WO2018122460A1

WO2018122460A1 - Transmission system for a vehicle and a method for changing rotation speed of drive shafts of a vehicle

Info

Publication number: WO2018122460A1
Application number: PCT/FI2017/050947
Authority: WO
Inventors: Kalle Pohjola; Heikki Pohjola
Original assignee: Finncat Oy
Priority date: 2016-12-29
Filing date: 2017-12-28
Publication date: 2018-07-05
Also published as: FI20166044L

Abstract

A transmission system for a vehicle comprises a primary shaft (10), a first planetary gear train (22a) and a second planetary gear train. The planetary gear trains comprise a ring gear (12), a carrier (14) for supporting planet gears (26), a first drive shaft mounted on the carrier of the first planetary gear train, a second drive shaft mounted on the carrier of the second planetary gear train, as well as secondary transmission devices for changing the rotation speeds of the ring gears of the first and second planetary gear trains. The secondary transmission devices comprise first control devices for changing the rotation speed of the ring gear of the first planetary gear train, and second control devices for changing the rotation speed of the ring gear of the second planetary gear train, the first and second control devices being independent of each other. Preferably, the ring gears are equipped with an external toothing (34), and said first and second control devices comprise a self- locking worm (20) arranged to engage the external toothing, and a control motor (18) for spinning the worm. In the method, the rotation speeds of the drive shafts of the vehicle are changed by adjusting the rotation speeds of the ring gears by secondary transmission devices independently from each other.

Description

TRANSMISSION SYSTEM FOR A VEHICLE AND A METHOD FOR CHANGING ROTATION SPEED OF DRIVE SHAFTS OF A VEHICLE

The invention relates to a transmission system for a vehicle, comprising a primary shaft, a first planetary gear train and a second planetary gear train, the planetary gear trains comprising a ring gear and a carrier for supporting planet gears, a first drive shaft mounted on the carrier of the first planetary gear train, and a second drive shaft mounted on the carrier of the second planetary gear train, as well as secondary transmission devices for changing the rotation speed of the ring gears of the first and second planetary gear trains. The invention also relates to a method for controlling the rotation speed of the drive shafts in a vehicle equipped with the transmission system according to the invention.

In vehicles, drive wheels or two track belts may be used as the driving structure. When driving straight forward on an anti-skid ground, all the drive wheels and track belts have the same rotation speed. When the vehicle makes a turn, the wheels or the track belt on the outside bend have to rotate faster than those on the inside bend, so that the vehicle could be steerable. A situation requiring different rotation speeds may also occur when the vehicle travels on surfaces or under conditions where the direction of propagation of the vehicle differs from the heading. For maintaining the capacity to propagate and the steerability of vehicles under various conditions, the vehicles are equipped with a transmission mechanism which makes it possible to distribute the driving force produced by the motor of the vehicle to the wheels or track belts in the appropriate way.

Document WO 87/04986 describes a driving and steering system for a vehicle having at least two driving wheels or tracks. The mechanism comprises two drive shafts, each equipped with a planetary gear set provided at the end of the shaft. The planetary gear sets comprise a sun gear which is subjected to the primary transmission of power generated by the motor of the vehicle. The drive shafts are mounted on carriers supporting the planet gears. The carriers are surrounded by a ring gear whose outer surface is provided with a toothing. The ring gears of the planetary gear sets are next to each other, and a conical gear is arranged between them, whereby the ring gears can be rotated in opposite directions by rotating the shaft connected to the conical gear so that the rotation speed of the drive shafts is changed. The transmission for changing the rotation speed of the drive wheels is often called the secondary transmission. The solution described in WO 87/04986 involves the problem that a relatively great power is needed for rotating the conical gear, which increases the manufacturing and operating costs of the mechanism. The conical gear has to be subjected to a retaining force also when driving straight forward, in order to keep the rotation speed of the drive shafts constant.

It is an aim of the invention to present a transmission system for a vehicle and a method for controlling the rotation speed of the drive shafts of a vehicle, by which problems involved in the state of art can be eliminated.

The aims of the invention are achieved by a transmission system and a method, which are characterised in what will be presented in the characterizing parts of the independent claims. Some advantageous embodiments of the invention will be presented in the dependent claims.

The invention relates to a transmission system for a vehicle, comprising a primary shaft, a first planetary gear train and a second planetary gear train. The planetary gear trains comprise a ring gear, a carrier for supporting the planet gears, a first drive shaft mounted on the carrier of the first planetary gear train, a second drive shaft mounted on the carrier of the second planetary gear train, as well as secondary transmission devices for changing the rotation speed of the ring gears of the first and second planetary gear trains. The secondary transmission devices comprise first control devices for changing the rotation speed of the ring gear of the first planetary gear train, and second control devices for changing the rotation speed of the ring gear of the second planetary gear train, the first and second control devices being independent of each other. Independence of the control devices refers to the fact that the rotation speed of the ring gear of each planet gear can be changed independently so that a change in the rotation speed of one ring gear will not affect the rotation speed of the other ring gear.

In a preferred embodiment of the transmission system according to the invention, the primary shaft has a first end and a second end, and the first planetary gear train is at the first end of the primary shaft, and the second planetary gear train is at the second end of the primary shaft.

In another preferred embodiment of the transmission system according to the invention, the ring gears are equipped with an external toothing, and said first and second control devices comprise a matching worm placed to engage the external toothing, and a control motor for rotating the worm. Preferably, the control motor is an electric motor.

The worm may be a so-called self-locking worm. The self-locking worm refers to the fact that the force possibly applied on the worm via the external toothing of the ring gear does not make the worm rotate. The self-locking capacity of the worm is achieved by the shape of the thread of the worm and the suitable pitch of the thread. Instead of complete self-locking capacity, the worm may be set to operate very close to the self-locking capacity, whereby the worm can be kept non-spinning by a very small force generated by the control motor. On the other hand, the ring gear and the drive shaft can be made to spin by releasing the control motor. Such a property may be utilized, for example, in vehicles equipped with ABS brakes.

A third preferred embodiment of the transmission system according to the invention comprises a control unit for controlling the operation of the control motors. The control unit may be a part of the electronic control system for the transmission of the vehicle.

The transmission system according to the invention may be the transmission system of a crawler driven vehicle, such as a snow mobile. Alternatively, the transmission system may be the transmission system of a wheeled vehicle or machine, such as an automobile or a tractor. The method according to the invention is applied in a vehicle equipped with a transmission system comprising a primary shaft, a first planetary gear train and a second planetary gear train. The planetary gear trains comprise a ring gear and a carrier for carrying planet gears. A first drive shaft is mounted on the carrier of the first planetary gear train, and a second drive shaft is mounted on the carrier of the second planetary gear train. In the method, the rotation speeds of the drive shafts of the vehicle are changed by adjusting the rotation speeds of the ring gears by secondary transmission devices. The method is characterized in that the rotation speed of the ring gear of the first planetary gear train and the rotation speed of the ring gear of the second planetary gear train are adjusted independently of each other.

In a preferred embodiment of the method according to the invention, when the vehicle turns in the direction pointed by the first drive shaft, the rotation speed of the first drive shaft is reduced by spinning the ring gear of the first planetary gear train in a direction opposite to the direction of rotation of the primary shaft, and the spinning of the ring gear of the second planetary gear train is prevented.

In a second preferred embodiment of the method according to the invention, when the vehicle turns in the direction pointed by the second drive shaft, the rotation speed of the second drive shaft is reduced by spinning the ring gear of the second planetary gear train in a direction opposite to the direction of rotation of the primary shaft, and the spinning of the ring gear of the first planetary gear train is prevented.

In some situations, the drive shafts of the vehicle may tend to spin at a speed higher than the driving speed of the vehicle. This is the case, for example, upon reverse braking when the vehicle is driven downhill. In such a situation, the ring gear of the planetary gear train can be rotated in the direction of rotation of the primary shaft by a very low force. Thus, it may be advantageous to control the rotation speeds of the drive shafts by accelerating the rotation speeds of the ring gears.

Consequently, in a third preferred embodiment of the method according to the invention, when the vehicle is turned in a direction pointed by the first drive shaft, the rotation speed of the second drive shaft is increased by spinning the ring gear of the second planetary gear train in the direction of rotation of the primary shaft. Correspondingly, when the vehicle is turned in a direction pointed by the second drive shaft, the rotation speed of the first drive shaft is increased by spinning the ring gear of the first planetary gear train in the direction of rotation of the primary shaft.

In a fourth preferred embodiment of the method according to the invention, the ring gear is rotated by a worm, preferably a self-locking worm.

The invention has the advantage of making it possible to change the rotation speed of the drive shafts by very little secondary energy.

The invention also has the advantage that the transmission system has a simple structure and is reliable in operation.

In the following, the invention will be described in detail. In the description, reference will be made to the appended drawings, in which Fig. 1 a shows, by way of an example, a transmission system according to the invention in a diagonal view from above, Fig. 1 b shows the transmission system of Fig. 1 a in a horizontal cross-sectional view, and

Figs. 2a, 2b, and 2c show, by way of example, parts of the transmission system according to the invention in reduced cross-sectional views. Figure 1 a shows, by way of an example, a transmission system according to the invention, seen diagonally from above, and Fig. 1 b shows the same transmission system in a cross-sectional view cut along the plane of the shafts. In the following, both figures will be described at the same time.

The transmission system comprises a frame housing 1 accommodating three parallel shafts. A primary shaft 10 is provided at the first end of the frame housing, an input shaft 2 at the second end, and an intermediate shaft 4 between the first and second shafts. The first end of the input shaft extends outside the frame housing, on its first side, and the second end of the intermediate shaft extends outside the frame housing, on its second side. The first end of the input shaft is intended to be connected to the motor of the vehicle in such a way that the motor is applied to bring the input shaft to a rotary motion. Gears 6 are provided around the input shaft and the intermediate shaft, the teeth of the gears meshing so that the rotary motion of the input shaft is transmitted to the intermediate shaft. A brake disc 5 is provided at the second end of the intermediate shaft extending outside the frame housing, for restricting the spinning of the intermediate shaft. A toothed disc 8 is provided around the intermediate shaft 4 and the primary shaft 10 which are encircled by a sprocket chain 9 transmitting the rotary motion of the intermediate shaft to the primary shaft.

A first planetary gear train 22a and a second planetary gear train 22b are provided at the first end and the second end of the primary shaft, respectively. The planetary gear trains are structurally identical and mirror images of each other. In a way to be described hereinbelow, the planetary gear trains are equipped with drive shafts so that the first drive shaft 16a connected to the first planetary gear train extends outside the frame housing 1 , on its first side, and the second drive shaft 16b connected to the second planetary gear train extends outside the frame housing, on its second side. The rotary motion of the primary shaft is transmitted by the planetary gear trains to a rotary motion of the drive shafts. Parts belonging to the driving structure of the vehicle and to be rotated, such as track wheels for rotating a track, or wheels rolling on the ground, may be attached to the drive shafts. The transmission system according to the invention is suitable for use in any vehicle having at least two drive wheels or rolls on different sides of the vehicle. Thus, the vehicle may be a car or a truck, a machine movable on wheels or tracks, or an off- road vehicle movable on wheels or tracks, for example a snow mobile. Figure 2a shows, by way of an example, a reduced view of a first planetary gear train 22a of a transmission system according to the invention. The figure shows the planetary gear train in cross-sectional view cut along a plane parallel with the primary shaft 10. The first planetary gear train is a mirror image of the second planetary gear train. Figure 2b shows the planetary gear train of Fig. 2a in a cross- sectional view cut along the plane A-A, and Fig. 2c shows it in a cross-sectional view cut along the plane B-B. In the following, all the figures will be described at the same time.

The planetary gear train comprises a sun gear 24 integrated at the end of the primary shaft 10 and having a toothing at its outer rim. The sun gear is surrounded by three planet gears 26, the toothing at their outer rim engaging the toothing of the sun gear. The sun gears are mounted on a disc-like carrier 14 by pins 30. A first drive shaft 16a is mounted on the outer surface of the carrier, its end extending outside the frame housing 1 through a shaft hole 32 mounted with bearings.

A ring gear 12 is provided on the first side of the sun gear, the primary shaft 10 extending through the central hole in the ring gear. A bearing 28 is provided between the outer surface of the primary shaft and the hole in the ring gear, allowing the rotation of the primary shaft in the hole of the ring gear. A collar encircles the outer rim of the ring gear, extending around the planet gears 26. An inner toothing 36 is provided on the inner surface of the collar, engaging the toothing of the planet gears. The rotary motion of the primary shaft is transmitted by the sun gear to the planet gears which mesh with the internal toothing of the ring gear, thereby rotating the carrier 14 and the first drive shaft 16a connected to it.

In the transmission system according to the invention, the outer surface of the ring gear is provided with an external toothing 34, and within the frame housing a worm 20 is provided whose threading engages the external toothing of the ring gear. A control motor 18 is provided within the frame housing, for rotating the worm in either direction of rotation (Fig. 2b). The control motor is an electric motor connected by electric conductors to the electric system of the vehicle (the electric conductors are not shown in the figure). When the worm is not rotated by the control motor, the ring gear 12 remains stationary with respect to the frame housing; in other words, it does not rotate around the primary shaft. The shape of the threading of the worm is selected so that the worm is self-locking; in other words, the worm will not rotate about its axis even if it were subjected to the force of the ring gear via the outer toothing 34 of the ring gear. The worm and the ring gear supported to it thus always assume a non-rotating state when the control motor is not in use.

By using the control motor, it is possible to rotate the worm in either direction of rotation, making the ring gear rotate with respect to the frame housing. When the ring gear is rotated in the same direction of rotation as the primary axis 10, the rotation speed of the first drive shaft 16a increases. Correspondingly, when the ring gear is rotated in a direction opposite to the direction of rotation of the primary axis, the rotation speed of the first drive shaft decreases. By using the control motor, it is thus possible to influence the rotation speed of the drive shaft even though the rotation speed of the primary shaft remains unchanged. The power of the control motor is substantially lower than the power of the motor driving the primary shaft of the vehicle, and the force applied to the ring gear is substantially lower than the force output by the motor of the vehicle and applied for driving the primary shaft. The power of the control motor may be, for example, 0.1 to 1 .0 kW, whereas the power of the motor of the vehicle, for driving the primary shaft, may be 2 to 500 kW. Consequently, the power generated by the control motor and applied to the ring gear is called secondary transmission.

The transmission system according to the invention further comprises a control unit 38 for controlling the operation of the control motors. The control unit may be a separate device, or it may be a part of the electronic control system for the transmission of the vehicle. The control unit detects a need for turning the vehicle and, on the basis of this, computes the optimal rotation speeds for the first and second drive shafts. For example, when the vehicle is turned to the right from the direction of travel, the rotation speed of the drive wheels or tracks on the right hand side of the vehicle is reduced to facilitate the turning of the vehicle. Correspondingly, when the vehicle is turned to the left, the rotation speed of the drive wheels or tracks on the left hand side of the vehicle is reduced. When the vehicle is turned, the rotation speed of its drive wheels or tracks on the side of the outside curve is maintained and the rotation speed of the drive wheels or tracks on the inner curve is decelerated. The control unit detects the turning angle of the vehicle e.g. on the basis of the position of the steering wheel or handlebar, and, on the basis of this, computes how much the rotation speed of the drive shaft to be decelerated has to be changed. After this, the control unit 38 controls the control motor 18 to rotate the worm 20 in such a way that the ring gear 12 rotates in a direction opposite to the direction of rotation of the primary shaft 10, whereby the rotation speed of the drive shaft to be decelerated is reduced. The rotation speed of the drive shaft on the side of the outside bend does not need to be changed, so that the ring gear of the planetary gear train connected to it is not rotated in either direction.

Consequently, in a vehicle equipped with a transmission system according to the invention, the control can be assisted by changing the rotation speed of the ring gear of only one of the two planetary gear trains. The invention makes this possible, because the rotation speed of the ring gears is controlled by control motors run independently of each other. In the most economic way, the control can be assisted by decelerating the rotation speed of the drive shaft on the side of the inner bend and maintaining the rotation speed of the drive shaft on the side of the outer bend. When the vehicle is turned, the rotation speed of its wheels on the side of the inner bend naturally tends to decrease, whereby the deceleration of the rotation speed of the ring gear requires very little power. In practice, for rotating the worm, power of the control motor is only needed for overcoming the friction of the worm. Thus, very low-power electric motors may be used as the control motors. Naturally, control motors may also be used for increasing the rotation speed of the ring gear if the rotation speed of the drive shaft is to be increased.

In the description presented above, the sun gears of the planetary gear trains are coupled directly to the ends of the primary shafts. The transmission between the planetary gear trains and the primary shaft may also be implemented in another way, for example by means of a reduction gear.

In the above description, the transmission system according to the invention was used for adjusting the rotation speed of drive wheels on a single shaft. The transmission system according to the invention may also be used in four-wheel drive vehicles, wherein the transmission system is mounted on the rear axle of the vehicle so that it adjusts the rotation speed of the drive wheels of the rear axle to the rotation speeds of the drive wheels of the front axle as well.

Some advantageous embodiments of the transmission system for a vehicle according to the invention have been described above. The invention is not limited to the solutions described above, but the inventive idea may be applied in different ways within the scope of the claims.

Claims

1 . A transmission system for a vehicle, comprising a primary shaft (10), a first planetary gear train (22a) and a second planetary gear train (22b), the planetary gear trains (22a, 22b) comprising a ring gear (12) and a carrier (14) for supporting planet gears (26), a first drive shaft (16a) mounted on the carrier (14) of the first planetary gear train (22a), and a second drive shaft (16b) mounted on the carrier (14) of the second planetary gear train (22b), as well as secondary transmission devices for changing the rotation speed of the ring gears (12) of the first and second planetary gear trains (22a, 22b), characterized in that said secondary transmission devices comprise first control devices for changing the rotation speed of the ring gear (12) of the first planetary gear train (22a), and second control devices for changing the rotation speed of the ring gear (12) of the second planetary gear train (22b), the first and second control devices being independent of each other.

2. The transmission system according to claim 1 , characterized in that the primary shaft (10) has a first end and a second end, and the first planetary gear train

(22a) is at the first end of the primary shaft (10), and the second planetary gear train (22b) is at the second end of the primary shaft (10).

3. The transmission system according to claim 1 or 2, characterized in that said ring gears (12) are equipped with an external toothing (34), and said first and second control devices comprise a matching worm (20) placed to engage the external toothing (34), and a control motor (18) for rotating the worm.

4. The transmission system according to claim 3, characterized in that said worm (20) is a self-locking worm (20).

5. The transmission system according to claim 2 or 3, characterized in that the control motor (18) is an electric motor.

6. The transmission system according to claim 3 to 5, characterized in that it comprises a control unit (38) for controlling the use of the control motors (18).

7. The transmission system according to any of the claims 1 to 6, characterized in that it is a transmission system for a tracked vehicle, such as a snow mobile.

8. The transmission system according to any of the claims 1 to 6, characterized in that it is a transmission system for a wheeled vehicle or machine, such as an automobile or a tractor.

9. A method for changing the rotation speed of the drive shafts (16a, 16b) of a vehicle equipped with a transmission system comprising a primary shaft (10), a first planetary gear train (22a) and a second planetary gear train (22b), the planetary gear trains (22a, 22b) comprising a ring gear (12) and a carrier (14) for supporting planet gears (26), the first drive shaft (16a) being mounted on the carrier (14) of the first planetary gear train (22a), and the second drive shaft (16b) being mounted on the carrier (14) of the second planetary gear train (22b), and wherein the rotation speeds of the ring gears (12) are adjusted by secondary transmission devices, characterized in that, in the method the rotation speed of the ring gear (12) of the first planetary train (22a) and the rotation speed of the ring gear (12) of the second planetary train (22b) are adjusted independently of each other.

10. The method according to claim 9, characterized in that when the vehicle is turned in the direction pointed by the first drive shaft (16a), the rotation speed of the first drive shaft (16a) is reduced by rotating the ring gear (12) of the first planetary gear train (22a) in a direction opposite to the direction of rotation of the primary shaft (10), and the rotation of the ring gear (12) of the second planetary gear train (22b) is prevented.

1 1 . The method according to claim 9 or 10, characterized in that when the vehicle is turned in the direction pointed by the second drive shaft (16b), the rotation speed of the second drive shaft (16b) is reduced by rotating the ring gear (12) of the second planetary gear train (22b) in a direction opposite to the direction of rotation of the primary shaft (10), and the rotation of the ring gear (12) of the first planetary gear train (22a) is prevented.

12. The method according to claim 9, characterized in that when the vehicle is turned in the direction pointed by the first drive shaft (16a), the rotation speed of the second drive shaft (16b) is increased by rotating the ring gear (12) of the second planetary gear train (22b) in the direction of rotation of the primary shaft (10).

13. The method according to claim 9 or 12, characterized in that when the vehicle is turned in the direction pointed by the second drive shaft (16b), the rotation speed of the first drive shaft (16a) is increased by rotating the ring gear (12) of the first planetary gear train (22a) in the direction of rotation of the primary shaft (10).

14. The method according to any of the claims 9 to 13, characterized in, that the ring gear (12) is rotated by a worm (20), preferably a self-locking worm (20).