been switched to the second position <Condition c>. If <Condition c> is satisfied, it means that a braking instruction that is an instruction to bring the electromagnetic brakes <NUM> into a braking state is provided to the brake controller <NUM> via the brake sensor <NUM>.

A condition that, in the stopped state, the brake operation part <NUM> has been switched to the first position <Condition d>. If <Condition d> is satisfied, it means that a releasing instruction that is an instruction to bring the electromagnetic brakes <NUM> into a released state is provided to the brake controller <NUM> via the brake sensor <NUM>. That is, this condition is satisfied at a stage before the electromagnetic brakes <NUM> are brought into a released state.

A condition that, in the travelling state, the brake operation part <NUM> has been switched to the second position, and a predetermined period of time has elapsed upon the number of rotations of the electric motors <NUM> decreasing to zero as a result of the motor controller <NUM> outputting a no-rotation instruction to the electric motors <NUM> <Condition e>. This predetermined period of time is, for example, <NUM> milliseconds. Upon <Condition e> being satisfied, excitation of the electromagnetic brakes <NUM> is stopped, and the electromagnetic brakes <NUM> enter a braking state.

A condition that, in the stopped state, the brake operation part <NUM> has been switched to the first position <Condition f>. If <Condition f> is satisfied, it means that a releasing instruction that is an instruction to bring the electromagnetic brakes <NUM> into a released state is provided to the brake controller <NUM> via the brake sensor <NUM>. That is, this condition is satisfied at a preparatory stage for recovering the travelling state after the transit stopped state. The electromagnetic brakes <NUM> are still in a braking state.

A condition that, in the emergency stopped state A, the brake operation part <NUM> has been switched to the second position <Condition g>. If <Condition g> is satisfied, it means that a braking instruction that is an instruction to bring the electromagnetic brakes <NUM> into a braking state is provided to the brake controller <NUM> via the brake sensor <NUM>.

A condition that, in the emergency stopped state B, the steering operation parts <NUM> are returned to the neutral positions <Condition h>. If <Condition h> is satisfied, it means that preparations for returning to the travelling state have been made.

As described above, not only simple control states such as a travelling state, a stopped state, and emergency stopped states, but also a transit stopped state is set between a travelling state and a stopped state, and thus control over the electromagnetic brakes <NUM> and the electric motors <NUM> is optimized. Also, the emergency stopped state A and the emergency stopped state B are set as the emergency stopped states, and thus control over a transition from an emergency stopped state to a normal travelling state and a normal stopped state is optimized.

The following describes one specific example of a grass mower according to the second example that is not claimed per se, with reference to the drawings. The grass mower according to the present example is a mid-mount type electric grass mower.

<FIG> is a side view of the electric grass mower (hereinafter simply referred to as the grass mower). This grass mower is provided with: a front wheel unit <NUM> that includes a left front wheel 101a and a right front wheel 101b that are of a caster type and can freely rotate; a drive wheel unit <NUM> that includes a left rear wheel 102a and a right rear wheel 102b; a vehicle body frame <NUM> that is supported by the front wheel unit <NUM> and the drive wheel unit <NUM>; a battery <NUM> that is located in a rear portion of the vehicle body frame <NUM>; a driver's seat <NUM> that is located forward of the battery <NUM>; a rollover protection frame <NUM> that is located rearward of the driver's seat <NUM> and stands upright; and a mower unit <NUM> that is suspended from the vehicle body frame <NUM> in a space below the vehicle body frame <NUM>, between the front wheel unit <NUM> and the drive wheel unit <NUM>, such that the mower unit <NUM> can be lifted and lowered by a lifting/lowering linkage mechanism <NUM>.

A floor plate <NUM>, on which the driver's feet can be placed, is provided forward of the driver's seat <NUM>, and a brake pedal <NUM> protrudes therefrom. Steering units <NUM> that include a left steering lever 115a and a right steering lever 115b are respectively provided on the left and right sides of the driver's seat <NUM>, each steering lever being swingable about a horizontal swing axis that extends in a direction that transverses the machine body. The rotational speed of the left rear wheel 102a can be changed using the left steering lever 115a, and the rotational speed of the right front wheel 101b can be changed using the right steering lever 115b. The rotational speeds of the left rear wheel 102a and the right rear wheel 102b can be individually changed, and a sharp turn can be realized by setting the directions of rotation of the rear wheels to be opposite to each other. Therefore, this grass mower is also referred to as a zero-turn mower.

As shown in <FIG>, the mower unit <NUM> is of a side discharge type, and is provided with a mower deck <NUM> and two rotary cutter blades <NUM>. The left cutter blade <NUM> and the right cutter blade <NUM> are arranged side by side in a direction that traverses the vehicle body. The mower deck <NUM> includes a top wall <NUM>, and a front wall <NUM> and a rear wall <NUM> that extend downward from the outer peripheral edge of the top wall <NUM>. The front wall <NUM> is continuous with a front portion of the outer peripheral edge of the top wall <NUM>, and the rear wall <NUM> is continuous with a rear portion of the outer peripheral edge. Right end areas of the front wall <NUM> and the rear wall <NUM> are cut out so as to form a cut grass discharge port <NUM>, which is covered by a cover <NUM>. The cutter blades <NUM> are located in an internal space of the mower deck <NUM>, which is defined by the top wall <NUM>, the front wall <NUM>, and the rear wall <NUM>.

Each cutter blade <NUM> has a band plate-like shape with cutting edges at both ends thereof. Also, wind stirring blades are formed on the back side of the cutting edges. During grass cutting work, grass that has been cut by the cutter blades <NUM> as a result of the grass mower travelling while rotating the cutter blades <NUM> is transported through the inside of the mower deck <NUM> by wind generated by the wind stirring blades of the cutter blades <NUM>, while being guided by baffle plates located in the mower deck <NUM>, and is discharged laterally outward of the mower deck <NUM> from the grass discharge port <NUM>.

As shown in <FIG>, rotation shafts <NUM> that extend downward penetrating through the top wall <NUM> of the mower deck <NUM> are held by the top wall <NUM> so as to be rotatable, using bearing units 121a. The cutter blades <NUM> are fastened and fixed to the lower ends of the rotation shafts <NUM> so as to be replaceable, using attachment bolts 121b. Input pulleys <NUM> are attached to the upper ends of the rotation shafts <NUM>.

As shown in <FIG>, a mower motor <NUM> that supplies power to the cutter blades <NUM> is mounted on a mounting platform <NUM> that protrudes rearward from the rear wall <NUM>. An output shaft <NUM> of the mower motor <NUM> is held in a vertical orientation inside a motor housing <NUM> so as to be rotatable, using a bearing, and the upper end of the output shaft <NUM> juts out of the motor housing <NUM>. An output pulley <NUM> is attached to this jutting portion of the output shaft <NUM>.

A belt <NUM> is hooked around the input pulleys <NUM> attached to the two rotation shafts <NUM>, the output pulley <NUM> attached to the output shaft <NUM> of the mower motor <NUM>, and a tension pulley unit <NUM> attached to the mower deck <NUM>. That is, in the present example, a mower power transmission mechanism MTS that establishes a power transmission path for transmitting power from the mower motor <NUM> to the cutter blades <NUM> is constituted by the output pulley <NUM> attached to the output shaft <NUM> of the mower motor <NUM>, the belt <NUM>, the tension pulley unit <NUM>, the input pulleys <NUM>, and the rotation shafts <NUM> to which the cutter blades <NUM> are fastened and fixed. If the belt <NUM> comes off from the input pulleys <NUM>, the output pulley <NUM>, or the tension pulley unit <NUM>, the belt <NUM> slips, or the cutter blades <NUM> fastened and fixed to the rotation shafts <NUM> come loose, power transmission is at least partially blocked, and an abnormality occurs in the power transmission path.

<FIG> shows a power system and a control system of the electric grass mower. A left motor <NUM> and a right motor <NUM>, which are travel motors that respectively rotate the left rear wheel 102a and the right rear wheel 102b, and the mower motor <NUM>, which rotates the cutter blades <NUM>, are supplied with power from an inverter <NUM>. The inverter <NUM> includes a travel motor inverter <NUM> that supplies power to the left motor <NUM> and the right motor <NUM>, and a mower motor inverter <NUM> that supplies power to the mower motor <NUM>. The inverter <NUM> drives are based on a control signal from a control device <NUM>. The inverter <NUM> is connected to the battery <NUM>, which is a power source.

A mower operation part <NUM>, a left steering angle detection sensor 191a, a right steering angle detection sensor 191b, a left motor rotation detection sensor 192a, a right motor rotation detection sensor 192b, a mower motor rotation detection sensor <NUM>, and a current detector <NUM> are connected to the control device <NUM>.

The mower operation part <NUM> is a manual operation part that is used to drive the mower motor <NUM> or stop the mower motor <NUM> from driving, selectively. In the present example, the mower operation part <NUM> is configured as a swing lever that is swingable to a first position (ON) and a second position (OFF). Upon the mower operation part <NUM> being operated to swing to the first position, an operation position detection sensor 190a provides the control device <NUM> with a drive instruction, which is an instruction to drive the mower motor <NUM>. Upon the mower operation part <NUM> being operated to swing to the second position, the operation position detection sensor 190a provides the control device <NUM> with a stop instruction, which is an instruction to stop the mower motor <NUM> from driving.

The left steering angle detection sensor 191a detects the swing angle of the left steering lever 115a. The right steering angle detection sensor 191b detects the swing angle of the right steering lever 115b. The left motor rotation detection sensor 192a detects the number of rotations of the left motor <NUM>. The right motor rotation detection sensor 192b detects the number of rotations of the right motor <NUM>. The mower motor rotation detection sensor <NUM> detects the number of rotations of the mower motor <NUM>.

The current detector <NUM>, which is built into the mower motor inverter <NUM>, detects a current flowing through the mower motor <NUM>.

As shown in <FIG>, the control device <NUM> receives detection signals input from a mower drive state detector <NUM>, a steering state detector <NUM>, and a travel state detector <NUM>. The mower drive state detector <NUM> includes the mower motor rotation detection sensor <NUM>, the current detector <NUM>, and so on. The steering state detector <NUM> includes the left steering angle detection sensor 191a and the right steering angle detection sensor 191b. The travel state detector <NUM> includes the left motor rotation detection sensor 192a and the right motor rotation detection sensor 192b.

The control device <NUM> includes functional units such as an input signal processor <NUM>, a left wheel speed calculator <NUM>, a right wheel speed calculator <NUM>, a travel motor controller <NUM>, a mower motor controller <NUM>, a mower abnormality detector <NUM>, and an abnormality notifier <NUM>, and these functional units are built as pieces of hardware or software. The input signal processor <NUM> has a sensor information processing function and an operational input processing function. The input signal processor <NUM> processes external signals from the travel state detector <NUM>, the steering state detector <NUM>, the mower drive state detector <NUM>, and so on, and converts the signals to pieces of information that can be internally used by the control device <NUM>.

The left wheel speed calculator <NUM> obtains the rotational speed (the number of rotations) of the left rear wheel 102a, i.e. the rotational speed (the number of rotations) of the left motor <NUM>, based on operational information received via the left steering angle detection sensor 191a, which detects the amount of movement of the left steering lever 115a operated by the driver. Similarly, the right wheel speed calculator <NUM> obtains the rotational speed (the number of rotations) of the right rear wheel 102b, i.e. the rotational speed (the number of rotations) of the right motor <NUM>, based on operational information received via the right steering angle detection sensor 191b, which detects the amount of movement of the right steering lever 115b operated by the driver.

The travel motor controller <NUM> provides the travel motor inverter <NUM> with control signals for supplying the left motor <NUM> and the right motor <NUM> with power that is required to achieve the rotational speed of the left motor <NUM> and the rotational speed of the right motor <NUM> obtained by the left wheel speed calculator <NUM> and the right wheel speed calculator <NUM>. The travel motor inverter <NUM> includes a left wheel power supplier 171a and a right wheel power supplier 171b. The rotational speeds of the left motor <NUM> and the right motor <NUM> change according to the amount of power individually supplied thereto by the left wheel power supplier 171a and the right wheel power supplier 171b. Therefore, the rotational speeds of the left rear wheel 102a and the right rear wheel 102b can be set different from each other, and the grass mower can turn due to the difference between the speeds of the left and right rear wheels.

Upon the mower operation part <NUM> being switched to the first position (ON) and the operation position detection sensor 190a providing the control device <NUM> with a first position detection signal, which is a drive instruction and is an instruction to drive the mower motor <NUM>, the mower motor controller <NUM> controls a mower motor power supplier 172a of the mower motor inverter <NUM> to drive the mower motor <NUM>.

In the present example, the mower abnormality detector <NUM> detects an abnormality that has occurred in the power transmission path established by the mower power transmission mechanism MTS, based on a detection signal from the current detector <NUM>, which is one of the components of the mower drive state detector <NUM>. Furthermore, upon the mower abnormality detector <NUM> detecting an abnormality that has occurred in the power transmission path, the mower motor <NUM> is forcibly stopped even if a drive instruction has been input using the mower operation part <NUM>. Note that, in order to recover the mower motor <NUM> from a forcibly stopped state, a recovery operation needs to be performed using the mower operation part <NUM>. Specifically, the mower operation part <NUM> is first returned from the second position to the first position and an instruction to stop the mower motor <NUM> is input to the control device <NUM>, and thereafter the mower operation part <NUM> is switched from the second position to the first position and a drive instruction is input to the control device <NUM>. Thus, the mower motor <NUM> starts driving again.

One specific abnormality detection method that can be employed by the mower abnormality detector <NUM> is to check the current value of the mower motor power supplier 172a, detected by the current detector <NUM> while the mower unit <NUM> is driving (while the cutter blades <NUM> are rotating). A current value under a no load condition or a normal load condition can be used as a reference value, and a value that is lower than this reference value by a predetermined amount can be used as an abnormality detection threshold value. In this case, if the current value falls below the predetermined value (the abnormality detection threshold value) despite the mower unit <NUM> being driven, the mower abnormality detector <NUM> can determine that an abnormality has occurred in the power transmission path from the mower motor <NUM> to the cutter blades <NUM>. In this regard, in order to prevent a sudden drop in the current value, which may be caused by a disturbance or the like, from being associated with the occurrence of an abnormality, it is preferable that an average of current values that have been measured over a period of time is used as a value that is to be compared with the abnormality detection threshold value.

The abnormality notifier <NUM> notifies the driver of the occurrence of an abnormality when the mower abnormality detector <NUM> detects an abnormality in the power transmission path, using a display <NUM> or a speaker <NUM> or both. If the mower abnormality detector <NUM> can discern between various types of abnormalities, e.g. between a power transmission failure in the mower power transmission mechanism MT such as disengagement of the belt and an attachment failure in which the cutter blades <NUM> and the rotation shafts <NUM> are improperly attached, based on the amount of a drop from the reference current value, it is preferable that the driver is notified of an abnormality such that the driver can discern the type of abnormality.

Next, the following describes an example of a flow of control for detecting an abnormality in the power transmission path in the grass mower, with reference to the flowchart shown in <FIG>.

This flowchart starts from a point in time when the grass mower is in a work standby state (#<NUM>). When the grass mower is in a work standby state, a main SW is ON and the mower operation part <NUM> is at the second position. To transition from a work standby state to a working state, the grass mower first requires that the mower operation part <NUM> is switched to the first position (#<NUM>). Upon the mower operation part <NUM> being switched to the first position (#<NUM>: "Yes" branch), the mower motor <NUM> starts rotating. The grass mower stands by until the number of rotations of the mower motor <NUM>, which has started rotating, reaches a rated number of rotations (#<NUM>: "No" branch). Although not shown in this flowchart, if the mower motor <NUM> does not reach the rated number of rotations within a predetermined period of time, the mower motor <NUM> is forcibly stopped. At this time, if the travel motors are driving, the travel motors are also forcibly stopped. If the mower motor <NUM> reaches the rated number of rotations within the predetermined period of time (#<NUM>: "Yes" branch), the current value of the mower motor <NUM> is obtained (#<NUM>). The current value thus obtained is compared with an abnormality detection threshold value that has been set in advance (#<NUM>). If the current value is no less than the abnormality detection threshold value (#<NUM>: "No" branch), it is determined that there is no abnormality, and furthermore, whether or not the mower operation part <NUM> has been switched to the second position is checked (#<NUM>). If the mower operation part <NUM> has been switched to the second position (#<NUM>: "Yes" branch), it means that mowing work has been suspended. Therefore, processing returns to step #<NUM> and the grass mower enters a work standby state. If the mower operation part <NUM> has not been switched to the second position, i.e. if the mower operation part <NUM> is still at the first position (#<NUM>: "No" branch), mowing work continues, and processing returns to step #<NUM> so that the current value of the mower motor <NUM> is obtained again.

At determination in step #<NUM>, if the current value is less than the abnormality detection threshold value, it is determined that there is an abnormality (#<NUM>: "Yes" branch), and the mower motor <NUM> is forcibly stopped (#<NUM>). At the same time, the abnormality notifier <NUM> performs abnormality notification (#<NUM>). Subsequently, recovery treatment is performed to address the abnormality (#<NUM>). For example, if the abnormality is disengagement of the belt <NUM>, the belt <NUM> is re-attached. To return to mowing work after recovery treatment has been completed, the grass mower first requires that whether or not the mower operation part <NUM> has been switched to the second position is checked (#<NUM>). If the mower operation part <NUM> has been switched to the second position (#<NUM>: "Yes" branch), the forcibly stopped state is cancelled, and processing returns to step #<NUM> so that the grass mower enters a work standby state. In step #<NUM>, if the mower operation part <NUM> is still at the first position (#<NUM>: "No" branch), the forcibly stopped state is not cancelled, and the cutter blades <NUM> do not start rotating.

Claim 1:
An electric travelling vehicle comprising:
a vehicle body (<NUM>);
a power device that includes an electric motor (<NUM>) that is driven by being excited, and an electromagnetic power-off brake (<NUM>);
a drive wheel (<NUM>) configured to be driven by power from the power device;
a steering operation part (<NUM>) configured to be displaced to a forward travel position, a neutral position, and a rearward travel position from one to another by a manual operation;
a motor controller (<NUM>) configured to control the electric motor (<NUM>) based on displacement of the steering operation part (<NUM>);
a brake controller (<NUM>) configured to bring the electromagnetic power-off brake (<NUM>) into a released state or a braking state; and
a travel state detector (<NUM>) configured to detect a travelling state that is accompanied with the released state, a stopped state that is accompanied with the braking state, and a transit stopped state that is accompanied with the braking state and is a transit state between the stopped state and the travelling state,
characterized in that:
the electric travelling vehicle comprises a brake operation part (<NUM>) of a manual operation type,
wherein the brake operation part (<NUM>) being configured to be switchable to a first position to make a request to bring the electromagnetic power-off brake (<NUM>) into the released state, and to a second position to make a request to bring the electromagnetic power-off brake (<NUM>) into the braking state,
a transition from the travelling state to the transit stopped state occurs on a condition that, in the travelling state, the steering operation part (<NUM>) has been returned to the neutral position and a predetermined first period of time has elapsed upon a rotational speed of the electric motor (<NUM>) decreasing below a very low rotational speed,
a transition from the transit stopped state to the stopped state occurs at least on a condition that, in the transit stopped state, the brake operation part (<NUM>) has been switched to the second position, and
a transition from the stopped state to the transit stopped state occurs at least on a condition that, in the stopped state, the brake operation part (<NUM>) has been switched to the first position.