Patent Application
20060278459
1. Field of the Invention
The present invention relates to a hydraulically driven vehicle.
2. Related Art
Conventionally, as disclosed in International Publication WO 2004/062956, there is a well-known hydraulically driven vehicle having a main transaxle and an auxiliary transaxle. The main transaxle supports main drive wheels, and comprises a hydraulic motor for driving the main drive wheels. The auxiliary transaxle supports a pair of auxiliary drive wheels, and comprises a pair of hydraulic motors for driving the respective auxiliary drive wheels. The vehicle has a hydraulic circuit fluidly connecting the hydraulic motors of the main and auxiliary transaxles to a hydraulic pump. In the hydraulic circuit, the hydraulic motor of the main transaxle and the pair of hydraulic motors of the auxiliary transaxle are connected in series to the hydraulic pump, and the hydraulic motors of the auxiliary transaxle are connected to the hydraulic pump in parallel to each other.
The left and right auxiliary drive wheels are steerable wheels. Both of the hydraulic motors of the auxiliary transaxle are variable in displacement so as to prevent drag of the steerable wheels or the main drive wheels. The hydraulic motors of the auxiliary transaxle are provided with respective movable swash plates moved according to steering operation of the vehicle, or according to change of left or right turning angle of the steerable wheels, so as to change rotary speed of the steerable wheels, i.e., generate difference between the main drive wheels and the auxiliary drive wheels, according to change of the left or right turning angle of the vehicle. However, the link mechanism for moving the two movable swash plates according to the turning of the steerable wheels is complicated, and expanded so as to reduce spaces for other parts. Further, the link mechanism requires a large operation force because of its small operational efficiency.
Further, the conventional main drive wheels are unsteerable wheels, which restrict reduction of the turning radius of the vehicle relative to the steering operation degree (i.e., improvement of replication of reduction of the turning radius of the vehicle to the steering operation).
An object of the present invention is to provide a hydraulically driven vehicle, in which a hydrostatic transaxle, supporting a pair of left and right steerable drive wheels and comprising a pair of hydraulic motors for driving the respective drive wheels, is provided with a simple and compact link mechanism for controlling displacement of the hydraulic motors during turning of a vehicle, and the turning radius of the vehicle relative to the steering operation can be further reduced.
To achieve the object, a hydraulically driven vehicle according to the present comprises a first transaxle, a second transaxle and a common hydraulic pressure source. The first transaxle includes a first transaxle casing, a pair of left and right first axles disposed in the first transaxle casing, a first hydraulic motor disposed in the first transaxle so as to drive the first axles, and a pair of left and right first drive wheels steerably disposed on left and right distal ends of the first transaxle casing and drivingly connected to the respective first axles. The second transaxle includes a second transaxle casing, a pair of left and right second axles disposed in the transaxle casing, a second fixed displacement hydraulic motor disposed in the second transaxle casing so as to drive one of the second axles, a third variable displacement hydraulic motor disposed in the second transaxle casing so as to drive the other second axle, and a pair of left and right second drive wheels steerably disposed on left and right distal sides of the second transaxle casing and drivingly connected to the respective second axles. A displacement of the third hydraulic motor is changed according to change of steered angles of the second drive wheels. The common hydraulic pressure source is provided for the first, second and third hydraulic motors. The first hydraulic motor and the pair of second and third hydraulic motors are fluidly connected in series to the hydraulic pressure source. The second hydraulic motor and the third hydraulic motor are fluidly connected in parallel to the hydraulic pressure source.
Therefore, the change of steered angles of the second drive wheels does not have to be transmitted to a fixed swash plate or another fixed displacement-setting member of the fixed displacement second hydraulic motor. Therefore, a link mechanism for moving a movable swash plate or another variable displacement-setting member of the variable displacement third hydraulic motor according to change of turning angle of the vehicle can be simple and compact in comparison with the conventional type transaxle having a pair of variable displacement hydraulic motors, thereby expanding a space around the hydrostatic transaxle for arrangement of other members, and increasing variation of layout in the vehicle. Further, when the displacement of the third hydraulic motor is reduced during turning of the vehicle so as to increase peripheral speed of the second drive wheel driven by the variable displacement third hydraulic motor, peripheral speed of the drive wheel driven by the fixed displacement second hydraulic motor is also increased according to the increase of peripheral speed of the second drive wheel driven by the third hydraulic motor so as to ensure smooth turning of the vehicle without drag of the drive wheels while keeping proper driving force. Further, in the first transaxle, the first drive wheels are also steerably disposed on left and right distal ends of first transaxle casing, thereby further reducing the turning radius of the vehicle relative to the steering operation degree, i.e., improving replication of reduction of the turning radius of the vehicle to the steering operation.
Preferably, the first transaxle casing is pivoted onto a vehicle frame so as to be horizontally rotatable, and wherein the left and right first drive wheels are unsteerably connected to the respective first axles.
Therefore, the left and right first drive wheels are assembled into the first transaxle without a complicated mechanism for making the first drive wheels steerable, thereby facilitating assembly.
Preferably, a pair of left and right steerable casings are relatively horizontally rotatably attached onto respective left and right ends of the first transaxle casing so as to support the respective first drive wheels, thereby making the first drive wheels steerable. A rotary member is pivoted on the first transaxle casing so as to be connected to a steering actuator. Each of a pair of link members is pivotally interposed between the rotary member and each of the steerable casings.
Therefore, in comparison with a space adjacent to the conventional transaxle supporting steerable wheels occupied by a tie rod connecting the left and right steerable casings, the major of a space adjacent to the present first transaxle with the above steering mechanism can be freely opened for transmission means such as hydraulic piping or a transmission shaft, or for another device or member, thereby expanding variation of layout and improving facility of assembly and maintenance.
Preferably, a pair of left and right steerable casings are relatively horizontally rotatably attached onto respective left and right ends of the second transaxle casing so as to support the respective second drive wheels, thereby making the second drive wheels steerable. The third hydraulic motor is provided with a displacement control section for controlling displacement of the third hydraulic motor. The displacement control section is connected to a link member extended from one of the steerable casings so as to enable the change of displacement of the third hydraulic motor according to change of steered angles of the second drive wheels.
Since the displacement control section changes the displacement of the third hydraulic motor correspondingly to the change of steered angles of the second drive wheels, the link member does not have to be extended adjacent to the steerable casing supporting the second drive wheel driven by the second hydraulic motor, thereby ensuring a large space for arrangement of another member (such as a steering actuator connected to this steerable casing or suction-and-delivery ports for fluidly connecting the second and third hydraulic motors to the hydraulic pressure source).
These, further and other objects, features and advantages will appear more fully from the following description with reference to accompanying drawings.
Referring to
An engine 10 is vibro-isolatingly supported on a front upper portion of vehicle frame 3 via vibro-isolating rubbers or the like, and covered with a bonnet 11. A steering wheel 12 is extended upwardly rearward at a rear end of bonnet 11, and a speed change pedal 13 is disposed at the bottom portion of the rear end of bonnet 11. Speed change pedal 13 is shaped like a seesaw such as to have a front portion depressed for setting forward traveling speed and a rear portion depressed for setting backward traveling speed. Speed change pedal 13 is linked to a speed change lever 14 pivoted on a casing of rear transaxle 1. A rear cover 15 is mounted on a rear upper portion of vehicle frame 3. A reservoir tank 28 is disposed in rear cover 15. A driver's seat 16 is mounted on rear cover 15.
Engine 10 has a downwardly vertical output shaft 10a on which pulleys 10b and 10c are fixed. An input shaft 17 (serving as a pump shaft of a later-discussed hydraulic pump P) projects upward from the casing of rear transaxle 1. A belt 18 is interposed between a pulley 17a fixed on input shaft 17 and pulley 10b on engine output shaft 10a, so as to drivingly connect hydraulic pump P in rear transaxle 1 to engine 10. Further, a cooling fan 17b is fixed on input shaft 17 so as to blow cooling air to the casing of rear transaxle 1.
A mower 20 is vertically movably suspended below vehicle frame 3 between front wheels 7 and rear wheels 9. An input pulley 20b is disposed on a top of mower 20. A belt 19 is interposed between pulley 10c on engine output shaft 10a and input pulley 20b so as to drivingly connect a rotary blade 20a in mower 20 to engine 10.
Hydraulic pump P, and hydraulic motor M1 for driving rear wheels 7 (axles 6) are disposed in the casing of rear transaxle 1. On the other hand, a pair of hydraulic motors M2 and M3 for driving respective left and right front wheels 9 (axles 8) are disposed in a casing of front transaxle 2. HST fluid pipes 23 and 26 including respective intermediate flexible hydraulic fluid hoses 23a and 26a are interposed between the casings of front and rear transaxles 1 and 2 so as to constitute an HST circuit HC1 including hydraulic pump P and hydraulic motors M1, M2 and M3.
HST circuit HC1 will be described with reference to
In the casing of rear transaxle 1, a fluid passage 21 is interposed between hydraulic pump P and hydraulic motor M1, a fluid passage 27 is interposed between hydraulic pump P and port 1b, and a fluid passage 22 is interposed between hydraulic motor M1 and port 1a.
In the casing of front transaxle 2, hydraulic motor M2 is fixed in displacement, and hydraulic motor M3 is variable in displacement. In the casing of front transaxle 2, a fluid passage 24 is extended from port 2a toward hydraulic motors M2 and M3, and a fluid passage 25 is extended from port 2b toward hydraulic motors M2 and M3. Fluid passage 24 bifurcates into a fluid passage 24a connected to hydraulic motor M2 and a fluid passage 24b connected to hydraulic motor M3. Fluid passage 25 bifurcates into a fluid passage 25a connected to hydraulic motor M2 and a fluid passage 25b connected to hydraulic motor M3.
In HST circuit HC1, hydraulic motor M1 of rear transaxle 1 and the pair of hydraulic motors M2 and M3 of front transaxle 2 are connected in series to hydraulic pump P. Hydraulic motors M2 and M3 in front transaxle 2 are fluidly connected to hydraulic pump P in parallel to each other so as to be rotatable relative to each other according to conditions of load or the like.
In HST circuit HC1, during forward traveling of the vehicle, fluid delivered from hydraulic pump P flows through fluid passage 21, hydraulic motor M1, hydraulic passage 22, port 1a, pipe 23, port 2a, fluid passage 24, the pair of hydraulic motors M2 and M3, fluid passage 25, port 2b, pipe 26, port 1b, and fluid passage 27, so as to return to hydraulic pump P. In other words, during forward traveling of the vehicle, pressurized fluid from hydraulic pump P is supplied to hydraulic motor M1 of rear transaxle 1 before the pair of hydraulic motors M2 and M3 of front transaxle 2. During backward traveling of the vehicle, the fluid circulation route in HST circuit HC1 is reversed, that is, pressurized fluid from hydraulic pump P is supplied to the pair of hydraulic motors M2 and M3 of front transaxle 2 before hydraulic motor M1 of rear transaxle 1.
Of course, forward traveling is more frequent than backward traveling. It is now assumed that the circulation route in HST circuit HC1 during each of forward and backward travels is opposite to the above-mentioned route. On the assumption, when the vehicle climbing over a step is caught on the step and front wheels 9 are stuck, hydraulic motor M1 of rear transaxle 1 cannot be supplied with fluid through hydraulic motors M2 and M3 of front transaxle 2, whereby rear wheels 7 also stop. For this reason, the vehicle may stop every time it climbs over a step. Considering this problem, actual HST circuit HC 1 is constructed as mentioned above so that fluid from hydraulic pump P is supplied to hydraulic motor M1 before hydraulic motors M2 and M3. Therefore, even if front wheels are stuck, hydraulic motor M1 is supplied with fluid from hydraulic pump P so as to drive rear wheels 7, thereby canceling the stuck condition of front wheels 9.
Additionally, a drive-mode setting valve may be interposed across pipes 23 and 26 between transaxles 1 and 2. The drive-mode setting valve is opened so as to complete connection between ports 1a and 2a and between ports 1b and 2b, thereby putting the vehicle into a four-wheel drive mode where fluid from hydraulic pump P circulates through hydraulic motors M1, M2 and M3. The drive-mode setting valve is closed so as to shut off ports 2a and 2b from ports 1a and 1b, and make a closed fluid circuit between hydraulic pump P and hydraulic motor M1 isolated from hydraulic motors M2 and M3, thereby putting the vehicle into a two-wheel drive mode where only hydraulic motor M1 is driven by fluid supplied from hydraulic pump P.
The casings of transaxles 1 and 2 are filled with fluid so as to form respective fluid sumps therein. The casing of rear transaxle 1 is provided with a drain port 1c from which a drainpipe 29 is connected to reservoir tank 28. The casing of front transaxle 2 is provided with a drain port 2c from which a drainpipe 30 is connected to reservoir tank 28. Therefore, reservoir tank 28 absorbs excessively expanded fluid in the respective fluid sumps of transaxles 1 and 2.
Rear transaxle 1 incorporates a charge pump 33 for supplying fluid to HST circuit HC1. As shown in
In the casing of rear transaxle 1, a charge fluid passage 34 is interposed between fluid passages 21 and 27 with hydraulic pump P therebetween, so as to charge fluid from charge pump 33 to hydraulically depressed one of fluid passages 21 and 27 via corresponding one of check valves 35. Charge fluid passage 34 is connected at a portion thereof between check valves 35 and 35 to a hydraulic pressure control valve 36, so as to drain excessive pressurized fluid via hydraulic pressure control valve 36 into the fluid sump in the casing of rear transaxle 1. Charge fluid passage 34 is also connected at the portion thereof between check valves 35 to suction line 31 via a check valve 39, in parallel to charge pump 33. Check valve 39 is opened when either fluid passage 21 or 27 is hydraulically depressed to open corresponding check valve 35 so as to absorb the suction port of charge pump 33 (suction line 31), thereby preventing cavitation in HST circuit HC1 during straight travel of the vehicle.
In the casing of rear transaxle 1, a differential gear unit 38 is disposed so as to differentially connect axles 6 to each other. Distal ends of axles 6 project oppositely laterally outward from the casing of rear transaxle 1 so as to be fixed to respective rear wheels 7 (alternatively, rear wheels 7 may be steerably connected to the distal ends of axles 6, as discussed later with reference to
Description will now be given on peripheral speed setting of rear wheels 7 and front wheels 9 depending on the output rotary speed setting of hydraulic motor M1 and the pair of hydraulic motors M2 and M3, and design of HST circuit HC1 in correspondence to the peripheral speed setting of wheels 7 and 9. In a general manner, hydraulic motor M1 and hydraulic motors M2 and M3 would be set in output rotary speed so as to equalize peripheral speeds of rear wheels 7 to those of front wheels 9 during straight travel of the vehicle. However, if the setting is excessively strict, peripheral speed difference between rear wheels 7 and front wheels 9 due to road conditions causes stiff travel of the vehicle. That is, on one occasion, the peripheral speeds of rear wheels 7 exceed those of front wheels 9 (i.e., the peripheral speeds of front wheels 9 become lower than those corresponding to the set output of hydraulic motors M2 and M3), so as to cause a condition where front wheels 9 rotate following rotation of rear wheels 7. On another occasion, the peripheral speeds of front wheels 9 exceed those of rear wheels 7 (i.e., the peripheral speeds of rear wheels 7 become lower than those corresponding to the set output of hydraulic motor M1), so as to cause a condition where rear wheels 7 rotate following rotation of front wheels 9.
Therefore, the output rotary speeds of hydraulic motors M1, M2 and M3 are actually set so that, during straight travel of the vehicle, peripheral speeds of rear wheels 7 strictly exceed those of front wheels 9. Due to this setting, front wheels 9 almost constantly rotate following rotation of rear wheels 7. Even if the slowing-down degree of rear wheels 7 is considerably large (the peripheral speeds of rear wheels 7 is considerably reduced to be lower than those corresponding to the set output of hydraulic motor M1), peripheral speeds of rear wheels 7 is still larger than peripheral speeds of front wheels 9, or equal to peripheral speeds of front wheels 9. Even if the reduced peripheral speeds of rear wheels 7 become lower than the peripheral speeds of front wheels 9, the major case is that the peripheral speed difference between rear wheels 7 and front wheels 9 is still small so that rear wheels 7 are rotated with a little assistance of front wheels 9, and the difference of reduced peripheral speeds of rear wheels 7 from peripheral speeds of front wheels 9 hardly becomes sincerely large. Consequently, the vehicle is substantially prevented from stiffly traveling.
However, due to the output speed setting of hydraulic motors M1, M2 and M3 for making peripheral speeds of rear wheels 7 exceed peripheral speeds of front wheels 9, i.e., for rotating front wheels 9 following rotation of rear wheels 7, hydraulic motors M2 and M3 receive opposite torque from respective axles 8 so as to act as pumps. Consequently, primary (suction) ports of hydraulic motors M2 and M3 are hydraulically depressed. This phenomenon remarkably happens during turning of the vehicle, especially during sharp turning of the vehicle, thereby causing cavitation in the HST circuit, and causing hunting of the vehicle. Therefore, HST circuit HC1 includes a check valve disposed on the suction side fluid passage of the pair of hydraulic motors M2 and M3 so as to introduce fluid from the outside of HST circuit HC1 into HST circuit HC1. During forward travel of the vehicle, the suction side fluid passage comprises fluid passages 22 to 24a and 24b between hydraulic motor M1 and the pair of hydraulic motors M2 and M3. During backward travel of the vehicle, the suction side fluid passage comprises fluid passages 21 to 25a and 25b between hydraulic motor M1 and the pair of hydraulic motors M2 and M3 through hydraulic pump P. In the embodiment of
Alternatively, check valve 40 to be opened during forward travel of the vehicle may be connected to fluid passage 24 or 24b in front transaxle 2. Alternatively, a check valve for absorbing fluid from the fluid sump in the casing of rear transaxle 1 may be connected to fluid passage 22 in rear transaxle 1 so as to have the same effect as check valve 40. On the other hand, in stead of check valve 39 in rear transaxle 1, a check valve may be connected to fluid passage 25, 25a or 25b in front transaxle 2 so as to introduce fluid from the fluid sump in the casing of front transaxle 2 to the suction side fluid passage of the pair of hydraulic motors M2 and M3 during backward travel of the vehicle.
In association with the peripheral speed setting such that peripheral speeds of rear wheels 7 exceed peripheral speeds of front wheels 9 during straight travel of the vehicle, fluid circulates in HST circuit HC1 during forward travel of the vehicle so as to flow from hydraulic pump P to the pair of hydraulic motors M2 and M3 through hydraulic motor M1. Therefore, during forward climbing a slope, rear wheels 9 can be effectively rotated for smooth climbing of the vehicle over a slope, because hydraulic motor M1 for driving rear wheels 7 weighed more than front wheels 9 is effectively supplied with fluid from hydraulic pump P before the pair of hydraulic motors M2 and M3 is supplied.
However, during forward descending a slope, front wheels 9 weighed more than rear wheels 7 require larger driving force than that for rear wheels 7. If the forward descending on a slope is more important than the forward ascending on a slope, the circulation route in HST circuit HC1 may be reversed so that, during forward travel of the vehicle, fluid from hydraulic pump P is supplied to hydraulic motor M1 through the pair of hydraulic motors M2 and M3.
Due to the above output setting of hydraulic motors M1, M2 and M3 and construction of HST circuit HC1, front wheels 9 receive driving forces from hydraulic motors M2 and M3 with the assistance of rotation of rear wheels 7. Therefore, the vehicle can travel straight without stiff movement, and the operation force required for steering front wheels 9 can be lightened so as to enable the vehicle to turn smoothly with the feeling of almost two-wheel drive mode travel. It may be said that acceleration of the forward wheels during turning of the vehicle is unnecessary. Due to this theory, as shown in
Referring to
Engine 10 is vibro-isolatingly supported on vehicle frame 3 via vibro-isolating rubbers or the like. Pulley 10b is fixed on output shaft 10a of engine 10. Input shaft 17 serves as the pump shaft of hydraulic pump P in the casing of pump unit 50. Input shaft 17 projects upward from a casing of pump unit 50 so as to be fixedly provided thereon with pulley 17a. Belt 18 is interposed between pulleys 10b and 17a so as to drivingly connect hydraulic pump P to engine 10. Cooling fan 17b is fixed on input shaft 17 above the casing of pump unit 50 so as to blow cooling air to the casing of pump unit 50 and reservoir tank 28 adjacent to the casing of pump unit 50. Pipes 51, 123 and 126, constituting a later-discussed HST circuit HC2, and drainpipes 52, 129 and 30 connected to reservoir tank 28 are partly disposed in an area blown by cooling wind generated from cooling fan 17b so as to enhance the effect of cooling fluid therein.
Pump unit 50 also obtains the vibro-isolating effect of engine 10 against vehicle frame 3. More specifically, pump unit 50 is vibro-isolatingly supported together with engine 10 onto vehicle frame 3. To get such vibro-isolating effect, engine output shaft 10a may be coaxially and integrally rotatably connected to input shaft 17, or single engine output shaft 10a may be extended so as to serve as input shaft 17 of pump unit 50.
Variable displacement hydraulic pump P in pump unit 50 is provided with movable swash plate Pa linked to speed change lever 14 pivoted on the casing of pump unit 50, and speed change lever 14 is linked to speed change pedal 13. By depression of speed change pedal 13, movable swash plate Pa is set in direction and angle so as to set the fluid delivery direction and amount of hydraulic pump P.
Mower 20 is disposed below vehicle frame 3 between front wheels 9 and rear wheels 7. Rotary blade 20a in mower 20 is drivingly connected to engine 10 via power transmission means, e.g., a belt transmission, such as the belt transmission of the vehicle shown in
A duct 92 is extended rearward from mower 20 so as to send grass mowed by rotary blade 20a. Rear transaxle 101 having no hydraulic pump is vertically and laterally slimed. Such rear transaxle 101 is laterally eccentrically disposed toward one of left and right sides of the vehicle (in this embodiment, leftward) so as to ensure a large space for duct 92 on the other right or left side of the vehicle (in this embodiment, right side). Therefore, duct 92 can have such a large capacity as to prevent wet grass from clogging therein.
Further, as shown in
Cooling fan 17b fixed on a bottom end of input shaft 17 of pump unit 50 blows upward cooling wind to adjoining pump unit 50 and reservoir tank 28 and fluid pipes so as to cool fluid therein. Additionally, as drawn in phantom lines, input shaft 17 may be extended upward from pump unit 50 so as to be provided thereon with another cooling fan 17b for blowing downward cooling wind. In this case, vehicle frame 3 is opened to lead the downward cooling wind to pipes.
Hydraulic motor M1 for driving rear wheels 7 (axles 6) are disposed in the casing of rear transaxle 101. On the other hand, a pair of hydraulic motors M2 and M3 for driving respective left and right front wheels 9 (axles 8) are disposed in the casing of front transaxle 2. An HST fluid pipe 51 is interposed between pump unit 50 and rear transaxle 101, an HST fluid pipe 123 between rear transaxle 101 and front transaxle 2, and an HST fluid pipe 126 between front transaxle 2 and pump unit 50, thereby constituting HST circuit HC2. Pipes 123 and 126 may be provided at intermediate portions thereof with flexible hoses, respectively, similar to fluid pipes 23 and 26 including flexible hoses 23a and 26a in the vehicle according to the first embodiment as shown in
HST circuit HC2 will be described with reference to
In the casing of pump unit 50 incorporates common hydraulic pump P for supplying fluid to hydraulic motors M1, M2 and M3. In the casing of pump unit 50, a fluid passage 121a is extended from hydraulic pump P to port 50a, and a fluid passage 127 from hydraulic pump P to port 50b. In the casing of rear transaxle 101, a fluid passage 121b is extended from hydraulic motor M1 to port 101a, and a fluid passage 122 from hydraulic motor M1 to port 101b. Fluid passages 121a and 121b and pipe 51 constitute a fluid passage 121 between hydraulic pump P and hydraulic motor M1.
Similar to front transaxle 2 of the vehicle shown in
In HST circuit HC2, hydraulic motor M1 of rear transaxle 101 and the pair of hydraulic motors M2 and M3 of front transaxle 2 are connected in series to hydraulic pump P. Hydraulic motors M2 and M3 in front transaxle 2 are fluidly connected to hydraulic pump P in parallel to each other.
In HST circuit HC1, during forward traveling of the vehicle, fluid delivered from hydraulic pump P flows through fluid passage 121 (i.e., fluid passage 121a, pipe 51 and fluid passage 121b), hydraulic motor M1, hydraulic passage 122, outwardly opened port 101b, pipe 123, outwardly opened port 2a, fluid passage 24, the pair of hydraulic motors M2 and M3, fluid passage 25, outwardly opened port 2b, pipe 126, outwardly opened port 50b, and fluid passage 127, so as to return to hydraulic pump P. In other words, during forward travel of the vehicle, pressurized fluid from hydraulic pump P is supplied to hydraulic motor M1 of rear transaxle 1 before the pair of hydraulic motors M2 and M3 of front transaxle 2. During backward travel of the vehicle, the fluid circulation route in HST circuit HC2 is reversed, that is, pressurized fluid from hydraulic pump P is supplied to the pair of hydraulic motors M2 and M3 of front transaxle 2 before hydraulic motor M1 of rear transaxle 1.
Such circulation route of HST circuit HC2 is set for the same reason as the circulation route setting of HST circuit HC1 of the vehicle shown in
Additionally, a drive-mode setting valve for switching drive mode of the vehicle between four-wheel drive mode and two-wheel drive mode may be interposed between hydraulic motor M1 and the pair of hydraulic motors M2 and M3 in HST circuit HC2.
The casings of pump unit 50 and transaxles 1 and 2 are filled with fluid so as to form respective fluid sumps therein. As shown in
Pump unit 50 incorporates charge pump 33 for supplying fluid to HST circuit HC2. As shown in
In the casing of pump unit 50, charge fluid passage 34 is interposed between fluid passages 121a and 127 with hydraulic pump P therebetween, so as to charge fluid from charge pump 33 to hydraulically depressed one of fluid passages 121 and 127 via corresponding one of check valves 35. Charge fluid passage 34 is connected at a portion thereof between check valves 35 and 35 to hydraulic pressure control valve 36, so as to drain excessive pressurized fluid via hydraulic pressure control valve 36 into the fluid sump in the casing of pump unit 50. Check valve 39 for preventing cavitation is interposed between charge fluid passage 34 and hydraulic pressure control valve 36 so as to bypass one of check valves 35.
Similar to rear transaxle 1 of the vehicle shown in
As the vehicle shown in
Referring to
Separated pump unit 50 and rear transaxle 101 are so compact as to be distributed on vehicle frame 3 while ensuring sufficient capacity in duct 192. In the present embodiment, pump unit 50 and reservoir tank 28 are laterally juxtaposed on vehicle frame 3 just in front of duct 192, and rear transaxle 101 is supported on vehicle frame 3 just above a fore-and-aft intermediate portion of duct 192. Cooling fan 17b fixed on a bottom end of input shaft 17 of pump unit 50 blows upward cooling wind to adjoining pump unit 50 and reservoir tank 28 and fluid pipes so as to cool fluid therein. Additionally, as drawn in phantom lines, input shaft 17 may be extended upward from pump unit 50 so as to be provided thereon with another cooling fan 17b for blowing downward cooling wind. In this case, vehicle frame 3 is opened to lead the downward cooling wind to pipes. Rear transaxle 101 may be disposed on vehicle frame 3 in front or rear of pump unit 50. Especially, as shown in
Rear transaxle 101 has left and right rear-wheel-driving output shafts 106 which are differentially connected to each other by differential gear unit 38 and extended oppositely outward from the casing of rear transaxle 1. As shown in
Left and right rear wheels 7 has respective axles 107 extended laterally proximally of the vehicle. Axles 107 are inserted into lower portions of respective chain casings 108, and sprockets 107a are fixed on the proximal ends of respective axles 107 in respective chain casings 108. In each of chain casings 108, a chain 109 is interposed between sprockets 106a and 107a so as to transmit the driving force of output shaft 106 to axle 107, thereby driving left and right rear wheels 7.
A drive system of the present vehicle is represented by the description of drive system of the vehicle according to the second embodiment with reference to
Front transaxle 2 incorporating fixed displacement hydraulic motor M2 and variable displacement hydraulic motor M3 will be described with reference to
Referring to a casing structure of front transaxle 2, as shown in FIGS. 10 to 12, a motor casing 201 is disposed between left and right axle casings 203, and detachably attached to each axle casing 203. Axle casings 203 incorporate respective axles 8. A spacer may be interposed between motor casing 201 and any of axle casings 203, if a tread between front wheels 9 has to be lengthened. Kingpin casings 204 are fixed on distal ends of respective axle casings 203, extended laterally outwardly downward at kingpin angles, and inserted into respective steerable casings 205. Steerable casings 205 are rotatable centered on the axes of respective kingpin casings 204.
As shown in
The motor assembly will be described with reference to
As best shown in
As shown in
To fix the motor assembly to an inside (front) surface of motor cover 202, as best shown in
As best shown in
Motor cover 202 with the motor assembly in motor casing 201 is fixedly provided with a pipe coupling block 70 on the rear surface thereof just in rear of center section 60. Pipe coupling block 70 is bored by fluid passages 70c and 70d, which are opened to respective fluid passages 60a and 60b via respective fluid passages 202a and 202b penetrating motor cover 202. Pipe couplings 70a and 70b are disposed at outer ends of respective fluid passages 70c and 70d, and project outward from pipe coupling block 70. Pipe couplings 70a and 70b serve as fluid ports 2a and 2b of each of HST circuits HC1 and HC2 shown in
In comparison with the case where pipe couplings 70a and 70b are directly attached to motor cover 202, pipe coupling block 70 with pipe couplings 70a and 70b is advantageous in increasing angle variation of pipe couplings 70a and 70b relative to fluid passages 60a and 60b and the like serving as fluid passages 24 and 25. Therefore, pipe coupling block 70 with pipe couplings 70a and 70b can be designed so that angles of pipes 23 (or 123) and 26 (or 126) coupled to respective pipe couplings 70a and 70b are optimized in relation to a later-discussed linkage for controlling the swash plate of hydraulic motor M3.
Alternatively, pipe coupling block 70 may be separated from motor cover 202 and supported on vehicle frame 3 or the like, so as to have pipes between pipe coupling block 70 and motor cover 202.
As shown in
As shown in
The linkage for controlling the displacement of hydraulic motor M3 will be described. As shown in
As shown in
As shown in
Pressure plate 78 is fastened to outer arm 77 so as to be shiftable relative to outer arm 77, so that, when cam plate 81 is disposed at the initial position, the bottom edge of pressure plate 78 is disposed horizontally to abut against the upper edge of cam plate 81 regardless of the initial position of swash plate pivot shaft 73 with inner and outer arms 74 and 77 adjusted by stopper pin 76. In this regard, outer arm 77 is bored by a pair of bolt holes. One of the bolt holes is disposed toward a tip of outer arm 77, and the other toward a basal end of outer arm 77. As shown in
Cam plate 81 is extended downward from camshaft 80. An acceleration rod 82 is pivotally connected at one end thereof to a bottom end of downwardly extended cam plate 81. Acceleration rod 82 is pivoted at the other end thereof onto one of left and right steerable casings 205. Preferably, the other end of acceleration rod 82 is pivoted onto a pivot pin 83 (as best shown in
As shown in
In this way, the cam system including cam plate 81 and pressure plate 78 abutting against each other, and arms 77 and 74 connected to pressure plate 78 so as to rotate integrally with movable swash plate 67 constitute the linkage for moving swash plate 67 of hydraulic motor M3 according to lateral rotation of steerable casings 205 during turning of the vehicle. The linkage is disposed on the outer surface of motor cover 202 in rear of variable displacement hydraulic motor M3. Pipe coupling block 70 is disposed on the outer surface of motor cover 202 in rear of the portion between hydraulic motors M2 and M3 adjacent to the linkage.
It is now assumed that both the hydraulic motors in front transaxle 2 are variable displacement hydraulic motors M3. The linkage must have a cam system for converting the push-and-pull movement of a rod for the lateral rotation of steerable casings 205 into rotation of movable swash plates 67 of both hydraulic motors M3. Therefore, the linkage must be complicated and large so as to substantially entirely cover the outer surface of motor cover 202 (the rear surface of front transaxle 2) in the left-and-right direction. Accordingly, a port member having ports for fluidly connecting both hydraulic motors M3 to hydraulic pump P and motor M1 (such as pipe coupling block 70) has to be disposed on a surface of rear transaxle 2, which is different from the outer surface of motor cover 202. For instance, the port member has to be attached to the front surface of front transaxle 2 opposite to the outer surface of motor cover 202. Pipes to be connected to the port member have to be extended along or beyond motor casing 201.
However, in front transaxle 2 of the present embodiment, one of the pair of hydraulic motors therein is fixed displacement hydraulic motor M2. The linkage for angle controlling of movable swash plate 67 does not have to be disposed on the outer (rear) surface of motor cover 202 in rear of hydraulic motor M2 or in rear of the portion between hydraulic motors M2 and M3, thereby ensuring a space in rear of the rear surface of front transaxle 2 for attaching pipe coupling block 70 and drain pipe coupling 71. Due to pipe coupling block 70 disposed at this position, pipes connected to front transaxle 2 from rear transaxle 1 (or from pump unit 50 and front transaxle 101) are streamlined so as to increase fluid circulation efficiency, and to reduce interference thereof with other parts or members.
A drive train from each motor shaft 61 to corresponding front wheel 9 will be described. As shown in
As best shown in
A top opening of kingpin casing 204 facing the inner space of kingpin casing 204, in which meshing bevel gears 86a and 87a are disposed, is wide so as to be adapted for economically forming kingpin casing 204 by die casting. Further, the wide opening facilitates easy and accurate forming of bearing grooves in the inner wall surface of kingpin casing 204. The opening is closed by a grommet after the bevel gears and others are completely disposed in kingpin casing 204.
The downwardly extended portion of kingpin casing 204 is inserted into steerable casing 205. Steerable casing 205 relatively rotatably supports the downwardly extended portion of kingpin casing 204 therein with bearings. In other words, steerable casing 205 is laterally rotatable around kingpin casing 204. Kingpin center shaft 87 is extended downward from a bottom end of kingpin casing 204, and fixedly provided on a bottom end thereof with a bevel gear 87b in steerable casing 205 below kingpin casing 204. Bevel gear 87b is journalled by a bottom portion of steerable casing 205.
A bearing cover support portion 205a is formed on a lateral distal end of steerable casing 205 so as to journal a proximal end of a center axis shaft 9a of front wheel 9 in a center hole thereof. A diametrically large bevel gear 89 is fixed on center axis shaft 9a and meshes with bevel gear 87b. A bearing cover 206 is fastened to bearing cover support portion 205a so as to cover bevel gear 89. Center axis shaft 9a is extended distally outward from bevel gear 89 so as to be pivoted onto bearing cover 206 via bearings, and further extended distally outward from bearing cover 206 so as to be connected at a distal end thereof to front wheel 9.
In this way, front wheels 8 can be steered by rotating steerable casing 205 around kingpin casing 204 while receiving the output force of respective hydraulic motors M2 and M3 through respective motor shafts 61, axles 8 and kingpin center shafts 87.
As mentioned above, the entire casing of front transaxle 2 is formed by joining motor casing 201 (with motor cover 202), left and right axle casings 203, kingpin casings 204, steerable casings 205 and bearing covers 206 to one another. A bearing for journalling a shaft is disposed at a junction between any adjoining casings of rear transaxle 2. The bearing is provided with no oil seal. In this regard, lube (also used as operation fluid for the HST) filled in motor casing 201, axle casings 203, kingpin casings 204, steerable casings 205 and bearing covers 206 can freely pass among these casings and covers. The costs for oil seals are saved. Oiling ports to fill entire front transaxle 2 with fluid (lube) can be reduced, and even only a single oiling port can be provided. Further, the total amount of fluid and the total surface area of hydraulic devices are increased so as to suppress heating of the hydraulic devices, thereby improving the hydraulic devices in endurance and mechanical efficiency.
The linkage from steering wheel 12 to steerable casing 205 will be described with reference to
As best shown in
Referring to
Some different designed center pin brackets 200 are prepared, and one corresponding to relative pivot positions of front transaxle 2 in a vehicle is selected to be fastened to stays 201a of motor casing 201. Therefore, front transaxle 2 can be standardized for various designed vehicles.
Center pin 5 is journalled at front and rear ends thereof by front axle bracket 4 fixed on the front end of vehicle frame 3. Front axle bracket 4 comprises a pair of left and right vertical side plates 4a, a vertical rear plate 4b connecting side plates 4a to each other, a front plate 4c, and a horizontal plate 4d connected between rear and front plates 4b and 4c.
Each of left and right side plates 4a has bolt holes 4h bored in a rear end portion thereof. Bolts are passed through bolt holes 4h of left and right side plates 4a so as to fasten left and right side plates 4a onto front end portions of respective left and right side plate portions of vehicle frame 3, thereby fixing front axle bracket 4 onto the front end portion of vehicle frame 3. Center pin 5 passed through center pin bracket 5 is journalled at the rear end portion by rear plate 4b, and at the front end portion by front plate 4c. Therefore, front transaxle 2 is swingably supported. Flexibility of hydraulic fluid hoses 23a and 26a permits the swing of front transaxle 2.
In this state, horizontal plate 4d covers the top of motor casing 201 disposed in front of the front end of vehicle frame 3. A pair of left and right stoppers 4e are hung down from the bottom surface of horizontal plate 4d. The position where one of stoppers 4e abuts against the top of plate portion 200a of center pin bracket 200 fixed on front transaxle 2 is defined as the limit swing position of front transaxle 2 centered on center pin 5. Stoppers 4e also serve as ribs for reinforcing horizontal plate 4d.
Further, horizontal plate 4d is at a lower degree than the top of the front end of vehicle frame 3. An engine muffler 10d is mounted on horizontal plate 4d, so as to be covered at a rear portion thereof with rear plate 4b, and at left and right end portions thereof with left and right side plates 4a. In this way, a suitable space for efficient radiation of engine muffler 10d is ensured in front axle bracket 4. Further, horizontal plate 4d protects front transaxle 2 from the heat radiated from engine muffler 10d.
As shown in
A part of each side plate 4a adjacent to corresponding bonnet bracket 4f is cut off and bent laterally inward of the vehicle so as to form a spring stay 4j, onto which an end of a spring for biasing bonnet 11 to its initial closed position is connected.
As shown in
Front axle bracket 4 may be replaced with a simple vertical plate covering the front end of vehicle frame 3, if the vehicle is a two-wheel drive vehicle having no front transaxle 2 incorporating the pair of hydraulic motors.
Referring to FIGS. 21 to 23, two type rear-wheel steering systems will be described. These steering systems are applicable to the respective four-wheel drive lawn tractors according to the first embodiment shown in
Referring to the rear-wheel steering system of
Rear transaxle 101 has longer and shorter axles 6. Shorter axle 6 is extended laterally outward from the end portion of the casing of rear transaxle 101 fastened to the bottom of first end portion 222c of rear wheel support frame 222, and fixed at the distal end thereof to one rear wheel 7. Longer axle 6 is further extended laterally outward from bearing 222e, and fixed at the distal end thereof to the other rear wheel 7.
Therefore, by rotating steering wheel 12, rear wheel support frame 222 rotates integrally with rear transaxle 101, left and right axles 6 and rear wheels 7 relative to vehicle frame 3 centered on pivot shaft 221, thereby steering rear wheels 7.
A structure of rear wheel support frame 222, and a structure of the casing of rear transaxle 101 with axles 6 to be supported by rear wheel support frame 222 may be different from those shown in
Referring to the rear wheel steering system of
An upper kingpin support portion 223b and a lower kingpin support portion 223c are extended laterally outward from each rear wheel support frame 223. The distal end of each axle 6 extended outward from the casing of rear transaxle 101 is disposed between upper and lower kingpin support portions 223b and 223c. The distal end of axle 6 is connected to center axis shaft 7a of rear wheel 7 via a universal joint 6a, so that rear wheel 7 with center axis shaft 7a can be substantially horizontal relative to axle 6.
Center axis shaft 7a is journalled in a bearing block 224. An upper arm 224a is extended from an upper portion of bearing block 224 so as to be pivotally connected to upper kingpin support portion 223b via a kingpin 225. A lower arm 224b is extended from a lower portion of bearing block 224 so as to be pivotally connected to lower kingpin support portion 223c via a kingpin 226. Upper and lower kingpins 225 and 226 are disposed coaxially, and the pivot of universal joint 6a is coaxially disposed between upper and lower kingpins 225 and 226.
A tie rod (not shown) is interposed between tie rod stays 224c extended from respective upper portions of bearing blocks 224, and connected to steering wheel 12. By rotating steering wheel 12, left and right bearing blocks 224 are substantially horizontally rotated around respective kingpins 225 and 226 so as to steer left and right rear wheels 7.
The rear wheel steering system shown in
A rotary plate 230 is pivoted through a vertical pivotal shaft 230a onto a bottom portion of the casing of rear transaxle 101 at the lateral middle position between left and right drive wheels 7. As shown in
Rotary plate 230, left and right link rods 231 and left and right arms 232 connected in the above mentioned way are disposed in principle so that, in the initial state (in the straight traveling state of rear wheels 7), when viewed in plan, as shown in
An arm 230b is pivoted at one end thereof onto pivotal shaft 230a so as to be rotatable integrally with rotary plate 230. Arm 230b is extended leftward or rightward from the end thereof pivoted onto pivotal shaft 230a, and pivotally connected at a tip thereof to a tip of a piston rod 233a of a rear wheel power steering cylinder 233. Piston rod 233a of rear wheel power steering cylinder 233 is selectively extended or contracted depending on whether steering wheel 12 is rotated rightward or leftward. Due to the telescopic movement of piston rod 233a, rotary plate 230 is rotated so that the angle between link rod 231 and arm 232 on one of left and right sides is expanded so as to turn the front end of corresponding rear wheel 7 laterally outward (in
In the vehicle shown in
Other structures, including rear transaxle 101, pump unit 50 and front transaxle 2, are the same as those in each of the above-mentioned embodiments. In this regard, the casing of rear transaxle 101 incorporates hydraulic motor M1 for driving left and right axles 6. Motor casing 201 of front transaxle 2 incorporates fixed displacement hydraulic motor M2 and variable displacement hydraulic motor M3 for driving respective left and right axles 8. Hydraulic motor M1 and the pair of hydraulic motors M2 and M3 are fluidly connected in series to hydraulic pump P in pump unit 50, and hydraulic motors M2 and M3 are fluidly connected in parallel to hydraulic pump P. Alternatively, pump unit 50 and rear transaxle 101 may be replaced with rear transaxle 1 incorporating hydraulic pump P together with hydraulic motor M1, and the steering system as shown in
Incidentally, the above-mentioned casing 12b serves as a hydraulic steering device casing, in which a directive control valve 235 for supplying fluid to power steering cylinders 233 and 234, and a hydraulic motor 236 for shifting directive control valve 235 are disposed. Hydraulic motor 235 is rotated in one of opposite directions selected depending on whether steering wheel 12 is rotated leftward or rightward, so as to telescopically move piston rods 233a and 234a of respective power steering cylinders 233 and 234. Further, ports 237 and 238 are provided on casing 12b so as to supply fluid to directive control valve 235 and hydraulic motor 236, and connected to a hydraulic pressure source outside casing 12b through pipes or the like. Preferably, the hydraulic pressure source is charge pump 33 in pump unit 50.
The hydrostatic transaxle and the hydraulically driven vehicle of the present invention are applicable to various vehicles such as working vehicles including disclosed lawn tractors. The illustrated vehicles have Ackerman-type steering systems. However, the peripheral speed setting of front and rear wheels, the structure of the hydraulic pump unit separated from the front and rear transaxles, and the like are applicable to vehicles having different steering systems, such as an articulated vehicle.
It is further understood by those skilled in the art that the foregoing description is a preferred embodiment of the disclosed apparatus and that various changes and modifications may be made in the invention without departing from the spirit and scope thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-256186 | Sep 2004 | JP | national |
| 2005-23438 | Jan 2005 | JP | national |
This application is a continuation-in-part of U.S. application Ser. No. 11/214,056, filed Aug. 30, 2005, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11214056 | Aug 2005 | US |
| Child | 11449859 | Jun 2006 | US |
