GB1597661A - Power shift transmission - Google Patents

Description

(54) POWER SHIFT TRANSMISSION (71) We, HANOMAG GESELLSCHAFT MIT BESCHRAENKTER HAFTUNG, a Company organised under the laws of the Federal Republic of Germany, of Hanomagstrasse 9, 3000 Hannover 91, Federal Republic of Germany, 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 vehicle transmissions, hereinafter referred to as being of the kind specified, having a hydrodynamic torque converter provided with internal vanes whose position is adjustable to vary the torque transmitted by the converter and a gear mechanism arranged to be driven by the torque converter and provided with gear ratios arranged to be selectively engaged by the operation of fluid pressure operated clutches in a fluid circuit.

Vehicle transmissions of the kind specified are used in a wide variety of vehicles such as, for example, lorries passenger cars, agricultural tractors and track laying vehicles such as dozers and excavators.

One of the problems with transmissions of the kind specified is that very high torque peaks occur in the gear mechanism during ratio changes under full load. This imposes excessive loads on the working parts of the gear mechanism, such as the bearing, gear wheels and clutches, leading to numerous break-downs and premature wear.

A further deficiency of transmissions of the kind specified is that if a ratio is engaged under full load, that is whiist the torque converter is delivering its normal torque output to the gear mechanism, an appreciable amount of slippage will occur in the clutch being engaged in order to select the ratio on account of the high torque being applied to the clutch by the torque converter.

As will be appreciated, this slippage results in the generation of an appreciable quantity of heat in the clutches of the gear mechanism.

This heat must be removed if premature failure of the clutches is to be avoided. This leads to problems since only a limited amount of heat can be dissipated from the clutches per unit area and the size of the clutches is normally limited by the space available in the vehicle.

It is an object of the present invention to provide an improved form of vehicle transmission of the kind specified which at least mitigates the clutch problems discussed above.

In accordance with the present invention there is provided a vehicle transmission of the kind specified in which the position of the internal vanes is adjustable by a fluid pressure operated servo motor arranged to be supplied with pressurized fluid from a source thereof, a pressure sensing means is disposed in said fluid circuit, an electro-magnet is connected with the sensing means, and a servo motor control valve is shiftable by the electromagnet to control the flow of pressurized fluid to the servo motor from the source to alter the position of the vanes dependent on the signal derived from the pressure sensing means, the pressure sensing means being arranged to signal to the electromagnet a reduction of the pressure level in said fluid circuit on commencement of a ratio change to bring about a reduction of the torque transmitted by the converter by alteration of the position of the vanes, and to signal to the electromagnet the re-establishment of the circuit pressure level consequent on completion of the ratio change to bring about an increase in the torque transmitted by the converter by a further alteration in the position of the vanes.

It will be evident that, since in a vehicle transmission in accordance with the present invention the torque delivered to the gear mechanism by the torque converter is reduced during a ratio change, the previously referred to problems of high torque peaks and excessive generation of heat in the clutches of the gear mechanism are greatly reduced. This means that for a given maximum torque converter output the size of the clutches required in the gear mechanism can be reduced as compared with previous arrangements, or alternatively, for a given clutch size a higher maximum torque converter output can be used.

Conveniently, the servo motor control valve may be a spool valve whose spool is axially shiftable by the electro-magnet, the spool being biassed against the axial shifting necessary to either decrease or increase the torque transmitted.

Also, the transmission may be provided with an adjustable time delay positioned between the pressure sensing means and the electro-magnet, the adjustable time delay being arranged to enable the response time of the servo motor to be adjusted.

One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a vehicle transmission embodying the present invention, and Figures 2 and 3 are graphical representations of the operating characteristics of a transmission of the kind specified not including and including the invention respectively.

Referring to Figure 1, "A" denotes the torque converter as a whole, this unit being driven by an input shaft 1 from a prime mover (not shown). "B" denotes the servo motor circuit for controlling the torque delivered by the torque converter and "C" denote the gear mechanism which is driven from the torque converter via shaft 5, meshing gears 6 and a gear mechanism input shaft 20.

The torque converter input shaft 1 drives a fly-wheel 2 which is secured to the impeller 3 of the torque converter. In the conventional manner during use of the torque converter fluid circulation takes place so that the turbine 21 is caused to rotated thus driving the associated torque converter output shaft 5. The circulation of fluid within the torque converter can be regulated (that is its direction of flow altered) by adjusting the position of the vanes 4 of the torque converter. This adjusts the amount of torque transmitted to the output shaft 5.

As previously described, the shaft 5 drives the gear mechanism input shaft 20 via the meshing gears 6. As can be seen from Figure 1, the housing 7 of the gear mechanism "C" houses a number of fluid pressure operated clutches 9 which can be selectively engaged to achieve the required operating ratio in the gear mechanism "C". The output from the gear mechanism "C" is in the form of the shaft 8. This output shaft may be used either to propel the vehicle or to drive some machine associated with or carried by the vehicle at any given time.

Fluid pressure for operation of the clutches 9 is provided by a gear pump 10 which is driven from the torque converter impeller 3 by the gear drive 11. The pump 10 supplies hydraulic fluid to the clutches via a pressure regulating valve 12 and a conventional ratio control device 13.

When a ratio is changed in the gear mechanism "C" the control device 13 dumps the pressure from the previously operative clutch 9 and applies fluid pressure to the new clutch 9 in order to engage the new desired ratio. This operating sequence results in the pressure level in the control device 13 being initially reduced and subsequently re-established.

This change in the pressure level in the control device 13 is sensed by a pressure sensing means 14 which is electrically connected with a relay 15 and an electro-magnet 16.

The electro-magnet 16 controls a gate valve 17 which controls the supply of hydraulic fluid to a servo motor 18 which adjusts the position of the vanes 4 of the torque connector "A".

The valve 17 is supplied with pressurized fluid from a separate gear pump 19 which is also driven from the gear drive 11. If desired the pump 10 could be used to supply fluid to the valve 17 and the relay 15 could be omitted if the transmission is set to operate on a fixed time lag.

In the arrangement shown the valve 17 is a spool valve whose spool is biassed at 22 against movement in one direction, for example, the spool could be biassed so that the necessary movement of the spool to cause the servo motor to adjust the vanes 4 to a position in which the torque converter output is reduced to a low level must be made against the action of the bias 22. Alternatively, the spool of valve 17 would be biassed in the opposite sense.

The sequence of operation of the transmission is as follows.

Operation of the control device 13 to engage a new ratio results in the reduction of the pressure level in the control device as described above. This pressure level reduction is sensed by the sensing means 14 which produces an electrical signal which causes the electro-magnet via the relay 15, to displace the spool of valve 17 to direct fluid to the servo motor 18 from the pump 19 to adjust the vanes 4 so as to reduce the torque transmitted by the torque converter to the gear mechanism "C" to a low level.

As the ratio change continues the pressure level in the control device 13 again builds up as the new clutch is pressurized as described above. This re-establishing of the pressure level in the control device 13 is sensed by the sensing means 14 and results in the deactivating of the electo-magnet 16 and hence the movement of the spool of the valve 17 to a position in which the servo motor 18 moves the vanes 4 to open up the torque converter and supply the normal torque input into the gear mechanism "C".

Figure 2 is a graphical representation of the variation with time of the operating characteristics of a transmission of the kind specified not fitted with the invention. Figure 3 is a similar representation of the same characteristics of a transmission of the kind specified embodying the invention.

In Figures 2 and 3 time (T) is plotted horizontally in seconds. Curves I show the variation of gear mechanism pressure in kp/cm2 (scale P), curves II show the variation of torque in mkp (scale Q), and curves III and IV show the variation of the input and output speeds respectively of the operative clutch in r.p.m. (scale R).

At point "a" the ratio change starts, causing the gear mechanism pressure to fall steeply. This fall is identifiable in both Figures 2 and 3 by the course taken by curve I in the section marked "b". It is only from point "c" that the pressure starts to build up to its original level, this building-up continues through the point "d", when the new clutch is filled with fresh fluid, until the slip phase "e" for the newly engaged clutch is ended. It is already evident at this point that with the arrangement as described in the invention the slip phase "e" is considerably shorter.

Point "f' denotes the point when the input and output speeds of the newly engaged clutch are the same and no slip is therefore taking place. This condition arises when the ratio change is completed. The point "g" corresponds to a condition in which the vehicle reverses in direction.

With the torque curve II the input torque is about the same. It rises during the ratio change phase to a relatively high peak value in transmissions not provided with the invention (Figure 2). By means of the adjustable converter arrangement of the present invention this torque peak, which occurs during the slip phase of the ratio change is cut down.

As will be appreciated, the shortening of the slip phase and the simultaneous reduction of the torque peak can only bring about a considerably smaller generation of heat by friction.

WHAT WE CLAIM IS: 1. A vehicle transmission of the kind specified in which the position of the internal vanes is adjustable by a fluid pressure operated servo motor arranged to be supplied with pressurized fluid from a source thereof, a pressure sensing means is disposed in said fluid circuit, an electro-magnet is connected with the sensing means, and a servo motor control valve is shiftable by the electro-magnet to control the flow of pressurized fluid to the servo motor from the source to alter the position of the vanes dependent on the signal derived from the pressure sensing means, the pressure sensing means being arranged to signal to the electromagnet a reduction of the pressure level in said fluid circuit on commencement of a ratio change to bring about a reduction of the torque transmitted by the converter by alteration of the position of the vanes, and to signal to the electro-magnet the re-establishment of the circuit pressure level consequent on completion of the ratio change to bring about an increase in the torque transmitted by the converter by a further alteration in the position of the vanes.

2. A transmission according to claim 1 in which the servo motor control valve is a spool valve whose spool is axially shiftable by the electro-magnet, the spool being biassed against the axial-shifting necessary to either decrease or increase the torque transmitted.

3. A transmission according to claim 1 or claim 2 in which an adjustable time delay is positioned between the pressure sensing means and the electro-magnet, the adjustable time delay being arranged to enable the response time of the servo motor to be adjusted.

4. A vehicle transmission of the kind specified, said transmission being constructed and arranged substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.

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

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. above. This re-establishing of the pressure level in the control device 13 is sensed by the sensing means 14 and results in the deactivating of the electo-magnet 16 and hence the movement of the spool of the valve 17 to a position in which the servo motor 18 moves the vanes 4 to open up the torque converter and supply the normal torque input into the gear mechanism "C". Figure 2 is a graphical representation of the variation with time of the operating characteristics of a transmission of the kind specified not fitted with the invention. Figure 3 is a similar representation of the same characteristics of a transmission of the kind specified embodying the invention. In Figures 2 and 3 time (T) is plotted horizontally in seconds. Curves I show the variation of gear mechanism pressure in kp/cm2 (scale P), curves II show the variation of torque in mkp (scale Q), and curves III and IV show the variation of the input and output speeds respectively of the operative clutch in r.p.m. (scale R). At point "a" the ratio change starts, causing the gear mechanism pressure to fall steeply. This fall is identifiable in both Figures 2 and 3 by the course taken by curve I in the section marked "b". It is only from point "c" that the pressure starts to build up to its original level, this building-up continues through the point "d", when the new clutch is filled with fresh fluid, until the slip phase "e" for the newly engaged clutch is ended. It is already evident at this point that with the arrangement as described in the invention the slip phase "e" is considerably shorter. Point "f' denotes the point when the input and output speeds of the newly engaged clutch are the same and no slip is therefore taking place. This condition arises when the ratio change is completed. The point "g" corresponds to a condition in which the vehicle reverses in direction. With the torque curve II the input torque is about the same. It rises during the ratio change phase to a relatively high peak value in transmissions not provided with the invention (Figure 2). By means of the adjustable converter arrangement of the present invention this torque peak, which occurs during the slip phase of the ratio change is cut down. As will be appreciated, the shortening of the slip phase and the simultaneous reduction of the torque peak can only bring about a considerably smaller generation of heat by friction. WHAT WE CLAIM IS:

1. A vehicle transmission of the kind specified in which the position of the internal vanes is adjustable by a fluid pressure operated servo motor arranged to be supplied with pressurized fluid from a source thereof, a pressure sensing means is disposed in said fluid circuit, an electro-magnet is connected with the sensing means, and a servo motor control valve is shiftable by the electro-magnet to control the flow of pressurized fluid to the servo motor from the source to alter the position of the vanes dependent on the signal derived from the pressure sensing means, the pressure sensing means being arranged to signal to the electromagnet a reduction of the pressure level in said fluid circuit on commencement of a ratio change to bring about a reduction of the torque transmitted by the converter by alteration of the position of the vanes, and to signal to the electro-magnet the re-establishment of the circuit pressure level consequent on completion of the ratio change to bring about an increase in the torque transmitted by the converter by a further alteration in the position of the vanes.

2. A transmission according to claim 1 in which the servo motor control valve is a spool valve whose spool is axially shiftable by the electro-magnet, the spool being biassed against the axial-shifting necessary to either decrease or increase the torque transmitted.

3. A transmission according to claim 1 or claim 2 in which an adjustable time delay is positioned between the pressure sensing means and the electro-magnet, the adjustable time delay being arranged to enable the response time of the servo motor to be adjusted.

4. A vehicle transmission of the kind specified, said transmission being constructed and arranged substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.