Motor vehicles – Steering by driving – Endless flexible track
Reexamination Certificate
1999-10-28
2001-07-17
Schwartz, Christopher P. (Department: 3613)
Motor vehicles
Steering by driving
Endless flexible track
C037S348000
Reexamination Certificate
active
06260642
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a steering control system for tracklaying vehicles such as bulldozers.
BACKGROUND ART
There is known a steering control system for a tracklaying vehicle such as bulldozers, in which a clutch and a brake are provided for each of the right and left drive wheels of the vehicle and controlled to cause right and left turns of the vehicle. In such a steering control system, when operating the steering lever so as to cause a right turn during traveling of the vehicle, the right clutch is disengaged and the right brake is actuated to stop only the right crawler belt, so that the vehicle turns to the right. Similarly, when operating the steering lever to cause a left turn, the left clutch is disengaged and the left brake is actuated to stop only the left crawler belt, so that the vehicle turns to the left.
The above steering control system is designed such that there is a predetermined time interval after clutch disengagement until brake actuation, or after brake release until clutch engagement, which relieves shocks occurring during steering control so that smooth turns can be carried out. If this time interval between clutch disengagement and brake actuation or between brake release and clutch engagement is made to be constant, it will cause a time period when the clutch and brake which have been operated by the steering lever are both in their released states during traveling of the vehicle on a slope, with the result that the vehicle undesirably turns in a direction opposite to a direction designated by operating the steering lever, due to the so-called “reverse steering phenomenon”.
An attempt to solve the above problem is disclosed, for instance, in Japanese Patent Publication (KOKAI) No. 4-366232 (1992) in which the time intervals between clutch disengagement and brake actuation and between brake release and clutch engagement are controlled according to the pitch forward or pitch aft angle of the vehicle with intent to prevent shocks occurring during operation of the steering lever and to prevent the reverse steering phenomenon.
A steering control system directed to performing smooth turns without shocks under various driving and operating conditions is disclosed, for instance, in Japanese Patent Publication (KOKAI) No. 5-8753 (1993) according to which, a time interval until a start of brake actuation or until a start of clutch engagement is automatically adjusted according to the operation speed of the steering lever, thereby achieving improved fine controllability.
These conventional steering control systems are, however, not designed to perform steering control taking into consideration the operating state of the tracklaying vehicle such as bulldozer's dozing operation and high speed driving state, and therefore this system cannot provide optimum control suited for each operating state. Another problem of these conventional control systems is such that since the control is designed mainly in view of the static characteristic of the clutches and brakes, it cannot achieve smooth and reliable turning control suited for each operating state.
The present invention is directed to overcoming the foregoing problems and a prime object of the invention is therefore to provide a steering control system for a tracklaying vehicle, which enables optimum steering performance according to various operating conditions of the tracklaying vehicle.
DISCLOSURE OF THE INVENTION
The above object can be accomplished by a steering control system for a tracklaying vehicle according to a first aspect of the invention (related to claim
1
). This steering control system for a tracklaying vehicle comprises a clutch and a brake provided for each of right and left drive wheels, electronic proportional control valves for controlling the clutches and the brakes, a steering lever, a steering command signal generator for generating a steering command signal according to the operating amount of the steering lever, and a controller for outputting a steering control signal to the electronic proportional control valves based on the output of the steering command signal generator,
wherein tractive force detecting means for detecting the tractive force of the vehicle is provided and
wherein if the tractive force detecting means determines that the vehicle is in a high load driving state, the controller outputs a steering control signal to the electronic proportional control valves in order to obtain a hydraulic characteristic for expanding the controlling region of a clutch and reducing the controlling region of a brake.
According to the first aspect of the invention, when little tractive force is imposed on the vehicle, that is, when the vehicle is turning during travel at a flat place, the turning torque of the inner crawler belt has a minus value while the turning torque of the outer crawler belt has a plus value so that the controlling region of a clutch is set to be small and the controlling region of a brake is set to be large. On the other hand, if the vehicle is in a high load state in which the vehicle is subjected to great tractive force, for instance, when the vehicle turns with high load being imposed on the blade in dozing operation, the controlling region of a clutch is expanded while the controlling region of a brake is reduced. In this way, the turning torque of the inner crawler belt has a plus value, maintaining a half-engaged clutch condition for long. In consequence, soil pushing by the front face of the blade can be smoothly carried out and an optimum turning characteristic free from shocks can be attained even in dozing operation.
According to a second aspect of the invention (related to claim
2
), there is provided a steering control system for a tracklaying vehicle comprising a clutch and a brake provided for each of right and left drive wheels, electronic proportional control valves for controlling the clutches and the brakes, a steering lever, a steering command signal generator for generating a steering command signal according to the operating amount of the steering lever, and a controller for outputting a steering control signal to the electronic proportional control valves based on the output of the steering command signal generator,
wherein pitch angle detecting means for detecting the pitch forward or pitch aft angle of the vehicle is provided and
wherein if the pitch angle detecting means determines that the vehicle is in a slope traveling state, the controller outputs a steering control signal to the electronic proportional control valves in order to obtain a hydraulic characteristic for inhibiting simultaneous release of a clutch and a brake.
According to the second aspect of the invention, if the vehicle is in a slope traveling state, a hydraulic characteristic for inhibiting simultaneous release of a clutch and a brake is obtained. In other words, control is so performed in a slope traveling state as to eliminate the disengaged region of a clutch to increase the braking force of a brake. Therefore, reverse turning (i.e., reverse steering) due to clutch disengagement during the descent of the vehicle on a slope and excessively large turning radius occurring during the ascent of the vehicle on a slope can be avoided so that an improved turning characteristic for the slope traveling state can be achieved.
In the second aspect of the invention, it is preferable that if the pitch angle detecting means determines that the vehicle is in the slope traveling state, the controller outputs a steering control signal to the electronic proportional control valves in order to obtain a hydraulic characteristic for setting the value of oil pressure for starting clutch disengagement and the value of oil pressure for starting brake actuation to be lower than those of normal driving (this feature corresponds to claim
3
). With this arrangement, clutching force and braking force can be corrected so as to increase, so that when driving on a slope, the operator can carry out steering operation with steering feeling similar to the feeling when dri
Morita Satoru
Okazawa Koji
Yamamoto Shigeru
Armstrong Westerman Hattori McLeland & Naughton LLP
Bartz C. T.
Komatsu Ltd.
Schwartz Christopher P.
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