This invention concerns a drive with a stepless transmission ratio which is designed to hydraulically transmit the driving force with variable speed from a drive shaft to the driven shaft of a machine. s.

It is used as a transmission device in hydraulic drives and in servomotors for the transmission of rotary motions and torques from a drive shaft to the driven shaft of a machine with stepless variable ratio between the number of revolutions of the drive shaft and the number of revolutions of the driven shaft. It is especially employed when the drive is used as a coupling to transmit large torques between the both shafts at maximum operating speed during extended operating periods.

The drive can be used for various purposes. It can be employed as an automatic gearbox in cars and lorries and as a stepless variable torque converter, i.e. the speed of the output shaft can be adjusted from zero to the same speed as the input shaft. Depending on the respective size of the pumps, the direction of rotation can even be reversed.

It is already common knowledge that a speed variator can be obtained by combining a hydraulic pump with a hydraulic motor.

In particular, it is already known how an axial reciprocating pump and an axial motor consisting of a reciprocating pump whose direction of rotation can be reversed can be combined by connecting them in a closed circuit.

The flow rate of the pump can be varied and can even be made negative. This is also possible for the motor. The speed of the motor can be decreased to an extremely low value by attributing a finite slewing angle to the motor, whilst the slewing angle attributed to the pump is zero. Conversely, the speed of the motor can be increased to an extremely high value by attributing a maximum slewing angle to the pump, whilst the slewing angle attributed to the motor is extremely small.

This provides the variator with an extremely wide variable flow rate range. The disadvantage of this variator is that the coupling of the pump to the motor at maximum speed for extended operating periods causes the oil to heat up (due to

turbulence and friction produced by an increased flowrate at maximum speed). The friction is mainly due to the narrow cross-section of the connecting pipes which must be able to withstand extremely high pressures.

In existing speed variators, the mechanical transfer of force or motion is completely hydraulic. The flow rate of the hydraulic fluid is at a maximum when the speed variator is running at high speed. A large amount of energy can be lost due to heat dissipation caused by the internal friction of the oil in the pump and in the pipes which connect the motor to the pump. The aim of the invention is to eliminate this disadvantage. In order to achieve this, the oil flow rate in the drive is kept to a minimum, and even reduced to zero when the motor and pump are running at the same speed so that the torque can be transferred with optimal efficiency and with no heating-up of the oil.

The invention conforms to the description given in the first paragraph of this specification . This drive is characterized by the connection between the hydraulic pump and the hydraulic motor which is formed by a cylindrical casing which is static in relation to the drive housing, and which is mounted on the drive shaft for the hydraulic pump and the hydraulic motor, consisting of two parts, the side wall of which has two pairs of diametrically-opposite semi¬ circular openings, the first part is static and contains a pair of openings through which hydraulic fluid is sucked out of the sleeve in order to supply the hydraulic pump and the hydraulic motor, and the second part which turns with the pump body of the hydraulic motor and has a pair of openings through which the oil is forced out of the hydraulic pump and the hydraulic motor.

A characteristic of the invention is that the hydraulic pump has a variable flow rate.

In a first particular embodiment, the hydraulic pump which has a variable flow rate, is a volumetric pump whose eccentricity can be varied.

In a second particular embodiment, one of the pumps is an axial reciprocating pump which has a slewabie pump body or a shackle plate with a variable slewing angle.

Other characteristics and details of the invention will be made apparent in the following detailed description which refers to the associated illustrations. These illustrations are examples which show an embodiment of the invention in great detail.

Figure 1 is a longitudinal cross-sectional view of an first embodiment of the drive as per the invention which contains two axial reciprocating pumps;

Figure 2 is a cross-sectional view as per the line ll-ll which passes through the pump housing of the drive shown in Figure 1 ;

Figure 3 is a cross-sectional view as per the line Ill-Ill which passes through the pump housing of the drive shown in Figure 1 and which shows the first position of the hydraulic motor.

Figure 4 is a longitudinal cross-sectional view which resembles the view of the drive shown in Figure 1 , where the pump housing is in the second position.

Figure 5 is a cross-sectional view as per the line IV-IV shown in Figure 1 , but with the pump housing of the hydraulic motor in the second position (almost aligned with the impeller of the motor so that a miminal flow rate results);

Figure 6 is a cross-sectional view which resembles the view of the drive shown in Figure 1 , where the disengaging arm is in the position which disengages the drive;

Figure 7 is an exploded view (in perspective) which shows a connecting sleeve which is located between the hydraulic pump and the hydraulic motor of the drive as per the invention, and

Figure 8 is a longitudinal cross-sectional view of a second embodiment of the drive as per the invention which contains two hydraulic pumps and a shackle plate.

The same reference numbers are used in these illustrations for identical or similar parts.

As per the invention shown in the Figure 1 , the drive 1 consists of a stepless transmission ratio which is designed to hydraulically transmit the driving force with variable speed from a drive shaft 2 to the driven shaft 3 of a machine which is not shown via a hydraulic pump 4 and a hydraulic motor 5 which are interconnected so that the suction side of the hydraulic pump 4 is connected to the pressure side of the hydraulic motor 5 and vice-versa.

A first embodiment of the drive 1 consists of the . hydraulic pump 4 and a vanes pump which has variable eccentricity,

whilst the hydraulic motor 5 is a non-variable volumetric vanes pump. The vanes pump 4 consists of a rotatable cylindrical pump body consisting of a rotor 9 which is centrally mounted in relation to the driven shaft 3 and a variable ring which is eccentrically mounted and which consists of two radial interconnected parts (an inner ring 7 which rotates at the same time and a controllable outermost ring 8 which does not rotate) and a rotating vanes holder 10. Likewise, the hydraulic motor 5 contains a rotatable cylindrical pump body 30 consisting of the rotor 9 which is centrally aligned with the driven shaft 3, a non-controllable eccentrical ring 13, and a rotating vanes holder 20.

Both of the vanes holders 10 and 20 have radial slots 47, in which the vanes 11 move up and down, either due to the action of springs, or due to centrifugal force produced when the rotor 9 rotates, which forces the vanes 11 against the eccentrical ring.

During the first half-revolution of the vanes holder 10 (i.e. the suction cycle of the pump), the eccentrical shape of the ring 7 causes the chambers 12 formed by the vanes 11 and the eccentric ring 7 to become become larger. During the remaining half-revolution of the vanes holder 10 (i.e. the extraction cycle of the pump), the eccentrical shape of the ring 7 causes the chambers 12 formed by the vanes 11 and the eccentric ring 7 to become become smaller.

Figure 1 illustrates how the the flow is discharged via shaft channels 14 and 15 and how the flow is input via the chambers 12 of the vanes pump 4.

A gearwheel 16 which is driven by a motor is mounted on the drive shaft 2 of the hydraulic pump 4. This gearwheel 16 drives a crown wheel 19 to which the rotor 9 of the hydraulic pump 4 is secured. The hydraulic pump is secured to a dividing wall and also drives the rotor 9 of the hydraulic motor 5. These three components and the vanes of the hydraulic pump 4 and the hydraulic motor 5 are directly driven by a drive mechanism consisting of the gearwheel 16, the crown wheel 19 and the drive shaft 2.

In the hydraulic motor 5, the ring 13 of the rotatable pump body 30 is eccentrically aligned with the drive shaft 3 in order to produce a sucking and pumping action.

The ring 8 (which has variable eccentricity) of the pump body of the hydraulic pump 4 and the rotatable pump body 30 of the hydraulic motor 5 are mounted in a common housing 31

which has removable sidewalls 32 which are secured by a series of bolts.

A sleeve 6 is located in the centre of the device. This sleeve connects the pressure side of the hydraulic motor 5 with the suction side of the vanes pump 4 and vice-versa.

The vanes in the hydraulic pump 4 and the hydraulic motor 5 rotate at the same speed and in the same direction.

In order to guarantee optimal operation of the drive 1 , the openings 17, 18 and 37, 38 which are located in the outermost tubes 35, 36, must always be equipped with suitable shaft channels 14, 15 which connect the various chambers 12 of the hydraulic pump 4 and the hydraulic motor 5 by means of the axial oil-supply and oil-discharge pipes 27, 28. The shaft channels 14, 15 of the hydraulic pump 4 and the hydraulic motor 5 which are located in the base of the rotor 9 rotate with the driven shaft 3. The coaxial channels, oil-supply and oil-discharge channels 27, 28 are constructed from three coaxial tubes 35, 36 and also 22 and 23. Holes 17, 18, 37, 38 are milled into the the outermost tubes 35 and 36. These holes are provided for the supply to the hydraulic pump 4 and the hydraulic motor 5. The smallest tube 23 has a sleeve which is secured by a cross-shaped cross-piece. The sleeve ensures that the hydraulic fluid flows from the pressure side to the suction side. The middlemost tube 22 is a separator which divides the outermost tubes 35 and 36 into two coaxial channels 27, 28. Part 35 is secured to the housing of the drive 1 and remains static whilst part 36 rotates with the driven shaft 3. The disengaging lever 25 is the control which disengages the drive. When the disengaging lever 25 is moved to the left or to the right, the openings 24 are uncovered in the tube 22 and the pressure difference between the coaxial supply- channels 27, 28 is eliminated so that the drive is disengaged.

The disengaging lever 25 also provides pressure protection and guards against any overpressure conditions which may occur in the coaxial channel 27 (due to the action of the helicoidial spring 48 which is supported by the housing 31 of the drive 1). Pressure protection is also provided to guard against any overpressure conditions which may occur in the coaxial channel 28 (due to the action of a spring 49 mounted on a plate which is forced against the sidewall of the sleeve.

The purpose of the control lever 26 is to move the eccentric ring 8 of the pump body of the hydraulic pump 4 up and down so that the eccentricity of the hydraulic pump 4 can be

varied and also to control the amount of oil ^" which is sucked in and forced out.

Operation

In the first embodiment shown in Figures 1 to 7, the hydraulic pump 4 and the hydraulic motor 5 of the drive consist of two vanes pumps. The vanes holders 10 and 20 of the hydraulic pump 4 and the hydraulic motor 5 which are enclosed by the rotor 9 rotate in the same direction and at the same speed. When the ring is eccentrically positioned in relation to the rotor 9, both vanes pumps alternately suck in and force out oil.

The hydraulic pump 4 and the hydraulic pump 5 are interconnected by coaxial channels 27, 28 so that the amount of oil which the pump 4 forces out is sucked in by the motor 5. The flow rate of the hydraulic pump 4 is identical to the flow rate of the hydraulic motor 5.

Since the eccentricity of the hydraulic motor 5 always remains the same, the flow rate of this motor also remains constant. When the hydraulic motor 5 is not operating, this is not a problem since the hydraulic pump 4 is the same pump with the same flow rate. When the eccentricity of the hydraulic pump 4 is decreased, the flow rate is consequently also decreased (i.e. the flow rate of the hydraulic pump is no longer identical to the flowrate of the hydraulic motor 5).

This change in the flow rate is compensated for by rotation of the pump body 30 of the hydraulic motor 5 which consists of the rotor 9 and the eccentric ring 13 which moves together with the driven shaft 3.

The pump body 30 of the hydraulic motor 5 is driven so that, due to the eccentricity, this oil can be sucked in and forced out. The hydraulic pump 4 is supplied with oil by the hydraulic motor 5. The hydraulic pump 4 can also discharge oil via the hydraulic motor 5. The change in eccentricity of the hydraulic pump 4 causes it to suck in less oil so that pressure builds up in the hydraulic motor 5 which causes the drive to rotate and also causes the pressure in the hydraulic pump 4 to build up so that the vanes holder moves.

A state of equilibrium is obtained by rotating the eccentric ring 13 of the hydraulic motor 5. During this action, the hydraulic pump 4 acts as a controller which controls the transmission ratio. If the eccentricity of the hydraulic pump 4 is increased, the eccentric ring 13 will rotate in the opposite direction.

From this, we can see that the device can be controlled in a stepless manner by only controlling the eccentricity of the hydraulic pump 4. The advantages of the device are as follows: at 100% transmission, there is no oil flow; only pressure differences are present. This provides the enormous advantage that turbulence cannot ooccur in the oil and heat is not generated as there is no friction between the oil and the wall. Another advantage is that the transmission can occur in a stepless manner.

The drive described in this invention posseses the same power transmission efficiency as a conventional plate coupling. It is a well-known fact that a plate coupling does not have efficiency losses. Unlike the conventional plate coupling, the drive described in this invention is gradually engaged via a stepless transmission ratio which can be controlled. Moreover, the drive operates silently. When compared with the hydraulic torque converter, the drive described in this invention provides transmission ratios which are not limited from 1 to 2.5 and which have improved efficiency.

Like speed variators, the drive 1 described in this invention operates quietly and has a stepless transmission which searches for ratios between zero and infinity, with the disadvantages of efficiency loss (from 3 to 5%), with no large oil flows, and with no significant generation of heat.

The drive is a hydrostatic torque converter which: operates in a stepless manner; has a transmission ratio of between zero and twice the driving speed; has a simple construction; has an efficiency loss which can be neglected, and has an oil flow which is directly proportional to the speed difference between the drive shaft and the driven shaft.

In a second embodiment, the hydraulic pump 4 and the hydraulic motor 5 are pumps which have a rotatable shackle plate. Each pump contains a rotatable pump body 30 in which several cylindrical chambers 39, 39' are housed. These chambers are parallel to the centre-line of the drive shaft 2, 2' of the pump. In each chamber 39, 39', a piston is driven in a reciprocating motion due to the rotation of the shackle plate 41 and by the pressure of the springs which are located on the inside of each of the pistons 40, 41 '. The' shackle plate is driven by a drive shaft parallel to the movement of the pistons. The supply to the pistons occurs

via the opening 17, 18, 37, 38. A crown wheel which is driven by the gearwheel 16 and the drive shaft 2 is mounted on the rotatable pump body 30 of the hydraulic pump 4.

The centre of the drive is identical to the first embodiment. It connects the supply and discharge pipes for the hydraulic pump with those for the hydraulic motor. It consists of a cylindrical sleeve 6 comprising two cylindrical parts 35, 36 which are aligned with each other.

The cylindrical wall of each part has two diametrically- opposite semi-circular openings 17, 18, and 37 which are used for the supply and discharge of oil into and out of the pump. At least one of the pumps has a variable flowrate. The oil flow rate which is forced through the hydraulic pump 4 is processed by the hydraulic motor and vice-versa. This causes a build-up of pressure and causes the hydraulic motor 5 to rotate and the eccentrical rotor 9 to be driven. The speed of the drive can be controlled in a stepless manner by controlling the inclination of the shackle plate of the hydraulic pump 4.

CLAIMS

1. A drive which has a stepless transmission ratio which is designed to hydraulically transmit the driving force with variable speed from a drive shaft (2) to the driven shaft (3) of a machine consists of a hydraulic pump (4) and a hydraulic ^" motor (5) which are interconnected so that the suction side of the hydraulic pump (4) is connected to the pressure side of the hydraulic motor and vice-versa, characterised by the fact that the connection between the hydraulic pump (4) and the hydraulic motor (5) is formed by a cylindrical sleeve (6) which is mounted on the rotary shaft of the hydraulic pump (4) and the hydraulic motor (5) and consists of two parts (35,36), of which the sidewall has two diametrically-opposite semi¬ circular openings (17, 18, 37, 38). The first part (35) is static and contains a pair of openings (17,18) for the supply to the hydraulic pump (4) and the hydraulic motor (5) by sucking in of the hydraulic fluid from the sleeve (6), and the second part (36) rotates with the pump body (19) of the hydraulic motor (5) and contains a pair of openings (37, 38) for forcing the oil out of the the hydraulic pump (4) and the hydraulic motor.

2. A drive according to claim 1 , characterised in that at least the hydraulic pump (4) or the hydraulic motor (5) has a controllable flow rate.