The present invention relates to a phaser for acting on two groups of cam lobes of a valve train of an internal combustion engine to change the phases of each of the two groups of lobes independently of one another relative to the phase of the engine crankshaft. Such a system is herein referred to as a dual phaser.
The use of phasers is becoming increasingly widespread on both gasoline and diesel engines. In the past, hydraulically operated phasers have offered a compact and cost-effective solution. However, more recently, electrically operated phasers have become popular due to the functional advantages that they offer. These advantages include (i) faster response time, (ii) more consistent response times over all engine operating conditions, particularly low temperatures when oil viscosity reduces the performance of hydraulically operated phasers, and (iii) reduced oil consumption and oil pump power consumption.
An electrically operated phaser generally consists of two main components, namely a gear set or harmonic drive that is mounted to the engine camshaft, and an electric motor which is mounted to a stationary part of the engine and positioned coaxially with the camshaft. There may be a drive coupling (such as an Oldham coupling) to allow for any small misalignment between the axes of the motor and the camshaft. Phase is adjusted using an electrically operated phaser by varying the speed of the electric motor relative to that of the camshaft. If the motor speed is synchronized with camshaft speed, then the prevailing phase setting is maintained. Reducing the motor speed relative to the camshaft will cause the phaser to move in one direction, increasing the motor speed will cause the phaser to move in the other direction. A typical example of an electrically operated phaser is to be found in U.S. Pat. No. 8,682,564.
In some variable valve systems, such as that shown in EP 1417399, a phaser is used to adjust the valve lift profile characteristics. In such a system, operation of the phaser affects engine power output and the faster response of an electrically operated phaser would offer drivability advantages.
Many twin camshaft engines are now being designed with multiple phasers and, in some cases, these are of different types, one camshaft utilizing a cost-effective hydraulically operated phaser whilst the other uses an electrically operated phaser for its additional speed and consistency. For example, some engines utilize an electrically operated phaser to control the intake valve timing and a hydraulically operated phaser to control the exhaust valve timing.
EP 3141711 shows a hybrid dual phaser having an electrically operated phaser and a hydraulically operated phaser combined into a single unit for independently controlling the timing of two groups of cam lobes mounted to an adjustable camshaft, which is also referred to herein as a concentric or as an assembled camshaft. This device could be applied to an engine having a single camshaft to allow independent control of intake and exhaust valve timing or it could be applied to an engine with a cam summation valvetrain system such that one output of the dual phaser controls valve lift and duration whilst the other output controls the lift timing.
The dual phaser of EP 3141711 shows how the hydraulic and electric sections of a hybrid phaser can be arranged and connected axially, but, in some applications, there is limited axial space available making it difficult to implement such a solution.
The invention therefore seeks to provide a hybrid dual phaser, comprised of a hydraulically operated phaser in combination with an electrically operated phaser, that has a reduced axial length and that offers a significant package space advantage in some applications.
According to the present invention, there is provided a hybrid dual phaser assembly for mounting to an engine camshaft to allow the timing of two sets of cam lobes to be phased independently of one another relative to a crankshaft of the engine, wherein the phaser assembly comprises an electrically operated phaser having intermeshing gears for transmitting torque to the camshaft and a phase control input driven by an electric motor to be mounted coaxially with the camshaft, and a hydraulically operated phaser having vanes movable within arcuate cavities, wherein the cavities of the hydraulically operated phaser are defined in part by an annular member that radially surrounds, and axially overlaps, a gear of the electrically operated phaser, which gear is rotatable relative to the annular member and forms radially inner boundary walls of the cavities.
By “axially overlaps” it is meant that at least one plane normal to the axis of rotation of the dual phaser assembly passes through both the electrically operated phaser and the hydraulically operated phaser. In this way, a dual phaser assembly of the invention combines an electrically operated phaser with a hydraulically operated phaser by arranging the arcuate working chambers radially around the electrically operated phaser in the same plane normal to the axis of rotation of the phaser. Packaging the electrically operated phaser radially inside the vane phaser minimizes the axial packaging space requirement whilst allowing the available radial space to be fully utilized.
The electrically operated phaser is controlled by the electric motor, which is mounted coaxially with the camshaft and the hydraulically operated phaser may be controlled by oil feeds connected to a proportional control valve via oil drillings in the camshaft.
The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:
The drive configuration of a first embodiment of the invention is shown in
The construction of the phaser of the first embodiment of the invention is shown in
The drive output of the hydraulically operated phaser is formed as an annular plate 122 partially defining three arcuate cavities 124. The inner radial surface of each cavity 124 is defined by the outer surface of the output member 136 of the electrically operated phaser. Each cavity 124 contains one of the vanes 114 connecting the front and rear plates 110,112. The three vanes 114 form a seal between the surface of the output gear 136 and the surface of the annular plate 122. The rear end plate 110 of the dual phaser is provided with three large slots 126 to allow access for a drive connection from the hydraulically operated phaser output plate 122 to the camshaft 160.
Timing feedback from the hydraulically operated phaser is provided by a timing wheel 130 integral to the annular plate 122, while timing feedback from the electrically operated phaser is provided by a timing wheel 134 formed as a plate fitted to the front of the dual phaser. This timing wheel 134 is connected for rotation with the electrically operated phaser output via three projections 138 on the output gear 136 of the electrically operated phaser that pass with clearance through cutouts 144 in the front plate 112 of the hydraulically operated phaser and are engaged by three small fixing screws 142 to secure the timing wheel 134 in position.
A bias spring 150 mounted to the rear end plate 110 of the phaser (shown only in
A phaser mounting plate 132 is fitted to the camshaft front bearing 162 via three fixing bolts 164, and this mounting plate provides three spigots 168, fitted with three bushes 169, for connection to the output plate 122 of the hydraulically operated phaser, the entire dual phaser being secured in place by three screws 171. The drive connection between the electrically operated phaser output gear 136 and the inner driveshaft of the camshaft is achieved via a drive coupling 170, such as an Oldham coupling, that can transmit drive torque without imposing any radial position constraint between the phaser and the inner shaft 172 of the camshaft 160, and a fixing bolt 140 to secure the axial position of the inner shaft to the electrically operated phaser output gear 136.
The internal gearset 120 has two gears that are fast in rotation with one another but have a different number of teeth. The first gear meshes with the internal input gear 118, and the second gear meshes with the output gear 136. The gear ratio between the input gear 118 and the first gear of the gearset 120 differs from the gear ratio between the second gear of the gearset 120 and the output gear 136. The difference between the two gear ratios causes the angular position of the output gear 136 to change relative to the input gear 118.
To maintain the same phase between the input from the crankshaft and the inner camshaft 172, the motor 180 must rotate the gearset 120 at the same speed as the input gear 118. If the motor 180 rotates at a speed different to the input gear 118, the first gear of the eccentric gearset 120 rotates and meshes at a different point within the input gear 118, causing rotation of the second gear and therefore the output gear 136. Once the desired phase is achieved, the motor 180 must again match the rotational speed of the input gear 118 to maintain the desired phase.
To avoid unnecessary repetition, components serving the same function in the different embodiments to be described herein have been allocated reference numerals with the same last two digits and will not be described again. Components of the first embodiment have numerals in the 100 series while those of the second, embodiments have numerals in the 200 series.
The second embodiment adopts the alternative drive configuration shown in
In
The timing wheel for the first set of cam lobes (not shown in
To maintain the same relative phase between the first and second set of cam lobes, the motor (not shown) must rotate at the same speed as the front plate 212. If the phase of the first set of cam lobes is to be changed relative to the phase of the second set of cam lobes, then the motor must compensate by adjusting its speed relative to the front plate 212.
Number | Date | Country | Kind |
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19173473.0 | May 2019 | EP | regional |