Motor vehicles – Steering by driving
Reexamination Certificate
1999-09-14
2001-06-05
Boehler, Anne Marie (Department: 3618)
Motor vehicles
Steering by driving
C180S248000, C180S249000
Reexamination Certificate
active
06241037
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a device for a differential gear for vehicles, comprising driving means capable of driving the vehicle and steering means capable of changing the direction of the vehicle, which differential gear comprises an input driving shaft, two output shafts connected to the vehicle's driving means, at least one hydraulic pump capable of delivering a hydraulic flow, and at least one hydraulic motor communicating with the hydraulic pump and arranged to the differential gear, capable of achieving a difference in rotational speed between the output shafts.
BACKGROUND TO THE INVENTION
Differential gears are used in principle in all types of vehicles if a differentiation in rotational speed is to be achieved between the driving wheels. This is due to that the wheels on a vehicle rotate at a different velocity when the vehicle turns, due to the fact that the wheels follow tracks with a different radius. However, the differential has the disadvantage that if one driving wheel has lower friction against the ground than the other driving wheel, the wheel with the lower friction will begin to spin and the vehicle loses propulsion power, due to the fact that the differential is torque-equalizing and thus both driving wheels will have the torque which the wheel with the lower friction can transmit.
To remedy this problem, a number of devices have been developed. The simplest is a differential lock, which quite simply locks the drive shafts to one another so that they are forced to rotate at the same velocity. This is normally only used in extreme cases as it places great strain on the transmission and tires.
One development of this is to arrange a differential brake. These comprise a braking device which often consists of disc packs. The brake is activated in various ways and slows down the differences in rotational speed, often due to the braking moment increasing as the driving torque increases. In advanced types of differential brakes, the braking moment can be changed via hydraulics controlled by a computer. This requires the rotational speed differences to be detected by sensors which sense the rotation of the shafts. The systems can be more or less sophisticated. being provided with information regarding the driving torque of the vehicle, steering deflection, velocity, gear selection and the like The differential brakes which are activated by the torque often have a certain preload, i.e. the discs already lie close to one another in the unloaded state. This is done deliberately in this way precisely on account of the fact that a differential gear is torque-equalizing. The preload is required to transmit a certain torque to the driving wheel which has the higher friction as stated above. The preload thus provides a certain straining effect at the differential even when this is not desirable.
The general limitation with differential brakes is that they cannot achieve a certain defined rotational speed difference between the drive shafts, but can only slow down a rotational speed difference which is too great.
ACCOUNT OF THE INVENTION
The object of the invention is to achieve differentiated control of the rotation of a vehicle's drive shafts starting out from the desired steering direction.
This is achieved according to one aspect of the invention according to the introduction characterized by means capable of regulating the hydraulic flow between the hydraulic pump and the hydraulic motor depending on the steering direction of the steering means and the velocity of the vehicle.
According to another aspect of the invention, this is characterized in that the hydraulic pump is of the displacement type and that the hydraulic motor is of the displacement type.
According to a further aspect of the invention, a device is obtained characterized in that the magnitude of the oil flow is controlled by the steering direction of the steering means, the flow being mainly zero when the steering direction of the steering means is straight forward, and that the oil flow gradually increases the more the steering direction of the steering means deviates from a propulsion direction straight forward, that the direction of the oil flow is controlled by whether the direction of steering of the steering means deviates to the left or right of this, and that the oil flow increases as the velocity increases.
According to a further aspect of the invention, a device is obtained characterized in that the pump is connected drivably to the vehicle's drive, which is arranged between the vehicle's engine and the two output shafts.
The great advantage of the device according to the invention is that differentiated steering and driving are obtained from the driving means starting out from the steering direction of the steering means, in which the driving of the drive shafts is effected primarily by mechanical means and control of the rotational speed differences between the drive shafts is achieved hydraulically. This rotational speed control is always effected starting out from the steering direction of the steering means and there is thus no reason to take into account, and control, the actually transferred torques or current rotational speed differences of the drive shafts, and attempt to correct the deviations as they occur
Due to the fact that the hydraulic pump is preferably connected to the vehicle's drive, which is arranged between the vehicle's gear box and the two output shafts, for example the cardan shaft, a direct link is obtained between the flow and the velocity of the vehicle, no special valve arrangements being required to regulate the oil flow in relation to the vehicle's velocity. Due to the fact that the hydraulic motor and the hydraulic pump are of the displacement type, in which the pump has variable displacement, and owing to the fact that they are arranged in a hydraulic system in which mainly all the oil which the pump delivers passes through the motor, a certain gear ratio exists between the rotating shafts of the pump and the motor for a certain setting of the pump's displacement, and this gear ratio is varied by varying the displacement.
Due to the fact that the pump is operated by a shaft of which the rate of rotation is directly proportional to the propulsion velocity of the vehicle and that the pump's displacement setting is linked to the vehicle's steering deflection, synchronization can be obtained between the driving wheels and the steering wheels, i.e. the difference in rotational speed of the driving wheels corresponds to the turning radius which the vehicle acquires from the current steering deflection.
It is also possible with the device according to the invention to combine the improved efficiency of the mechanical transmission with a system which precisely controls the difference in rotational speed between the drive shafts and thereby gives the vehicle a steering capacity of a precision which, as far as is known, was previously only possible with vehicles driven by hydraulic motors.
The device according to the invention thus functions without sensors which sense the rotational speed differences between the driving wheels or other electronics which are to control differential brakes or the like.
Further aspects and advantages of the present invention will be evident from the detailed description of a number of conceivable embodiments and variants and from the following patent claims.
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PCT Application (PCTSE98/00546) Published by WIPO No. 98/43845, Oct. 8, 1998.
Boehler Anne Marie
Kilpatrick & Stockton LLP
Marcou George T.
Unic Aktiebolag
Winner Tony
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