Machine element or mechanism – Gearing – With fluid drive
Patent
1991-07-01
1992-05-12
Braun, Leslie A.
Machine element or mechanism
Gearing
With fluid drive
747311, 192103F, F16H 4702
Patent
active
051117169
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission for a hydraulically driven vehicle, and more particularly, to an automatic transmission for a hydraulic excavator or the like which has an auxiliary speed change gear capable of shifting between high and low speed ranges.
2. Description of the Related Art
In a conventional hydraulic excavator or the like which has an upper swivel body and a lower travel body and which runs with an hydraulically driven motor provided with an auxiliary speed change gear capable of changing between high and low speed ranges, the auxiliary speed change gear is of constant-mesh type and is manually operated by means of an operation lever to change speeds between high and low speeds. Speed change operation therefore requires that the vehicle be stopped temporarily, and is thus troublesome: it is difficult to conduct speed change operation quickly and smoothly.
An auxiliary speed change gear which employs a wet multiple disk clutch hydraulically operated to change between high and low speed ranges by means of an operation valve has also been proposed in, for example, Japanese Utility Model Laid-Open No. 172817/1986. With this auxiliary speed change gear, an operation of shifting a speed changing gear from low to high speed, which is conducted while the vehicle is running at a high speed, may cause overrun of the hydraulically driven motor and damage the hydraulic motor or a low speed clutch.
SUMMARY OF THE INVENTION
In view of the aforementioned drawbacks of the prior techniques, an object of the present invention is to provide an automatic transmission for a hydraulically driven auxiliary speed change gear which assures easy speed changing gear shifting operation during travel and which eliminates damage to an hydraulically driven motor or the like.
To this end, the present invention provides an automatic transmission for a hydraulically driven auxiliary speed change gear which is a power transmitting speed change gear including a hydraulically driven motor and an auxiliary speed change gear provided with hydraulically operated clutches to shift between high and low speed ranges. In this automatic transmission, an automatic change-over valve is provided in a hydraulic circuit which connects cylinders of the high and low speed clutches to a clutch operating hydraulic pump. One end of the automatic change-over valve is connected to the hydraulic circuit connected to the discharge side of the pump by a conduit pipe, and an automatic speed changing valve is provided in the conduit pipe. A rotation sensing hydraulic pump coupled to an input shaft of the auxiliary speed change gear is connected to one end of the automatic speed changing valve and to the other end of the automatic speed changing valve through an orifice. The other end of the automatic speed changing valve is connected to a hydraulic circuit which is located between the low-speed clutch and the automatic change-over valve by a conduit pipe. The rotation sensing hydraulic pump may be connected not to the input shaft of the auxiliary speed change gear but to an output shaft thereof. Alternatively, the input shaft of the auxiliary speed change gear may be connected to an annular centrifugal hydraulic pressure detecting chamber which is employed in place of the rotation sensing hydraulic pump and the orifice. In that case, a pressure detecting pipe inserted in this chamber is connected to one end of the automatic speed change valve.
In a case where the combination of the orifice and the rotation sensing hydraulic pump coupled to an input or output shaft of the auxiliary speed change gear is employed, the automatic speed changing valve is controlled by utilizing a difference in the discharge pressure of the rotation sensing hydraulic pump which varies in accordance with the rotation speed of the hydraulically driven motor and the discharge pressure which has passed through the orifice, to change over the automatic change-over valve due to the pilot pressure from the auto
REFERENCES:
patent: 3529705 (1970-09-01), Cudnohufsky
patent: 4368798 (1983-01-01), Meyerle et al.
patent: 4480502 (1984-11-01), Nembach
patent: 4528871 (1985-07-01), Nembach
patent: 4899542 (1990-02-01), Iino
patent: 4947687 (1990-08-01), Martini et al.
Matsuda Haruyuki
Sato Masayuki
Braun Leslie A.
Kabushiki Kaisha Komatsu Seisakusho
Stavish Matthew
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