Power plants – Pressure fluid source and motor – Methods of operation
Patent
1997-05-08
1998-07-28
Denion, Thomas E.
Power plants
Pressure fluid source and motor
Methods of operation
60448, 60449, F16D 3100
Patent
active
057848831
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for controlling a speed change of a hydraulic driving apparatus for a vehicle and to a speed changing device, and more particularly, to a method for controlling a speed change of a hydraulic driving apparatus for use in construction vehicles, agricultural machinery, automobiles, etc., and to a speed changing device.
BACKGROUND ART
Hitherto, various types of power transmission devices for use in construction vehicles, agricultural machinery, automobiles, etc., such as the mechanical type, the hydraulic type, and the electric type, have been proposed and used. With regard to small vehicles for construction machines, those of the hydraulic type have been used relatively often. This is because the hydraulic type can change its running speed from zero to infinity, and its merit-of excellent operability has been highly regarded. On the other hand, the hydraulic type has disadvantages of lower efficiency and higher cost as compared to the mechanical type. However, operating machines for digging, earth moving, etc., are mounted in construction equipment, such as a wheel hydraulic excavator, and all of the power from an engine is converted by a hydraulic pump in order to actuate the operating machines, so that the use of hydraulic driving apparatuses may becomes less expensive conversely. When such hydraulic driving apparatuses are used, there are two types: closed circuit and open circuit. They have different characteristics, and they are used in accordance with the purpose.
For example, in construction machines used mainly for the purpose of traveling, when large amounts of flowing oil pressure is required, the open circuit type is used. Closed center load sensing circuits have been used in operating machines in terms of improvement in operability, and closed center valves are adopted therein. On the other hand, when traveling efficiency or controllability is emphasized, the closed circuit type is used, and a hydraulic travel pump and an operating machine hydraulic pump are used therein.
In addition, a circuit using a counterbalance valve, shown in FIG. 37, has been known; and it controls the return oil from the counterbalance valve to effect speed control (runaway prevention) when descending a slope. This construction comprises a variable displacement hydraulic pump 210, driven by a driving source 1 such as an engine; a capacity control device 211, for controlling the capacity of the hydraulic pump 210; a forward-reverse directional control valve 212; solenoid operated proportional valves 213 (forward) and 214 (reverse), for controlling the forward-reverse directional control valve 212; a counterbalance valve 215, connected to the forward-reverse directional control valve 212; a variable displacement hydraulic motor 216, for receiving the pressurized oil from the counterbalance valve 215; and a capacity control device 217, for controlling the capacity of the hydraulic motor 216.
However, the above-described conventional circuit encounters the following problems.
i) The use of the counterbalance valve in a traveling circuit reduces the efficiency because the valve is controlled by restriction. Moreover, since heat is generated while traveling, a large cooler and an engine of larger output are required, so that the size and cost of the vehicle increases.
ii) The use of the closed center valve, in the traveling circuit of a vehicle emphasizing workability, encounters a similar malfunction because the valve is controlled by restriction similar to the counterbalance valve. Particularly, in a high-speed, long-distance traveling vehicle, the resistance increases, reducing efficiency, and the heating value also increases so that a large cooler is required.
iii) The gradients of change of the engine rotational speed are taken on the same line during low speed operation and during high speed operation, so that follow-up properties of the engine with respect to the depressed amount of the brake pedal is bad or oversensitive during either of low speed operation a
REFERENCES:
patent: 5184466 (1993-02-01), Schniederjan et al.
Hiraki Hikosaburo
Kanayama Noboru
Makida Ryutaro
Ohkura Yasunori
Denion Thomas E.
Karimi Bijan N.
Komatsu Ltd.
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