GB1561952A

GB1561952A - Transmission systems

Info

Publication number: GB1561952A
Application number: GB3224877A
Authority: GB
Original assignee: PROIZV OBIEDINE; TS NAUCH ISSLED AVTOMOBIL I AV
Current assignee: PROIZV OBIEDINE; TS NAUCH ISSLED AVTOMOBIL I AV
Priority date: 1977-08-01
Filing date: 1977-08-01
Publication date: 1980-03-05

Description

(54) IMPROVEMENTS IN OR RELATING TO TRANSMISSION SYSTEMS (71) We, TSENTRALNY NAUCHNO ISSLEDOVATELSKY AVTOMOBILNY I AVTO MOTORNY INSTITUT "NAMI", a Corporation organised and existing under the laws of the Union of Soviet Socialist Republics, of Avtomotornaya ulitsa 2, Moscow, U.S.S.R., anl PROIZVODSTVENNOE OBIEDINE NIE "Bxz;", a Corporation organised and existing under the laws of the Union of Soviet Socialist Republics, of Bryansk, U.S.S.R., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to hydraulic transmissions for vehicles.

According to one aspect of the present invention there is provided a hydraulic transmission for a vehicle, the transmission comprising a transmission clutch; a hydraulic torque converter kinematically connected with the said transmission clutch and including an impeller, a turbine and a direct drive clutch actuable to lock together the said impeller and turbine; a vehicle engine shaft speed pickup arranged to cause actuation of the direct drive clutch by means of hydraulic fluid pressure upon the engine shaft speed reaching a predetermined value; a transmission clutch engaging and disengaging arrangement comprising a power cylinder whose movable member is mechanically connected with the operating member of the transmission clutch, an air pressure source and a valve controllable by a driver of the vehicle to cause disengagement and engagement of the transmission clutch by connection of the power cylinder respectively to the said air pressure source and to atmosphere through a throttling orifice; and a valve arrangement connected through the driver controllable valve to the power cylinder and providing a further route for communication of the power cylinder with the atmosphere, said valve arrangement being actuated by hydraulic fluid pressure in response to a signal from said vehicle engine shaft speed pickup.

According to another aspect of the present invention, there is provided a hydraulic transmission for a vehicle, the transmission comprising a transmission clutch, a hydraulic torque converter, a direct drive clutch for locking friction elements of the hydraulic torque converter, a vehicle engine shaft speed pick up arranged tto control the direct drive clutch, clutch operating means for engaging and disengaging the transmission clutch in response to movement of a gear change lever, said clutch operating means comprising a pneumatic power cylinder so arranged that engagement of the transmission clutch is effected by allowing air under pressure to escape from the said power cylinder by way of a first passage through a throttling orifice, and a valve actuated by a means of hydraulic fluid pressure in response to a predetermined engine shaft speed being reached to provide a second passage by which air under pressure can escape from the said clutch control means whereby engagement of the said transmission cltuch is effected more quickly at and above the said predetermined engine speed.

The invention will now be particularly described by way of example with reference to the accompanying diagrammatic drawings in which: Figure 1 is a part-sectional schematic diagram of a vehicle hydraulic transmission including a first form of valve arrangement; Figure 2 is a section through another form of the valve arrangement; Figure 3 is a section through yet another form of the valve arrangement; and Figure 4 is a graph of pressure variation in a power cylinder of the transmission during engagement of a transmission clutch.

The illustrated hydraulic transmission comprises a casing 1 (Figure 1) which accommodates a transmission clutch 2 and a hydraulic torque converter 3. The vehicle engine shaft (not shown) is connected to an impeller 4 of the torque converter 3. A turbine 5 of the torque converter 3 is fixedly mounted on a shaft 6 which is attached to a flywheel 7 of the transmission clutch 2.

A stator 8 of the torque converter 3 is supported in the casing 1 via a freewheel bearing 9. The torque converter 3 incorporates a direct drive clutch 10 arranged to lock the impeller 4 and the turbine 5 together. The direct drive clutch 10 includes a casing which is rigidly secured to the impeller 4. A disc 11 of the clutch 10 is mounted on the turbine 5 such that it is situated within the casings and arranged to move in a direction parallel with the axis of the shaft 6. A pressure plate 12 is slidably mounted inside the casing 13 on a hollow hub integral with the casing 13 such that a variable-volume chamber 14 is formed between the pressure plate 12 and the casing 13. This variable volume chamber 14 communicates with a selector valve 18 by way of a hole 15 through the hub wall, a passage 16 provided in the shaft 6, and a hydraulic fluid line 17. A space 19 in the torque converter 3 communicates via a passage 20 and a hydraulic fluid line 21 with the selector valve 18. The selector valve 18 comprises a body 22 and a spring-loaded spool 23. The valve body 22 has holes to receive the hydraulic fluid lines 17 and 21. The selector valve 18 communicates with a pump 26 via a hvdraulic fluid supply line 25. The pump 26 is connected to a hydraulic fluid reservoir 27. A limiting valve 28 is fitted between the hydraulic fluid supply line 25 and the fluid reservoir 27 to prevent excess pressures building up in the supply line 25. A hydraulic fluid return line 25a is directly connected between the selector valve 18 and the reservoir 27. The position of the spool 23 controls the communication of the line 21 with the hydraulic fluid supply line 25 and communication of the line 17 with the return line 25a and the supply line 25. The spool 23 of the selector valve 18 is mechanically controlled by a vehicle engine shaft speed pickup in the form of a centrifugal governor 24. Depending on the speed of the engine shaft, the centrifugal governor 24 pushes the spool 23 into the body 22 against the action of the spring.

The interior of the torque converter 3 communicates via a hydraulic fluid line 29, a limiting valve 30 and a hydraulic fluid cooler 31 with the hydraulic fluid reservoir 27.

Engagement and disengagement of the transmission clutch 2 is effected by means of a clutch operating arrangement 32 which includes a pneumatic power cylinder 33 whose movable member (in the present example its piston) 34 is mechanically connected with a pressure plate 35 of the transmission clutch 2.

The mechanical connection between the piston 34 and the pressure plate 35 is formed by a piston rod 36, a lever 37, a clutch release element 38 and a disc spring 39.

The transmission clutch 2 has a driven disc 40 arranged to be clamped to the flywheel 7 by the pressure plate 35.

A space 41 in the power cylinder 33 communicates via a pipeline 42 with a valve 43 which is arranged to connect the space 41 to an air pressure source 44 and the atmosphere via a throttling orifice 45. The valve 43 is actuated by an electromagnet 47 which is fed from a storage battery 46 and is energised by means of a switch 48 connected with a gearchange lever 49 of a gearbox 50. Thus the action of the valve 43 is controlled by the driver of the vehicle.

The space 41 in the power cylinder 33 can also communicate with the atmosphere via a valve arrangement 51 which is connected to the controllable valve 43 and is actuated by hydraulic fluid pressure in response to a signal from the centrifugal governor 24 (in the present example, this signal is the pressure increase effecting engagement of the direct drive clutch 10). The provision of the valve arrangement 51 means that the time taken to engage the transmission clutch 2 when the vehicle is moving at comparatively high speeds is reduced. The valve arrangement 51 comprises a cylinder 52 accommodating a spring-loaded piston 53 with a piston rod 54. The piston 53 defines in the cylinder 52 a variable-volume space 55 which communicates via a hydraulic fluid line 56 with the line 17 and the selector valve 18. The cylinder space 57 which accommodates the piston rod 54 is in constant communication with the atmosphere through a passage 58. A closure member 59, loaded by a spring 59a is provided between the cylinder space 57 and a space 60 which communicates via a line 61, the valve 43 and the line 42 with the space 41 in the power cylinder 33. The space 60 is defined by a cover 62 and a part 63 rigidly attached to the cylinder 52. The valve arrangement 51 is very simple in construction but also very reliable in operation.

The valve arrangement 51 can be variously modified and two such modified arrangements are shown in Figures 2 and 3 respectively. The Figure 2 valve arrangement 65 has a cover 64 made of a resilient material. viz. rubberized fabric. The cover 64 can also be made of other suitable materials. In this embodiment, the closure member 59 is fixed to the cover 64 and the spring 59a is fitted between the cover 64 and a part 66.

This constructional arrangement of the cover 64 improves the process of engaging the clutch when the vehicle is moving off from rest.

In the Figure 3 valve arrangement 67 the cover 64 is again made of a resilient material but it closes the axial hole in the part 63 which is rigidly attached to the cylinder 52 directly. A closure member 68 is attached to the side of the cover 64 remote from the axial hole in the part 63.

The spring 59a is fitted between the closure member 68 and the part 66.

The use of a resilient material for the cover 64 and a rigid connection between the cover 64 and the closure member 59 increases the life of the hydraulic transmission.

Operation of the hydraulic transmission will now be described.

With the vehicle engine running, the driver begins to select the required gear using the gear lever 49 in the gearbox 50, whereby the contacts of the switch 48 close and electric current flows through the winding of the electromagnet 47. The movable member 69 (Figure 1) of the valve 43 moves upwards so that the space 41 in the power cylinder 33 communicates with the air pressure source 44 whereupon the transmission clutch 2 disengages.

When the gearchange is complete, the drive releases the gearchange lever 49, the contacts of the switch 48 open and the winding of the electromagnet 47 is de-energized.

Consequently, the movable member 69 of the valve 43 moves downwards to the position shown in Figure 1, thereby isolating the air pressure source 44 and putting the space 41 in the power cylinder 33 in communication with the atmosphere through the throttling orifice 45. As a result, the transmission clutch 2 re-engages.

Variation of the air pressure in the space 41 during the clutch engagement process is illustrated by curve C1 in Figure 4 wherein the symbols represent the following: P = pressure in the space 41 in the power cylinder 33, t = engaging time of the clutch 2.

t1 = point in time at which clutch en- gagement starts, t,l = point in time at which clutch en gagement ends, P1 = pressure equal to that in the air pressure source 44, P:2 = air pressure at which the pressure plate 35 takes up the clearance of the driven disc 40 and the clutch 2 starts transmitting frictional torque.

When the vehicle is moving off from rest, clutch operating arrangement 32 operates as described above smoothly engaging the transmission clutch 2 and avoiding jerky vehicle starting.

As the vehicle engine accelerates, the speed of the torque converter impeller 4 and, consequently, of the torque converter turbine 5, which communicates with the drive wheels of the vehicle via the gearbox 50 increases.

For subsequent gearchanges, the clutch is disengaged and engaged in a similar manner to that already described.

As the speeds of the engine and vehicle increase, the centrifugal governor 24 moves the spool 23 to the right, whereby the pressure of the hydraulic fluid in the space 14 increases and the pressure of the hydraulic fluid in the space 19 decreases. As a result, the pressure plate 12 moves to the right, displacing the disc 11 and thereby locking together the torque converter impeller 4 and turbine 5.

As well as the rise of hydraulic fluid pressure in the space 14, the fluid pressure in the space 55 of the cylinder 52 also increases. This pressure build-up moves the piston 53 to the right whereupon the piston rod 54 moves the closure member 59 in the same direction. This means that the space 60 is open to atmosphere and since the space 60 and the space 41 are connected together when the transmission clutch 2 is engaged, the space 41 is also open to the atmosphere via the passage 58 as well as through the throttling orifice 45.

Thus at high speeds, although disengagement of the transmission clutch 2 for making a gearchange is effected as described previously, clutch engagement upon completion of the gearchange is effected much faster since air under pressure issues from the space 41 in the power cylinder 33 through the throttling orifice 45 and also through the passage 58 as the closure member 59 is open.

The clutch engagement process employing the valve arrangement 51 is illustrated by the curve C2 in Figure 4. Owing to faster engagement of the transmission clutch, slip is reduced substantially and consequently the reliability and life of the hydraulic transmission is increased. Furthermore, the duration of power flow interruption after gearchange is reduced by the difference t11-t21, where t21 is the point in time at which the clutch engagement process ends.

With the valve arrangements 65 and 67 employing a resilient cover 64, the process of engaging the transmission cltuch 2 after gearchange in the gearbox 50 (when the vehicle is moving with the torque converter in direct drive) also follows the curve C2 since the valve 59 is again open.

When the vehicle first starts to move the pressure of the hydraulic fluid in the space 55 is zero, and the decrease of air pressure in the power cylinder space 41 to a value P2 follows the curve C2 However, further pressure drop from P2 to zero will follow the curve C3.

This is attributed to the fact that during the process of engagement of the transmission clutch 2, when the air pressure in the space 60 varies between P1 and P2, the pressure acting on the resilient cover 64 is sufficient to overcome the load of the spring on the closure member 59 and unseats the closure member 59 from the part 63.

But when the pressure drops below P2, it is insufficient to keep the closure member 59 open, and so it becomes tightly seated on the part 63. Therefore, during the remainder of the engagement process of the transmission clutch 2 air pressure is released from the space 41 of the power cylinder 33 into the atmosphere through the throttling orifice 45 only.

As stated earlier, the transmission clutch 2 starts transmitting torque only when the pressure in the space 41 has dropped below P2.

Therefore, the described process of transmission clutch engagement in starting the vehicle cannot cause jerks, whereas the total time to engage the transmission clutch 2 is decreased by the difference t11-t31 where t31 is the point in time at which clutch engagement ends when moving off from rest.

Ten heavy-duty truck hydraulic transmissions constructed as described above have been throughly tested under various climatic and mountainous terrain conditions.

The tests have shown the hydraulic transmission has good operating characteristics and that the transmission clutch is particularly reliable and has a long life.

From the foregoing it can be seen that the clutch of the vehicle hydraulic transmission is operated by a power cylinder wherein the variation of air pressure during the clutch engagement process is correlated with the mode of operation of the torque converter.

The torque-speed characteristics of the described hydraulic transmission are very good due to the reduction in the transmission clutch engagement time.

WHAT WE CLAIM IS: I. A hydraulic transmission for a vehicle, the transmission comprising a transmission clutch; a hydraulic torque converter kinematically connected with the said transmission clutch and including an impeller. a turbine and a direct drive clutch actuable to lock together the said impeller and turbine; a vehicle engine shaft speed pickup arranged to cause actuation of the direct drive clutch by means of hydraulic fluid pressure upon the engine shaft speed reaching a predetermined value; a transmission clutch engaging and disengaging arrangement comprising a power cylinder whose movable member is mechanically connected with the operating member of the transmission clutch, an air pressurt source, and a valve - contrdllable by a driver of the vehicle to cause disengagement and engagement of the transmission clutch by connection of the power cylinder respectively to the said air pressure source and to atmosphere through a throttling orifice; and a valve arrangement connected through the driver controllable valve to the power cylinder and providing a further route for communication of the power cylinder with the atmosphere, said valve arrangement being actuated by hydraulic fluid pressure in response to a signal from said vehicle engine shaft speed pickup.

2. A transmission according to claim 1, in which the valve arrangement is actuated jointly with the direct drive clutch.

3. A transmission as claimed in claim 1 or claim 2, wherein the valve arrangement comprises a cylinder accommodating a piston with a piston rod, means for feeding hydraulic fluid under pressure into the piston end of said cylinder, the rod end of the cylinder being in constant communication with the atmosphere, a spring-loaded closure member arranged to interact with the free end of the piston rod and a cover fitted to the rod end of the said cylinder to enclose a space which is in communication with the power cylinder, and separable from the rod end of the cylinder by means of the closure member.

4. A transmission, as claimed in claim 3, wherein the said cover is made of a resilient material and is rigidily connected to the spring-loaded closure member.

5. A hydraulic transmission for a vehicle, the transmission comprising a transmission clutch, a hydraulic torque converter, a direct drive clutch for locking friction elements of the hydraulic torque converter, a vehicle engine shaft speed pick up arranged to control the direct drive clutch, clutch operating means for engaging and disengaging the transmission clutch in response to movement of a gearchanger lever, said clutch operating means comprising a pneumatic power cylinder so arranged that engagement of the transmission clutch is effected by allowing air under pressure to escape from the said power cylinder by way of a first passage through a throttling orifice, and a valve actuated by means of hydraulic fluid pressure in response to a predetermined engine shaft speed being reached to provide a second passage by which air under pressure can escape from the said clutch control means whereby engagement of the said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

55 is zero, and the decrease of air pressure in the power cylinder space 41 to a value P2 follows the curve C2 However, further pressure drop from P2 to zero will follow the curve C3.

This is attributed to the fact that during the process of engagement of the transmission clutch 2, when the air pressure in the space 60 varies between P1 and P2, the pressure acting on the resilient cover 64 is sufficient to overcome the load of the spring on the closure member 59 and unseats the closure member 59 from the part 63.

But when the pressure drops below P2, it is insufficient to keep the closure member 59 open, and so it becomes tightly seated on the part 63. Therefore, during the remainder of the engagement process of the transmission clutch 2 air pressure is released from the space 41 of the power cylinder 33 into the atmosphere through the throttling orifice 45 only.

As stated earlier, the transmission clutch 2 starts transmitting torque only when the pressure in the space 41 has dropped below P2.

Therefore, the described process of transmission clutch engagement in starting the vehicle cannot cause jerks, whereas the total time to engage the transmission clutch 2 is decreased by the difference t11-t31 where t31 is the point in time at which clutch engagement ends when moving off from rest.

Ten heavy-duty truck hydraulic transmissions constructed as described above have been throughly tested under various climatic and mountainous terrain conditions.

The tests have shown the hydraulic transmission has good operating characteristics and that the transmission clutch is particularly reliable and has a long life.

From the foregoing it can be seen that the clutch of the vehicle hydraulic transmission is operated by a power cylinder wherein the variation of air pressure during the clutch engagement process is correlated with the mode of operation of the torque converter.

The torque-speed characteristics of the described hydraulic transmission are very good due to the reduction in the transmission clutch engagement time.

WHAT WE CLAIM IS: I. A hydraulic transmission for a vehicle, the transmission comprising a transmission clutch; a hydraulic torque converter kinematically connected with the said transmission clutch and including an impeller. a turbine and a direct drive clutch actuable to lock together the said impeller and turbine; a vehicle engine shaft speed pickup arranged to cause actuation of the direct drive clutch by means of hydraulic fluid pressure upon the engine shaft speed reaching a predetermined value; a transmission clutch engaging and disengaging arrangement comprising a power cylinder whose movable member is mechanically connected with the operating member of the transmission clutch, an air pressurt source, and a valve - contrdllable by a driver of the vehicle to cause disengagement and engagement of the transmission clutch by connection of the power cylinder respectively to the said air pressure source and to atmosphere through a throttling orifice; and a valve arrangement connected through the driver controllable valve to the power cylinder and providing a further route for communication of the power cylinder with the atmosphere, said valve arrangement being actuated by hydraulic fluid pressure in response to a signal from said vehicle engine shaft speed pickup.
2. A transmission according to claim 1, in which the valve arrangement is actuated jointly with the direct drive clutch.
3. A transmission as claimed in claim 1 or claim 2, wherein the valve arrangement comprises a cylinder accommodating a piston with a piston rod, means for feeding hydraulic fluid under pressure into the piston end of said cylinder, the rod end of the cylinder being in constant communication with the atmosphere, a spring-loaded closure member arranged to interact with the free end of the piston rod and a cover fitted to the rod end of the said cylinder to enclose a space which is in communication with the power cylinder, and separable from the rod end of the cylinder by means of the closure member.
4. A transmission, as claimed in claim 3, wherein the said cover is made of a resilient material and is rigidily connected to the spring-loaded closure member.
5. A hydraulic transmission for a vehicle, the transmission comprising a transmission clutch, a hydraulic torque converter, a direct drive clutch for locking friction elements of the hydraulic torque converter, a vehicle engine shaft speed pick up arranged to control the direct drive clutch, clutch operating means for engaging and disengaging the transmission clutch in response to movement of a gearchanger lever, said clutch operating means comprising a pneumatic power cylinder so arranged that engagement of the transmission clutch is effected by allowing air under pressure to escape from the said power cylinder by way of a first passage through a throttling orifice, and a valve actuated by means of hydraulic fluid pressure in response to a predetermined engine shaft speed being reached to provide a second passage by which air under pressure can escape from the said clutch control means whereby engagement of the said

transmission clutch is effected more quickly at and above the said predetermined engine speed.
6. A hydraulic transmission for a vehicle according to claim 5, wherein said value is arranged such that the said second passage is also open to allow air under pressure to escape during a first portion of clutch engagement when the vehicle is starting from rest.
7. A hydraulic transmission for a vehicle substantially as herein described with reference to the accompanying drawings.

E r MYTTTS\T o r