Interrelated power delivery controls – including engine control – Transmission control – Engine controlled by transmission
Reexamination Certificate
2000-02-29
2001-08-21
Wright, Dirk (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Engine controlled by transmission
Reexamination Certificate
active
06277050
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an engine speed control system for a work vehicle such as a bulldozer.
BACKGROUND ART
Generally, excavating and earth moving operation by use of a work vehicle such as a bulldozer is often carried out with the vehicle engine being in full operation. In such operation, when the drive of the vehicle is switched from a forward speed range to a reverse speed range or vice versa, or when the operation of the vehicle is suspended for a while with the engine running, fully operated engine generates extremely high noise and causes high fuel consumption. To cope with such situations, the operator depresses the decelerator pedal or turns the fuel throttle dial to its low idle side, thereby reducing engine speed. However, if the operator depresses the decelerator pedal or turns the fuel throttle dial in every vehicle suspension, it will impose serious burden on the operator.
To solve this problem, there have been proposed various techniques for reducing engine speed by actuating an automatic decelerator when work implement levers are brought into their neutral position to stop the work implements.
For instance, Japanese Patent Publication (KOKOKU) Gazette No. 5-52411 (1993) discloses a technique wherein engine speed is slightly reduced by actuating the automatic decelerator for a short time, upon placement of all the work implement levers in their respective neutral positions and after the engine is maintained at this reduced speed for a specified time, the automatic decelerator is again operated to further reduce engine speed. Another technique is disclosed in Japanese Patent Publication (KOKOKU) Gazette No. 60-38561 (1985) according to which, when a low speed drive control command has been issued, a low engine speed drive is instructed after an elapse of a predetermined delay time after all the operation levers are placed in their neutral positions, and measurement of the delay time is cleared at the time when at least one of the operation levers is actuated before an elapse of the delay time. Japanese Patent Publication (KOKOKU) Gazette No. 61-34327 (1986) discloses a system which is arranged such that a supply of fuel to the internal combustion engine is stopped provided that the running condition of the internal combustion engine meets a specified level, and if the gear position of the transmission is changed from its neutral position to a non-neutral position, an interruption in fuel supply will be inhibited to prevent engine stall.
The conventional techniques disclosed in these publications, however, suffer from the problem that when operation is resumed after suspension with the engine running at a reduced speed and engine speed is restored to an initial speed, occurrence of an instantaneous impact load is unavoidable at the time of engagement of the gear shift clutch of the transmission.
The present invention is directed to overcoming the foregoing problems and the prime object of the invention is, therefore, to provide an engine speed control system for a work vehicle which reduces engine speed when operation is suspended for a while in order to reduce engine noise and suppress fuel consumption, the system enabling a reduction in a possible instantaneous impact load which would occur at the time of engagement of the gear shit clutch when operation is resumed after suspension.
DISCLOSURE OF THE INVENTION
The above object can be accomplished by an engine speed control system for a work vehicle according to a first aspect of the invention, the system comprising: lever position detecting means for detecting the position of a forward/reverse drive shift operation lever for selectively determining the forward or reverse speed range of the work vehicle, engine speed detecting means for detecting the speed of an engine, and a controller for controlling the speed of the engine to a specified value based on detection signals respectively sent from these detecting means,
the controller being designed such that if the lever position detecting means determines that the forward/reverse drive shift operation lever has been shifted to a neutral position when the work vehicle was in a work-loaded condition, the speed of the engine is immediately reduced to a first specified engine speed to be limited thereto and then further reduced to a second specified engine speed to be limited thereto, after the first specified engine speed is maintained for a first specified period of time, and if the lever position detecting means determines that the forward/reverse drive shift operation lever has been shifted from the neutral position to a forward drive position or a reverse drive position while the engine being kept at the first specified engine speed or the second specified engine speed, the speed of the engine is controlled so as to cancel the limitation of the engine speed to the first or second specified engine speed after an elapse of a second specified period of time after the determination.
According to the first aspect of the invention, if it is determined that the state of the work vehicle has been changed from a work-loaded condition to a non-loaded condition by shifting the forward/reverse drive shift operation lever to its neutral position, engine speed is automatically, immediately reduced to a first specified engine speed and limited to it. If the forward/reverse drive shift operation lever is not shifted to a forward or reverse drive position even when the first specified engine speed is maintained for a time that is not less than a first specified time period, engine speed is further reduced and limited to a second specified engine speed which is lower than the first specified engine speed. In this way, not only can engine noise be reduced during vehicle suspension but also useless fuel consumption can be suppressed. If it is determined that the forward/reverse drive shift operation lever has been shifted from its neutral position to a forward or reverse drive position (that is, the operation of the vehicle has been resumed) while the engine is kept at the first or second specified engine speed, the limitation of the engine speed to the first or second specified engine speed is cancelled after an elapse of a second specified period of time after the determination. With this arrangement, when the vehicle resumes operation after suspension, the engine is able to quickly return to an engine speed which corresponds to the load of an operation to be carried out after the resumption. Further, since there is proved a delay time (i.e., the second specified period of time) for the restoration, engagement of the gear shift clutch can be completed within this delay time, which ensures that occurrence of an impact load due to clutch engagement during the restoration is prevented.
In the invention, the lever position detecting means preferably detects the position of the forward/reverse drive shift operation lever by detecting a pilot oil pressure for a transmission shifting oil pressure.
Preferably, in the invention, the first specified engine speed is set to a value (e.g., 2,000 rpm) that is slightly lower than a high idle engine speed (e.g., 2,150 rpm) while the second specified engine speed is set to a value equal to a low idle engine speed (e.g., 650 rpm).
It is preferable that the first specified period of time be set to 3 to 5 sec. and the second specified period of time be set to about 1 sec.
According to a second aspect of the invention, there is provided an engine speed control system for a work vehicle, the system comprising: lever position detecting means for detecting the position of a forward/reverse drive shift operation lever for selectively determining the forward or reverse speed range of the work vehicle, engine speed detecting means for detecting the speed of an engine, and a controller for controlling the speed of the engine to a specified value based on detection signals respectively sent from these detecting means,
the controller being designed such that if the lever position detecting means determines that the forward/reverse d
Nakagawa Tomohiro
Okada Toshikazu
Armstrong, Westerman, Hattori, McLeland & Naughton, LLP.
Komatsu Ltd.
Wright Dirk
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