GB2041468A

GB2041468A - Improvements in gearboxes

Info

Publication number: GB2041468A
Application number: GB8004069A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-02-10
Filing date: 1980-02-07
Publication date: 1980-09-10
Also published as: FR2448450A1; FR2448450B1; GB2041468B; DE2905097A1

Abstract

A double-acting working cylinder for changing the ratio in a two-ratio gearbox in series with a four-ratio gearbox is controlled by a valve with two motor ports (41, 42) and inlet and exhaust ports (40, 45). Movement of a selector cam (3) from a neutral position (C) to a position (D) causes motor port (42) to be pressurised to establish low ratio, and movement of the cam to position (B) causes port (41) to be pressurised for high ratio. Further operation of the cam after low or high ratio has been established, i.e. to the range (E) or (A) selects ratios in the four-ratio gearbox. A coupling (10) between cam follower 9 and valve stem 8 is automatically released when the cam is in the range (E) or (A), allowing the valving parts to be returned to neutral by springs. Thus, rapid movement of the cam from (C) to (E) or (A) not allowing sufficient time at position (D) or (B) for low of high ratio to be established results in the two-speed gearbox being placed in neutral. <IMAGE>

Description

SPECIFICATION Improvements in gearboxes The invention relates to a shift device for changing the transmission ratio of a group change gearbox of a commercial vehicle.

A known shift device for such purpose has a control cam which, commencing from a neutral central position, has only two shift positions for "fully engaged". In a shift device of this type, it may so happen a new gear is already engaged in the step-change gearbox during a rapid gear-change operation and the clutch is re-engaged before the group change gearbox has completed its gearshift operation.

The group change gearbox is then liable to be destroyed.

The present invention provides a shift device for changing the transmission ratio of a group change gearbox of a commercial vehicle, comprising a double-acting working cylinder for effecting the ratio change a four port, four position valve for controlling the doubleacting working cylinder, and a control cam for actuating the valve, the multi-position valve having two double-seat valves and having a valve stem whose length is variable in three stages by means of a travel-dependent snap device.

Upon changing the gears, an additional stroke is imparted to the four-port, four-position valve by way of the control cam and the working chamber of the cylinder is vented.

The group change gearbox thereby assumes its neutral state if the gear-change operation has not yet been concluded. Thus, in such a case, no forces can be transmitted upon coupling the engine and damage to the group transmission is avoided.

A further advantage is that, upon actuation of the group change gearbox, that working chamber of the actuating cylinder which is the last to be vented remains vented, thus ensuring a rapid and reliable gear-change operation.

The invention is further described, by way of example, with reference to the drawings, in which: Figure 1 shows a gear shift device diagrammatically with a four port, four position valve and an actuating cam, Figure 2 is a diagram of the gear arrangement, Figure 3 is a section through the four port, four position valve with control cam and venting diagram, and Figure 4 is a diagrammatic illustration of actuation of the transmission unit.

A gear shift device has a four port, four position valve 1. The multi-position valve 1 is intended for controlling the air supply to a double-acting working cylinder 4 of a group change gearbox (not illustrated). The group change gearbox has two ratios and is arranged at the input side of a four-speed stepchange gearbox so that, in all, eight ratios are available, in addition to the usual "crawl" and "reverse" ratios. A valve stem 2 is provided for actuation of the multi-position valve 1 and is adjustable by way of a control cam 3. To improve comprehension, the control cam 3 is illustrated in two different ways. It is shown diagrammatically by dash-dot lines on the one hand and, on the other hand, it is shown in perspective by solid lines, various zones of the control cam 3 being denoted by the capital letters A, B, C, D, E.When the valve stem 2 is engaged by the zone C, the four port, four position valve 1 is in a neutral or transition position, and, when the valve stem 2 is engaged by the zone B or D, the multi-position valve is put into its air-admission position in which the working cylinder 4 engages the group change gearbox in the selected one of its ratios. However, the admission of air into the working cylinder 4 is interrupted when the zone A or E reaches the valve stem 2 and the multi-position valve automatically snaps back into its neutral central position in which the working cylinder 4 is vented.

The gears 1 to 4, R (reverse) and C (crawl) are engaged with the actuating zone D effective, and the gears 5 to 8 are engaged with the actuating zone B effective (see Fig. 2).

The sectional illustration of Fig. 3 shows that the four port, four position valve 1 has a housing incorporating a multiply stepped through bore 5. A partition 6 is fitted in the housing and has a central hole 7 through which a portion 8 of the valve stem 2 passes in a sealed manner. A portion 9 of the valve stem 2 extends outwardly and is intended for cooperation with the control cam 3. The two portions 8 and 9 af the valve stem are located one behind the other normally with an amount x of axial clearance therebetween, and are couplable and de-couplable by way of a snap device 1 0.

The snap device 10 comprises an annular groove 11 in the stem portion 8, spherical members 1 2 normally located in the annular groove 11, a tubular member 13 which is slidably mounted on the stem portion 8 and which is provided with radial openings 1 4 for receiving the spherical members 12, and an annular sliding block 1 5 which is slidingly mounted on the tubular member 1 3 and which incorporates two annular chambers 1 6 and 1 7 for entry of the spherical members 1 2 during de-coupling and an annular ridge portion 1 8 which is disposed between the two annular chambers 1 6 and 1 7 and which is intended for displacing the spherical members 1 2 into the annular groove 11 for the purpose of the coupling together the two stem portions 8 and 9.

The sliding block 1 5 is retained in its illustrated position by means of two centering springs 19 and 20. A strong spring 21 en sures that one end of the tubular member 1 3 always remains in abutment with the stem portion 9. A diaphragm 22 secured to the stem portion 9 externally seals a chamber 23 which accommodates the snap device 10. A weaker spring 24 also abuts against the tubular member 1 3 and its other end abuts against the stem portion 8 by way of a disc 25.

Two double-seat valves 27 and 28 are fitted in a valve chamber 26 disposed on the other side of the partition 6 remote from the snap device 10. Each double-seat valve 27 and 28 has a valve seat 29 and 30 respectively which is secured relative to the housing, and a movable valve seat 31 and 32 respectively. The latter valve seats are arranged on the portion 8 of the valve stem. A closure member 33 of the double-seat valve 22 is in the form of a disc and is acted upon by a valve spring 34. On the other hand, a closure member 35 of the double-seat valve 28 is in the form of a ring which sealingly surrounds the stem portion 8 by means of an annular sealing lip 36. A valve spring is mounted on the closure member 35 and is designated 37.

A valve stem spring 38 acts upon the stem portion 8 and seeks to urge the portion 8 to the right. The valve stem spring 38 is supported by a stop 39 comprising an annular disc and a spring ring so that the stem spring 38 no longer acts on the stem portion 8 when the latter is displaced to the right from its illustrated neutral position.

The valve chamber 26 has a compressed air port 40, a load port 41 in the region of the double-seat valve 27, and a load port 42 in the region of the double-seat valve 28. The two load ports 41 and 42 are connected by way of lines (not illustrated in Fig. 3 but see Figs. 1 and 4) to the double-acting working cylinder 4 which actuates the group change gearbox. A common atmospheric air connection for the two double-seat valves 27 and 28 is provided by a coaxial bore 43 in the stem portion 8 and leads into the chamber 23 by way of a radial passage 44 and then to the atmosphere by way of an exhaust port 45.

Fig. 4 is a diagram of the entire system.

The four position, four port valve 1 will be seen. Furthermore, Fig. 4 shows a compressed air reservoir 50 and the working cylinder 4 for a gear-shift lever 52, shown in its two end positions, for the group change gearbox (not illustrated).

When in its illustrated position, the valve stem 2 is located on the neutral zone C of the control cam 3. The stem portion 8 is coupled to the stem portion 9 by way of the snap device 11, since the spherical members 1 2 are located in the annular groove 11. The two double-seat valves 27 and 28 are both in their venting positions in which the load ports 41 and 42 are both connected to the exhaust port 45.

Upon changing a gear, the control cam 3 is moved such that the stem 2 reaches the gear change zone B or D. Either the double-seat valve 27 or the double-seat valve 28 is then fully actuated, that is to say, the venting operation is shut off and the valve closure member 33 or 35 is removed from its respec tive valve seat 29 or 30. The working cylinder 4 receives compressed air by way of the load port 41 or 42 and changes over the group change gearbox. The group change gearbox then establishes its ratio for the gears 5, 6, 7, 8 when air is admitted to the load port 41, or establishes the ratio for the other gears when the load port 42 receives compressed air (see air-admission diagram on the right of Fig. 3).

The valve stem 2 reaches the gear-change zone A or E when a gear change operation is completed to engage a ratio of the step change gearbox. Thus, an additional stroke is imparted to the valve stem 2 by way of the control cam 3 and uncouples the snap device 10. The two portions 8 and 9 of the valve stem are no longer rigidly interconnected, and the valve stem 2 becomes either shorter or longer so that the changed-over double-seat valve 27 or 28 automatically returns to its starting position in which admission of air to the working cylinder is again interrupted and venting takes place.

The spherical members 12 register with the annular chamber 16 or 1 7 during the course of the additional stroke and can thus snap out of the annular groove 11. The force of the spring 38 or 24 returns the stem portion 8 to its starting position. When the stem portion 9 again engages the gear-change zone C, the snap device 10 re-engages by virtue of the fact that the annular ridge portion 18 presses the spherical members 12 into the annular groove 11. Thus, the valve stem 2 has again assumed its original length.

It will be seen that intermediate admission of air to the working cylinder 4 does not take place upon gear shift of the 4 speed step change gearbox. Thus, a short gear-shift times are obtained.

It is also advantageous that the working cylinder 4 is immediately vented when the speed change involving changing the ratio of the group change gearbox (i.e. from 4th to 5th gear) is actuated too rapidly or in the vent of other faults. Thus, damage to the group change gear-box is avoided.

Claims

1. A shift device for changing the trans mission ratio of a group change gearbox of a commerical vehicle, comprising a double-act ing working cylinder for effecting the ratio change, a four port, four position valve, for controlling the double-acting working cylinder, and a control cam for actuating the valve, the multi-position valve having two double-seat valves and having a valve stem whose length is variable in three stages by means of a travel dependent snap device.

2. A shift device as claimed in claim 1, in which the change in the length of the valve stem from its medial second stage length to its first and third stage lengths is equal respectively to the valve stroke of one or other of the two double-seat valves.

3. A shift device as claimed in claim 1 or 2, in which the valve stem comprises two portions which are located one behind the other normally with an amount of axial clearance therebetween and which are couplable and uncouplable by way of the snap device.

4. A shift device as claimed in claim 3, in which one portion of the valve stem carries two outlet valve seats respectively of the two double-seat valves and incorporates a part of the snap device.

5. A shift device as claimed in claim 4, in which one end of the other portion of the valve stem abuts against the control cam and its other end has a contact surface for the one portion of the stem.

6. A shift device as claimed in claim 4 or 5, in which the snap device part incorporated in the one stem portion comprises an annular groove therein.

7. A shift device as claimed in claim 4, 5, or 6, in which the snap device includes spherical members received in radial opening provided in a tubular member which encircles the one stem portion which carries the two outlet seats, the spherical members cooperating with said one stem portion.

8. A shift device as claimed in claim 7, in which an annular sliding block is slidingly mounted on the tubular member and is provided with two annular chambers for entry of the spherical members and with an annular ridge portion disposed between the two annular chambers for the purpose of displacing the spherical members into that portion of the valve stem which carries the two outlet seats.

9. A shift device as claimed in any of claims 1 to 7, in which a "snap point" of the snap device is determined by an actuating surface of the control cam by which an additional displacement is imparted to the valve stem for the purpose of decoupling the snap device.

1 0. A shift device for changing the transmission ratio of a group change gearbox, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.