DEVICE FOR CONTROLLING VARIABLE CAPACITY MOTOR OF HYDRAULIC DRIVE VEHICLE

Abstract: A device for controlling the variable capacity motor (2) incorporated in a hydraulic drive vehicle, wherein means (201) for reducing the oil pressure for controlling the motor is provided to pilot hydraulic piping (15) extending from control pump (3) for controlling the capacity of the motor (2), and change over valves (202), (203) are provided for performing changeover between operation and non-operation of said pressure reduction means (201). The above structure serves to control the minimum capacity of the variable capacity hydraulic motor while reducing the pressure of pilot oil introduced from the control pump and, when a pressure in the main circuit exceeds a preset value, the changeover valves operate even when the pressure reduction means is in operation so as to cancel such operation for continuously controlling the vehicle.

Description: TECHINICAL FIELD The present invention relates to a vehicle hydraulic drive device with the features of the first part of claim 1, which is known from GB-A-2 089 006. Further, reference is made to EP-A-0 396 781. BACKGROUND TECHNOLOGY Illustrated in Fig. 13 is a conventional hydraulic circuit of an infinite variable-speed hydraulic drive vehicle which has a variable capacity hydraulic pump and a motor. In the same figure, a part of the output of an engine 5 drives a working machine hydraulic pump 4 and acts upon a working machine hydraulic cylinder 52 by way of a working machine hydraulic circuit 51. Remaining output of the engine 5 drives the control pump 3 and a hydraulic pump 1 in which oil pressure is generated. The oil pressure thus generated at the hydraulic pump 1 flows through main circuits 24 and 25, rotates the variable capacity motor 2, thereby forming a driving force. Designated at 6 is a pump control valve for controlling the capacity of the hydraulic pump 1, 7 is a pump capacity control cylinder, 8, 8 are main relief valves and 10 is a filter. Oil under pressure, which flows from the pump control valve 6 to the motor control oil line 11, is introduced into one end of the motor control valve 14, whereby the oil introduced into the motor control valve 14 operates to introduce the oil under high pressure, which is introduced by a pilot hydraulic piping 16 from the main circuits 24 and 25, into a motor capacity control cylinder 31. That is, the pump capacity control cylinder 7 and a motor capacity control cylinder 31 are controlled by the pump control valve 6 and the motor control valve 14 so that the capacity of the pump 1 and the capacity of the hydraulic motor 2 are arbitrarily varied, thereby varying the traveling speed of the vehicle. A graph representing a traveling performance curve of the conventional hydraulic drive vehicle, as explained in Fig. 13, will be described with reference to Fig. 14. As illustrated in the same figure, in the infinite variable-speed hydraulic drive vehicle having the conventional variable capacity hydraulic motor, both the traveling driving force and the traveling speed are continuously varied so that they are automatically and continuously varied without changing operation from the maximum driving force (traveling speed is 0) to the maximum speed. Accordingly, since the driver can control the traveling speed and the driving force, it is possible to travel the vehicle easier than a vehicle provided with a mechanical speed change gear. The conventional hydraulic drive vehicle has an advantage that the traveling operation is easy. However, in the industrial vehicle provided with a loading apparatus such as a shovel loader, the working machine pump 4 of the loader is also driven by the engine in the same way as the hydraulic drive pump 1. Since the maximum rising speed of the loader is proportional to the engine speed, the rising speed of the loader is also controlled by the travel of the accelerator pedal in the same way as the traveling speed. Accordingly, in case that the hydraulic drive vehicle travels while raising the loader at the narrow working site, the working efficiency is improved, when the loader rises at the maximum speed and the vehicle travels at low speed. However, there was such a serious problem that when the loader rises at the maximum speed, the traveling speed is at the same time increases at the maximum. This problem will be described with reference to Fig. 15 which depend on the engine speed of the engine 5 Pst1'', ........ Pst5'' represent pressures of a pilot hydraulic piping 15. The relation between the capacity of the motor (horizontal axis) and the pressure P H'' (vertical axis) in the main hydraulic circuits 24 and 25 is varied by the pilot pressures Pst1'' ........ Pst5''. In case that the traveling speed is accelerated at full throttle so as to rise the loader at the maximum speed, as the pilot pressure rises to Pst1'' and thereafter the traveling load decreases, the pressure P H '' decreases as the traveling load decreases. At this time, the traveling speed increases as the capacity of the motor moves along the characteristic line of the pilot pressure and reaches the minimum. At this time, the traveling speed reaches the maximum speed, which causes the problem in the working site having small traveling range. To solve the matching problem between the traveling speed and the rising speed of the loader, the multiple speed gear change method is conventionally employed wherein the maximum traveling speed is reduced while the capacity of the motor is fixed to be the maximum or the mechanical speed change gear is connected to the motor. However, there was a problem in the former that the traveling speed is limited to the low speed since the capacity of the motor is fixed as illustrated in Fig. 16 and a problem in the latter that the device cannot match exactly with the working condition since the maximum driving force is not obtained at high range as illustrated in Fig. 17. To solve these problems, the applicant proposed a means, which disclosed in Japanese Utility Application No. JP-U-63-144985 (EP-A-396 781) and is provided with a means which is capable of operating to control the minimum capacity of the variable capacity hydraulic motor, thereby continuously controlling the maximum traveling speed in response to the oil pressure in the high pressure side of the main circuit which is connected to the variable capacity hydraulic motor of the hydraulic pump and the pilot oil pressure from the control pump which operates the motor capacity control cylinder for controlling the capacity of the variable capacity hydraulic motor. A motor control valve 14 of this device, as disclosed in Japanese Utility Model Application No. JP-U-63-144985, controls the motor control oil pressure by balancing the control oil pressure with the main circuit oil pressure, but it had the following problems. (1) The motor control oil pressure is liable to vary by the variation of the main circuit oil pressure which is caused by the control of the traveling speed. (2) A structure is complex and rather expensive. It is therefore an object of the present invention to solve these problems of the conventional device and to provide a device for controlling the variable capacity motor which is simple in structure and low in cost and has a traveling characteristic which is not influenced by the variation of the main circuit oil pressure. DISCLOSURE OF THE INVENTION To achieve the above object, the present invention provides a device with the features of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 to 5 are deleted. Fig. 6 is a hydraulic circuit diagrams according to an embodiment of the present invention, Fig. 7 is a graph showing a characteristic of a pressure control valve in Fig. 6, Fig. 8 is a graph showing a control characteristic of the variable capacity hydraulic motor of the hydraulic circuit in Fig. 6, Fig. 9 is a graph showing the control of the maximum traveling speed of the hydraulic drive vehicle employing the hydraulic circuit in Fig. 6, Figs. 10 and 11 are deleted, and Figs. 12 to 17 showing conventional device and characteristics thereof. Fig. 6 is a view showing an embodiment of the present invention. Components same as those in Fig. 13 are denoted at same numerals and the explanation thereof are omitted. A feature of this embodiment resides in adding a traveling speed cut-off device 222 to the conventional hydraulic circuit as illustrated in Fig. 13. This embodiment comprises the pilot hydraulic piping 15 which supplies the oil under pressure from the control pump 3 to the motor control valve 14, a pilot hydraulic piping 217 which extends from the pilot hydraulic piping 15 and is connected to one end of a pressure reduction type pressure control valve 219 and a pilot hydraulic piping 218 which supplies the oil under pressure from the main circuit 24 or 25 at the high pressure side to the motor control valve 14 is connected to another end of the reduction type pressure control valve 219. The pressure control valve 219 is balanced by difference between the pressure in the pilot hydraulic piping 217 and the pressure in the pilot hydraulic piping 218 and a spring 220. Resilience force of the spring 220 can be arbitrarily adjusted by a lever 221. Operations of the hydraulic circuit according to the embodiments set forth above will be described hereinaffer. Since a pressure P H of the main circuit 24 or 25 at the high pressure side (hereinafter referred to as main circuit pressure) is also applied to the pilot hydraulic piping 218, the pressure in the pilot hydraulic piping 217 is controlled by switching over the pressure regulating valve 219 to a position 219a in case the following expression is established P st · A ≦ PH · B+F while the pressure in the pilot hydraulic piping 217 is controlled by switching over the pressure regulating valve 219 to a position 219b in case the following expression is established. P st · A > P H · B+F where P st is a control pressure in the pilot hydraulic piping 217, F is a resilient force of the spring 220, B is an area of the pressure control valve 219 for receiving the pressure at the side of the pilot hydraulic piping 218, and A is an area of the pressure control valve 219 for receiving the pressure at the pilot hydraulic piping 217. A characteristic of the pressure control valve 219 is illustrated in Fig. 7. In the same figure, straight lines X₁, X₂, X₃ .... . show the characteristic when the pressure regulating valve 219 is switched over from the position 219a to the position 219b, which is continuously varied when the spring 220 is operated by the lever 221. A graph in Fig. 8 represents the relation between the main circuit pressure P H in the hydraulic circuit in Fig. 6, the capacity of the motor and the pilot pressure P st , i.e. the control characteristic of the variable capacity hydraulic motor 2 and corresponds to the graph in Fig. 15 of the conventional hydraulic circuit in Fig. 13. As evident from the graph in Fig. 8, the capacity of the motor is minimum at the matching lines Y₁, Y₂, Y₃ .... . Since the minimum capacity of the motor can be controlled arbitrarily, it is possible to control the maximum traveling speed continuously between Z₁ to Z₇ as illustrated in Fig. 9. INDUSTRIAL UTILIZATION The following conspicuous effects can be obtained by the present invention having the arrangement as set forth above in detail. (1) Since the traveling speed alone can be arbitrarily regulated while the traveling performance, which is the feature of the infinite variable-speed hydraulic drive vehicle, is maintained, it is possible to obtain the optimum speed for the working condition, thereby remarkably improving the matching between the loading or working speed and the traveling speed. (2) When the traveling speed is slower than the controlled speed according to the speed control means of the present invention, it is possible to obtain the same traveling performance as that which is obtained when the traveling speed is not controlled, hence the traveling performance is not influenced by the variation of the main circuit pressure. (3) Since the pressure reduction means for reducing the control pressure for determining the traveling speed and the changeover means for switching over the pressure reduction means by the main circuit pressure (or traveling speed) are separately provided, it is possible to structure the present device by the existing devices, which can be realized at relatively low cost and can be adjusted with ease. In case that pressure reduction type pressure control valve is provided in series in the motor control circuit, when the pressure regulating valve is positioned at the position 219b (when pressure is reduced), it is possible to lessen the pressure reduction in the upstream circuit, which dispenses with a fixed orifice, thereby improving a response of the variation of the capacity of the motor relative to the variation of the motor control pressure. As mentioned above, according to the present invention, the matching between the traveling speed and the loading speed are suitably made under the working condition. The traveling performance is not influenced by the variation of the main circuit pressure, hence is suitably employed in the device for controlling variable capacity motor of hydraulic drive vehicle , the maximum traveling speed of which should be controlled in response to the working condition.

Claims: A vehicle hydraulic drive device having a variable capacity hydraulic drive pump (1) driven from an engine (5), a variable capacity hydraulic motor (2) driven from the hydraulic drive pump (1), a main fluid supply circuit (24, 25) connected between the drive pump (1) and the motor (2) for supplying pressure fluid to the motor (2) to effect driving thereof, pump control valve means (6) for controlling the capacity of the drive pump (1), a control pump (3) driven from the engine (5) and having a fluid pressure outlet communicating with said pump control valve means (6), fluid pressure cylinder means (31) coupled to said motor (2) for varying the capacity thereof, motor control valve means (14) for controlling flow of pressure fluid from said main circuit (11) to said cylinder means (31) to control activation thereof, a pilot pressure conduit (15) connected to said motor control valve means (14) for supplying pilot pressure fluid from said control pump (3) to a pilot of said motor control valve means (14) to control shifting thereof, and a fluid flow cut-off valve means (222) connected in series with said pilot pressure conduit (15) to open and close said pilot pressure conduit (15) for controlling flow of pilot pressure fluid to a pilot of said motor control valve means (222), and pilot control conduit (218) connected between a first pilot of said cut-off valve means (222) and said main circuit (24, 25) for supplying pressure fluid therethrough for controlling said cut-off valve means (222), characterized in that said cut-off valve means (222) is a pressure reduction-type pressure valve having said control conduit (218) connected to a first said pilot at one end thereof, and said pilot pressure conduit (11) downstream of said pressure valve (219) having a pilot conduit portion connected to a second pilot at the other end of said pressure valve (219). A device according to Claim 1, including a solenoid actuated changeover valve (219) associated with said pilot conduit portion for controlling flow of pressure fluid therethrough. A device according to Claim 1 or 2, including adjustable biasing means (220) for normally urging the pressure valve (219) into an open position wherein upstream and downstream portions of said pilot pressure conduit (11) are in fluid communication with one another.

Inventors: IKARI MASANOR KOMATSU MEC KABU, IKARI, MASANOR KOMATSU MEC KABUSHIKI KAISHA
Applicants: KOMATSU MEC CORP, KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO, KOMATSU MEC CORPORATION
Application year: 1990
Main classification: F16H61
IPC codes: F16H61