CA2008280C - Hydraulic propelling apparatus for a vehicle - Google Patents
Hydraulic propelling apparatus for a vehicleInfo
- Publication number
- CA2008280C CA2008280C CA 2008280 CA2008280A CA2008280C CA 2008280 C CA2008280 C CA 2008280C CA 2008280 CA2008280 CA 2008280 CA 2008280 A CA2008280 A CA 2008280A CA 2008280 C CA2008280 C CA 2008280C
- Authority
- CA
- Canada
- Prior art keywords
- hydraulic
- swash plate
- oil pressure
- control valve
- vehicle
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H61/00—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing
- F16H61/38—Control of exclusively fluid gearing
- F16H61/40—Control of exclusively fluid gearing hydrostatic
- F16H61/46—Automatic regulation in accordance with output requirements
- F16H61/478—Automatic regulation in accordance with output requirements for preventing overload, e.g. high pressure limitation
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02F—DREDGING; SOIL-SHIFTING
- E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
- E02F9/20—Drives; Control devices
- E02F9/22—Hydraulic or pneumatic drives
- E02F9/2253—Controlling the travelling speed of vehicles, e.g. adjusting travelling speed according to implement loads, control of hydrostatic transmission
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H61/00—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing
- F16H61/38—Control of exclusively fluid gearing
- F16H61/40—Control of exclusively fluid gearing hydrostatic
- F16H61/42—Control of exclusively fluid gearing hydrostatic involving adjustment of a pump or motor with adjustable output or capacity
- F16H61/423—Motor capacity control by fluid pressure control means
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H61/00—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing
- F16H61/38—Control of exclusively fluid gearing
- F16H61/40—Control of exclusively fluid gearing hydrostatic
- F16H61/42—Control of exclusively fluid gearing hydrostatic involving adjustment of a pump or motor with adjustable output or capacity
- F16H61/433—Pump capacity control by fluid pressure control means
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H61/00—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing
- F16H61/38—Control of exclusively fluid gearing
- F16H61/40—Control of exclusively fluid gearing hydrostatic
- F16H61/46—Automatic regulation in accordance with output requirements
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Mining & Mineral Resources (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Control Of Fluid Gearings (AREA)
- Fluid-Pressure Circuits (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A hydraulic propelling apparatus for a vehicle comprising a hydraulic pump driven by a vehicle engine, and a hydraulic motor connected to a propelling transmission of the vehicle. The hydraulic motor includes a swash plate rotatable by a switch mechanism between a high speed position and a low speed position. The switch mechanism includes a hydraulic cylinder, and an oil line extending to this hydraulic cylinder includes a throttle for retarding the rotation of the swash plate to the low speed position.
A hydraulic propelling apparatus for a vehicle comprising a hydraulic pump driven by a vehicle engine, and a hydraulic motor connected to a propelling transmission of the vehicle. The hydraulic motor includes a swash plate rotatable by a switch mechanism between a high speed position and a low speed position. The switch mechanism includes a hydraulic cylinder, and an oil line extending to this hydraulic cylinder includes a throttle for retarding the rotation of the swash plate to the low speed position.
Description
The present invention relates to a hydraulic propelling apparatus for a vehicle, which utilizes a hydrostatic transmission comprising a variable displacement hydraulic pump and a hydraulic motor driven by pressure oil supplied from the hydraulic pump.
Japanese Utility Model Publication Kokai No. 61-19158 dicloses an apparatus comprising a hydraulic pump having an angularly variable swash plate, and a hydraulic motor having an angularily fixed swash plate. In operation, the swash plate of the hydraulic pump is rotated to cause a plurality of pistons to deliver pressure oil to a plurality of pistons of the hydraulic motor. As a result, the pistons of the hydraulic are moved back and forth in fixed cycles to rotate the swash plate of the hydraulic motor. Futhermore, the rotational rate tranmitted to the hydraulic motor is adjustable by-varyinq the swash plate angle of the hydraulic pump.
A hydrostatic transmission may be used in the propelling system of a vehicle, with the swash plate angle of the hydraulic motor switchable for two, h,~ h X
- ` .... - -- . -. . ,. ~ : . ., . , :,. `: ..
, ~ 2008280 and law, speeds. In this case, the following inconvenience may be encountered when the swash plate angle is switched from hi8h speed to low speed while the vehicle is running.
When the swash plate angle is switched from high - speed to low speed, the dynamic inertial force of the vehicle will act on the hydraulic motor. This means that the propelling system imparts a force to rotate the output shaft of the hydraulic motor at the rate prevailing immediately before the swash plate angle is switched. When the output shaft of the hydraulic motor is rotated by the force applied from the propelling system, the rotational rate may exceed an aliowable rotational rate, resulting in dama8e to the apparatus.
More particularly, when the output shaft of the hydraulic motor is rotated in the accelerating direction by the external force as described above, the hydraulic motor functions as if a hydraulic pump to discharge pressure oil. As a result, not only the two oil lines connected to the hydraulic motor are reversed with respect to the hi8h pressure and low pressure sides, but the relief valve disposed between the two oil lines is opened. This nullifies the 2$ funotion of n~ine brak- - in p-ssen~er vehiolo.
Even if the hydraulic pump operates normally, it .
,... , . : .
.. . .
.. . . " .~ .
2~08280 inevitably allows acceleration of the output shaft as described above, which results in damage to the apparatus.
The upper limit of the allowable rotational rate of the hydraulic motor is set on the basis of working strokes of the pistons within a unit time. The rotational rate occurring when the working strokes reach a certain value is set to be the allowable rotational rate. The upper limit of the allowable rotational rate has a greater value when the swash plate angle is set to the high speed than when it is set to the low speed.
That is, where the motor of the conventional hydrostatic transmission has two, high and low, speeds, the swash plate of the motor may be rapidly changed from high speed to low speed, and the dynamic inertia of the vehicle applies an excessive load to the motor.
In one aspect, the invention provides a hydraulic propelling apparatus for a vehicle comprising: a hydraulic pump and a charge pump driven by a vehicle engine; a hydraulic motor including a swash plate having a high speed pofiition; and a swash plate low speed position, said hydraulic motor being operatively connected to a propelling transmission of the vehicle; a swash plate position switching mechanism movable between a first position corresponding to said swash plate high speed position and a second position corresponding to said swash plate low speed position: a three-position hydraulic control valve, a first oil pressure ~ ' ' ~ ' ` ' ~; 1, . ' :
s supply line connected between said charge pump and said . three-position hydraulic control valve, a second oil pressure line connected between said three-position hydraulic control valve and said swash plate position switching mechanism for conducting oil under pressure to and from said swash plate position switching mechanism; damper means comprising a throttle mechanism in said second oil pressure line between said three-position control valve and said swash plate position switching mechanism, said swash plate position switching mechanism including: a hydraulic cylinder having a hydraulic piston movable from said first position to said second position, and elastic means for urging said hydraulic piston from said second position back to said first position;
said three-position hydraulic control valve controls a supply lS oil pressure to the hydraulic cylinder for switching said swash plate from said first swash plate position to said second swash plate position, said hydraulic control valve being movable between a high speed position for supplying the hydraulic cylinder with oil pressure from said charge pump, a low speed position for connecting the hydraulic cylinder and said second oil pressure line with a supply tank, and a braking position for connecting the hydraulic cylinder, said second oil pressure line and said first oil pressure line to the supply tank: and a negative hydraulic brake connected to the first oil pressure line and a propelling system for releasing a braking condition of the propelling system.
... ~ . ................... . .. ~ .
- :: .
200~280 In a preferred embodiment of the above aspect, the hydraulic propelling apparatus further includes a one-way control valve in a third oil pressure line which bypasses said damper means which permits oil under pressure to flow from said three-position control valve to said swash plate position switching mechanism.
- 4a -.~, ~..
- , . .. . . . ..
- . ,, -- : ~. - ,: ~ , . -2~08~80 ~ he drawings show a hydraulic propelling apparatus for a vehicle according to the present invention, in which:-Fig.l is a side elevation of a wheel loader equippedwith the apparatus according to the present invention, Figs. 2A and 2B are diagrams showing hydraulic circuitry of the wheel loader, Fig.3 is a graph showing the allowable rotational rate of a hydraulic motor.
Fig. 4 is a partial diagram showing modified h~draulic circuitry, and Fig.5 is a partial diagram showing a throttle in a different embodiment.
Referring to Fig.l, a wheel loader, which is one example of vehicles, comprises a front vehicle body 2 having right and left drive wheels 1, and a rear vehicle body 4 having right and left drive wheels 3. The front and rear vehicle bodies 2 and 4 are interconnected to be pivotable relative to each other about a vertical axis Y. A steering cylinder 5 is mounted between the front and rear vehicle bodies 2 and 4.
The front vehicle body 2 carries a shovel 7 vertically movable by a pair of right and left arms 6, .
,.
. :' '' ' ' - ~
~ , ': :.
lift cylinders 8 for driving the arms 6, and a tilt cylinder 9 for driving the shovel 7. The rear body 4 carries an engine 10, a driver's seat 11, a steering wheel 12, and a drive system for transmitting power to the front and rear wheels 1 and 3.
The wheel loader includes a hydraulic system for controlling the above three types of cylinders 5, 8 and 9j and a hydraulic system for driving the wheels 1 and 3 as shown in Figs. 2A and 2B, respectively.
These hydraulic systems include a variable displacement hydraulic pump 13, a working pump 14 and a charge pump 15 driven by the engine 10. The variable displacement pump 13 supplies pressure oil through oil lines 16 to a hydraulic motor 17 having a swash plate angle switchable for two, high and low, speeds, and an output shaft 17a connected to the propelling system. The working pump 14 supplies pressure oil to a control valve 18 for controlling the steering cylinder S, a control valve 19 for controlling the tilt cylinder 9, and a control valve for controlling the lift cylinders 8. Part of pressure oil from the char8e pump lS flows to an electromagnetic valve 22 for controlling a servo cylinder 21 which adjusts the displacement of the variable displacement pump 13. Another part of the pressure oil from the charge pump 15 flows to the .., .. . . . ~ , .
,. ~ .. .
;~ :
~, ': propelling oil lines 16 as charging oil. Thef~. remaining part of the pressure oil from the charge : pump 15 flows through a switch valve 23 to a hydraulic cylinder 24 for switching the swash plate angle of the : 5 hydraulic motor 17, and to a negative brake 25 mounted in the propelling system.
The negative brake 25 is released by the pressure :~ applied by the charge pump 15, and brakes the :~. propelling system whenever the engine 10 is stopped.
A separate oil line 27 is provided so that the brake 25 is operable also by a foot pedal 26 during a run of the vehicle.
. In this wheel loader, the hydraulic pump 13 and hydraulic motor 17 constitute a stepless change speed apparatus A. One of the forward and backward traveling directions may be selected by operating a cont.ol lever 28 provided laterally of the steering wheel 12. For this purpose, a switch 29 interlocked with the control lever 28 transmits a signal to a control unit 30 for controlling the electromagnetic 3 valve 22.
The pressure oil from the charge pu~p 15 is delivered to the electromagnetic valve 22 through two oil lines 32 divided by an orifice 31, so that the amount of operation of the servo cylinder 21 increases with the rotational rate of the engine 10. The . -7-.
. .
::. . ` . .'-' ~
.
pressure oil operates the servo cylinder 21 to a position where the differential pressure due to a variation in the rotational rate of the engine 10 balances with a neutral spring 33 mounted in the servo cylinder 21.
The hydraulic cylinder 24 has a hydraulic piston 24' movable by the pressure oil supplied thereto for setting the angle of the swash plate (not shown) of the hydraulic motor 17 to the high speed, the swash plate ange being set to the low speed when the pressure oil is exhausted. An oil line 35 connected to the hydraulic cylinder 24 includes a throttle mechanism 36 for checking a sudden and rapid switching of the swash plate angle as described later.
~5 The switch valve 23 is movable to three positions, i.e. a high speed position H, a low speed position L and a parking position P.
The way in which the hydraulic circuitry of Figs.
2A and 2B operates will be described next. Assume that, when the vehicle is running with the swash plate angle of the hydraulic motor 17 set to the hi8h speed, pressure oil is exhausted from the hydraulic cylinder 24 to switch the swash plate angle of the hydraulic motor 17 to the low speed. This exhaust oil is checked by the throttle mechanism 36, and therefore the swash plate of the hydraulic motor 17 is switched .~: .
~ ~ . . .. .
200~280 to the low speed relatively slowly under the force of a spring 34. Even when this switching operation is carried out while the vehicle is running at a relatively high speed, the deceleration of the vehicle due to the oil line resistance within the stepless change speed apparatus and the mechanical resistance of the propelling system allows the switching operation to be completed smoothly without increasing the rotation of the output shaft 17a of the hydraulic motor 17 over the allowable rotational rate.
Thus, the hydraulic control system is rationally constructed for changing the swash plate angle of the hydraulic motor 17 for two, high and low, speeds.
This construction protects the hydraulic motor 17 from damage even if a change speed operation is effected through the hydraulic control system while the vehicle is running at a relatively high speed.
Fig. 3 is a graph showing the upper limit of the allowable rotational rate of the hydraulic motor 17 described with reference to the swash plate angle.
~- When, for example, the swash plate an81e is rapidly changed from a high speed position H to a low speed position L, the rotation remains below the allowable rotational rate according to the present invention as shown in a bro~en line arrow. In contrast, the rotation would exceeds the upper limit of the _g_ :. ,~ . .
... . ..
., : : ,,.: " ,,, . :: .
:~ , . : - -:
200~280 allowable rotational rate in the prior art as shown in a phanto~ line.
The described embodiment may be modified by including a check valve S0 connected parallel to the throttle mechanism 36 as shown in Fig. 4, so that the throttling action is effective only at exhaustin8 times. Further, as shown in Fig. 5, a constricted oil line portion 60 may be formed between a control spool and a land of the switch valve 23 for use as a throttle.
... .
. :
.
Japanese Utility Model Publication Kokai No. 61-19158 dicloses an apparatus comprising a hydraulic pump having an angularly variable swash plate, and a hydraulic motor having an angularily fixed swash plate. In operation, the swash plate of the hydraulic pump is rotated to cause a plurality of pistons to deliver pressure oil to a plurality of pistons of the hydraulic motor. As a result, the pistons of the hydraulic are moved back and forth in fixed cycles to rotate the swash plate of the hydraulic motor. Futhermore, the rotational rate tranmitted to the hydraulic motor is adjustable by-varyinq the swash plate angle of the hydraulic pump.
A hydrostatic transmission may be used in the propelling system of a vehicle, with the swash plate angle of the hydraulic motor switchable for two, h,~ h X
- ` .... - -- . -. . ,. ~ : . ., . , :,. `: ..
, ~ 2008280 and law, speeds. In this case, the following inconvenience may be encountered when the swash plate angle is switched from hi8h speed to low speed while the vehicle is running.
When the swash plate angle is switched from high - speed to low speed, the dynamic inertial force of the vehicle will act on the hydraulic motor. This means that the propelling system imparts a force to rotate the output shaft of the hydraulic motor at the rate prevailing immediately before the swash plate angle is switched. When the output shaft of the hydraulic motor is rotated by the force applied from the propelling system, the rotational rate may exceed an aliowable rotational rate, resulting in dama8e to the apparatus.
More particularly, when the output shaft of the hydraulic motor is rotated in the accelerating direction by the external force as described above, the hydraulic motor functions as if a hydraulic pump to discharge pressure oil. As a result, not only the two oil lines connected to the hydraulic motor are reversed with respect to the hi8h pressure and low pressure sides, but the relief valve disposed between the two oil lines is opened. This nullifies the 2$ funotion of n~ine brak- - in p-ssen~er vehiolo.
Even if the hydraulic pump operates normally, it .
,... , . : .
.. . .
.. . . " .~ .
2~08280 inevitably allows acceleration of the output shaft as described above, which results in damage to the apparatus.
The upper limit of the allowable rotational rate of the hydraulic motor is set on the basis of working strokes of the pistons within a unit time. The rotational rate occurring when the working strokes reach a certain value is set to be the allowable rotational rate. The upper limit of the allowable rotational rate has a greater value when the swash plate angle is set to the high speed than when it is set to the low speed.
That is, where the motor of the conventional hydrostatic transmission has two, high and low, speeds, the swash plate of the motor may be rapidly changed from high speed to low speed, and the dynamic inertia of the vehicle applies an excessive load to the motor.
In one aspect, the invention provides a hydraulic propelling apparatus for a vehicle comprising: a hydraulic pump and a charge pump driven by a vehicle engine; a hydraulic motor including a swash plate having a high speed pofiition; and a swash plate low speed position, said hydraulic motor being operatively connected to a propelling transmission of the vehicle; a swash plate position switching mechanism movable between a first position corresponding to said swash plate high speed position and a second position corresponding to said swash plate low speed position: a three-position hydraulic control valve, a first oil pressure ~ ' ' ~ ' ` ' ~; 1, . ' :
s supply line connected between said charge pump and said . three-position hydraulic control valve, a second oil pressure line connected between said three-position hydraulic control valve and said swash plate position switching mechanism for conducting oil under pressure to and from said swash plate position switching mechanism; damper means comprising a throttle mechanism in said second oil pressure line between said three-position control valve and said swash plate position switching mechanism, said swash plate position switching mechanism including: a hydraulic cylinder having a hydraulic piston movable from said first position to said second position, and elastic means for urging said hydraulic piston from said second position back to said first position;
said three-position hydraulic control valve controls a supply lS oil pressure to the hydraulic cylinder for switching said swash plate from said first swash plate position to said second swash plate position, said hydraulic control valve being movable between a high speed position for supplying the hydraulic cylinder with oil pressure from said charge pump, a low speed position for connecting the hydraulic cylinder and said second oil pressure line with a supply tank, and a braking position for connecting the hydraulic cylinder, said second oil pressure line and said first oil pressure line to the supply tank: and a negative hydraulic brake connected to the first oil pressure line and a propelling system for releasing a braking condition of the propelling system.
... ~ . ................... . .. ~ .
- :: .
200~280 In a preferred embodiment of the above aspect, the hydraulic propelling apparatus further includes a one-way control valve in a third oil pressure line which bypasses said damper means which permits oil under pressure to flow from said three-position control valve to said swash plate position switching mechanism.
- 4a -.~, ~..
- , . .. . . . ..
- . ,, -- : ~. - ,: ~ , . -2~08~80 ~ he drawings show a hydraulic propelling apparatus for a vehicle according to the present invention, in which:-Fig.l is a side elevation of a wheel loader equippedwith the apparatus according to the present invention, Figs. 2A and 2B are diagrams showing hydraulic circuitry of the wheel loader, Fig.3 is a graph showing the allowable rotational rate of a hydraulic motor.
Fig. 4 is a partial diagram showing modified h~draulic circuitry, and Fig.5 is a partial diagram showing a throttle in a different embodiment.
Referring to Fig.l, a wheel loader, which is one example of vehicles, comprises a front vehicle body 2 having right and left drive wheels 1, and a rear vehicle body 4 having right and left drive wheels 3. The front and rear vehicle bodies 2 and 4 are interconnected to be pivotable relative to each other about a vertical axis Y. A steering cylinder 5 is mounted between the front and rear vehicle bodies 2 and 4.
The front vehicle body 2 carries a shovel 7 vertically movable by a pair of right and left arms 6, .
,.
. :' '' ' ' - ~
~ , ': :.
lift cylinders 8 for driving the arms 6, and a tilt cylinder 9 for driving the shovel 7. The rear body 4 carries an engine 10, a driver's seat 11, a steering wheel 12, and a drive system for transmitting power to the front and rear wheels 1 and 3.
The wheel loader includes a hydraulic system for controlling the above three types of cylinders 5, 8 and 9j and a hydraulic system for driving the wheels 1 and 3 as shown in Figs. 2A and 2B, respectively.
These hydraulic systems include a variable displacement hydraulic pump 13, a working pump 14 and a charge pump 15 driven by the engine 10. The variable displacement pump 13 supplies pressure oil through oil lines 16 to a hydraulic motor 17 having a swash plate angle switchable for two, high and low, speeds, and an output shaft 17a connected to the propelling system. The working pump 14 supplies pressure oil to a control valve 18 for controlling the steering cylinder S, a control valve 19 for controlling the tilt cylinder 9, and a control valve for controlling the lift cylinders 8. Part of pressure oil from the char8e pump lS flows to an electromagnetic valve 22 for controlling a servo cylinder 21 which adjusts the displacement of the variable displacement pump 13. Another part of the pressure oil from the charge pump 15 flows to the .., .. . . . ~ , .
,. ~ .. .
;~ :
~, ': propelling oil lines 16 as charging oil. Thef~. remaining part of the pressure oil from the charge : pump 15 flows through a switch valve 23 to a hydraulic cylinder 24 for switching the swash plate angle of the : 5 hydraulic motor 17, and to a negative brake 25 mounted in the propelling system.
The negative brake 25 is released by the pressure :~ applied by the charge pump 15, and brakes the :~. propelling system whenever the engine 10 is stopped.
A separate oil line 27 is provided so that the brake 25 is operable also by a foot pedal 26 during a run of the vehicle.
. In this wheel loader, the hydraulic pump 13 and hydraulic motor 17 constitute a stepless change speed apparatus A. One of the forward and backward traveling directions may be selected by operating a cont.ol lever 28 provided laterally of the steering wheel 12. For this purpose, a switch 29 interlocked with the control lever 28 transmits a signal to a control unit 30 for controlling the electromagnetic 3 valve 22.
The pressure oil from the charge pu~p 15 is delivered to the electromagnetic valve 22 through two oil lines 32 divided by an orifice 31, so that the amount of operation of the servo cylinder 21 increases with the rotational rate of the engine 10. The . -7-.
. .
::. . ` . .'-' ~
.
pressure oil operates the servo cylinder 21 to a position where the differential pressure due to a variation in the rotational rate of the engine 10 balances with a neutral spring 33 mounted in the servo cylinder 21.
The hydraulic cylinder 24 has a hydraulic piston 24' movable by the pressure oil supplied thereto for setting the angle of the swash plate (not shown) of the hydraulic motor 17 to the high speed, the swash plate ange being set to the low speed when the pressure oil is exhausted. An oil line 35 connected to the hydraulic cylinder 24 includes a throttle mechanism 36 for checking a sudden and rapid switching of the swash plate angle as described later.
~5 The switch valve 23 is movable to three positions, i.e. a high speed position H, a low speed position L and a parking position P.
The way in which the hydraulic circuitry of Figs.
2A and 2B operates will be described next. Assume that, when the vehicle is running with the swash plate angle of the hydraulic motor 17 set to the hi8h speed, pressure oil is exhausted from the hydraulic cylinder 24 to switch the swash plate angle of the hydraulic motor 17 to the low speed. This exhaust oil is checked by the throttle mechanism 36, and therefore the swash plate of the hydraulic motor 17 is switched .~: .
~ ~ . . .. .
200~280 to the low speed relatively slowly under the force of a spring 34. Even when this switching operation is carried out while the vehicle is running at a relatively high speed, the deceleration of the vehicle due to the oil line resistance within the stepless change speed apparatus and the mechanical resistance of the propelling system allows the switching operation to be completed smoothly without increasing the rotation of the output shaft 17a of the hydraulic motor 17 over the allowable rotational rate.
Thus, the hydraulic control system is rationally constructed for changing the swash plate angle of the hydraulic motor 17 for two, high and low, speeds.
This construction protects the hydraulic motor 17 from damage even if a change speed operation is effected through the hydraulic control system while the vehicle is running at a relatively high speed.
Fig. 3 is a graph showing the upper limit of the allowable rotational rate of the hydraulic motor 17 described with reference to the swash plate angle.
~- When, for example, the swash plate an81e is rapidly changed from a high speed position H to a low speed position L, the rotation remains below the allowable rotational rate according to the present invention as shown in a bro~en line arrow. In contrast, the rotation would exceeds the upper limit of the _g_ :. ,~ . .
... . ..
., : : ,,.: " ,,, . :: .
:~ , . : - -:
200~280 allowable rotational rate in the prior art as shown in a phanto~ line.
The described embodiment may be modified by including a check valve S0 connected parallel to the throttle mechanism 36 as shown in Fig. 4, so that the throttling action is effective only at exhaustin8 times. Further, as shown in Fig. 5, a constricted oil line portion 60 may be formed between a control spool and a land of the switch valve 23 for use as a throttle.
... .
. :
.
Claims (2)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A hydraulic propelling apparatus for a vehicle comprising:
a hydraulic pump and a charge pump driven by a vehicle engine;
a hydraulic motor including a swash plate having a high speed position; and a swash plate low speed position, said hydraulic motor being operatively connected to a propelling transmission of the vehicle;
a swash plate position switching mechanism movable between a first position corresponding to said swash plate high speed position and a second position corresponding to said swash plate low speed position;
a three-position hydraulic control valve, a first oil pressure supply line connected between said charge pump and said three-position hydraulic control valve, a second oil pressure line connected between said three-position hydraulic control valve and said swash plate position switching mechanism for conducting oil under pressure to and from said swash plate position switching mechanism;
damper means comprising a throttle mechanism in said second oil pressure line between said three-position control valve and said swash plate position switching mechanism, said swash plate position switching mechanism including:
a hydraulic cylinder having a hydraulic piston movable from said first position to said second position, and elastic means for urging said hydraulic piston from said second position back to said first position;
said three-position hydraulic control valve controls a supply oil pressure to the hydraulic cylinder for switching said swash plate from said first swash plate position to said second swash plate position, said hydraulic control valve being movable between a high speed position for supplying the hydraulic cylinder with oil pressure from said charge pump, a low speed position for connecting the hydraulic cylinder and said second oil pressure line with a supply tank, and a braking position for connecting the hydraulic cylinder, said second oil pressure line and said first oil pressure line to the supply tank; and a negative hydraulic brake connected to the first oil pressure line and a propelling system for releasing a braking condition of the propelling system.
a hydraulic pump and a charge pump driven by a vehicle engine;
a hydraulic motor including a swash plate having a high speed position; and a swash plate low speed position, said hydraulic motor being operatively connected to a propelling transmission of the vehicle;
a swash plate position switching mechanism movable between a first position corresponding to said swash plate high speed position and a second position corresponding to said swash plate low speed position;
a three-position hydraulic control valve, a first oil pressure supply line connected between said charge pump and said three-position hydraulic control valve, a second oil pressure line connected between said three-position hydraulic control valve and said swash plate position switching mechanism for conducting oil under pressure to and from said swash plate position switching mechanism;
damper means comprising a throttle mechanism in said second oil pressure line between said three-position control valve and said swash plate position switching mechanism, said swash plate position switching mechanism including:
a hydraulic cylinder having a hydraulic piston movable from said first position to said second position, and elastic means for urging said hydraulic piston from said second position back to said first position;
said three-position hydraulic control valve controls a supply oil pressure to the hydraulic cylinder for switching said swash plate from said first swash plate position to said second swash plate position, said hydraulic control valve being movable between a high speed position for supplying the hydraulic cylinder with oil pressure from said charge pump, a low speed position for connecting the hydraulic cylinder and said second oil pressure line with a supply tank, and a braking position for connecting the hydraulic cylinder, said second oil pressure line and said first oil pressure line to the supply tank; and a negative hydraulic brake connected to the first oil pressure line and a propelling system for releasing a braking condition of the propelling system.
2. A hydraulic propelling apparatus as claimed in claim 1, which includes a one-way control valve in a third oil pressure line which bypasses said damper means which permits oil under pressure to flow from said three-position control valve to said swash plate position switching mechanism.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1367989A JPH02195074A (en) | 1989-01-23 | 1989-01-23 | Hydraulic structure of vehicle |
| JP1-13679 | 1989-01-23 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2008280A1 CA2008280A1 (en) | 1990-07-23 |
| CA2008280C true CA2008280C (en) | 1993-09-21 |
Family
ID=11839873
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2008280 Expired - Fee Related CA2008280C (en) | 1989-01-23 | 1990-01-22 | Hydraulic propelling apparatus for a vehicle |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPH02195074A (en) |
| CA (1) | CA2008280C (en) |
| DE (1) | DE4001888A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19620665C1 (en) | 1996-05-22 | 1997-06-12 | Brueninghaus Hydromatik Gmbh | Hydraulic control system for dredger slewing gear |
| DE19625393A1 (en) * | 1996-05-22 | 1998-01-02 | Brueninghaus Hydromatik Gmbh | Slewing gear control with double-sided braking |
| CN115324150B (en) * | 2022-08-25 | 2023-09-05 | 江苏徐工工程机械研究院有限公司 | Control method of backhoe loader and backhoe loader |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1528473B2 (en) * | 1966-02-11 | 1974-10-17 | Linde Ag, 6200 Wiesbaden | Setting device for an adjustable hydraulic motor |
| DE2422480A1 (en) * | 1974-05-09 | 1975-11-13 | Kloeckner Humboldt Deutz Ag | Hydrostatic vehicle transmission system - has control system damper throttle bypassed by valve at low pressure |
| JPS57107666U (en) * | 1980-12-24 | 1982-07-02 | ||
| JPS58131412A (en) * | 1982-01-28 | 1983-08-05 | Hideo Nakagawa | Fluid pressure cylinder |
| JP2509884B2 (en) * | 1987-03-23 | 1996-06-26 | 油谷重工株式会社 | Travel speed switching device for hydraulic traveling vehicle |
| JPH07106690B2 (en) * | 1987-03-23 | 1995-11-15 | 油谷重工株式会社 | Travel speed switching device for hydraulic traveling vehicle |
-
1989
- 1989-01-23 JP JP1367989A patent/JPH02195074A/en active Pending
-
1990
- 1990-01-22 CA CA 2008280 patent/CA2008280C/en not_active Expired - Fee Related
- 1990-01-23 DE DE19904001888 patent/DE4001888A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02195074A (en) | 1990-08-01 |
| CA2008280A1 (en) | 1990-07-23 |
| DE4001888C2 (en) | 1993-09-02 |
| DE4001888A1 (en) | 1990-08-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |