CA2017690C - Power steering system of the outboard motor - Google Patents

Abstract

A power steering system of an outboard motor for steering an outboard motor body disposed at an outside of a rear portion of a hull and usually including a manual steering system mounted on the hull for operating a steering element to manually steer the outboard motor body. A power unit is operatively connected to the manual steering system and including an electric motor for applying a steering asist force to said manual steering system. The power unit is located at a portion capable of effectively utilizing an inner space of the hull and the electric motor of the power unit is controlled by a control unit in accordance with the navigation conditions of the hull and the outboard motor detected by sensor means. The sensor means includes various sensors such as steering torque sensor and engine speed sensor.

Description

POWER STEERING SYSTEM OF THE OUTBOARD MOTOR

BACKGROUND OF THE INVENTION
The present invention relates to a power steer-ing system of the outboard motor particularly having an improved power unit for applying a steering assist force to a manual steering system, and for suitably controlling the steering assist force.
A conventional manually operative steering system of an outboard motor provides such a problem as that the steering load increases, which may results in the difficulty of the steering operation, in accordance with navigation conditions, such as wind or wave condition, hull speed, trim angle of the outboard motor body and the like conditions.
In order to obviate the problem encountered to the conventional manual steering system, a hydraulic power steering system has been proposed.
A proposed hydraulic power steering system is generally composed of the manual power steering system and a power unit equipped with a hydraulic pump for generating a steerng assist force. The power unit applies the steering assist force to the manual power steering system.
However, the hydraulic power steering system ,, ~- 201 76qO
described above utilizes a power source of the outboard motor itself as a power source of the hydraulic pump. Accordingly, the steering assist force generated by the hydraulic pump is changed in response to the rotations per minute of the engine, i.e. engine speed, mounted on the outboard motor, which may not be suitably controlled according to the navigation conditions.
SUMMARY OF THE INVENTION
An object of this invention is to substantially eliminate the defects or drawbacks of the conventional technology and to provide a power steering system of the out-board motor capable of easily and suitably steering a outboard motor body by a little steering load free from the changes of the navigation conditions.
Another object of this invention is to provide a power steering system of the outboard motor capable of reducing an occupied space of the power steering system required in the hull to thereby apply to a small sized hull.
These and other objects can be achieved according to the present invention, in one aspect, by providing a power steering system for an outboard motor, for steering an outboard motor body of said outboard motor which is disposed outside of a rear portion of a hull of a watercraft and which is provided with an engine and a propeller driven by means of said engine, comprising: a manual steering system mounted upon said hull for operating a steering element in order to manually steer said outboard motor body; a power unit operatively connected to said manual steering system and including an B

20176qO 27860-6 electric motor for applying a steering assist force to said manual steering system; a sensor means provided with a steering torque sensor for detecting steering torque applied to said steering element of said manual steering system during operation thereof, an engine speed sensor for detecting engine speed, and a steering angle sensor for detecting a steering angle and a steering direction of said outboard motor body when steered by said manual steering system; and a control means operatively connected to said sensor means for controlling said electric motor of said power unit by determining said steering assist force in response to said steering torque detected by said steering torque sensor and adjusting said determined steering assist force in response to said engine speed and said steering angle respectively detected by means of said engine speed sensor and said steering angle sensor.
In preferred embodiments of the one aspect of the present invention, the sensor means operatively connected to the control means is provided with a steering torque sensor for detecting steering torque during operation of the manual steer-ing system and engine speed sensor for detecting engine speedand a steering sensor for detecting steering angle and steering direction of the outboard motor body steered by the manual steering system.
The control means controls the electric motor of the power unit so as to determine the power assist force in response to the steering torque detected by the steering torque sensor and then to convert the determined force in response to the 201 76~0 engine speed and the steering angle respectively detected by the engine speed sensor and the steering angle sensor.
The sensor means comprises a thrust sensor operatively connected to the control means for detecting thrust force generated by the propeller of the outboard motor.
The control means controls the electric motor of the power unit so as to generate the steering assist force in proportion to the thrust force detected by the thrust sensor.
The outboard motor is provided with a power trim-tilt system for automatically trimming and tilting the outboard motor body and the thrust sensor directly detects pressure of a pressure oil operating the power trim-tilt system to indirectly detect the thrust generated by the propeller.
In another aspect of the present invention, there is provided a power steering system for an outboard motor having an outboard motor body and means for mounting the motor body on a transom having a front surface defining the rear of a water-craft hull interior space, the outboard motor being provided with an engine and a propeller driven by means of said engine, said steering system comprising: a manual steering system mounted upon said hull for operating a steering element in order to manually steer said outboard motor body; and a power unit operatively connected to said manual steering system and including an electric motor for applying a steering assist force to said manual steering system, and transmission means for transmitting power generated by said electric motor to said manual steering system, said electric motor being within a ._ motor box means located outside of said hull interior space and said outboard motor body and to the rear of the transom front surface when the motor body is mounted on the transom, and said transmission means being disposed within a trans-mission box means which is also located outside of said hull interior space and said outboard motor body and to the rear of the transom front surface when the motor body is mounted on the transom.
In preferred embodiments, the transmission means is accommodated in a transmission box means located outside the hull. The hull is provided with a transom at the rear portion thereof and the transmission means comprises reduction gears, a rack and a pinion, the reduction gears being accommodated in a gear box located outside the hull, the rack and pinion being accGmmodated in a rack box located above a surface of the transom.
According to the present invention of the characters and structures described above, there is provided a power steering system for an outboard motor, for steering an outboard motor body of said outboard motor which is disposed outside of a rear portion of a hull of a watercraft and which is provided with an engine and a propeller driven by means of said engine, comprising: a manual steering system mounted upon said hull for operating a steering element in order to manually steer said outboard motor body; a power unit operatively connected to said manual steering system and including an electric motor for applying a steering assist force to said manual steering 201 76~0 27860-6 system; a sensor means provided with a thrust sensor for detecting a thrust force generated by means of said propeller of said outboard motor; and control means operatively connected to said sensor means for controlling said electric motor of said power unit by determining said steering assist force in proportion to said thrust force detected by means of said thrust sensor.

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In addition, the control means sets the steering asist force to be proportional to the thrust force generated by the propepper of the outboard motor and affecting the steering load, so that the steering asist force can be controlled so as to correspond to the fluctuation of the steering load. Thus, the power steering system can easily and suitably steer the outboard motor body by a little load free from the navigation conditions, thereby improving the steering feeling.
Furthermore, according to the present invention, the power steering system camprises the motor box in which the electric motor of the power unit is accommoated and the transmission box in which the transmission means for transmitting the steering asist force generated by the electric motor to the manual steering system is accommodated. The motor box and the transmission box are located outside the rear portion of the hull at which the outboard motor is disposed, thereby reducing the location space of the power steering system required in the hull and, hence, the power steering system can be applied to a small sized craft to improve the usage thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

2 ~ 9 0 For a better understanding of the present invention and to show how the same is carried out, reference is now made to, by way of preferred embodiments, to the accompanying drawings, in which:
Fig. 1 is a block diagram mainly representing a controller of a power steering system of an outboard motor of the first embodiment according to the present invention;
Fig. 2 is a side view of the outboard motor to which a power steering system provided with the controller shown in Fig. 1 is applied;
Fig. 3 is a front view of the power steering system of the first embodiment;
Fig. 4 is a longitudinal sectional view of the power steering system shown in Fig. 3;
Fig. 5 is an enlarged perspective view of a portion enclosed by V shown in Fig. 4;
Fig. 6 is an illustration representing an arrangement of a steering angle sensor shown in Fig. 4;
Fig. 7 is a sectional view representing a geer tooth of a pinion shown in Fig. 6;
Fig. 8 is a flowchart representing control condition of the controller shown in Fig. l;
Fig. 9 is a graph representing the relationship between the steering torque and the current value - 2 ~ Q
supplied to a motor, which is memorized in a ROM shown in Fig. l;
Fig. 10 is a graph representing the relation-ship between the engine speed, the steering angle and the current value to the motor, which are memorized in RAM
shown in Fig. l;
Fig. llA is a plan view representing the arrangement of a detecting gear of one modification of the first emboeiment;
Fig. llB is an enlarged sectional view of the portion enclosed by XIB shown in Fig. llA;
Fig. 12 is a block diagram mainly representing a controller of a power steering system of the second embodiment according to the present invention;
Fig. 13 is a perspective view of the power steering system including the controller shown in Fig. 12;
Fig. 14 is a front view of the power steering system of the second embodiment shown in Fig. 12;
Fig. 15 is a longitudinal sectional view of the power steering system shown in Fig. 14;
Fig. 16 is a front view of a power trim-tilt system accommodated in the outboard motor body shown in Fig. 14;
Fig. 17 is a side view of the power trim-tilt system shown in Fig. 16;

~' ~ o ~ a Fig. 18 is a front view of a thrust sensor of the power trim-tilt system shown in Figs. 12 and 16;
Fig. 19 is a schematic sectional view of the power trim-tilt system shown in Figs. 16 and 17;
Fig. 20 is a graph generally representing the relationship between the engine speed and the thrust force generated by a propeller;
Fig. 21 is a partial perspective view of the power steering system of the third embodiment according to the present invention;
Fig. 22 is a longitudinal sectional view partially representing the power steering system shown in Fig. 21;
Fig. 23 is a side view of the outboard motor including the power steering system shown in Figs. 21 and 22;
Fig. 24 is a perspective view of a conventional manual steering system; and Fig. 25 is a side view representing the tilt-up and tilt-down conditions of the outboard motor body shown in Fig. 24.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
In advance of the detailed description of preferred embodiments of the present invention, the 20~ 7~

conventional art will be described hereunder with reference to Figs. 24 and 25.
Referring to Fig. 24 showing a steering system of an outboard motor operative manually, when an operator handles a steering wheel 2 equipped at a driving portion in a hull 1, a gear in a gear box 4 is rotated through a steering shaft 3. In response to the rotation of the gear, an inner cable 6 of a steering cable 5 is recipro-cated axially forwardly or backwardly (push-pull motion).
The steering cable 5 comprises an outer cable 7 and the inner cable 6 coaxially located therein.
The front end of the inner cable 6 slightly extends beyond the front end of the outer cable 7 and is connected to one end of a drag link 9 of a link mechanism 8. The drag link 9 has an L-shaped structure and has the other end connected to one end of a steering bracket lO
to be rotatable. The other end of the steering bracket 10 is secured to a body 12 of the outboard motor 11.
As shown in Fig. 25, the outboard motor body 12 comprises a drive shaft housing 13 including a drive shaft, not shown. The outboard motor body 12 is supported by a swivel bracket 14 through a pilot shaft, not shown, secured to the drive shaft housing 13 to be horizontally rotatable or steerable around the pilot shaft. The swivel bracket 14 is supported to be rotatable i.e. tiltable, in 2~17~

a vertical direction by a clamp bracket shaft 15 horizon-tally mounted between a lateral pair of clamp brackets 16 and 16, by which a transom la of the hull 1 is held to thereby secure the outboard motor body 12 to the hull 1.
According to the structure described above, the outboard motor body 12 is horizontally bilaterally swung about the pilot shaft by the push-pull motion of the inner cable 6 of the steering cable 5 through the link mechanism 8, thus the outboard motor body 12 being steered.
However, with respect to the manual steering system of the conventional type described above, the maneuvaring of the outboard motor 11 may involve much labour by the increasing of the steering load applied during the steering operation due to the navigation conditions, such as wind or wave condition, hull speed, trim angle of the outboard motor 11.
In order to obviate the defect of the conven-tional manual steering system and, hence, to reduce the steering load, a conventional technology provides a hydraulic power steering system of the outboard motor.
However, the hydraulic power steering system of prior art utilizes a power source of the outboard motor itself as a power source for driving a hydraulic pump. Accordingly, an steering assist force generated by the hydraulic pump is changed in response to rotations per minute of the 2Q~7~

drive shaft and may not be suitably controlled in accor-dance with the navigation conditions.
A power steering system according to the present invention conceived for substantially eliminating the defects or drawbacks encountered to the prior art des-cribed above will be described hereunder with reference to Figs. 1 to 23.
Referring to 1 to 10 representing first embodi-ment according to the present invention, Fig. 3 shows a front view of a power steering system 20 of one embodiment of the present invention. Referring to Fig. 3, the power steering system 20 comprises a manual steering system 21 and a power unit 22 and the manual steering system 21 is of the type substantially the same as that shown in Figs.
24 and 25, so that the like reference numerals are added to elements or members corresponding to those shown in Figs. 24 and 25 and the details thereof are now omitted herein.
The power unit 22 acts to apply a steering assist force directed to the same direction as the manual steering force of the manual steering system 21 to an input end of the link mechanism 8 to thereby reduce the steering load. The power unit 22 comprises a motor box 23 in which a motor, not shown, is accommodated, a gear box 24 in which a reduction gear is accommodated and a sensor 201~

box 25 in which a torque sensor, not shown, is incorporated.
As shown in Fig. 4, the motor box 23 and the gear box 24 are integrally coupled with a rack box 27 in which a rack 26 is accommodated and the integral structure is secured to an upper portion of the swivel bracket 14 of the outboard motor 11 by means of bolts.
The sensor box 25 is secured to one of the paired clamp brackets 16 through a support arm 28 and slidably accomodates a sensor rod, not shown, therein.
The sensor rod has one end secured to a terminal end of the outer cable 107 by a stationary arm 28a. The other end of the sensor rod is operatively connected to a potentiometer, not shown, accomodated in the sensor box 25. The potentiometer and the sensor rod described above constitute a steering torque sensor 32 as shown in Fig. 1.
When the inner cable 6 is pushed or pulled with respect to the outer cable 7 by the manual operation of the steering wheel 2, the reaction force applied to the outer cable 7 by the push or pull motion of the inner cable 6, i.e. the steering load, is transmitted to the sensor rod through the stationary arm 28a. The displace-ment of the sensor rod is detected by the potentiometer in the sensor box 25 and a signal, i.e. steering torque signal, representing the displacement detected by the 2 Q ~

potentiometer is transmitted to a controller 29 described later herein.
As shown in Fig. 3, the rack box 27 has axial ends to which shrinkable cylindrical bellows 31 and 31 are coaxially secured and the rack 26 is liquid-tightly accommodated in the rack box 27 in an axially reciprocating manner. The rack 26 has one axial end (right end as viewed in Fig. 4) secured to a stay 26a and, as shown in Fig. 5, the stay 26a is connected to a bent end 9a of the drag link 9 in a direction normal thereto by means of a washer 33 and a nut 34. The rack 27 is engaged with a pinion 30 at an intermediate portion thereof, which is fixed to a pinion shaft 30a. The pinion shaft 30a is operatively connected to the motor shaft 37 of the motor 38, shown in Fig. 1, through a reduction gears 35 and 36 which are in the form of bevel gears and engaged with each other. Accordingly, when the motor 38 is driven, the pinion 30 is rotated through the reduction gears 35 and 36 to thereby move the rack 26 in the linear direction thereof, whereby the rotating power of the motor 38 is transmitted to the link mechanism 8 as the steering assist force for reducing the steering load to thereby easily steer the outboard motor body 12.
Referring to Fig. 1, an engine speed sensor 39 detects the rotations per minute of the engine (i.e.

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engine speed), not shown, mounted in the outboard motor body 12 and transmits a signal representing the engine speed, i.e. engine speed signal, to the controller 29.
A steering angle sensor 40 is utilized a non-contact electromagnetic sensor and arranged in opposing state to the pinion 30 as shown in Fig. 6. When an operator handles the steering wheel 2 to move the inner cable 6 of the steering cable 5 and to rotate the pinion 30 through the stay 26a and rack 26, the steering angle sensor 40 counts the numbers of gear teeth 41 of the pinion 30 to thereby detect the steering angle of the outboard motor body 12. Referring to Fig. 7, each of the gear teeth 41 of the pinion 30 has a top land 42 on which a cutout portion 43 is formed so as not to damage to the strength of the pinion 30. The cutout portion 43 is formed to be in such asymmetrical manner as that the position of the cutout portion 43 is set with distances L
and M respectively from bilateral ends of the top land 42. Accordingly, when the steering angle sensor 40 detects this asymmetrical cutout portion 43, detected voltage waveforms of the gear teeth 41 of the pinion 30 are asymmetrical, thus detecting a direction of rotation of the pinion 30, i.e. a steering direction of the outboard motor body 12. The steering angle sensor 40 transmits signals representing these steering angle - ~ o ~
and steering direction described above as steering angle-direction signals to the controller 29.
Referring to Fig. 1, the controller 29 is composed of a central processing unit (CPU) 44, memories provided with a read only memory (ROM) 45 and a random access memory (RAM) 46 and a signal converter provided with an analog-to-digital converter (A-D converter) 47 and a digital-to-analog converter (D-A converter) 48.
The ROM 45 has a data-table, as shown in Fig.
9, representing relationship between the steering torque T and current value A supplied to the motor 30. The steering assist force applied to the link mechanism 8 from the power unit 22 is determined in accordance with the current value A supplied to the motor 30. Referring to Fig. 8, CPU 44 reads the steering torque signal and the engine speed signal from the steering torque sensor 32 and the engine speed sensor 39 respectively through the A-D converter 47 in condition of switch ON, and then determines the current value A supplied to the motor 38 for generating the steering assist force corresponding to the steering torque T represented by the steering torque signal with reference to the data-table memorized in the ROM45.
The RAM 46 has a data-table, as shown in Fig.
10, representing the relationship between the steering 2~ 7~

angle ~ , the engine speed R and current values A' and A"
supplied to the motor 38. Referring to Fig. 8, the CPU
44 continually reads the steering angle ~ through the A-D converter 47 during the operation of a shift device accomodated in the outboard motor body 12. The CPU 44 then memorizes said steering angle ~ to the RAM 46 and simultaneously calculates so as to adjust the current value A determined by the data-table memorized in the ROM 45.
Namely, the characteristics of the current values A' and A" memorized in RAM 46, as shown in Fig.
10, are different in accordance with the engine speed R
even in the same steering angle ~ . The CPU 44 selects one of these characteristics of the current values A' and A" in accordance with the engine speed signal transmitted from the engine speed sensor 39 and, for example, selects a characteristic represented by a full line P as viewed in Fig. 10 in a case where the enginespeed R is more than 5500 r.p.m. This characteristic represented by the full line P designates the supplying current value A
determined by the data-table as shown in Fig. 9 in a case where the steering angle~ is less than steering anglea ( ~
< a ) , and designates the supplying current value A' determined by a formula described such as A' = A - X ( ~ - a ) 2 ~ ~ 7 ~
in a case where the steering angle~ is more than a steering angle a and less than a steering angle ~ ( a ~ ~
< ~; a < ~ ), thus reducing the steering assist force settled by the supplying current value A'. The letter X
represents a gradient of the full line P as shown in Fig. 10 in condition of a ~ ~ < ~ . The characteristic represented by the full line P designates then a supplying current value A" determined by a formula described such as A " = A - X ( ,~ -- a ) in a case where the steering angle~ is more than a steering angle~ ( ~ 2 ~ ). As this supplying current value A" is constant, the steering assist force settled by the current value A" is also constant. Accordingly to the manner described above, when the engine speed R is high and the steering angle ~ is large, the controller 29 operates to reduce the current value supplied to the motor 38, thus avoiding the turn-over, for example, of the hull 1.
Referring to Fig. 1, the current value A, A' or A" supplied to the motor 38 is transmitted to a driver 49 through the D-A converter 48, which amplifies the current value from the controller 29 so as to drive the motor 38 and then flows the amplified current to the motor 38.
According to the described first embodiment, ---- 2~7~,,,`i~
the controller 29 adjusts the supplying current value A
to the motor determined by the steering torque T from the steering torque sensor 32 in accordance with the engine speed R and the steering angle ~ respectively detected by the engine speed sensor 39 and the steering angle sensor 40. In a case where the engine speed R is high, the controller 29 preferably supplies to the motor 38 the current value less than the supplying current value A
determined by the steering torque T so as to reduce the steering assist force, so that the steering assist force can be suitably controlled in accordance with the navigation conditions. Thus, the power steering system of the outboard motor can easily and suitably steer the outboard motor body with a little steering load.
Fig. llA shows a fragmentary plan view of one modification according to the first embodiment. In this first modification, the pinion 30 and a detecting gear 50 is coaxially located to the pinion shaft 30a, and the detecting gear 50 has gear teeth 41 provided with the cutout portion 43 as shown in Fig. 7 so as to detect the direction of rotation of the pinion 30 or has gear teeth 51, as shown in Fig. llB, respectively provided with larger cutout portions 52 so as to detect the same. The shapes of the teeth of the detecting gear 50 provided with the cutout portion 43 or 52 is detected by the 2 ~ ~L rl ~ ~ ~

steering angle sensor 40. According to this modification, these cutout portions 43 and 52 are larglycut regardless of the strength of the pinion 30, thus correctly detecting the steering direction of the outboard motor body 12 by means of a voltage wave of the detecting gear 50.
In another modification of the first embodiment, the steering sensor 40 may be arranged to directly detect the rotation of the motor 38 so as to detect the steering direction of the outboard motor body 12.
Referring to Figs. 12 to 20 representing the second embodiment according to the present invention, Fig. 13 shows a perspective view of a power steering system 60 of the second embodiment of the present invention, in which like reference numerals are added to portions or members corresponding to those used for the first embodiment shown in Figs. 1 to 10 and detailed description thereof is now omitted herein.
In the second embodiment, the power steering system 60 is applied to the outboard motor 11 in which a power trim-tilt system 62 is accommodated, as shown in Figs. 16 and 17, and comprises the manual steering system 21 and a power unit 61.
The power unit 61 comprises a thrust sensor 63 20 1 76~0 as shown in Figs. 12, 16 and 18, the motor box 23, as shown in Figs. 13 to 15, in which a motor 38 for generating the steering assist force is accommodated, the gear box 24 in which the reduction gears 35 and 36 for transmitting a turning force are accommodated and the rack box 27 in which the rack 26 and pinion 30 for transmitting the turning force from the gears 35 and 36 to the drag link 9 of the link mechanism 8 through the stay 26a are incorporated.
The thrust sensor 63, as described later in detail, detects a thrust of a propeller 64, as shown in Fig. 2, of the outboard motor 11 and transmits a thrust signal representing said thrust to controller 65 as shown in Figs. 12 and 13.
Referring to Fig. 12, the controller 65 is composed of an arithmetic unit 66, an output unit 67 for a torque control signal and a motor control unit 68, and the arithmetic unit 66 calculates and determines the steering assist force in proportion, for example, to said thrust represented by said thrust signal and transmits an assist force control signal representing the steering assist force to the motor control unit 68 through the output unit 67 as output end. The motor control unit 68 manipulates, and preferably amplifies the assist force contrl signal and transmits the amplified signal to the 2 ~ Q

motor 38. Thus it is that the controller 65 controls the rotation of the motor 38 to generate the suitable steering assist force.
Namely, the steering load applied to the steer-ing wheel 2 during the steering operation is generally affected at the thrust force generated by the propeller 64 and the force applied to the outboard motor body 12 in the rectangular direction of the axis of the propeller 64 or the moment around the pirot shaft, not shown, applied to the outboard motor body 12. The applied force and the moment respectively described above are proportional to the thrust force generated by the propeller 64.
Accordingly, the controller 65 controls the steering assist force generated by the motor 38 to be in proportional to the thrust force of propeller 64, thus suiting the steering assist force to fluctuation of the steering load, whereby the steering feeling can be improved.
Referring to Fig. 20, in a sliding or running craft such as a motor boat, the thrust force generated by the propeller 64 during the engine operation is maximum before the sliding of the craft and is constant during the sliding manner of the craft. In this case, the controller 65 controls the steering assist force generated by the motor 38 to rapidly increase before the 2 ~

sliding of the craft and to be constant during the sliding of the craft in response to the thrust force generated by the propeller 64 described above.
As shown in Figs. 16 and 17, the power trim-tilt system 62 is composed of a pair of trim cylinders 69a and 69b accommodated in the outboard motor body 12, a tilt cylinder 70 arranged between the trim cylinders 69a and 69b in the outboard motor body 12 and an oil pump 71 located outside the outboard motor body 12. Referring to Fig. 19, the oil pump 71 supplies a pressure oil to an inner upper chamber and an inner lower chamber of the tilt cylinder 70 through a tilt-down tube 72 and a tilt-up tube 73 respectively to thereby slide a piston rod 74 incorporated in the tilt cylinder 70 downwardly and upwardly, whereby the outboard motor body 12 can be automatically tilted down and tilted up respectively. The oil pump 71 also supplies the pressure oil to an inner upper chamber and an inner lower chamber of trim cylinder 69a and 69b through a trim-down tube 75 and a trim-up tube 76 respectively to thereby slide piston rods 77a and 77b respectively incorporated in the trim cylinders 69a and 69b downwardly and upwardly. Thus, the outboard motor body 12 can be automatically trimed down and trimed up within the range of the tilt angle.
The trim-up tube 76 is interposed between an 2 Q ~ 4 ~
..
output end of the oil pump 71 and the inner lower chambers of the trim cylinders 69a and 69b so as to supply the pressure oil in the oil pump 71 into the inner lower chambers. The thrust sensor 63 is arranged to the trim-up tube 76 and, as shown in Fig. 18, composed of a pressure sensor 78 and a sensor body 79 which is of a liquid-tight hollow box structure and secured to the trim-up tube 76. The pressure sensor 78 is accommodated in the sensor body 79 and adapted to detect the pressure of the pressure oil in the trim-up tube 76 and then transmits an electric signal representing the detected pressure to the arithmetic unit 66 of the controller 65 through a signal cable 80. The pressure oil in the trim-up tube 76 applies to the outboard motor body 12 the force which is substantially the same level as that of the thrust force generated by the propeller 65 in a direction opposite to the thrust force direction to thereby hold the hull 1 in a predetermined navigation state with the bow thereof lifted up. Accordingly, the thrust force generated by the propeller 64 can be indirectly detected by the thrustsensor 63 which directly detects the pressure of the pressure oil in the trim-up tube 76.
The arithmetic unit 66 of the controller 65, as shown in Fig. 12, has a data-table representing the ~Q~ 7~

relative relationship between the pressure of the pressure oil in the trim-up tube 76 and the thrust force generated by the propeller 64 and the arithmetic unit 66 reads the thrust force corresponding to the detected signal from the thrust sensor 63 according to the data-table. The arithmetic unit 66, further, culculates and determins the steering assist force proportional to the thrust force read in the described manner and transmits the assist force control signal representing the steering assist force determined in the described manner to the motor control unit 68 through the output unit 67. The motor control unit 68 manipulates, preferably amplifies the assist force control signal and then transmits the amplified signal to the motor 38, whereby the controller 65 enables the motor 38 to generate the suitable steering assist force corresponding to the fluctuation of the steering lood.
According to the described second embodiment, the controller 65 enables the motor 38 to generate the suitable steering assist force corresponding to the fluctuation of the steering load which is generally affected by the thrust force generated by the propeller 64 and the like force, thus reducing the steering load applied to the steering wheel 2 and, hence, the steering feeling can be improved by the suitable steering assist - 2~7~

force corresponding to the fluctuation of the steering load.
In addition, the thrust sensor 63 indirectly detects the thrust force generated by the propeller 65 in a manner of directly detecting the pressure of the pressure oil in the trim-up tube 76 of the existing power trim-tilt system 62, so that the thrust sensor 63 can be made compact and simplified with reduced cost.
In the first modification of the second embodi-ment, the thrust sensor 63 may be arranged to the tilt-up tube 73 of the power trim-tilt system 62 to thereby directly the pressure of the pressure oil in the tilt-up tube 73, thus indirectly detecting the thrust force generated by the propeller 64, because the pressure oil is also supplied to the tilt cylinder 70 as well as the trim cylinders 69a and 69b during the trim-up operation.
In the second modification of the second embodiment, the power trim-tilt system 62 is composed of a single hydraulic cylinder for attaining both power trim effect and power tilt effect. The thrust sensor may be mounted to a tube through which the pressure oil is supplied from the oil pump 71 to the inner chamber of the hydraulic cylinder described above, thus indirectly detecting the thrust force generated by the propeller 64.
Referring to Figs. 21 to 23 representing the 2 ~ ~ 7 ~1 ~J' ~

third embodiment according to the present invention, Fig.
21 shows a partial perspective view of a power steering system 90 of the third embodiment of the present invention, in which like reference numerals are added to portions or members corresponding to those used for the first embodiment shown in Figs. l to 10 and detailed description thereof is now omitted herein.
In the third embodiment, the power steering system 90 comprises the manual steering system 21 and a power unit 91. Referring to Figs. 21 and 22, the power unit 91 is provided with a motor box 92 in which a motor 38 is accommodated, a gear box 93 in which the reduction gears 35 and 36 are accommodated, a rack box 94 in which a rack 97 and a pinion 96 are incorporated and a sensor box 95 in which a potentiometer and a sensor rod constituting the steering torque sensor 32 are accommo-dated. The reduction gears 35 and 36, the rack 97 and the pinion 96 are constructed as a transmission means for transmitting the steering assist force generated by the motor 38 to the link mechanism 8 of the manual steering system 21. The motor box 92 and the gear box 93 are located outside the transom la of the hull, and the rack box 94 is disposed above, as viewed, an upper end surface of the transom la in parallel relationship thereto. The sensor box 95 is coaxially mounted to the outer periphery of the inner cable 6 of the steering cable 5.
Namely, the motor box 92 is arranged outside the transom in such a manner as that the longitudinal direction of the motor box 92 corresponds to the upward and downward direction as viewed, and the gear box 93 is integrally secured to the upper, as viewed, portion of the motor box 92. The reduction gear 35 secured to the motor shaft, not shown, is substantially perpendicularly engaged with the reduction gear 36 secured to the pinion shaft 96a extending horizontally as viewed, whereby the rotating force of the motor 38 changes to the horizontal direction from the vertical direction as shown in Fig.
21.
The rack box 94 which accommodates a pinion shaft 96a as well as the rack 97 and the pinion 96 is mounted to one of the cramp brackets 16 in the coaxial relationship with respect to the cramp bracket shaft 15 interposed between the cramp brackets 16 and 16. One of the bellows 31 is attached to the rack box 94 and the other thereof is attached to the end portion of the clamp bracket shaft 15 in a manner of outwardly extending from the other one of the clamp brackets 16. The rack 97 is coaxially accommodated in the rack box 94 and the hollow clamp bracket shaft 15 in an axially reciprocating manner and both the axial end of the rack 97 is incorpo-2 ~
rated in the bellows 31. The most outward end portion97a, i.e. the most rightward end as viewed in Fig. 22, of the rack 97 extends outside bellow 31 and is perpend-cularly connected to the stay 26a through a free joint device 98 to thereby transmit the axial reciprocation of the rack 97 to the outboard motor body 12 through the link mechanism 8, whereby the outboard motor 12 can be steered in the bilateral direction.
According to the third embodiment described above, the motor box 92 and the gear box 93 are located outside the transom la of the hull 1 and the rack box 97 is disposed above the transom la out of the steering cable 5, so that the power unit 91 composed of the motor box 92, the gear box 93, the rack box 94 and the like member is not mounted inside the hull 1, thus preventing the reduction of the space of the hull 1. Accordingly, the power steering system 90 is applied to a small sized craft, for example a small sized motor boat, which has no sufficient space, thereby improving the utility of the power steering system 90.
It is to be understood by persons skilled in the art that the present invention is not limited to the described embodiments and many other modifications and changes may be made without departing from the spilit and scope of the appended claims.

Claims (9)

1. A power steering system for an outboard motor, for steering an outboard motor body of said outboard motor which is disposed outside of a rear portion of a hull of a watercraft and which is provided with an engine and a propeller driven by means of said engine, comprising:
a manual steering system mounted upon said hull for operating a steering element in order to manually steer said outboard motor body;
a power unit operatively connected to said manual steering system and including an electric motor for applying a steering assist force to said manual steering system;
a sensor means provided with a steering torque sensor for detecting steering torque applied to said steering element of said manual steering system during operation thereof, an engine speed sensor for detecting engine speed, and a steering angle sensor for detecting a steering angle and a steering direction of said outboard motor body when steered by said manual steering system; and a control means operatively connected to said sensor means for controlling said electric motor of said power unit by determining said steering assist force in response to said steering torque detected by said steering torque sensor and adjusting said determined steering assist force in response to said engine speed and said steering angle respectively detected by means of said engine speed sensor and said steering angle sensor.

2. A power steering system as set forth in claim 1, wherein said steering angle sensor comprises:
pinion means operatively connected to said manual steering system so as to rotate in either one of two opposite directions, said pinion means comprising a plurality of gear teeth; and sensor means disposed adjacent to said pinion means at a fixed position past which each of said gear teeth can movably pass as said pinion is rotated in either one of said two opposite directions for counting said gear teeth moved past said fixed position whereby said steering angle of said outboard motor body can be detected.

3. A power steering system as set forth in claim 2, wherein:
each of said gear teeth has a radially outer land portion defined thereon; and notch means are defined within said land portion of each of said gear teeth in an asymmetrical manner with respect to a longitudinal axis of each of said gear teeth such that said notch means is located at different distances from side portions of each of said gear teeth, whereby said sensor means can determine sald steering direction of said outboard motor body.

4. A power steering system as set forth in claim 2, wherein:
each of said gear teeth of said pinion means comprises large and small land portions radially offset with respect to each other in a stepped manner such that together, asymmetrical land portions are defined upon each one of said gear teeth with respect to a longitudinal axis of each one of said gear teeth and with respect to side portions of each one of said gear teeth, whereby said sensor means can determine said steering direction of said outboard motor body.

5. A power steering system for an outboard motor having an outboard motor body and means for mounting the motor body on a transom having a front surface defining the rear of a watercraft hull interior space, the outboard motor being provided with an engine and a propeller driven by means of said engine, said steering system comprising:
a manual steering system mounted upon said hull for operating a steering element in order to manually steer said outboard motor body; and a power unit operatively connected to said manual steering system and including an electric motor for applying a steering assist force to said manual steering system, and transmission means for transmitting power generated by said electric motor to said manual steering system, said electric motor being within a motor box means located outside of said hull interior space and said outboard motor body and to the rear of the transom front surface when the motor body is mounted on the transom, and said transmission means being disposed within a transmission box means which is also located outside of said hull interior space and said outboard motor body and to the rear of the transom front surface when the motor body is mounted on the transom.

6. A power steering system according to claim 5, wherein said transmission means comprises reduction gears, a rack and a pinion, said reduction gears being accommodated in a gear box located outside of the hull interior space and to the rear of the transom front surface, said rack and pinion being accommodated in a rack box located above the transom and to the rear of the transome front surface when the motor body is mounted on the transom.

7. A power steering system as set forth in claim 6, wherein:
said motor box means is disposed in a substantially vertical orientation with respect to said hull of said water-craft;
said gear box is operatively connected to an upper end of said motor box means; and said rack box is disposed horizontally and parallel to the transom of said watercraft, whereby a compact arrangement of said power steering system, with respect to said manual steering system, is achieved.

8. A power steering system for an outboard motor, for steering an outboard motor body of said outboard motor which is disposed outside of a rear portion of a hull of a watercraft and which is provided with an engine and a propeller driven by means of said engine, comprising:

a manual steering system mounted upon said hull for operating a steering element in order to manually steer said outboard motor body, a power unit operatively connected to said manual steering system and including an electric motor for applying a steering assist force to said manual steering system;
a sensor means provided with a thrust sensor for detecting a thrust force generated by means of said propeller of said outboard motor; and control means operatively connected to said sensor means for controlling said electric motor of said power unit by determining said steering assist force in proportion to said thrust force detected by means of said thrust sensor.

9. A power steering system according to claim 8, wherein said outboard motor is provided with a power trim-tilt system for automatically trimming and tilting the outboard motor body and said thrust sensor directly detects the pressure of pressurized oil operating the power trim-tilt system so as to indirectly detect the thrust generated by the propeller.