Patent Publication Number: US-7581339-B2

Title: Snow removing machine

Description:
FIELD OF THE INVENTION 
   The present invention relates to self-propelled snow removing machines including left and right running devices and an auger. 
   BACKGROUND OF THE INVENTION. 
   In many snow removing machines provided with an auger, there is employed a technique in accordance with which the auger is varied in height in accordance with conditions of snow removal work. When the snow removing machine should travel, it can do so more efficiently with the lower end surface of the auger positioned higher. When, on the other hand, the snow removing machine should remove snow, it can do so more efficiently with the lower surface of the auger positioned lower. Further, in many cases, the height of the auger is adjusted in accordance with road surface irregularity or unevenness. Where the auger height is adjusted through manual input operation by a human operator, the input operation tends to be a great load on the human operator. 
   Auger-type snow removing machines, constructed to move the lower end surface of the auger in an upward/downward direction in order to reduce a load on a human operator, are known, for example, from Japanese Patent Post-Exam Publication No. SHO-61-30085 and Japanese Utility Model Laid-Open Publication Nos. SHO-63-194927 and SHO-64-31418. 
     FIG. 20  is a side view showing the conventional auger-type snow removing machine disclosed in SHO-61-30085. The auger-type snow removing machine  200  of  FIG. 20  is a self-propelled vehicle, in which a vehicle body frame  204  having an engine  203  mounted thereon is vertically pivotably connected at its rear end portion to a running-device frame  202  having left and right running devices  201  mounted thereon. Further, in the disclosed auger-type snow removing machine  200 , an auger housing  205  and blower case  206  are rollably connected to a front end portion of the vehicle body frame  204 . 
   The left and right running devices  201  are in the form of left and right crawlers. The auger housing  205  houses an auger  207 , and the blower case  206  houses a blower  208 . The snow removing machine  200  can travel with output power of the engine  203  transmitted via a transmission device  209  to the running devices  201 . Switching between forward and rearward running and between left and right turning of the running devices  201  can be effected by the human operator manipulating operation levers  211  etc. Snow can be removed by the output power of the engine  203  being transmitted via a belt transmission mechanism  213  to the auger  207  and blower  208 . 
   Front portion of the vehicle body frame  204  can be moved in the upward/downward direction via an auger housing elevator mechanism  222  by the human operator pivoting an auger-housing-posture manipulating lever  221  in a forward/rearward direction, in response to which the auger housing  205  can be moved in the upward/downward direction. 
   Further, the auger housing  205  and blower case  206  can be rolled via a rolling drive mechanism  223  by the human operator pivoting the auger-housing-posture manipulating lever  221  in a leftward/rightward direction. 
   In general, when the snow removing machine  200  is to be turned in a desired direction, one of the running devices  201 , which is located inwardly of the other as viewed in the turning direction, is slowed down. However, a coefficient of friction between a snow surface and the running devices  201  is smaller than a coefficient of friction between an ordinary road surface and the running devices  201 . Furthermore, even when one of the running devices  201  (hereinafter “inner running device”) which is located inwardly of the other (hereinafter “outer running device”) as viewed in the turning direction is slowed down as the snow removing machine  200  is turned during low-speed travel, e.g. immediately before stoppage of the machine  200 , there can be created only an extremely small difference in traveling speed between the inner running device  201  and the outer running device  201 . 
   Particularly, the running devices  201 , which are in the form of crawlers, present a great ground contact capability and great driving force inherent to the crawlers. If the speed difference between the left and right crawlers is small, the tractive force of the inner crawler  201  is not so great as compared to the tractive force of the outer crawler; namely, the speed difference between the inner and outer crawlers can not increase as required. Thus, it tends to be difficult to attain a desired turning radius when the human operator performs operation for switching from the straight travel to the turning travel, and further improvements must be made in order to allow the snow removing machine  200  to smoothly switch from the straight travel to the turning travel. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing prior art problems, it is an object of the present invention to provide a technique which can effectively improve turning performance of a snow removing apparatus equipped with left and right running devices and an auger. 
   In order to accomplish the above-mentioned object, the present invention provides an improved snow removing machine, which comprises: left and right running devices mounted on a running-device frame; an auger housing having an auger housed therein and rollably mounted on the running-device frame; a rolling drive mechanism for rolling the auger housing; a turning operator operable to turn the snow removing machine; and a control section for, in response to operation of the turning operator, not only performing control to drive the left and right running devices to thereby turn the snow removing machine in a desired turning direction. Also, in response to the operation of the turning operator, the control section issues a drive instruction to the rolling drive mechanism to roll the auger housing in an inward direction, as viewed in the turning direction of the snow removing machine, such that a portion of one of side edges of the auger housing, located inwardly of the other side edge as viewed in the turning direction, is brought into contact with the ground surface. 
   By the control section issuing a drive instruction to the rolling drive mechanism in response to human operator&#39;s operation of the turning operator, the auger housing can be rolled in the inward direction, as viewed in the turning direction of the snow removing machine. In this way, the portion of one of the side edges of the auger housing (i.e., “inner side edge”), located inwardly of the other side edge as viewed in the turning direction, is brought into contact with the ground surface, e.g. bite into a snow surface on the ground. 
   With the “inner” side edge of the auger housing caused to contact the ground surface, there is produced a new traveling resistance against the inner side edge, and thus, the machine can turn about the portion of the ground-contacting inner side edge as a pivot center. 
   Thus, as the human operator operates the turning operator, not only one of the running devices, located inwardly of the other running device as viewed in the turning direction, can be slowed down but also the auger housing can be rolled in such a manner as to cause the inner side edge to contact the ground surface, which can thereby enhance the turning performance of the snow removing machine. Therefore, by the human operator operating the turning operator, the snow removing machine can be smoothly switched from straight travel to turning travel. As a result, the snow removing machine of the invention can be highly maneuverable and usable with ease and, therefore, can efficiently perform snow removal work even in small working areas. 
   The snow removing machine of the invention may further comprise left and right operating handles extending from a rear portion of the running-device frame, and the turning operator may comprise left and right turning operators, such as left and right operation levers operable by the hands of a human operator holding the left and right operating handles, or left and right push-button switches provided between the left and right operating handles at positions within ranges operable by the hands of the human operator holding the left and right operating handles. Thus, the human operator can also operate the left and right turning operator members with the same hands holding the operating handles to manipulate the snow removing machine. Therefore, it is not necessary to rehold or release or let go of any of the left and right operating handles each time the human operator performs operation for turning the snow removing machine to the left or right. As a consequence, the present invention can enhance the operability of the snow removing machine and allows the human operator to turn the machine with ease. With such an enhanced turning operability and turning capability of the snow removing machine, the overall performance of the machine can be significantly improved. Further, because only the operation levers or push buttons have to be provided near the left and right operating handles for purposes of turning the machine, the present invention can reduce the number of components necessary to implement the turning operator and thereby simplify the construction of the turning operator. 
   The snow removing machine may further comprise an auger-housing-posture manipulating lever for operating the rolling drive mechanism to roll the auger housing in accordance with a snow surface during snow removal work using the auger. In this case, the auger-housing-posture manipulating lever may be caused to also function as the turning operator. Thus, it is possible to dispense with the separate or dedicated turning operator. Even though the snow removing machine has no dedicated turning operator, the human operator can use the auger-housing-posture manipulating lever to readily perform operation for turning the machine. Thus, the present invention can achieve an enhanced turning operability, sufficient turning performance and hence enhanced overall performance of the snow removing machine. Since the number of necessary operator members can be minimized, such inventive arrangements can be suitably applicable to snow removing machines that have to be small in size or have other spatial limitations. Further, because the number of necessary component parts can be reduced, it is possible to reduce the manufacturing cost of the snow removing machine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Certain preferred embodiments of the present invention will hereinafter be described in detail, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a side view showing a snow removing machine in accordance with a first embodiment of the present invention; 
       FIG. 2  is rear end view of an auger housing and blower case in the snow removing machine of the invention; 
       FIG. 3  is a perspective view taken in a direction of arrow  3  in  FIG. 1 ; 
       FIG. 4  is a block diagram of a control system in the snow removing machine of the invention; 
       FIG. 5  is a diagram explanatory of operation of a direction/speed control lever employed in the snow removing machine of the invention; 
       FIG. 6  is a sectional view showing an auger-housing-posture manipulating lever and related switches employed in the snow removing machine of the invention; 
       FIG. 7  is a flow chart showing a portion of an example flow of control operations performed by a control section in the snow removing machine of the invention; 
       FIG. 8  is a flow chart showing another portion of the flow of control operations performed by the control section in the snow removing machine of the invention; 
       FIG. 9  is a flow chart showing still another portion of the flow of control operations performed by the control section in the snow removing machine of the invention; 
       FIG. 10  is a flow chart showing the remaining portion of the flow of control operations performed by the control section in the snow removing machine of the invention; 
       FIG. 11  is a diagram showing behavior of the control section in the snow removing machine of the invention; 
       FIG. 12  is a view explanatory of behavior of the snow removing machine of the present invention; 
       FIG. 13  shows an auger-housing-posture manipulating lever employed in a snow removing machine according to a second embodiment of the invention; 
       FIG. 14  is a flow chart showing a portion of an example flow of control operations performed by a control section in the second embodiment; 
       FIG. 15  is a flow chart showing another portion of the example flow of control operations performed by the control section in the second embodiment; 
       FIG. 16  is a flow chart showing still another portion of the example flow of control operations performed by the control section in the second embodiment; 
       FIG. 17  is a flow chart showing the remaining portion of the example flow of control operations performed by the control section in the second embodiment; 
       FIG. 18  is a diagram showing behavior of the control section in the second embodiment; 
       FIG. 19  is also a diagram showing the behavior of the control section in the second embodiment; and 
       FIG. 20  is a side view of a conventionally-known auger-type snow removing machine. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   It should be noted that the terms “front”, “rear”, “left”, “right”, “upper”, “lower”, etc. represent various directions as viewed by a human operator operating the snow removing machine. 
     FIG. 1  is a side view showing a snow removing machine in accordance with a first embodiment of the present invention, the snow removing machine  10  of  FIG. 1  is a self-propelled vehicle, in which a snow removal work section  13  and an engine  14  for driving the snow removal work section  13  are mounted on a vehicle body frame (second frame)  15 , and in which the vehicle body frame  15  is vertically pivotably connected at its rear end portion to a running-device frame (first frame)  12  having left and right running (transporting) devices  11 L and  11 R mounted thereon. Further, in the snow removing machine  10 , a front portion of the vehicle body frame  15  can be moved in an upward/downward direction (i.e., vertically pivoted) via an auger housing elevator mechanism  16 . Left and right operating handles  17 L and  17 R extend upwardly and rearwardly from a rear portion of the running-device frame  12 , and grips  18 L and  18 R are fixed to the respective digital ends of the left and right operating handles  17 L and  17 R. 
   The running-device frame  12  and vehicle body frame  15  together constitute a machine body  19 . On the running-device frame  12 , there are also mounted left and right electric motors  21 L and  21 R for driving the left and right running devices  11 L and  11 R. The left and right running devices  11 L and  11 R include left and right crawler belts  22 L and  22 R, left and right driving wheels  23 L and  23 R disposed on rear portions of the devices  11 L and  11 R, and left and right driven wheels  24 L and  24 R disposed on front portions of the devices  11 L and  11 R. 
   The left crawler belt  22 L can be driven by the left electric motor  21 L via the left driving wheel  23 L, while the right crawler belt  22 R can be driven by the right electric motor  21 R via the right driving wheel  23 R. 
   The snow removal work section  13  includes an auger housing  25 , a blower case formed integrally with the rear surface of the auger housing  25 , an auger  31  housed in the auger housing  25 , a blower housed in the blower case  26 , and a shooter  33 . On rear lower end portions of the auger housing  25 , there are mounted a scraper  27  and left and right sleds  28 L and  28 R. 
   The engine  14  is a snow-removing drive source for driving the snow removal work section  13  via a snow-removing-power transmission mechanism  34 . The snow-removing-power transmission mechanism  34  includes a driving pulley  36  connected via an electromagnetic clutch  35  to a crank shaft  14   a  of the engine  14 , a transmission belt  37 , and a rotation shaft  39  having a driven pulley  38  mounted thereon. 
   The output power of the engine  14  is transmitted to the auger  31  and blower  32  via the crankshaft  14   a,  electromagnetic clutch  35 , driving pulley  36 , transmission belt  37 , driven pulley  38  and rotation shaft  39 . Snow gathered by the auger  31  can be thrown far away from the machine  10  by the blower  32  through the shooter  33 . 
   The auger housing elevator mechanism  16  is an actuator having a piston movable out of and into a cylinder. This actuator is an electric hydraulic cylinder where the piston is caused to expand and contract by hydraulic pressure produced by means of a not-shown hydraulic pump driven by an electronic motor  16   a  ( FIG. 4 ). The electronic motor  16   a  is an elevator drive source fixed to a side portion of the cylinder of the auger housing elevator mechanism  16 . 
   The human operator can manipulate the snow removing machine  10  via the operating handles  17 L and  17 R while walking behind the machine  10 . In the illustrated example, an operation box  41 , control section  61  and battery  62  are arranged, in a top-to-bottom direction in the mentioned order, between the operating handles  17 L and  17 R. Reference numeral  63  represents a machine cover. 
     FIG. 2  is rear end view of the auger housing and blower case in the first embodiment of the present invention. In the snow removing machine  10 , as shown in  FIGS. 1 and 2 , the auger housing  25  and blower case  26  are rollably mounted on the running-device frame  12 ; the auger housing  25  is rolled by means of a rolling drive mechanism  70 . 
   More specifically, the rotation shaft  39  extending forward/rearward direction of the machine  10  is rotatably supported not only on a front end portion of the vehicle body frame  15  via a bearing  71 , but also on the blower case  26  via a bearing (not shown). Thus, the auger housing  25  and blower case  26  are connected to the vehicle body frame  15  so that they are rotatable (or rollable) about the rotation shaft  39  in clockwise and counter-clockwise as viewed from the human operator (see  FIG. 12 ). 
   As set forth above, the running-device frame  12  has the vehicle body frame  15  connected thereto. In this way, the auger housing  25  and blower case  26  are rollably connected to the running-device frame  12 . As a result, the auger housing  25  is movable up and down and rollable relative to the running-device frame  12 . 
   The rolling drive mechanism  70  is an actuator having a piston (rod)  73  movable out of and into a cylinder  72 . This actuator is an electric hydraulic cylinder where the piston is caused to expand and contract by hydraulic pressure produced by means of a not-shown hydraulic pump driven by an electronic motor  74 . The electronic motor  74  is a rolling drive source fixed to a side portion of the cylinder  72  of the rolling drive mechanism  70 . 
   The rolling drive mechanism  70  is connected at one end (i.e., lower end of the cylinder  72 ) to the vehicle body frame  15  for pivotal movement in the leftward/rightward direction, and connected at the other end (i.e., distal end of the piston  73 ) to the rear surface of the blower case  26 . Thus, the auger housing  25  and blower case  26  can be rolled by means of the rolling drive mechanism  70 . As set forth above and shown in  FIGS. 1 and 2 , the left and right sleds  28 L and  28 R are provided on left lower end portions of the auger housing  25 . 
     FIG. 3  is a perspective view taken in a direction of arrow  3  in  FIG. 1 , which particularly shows an operation section  40  of the snow removing machine  10 . As shown, the operation section  40  includes the above-mentioned operation box  41 , a travel-standby lever  41  and left turning operation lever  43 L provided on the left operating handle  17 L near the left grip  18 L, and a right turning operation lever  43 R provided on the right operating handle  17 R near the right grip  18 R. 
   The travel-standby lever  42  is an operating member acting on a switch  42   a  ( FIG. 4 ). The switch  42   a  is turned off when the lever  42  is brought to a released or free position (i.e., position illustrated in the figure) by resilient pulling action of a return spring. When the human operator uses his or her left hand to hold and depress the travel-standby lever  42  toward the left grip  18 L, the switch  42   a  is turned on. 
   The left and right turning switches  43 La and  43 Ra are each turned off when the corresponding left or right turning operation lever  43 L or  43 R is brought to a released free position (i.e. position illustrated in the figure) by resilient pulling action of a return spring. When the human operator uses his or her left hand to hold and depress the left turning operation lever  43 L toward the left grip  18 L, the left turning switch 43 La is turned on. Similarly, when the human operator uses the right hand to hold and depress the right turning operation lever  43 R toward the right grip  18 R, the right turning switch  43 Ra is turned on. Whether or not the left or right turning operation lever  43 L or  43 R is being held by the human operator is detectable on the basis of the ON/OFF state of the corresponding turning switch  43 La or  43 Ra. 
   Referring now to  FIG. 3  in combination with  FIG. 1 , the operation box  41  includes, on its rear surface  41   a  (i.e., surface closer to the human operator), a main switch  44 , a choke knob  45  operable when the engine  14  is started, and a clutch operating switch (or auger switch)  46  for turning on/off the electromagnetic clutch  34 . The engine  14  can be activated by inserting a key in the main switch (key switch)  44  and turning the inserted key to a start position “ST”. 
   The operation box  41  includes, on its upper surface  41   b,  a shooter operating lever  51  for changing an operating direction of the shooter  33 , an auger-housing-posture manipulating lever  52 , a direction/speed control lever (forward/rearward-traveling-speed adjusting lever)  53 , and a throttle value  54  for adjusting the number of rotations of the engine  14 . 
   The auger-housing-posture manipulating lever  52  is an operating member for operating the auger housing elevator mechanism  16  and rolling drive mechanism  70  to move the auger housing  25  upward or downward in accordance with the snow surface during snow removal work using the auger  31 . 
   The piston of the auger housing elevator mechanism  16  can be caused to expand by the human operator pivoting the auger-housing-posture manipulating lever  52  rearward from a neutral position shown in  FIG. 3 . Further, the piston of the auger housing elevator mechanism  16  can be caused to contract by the human operator pivoting the auger-housing-posture manipulating lever  52  forward from the neutral position shown in  FIG. 3 . The piston  73  ( FIG. 2 ) of the rolling drive mechanism  70  can be caused to contract by the human operator pivoting the auger-housing-posture manipulating lever  52  leftward from the neutral position shown in  FIG. 3 . Further, the piston of the rolling drive mechanism  70  can be caused to expand by the human operator pivoting the auger-housing-posture manipulating lever  52  rightward from the neutral position shown in  FIG. 3 . 
     FIG. 4  is a block diagram of a control system in the snow removing machine  10 , which particularly shows various components and information transmission paths in the control section  61 . Flows of instructions in the control section  61  are indicated in the figure by broken lines; however, these flows are just for illustrative purposes. 
   The snow removable work section  13  and related components operate as follows. Power generator  81  is driven by a portion of the output of the engine  14 , and electric power thus produced by the generator  81  is supplied to the battery  62 , electric motors  21 L and  21 R and other electric equipment. The remaining portion of the output of the engine  14  is supplied to rotate the auger  31  and blower  32 . Reference numerals  82 L and  82 R represent rotation sensors for measuring rotating speeds of the left and right electric motors  2   1 L and  21 R. 
   Once the human operator operates the clutch operating switch  46  while griping the travel-standby lever  42 , the electromagnetic clutch  35  is brought to a connecting state so that the auger  31  and blower  32  can be driven to rotate by the power of the engine  14 . The electromagnetic clutch  35  can be brought back to a disconnecting state by the human operator shifting the travel-standby lever  42  to the free position or again operating the clutch operating switch  46 . 
   The running devices  11 L and  11 R and related components operate as follows. The snow removing machine  10  includes left and right electromagnetic brakes  83 L and  83 R that function like parking brakes of ordinary vehicles. Specifically, the respective rotation shafts of the left and right motors  21 L and  21 R can be braked by the corresponding electromagnetic brakes  83 L and  83 R. During parking of the snow removing machine  10 , the electromagnetic brakes  83 L and  83 R are kept in a braking (i.e., ON) state under control of the control section  61 . The electromagnetic brakes  83 L and  83 R can be shifted to a non-braking (OFF or open) state once the direction/speed control lever  53  is shifted to a forward or rearward travel (i.e., advance or retreat) position while 1) the main switch  44  is in the “ON” position and 2) the travel-standby lever  42  is being gripped by the human operator. 
     FIG. 5  is a diagram explanatory of operation of the direction/speed control lever  53  employed in the snow removing machine  10 . As seen in  FIG. 5 , the direction/speed control lever  53  is reciprocatively movable in opposite directions as indicated by arrows Ad and Ba. As the direction/speed control lever  53  is shifted or turned from a “neutral” region to a “forward travel” region, the vehicle  10  can move forward. In the “forward travel” region, speed control can be performed such that the machine  10  is variable in forward traveling speed between a lowest speed Lf and a highest speed Hf. Similarly, as the direction/speed control lever  53  is shifted or turned from the “neutral” region to a “rearward travel” region, the vehicle  10  can move rearward. In the “rearward travel” region, speed control can be performed such that the machine  10  is variable in rearward traveling speed between a lowest speed Lr and a highest speed Hr. In the illustrated example of  FIG. 5 , voltages corresponding to the various positions of the direction/speed control lever  53  are generated via a potentiometer. For example, the potentiometer  53   a  generates 0 volt (V) when the direction/speed control lever  53  is at the highest-rearward-traveling-speed position, 5 V when the lever  53  is at the highest-forward-traveling-speed position, and 2.3 V-2.7 V when the lever  53  is in the neutral region, as indicated on a left end area of the figure. In this way, the single direction/speed control lever  53  can set both a desired one of the forward and rearward travel directions and a desired speed between the highest and lowest travel speeds; this is why the direction/speed control lever  53  is so named. 
   Referring back to  FIG. 4 , the control section  61 , in accordance with position information of the direction/speed control lever  53  received from the potentiometer  53   a,  rotates the left and right electric motors  21 L and  21 R via left and right motor drivers  84 L and  84 R. The control section  61  detects the respective numbers of rotations of the motors  21 L and  21 R via the rotation sensors  82 L and  82 R and performs feedback control so that the rotating speeds of the motors  21 L and  21 R assume predetermined values on the basis of detection signals given from the sensors  82 L and  82 R. As a consequence, the left and right driving wheels  21 L and  21 R can rotate in desired directions and at desired speeds, so that the snow removing machine  10  can be brought to desired traveling conditions. 
   During travel of the snow removing machine  10 , the machine  10  is braked in the following manner. For the braking purposes, the left and right motor drivers  84 L and  84 R each include a regenerative brake circuit  85 L or  85 R, and a short-circuit brake circuit  86 L or  86 R as a brake means. 
   While the human operator is gripping the left turning operation lever  43 L to keep the left turning switch  43 La in the ON state, the control section  61  activates the left regenerative brake circuit  85 L to thereby lower the speed of the left electric motor  21 L. Similarly, while the human operator is gripping the right turning operation lever  43 R to keep the right turning operation switch  43 Ra in the ON state, the control section  61  activates the right regenerative brake circuit  85 R to thereby lower the speed of the right electric motor  21 R. 
   Namely, the snow removing machine  10  can be turned to the left only while the human operator is gripping the left turning operation lever  43 L, and the snow removing machine  10  can be turned to the right only while the human operator is gripping the right turning operation lever  43 R. 
   Then, the snow removing machine  10  can be caused to stop traveling by the human operator
         (1) releasing the travel-standby lever  42 ,   (2) returning the main switch  44  to the OFF position, or   (3) returning the direction/speed control lever  53  to the neutral position.       

     FIG. 6  is a sectional view showing the auger-housing-posture manipulating lever  52  and related switches. As shown in  FIG. 6 , the auger-housing-posture manipulating lever  52  is supported at one end within a case  91  in such a manner that the lever  52  is pivotable in forward/rearward and leftward/rightward directions. The auger-housing-posture manipulating lever  52  is also normally biased by a resilient member  92  so that it can automatically return to a neutral position Ne. Namely, the auger-housing-posture manipulating lever  52  is a lever mechanism that automatically returns to the neutral position Ne when released. On the inner surface of the case  91 , there are provided four rolling switches, i.e. front and rear rolling switches and left and right rolling switches, of which only the left and right rolling switches  93 L and  93 R are shown in the figure. 
   As seen from  FIGS. 3 and 6 , the left rolling switch  93 L is turned on in response to human operator&#39;s pivoting operation of the auger-housing-posture manipulating lever  52  from the neutral position Ne to a left rolling position Le (namely, left rolling operation) and kept in the ON state only while the auger-housing-posture manipulating lever  52  is in the left rolling position Le. Similarly, the right rolling switch  93 R is turned on in response to human operator&#39;s pivoting operation of the auger-housing-posture manipulating lever  52  from the neutral position Ne to a right rolling position Ri (namely, right rolling operation) and kept in the ON state only while the auger-housing-posture manipulating lever  52  is in the right rolling position Ri. 
   Further, as seen from  FIGS. 4 and 6 , the electric motor  16   a  of the auger housing elevator mechanism  16  is shiftable between forward and reverse rotations in response to human operator&#39;s pivoting operation of the auger-housing-posture manipulating lever  52  in the forward/rearward directions, so that the piston of the auger housing elevator mechanism  16  can be caused to expand or contract. 
   Furthermore, as seen from  FIGS. 2 and 6 , the left rolling switch  93 L is turned on in response to the left rolling operation of the auger-housing-posture manipulating lever  52 , so that the electric motor  74  of the rolling drive mechanism  70  rotates in the forward direction to cause the piston  73  to contract. As a consequence, the auger housing  25  and blower case  26  are rolled to the “left” (i.e., in the counterclockwise direction as viewed from the human operator as seen in  FIG. 12 ). The right rolling switch  93 R is turned on in response to the right rolling operation of the auger-housing-posture manipulating lever  52 , so that the electric motor  74  of the rolling drive mechanism  70  rotates in the reverse direction to cause the piston  73  to expand. As a consequence, the auger housing  25  and blower case  26  is rolled to the “right” (i.e., in the clockwise direction as viewed from the human operator as seen in  FIG. 12 ). 
   Note that the aforementioned left and right turning operator members may be in the form of left and right turning operation switches  47 L and  47 R of  FIG. 3  rather than the left and right turning operation levers  43 L and  43 R. In such a case, the left and right turning operation switches  47 L and  47 R are provided on the operation box  41  between the operating handles  17 L and  17 R at positions within ranges operable by the two hands of the human operator holding the left and right grips  18 L and  18 R. 
   The left turning operation switch  47 L is a push-button switch including a push button  48 L oriented toward the rear of the snow removing machine  10  (i.e., toward the human operator). The left turning operation switch  47 L is an automatically-reset switch that is kept ON to generate a predetermined switch signal only while the push button  48 L is being depressed by the human operator. 
   Similarly, the right turning operation switch  47 R is a push-button switch including a push button  48 R oriented toward the rear of the snow removing machine  10  (i.e., toward the human operator). The right turning operation switch  47 R is an automatically-reset switch that is kept ON to generate a predetermined switch signal only while the push button  48 R is being depressed by the human operator. 
   These left and right turning operation switch  47 L and  47 R take the place of the left and right turning switches  43 La and  43 Ra of  FIG. 4 . 
   More specifically, the left turning switch  47 L and its push button  48 L are provided on a left end portion of the rear surface  41   a  of the operation box  41  inwardly of the left grip  18 L (namely, located closer than the grip  18 L to a longitudinal centerline CL of the machine  10 . The right turning switch  47 R and its push button  48 R are provided on a right end portion of the rear surface  41   a  of the operation box  41  inwardly of the right grip  18 L (namely, located closer than the grip  18 L to the longitudinal centerline CL of the machine  10 . 
   When the human operator grips the left and right operating handles  18 L and  18 R with both hands, the thumb of each of the hands is generally located between the handles  18 L and  18 R, i.e. the thumb nail faces inward (toward the longitudinal centerline CL). The snow removing machine  10  can be turned left only when the human operator is depressing the push button  48 L of the left turning operation switch  47 L with the thumb of the left hand extended forward while gripping the left and right grips  18 L and  18 R. Similarly, the snow removing machine  10  can be turned right only when the human operator is depressing the push button  48 R of the right turning operation switch  47 R with the thumb of the right hand extended forward. In this way, the human operator can perform desired turning operation extremely easily with a small force without releasing or letting go of any of the left and right grips  18 L and  18 R. 
   Now, with primary reference to flow charts of  FIGS. 7-10 , a description will be made about a flow of various control operations performed by the control section  61  of  FIG. 4  in the case where the control section  61  is implemented by a microcomputer. For example, this control flow is started up in response to turning-on of the main switch  44  and brought to an end in response to turning-off of the main switch  44 . 
     FIG. 7  is a flow chart showing a portion of an example flow of control operations performed by the control section  61 . 
   Step ST 01  of  FIG. 7 : A predetermined initialization process is performed; specifically, various flags, such as a left rolling flag Fro, right rolling FRro, preceding left rolling flag bFLr and preceding right rolling flag bFRr, are all set at an initial value “0”, and a left roll amount Lro and right roll amount Rro are also set to “0”. The left rolling flag FLro is a flag indicating whether or not the auger housing  25  should be rolled to the left (in the counterclockwise direction), and the right rolling flag FRro is a flag indicating whether or not the auger housing  25  should be rolled to the right (in the clockwise direction). 
   Step ST 02 : Signals from various switches are read. 
   Step ST 03 : A determination is made as to whether the snow removing machine  10  is currently moving forward. With a YES determination, the control section  61  proceeds to step ST 04 , while, with a NO determination, the control section  61  branches to step ST 06 . It is determined that the snow removing machine  10  is currently traveling forward, if the aforementioned three conditions, i.e. the condition that the main switch  44  is in the ON position, the condition that the travel-standby lever  42  is currently being gripped by the human operator and the condition that the direction/speed control lever  53  is in the “forward travel” region, have been met. 
   Step ST 04 : Current traveling speed Sf of the snow removing machine  10  is measured; for example, it may be measured on the basis of the rotating speeds of the electric motors  21 L and  21 R measured via the rotation sensors  82 L and  82 R. 
   Step ST 05 : A determination is made as to whether the traveling speed Sf of the snow removing machine  10  is lower than a preset reference speed So. With a YES determination, the control section  61  proceeds to an out-connector A 1 , while, with a NO determination, the control section  61  branches step ST 06 . 
   When the snow removing machine  10  is to be turned during high-speed travel of the machine  10 , the control section  61  performs control to gradually slow down the left or right running device  11 L or  11 R. The human operator can cause the snow removing machine  10  to make a rapid turn, by rolling the auger housing  25  to cause a portion of one of the side edges of the auger housing  25 , which is located inwardly of the other side edge as viewed in the turning direction, to contact the ground surface. For that purpose, the reference speed So is set within a speed range that permits rapid turns, e.g. 0.3 m/sec close to a speed in a stop (i.e., non-traveling) state of the vehicle. 
   Step ST 06 : The left rolling flag FLro and right rolling flag FRro are each set at “0”, and then the control section  61  proceeds to an output-connector A 2 . 
     FIG. 8  is a flow chart showing another portion of the flow of control operations performed by the control section  61 . 
   Step ST 11 : The control section  61  reads left and right slow-down rates GsL and GsR to be applied when the snow removing machine  10  is to be turned. The left and right slow-down rates GsL and GsR are expressed in percentage and vary in accordance with a degree of slow-down to be effected for one of the left and right running devices  11 L or  11 R which is located inwardly of the other  11 R or  11 L as viewed in the turning direction. 
   When the snow removing machine  10  is to be turned, one of the left and right running devices  11 L or  11 R which is located inwardly of the other  11 R or  11 L as viewed in the turning direction, i.e. the “inner” running device  11 L or  11 R, is slowed down in the present invention. Whether or not and how rapidly the human operator wants to turn the snow removing machine  10  is determined, in the illustrated example, in accordance with a value of the left or right slow-down rates GsL or GsR to be applied to the “inner” running device  11 L or  11 R. Namely, a greater value of the left or right slow-down rates GsL or GsR indicates that the human operator wants to turn the snow removing machine  10  more rapidly. 
   Step ST 12 : A determination is made as to whether the right slow-down rate GsR is smaller than a preset small rate threshold value GL (GsR&lt;GL). With a YES determination, the control section  61  moves on to step ST 13 , while, with a NO determination, the control section  61  branches to step ST 14 . The preset small rate threshold value GL is expressed in percentage (%) and set at, for example, 40% in this case. If the right slow-down rate GsR is equal to or greater than the preset small rate threshold value GL (NO determination at step ST 12 ), it means that the human operator wants to turn the snow removing machine  10  to the right, so that left rolling control is turned off (canceled). 
   Step ST 13 : The left slow-down rate GsL is compared to the preset small rate threshold value GL and great-rate threshold value GH. The preset great rate threshold value GH is also expressed in percentage (%) and set at, for example, 60% in this case. If the left slow-down rate GsL is smaller than the preset small rate threshold value GL (GsL&lt;GL), the control section  61  judges that it is not necessary to rapidly turn the machine  10  to the left and goes to step ST 14 . If the left slow-down rate GsL is greater than the preset great rate threshold value GH (GH&lt;GsL), the control section  61  judges that it is necessary to rapidly turn the machine  10  to the left and branches to step ST 15 . If the left slow-down rate GsL is in the range from the small rate threshold value GL to the great rate threshold value GH (GL≦GsL≦GH), the control section  61  judges that the current state should be maintained and goes to step ST 16 . 
   Step ST 14 : The left rolling flag FLro is set at “0”, and then the control section  61  proceeds to step ST 16 . 
   Step ST 15 : The left rolling flag FLro is set at “1”, and then the control section  61  proceeds to step ST 16 . 
   Step ST 16 : A determination is made as to whether the left slow-down rate GsL is smaller than the preset small rate threshold value GL (GsL&lt;GL). With a YES determination, the control section  61  moves on to step ST 17 , while, with a NO determination, the control section  61  branches to step ST 18 . If the left slow-down rate GsL is equal to or greater than the preset small rate threshold value GL (NO determination at step ST 16 ), it means that the human operator wants to turn the snow removing machine  10  to the left, so that right rolling control is turned off (canceled). 
   Step ST 17 : The right slow-down rate GsR is compared to the preset small rate threshold value GL and great rate threshold value GH. If the right slow-down rate GsR is smaller than the preset small rate threshold value GL (GsR&lt;GL), the control section  61  judges that it is not necessary to rapidly turn the machine  10  to the right and goes to step ST 18 . If the left slow-down rate GsR is greater than the preset great rate threshold value GH (GH&lt;GsR), the control section  61  judges that it is necessary to rapidly turn the machine  10  to the right and branches to step ST 19 . If the right slow-down rate GsR is in the range from the small rate threshold value GL to the great rate threshold value GH (GL≦GsR≦GH), the control section  61  judges that the current state should be maintained and goes to an out-connector A 2 . 
   Step ST 18 : The right rolling flag FRro is set at “0”, and then the control section  61  proceeds to the out-connector A 2 . 
   Step ST 19 : The right rolling flag FRro is set at “1”, and then the control section  61  proceeds to the out-connector A 2 . 
     FIG. 9  is a flow chart showing still another portion of the flow of control operations performed by the control section  61 . 
   Step ST 21 : Newest value of the left rolling flag FLro (hereinafter “new left rolling flag value FLro”) is compared to the preceding value of the left rolling flag (hereinafter “preceding left rolling flag value bFLr”). If the preceding left rolling flag value bFLr is “1” and new left rolling flag value FLro is “0”, the control section  61  judges that left rolling of the auger housing  25  responsive to left turning operation is to be terminated and goes to step ST 22 . If the preceding left rolling flag value bFLr is “0” and new left rolling flag value FLro is “1”, the control section  61  judges that left rolling of the auger housing  25  is to be started in response to left turning operation and goes to step ST 23 . If the new left rolling flag value FLro agrees with the preceding left rolling flag value bFLr, the control section  61  judges that the current state is to be maintained and goes to step ST 24 . 
   Step ST 22 : The left roll amount Lro is set to “0”, and then the control section  61  proceeds to step ST 24 . 
   Step ST 23 : The left roll amount Lro is set to α, and then the control section  61  proceeds to step ST 24 . “α” represents a predetermined roll amount in a range for rolling the auger housing  25  to the left or right from the neutral position. The predetermined roll amount α is set, for example, at a value that can cause an end portion of the inner side edge of the auger housing  25  (i.e., sled  28 L or  28 R), as viewed in the turning direction, to contact the ground surface. 
   Step ST 24 : The preceding left rolling flag value bFLr is rewritten with the new left rolling flag value FLro, and then the control section  61  goes to step ST 25 . 
   Step ST 25 : Newest value of the right rolling flag FRro (hereinafter “new right rolling flag value FRro”) is compared to the preceding value of the right rolling flag (hereinafter “preceding right rolling flag value bFRr”). If the preceding right rolling flag value bFRr is “1” and new right rolling flag value FRro is “0”, the control section  61  judges that right rolling of the auger housing  25  responsive to right turning operation is to be terminated and goes to step ST 26 . If the preceding right rolling flag value bFRr is “0” and new right rolling flag value FRro is “1”, the control section  61  judges that right rolling of the auger housing  25  is to be started in response to right turning operation and goes to step ST 27 . If the new right rolling flag value FRro agrees with the preceding right rolling flag value bFRr, the control section  61  judges that the current state is to be maintained and goes to step ST 28 . 
   Step ST 26 : The right roll amount Rro is set to “0”, and then the control section  61  proceeds to step ST 28 . 
   Step ST 27 : The right roll amount Rro is set to α, and then the control section  61  proceeds to step ST 28 . “α” represents the same predetermined roll amount as used at step ST 23  above. 
   Step ST 28 : The preceding right rolling flag value bFRr is rewritten with the new right rolling flag value FRro, and then the control section  61  goes to an out-connector A 3 . 
     FIG. 10  is a flow chart showing the remaining portion of the flow of control operations performed by the control section  61 . 
   Step ST 31 : A determination is made as to whether the left rolling switch  93 L (see  FIG. 6 ) is ON or not. With a YES determination, the control section  61  proceeds to step ST 32 , while, with a NO determination, the control section  61  goes to step S 34 . Note that the left rolling switch  93 L is ON if the auger-housing-posture manipulating lever  52  is being operated to effect left rolling. 
   Step ST 32 : The left and right roll amounts Lro and Rro are each set to “0”, and then the control section  61  proceeds to step ST 33 . 
   Step ST 33 : The control section  61  issues a left rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via an out-connector A 4  of  FIG. 10  and in-connector A 4  of  FIG. 7 . Namely, the control section  61  issues a control signal for starting the left rolling operation of the auger housing  25  and a control signal for stopping the right rolling operation of the auger housing  25 . In this way, the auger housing  25  is caused to roll to the left while the human operator is operating the auger-housing-posture manipulating lever  52  to effect left rolling during the snow removal work. 
   Step ST 34 : A determination is made as to whether the right rolling switch  93 R (see  FIG. 6 ) is ON or not. With a YES determination, the control section  61  proceeds to step ST 35 , while, with a NO determination, the control section  61  goes to step S 37 . Note that the right rolling switch  93 R is ON while the auger-housing-posture manipulating lever  52  is being operated to effect right rolling. 
   Step ST 35 : The left and right roll amounts Lro and Rro are each set to “0”, and then the control section  61  proceeds to step ST 36 . 
   Step ST 36 : The control section  61  issues a right rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector A 4  of  FIG. 10  and in-connector A 4  of  FIG. 7 . Namely, the control section  61  issues a control signal for starting the right rolling operation of the auger housing  25  and a control signal for stopping the left rolling operation of the auger housing  25 . In this way, the auger housing  25  is caused to roll to the right while the human operator is operating the auger-housing-posture manipulating lever  52  to effect right rolling during the snow removal work. 
   Step ST 37 : A determination is made as to whether the value of the left rolling flag FLro is “1” and the left roll amount Lro is greater than “0” (i.e., FLro=1 and Lro&gt;0). If answered in the affirmative, the control section  61  judges that left rolling is to be effected and moves on to step ST 38 , while, if answered in the negative, the control section  61  branches to step ST 40 . 
   Step ST 38 : Subtraction is performed on the left roll amount Lro while an addition is performed on the right roll amount Rro, and then the control section  61  proceeds to step ST 39 . For example, each time this step is reached, a predetermined very small amount is subtracted from the left roll amount Lro while the same predetermined very small amount is added to the right roll amount Rro. 
   Step ST 39 : The control section  61  issues a left rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector A 4  of  FIG. 10  and in-connector A 4  of  FIG. 7 . Namely, the control section  61  issues a control signal for starting the left rolling operation of the auger housing  25  and a control signal for stopping the right rolling operation of the auger housing  25 . 
   Step ST 40 : A determination is made as to whether the value of the right rolling flag FRro is “1” and the right roll amount Rro is greater than “0” (i.e., FRro=1 and Rro&gt;0). If answered in the affirmative, the control section  61  judges that right rolling is to be effected and moves on to step ST 41 , while, if answered in the negative, the control section  61  branches to step ST 43 . 
   Step ST 41 : Addition is performed on the left roll amount Lro while a subtraction is performed on the right roll amount Rro, and then the control section  61  proceeds to step ST 42 . For example, each time this step is reached, the predetermined very small amount is added to the left roll amount Lro while the same predetermined very small amount is subtracted from the right roll amount Rro. 
   Step ST 42 : The control section  61  issues a right rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector A 4  of  FIG. 10  and in-connector A 4  of  FIG. 7 . Namely, the control section  61  issues a control signal for stopping the left rolling operation of the auger housing  25  and a control signal for starting the right rolling operation of the auger housing  25 . 
   Step ST 43 : A determination is made as to whether the value of the left rolling flag FLro is “0” and the right roll amount Rro is greater than “0” (i.e., FLro=0 and Rro&gt;0). If answered in the affirmative, the control section  61  judges that right rolling is to be effected to return the auger housing  25  to the original neutral position and moves on to step ST 44 , while, if answered in the negative, the control section  61  branches to step ST 46 . 
   Step ST 44 : Subtraction is performed on the right roll amount Rro, and then the control section  61  proceeds to step ST 45 . For example, each time this step is reached, the predetermined very small amount is subtracted from the right roll amount Rro. 
   Step ST 45 : The control section  61  issues a right rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector A 4  of  FIG. 10  and in-connector A 4  of  FIG. 7 . Namely, the control section  61  issues a control signal for stopping the left rolling operation of the auger housing  25  and a control signal for starting the right rolling operation of the auger housing  25 . 
   Step ST 46 : A determination is made as to whether the value of the right rolling flag FRro is “0” and the left roll amount Lro is greater than “0” (i.e., FRro=0 and Lro&gt;0). If answered in the affirmative, the control section  61  judges that left rolling is to be effected to return the auger housing  25  to the original neutral position and moves on to step ST 47 , while, if answered in the negative, the control section  61  branches to step ST 49 . 
   Step ST 47 : Subtraction is performed on the left roll amount Lro, and then the control section  61  proceeds to step ST 48 . For example, each time this step is reached, the predetermined very small amount is subtracted from the left roll amount Lro. 
   Step ST 48 : The control section  61  issues a left rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector A 4  of  FIG. 10  and in-connector A 4  of  FIG. 7 . Namely, the control section  61  issues a control signal for starting the left rolling operation of the auger housing  25  and a control signal for stopping the right rolling operation of the auger housing  25 . 
   Step ST 49 : The control section  61  issues a stop instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector A 4  of  FIG. 10  and in-connector A 4  of  FIG. 7 . Namely, the control section  61  issues a control signal for stopping the left rolling operation of the auger housing  25  and a control signal for stopping the right rolling operation of the auger housing  25 . 
     FIG. 11  is a diagram showing behavior of the control section  61  employed in the first embodiment of the present invention, which particularly shows relationship among the left slow-down rate GsL, left roll amount Lro, right roll amount Rro and rolling operation of the rolling drive mechanism  70  when the snow removing machine  10  is to be turned left, with the horizontal axis representing an elapsed time. 
   In left turning of the snow removing machine  10 , the left roll amount Lro is set to the value α once the left slow-down rate GsL increases above the great rate threshold value GH, from which time on the predetermined subtraction and addition are successively performed on the left roll amount Lro and right roll amount Rro, respectively, in accordance with the passage of the time, so that the rolling drive mechanism  70  starts rolling the auger housing  25  to the left. 
   At the beginning of a predetermined time period (e.g., one sec.) t 1 , the left roll amount Lro starts decreasing while the right roll amount Rro starts increasing, and, at the end of that predetermined time period t 1 , the decreasing left roll amount Lro reaches zero while the increasing right roll amount Rro reaches the value α, upon which the predetermined subtraction on the left roll amount Lro and the predetermined addition on the right roll amount Rro are terminated and the rolling drive mechanism  70  terminates the left rolling operation. As a result, the auger housing  25  tilts to the left through a predetermined angle. 
   Then, once the left slow-down rate GsL decreases below the small rate threshold value GL, the predetermined subtraction starts to be successively performed on the right roll amount Rro, in accordance with the passage of the time, so that the rolling drive mechanism  70  starts rolling the auger housing  25  to the right (i.e., back to the neutral position). 
   At the end of the predetermined time period t 1 , the decreasing right roll amount Rro reaches the zero level, upon which the predetermined subtraction on the right roll amount Rro is terminated and the rolling drive mechanism  70  terminates the right rolling operation. As a result, the auger housing  25  returns to the original neutral position. 
   If, in left turning of the snow removing machine  10 , a time period t 2 , from the time point when the left slow-down rate GsL increases above the great rate threshold value GH to the time point when the left slow-down rate GsL decreases below the small rate threshold value GL, is smaller in length than the above-mentioned predetermined time period t 1 , then the left roll amount Lro does not decrease to the zero level and the right roll amount Rro does not increase to the α level. As a consequence, the auger housing  25  only rolls to the left partway. 
   Now that the left slow-down rate GsL has decreased below the small rate threshold value GL, the subtraction starts to be performed successively on the right roll amount Rro, in accordance with the passage of the time, until the right roll amount Rro reaches the zero level at the end of the next predetermined time period t 2 , upon which the subtraction on the right roll amount Rro is terminated and the rolling drive mechanism  70  terminates the right rolling operation. As a result, the auger housing  25  returns to the original neutral position. 
   As apparent from the foregoing, when the snow removing machine  10  is to be turned to the left rapidly, the human operator increases the slow-down rate of the left running device  11 L ( FIG. 4 ) that is located inwardly of the right running device  11 R as viewed in the turning direction. Therefore, the left slow-down rate GsL takes a value greater than the great rate threshold value GH (GsL&gt;GH). Thus, in this case, the left turn can be appropriately assisted by the auger housing  25  being rolled to the left into contact with the ground surface. 
   When the snow removing machine  10  is to be turned to the right rapidly, on the other hand, the right turn can be appropriately assisted by the auger housing  25  being rolled to the right into contact with the ground surface in a similar manner to the left turn. 
     FIG. 12  is a view explanatory of behavior of the snow removing machine of the present invention, which particularly shows arrangements of the auger housing  25 , blower case  26  and rolling drive mechanism  70  as viewed from behind these components  25 ,  26  and  70 . 
   (a) of  FIG. 12  shows the auger housing  25  in the neutral position in a manner corresponding to  FIG. 2 . As the snow removing machine  10  is turned to the left in this state, the electric motor  74  of the rolling drive mechanism  70  is rotated in the forward direction so that the piston  73  contracts. As a consequence, the auger housing  25  rolls to the left (i.e., counterclockwise as seen in  FIG. 12 ), so that the left sled  28 L (i.e., inner side edge of the auger housing  25  as viewed in the leftward turning direction) is caused to contact the ground surface and bite into snow on the ground surface. 
   Then, the electric motor  74  is rotated in the reverse direction so that the piston  73  expands. As a consequence, the auger housing  25  returns to the original neutral position as illustrated in (a) of  FIG. 12 . 
   On the other hand, as the snow removing machine  10  is turned to the right when the auger housing  25  is in the neutral position as illustrated in (a) of  FIG. 12 , the electric motor  74  of the rolling drive mechanism  70  is rotated in the reverse direction, so that the auger housing  25  rolls to the right (i.e., clockwise as seen in  FIG. 12 ), so that the right sled  28 R (i.e., inner side edge of the auger housing  25  as viewed in the rightward turning direction) is caused to contact the ground surface and bite into snow on the ground surface. 
   The foregoing description may be summed up as follows. As illustrated in  FIGS. 4 and 12 , the control section  61  issues a drive instruction to the rolling drive mechanism  70  in response to human operator&#39;s operation of the left or right turning operator member (left or right turning operation lever  43 L or  43 R, or left or right turning operation switch  47 L or  47 R). On the basis of such a drive instruction from the control section  61 , the auger housing  25  can be rolled in such a manner as to cause the end portion of one of the side edges (i.e., inner side edge, more specifically, left or right sled  28 L or  28 R) of the auger housing  25 , which is located inwardly of the other (right or left sled  28 R or  28 L) as viewed in the turning direction, to contact the ground surface biting into a snow surface gr. 
   With the end portion of the “inner” side edge of the auger housing  25  contacting the ground surface, there is produced a new traveling resistance in the inner side edge of the snow removing machine  10 , and thus, the machine  10  can turn about the portion of the side edge contacting the ground surface. 
   Thus, as the human operator operates any one of the turning operator members, not only one of the running devices  11 L or  11 R, located inwardly of the other running device  11 R or  11 L as viewed in the desired turning direction, is slowed down but also the auger housing  25  is rolled in such a manner as to cause the inner side edge to contact the ground surface, which can effectively enhance the turning performance of the snow removing machine  10 . Therefore, when the human operator has operated any one of the turning operator members, the snow removing machine  10  can be smoothly switched from the straight travel to the turning travel. As a result, the snow removing machine  10  can be highly maneuverable and usable with ease and, therefore, can efficiently perform snow removal work even in small working areas. 
   Further, in the snow removing machine  10 , as illustrated in  FIGS. 3 and 4 , the left and right turning operator members in the first embodiment are implemented by the left and right operation levers (left and right turning operation levers  43 L and  43 R) operable with the same hands holding the grips  18 L and  18 R fixed to the left and right operating handles  17 L and  17 R that extend rearwardly from a rear portion of the running-device frame  12 . Alternatively, the left and right turning operator members may be implemented by the left turning and right turning push-button switches (left and right turning operation switches  47 L and  47 R) provided between the operating handles  17 L and  17 R and at positions within ranges operable by the same hands holding the left and right grips  18 L and  18 R. 
   Thus, the human operator can also operate the left and right turning operator members with the two hands while manipulating the snow removing machine  10  with the same hands. Therefore, it is not necessary to rehold or release or let go of any of the left and right grips  18 L and  18 R each time the human operator performs operation for turning the snow removing machine  10  to the left or right. As a consequence, the present invention can effectively enhance the operability of the snow removing machine  10  and allows the human operator to turn the machine  10  with ease. With such an enhanced turning operability and turning capability of the snow removing machine  10 , the overall performance of the machine  10  can be significantly improved. 
   Further, because only the operation levers or push buttons have to be provided near the left and right operating handles  17 L and  17 R for purposes of turning the machine  10 , the present invention can reduce the number of components necessary to provide the turning operator members and thereby simplify the constructions of the turning operator members. 
   When the snow removing machine  10  is traveling on a soft ground, such as a snowy ground, the left and/or right running device  11 L and/or  11 R might get stuck in the ground; in such a case, the left and/or right running device  11 L and/or  11 R may just run idle digging in the ground. 
   Further, when the snow removing machine  10  is traveling on a snowy soft ground, for example, the machine  10  may encounter a great resistance ahead due to a great amount and great density of the snow. Where there is a likelihood of the left and/or right running device  11 L and/or  11 R getting stuck in the snowy soft ground, the human operator of the inventive snow removing machine  10  can break the snow ahead by repetitively rolling the auger housing  25  to the left and/or right (i.e., in the counterclockwise/clockwise direction) by alternately operating the left and right turning operator members with the two hands holding the grips  18 L and  18 R while manipulating the machine  10  with the same hands. As a consequence, the resistance against forward travel due to the snow in front can be effectively reduced, so that the controllability or maneuverability and traveling performance of the snow removing machine  10  can be even further enhanced. 
   The following paragraphs describe a modification of the above-described snow removing machine  10  (i.e., snow removing machine according a second embodiment of the present invention), with primary reference to  FIGS. 13-19 . 
   The snow removing machine  10  according to the second embodiment is characterized in that the auger-housing-posture manipulating lever itself  52 A is equipped with the functions of the left and right turning operator members (left and right turning operation levers  43 L and  43 R, or left and right turning operation switches  47 L and  47 R. Thus, in the second embodiment, there is no need to provide the left and right turning operation levers  43 L and  43 R, or left and right turning operation switches  47 L and  47 R employed in the above-described first embodiment 
   The other arrangements of the second embodiment are similar to those shown in  FIGS. 1-5  and will not be described here to avoid unnecessary duplication. 
     FIG. 13  shows the modified auger-housing-posture manipulating lever  52 A employed in the second embodiment. This modified auger-housing-posture manipulating lever  52 A is generally similar in construction to the auger-housing-posture manipulating lever  52  shown in  FIG. 6 , but different therefrom in that it includes a potentiometer provided in place of the left and right rolling switches  93 L and  93 R. 
   The modified auger-housing-posture manipulating lever  52 A is reciprocatively pivotable by the human operator as indicated by arrows Le and Ri. The auger housing  25  (see  FIG. 4 ) can be rolled to the left (i.e., counterclockwise as viewed from the human operator) by the human operator pivoting the auger-housing-posture manipulating lever  52 A to a “left rolling” region from a “stop region” (neutral position), and, in the “left rolling” region, control can be performed on the left rolling between a maximum left rolling operation amount Lomax and a minimum left rolling operation amount Lomin. 
   Similarly, the auger housing  25  can be rolled to the right (i.e., clockwise as viewed from the human operator) by the human operator pivoting the auger-housing-posture manipulating lever  52 A to a “right rolling” region from the “stop region” (neutral position), and, in the “right rolling” region, control can be performed on the right rolling between a maximum right rolling operation amount Romax and a minimum right rolling operation amount Romin. 
   As indicated in a lower end area of the figure, the potentiometer in the modified auger-housing-posture manipulating lever  52 A generates different voltages corresponding to various operating positions of the lever  52 A, i.e. 0 V when the lever  52 A is at a position corresponding to the maximum right rolling operation amount, 5 V when the lever  52 A is at a position corresponding to the maximum left rolling operation amount, and 2.3 V-2.7 V when the lever  52 A is in the stop (neutral) region. 
   Namely, the auger-housing-posture manipulating lever  52 A is a rolling operation lever operable to effect left and right (counterclockwise and clockwise) rolling of the auger housing  25 . Thus, the auger-housing-posture manipulating lever  52 A will hereinafter be referred to also as “rolling operation lever  52 A” where appropriate. 
   The auger-housing-posture manipulating lever  52 A is also pivotable in a direction perpendicular to the leftward/rightward pivoting direction indicated by arrows Le and Ri, to cause the auger housing  25  to move in the upward/downward direction (i.e., ascend or descend). 
   Next, with primary reference to flow charts of  FIGS. 14-17 , a description will be made about a flow of various control operations performed by the control section  61  in the snow removing machine  10  according to the second embodiment. 
     FIG. 14  is a flow chart showing a portion of an example flow of control operations performed by the control section  61  in the second embodiment. 
   Step ST 101 : a predetermined initialization process is performed; specifically, various flags, such as a left rolling flag Fro, right rolling flag FRro, left turning flag FLtu, right turning flag FRtu, preceding left turning flag bFLt and preceding right turning flag bFRt, are all set at “0”, and a timer-counted time Tc is also set at “0”. 
   Step ST 102 : The control section  61  reads rolling instructions given from the rolling operation lever  52 A, namely, a rolling operation direction and right and left rolling operation amounts Ro and Lo of the rolling operation lever  52 A (auger-housing-posture manipulating lever  52 A). The rolling operation amounts Ro and Lo are each expressed in percentage (%). 
   Step ST 103 : A determination is made as to whether the right rolling operation amount Ro is smaller than a preset small operation-amount threshold value SL (Ro&lt;SL). With a NO determination, the control section  61  branches to step ST 104 , while, with a YES determination, the control section  61  proceeds to step ST 107 . The small operation-amount threshold value SL is expressed in percentage (%) and set at, for example, 10% in this case. If the right rolling operation amount Ro is equal to or greater than the preset small operation-amount threshold value SL (NO determination at step ST 103 ), it means that the human operator wants to turn the snow removing machine  10  to the right, so that left rolling control is turned off (canceled). 
   Step ST 104 : The control section  61  sets a value “0” as the counted time Tc of the timer contained in the control section  61 , and then goes to step ST 105 . 
   Step ST 105 : The left rolling flag FLro is set at “0”, and then the control section  61  proceeds to step ST 106 . The left rolling flag FLro is a flag indicating whether or not the auger housing  25  should be rolled to the left to effectively perform snow removal work. 
   Step ST 106 : The left turning flag FLtu is set at “0”, and then the control section  61  proceeds to an out-connector B 1 . The left turning flag FLtu is a flag whether or not the auger housing  25  should be rolled to the left in order to turn the snow removing machine  10  to the left. 
   Step ST 107 : The left rolling operation amount Lo is compared to the preset small operation-amount threshold value SL and great operation-amount threshold value SH. The preset great operation-amount threshold value SH, which is greater than the small operation-amount threshold value SL, is expressed in percentage (%) and set at, for example, 60% in this case. If the left rolling operation amount Lo is smaller than the preset small operation-amount threshold value SL (Lo&lt;SL), the control section  61  judges that there has been no intended left rolling operation by the human operator, and branches to step ST 104 . 
   If the left rolling operation amount Lo is greater than the preset great operation-amount threshold value SL (SH&lt;Lo), the control section  61  judges that the human operator has operated the rolling operation lever  52 A to the left in order to turn the snow removing machine  10  to the left, and branches to step ST 108 . 
   If the left rolling operation amount Lo is in the range from the small operation-amount threshold value SL to the great operation-amount threshold value SH (SL≦Lo≦SH), the control section  61  judges that the human operator has operated the rolling operation lever  52 A to the left in order to perform snow removal work, and moves on to step ST 111 . 
   Step ST 108 : The control section  61  sets the timer-counted time Tc at a preset predetermined reference time To, and then goes to step ST 109 . 
   The reference time To is a slight delay time necessary to invert the value of the left rolling flag FLro from “0” to “1” (see later-described step ST 114 ) after the value of the left turning flag FLtu is inverted from “1” to “0” (see later-described step ST 116 ), and this reference time To is, for example, 100 msec. With the provision of such a delay time, the snow removing machine  10  can be reliably switched from the rolling operation for a left turn to the rolling operation for snow removal work. 
   Step ST 109 : The left rolling flag FLro is set at “0”, and then the control section  61  proceeds to step ST 110 . 
   Step ST 110 : The left turning flag FLtu is set at “1”, and then the control section  61  proceeds to the out-connector B 1 . 
   Step ST 111 : A determination is made as to whether the left turning flag FLtu is currently at the value “0”. With a YES determination, the control section  61  proceeds to step ST 112 , while, with a NO determination, the control section  61  branches to step ST 115 . 
   Step ST 112 : A determination is made as to whether the timer-counted time Tc is greater than “0” (zero). With a YES determination, the control section  61  proceeds to step ST 113 , while, with a NO determination, the control section  61  branches to step ST 114  judging that the reference time To has passed (see later-described step ST 108 ). 
   Step ST 113 : Subtraction is performed on the timer-counted time Tc, and then the control section  61  proceeds to the out-connector B 1 . For example, each time this step is reached, a predetermined time is subtracted from the timer-counted time Tc. 
   Step ST 114 : The left rolling flag FLro is set at “1”, and then the control section  61  proceeds to the out-connector B 1 . 
   Step ST 115 : A determination is made as to whether the left rolling operation amount Lo is smaller than a preset medium operation-amount threshold value SM (Lo&lt;SM). With a YES determination, the control section  61  proceeds to step ST 116 , while, with a NO determination, the control section  61  proceeds to the out-connector B 1 . The medium operation-amount threshold value SM, which is greater than the small operation-amount threshold value SL, is expressed in percentage (%) and set at, for example, 40% in this case. 
   If (Lo&lt;SM), it means that the human operator has stopped left turning operation. In this way, a hysteresis characteristic is imparted to the medium operation-amount threshold value SM, used for terminating the turning operation, with respect to the great operation-amount threshold value used for starting the turning operation. 
   Step ST 116 : The left turning flag FLtu is set at “0”, and then the control section  61  proceeds to the out-connector B 1 . 
     FIG. 15  is a flow chart showing another portion of the example flow of control operations performed by the control section  61  in the second embodiment. 
   Step ST 123 : A determination is made as to whether the left rolling operation amount Lo is smaller than the preset small operation-amount threshold value SL (Lo&lt;SL). With a NO determination, the control section  61  branches to step ST 124 , while, with a YES determination, the control section  61  proceeds to step ST 127 . If the right rolling operation amount Ro is equal to or greater than the preset small operation-amount threshold value SL (NO determination at step ST 123 ), it means that the human operator wants to turn the snow removing machine  10  to the left, so that right rolling control is turned off (canceled). 
   Step ST 124 : The control section  61  sets a value “0” as the counted time Tc of the timer, and then goes to step ST 125 . 
   Step ST 125 : The right rolling flag FRro is set at “0”, and then the control section  61  proceeds to step ST 126 . The right rolling flag FRro is a flag indicating whether or not the auger housing  25  should be rolled to the right to effectively perform snow removal work. 
   Step ST 126 : The right turning flag FRtu is set at “0”, and then the control section  61  proceeds to an out-connector B 2 . The right turning flag FRtu is a flag whether or not the auger housing  25  should be rolled to the right in order to turn the snow removing machine  10  to the right. 
   Step ST 127 : The right rolling operation amount Ro is compared to the preset small operation-amount threshold value SL and great operation-amount threshold value SH. 
   If the right rolling operation amount Ro is smaller than the preset small operation-amount threshold value SL (Ro&lt;SL), the control section  61  judges that there has been no intended right rolling operation by the human operator, and branches to step ST 124 . 
   If the right rolling operation amount Ro is greater than the preset great operation-amount threshold value SH (SH&lt;Ro), the control section  61  judges that the human operator has operated the rolling operation lever  52 A to the right in order to turn the snow removing machine  10  to the right, and branches to step ST 128 . 
   If the right rolling operation amount Ro is in the range from the small operation-amount threshold value SL to the great operation-amount threshold value SH (SL≦Ro≦SH), the control section  61  judges that the human operator has operated the rolling operation lever  52 A to the right in order to perform snow removal work, and moves on to step ST 131 . 
   Step ST 128 : The control section  61  sets the timer-counted time Tc at a preset reference time To, and then goes to step ST 129 . Similarly to the preset reference time To explained above in relation to step ST 108 , this reference time To is a slight delay time necessary to invert the value of the right rolling flag FRro from “0” to “1” after the value of the right turning flag FRtu is inverted from “1” to “0”. 
   Step ST 129 : The right rolling flag FRro is set at “0”, and then the control section  61  proceeds to step ST 130 . 
   Step ST 130 : The right turning flag FRtu is set at “1”, and then the control section  61  proceeds to the out-connector B 2 . 
   Step ST 131 : A determination is made as to whether the right turning flag FRtu is currently at the value “0”. With a YES determination, the control section  61  proceeds to step ST 132 , while, with a NO determination, the control section  61  branches to step ST 135 . 
   Step ST 132 : A determination is made as to whether the timer-counted time Tc is greater than “0” (zero). With a YES determination, the control section  61  proceeds to step ST 133 , while, with a NO determination, the control section  61  branches to step ST 134  judging that the reference time To has passed (see later-described step ST 128 ). 
   Step ST 133 : Subtraction is performed on the timer-counted time Tc, and then the control section  61  proceeds to the out-connector B 2 . For example, each time this step is reached, a predetermined time is subtracted from the timer-counted time Tc. 
   Step ST 134 : The right rolling flag FRro is set at “1”, and then the control section  61  proceeds to the out-connector B 2 . 
   Step ST 135 : A determination is made as to whether the right rolling operation amount Ro is smaller than the preset medium operation-amount threshold value SM (Ro&lt;SM). With a YES determination, the control section  61  proceeds to step ST 136 , while, with a NO determination, the control section  61  proceeds to the out-connector B 2 . 
   Step ST 136 : The right turning flag FRtu is set at “0”, and then the control section  61  proceeds to the out-connector B 2 . 
     FIG. 16  is a flow chart showing still another portion of the example flow of control operations performed by the control section  61  in the second embodiment. 
   Step ST 141 : Newest value of the left turning flag FLtu hereinafter “new left turning flag value FLtu”) is compared to the previous value of the left turning flag FLtu (hereinafter “preceding left turning flag value bFLt”). If the preceding left rolling flag value bFLt is “1” and new left turning flag value FLtu is “0”, the control section  61  judges that left rolling of the auger housing  25  responsive to turning operation is to be terminated and goes to step ST 142 . If the preceding left turning flag value bFLt is “0” and new left rolling flag value FLtu is “1”, the control section  61  judges that left rolling of the auger housing  25  is to be started in response to leftward turning operation and goes to step ST 143 . If the new left turning flag value FLtu agrees with the preceding left turning flag value bFLt, the control section  61  judges that the current state is to be maintained and goes to step ST 144 . 
   Step ST 142 : The left roll amount Lro is set to “0”, and then the control section  61  proceeds to step ST 144 . 
   Step ST 143 : The left roll amount Lro is set to α, and then the control section  61  proceeds to step ST 144 . As explained above in relation to step ST 23 , “α” represents a predetermined roll amount in a range for rolling the auger housing  25  from the neutral position, and is set, for example, at a values that causes an end portion of the “inner” side edge, as viewed in the turning direction, of the auger housing  25  (sled  28 L or  28 R) to contact the ground surface. 
   Step ST 144 : The preceding left turning flag value bFLt is rewritten with the new left rolling flag value FLro, and then the control section  61  goes to step ST 145 . 
   Step ST 145 : Newest value of the right turning flag FRtu (hereinafter “new left turning flag value FRtu”) is compared to the preceding value of the right turning flag bFRt (hereinafter “preceding right turning flag value bFRt”). If the preceding turning flag value bFRt is “1” and new right turning flag value FRtu is “0”, the control section  61  judges that right rolling of the auger housing  25  responsive to turning operation is to be terminated and goes to step ST 146 . If the preceding right turning flag value bFRt is “0” and new right turning flag value FRtu is “1”, the control section  61  judges that right rolling of the auger housing  25  is to be started in response to turning operation and goes to step ST 147 . If the new right turning flag value FRtu agrees with the preceding right turning flag value bFRt, the control section  61  judges that the current state is to be maintained and goes to step ST 148 . 
   Step ST 146 : The right roll amount Rro is set to “0”, and then the control section  61  proceeds to step ST 148 . 
   Step ST 147 : The right roll amount Rro is set to α, and then the control section  61  proceeds to step ST 148 . “α” represents the same predetermined roll amount as used at step ST 143  above. 
   Step ST 148 : The preceding right turning flag value bFRt is rewritten with the new right turning flag value FRtu, and then the control section  61  goes to an out-connector B 3 . 
     FIG. 17  is a flow chart showing the remaining portion of the flow of control operations performed by the control section  61  in the second embodiment. 
   Step ST 151 : A determination is made as to whether the value of the left rolling flag FLro is “1” or not. With a YES determination, the control section  61  proceeds to step ST 152 , while, with a NO determination, the control section  61  branches to step ST 154 . 
   Step ST 152 : The left and right roll amounts Lro and Rro are each set to “0”, and then the control section  61  proceeds to step ST 153 . 
   Step ST 153 : The control section  61  issues a left rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 102  by way of an out-connector B 4  of  FIG. 17  and in-connector B 4  of  FIG. 14 . Namely, the control section  61  issues a control signal for starting the left rolling operation of the auger housing  25  and a control signal for stopping the right rolling operation of the auger housing  25 . In this way, the auger housing  25  is caused to roll to the left while the human operator is operating the auger-housing-posture manipulating lever  52 A to effect snow removal work. 
   Step ST 154 : A determination is made as to whether the value of the right rolling flag FRro is “1” or not. With a YES determination, the control section  61  proceeds to step ST 155 , while, with a NO determination, the control section  61  branches to step ST 157 . 
   Step ST 155 : The left and right roll amounts Lro and Rro are each set to “0”, and then the control section  61  proceeds to step ST 156 . 
   Step ST 156 : The control section  61  issues a right rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 102  by way of the out-connector B 4  of  FIG. 17  and in-connector B 4  of  FIG. 14 . Namely, the control section  61  issues a control signal for stopping the left rolling operation of the auger housing  25  and a control signal for starting the right rolling operation of the auger housing  25 . In this way, the auger housing  25  is caused to roll to the right while the human operator is operating the auger-housing-posture manipulating lever  52 A to effect snow removal work. 
   Step ST 157 : A determination is made as to whether the value of the left turning flag FLtu is “1” and the left roll amount Lro is greater than “0” (i.e., FLtu=1 and Lro&gt;0). If answered in the affirmative, the control section  61  judges that left rolling is to be effected for a left turn of the machine  10  and moves on to step ST 158 , while, if answered in the negative, the control section  61  branches to step ST 160 . 
   Step ST 158 : Subtraction is performed on the left roll amount Lro while an addition is performed on the right roll amount Rro, and then the control section  61  proceeds to step ST 159 . For example, each time this step is reached, a predetermined very small amount is subtracted from the left roll amount Lro while the predetermined very small amount is added to the right roll amount Rro. 
   Step ST 159 : The control section  61  issues a left rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector B 4  of  FIG. 17  and in-connector B 4  of  FIG. 14 . Namely, the control section  61  issues a control signal for starting the left rolling operation of the auger housing  25  and a control signal for stopping the right rolling operation of the auger housing  25 . 
   Step ST 160 : A determination is made as to whether the value of the right turning flag FRtu is “1” and the right roll amount Rro is greater than “0” (i.e., FRtu=1 and Rro&gt;0). If answered in the affirmative, the control section  61  judges that right rolling is to be effected for a right turn of the machine  10  and moves on to step ST 161 , while, if answered in the negative, the control section  61  branches to step ST 163 . 
   Step ST 161 : Addition is performed on the left roll amount Lro while a subtraction is performed on the right roll amount Rro, and then the control section  61  proceeds to step ST 162 . For example, each time this step is reached, a predetermined very small amount is added to the left roll amount Lro while the predetermined very small amount is subtracted from the right roll amount Rro. 
   Step ST 162 : The control section  61  issues a right rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector B 4  of  FIG. 17  and in-connector B 4  of  FIG. 14 . Namely, the control section  61  issues a control signal for stopping the left rolling operation of the auger housing  25  and a control signal for starting the right rolling operation of the auger housing  25 . 
   Step ST 163 : A determination is made as to whether the value of the left turning flag FLtu is “0” and the right roll amount Rro is greater than “0” (i.e., FLtu=0 and Rro&gt;0). If answered in the affirmative, the control section  61  judges that right rolling is to be effected to return the auger housing  25  to the original neutral position and moves on to step ST 164 , while, if answered in the negative, the control section  61  branches to step ST 166 . 
   Step ST 164 : Subtraction is performed on the right roll amount Rro, and then the control section  61  proceeds to step ST 165 . For example, each time this step is reached, a predetermined very small amount is subtracted from the right roll amount Rro. 
   Step ST 165 : The control section  61  issues a right rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 02  via the out-connector B 4  of  FIG. 17  and in-connector B 4  of  FIG. 14 . Namely, the control section  61  issues a control signal for stopping the left rolling operation of the auger housing  25  and a control signal for starting the right rolling operation of the auger housing  25 . 
   Step ST 166 : A determination is made as to whether the value of the right turning flag FRtu is “0” and the left roll amount Lro is greater than “0” (i.e., FRtu=0 and Lro&gt;0). If answered in the affirmative, the control section  61  judges that left rolling is to be effected to return the auger housing  25  to the original neutral position and moves on to step ST 167 , while, if answered in the negative, the control section  61  branches to step ST 169 . 
   Step ST 167 : Subtraction is performed on the left roll amount Lro, and then the control section  61  proceeds to step ST 168 . For example, each time this step is reached, a predetermined very small amount is subtracted from the left roll amount Lro. 
   Step ST 168 : The control section  61  issues a left rolling instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 102  via the out-connector B 4  of  FIG. 17  and in-connector B 4  of  FIG. 14 . Namely, the control section  61  issues a control signal for starting the left rolling operation of the auger housing  25  and a control signal for stopping the right rolling operation of the auger housing  25 . 
   Step ST 169 : The control section  61  issues a stop instruction to the electric motor  74  of the rolling drive mechanism  70  and then reverts to step ST 102  via the out-connector B 4  of  FIG. 17  and in-connector B 4  of  FIG. 14 . Namely, the control section  61  issues a control signal for stopping the left and right rolling operation of the auger housing  25 . 
     FIG. 18  is a diagram showing behavior of the control section  61  employed in the second embodiment, which particularly shows relationship among the left rolling operation amount Lo, left turning flag FLtu and left rolling flag FLro, right roll amount Rro and rolling operation of the rolling drive mechanism  70  when the snow removing machine  10  is to be turned left, with the horizontal axis representing the elapsed time. 
   In left turning of the second embodiment, once the left rolling operation amount Lo increases above the preset small operation-amount threshold value SL, the value of the left rolling flag FLro is inverted from “0” to “1”. Then, once the left rolling operation amount Lo further increases to exceed the great operation-amount threshold value SH, the value of the left rolling flag FLro is inverted from “1” to “0” and the value of the left turning flag FLtu is inverted from “0” to “1”. Then, the value of the left turning flag FLtu is inverted from “1” to “0” once the left rolling operation amount Lo decreases below the medium operation-amount threshold value SM. Then, the value of the left tolling flag FLro is inverted from “0” to “1” upon passage of the slight reference time To from the time point when the left rolling operation amount Lo has decreased below the medium operation-amount threshold value SM. Thence, once the left rolling operation amount Lo further decreases to fall below the small operation-amount threshold value SL, the value of the left rolling flag FLro is inverted from “1” to “0”. 
   Further, if, in left turning of the machine  10 , the left rolling operation amount Lo increases above the great operation-amount threshold value SH and then decreases past the medium operation-amount threshold value SM to fall below the small operation-amount threshold value SL before the passage of the following reference time To, the value of the left rolling flag FLro is left unchanged from “0”. 
     FIG. 19  is another diagram showing the behavior of the control section  61  employed in the second embodiment, which particularly shows relationship among the left turning flag FLtu, left roll amount Lro, right roll amount Rro and rolling operation of the rolling drive mechanism  70 , with the horizontal axis representing the elapsed time. 
   In left turning of the second embodiment, once the value of the left turning flag FLtu is inverted from “0” to “1”, the left roll amount Lro is set to “α”, from which time on the predetermined subtraction and addition are successively performed on the left roll amount Lro and right roll amount Rro, respectively, in accordance with the passage of the time, so that the rolling drive mechanism  70  starts rolling the auger housing  25  to the left. 
   At the end of a predetermined time period t 1 , the decreasing left roll amount Lro reaches “0” while the increasing right roll amount Rro reaches “α”, upon which the predetermined subtraction on the left roll amount Lro and the predetermined addition on the right roll amount Rro are terminated and the rolling drive mechanism  70  stops rolling the auger housing  25 . As a result, the auger housing  25  tilts to the left through a predetermined angle. 
   Then, once the value of the left turning flag FLtu is inverted from “1” to “0”, the subtraction starts to be performed successively on the right roll amount Rro, in accordance with the passage of the time, and the rolling drive mechanism  70  starts rolling the auger housing  25  to the right (returning the auger housing  25  to the neutral position). At the end of the following predetermined time period t 1 , the decreasing right roll amount Rro reaches “0”, upon which the predetermined subtraction on the right roll amount Rro is terminated and the rolling drive mechanism  70  stops rolling the auger housing  25 . As a result, the auger housing  25  returns to the original neutral position. 
   If, in left turning of the snow removing machine  10 , a time period t 2  when the value of the left turning flag FLtu is kept at “1”, is shorter than the above-mentioned predetermined time period t 1 , then the left roll amount Lro does not decrease to the zero level and the right roll amount Rro does not increase to the α level. As a consequence, the auger housing  25  only rolls to the left partway. 
   Starting at the time point when the left turning flag FLtu has been inverted from “1” to “0”, the predetermined subtraction is performed successively on the right roll amount Ryo, in accordance with the passage of the time, until the right roll amount Ryo decreases to the zero level at the end of the predetermined time period t 2 . When the right roll amount Ryo has decreased to the zero level, the predetermined subtraction on the right roll amount Ryo is terminated, and the rolling drive mechanism  70  stops rolling the auger housing  25 . As a result, the auger housing  25  returns to the original neutral position. 
   When the snow removing machine  10  is to be turned to the right, the control section  61  performs control to allow the auger housing  25  to be rolled to the right in generally the same manner as when the snow removing machine  10  is to be turned to the left. 
   As apparent from the foregoing, the second embodiment can achieve the following novel advantageous results as well as those attained by the first embodiment of  FIGS. 1-12 . 
   Namely, in the second embodiment, the auger-housing-posture manipulating lever  52 A, which fundamentally operates the rolling drive mechanism  70  for rolling the auger housing  25  in accordance with the snow surface during snow removal work using the auger  31 , is designed to function also as the turning operator member. Thus, in this case, there is no need to provide separate turning operation levers on the machine  10 . 
   More specifically, three operation-amount threshold values SL, SM and SH are set in the second embodiment. The rolling operation amounts Lo and Ro of the auger-housing-posture manipulating lever  52 A are compared to the three operation-amount threshold values SL, SM and SH, so that, with the auger-housing-posture manipulating lever  52 A alone, the human operator can perform both (1) auger-housing rolling operation to assist turning of the machine  10  and (2) auger-housing rolling operation to assist snow removal work. 
   Even though the snow removing machine  10  according to the second embodiment of the invention has no dedicated turning operator member, the human operator can use the auger-housing-posture manipulating lever  52 A to readily perform operation for turning the machine  10 . Thus, the second embodiment can achieve an enhanced turning operability, sufficient turning performance and hence enhanced overall performance of the snow removing machine  10 . Since the number of necessary operation members can be minimized, the basic principles of the second embodiment can be suitably applicable to snow removing machines that have to be small in size or have other spatial limitations. Further, because the number of necessary components can be reduced, the second embodiment can reduce the manufacturing cost of the snow removing machine  10 . 
   The snow removing machine  10  of a type where the left and right running devices  11 L and  11 R are not controlled independently of each other can not make a turn by slowing down one of the running devices. Thus, normally, the snow removing machine  10  has to be turned by the human operator displacing the machine manually by his or her own force. With the second embodiment, however, the human operator can operate the auger-housing-posture manipulating lever  52 A to roll the auger housing  25 , in a direction corresponding to a desired turning direction of the snow removing machine  10 , so as to cause the end portion of one of the side edges of the auger housing  25 , located inwardly of the other side edge as viewed in the turning direction, to contact the ground surface. Thus, the snow removing machine  10  can be appropriately turned with the portion of the ground-contacting inner side edge as a pivot center. 
   Because the left and right running devices  11 L and  11 R are not controlled independently of each other, the cost of the machine  10  can be lowered. Further, because any one of the left and right running devices  11 L and  11 R is not slowed down in turning the snow removing machine  10 , a sufficiently-great force for running the machine  10  can always be secured reliably. 
   Driving sources for the running devices  11 L and  11 R may be other than the electric motors  21 L and  21 R. For example, the engine  14  may be used as the driving source for the running devices  11 L and  11 R, in which case the output power of the engine  14  is transmitted, via a hydrostatic continuously variable transmission, to the running devices  11 L and  11 R. The hydrostatic continuously variable transmission is a well-known continuously variable transmission capable of rotating left and right output shafts in forward and reverse directions and stopping the rotations of the output shafts, independently of each other, in response to power received via input shafts. 
   Further, each of the auger housing elevator mechanism  16  and rolling drive mechanism  70  may be other than the electric hydraulic cylinder of the type that expands and contracts the piston with hydraulic pressure produced from the hydraulic pump by the electric motor integrally fixed to the cylinder; for example, it may comprise a combination of a hydraulic device and hydraulic cylinder provided separately from each other. 
   Further, the above-mentioned predetermined time t 1  is a time period over which the left or right roll amount Lro or Rro decreases from the “α” level to the “0” level; namely, the predetermined time t 1  corresponds to the predetermined roll amount α. Thus, the predetermined roll amount α may be replaced with the predetermined time t 1 . 
   Furthermore, the determination as to whether the left or right roll amount Lro or Rro has decreased from the “α” level to the “0” level may be made on the basis of an output from a position sensor that detects a roll amount of the auger housing  25 , instead of the subtraction and addition of the predetermined roll amount α or the passage of time. 
   Furthermore, when the auger housing  25  is already in a position rolled partway, the predetermined roll amount α may be subtracted a predetermined number of times corresponding to the partway-rolled position (e.g., step ST 23  or T 27  of  FIG. 9 ). Thus, when the snow removing machine  10  is to be turned, the auger housing  25  may be rolled only by an amount necessary to assist the turning. 
   In the snow removing machine  10  according to the second embodiment, rolling operation via the auger-housing-posture manipulating lever  52 A may be dispensed with, and the functions of the auger-housing-posture manipulating lever  52 A may be performed by turning operator members (e.g., left and right turning operation levers  43 L and  43 R or left and right turning operation switches  47 L and  47 R). In such a case, only the left and right turning operation levers or the left and right turning operation switches can perform both (1) auger-housing rolling operation to assist turning of the machine  10  and (2) auger-housing rolling operation to assist snow removal work. 
   Further, in the snow removing machine  10  according to the second embodiment, the auger-housing rolling operation to assist turning of the machine  10  may be permitted only when the condition that the machine  10  is traveling forward at low speed has been met, as in the first embodiment of  FIGS. 1-12 . In this case, steps ST 02 -ST 06  of  FIG. 7  may be added between steps ST 101  and ST 102  of  FIG. 14 . At step ST 106 , the left rolling flag FLro and right rolling FRro are each set at “0” and the left turning flag FLtu and right turning FRtu are each set at “0”, after which then the control section  61  proceeds to the output-connector B 2 . 
   Obviously, various minor changes and modifications of the present invention are possible in the light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.