Cable steering device

A cable steering device in which the steering torque of a steering wheel is transmitted to wheels by a driven pulley provided in a driven pulley housing, cables, a follower pulley provided in a follower pulley housing and a gear box, and a power steering motor for assisting in the generation of the steering torque is provided in the follower pulley housing and not in the gear box.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a cable steering device in which a steering wheel 
and a gear box are connected to each other by flexible cables, such as 
Bowden cables. 
2. Description of the Related Art 
In a conventional steering device for a vehicle, a lower end of a steering 
shaft having a steering wheel at an upper end thereof is connected to a 
gear box so that a steering torque inputted to the steering wheel is 
transmitted to a rack and pinion mechanism provided in the gear box via 
the steering shaft. 
However, when the steering wheel and the gear box are connected to each 
other using the steering shaft, it is difficult to freely select a 
position of the steering wheel relative to the gear box. Therefore, the 
degree of freedom of designing the apparatus is greatly restricted and 
further, the gear box cannot be commonly used in both a right-hand steered 
vehicle and left-hand steered vehicle. In addition, the vibration inputted 
from the road surface to tires and the vibration of an engine are inputted 
to the steering wheel via the steering shaft, so that such vibrations 
detract from calmness in the interior of the vehicle and riding comfort. 
Therefore, a cable steering device employing flexible transmission means, 
such as Bowden cables instead of a conventional steering shaft has been 
proposed in Japanese Patent Application Laid-Open No. 8-2431. 
When a steering device is formed in this manner, it becomes possible to 
freely select a position of a steering wheel relative to a gear box, and, 
moreover, the vibration of the gear box is rarely transmitted to the 
steering wheel. This solves the above-mentioned various problems. 
A known electric power steering device is provided with an actuator, which 
comprises a power steering motor, on the outside of a gear box, and the 
wheels are steered by driving a steering rod housed in the gear box, by 
this actuator. 
If a cable steering device and an electric power steering device are 
combined with each other with an actuator provided on a gear box, the 
degree of freedom of designing the electric power steering device with 
respect to the dimensions and shape thereof is reduced and it becomes 
difficult to place the electric power steering device in a narrow engine 
room. 
SUMMARY OF THE INVENTION 
The present invention has been developed in view of these facts, and is 
directed to improving the degree of freedom of designing a cable steering 
device having an electric power steering device, with respect to the 
dimensions and shape thereof, and enabling this apparatus to be housed 
more easily in a small engine room. 
In the present invention, an operation of the steering wheel made by a 
driver is transmitted to the wheels via the driven pulley, cables, 
follower pulley and gear box. In the meantime, the power assist means is 
operated on the basis of the steering wheel operating torque detected by a 
steering torque detecting means, and the driver's steering wheel operating 
action is thereby assisted. Since the power assist means is provided in a 
follower pulley housing in which the follower pulley is housed, the device 
can be placed in an engine room more easily by miniaturizing and 
simplifying the gear box. Moreover, a gear box of an existing manual 
steering apparatus can be used as it is. 
In one preferred embodiment of the invention, when the power steering motor 
constituting the power assist means is rotated, the driving force is 
transmitted from a worm mounted on the output shaft thereof to a worm 
wheel mounted on the follower pulley or the rotary shaft thereof, whereby 
the driver's steering operation is assisted. 
When the power steering motor constituting the power assist means in the 
invention is rotated, the driving force is transmitted to the follower 
pulley connected directly to the output shaft of the power assist means or 
the rotary shaft of the follower pulley, whereby the driver's steering 
operation is assisted. 
In another embodiment of the invention, when the power steering motor 
constituting the power assist means is rotated, the driving force is 
transmitted from a spur gear mounted on the output shaft thereof to a spur 
gear mounted on the follower pulley or on the rotary shaft of the follower 
pulley, whereby the driver's steering operation is assisted. 
In still another embodiment of the invention, when the power steering motor 
constituting the power assist means is rotated, the driving force is 
transmitted from a bevel gear mounted on the output shaft thereof to a 
bevel gear mounted on the follower pulley or on the rotary shaft of the 
follower pulley, whereby the driver's steering operation is assisted. 
In a further embodiment of the invention the output shaft of the power 
steering motor is provided in parallel with a pair of cables extending 
from the follower pulley, and the power steering motor is located between 
the two cables.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The best mode for carrying out the present invention will now be described 
with reference to the embodiments thereof shown in the attached drawings. 
As shown in FIG. 1, a driven pulley housing 2 provided in front of a 
steering wheel 1 of an automobile and a follower pulley housing 4 provided 
above a gear box 3 are connected to each other by two Bowden cables 5, 6. 
The tie rods 7L, 7R extending from both end portions of the gear box 3 in 
leftward and rightward directions of a vehicle body are connected to 
knuckles (not shown) supporting left and right wheels W.sub.L, W.sub.R. 
As shown in FIG. 2, a driven pulley 11dr is mounted fixedly on a rotary 
shaft 10dr which is supported rotatably in the driven pulley housing 2 and 
rotated with the steering wheel 1. The two Bowden cables 5, 6 comprise 
outer tubes 5o, 6o, and inner cables 5i, 6i housed slidably in the 
interior of the outer tubes, and one end portion of each of the inner 
cables 5i, 6i is fixed by being wound a plurality of times along a helical 
pulley groove formed in an outer circumference of the driven pulley 11dr, 
one end portion of each of the outer tubes 5o, 6o being supported slidably 
in the driven pulley housing 2. 
Spring seats 12, 13 are formed by enlarging the diameter of one end portion 
of each of the outer tubes 5o, 6o and positioned between an end wall 
2.sub.1 and an intermediate wall 2.sub.2 formed in the driven pulley 
housing 2. Springs 14, 15 are compressed between the intermediate wall 
2.sub.2 of the driven pulley housing 2 and the spring seats 12, 13 urge 
the two outer tubes 5o, 6o in the direction in which the outer tubes 5o, 
6o are pushed out of the driven pulley housing 2. Accordingly, the spring 
seats 12, 13 of the two outer tubes 5o, 6o are movable in the longitudinal 
direction (lengthwise direction of the Bowden cables 5, 6) in accordance 
with the expansion and contraction of the springs 14, 15. A pair of 
differential transformers 16, 17 are provided on the intermediate wall 
2.sub.2 of the driven pulley housing 2 as steering torque detecting means. 
The detecting elements 16.sub.1, 17.sub.1 of these differential 
transformers 16, 17 are connected to the spring seats 12, 13 respectively. 
When the rotary shaft 10dr is rotated in a direction of an arrow A by 
operating the steering wheel 1, tension of the inner cable 5i increases to 
cause the outer tube 5o to be drawn in a direction of an arrow B against 
the spring 14, and the spring seat 12 of the outer tube 5o moves the 
detecting element 16.sub.1 of the differential transformer 16 in the 
direction of the arrow B. Since tension of the inner cable 6i decreases, 
the outer tube 6o is pressed in a direction of an arrow C due to a 
resilient force of the spring 15, so that the spring seat 13 of the outer 
tube 6o moves the detecting element 17.sub.1 of the differential 
transformer 17 in the direction of the arrow C. 
The steering torque inputted to the steering wheel 1 is proportional to a 
tension difference between the two inner cables 5i, 6i, and a relative 
amount of movement of the two outer tubes 5o, 6o is proportional to this 
tension difference. Accordingly, the steering torque can be determined by 
detecting the relative amount of movement of the two outer tubes 5o, 6o by 
the differential transformers 16, 17. The steering torque thus detected is 
arithmetically processed with other control signals in an electronic 
control unit U. On the basis of the results, the feedback of the steering 
assist torque generated by a power steering motor 24 which will be 
described later is controlled so that the tension difference between the 
inner cables 5i, 6i, i.e. the relative amount of movement of the outer 
tubes 5o, 6o becomes substantially constant. 
When the steering wheel 1 is rotated in the direction of an arrow A' in 
FIG. 2, the steering torque of the steering wheel 1 can also be detected 
in the same manner as in the case where the steering wheel 1 is rotated in 
the mentioned direction of the arrow A. 
As shown in FIGS. 1 and 3, a follower pulley 11dn is mounted fixedly on a 
rotary shaft 10dn supported rotatably in the follower pulley housing 4, 
and the other end portions of the two inner cables 5i, 6i are fixed by 
being wound a plurality of times along a helical pulley groove formed in 
an outer circumference of the follower pulley 11dn. The other end portions 
of the outer tubes 5o, 6o for the two Bowden cables 5, 6 are fixed to the 
follower pulley housing The rotary shaft 10dn, which projects from the 
follower pulley housing 4 into the interior of the gear box 3, is mounted 
at a free end portion thereof with a pinion 21, which is meshed with a 
rack 23 formed on a steering rod 22 supported in the interior of the gear 
box 3 so that the steering rod can be laterally moved. 
The power steering motor 24 is supported on the follower pulley housing 4, 
in which a worm 26 provided on an output shaft 25 is meshed with a worm 
wheel 27 mounted on the rotary shaft 10dn. Therefore, a torque of the 
power steering motor 24 is transmitted to the rotary shaft 10dn via the 
worm 26 and the worm wheel 27. 
The operation of the embodiment of the present invention having the 
above-described construction will now be described. 
When the steering wheel 1 is operated so as to turn the vehicle, the rotary 
shaft 10dr in FIG. 2 is rotated with the driven pulley 11dr. As a result, 
one inner cable 5i, 6i of the Bowden cables 5, 6 is drawn, and the other 
inner cable 5i, 6i is slackened. Consequently, the rotation of the driven 
pulley 11dr is transmitted to the follower pulley 11dn to cause the rotary 
shaft 10dn to rotate, and to transmit the steering torque to the wheels 
W.sub.L, W.sub.R via the pinion 21, rack 23 and steering rod 22 in the 
gear box 3. 
When the differential transformers 16, 17 detect the steering torque 
applied to the steering wheel 1, the power steering motor 24 generates 
torque in accordance with the steering torque. Consequently, the rotary 
shaft 10dn is rotated via the worm 26 and worm wheel 27, to assist the 
driver's steering wheel operating action. The worm gear comprising the 
worm 26 and worm wheel 27 can take a large reduction ratio, so that a 
small output power steering motor 24 can produce a sufficiently large 
steering assist force. 
Since the power steering motor 24 is provided in the follower pulley 
housing 4, it becomes unnecessary to provide a power steering motor in the 
gear box 3. This improves the degree of freedom in designing the inside of 
the engine room by reducing the dimensions and simplifying the 
construction of the gear box 3. Moreover, a gear box for a manual steering 
device can be used as it is for the device according to present invention 
to contribute to the reduction of the cost. 
A second embodiment of the present invention will now be described with 
reference to FIGS. 4 and 5. 
In the second embodiment, the output shaft 25 of the power steering motor 
24 is connected directly to the rotary shaft 10dn of the follower pulley 
11dn, and the worm 26 and worm wheel 27 in the first embodiment are 
omitted. Accordingly, the number of parts can be reduced. 
A third embodiment of the present invention will now be described with 
reference to FIGS. 6 and 7. 
In the third embodiment, the output shaft 25 of the power steering motor 24 
is provided in parallel with the rotary shaft 10dn of the follower pulley 
11dn, and the small-diameter spur gear 28 mounted on this output shaft 25 
is meshed with a large-diameter spur gear 29 mounted on the rotary shaft 
10dn of the follower pulley 11dn. The cost of the device of this 
embodiment is less than that of the first embodiment in which a worm gear 
is used, and, moreover, the power transmission efficiency of the device of 
this embodiment is higher. 
A fourth embodiment of the present invention will now be described with 
reference to FIGS. 8 and 9. 
In the fourth embodiment, the output shaft 25 of the power steering motor 
24 is provided at right angles to the rotary shaft 10dn of the follower 
pulley 11dn, and a small-diameter bevel gear 30 mounted on this output 
shaft 25 is meshed with a large-diameter bevel gear 31 mounted on the 
rotary shaft 10dn of the follower pulley 11dn. The power steering motor 24 
is disposed (refer to FIG. 9) between a pair of Bowden cables 5, 6 
extending from the follower pulley 11dn, as viewed in the axial direction 
of the axis of the rotary shaft 10dn of the follower pulley 11dn. Since 
the bevel gears 30, 31 are thus used, the degree of freedom of designing 
the device can be improved by crossing at an arbitrary angle the output 
shaft 25 of the power steering motor 24 and the rotary shaft 10dn of the 
follower pulley 11dn. Moreover, the power steering motor 24 can be located 
compactly in a dead space between the two Bowden cables 5, 6. 
As described in the first to fourth embodiments, in which the power 
steering motor 24 is provided in an arbitrary posture in an arbitrary 
position in the follower pulley housing 4, the degree of freedom of 
designing the power steering device is improved, and it becomes easier to 
arrange parts in the interior of the engine room. 
In the embodiments of the present invention described in detail above, 
various changes in the design thereof which do not depart from the gist of 
the present invention may be made. For example, in the first embodiment, 
the worm wheel 27 may be provided on the follower pulley 11dn instead of 
being mounted on the rotary shaft 10dn. In the second embodiment, the 
output shaft 25 of the power steering motor 24 may be connected directly 
to the follower pulley 11dn instead of being connected directly to the 
rotary shaft 10dn. In the third embodiment, the large-diameter spur gear 
29 may be provided on the follower pulley 11dn instead of being mounted on 
the rotary shaft 10dn. In the fourth embodiment, the large-diameter bevel 
gear 31 may be provided on the follower pulley 11dn instead of being 
mounted on the rotary shaft 10dn. 
According to the present invention as described above, the power assist 
means is provided in the follower pulley housing in which the follower 
pulley is housed, and, therefore, it is not necessary to provide the power 
assist means in the gear box. Accordingly, accommodation of the gear box 
in the engine room can be done easily by miniaturizing and simplifying the 
gear box. Moreover, the gear box in an existing manual steering apparatus 
can be used as it is. 
According to one embodiment of the invention, the power assist means 
comprises a power steering motor, and a worm mounted on the output shaft 
of the power steering motor is meshed with a worm wheel mounted on the 
follower pulley or the rotary shaft of the follower pulley. Therefore, the 
driving force of the power steering motor compactly integrated in the 
follower pulley housing can be transmitted reliably to the gear box. 
Moreover, the power steering motor can be miniaturized owing to the 
utilization of a worm gear of a large reduction ratio. 
According to a further embodiment of the invention, the power assist means 
comprises a power steering motor, the output shaft of which is connected 
directly to the follower pulley or the rotary shaft of the follower 
pulley. Therefore, the driving force of the power steering motor compactly 
integrated in the follower pulley housing can be transmitted reliably to 
the gear box. Moreover, since a separate gear is not required, the number 
of parts decreases. 
According to another embodiment of the invention the power assist means 
comprises a power steering motor, and a spur gear mounted on the output 
shaft of the power steering motor is meshed with a spur gear mounted on 
the follower pulley or the rotary shaft of the follower pulley. Therefore, 
the driving force of the power steering motor compactly integrated in the 
follower pulley housing can be transmitted reliably to the gear box. 
Moreover, the cost can be reduced owing to the employment of an 
inexpensive spur gear set. 
According to a still further embodiment of the invention, the power assist 
means comprises a power steering motor, and a bevel gear mounted on the 
output shaft of the power steering motor is meshed with a bevel gear 
mounted on the follower pulley or the rotary shaft of the follower pulley. 
Therefore, the driving force of the power steering motor compactly 
integrated in the follower pulley housing can be transmitted reliably to 
the gear box. Moreover the output shaft of the power steering motor and 
the rotary shaft of the follower pulley may be arranged in an arbitrary 
direction, so that the degree of freedom of determining the layout of the 
parts of the device can be increased. 
According to a still further embodiment of the invention, the power 
steering motor is disposed between a pair of cables extending from the 
follower pulley, as viewed in a plane normal to the axis of the rotary 
shaft of the follower pulley, so that the follower pulley housing, power 
steering motor and cables can be compactly arranged.