WO2013097880A1

WO2013097880A1 - Hydraulically actuated continuously variable transmission for a vehicular drive line provided with an engine

Info

Publication number: WO2013097880A1
Application number: PCT/EP2011/006599
Authority: WO
Inventors: Francis Maria Antonius Van Der Sluis; Peter Verhoeven; Adrianus VAN TREIJEN; Antonius Embregt Van Hout
Original assignee: Robert Bosch Gmbh
Priority date: 2011-12-29
Filing date: 2011-12-29
Publication date: 2013-07-04
Also published as: CN104160180A

Abstract

A continuously variable transmission (1) for transmitting a driving force of an engine (VE) to a load (DW) to be driven, in particular in a vehicular drive line, provided with two hydraulic pumps (10, 11) for realising a pressurised supply of hydraulic transmission fluid for the actuation of the transmission (1), whereof a first pump (10) is driven by the engine (VE) and whereof a second pump (11) is driven by an electric motor independently from the engine (VE), and with a main hydraulic line (13), an auxiliary hydraulic line (15) and a line pressure valve (14) that control a pressure (Pline) in the main line (13) by allowing a surplus of transmission fluid to flow from the main line (13) into the auxiliary line (15), wherein the first pump (10) is connected to the main line (13) and wherein the second pump (11) is connected to the auxiliary line (15).

Description

HYDRAULICALLY ACTUATED CONTINUOUSLY VARIABLE TRANSMISSION FOR A VEHICULAR DRIVE LINE PROVIDED WITH AN ENGINE

The present invention relates to a continuously variable transmission as defined in the preamble of the following claim 1. Such a continuously variable transmission is generally known, and e.g. described in the European patent publication EP 0 798 492 A1 and is typically applied in the drive line of a passenger vehicle between the engine and the drive wheels thereof.

The known continuously variable transmission, which may be one of several known types, provides a transmission ratio that may be controlled to an arbitrary value within a range of transmission ratios covered by said transmission by an electro- hydraulic actuation system thereof. In addition to the said ratio control, the actuation system of the transmission also controls the torque that is transmissible by the transmission. Further, i.e. in addition to these two main functions of ratio and torque control, the said actuation system also performs the so-called auxiliary functions of the transmission, which normally include at least the lubrication of the transmission and the opening and closing of clutches thereof.

Typically, the two main actuation functions of transmission ratio control and of transmission torque control of the actuation system of the transmission require the largest flow of hydraulic transmission fluid at the highest pressure level. Although in the known transmission such a high pressure level may be realised and controlled without extraordinary difficulty per se, it is in particular the large flow of transmission fluid at such high pressure level that puts high demands on the lay-out and/or components of the electro-hydraulic actuation system of the transmission. Such high demands is especially problematic when a hydraulic pump of the actuation system is mechanically driven by the engine of the drive line in which the transmission is applied, since such pump must provide the required flow of transmission fluid even at a low engine speed, when the pump is driven only marginally. Thus, such known, engine driven pump is designed with a considerable stroke volume such that it provides a sufficient flow of transmission fluid also at the said low engine speed. As a result, at a high engine speed, far too much transmission fluid is circulated by the known engine driven pump and unnecessary efficiency losses occur.

It is therefore a general development aim to improve the efficiency of the transmission by reducing the flow of transmission fluid required for, in particular, the said two main actuation functions of the actuation system. This development aim has for instance been pursued by further increasing the pressure level applied thereto and by modifying the design of the transmission in the manner described in the above- mentioned European publication. According to this latter publication, the so-called V- angle defined by the side faces of the drive belt, as well as between the conical discs of the pulleys is reduced from its conventional value of 22.0 degrees to, effectively, a value in the range between 9.1 and 19.3 degrees.

In fact, the known development efforts to reduce the flow of transmission fluid, required by the actuation system for performing its two main actuation functions of ratio and torque control, have been so successful that in some transmission designs the auxiliary actuation functions of the actuation system became the limiting factor for the minimally required flow of transmission fluid, i.e. for the minimally required pumping capacity of the hydraulic pump instead.

It is an object of the present invention to enable the further optimisation of the known transmission in terms of its overall efficiency and of the efficiency of its electro- hydraulic actuation system in particular.

According to the invention such object is realised by providing the electro-hydraulic actuation system with two hydraulic pumps, whereof one is driven by the vehicle engine and the other one is electrically powered by an electric motor, i.e. independently from the vehicle engine, and by arranging the electro-hydraulic actuation system as per claim 1 hereinafter.

The electro-hydraulic actuation system according to the invention can be operated in three modes, namely

(i) either with the electrically powered pump providing hydraulic fluid for both the main and the auxiliary actuation functions thereof, i.e. fully independent from the vehicle engine,

(ii) or with the electrically powered pump providing hydraulic fluid for the auxiliary actuation functions thereof and with the engine driven pump providing hydraulic fluid for the said two main actuation functions thereof,

(iii) or with the engine driven pump providing hydraulic fluid for both the main and the auxiliary actuation functions thereof.

In the electro-hydraulic actuation system according to the invention, in an operational condition wherein the flow of transmission fluid provided by the engine driven pump is insufficient for performing both the main and the auxiliary actuation functions, the electrically powered pump can be activated to provide a further flow of transmission fluid specifically for the auxiliary actuation functions. Hereby, i.e. by effectively decoupling the supply of transmission fluid to the said two main actuation functions on the one hand and the auxiliary actuation functions on the other hand, it has been favourably made possible to operate the electrically powered pump at a considerably lower pressure level than what is required by the said two main actuation functions. As a result, the electrically powered pump can be designed and operated efficiently, i.e. optimised solely for providing transmission fluid for the auxiliary actuation functions of the actuation system, whereas the design of the engine driven pump can be optimised solely for the said two main actuation functions thereof. In transmission design according to the invention, a low(-er) fluid flow requirements of the said two main actuation functions can be fully utilised to optimise the design and efficiency of the engine driven pump.

An additional advantage of the electro-hydraulic actuation system according to the invention is that the vehicle engine can be switched off in, for example, hybrid vehicle drive lines and/or vehicles with what is called start-stop engine control, such that the engine driven pump is not driven at all. In this latter "engine-stop" operational condition the electrically powered pump provides hydraulic fluid not only for the auxiliary actuation functions of the actuation system, but also for the said two main actuation functions thereof. It is noted that this latter functionality and operation of the actuation system is, as such, already known in the art and is, for instance, described in the German patent application DE-A-41 34 268.

The invention will now be elucidated further along a drawing in which:

figure 1 is a schematic representation of a prior art and to be improved continuously variable transmission,

figure 2 represents the novel hydraulic configuration of the transmission according to the invention and

figure 3 illustrates three operating modes of the novel transmission configuration of figure 2.

In the figures, identical references relate to corresponding technical functions or structures, as the case may be.

Figure 1 schematically shows the known continuously variable transmission 1 such as is typically applied in the drive line of a passenger vehicle between the engine VE and the drive wheels DW thereof. The known transmission comprises a mechanical system MS for realising and changing a transmission speed ratio and a transmission torque ratio between an input shaft 2 and an output shaft 3 of the transmission 1 , and an electro-hydraulic actuation system AS for the control of the transmission 1 , i.e. of the main and the auxiliary functions of the transmission 1. These main functions of the transmission 1 are the control of the transmission speed and/or torque ratio and the control of torque that is transmissible by the transmission 1 between the in- and output shafts 2, 3 thereof. The actuation system AS typically controls a number of further or auxiliary actuation functions AAF-I, AAF-II of the transmission 1 that typically include at least the active lubrication of moving parts AAF-I and the actuation of a clutch AAF-II of the drive line for rotationally connecting or disconnecting the vehicle engine VE and the driven wheels DW.

In this particular illustrative example the mechanical system MS of the known transmission 1 comprises a flexible belt 4 that is wrapped around two transmission pulleys 5 and 6 that are respectively provided on input shaft 2 and the shaft 3 of the transmission 1. The pulleys 5 and 6 each comprise two pulley discs that provide effectively conically shaped contact surfaces for the belt 4 that is frictionally engaged with such discs. The pulley discs of each respective pulley 5 or 6 are urged towards each other under the influence of a hydraulic pressure exerted in a pressure chamber 7 or 8 of a piston-and-cylinder assembly of that respective pulley 5 or 6. By simultaneously exerting an input pulley pressure Pin in the input pulley pressure chamber 7 and an output pulley pressure Pout in the output pulley pressure chamber 8, the belt 4 is not only tensioned between the pulleys 5, 6, such that torque can be transmitted between the input shaft 2 and the output shaft 3 of the transmission 1 , but also assumes a certain radial position between the pulley discs of each pulley 5, 6, which radial position represents and provides a certain transmission ratio of the transmission 1.

The input pulley pressure Pin and output pulley pressure Pout are controlled by the actuation system AS that, in doing so, thus controls the two main actuation functions of transmission ratio control and of transmission torque control. For performing such two main actuation functions, the actuation system AS is provided with an electrical control unit (not shown) that based on several input signals, in a well-known manner, generates output signals for the operation of two pulley pressure valves 23 and 27 that set the pressure Pin, Pout in the input pulley pressure chamber 7 and the output pulley pressure chamber 8 respectively.

The known actuation system AS is further provided with two hydraulic pumps 10 and 11 that draw hydraulic transmission fluid from a reservoir 12 and that pump such fluid into a main hydraulic line 13 of the actuation system AS, which main line 13 is connected to the said two pressure valves 23 and 27. The pressure level in this main line 13 or line pressure Pline should thus always be at least as high as the highest of the input pulley pressure Pin and the output pulley pressure Pout. The line pressure Pline is set by means of a line pressure valve 14, which valve 14 is also operated by the electrical control unit (not shown) of the actuation system AS. The line pressure valve 14 passes any surplus of transmission fluid from the main line 13 into an auxiliary hydraulic line 15. The pressure level in this auxiliary line 15 or auxiliary pressure Paux will thus always be lower than the line pressure Pline and is set by means of an auxiliary pressure valve 16. The auxiliary pressure valve 16 may be passively controlled to set a constant auxiliary pressure Paux, however, in the presently illustrated embodiment this valve 16 is also operated by the electrical control unit (not shown) of the actuation system AS. The said auxiliary actuation functions AAF-I and AAF-II of the transmission 1 are operated and controlled by the actuation system AS while using transmission fluid supplied from this auxiliary line 15. At least in the present example of the known actuation system AS the auxiliary pressure valve 16 passes any remaining excess transmission fluid from the auxiliary line 5 back into the reservoir 12. In this latter respect it is noted that also the transmission fluid that is used for, in or by the said main and auxiliary actuation functions of the actuation system AS, is, after such use, also returned to the reservoir 12, such that the hydraulic parts of the actuation system AS form a closed circuit wherein the transmission fluid is circulated by the pumps 10, 11 , at least during operation of the transmission 1.

In this known actuation system AS, a first pump 10 of the two hydraulic pumps 10, 11 is mechanically driven by the vehicle engine VE such that a flow of transmission fluid provided by this first pump 10 is determined by the (rotational) speed of the (crankshaft of the) vehicle engine VE. Further, a second pump 11 of the two hydraulic pumps 10, 11 is electrically powered, i.e. is driven by an electric motor independent from the vehicle engine VE. The second pump 1 1 may thus be activated on demand and to a variable extent, in particular during dynamic operation of the mechanical system MS of the transmission 1 or when the vehicle engine VE, and hence also the first pump 10, is stopped. A one-way or check valve 17, 18 is provided between each pump 10, 1 1 and the main line 13 to prevent that, when either pump 10, 11 is stopped, transmission fluid flows back into the reservoir 12 from the main line 13 via such respective pump 10, 1 1.

As has already been noted in the introductory part, this known transmission 1 has a good overall efficiency, in particular in comparison with the more conventional transmission design that includes only the engine driven pump 10. However, in accordance with the invention even the transmission design of figure 1 hereof could still be improved upon in terms of the overall transmission efficiency, which improved transmission design is schematically illustrated in figure 2.

Figure 2, i.e. the transmission 1 depicted therein, largely corresponds to the known transmission 1 of figure 1 , however, including two important differences. A first difference is that the second, i.e. the electrically powered pump 11 of the said two hydraulic pumps 10, 11 is connected to, i.e. pumps transmission fluid into the auxiliary line 15 of the actuation system AS. Moreover, the pumping capacity of the first, i.e. the engine driven pump 10 can be tailored to the said two main actuation functions of the actuation system AS, even at a low engine speed, i.e. without having to take into account the pumping capacity that would, otherwise, additionally be required for the auxiliary actuation functions AAF-I, AAF-II.

This first difference, i.e. the feature of the electrically powered pump 11 being connected to the auxiliary line 1.5, i.e. downstream of the line pressure valve 14, thus favourably allows for an improvement of the efficiency of the transmission by reducing the pumping capacity of the engine driven pump 10.

A second difference between the transmission 1 according to the invention of figure 2 and the known transmission 1 of figure 1 is that a bypass hydraulic line 20 is provided between the main line 13 and the auxiliary line 15, thus bypassing the line pressure valve 14, which bypass line 20 includes a further check valve 21 and which bypass line 20 is provided in parallel with and the line pressure valve 14. The further check valve 21 of the bypass line 20 is fitted such that transmission fluid is allowed to flow from the auxiliary line 15 into the main line 13 -provided that the auxiliary pressure Paux is higher than the line pressure Pline-, but not in the opposite direction. As a result, the electrically powered pump 11 can still support the engine drive pump 10 by providing a flow of transmission fluid not only to and for the said auxiliary actuation functions AAF-I, AAF-II of the actuation system AS of the transmission 1 , but also to and for the said two main actuation functions of transmission ratio control and of transmission torque^"eont ol thereof.

In combination with the above-described first difference, this second difference, i.e. the feature of the said bypass line^N20 and the further check valve 21 connecting the auxiliary line 15 to the main line 13, thus favourably allows the vehicle engine to be switched-off during operation of the transmission 1 in the known manner.

The electro-hydraulic actuation system AS according to the invention of figure 2 can be operated in three different modes that are illustrated in figures 3A, 3B and 3C respectively. In these figures 3A, 3B and 3C the part or parts of the actuation system AS that are supplied with transmission fluid from or by the electrically powered pump 11 are indicated by the dashed thick lines, whereas the part or parts of the actuation system AS that are supplied with transmission fluid from or by the engine driven pump 10 are indicated by the solid thick lines.

In a first operating mode of the electro-hydraulic actuation system AS, illustrated in figure 3A, only the engine driven pump 10 is pumping transmission fluid. That is to say, that the flow of transmission fluid generated by the engine driven pump 10 is sufficient for allowing the actuation system AS to perform both the two main actuation functions "MAF" of ratio and torque control and any auxiliary actuation functions "AAF" thereof. In this first operating mode, the electrically powered pump 11 is, or at least can be, deactivated completely.

In a second operating mode of the electro-hydraulic actuation system AS, illustrated in figure 3B, both the engine driven pump 10 and the electrically powered pump 11 are pumping transmission fluid. That is to say, that the flow of transmission fluid generated by the engine driven pump 10 is insufficient to fully perform for the auxiliary actuation functions "AAF" of the actuation system AS in addition to the two main actuation functions "MAF" thereof. In this second operating mode the electrically powered pump 11 is activated to generate an additional flow of transmission fluid for allowing the actuation system AS to perform the auxiliary actuation functions "AAF" thereof in full as well.

In a third operating mode of the electro-hydraulic actuation system AS, illustrated in figure 3C, the vehicle engine and hence the engine driven pump 10 are deactivated and only the electrically powered pump 11 is pumping transmission fluid. That is to say, that the electrically powered pump 11 is activated to such an extend that the flow of transmission fluid generated thereby is sufficient for allowing the actuation system AS to perform both the two main actuation functions "MAF" of ratio and torque control and any auxiliary actuation functions "AAF" thereof.

The invention is not limited to the examples discussed above, but additionally covers the various amendments and modifications thereof that are possible without deviating from the scope of the invention as defined by the preceding description, by the attached drawings and all the features illustrated therein and by all the details of the following set of claims.

Claims

1. Continuously variable transmission (1 ) for transmitting a driving force of an engine (VE) to a load (DW) to be driven, in particular in a vehicular drive line, provided with two hydraulic pumps (10, 11) for realising a pressurised supply of hydraulic transmission fluid for the actuation of the transmission (1), whereof a first pump (10) is driven by the engine (VE) and whereof a second pump (11) is driven by an electric motor independently from the engine (VE), and with a main hydraulic line (13), an auxiliary hydraulic line (15) and a line pressure valve (14) that control a pressure (Pline) in the main line (13) by allowing a surplus of transmission fluid to flow from the main line (13) into the auxiliary line (15), wherein the first pump (10) is connected to the main line (13), characterised in that the second pump (11) is connected to the auxiliary line (15) instead.

2. Continuously variable transmission (1) according to claim 1 , characterised in that a bypass hydraulic line (20) with a check valve (21) is provided between the main line (13) and the auxiliary line (15), which check valve (21) is arranged to allow a flow of transmission fluid through the bypass line (20) from the auxiliary line (15) to the main line (13) and to obstruct an oppositely directed flow of transmission fluid.

3. Method of operating the continuously variable transmission (1) according to claim 1 or 2, characterised in that the operation of the transmission includes two main transmission actuation functions (MAF) of transmission ratio control and of transmission transmissible torque control and one or more auxiliary transmission actuation functions (AAF), such as for example lubrication and/or transmission clutch control, and in that the two main transmission actuation functions (MAF) are performed using transmission fluid drawn from the main line (13) and the one or more auxiliary transmission actuation functions (AAF) are performed using transmission fluid drawn from the auxiliary line (15).