Power tilt cylinder device

In a power tilt cylinder device 100, an opening/closing valve 61 in a rod guide 18A supplies a hydraulic fluid from a second duct line 44 to the opposite piston side space 22B of a free piston 25 of the cylinder device 100, in an upper limit of upward tilting for pushing out a piston rod 19 to the outside of a cylinder 18, this valve is pushed opened by a piston 20, and a fluid supplied from a pump 33 to the second duct line 44 is guided to a first chamber 21.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a power tilt cylinder device of a vessel 
propelling device or boat motor. 
2. Discussion of the Background Art 
Conventionally, as a power tilt cylinder device used for a vessel 
propelling device of an inboard or an outboard motor, etc., there has been 
available a cylinder device, which is provided between a vessel body and a 
propelling unit and in which the propelling unit is supported so as to be 
tilted against the vessel body by supplying a hydraulic fluid to or 
discharging a hydraulic fluid from the cylinder device. This cylinder 
device is composed of a cylinder, a piston rod inserted into this cylinder 
and extended to the outside of the cylinder via a rod guide, a piston 
fixed on a piston rod end part inside the cylinder for plotting and 
forming a first chamber of a piston rod housing side and a second chamber 
of a piston rod non-housing side in the cylinder and a free piston for 
plotting the second chamber into a piston side space and an opposite 
piston side space. 
In the power tilt cylinder device, an upper limit position is decided by 
the contact of the piston with the rod guide during upward tilting, which 
is carried out for supplying a hydraulic fluid discharged from a pump to 
the second chamber. During this period, it is necessary to control an 
increase in the inner pressure of the cylinder in order to protect the 
cylinder. 
In the conventional technology for controlling an increase in the inner 
pressure of the cylinder during a upward tilting operation, there is 
available a technology, whereby in the case of a hydraulic circuit with no 
free pistons provided in the second chamber of the cylinder, an 
opening/closing valve for connecting the first and second chambers to each 
other and an operating member for opening this opening/closing valve are 
arranged in the piston, the operating member is pressed and moved by being 
brought into contact with the rod guide during upward tilting and operates 
to open the opening/closing valve of the piston, and thus the first and 
second chambers are caused to be communicated with each other. According 
to this technology, when the operating member is brought into contact with 
the rod guide provided in the piston in the upper limit position of upward 
tilting, the opening/closing valve is opened and thereby the first and 
second chambers are caused to be communicated with each other. As a 
result, the fluid, which has been supplied to the second chamber, flows 
away to the first chamber, and this is then discharged from the first 
chamber and an increase in the inner pressure of the cylinder can be 
controlled. However, in this conventional technology, if a free piston is 
provided in the second chamber of the cylinder, even when the 
opening/closing valve of the piston is opened, and flowing of a fluid 
supplied to the opposite piston side space of the free piston in the 
second chamber is interrupted by the free piston, and this makes it 
impossible for a fluid to flow away to the first chamber side as that 
described above. For this reason, a free piston cannot be provided. 
Furthermore, in the foregoing conventional technology, a shock valve is 
provided in the piston. When the pressure of the first chamber of the 
cylinder suddenly increases, which occurs, for instance during rapid 
movement of a propelling unit jumping-up period caused by a collision 
between the running propelling unit and an underwater obstacle, this shock 
valve serves to cause this hydraulic fluid to escape from the first 
chamber to the second chamber. However, a return valve for returning the 
hydraulic fluid from the second chamber to the first chamber after such a 
collision cannot be provided in the piston. This is because if such a 
return valve is provided in the piston, which does not have any free 
pistons, a hydraulic fluid supplied to the second chamber for upward 
tilting flows away through the return valve to the first chamber and this 
makes it impossible to perform upward tilting. That is, this conventional 
technology is disadvantaged by the fact that since a return valve cannot 
be provided in the piston, the propelling unit cannot return to its 
original position immediately after the upward movement caused by its 
collision with an obstacle. 
Efforts were made to eliminate this disadvantage. For example, there was 
disclosed a device in Japanese Unexamined Patent Publication (JP-A) No. 
60-1097, in which a free piston is provided in the second chamber of the 
cylinder and the piston is equipped with both shock and return valves. 
According to this device, since the piston has the return valve, the 
propelling unit can return to its original position immediately after the 
upward movement caused by its collision with an obstacle. 
However, in a power tilt cylinder device like that disclosed in Japanese 
Unexamined Patent Publication (JP-A) No. 60-1097, as described above, it 
is impossible to control an increase in the inner pressure of the cylinder 
by providing in the piston an opening/closing valve, which is opened in 
the upper limit position of upward tilting for causing the first and 
second chambers to be communicated with each other, and causing a 
hydraulic fluid to escape from the second to the first chamber. 
Therefore, in the conventional technology described in this Japanese 
Unexamined Patent Publication (JP-A) No. 60-1097, in a duct line for 
interconnecting a pump and the second chamber, a relief valve for escaping 
the inner pressure increase of the second chamber during upward tilting to 
a reservoir is provided. It is necessary to set the opening pressure of 
this relief valve to a pressure higher than that of the second chamber in 
order that the valve may not be opened by the pressure of the second 
chamber during upward tilting (pump discharging pressure) and the normal 
running position of the propelling unit may be stably maintained. 
Therefore, each time upward tilting reaches its upper limit position, the 
relief valve is opened after the discharging pressure of the pump 
increases to exceed the high opening pressure of the relief valve. As a 
result, improvements are required in terms of power consumption and pump 
durability. 
SUMMARY OF THE INVENTION 
An object of the present invention to provide a free piston and to quickly 
control an increase in the inner pressure of a cylinder in the upper limit 
position of upward tilting in a power tilt cylinder device. 
In accordance with an aspect of the invention, a power tilt cylinder device 
is provided between a vessel body and a propelling unit, and the 
propelling unit is supported so as to be tilted against the vessel body by 
supplying a hydraulic fluid from a pressure supplying device to the 
cylinder device and alternatively discharging a hydraulic fluid from the 
cylinder device. The cylinder device has a cylinder, a piston rod inserted 
into this cylinder and extended to the outside of the cylinder via a rod 
guide, a piston fixed in a piston rod end part in the cylinder for 
plotting and forming a first chamber of a piston rod housing side and a 
second chamber of a piston rod non-housing side and a free piston for 
plotting the second chamber into a piston side space and an opposite 
piston side space. The piston is provided with a shock valve which is 
opened when the first chamber is suddenly compressed, and a return valve 
for returning a fluid in the piston side space to the first chamber by a 
dead weight of the propelling unit. The power tilt cylinder device has a 
first duct line for interconnecting the pressure supplying device and the 
first chamber, a second duct line for interconnecting the pressure 
supplying device and the opposite piston side space of the free piston, 
and an opening/closing duct line which branches off from the second duct 
line and is connected to the first chamber via a opening/closing valve of 
the rod guide. The opening/closing valve supplies a hydraulic fluid from 
the second duct line to the opposite piston side space of the free piston 
of the cylinder device, discharges the hydraulic fluid from the first 
chamber and pushes out the piston rod to the outside of the cylinder. This 
valve is pushed open by the piston in an upper limit of upward tilting, in 
which the piston comes into contact with the rod guide. A fluid supplied 
to the second duct line by the pressure supplying device is guided to the 
first chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 4, a clamp bracket 12 is fixed in the stern plate 11A of a 
vessel or boat body 11, and a swivel bracket 14 is pivotally attached to 
the clamp bracket 12 via a tilt shaft 13 so as to be tilted approximately 
around a horizontal axis, that is, to be tilted up and down. A propelling 
unit 15 is pivotally attached to the swivel bracket 14 via a steering 
shaft, not shown, so as to be rotated around the steering shaft. An engine 
unit 16 is placed on the upper part of the propelling unit 15, and a 
propeller 17 is provided in the lower part of the propelling unit 15. An 
outboard motor 10 causes the propelling unit 15 to be tilted by a tilt 
cylinder device 100, described below. 
The base end part of the cylinder 18 of the tilt cylinder device 100 is 
connected to the clamp bracket 12 by a pin, and the tip part of a piston 
rod 19, which is inserted into the cylinder 18 and extended to the outside 
of the cylinder 18 via a rod guide 18A, is connected to the swivel bracket 
14 by a pin. The inside of the cylinder 18 is plotted into the first 
chamber 21 of a piston rod 19 housing side and the second chamber 22 of a 
piston rod 19 non-housing side by a piston 20, which is fixed in the end 
part of the piston rod 19. 
A shock valve 23 and a return valve 24 are arranged side by side in the 
piston 20. The shock valve 23 is closed by a spring 23A, and opened when a 
pressure inside the first chamber 21 abnormally increases, which occurs 
under the influence of an impact force given by collision with an 
underwater obstacle, and the increased pressure exceeds a specified 
pressure value. This makes it possible to transfer hydraulic fluid in the 
first chamber 21 to the second chamber 22 (piston side space 22A). The 
return valve 24 is opened when a pressure inside the second chamber 22 
(piston side space 22A) exceeds a specified pressure value under the 
influence of the dead weight of the upward tilted propelling unit 15 after 
the impact force given by the collision with the underwater obstacle has 
been absorbed. 
A free piston 25 is arranged close to the piston 20 in the second chamber 
22. The free piston 25 plots the second chamber 22 into a piston side 
space 22A and an opposite piston side space 22B. The free piston 25 
remains in a fixed position before and after the absorption of the impact, 
which arises due to the collision with the underwater obstacle. Therefore, 
the amount of hydraulic fluid transferred from the first chamber 21 to the 
second chamber 22 (piston side space 22A) through the shock valve 23 and 
the amount of the hydraulic fluid returned from the second chamber 22 
(piston side space 22A) to the first chamber 21 through the return valve 
24 can be made the same, and the returning position of the piston rod 19 
with respect to the cylinder 18 after the impact absorption can be matched 
with the remaining position of the same before the impact absorption. 
Next, the operation circuit of the foregoing tilt cylinder device 100 will 
be described. 31 represents a reservoir, which can store hydraulic fluid. 
32 represents a reversible type DC motor and 33 a reversible type gear 
pump. The pump 33 can be selectively rotated forward or backward by the 
motor 32. 34 represents an opening/closing device, which has a shuttle 
piston 35, a first check valve 36 and a second check valve 37. A first 
shuttle space 38 is formed in the first check valve 36 side of the shuttle 
piston 35, and a second shuttle space 39 is formed in the second check 
valve 37 side of the same. That is, the first check valve 36 is opened by 
fluid pressure, which is supplied via a duct line 42 during the forward 
rotation of the pump 33, and the second check valve 37 is opened by fluid 
pressure, which is supplied via a duct line 43 during the backward 
rotation of the pump 33. The shuttle piston 35 operates so as to open the 
second check valve 37 by means of fluid pressure, which arises because of 
the forward rotation of the pump 33 and the first check valve 36 by means 
of fluid pressure, which arises because of the backward rotation of the 
pump 33. 
The first check valve 36 of the opening/closing device 34 and the second 
chamber 22 (opposite piston side space 22B) of the cylinder 18 communicate 
with each other by a duct line 44. Also, the second check valve 37 of the 
opening/closing device 34 and the first chamber 21 of the cylinder 18 
communicate with each other by a duct line 45. 
A check valve 48 is provided in the middle part of a duct line 42A, which 
is linked to the duct line 42. More particularly, when the piston rod 19 
of the cylinder 18 reaches a maximum shrinking position and no fluid is 
returned from the second chamber 22 of the cylinder 18 to the pump 33 
during the tilting-down operation of the outboard motor 10, if the pump 33 
is to operate, the check valve 48 is opened, and thereby hydraulic fluid 
can be supplied from the reservoir 31 to the pump 33. 
A check valve 49 is provided in the middle part of a duct line 43A, which 
is linked to the duct line 43. More particularly, the inner capacity of 
the cylinder 18 increases by an amount equivalent to the leaving capacity 
of the piston rod 19 from the cylinder 18 during the upward tilting 
operation of the outboard motor 10, and this results in the shortage of 
the circulation amount of hydraulic fluid. Thus, the check valve 49 is 
opened and fluid can be supplied from the reservoir 31 to the pump 33 to 
compensate for the shortage of the circulation amount. 
A down relief valve 50 is connected to the middle part of the second duct 
line 43 via a duct line 43B. More particularly, the capacity of the 
cylinder 18 decreases by an amount equivalent to the entering capacity of 
the piston rod 19 into the cylinder 18 during the downward tilting 
operation of the outboard motor 10, and this results in the surplus of the 
circulation amount of hydraulic fluid. Thus, the down relief valve 50 is 
opened and fluid having been discharged from the pump 33 can be returned 
to the reservoir 31. 
A relief valve 51 for the second chamber is connected to the middle part of 
the second duct line 44. More particularly, when the propelling unit 15 
collides with an underwater obstacle and a pressure in the second chamber 
22 of the cylinder 18 abnormally increases during backward sailing, in 
which the propelling unit 15 is held in an optional upper position, the 
relief valve 51 for the second chamber is opened and thereby pressure 
increased hydraulic fluid can be returned to the reservoir 31. 
A manual valve 52 is provided via a bypass duct line 46 between the first 
duct line 45, which is communicated with the first chamber 21 of the 
cylinder 18, and the second duct line 44, which is communicated with the 
second chamber 22. More particularly, the first and second chambers 21 and 
22 of the cylinder 18 can be communicated with each other by opening the 
manual valve 52 and the piston rod 19 is manually extended or contracted. 
Thereby, the propelling unit 15 can be freely swung between its lower 
position and its maximum tilted-up position. 
In order to protect the cylinder 18 by causing hydraulic fluid supplied to 
the second chamber 22 to escape in the tilted-up upper limit position of 
the outboard motor 10, the tilt cylinder device 100 has a structure 
described below. 
The tilt cylinder device 100 has an opening/closing duet line 60 in 
addition to the foregoing first duct line 45, which interconnects the pump 
33 and the first chamber 21, and the second duct line 44, which 
interconnects the pump 33 and the opposite piston side space 22B of the 
free piston 25. The opening/closing duct line 60 branches off from the 
second duct line 44, and this can be connected to the first chamber 21 via 
the opening/closing valve 61 in the rod guide 18A. The opening/closing 
valve 61 is closed by a spring 62 so as not to be opened by a hydraulic 
fluid pressure in the first chamber 21, which increases when the 
propelling unit 15 collides with an underwater obstacle. 
Therefore, in the tilt cylinder device 100, as shown in FIG. 3A, the 
opening/closing valve 61 supplies a hydraulic fluid from the second duct 
line 44 to the opposite piston side space 22B of the free piston 25, 
discharges the hydraulic fluid from the first chamber 21 and pushes out 
the piston rod 19 to the outside of the cylinder 18. In the upper limit 
position of upward tilting, in which the piston 20 comes into contact with 
the rod guide 18A, the rod projecting part 61A is pressed by the piston 20 
so as to open this valve 61, and thereby the hydraulic fluid, which has 
been supplied to the second duct line 44 through the pump 33, can be 
guided not to the second chamber 22 but to the first chamber 21 from the 
opening/closing duct line 60. The rod guide 18A has a groove-like flow 
passage 63 for communicating the opening/closing duct line 60 and the 
first duct line 45 with each other in its inner surface, with which the 
piston 20 comes into contact. Thus, the hydraulic fluid, which has been 
supplied from the second duct line 44 to the second chamber 22, escapes 
through the opening/closing duct line 60 and the opening/closing valve 61 
to the first chamber 21, and this is then discharged from the first 
chamber 21 (groove-like flow passage 63) to the outside (first duct line 
45) of the cylinder 18. 
When the tilt cylinder device 100 performs downward tilting from the upper 
limit position of upward tilting, as shown in FIG. 3B, the hydraulic fluid 
supplied to the first chamber 21 closes the return valve 24 of the piston 
20 and presses down the piston 20. The opening/closing valve 61 is not 
opened by inner pressure of the first chamber 21 during this downward 
tilting period. 
Next, the operation of the tilt cylinder device 100 will be described. 
(Upward tilting operation) 
The upward tilting operation of the outboard motor 10 is as follows. 
When the motor 32 is actuated for upward tilting and the pump 33 is rotated 
forward, fluid discharged from the pump 33 enters the opposite piston side 
space 22B of the second chamber 22 of the cylinder 18 after passing 
through the duct line 42, the first check valve 36 and the second duct 
line 44, pushes up the piston rod 19 and enables the propelling unit 15 to 
be tilted from a lower position indicated by a solid line shown in FIG. 1 
to an upper position indicated by a 2-dotted chain line. Fluid in the 
first chamber 21 of the cylinder 18 is returned to the pump 33 through the 
duct line 45, the second check valve 37 and the duct line 43. 
During this upward tilting period, in the upper limit position of upward 
tilting, in which the piston rod 19 reaches its maximum extended position, 
the piston 20 coming into contact with the rod guide 18A pushes open the 
opening/closing vane 61, and thereby the opening/closing duct line 60 is 
opened. Thus, the hydraulic fluid, which has been supplied from the second 
duct line 44 to the second chamber 22, escapes through the opening/closing 
duct line 60 and the opening/closing valve 61 to the first chamber 21, and 
is then discharged from the first chamber 21 to the outside of the 
cylinder 18. In this manner the inner pressure increase of the cylinder 18 
is controlled. 
During this period, the opening/closing valve 61 is always pushed by the 
piston 20 in the upper limit position of upward tilting and immediately 
opened. Thus, the inner pressure increase of the cylinder 18 is quickly 
controlled, and this makes it possible to reduce power consumption and 
improve pump durability. 
(Downward tilting operation) 
The downward tilting operation of the outboard motor 10 is as follows. 
When the motor 32 is actuated for downward tilting and the pump 33 is 
rotated backward, fluid discharged from the pump 33 enters the first 
chamber 21 of the cylinder 18 after passing through the duct line 43, the 
second check valve 37 and the duct line 45, and presses down the piston 
rod 19. Fluid in the second chamber 22 of the cylinder 18 is returned to 
the pump 33 through the duct line 44, the first check valve 36 and the 
duct line 42. 
(Rapid upward movement or jumping-up operation) 
The jumping-up operation of the outboard motor 10 following its collision 
with an underwater obstacle is as follows. 
When an underwater obstacle comes into collision with the propelling unit 
15, a large tensile force is applied on the piston rod 19, the pressure of 
the first chamber 21 of the cylinder 18 is increased, the shock valve 23 
is opened, hydraulic fluid in the first chamber 21 is transferred to the 
piston side space 22A of the second chamber 22, the piston rod 19 is 
extended, which causes the propelling unit 15 to jump up, and the impact 
force is absorbed. After the absorption of the impact force, a pressure in 
the piston side space 22A is increased by dead weight of the propelling 
unit 15, the return valve 24 is then opened, the hydraulic fluid in the 
piston side space 22A is returned to the first chamber 21, and the 
propelling unit 15 is returned to a position before its jumping up by 
contracting the piston rod 19. Furthermore, as described above, in this 
embodiment, the free piston 25 is provided in the second chamber 22. Thus, 
the amount of hydraulic fluid transferred from the first chamber 21 to the 
second chamber 22 and the amount of the hydraulic fluid returned from the 
second chamber 22 to the first chamber 21 are the same before and after 
the impact absorption. Thereby, the returning position of the piston rod 
19 after the impact absorption can be matched with its lower position 
before the impact absorption. 
Apparent from the foregoing, according to the present invention, in the 
power tilt cylinder device, the free piston is provided and it is possible 
to quickly control the inner pressure increase of the cylinder in the 
upper limit position of upward tilting. 
The entire disclosure of Japanese Patent Application No. 8-91754 filed on 
Mar. 22, 1996 including specification, claims, drawings and summary are 
incorporated herein by reference in its entirety. 
While there has been described a preferred embodiment of the invention with 
reference to the accompanying drawings, it is to be understood that a 
specific constitution of the invention is not limited to this embodiment 
and various modifications are possible without departing from the spirit 
and scope of the invention, and it is intended to cover in the appended 
claim all such modifications as fall within the invention.