Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
2001-04-25
2003-10-14
Marmor, Charles A (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
C184S006280, C184S027200
Reexamination Certificate
active
06631651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic circuit for an automated twin clutch transmission for motor vehicles, comprising a countershaft transmission with two parallel power transmission branches, and two main clutches, comprising:
a high pressure circuit having at least one actuator for the countershaft transmission and/or the main clutches,
a low pressure circuit for lubrication and/or cooling of elements of the twin clutch transmission, and
a first adjustment pump for providing a variable high pressure for the high pressure circuit.
Further, the present invention relates to a twin clutch transmission having such a hydraulic circuit.
2. Description of the Related Art
It is a recent tendency to use automated countershaft transmissions and spur gear transmissions in motor vehicles. In such transmissions, manipulating drives operate the shift clutches, particularly synchronizer units, and the starting and separating main clutch.
These automated manual transmissions suffer from an interruption of the traction force during a shifting process, cf. “Automatisierte Kraftfahrzeuggetriebe”, Hans-Joachim Förster, Springer Verlag, Germany.
In contrast thereto, the so-called twin clutch transmissions can perform power shifts.
Twin clutch transmissions comprise two main clutches at the input side which can be manipulated separately from each other, wherein one of the clutches is usually assigned to the even gears and the other clutch is usually assigned to the odd gears. A gear change of successive gears is made by operating the two input side main clutches in an interleaving manner. The load at the input side is continuously passed from one power transmission branch of the transmission to the other branch. Thus, power shifts can be performed without interruption of traction force.
A hydraulic circuit for controlling a twin clutch transmission is partially disclosed in the “Automobiltechnische Zeitung ATZ 89 (1987, 9), Porsche twin clutch transmission (in the following referred to as “PDK”).
In the PDK, the hydraulic energy generation is divided into two circuits. A pressure-controlled adjustment pump working according to the vane-cell principle supplies the hydraulic control circuit. In the low pressure circuit that is used for lubrication purposes, a constant pump is operated. The two clutches are controlled by proportional pressure reducer valves. The three synchronizer units are each actuated by two 3/2-port control valves, i.e. in total six control valves.
The pressure controlled vane-cell pump for the high pressure circuit is operated on demand. The constant pump for the low pressure circuit supplies the oil in dependence on the speed of the combustion engine.
Constant pumps are advantageous as hydraulic energy supply systems in mobile applications, due to high robustness, low weight, small size and low costs. The supply volume is derived from the requirements at extreme conditions. For all other operational conditions, the supplied amount of volume flow exceeds the necessary amount of volume flow, cf. lecture notes of the lecture “Fluidtechnik für mobile Anwendungen”, RWTH Aachen, 1
st
edition, 1990, Prof. Dr.-Ing. W. Backé, Prof. Dr.-Ing. J. Helling.
In the PDK, the supply volume is determined both in the low pressure circuit as well as in the high pressure circuit by the hydraulic operation condition at low engine speeds. With increasing differential speed, the discrepancy between the available supply flow of the pump and the necessary volume flow of the loads increases. Excessive hydraulic power has to be dissipated as a loss volume flow, using a suitable valve control. The losses are generated in a tertiary energy carrier (chemical→mechanical→hydraulic). An electronic control of the pressure level can reduce the influence of the hydraulic circuit. It is the object to reduce the loss producing counterpressure.
Pressure-controlled adjustment pumps allow to adapt the volume flow to the demand. The dependency from the engine speed exists only at maximum adjustment. Thus, those pumps are close to being an optimum solution from an energetic viewpoint, because the volume flow has the highest contribution to losses.
Within a project DKG 430 it was proposed by the assignee of the present invention, to provide an adjustment pump not only for the high pressure circuit but also for the low pressure circuit. Thereby, the energy consumption can be further optimized. However, this solution needs improvement with respect to costs and weight.
For the control or closed-loop control of the clutch function, the PDK uses proportional 3/3-port pressure reducer valves. These valves convert an impressed magnetic coil current into a hydrostatic pressure. The hydrostatic pressure acts onto the manipulating area of a hydraulic cylinder and impresses a manipulating force onto the clutch mechanics.
The hydraulic mechanical closed-loop control is made via a mechanical balance at the valve gate.
Proportional pressure reducer valves have, in general, the following disadvantages:
The magnetic hysteresis results in a width of backlash in the hydrostatic pressure.
The hydraulic mechanical control of the pressure reducer valve is subject to thermal influences. Stability and attenuation are changed with changes in temperature.
In dynamic processes where volume changes arise in the hydraulic drive (cylinder), the direct pressure feedback cuts off or on the volume flow before the target pressure is achieved. This has a negative influence on the movements that have to be made. The open-loop transfer function in which elasticity, compressibility, friction and inertia act, does not allow an exact assignment of magnetic current to the momentary hydrostatic pressure of dynamic processes.
In general, the hydraulic clutch control of the PDK has the following disadvantages:
The dynamics limit the momentary supply volume of the pump. The adjustment process of the pump requires reaction time. In this time, the pump adapts its feed volume to the induced demand of the drives. A constant pump supplies the momentary supply flow of the pump. In the constant pump, an increase of the supply amount leads to higher losses at higher rotational speeds.
The lack of electronic feedback of the pressure is disadvantageous for the control optimization; any diagnosis for monitoring the clutch function is made difficult.
In the PDK, there exists a safety hazard because of transmission blockages in case of malfunctions of the pressure reducer valves.
The dry main clutches used in the PDK are difficult to control.
On the other hand, wet clutches need an active cooling oil control in view of the effect of the impressed cooling oil amount on the drag torque of the clutch; the constructional expenditure is increased if this object is to be solved by a magnetic valve.
The operation of the synchronizer units in the PDK is performed on an electro-hydraulic basis. Each synchronizer unit is controlled by a drive, consisting of a double-acting cylinder and two 3/2-port control valves. The cylinder drive comprises two springs. In a fail safe position, the cylinder is in its central position. In this cylinder position, the synchronizer unit is in its neutral position.
In view of the fact that each synchronizer unit needs a double-acting cylinder and two 3/2-port control valves, the PDK has high costs, requires a high technical expenditure and a large amount of elements.
The actuating forces cannot be proportioned with the control valves which are on-off valves. Thus, shift noises occur, the load on the elements is high, the synchronizer force cannot be adjusted and the position cannot be closed-loop controlled (neutral, synchronous).
In view of the fact that the fixation is made by means of springs, the pressure has to maintain the engaged gear, the costs are high. Further, disengagement of a gear has to be made by spring forces.
Also, there are no means for externally locking inadmissible actuations of synchronizer units.
It is also known in the art to actuate the synchronizer units of
Getrag Getriebe-und-Zahnrad-fabrik Hermann Hagenmeyer GmbH & Cie
Ho Ha
Knobbe Martens & Olson Bear LLP.
Marmor Charles A
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