The present invention relates to a method and arrangement for operating a drive for a plurality of auxiliary devices arranged on an internal-combustion engine in a motor vehicle, having a differential gear arranged between the internal-combustion engine and the auxiliary devices.
In order to meet the current or voltage requirement of electrical consumers in a motor vehicle, a timed exciting current is fed to a rotary current generator. When there is, for example, a first low rotational generator speed, the exciting current is switched on and off by a regulator at predetermined intervals in such a manner that a specific first medium exciting current is adjusted in the case of a constant wiring voltage. So that the wiring voltage which is permissible for the wiring of the motor vehicle is regulated to its desired value when a second higher rotational generator speed occurs, the regulator changes the timing signal in such a manner that the switched-off time fractions increase and a second medium exciting current is adjusted which is lower than the first. As a result, the wiring voltage, which is a function of the exciting current and the rotational speed and is induced in the generator, remains constant.
It is known to arrange a transmission between an output of an internal-combustion engine and a drive of auxiliary devices. The transmission, as a function of parameters, carries out an adaptation of the rotational driving speed of the auxiliary devices to the rotational output speed of the internal-combustion engine. For example, in the German Patent Document DE-PS 31 24 102, a consumer-current-dependent change-over between a higher and a lower rotational driving speed of an electric generator is disclosed. The transmission connected in front of the electric generator has a clutch actuated by a control device. The clutch carries out the rotational speed change-over in such a manner that the higher rotational driving speed will be maintained only when a low rotational speed of the internal-combustion engine and at the same time a high current requirement, is present at the electric generator. The current requirement is fed to a regulator for the exciting current which, in turn, is fed to the control device.
In the German Patent Document DE-OS 28 01 812, a planetary transmission is arranged coaxially on a crankshaft end. The sun gear of the planetary transmission is provided with an electromagnetically stallable clutch disk. The ring gear of the planetary transmission drives auxiliary devices. When the sun gear is free, all auxiliary devices are driven at a low rotational speed. When the sun gear is fixed, the rotational output speed of the ring gear will increase so that all auxiliary devices are driven at a joint higher rotational speed. The change-over of the clutch disk takes place as a function of several parameters, for example, of the battery charging current or the cooling water temperature of the internal-combustion engine.
From the above-mentioned prior art, it is known to change over the rotational speed of the drive of the auxiliary devices as a function of parameters between a low and a higher rotational speed. A continuous adaptation or a disconnecting of one or several auxiliary devices is not possible.
It is an object of the invention to provide a method and arrangement for operating a drive for auxiliary devices of an internal-combustion engine which permits a controlled drive of individual auxiliary devices according to the requirements.
This and other objects are achieved by the present invention which provides a method of operating a drive for a plurality of auxiliary devices arranged on an internal-combustion engine in a motor vehicle, having a differential gear arranged between the internal-combustion engine and the auxiliary devices. The method includes switching on and off with a regulator in a timed manner an exciting current. The exciting current is supplied to a first auxiliary device as a function of a rotational speed of the generator such that a wiring voltage induced in the auxiliary device remains substantially constant, wherein the first auxiliary device is a rotary current generator. A signal of the internal-combustion engine is supplied to the regulator as a function of at least one of a load and a cooling water temperature of the internal-combustion engine. This thereby affects the timing of the regulator so as to change a driving torque supplied to the rotary current generator. A rotational generator speed and therefore a rotational driving speed of at least a second auxiliary device is changed by the differential gear to maintain the wiring voltage.
The aforementioned objects are also achieved by an embodiment of the present invention which provides an arrangement for operating a drive for a plurality of auxiliary devices arranged on an internal-combustion engine in a motor vehicle, having a differential gear arranged between the internal-combustion engine and the auxiliary devices. A regulator switches on and off in a timed manner an exciting current supplied to a first auxiliary device as a function of a rotational speed of the generator such that a wiring voltage induced in the first auxiliary device remains substantially constant. A signal of the internal-combustion engine is supplied to the regulator as a function of at least one of a load and a cooling water temperature of the internal-combustion engine to thereby affect the timing of the regulator so as to change a driving torque supplied to the first auxiliary device. A rotational generator speed is changed and therefore a rotational driving speed of at least a second auxiliary device is also changed by the differential gear to maintain the wiring voltage, wherein the differential gear is a planetary transmission. The planetary transmission has first and second outputs. The first output has a ring gear. The first auxiliary device is coupled to the ring gear. The second output has a sun gear. The second auxiliary device is coupled to the sun gear. A planet carrier is coupled to a crankshaft.
Via the intervention into the exciting current fed to the rotary current generator (electric generator), in combination with a differential gear arranged between the internal-combustion engine and the auxiliary devices, this method permits a drive of individual auxiliary devices, such as a water pump, that is controlled according to the requirements.
The power supplied by the internal-combustion engine to the differential gear in the case of a constant rotational speed may be considered to be constant. As a function of the construction of the transmission, the supplied power is distributed to these assemblies at a torque ratio that is constant at first. The required driving torque of the water pump may be considered to be constant while that of the electric generator depends on the intensity of the exciting current.
In the case of a cold start of the internal-combustion engine, a signal is, for example, supplied to the regulator. The signal is a function of the cooling water temperature and changes the timing of the exciting current of the electric generator. When the internal-combustion engine is cold, only a low cooling water throughput or no cooling water throughput at all is desired. The wiring voltage induced in the electric generator is a direct function of the exciting current and of the rotational driving speed of the electric generator. When the exciting current falls and the driving torque of the electric generator is therefore reduced by a certain amount, the rotational driving speed is increased by means of the differential gear. The wiring voltage is therefore kept constant.
Because of the compensating effect of the planetary transmission, the rotational driving speed of the water pump will be reduced.
Advantageously by using this method, when the rotational speed of the internal-combustion engine is low, a high transmission ratio can be achieved with respect to the electric generator. This allows the electric requirements to be covered, for example, also at the idling speed of the engine. On the other hand, it is possible to lower the transmission ratio in the case of high rotational speeds of the internal-combustion engine. As a result, the power consumption and the noise emission caused by the fan wheel of the electric generator will be reduced. The electric generator can therefore be operated in a favorable efficiency range of its characteristic diagram.
Additional advantages are achieved with respect to the second auxiliary device, for example, a water pump. In the case of the known design of a conventionally driven water pump, the power consumption relates to the cooling water flow rate of the internal-combustion engine at full load and maximal rotational speed. In the case of a partial load and low rotational speeds, the cooling requirements of the internal-combustion engine will be reduced to up to a third of the maximal cooling power. The method according to the invention allows a drive of the water pump which is controlled according to the demand. In this case, when the cooling water temperature is low, the differential gear reduces the rotational driving speed of the water pump and, when the internal-combustion engine is warmed up, increases it corresponding to the increased cooling requirements.
In an advantageous embodiment of the invention, the supply of the signal that is a function of the load or the cooling water temperature only takes place when it falls below a predetermined limit value for the cooling water temperature. When the actual cooling water temperature is below the limit value, the timing of the exciting current will be changed in such a manner that this exciting current will fall. As a result, the driving torque of the electric generator will be reduced, and its rotational speed will rise. Consequently, the rotational speed of the water pump will decrease.
In certain embodiments, a locking device is arranged between the output of the planetary transmission and the water pump. The locking device stops the water pump in the case of a cold start. This increases the rotational speed of the electric generator. With a controllable design of this locking device, the cooling power can in addition be regulated between one third and zero of the maximal cooling power.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.