Reduction-addition unit particularly suitable for industrial machines

Abstract: Reduction-distribution unit for gearshift units, particularly for industrial machines, comprising a first hydrostatic motor (1) and a second hydrostatic motor (2) which are operatively associated for the transmission of the motion to the axles. Said unit also comprises an epicyclic train (10) which adds the power of said hydrostatic motors (1,2), said first motor (1) being associated with the shaft (11) of the sun gear (12) and said second motor (2) being associated with the shaft (16) of the crown gear (15) of said epicyclic train (10).

Description: The present invention relates to a reduction-addition unit particularly suitable for industrial machines. As known, gearshift units are frequently used in industrial machines, for example earth-moving machines; those units are formed by a variable-displacement hydrostatic pump connected to the thermal engine and by a variable-displacement hydrostatic motor which is connected to the wheels. This known solution has the severe disadvantage of having a limit in the obtainable conversion ratio, which is approximately equal to three times, by adjusting the displacement of the pump, and to another three times by adjusting the displacement of the motor, for a total of approximately nine times. This aspect limits the maximum speed of these vehicles to approximately 18 km/h with an operating speed of approximately 2 km/h under maximum traction stress. Power-shift units with two-three speeds have been studied in order to try and obviate this limit, and ensure a working speed comprised between 2 and 10 km/h, a possible intermediate speed comprised between approximately 4 and 20 km/h and a travel speed which is comprised between 7.6 and 38 km/h. A problem shown by power-shift units mounted downstream of the hydrostatic motor is constituted by the inertia in the variation of the displacement of the pump or of the hydrostatic motor during power-shifting, which is a necessary condition in order to vary the rotation rate due to the non-compressibility of the fluid. It is therefore necessary to intervene synchronously both on the power-shift unit and on the hydrostatic unit, which must necessarily be equipped with an electronic adjustment; quality in the gear shifting step is generally unsatisfactory. As an alternative, two hydrostatic motors with conventional adding gear systems have also been used; said motors exploit the possibility of making one of the two motors run idle at high rpm, thus increasing the conversion ratio, since at low speeds both motors operate and add their torques proportionately to their displacement, distributing the flow-rate of the pump. However, the motor which is driven idle at high rpm absorbs considerable power, so that other solutions have been sought to improve the system by disconnecting the inoperative motor by means of a clutch and by locking it with a brake. All the above described solutions have however generally turned out to be complicated from a constructive point of view and to have a relatively low efficiency. EP-A-0 322 202 discloses a reduction-distribution unit as defined in the preamble of the appended claim 1. The aim of the invention is indeed to eliminate the disadvantages described above by providing a reduction-addition unit for gearshift units particularly for industrial machines which allows to obtain a very high conversion ratio without thereby having constructive complications, without requiring intervention on the adjustment of the hydrostatic units arranged upstream and thus obtaining a high quality in gear shifting without the use of modulations; this is possible since the system, during its operation, passes without discontinuities through a series of mechanical and hydraulic equilibrium conditions. Within the scope of the above described aim, a particular object of the invention is to provide a reduction-addition unit which minimizes power loss, thus obtaining a very high useful efficiency. Another object of the present invention is to provide a reduction-addition unit which, by virtue of its peculiar characteristics, is capable of giving the greatest assurances of reliability and safety in use. Not least object of the present invention is to provide a reduction-addition unit which can be easily obtained starting from commonly commercially available elements and materials and is furthermore competitive from a merely economical point of view. The above described aim, the objects mentioned and others which will become apparent hereinafter are achieved by a reduction-addition unit as defined in the appended claim 1. Further characteristics and advantages will become apparent from the dependent claims and further from the description of a preferred but not exclusive embodiment of a reduction-addition unit for gearshift units particularly for industrial machines, according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: figure 1 is a schematic sectional view of the reduction-addition unit according to the invention; figure 2 is a view of the reduction-addition unit with a different structural configuration. With reference to the above figures, and in particular to figure 1, the reduction-addition unit for gearshift units of industrial machines, particularly for earth-moving machines, comprises a first hydrostatic motor 1 and a second hydrostatic motor 2 which are operatively associated with an epicyclic train, which is generally indicated by the reference numeral 10, and is operatively associated with the axles for the transmission of the motion by means of the gear 4. An epicyclic train 10 is interposed between the first motor 1 and the second motor 2, adds the power of the hydrostatic motors and has a first shaft 11 to which the sun gear 12, associated with the first motor 1, is connected. The outer crown gear 15 of the epicyclic train is associated with a second shaft 16 which is operatively associated with the second hydrostatic motor 2. The epicyclic train furthermore comprises a plurality of planet gears 20 which mesh with the internal set of teeth of the crown gear 15 and are rotatably supported by a spider 21 on which a transmission gear 22 is keyed; said gear 22 meshes with the gear 4 which transmits the motion to the axle. To the above it should also be added that a first brake 30 is associated at the first shaft 11 and a second brake 31 is associated at the second shaft 16. The reduction-addition unit thus provided has a fundamental ratio τo which is advantageously comprised between -54 and -1, so as to operate as high-ratio (1-τo) reduction unit when, in a first step, only the hydrostatic motor associated with the sun gear rotates while the outer crown gear is locked by the second brake 31 associated with the second shaft and the output is connected to the gear 4. The condition of maximum torque in output is obtained when the variable-displacement pump delivers the maximum allowed pressure and the hydrostatic motor operates at maximum displacement. The first step of conversion is obtained, as in conventional cases, by reducing by approximately three times the displacement of the motor associated with the sun gear (vehicle speed between 2 and 5.5 km/h). Adjustment stops when the torque of the first hydrostatic motor in operation is such as to obtain the equilibrium of the epicyclic train, since the torque of the brake is identical to that which can be delivered by the idle motor. At this point it is possible to release the brake 31 and the previously idle motor 2 accelerates while the previously running motor 1 decelerates until the same rotation rate is obtained, balancing the flow-rate of the pump between the two hydrostatic motors. The obtainment of equal speeds can be easily achieved by means of a trim adjustment of the displacement of one of the two hydrostatic motors. Such step is not essential for the proper functioning of the invention, as will be better explained hereinafter and is only cited for the sake of the completeness of the description. The second step of conversion is performed by varying the displacement of the hydrostatic pump, increasing the flow-rate and decreasing the pressure of the fluid as in a normal application. The rigid rotation of the adder epicyclic train allows a better efficiency in the central operating step which is comprised for example between 5.5 and 13 km/h. The third step begins by locking the brake 30 associated with the first motor and with the sun gear and by allowing the motor 2 connected to the crown gear to accelerate to an equal output speed. This step is then performed by reducing the displacement of the hydrostatic motor 2 associated with the crown gear by approximately three times, consequently increasing the rotation rate and therefore the speed from 13 km/h to 38 km/h. With reference to figure 2, the distribution unit comprises, besides the first hydrostatic motor 1 and the second hydrostatic motor 2, which are operatively associated with the epicyclic train which is generally indicated by the reference numeral 10 and is connected to the axles 11 for the transmission of the motion by means of the gears 4, a pair of gears 42 and 43 which are interposed between the first motor 1 and the shaft 11 and a second pair of gears 40, 41 which is interposed between the motor 2 and the shaft 16. The function of the gears 40, 41, 42, 43 is to allow to vary the dimensions of the applied motors and the obtainable overall conversion ratio without modifying the epicyclic train 10 which adds the power of the hydrostatic motors. The disengageable coupling for forward traction 50 and the emergency steering pump 51 do not constitute an essential element of the invention and are illustrated only for the sake of the completeness of the configuration. Assuming a maximum vehicle speed equal to 38,18 Km/h (40 + 5% Km/h - 10% regulator) and a minimum work speed of 2 Km/h (typical for loading shovels) the total conversion ratio (t.c.r.) is 38,18/2 = 19,09. A more general diagram may be where t A and t B are the gear ratios of the kinematic chains generic for i-ratios interposed between the motors A and B, t epc is the gear ratio of the adder epicyclic train, t Aepc is the total gear ratio relative to motor A, t Bepc is the total gear ratio relative to motor B. Assuming that the two hydrostatic motors (A and B) are equal and c is the conversion ratio of the motor, the equilibrium equations of the transmission in the various operating stages from the condition of maximum speed could be written: where A' and B' are the maximum displacements of motors A and B, expressed in cm³/rotation and where t i is the gear ratio in the i-th speed. Considering three particular cases to exemplify the possibilities of the invention: case 1) motor A directly connected to the sun gear of the epicyclic reduction unit motor B directly connected to the crown gear of the epicyclic reduction unit thence t A = t B = 1 supposing the adjustment of the pump and of the motors constant and equal to c, it is obtained that We could then write now, indicating by 1 the crown gear, 2 the sun gear, 3 the spider and M₁, M₂, M₃ the corresponding acting torques, it is obtained that where t o is the basic ratio of the epicycloid and then we could write This value could be suitably approximated with an epicycloid with the following characteristics: crown gear Z = 59 sun gear Z = 22 planetary gear Z = 17 which gives a t o = -2,6818. case 2) Motor A directly connected to the sun gear of the epicyclic reduction unit Motor B connected to the crown gear of the epicyclic reduction unit through a two-speed gearshift supposing the adjustment of the pump and of the motors constant to c it is obtained that We could then write t A * t Bepc = t IIB * t Bepc * c and t IB * t Bepc = t IIB * t Bepc *c² from which assuming for t o the value previously obtained t o = -2,6818 it is obtained choosing thereafter t A = 1,033 (Z 31/30) the two ratios t IB = 5,792665 t IIB = 1,32575 are obtained. The system configuration will then be the following case 3) Motor A connected to the sun gear of the epicyclic reduction unit through a two-speed gearshift Motor B connected to the crown gear of the epicyclic reduction unit through a two-speed gearshift supposing the adjustment of the pump and motors constant and equal to c, it is obtained that We could then write the equilibrium equations t IIA * t Aepc = t IIB * t Bepc * c t IB = t IIB * c² t IA = t IIA * c² t IA * t Aepc = t IIB * t Bepc * c³ from which t IIA = 1,⊘33 t IIB = 1,5364 t IA = 3,3617 t IB = 5 and the system configuration will be Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: Reduction-addition unit for gearshift units, particularly for industrial machines, comprising a first hydrostatic motor (1,A) and a second hydrostatic motor (2,B) which are operatively associated for the transmission of the motion to axles, whereby said unit comprises an epicyclic train (10) with a sun gear (12), a crown gear (15), and a spider, each having a shaft (11,16,21), whereby said epicyclic train (10) adds the power of said hydrostatic motors (1,2), said first motor (1,A) is associated with the shaft (11) of the sun gear (12) and said second motor (2, B) is associated with the shaft (16) of the crown gear (15) of said epicyclic train 10, while the power is transmitted to the axles by the shaft (21) of the spider of said epicyclic train, and wherein said shaft (16) of the crown gear (15) is associated with a brake (31), characterized in that it comprises a further brake (30) associated with said shaft (11) of the sun gear (12). Reduction-addition unit according to claim 1, characterized in that it comprises conventional trains (40,41,42,43) interposed between said motors (1,A;2,B) and the shafts (11,16) for connection to said epicyclic train (10), for the adaptation of hydrostatic motors (1,A;2,B) with different characteristics without varying the equilibrium of said epicyclic train (10). Reduction-addition unit according to claim 1, characterized in that it comprises simple and/or multiple friction clutches between said motors (1,A;2,B) and the shafts for connection to said epicyclic train (10). Reduction-addition unit according to claim 1, characterized in that it comprises between said first motor (1,A) and the shaft (11) for connection to the sun gear (12) of the adder epicyclic train (10) a two- or more-speed gearshift. Reduction-addition unit according to claim 1 or claim 4, characterized in that it comprises between said second motor (2,B) and the shaft (16) for connection to the crown gear (15) of the adder epicyclic train (10) a two- or more-speed gearshift.

Inventors: HURTH FRITZ CARL ANTON, HURTH, FRITZ CARL ANTON
Applicants: CLARK HURTH COMPONENTS SPA, CLARK-HURTH COMPONENTS S.P.A.
Application year: 1991
Main classification: F16H47
IPC codes: F16H47, F16H37