Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Construction or agricultural-type vehicle
Reexamination Certificate
2002-03-22
2003-11-25
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Construction or agricultural-type vehicle
C180S006200, C477S001000, C475S019000, C475S027000
Reexamination Certificate
active
06654676
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a steering system for a tracklaying vehicle, which includes a pair of brakes provided for right and left output shafts and is designed to transmit the driving force of a hydraulic motor to the respective output shafts through a differential steering means.
BACKGROUND ART
In a known steering system for a tracklaying vehicle such as a bulldozer, the hydraulic motor is driven by a hydraulic pump actuated by the engine and the output of the hydraulic motor is transmitted to the right and left output shafts through a differential steering means such as a planetary gear mechanism, thereby making the rotational speeds of the right and left sprockets different from each other to turn the vehicle.
Such a steering system for a tracklaying vehicle suffers from the problem that since the hydraulic motor receives a reaction force caused by the turning resistance of the vehicle when the vehicle turns and the reaction force acting on the hydraulic motor increases as the radius of turn of the vehicle becomes small, a radius of turn exceeding the capacity of the hydraulic pump and the hydraulic motor cannot be obtained. In addition, the steering system employing the hydraulic motor also presents such a problem that all the power required for turns is obtained from oil pressure and therefore allowance has to be made for engine power.
An attempt to solve the above problems has been made in Japanese Patent Application No. 63-235173 (1988). This publication teaches a system in which the closed circuit for the hydraulic pump and the hydraulic motor is provided with right and left steering brake valves and a transverse shaft is provided with a pair of brakes. In this system, when the operating position of the steering lever becomes more than or equal to an intermediate operational amount, the output of the hydraulic motor is set to zero and either the right or left sprocket is braked, whereby the reaction force is prevented from working on the hydraulic motor when a turn with a small turning radius (e.g., pivot turn) is carried out.
The technique disclosed in the above publication, however, has revealed the following problem. Regarding the relationship between a timing for braking a sprocket by a brake and a timing for disconnecting the hydraulic motor from a driving power source, if the braking timing is slower than the disconnecting timing, the relative speed of the right and left sprockets is dependent only on the load of the road surface applied to the respective crawler belts, so that the radius of turn of the vehicle cannot be made to be constant. On the other hand, if the braking timing is quicker than the disconnecting timing, the vehicle gets a great shock at the instant the vehicle starts a pivot turn, in some cases depending on the relationship between the timings.
To solve such a problem, the present inventors have already suggested a steering method for a tracklaying vehicle in the previous invention (Japanese Patent Application No. 2000-83329). According to this method, when the vehicle makes a pivot turn, after actuation of the brake for either one of the right and left output shafts and a transmission of a driving force from the hydraulic motor to the differential steering means have been carried out concurrently for a specified period of time, the transmission of the driving force from the hydraulic motor to the differential steering means is interrupted. The previous invention also discloses a method for controlling the rotational speed of the engine so as to be less than or equal to a specified value during a pivot turn of the vehicle in order to prevent an unfavorable situation such as when either one of the drive shafts is stopped by actuation of its corresponding brake, the hydraulic motor receives a driving force from the other drive shaft being rotated and, in consequence, the rotation of the motor overruns.
However, in cases where the motor overrun prevention method disclosed in the previous invention is adopted, there arise other problems. Specifically, the rotational speed of the motor deviates from the desired value in some cases depending on the surface condition of the road on which the tracklaying vehicle is traveling, or the engine may be excessively throttled down, resulting in a shortage of power during a pivot turn.
The invention is directed to overcoming the foregoing problems and a primary object of the invention is therefore to provide a steering system for a tracklaying vehicle which is capable of preventing overrun of the motor during a pivot turn irrespective of the load of the road surface and does not cause a shortage of power during a turn.
DISCLOSURE OF THE INVENTION
The above object can be accomplished by a steering system for a tracklaying vehicle according to the invention wherein a pair of brakes are provided for right and left output shafts and the driving force of a hydraulic motor is transmitted to the right and left output shafts through differential steering means, the system comprising:
(a) brake actuating means for independently actuating the right and left brakes;
(b) driving force transmission interrupting means for interrupting a transmission of a driving force from the hydraulic motor to the differential steering means;
(c) pivot turn control instruction signal detecting means for detecting an issue of a vehicle pivot turn control instruction signal;
(d) vehicle speed detecting means for detecting the vehicle body speed of the vehicle;
(e) controlling means for controlling the brake actuating means and the driving force transmission interrupting means in response to an output from the pivot turn control instruction signal detecting means such that after actuation of a brake for either one of the right and left output shafts by the brake actuating means and a transmission of a driving force from the hydraulic motor to the differential steering means are carried out concurrently for a specified period of time, the driving force transmission interrupting means interrupts the transmission of the driving force from the hydraulic motor to the differential steering means,
wherein the controlling means controls an engine such that the vehicle body speed of the vehicle detected by the vehicle speed detecting means during a pivot turn of the vehicle becomes equal to a specified value.
In the invention, during a pivot turn, actuation of a brake for either one of the right and left output shafts and a transmission of a driving force from the hydraulic motor to the differential steering means are concurrently carried out for a specified time and thereafter, the transmission of the driving force from the hydraulic motor to the differential steering means is interrupted thereby bringing the hydraulic motor into its free condition. Accordingly, trouble caused by an unfavorable situation such as when the timing for the brake actuation is delayed and the free condition of the hydraulic motor continues until the brake is actuated can be avoided. In other words, the problem of having the relative speed of the right and left sprockets be dependent upon only the load of the road surface exerted on the respective crawler belts can be avoided. In addition, that the present invention prevents the vehicle from getting a great shock at the instant of a pivot turn. Further, during a pivot turn, the transmission of a driving force from the hydraulic motor to the differential steering means is interrupted so that a reaction force from the road surface does not act on the hydraulic motor, and therefore, it is possible to make a pivot turn with a conventional hydraulic motor of a small capacity. Since the controlling means of the invention controls the engine such that the vehicle body speed of the vehicle detected by the vehicle speed detecting means during a pivot turn of the vehicle becomes equal to a specified value, the present invention also avoids the possibility that while one of the drive shafts is stopped by actuation of its corresponding brake, the hydraulic motor receives a driving force from the rotating one o
Nakagawa Tomohiro
Suzuki Kazuyuki
Yamamoto Shigeru
Cuchlinski Jr. William A.
Hemandez Olga
Komatsu Ltd.
Rader & Fishman & Grauer, PLLC
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