GB1602398A

GB1602398A - Apparatus for operation of transmission clutches or brakes by means of pressure medium

Info

Publication number: GB1602398A
Application number: GB21759/78A
Authority: GB
Original assignee: Hurth Verwaltungs GmbH
Current assignee: Hurth Verwaltungs GmbH
Priority date: 1977-06-25
Filing date: 1978-05-24
Publication date: 1981-11-11
Also published as: IT1156160B; FR2395430B3; IT7848804A0; FR2395430A1; DE2728737A1

Description

(54) APPARATUS FOR OPERATION OF TRANSMISSION CLUTCHES OR BRAKES BY MEANS OF PRESSURE MEDIUM (71) We, HURTH VERWALTUNGS GmbH, of 36 Moosacher Strasse, Munich, Germany, a German Body Corporate, 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 invention relates to apparatus for the selective control of transmission clutches or brakes.

The object of the invention is to provide apparatus for the selective operation of pressure medium-operated clutches or brakes, in which only a single differential pressure valve is required for all the clutches or brakes; at the same time the apparatus is to operate rapidly and reliably and have a compact shape which facilitates installation.

It has been found that such apparatus operates reliably with a single differential pressure valve only if it can be ensured that the line leading to the actuating member (plunger) of the differential pressure valve remains substantially unpressurized during all control functions, until the piston or the like of the driven clutch or brake cylinder bears on the friction surfaces, for example the plates. Furthermore, a quantity of pressure medium, but not pressure, is required for displacing the clutch or brake piston, while only pressure and no quantity of fluid is required after the friction members are in contact. An advantage of the invention is that there is provided a control element in the apparatus which will control both operations in a simple manner.

The present invention resides in apparatus for the selective control of a plurality of friction devices of a transmission by means of a pressure medium, wherein in operation at least one friction device is engaged and at least one other friction device is disengaged, the engagement being gradual and the disengagement faster, which apparatus includes a changeover valve for selecting the friction device(s) to be engaged and disengaged and directing pressure medium to the said device(s) to be engaged, and a pressure control device adapted to delay engagement which control device includes a differential pressure valve having an actuating plunger of relatively larger diameter, a control spool of relatively small diameter, and a spring therebetween, whereby in operation the control spool controls the engagement pressure of the friction device(s) to be engaged according to the spring force and the actuating plunger is moved with a delay from an initial position to an end position thereby to increase the spring force acting on the control spool, the differential pressure valve being connectable to all the friction devices, and a flow control valve connected to the differential pressure valve and arranged to respond to the flow of pressure medium towards the friction devices and to interrupt the supply of actuating pressure to the actuating plunger until the flow control valve senses a cessation of flow whereby in operation the plunger will remain in its initial position until the friction members of the selected friction device(s) are engaged.

The term "friction device" herein and in the claims means a friction clutch or a friction brake.

The above mentioned control element is the said flow control valve. The features of claim 2 result in a simple construction for the flow control valve and a compact construction is achieved with the features of claim 3. The apparatus is reduced to the smallest space by the application of the features of claim 4.

Smooth operation of the clutches or brakes is achieved by the features of claim 5 and the features of claim 6 ensure reliable operation.

The functionality of the apparatus is assisted by the features of claim 8.

A device which can be simply installed and quickly exchanged is obtained by the features of claim 7.

Further advantages and features are disclosed in the description hereinbelow with reference to the accompanying drawings in which: Figure 1 is a hydraulic circuit diagram for a transmission which is provided with two hydraulically operable clutches and is driven by a hydrodynamic converter, Figure 2 is a section through a valve assembly relating to the hydraulic circuit according to Figure 1, in its neutral position, Figure 3 shows the baseplate of the valve assembly according to Figure 2, and Figure 4 shows the pressure characteristic in the clutches which are controlled by the hydraulic system according to Figure 1.

The hydraulic control system according to Figure 1 controls hydraulically operable clutches 1 and 2 of a two-speed transmission which is driven via a hydrodynamic converter 3. A pump 4 draws the operating medium, for example oil via filter 5 from a storage tank 6 and delivers it into a delivery duct 7. The delivery duct is divided into a first branch duct 8 and a second branch duct 9. A relief valve 10, the discharge of which is returned to the storage tank, is provided for the delivery duct.

The first branch duct 8 leads to a pressure regulating valve 11 whose regulating spool 12 closes the said branch duct in one operating state and in another operating state admits oil to pass from the first branch duct into the lubricating circuit 13 of the transmission. When required, an oil cooler 14 can be connected to the lubricating circuit by means of a bypass line.

The regulating spool 12 is operated by an actuating plunger 15 via a spring 16. The plunger 15 is biased by the oil pressure in the manner described below.

The second branch duct 9 leads via a precision filter 17 to a regulating circuit 18, including a duct 19 leading via an orifice diaphragm 20 and a further duct 21 to a rotary changeover valve 22. A line 23, extending into the oil pressure chamber 24 behind the plunger 15, branches off between the orifice diaphragm 20 and the rotary valve 22. "Orifice diaphragm" refers to a restrictor with a relatively short restrictor bore, a feature which achieves substantial independence from viscosity and temperature.

The valves 11 and 22, a controll spool 30 coupled to the spool 12, and a flow control valve 33, are all incorporated in a valve assembly shown in Figures 2 and 3, having a casing 39.

A chamber 25 (Figure 2) in the valve assembly, downstream of the precision filter 17, communicates with a control chamber 31 of valve 33 via a duct 26, a groove 27 in the rotary member of valve 22, a duct 28 in the latter and a port 29 in spool 30 (described below); the control chamber 31 is formed in the spool 32 of the flow control valve 33, which is housed in the said rotary member. A shank of the spool 32 is guided in sealing-tight manner in the spool 30 so as to be longitudinally and axially slidable therein. An end of the spool 30 as well as an end of the spool 32 face an end of the spool 12 and can bear thereon.

At the end which is distal from the spool 12, the control chamber 31 is closed by a collar 34 whose circumference does not closely adjoin the wall of an axial bore 35 in the spool 30 but leaves an annular gap which forms a first restrictor 36. This first restrictor is shown diagrammatically in a bypass line in the hydraulic circuit diagram of Figure 1.

The axial bore 35 of the spool 30 also forms the connecting duct 35a in the hydraulic circuit diagram of Figure 1.

The axial bore 35 communicates via radial ports with an annular groove 37 which, in specific operating states, is aligned with a hydraulic oil duct 38 situated in the rotary valve 22.

The rotary member of valve 22 is rotatably guided in sealing-tight manner in a casing 39.

Longitudinal displacement of the rotary valve member is prevented by a pin 40. The rotary valve member can be rotated by means of a lever 41 so that the hydraulic oil duct 38 can be optionally aligned with the ducts 42, 43 (Figure 3) and can communicate with the clutch lines 44, 45. The particular clutch line which is not charged with hydraulic oil is connected to one of the discharge ducts 46, 47 which returns to the storage tank the oil of the clutch which is to be depressurized. The rotary valve can therefore assume three positions.

I. Clutch 1 engaged, clutch 2 disengaged O. Both clutches disengaged II Clutch 2 engaged, clutch 1 disengaged On the side which is distal from the regulating spool 12 the axial bore 35 of the spool 30 is closed with a plug 48 which is provided with a bore that acts as a second restrictor 49. The oil is conducted through the restrictor 49 into a control chamber 50 above the spool 30. In Figure 1 the second restrictor 49 is shown in a bypass duct. The different positions of the control means 22, 30, 33 are shown side by side in the diagram of Figure 1.

An annular groove 55 is associated with the port 29, and on the side of groove 55 distal from the annular groove 37, a third annular groove 51 is provided in the spool 30 which, in specific operating states, is in alignment with a duct 52 situated in the rotary member of valve 22. The duct 52 communicates with an annular duct 53 that extends into the duct 21 (Figure 1 and 2). The annular duct 53 also communicates via the duct 23 formed in the baseplate 54 (Figure 3) with a space 24 beneath the plunger 15. The bore for the diaphragm 20 (see Figure 3) also extends into the annular duct 53, thus embodying the circuit according to Figure 1 in the valve assembly illustrated in Figures 2 and 3.

The groove 51 is sufficiently wide that the annular duct 53 is connected via the duct 52 and the groove 51 to the discharge duct 46 when the spool 30 is slid downwardly. In the same operating state the groove 27 will communicate via the duct 28 and via the annular groove 55 associated with the port 29, with the duct 52, which is connected to the discharge duct 46 as described above.

If the spool 32 is slid upwardly from the position according to Figure 2 the annular duct 53 will also communicate with the discharge duct 46 (designated 46a in Figure 1) via the space beneath the spool 32 and via the gap 56 (Figure 2) of the regulating spool 12. The valve assembly according to Figures 2 and 3 therefore also embodies the connection 57 shown diagrammatically in Figure 1.

A plunger 60 longitudinally is slidably guided in sealing-tight manner in a cylinder 59, which is mounted by means of screws 58 on the rotary valve member and is disposed on the far side of the lever 41 as seen from the casing 39 (Figure 2). The plunger 60 can be biased with hydraulic oil through a delivery line 61. The oil pressure is opposed by a spring 62. The motion of the plunger 60 is transmitted by means of a pin 63 to the control spool 30. With this device, which is also known as an inching device, it is possible to deliberately act on the control spool 30 and therefore on the entire control circuit 18. The inching device can also be mechanically actuated.

The valve combination 15, 30 acts as a differential pressure valve in which the pressure ratio P, = surface of the plunger 15 P surface of the control spool 30 Only one differential pressure valve 15, 30 is provided for both control position I and II of the rotary valve 22, a feature made possible by the invention owing to the lines 23, 21, 57 which lead to the plunger 15 communicating with the discharged oil during all control functions until the plates of the control clutch are in contact. In order to achieve this the lines 21. 23, 57 are connected to the discharge duct 46 (see also Figure 2) by means of the rotary valve 22 in position "0". The first restrictor 36, which acts as a flow control valve on the spool 32, also connects the lines 23, 57 to the discharge duct 46 (46a in Figure 1) in control positions I or II. No substantial amount of oil flows as soon as the plates in the pressure biased clutch make contact and the aforementioned flow control valve closes.

The device (inching device) for deliberately acting on the hydraulic control function is designed so that the clutches can be controlled either by means of a hydraulic brake system of a vehicle, not shown, or by means of a separate hydraulic system. The pressure required in the clutch cylinders la, 2a for reducing the control pressure to zero corresponds approximately to the opening pressure of a shoe brake. The reduction of the control pressure can be divided into three phases.

a) Direct control of the pressure regulating valve 11, reduction of the control pressure approximately to the level of the lubricating oil pressure.

b) Opening of the duct 21, 23, 57 through the annular groove 51 on the control spool 30.

c) Connecting the control pressure in the affected clutch cylinder to the discharge duct while simultaneously restricting the supply by means of the control land on the control spool 30.

The delivery regulation of control pressure (inching device) is normally adjusted so that a residual pressure is maintained in the control circuit. The residual pressure ensures that on the one hand the plates in the affected clutch are not under pressure and on the other hand the piston in the clutch cylinder la or 2a does not return into the starting position so that no delay occurs on re-engagement of the clutch.

The graph of Figure 4 shows the pressure characteristic during the clutch operation. The solid line 71 refers to the control pressure in the clutch 1, the chain line 72 to the control pressure in the clutch 2, and the dashed line 73 refers to the differential pressure in the line 23, 21, 57, depending on the area difference between the spool 30 and plunger 15. The numeral 74 refers to the so-called changeover time, i.e. the time from disengagement of the clutch 1 to contact of the friction members, for example plates, of the clutch 2. The numeral 75 refers to the time required for building up the pressure.

In the first control state the pressure in the clutch 1 has a maximum value. The pressure in the other clutch 2 is zero. The differential pressure 73 is equal to the pressure 71 in the engaged clutch because the diaphragm 20 ensures pressure equalization.

If the rotary valve is changed from position I into "0" the control pressure 71 and the differential pressure 73 will first drop substantially suddenly to zero. In position "II" a pilot pressure 76 will be built up in the clutch 2 in dependence on the spring 16 in the pressure regulating valve 11. The space 24 beneath the plunger 15 initially remains unpressurized via 23, 57, 56, 46 or 46a since, owing to the presence of the first restrictor 36, the flow control valve 32 moves in the outward direction when oil flows into the clutch cylinder 2a in Figure 2. As soon as the clutch cylinder 2a is filled the flow ceases, the flow control valve 32, 36 closes and the differential pressure 73 and therefore the control pressure 72 rises. When the full control pressure 72 is reached the entire hydraulic system will be filled with hydraulic oil and the pressure beneath the plunger of the differential pressure valve rises suddenly to the full value via the third restrictor or diaphragm 20.

An example with two controllable clutches has been selected to explain the invention.

The invention can also be applied to changeover and/or reversing transmissions which are controlled with more than two clutches, and to transmissions controlled by means of friction brakes.

WHAT WE CLAIM IS: 1. Apparatus for the selective control of a plurality of friction devices of a transmission by means of a pressure medium, wherein in operation at least one friction device is engaged and at least one other friction device is disengaged, the engagement being gradual and the disengagement faster, which apparatus includes a changeover valve for selecting the friction device(s) to be engaged and disengaged and directing pressure medium to the said device(s) to be engaged, and a pressure control device adapted to delay engagement which control device includes a differential pressure valve having an actuating plunger of relatively large diameter, a control spool of relatively small diameter, and a spring therebetween, whereby in operation the control spool controls the engagement pressure of the friction device(s) to be engaged according to the spring force and the actuating plunger is moved with a delay from an initial position to an end position thereby to increase the spring force acting on the control spool, the differential pressure valve being connectable to all the friction devices, and a flow control valve connected to the differential pressure valve and arranged to respond to the flow of pressure medium towards the friction devices and to interrupt the supply of actuating pressure to the actuating plunger until the flow control valve senses a cessation of flow whereby in operation the plunger will remain in its initial position until the friction members of the selected friction device(s) are engaged.

2. Apparatus according to claim 1, in which the flow control valve comprises a spool which is longitudinally slidably guided in a bore, said bore and spool defining a control chamber and a first restrictor which extends from the control chamber.

3. Apparatus according to claim 1 or 2, in which the flow control valve is disposed in the control spool of the differential pressure valve.

4. Apparatus according to claim 3, in which the control spool which contains the flow control valve is disposed in a movable member of the changeover valve.

5. Apparatus according to claim 3 or 4, when dependent on claim 2, in which the bore is an axial bore in the control spool and is connected via a second restrictor to a control chamber which is formed by the control spool of the differential pressure valve and a cylinder in which the control spool is longitudinally slidably guided.

6. Apparatus according to claim 2, or any of claims 3 to 5 when dependent thereon, including a further restrictor between a delivery duct upstream of the first restrictor and a pressure chamber of the actuating plunger of the differential pressure valve.

7. Apparatus according to claim 6 when dependent on claim 5, in which the differential pressure valve, the first, second and further restrictors, the changeover valve and a filter disposed in a pressure medium delivery line are all situated in a single casing.

8. Apparatus according to any preceding claim in which the control spool of the differential pressure valve is provided with grooves which are adapted to, depending on the position of the control spool, admit pressure medium to the friction device(s) to be engaged or depressurize selected friction device(s) and a pressure chamber of the actuating plunger of the differential pressure valve.

9. Apparatus according to any preceding claim comprising means by which the position of the control spool of the differential pressure valve can be deliberately influenced, for example by a braking system of a vehicle.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. In the first control state the pressure in the clutch 1 has a maximum value. The pressure in the other clutch 2 is zero. The differential pressure 73 is equal to the pressure 71 in the engaged clutch because the diaphragm 20 ensures pressure equalization. If the rotary valve is changed from position I into "0" the control pressure 71 and the differential pressure 73 will first drop substantially suddenly to zero. In position "II" a pilot pressure 76 will be built up in the clutch 2 in dependence on the spring 16 in the pressure regulating valve 11. The space 24 beneath the plunger 15 initially remains unpressurized via 23, 57, 56, 46 or 46a since, owing to the presence of the first restrictor 36, the flow control valve 32 moves in the outward direction when oil flows into the clutch cylinder 2a in Figure 2. As soon as the clutch cylinder 2a is filled the flow ceases, the flow control valve 32, 36 closes and the differential pressure 73 and therefore the control pressure 72 rises. When the full control pressure 72 is reached the entire hydraulic system will be filled with hydraulic oil and the pressure beneath the plunger of the differential pressure valve rises suddenly to the full value via the third restrictor or diaphragm 20. An example with two controllable clutches has been selected to explain the invention. The invention can also be applied to changeover and/or reversing transmissions which are controlled with more than two clutches, and to transmissions controlled by means of friction brakes. WHAT WE CLAIM IS:

1. Apparatus for the selective control of a plurality of friction devices of a transmission by means of a pressure medium, wherein in operation at least one friction device is engaged and at least one other friction device is disengaged, the engagement being gradual and the disengagement faster, which apparatus includes a changeover valve for selecting the friction device(s) to be engaged and disengaged and directing pressure medium to the said device(s) to be engaged, and a pressure control device adapted to delay engagement which control device includes a differential pressure valve having an actuating plunger of relatively large diameter, a control spool of relatively small diameter, and a spring therebetween, whereby in operation the control spool controls the engagement pressure of the friction device(s) to be engaged according to the spring force and the actuating plunger is moved with a delay from an initial position to an end position thereby to increase the spring force acting on the control spool, the differential pressure valve being connectable to all the friction devices, and a flow control valve connected to the differential pressure valve and arranged to respond to the flow of pressure medium towards the friction devices and to interrupt the supply of actuating pressure to the actuating plunger until the flow control valve senses a cessation of flow whereby in operation the plunger will remain in its initial position until the friction members of the selected friction device(s) are engaged.

10. Apparatus as claimed in any preceding claim in which the changeover valve is a

rotary valve.

11. Apparatus for selectively controlling transmission clutches, substantially as herein described with reference to and as shown in the accompanying drawings.