GB1582237A

GB1582237A - Powershift transmission

Info

Publication number: GB1582237A
Application number: GB3715376A
Authority: GB
Original assignee: Brockhouse Transmissions Ltd
Current assignee: Brockhouse Transmissions Ltd
Priority date: 1977-09-08
Filing date: 1977-09-08
Publication date: 1981-01-07

Description

(54) POWERSHIFT TRANSMISSION (71) We, BROCKHOUSE TRANSMISSIONS LIMITED, a British Company of Victoria Works, Hill Top, West Bromwich, in the County of Stafford, 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: This invention relates to a powershift transmission of the type, hereinafter referred to as the type described, having constantly meshing gears and clutches for selectively coupling said gears to rotatable shafts to provide a desired gear ration between input and output shafts of the transmission and in which more than one of said clutches is engaged concurrently during torque transmission.

For example, the transmission may comprise a first set of constant mesh gears and selectively engageable clutches to provide a first set of speed ratios and, downstream thereof, a second set of constant mesh gears and selectively engageable clutches to provide a second set of speed ratios used in conjunction with the first ratios. As a result the clutches of the second set may have to transmit a greater torque than do the clutches of the first set and this is a disadvantage as it increases the cost of the clutches and also the space required therefor. Even if the second clutches carry a lower torque than the first clutches, as may be the case depending on the ratios concerned, they are still longer than would be preferable.

It is accordingly an object of the present invention to provide a power shift transmission of the type described wherein the abovementioned disadvantage is overcome or is reduced.

According to the present invention we provide a powershift transmission having constantly meshing gears and clutches for selectively coupling said gears to associated shafts to provide desired gear ratios between input and output shafts of the transmission and in which more than one of said clutches are in engagement concurrently during torque transmission, a clutch control means operable to control engagement and disengagement of the clutches and including electrically operated means to cause one of said clutches to engage after another on at least some ratio changes.

The control means may include means to provide a first electric signal to cause engagement of said one clutch and means to provide a second electric signal to cause engagement of said other clutch and a time delay means whereby said second signal is provided a predetermined time after said first signal.

The clutches may be fluid operated and the control means may include a plurality of electrically operated fluid supply valves adapted to supply fluid to the clutches and the control means may include means to provide a first electric signal to at least one of said valves and means to provide a second electric signal to at least another one of said valves and a time delay means whereby said second signal is provided a predetermined time after said first signal.

The transmission may comprise a first set of constant mesh gears and selectively engageable clutches to provide a first set of speed ratios and, downstream thereof, a second set of constant mesh gears and selectively engage able clutches to provide a second set of speed ratios, the clutches of the first set engaging after those of the second set whereby when the clutches of the second set engage no driving torque is transmitted by the transmission and hence the clutches do not have to be capable of handling the dynamic driving torque of the transmission upon engagement. As a result the overall size and number of plates of the clutch can be reduced by choosing clutch facing material with a higher static coefficient of friction than dynamic and ability to ignore wear aspects of clutch facings. In addition a higher loading pressure may be provided since allowable clutch face pressure for static operations can be higher than for dynamic ones, thus again contributing to reduction in size and number of plates in the clutch compared with that which would be required if the clutch had to be capable of transmitting driving torque upon engagement.

The last to engage clutches may be modulated in conventional manner.

The gears and clutches of the first set may permit selection of forward or reverse and of first or second speed ratios in either forward or reverse whilst the gears and clutches of the second set may provide a range change thereby providing a thrid and fourth speed ratio in forward or reverse.

The transmission may comprise an input shaft carrying a first clutch drum which is in constant mesh with a second clutch drum on a reverse shaft, each clutch drum having a pair of clutches, each clutch of which is capable of engaging an associated gear to the shaft which carries the drum, the gears on the input and reverse shafts being in constant mesh with a pair of gears fixed to a lay shaft and gears fixed to the lay shaft being in constant mesh with two further gears which can be clutched to an output shaft.

Engagement of one clutch on the input shaft provides a first forward ratio whilst engagement of the other clutch provides a second forward ratio, engagement of a clutch on the reverse shaft provides a first reverse ratio and engagement of the other clutch of the reverse shaft provides a second reverse ratio.

Engagement of one clutch on the output shaft provides a low range and hence gives an overall first or second ratio depending upon which of the clutches on the forward or reverse shaft are engaged whilst engagement of the other clutch provides a high range and thus an overall third or fourth ratio again depending upon which clutch is engaged on the forward or reverse shaft.

The invention will now be described in more detail by way of example with reference to the accompanying drawings wherein: - Figure 1 is a longitudinal cross-sectional view of a four speed forward and reverse powershift transmission embodying the invention, Figure 2 is a longitudinal cross-sectional view through a pressure valve in the clutch control system of the transmission of Figure 1, and Figure 3 is a diagrammatic representation of the electrical clutch control system of the transmission shown in Figure 1.

Referring to the drawings there is illustrated a powershift transmission comprising a casing 10 within which is provided a hydro-dynamic coupling 11 and a powershift gearbox 12. The coupling 11 is of generally conventional form consisting of the usual annular hollow two-part shell. The half of the shell which is more remote from the engine comprises a vaned impeller 13 driven by a driving member 14 connected to the engine of the vehicle and mounted on a bearing 15.

In the other half of the shell, that is the half nearer to the engine, there is mounted a vaned turbine 16. The impellor 13 and turbine 16 constitute torque transmitting elements through which the torque is transmitted. Disposed at the inner periphery of the path of the fluid within the coupling is a vaned reaction element 17 which is held against rotation under torque conversion conditions by a suitable conventional overrunning device 18.

The turbine 16 of the coupling is carried on one end of an output shaft 19 which extends through the impellor 13 and is rotatably mounted on bearings 20. The output shaft 19 constitutes an input shaft to the powershift gear box 12 and carries a Duplex hydraulically operated clutch 21 of a forward drive means.

The clutch 21 compnses a drum 22 connected by a median web 23 for rotation with the shaft 19 and slidably mounted within the drum 22 are a pair of pistons 24a, 24b, each piston 24a, 24b is adapted respectively to act on sets of clutch plates 25a, 25b and 26a and 26b respectively. The clutch plates 25a are keyed to the drum 22 whilst the clutch plates 25b are keyed to a second speed ratio gear 27.

The clutch plates 26a are keyed to the drum 22 and the plates 26b to a first speed ratio gear 28.

In use, the piston 24a can be urged by hydraulic fluid to the left in Figure 1 to press the clutch plates 25a and 25b together and against a stop member 25c so as to connect the gear 27 to the drum 22.

Alternatively, the piston 24b can be operated to urge the clutch plates 26a and b together and against the stop member 26c to connect the gear 28 to the drum 22.

Belleville springs 29 are provided normally to maintain the pistons 24a and 24b out of drive transmitting engagement with the clutch plates.

The drum 22 has a gear teeth 30a which mesh with gear teeth 30b formed on a drum 31 of a reverse clutch 32. The clutch 32 is of the same construction as the clutch 21 and hence will not be described further except to say that the clutch is operable to connect a first reverse ratio gear 33 or a second reverse ratio gear 34 to the drum 31.

The first forward gear 28 and the first reverse gear 33 are both in mesh with a gear 35 fixed to lay shaft L mounted in bearings 36.

Likewise the second forward and reverse gears 27 and 34 are both in mesh with a gear 37 fixed to the lay shaft L.

The lay shaft L also carries a gear 38 which is in constant mesh with a low range gear 39 which can be engaged by a clutch 40 with an output shaft 0 of the transmission rotatably mounted in bearings 42. The gear 37 carried by the lay shaft L is in constant mesh with a high range gear 41 which can be clutched by a clutch 43 to the output shaft 41.

The clutches 40 and 43 are of basically the same construction as the hereinbefore described clutches 21 and 32 although they differ in detail as may be seen from Figure 1. The precise construction of the clutches however does not form part of the present invention and so further description of the clutches is not considered necessary.

It is, however, to be noted that the clutches 43 and 40 are of relatively compact construction.

In use, the clutch control means, hereinafter described in more detail, may be actuated to engage either the clutch 24b or 24a to give first or second forward drive through the gears 28, 35 or 27, 37 respectively to the lay shaft L or the reverse clutch 32 may be engaged to give first or second reverse drive through the gears 33,35 and 34,37 respectively to the lay shaft L.

One of the clutches 40 or 43 is also engaged to give either an overall first or second ratio or a third and fourth ratio depending upon whether it is the clutch 40 or the clutch 43 respectively which is engaged.

Because the clutches 40 and 43 have to transmit the input torque provided by the coupling 11 multiplied by the gear ratio afforded by the clutches 21 or 32, conventionally the clutches 40 and 42 would have to be capable of transmitting relatively high torque and engaging under torque transmitting conditions.

(The actual torque values may be no higher than the clutches 21, 32 and depends on gear ratios used).

However, as a result of the present invention the overall size and number of plates in the clutches 43 and 40 may be reduced compared to that conventionally required and in addition a higher loading pressure may be provided as hereinafter to be described.

Referring now to Figure 2, the hydraulic fluid which is provided from a pressure source for operating the clutches hereinbefore described is fed to a valve 50 at an inlet port 51.

Slidably mounted within the valve 50 is a piston 52 and the fluid fed via the inlet 51 acts on the surface 53 of the piston 52 to force the piston downwardly in Figure 2 against the bias of a spring 54.

When the piston 52 is displaced downwardly it connects the space above the piston with a passage 55 which provides fluid to act on the surface 56 of a second piston 57 slidably mounted in the valve 50 and movement of which is opposed by a spring 58.

The space 59 below the surface 56 is connected by a passage 60 to the space 61 below the surface 62 of the piston 52.

Hydraulic fluid for operating the clutches 40 and 43 is fed from a connection to the inlet 51 whilst hydraulic fluid for operating the clutches 21 and 32 is fed from a passage which communicates with the passage 55.

In use, hydraulic fluid fed to the inlet 51 displaces the piston 52 downwardly when the pressure of the fluid in the inlet 51 balances the pressure applied by the spring 54 and the pressure of fluid in the region 59 below the surface 56 of the piston 57, fed into the region 61 by the by-pass 60. This fluid pressure will be determined by the strength of the spring 58.

In the example under discussion the springs are of equal strength and exert a pressure equivalent to 125 PSI. Thus, the fluid fed to the clutches 40 and 43 will be at a pressure of 250 PSI whilst that fed to the clutches 21 and 31 will be at a pressure of 125 PSI.

Although in this example the springs have been described as being of the same rate and the pistons are also identical if desired the springs be of a different rate and the pistons may also be dissimilar. It is, however, convenient for similar components to be used for production reasons.

Referring now to Figure 3, there is illustrated diagrammatically an electrical circuit of the clutch control means. The clutch control means includes two manually operable levers, namely a forward and reverse lever 70 provided in a forward and reverse control means 69 and a speed ratio change lever 71 provided in a change speed control means 72. The forward and reverse lever 70 can engage forward, neutral and reverse contacts F, N and R respectively.

The contact N is connected to a starter circuit by a line N1 whilst the forward and reverse contacts are connected by lines F1 and R1 respectively to the change speed means 72.

In the change speed control means 72 the lever 71 can cause engagement of a first forward and first reverse contact 1 F, 1R a second forward and second reverse contact 2F, 2R, a third forward and third reverse contact 3F, 3R and a fourth forward and fourth reverse contact 4F and 4R respectively the forward or reverse selection being controlled by position of control means 69.

The line R1 relates to the contacts 1 R - 4R whilst the line F1 relates to the contacts 1 F - 4F and connections are taken from the contacts 1F - 4F and 1R - 4R to operate appropriate solenoids, as illustrated in Figure 3.

The speed ratio control means is also provided with a source of current via lines 73, 74 and 75 whilst a line 76 from this control means provides an input to an electrical delay means 77 whilst the output thereof is fed by line 78 to provide the input 79 for the forward and reverse contacts F and R of the reverse change means 69.

The line 74 is provided with range change contacts RC1-2 and RC3-4 whilst the line 75 is provided with delay contacts D1-2 and D3-4.

Contacts RC1-2 and RC3-4 select the appropriate range clutch 40 or 43 and contacts D1-2 D34 control the delay circuit (via 76).

In use, when the lever 71 is moved to the first position it will cause engagement of the contacts 1F and 1R and the contacts RC1-2; thus selecting a first gear ratio and a first range.

Depending upon whether the lever 70 has energised the lines F1 or R1 appropriate forward or reverse solenoids will also be energised. The contacts D1-2 are also engaged thus completing the circuit to the F/R control 69 via the delaying device 77.

When the lever 71 is moved from the first to the second position contact will be maintained with the contacts RC 1-2 and D1-2 and contact will be broken with the contacts 1F and 1R and made with contacts 2F and 2R, thus causing energisation of the solenoids for the second gear ratio in forward or reverse depending again upon the position of the lever 70. This movement does not change selection of the range clutch which remains engaged and hence the delay device 77 does not operate.

However when the lever is moved to the third position contact is broken with 2F and 2R and made with 3F and 3R and contact is broken with contacts RC 1-2 and D1-2 and made with contacts RC34 and D34, thus causing a break in the power supply to the delay unit 77 which ensures that there is an adequate delay, for example 0.5 seconds, after the lever 71 engages the contacts RC34 and D34 before the solenoids for the ratio clutches 21 or 32 can be engaged thereby ensuring that the range clutches 40 or 43 are engaged before the clutches 21, 32.

Thus the delay device 77 only operates when shifting across the 2-3, 3-2 gap. These shifts operate the delay: 1-3/1-4/2-3/2-4//4- 2/4- 1/3 -2/3 - 1) This ensures that when the clutches 40 and 43 do engage the transmission is not transmitting torque, except for inertial torque of parts in the transmission which can be ignored, thereby permitting the clutches 40 and 43 to be made relatively less large than would otherwise be the case as hereinbefore described.

If desired the clutches 21 and 32 may be modulated in conventional manner.

WHAT WE CLAIM IS: 1. A powershift transmission having constantly meshing gears with clutches for selectively coupling said gears to associated rotatable shafts to provide desired gear ratios between input and output shafts of the transmission and in which more than one of said clutches are in engagement concurrently during torque transmission, a clutch control means operable to control engagement and disengagement of the clutches and including electrically operated means to cause one of said clutches to engage after another on at least some ratio changes.

2. A transmission according to Claim 1 wherein the control means includes means to provide a first electric signal to cause engagement of said one clutch and means to provide a second electric signal to cause engagement of said other clutch and a time delay means whereby said second signal is provided a predetermined time after said first signal.

3. A transmission according to Claim 1 wherein the clutches are fluid operated and the control means includes a plurality of electrically operated fluid supply valves adapted to supply fluid to the clutches and the control means includes means to provide a first electric signal to at least one of said valves and means to provide a second electric signal to at least another one of said valves and a time delay means whereby said second signal is provided a predetermined time after said first signal.

4. A transmission according to any one of the preceding claims wherein the transmission comprises a first set of constant mesh gears and selectively engageable clutches to provide a first set of speed ratios and, downstream thereof, a second set of constant mesh gears and selectively engageable clutches to provide a second set of speed ratios, the clutches of the first set engaging after those of the second set whereby when the clutches of the second set engage no driving torque is transmitted by the transmission and hence the clutches do not -have to be capable of handling the dynamic driving torque of the transmission upon engage ment.

5. A transmission according to any of the preceding claims wherein the last to engage clutches are modulated in conventional manner.

6. A transmission according to Claim 4 or Claim 5 when dependent on Claim 4 wherein the gears and clutches of the first set permit selection of forward or reverse and of first or second speed ratios in either forward or reverse whilst the gears and clutches of the second set provide a range change thereby providing a third and fourth speed ratio in forward or reverse.

7. A transmission according to any one of the preceding claims wherein the transmission comprises an input shaft carrying a first clutch drum which is in constant mesh with a second clutch drum carried on a reverse shaft, each clutch drum having a pair of clutches, each clutch of which is capable of engaging an associated gear to the shaft which carries the drum, the gears on the input and reverse shafts being in constant mesh with a pair of gears fixed to a lay shaft and gears fixed to the lay shaft being in constant mesh with two futther gears which can be clutched to an output shaft.

8. A transmission according to Claim 7 wherein engagement of one clutch on the input shaft provides a first forward ratio whilst engagement of the other clutch provides a second forward ratio, engagement of a clutch on the reverse shaft provides a first reverse ratio and engagement of the other clutch of the reverse shaft provides a second reverse ratio.

9. A transmission according to Claim 8 wherein engagement of one clutch on the output shaft provides a low range and hence gives an overall first or second ratio depending upon which of the clutches on the forward or reverse shaft are engaged whilst engagement of the other clutch provides a high range and thus an overall third or fourth ratio again depending upon which clutch is engaged on the forward or reverse shaft.

10. A transmission substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. However when the lever is moved to the third position contact is broken with 2F and 2R and made with 3F and 3R and contact is broken with contacts RC 1-2 and D1-2 and made with contacts RC34 and D34, thus causing a break in the power supply to the delay unit 77 which ensures that there is an adequate delay, for example 0.5 seconds, after the lever 71 engages the contacts RC34 and D34 before the solenoids for the ratio clutches 21 or 32 can be engaged thereby ensuring that the range clutches 40 or 43 are engaged before the clutches 21, 32. Thus the delay device 77 only operates when shifting across the 2-3, 3-2 gap. These shifts operate the delay: 1-3/1-4/2-3/2-4//4- 2/4- 1/3 -2/3 - 1) This ensures that when the clutches 40 and 43 do engage the transmission is not transmitting torque, except for inertial torque of parts in the transmission which can be ignored, thereby permitting the clutches 40 and 43 to be made relatively less large than would otherwise be the case as hereinbefore described. If desired the clutches 21 and 32 may be modulated in conventional manner. WHAT WE CLAIM IS:

1. A powershift transmission having constantly meshing gears with clutches for selectively coupling said gears to associated rotatable shafts to provide desired gear ratios between input and output shafts of the transmission and in which more than one of said clutches are in engagement concurrently during torque transmission, a clutch control means operable to control engagement and disengagement of the clutches and including electrically operated means to cause one of said clutches to engage after another on at least some ratio changes.