JP2005193788A - Electric power steering device of snowmobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device of a snowmobile capable of providing comfortable steerability to a driver under any situation in which the snowmobile is used. <P>SOLUTION: The electric power steering device 3 of the snowmobile 1 is arranged in an engine room 30. A controller 5 controls the output of an assist motor 4 according to the vehicle speed and the steering force of the snowmobile 1. The output of the assist motor 4 is decelerated, and provided to a steering mechanism as the assist force to assist the steering force of a steering wheel 45. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering device for a snow vehicle having a four-cycle engine mounted on a front portion of a vehicle body and a steering mechanism for transmitting a steering force of a steering handle to a steering sled.

  Conventionally, in a snow vehicle that runs on the snow (snowmobile), the two skis provided on the left and right of the front of the vehicle body are steered by the steering handle. Compared to a four-wheeled vehicle that steers, the friction resistance between the snow surface and skis is smaller than the friction resistance between the road surface and tires, so it is considered unnecessary to equip snow vehicles with a power steering device. It has been.

  Many four-wheeled vehicles are equipped with an electric power steering device in order to reduce the steering force of the steering wheel. This electric power steering device is connected to a steering mechanism that steers wheels, and has an auxiliary force device that uses an electric motor as a drive source. The auxiliary power device applies an auxiliary force to the steering mechanism. In an electric power steering device for a four-wheeled vehicle, generally, a controller controls the drive current of the electric motor in accordance with the steering force and the vehicle speed, and the output of the electric motor has an appropriate auxiliary force with respect to the steering direction. It is controlled to become.

Some electric power steering devices for four-wheeled vehicles control the driving current of the electric motor by discriminating road surface conditions and running conditions. As a method for determining the road surface condition and the traveling state, a method of determining whether the host vehicle is traveling or stopped by using a vehicle speed sensor or a torque sensor (for example, refer to Patent Document 1), and estimating a road surface anti-torque, a low μ road or a high There are a method for determining whether the vehicle is a μ road (for example, see Patent Document 2), a method for determining whether the vehicle is traveling on a bad road (for example, see Patent Document 3), or the like.
JP 2000-142433 A JP 2001-233231 A JP 2003-137121 A

  However, with the recent four-cycle engine accompanying environmental problems, a four-cycle engine is also being installed in snow vehicles. The vehicle weight tends to increase due to the installation of this 4-cycle engine, and in general snow vehicles, the engine is mounted on the front of the vehicle body. Is required. In particular, in forests and mountains, there are many obstacles and it is necessary to frequently perform avoidance operations, and since there are many deep snow roads and steep climb slopes, the frequency of the driver's steering operation with a large steering force increases, It is difficult to obtain comfortable steering.

  The present invention has been made in view of the above problems, and provides an electric power steering device for a snow vehicle that can give a driver a comfortable steering performance in any situation where the snow vehicle is used. With the goal.

  In order to achieve the above object, the present invention provides an electric power steering apparatus for a snow vehicle having a four-cycle engine mounted on a front portion of a vehicle body and a steering mechanism for transmitting a steering force of a steering handle to a steering sled. , An electric motor, an auxiliary force mechanism for converting the output of the electric motor into an auxiliary force for assisting the steering force, and applying the auxiliary force to the steering mechanism, and depending on the vehicle speed and the steering force of the snow vehicle Control means for controlling the output of the electric motor, and at least the electric motor and the auxiliary force mechanism are provided in an engine room of the snow vehicle.

  In addition, the control means includes a traveling state determination unit that determines a traveling state of the snow vehicle, and the electric motor according to the vehicle speed and the steering force of the snow vehicle based on a determination result by the traveling state determination unit. It is preferable to have correction means for correcting the output.

  Further, the traveling state determination means is configured to control the output of the electric motor based on the traveling state of the snow vehicle based on the vehicle speed and the steering force of the snow vehicle. It is determined whether the driving state corresponds to a decrease correction mode for correcting the output of the motor to be decreased or an increase correction mode for correcting the output of the electric motor to be increased with respect to the normal mode. Preferably, the means corrects the output of the electric motor according to the vehicle speed and the steering force of the snow vehicle based on a mode corresponding to the traveling state of the snow vehicle.

  Further, the traveling state determination means is a traveling state in which the traveling state of the snow vehicle corresponds to any of the modes based on the vehicle speed of the snow vehicle and the throttle opening or engine speed of the snow vehicle. It is preferable to determine whether or not.

  The vehicle further includes an external input unit operated by a driver of the snow vehicle, and the travel state determination unit, when receiving an input from the external input unit, travels the snow vehicle regardless of the travel state of the snow vehicle. It is preferable to determine that the state is a traveling state corresponding to the increase correction mode.

  According to the present invention, since the output of the electric motor is controlled in accordance with the vehicle speed and steering force of the snow vehicle, an appropriate assisting force is given to the steering mechanism, and the driver can be used in any situation where the snow vehicle is used. Can give a comfortable steering.

  In addition, the electric power steering device of the present invention is lighter in weight and smaller in installation space than a hydraulic one, so the engine room is occupied by a four-cycle engine, and the engine room In a snow vehicle in which an empty space is limited, at least the electric motor and the auxiliary force mechanism can be easily arranged in the engine room of the snow vehicle. Moreover, the increase in the vehicle weight of a snow vehicle can be suppressed.

  Further, according to the present invention, the running state of the snow vehicle is determined, and the output of the electric motor corresponding to the vehicle speed and the steering force of the snow vehicle is corrected based on the determination result. A comfortable steering performance can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a snow vehicle equipped with an electric power steering apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the snow vehicle (snowmobile) 1 includes a vehicle body 31 having a monocoque frame structure. Here, in the following description, the front-rear direction and the left-right direction of the snow vehicle 1 are directions based on the driver. A front frame (engine mount frame) 31a of the vehicle body 31 is mounted with a three-cylinder four-cycle engine (hereinafter simply referred to as an engine) 2 and is covered with an engine hood 39 defining an engine room 30 from above. ing. A pair of left and right steering sleds 32 are arranged at the lower portion of the front frame 31a so as to be able to swing in the left-right direction. A sled house portion 40 protruding upward in the engine room 30 is formed in the front portion of the front frame 31a. In the sled house portion 40, a suspension for suspending and buffering each steering sled 32 is provided. The link part 41 of the steering mechanism is accommodated.

  On the upper part of the rear frame 31b of the vehicle body 31, a bowl-shaped seat 42 is provided. Steps 43 (left and right side steps) are respectively provided on the left and right sides of the seat 42 in the vehicle body width direction in the rear frame 31b.

  A driving crawler 34 is disposed below the rear frame 31 b of the vehicle body 31. The crawler 34 includes a drive wheel 35 disposed at the front end of the rear frame 31b, a driven wheel 36 disposed at the rear end of the rear frame 31b, a plurality of intermediate wheels 37, and a suspension that suspends and cushions them. It has a mechanism 38 and a track belt 33 that circulates around each wheel. The drive wheels 35 are attached to a drive shaft (track shaft) 35a driven by the output of the engine 2, and the rotational speed of the drive shaft 35a is detected in the vicinity of the drive shaft 35a to obtain the vehicle speed of the snow vehicle 1. A vehicle speed sensor 55 is provided.

  A steering shaft 44 extending in a state of being slightly tilted rearward in the engine room 30 upward is disposed at a position immediately before the seat 42 in the rear portion of the engine hood 39. A bar-like steering handle 45 is provided at the upper end of the steering shaft 44. The steering shaft 44 is connected to the intermediate shaft 50 via the electric power steering device 3 disposed in the engine room 30, and the intermediate shaft 50 is connected to the link portion 41 of the steering mechanism. As a result, a steering mechanism that transmits the steering force of the steering handle 45 to the steering sled 32 through the steering shaft 44, the electric power steering device 3, the intermediate shaft 50, and the link portion 41 of the steering mechanism is configured.

  Next, the steering mechanism in the snow vehicle 1 will be described in detail with reference to FIG. FIG. 2 is a perspective view showing a main part of the steering mechanism in the snow vehicle 1.

  As shown in FIG. 2, the steering shaft 44 provided with a steering handle 45 at its upper end is inserted into a column assembly 51 fixed to the vehicle body 31 side, and its lower end is connected to the electric power steering device 3 as an input shaft. Is done.

  The electric power steering device 3 includes an assist motor 4 formed of a DC electric motor, a column case 54, and a controller 5 for controlling the assist motor 4. The column case 54 incorporates a deceleration mechanism and a torque detection device that decelerates the output of the assist motor 4 and applies the decelerated output as an assisting force for assisting the steering torque of the steering handle 45. The controller 5 is attached to the column case 54 via a bracket (not shown). The electric power steering device 3 is provided with an output shaft for outputting a steering force, and this output shaft is connected to the input side of the universal joint 52. An intermediate shaft 50 is connected to the output side of the universal joint 52.

  Next, the configuration of the electric power steering device 3 will be described with reference to FIGS. 3 and 4. 3A is a longitudinal sectional view of the main part of the electric power steering apparatus of FIG. 2, and FIG. 3B is a sectional view obtained along the line AA of FIG. 3A. is there. FIG. 4 is a perspective view showing the internal structure of the electric power steering apparatus 3 of FIG.

  As shown in FIGS. 3A and 4, the electric power steering device 3 includes an input shaft 17 integrally formed at the lower end portion of the steering shaft 44 inserted through the column assembly 51, and is coaxial with the input shaft 17. The output shaft 18 is rotatably supported in the column case 54. The end of the input shaft 17 is connected to one end of the output shaft 18 via a cylindrical sensor shaft 8 and a torsion bar 9 inserted coaxially into the sensor shaft 8. The other end of the output shaft 18 is connected to the universal joint 52 (see FIG. 4).

  The sensor shaft 8 includes a shaft member that extends coaxially with the input shaft 17, and one end of the sensor shaft 8 is coupled to the input shaft 17. The other end of the sensor shaft 8 is engaged with the output shaft 18 so as to allow only a certain angle of rotation and not to rotate any further. The torsion bar 9 is a member that elastically connects the input shaft 17 and the output shaft 18, one end of which is coupled to the input shaft 17 and the other end is coupled to the output shaft 18.

  A slider 10 is inserted into the sensor shaft 8 so as to be slidable in the axial direction of the sensor shaft 8. A ball groove 11 extending in a spiral shape is formed on the outer periphery of the lower end portion of the sensor shaft 8. The ball groove 11 has a shape capable of receiving a part of the steel ball 13. On the outer periphery in the vicinity of the upper end portion of the slider 10, a groove portion 10a that engages with an engaging portion 7a (shown in FIGS. 3B and 4) of a lever 7 of a torque sensor to be described later is formed. A ring 12 surrounding the outer periphery of the lower end of the sensor shaft 8 is attached to the lower end of the slider 10 via a cross guide 19, and a hole for receiving the steel ball 13 is provided in the cross guide 19. The steel ball 13 is held by the ring 12, the hole of the cross guide 19, and the ball groove 11, and can move along the ball groove 11.

  A worm wheel 14 is attached to one end of the output shaft 18. The worm wheel 14 is engaged with a worm gear 15 attached to the drive shaft 4 a of the assist motor 4, whereby the rotation of the drive shaft 4 a is decelerated and transmitted to the output shaft 18.

  As shown in FIG. 4, the assist motor 4 has a clutch 16 interposed between its output shaft and the drive shaft 4a. The controller 5 controls the connection and disconnection operation of the output shaft of the assist motor 4 and the drive shaft 4 a by the clutch 16. The controller 5 normally holds the output shaft of the assist motor 4 and the drive shaft 4a in a connected state, and disconnects the output shaft of the assist motor 4 and the drive shaft 4a when the assist motor 4 fails. Thus, the clutch 16 is controlled. Thereby, the steering state by the steering handle 45 is ensured as a state in which manual steering operation is possible, and fail-safe can be achieved.

  The electric power steering device 3 has a torque detection device as described above. The torque detection device includes a sensor shaft 8, a torsion bar 9, a slider 10, a cross guide 19, a ring 12, a steel ball 13, a torque sensor 6, and the like. As shown in FIGS. 3B and 4, the torque sensor 6 is attached to the column case 54. An eccentric cam-like lever 7 is attached to the torque sensor 6, and an engaging portion 7 a that engages with the groove portion 10 a of the slider 10 is provided on the lever 7. As will be described later, the lever 7 is configured to convert the axial movement of the sensor shaft 8 of the slider 10 into a rotational movement and transmit it to the torque sensor 6.

  Here, when a steering torque acts on the steering handle 45, the input shaft 17 is rotated. As a result, the torsion bar 9 is slightly twisted to cause a rotational displacement corresponding to the steering torque between the input shaft 17 (sensor shaft 8) and the output shaft 18. However, the engagement between the sensor shaft 8 and the output shaft 18 is restricted so that no more than a predetermined rotational displacement occurs between the input shaft 17 (sensor shaft 8) and the output shaft 18.

  When a rotational displacement occurs between the sensor shaft 8 and the output shaft 18, the steel ball 13 moves along the ball groove 132, and the slider 10 moves in the axial direction of the sensor shaft 8 as the steel ball 13 moves. The amount of movement of the moving slider 10 corresponds to the amount of rotational displacement generated between the sensor shaft 8 and the output shaft 18. When the slider 10 moves in the axial direction of the sensor shaft 8, the movement in the axial direction of the slider 10 is converted into movement in the rotational direction via the lever 7 of the torque sensor 6 and transmitted to the torque sensor 6. The torque sensor 6 takes out the rotation amount and direction of the lever 7 as a change value of the potentiometer in the torque sensor 6, and outputs a voltage signal indicating the change value to the controller 5. That is, by detecting the axial displacement of the slider 10 by the torque sensor 6, the steering torque acting on the input shaft 17 and its direction are detected.

  Further, as shown in FIG. 7, the torque sensor 6 outputs two main and sub voltage signals to the controller 5 as voltage signals corresponding to the steering torque when the driver performs the steering operation. The controller 5 can input these two main and sub voltage signals, calculate the difference between them, and detect whether the torque sensor 6 is abnormal.

  Further, the controller 5 detects the steering torque of the steering 45 based on the main output voltage from the torque sensor 6 and determines the rotation direction thereof. Here, when the torque sensor 6 has an output voltage characteristic as shown in FIG. 7, for example, the controller 5 goes straight when the main output voltage of the torque sensor 6 is 2.5V, and to the right when it exceeds 2.5V. When the steering torque in the rotational direction is less than 2.5V, it is determined that the steering torque in the left rotational direction is generated.

  Next, the operation of the electric power steering device 3 will be described with reference to FIG. FIG. 5 is a diagram illustrating the operation of the electric power steering apparatus 3 of FIG. 2, in which (a) shows the steering neutral time, (b) shows the steering left rotation, and (c) shows the steering right rotation. Show.

  When the steering handle 45 is in the neutral position, as shown in FIG. 5A, the position of the slider 10 is in the neutral position, so that the assist motor 4 is not driven.

  When the steering handle 45 is rotated to the right, as shown in FIG. 5C, the input shaft 17 of the steering shaft 44 rotates to the right, and the output shaft 18 also tries to rotate via the torsion bar 9, but the output shaft 18 Since road surface resistance (snow surface resistance) acts on the torsion bar 9, torque is applied to the torsion bar 9, and the torsion bar 9 is twisted, causing a shift in the rotation amount between the input shaft 17 and the output shaft 18. As a result, the ball groove 11 of the input shaft 17 shifts to the left with respect to the output shaft 18, and the slider 10 moves downward together with the steel ball 13. At this time, since the lever 7 of the torque sensor 6 rotates to the right, a rightward force corresponding to the steering torque is transmitted from the assist motor 4 to the worm wheel 14 via the worm gear 15, and an auxiliary force acts on the output shaft 18. .

  When the steering handle 45 is rotated to the left, as shown in FIG. 5B, the slider 10 moves upward, and an auxiliary force in the direction opposite to the right rotation acts on the output shaft 18.

  Next, the configuration of the controller 5 of the electric power steering apparatus 3 will be described with reference to FIG. FIG. 6 is a block diagram showing a configuration of the controller 5 of the electric power steering apparatus 3 of FIG.

  As shown in FIG. 6, the controller 5 includes, for example, a memory and a CPU. Power is supplied to the controller 5 from the battery 22 via the ignition switch 23. The controller 5 determines the motor drive current of the assist motor 4 based on the outputs of the torque sensor 6, the vehicle speed sensor 55, the throttle opening sensor 20 that detects the throttle opening, and the engine rotation speed sensor 21 that detects the engine rotation speed. The output of the assist motor 4 is controlled.

  Further, as described above, the controller 5 has a function of inputting two main and sub voltage signals from the torque sensor 6 and calculating the difference between them to detect whether the torque sensor 6 is abnormal. When an abnormality of the torque sensor 6 is detected, the driver is notified of this by any one of lighting of an LED, display of a message, voice, and the like. Further, the controller 5 determines the magnitude of the steering torque of the steering 45 and the rotation direction thereof based on the main output voltage from the torque sensor 6 (see FIG. 7). Further, as described above, the controller 5 can perform control for disconnecting the connection between the output shaft of the assist motor 4 and the drive shaft 4a when the assist motor 4 fails. Has a function of notifying the driver that the vehicle has failed.

  Next, the control configuration of the assist motor 4 in the controller 5 will be specifically described.

  Based on the outputs of the vehicle speed sensor 55 and the throttle opening sensor 20, the controller 5 corresponds to any of the three traveling modes in which the traveling state (or road surface state) of the snow vehicle 1 is set in advance. A motor drive current value to be supplied to the assist motor 4 based on the travel mode determination means 25 for determining whether the vehicle is a vehicle, the outputs of the torque sensor 6 and the vehicle speed sensor 55 and the travel mode corresponding to the travel state of the snow vehicle 1. Motor drive current control means 26 for controlling. The travel mode determination unit 25 and the motor drive current control unit 26 are configured by a CPU in the controller 5 executing a predetermined program stored in a memory.

  Here, as the three preset driving modes, a normal mode in which the motor drive current to the assist motor 4 is determined based on the vehicle speed and steering torque of the snow vehicle, Downhill / rapid deceleration mode (decrease correction mode) for correcting the motor drive current to decrease, and climb / deep snow mode (increase correction mode) for correcting the motor drive current to the assist motor 4 relative to the normal mode. )

  In the present embodiment, the travel mode determination map shown in FIG. 9 is used to easily determine which travel mode the road surface condition while the snow vehicle 1 is traveling or the travel state of the snow vehicle 1 corresponds to. It is done. As shown in FIG. 9, this travel mode determination map is set in three travel modes with the vehicle speed and the throttle opening as parameters, and is stored in advance in a memory in the controller 5.

  The traveling state corresponding to the normal mode is a traveling state (for example, the throttle opening is a partial state) set on the assumption that the road surface is flat and snow-capped or the vehicle travels at a constant speed. The traveling state corresponding to the downhill / rapid deceleration mode is a traveling state set on the assumption that the snow vehicle 1 is down a slope or is in a sudden deceleration state. The traveling state corresponding to the climbing / deep snow mode is a traveling state set on the assumption that, for example, the snow vehicle 1 is climbing up a steep slope or traveling in deep snow.

  The motor driving current control means 26 selects a corresponding steering torque / motor driving current characteristic from the driving mode-specific motor driving current control map shown in FIG. 10 according to the vehicle speed and the driving mode, and the selected steering torque / motor driving is selected. A motor drive current value corresponding to the steering torque input to the current steering handle 45 is determined using the current characteristics.

  The motor drive current control map for each travel mode shown in FIG. 10 should be supplied to the assist motor 4 according to the steering torque input to the steering handle 45 with the vehicle speed and the travel mode determined by the travel mode determination means 25 as parameters. It is used to determine the motor drive current value. In this driving mode-specific motor drive current control map, the steering torque / motor drive current characteristics a1, a2, and a3 indicate the motor drive current supplied to the assist motor 4 according to the steering torque when the snow vehicle 1 is at low speed. The steering torque / motor drive current characteristics b1, b2, and b3 indicate absolute values of the motor drive current supplied to the assist motor 4 in accordance with the steering torque at the middle speed. The steering torque / motor drive current characteristics c1, c2, and c3 indicate the absolute value of the motor drive current supplied to the assist motor 4 in accordance with the steering torque at high speed.

  Here, the steering torque / motor driving current characteristics a1, b1, and c1 are characteristics when it is determined that the traveling state corresponds to the normal mode, and the steering torque / motor driving current characteristics a2, b2, and c2 are uphill when the traveling state is / Characteristics when determined to correspond to the deep snow mode, a3, b3, and c3 are characteristics when the traveling state is determined to correspond to the downhill / rapid deceleration mode.

  Further, as shown in FIG. 6, an external input means 24 for forcibly setting the traveling mode is provided. The external input means 24 is provided on the steering handle 45 so that the driver can easily operate, for example. It is composed of switches. When there is an input from the external input unit 24, for example, when the switch is turned on, the traveling mode determination unit 25 determines whether the traveling state of the snow vehicle 1 is the climbing / deep snow mode (increase correction mode) regardless of the traveling state of the snow vehicle 1. ) Is determined to be in the traveling state corresponding to.

  Next, drive control of the assist motor 4 by the controller 5 will be described with reference to FIG. FIG. 8 is a flowchart showing a drive control procedure for the assist motor 4 by the controller 5 of the electric power steering apparatus 3 of FIG. This process is executed by the CPU in the controller 5 according to a predetermined program in the memory, and the process includes a process by the traveling mode determination unit 25 and the motor drive current control unit 26.

  As shown in FIG. 8, the controller 5 determines whether or not the throttle opening exceeds the reference throttle opening (for example, the throttle opening A shown in FIG. 9) for starting the running mode determination based on the output of the throttle opening sensor 20. Is determined (step S1). Here, when the throttle opening does not exceed the reference throttle opening, the controller 5 determines that the traveling state is the normal mode, and sets the traveling mode to the normal mode (step S3). On the other hand, when the throttle opening degree exceeds the reference throttle opening degree, the controller 5 shows the traveling state based on the output of the vehicle speed sensor 55 (vehicle speed) and the output of the throttle opening degree sensor 20 (throttle opening degree). It is determined whether it corresponds to any of the travel modes in the travel mode determination map shown in FIG.

  Then, when it is determined by the determination in step S2 that the traveling state corresponds to the normal mode, the controller 5 sets the traveling mode to the normal mode (step S3). On the other hand, when it is determined by the determination in step S2 that the traveling state corresponds to the climbing / deep snow mode, the controller 5 sets the traveling mode to the climbing / deep snow mode (step S4). On the other hand, when it is determined by the determination in step S2 that the traveling state corresponds to the downhill / rapid deceleration mode, the controller 5 sets the traveling mode to the downhill / rapid deceleration mode (step S5).

  When the travel mode corresponding to the travel state is set in this way, the controller 5 determines whether or not the steering torque is input based on the output of the torque sensor 6 (step S6), and the input of the steering torque is performed. If there is, the controller 5 selects the corresponding steering torque / motor drive current characteristic from the drive mode-specific motor drive current control map shown in FIG. 10 according to the set travel mode and vehicle speed, and the selected A motor driving current value corresponding to the steering torque input to the current steering handle 45 is determined using the steering torque / motor driving current characteristic (step S7). Then, the motor drive current having the determined value is supplied to the assist motor 4. Next, the controller 5 returns to step S1.

  In the present embodiment, when the throttle opening is equal to or less than the reference throttle opening, the normal mode is set regardless of the vehicle speed, but other driving modes may be used instead. . Further, the reference throttle opening may be set in consideration of the play of the throttle of the snow vehicle 1 or may be set arbitrarily.

  As described above, according to the present embodiment, the snow vehicle 1 is provided with the electric power steering device 3 that gives an assisting force to the steering force of the steering handle 45, so that the snow vehicle 1 can be used under any circumstances. Therefore, the driver can be provided with a comfortable steering performance.

  In addition, the electric power steering device 3 is lighter in weight and smaller in installation space than the hydraulic one, so that the engine room 30 is occupied by the engine 2 and the free space in the engine room 30 is limited. In the snow vehicle, the electric power steering device 3 can be easily arranged in the engine room 30. Moreover, the increase in the vehicle weight of the snow vehicle 1 can be suppressed.

  Further, since the traveling state of the snow vehicle 1 is determined from the vehicle speed of the snow vehicle 1 and the engine throttle opening, and the motor drive current is controlled according to the traveling state, comfortable steering performance according to the road surface condition and the traveling state is achieved. Can be given to the driver. Further, since the traveling state of the snow vehicle 1 is determined by the vehicle speed of the snow vehicle 1 and the engine throttle opening, the road surface condition and the traveling state can be easily determined without providing a special sensor.

  Further, the external input means 24 can determine that the traveling state of the snow vehicle 1 is a traveling state corresponding to the uphill / deep snow mode (increase correction mode) regardless of the traveling state of the snow vehicle 1. As a result, it is possible to increase the assisting force that is intentionally given to a driver who feels that the steering operation is heavy, such as a woman or an elderly person, and to improve usability. The external input means 24 may be optionally attached.

  In the present embodiment, a travel mode determination map using the vehicle speed and the throttle opening as parameters is used for determination of the travel state. However, the vehicle speed and the output (engine speed) of the engine speed sensor 21 are parameters. A travel mode determination map may be used. Also in this case, the motor drive current is determined by the same procedure as that shown in FIG.

  By the way, in the above embodiment, every time the driving mode is updated, the motor driving current to the assist motor 4 is determined using the driving motor driving current control map for each driving shown in FIG. A motor drive current for a travel mode other than the normal mode may be determined by adding (or multiplying) a predetermined correction value to the motor drive current according to the mode. For example, as shown in FIG. 10, assuming that the motor drive current in the normal mode is Im and the motor drive current in a travel mode other than the normal mode (for example, the uphill / deep snow mode) is Im ′, On the other hand, the motor drive current Im ′ for the travel modes other than the normal mode is determined.

Im ′ [A] = Im [A] + traveling state correction value Im ′ [A] = Im [A] × traveling state correction rate The traveling state correction value and the traveling state correction rate are normally set according to changes in the traveling mode. This is a correction value that is added to or multiplied by the motor drive current in the mode. For example, regarding the running state correction value or the correction rate for the uphill / deep snow mode, the correction value> 0 [A] or the correction rate> 1, and the motor drive current is increased. On the other hand, regarding the traveling state correction value or the correction rate for the downhill / rapid deceleration mode, the correction value <0 [A] or the correction rate <1, and the motor drive current is reduced. Thus, the motor drive current for each travel mode can be determined without using the control map shown in FIG.

  In the above embodiment, the vehicle speed-throttle opening travel mode determination map shown in FIG. 9 is used as a method for determining the road surface condition and the travel state. However, the travel state is divided into more modes. May be. This is effective, for example, when assuming a traveling state where different assisting forces are required on ice, downhill, or acceleration / deceleration. However, in this case, an inclination sensor or the like is necessary to perform acceleration / deceleration determination.

  In the above-described embodiment, the road surface condition and the like are simply determined by the travel mode determination map shown in FIG. 9 to set the travel mode, and the motor drive current is determined from the motor drive current control map for each travel mode shown in FIG. However, instead of this, in order to simplify the control, the motor drive current is simply determined according to the vehicle speed and steering torque under all driving conditions without determining the driving condition. You may adopt the method of doing. For example, the motor drive current according to the vehicle speed and the steering torque may be determined using a motor drive current control map as shown in FIG. The motor drive current control map shown in FIG. 11 is a normal four-wheel control map.

  Further, in the above embodiment, the torsion bar type is used as the torque detection device, but it goes without saying that other types such as a magnetostriction type may be used instead. Nor.

1 is a side view showing a snow vehicle equipped with an electric power steering apparatus according to an embodiment of the present invention. 1 is a perspective view showing a main part of a steering mechanism in a snow vehicle 1. FIG. (A) is a longitudinal cross-sectional view of the principal part of the electric power steering apparatus of FIG. 2, (b) is sectional drawing obtained along the AA line of (a). It is a perspective view which shows the internal structure of the electric power steering apparatus 3 of FIG. FIG. 3 is a diagram illustrating an operation of the electric power steering apparatus 3 of FIG. 2, where (a) shows a steering neutral time, (b) shows a steering left rotation, and (c) shows a steering right rotation. It is a block diagram which shows the structure of the controller 5 of the electric power steering apparatus 3 of FIG. It is a figure which shows the output voltage characteristic of the torque sensor 6 of FIG. 3 is a flowchart showing a drive control procedure for the assist motor 4 by a controller 5 of the electric power steering apparatus 3 of FIG. 2. It is a figure which shows an example of the driving mode determination map which uses a vehicle speed and throttle opening as a parameter. It is a figure which shows the motor drive current control map classified by traveling mode corresponding to the traveling mode discrimination | determination map of FIG. It is a figure which shows the other example of a motor drive current control map.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Snow vehicle 2 Engine 3 Electric power steering apparatus 4 Assist motor 5 Controller 6 Torque sensor 7 Lever 8 Sensor shaft 9 Torsion bar 10 Slider 14 Worm wheel 15 Worm gear 20 Throttle opening sensor 21 Engine speed sensor 24 External input means 25 Travel mode Determination means 26 Motor drive current control means 32 Steering sled

Claims (5)

An electric power steering device for a snow vehicle having a four-cycle engine mounted on a front portion of a vehicle body and a steering mechanism for transmitting a steering force of a steering handle to a steering sled,
An electric motor;
An auxiliary force mechanism for converting the output of the electric motor into an auxiliary force for assisting the steering force and applying the auxiliary force to the steering mechanism;
Control means for controlling the output of the electric motor according to the vehicle speed of the snow vehicle and the steering force;
An electric power steering apparatus for a snow vehicle, wherein at least the electric motor and the auxiliary force mechanism are provided in an engine room of the snow vehicle.   The control means determines the output of the electric motor according to the vehicle speed and the steering force of the snow vehicle based on a determination result by the driving condition determination means and a determination result by the driving condition determination means. The electric power steering apparatus for a snow vehicle according to claim 1, further comprising correction means for correcting. The running state determination means is a normal mode in which the running state of the snow vehicle controls the output of the electric motor based on the vehicle speed and the steering force of the snow vehicle, and the output of the electric motor with respect to the normal mode. Determining whether the driving state corresponds to a decrease correction mode for correcting the output to decrease, or an increase correction mode for correcting to increase the output of the electric motor with respect to the normal mode,
The snow correction device according to claim 2, wherein the correction unit corrects an output of the electric motor according to a vehicle speed and the steering force of the snow vehicle based on a mode corresponding to a traveling state of the snow vehicle. Electric power steering device for cars.   The traveling state determination means determines whether the traveling state of the snow vehicle corresponds to one of the modes based on the speed of the snow vehicle and the throttle opening or engine speed of the snow vehicle. The electric power steering apparatus for a snow vehicle according to claim 3, wherein the determination is made. Comprising external input means operated by a driver of the snow vehicle,
The traveling state determination means determines that the traveling state of the snow vehicle is a traveling state corresponding to the increase correction mode regardless of the traveling state of the snow vehicle when input from the external input unit. The electric power steering apparatus for a snow vehicle according to claim 3.

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