Acceleration modulator for a hydraulic driving system

An acceleration regulator in the driving system of an automotive vehicle comprising an element for transmitting displacement comprising a first portion and a second portion; a differential mechanism having a first input terminal connected to the first portion of the element, a second input terminal, an an output terminal connected to the second portion of the element, and being so arranged that the amount of operation applied through the first portion of the element to the first input terminal is modulated differentially by the piston of the second input terminal so that the modulated amount of operation is taken out at the output terminal; and a fixing mechanism for variably fixing the position of the second input terminal of the differential mechanism, the fixing mechanism being so arranged that when the hydraulic pressure in the hydraulic circuit of the driving system rises to a preset level slightly lower than the relief pressure of the circuit, the second input terminal of the differential mechanism is moved to a position where the amount of output available at the output terminal of the differential mechanism decreases.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus for modulating acceleration in the 
driving system of an automotive vehicle such as an automobile or a tractor 
provided with a hydraulic transmission. 
Generally, a driving system for an automtive vehicle such as a tractor 
provided with a hydraulic transmission comprises an engine as a prime 
mover, a hydraulic pump driven by the engine to produce a hydraulic 
pressure, and a hydraulic motor connected through a hydraulic circuit to 
the pump so that the motor is driven by the output pressure of the pump to 
produce a motive force for driving the wheels of the vehicle. Either the 
pump or the motor or both are of a variable displacement type, so that the 
transmission ratio may be changed by changing the displacement of either 
or both of the pump and the motor. 
In this system, the output of the engine is controlled by an accelerator 
provided with a pedal or the like in such a manner that the amount of 
operation applied to the accelerator pedal is transmitted through a 
displacement transmitting element such as a wire to the throttle valve of 
a carburetor for the engine. 
Normally, the system of the above type is used in the range in which the 
output pressure of the hydraulic pump remains lower than the relief 
pressure of the hydraulic circuit including the pump and the motor. Under 
the normal condition, the absorption torque is the product of the output 
pressure of the pump and the displacement thereof. 
In a system in which the outupt of the engine can be freely controlled by 
stepping on the accelerator pedal, it often happens that the output of the 
engine is increased to such an unnecessarily high level that the pressure 
in the hydraulic circuit reaches the relief pressure, whereupon the excess 
hydraulic operating fluid is discharged out of the circuit through a 
relief valve, with resulting waste of energy and abnormal rise of the 
temperature of the hydraulic operating fluid. This is a great 
disadvantage. 
The object of the invention is to provide an apparatus for modulating 
acceleration in the driving system of an automotive vehicle, which 
completely eliminates the above-mentioned and other disadvantages of the 
conventional systems. 
The invention will be described with reference to the accompanying drawings 
.

SUMMARY OF THE INVENTION 
The acceleration modulator of the invention is incorporated into a 
hydraulic driving system which comprises a prime mover the output of which 
varies with the amount of operation applied to the terminal for 
controlling energy supply to the prime mover, a hydraulic pump driven by 
the prime mover, a hydraulic motor for driving the wheels of a vehicle, 
and a hydraulic circuit for connecting the pump and the motor to operate 
the motor with the output pressure of the pump thereby to drive the 
vehicle wheels. 
Briefly stated, the acceleration regulator of the invention comprises: an 
element for transmitting displacement comprising a first portion and a 
second portion; a differential mechanism having a first input terminal 
connected to the first portion of the element, a second input terminal, 
and an output terminal connected to the second portion of the elemnet, and 
being so arranged that the amount of operation applied through the first 
portion of the element to the first input terminal is modulated 
differentially by the the position of the second input terminal so that 
the modulated amount of operation is taken out at the output terminal; and 
a fixing mechanism for variably fixing the position of the second input 
terminal of the differential mechanism, the fixing mechanism being so 
arranged that when the hydraulic pressure in the hydraulic circuit of the 
driving system rises to a preset level slightly lower than the relief 
pressure of the circuit, the second input terminal of the differential 
mechanism is moved to a position where the amount of output available at 
the output terminal of the differential mechanism decreases. 
So long as the hydraulic pressure in the hydraulic circuit remains below 
the preset level adjacent to the relief pressure of the hydraulic circuit, 
the fixing mechanism holds the second input terminal of the differential 
mechanism at a fixed position. Under the condition, the amount of 
operation applied to the first portion of the displacement transmitting 
element and transmitted to the first input terminal of the differential 
mechanism is not changed but taken out at the output terminal of the 
differential mechanism so as to be transmitted to the control terminal of 
energy supply to the prime mover. In this case the output of the prime 
mover can be controlled in substantially the same manner as if there were 
no differential mechanism interposed between the first and second portions 
of the displacement transmitting element. 
When an excessive amount of operation has been applied to the first portion 
of the displacement transmitting element so that the output of the prime 
mover increases thereby to cause the system pressure in the hydraulic 
circuit to exceed the preset level slightly lower than the relief pressure 
of the circuit, the fixing mechanism operates in response to the increased 
system pressure to change the fixed position of the second input terminal 
of the differential mechanism so as to reduce the amount of displacement 
to be taken out at the output terminal of the differential mechanism. As a 
result, as the excessive amount of operation applied to the first portion 
of the displacement transmitting element is delivered to the control 
terminal of energy supply to the prime mover, the amount is reduced to 
such a relatively low level as to prevent unnecessary increase of the 
output of the prime mover. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is schematically shown a driving system for an 
automotive vehicle, into which the acceleration modulator of the invention 
is incorporated as shown as a mere block 1. The driving system can be 
employed in a tractor, for example, and comprises an engine 2 as a prime 
mover, a hydraulic pump 3 driven by the output of the engine 2, a 
hydraulic motor 5 driven by the output hydraulic pressure of the pump 3, 
and a hydraulic circuit 4 connecting the pump and the motor. The motor 5 
produces an output to drive the wheels of a vehicle shown as a mere block 
10. 
The pump 3 and the motor 5 are of a variable displacement type, so that the 
transmission ratios of the driving system can be varied continuously by 
changing the displacement of either or both of the pump and the motor. The 
hydraulic circuit 4 is provided with a relief valve 6 to define the upper 
limit of the system pressure thereby to prevent destruction of the circuit 
4. The output of the engine 2 is controlled by the amount of operation on 
an accelerator pedal 7 transmitted through an element such as a wire 8 for 
transmitting the displacement of the pedal 7 to a fuel control terminal 9 
of the engine 2 such as a throttle valve in a carburetor, not shown, for 
the engine. 
In accordance with the invention, the wire 8 comprises two portions, that 
is, the forward portion 8a connected at one end thereof to the accelerator 
pedal 7 and the rear portion 8b connected at one end thereof to an 
operating rod 9a for controlling the throttle valve 9. 
The acceleration modulator 1 of the present invention is provided between 
the other end of the forward wire portion 8a and the other end of the rear 
wire portion 8b. One form of the modulator 1 is shown in detail in FIGS. 2 
through 5, comprising a differential gear mechanism 11 having a first and 
a second input terminal and an output terminal and so designed as to 
subtract the amount of operation applied to the second input terminal from 
the amount of operation applied to the first input terminal and produce an 
amount of operation corresponding to the result of subtraction at the 
output terminal, and a mechanism 12 for variably fixing the position of 
the second input terminal of the differential gear mechanism 11. 
The differential gear mechanism 11 is enclosed in a casing 13, which 
supports the forward portion 8a of the wire 8 by a first lateral wall 13a 
thereof and the rear portion 8b of the wire by a second lateral wall 13b 
thereof extending at right angles with the first lateral wall 13a. In 
particular, the forward and rear wire portions 8a and 8b pass through 
bearing sleeves 14.sub.1 and 14.sub.2, respectively, to be slidably 
supported thereby. The sleeves 14.sub.1 and 14.sub.2 are mounted on the 
lateral side walls 13a and 13b of the casing 13 by means of retainers 
15.sub.1 and 15.sub.2, respectively. 
The forward wire portion 8a has its rear end 8A engaged with a recess 16a 
formed on the periphery of an input pulley 16 constituting the first input 
terminal of the differential gear mechanism 11. The rear wire portion 8b 
has its forward end 8B engaged with a recess 17a formed on the periphery 
of an output pulley 17 constituting the output terminal of the 
differential gear mechanism 11. The wire portions 8a and 8b run partially 
about the pulleys 16 and 17, respectively. 
In the illustrated embodiment, the differential gear 11 is of the planetary 
type comprising a ring gear 18, a sun gear 19 secured to a shaft 19a and 
arranged within the ring gear 18 coaxially therewith, a gear retainer 21 
arranged rotatably and coaxially with both the sun gear 19 and the ring 
gear 18, and a plurality, say, three planetary gears 22 rotatably 
supported on the gear retainer 21 by means of a pin 21a and engaged with 
both the ring gear 18 and the sun gear 19. The previously mentioned input 
pulley 16 is mounted on the ring gear 18 for simultaneous rotation 
therewith, and the previously mentioned output pulley 17 is mounted on the 
shaft 19a for simultaneous rotation therewith. 
The gear retainer 21 has its under side fixed to a hollow cylindrical input 
shaft 23, which constitutes the second input terminal of the differential 
gear mechanism 11, for simultaneous rotation therewith. The input shaft 23 
is rotatably supported by a pair of radial bearings 24 mounted in a boss 
13c formed inside the casing 13. The ring gear 18 is mounted by a bearing 
25 on the gear retainer 21 fixed to the upper end of the input shaft 23. 
The support shaft 19a of the sun gear 19 is rotatably supported on the 
input shaft 23 and the gear retainer 21 by means of bearings 26 and 27. 
The previously mentioned fixing mechanism 12 engages the input shaft 23 so 
as to fix the shaft at a desired angular position, which can be changed as 
will be described presently. 
As shown in FIG. 5, the fixing mechanism 12 comprises a cylinder 31 formed 
in the casing 13 in association with the boss 13c, and a piston 32 
slidably disposed in the chamber of the cylinder 31 so as to be operated 
by the pilot pressure taken out of the hydraulic pressure circuit 4 as 
will be described presently. The piston 32 is formed on the exterior 
surface thereof with a rack 33 extending axially of the piston and 
engaging a pinion gear 34 formed on the exterior circumferential surface 
of the input shaft 23. 
In further detail, the cylinder 31 extends perpendicularly to the input 
shaft 23 and is provided at the opposite ends with a pair of caps 35 and 
36 and a plug 35a liquid-tightly closing the cylinder chamber as shown in 
FIG. 5. The piston 32 is a hollow cylindrical member open at one end and 
closed at the other, with a compression coil spring 37 enclosed therein to 
normally urge the piston 31 against the inner face of the cylinder plug 
35a. In the cylinder plug 35a there is formed a passage 38 connected to a 
device 41 for taking out a pilot pressure so that the pilot pressure taken 
out of the hydraulic circuit 4 is introduced through the passage 38 into a 
pilot pressure chamber 39 formed in the inner end face of the plug 35a 
defined by the closed end of the piston 32. 
As schematically shown in FIG. 6, the device 41 for taking out a pilot 
pressure has an inlet port 42 through which the system pressure in the 
hydraulic circuit 4 the upper limit of which is defined by the previously 
mentioned relief valve 6 is introduced into the device 41, an outlet port 
44 through which the pressure is discharged into a reservoir tank 43 shown 
in FIG. 1, a series combination of a first relief valve 45 and a 
restrictor 46 connected between the inlet and outlet ports 42 and 44, a 
pilot pressure port 47 connected between the first relief valve 45 and the 
restrictor 46 for a pilot pressure to be taken out therefrom, and a second 
relief valve 48 connected in parallel with the restrictor 46 to regulate 
the pilot pressure to be taken out. 
The operating pressure of the first relief valve 45 is set to a level a 
little lower than that of the relief valve 6 in the hydraulic circuit 4. 
The pilot pressure port 47 is connected to the passage 38 in the cylinder 
plug 35a. 
A sensor 51 detects the opening of the throttle valve 9, that is, converts 
the rotational angle of the support shaft 19a of the sun gear 19 in the 
previously mentioned differential mechanism 11 to a corresponding 
electrical signal, which is used for controlling the HST or HMT 2. 
The system of the invention operates in the following manner. 
So long as the system pressure in the hydraulic circuit 4 remains below the 
preset pressure level of the device 41 a little lower than the preset 
pressure of the relief valve 6, no pilot pressure will be supplied from 
the device 41 to the fixing mechanism 12, so that the spring 37 keeps the 
piston 32 abutting on the inner face of the cylinder plug 35a and 
consequently the input shaft 23 of the differential mechanism 11 at a 
predetermined angular position and the planetary gears 22 at predetermined 
waiting positions. Under the condition, the amount of displacement of the 
accelerator pedal 7 is transmitted to the input pulley 16 and thence 
through the ring gear 18, the planetary gears 22, the sun gear 19 and the 
support shaft 19a thereof successively to the output pulley 17 fixed to 
the upper end of the shaft 19a, so that the pulley 17 is rotated in the 
direction opposite to that of rotation of the input pulley 16 so as to 
pull the rear portion 8b of the accelerator wire 8 thereby to control the 
opening of the throttle valve 9 in accordance with the amount of operation 
on the accelerator pedal 7. 
If the accelerator pedal 7 has been operated excessively so that the 
resulting increase in the output of the engine 2 causes the system 
pressure in the hydraulic circuit 4 to exceed the pressure preset level of 
the device 41 a little lower than the relief pressure of the relief valve 
6 in the circuit 4, the first relief valve 45 in the device 41 is opened 
to introduce into the pressure chamber 39 of the fixing mechanism 12 a 
pilot pressure the upper level of which is defined by the opening pressure 
of the second relief valve 48. The pilot pressure introduced into the 
chamber 39 urges the piston 32 away from the cylinder plug 35a against the 
force of the spring 37, thereby to cause the input shaft 23 of the 
differential mechanism 11 engaged by the rack 33 on the piston 32 to 
rotate about the axis of the input shaft 23 for an angle corresponding to 
the pilot pressure, whereupon the positions of the planetary gears 22 on 
the gear retainer 21 change thereby to reduce the output angular 
displacement of the sun gear 19. This means that the amount of angular 
displacement of the input shaft 23 of the differential mechanism 11 has 
been subtracted from the amount of operation on the accelerator pedal 7 
transmitted to the input pulley 16, and the resulting reduced amount of 
displacement is taken out from the output pulley 17 so as to control the 
opening of the throttle valve 9. 
With the apparatus of the invention as described above in detail, even when 
the accelerator pedal 7 has been excessively operated by mistake, the 
output of the engine 2 is automatically restricted to prevent the system 
pressure from reaching the relief pressure level thereby to prevent a 
large amount of working fluid from being returned to the tank 43 through 
the relief valve 6, with resulting marked reduction of energy loss and 
effective prevention of abnormal rise of the temperature of the working 
fluid. 
Since the displacement of the forward portion 8a of the wire 8 is 
transmitted through a gear type differential mechanism, that is, the 
differential mechanism 11 to the wire rear portion 8b, there is scarcely 
any error, delay or loss in transmission of movement, so that the operator 
can control the throttle valve 9 as effectively as if there were no 
acceleration modulator and without deterioration of the feeling of 
operating the throttle valve. 
Advantageously the throttle position sensor 51 is secured to the lower 
portion of the shaft 19a which projects outside the casing 13 as in the 
illustrated embodiment of the invention, so that the sensor 51 is scarcely 
affected by the vibration of the engine. 
A preferred embodiment of the invention having been described above in 
detail, the invention is not limited to the illustrated embodiment, but 
there may be many modifications. For example, it is possible to use other 
prime movers than the engine to dirve the hydraulic pump. The differential 
gear mechanism and the element for transmitting displacement are not 
limited to the illustrated forms. 
The acceleration modulator of the invention can be easily incorporated into 
a driving system and prevent loss of energy and abnormal temperature rise 
of the working fluid which would otherwise be caused by excessive 
operation of acceleration of the driving system, and this is possible 
without damaging the feeling of operation of acceleration. Since the 
element for transmitting displacement comprises a wire, it enables easy 
connection to the differential gear and proper and reliable control of 
acceleration.