Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-12-17
2003-04-01
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C180S422000, C318S432000, C318S433000
Reexamination Certificate
active
06542801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric power steering system.
2. Description of the Related Art
As a first conventional example of a power steering system for a forklift truck, there is known a power steering system in which rear wheels disposed at a rear position of a main body of the forklift truck are used as steering wheels and in which a steering mechanism for operating the steering wheels to turn to thereby turn the vehicle itself and a steering wheel disposed at a front position of the main body of the vehicle are mechanically coupled to each other via a torque transmission mechanism consisting of a chain or a shaft. In this power steering system, the rotational torque of the steering wheel is detected by a torque sensor disposed at a rear end portion of the torque transmission mechanism, and the rear steering wheels are operated to turn as a steering motor provided on the steering mechanism is driven based on a detected value detected by the torque sensor.
As a second example of a conventional power steering system for the forklift truck, there is known a power steering system comprising, as shown in a block diagram of
FIG. 5
, an operating speed sensor
11
for detecting the operating speed of a steering wheel which is the turning speed thereof, an actual steering speed sensor
12
for detecting an actual operating speed which is an actual turning speed by a steering mechanism, a micro computer
13
which is a controller for calculating a target operating speed which is a target turning speed for the steering mechanism and comparing the actual steering speed detected by the actual steering speed sensor
12
with the target steering speed so calculated for calculation of a deviation and a motor a driving device
15
which is a driving device for driving a steering motor
14
provided on the steering mechanism in response to the deviation so calculated.
As a third example of a conventional power steering system for the forklift truck, there is known a power steering system comprising, as shown in a block diagram of
FIG. 6
, an operating angle sensor
111
for detecting the operating angle of a steering wheel which is the turning angle thereof, an actual steering angle sensor
112
for detecting an actual operating angle which is an actual turning speed by a steering mechanism or a so-called steering angle of a steering wheel, a micro computer
113
which is a controller for calculating a target operating angle which is a target turning angle for the steering mechanism based on the operating angle detected by the operating angle detecting sensor and comparing the actual steering angle detected by the actual steering angle sensor
112
with the target steering angle so calculated for calculation of a deviation and a motor a driving device
115
which is a driving device for driving a steering motor
114
provided on the steering mechanism in response to the deviation so calculated. In addition, the operating angle of the steering which is the turning angle thereof is calculated in response to the number of times of turns of the steering wheel, and there exists an established proportional relationship between the number of times of turns and the operating angle that the number of times of turns increases as the operating angle increases.
However, in the power steering system according to the first conventional example, since the steering wheel and the steering mechanism are mechanically coupled to each other, it is not easy to change the turning speed ratio between the two members.
Moreover, in the power steering system according to the second conventional example, the target steering speed for the steering mechanism is only calculated based on the simple set ratio relative to the operating speed, and in reality the turning speed ratio between the steering handle and the steering mechanism is set as a fixed value. Namely, in vehicles in general including forklift trucks, since it is important to maintain good straight line vehicle stability by preventing the wandering of a vehicle that occurs while the vehicle is running at high speed, it is the normal practice that the set ratio of the target steering speed of the steering mechanism relative to the operating speed is set as a fixed value by using the straight line vehicle stability at a high vehicle speed as a reference and that the target steering speed of the steering mechanism is calculated as a result of the multiplication of the set ratio by the operating speed.
For forklift trucks as loading vehicles which are different from those developed mainly for running, however, it is imperative to be used to load and unload freight while being run at low speed, and therefore, forklift trucks are operated back and forth restlessly and repeatedly and the steering wheel frequently needs to be turned in a condition in which the vehicle is nearly stationary as in so-called stationary steering. Then, as long as the fixed set ratio set based on the straight line vehicle stability at the high vehicle speed as a reference is used, the turning speed or operating speed of the steering wheel has to be increased in despite of the fact that the target steering speed of the steering mechanism is relatively slow, and therefore there is caused a problem that the operator gets exhausted before long after the initiation of operating the forklift truck or a muscular disorder is caused.
Moreover, in the power steering system according to the third conventional example, the target steering angle for the steering mechanism is only calculated based on the simple set ratio relative to the operating angle, and in reality the turning angle ratio between the steering handle and the steering mechanism is set as a fixed value.
Namely, in vehicles in general including forklift trucks, since it is important to maintain good straight line vehicle stability by preventing the wandering of a vehicle that occurs while the vehicle is running at high speed, it is the normal practice that the set ratio of the target steering angle of the steering mechanism relative to the operating angle is set as a fixed value by using the straight line vehicle stability at a high vehicle speed as a reference and that the target steering angle of the steering mechanism is calculated as a result of the multiplication of the set ratio by the operating speed. Note that in forklift trucks it is common that the number of times of turns of the steering wheel relative to the overall movable range of the steering mechanism is set to 5 to 8 turns.
For forklift trucks as loading vehicles which are different from those developed mainly for running, however, it is imperative to be used to load and unload freight while being run at low speed, and therefore, forklift trucks are operated back and forth restlessly and repeatedly and the steering wheel frequently needs to be turned in a condition in which the vehicle is nearly stationary as in so-called stationary steering. Then, as long as the fixed set ratio set based on the straight line vehicle stability at the high vehicle speed as a reference is used, the number of times of turns of the steering wheel needs to be increased so that the steering angle is also increased in despite of the fact that the target steering angle of the steering mechanism is relatively small, and as a result of this, there is caused a problem that the operator gets exhausted before long after the initiation of operating the forklift truck or a muscular disorder is caused.
SUMMARY OF THE INVENTION
The present invention has been made in view of the inconveniences inherent in the conventional examples.
An object of the invention is to provide a power steering system in which a set ratio of a target steering speed for a steering mechanism relative to the steering speed of a steering wheel is variable, and in which there is no risk of the operator of a forklift truck getting exhausted before long after the initiation of the operation of the vehicle or a muscular disorder being caused.
Another object of the inv
Cuchlinski Jr. William A.
Nippon Yusoki Co., Ltd.
Sughrue & Mion, PLLC
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