Machine element or mechanism – Rotary member or shaft indexing – e.g. – tool or work turret – Preselected indexed position
Patent
1986-12-16
1989-06-06
Braun, Leslie A.
Machine element or mechanism
Rotary member or shaft indexing, e.g., tool or work turret
Preselected indexed position
B60K 4106
Patent
active
048360570
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of controlling a plurality of speed change clutches which are incorporated in a gear type transmission.
BACKGROUND OF THE INVENTION
A gear type transmission having a plurality of speed change clutches incorporated therein is so constructed that change of speed stages is carried out by making selective engagement among the speed change clutches and therefore so-called speed change shock occurs during engagement among the speed change clutches. As is well known for any expert in the art, the larger an amount of slippage of the speed change clutches, the smaller the speed change shock. On the other hand, increase of an amount of slippage leads to increase of an amount of heat generated by the speed change clutches. Due to the fact that construction machine such as dump truck or the like has considerably high intensity of torque transmitted by the speed change clutches compared with that of passenger car or the like, a large amount of heat is generated by slippage.
In view of the above-mentioned fact construction machine is so designed that clutch hydraulic pressure is caused to increase gradually (in the form of modulation) to such an extent that an amount of slippage does not increase excessively.
Torque transmitted by means of the speed change clutches varies considerably in dependence on the running state of a vehicle. Specifically, torque to be transmitted in the case where an article having heavy weight is loaded on the vehicle is remarkably different from that in the case where no article is loaded thereon.
Since clutch hydraulic pressure is hitherto caused to increase gradually with the use of mechanical type modulation valves, it results that clutch hydraulic pressure has fixed gradual increase characteristics and thereby this leads to an occurrence of such malfunctions that a high intensity of speed change shock appears under a certain running state of vehicle and an amount of slippage increases unnecessarily.
One of objects of the present invention is to inhibit an occurrence of malfunctions as mentioned above.
On the other hand, a conventional transmission in which clutch hydraulic pressure is caused to increase gradually with the use of mechanical type modulation valves has the following drawbacks.
Specifically, FIG. 27 schematically illustrates an example of a gear type transmission employed for dump truck or the like. As is apparent from the drawing, the transmission is equipped with speed change clutches 401, 402, 403 and 404 for selecting one of speed stages comprising first speed, second speed, third speed and rearward movement.
It has been found with respect to the conventional transmission as constructed in the above-described manner that so-called speed change shock occurs when hydraulic pressure is abruptly exerted on the speed change clutches 401 to 404. To obviate this problem the transmission is so constructed that a mechanical type modulation valve 410 and a quick return valve 411 are interposed between switching valves 405 to 408 hydraulically connected to the speed change clutches 401 to 404 and a hydraulic pump 409.
The modulation valve 410 and the quick return valve 411 have a function for gradually increasing hydraulic pressure, for instance, in the clutch 410 in the purely mechanical manner (in the form of modulation) when a switching valve 405 is shifted by activating an electromagnetically actuated valve 412 for the purpose of controlling of pilot pressure which is operatively connected to the switching valve 405. By virtue of the function as mentioned above hydraulic pressure exerted on the clutch 401 is caused to increase with a constant gradient (time change rate), resulting in speed change shock being reduced. When any one of the electromagnetically actuated valves 413, 414 and 415 is activated, clutch hydraulic pressure in the speed change clutch operatively associated with the thus selected electromagnetically actuated valve is caused to increase gradually.
Now, consideration is taken into account, for instanc
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"Electronic/Hydraulic Transmission Control System for Off-Highway Hauling Vehicles", by Morris and Sorrells, pp. 1-7, S.A.E. 850783, publ. 1985.
Asayama Yoshio
Okura Yasunori
Takitani Yukitaka
Tsubota Makio
Braun Leslie A.
Diehl Dwight G.
Kabushiki Kaisha Komatsu Seisakusho
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