The present invention relates to a gear device for steplessly variable transmission, comprising an epicyclic gear having a central sun wheel, planetary wheels, and an outer annulus and a planetary wheel carrier for mounting of the planetary wheels, and an output shaft, whereby the annulus is coupled to an appliance for controlled, adjustable rotation.

It is well known that the rotation of the annulus influences the transmission ratio between the sun wheel and the planetary wheel carrier. US Patent 4341132 describes a device as mentioned above. Operational energy for a hydraulic circuit is taken from the input shaft of the gear, which for instance may be the output shaft from a motor. Means are provided for adjusting the influence on the annulus, in order that it can be brought to rotate with different speeds or kept at rest. In order to achieve large transmission ratios the annulus has to rotate relatively fast, and all of the drive energy must be transmitted via the hydraulic system, which has a relatively small efficiency.

US Patent 4382392 describes a gear device which comprises two serially coupled epicyclic gears, for the achievement of a large variation of the transmission ratio. The device is mechanically complicated and requires a large power consump¬ tion.

The present invention provides a gear device being charac¬ terized by the features appearing from the succeeding claim 1.

The invention is based on the acknowledgement that the annulus of the epicyclic gear should be mechanically driven, in order to keep the power consumption low. This is achieved in that a differential is interconnected for transmitting the input power to the sun wheel.of the epicyclic gear, from one of the driving wheels in the differential, whereby the other

driving wheel is coupled to an adjustment wheel which can transmit a torque to the annulus, and whereby the adjustment driving appliance is used to determine the torque to be transmitted to the annulus.

The invention is not limited to a hydraulically operated adjustment, in that for instance also an electrical adjust¬ ment can be used. The adjustment driving appliance will directly influence the rotation of the annulus of the epicyclic gear, but as the adjustment driving appliance is also coupled to the sun wheel of the epicyclic gear, indirectly via the differential, it will simultaneously influence the rotation of the sun wheel.

When the gear device is used in a vehicle it is able to cause a steplessly variable shifting down, i.e. a reduced rotation¬ al speed of the output shaft from the epicyclic gear relatively to the input shaft of the differential. Also a shifting up, i.e. driving in overdrive, and reverse can be achieved.

The invention will hereinafter be explained more detailed, with reference to the accompanying drawings, which show an example of an embodiment of a gear device according to the invention.

Fig. 1 shows the gear device somewhat diagramatically, and the epicyclic gear and the differential are shown partly in an axial longitudinal section.

Fig. 2 shows diagrammatically the wheels incorporated in the epicyclic gear and a transmission wheel for controlling the annulus of the epicyclic gear, seen axially.

Fig. 1 shows an input shaft 1, which for instance may be directly coupled to a motor (internal combustion engine, electric motor) . The shaft l.has a toothed gear 2, shown as a pinion, in engagement with a toothed ring on a differential

housing 4. It will be appreciated that the shaft 1 can have any direction relatively to the differential housing 4. The differential 3 contains in a known manner planetary wheels 5, usually two, being in driving engagement with two drive wheels 6 and 7, each having a drive shaft 8 and 9 protruding from the differential housing on respective sides thereof.

One drive shaft 8 is in fixed connection with a central sun wheel 12 in an epicyclic gear 10. The epicyclic gear furthermore comprises planetary wheels 13, usually at least three in order to secure centering, distributed around the sun wheel 12. The planetary wheels 13 are surrounded by an annulus 14. All the wheels are toothed. The mutual location and engagement of the wheels appear more clearly from Fig. 2, which shows the sun wheel 12, three planetary wheels 13 distributed with angular spacings of 120° and the annulus 14. The annulus is also toothed on the outside, and is in engagement with a transmission wheel 20. The purpose of this will be further explained in the following. Moreover, the epicyclic gear comprises a planetary wheel carrier 11 which is in fixed connection with an output shaft 16, which for instance may be in driving connection with vehicle wheels, through a not shown differential. The planetary wheels 13 are mounted for rotation in the planetary wheel carrier 11, and in order to achieve a bilateral and stable mounting of the planetary wheels 13 they are also mounted in a mounting disc 15.

The second drive shaft 9 protruding from the differential housing 4 carries an adjustment wheel 17, which via a transmission wheel 18 and a transmission shaft 19 is in connection with said transmission wheel 20 and thereby in connection with the annulus 14 of the epicyclic gear.

All the crossed rectangles are diagrammetrical representa¬ tions of bearings, which for instance may be conventional ball or roller bearings. In order not to complicate the

drawings a housing needed for mounting of the bearings and for keeping the gear device together as a unit is not shown.

It will appear from the above that when power is supplied to the gear device through the input shaft 1 it is possible to achieve rotation of both of the output drive shafts 8 and 9 from the differential 3. Except from a certain frictional loss a corresponding power can be taken out through the output shaft 16 from the epicyclic gear 10.

For controlling of the gear device this comprises a control appliance, which in the example shown comprises a hydraulic pump 21, a hydraulic motor 22 being in driving connection with the adjustment wheel 17 through a shaft 23, and a control unit 24. It will be appreciated that the motor can be coupled to the adjustment system anywhere between the drive shaft 9 and the annulus 14, and it will be appreciated that the hydraulic pump 21 and the motor 22 can be replaced by an electric motor. In the example shown the pump is driven by the input shaft 1. The motor 22 can influence the adjustment wheel 17 in four different ways, by braking of the wheel, by keeping the wheel at rest ( no rotation ) , by driving the wheel at a higher rotational speed than that in which the wheel is driven by the differential 3, and by reversing the wheel. The annulus 14 will of course be influenced cor¬ respondingly, and also the rotation of the sun wheel 12 will be influenced. Under the premise that the input shaft 1 rotates with a constant rotational speed braking of the adjustment wheel 17 ( and the annulus 14 ) will cause an increased rotational speed of the sun wheel 12 and of the planetary wheel carrier 11 ( and the output shaft 16 ) , i. e. the transmission ratio between the input shaft 1 and the output shaft 16 will be changed, and to a larger degree than if the adjustment merely influenced the adjustment wheel 17 and the annulus 14. Correspondingly, positive driving of the adjustment wheel 17 and the annulus 14 by means of the motor 22 will cause that the ^' rotational speed of the sun wheel 12 decreases, and the transmission ratio between the input shaft

1 and the output shaft 16 will also in this case be changed to a larger degree than by adjustment of the rotational speed of only the adjustment wheel 17 and the annulus 14.

When using a hydraulic pump for driving a hydraulic motor the pump may conveniently be an axial piston pump which may be adjusted steplessly. The pump is controlled by the control unit 24, which must be adapted to what is desired to achieve with the gear device.

When the gear device is to be used in a vehicle, no releas- able coupling ( clutch ) between the driving engine and the gear device is needed. For starting of the driving engine and running at idling speed without driving of the output shaft 16, provision may be made in order that the sun wheel 12 and the annulus 14 rotate in mutually opposite direction. nd at such rotational speeds that the planetary wheel carrier 11 and the output shaft do not rotate. Alternatively a releas- aole coupling may be employed, but this is not to be used during driving.

If an electric motor is employed in stead of the hydraulic mo-or 22, this may for braking of the adjustment wheel 17 be adapted to act as a generator.

For a certain rotational speed of the input shaft 1 there will for the shown embodiment of the gear device be a rotational speed for the drive wheel 7 in the differential, i.e. for the shaft 9 and the adjustment wheel 17, which implies that the planetary wheel carrier 11 and the output shaft 16 do not rotate. This rotational speed for the drive wheel 7 constitutes a partition between the two directions of rotation of the planetary wheel carrier 11 and the output shaft 16.

It will be appreciated that the gear device according to the invention can be designed in many ways also with respect to the mechanical structure and that the shown transmission

ratios within the epicyclic gear 10 and in the transmission from the shaft 9 to the annulus 14 via the adjustment wheel

17 and the transmission wheels 18 and 20 and the shaft 19 can be chosen within wide limits. The mutual location of the units can be different from that shown. For instance the motor 22, or an electric motor substituting it, can be coupled anywhere in the adjustment system for the annulus 14, also directly thereto.