A motor-driven vehicle includes: a motor, a first rotational shaft to be driven to rotate by the motor, a clutch, a second rotational shaft to be driven to rotate by the motor via the clutch, an arm configured to rotate in association with rotation of the second rotational shaft, and at least two wheels, wherein each of the at least two wheels being attached to the arm at a position offset from a rotation center of the arm, and each of the at least two wheels being rotatable in association with rotation of the first rotational shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2020-190506 filed on Nov. 16, 2020, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The technology disclosed herein relates to a motor-driven vehicle. In particular, the technology relates to a structure of a vehicle configured to ascend or descend a staircase.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 7-2154 (JP 7-2154 A) describes a motor-driven vehicle having two wheels attached to each arm and configured to ascend or descend steps by using rotation of the arms and rotation of the wheels.

SUMMARY

The motor-driven vehicle described above has arm motors and wheel motors. Therefore, a problem arises in that the motor-driven vehicle has a large number of motors.

A motor-driven vehicle according to one aspect disclosed herein includes a motor, a first rotational shaft to be driven to rotate by the motor, a clutch, a second rotational shaft to be driven to rotate by the motor via the clutch, an arm configured to rotate in association with rotation of the second rotational shaft, and at least two wheels, each of the at least two wheels being attached to the arm at a position offset from a rotation center of the arm, and each of the at least two wheels being rotatable in association with rotation of the first rotational shaft.

According to the aspect described above, the at least two wheels can be rotated by the first rotational shaft by disengaging the clutch. Further, the arm can be rotated by the second rotational shaft by engaging the clutch. The arm and the wheels can be driven by one motor. The number of motors can be reduced as compared to a case where an arm motor and a wheel motor are provided individually.

In the aspect described above, the motor-driven vehicle may further include a brake configured to restrict the rotation of the second rotational shaft. According to the aspect described above, the arm can be fixed.

In the aspect described above, the motor-driven vehicle may further include a processor configured to selectively execute a first mode in which the clutch is disengaged and the brake is operated, or a second mode in which the clutch is engaged and the brake is released. According to the aspect described above, the arm can be fixed by the brake in the first mode. In the second mode, the arm can be rotated by engaging the clutch.

In the aspect described above, the motor-driven vehicle may further include a sun gear located at the rotation center of the arm and rotatable in association with the rotation of the first rotational shaft, and planetary gears located at rotation centers of the at least two wheels and engaging with the sun gear. A central axis of the first rotational shaft and a central axis of the second rotational shaft may be coaxial. According to the aspect described above, the at least two wheels can be rotated in association with the rotation of the first rotational shaft. Further, the at least two wheels can be rotated about the rotation center of the arm.

In the aspect described above, a gear ratio among the second rotational shaft, the sun gear, and the planetary gears may be (n+1):1:−n. The negative sign of the value in the ratio indicates that the elements rotate in opposite directions. According to the aspect described above, it is possible to achieve an operation in which the arm rotates relative to a vehicle body without rotating the wheels relative to the vehicle body.

In the aspect described above, the second rotational shaft may be a hollow shaft. The first rotational shaft may penetrate the second rotational shaft. According to the aspect described above, the central axis of the first rotational shaft and the central axis of the second rotational shaft can be coaxial.

In the aspect described above, the motor-driven vehicle may further include a first driving shaft to be driven to rotate by the motor, a second driving shaft to be driven to rotate by the motor via the clutch, a first power transmission mechanism connecting the first driving shaft and the first rotational shaft, and a second power transmission mechanism connecting the second driving shaft and the second rotational shaft. According to the aspect described above, the arm and the wheels can be driven by one motor.

DETAILED DESCRIPTION OF EMBODIMENTS

First Embodiment

Structure of Vehicle1

FIG.1is a schematic top view of a vehicle1. In a coordinate system ofFIG.1, a symbol “F” represents a forward vehicle direction. A symbol “U” represents an upward vehicle direction. A symbol “L” represents “left” when the front of the vehicle is viewed from the rear. In the other figures, the coordinate system has the same meanings.

The vehicle1includes a front vehicle2, a rear vehicle3, and a direct-drive actuator4. The direct-drive actuator4is a member that couples the front vehicle2and the rear vehicle3. A processor10causes the direct-drive actuator4to extend or contract to variably control a distance between the front vehicle2and the rear vehicle3. The front vehicle2includes the processor10and a pair of right and left units11and12. The rear vehicle3includes a pair of right and left units13and14. The processor10includes a central processing unit (CPU) and a memory (both are not illustrated), and is communicable with the units11to14and the direct-drive actuator4. Since the units11to14have the same structure, the unit11is mainly described below.

FIG.2is a schematic top view of the unit11. The unit11includes a driver20, a first rotational shaft41, a second rotational shaft42, an arm43, a sun gear50, planetary gears51and52, and wheels61and62.FIG.3is a side view of the unit11that is viewed from the right of the vehicle1. InFIG.3, the first rotational shaft41, the second rotational shaft42, the arm43, the sun gear50, and the planetary gears51and52are taken in the illustration.

The second rotational shaft42is a hollow shaft. The first rotational shaft41penetrates the second rotational shaft42. Thus, the first rotational shaft41and the second rotational shaft42have the same central axis CA. That is, the first rotational shaft41and the second rotational shaft42are coaxial. The arm43is connected to one end of the second rotational shaft42. A pulley35is arranged at the other end of the second rotational shaft42. The second rotational shaft42can be driven to rotate by transmitting power to the pulley35via a belt34. The arm43rotates in a direction of an arrow A3inFIG.3in association with the rotation of the second rotational shaft42.

The sun gear50is located at the central axis CA that is a rotation center of the arm43. The sun gear50is connected to one end of the first rotational shaft41. A pulley33is arranged at the other end of the first rotational shaft41. The first rotational shaft41can be driven to rotate by transmitting power to the pulley33via a belt32. The sun gear50rotates in a direction of an arrow A0inFIG.3in association with the rotation of the first rotational shaft41.

The planetary gears51and52are rotatably attached to positions offset from the central axis CA that is the rotation center of the arm43. The planetary gear51engages with the sun gear50with its central axis located at a rotation center PC1of the wheel61. The planetary gear52engages with the sun gear50with its central axis located at a rotation center PC2of the wheel62. Thus, the wheels61and62rotate in directions of arrows A1and A2inFIG.3in association with the rotation of the first rotational shaft41. The planetary gears51and52have the same number of teeth. The wheels61and62have the same diameter.

Rotational shafts of the planetary gears51and52are fixed onto the arm43serving as a carrier. Torques of the planetary gears51and52are transmitted by the sun gear50. Thus, the unit11has a structure similar to that of a planetary-gearing speed reducer.

The driver20drives the first rotational shaft41and the second rotational shaft42to rotate. The driver20includes a motor21, a first speed reducer22, a first driving shaft23, a pulley24, a clutch25, a second driving shaft26, gears27and28, a brake29, a second speed reducer30, a pulley31, the belts32and34, and the pulleys33and35.

The motor21is connected to the first driving shaft23via the first speed reducer22. The first driving shaft23is connected to the first rotational shaft41by a first power transmission mechanism TM1including the pulley24, the belt32, and the pulley33. Thus, the first rotational shaft41can be driven to rotate by the motor21.

The first rotational shaft41engages with the second driving shaft26via the clutch25. The second driving shaft26is connected to a second power transmission mechanism TM2via the second speed reducer30. The second power transmission mechanism TM2includes the pulley31, the belt34, and the pulley35, and connects the second driving shaft26and the second rotational shaft42. Thus, the second rotational shaft42can be driven to rotate by the motor21via the clutch25. The second rotational shaft42is connected to the brake29via the gears27and28. The brake29restricts the rotation of the second rotational shaft42.

The processor10can selectively operate the units11to14in a first mode or a second mode. In the first mode, the clutch25is disengaged. In the second mode, the clutch25is engaged and the brake29is released. In some embodiments, it is not desirable to simultaneously drive the clutch25and the brake29. This is because a torque of the motor21is transmitted to the brake29and the motor21has an excessive load when the clutch25and the brake29are driven simultaneously. Details of the first and second modes are described later.

Operations in First Mode

In the first mode, the wheels61and62rotate about their axes. In the first mode, the clutch25is disengaged. The first driving shaft23can be driven to rotate by the motor21without rotating the second driving shaft26. A driving force of the first driving shaft23is transmitted to the first rotational shaft41via the first power transmission mechanism TM1(pulley24, belt32, and pulley33), and the sun gear50is driven to rotate. Thus, the planetary gears51and52rotate and the wheels61and62rotate.

When the brake29is driven, the arm43can be held stationary. The wheels61and62can be rotated with the arm fixed. When the brake29is released, a driving torque of the arm43can be set to 0. The arm43is rotated by forces received by the wheels61and62from the ground. Thus, the arm43can be rotated in conformity with the shape of irregularities of a traveling surface as illustrated inFIG.4. The arm43can function as a suspension that appropriately holds the wheels61and62on a road surface.

Operations in Second Mode

In the second mode, the wheels61and62rotate about the central axis CA of the arm43. In the second mode, the clutch25is engaged and the brake29is released. Both the first driving shaft23and the second driving shaft26can be driven to rotate by the motor21. As described above, the driving force of the first driving shaft23is transmitted to the wheels61and62via the first rotational shaft41. A driving force of the second driving shaft26is transmitted to the second rotational shaft42via the second speed reducer30and the second power transmission mechanism TM2(pulley31, belt34, and pulley35), and the arm43is driven to rotate. That is, when the clutch25is engaged, the torque of the motor21is transmitted both to the wheels61and62and to the arm43.

The rotation speeds of the wheels61and62in the second mode are determined by constants in a speed reducing system. In the vehicle1described herein, a gear ratio (or torque ratio) among the second rotational shaft42, the sun gear50, and the planetary gear51is set to “(n+1):1:−n”. In other words, an angular velocity ratio among the second rotational shaft42, the sun gear50, and the planetary gear51is set to “n:n(n+1):−(n+1)”. The angular velocity ratio between the sun gear50and the planetary gear51is determined depending on the gear ratio between the sun gear50and the planetary gear51. The angular velocity ratio between the sun gear50and the second rotational shaft42is determined depending on a gear ratio obtained in consideration of three elements that are the first power transmission mechanism TM1, the second speed reducer30, and the second power transmission mechanism TM2. This is because the sun gear50and the second rotational shaft42are connected via the first power transmission mechanism TM1(pulley33, belt32, and pulley24), the second speed reducer30, and the second power transmission mechanism TM2(pulley31, belt34, and pulley35).

By using the gear ratio described above, an operation in which “the arm43rotates relative to a vehicle body without rotating the wheels61and62relative to the vehicle body” can be achieved in the second mode. Thus, a staircase ascending/descending operation can securely be executed as described later.

Conditions to be Satisfied by Speed Reducing System

Description is given of the principle that can achieve the operation in which “the arm43rotates relative to the vehicle body without rotating the wheels61and62relative to the vehicle body” by setting the gear ratio among the second rotational shaft42, the sun gear50, and the planetary gear51to “(n+1):1:−n” and rotating the second rotational shaft42and the planetary gear51in opposite directions.

Since the central axis of the planetary gear51is fixed to the arm43, an angular velocity ωpof the planetary gear51in a coordinate system fixed to the vehicle body is the sum of an angular velocity ωaof the arm43in the coordinate system fixed to the vehicle body and an angular velocity ωapof the planetary gear51in a coordinate system fixed onto the arm43. Thus, Expression (1) is established.
ωp=ωa+ωapExpression (1)

It is assumed that “ωs” represents an angular velocity of the sun gear50in the coordinate system fixed to the vehicle body. An angular velocity ωasof the sun gear50in the coordinate system fixed onto the arm43is represented by Expression (2).
ωas=ωs−ωaExpression (2)

When the gear ratio between the sun gear50and the planetary gear51is 1:−n, the angular velocity ratio between the sun gear50and the planetary gear51is n:−1. The negative sign of the value in the ratio indicates that the gears rotate in opposite directions. Thus, the angular velocity ωapof the planetary gear51in the coordinate system fixed onto the arm43is represented by Expression (3).
ωap=−ωas/n=−(ωs−ωa)/nExpression (3)

Based on the above, the angular velocity ωpof the planetary gear51in the coordinate system fixed to the vehicle body is represented by Expression (4).
ωp=ωa−(ωs−ωa)/nExpression (4)

When a condition that the planetary gear51does not rotate relative to the vehicle body, that is, ωp=0 is substituted into Expression (4), Expression (5) is obtained.
ωs=(n+1)ωaExpression (5)

As understood from Expression (5), the gear ratio between the second rotational shaft42and the sun gear50is (n+1):1.

Thus, the condition that the planetary gear51does not rotate relative to the vehicle body is “(n+1):1:−n” in terms of the gear ratio among the second rotational shaft42, the sun gear50, and the planetary gear51. However, a condition “n≠−1, 0” exists. This is because the gear ratio cannot be 0.

Devised Points in Mechanism and Specific Examples of Setting Values in Speed Reducing System

In some embodiments, a gear ratio from the motor21to the sun gear50is larger than 7 and smaller than 40. In some embodiments, a gear ratio from the motor21to the arm43is larger than 27 and smaller than 113. To achieve those gear ratios, several constraints exist. The first constraint is that a speed reducer having a large gear ratio increases in its size and mass. The second constraint is that the gear ratio can only be set to about 2 in power transmission using a pulley as in the first power transmission mechanism TM1and the second power transmission mechanism TM2.

The unit11herein includes the following mechanism to address those constraints. The first speed reducer22is arranged immediately next to the motor21, and power is transmitted to the sun gear50through speed reduction via the first power transmission mechanism TM1. The second speed reducer30is arranged at a position succeeding the clutch25that switches torque transmission to the arm43. Thus, the gear ratio up to the arm43can be increased. The brake29for holding the arm43stationary is arranged at a position preceding the second speed reducer30. Thus, a holding torque of the brake29can be reduced.

A table ofFIG.5illustrates specific examples of setting values in the speed reducing system according to this embodiment.FIG.5illustrates examples of setting values in the speed reducing system in a case of n=2. That is, the gear ratio among the second rotational shaft42, the sun gear50, and the planetary gear51is “3:1:−2” in this example. In this case, the planetary gear51rotates opposite to the second rotational shaft42and the sun gear50.

The staircase ascending/descending operation of the vehicle1is described with reference toFIG.6toFIG.8. To facilitate understanding,FIG.6toFIG.8illustrate a case where the vehicle1has one vehicle body. Each arm43is represented simply by a straight line. The first mode is used during traveling along flat ground. The vehicle1travels in a traveling direction D1(rightward in the drawing sheets) by driving the wheels. As illustrated inFIG.6, the wheel62abuts against a vertical face VP of a step, and the vehicle1stops.

The first mode is switched to the second mode. The arm43is rotated relative to the vehicle1without rotating the wheels61and62relative to the vehicle1. Thus, as indicated by an arrow A11inFIG.7, the wheel61can be lifted about the wheel62serving as a pivot and brought into contact with the surface of a tread HP.

By continuously using the second mode, the wheel62can be lifted about the wheel61serving as a pivot as indicated by an arrow A12inFIG.8. Thus, the wheel62can be positioned above the tread HP.

In the state ofFIG.8, the second mode is switched to the first mode. That is, the arm43can be held stationary by driving the brake29. Thus, the posture inFIG.8can be kept. The wheel61can be driven to rotate by disengaging the clutch25and driving the motor. Thus, the vehicle1can travel in the traveling direction D1. When the wheel61comes into contact with a next vertical face VP, the vehicle1stops and the first mode is switched to the second mode. Then, the operations described above are repeated to ascend the staircase.

Effects

In a case where the mode for rotating the wheels61and62and the mode for rotating the arm are independently controlled in related art, both a motor for driving the wheels61and62and a motor for driving the arm43are necessary. However, a problem arises in terms of an increase in costs and weight because two motors are necessary per unit. The vehicle1disclosed herein employs the mechanism in which both the wheels61and62and the arm43are driven by one motor21. That is, the wheels61and62can be rotated by the first rotational shaft41and the sun gear50by disengaging the clutch25. Further, the arm43can be rotated by the second rotational shaft42by engaging the clutch25. The number of motors can be reduced as compared to the case where the wheel drive motor and the arm drive motor are provided individually. The costs and weight can be reduced.

In the staircase ascending/descending mechanism described inFIG.7andFIG.8, it is necessary that the wheel serving as the pivot be held stationary to rotate the arm. In the related art, the wheel serving as the pivot is fixed by an external factor that is friction between the wheel and the tread. Under a condition that the mass of the vehicle body or a load is large in a low-friction environment, wheel idling is likely to occur rather than arm rotation. That is, the related art has a problem that the wheel slips and the vehicle cannot ascend or descend the staircase well in a case of a low coefficient of friction between the tread and the wheel. In the vehicle1disclosed herein, the planetary gearing mechanism is used and the gear ratio among the second rotational shaft42, the sun gear50, and the planetary gear51is set to “(n+1):1:−n”. This structure can achieve the operation in which “the arm43rotates relative to the vehicle body without rotating the wheels61and62relative to the vehicle body”. Thus, the wheel61or62serving as the pivot can be held stationary while a driving force is applied from the motor. That is, a braking mechanism that prevents wheel idling can be achieved by the driving force of the motor. Thus, the staircase ascending/descending operation can securely be executed even under the low-friction environment.

Second Embodiment

FIG.9is a schematic top view of a vehicle1aaccording to a second embodiment. Components similar to those in the vehicle1of the first embodiment are represented by the same reference symbols to omit their description. Components unique to the second embodiment are suffixed with “a” for distinction. In the vehicle1a, the structure of the rear vehicle3is similar to that in the first embodiment. That is, the rear vehicle3includes two motors21and two right and left first rotational shafts41. The structure of a front vehicle2aof the vehicle1adiffers from the structure of the front vehicle2in the first embodiment. That is, the front vehicle2aincludes one motor21and one first rotational shaft41acommon to right and left sides. The front vehicle2ais mainly described below.

The motor21is connected to a first driving shaft23a1via the first speed reducer22. The first driving shaft23a1is connected to the first rotational shaft41aby the first power transmission mechanism TM1. The first rotational shaft41ais a single shaft for simultaneously rotating the right and left wheels of the front vehicle2a. The sun gears50are arranged at both ends of the first rotational shaft41ain a vehicle width direction.

The first driving shaft23a1is connected to a first driving shaft23a2by a third power transmission mechanism TM3aincluding pulleys and a belt. The first driving shaft23a2engages with a second driving shaft26a1on the right side of the vehicle via a clutch25a1, and with a second driving shaft26a2on the left side of the vehicle via a clutch25a2. The second driving shaft26a1is connected to a brake29a1and to the second rotational shaft42on the right side of the vehicle via a second power transmission mechanism TM2a1. The second driving shaft26a2is connected to a brake29a2and to the second rotational shaft42on the left side of the vehicle via a second power transmission mechanism TM2a2.

Operations of Front Vehicle2a

In the first mode, the clutches25a1and25a2are disengaged. The driving force of the motor21is transmitted to the first rotational shaft41avia the first driving shaft23a1and the first power transmission mechanism TM1. Thus, the right and left wheels61and62of the front vehicle2arotate at the same rotation speed. The vehicle1acan be steered by controlling the right and left wheels of the rear vehicle3independently of each other.

In the second mode, the clutches25a1and25a2are engaged and the brakes29a1and29a2are released. The driving force of the motor21is transmitted to the right and left second rotational shafts42via the first driving shaft23a1, the third power transmission mechanism TM3a, the first driving shaft23a2, the clutches25a1and25a2, the second driving shafts26a1and26a2, and the second power transmission mechanisms TM2a1and TM2a2. Thus, the right and left arms43of the front vehicle2arotate at the same rotation speed.

In the vehicle1aaccording to the second embodiment, the number of motors can further be reduced from four to three as compared to the vehicle1of the first embodiment (FIG.1). It is possible to increase the effect of reducing the costs and weight.

Third Embodiment

FIG.10is a schematic top view of a vehicle1baccording to a third embodiment. Components unique to the third embodiment are suffixed with “b” for distinction. The structure of the front vehicle2aof the vehicle1bis similar to that in the second embodiment, and therefore description of the structure is omitted. The structure of a rear vehicle3bof the vehicle1bdiffers from the structure of the rear vehicle3in each of the first and second embodiments. That is, the rear vehicle3bincludes one motor21. The rear vehicle3bis mainly described below.

The motor21is connected to a first driving shaft23b1via the first speed reducer22. The first driving shaft23b1is connected to a first driving shaft23b3by a clutch38band a fourth power transmission mechanism TM4b. The first driving shaft23b1is connected to the first driving shaft23b3also by gears36and37, a first driving shaft23b2, a clutch39b, and a fifth power transmission mechanism TM5b. The first driving shaft23b3is connected to the first rotational shaft41on the right side of the vehicle by a first power transmission mechanism TM1b1. The first driving shaft23b3is connected to the second rotational shaft42on the right side of the vehicle via a clutch25b1and a second power transmission mechanism TM2b1.

The first driving shaft23b1is connected to a first driving shaft23b4by a sixth power transmission mechanism TM6b. The first driving shaft23b4is connected to the first rotational shaft41on the left side of the vehicle by a first power transmission mechanism TM1b2. The first driving shaft23b4is connected to the second rotational shaft42on the left side of the vehicle via a clutch25b2and a second power transmission mechanism TM2b2.

Operations of Rear Vehicle3b

In the first mode, the clutches25b1and25b2are disengaged. To rotate the right and left wheels of the vehicle in the same direction (travel straightforward), the clutch38bis engaged and the clutch39bis disengaged. The driving force of the motor21is transmitted to the first rotational shaft41on the right side of the vehicle via the first driving shaft23b1, the clutch38b, the fourth power transmission mechanism TM4b, the first driving shaft23b3, and the first power transmission mechanism TM1b1. The driving force of the motor21is transmitted to the first rotational shaft41on the left side of the vehicle via the sixth power transmission mechanism TM6b, the first driving shaft23b4, and the first power transmission mechanism TM1b2.

To rotate the right and left wheels of the vehicle in opposite directions (make a spin turn), the clutch38bis disengaged and the clutch39bis engaged. A driving force of rotation opposite to that of the first driving shaft23b1is transmitted to the first driving shaft23b2by the gears36and37. The driving force of the first driving shaft23b2is transmitted to the first rotational shaft41on the right side of the vehicle via the clutch39b, the fifth power transmission mechanism TM5b, the first driving shaft23b3, and the first power transmission mechanism TM1b1.

In the second mode, the clutches25b1and25b2are engaged and brakes29b1and29b2are released. The driving force of the first driving shaft23b3is transmitted to the second rotational shaft42on the right side of the vehicle via the clutch25b1and the second power transmission mechanism TM2b1. The driving force of the first driving shaft23b4is transmitted to the second rotational shaft42on the left side of the vehicle via the clutch25b2and the second power transmission mechanism TM2b2.

In the vehicle1baccording to the third embodiment, the number of motors can further be reduced from four to two as compared to the vehicle1of the first embodiment (FIG.1). It is possible to increase the effect of reducing the costs and weight.

Although the specific examples of the present disclosure are described above in detail, the examples are only illustrative and are not intended to limit the claims. The technologies described in the claims encompass various modifications and changes to the specific examples described above. The technical elements described herein or illustrated in the drawings exert technical utility solely or in various combinations, and are not limited to the combination described in the claims as filed. The technologies described herein or illustrated in the drawings may simultaneously achieve a plurality of objects, and exert technical utility by achieving one of the objects.

MODIFIED EXAMPLES

The number of planetary gears mounted on the arm is not limited to two, and may be three or more. For example, three planetary gears may radially be mounted about the central axis CA of the arm43. The sun gear may engage with the three planetary gears.

The power transmission mechanism is not limited to the structure including the pulleys and the belt. For example, the power transmission mechanism may include a chain or gears.