PTO transmission system in a work vehicle

A PTO transmission system in a vehicle for transmitting power to a PTO shaft driving an implement comprises a planetary drive unit having first and second input and output coupled to the PTO shaft. The first and second inputs are coupled to an output shaft of the vehicle engine and to an output shaft of a drive motor, respectively. A control system controls the transfer of power from a power source to the drive motor. The power source is a variable power generating source driven by the PTO shaft. The drive motor is configured and adapted to decrease or increase the rotational speed of the output of the planetary drive unit on an increase or decrease of the power transferred to it, respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage filing of International Application Serial No. PCT/EP2012/052721, entitled “PTO TRANSMISSION SYSTEM IN A WORK VEHICLE,” filed Feb. 16, 2012, which claims priority to Italian Application Serial No. TO2011A000136, filed Feb. 17, 2011, each of which is incorporated by reference herein in its entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to a PTO transmission system in a work vehicle for transmitting power to a PTO shaft driving an implement.

BACKGROUND OF THE INVENTION

The present invention relates to a PTO transmission system in an agricultural or industrial vehicle, that is, a work vehicle, for transmitting power to a PTO shaft driving an implement, said vehicle comprising an engine and ground drive wheels driven by main or traction drive transmission means comprising a continuously variable transmission (CVT) or a power shift transmission, wherein the PTO transmission system comprises a planetary drive unit having first and second input means and output means, said first input means being adapted to be coupled to an output shaft of said engine, said second input means being adapted to be coupled to an output shaft of drive motor means and said output means being adapted to be coupled to said PTO shaft, said output means having a rotational speed which is a function of a rotational speed of the first and second input means; power source means; and control means adapted to control the transfer of power from said power source means to said drive motor means and coupled to sensor means adapted to sense the vehicle wheel speed and the PTO shaft speed.

Present day agricultural or industrial vehicles and specifically tractors comprise electronic engine controls and continuously variable transmissions (CVT) or power shift transmissions in an effort to provide optimum performance and fuel efficiency.

On the other hand, most PTO driven implements require a constant drive shaft speed or a drive shaft speed governed by other considerations to insure proper operation.

Therefore, PTO transmission systems for agricultural or industrial vehicles for transmitting power to a PTO shaft driving an implement or variable transmissions between the PTO shaft and drive means on the implement itself have been designed in an effort to allow the control the working speed of such implements independent from the wheel speed of the vehicle or the speed of rotation of the engine thereof.

Examples for such PTO transmission systems may be found in U.S. Pat. No. 6,692,395-B2 or the DE-A1-196 21 391. These PTO transmission systems use planetary gear units having two input shafts driven by the engine and an auxiliary drive motor, and an output shaft for driving the PTO shaft. By changing the speed of rotation of the auxiliary drive motor, the speed of the PTO shaft may be varied in relation to the engine speed. The energy consumption of such auxiliary drives is relatively high and it still is not possible to readily adapt the PTO transmission system to different implements and working conditions.

The present invention is directed to a PTO transmission system and a method of operating thereof, wherein the power consumption is reduced and which is readily adaptable to different implements and working conditions.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a PTO transmission system in an agricultural or industrial vehicle for transmitting power to a PTO shaft driving an implement, said vehicle comprising an engine and ground drive wheels driven by main transmission means comprising a continuously variable transmission (CVT) or a powershift transmission; said PTO transmission system comprising: a planetary drive unit having a first and second input means and output means, said first input means being adapted to be coupled to an output shaft of said engine, said second input means being adapted to be coupled to an output shaft of drive motor means and said output means being adapted to be coupled to said PTO shaft; control means operable to control the engine rpm, the transmission ratio of said transmission means and said drive motor means; and an engine speed sensor, a PTO shaft speed sensor, operable to measure engine speed and PTO shaft speed respectively, and coupled to said control means; a target PTO speed; and characterized in that said control means may be operable to control the engine rpm, the gear ratio of said transmission means and said drive motor means to obtain a PTO output shaft speed corresponding said target PTO speed is provided.

The PTO output shaft speed may be adapted in an optimum manner to the working environment such that the working efficiency is optimized.

The control may preferably be connected to an operator actuable mode selector means for selecting a plurality of working modes.

The selector means provided by an operator actuable mode selector means, said input signals defining a predetermined combination of control parameters for the engine speed, the wheel speed and the PTO speed.

According to the invention one working mode may be selected wherein said target PTO speed is defined by GPS mapping information or ISO-bus connected sources or operator input.

This working mode permits an optimization of the operation of the implement based on GPS data of ISOBUS input devices and an improved fuel efficiency.

A further working mode may be selected wherein said target PTO speed is a function of the wheel speed.

As a result, the rotational speed of the output means of the planetary drive unit and thereby the PTO shaft is readily adaptable to different implements and working conditions, at the same time optimizing the fuel and working efficiency.

Further, said target PTO speed may be proportional to the wheel speed in a first wheel speed zone and said target PTO speed is constant in a second wheel speed zone, above a threshold wheel speed.

Moreover, the invention may further comprise a torque sensor, coupled to the control unit, and an even further working mode may be selected wherein the target PTO speed is based on a constant target PTO load.

According to a second aspect of the present invention a method according to claim6is provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

InFIG. 1, an embodiment of the PTO transmission system in an agricultural or industrial vehicle for transmitting power to a PTO shaft8driving an implement is shown.

The vehicle30is only schematically shown and comprises an engine1and drive wheels16(only one being shown) driven by traction drive or main transmission means15comprising a continuously variable transmission (CVT) or a power shift transmission.

The PTO transmission system comprises a planetary drive unit3having first and second input shafts2,5and an output shaft4. The input shafts2,5may be for instance coupled to or in engagement with the sun gear and the ring gear, respectively, of the planetary drive unit3, whereas the planet gear carrier planetary drive unit3may be coupled to the output shaft4.

The first input shaft is an output shaft2of the engine1, whereas the second input shaft is an output shaft5of drive motor means7. The output shaft4of planetary drive unit3is coupled to a PTO shaft8.

With this planetary drive unit3, the output shaft4has a rotational speed ωPTO which is a function of a rotational speed ωE and ωHM of the first and second input shafts2,5, respectively. The drive motor means7therefore is adapted to decrease or increase the rotational speed ωPTO of said output shaft4of said a planetary drive unit3on an increase or decrease of the power transferred to it, respectively, under control of said control means11.

A variable power source6which may comprise a variable displacement hydraulic pump drivingly connected to the PTO shaft8and controlled by control means11, and said drive motor7may comprise a hydraulic motor driven by said pump6via hydraulic lines9and10. The variable displacement pump and hydraulic motor work together as a hydrostatic drive.

Alternatively, the variable power source6may comprise an electric generator drivingly connected to said PTO shaft8and controlled by a control system or control means11. In this case, the drive motor7may comprise an electric motor driven by said generator.

The control means11is adapted to control the transfer of power from said power source6to said drive motor means7and is coupled to sensor means illustrated inFIG. 1sensing the vehicle wheel speed60, the engine speed61, and the PTO shaft speed and the PTO torque, collectively62.

Further, the control means11is connected to an electronic engine control unit13and an electronic transmission control unit14of said traction drive or main transmission means15via any of the conventional bus systems17known in this field.

The control means11further comprises operator actuable selecting means12for selecting any one of a plurality of working modes of said PTO transmission system. This control means is adapted to further control the engine speed, a gear ratio of the main transmission means and the PTO speed in response to input signals provided by the operator actuable mode selector or selector means12, said input signals defining a predetermined combination of control parameters for the engine speed, the wheel speed and the PTO speed. These input signals may define a predetermined combination of the engine speed and a gear ratio of the main transmission means15operative to reduce the power fed to said drive motor means (6,51) to a minimum.

In another working mode, these input signals may define a predetermined combination of the engine speed and a gear ratio of the main transmission means operative maintain the PTO speed at a selected speed.

The operator actuable mode selector means (12) are further operative to generate said input signals defining a predetermined combination of control parameters for the engine speed, the wheel speed and the PTO speed in response to external signals comprising one or more of GPS signals, ISOBUS signals, PTO torque signals and signals generated by the implement20.

The drawings of the embodiments ofFIGS. 2 to 4only show the hydraulic components of the PTO drive system and use the same control means11,12,13and14as inFIG. 1, so that this control system is not set out in these drawings again.

InFIG. 2, the hydraulic pump comprises a standard load sensing pump51which is anyhow provided on the vehicle and is constantly driven by the output shaft2aengine1preferably via a gearbox50. This pump is controlled by the control means11and feed the drive means7via a hydraulic compensator52, again under control of said control means11.

The first input means of the planetary gear3comprises an engine shaft section2bcoupled to the engine output shaft section2avia a clutch53permitting to completely shut off the PTO system if not in use.

The output shaft of the planetary gear is optionally coupled to the PTO shaft8via a PTO gearbox54to reduce the size and cost of the hydraulic components of the system.

FIG. 2Ashows the relationship between the engine (ICE) speed on the horizontal axis and the PTO speed on the vertical axis. The PTO speed may be varied between a minimum flow and a maximum flow of the engine1, and between these graphs, a reliable operation is possible.

In the embodiment ofFIG. 3, the drive means7of the second input means5of the planetary gear3is powered by an additional pump51which is a variable displacement pump driven via a clutch53at the output of the engine1and a gearbox50on the second output shaft section2bof the engine1extending to the planetary gear3. The drive means comprises a standard hydraulic motor7. The pump51is controllable via the control means11shown inFIG. 1.

To permit a complete shut-off of the PTO system, the PTO clutch50between the sections2aand2bof the output shaft of the engine1may be disengaged.

A PTO gearbox54may be provided at the output end of the PTO shaft as inFIG. 2.

FIG. 4differs from the embodiment ofFIG. 3in that both pump51and motor7have a variable displacement and are both controlled by the control means11.

In the following, examples of working modes of the PTO system ofFIGS. 1 to 4will be described.

As exemplified inFIG. 5, these working modes may comprise a first working mode wherein the operator selects at said input means12a constant PTO speed and a constant wheel speed. The electronic engine control unit13automatically controls the engine speed and electronic transmission control unit14automatically selects one of the selectable gears thereof for maintaining this constant wheel speed. The PTO speed is constant independently from the engine speed. Therefore, even if the combination of the vehicle30and the implement rides uphill or downhill, the PTO speed is constant, and only the engine speed and the selected gear change.

In this example, on even ground at position A, the vehicle speed is 10 km/h, the engine speed is 1900 rpm, and the gear selected is gear10. At the uphill position B, the engine speed is automatically increased to 2200 rpm, and gear9is selected. At the downhill position C, the engine speed is automatically decreased to 1600 rpm, and gear11is selected. At all positions, the PTO speed is kept constant at for instance 1000 rpm.

InFIG. 6, a second working mode is shown, wherein the operator selects at said input means12a PTO speed proportional to a predetermined wheel speed selected by the operator or automatically controlled, the electronic engine control unit13being adapted to automatically control the engine speed and electronic transmission control unit14being adapted to automatically select one of the selectable gears thereof for maintaining said predetermined wheel speed. In this working mode, the engine speed is kept constant at 1900 rpm and the PTO speed is always kept proportional to the wheel speed so that for instance at position D, the PTO speed is 1000 rpm, whereas the wheel speed is 10 km/h. The selected gear is10. At uphill position E, the wheel speed reduces to 9 km/h, the PTO speed is proportionally reduced to 900 rpm, and gear9is automatically selected. At downhill position F, the wheel speed increases again to 10 km/h with a proportional PTO speed of 1000 rpm, and gear11is selected. This working mode results in a uniformity of operation of the implement independently from the wheel speed and an improved fuel efficiency.

In the situation ofFIG. 6, a third working mode may be selected, wherein said PTO speed is determined as a function of a GPS map or a ISOBUS request, the wheel speed is selected by the operator or automatically controlled, the electronic engine control unit13being adapted to automatically control the engine speed and electronic transmission control unit14being adapted to automatically select one of the selectable gears thereof for maintaining said constant wheel speed. In this working mode, the PTO speed is a function of a GPS map or a ISOBUS request, and the wheel speed is kept constant at 10 km/h so that for instance at position D, the PTO speed is 900 rpm, whereas the engine speed is 1900 rpm. The selected gear is10. At uphill position E, the engine speed increases to 2200 rpm whereas the PTO speed is increased to 1000 rpm in view of the operation based on a function of GPS map data or a ISOBUS request, and gear9is automatically selected. At downhill position F, the engine speed decreases to 1600 rpm, whereas the PTO speed is still 1000 rpm, and gear11is selected. This working mode results in an optimization of operation based on a function of the GPS map data or the ISOBUS request and an improved fuel efficiency.

There may be any kind of functional relation between the vehicle wheel speed and the PTO speed, it should not always be a proportional relation. The operator may for instance define two working points where a certain PTO speed is selected for a specific wheel speed. A line through these working points may define such a relation between the PTO speed and the wheel speed for the entire wheel speed range.

A threshold wheel speed can be defined to allow a different strategy below and above said threshold. Below said threshold the relation between the PTO speed and the wheel speed could be a proportional relation while above said threshold the PTO speed may be fixed, defining a saturation zone.

Referring toFIG. 6also a fourth working mode may be explained wherein the operator selects at said input means12a predetermined PTO speed and a predetermined or automatically controlled wheel speed, the electronic engine control unit13being adapted to automatically control the engine speed and said electronic transmission control unit14being adapted to automatically select one of the selectable gears thereof for maintaining said predetermined or automatically controlled wheel speed. In this working mode, the wheel speed is kept constant at 10 km/h and the operator selects continuously a desired PTO speed, so that for instance at position D, the PTO speed is selected as 900 rpm, whereas the engine speed automatically controlled to 1900 rpm. The selected gear is10. At uphill position E, the engine speed increases to 2200 rpm, and the operator has selected a PTO speed of 1000 rpm. Gear9is automatically selected. At downhill position F, the engine speed decreases to 1600 rpm and gear11is selected. The selected PTO speed is kept to 1000 rpm. This working mode permits an optimization of operation of the implement based on operator's input and may result in improved fuel efficiency.

In a fifth working mode, a PTO speed resulting in a constant PTO power is automatically controlled by said control means11, the wheel speed is selected by the operator or automatically controlled, the engine speed is selectable by the operator or automatically controlled by said electronic engine control unit13, and a gear is selectable by the operator or automatically selected by said electronic transmission control unit14. In this working mode, the PTO output power is kept constant. When the load on the PTO increases, the PTO speed is decreased in order to not exceed an adjustable power limit or to keep a constant output power. The benefit of this working mode is that similar to the draft mode for the rear implement: the output power is maximized. A torque sensor on the PTO shaft8measures the load on said shaft8and said control means11adapts the PTO speed to keep the PTO output power constant.

In a sixth working mode, a soft soil treatment is desired. In this working mode, the PTO speed is automatically controlled by said control means11in response to the load acting on said PTO shaft8, the wheel speed is selected by the operator or automatically controlled, the electronic engine control unit13controls the engine speed in response to and operator input or automatically, and a variable gear is selected by the operator or automatically selected by the electronic transmission control unit14. The PTO speed is automatically reduced when the load is low enough, e.g. below a predefined threshold. As an example for this working mode, a soil cultivator may be considered. If the soil is hard the mechanical work to prepare the soil is higher than when the soil is softer. With a softer soil the full PTO speed is not necessary, so it is reduced. By reducing the PTO speed when not necessary, fuel consumption is reduced, and an optimized treatment is obtained. This is shown in the diagram ofFIG. 4wherein the working conditions in hard and soft soil are indicated. This working mode avoids an increase of the PTO speed beyond a control target in soft soil and even decreases the working point to a lower PTO speed of 540 rpm when operating in soft soil. In hard soil, the control target of 1000 rpm is automatically controlled.

In spite of the fact that specific working modes have been set out above, desired combinations of the specifics of these working modes are envisaged and possible.

In all working modes, a PTO speed, a tractor wheel speed, an engine speed and a variable gear are selected and/or automatically controlled according to a selected working mode within safe margins to avoid an engine stall on a sudden increase of the load on the PTO shaft. When the engine speed is lower than the rated speed (i.e. 1900 rpm), the engine may have power enough but the torque margin is reduced. In case of a sudden PTO load increase, if the PTO speed is kept constant, the engine would stall, therefore the PTO speed is temporarily reduced to virtually increase the torque margin. This has the benefit that the operator can work very close to the maximum engine power and efficiency (i.e. 1900 rpm) without the risk to stall the engine in case of sudden load variations. Higher efficiency (better engine working point) and higher productivity (works closer to max engine speed) are achieved.