Control valve for steering clutch and brake

A control valve for a hydraulically actuated steering clutch and steering brake are provided. The valve comprises a valve housing having a plurality of bores therein, right and left hand operating rods and first, second and third spools slidably disposed within said respective bores. The spools are normally urged towards a neutral position where the hydraulic fluid from a hydraulic pressure supply source is discharged, through a drain circuit. The first and third spools are arranged such that when either of the right and left hand operating rods is moved on a predetermined stroke, the hydraulic fluid delivered by the supply source is supplied into either the pressure chamber of a right hand steering clutch or that of a left hand steering clutch, and when the operating rod is moved on a further predetermined stroke, the hydraulic fluid is supplied into either the pressure chamber of a right hand steering brake or that of a left hand steering brake, whereby the steering clutch and the steering brake can be controlled by a common control valve.

BACKGROUND OF THE INVENTION 
This invention relates to a steering clutch and brake for controlling the 
travelling of a tractor such as bulldozer, and more particularly to a 
control valve for a hydraulically actuated steering clutch and brake. 
Conventional control valves for a steering clutch and brake of this type 
are either actuated by independent operating rods, respectively or 
actuated in interlocked relationship by a common operating rod, but in 
either case, the steering clutch and the steering brake are actuated by 
means of respective control valves. 
Therefore, the conventional control device is disadvantageous in that a 
separate operating rod is required for each of the steering clutch and the 
steering brake so that the entire structure becomes complicated, and the 
respective operating rods have to be adjusted in length in such a manner 
that after the steering clutch is released, the steering brake is 
controlled. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a control 
valve which can be commonly used for controlling a hydraulically actuated 
steering clutch and steering brake.

Further FIG. 1 is a view showing a condition wherein the right and left 
steering brakes 101R and 101L are not operated and, at the same time, the 
right and left steering clutches 32R and 32L are engaged so as to permit 
forward drive on the vehicle because no operating rod or pedal is 
actuated, while FIG. 2 is a view showing a condition wherein the right 
operating rod 23R is actuated so as to disengage the right steering clutch 
32R and exert an ordinary braking force on the right steering brake 101R 
for the purpose of turning the vehicle to the right. 
The "neutral position" of the first and second spools described in the 
present claim means the state illustrated by FIG. 1. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawing, reference numeral 1 indicates a valve housing which has 
formed therein first, second and third bores 2, 3 and 4. Within the first, 
second and third bores 2, 3 and 4 are slidably disposed first, second and 
third spools 5, 6 and 7. 
First to sixth ports 8 to 13 are formed in the first bore 2, and seventh 
port 14 is formed in the second bore 3. Eighth to thirteenth ports 15 to 
20 are formed in the third bore 4. 
The operative relationship between the ports and the spools and also the 
detailed structure thereof will now be described below together with their 
operations. 
(I) Neutral state 
The hydraulic fluid discharged from a hydraulic pressure supply source P 
flows through the seventh port 14, passages 21 and 22 and first and eighth 
ports 8 and 15 into pressure receiving chamber 107a for the emergency 
brake defined within the right and left brake actuating cylinders 100. 
Each of the right and left brake operated cylinders 100 contains a first 
piston 105 having a piston rod 104 connected through a linkage 102 to a 
brake band 103 of each of the right and left steering brakes 101, and a 
second piston 107 having slidably fitted on the piston rod 104 and being 
urged by a spring 106 toward the first piston 105. When hydraulic fluid is 
supplied to the pressure receiving chamber 105a for the ordinary brake of 
the first piston 105 or hydraulic fluid in the pressure receiving chamber 
107a for the emergency brake of the second piston 107 is discharged, the 
brake band 103 is actuated, and when hydraulic fluid in the pressure 
receiving chamber 105a for the ordinary brake is discharged or hydraulic 
fluid is supplied to the pressure receiving chamber 107a for the emergency 
brake, the brake band 103 is released. Therefore, both the right and left 
steering brakes 101 are released in a neutral state. 
(II) When the right hand operating rod 23R is gradually operated 
The actuating member 24 urges a first push rod 25 to the right in the 
drawing thereby to move the first spool 5 towards the right through the 
action of the spring 26 so that the fifth port 12 is connected with the 
sixth port 13 through a reduced diameter portion 27, while the second 
spool 6 is moved to the right in the drawing through the second push rod 
28 and spring 29 so that the seventh port 14 is connected with the fifth 
and twelfth ports 12 and 19 through the reduced diameter portion 30 and 
passages 31 and 32. Therefore, the hydraulic fluid discharged from the 
hydraulic pressure supply source P flows through the seventh port 14, the 
reduced diameter portion 30, the passage 31, the fifth port 12, the 
reduced diameter portion 27 and the sixth port 13 into the pressure 
chamber 32a of the right steering clutch 32R so that the right side 
steering clutch 32R is moved against the force of the spring 33 in the 
direction as shown by II In which the power transmission is interrupted. 
Then the pressure chamber 34a defined by a load piston 34 of the second 
spool 6 is connected through the aperture 35 with the passages 31 and 32. 
Therefore, if the pressure in the pressure chamber 32a of the clutch is 
increased, the pressure in the pressure chamber 34a of the load piston 34 
is also increased so that the second piston 6 is moved to the left in the 
drawing against the action of the spring 29 so as to interrupt the 
communication between the seventh port 14 and the passage 31. Then, when 
the spring load by the operation of the second push rod 28 is balanced 
with the urging force of the load piston 34, the second spool 6 interrupts 
the communication between the seventh port 14 and the passage 31. When the 
right hand operating rod 23R is moved further to the right thereby to 
operate the second push rod 28, then the load of the spring 29 is 
increased, and consequently the second spool 6 is moved towards the right 
in the drawing so that the seventh port 14 is allowed to communicate with 
the passage 31 thereby increasing the pressure in the pressure chamber 32a 
of the right hand steering clutch 32. 
In other words, the pressure in the pressure chamber 32a of the right hand 
steering clutch 32R is increased in proportion to the stroke of the right 
hand operating rod 23R as shown in FIG. 3. 
When the right hand operating rod 23R is further operated, the first spool 
5 is further urged to the right so that the second port 9 is connected 
through the reduced diameter portion 36 with the third port 10, and 
consequently the hydraulic fluid delivered by the hydraulic pressure 
supply source P flows through the seventh port 14, the passage 37, the 
second port 9 and the third port 10 into the pressure receiving chamber 
105a for the ordinary brake of the brake cylinder 100. When the hydraulic 
pressure in the pressure receiving chamber 105a for the ordinary brake is 
increased, the hydraulic fluid flows through the aperture 38 into the 
pressure chamber 39a of the load piston 39 so as to urge the first spool 5 
to the left in the drawing against the repulsion force of the spring 26, 
thereby to shut off the communication between the second port 9 and the 
third port 10 at a position where the hydraulic pressure in the pressure 
receiving chamber 105a for the ordinary brake is balanced with the 
repulsion force of the spring 26. 
When the right hand operating rod 23R is moved further to the right in the 
drawing, the repulsion force of the spring 26 is increased so that the 
hydraulic pressure in the pressure receiving chamber 105a for the ordinary 
brake is increased. Consequently, the first piston 105 is moved to the 
left in the drawing so that the right hand steering brake 101R is actuated 
by the brake band 103. In other words, the hydraulic pressure in the 
pressure receiving chamber 105a for the ordinary brake of the brake 
cylinder 100 is increased in response to the stroke of the operating rod 
as shown in FIG. 3. 
(III) When a right hand brake operating rod 44R is operated, the first push 
rod 25 is moved to the right in the drawing against the repulsion force of 
the spring 26. However, since the communication between the seventh port 
14 and the passage 31 is not allowed because the second push rod 28 is not 
moved, the hydraulic pressure in the pressure chamber 32a of the clutch is 
not increased. Therefore, the hydraulic pressure in the pressure receiving 
chamber 105a for the ordinary brake of the brake cylinder 100 is increased 
in response to the stroke of the operating rod 44R in such a state that 
the clutch is held in contact. Further, when the right hand brake 
operating rod 44R is operated to its stroke end, the first port 8 and the 
passage 21 are allowed to communicate with the drain 40 through the 
reduced diameter portion 44 of the first push rod 25. Therefore, the 
hydraulic fluid within the pressure receiving chamber 107a for the 
emergency brake of the brake cylinder 100 flows instantaneously out to the 
drain so that the second piston 107 is moved to the left in the drawing by 
the repulsion force of the spring 106 and the first piston 105 is also 
moved to the left, thereby actuating the right hand steering brake 101R by 
the brake band 103. In other words, emergency braking is effected. 
In this case, there is provided an arrangement in which the right hand 
operating rod 23R is held up with a stopper before the communication 
between the reduced diameter portion 44 of the first push rod 25 and the 
first port 8 is allowed. 
(IV) When the right hand operating rod 23R returns from the stroke end. 
The third port 10 is connected through the reduced diameter portion 41 and 
the fourth port 11 with the drain so as to discharge the hydraulic fluid 
within the first pressure receiving chamber 105a for the ordinary brake 
through the drain. As a result, the first piston 105 is returned 
rightwards in the drawing so that the brake band 103 is disengaged to 
release the right hand steering brake 101R. 
When the right hand operating rod 23R is returned further, the sixth port 
13 is allowed to communicate through the groove 42 formed on the 
peripheral surface of the one side end of the first spool 5 with the drain 
45 and consequently the hydraulic fluid within the pressure chamber 32a of 
the right hand steering clutch 32R is drained so that the clutch is moved 
to the power transmission position I by the repulsion force of the spring 
33. 
Then the hydraulic fluid within the pressure chamber 39a of the load piston 
39 is drained through the drain aperture 43 and the drain port 12. 
The operation of the control valve when the left hand operating rod 23L is 
operated is similar to that as described in the above paragraphs (II) to 
(IV), and accordingly it is omitted. 
It will be understood from the foregoing description that since the control 
valve of this invention is thus constructed, either of the right and left 
operating rods 101R and 101L and either one of the steering clutches 32R 
and 32L can be operated. 
It will also be understood that the steering brake and steering clutch can 
be controlled by means of a single control valve, and only one rod for 
connecting the operating rod 23 with the control valve may be provided at 
the right and left sides, respectively. Thus, the structure becomes simple 
and it is not necessary to adjust the length of operating rod for 
controlling the timing of actuation of the steering brake and steering 
clutch. 
With further reference to FIG. 3, hydraulic pressure in the clutch chamber 
32a becomes a constant pressure equal to the hydraulic pressure supplied 
from the hydraulic pressure supply source P when the operating rod 23R or 
23L is moved in a predetermined stroke (80 mm) because, at that time, the 
second spool 6 is directly urged by the operating rod 23R or 23L without 
interposing the spring 29 therebetween. On the other hand, until the 
operating rod 23R or 23L takes the predetermined stroke, the hydraulic 
pressure in the clutch chamber 32a is increased in proportion to the 
stroke of the operating rod while the clutch 32R or 32L is in a 
semi-engaging state which is one of the characteristic features of the 
present invention. 
As to hydraulic pressure in the ordinary steering brake chamber 105, this 
is controlled by the operation of the first spool 5 and depends on the 
resilient force of the spring 26a. And, since the ordinary steering brake, 
according to the valve apparatus of the present invention, is applied 
after the steering clutch is disengaged, steering such brake is applied by 
the operating rod 23R or 23L after the operating rod 23R or 23L increases 
beyond the aforesaid predetermined stroke. Further, it is a characteristic 
feature of the steering brake function of the present invention that the 
ordinary steering brake is distinguished from the emergency steering brake 
by the difference of the resilient force between the springs 26a and 26b; 
that is, in order to apply the emergency steering brake, it is necessary 
to apply a large operating force to the operating rod 23R or 23L as 
compared with the application of the ordinary steering brake. By the above 
function, an operator of the vehicle can determine the distinction between 
the ordinary steering brake and the emergency one during operation. 
It is further necessary to increase the operating force of the operating 
rod 23R or 23L in proportion to the increase of hydraulic pressure in the 
clutch chamber 32a, the pressure receiving chamber 105a for the ordinary 
brake and the pressure receiving chamber 107a for the emergency brake 
because each of the first, second and third spools 5, 6 and 7 acts as a 
pressure reducing valve.