Patent Description:
An electrically heated catalyst that is heated by energizing a heating element has been described. Such a catalyst is accommodated in and attached to a tubular case, while being electrically insulated from the case. Particulate matter or condensed water in exhaust gas may adhere to such an electrically heated catalyst. In this case, short circuits occur between the catalyst and the case, so that current also flows through the case. Therefore, the case is required to have insulation properties.

In order to ensure the insulation properties of the case, for example, the catalyst device disclosed in <CIT> includes a case with an end portion formed as an insulating portion.

Even in the catalyst device disclosed in the above publication, particulate matter may be deposited on the insulating portion of the end portion of the case. Therefore, it is necessary to improve the insulation properties at the insulating portion of the case end portion by preventing deposition of particulate matter.

<CIT> provides a catalytic converter that is provided at the exhaust pipe of an internal combustion engine. <CIT> provides an exhaust passage structure for an internal combustion engine, which includes an exhaust gas catalyst, a bypass passage and a waste gate valve.

In one general aspect, a catalyst device is configured to be disposed in an exhaust passage of an internal combustion engine including a forced-induction device. The catalyst device includes a catalyst configured to purify exhaust gas, a heating element configured to heat the catalyst by generating heat when energized, and a case that is a pipe accommodating the catalyst and the heating element. A direction in which exhaust gas flows through the exhaust passage is defined as a gas discharging direction. The case includes an end portion on an upstream side in the gas discharging direction. The heating element includes an end on an upstream side in the gas discharging direction. The end portion of the case is an insulating portion that insulates electricity and protrudes toward an upstream side of the end of the heating element in the gas discharging direction. The catalyst device further includes an outer tube that is separated from the end portion of the case in a radial direction to cover the end portion. The outer tube is formed by a turbine housing that houses a turbine wheel of the forced-induction device.

When the temperature of the outer tube is lower than the temperature of the end portion of the case, particulate matter collected on the end portion of the case moves to the inner circumferential surface of the outer tube due to thermophoresis. This prevents deposition of particulate matter in the insulating portion. Prevention of deposition of particulate matter in the insulating portion improves the insulation properties of the insulating portion.

In this regard, the outer tube in the above-described configuration is formed by the turbine housing of the forced-induction device. Since such a turbine housing has a large thermal capacity, the temperature rise of the turbine housing is slow, for example, during cold start. This encourages the temperature of the outer tube to be lower than the temperature of the end portion of the case, which is exposed to exhaust gas. This improves the insulation properties of the insulating portion at the end portion of the case.

In the above-described catalyst device, the outer tube may be entirely formed by the turbine housing.

With this configuration, the thermal capacity of the outer tube is larger than that in a case in which part of the outer tube is formed by the turbine housing. This further encourages the temperature of the outer tube to be lower than the temperature of the end portion of the case. This further improves the insulation properties of the insulating portion at the end portion of the case.

In the above-described catalyst device, the end portion of the case may include an edge on an upstream side in the gas discharging direction. A diameter of an outlet of the turbine wheel on a downstream side in the gas discharging direction may be defined as an outlet diameter. A diameter of the edge of the end portion may be set to be larger than the outlet diameter. A shortest distance between the edge and an inner circumferential surface of the turbine housing may be set to a distance greater than or equal to a shortest distance that allows insulation at a maximum voltage supplied to the heating element.

With this configuration, the exhaust gas that has passed through the turbine wheel does not easily flow into the space between the outer tube and the end portion of the case, and most of the exhaust gas flows into the case, which accommodates the catalyst. Therefore, it is possible to limit a decrease in the turbine efficiency of the forced-induction device caused by such a space.

In the above-described catalyst device, the turbine housing may be formed by a casting, and the catalyst device may include the turbine housing.

With this configuration, since the turbine housing is formed by the casting, the thermal capacity of the turbine housing is increased as compared with a case in which the turbine housing is formed by a metal plate. An increase in the thermal capacity of the turbine housing causes the temperature of the turbine housing to be less likely to increase. This encourages the temperature of the outer tube to be lower than the temperature of the end portion of the case.

Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, except for operations necessarily occurring in a certain order.

A catalyst device <NUM> according to an embodiment will now be described with reference to <FIG> and <FIG>.

As shown in <FIG>, an internal combustion engine <NUM> includes a forced-induction device <NUM> that supercharges intake air flowing through an intake passage <NUM> using exhaust gas flowing through an exhaust passage <NUM>. The forced-induction device <NUM> includes a turbine housing <NUM>, which houses a turbine wheel. The catalyst device <NUM> is connected to the downstream side of the turbine housing <NUM>. The catalyst device <NUM> is an electrically heated catalyst device and includes a heating element that generates heat when energized. The arrow in <FIG> represents a gas discharging direction, which is a flow direction of the exhaust gas discharged from the internal combustion engine.

<FIG> shows an axis C1, which is a straight line extending along the central axis of the catalyst device <NUM>. Like <FIG>, <FIG> shows an arrow indicating a gas discharging direction.

As shown in <FIG>, the catalyst device <NUM> includes a catalyst support <NUM>, which supports a catalyst for purifying exhaust gas. The catalyst device <NUM> includes a case <NUM>, which is a pipe accommodating the catalyst support <NUM>. The catalyst device <NUM> includes a mat <NUM>, which fixes the catalyst support <NUM> to an accommodation portion <NUM> of the case <NUM>. The catalyst device <NUM> includes two electrodes <NUM> for energizing the catalyst support <NUM>.

Next, the structure of the catalyst device <NUM> on the upstream side in the gas discharging direction will be described. The structure on the downstream side in the gas discharging direction may be symmetrical with the structure on the upstream side. Alternatively, the structure on the downstream side may be a single-wall pipe structure with the case <NUM>, which accommodates the catalyst support <NUM>.

The catalyst support <NUM> has a columnar outer shape with its central axis agreeing with the axis C1. The catalyst support <NUM> is a porous body. One example of the catalyst support <NUM> has a honeycomb structure in which channels extending in the gas discharging direction are defined.

As shown in <FIG>, the electrodes <NUM> are connected to the catalyst support <NUM>. When a voltage is applied across the electrodes <NUM>, current flows through the catalyst support <NUM>. When current flows through the catalyst support <NUM>, the electrical resistance of the catalyst support <NUM> causes the catalyst support <NUM> to generate heat. That is, the catalyst support <NUM> is an object that generates heat according to the electrical resistance when energized. In other words, the catalyst support <NUM> is a heating element, which generates heat when energized. The catalyst support <NUM> is made of, for example, a ceramic containing silicon carbide.

The mat <NUM> covers a surface that corresponds to the side surface of the column of the catalyst support <NUM>. The mat <NUM> is an insulating body having a low electric conductivity. The mat <NUM> is made of, for example, an inorganic fiber having alumina as a major component. Since the catalyst support <NUM> is covered with the mat <NUM>, no current flows through the case <NUM> when the catalyst support <NUM> is energized.

The case <NUM> is a pipe made of metal such as stainless steel. The axis C1 agrees with a straight line extending along the central axis of the case <NUM>. The case <NUM> includes the accommodation portion <NUM> and an end portion <NUM>, which is located on the upstream side in the gas discharging direction of the accommodation portion <NUM>. The catalyst support <NUM> is accommodated in the case <NUM> and includes an end face on the upstream side in the gas discharging direction. This end face is referred to as a catalyst upstream end 31A. The end portion <NUM> of the case <NUM> is a portion of the case <NUM> located on the upstream side of the catalyst upstream end 31A. The accommodation portion <NUM> is a portion of the case <NUM> located on the downstream side of the catalyst upstream end 31A. A diameter of a circle defined by the inner circumferential surface of the accommodation portion <NUM> is referred to as an inner diameter of the accommodation portion <NUM>. The length of the inner diameter of the accommodation portion <NUM> is twice the distance from the axis C to the inner circumferential surface of the accommodation portion <NUM>. The inner diameter of the accommodation portion <NUM> is constant in the direction in which the axis C1 extends. The end portion <NUM> of the case <NUM> protrudes further upstream in the gas discharging direction than the catalyst upstream end 31A. The surface of the end portion <NUM> of the case <NUM> is covered with an insulating material. The insulating material that covers the entire end portion <NUM> forms an insulating layer on the end portion <NUM>. Thus, the end portion <NUM> of the case <NUM> corresponds to an insulating portion.

The accommodation portion <NUM> of the case <NUM> has electrode insertion holes <NUM>, into which the electrodes <NUM> are inserted. The electrodes <NUM>, which are connected to the catalyst support <NUM>, protrude outside the case <NUM>, via the electrode insertion holes <NUM>. The electrode insertion holes <NUM> are closed by electrode holding portions <NUM>. The electrode holding portions <NUM> fix the electrodes <NUM> inserted in the electrode insertion holes <NUM>. The electrode holding portions <NUM> are insulating bodies having a low electric conductivity. Since the electrode holding portions <NUM> support the electrodes <NUM>, current does not flow to the case <NUM>.

The end portion <NUM> of the case <NUM> includes a constant diameter portion <NUM>, which is located at the upstream end in the gas discharging direction of the case <NUM>, and a decreasing diameter portion <NUM>, which is located between the constant diameter portion <NUM> and the accommodation portion <NUM> to connect the constant diameter portion <NUM> and the accommodation portion <NUM> to each other. A diameter of a circle defined by the inner circumferential surface of the constant diameter portion <NUM> is referred to as an inner diameter D of the constant diameter portion <NUM>. The length of the inner diameter D of the constant diameter portion <NUM> is twice the distance from the axis C1 to the inner circumferential surface of the constant diameter portion <NUM>. The inner diameter D of the constant diameter portion <NUM> is constant in the direction in which the axis C1 extends. The inner diameter D of the constant diameter portion <NUM> is smaller than the inner diameter of the accommodation portion <NUM>. An edge <NUM> of the constant diameter portion <NUM> on the upstream side in the gas discharging direction is an opening through which exhaust gas flows into the case <NUM>.

The decreasing diameter portion <NUM> of the end portion <NUM> has the shape of pipe that is tapered such that the distance to the axis C1 decreases toward the upstream end in the gas discharging direction. That is, the inner diameter of an inner circumferential surface 22B of the decreasing diameter portion <NUM> decreases toward the upstream end in the gas discharging direction.

The catalyst device <NUM> includes an outer tube <NUM> that is separated from the end portion <NUM> of the case <NUM> in a radial direction to cover the end portion <NUM>. The outer tube <NUM> is formed by a connecting pipe <NUM> and an enlarged diameter portion <NUM> of the turbine housing <NUM>.

The connecting pipe <NUM> is made of metal such as stainless steel. A downstream end <NUM> of the connecting pipe <NUM>, which is located at the downstream end in the gas discharging direction, is joined to an outer circumferential surface 22A of the decreasing diameter portion <NUM>. An inner circumferential surface 120B of the connecting pipe <NUM> is separated in the radial direction from the end portion <NUM> so as to cover the decreasing diameter portion <NUM> of the end portion <NUM>. The connecting pipe <NUM> includes a flange <NUM> at an upstream end in the gas discharging direction.

The turbine housing <NUM> is formed by a casting made of a metal material such as cast iron or an aluminum alloy. The turbine housing <NUM> includes a wheel accommodating portion <NUM>, which accommodates a turbine wheel <NUM>. The turbine housing <NUM> includes a cylindrical gas discharge portion <NUM>, through which the exhaust gas that has passed through the turbine wheel <NUM> flows. The central axis of the gas discharge portion <NUM> agrees with the axis C1. The inner diameter of the gas discharge portion <NUM> is constant in the direction in which the axis C1 extends. When the diameter of the outlet end of the turbine wheel <NUM> on the downstream side in the gas discharging direction is defined as an outlet diameter Dt, the inner diameter of the gas discharge portion <NUM> is slightly larger than the outlet diameter Dt. An opening <NUM> of the gas discharge portion <NUM> on the downstream side in the gas discharging direction is located on the upstream side in the gas discharging direction with respect to the edge <NUM> of the end portion <NUM>. The turbine housing <NUM> includes the enlarged diameter portion <NUM>. The enlarged diameter portion <NUM> is formed on the downstream side in the gas discharging direction with respect to the opening <NUM> of the gas discharge portion <NUM>. The inner diameter of the enlarged diameter portion <NUM> is larger than the inner diameter of the gas discharge portion <NUM>. An inner circumferential surface 112B of the enlarged diameter portion <NUM> is spaced apart in the radial direction from the end portion <NUM> so as to cover the end portion <NUM>. The enlarged diameter portion <NUM> includes a flange <NUM> at a downstream end in the gas discharging direction. The flange <NUM> of the enlarged diameter portion <NUM> and the flange <NUM> of the connecting pipe <NUM> are connected to each other, so that the downstream end of the turbine housing <NUM> in the gas discharging direction is fixed to the case <NUM>.

The inner diameter D, which is the diameter of the edge <NUM> of the end portion <NUM>, is set to be larger than the outlet diameter Dt of the turbine wheel <NUM>. A shortest distance L between the edge <NUM> and the inner circumferential surface 112B of the turbine housing <NUM> is set to a distance greater than or equal to a shortest distance Lα that allows insulation at a maximum voltage supplied to the catalyst support <NUM>. In the present embodiment, the positional relationship between the edge <NUM> and the inner circumferential surface 112B is determined such that the shortest distance L is equal to the shortest distance Lα at which insulation is possible.

Operation and advantages of the present embodiment will now be described.

In this regard, the outer tube <NUM> of the present embodiment is partially formed by the turbine housing <NUM> of the forced-induction device <NUM>. Since the turbine housing <NUM> having such a structure has a large thermal capacity, the temperature rise of the turbine housing <NUM> is slow, for example, during cold start. This encourages the temperature of the outer tube <NUM> to be lower than the temperature of the end portion <NUM> of the case <NUM>, which is exposed to exhaust gas. This improves the insulation properties of the insulating portion at the end portion <NUM> of the case <NUM>.

The above-described embodiment may be modified as follows. The above-described embodiment and the following modifications can be combined as long as the combined modifications remain technically consistent with each other.

The outer tube <NUM> of the above-described embodiment is formed by the connecting pipe <NUM> and the turbine housing <NUM>. Alternatively, the entire outer tube <NUM> may be formed by the turbine housing <NUM>.

<FIG> illustrates one example of this modification. As shown in <FIG>, the catalyst device <NUM> of the modification does not include the connecting pipe <NUM>. The enlarged diameter portion <NUM> of the turbine housing <NUM> includes a downstream end <NUM> located at an end on the downstream side in the gas discharging direction. The downstream end <NUM> is joined to the outer circumferential surface 22A of the decreasing diameter portion <NUM>.

With this modification, the thermal capacity of the outer tube <NUM> is larger than that in a case in which part of the outer tube <NUM> is formed by the turbine housing <NUM>. This further encourages the temperature of the outer tube <NUM> to be lower than the temperature of the end portion <NUM> of the case <NUM>. This further improves the insulation properties of the insulating portion at the end portion <NUM> of the case <NUM>. In this modification, the downstream end <NUM> may be joined to the outer peripheral surface of the accommodation portion <NUM> of the case <NUM>.

In the above-described embodiment, the downstream end <NUM> of the connecting pipe <NUM> may be joined to the outer circumferential surface of the accommodation portion <NUM> of the case <NUM>.

The above-described embodiment illustrates the case <NUM>, which includes the decreasing diameter portion <NUM>. The case <NUM> does not necessarily include a decreasing diameter portion. For example, the inner diameter of the end portion of the case <NUM> may be constant in the direction in which the axis along the central axis of the catalyst device extends.

In the above-described embodiment, the case <NUM> including the constant diameter portion <NUM> is illustrated. The case <NUM> does not necessarily include a constant diameter portion. That is, the constant diameter portion may be omitted from the end portion <NUM> of the case <NUM>. For example, a pipe may be employed in which the distance to the central axis of the catalyst device decreases toward the upstream end in the gas discharging direction.

Claim 1:
A catalyst-turbocharger combination comprising:
a catalyst device (<NUM>) configured to be disposed in an exhaust passage (<NUM>) of an internal combustion engine (<NUM>); and
a forced-induction device (<NUM>) including a turbine housing (<NUM>) that houses a turbine wheel (<NUM>),
the catalyst device (<NUM>) comprising:
a catalyst configured to purify exhaust gas;
a heating element (<NUM>) configured to heat the catalyst by generating heat when energized; and
a case (<NUM>) that is a pipe accommodating the catalyst and the heating element (<NUM>), wherein
a direction in which exhaust gas flows through the exhaust passage (<NUM>) is defined as a gas discharging direction,
the case (<NUM>) includes an end portion (<NUM>) on an upstream side in the gas discharging direction,
the heating element (<NUM>) includes an end (31A) on an upstream side in the gas discharging direction,
the end portion (<NUM>) of the case (<NUM>) protrudes toward an upstream side of the end (31A) of the heating element (<NUM>) in the gas discharging direction, and is an insulating portion that insulates electricity,
a surface of the end portion (<NUM>) of the case (<NUM>) is covered with an insulating material, such that the end portion (<NUM>) of the case (<NUM>) is an insulating portion,
the catalyst device (<NUM>) further comprises an outer tube (<NUM>) that is separated from the end portion (<NUM>) of the case (<NUM>) in a radial direction to cover the end portion (<NUM>),
the outer tube (<NUM>) is formed by the turbine housing (<NUM>), and
the turbine housing (<NUM>) includes a cylindrical gas discharge portion (<NUM>) that is coaxial with the catalyst device (<NUM>).