1. Field of the Invention
The present invention relates to a multiple-gear transmission applied in a tractor or other vehicle.
2. Description of the Related Art
Because the total vehicle weight of a tractor-trailer that can pull a trailer varies considerably depending on whether the trailer is attached or not, an auxiliary transmission may be mounted to the main transmission for switching between high and low speeds in order to improve drive performance. This type of auxiliary transmission may include a splitter mounted on the input side of the main transmission and a range gear mounted on the output side of the main transmission as disclosed in Japanese Patent Application Laid-Open Publication No. 8-159258.
The conventional splitter has only the two positions of high speed (HIGH) and low speed (LOW), and it must be in one of these two positions at all times.
However, this construction gives rise to the following problem. That is, many long-distance drivers take naps while running the air conditioner. In these circumstances, because the engine drive power is transmitted to a counter shaft of the main transmission via the splitter when the vehicle is parked and the engine is idling, a counter gear mounted to the counter shaft and a main gear mounted to a main shaft in a transmission casing are engaged and rotating at all times, and therefore a rattling noise occurs due to the colliding of the gear teeth. This ratting noise is conveyed to the interior of the vehicle, and heard by the sleeping driver.
To address this problem, such measures as changing the clutch damper characteristics or additionally providing a scissors gear may be possible. However, because the drive power is conveyed to the counter shaft in any event, these are not fundamental solutions. They would also increase the total length of the transmission assembly (main and auxiliary transmissions), which makes mounting of the transmission assembly difficult.
Accordingly, the inventor of the present invention has proposed a solution to the problem described above in Japanese Patent Application No. 11-819915 or corresponding U.S. patent application Ser. No. 09/707,897 filed Nov. 7, 2000, entitled xe2x80x9cMULTI-STAGE TRANSMISSION OF VEHICLExe2x80x9d the entire disclosures of which are incorporated herein by reference and referred to as xe2x80x9cpreceding invention.xe2x80x9d In this proposed technology, the splitter has a neutral position in addition to high and low gear positions. The drive power transmission is interrupted at the splitter by shifting the splitter to the neutral position. Therefore, if the splitter is brought into the neutral condition, the counter shaft rotation is stopped, and the noise caused by the engaging and rattling of the gears can be eliminated.
In the meantime, a problem of insufficient lubrication may arise when the splitter is left in the neutral position for a long period of time, because oil cannot be circulated or splashed by the counter gear and the oil pump cannot be driven for a long period of time. Various parts in the transmission casing should be lubricated by the oil supplied upon rotation of the counter gear and/or oil pump. In the preceding invention, therefore, the splitter is intermittently shifted between the neutral position and a different position, such that the counter gear is rotated at predetermined intervals, and lubrication is intermittently carried out.
However, the preceding invention entails another problem that when the vehicle is unused for a long period of time for maintenance, etc., oil completely falls off from the shaft support areas (bearings), synchro units, gallery, etc. in the transmission. If the splitter does not have a neutral position, and is locked in either the HIGH or LOW position, the counter shaft begins to rotate upon starting of the engine, thereby initiating lubrication. Therefore, the driver can move the vehicle after a relatively short period of time after the engine is started. However, in the case of the preceding invention, if the splitter is in the neutral position, lubrication does not occur even when the engine is started. As a result, if the driver attempts to move the vehicle in this state, there is no oil circulating among the various transmission components, and the problem of insufficient lubrication occurs.
An object of the present invention is to provide lubrication to the various transmission components and eliminate the problem of insufficient lubrication in a multiple-gear vehicle transmission equipped with a splitter having a neutral position.
According to one aspect of the present invention, there is provided a multiple-gear vehicle transmission including a main transmission and a splitter that operates as an auxiliary transmission on the input side of the main transmission, wherein the splitter has a neutral position in addition to high and low gear positions, and wherein the multiple-gear transmission has splitter control means that intermittently shifts the splitter between the neutral position and a high (or low) gear position, and splitter neutral shift prohibition means that prohibits the splitter from being shifted to the neutral position when the engine is starting up. By shifting the splitter into the high or low gear position, a counter shaft is caused to rotate and various parts in a transmission casing are lubricated by oil that is splashed up by the counter shaft or delivered by an oil pump attached to the counter shaft. When the splitter is shifted to the neutral position, on the other hand, the counter shaft does not rotate. In a certain period from starting of the engine, sufficient lubrication oil may not penetrate to the parts in the transmission casing. Thus, the counter shaft is caused to rotate to insure sufficient lubrication to these parts. After a while, the splitter is intermittently shifted between the high gear position and neutral so that the lubrication takes place intermittently.
The splitter neutral shift prohibition means may prohibit the splitter from shifting to the neutral position until a prescribed period of time has elapsed after the engine is started.
The splitter neutral shift prohibition means may prohibit the splitter from shifting to the neutral position until a vehicle speed has exceeded a prescribed value after the engine is started.
A range gear that operates as another auxiliary transmission may be provided on the output side of the main transmission.