A TRANSMISSION SYSTEM FOR A VEHICLE Field of the invention

This invention relates to a transmission system for a vehicle. More particularly, it relates to a transmission system for a hybrid vehicle.

Background of the invention

Power from the engine is transmitted to the wheels through transmission systems. There are two types of transmission systems, namely manual transmission and continuous variable transmission (CVT). In manual transmission, a gear box with simple gear arrangements using spur or helical gears are assembled for achieving different gear ratios. The gear ratios are achieved in terms of steps. However, in manual transmission, due to the fixed number of gear ratios the output gear ratios are in steps and fixed. This reduces the flexibility of the power train. The next type of transmission system is the CVT. In CVT, a primary sheave is connected to a crankshaft and a secondary sheave is connected to the transmission side of the vehicle. The primary sheave and the secondary sheave is connected through a belt. This configuration enables seamless variable gear ratio, however such an arrangement causes major transmission losses.

Hence there is need for a transmission system which has similar transmission efficiency as the manual transmission and the seamless variable gear arrangement and minimal transmission losses.

Brief description of the accompanying drawings

Figure 1 illustrates a schematic representation of a transmission system, in accordance with an embodiment of the present disclosure; and

Figure 2 is a graph that illustrates working of a transmission system, in accordance with an embodiment of the present disclosure. Figure 3 illustrates a schematic representation of a transmission system, in accordance with another embodiment of the present disclosure.

Detailed description

The transmission system for a vehicle comprises planetary gear arrangement (10) coupled between a crankshaft (20) and a transmission shaft (22). The planetary gear arrangement (10) comprises an inner sun gear (12), an outer ring gear (18) and at least two planetary gears (14a) & (14b) meshed with the sun gear (12) and a ring gear (18). The transmission system is characterized by a motor (30) coupled to one of the sun gear (12), the ring gear (18) and the two planetary gears (14a) & (14b) for controlling rotation of the transmission shaft (22) such that a plurality of gear ratios are obtained. The working of the transmission system is explained in detail using various embodiments in below paragraphs.

In first embodiment, the sun gear (12) shaft is in communication with the crankshaft (20) of the vehicle, the two planetary gears (14a) & (14b) are in communication with the transmission shaft (22) and the ring gear (18) is coupled to the motor (30). The working of the first embodiment is explained below with reference to Figure 1.

In accordance with the second embodiment, the sun gear shaft (12a) is in communication with the crankshaft (20) of the vehicle, the ring gear (18) is in communication with the transmission shaft (22) and the four planetary gears (14a), (14b), 14c) & (14d) are coupled to the motor (30). The working of the first embodiment is explained below with reference to Figure 3 in the following paragraphs.

In accordance with the third embodiment, the ring gear (18) is in communication with the crankshaft (20) of the vehicle, the sun gear shaft (12a) is in communication with the transmission shaft (22) and the two planetary gears (14a) & (14b) are coupled to the motor (30). In accordance with the fourth embodiment, the two planetary gears (14a) & (14b) are in communication with the crankshaft (20) of the vehicle, the sun gear shaft (12a) is in communication with the transmission shaft (22) and the ring gear (18) is coupled to the motor (30).

In accordance with the fifth embodiment, the two planetary gears (14a) & (14b) are in communication with the crankshaft (20) of the vehicle, ring gear (18) is in communication with the transmission shaft (22) and the sun gear shaft (12a) is coupled to the motor (30).

In accordance with the sixth embodiment, the ring gear (18) in communication with the crankshaft (20) of the vehicle, two planetary gears (14a) & (14b) are in communication with the transmission shaft (22) and sun gear shaft (12a) is coupled to the motor (30).

There are various other embodiments possible, in which one of the sun gear, ring gear or the planetary gear is connected to the input or crankshaft (20), while the second gear is connected to the output or transmission shaft (22), and the third gear is connected to motor (30). The rotation of the motor (30) is selectively controlled to achieve desired gear reduction ratios.

The motor (30) that drives the various shafts is rotated by current supplied by an electronic controller. The electronic controller may be a processor that receives vehicle information from various sources. The electronic controller determines a crankshaft rotation speed of the vehicle from a crankshaft sensor determines gear reduction required to operate the vehicle and then transmits the current for operating the motor (30) based on the crankshaft rotation speed and the gear reduction required.

The transmission system according to the first embodiment is explained in detail with reference to Figure 1. The sun gear (12) is mounted on a sun gear shaft (12a) and in communication with a crankshaft (20) of the vehicle. In some embodiments, the sun gear (12) may be mounted directly on the crankshaft (20). The two planetary gears (14a) & (14b) are coupled to a planet carrier shaft (16). The planet carrier shaft (16) is connected to a transmission shaft (22) of the vehicle. The ring gear (18) is driven by a motor (30). The ring gear (18) can even be driven by the engine crankshaft (20) in some cases for obtaining a plurality of gear ratios at the transmission shaft (22).

The diameter of the sun gear (12) is greater than the planetary gears (14a) & (14b) but lesser than the ring gear (18). The diameter of the planetary gears (14a) & (14b) are lesser than the sun gear (12) and the ring gear (18). Usually all the planetary gears (14a) & (14b) will have equal diameters and have equal number of teeth. The diameter of the ring gear (18) is larger than the diameter of the sun gear (12) and the planetary gear (14a) & (14b). The diameter of the sun gear (12), the planetary gears (14a) & (14b) and the ring gear (18) is chosen based on the maximum gear ratio required. In some cases, the diameter of the Sun gear (12) can be lower than the planetary gear (14a) & (14b) based on the overall gear ratio required.

Also, the number of teeth present in the sun gear (12), planetary gears (14a) & (14b) and the ring gear (18) is defined based on smoothness expected during gear change and band between maximum gear ratio to minimum gear ratio. It should be noted that, larger the number of teeth present in each of the gears, smoother the gear change occurs without any jerks during gear change.

The sun gear shaft (12a) is in communication with the crankshaft (20) through a first connector (24). Examples of the first connector (24) include, but are not limited to, a belt drive connector or a gear drive connector or a direct drive where the sun gear (12) is mounted directly on the crankshaft (20). Since, the sun gear shaft (12a) is connected to the crankshaft (20), the sun gear shaft (12a) rotates with the speed equal to the rotation of the crankshaft (20).

The planetary gears (14a) & (14b) are coupled to a single planet carrier shaft (16). In one embodiment, there may be two planetary gears (14a) & (14b). In another embodiment, there may be three planetary gears and in yet another embodiment, there may be four planetary gears. The number of planetary gears used is decided based on maximum torque required. It should be noted that higher the torque required, higher will be the number of the planetary gears. If lower torque is required for an application then the lesser number of planetary gears are used. The planet carrier shaft (16) is connected to the transmission shaft (22) through a second connector (26). The second connector (26) may be a gear drive connector. The transmission shaft (22) is connected to a final reduction means through a clutch. The clutch may be controlled manually or automatically. Hence, the transmission shaft (22) rotation will be equal to the planet carrier shaft (16) rotation. Therefore the transmission shaft (22) is connected to wheels (rear wheel) of the vehicle through the final reduction means which may be gear box or chain and sprocket assembly or a belt drive.

The ring gear (18) is mounted on a ring gear shaft (18a). The ring gear shaft (18a) is driven by a motor (30) through a gear (19). In an embodiment of the invention, the motor (30) selectively coupled or decoupled to the ring gear shaft (18a) through a clutch (not shown in figure) Examples of the motor (30) include, but are not limited to, an electric motor, a pneumatic motor and a hydraulic motor. Speed of rotation of the ring gear (18) enables the transmission system in obtaining plurality of gear ratios. According to this disclosure, plurality of gear ratios refer to infinite gear ratios. The speed of the ring gear (18) controls speed of rotation of the sun gear (12). Further, the speed of rotation of the sun gear (12) controls speed of rotation of the planetary gears (14a) & (14b). The speed of rotation of the planetary gear is thus obtained at the transmission shaft (22). Hence, controlling the speed of rotation of the ring gear (18) by the motor (30) is responsible for obtaining various gear ratios at the transmission end of the vehicle. The speed of motor (30) is proportional to the speed of rotation of the ring gear (18). The speed of the motor (30) depends on current wheel speed, current engine speed and gear ratio required at the transmission shaft (22).

Working of the embodiment disclosed in the above paragraphs are explained with reference to the graph illustrated in Figure 2. According to the graph, curve 205 represents speed of crankshaft (20), curve 210 represents speed of transmission shat (22), curve 215 represent speed of rotation of the motor (30) and the curve 220 represent gear ratio .

Initially the crankshaft (20) rotation (engine speed) is low, for example at about 2000 rpm. This means the sun gear shaft (12a) is also rotating at 2000 rpm and hence the sun gear (12) also rotates at 2000 rpm. As the sun gear (12) is rotating at 2000 rpm, simultaneously the ring gear (18) is also rotating. The ring gear (18) is rotated by the motor (30). The motor (30) rotates the ring gear shaft (18a) at speed ranging from 0-500 rpm but in the direction opposite to the rotation of the sun gear shaft (12a) and hence the ring gear (18) rotates in the direction opposite to the sun gear (12). Such rotation of the ring gear (18) in the opposite direction will limit the speed of rotation of the sun gear (12) through the planetary gears (14a) & (14b) that are connected in between the sun gear (12) and the ring gear (18).

Such limitation of the speed of rotation of the sun gear (12), will reduce speed of rotation of the planetary gears (14a) & (14b) and the planet carrier shaft (16). In some cases, the planetary gears (14a) & (14b) may not rotate as the speed of rotation of the sun gear (12) due to the reverse rotation of ring gear (18). When the planetary gears (14a) & (14b) do not rotate, the planet carrier shaft (16) also does not rotate. When planet carrier shaft (16) is not rotating, the transmission shaft (22) will not rotate and hence the wheel of the vehicle will not rotate and the vehicle is in stand still mode. This condition can be considered that the vehicle is in neutral gear.

As the engine speed increases, the crankshaft (20) rotation increases, for example, the speed of rotation of the crankshaft (20) may be in the range of 2000-4000 rpm. Hence, the sun gear shaft (12a) rotates in the range of 2000-4000 rpm thereby the sun gear (12) is also rotating with the same speed since the sun gear (12) is mounted on the sun gear shaft (12a). When the crankshaft (20) is rotating at 2000-4000 rpm, the motor (30) is adapted to rotate the ring gear shaft (18a) in the speed range of 100-1000 rpm and in the same direction of rotation as the sun gear shaft (12a). Hence the ring gear (18) also rotates in the speed range of 100-1000 rpm and in the same direction of rotation as the sun gear shaft (12a).

The sun gear (12) rotating at 2000-4000 rpm and the ring gear (18) rotating at 100-1000 rpm in the same direction causes a gear ratio at the planet carrier shaft (16). Also, the reduction ratio is such that sufficient torque is produced for initial movement of the vehicle. The gear ratio at the planet carrier shaft (16) according to this example causes the planet carrier shaft (16) to rotate in the speed ranging between 1000-2500 rpm. Hence, when the sun gear shaft (12a) is rotating 2000-4000 rpm and the ring gear shaft (18a) is rotating at 100-1000 rpm in the same direction as the rotation of the sun gear shaft (12a), then the planet carrier shaft (16) rotates in the speed ranging between 1000-2500 rpm. Since torque is high, planet carrier shaft (16) rotates at low speeds such as 1000-2500 rpm.

The rotation of the planet carrier shaft (16) between 1000-2500 rpm rotates the transmission shaft (22) at 1000-2500 rpm. From the transmission shaft (22), the rotational speed is thus transmitted to the wheels. There can be additional reduction ratio between the transmission shaft (22) to the wheel to ensure sufficient torque at the wheel. The vehicle speed when the transmission shaft (22) is rotating at 1000-2500 rpm may be ranging from 5-15 kmph. At this speed, vehicle gear is analogous to first gear.

When the engine speed further increases, for example speeds ranging between 4000-6000 rpm, the sun gear shaft (12a) also rotates approximately in the range of 4000-6000 rpm. Hence the sun gear (12) is also rotating in the range of 4000-6000 rpm. When the crankshaft (20) is rotating at between 4000-6000 rpm, the motor (30) is adapted to rotate the ring gear (18) in the range of 1500-2500 rpm through the ring gear shaft (18a) in the same direction as rotation of the sun gear shaft (12a).

The rotation of the sun gear shaft (12a) 4000-6000 rpm and the rotation of the ring gear (18) between 1500-2500 rpm provides a corresponding gear ratio at the planetary gears (14a) & (14b). The gear ratio is such that the planet carrier shaft (16) rotates in the speed ranging between 2000-4000 rpm. This provides relatively lesser amount of torque when compared to the crankshaft (20) being rotated between 2000-4000 rpm. Since the planet carrier shaft (16) is connected to the transmission shaft (22), the transmission shaft (22) also approximately rotates between 2000-4000 rpm. When the transmission shaft (22) is rotating at speeds ranging between 2000-4000 rpm, the vehicle speed may be between 15-30 kmph. Vehicle speed of 15-30 kmph is analogous to vehicle being driven at second gear. Also, it should be noted that, since here torque is relatively low, speed is slightly higher.

As the engine speed further increases, for example, 6000-8000 rpm. The crankshaft (20) is rotated at 6000-8000 rpm and hence the sun gear (12) also rotates at speeds ranging from 6000-8000 rpm. At this engine speed, the motor (30) is adapted to rotate the ring gear (18) in the range of 2000-4500 rpm though the ring gear shaft (18a).

Speed of rotation of the sun gear (12) between 6000-8000 rpm and the ring gear (18) between 2000-4500 rpm causes a gear ratio at the planetary gears (14a) & (14b). Hence the planet carrier shaft (16) rotates at speed corresponding to the gear ratio obtained. The planet carrier shaft (16) rotates in the speed ranging between 4500-6000 rpm. Therefore the transmission shaft (22) also rotates at 4500-6000 rpm. Here, speed is high and torque is low. As the transmission shaft (22) rotates at 4500-6000 rpm, a corresponding vehicle speed obtained is 35-50 kmph. At this speed, the vehicle gear is analogous to third gear.

When the engine speed further increases, for example, the crankshaft (20) is rotating at speeds ranging from 8000-10000 rpm. Hence sun gear (12) also rotates between 8000- 10000 rpm.

At this engine speed, the motor (30) is adapted to rotate the ring gear (18) in the speed range of 4500- 10000 rpm, through the ring gear shaft (18a), in the same direction as the rotation of the sun gear shaft (12a).

When the sun gear (12) is rotating 8000-10000 rpm and the ring gear (18) is rotating at 4500- 10000 rpm then corresponding gear ratio achieved is such that the planetary gears (14a) & (14b) are rotating between 6000-10000 rpm and hence the planet carrier shaft (16) also rotates in the speeds ranging between 6000-10000 rpm. Hence the transmission shaft (22) also rotates at 6000-10000 rpm. At such high speeds, torque required is very low compared to the engine speeds mentioned in above paragraphs. The rotation of the transmission shaft (22) is further transmitted to the wheels. The corresponding vehicle speed when the transmission shaft (22) is rotating at 6000- 10000 rpm will be in the range of 55-85 kmph. When the vehicle is moving at such high speed, the moment of inertia of the vehicle enables the low torque requirement to keep the vehicle moving. At this vehicle speed, the vehicle gear is analogous to fourth gear.

Therefore according to the embodiment described in the above paragraphs, by controlling speed of rotation of the ring gear shaft (18a) by the motor (30), a plurality of gear ratios can be obtained. Also, the motor (30) can adjust the speed of rotation of the ring gear (18) as per the engine speed, vehicle speed and desired reduction ratio through an electronic controller. The electronic controller can read the engine speed and provide a corresponding current to the motor (30) for rotating the ring gear shaft (18a). The current provided to the motor (30) depends on the engine speed vehicle speed and desired reduction ratio. By controlling the speed of the ring gear shaft (18a) in conjunction with the rotation of the sun gear shaft (12a), an appropriate reduction ratio is achieved thus ensuring the planet carrier shaft (16) rotates in accordance with the achieved reduction ratio. Hence by controlling speed of rotation of the ring gear shaft (18a), various gear ratios can be achieved with a single set of planetary gear arrangement (10) and a motor (30). Also there is a provision to alter the number of teeth on the sun gear (12), planetary gears (14a) & (14b) and the ring gear (18) can be altered depending on the smoothness required during gear (18) change. Such design of the transmission system results in reduced size, weight, complexity and cost of the transmission system.

The transmission system in accordance with second embodiment is described in the following paragraphs. The transmission system comprises an inner sun gear (12), an outer ring gear (18) and four planetary gears (14a), (14b), (14c) & (14d) meshed with the sun gear (12) and the ring gear (18). The sun gear (12) is mounted on a sun gear shaft (12a) and in communication with a crankshaft (20) of the vehicle. In some cases, the sun gear (12) can also be mounted on the crankshaft itself. If the sun gear (12) is mounted on the sun gear shaft (12a) then the sun gear shaft (12a) and the crankshaft is connected through a connector (not shown in figure). The ring gear (18) is mounted on a ring gear shaft (18a) and in communication with a transmission shaft of the vehicle. In some cases the ring gear (18) can be directly mounted on the transmission shaft. If the ring gear (18) is mounted on the ring gear shaft (18a), then the ring gear shaft (18a) and the transmission shaft is connected by a connector (not shown in figure). The planetary gears (14a), (14b), (14c) & (14d) are coupled to a planet carrier shaft (16). It should be noted that, the number of planetary gears can be more than two depending on the application of use of the transmission system. The planet carrier shaft (16) is driven by a motor (30) for obtaining a plurality of gear ratios.

The transmission system in accordance with the second embodiment is disclosed in the below paragraphs in accordance with Figure 3. For example, the transmission system disclosed in accordance with this embodiment is used in lawnmowers. Lawnmowers are used in application where the requirement is high torque and low speed.

In such cases, the sun gear (12) is rotated by a primary motor (30). The primary motor (30) rotates the crankshaft (20) and thereby rotating the sun gear (12). The planet carrier shaft (16) is driven by a secondary motor (30), for rotating the planetary gears (14a), (14b), (14c) & (14d), in the direction opposite to the rotation of the sun gear (12). The planetary gears (14a), (14b), (14c) & (14d) are being rotated at a particular speed such that an appropriate reduction ratio is achieved at the ring gear (18). The speed of motor (30) for rotating the planetary gears (14a), (14b), (14c) & (14d) at that particular speed depends on the speed of the crankshaft (20) and reduction ratio required at the transmission shaft (22). Since ring gear (18) is connected to the transmission shaft (22), the transmission shaft (22) rotates at the speed equivalent to the speed of the ring gear (18). The blades of the lawnmower may be mounted on the transmission shaft (22). Hence, rotation of the transmission shaft (22) causes rotation of blades at speed equivalent to the speed of the ring gear (18) rotation. The reduction ratio achieved is such that speed of the transmission shaft (22) is low and hence torque is high. Such high torque is utilized for cutting the grass on the surface. Hence, such configuration of the transmission system can be used in lawnmowers.

Therefore, by connecting the sun gear (12) to the crankshaft (20) and the ring gear (18) to the transmission shaft (22) and enabling a motor (30) to control speed of rotation of the planetary gears (14a) & (14b) we can obtain high torque with low speeds at the output. Such configuration can be used for lawnmowers for cutting grass on the surface.

The transmission system in accordance with third embodiment is described in the following paragraphs.

The transmission system in accordance with the third embodiment comprises an inner sun gear (12), outer ring gear (18) and at least two planetary gears (14a) & (14b) meshed with the sun gear (12) and the ring gear (18). The ring gear shaft (18a) is mounted on either a ring gear shaft (18a) or mounted directly on the crankshaft (20) of the vehicle. If the ring gear (18) is mounted on the ring gear shaft (18a) then the ring gear shaft (18a) and the crankshaft (20) is connected through a connector for transmitting for rotating the ring gear (18).

The sun gear (12) is mounted on the sun gear shaft (12a). In some cases the sun gear (12) is directly mounted on the transmission shaft (22). If the sun gear (12) is mounted on the sun gear shaft (12a) then the sun gear shaft (12a) and the transmission shaft (22) are connected through a connector for transmitting rotation of the ring gear (18) to the transmission shaft (22). The two planetary gears (14a) & (14b) are coupled to a planet carrier shaft (16). The planet carrier shaft (16) is driven by a motor (30) for rotating the planetary gears (14a) & (14b) such that the sun gear (12) may be rotated at required gear ratios. The speed of the motor (30) for driving the planetary gears (14a) & (14b) depends on the speed of the crankshaft (20) and the gear ratio required at the transmission shaft (22).

Let us consider that the transmission system disclosed in accordance with third embodiment is used in a leaf cutting machine.

For the leaf cutting machine, torque required is low since leaves do not provide high resistance to cutting. However, the machine needs to be operated at high speeds so that the leaves are cut evenly to obtain desired shape. Hence, the leaf cutting machine requires low torque and high speed.

To obtain low torque and high speed, the ring gear (18) is connected to the crankshaft (20). The crankshaft (20) is connected to a primary motor (30) so that it rotates the crankshaft (20). The planet carrier shaft (16) is driven by a secondary motor (30) and hence the planetary gears (14a) & (14b) begin to rotate at a speed equivalent to speed of rotation of the planet carrier shaft (16). Speed of rotation of the planetary gears (14a) & (14b) causes an effect in the speed of rotation of the sun gear (12) and hence the sun gear (12) rotates at a speed that corresponding to a particular reduction ratio required at the transmission shaft (22). The sun gear (12) now rotates the sun gear shaft (12a) or the transmission shaft (22) at a speed that correspond to the achieved reduction ratio. The reduction ratio achieved is such that the transmission shaft (22) rotates at high speed when compared to the crankshaft (20). The transmission shaft (22) is connected to the blades of the leaf cutter so that leaves are cut quickly to achieve even leaf cutting.

Hence, by connecting the ring gear (18) gear to the crankshaft (20), the sun gear (12) to the transmission shaft and enabling the motor (30) to control speed of the planetary gears (14a) & (14b) to get required reduction ratio we can obtain low torque with high speeds at the output. Such configuration can be used for leaf cutter machine. Therefore according to current disclosure, by using a single planetary gear arrangement (10) along with a motor, various gear reduction ratios can be achieved in the transmission system. Such an arrangement is simple and requires minimal hardware components when compared to prior arts that require multiple sets of planetary gear arrangement (10) in the transmission system.

Also it should be noted that, the configurations using the planetary gear arrangement (10) is not limited to the six embodiments described above. Various other combinations or configurations are also possible using a single planetary gear arrangement (10) along with a motor for achieving various gear reduction ratios at the output in a transmission system. Additionally, it should be noted that although various embodiments are possible, figures are included only for two embodiments.

It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to the diameter of the gears, number of teeth in the gears, type of motor (30) for driving the gears are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.