Transmission for a hydraulic hybrid vehicle, comprising a planetary gear train linked to a pump by a speed reducer

Abstract

A transmission for a hydraulic hybrid motor vehicle includes a planetary gear train (30) capable of differential operation. The planetary gear train has a first element (32) linked to an internal combustion engine (34), a second element (40) linked to drive wheels (22) of the vehicle, and a third element (36) linked to a hydraulic pump (64). The transmission (1) further includes a hydraulic machine which drives the drive wheels (22) by way of a link between the third element (36) of the planetary gear train (30) and the hydraulic pump (64). This link includes a speed reducer (38, 60) that provides, when the whole of the planetary gear train is rotating at the same speed, a reduction in the speed of rotation of the pump relative to that of the internal combustion engine (34) that is greater than a value of approximately two.

Claims

1. A method for evaluating the noise level of a hydraulic machine with axial pistons installed in a transmission of a hydraulic hybrid automotive vehicle; the vehicle having driving wheels and a combustion engine; said transmission comprising a planetary gear set which can function as a differential; the planetary gear set comprising a first element connected to said combustion engine, a second element connected to the driving wheels, and a third element connected to a hydraulic pump; said transmission additionally comprising means for delivering torque supplied by a hydraulic pump to the driving wheels; and wherein a connection between the third element of the planetary gear set and the hydraulic pump comprises a speed reducer which reduces the rotational speed of the pump relative to the speed of the combustion engine when all of the elements of the planetary gear set run at the same speed; the method comprising determining the noise level of the hydraulic machine as a function of the Log.sub.10 of the rotational speed of the hydraulic machine, the Log.sub.10 of the displacement of the hydraulic machine, and a constant.

2. A transmission for a hydraulic hybrid automotive vehicle having driving wheels and a combustion engine; the transmission comprising a planetary gear set which can function as a differential; the planetary gear set comprising a first element connected to the combustion engine, a second element connected to the driving wheels, and a third element connected to a hydraulic pump; said transmission additionally comprising a hydraulic machine adapted to drive the driving wheels; and wherein a connection between the third element of the planetary gear set and the hydraulic pump comprises a speed reducer which reduces the rotational speed of the pump relative to the speed of the combustion engine when all of the elements of the planetary gear set run at the same speed; wherein the value of said reduction of the rotational speed of the pump corresponds to a noise level of the hydraulic pump; said noise level of the hydraulic pump being determined via the following equation:
Xlog.sub.10(Speed rev/min)+Ylog.sub.10(Displacement in cm.sup.3) +K=noise level in dBA; with the constant K being between 5 and 15.

3. The transmission according to claim 2, wherein the speed reducer comprises two parallel shafts; said two shafts defining input and output shafts of the speed reducer.

4. The transmission according to claim 3, wherein the speed reducer input shaft is directly connected to the third element of the planetary gear set and carries a driving gear which meshes with a driven gear carried by the output shaft of the speed reducer, and wherein the output shaft is directly connected to the pump; wherein these two gears define a reduction ratio of the speed reducer.

5. The transmission according to claim 4 wherein the reduction ratio is approximately 2.2.

6. The transmission according to claim 2, wherein the first element of the planetary gear set is a ring gear, the second element is a planet carrier, and the third element is a sun gear.

7. The transmission according to claim 2 wherein the planetary gear set comprises a locking means.

8. The method according to claim 1, wherein the noise level of the hydraulic machine is calculated by the equation:
XLog.sub.10(speed in rev/min)+YLog.sub.10(displacement in cm.sup.3)+K=noise level in dBa. where K is the constant and is between 5 and 15.

9. A transmission for a hydraulic hybrid automotive vehicle comprising a planetary gear set capable of functioning in differential mode; said planetary gear set comprising a first element connected to a combustion engine, a second element connected to the driving wheels and a third element connected to a hydraulic pump; said transmission further comprising means for driving the driving wheels, said means comprising a hydraulic machine and an output differential; a connection between the output differential and the hydraulic machine comprising a speed reducer that reduces the rotational speed of the hydraulic machine when the hydraulic machine drives the driving wheels; wherein the value of said reduction in speed of the hydraulic machine corresponds with a noise level of the hydraulic machine evaluated according to the equation:
XLog.sub.10(speed in rev/min)+YLog.sub.10(displacement in cm.sup.3)+K=noise level in dBa, where K is a constant between 5 and 15.

10. The transmission according to claim 8, wherein said transmission is incorporated in a hybrid automotive vehicle.

11. The method of claim 1, wherein the noise level of the hydraulic machine is calculated according to the following equation:
Xlog.sub.10(Speed rev/min)+Ylog.sub.10(Displacement in cm.sup.3)+K=noise level in d BA; wherein, the K is the constant and is between 5 and 15.

12. The method according to claim 11 wherein X is 20 and Y is 3, such that the noise level of the hydraulic machine in dBa is calculated by the equation:
20Log.sub.10(speed in rev/min)+3Log.sub.10(displacement in cm.sup.3)+K.

13. The method according to claim 8 wherein X is 20 and Y is 3, such that the noise level of the hydraulic machine in dBa is calculated by the equation:
20Log.sub.10(speed in rev/min)+3Log .sub.10(displacement in cm.sup.3)+K.

14. The method according to claim 1 further comprising a step of controlling the speed of the hydraulic pump in response to the calculated noise level of the pump.

15. The method for evaluating the noise level of the hydraulic machine according to claim 11, wherein the value X is substantially equal to twenty, and the Y value is substantially equal to three.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and other features and advantages will appear more clearly upon reading the following description given as an example, with reference to the accompanying drawing of FIG. 1 which is a diagram of a transmission according to the invention.

DETAILED DESCRIPTION

(2) FIG. 1 shows a transmission 1 comprising six shafts arranged parallel to each other. A variable displacement hydraulic machine 2 is connected to a first input shaft 4 of the transmission, which supports a freely rotating drive gear 6 that can be connected to the input shaft by engaging a first synchronizer sleeve 8.

(3) The drive gear 6 of the first input shaft 4 meshes with a driven gear 12 connected to a first intermediate shaft 16, which carries a first output gear 14 fixed on the intermediate shaft 16. The first output gear 14 meshes with a ring gear 18 of an output differential 20, in order to distribute the power to the two driving wheels 22 of the vehicle.

(4) This makes it possible for the hydraulic machine 2 to directly drive the driving wheels 22 of the vehicle when the first synchronizer sleeve 8 is engaged.

(5) An internal combustion engine 34, arranged along the main axis A, directly drives an outer ring gear 32 of a planetary gear set 30 disposed along the same main axis A. The planetary gear set comprises a central sun gear 36 which is fixed to a shaft 52 carrying a fixed gear 38 at its end opposite to the engine.

(6) The planetary gear set 30 includes a planet carrier 40 with planet gears meshing with both the ring gear 32 and the sun gear 36. The planet carrier is connected to a fixed driving gear 42.

(7) When engaged, a second synchronization sleeve 50 installed axially between the fixed driving gear 42 of the planet carrier 40 and the fixed gear 38 of the shaft 52 on which the sun gear 36 is mounted, connects the planet carrier 40 with the sun gear 36. The planetary gear set 30 is then locked and all of its elements rotate at the same speed.

(8) The fixed driving gear 42 of the planetary carrier 40 meshes with a fixed driven gear 44 which is connected to a second intermediate shaft 46 on which a second fixed output gear 48 is mounted. This second output gear 48 meshes with the ring gear 18 of the output differential 20.

(9) This makes it possible for the combustion engine 34 to directly drive the driving wheels 22 of the vehicle when the second synchronization sleeve 50 is engaged. The connection between the combustion engine 34 and the driving wheels 22 is then made with a gear ratio defined by the two successive meshing gear sets, resulting in a small speed reduction. This ratio is the longest ratio, it is used for high vehicle speeds with good efficiency because it employs only a mechanical transmission comprising only two pairs of meshing gears.

(10) The gear 38 fixed to the shaft 52 meshes with a driven gear 60 fixed to the pump shaft 62, which is permanently connected to a variable displacement hydraulic pump 64.

(11) When the second synchronization sleeve 50 is disengaged, the planetary gear set 30 functions as a differential distributing the torque of the combustion engine 34, by delivering a first torque applied by the planet carrier 40 to the output differential 20, and a second torque applied by the sun gear 36 to the pump 64.

(12) The pump 64 and the hydraulic machine 2 are connected to high pressure and low pressure accumulators, which constitute energy reserves.

(13) The driving gear 38 fixed to the shaft 52 of the sun gear 36 and the driven gear 60 fixed to the pump shaft 62 constitute a speed reducer which in this example reduces the rotational speed of the pump 64 by a ratio of 2.2. In this way, when the combustion engine 34 rotates at a speed of 3000 rev/min, and the second synchronization sleeve 50 is engaged, the pump 64 rotates at a speed of 1364 rev/min.

(14) Subsequently, to compensate for the reduction in speed and to obtain a substantially equivalent mechanical power, the displacement of the pump 64 is increased. In this way, a less noisy pump 64 is obtained.

(15) Through a series of tests of several hydraulic pumps offered by different vendors, having pistons arranged parallel to the axis, the following mathematical relationship was established to estimate the acoustic level of these machines:
20log.sub.10(Speed rev/min)+3log.sub.10(Displacement in cm.sup.3)+K=noise level in dBa;

(16) where the constant K is between 5 and 15 according to the technology of the hydraulic machine.

(17) In practice, for a hydraulic pump having a capacity of 17 cm.sup.3 and rotating at a speed of 3000 rev/min, with a constant K=9.8, a sound level of 83 dBa is obtained with this mathematical relationship. With the same type of pump having a displacement of 31 cm.sup.3, installed in a transmission 1 according to the invention comprising the 2.2 reduction ratio, a sound/noise level is obtained of 77 dBa, or a reduction of approximately 6 dBa.

(18) Note that the displacement of the pump 64 is multiplied by a value slightly smaller than two, which is close to the reduction ratio of the gears driving the pump 64. Since the loss of the pump 64 is not proportional to its displacement, the mechanical power of the pump and its performance are similar to those of the original pump at the reduced displacement and higher speed.

(19) Using a similar calculation method in order to predict the noise level, the speed of the hydraulic machine 6, comprising radial pistons, can be reduced to lower the noise.

(20) In general, this calculation method provides in a simple manner a good estimate of the sound/noise level of a hydraulic machine with axial pistons, as a function of its displacement and its rotational speed, and can be used to calculate the reduction ratio required for driving the machine.