VARIABLE CAPACITY PUMP CONTROLLER OF HYDRAULICALLY DRIVEN WHEEL

Abstract: This invention relates to a variable capacity pump controller for an industrial vehicle such as a shovel loader using a static hydraulic driving system. In a hydraulically driven vehicle equipped with a variable capacity hydraulic pump (P), the controller of the invention includes variable throttle devices (11, 13), (21, 24), (31, 35), (41, 46) which are disposed in pilot hydraulic circuits (10, 12), (20, 22), (30, 32), (40, 42) of a pump capacity control cylinder (C) for controlling the capacity of a variable capacity hydraulic pump (P) and operate in such a manner as to change the operation speed of the pump capacity control cylinder (C) in accordance with the oil pressure of a main hydraulic circuit (S). According to this construction, the variable throttle device operates in such a manner as to open a check valve or a throttle valve in the pilot circuit of the pump capacity control cylinder when the hydraulic driving main circuit is at a high pressure. Therefore, a return hydraulic circuit of the pump control cylinder is expanded to speed up the reducing speed of the pump capacity and to prevent an excessive torque to an engine.

Description: TECHNICAL FIELD The present invention relates to a control system for a variable capacity pump in a hydrostatic drive for a vehicle according to the preamble of claim 1. Variable capacity pump controllers of hydraulically driven wheels are adapted for controlling a variable capacity hydraulic pump adapted for increasing and decreasing the rpm's of an engine of a vehicle in accordance with a driving load in an industrial vehicle such as a shovel loader using a static hydraulic driving system. A control system for a variable capacity pump according to the preamble of claim 1 is already disclosed in FR-A-2 231 537 in which a pilot pump is unloaded or escaped to a tank when the oil pressure of a main hydraulic circuit becomes high to thereby decrease pump capacity. This circuit constitutes simply an unload circuit. That is, when oil pressure of a main hydraulic circuit becomes high, oil from the pilot pump is escaped to a tank by switching a selector valve 34. However, this does not take into account that a transition is comparatively slow, so that a sharp increase of driving load is not followed by a sharp reduction of speed of the pump capacity in the embodiment of FR-A-2 231 537. Consequently the rpm's of the engine decrease significantly in this short time. In another document, GB-A-1 415 977, the rapid change in the output flow rate of a variable capacity pump is to be smoothened out, moderated, so that completely non-jerky transition is possible. This prolongs the answering time of the system. Fig. 7 and 8 are views explaining systems of a conventional variable capacity pump controller of a hydraulically driven wheel. In Fig. 7, a variable capacity control cylinder C for controlling a variable capacity hydraulic pump P (hereinafter referred to as variable pump) has a pilot circuit a provided with a throttle valve b wherein the operation speed of the pump capacity control cylinder C can be changed at the same speed in both directions to increase and reduce the pump capacity. Designated at E is an engine, A is a control pump, V is a control valve, K is a charge circuit, M is a motor and S is a main circuit. In Fig. 8, a pilot circuit a includes a one way throttle valve d composed of a throttle valve d 1 and a check valve d 2 in which a pressurized oil flows through the check valve d 2 in the direction to increase the pump capacity while pressurized oil flows through the throttle valve d 1 , in the direction to decrease the capacity whereby travelling performance and stability of the vehicle and compatible with each other by increasing the acceleration at the time of accelerating the speed of the vehicle and decreasing the reduction rate at the time of reducing the speed. In the conventional variable capacity pump controller of a hydraulically driven wheel as illustrated in Fig. 7 and 8, the acceleration and deceleration of the vehicle is regulated and the operational instability at the time of switching to forward or backward motion and varying an rpm of the engine are improved by controlling the operation speed of the pump capacity control cylinder C having the throttle valve b or a one way throttle valve d in the pilot circuit thereof. The conventional variable capacity pump controller operates effectively in a normal travelling state but has the following problem in an excavating and loading operation by the shovel loader and the like. That is, when the vehicle carries out the excavation and loading operations, the driving load increases sharply. At this time, the variable pump P tends to pull back the pump capacity control cylinder C in the direction to reduce the pump capacity due to the increase of the oil under pressure in the main circuit S. However, an amount of oil to be escaped from the control cylinder C is limited due to the presence of the throttle valve b or d 1 in the pilot circuit a whereby the reducing speed of the pump capacity is reduced and a torque of the variable pump P to be applied to the engine is increased, which causes the problem of decreasing the rpm of the engine. As a result, there were other problems in that the loading efficiency is decreased and the engine stops since an excessive torque is applied to the engine in case that the pressurized oil is used for controlling the variable pump and performing the excavating and loading operations. It is therefore object of the present invention to accelerate the transition of a variable capacity pump, so that a sharp increase of driving load is advantageously followed by a sharp reduction of speed of the pump capacity, so that the rpm's of the engine do not decrease significantly in this short time. To achieve the above object, the present invention provides a variable capacity pump controller in a hydrostatic drive for a vehicle with the features of claim 1. According to this construction, the variable throttle device operates in such a manner as to open a check valve or a throttle valve in the pilot circuit of the pump capacity control cylinder when the hydraulic driving main circuit is at a high pressure. Therefore, a return hydraulic circuit of the pump control cylinder is expanded to speed up the reducing speed of the pump capacity and to prevent an excessive torque to an engine. Figs. 1 to 4 are hydraulic circuit diagrams of the variable capacity pump controller according to the first to fourth embodiments of the present invention; Figs. 5 and 6 are hydraulic circuit diagrams of the variable capacity pump controller according to modified examples of the first embodiment; Figs. 7 and 8 are hydraulic circuit diagrams of the conventional variable capacity pump controller; and Fig. 9 is a chart showing change of discharge rate of a pump relative to oil pressure of a main circuit. The embodiments of the present invention will be described more in detail with reference to Figs. 1 to 6 and 9. Fig. 1 is the hydraulic circuit diagram explaining the system of the variable capacity pump controller according to the first embodiment of the present invention. Constituents of the variable capacity pump controller in Fig. 1 same as those of the conventional variable capacity pump controller in Fig. 9 have same numerals. In Fig. 1, a pilot circuit 10 of a pump capacity control cylinder C has a one way throttle valve 11 (11 1 is a throttle valve and 11 2 is a check valve) and a pilot operated directional control valve 13 connected to a pilot pipe 12 in a main circuit S. Since the directional control valve 13 is disposed in parallel with the one way valve 11 in the pilot circuit 10, the directional control valve 13 opens when the oil pressure of the main hydraulic circuit S exceeds a setting of the directional control valve 13. As a result, the pressurized oil in the control cylinder C flows through the directional control valve 13 so that the reducing speed of the discharging rate of the variable pump P is increased. Fig. 2 is the hydraulic circuit diagram explaining the system of the variable capacity pump controller according to the second embodiment of the present invention. In Fig. 2 a pilot circuit 20 of the pump capacity control cylinder C has a throttle valve 21 and a pilot operated check valve 24. The check valve 24 is operable by an oil pressure in the main circuit S which is supplied through a pilot pipe 22. The check valve 24 is disposed in parallel with the throttle valve in the pilot circuit 20. The pressurized oil in the control cylinder C flows through a communicating position 24b of the check valve 24 since the checking position 24a is switched to the communicating position 24b when the oil pressure of the main hydraulic circuit S exceeds a setting pressure of the check valve 24 so that the reducing speed of the discharging capacity of the variable pump P is increased. In Fig. 3 showing the circuit diagram of the third embodiment, a pilot circuit 30 of the pump capacity control cylinder C has a one way throttle valve 31, which has a piston 35 operable by the oil pressure of the main circuit S which is supplied through a pilot pipe 32. When the oil pressure in the main hydraulic circuit S becomes greater than the resilience force of the spring of the piston 35, the piston 35, even if it is in the checking position 31a, switches the one way throttle valve 31 in a checking position 31a to a communicating position 31b so that the pressurized oil in the control cylinder C flows through a communicating position 31b. As a result, the reducing speed of the discharging capacity of the variable pump is increased. In Fig. 4 showing the circuit diagram of the fourth embodiment, a pilot circuit 40 of the pump capacity control cylinder C has a check valve 41 and a pilot operated variable throttle valve 46 which is disposed in parallel with the check valve 41 and operable by the oil pressure of the main circuit S which is supplied through a pilot hydraulic pipe 42. When the pressurized oil of the main circuit S increases, it becomes greater than the resilience force of the pilot operated throttle valve 16 so that the throttling area in the throttle valve 41 is increasingly expanded from a throttling position toward a communicating position. As a result, the pressurized oil in the control cylinder C increases its flowing speed as the oil pressure of the main circuit S becomes higher so that reducing speed of the discharging capacity of the variable pump is increased. Modified examples of the variable capacity pump controller according to the first to fourth embodiments of the present invention will be described with reference to Figs. 5 and 6. The modified examples relate particularly to the pilot pipes. In Fig. 5, connected to a shuttle valve 53 is a pilot pipe 52 of the main circuit S and a pipe 59 connected to a line 56. The line 56 is connected to a working pump 57 and a working operation valve 58. The higher pressurized oil of those from the pilot pipe 52 and from the line 59 is supplied to the pilot pipe 54. In Fig. 6, connected to a multistage piston 61 is a pilot pipe 62 and a pilot pipe 69 connected to the line 56. The multistage piston 61 is connected to a pilot pipe 64. The pressurized oil supplied from the pilot pipe 62 and that supplied from the pilot pipe 69 are totaled in the multistage piston 61 and the thus totaled amount of the pressurized oil is supplied to the pilot pipe 64. Although the pilot pipes as illustrated in Figs. 5 and 6 are modified examples of the first embodiment, they can be applied to the second to fourth embodiments with ease. Fig. 9 is a chart showing change of discharge rate of a pump relative to oil pressure of a main circuit. When the pressure of the main circuit is greater than each of the setting pressures of the directional control valves (13 in Fig. 1, 24 in Fig. 2, 35 in Fig. 3 and 46 in Fig. 4), the reducing speed of the pump capacity is speeded up compared with the conventional variable capacity pump controller. The following effect can be obtained since the reducing speed of the pump capacity is speeded up compared with the conventional variable capacity pump controller when the oil pressure of the main circuit is greater than the set pressure of the directional control valve. (1) Even if the oil pressure of the main circuit increases sharply when the vehicle digs by the bucket thereof for excavating and loading purposes, the reducing speed of the pump capacity is speeded up to prevent the torque applied to the engine from being excessive whereby the rpm of the engine is less lowered. (2) Since the main circuit can select the reducing speed of the pump capacity at the optimum value at the high or the low pressure, it is possible to decelerate gently the speed of the vehicle when the hydraulic main circuit is at low pressure at the traveling on a flat road, whereby the reduction rate at the time of reducing the rpm of the engine and at the time of changing the gear to the forward or backward direction. As mentioned above, according to the present invention, since a return hydraulic circuit of the pump control cylinder is expanded to speed up the reducing speedof the pump capacity and to prevent the excessive torque applied to the engine, it is preferably adapted for a variable capacity pump controller of hydraulically driven wheel.

Claims: A control system for a variable capacity pump in a hydrostatic drive for a vehicle, comprising a variable capacity hydraulic pump (P) in a main hydraulic circuit (S), a control pump (A), a variable capacity control cylinder (C) for controlling the pumping capacity of said variable capacity hydraulic pump (P), and a pilot hydraulic circuit (20; 40; 10) having a variable throttle device (V), (21, 24); (41, 46) for varying the pressure of said variable capacity control cylinder (C), wherein said variable throttle device (V); (21, 24); (41, 46) comprises a throttle valve (21; 46; 11 1 ) and a check valve (24; 41; 11 2 ) for controlling the capacity control cylinder (C), means (22; 42) for operating a pilot-operated valve (24; 46; 13) in response to the pressure of the hydraulic fluid in said main hydraulic circuit (S), so as to discharge hydraulic fluid through said pilot-operated valve (24; 46; 13) additionally to the throttle valve (21; 46) from said variable capacity control cylinder (C) when the pressure of the hydraulic fluid in said main hydraulic circuit (S) is high, speeding up the reducing rate of the pump capacity and thereby preventing excessive torque to an engine (M), characterized in that pressurized hydraulic fluid flows through the check valve (24; 41) in the direction to increase the pump capacity. A control system for a variable capacity pump according to claim 1, characterized in that the pilot-operated valve is a check valve (24) operable by an fluid pressure supplied through a pilot pipe (22) and disposed in parallel with the throttle valve (21) between control valve (V) and pump capacity control cylinder (C). A control system for a variable capacity pump according to claim 1, characterized in that the pilot-operated valve is a throttle valve (46) operable by an fluid pressure supplied through a pilot pipe (42) and disposed in parallel with the check valve (41) between control valve (V) and pump capacity control cylinder (C). A control system for a variable capacity pump according to claim 1, characterized in that the pilot-operated valve is a pilot operated directional control valve (13) operable by an fluid pressure supplied through a pilot pipe (12) and disposed in parallel with the throttle valve (11 1 ) and the check valve (11 2 ) between control valve (V) and pump capacity control cylinder (C). A control system for a variable capacity pump according to claim 4, characterized by a pilot pipe (52), a pipe (59) connected to a line (56) between a working pump (57) and a working operation valve (58), and two check valves providing the higher pressurized fluid from those two pipes (57, 59) to a pilot pipe (54) connected with the control valve (13). A control system for a variable capacity pump according to claim 4, characterized by a pilot pipe (62), a pipe (69) connected to a line (56) between a working pump (57) and a working operation valve (58), and a multistage piston (61) providing a pressurized fluid totalled in amount from the amounts of those two pipes (57, 59) to a pilot pipe (64) connected with the control valve (13).

Inventors: IKARI MASANORI, IKARI, MASANORI, IKARI, MASANORI 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: F04B49, F16H61, E02F9